Coatings for High-Temperature Environments: Anti-Corrosion and Anti-Wear Applications (Engineering Materials) 3031455339, 9783031455339

Table of contents :
Preface
Acknowledgements
About This Book
Contents
Corrosion Resistant Coatings for High Temperature Environment
Corrosion Under Insulation for Hot Structural Components
1 Introduction
2 Case Studies of Corrosion Under Insulation (CUI)
3 Fundamental Concepts of Corrosion and CUI
3.1 Environmental Factors
3.2 Other Factors
3.3 On-Site Non-destructive Testing (NDT) Methods for CUI
4 Concepts and Methods for CUI Protection
4.1 Recognized and Generally Accepted Good Engineering Practices (RAGAGEPs)
4.2 Modified Thermal Insulation Structures
4.3 Anti-CUI Coatings
5 Materials of Anti-CUI Coatings
5.1 Polymer Coatings
5.2 Metallic Pigment Coatings
6 Standardization Laboratory Test for Anti-CUI Coatings
6.1 ASTM G189-07(2021)
6.2 ISO 19277:2018
7 Summary
References
Development of Coating-Resistant Materials at High Temperatures for Waste-to-Energy Plant Application
1 Introduction
1.1 WTE Boiler Corrosion Environment
2 HTC-Resistant Materials and Coatings Technological Advances
2.1 CRCs for WWTs
2.2 Alloy Tubes with Corrosion Resistance and Superheater Coatings
3 Materials and Coatings Corrosion Mechanisms
3.1 Resources Corrosion Mechanisms
3.2 Spray Coatings Deterioration Mechanisms
4 Corrosion-Resistant Substances and Coatings: Application Trends
4.1 Coatings for Waterwall Tubes
4.2 Superheaters Corrosion‐Resistant Alloys and Coatings
5 Decline Mechanisms and Design of Coatings
5.1 Formation and Breakdown of Protective Oxides Layer
5.2 Erosion and Erosion/Corrosion-Resistant Materials and Coatings
5.3 Durability of Alloy and Ceramic Spray Coatings
6 Conclusion
References
Composite Enamel Coatings for Thermal Shock and Chloride Corrosion Coupled Environments
1 Introduction
2 Surface and Microstructural Characterization of Composite Enamel Coatings
2.1 Silicon Nitride/Enamel Composite Coatings
2.2 Silicon Carbide/Enamel Composite Coatings
2.3 Enamel/Steel Interface Analysis
3 Mechanical Properties of Composite Enamel Coatings
3.1 Strength of Coated Steel
3.2 Adhesion of Coating to Steel Substrate
3.3 Hardness and Indentation Cracking Resistance
3.4 Impact Resistance
4 Thermal Shock Resistance of Composite Enamel Coatings
4.1 Thermal Shock Damages
4.2 Dilatometric Analysis
4.3 Residual Stress Analysis
4.4 Microstructure-Dependent Thermal Shock Resistance
5 Corrosion Resistance of Composite Enamel Coatings
5.1 Corrosion Morphology Evolution
5.2 Electrochemical Study
5.3 Salt-Spray Test
5.4 Corrosion Evolution Mechanism
6 Summary
References
Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear Fuel Tubes Against Accidental Temperature Corrosion in Water-Cooled Nuclear Reactors
1 Introduction
2 PCD Coating on ZIRLO Substrate: History of Application
3 Growth of PCD Layer on ZIRLO Substrate
4 Cr Coating on ZIRLO Substrate
5 Hot Steam Oxidation
5.1 Hot Steam Oxidation of PCD-Coated ZIRLO
5.2 Corrosion of ZIRLO Coated by Magnetron-Sputtered Cr
5.3 Hot Steam Oxidation of PCD and Cr-Coated ZIRLO
6 Summary
References
Silicon-Based Technologies for High-Temperature Coatings and Their Corrosion Behaviours
1 Introduction
2 Types of Silicon-Based Coating
2.1 Protective Coating
2.2 Conductive Coating
2.3 Bond Coating
2.4 Dip Coating
2.5 Spin Coating
2.6 Spray Coating
2.7 Preceramic Polymers
2.8 Particle-Filled Coatings
3 Properties of Coating
3.1 Permeability
3.2 Adhesion
4 Mechanisms of Adhesion
5 Properties of Silicon-Based Technology and Their Application
5.1 Primers
5.2 Heat-Resistant Coatings
5.3 Industrial Maintenance Coatings
5.4 Hygienic Coatings
5.5 Abrasion-Resistant Coatings
6 Benefits of Silicon-Based Additives
7 High-Temperature Corrosion-Resistant Ceramic Coating
8 Corrosion-Resistant Coatings for High-Temperature Applications
9 Conclusions and Future Outlook
References
High Temperature Wear Resistance Coatings
A New Solution to Save Production Costs in the Deposition of the Wear-Resistant Coating
1 Introduction
2 Definitions and Phenomena
2.1 Thermal Spray
2.2 Tribology
2.3 Lubrication and Lubricant
2.4 Wear and Wear Resistance
2.5 Gas Generation Plasma
2.6 Amorphous Alloy
2.7 Coefficient of Friction
2.8 Enthalpy
2.9 The Adhesion and Cohesion Bond
2.10 Deposition Coating
3 Materials for High-Temperature Coating
3.1 The Improvement of Wear-Resistant Materials
3.2 Relation Between the Wear and Hardness
3.3 Relation Between the Wear and Friction
4 Methodology for Evaluating the Performance of the Deposition
4.1 Porosity—Its Influence on the Quality of Coating
4.2 Measurement of the Wear Resistance
4.3 Corrosion Test
4.4 Adhesive Test
4.5 Thermal Insulation Test
4.6 Hardness Testing
4.7 Measurement of Enthalpy
4.8 Determination of the Velocity of Particles in Plasma Spraying
5 Conclusions
References
Wear/Erosion Resistant High-Temperature Coatings
1 Introduction
2 Technology Advancement in High-Temperature Erosive Wear Resistance
3 Parameters Influencing Erosive Wear
4 Advance Coating Techniques
4.1 Thermal Spray Techniques
5 Erosive Wear Resistance of Ceramic Coatings
6 Erosive Wear Resistance of Metallic Coatings
7 Erosive Wear Resistance of Composite Coatings
8 Erosive Wear Resistance of Super Alloy Coatings
9 Coatings Failure at High-Temperature Conditions
9.1 High-Temperature Oxidation
9.2 Hot Corrosion
9.3 Solid-State Diffusion
10 Summary and Future Scope
References
Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni High Entropy Alloys Coatings Prepared by Laser Cladding
1 Introduction
1.1 Protection Requirement for Oxidation/Wear Resistance at High Temperature
1.2 High-Entropy Alloy Properties
1.3 Laser Cladding High-Entropy Alloys Coatings
2 The Microstructure Co–Cr–Fe–Nb–Ni Coating
2.1 Effect of Cr Content on the Microstructure
2.2 Effect of Si Addition on the Microstructure
2.3 Effect of C Addition on the Microstructure
2.4 Effect of CeO2 Addition on the Microstructure
3 The Oxidation Behavior of Co–Cr–Fe–Nb–Ni Coatings
3.1 The Role of Cr on Wet Mixture Gas Oxidation
3.2 The Role of Si on Wet Mixture Gas Oxidation
3.3 The Influence of C and CeO2 on High-Temperature Oxidation
4 The Wear Mechanisms of Co–Cr–Fe–Nb–Ni Coatings
4.1 The Influence of C Addition on Hardness
4.2 The Wear Mechanisms of HEAs Coatings at Elevated Temperature
5 Comparison of HEAs Coatings to Electroplated Hard Cr
5.1 The Oxidation Behavior of Two Coatings
5.2 The Wear Behavior of Two Coatings
6 Conclusion
References
The Boriding Process for Enhancing the Surface Properties of High-Temperature Metallic Materials
1 The Boriding Process
1.1 The Boriding Techniques
2 The Adhesion Resistance of Boride Coating on Metallic Substrates
3 High-Temperature Wear of Boride Coatings
3.1 High-Temperature Wear Resistance of Borided Steels
3.2 High-Temperature Wear Performance of Borided Ni-Base Superalloys
4 Oxidation and Corrosion Resistance of Boride Coatings in Aggressive Environments
4.1 Oxidation Behavior of Borided Metallic Materials
4.2 Corrosion Resistance of Boride Coatings to Neutral and Acidic Solutions
5 Tribocorrosion of Borided Metallic Materials
References
Tribological Characterization of Electroless Nickel Coatings at High Temperatures
1 Introduction
2 Deposition of EN Coatings
3 Coating Characteristics
4 High-Temperature Tribological Behaviour of EN Coatings
4.1 Performance of Ni–P Coatings at High Temperatures
4.2 Performance of ENB Coatings at High Temperatures
5 Conclusions and Future Directions
References
Heat Resistant Coatings
Thin Chromium-Based Coatings for Internal Combustion Automobile Engine Valve Protection
1 Introduction
2 Operating Conditions of the Internal Combustion Automobile Engine Valves
3 Methods for Testing the Oxidation Resistance of Materials Used in the Manufacture of Engine Valves
4 Corrosion Behavior of Popular Automobile Engine Valve Steels at High Temperatures
4.1 Oxidation in Air Atmosphere
4.2 Oxidation in Combustion Gasses of Fuels Containing Bio-Additions
4.3 Oxidation in Combustion Gasses of LPG Fuel
5 Thin Chromium-Based Coating Protective Properties Against High Temperature Oxidation of Valve Steels
5.1 Chromium Coatings
5.2 Chromium–Nickel Coatings
6 Summary
References
Protective Coatings for High-Temperature Thermoelectric Materials
1 Thermoelectric Materials—Introduction
2 Coatings
2.1 Background of Coating Techniques
2.2 Components of Coating Materials and Its Importance
2.3 Different Stages to Coat Materials
2.4 Coatings for High Temperature
2.5 Challenges in High-Temperature (HT) Coatings
2.6 Different Types of Coatings
3 Applications
3.1 Coatings for Gas Turbines
3.2 Coatings for Solar Thermal Power
3.3 Coatings for Space Applications
3.4 Coatings for Marine Applications
4 Existing Materials for Protective Coatings
4.1 Superalloys
4.2 Ceramics
4.3 Intermetallics
4.4 Refractory Materials
5 Explored High-Temperature Protective Coatings for TEM
6 Future Outlook
7 Summary
References
Electrically Insulating Corrosion-Resistant Tritium Permeation Barrier Coatings for High Temperature Liquid Metal Breeders of Nuclear Fusion Reactors
1 Introduction
2 Experimental Methods and Materials
3 Results and Discussions
3.1 Coating Observations
3.2 Electrical Insulation Performance in High Temperature Molten PbLi Environment
4 Metallographic Investigations
5 Applications and Outlook
5.1 Development of a Two-Phase Detection Probe for High Temperature Liquid Metal Systems
5.2 Development of Electrically Decoupled Liquid Metal Flow Channels
6 Conclusions
Appendix A: Estimation of Volumetric Electrical Resistivity and Coating Resistance
References
Silicone-Based Coatings for High-Temperature Applications
1 Introduction
2 Silicone Materials and Their Unique Properties
3 Types of Silicone Coatings and Its Performance at High Temperature
3.1 Silanes
3.2 Polydimethylsiloxane (PDMS)
3.3 Silicone Polyethers
3.4 Silicone Resins
3.5 Silicone Elastomers
4 High-Temperature Coating Applications of Silicone Materials
4.1 Aerospace and Aviation
4.2 Automotive Industry
4.3 Oil and Gas Industries
5 Factors Affecting the Performance of Silicone Coatings in High-Temperature Environments
6 Performance of Silicone-Based Coatings in High-Temperature Applications
6.1 Effects of Temperature, Stress, and Exposure Time on the Performance of Silicone-Based Coatings
6.2 Comparison of the Performance of Silicone-Based Coatings with Other High-Temperature Coating Materials
7 Future Directions and Conclusions
7.1 Future Research Directions on the Development of Advanced Formulations and Manufacturing Processes
7.2 Conclusion and Recommendations for Future Work in the Field of Silicone-Based Coatings for High-Temperature Applications
References
Heat Resistant Coatings—An Overview
1 Introduction
2 Requirement for Heat Resistant Coating
3 Classification of Heat Resistant Coating Materials
3.1 Ceramic Heat Resistant Coating Materials
3.2 Metallic Heat Resistant Coating Materials
3.3 Nanostructured Heat Resistant Coating Materials
4 Preparation of Heat Resistant Coating Materials
4.1 Electron Beam—Physical Vapor Deposition Method (EB-PVD)
4.2 Plasma Spray Method
4.3 Chemical Vapor Deposition Method (CVD)
5 Properties of Heat Resistant Coating Materials
5.1 Mechanical Properties
5.2 Thermo Physical Properties
5.3 Failure Behavior
6 Performance of Heat Resistant Coating Materials
6.1 Oxidation
6.2 Failure Mechanisms
6.3 Degradation Mechanisms
7 Newer Materials for Heat Resistant Coating
7.1 Chemically Modified Yttria Stabilized Zirconia (YSZ)
7.2 Pyrochlore Oxides (A2B2O7)
7.3 Lanthanum Cerium Oxide (La2Ce2O7)
7.4 Silicates
7.5 Rare Earth Oxides
7.6 Y3Al5O12
7.7 Lanthanum Aluminates
7.8 LaPO4
7.9 Metal–Glass Composite (MGC)
8 Conclusion
References

Citation preview

Engineering Materials

Amirhossein Pakseresht Kamalan Kirubaharan Amirtharaj Mosas   Editors

Coatings for High-Temperature Environments Anti-Corrosion and Anti-Wear Applications

Engineering Materials

This series provides topical information on innovative, structural and functional materials and composites with applications in optical, electrical, mechanical, civil, aeronautical, medical, bio- and nano-engineering. The individual volumes are complete, comprehensive monographs covering the structure, properties, manufacturing process and applications of these materials. This multidisciplinary series is devoted to professionals, students and all those interested in the latest developments in the Materials Science field, that look for a carefully selected collection of high quality review articles on their respective field of expertise. Indexed at Compendex (2021) and Scopus (2022)

Amirhossein Pakseresht · Kamalan Kirubaharan Amirtharaj Mosas Editors

Coatings for High-Temperature Environments Anti-Corrosion and Anti-Wear Applications

Editors Amirhossein Pakseresht FunGlass—Centre for Functional and Surface Functionalized Glass Alexander Dubˇcek University of Trenˇcín Trenˇcín, Slovakia

Kamalan Kirubaharan Amirtharaj Mosas FunGlass—Centre for Functional and Surface Functionalized Glass Alexander Dubˇcek University of Trenˇcín Trenˇcín, Slovakia

ISSN 1612-1317 ISSN 1868-1212 (electronic) Engineering Materials ISBN 978-3-031-45533-9 ISBN 978-3-031-45534-6 (eBook) https://doi.org/10.1007/978-3-031-45534-6 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

Preface

Materials are exposed to temperatures that change their physical and chemical properties due to environmental reactions with the material and its surface. The science and technology of surface modification of materials have become more important over the past few decades. The best way to protect materials from oxidation and hot corrosion is through the application of coatings. Researchers thought that applying a suitable coating can be a good strategy to protect the underlying material by acting as a potential barrier between the material and the environment, so it has been constantly improved and developed. High-temperature coatings are a technologically significant, cost-effective, and rapidly expanding field. Over the past few decades, coatings have come a long way and are now used for protection against high-temperature oxidation and wear. While limiting the heat exposure of structural components, these coatings protect those parts that are exposed to high temperatures, extending the life of the components, and lowering oxidation, thermal fatigue, wear, hot corrosion, and erosion. There are different kinds of coatings made from ceramics, intermetallics, cermets, organosilicon polymers, and other materials with good thermal stability. These kinds of coatings are an important part of how different coating techniques are developed. There is much useful information available regarding anti-wear and anti-corrosion coatings for high-temperature environments and how they perform. However, this knowledge is spread through conference proceedings, book chapters, monographs, journals, and published industrial reports. The authors decided to put this collective information together under the theme of coatings for high-temperature environments. This book covers coatings used for high-temperature environments, especially corrosion and wear applications. In addition, this book also addresses the basic understanding of materials and their selection, basic principles of physical and chemical metallurgy, design considerations, manufacturing methods, performance upgrades, and different methods for evaluating the coating microstructure and application. This book covers coatings for high-temperature environments, especially for corrosion and anti-wear applications. It also includes fundamental studies, including creating coating architecture, methods of preparation, and coating performances for the temperature range of applications. v

vi

Preface

Organization of the Chapter Corrosion-resistant materials are becoming increasingly in demand. The fundamental concepts of corrosion and materials used for corrosion under insulation are discussed in Chapter “Corrosion Under Insulation for Hot Structural Components”. Chapter “Development of Coating-Resistant Materials at High Temperatures for Waste-to-Energy Plant Application” discusses the development of coating-resistant materials at high temperatures for waste-to-energy plant applications. The development of suitable software for such applications that can effectively protect against corrosion is studied in this chapter. Recent investigations of silicon carbide- and silicon nitride-based composite enamel coatings for thermal shock and chloride corrosion coupled environments are discussed in Chapter “Composite Enamel Coatings for Thermal Shock and Chloride Corrosion Coupled Environments”. Chapter “Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear Fuel Tubes Against Accidental Temperature Corrosion in Water-Cooled Nuclear Reactors” discusses the combinations of polycrystalline diamond and magnetron-sputtered Cr double coating for their ability to protect nuclear fuel tubes against corrosion at accident temperatures in a watercooled nuclear reactor environment. Silicon-based technology and the application of silicon-based coatings to protect metallic alloys from high temperatures are discussed in Chapter “Silicon-Based Technologies for High-Temperature Coatings and Their Corrosion Behaviours”. Chapter “A New Solution to Save Production Costs in the Deposition of the Wear-Resistant Coating” focused on the updated achievements with air plasma spraying using the Fe-based amorphous coating to deposit a competitive wear resistance coating. The methodology for the evaluation of wear resistance coatings, standards, and their relationship between wear, hardness, and friction is briefly described in Chapters “A New Solution to Save Production Costs in the Deposition of the Wear-Resistant Coating” and “Wear/Erosion Resistant High-Temperature Coatings”. The protection requirement for wear-resistant coatings at high temperature using high-entropy alloys is discussed in Chapter “Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni High Entropy Alloys Coatings Prepared by Laser Cladding”. The effect of the addition of elements with respect to the microstructure and hardness is discussed in this chapter. Boride-based coatings are stable at high temperatures due to their high melting point, which allows them to maintain their hardness and oxidation resistance up to 1000 °C, with the possibility of increasing the high-temperature wear resistance of metallic materials. Various boriding methods for the formation of boride coatings on high-temperature metallic materials to improve their performance for diverse high-temperature applications are discussed in Chapter “The Boriding Process for Enhancing the Surface Properties of High-Temperature Metallic Materials”. The properties such as wear, adhesion, oxidation, corrosion, and tribo-corrosion of borided materials are explained well in this chapter. Finally, Chapter “Tribological Characterization of Electroless Nickel Coatings at High Temperatures” presents various aspects of high-temperature tribological characterization of electroless nickel coatings.

Preface

vii

Chapter “Thin Chromium-Based Coatings for Internal Combustion Automobile Engine Valve Protection” presents the latest findings concerning the impact of various liquid fuel types on the course of high-temperature corrosion on internal combustion engine valves and a method to increase the heat resistance by applying chromiumbased metallic coatings. The corrosion behavior of automobile engine valve steels under an air atmosphere and combustion gases was discussed. High-temperature thermoelectric materials for a variety of high-temperature applications are discussed in Chapter “Protective Coatings for High-Temperature Thermoelectric Materials”. Chapter “Electrically Insulating Corrosion-Resistant Tritium Permeation Barrier Coatings for High Temperature Liquid Metal Breeders of Nuclear Fusion Reactors” examines the experimental investigations on AlPO4 -bonded Al2 O3 coatings to assess the deposition feasibility, electrical insulation integrity, and thermal/chemical stability in static molten lead–lithium (PbLi) alloy materials for fusion reactor applications. The use of different types of silicone-based coatings for high-temperature applications is discussed in Chapter “Silicone-Based Coatings for High-Temperature Applications”. The factors affecting the performance of the coatings were also briefly discussed. Chapter “Heat Resistant Coatings—An Overview” summarizes an overview of ceramic materials used for heat resistance coatings, their properties, and their processing methods.

Conclusion The main aim of the book, “Coatings for high temperature environments: Anticorrosion and anti-wear applications”, is to offer a comprehensive overview of the advancements, potential challenges, and applications of a wide variety of materials in the field of high-temperature coatings. By the contribution of leading researchers, engineers, and industrial experts in this book, we hope that this book will serve as a valuable resource for academicians, students, researchers, and industrial experts seeking to improve their knowledge in the field of high-temperature coatings. Trenˇcín, Slovakia

Amirhossein Pakseresht Kamalan Kirubaharan Amirtharaj Mosas

Acknowledgements

We would like to extend our heartfelt thanks and appreciation to all the contributing authors who have shared their knowledge and expertise in this book. This book would not be possible without their dedication and excellent contributions in their respective disciplines. The editors would like to thank the reviewers for their helpful contributions in improving the chapter contents, cohesion, and narrative of each chapter. The majority of the contributing authors also worked as reviewers, and we would like to thank them for their tireless efforts in completing the reviewing process in such a short period of time. The editors would like to thank the readers of the high-temperature coating community for providing inspiration for this work. We feel this book will be extremely beneficial to their studies and research. Finally, we would like to thank the Springer Nature publisher personnel for their assistance from the beginning of the book proposal submission process. This would not have been feasible without their prompt assistance. We would also like to thank the editorial and production teams for their dedicated efforts and for making the publication possible. Finally, the editors would like to express their gratitude to the FunGlass center at Alexander Dubcek University in Trencin, Slovakia, for providing us with a dynamic environment in which to complete this book. This work is a part of dissemination activities of project FunGlass. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 739566. Also, this work was supported by the VEGA grant no. 1/0171/21 and APVV grant no. APVV-22-0070. Trenˇcín, Slovakia

Amirhossein Pakseresht Kamalan Kirubaharan Amirtharaj Mosas

ix

About This Book

This book addresses the recent trends in high-temperature coatings that are used to provide oxidation and wear resistance to metallic/ceramic components in extreme environments. Ceramics, intermetallics, organosilicon polymers, cermets, and other materials with great thermal stability have long been recognized for these applications. This book introduces the state of the art in coating materials and processes for high-temperature environments and identifies areas for improvement in materials selection, performance upgrades, design considerations, and manufacturing methods. The book covers a variety of high-temperature coatings prepared through various synthesis processes such as thermal spraying, physical vapor deposition, electrodeposition, and sol–gel methods. It covers corrosion/oxidation, phase stability, and thermal and mechanical behavior of high-temperature coating materials having greater thermal stability. With contributions from international researchers active in the field, this edited book features the most recent and up-to-date literature references for a broad readership consisting of academic and industrial professionals. It is suitable for graduate students as well as scientists and engineers working in the area of anti-corrosionand anti-wear-resistant high-temperature coatings for industrial applications.

xi

Contents

Corrosion Resistant Coatings for High Temperature Environment Corrosion Under Insulation for Hot Structural Components . . . . . . . . . . . I-Tseng Liu, Yi-Chen Weng, and Ying-Chih Liao

3

Development of Coating-Resistant Materials at High Temperatures for Waste-to-Energy Plant Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ankita Kumari, Priyanka Sati, and Sudesh Kumar

31

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion Coupled Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dongming Yan and Hao Qian

53

Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear Fuel Tubes Against Accidental Temperature Corrosion in Water-Cooled Nuclear Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Irena Kratochvílová, Petr Ashcheulov, Jakub Luštinec, Jan Macák, Petr Sajdl, and Radek Škoda

83

Silicon-Based Technologies for High-Temperature Coatings and Their Corrosion Behaviours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Priyanka Sati, Ankita Kumari, and Sudesh Kumar High Temperature Wear Resistance Coatings A New Solution to Save Production Costs in the Deposition of the Wear-Resistant Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Trung Dao Duy and Vu Duong Wear/Erosion Resistant High-Temperature Coatings . . . . . . . . . . . . . . . . . . 161 S. Arulvel, D. Dsilva Winfred Rufuss, Jayakrishna Kandasamy, P. Kumaravelu, R. Prayer Riju, and P. U. Premsuryakanth

xiii

xiv

Contents

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni High Entropy Alloys Coatings Prepared by Laser Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Jin Zhang and Minyu Ma The Boriding Process for Enhancing the Surface Properties of High-Temperature Metallic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 I. E. Campos Silva, A. Günen, M. Serdar Karaka¸s, and A. M. Delgado Brito Tribological Characterization of Electroless Nickel Coatings at High Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Arkadeb Mukhopadhyay, Tapan Kumar Barman, and Prasanta Sahoo Heat Resistant Coatings Thin Chromium-Based Coatings for Internal Combustion Automobile Engine Valve Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 Zbigniew Grzesik and Grzegorz Smoła Protective Coatings for High-Temperature Thermoelectric Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 S. Nanthini, Pandiyarasan Veluswamy, and H. Shankar Electrically Insulating Corrosion-Resistant Tritium Permeation Barrier Coatings for High Temperature Liquid Metal Breeders of Nuclear Fusion Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Abhishek Saraswat, Chandrasekhar Sasmal, Ashokkumar Prajapati, Rajendraprasad Bhattacharyay, Paritosh Chaudhuri, and Sateesh Gedupudi Silicone-Based Coatings for High-Temperature Applications . . . . . . . . . . . 385 T. Dharini, Anand Krishnamoorthy, and P. Kuppusami Heat Resistant Coatings—An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 A. Anitha, A. Hemalatha, and P. Udhayakumar

Corrosion Resistant Coatings for High Temperature Environment

Corrosion Under Insulation for Hot Structural Components I-Tseng Liu, Yi-Chen Weng, and Ying-Chih Liao

Abstract Corrosion under insulation (CUI) is a common issue for hot structural components covered by thermal insulation materials and aluminum cladding for energy-saving and anti-scalding purposes. Environmental and human factors causing CUI are discussed in this chapter, providing readers deep insights into CUI prevention. Even though CUI is difficult to manage simply through visual inspection, on-site non-destructive testing (NDT) methods can facilitate detection process and provide clear guidelines for finding high-risk components under claddings. Moreover, the concepts of recognized and generally accepted good engineering practices (RAGAGEPs) and process safety management (PSM) can serve as the rule of thumb for diminishing the risk of CUI. CUI prevention strategies are also summarized in this chapter. Among them, anti-CUI coatings before cladding are the most feasible strategy due to the acceptable cost and easy processing. Anti-CUI coatings are formulated with proper resin and pigment system based on the operating temperature of hot structural components and followed by standard laboratory tests, such as ASTM G189-07(2021) and ISO 19277:2018 elaborated in this chapter. These test methods can provide meaningful performance evaluations of anti-CUI coatings, and give helpful guidelines for both formulation development and screening of commercially available coatings. Keywords Corrosion under insulation (CUI) · Non-destructive testing · RAGAGEPs · Anti-CUI coatings · Polymer and metallic pigmented coatings · Standard laboratory test

I-T. Liu · Y.-C. Weng · Y.-C. Liao (B) Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_1

3

4

I-T. Liu et al. Abbreviation

Explanation

AMPP

Association for Materials Protection and Performance

API

American Petroleum Institute

ASTM

American Society for Testing and Materials International

CDU

Crude Distillation Unit

CoC

Cost of Corrosion

CR

Computed Radiography

CTE

Coefficient of Thermal Expansion

CUI

Corrosion Under Insulation

DFT

Dry Film Thickness

IMPM

Inert Multi-polymeric Matrix

IR

Infrared

ISO

International Organization for Standardization

LGO

Light Gas Oil

MIO

Micaceous Iron Oxide

NACE

National Association of Corrosion Engineers

NDT

Non-destructive Testing

PEC

Pulsed Eddy Current

PSM

Process Safety Management

PTFE

Polytetrafluoroethylene

PVC

Pigment Volume Concentration

RAGAGEPs

Recognized and Generally Accepted Good Engineering Practices

ROI

Return on Investment

SCC

Stress Corrosion Cracking

SGP

Saturate Gas Plant

SSPC

Steel Structures Painting Council

TMIC

Titanium-Modified Inorganic Copolymer

TSA

Thermal Sprayed Aluminum

UT

Ultrasonic Technology

1 Introduction The annual cost of corrosion (CoC) is approximately estimated to be US$ 2.5 trillion, which is 3.4% of the world’s GDP [1]. Statistics illustrate that 40–60% of piping maintenance expenditures are related to corrosion under insulation (CUI) or other relevant issues [2]. Corrosion control is an intuitive method to avoid economic loss, but lessons are learned after disastrous events, accidents, shutdowns, and production

Corrosion Under Insulation for Hot Structural Components

5

Scheme 1 Corrosion types

loss. Battling for corrosion protection and treatment is a never-ending war. Corrosion is an electrochemical reaction between electrolytes (e.g., water and water-leachable ions) and electrode pairs (e.g., metal surface), and can be classified into seven types by mechanism (Scheme 1): uniform corrosion [3, 4], galvanic corrosion [5, 6], crevice corrosion [7, 8], pitting corrosion [9, 10], intergranular corrosion [11, 12], erosion corrosion [13, 14], and stress corrosion cracking [15, 16]. CUI is the external corrosion that occurs on carbon steel, low-alloy, and austenitic/ duplex stainless-steel equipment (e.g., piping systems, pressure vessels, tanks, and reactors) which are covered with thermal insulation materials [17]. Hot structural components at certain conditions are prone to suffer from CUI issue. There are three main causes for CUI: (1) insulation materials satiated with water (rainfall and condensation from cooling towers), (2) corrosive ions (from surroundings or thermal materials themselves), and (3) periodic change of temperature and humidity (environmental conditions or processing). CUI is a corrosion phenomenon specified in hot structural components covered by insulation materials. Practically, CUI is the combination of different corrosion types mentioned above. Based on practical experiences, temperature is the most critical factor for CUI. As indicated in professional guidelines (Table 1), CUI is not limited to high-temperature conditions (i.e., it also happens under cryogenic conditions). For example, CUI could happen on insulated carbon steel at temperatures ranging from −12 to 177 °C with high possibility. On the other hand, CUI on austenitic/duplex stainless steel occurs at higher temperatures ranging from 50 to 205 °C [17–20]. Due to page limitation, in this chapter, we will focus on high-temperature conditions. Corrosion at high temperatures has a unique characteristic among all kinds of corrosion. At high temperatures, small molecules (e.g., chlorides, sulfides, and hydrogen) can easily diffuse into metals, and may accumulate or precipitate in the

6 Table 1 Temperature range for CUI occurrence

I-T. Liu et al.

Guideline API 510/570

Temperature range Carbon steel ( °C)

Stainless steel ( °C)

−12 ~ 177

60 ~ 205

EFC 55

−4 ~ 175

>60

NACE SP0198

−4 ~ 175

50 ~ 175

API: American Petroleum Institute EFC: European Federation of Corrosion NACE: National Association of Corrosion Engineers (NACE and SSPC merged into AMPP at 2021)

grain boundaries of metal. As a result, stress accumulation occurs in metal parts, and therefore CUI is often accompanied by stress corrosion cracking (SCC). Because high-temperature (>100 °C) processing and fabrication are commonly used in petrochemical industries, heat loss, energy consumption, and personnel anti-scalding are inevitable issues when handling hot structural components. Before the 1970s, thermal insulation was mainly used for components over 150 °C. At these temperatures, nearly no moisture is present on the insulated metal surfaces. Thus, CUI is limited because of the low-humidity environment. Things changed upon the rise of oil and gas industries in the 1970s when insulation materials were widely installed on components below 150 °C for energy-saving purposes [21]. Since then, CUI became a prevalent issue. In general, thermal insulation materials like fiberglass, mineral wool, and calcium silicate are covered directly on hot components and followed by aluminum cladding for waterproofing considerations [21]. Practically, aluminum cladding will deform and unseal due to human trampling and silicone sealant aging. These issues reduce the water protection capability of the insulated parts. Thus surrounding moisture can penetrate through pinholes or gaps and be absorbed by insulation materials. From experience, insulation materials can absorb water about three to five times their original weight [22]. The satiated insulation materials not only provide moisture sources for corrosion on metals but also incubate a great environment for CUI, because water evaporation is prohibited even under temperatures higher than the boiling point of water (100 °C) between metal and insulation layers. Meanwhile, it is nearly impossible to observe and diagnose corrosion by visual inspection without removing the insulation materials.

2 Case Studies of Corrosion Under Insulation (CUI) CUI has caused devastating accidents in the past decades. On April 16, 2001, a serious fire explosion incident happened at ConocoPhillips Humber Refinery [23]. From the investigation report, CUI occurred at an elbow connected to a section of pipes on the saturate gas plant (SGP), downstream of a water-into-gas injection point. The

Corrosion Under Insulation for Hot Structural Components

7

corrosion led to pipe connection failure, and high-pressure flammable gas (ethane/ propane/butane) leaked out from the corroded 6-inch pipe. After leaking for 20–30 s, flammable gas ignited into a catastrophic explosion as shown in Fig. 1a. Damage to the SGP and adjacent plants is shown in Fig. 1b, c. Fortunately, upon the explosion, most of the employees were inside buildings preparing for shift handover, and only a few employees were on-site. Thus, no serious injury occurred. There was only a short-term impact on the operation after this accident. Another case for CUI is Chevron’s crude unit fired on August 6, 2012 [24, 25]. The light gas oil (LGO) sidedraw from a crude distillation unit (CDU) deviated from

Fig. 1 a The fire and secondary fireball, b damage to the SGP, c adjacent plant. Courtesy Public report of the fire and explosion at the ConocoPhillips Humber refinery, Health and Safety Executive, 2001. https://www.yumpu.com/en/document/view/22334776/public-report-of-the-fire-andexplosion-at-the-conocophillips-hse

8

I-T. Liu et al.

the routine process. LGO leaked out from the rupture of the serving pipeline and the leakage was ignited 2 min later. After the explosion, the burned oil resulted in a vast amount of black smoke, which can be seen miles away (Fig. 2). Unfortunately, 19 company employees lose their lives in this accident, and approximately 15,000 people from neighboring communities suffered from respiratory problems in the following years. Investigation revealed that critical factors for this accident were: (1) inadequate design standard (ASTM A53) before 1985, which did not specify the silicon content in carbon steel pipe. (2) Failure to identify and monitor the high corrosion rate, which was due to the combination of CUI and high silicon content of the pipe. (3) Improper operation by firefighters. Insulation materials were removed immediately and caused severe chemical leaking from the unwrapped pipe. These devastating accidents show the importance of CUI material selection for chemical leakage prevention, and continuous CUI monitoring can help preventing hazardous explosion. Besides material mismatch, CUI issues may also occur even under regular operations. The following case of CUI can be attributed to improper annual maintenance. As shown in Fig. 3a, compressed propylene leakage from a pipe was identified onsite. The main leakage component was a pipe connected to the inlet of a propylene reactor. From annual inspections, no decrease in pipe wall thickness was observed by guided wave ultrasonic technology (UT) testing. However, from metallographic analysis, transgranular cracks grew dendritically from the pipe surface into the pipe (Fig. 3b), illustrating stress corrosion at the leakage area. Moreover, from the SEM image, crack morphology was characterized in a brittle fracture manner and chloride deposition was found near the crack. From the elemental analysis, silicon and calcium were also found (Fig. 3c). Those images give clear evidence that leachable ions were carried out by water from the calcium silicate insulations. In theory, however, severe corrosion from the leached ions was impossible for this piping area, because the regular working temperature was 37 °C, much lower than the corrosion

Fig. 2 Chevron’s crude unit fire. a Seconds after ignition, b Rupture of pipe component (with insulation removal). Courtesy Final investigation report-Chevron Richmond refinery pipe rupture and fire, U.S. Chemical Safety and Hazard Investigation Board, 2012. https://www.csb.gov/che vron-refinery-fire/

Corrosion Under Insulation for Hot Structural Components

9

Fig. 3 a Propylene leakage from an inlet pipe (with insulation removed), b Crack morphology and growth direction from metallographic analysis, c SEM image and EDX analysis for the crack area. Courtesy The failure analysis on the inlet pipe of propadiene reactor of low-temperature unit in naphtha cracking plan, Linyuan Petrochemical Plant, 2011

occurring temperature. However, the reactor maintenance required a catalyst regeneration process every year. During the regeneration, the temperature of the inlet pipe turned out to be 100 °C, a temperature high enough to trigger corrosion. This periodic high-temperature processing was the major reason for this CUI accident, and was found in many other reactors in this plant [26].

3 Fundamental Concepts of Corrosion and CUI Corrosion is an electrochemical oxidation–reduction reaction. The reaction is composed of metal oxidation and water reduction. For example, the corrosion of iron is a stepwise oxidation reaction (i.e., from Fe to Fe2+ and further to Fe3+ ), while the corrosion of aluminum is a single-step oxidation reaction (i.e., Al–Al3+ ). Meanwhile, volume or density changes (expansion for most cases) are often accompanied by corrosion. This phenomenon gives rise to more metal surface exposure to moisture or air, and favors continuing oxidation. But few materials, such as aluminum

10

I-T. Liu et al.

and stainless steel, can form dense oxidation layers to stop further oxidation reactions. In the corrosion process, reduction/oxidation products may vary according to the redox reaction conditions, such as alloy composition, temperature, moisture, water-leachable ions, and pH value [27, 28]. Major factors are discussed below in the detail.

3.1 Environmental Factors 3.1.1

Temperature

Temperature plays an important role in the corrosion process because it affects the chemical reactions both thermodynamically and kinetically. From a kinetics perspective, an increase in temperature will increase the reaction rates of corrosion, including the diffusion of the ions and the corrosion products. There is a rule of thumb that the corrosion rate of a metal doubles for every 10 °C increase in temperature [28]. Theoretically, from a thermodynamics perspective, free energy (G) is the driving force for a reaction. Free energy is governed by enthalpy (H), entropy (S), and temperature (T ) as G = H − T S

(1)

For most reactions, entropy generation S is positive, and therefore free energy decreases with increasing temperature. In other words, high temperature leads to more negative free energy so that corrosion reaction is thermodynamically favorable and spontaneous at high temperatures. Ellingham diagrams are often adopted to determine the temperature dependence of the stability of metal oxides. An Ellingham diagram illustrates how the free energy changes with the temperature and pressure of oxygen [29]. The higher stability of the metallic oxide is shown at the lower position of the lines in the Ellingham diagram (i.e., low temperature and oxygen pressure). Ellingham diagram for common metal oxides is shown in Fig. 4 [29].

3.1.2

Moisture

Moisture can interact with metals through the following reaction: M(s) + H2 O(g) → MO(s) + H2(g)

(2)

If oxygen is present in the environment, hydrogen would be oxidized to water vapor and thus corrosion of metal keeps happening until oxygen or metal is consumed. Moreover, some metal oxides even form volatile products when reacting with water vapor, such as ferrous oxide and ferric oxide:

Corrosion Under Insulation for Hot Structural Components

11

Fig. 4 Ellingham diagram for several common metal oxides [29]

FeO(s) + H2 O(g) → Fe(OH)2(g)

(3)

2Fe2 O3(s) + 4H2 O(g) → 4Fe(OH)2(g) + O2(g)

(4)

These metal hydroxides evaporate and cannot form a protection layer for the interior metals. Furthermore, from Le Chatelier’s principle, formation of evaporative hydroxides in an open environment might quickly reduce the oxide’s thickness and deteriorate the corrosion.

12

3.1.3

I-T. Liu et al.

Ion Effect

The presence of ions can accelerate corrosion reactions. Particularly, chlorideinduced corrosion [30] has drawn lots of attention because chloride ions not only dissolve many metals (e.g., iron and chromium) but also break down the passive layer (e.g., Fe2 O3 or Fe3 O4 ) of steels. For rebar, chloride ions are adsorbed in the passive layer and react with iron to form chlorides and hydroxides through the following reactions [30]: Fe → Fe2+ + 2e−

(5)

Fe2+ + 2Cl− → FeCl2

(6)

FeCl2 + 2H2 O → Fe(OH)2 + 2H+ + 2Cl−

(7)

Because the chloride ion, as a catalyst, changes the reaction routes, the corrosion reaction would continue once the passive layer is destroyed.

3.1.4

pH Value

A Pourbaix diagram, or a potential-pH diagram, is useful for determining the stability of metals [31] because most of the oxidation reactions are affected by pH value. The Pourbaix diagram of Fe–H2 O system, for example, is shown in Fig. 5 [31]. The pH value is plotted against the redox potential concerning the standard hydrogen electrode calculated by the Nernst equation. In this diagram, the vertical line represents a pH-dependent reaction, while the horizontal line represents a potential-dependent reaction involving electron transfer. In addition, a Pourbaix diagram can be divided into three major regions, which represent three possible states of a metallic material: (1) immunity, (2) passivity, and (3) corrosion. In the immunity region, metals are immune from corrosion and thus are safe to use. In the passivity region, oxides or hydroxides tend to form on the surface of metals, protecting the metals from exposure to the environment. No corrosion will happen in this region. Nonetheless, in the corrosion region, a metal is thermodynamically favorable in transforming to its ionic or soluble species.

3.2 Other Factors Corrosion rate is strongly affected by temperature for both open and closed systems [20]. In general, the corrosion rate decreases at higher temperatures in an open system, but increases in a closed system (CUI) as shown in Fig. 6.

Corrosion Under Insulation for Hot Structural Components

13

Fig. 5 Pourbaix diagram for iron at 25 °C [31]

3.2.1

Insulation Materials

Insulation materials are used to retard the heat flow and thus reduce energy loss and consumption. In general, insulation materials can be divided into two categories: (1) fibers or blankets (e.g., fiberglass and mineral wool) and (2) cells (e.g., cellular glass, phenolic foam, and nitrile rubber). Once thermal insulation materials are adopted, the pipeline system will change from an open system to a closed system, and CUI becomes an inevitable issue. A small amount of water that goes inside the insulation system will cause severe corrosion. Things become worse when materials are prone to absorb water. Trapped water inside gaps can leach contaminants like chlorides and sulfides from thermal insulation materials. These ions accelerate and change the mechanism of corrosion. Even though thermal insulation materials are covered by aluminum cladding, moisture will not go inside the system in most circumstances. However, some human factors may be overlooked and incubate CUI.

14

I-T. Liu et al.

Fig. 6 Temperature dependence of corrosion rate of steel. Corrosion rates for closed system, open system, and CUI are shown in solid line, dashed line, and hollow circles, respectively. Courtesy NACE SP0198-Control of corrosion under thermal insulation and fireproofing materials-a systems approach, 2017 edition

3.2.2

Human Factors

Insulation materials are covered with aluminum cladding for structural and waterproof consideration. However, human factors caused by incorrect usage may increase the risk of CUI. Human trampling is common due to a lack of safety consciousness and discipline, which cause deformation and gaps in the aluminum cladding. Water from surroundings, such as rainfall and cooling towers, will be absorbed by insulation materials and cause CUI. Moreover, a mismatch for silicone sealants under certain environments may cause potential risks for aging. Practically, the edges and gaps of aluminum cladding are sealed with incorrect silicone sealants, which are prone to age and crack under UV exposure and highly humid conditions. Moisture penetrates the insulation materials through the cracks thereafter. Fortunately, the risk

Corrosion Under Insulation for Hot Structural Components

15

of CUI can be diminished by proper personnel training and regulations. Also, some non-destructive testing (NDT) methods can help with corrosion management.

3.3 On-Site Non-destructive Testing (NDT) Methods for CUI CUI is difficult, or even impossible, to manage by only visual inspections. At the same time, insulation removal for inspection is not feasible due to high costs (scaffolding and non-reusable insulation), time limit (annual shut down for maintenance), and huge manpower requirements. Therefore, NDT methods are beneficial for CUI management [32]. From a safety perspective, occupational safety, mechanical integrity, and process safety are three foundations of process safety management (PSM). Among them, mechanical integrity is often overlooked with lowest priority. As a result, CUI issues will only be aware until near-miss events or accidents occur. The ideas for NDT methods are to identify CUI from two aspects: (1) corrosion reaction. Corrosion is an endothermic reaction, which can be recognized by infrared (IR) thermography. (2) Wall thickness of structural components: corrosion usually leads to decreases in wall thickness, which can be recognized by pulsed eddy current (PEC) testing for instance. With these tools, CUI can be managed without insulation removal. Once the NDT methods are applied, resource configuration for maintenance and protection can be optimized. Some of the proven and generally accepted NDT methods are [33–38]. • • • • • •

IR thermography. Neutron backscatter. Guided wave UT. Profile radiography. Computed radiography (CR). PEC testing.

4 Concepts and Methods for CUI Protection CUI is quite complex and strongly depends on environmental conditions and the temperature profiles of structural components. Therefore, some guidelines and concepts of process safety management (PSM) are essential and referred to as recognized and generally accepted good engineering practices (RAGAGEPs). These practices are commonly used to reduce mistakes.

16

I-T. Liu et al.

4.1 Recognized and Generally Accepted Good Engineering Practices (RAGAGEPs) American Petroleum Institute (API) and Association for Materials Protection and Performance (AMPP) are the common RAGAGEPs addressing general problems of CUI cases. AMPP was created when the National Association of Corrosion Engineers (NACE) and Steel Structures Painting Council (SSPC) united in 2021 after more than 145 combined years of corrosion control and protective coatings. Guidelines for CUI and corrosion-related issues are listed below. Readers can check out the details by looking into the standard documents. • API 583, Corrosion Under Insulation and Fireproofing. • API 571, Damage Mechanism Affecting Fixed Equipment in the Refining Industry. • API 570, Piping Inspection Code: In-service Inspection, Rating, Repair, Alternation, of Piping System. • API RP 580, Risk-Based Inspection. • API RP 581, Risk-Based Inspection Technology. • API 585, Pressure Equipment Integrity Incident Investigation. • NACE SP0198, Control of Corrosion Under Thermal Insulation and Fireproofing Materials-A System Approach.

4.2 Modified Thermal Insulation Structures Practically, fiberglass, mineral wool, and calcium silicate are commonly used as insulation materials. However, these materials are prone to uptake and trap moisture inside metal/insulation gaps, even in the circumstances that the working temperature of components is higher than the boiling point of water. The absorbed water will further leach corrosive ions (e.g., chlorides) from insulation materials. Waterleachable ions facilitated corrosion thereafter. Also, the thermal conductivity of thermal insulation materials significantly decreases after water uptake (70% increase in thermal conductivity with 4% water uptake by volume). Therefore, water removal is the most effective way to prevent hot structural components from CUI. Nowadays, improvements in thermal insulation materials are made to diminish water absorption amount and residence time in closed pipeline/insulation systems.

4.2.1

Insulation Cladding

Aerogel Blankets Aerogels are naturally mesoporous (porosity > 90%) materials and have high specific surface area (S BET = 600–1000 m2 /g), low bulk density (ρ = 0.0030–0.35 g/cm3 ),

Corrosion Under Insulation for Hot Structural Components

17

and low thermal conductivity (k = 0.015–0.14 W/m K) [39]. Aerogels are made from precursors such as water glass or alkylsilane via the sol–gel method. Precursors hydrolyze in acid conditions (e.g., HCl) to form sol, followed by being base-catalyzed (e.g., NH4 OH) to form a cross-linked network of alcogels thereafter. The solvent in alcogels can be removed by ambient drying, freeze drying, or supercritical drying process. Aerogel monoliths are obtained after the processes mentioned above [40]. However, aerogel monoliths are brittle and limited in a few specific engineering applications [41]. Thus, aerogels are commonly incorporated with blankets to enhance their flexibility. In the manufacturing process, blankets are immersed completely in precursor solutions, and the gelling reaction is triggered after the immersion process. Then, blankets are immersed in a solvent (e.g., ethanol) for aging and a drying process is followed to remove the residue solvents. Aerogel blankets exhibit low thermal conductivity (0.013–0.014 W/m K) when compared with conventional thermal insulation material (rock wool: 0.033–0.045 W/m K, calcium silicate: 0.045–0.065 W/ m K, and glass wool: 0.03–0.045 W/m K) [42]. Therefore, a thinner insulation design is possible with the same level of thermal management. Also, aerogel blankets have low water uptake under high temperature (>300 °C) and thus can be used with long-term stability. Nonetheless, the high price of aerogel blankets leads to practical concerns for their applications.

Waterproof Enhancement of Insulation Materials To diminish water uptake, insulations can be modified by water repellent agents, which reduces the risk of CUI. Water repellent agents can be classified into three types: (1) mineral oil-based additives, (2) silicone oil-based additives, and (3) inorganic resin additives. For mineral oil-based additives, the agent starts to decompose at 150 °C and the degradation products can be removed easily by water. Therefore, long-term usage is not recommended. As a result, silicone oil-based additives are developed to enhance thermal stability. The silicone oil-based insulation materials have excellent waterproof performances below 250 °C. However, for conditions of higher temperature, silicone oil undergoes phase separation in the insulation materials. This phenomenon leads to local defects, such as pinholes or channels on insulations, resulting in higher water uptake. Therefore, silicone oil-based additives are not favorable in insulation materials for temperature higher than 250 °C. Last but not least, inorganic resin additives own the highest thermal stability (~250 °C) and are immobile in insulations under high temperature.

Non-contact Insulation System To reduce the residence time of water, non-contact insulations are designed. The idea is to achieve fast moisture/water evaporation through the separation of the insulation and hot components by creating cavities. The non-contact system is a combination

18

I-T. Liu et al.

Fig. 7 Non-contact (or distance-insulation) insulation system [21]

of polytetrafluoroethylene (PTFE) spacers and perforated aluminum plates as shown in Fig. 7 [21]. With this design, the initiation of CUI and corrosion rate can be controlled.

4.2.2

Thermal Insulation Coatings

Although modified insulation cladding can reduce the risk of CUI issues, the existing gaps between insulation materials and structural components still allow water ingress to a certain degree. By using insulation coating, these gaps no longer exist and water uptake can be reduced significantly. With proper material design, thermal insulation coatings can stop moisture from reaching structural metal components. Insulation coatings are formulated by pigments, binders, and additives for dispersing and rheological consideration. Pigments of low thermal conductivity, such as (hollow) ceramic pigment and silica aerogel powder or granulates, are commonly used. Meanwhile, UV resistance and thermal shock resistance are important concerns for outdoor applications. Acrylic (silicone-acrylic and acrylic urethane) resin and silicate are suitable polymeric binding materials. As a rule of thumb, acrylic insulation coating should be used for conditions below 170 °C, while silicate should be used below 205 °C [43]. Practically, the coefficient of thermal expansion (CTE) is a crucial parameter for thermal shock resistance. Dry film thickness (DFT) per coat is a critical consideration for cost. Silicate is limited for its low DFT per coat. Among all commercial products, waterborne acrylic resin with silica aerogel is the most commonly used. Due to the high thermal conductivity of ceramic pigments, high pigment volume concentration (PVC) is usually formulated for better thermal insulation property. However, ceramic pigment coating with high PVC is limited for its poor thermal shock resistance, which often leads to coating cracks.

Corrosion Under Insulation for Hot Structural Components

19

Because of the water impermeability (or relatively low permeability), thermal insulation coatings on pipes are feasible for both hot and cold (anti-sweating) conditions. Compared with conventional insulation materials, insulation coating only needs one-step application. But the coating thickness is constrained to approximately 0.5–20 mm (20–790 mil). Besides the simple one-step process, insulation coatings can also be combined with an anti-corrosive primer to reach a longer lifetime [20].

4.3 Anti-CUI Coatings Insulation coatings are limited by DFT per coat and are costly due to high pigment fractions. From an economic perspective, the return on investment (ROI) of insulation coating expenditure against energy saving is debatable in different countries and regions. Therefore, the alternative solution for CUI protection is applying anti-CUI coatings inside insulation claddings. Coatings for this application must be highly thermal resistant. Therefore, epoxy resin (e.g., phenolic and novolac) and an inorganic copolymer or inert multi-polymeric matrix (IMPM) are suitable materials. Because solar radiation is blocked by the outside insulation claddings, UV resistance is not a critical issue for coatings of this design. Pigments such as aluminum powder, micaceous iron oxide (MIO), and montmorillonite are commonly formulated with the aforementioned polymeric resins to improve corrosion resistance. Aluminum powder can provide cathodic protection, while layered MIO and montmorillonite can provide tortuous paths, which can diminish ion diffusivity and increase the service life of coated metal components. In general, phenolic and novolac epoxy resin coating (2K) should be used for conditions below 170 and 205 °C, respectively, while inorganic copolymer and IMPM (1K) can reach up to 400–650 °C. However, inorganic copolymer and IMPM are not the ones for all solutions even though the price is comparable to novolac epoxy. For high-temperature corrosion protection, water and oxygen solubility dominate the corrosion rate below 200 °C. Notice should be taken that inorganic copolymer or IMPM is not recommended for conditions below 200 °C due to the higher moisture permeability than that of phenolic and novolac epoxy. As a rule of thumb, phenolic and novolac epoxies are preferred for operating temperatures below 205 °C, and inorganic copolymer or IMPM is preferred above 205 °C. Last but not least, from a material perspective, chloride content in insulation materials is also crucial for CUI protection. The chloride extraction method is guided by ASTM C871 [44] and the acceptable level is guided by ASTM C795 [45]. Generally, chloride extraction from insulation materials should be lower than 10 ppm. In this section, several methods are mentioned for either trying to reduce the water uptake or dredging the moisture. Conventional thermal insulation systems are modified to enhance the water-repelling property and reduce the water absorption rate (I.). Others are dedicated to creating channels or spacers in insulations for water removal convenience (II.). For coatings, thermal insulation coatings can replace insulation materials for conditions below 170°C (III.). For higher temperature, anti-CUI

20

I-T. Liu et al.

Fig. 8 Strategies for CUI protection

coating before insulation materials cladding is more applicable. High thermal resistance and low moisture permeability of anti-CUI coating can prevent moisture from reaching components (IV). Strategies for CUI protection are shown in Fig. 8.

5 Materials of Anti-CUI Coatings Corrosion at high-temperature conditions involves the participation of moisture. Therefore, covering a moisture barrier over metal components can greatly reduce the risks of corrosion. To serve as diffusion barriers for moisture and corrosive ions, coatings must possess certain barrier properties, such as high thermal shock resistance, proper CTE, high-transition glass temperature (T g ), high decomposition temperature, etc. For instance, crosslinking materials are commonly used for high T g and high decomposition temperature consideration. However, if the crosslinking density is too high, thermal shock resistance and CTE would be too low, resulting in cracks after a short operating period. Therefore, materials suitable for CUI protection are very limited due to the trade-off between the contradicting properties mentioned above. Nonetheless, materials for anti-CUI coatings can be customized according to operation requirements. The following materials have acceptable properties and affordable costs for on-site protection and maintenance.

Corrosion Under Insulation for Hot Structural Components

21

5.1 Polymer Coatings 5.1.1

Epoxy

Conventional epoxies pigmented with aluminum spheres or flakes have been used for decades. Diglycidyl ether of bisphenol-A (DGEBA) and diglycidyl ether of bisphenol F (DGEBF) are commonly used epoxy compounds. However, regular epoxy materials can only work for operating temperatures around 120–150 °C. For higher operation temperatures, either phenolic or novolac epoxy is adopted.

5.1.2

Phenolic/Novolac Epoxy

Phenolic/novolac epoxies are better in thermal stability than conventional epoxies. This property can be attributed to the benzene structure in the crosslinking network. The tailored phenolic/novolac epoxy coatings can reach a high maximum operating temperature up to 230 °C [46]. Aside from epoxies, hardeners also play important roles in thermal resistance. For reaction consideration, polyamines, anhydrides, and polyamides are most commonly used [47]. Among them, polyamines are widely used for open time/pot-life of 1–2 h, which is feasible for on-site operation at room temperature (25 °C). The functionality of hardeners can also affect coating properties significantly by changing the crosslinking density of polymer networks. For example, polymer networks with high crosslinking density show better chemical resistance and lower flexibility, and vice versa. However, thick coatings usually show unreleased stress during curing, and thus coating cracks are commonly observed at the corner of components during temperature cycling operations. Practically, total DFT is regularly controlled below 250 μm.

5.1.3

Silicone/Silicate

Silicone/silicate coatings are prepared when inorganic silicone pigments are added to a coating. The working temperature of silicone/silicate can reach up to 400 °C. However, they are quite expansive and vulnerable to acids, alkalis, and warm moisture conditions, resulting in a short lifetime of corrosion protection. Besides, cracks are commonly observed if silicone/silicate-based materials are designed for high DFT operation. Once cracks appear, the corrosion resistance declines significantly due to moisture/water and ion penetration. Therefore, silicone/silicate coatings are generally applied with DFT of 25 μm.

22

5.1.4

I-T. Liu et al.

Organic–Inorganic Hybrid

This type of coating was first introduced in the 1990s for higher thermal stability aspirations. The modified organic–inorganic hybrid CUI coatings are widely used in the late 1990s and are dominated by two types: • TMIC, titanium-modified inorganic copolymer. • IMPM, inert multi-polymeric matrix. The higher bond energy of Si–O (454.2 kJ/mol) than C–C (355.6 kJ/mol) leads to better thermal stability [48]. Meanwhile, the materials can also be used for cryogenic (e.g., −196 °C) conditions. From a cost perspective, commercially available antiCUI coatings of organic–inorganic hybrid are close to or slightly higher than coatings of phenolic/novolac epoxy. On the other hand, a mismatch between organic–inorganic hybrid can easily lead to microcracks in these coating materials. Thus, the hybrid materials might have lower performances than original expectations even at temperatures below 200 °C. At this temperature range, moisture permeability (solubility × diffusivity) dominates the corrosion resistance, while the thermal stability of resin dominates the corrosion resistance for temperature above 200 °C. Since organic–inorganic hybrids generally have relatively higher moisture permeability than epoxies, it is highly recommended that organic–inorganic hybrid materials should not be used in the moisture permeability-dominated CUI preventions.

5.2 Metallic Pigment Coatings 5.2.1

Zinc Coating

Zinc (rich) coatings are widely used for atmospheric corrosion protection due to their higher oxidation potential than carbon steel. Nowadays, off-shore (e.g., wind turbines) and photovoltaic brackets (e.g., agro-photovoltaics) protection are drawing people’s attention due to the booming demand for green/renewable energy. However, zinc-pigmented coatings are seldom or even prohibited in anti-CUI coatings, because zinc and carbon steel undergo polarity inversion at about 60 °C [49], and thus zinc will no longer protect carbon steel from corrosion beyond this temperature. What’s worse, zinc will corrode carbon steel and shorten the lifetime of metallic components instead.

5.2.2

Thermal Sprayed Aluminum (TSA)

TSA is a protection method that applied molten aluminum on metallic components [50]. TSA has a maximum operating temperature of 660 °C (melting point of aluminum). A dense protective layer of Al2 O3 is formed on the surface of the

Corrosion Under Insulation for Hot Structural Components

23

aluminum and can slow down or even stop the corrosion reaction. Notice should be taken that, in general, TSA has a porosity of 5–15 %, and sealer paints are often applied thereafter. TSA possesses a long lifetime that can reach up to 20 years without any maintenance. Nonetheless, TSA might accompany fire and spark during operation, and is prohibited in most on-site applications. As a result, TSA is only applicable in certain special circumstances.

6 Standardization Laboratory Test for Anti-CUI Coatings Coating formulations designed for CUI protection need to be qualified by standard lab tests before being applied to field operations. Standard lab tests can give clear insights into coating properties and can be classified into two sections: (1) instrumental analysis tests, such as thermal, mechanical, and chemical resistance; (2) corrosion resistance under high temperature, such as multi-phase CUI simulation test. Several test methods are summarized in Table 2. Instrumental analysis tests are well established both in test methodology and equipment. These tests can tell preliminary properties but are not able to give clear insights into CUI protection. As a result, multi-phase CUI simulation tests are proposed to simulate the periodic temperature and moisture changes in regular Table 2 Test methods for anti-CUI coatings Characteristics

Standardization

Descriptions

Dry heat resistance

ASTM D2485B

• Test panels are exposed in muffle furnace at an agreed temperature for 24 h • Panels are allowed to cool under ambient or water to room temperature • If no deterioration is observed, the panels are exposed in a natural salt spray (ASTM B117) for 24 h

ASTM E2402

• TGA

Thermal shock resistance

ISO 19277

• Test panels are exposed in muffle furnace at agreed temperature and quenched in water – 150 °C for phenolic and novolac epoxy – 400 °C for inorganic copolymer and IMPM • Repeat test cycle for 20 times and ranking thermal shock resistance by visual inspection (ISO 4628)

Corrosion resistance

ASTM G189-07 CUI simulation cell • Monitored by electrochemical current flow and weight loss ISO 19277

Multi-phase CUI cyclic corrosion test

ISO 19277

Cyclic insulated pipe test (CIPT)

24

I-T. Liu et al.

on-site operations. Unfortunately, no single equipment or instruments are commercially available. Nonetheless, ASTM G189-07(2021) [51] and ISO 19277:2018 [52] standards can be general guidance for simulation test setup.

6.1 ASTM G189-07(2021) ASTM G189-07(2021) can simulate moisture effect on CUI potential. The apparatus designed in ASTM G189-07(2021) is composed of two parts: (1) CUI simulation cell and (2) heat oil circulation as shown in Fig. 9a. For the CUI simulation cell, the coating is applied on the outer surface of metallic rings, which are electrically isolated by PTFE compartments with each other as shown in Fig. 9b labeled by the yellow arrows [53]. Metallic rings are covered by insulations, which have an inlet and outlet for 0.01 wt% (100 ppm) NaCl solution (or acidified by H2 SO4 –pH 6 if needed) on top and bottom, respectively, as shown in Fig. 9c [53]. Corrosive liquid can be controlled by a peristaltic pump for facilitated corrosion tests. Simulation conditions are also suggested in ASTM G189-07(2021) as shown in Fig. 9 d. For most situations, the testing temperature is set at 175 °C during the test; however, these conditions are not mandatory. Temperature and NaCl solution flow rate can both be specified by the user’s needs. The CUI resistance of the coatings is monitored by electrochemical current flow and weight loss of metallic rings. The corrosion rate can be calculated by the following equation [51]: Corrosion Rate = (K × M)/( A × T × D)

(8)

where K is a constant (3.45 × 106 mil/year; 8.76 × 104 mm/year), M is the mass loss ([=] g) calculated by pre-exposure mass (M i ) minus the post-exposure (after cleaning) mass (M f1 ) for the ring specimens, A is the exposed area ([=] cm2 ), T is the time of exposure ([=] h), and D is the density of ring specimens ([=] g/cm3 ). Corrosion rate change with specified conditions is shown in Fig. 9e. Because ASTM G189-07(2021) does not consider the effect of thermal stress and thermal shock resistance on CUI, these tests usually need to be combined with other instrumental analyses to evaluate the possibility of on-site CUI.

6.2 ISO 19277:2018 ISO 19277:2018 provides two different methods for high-temperature CUI simulation: (1) multi-phase CUI cyclic corrosion test and (2) vertical pipe test.

Corrosion Under Insulation for Hot Structural Components

25

Fig. 9 a CUI-cell design, b, c cell without insulations showing spacers, samples, and dam [53], d suggested simulation conditions, e corrosion rate for metallic rings protected by coatings. Courtesy ASTM G189-07(2021)-Standard Guide for Laboratory Simulation of Corrosion Under Insulation, 2021 edition

6.2.1

Multi-phase CUI Cyclic Corrosion Test

This testing cycle is composed of three stages: (1) hot–dry, (2) hot and wet, and (3) ambient environment, which corresponds to the conditions of dry heat, wet heat, thermal shock, intermittent boiling water, steam interface, and shutdown time. The test chamber is made up of 316 stainless steel and filled with 5 wt% NaCl solution and a heating conduit in the center of the chamber. Anti-CUI coatings are applied on the outer surface of metallic square rings, which is similar to ASTM G189-07(2021). The coated rings are scribed with an X-cut on all four sides and worn in series on the heating conduit, in which hot oil is circulated, and all coating rings are heated by the conduits as shown in Fig. 10a [43]. Test rings undergo 15 cycles of 4 h of hot–wet and 4 hours of hot–dry stages, followed by 48 hours of ambient cooling, with the entire cycle repeated 6 times (6 weeks). Temperature for hot stages can be set as 150 and 175 °C for CUI-2 and CUI-3 classification, respectively. The test procedures are shown in Fig. 10b [52]. Coatings at the interface of liquid and gas phases can illustrate CUI resistance, because of immersion in NaCl solution and the hot–dry condition. Coatings before and after 6 weeks of testing are shown in Fig. 10c [43].

26

I-T. Liu et al.

Fig. 10 Equipment design, b test procedures defined in ISO 19277:2018, c coatings before and after 6 weeks of testing (Courtesy for a and c: CUI, practical approach from a coating perspective, The 10th Tank & Refinery Conference, PPG, 2017. Courtesy for b: ISO 19277:2018-Petroleum, Petrochemical and Natural Gas Industries-Qualification Testing and Acceptance Criteria for Protective Coating Systems Under Insulation, 2018)

6.2.2

Vertical Pipe Test

The vertical pipe test is designed to test the resistance of anti-CUI coatings for simulated CUI conditions. The process includes temperature cycling for high temperatures and periods of shutdown. Because the hotplate is placed at the bottom of the pipe, the corrosion resistance of anti-CUI coatings is non-uniform along the specimen due to the temperature gradient. Meanwhile, 1 wt% NaCl solution uptake by insulation materials is also considered. A schematic diagram of the vertical pipe test is shown in Fig. 11. At the beginning of the test, 1 liter of 1 wt% NaCl solution is poured into the insulated pipe from the top. The pipe is placed onto a hotplate at 500 °C (or specified temperature) for 8 h. After that, the pipe is transferred to another vessel. Fresh 1 wt% NaCl solution is poured into the pipe and kept cooling under ambient conditions for another 16 h. The testing cycle is repeated 5 days per week for 6 weeks. After testing, the pipe is cut into 11 sections from the bottom 50 mm and rated by the guidance

Corrosion Under Insulation for Hot Structural Components

27

Fig. 11 Sectional view of vertical pipe test

of ISO 4628-2, 4628-3, 4628-4, and 4628-5. The limitation is that systematic error may exist due to the variance of the solution composition along the pipe.

7 Summary Corrosion under insulation (CUI) is a corrosion reaction in closed system and draws wide attention after devastating accidents in the past decades. Three case studies are discussed at the beginning of this chapter. Fundamental concepts of corrosion are reviewed to help readers understand the effects of environmental and human factors on CUI. Even though CUI is almost impossible to be managed by visual inspection, on-site non-destructive testing (NDT) methods can give clear clues about which components are of high risk under claddings. Moreover, guidance of recognized and generally accepted good engineering practices (RAGAGEPs) and process safety management (PSM) is highly recommended. In insulation system design, modification of insulation materials can be dedicated to reducing the risks of CUI. Also, applying anti-CUI coating before insulation cladding is another applicable and affordable method. As a rule of thumb, resin systems of anti-CUI coatings are determined by the operating temperature of hot structural components. Some coatings with high thermal resistance, such as IMPM, may not be recommended in low temperature (i.e., 3 >3 3 >3 3 >3

– –

Tertiary SH 621/445 steam inlet (Alloy 625)

1.82

3

YSZ/625 YSZ/ NiCrSiB

>3 >3

>1.5 >1.5

5 Decline Mechanisms and Design of Coatings 5.1 Formation and Breakdown of Protective Oxides Layer The gas temperature, in particular, the temperature gradient T (the difference between the gas temperature and the metal temperature), is thought to be the primary cause of the condensation and depositing of the corrosive vapour components in the gas [47]. The deposits with high T have a high chloride content and are more likely to produce low melting deposits than other deposits. Furthermore, it is well known that the amounts of Cl, SO4 , alkalis and heavy metals affect the deposits’ corrosiveness as well as their physical properties, such as their permeability and the volume of molten

Development of Coating-Resistant Materials at High Temperatures …

45

phase [40]. It is believed that corrosive gas components must penetrate the deposits and oxidising elements like oxygen must be present in order to maintain the corrosion processes. Additionally, in actual plants, the use of soot blowers and changing gas temperatures result in significant thermal cycling that affects the surface of the tubes. This type of corrosion is referred to as “molten salt induced corrosion” [65] because the gaseous corrosion process becomes active as the amount of deposits increases and a portion of the deposit’s melts. If the protective oxide layer breaks down, corrosive material will get into the base material and scale lamellae will form as a result of the partial gaseous state fluctuating. CRMs must have the capacity to form and self-heal a robust protective oxide layer, which is comparable to a ceramic coating film, when used in harsh, corrosive environments. Based on the structure and properties of the corrosion products that disperse as chlorides, sulphates and oxides from the flue gas side to the corrosion interface, it is believed that steady-state corrosion is caused by high-temperature gaseous reactions, specifically chlorination/suffixation/oxidation. The effects of critical factors like temperature gradient, temperature fluctuation and the amount of molten ash on corrosion rates were quantitatively examined in coating experiments [65, 66].

5.2 Erosion and Erosion/Corrosion-Resistant Materials and Coatings As the primary systems for the combustion of mixed, inhomogeneous solid fuels like waste and biomass, FBC boilers are gaining popularity. The bubbling fluidized bed combustor (BFBC) and the circulating fluidized bed combustor are two examples of commonly used furnace types. Because solid fuels combine with sand flow, which is typically maintained in the furnace at a temperature of 800–900 °C, erosion or E-C damages on WWTs, SHTs and heat exchanger tubes placed in the furnace have been noted. These damages are impacted by the movement of sand and ash particles. The combined effects of mechanical erosion and corrosion almost always result in damage rates that exceed a few millimetres per month. (1) Damage to protective oxide layers, such as that brought on by soot blower assault on SHTs and low-velocity solid particle erosion on furnace tubes, speeds up the corrosion process. It is essential to increase materials’ corrosion resistance and to fortify protective oxide coatings in order to prevent damage in this circumstance. (2) Material surfaces can be eroded or abraded mechanically. The speed of degradation is controlled by this mechanical fracture at the surface. This kind of damage is frequently influenced by high-velocity combustion gas flow, which moves at few 10–100 m/s and contains solid sand and ash particles. (3) The scenario in the middle of (a) and (b) is mixing of corrosion and erosion, and it is thought that flue gas moving at just a few tens of metres per second or less has an impact on it. It is assumed that this type of accelerated corrosion causes a lot of tube damage in actual boilers.

46

A. Kumari et al.

Mechanical erosion is thought to be severe at particle speeds greater than a few m/s; however, damage processes switch to E-C at relatively low particle speeds and severely corrosive conditions [65, 66]. When selecting the applied coatings for actual FBC boilers, field tests are frequently the most reliable method of estimating lifespan. As an illustration, various hard CRC materials, as seen below, have been used for a variety of applications, most notably FBC boilers. (a) Weld Overlays: High Cr martensitic stainless steels, hard facing materials. (b) Laser Claddings: WC-Co, WC-NiCr, Cr carbide-NiCr, WCr carbide–NiCr. (c) Thermal Sprays: WC-NiCr, WC/Cr carbide–NiCr, WC-NiCrB, NiCrSiB, WC/ Cr carbide–Ni–Fe, etc. (d) Ceramic Linings: Al2 O3 -rich, SiC-rich refractories and fine ceramics. The most important factor (a) is weldability, and by utilising current cored wire and nano-powder technologies, various types of ceramic materials may be used in (b) and (c). For achieving excellent coating qualities, it’s important to consider the powder and wire design in addition to the coating process. Calculating and assessing the damage to FBC boilers’ extent is challenging. As a result, the coatings were frequently selected while taking availability, cost and performance into account based on the outcomes of field tests. Furthermore, E-C phenomena and damage rates are challenging to realise in condensed laboratory tests because the various contributions of corrosion and erosion are unknown. The creation of testing and assessment technologies is considered to be one of the most crucial issues for upcoming advancements.

5.3 Durability of Alloy and Ceramic Spray Coatings The ways that spray coating layers that have spent a lot of time in corrosive environments like boilers deteriorate. Corrosive gases like HCl and Cl2 penetrating the coating/base material interaction lead to the degradation of the covering layer and corrosion of the basic material. The adhesive strength is subsequently decreased, the coating layer “swells” or “cracks” and eventually the peel comes off (Fig. 3). Durability is governed by material factors such as open porosity, CRC corrosion rate, base material bonding strength, thermal expansion coefficient and residual stress. The physical properties of the coating are significantly influenced by the spraying conditions. Recently, using tiny electric resistance methods, a quantitative lifespan evaluation approach for boilers based on these degradation mechanisms was developed and implemented [56].

Development of Coating-Resistant Materials at High Temperatures …

47

Fig. 3 Mechanisms of coating layer deterioration from thermal spraying in an extremely corrosive environment (Redrawn) [9]

6 Conclusion In recent years, a slew of new requirements, such as pollution control, improved power generation efficiency, material recycling and so forth, have been placed on WTE plants. A more complex and varied HTC environment for the plants is the result of different combustion techniques and plant system implementations. It is believed that a key focus in the creation and application of corrosion prevention technologies is the use of the proper material in the right place at an affordable price. The performance and durability of WTE plants have increased thanks to the development of corrosion-preventing CRM and CRC technologies. The creation of software to successfully apply these corrosion prevention techniques to WTE boilers is one of the future research topics. These difficulties must be overcome by the engineers and researchers developing CRMs and CRCs. Recent performance standards for biomass and WTE facilities include those for material recycling, high electric power generating efficiency and pollution suppression. Due to the use of various combustion methods and plant systems, the hightemperature corrosive environment of the plants is growing and diversifying. The primary fundamental mechanisms that underlie high-temperature corrosion and E-C are thought to be constant across all plants. CRMs and CRCs are believed to have been created and implemented with the objective of placing the appropriate material in the appropriate location at a reasonable total cost. High-temperature parts now perform and last longer thanks to improvements in coating, CRM and CRC technologies. To achieve long lifetime, it is necessary for material information and plant design/operation to work together. Future research on corrosion and erosion in harsh high-temperature environments is expected to cover a wide range of topics, and engineers and scientists are expected to rise to the challenge of using CRMs and CRCs to find a solution.

48

A. Kumari et al.

Acknowledgements It is my proud privilege and special appreciation towards Department of Chemistry, Vigyan Mandir, Banasthali Vidyapith, Rajasthan. We are also thankful to reviewers for their most valuable suggestions, guidance and constructive criticism that made it possible for the work to get published. Conflict of Interest No conflict of interest. Research Funding No funding available.

References 1. Kawahara, Y.: Recent trends and future subjects on high temperature corrosion prevention technologies in high efficiency waste-to-energy plants. Zairyo-to-kankyo 54(5), 183–94 (2005) 2. Kaihara, Y., Kawahara, Y.: Recent trend of corrosion resistant tube materials and improvements of corrosion environments in WTE plants. In: CORROSION. OnePetro (2001) 3. Kawahara, Y.: Japanese. J. High Temp. Soc. Jpn. 28(5), 202–212 (2002) 4. Kawahara, Y., Nakamura, M., Tsuboi, H., Yukawa, K.I.: Evaluation of new corrosion resistant superheater tubings in high efficiency waste-to-energy plants. In: Corrosion 97. OnePetro (1997) 5. Otsuka, N., Fukuda, Y., Kawahara, Y., Hosoda, T.: Laboratory corrosion tests for simulating fireside wastage of superheater materials in waste incinerators. Mater. Corros. 51(4), 236–241 (2000) 6. Kawahara, Y., Kira, M.: Corrosion prevention of waterwall tube by field metal spraying in municipal waste incineration plants. Corrosion 53(3), 241–251 (1997) 7. Fukuda, Y., Hitachi, K.K.B., Kawahara, K., Hosoda, T.: Application of high velocity flame sprayings for the superheater tubes in waste incinerators. In: CORROSION 2000. OnePetro (2000) 8. Lai, G.Y.: Corrosion mechanisms and alloy performance in waste-to-energy boiler combustion environments. In: North American Waste-to-Energy Conference, vol. 3736, pp. 91–98 (2004) 9. Kawahara, Y.: Application of high temperature corrosion-resistant materials and coatings under severe corrosive environment in waste-to-energy boilers. J. Therm. Spray Technol. 16(2), 202– 213 (2007) 10. Kawahara, Y.: Handbook of advanced ceramics: Chapter 10.3. In: Application of HighTemperature Corrosion-Resistant Ceramics and Coatings under Aggressive Corrosion Environment in Waste-To-Energy Boilers. Elsevier Inc. (2013) 11. Errington, E., Guo, M., Heng, J.Y.: Environmental impacts of rice husk-derived silica under uncertainty: is “Bio” better?. In: Computer Aided Chemical Engineering, vol. 51, pp. 1615– 1620. Elsevier (2022) 12. Rademakers, P.F.: Materials for advanced power engineering. In: Proceedings of the 6th Liege Conference Part II 1998, vol. 751 13. Kawahara, Y., Nakagawa, Y., Sakurada, T., Kamakura, H., Kira, M., Imaizumi, Y.: Life evaluation of ZrO2 /Ni base alloy plasma jet coating systems in high efficiency WTE boiler superheaters. In: CORROSION. OnePetro (2004) 14. Ali, O., Ahmed, R., Faisal, N.H., Al-Anazi, N.M., Elakwah, Y.O., Goosen, M.F.: Nanoindentation evaluation of suspension thermal sprayed nanocomposite WC-Co coatings. Key Eng. Mater. 16(735), 225–229 (2017) 15. Kawahara, Y., Li, X., Nakagawa, Y., Imaizumi, H., Katoh, T., Nakajima, H.: Laboratory corrosion tests of new Weldoverlay materials in simulated environment of high efficiency WTE boilers. In: Proceedings of 48th Conference of JSCE Materials and Environments, C-308, p. 431 (2001)

Development of Coating-Resistant Materials at High Temperatures …

49

16. Kawahara, Y., Orita, N., Takahashi, K., Nakagawa, Y.: Demonstration test of new corrosionresistant boiler tube materials in high efficiency waste incineration plant. Tetsu-to-Hagane 87(8), 24 (2001) 17. Ulan kyzy, S., Völkl, R., Munz, O., Fischer, T., Welzenbach, S., Glatzel, U.: Thermo-physical properties of Hastelloy X and Haynes 214 close to the melting range. Mater. Sci. Technol. 36(10), 1012–1019 (2020) 18. Brennan, M.S., Gassmann, R.C.: Corrosion/2000, Paper No. 235 (Orlando, FL), NACE (2000) 19. Takeuchi, Y., Kawahara, Y., Hosoda, T.: Application of composite tubes plasma-weld-overlayed with Ni–Cr–Mo Alloy for Superheater in Waste Incinerators, Corrosion/2000, Paper No. 261 (Orlando, FL), NACE (2000) 20. AB Sandvik. Steel Technical Report 21. A Hosseini, V., Hurtig, K., Eyzop, D., Östberg, A., Janiak, P., Karlsson, L.: Ferrite content measurement in super duplex stainless steel welds. Weld. World 63(2), 551–563 (2019) 22. Yokono, M., Matsumoto, A., Noguchi, M., Yakuwa, H., Miyasaka, M., Miyoshi, K., Kosaka, K., Fukuda, Y.: Corrosion/99, Paper No. 87 (San Antonio, TX), NACE (1999) 23. Ishizuka, T., Mimura, H., Takahashi, T., Kurita, M., Hirayama, N., Mori, K.: Proceedings of High Temperature Corrosion and Protection/2000 (Lusutsu, Japan) (2000) 24. Eklund, J.: High temperature corrosion of FeCrAl alloys in biomass-and waste-fired boilers-the influence of alloying elements in prediction and mitigation of corrosion in harsh environments. Doctoral dissertation, Chalmers Tekniska Hogskola (Sweden) 25. Smith, G.D., Lipscomb, W.G.: Corrosion/89, Paper No. 201 (New Orleans, LA), NACE (1989) 26. Haggblom, E., Nylöf, L.: Materials for Advanced Power Engineering, Part II, D. Coutsouradis et al. Ed. 27. Kawahara, Y., Sasaki, K., Nakagawa, Y.: Development and application of high Cr-high Si–Fe– Ni alloys to high efficiency waste-to-energy boilers. In: Materials Science Forum, vol. 522, pp. 513–522. Trans Tech Publications Ltd. (2006) 28. Antony, C.M., Lai, G.Y., Tackett, J.W., Bickel, E.J.: Pressure Vessels Pipe Div., 262. In: ASME, vol. 57 (1993) 29. Yamamoto, S., Natori, A., Yamadera, Y., Otsuka, N., Kubo, T., Ogawa, K.: KaryokuGensiryoku-Hatsuden 47(7), 6 (1996) 30. Li, H., Liu, H., Bai, M., Zhang, X., Chi, H., Chen, T., Yu, Y., Yao, H.: Insight into the corrosion resistance of Mo-added NiCrBSi coating in simulated waste incineration environment. Corros. Sci. 15(216), 111085 (2023) 31. Brill, U., Klöwer, J., Maasen, E., Richter, H., Schwend, W., Venkateswarlu, J.: Corrosion, vol. 53, p 1585 (1994) 32. Matsui, T., Wakita, S., Takizawa, H., Kawahara, K., Hosoda, T.: Development of Ni–Cr–Mo alloy for the superheater tube applications. In: CORROSION 2000. OnePetro (2000) 33. Kawase, M., Ido, A., Morinaga, M.: Development of SiO2/TiO2/Al2O3-based/TiO2 coating for preventing sulfide corrosion in thermal power plant boilers. Appl. Therm. Eng. 5(153), 242–249 (2019) 34. Okada, M., Toyama, K., Ichihasgi, H.: Technical Report of Sumitomo Metal Industries. Ltd. 41, 189 (1989) 35. Shiyo, A., Isomoto, T., Yoshiba, M., Hirayama, N., Urabe, T., Nagashima, K.: Proceedings of the 10th Conference of the Japan Society of Waste Management Experts, C5–3, p. 749 (1999) 36. Shiyo, A., Isomoto, T., Toyama, K., Urabe, T., Yoshiba, M.: J. Jpn. Inst. Metals 66(6), 554 (2002) 37. Ejaz, M.: Metal dusting of laser-treated alloy 800H. The University of Manchester, United Kingdom (2009) 38. Miller, P.D., Kravse, H.H., Vaughan, D.A., Boyd, W.K.: The mechanism in high temperature corrosion in municipal incinerators. Corrosion 28(7), 274–282 (1972) 39. Kawahara, Y., Kira, M.: Effect of physical properties of molten deposits on high temperature corrosion of alloys in waste incineration environment. Zairyo-to-Kankyo 46(1), 8–15 (1997) 40. Kawahara, Y.: An overview on corrosion-resistant coating technologies in biomass/waste-toenergy plants in recent decades. Coatings 6(3), 34 (2016)

50

A. Kumari et al.

41. Uekado, M., Kamei, Y., Nakamura, M.: Effect of static stress on high temperature corrosion behavior of boiler tubes in waste incineration environment. In: CORROSION 2000. OnePetro (2000) 42. Izzuddin, H.: Effect of MO during the oxidation of NI20CR-XMO alloys AT 570 °C. Metalurgi 36(3), 103–108 (2022) 43. Bojanowska, M., Chmiel, J., Soza´nska, M., Chmiela, B., Grudzie´n, J., Halska, J.: Issues of corrosion and degradation under dusty deposits of energy biomass. Energies 14(3), 534 (2021) 44. Kumar, M., Singh, H., Singh, N.: Production of nanostructure Ni–20Cr coatings for hightemperature applications. Thermal Spray Technol. 1, 1–23 (2013) 45. Matsubara, Y., Sochi, Y., Tanabe, M., Takeya, A.: Advanced coatings on furnace wall tubes. J. Therm. Spray Technol. 16(2), 195–201 (2007) 46. Al-Samarai, R.A., Mahmood, A.S., Ahmed, O.M.: Influence of WS2 nanoparticles lubricants on physical characteristics of wrought aluminium alloys. Iraqi J. Sci. 26, 1240–1250 (2019) 47. Brennan, M., Gassmann, R.: Laser cladding of nickel and iron base alloys on boiler waterwall panels and tubes. In: CORROSION 2000. OnePetro (2000) 48. Kawahara, Y., Orita, N., Takahashi, K., Nakagawa, Y.: Demonstration test of new corrosionresistant boiler tube materials in high efficiency waste incineration plant. Tetsu-to-Hagané 87(8), 544–551 (2001) 49. Sadeghi, E., Markocsan, N., Joshi, S.: Advances in corrosion-resistant thermal spray coatings for renewable energy power plants. Part I: effect of composition and microstructure. J. Thermal Spray Technol. 28(8), 1749–1788 50. Wilson, A., Forsberg, U., Lunderg, M., Nylöf, L.: Composite tubes in waste incineration boilers. In: Proceedings of the Stainless-Steel World/99, Den Haag, The Netherlands (1999) 51. Kawahara, Y.: Controlling factors of localized corrosion in boiler combustion gas environments. Oxid. Met. 85(1), 127–149 (2016) 52. Galetz, M.C., Montero, X., Mollard, M., Günthner, M., Pedraza, F., Schütze, M.: The role of combustion synthesis in the formation of slurry aluminization. Intermetallics 1(44), 8–17 (2014) 53. Wang, Y., Wang, X., Wang, M., Tan, H.: Formation of sulfide deposits and high-temperature corrosion behavior at fireside in a coal-fired boiler. Energy Fuels 34(11), 13849–13861 (2020) 54. Eaton, H.E., Linsey, G.D.: Accelerated oxidation of SiCCMC’s by water vapor and protection via environmental barrier coating approach. J. Eur. Ceram. Soc. 22(14–15), 2741–2747 (2002) 55. Wang, G., Liu, H., Chen, T., Zhang, X., Li, H., Yu, Y., Yao, H.: Comparative investigation on thermal corrosion of alloy coatings in simulated waste incinerator environment. Corros. Sci. 15(189), 109592 (2021) 56. Strach, L, Wasyluk, D.T.: Experience with silicon-carbide tiles in mass-fired refuse boilers. Mater. Perform. (United States) 32(12) (1993) 57. Kawahara, Y.: High temperature corrosion mechanisms and effect of alloying elements for materials used in waste incineration environment. Corros. Sci. 44(2), 223–245 (2002) 58. Tanaka, Y., Komai, N., Suganuma, H.: Coal ash corrosion properties of Ni-based alloy for advanced-USC boilers. In: Advances in Materials Technology for Fossil Power Plants: proceedings from the Sixth International Conference, p. 303, Santa Fe, New Mexico, USA. ASM International (2011) 59. Fukuda, Y., Kawahara, Y.: Evaluation of corrosion resistance of waste incinerator superheater tubes coated by high velocity thermal spray. Nippon Kinzoku Gakkaishi (1952) 66(6), 563–568 (2002) 60. Dooley, R., Wiertel, E.: A survey of erosion and corrosion resistant materials being used on boiler tubes in waste to energy boilers. In: North American Waste-to-Energy Conference, vol. 48807, pp. 37–41 61. Tallman, S., Luo, Y., Buckley, P.J.: Business models in global competition. Glob. Strateg. J. 8(4), 517–535 (2018) 62. Zahs, A., Spiegel, M., Grabke, H.: The influence of alloying elements on the chlorine-induced high temperature corrosion of Fe–Cr alloys in oxidizing atmospheres. Mater. Corros. 50(10), 561–578 (1999)

Development of Coating-Resistant Materials at High Temperatures …

51

63. Kawahara, Y.: Evaluation of high-temperature corrosion life using temperature gradient corrosion test with thermal cycle component in waste combustion environments. Mater. Corros. 57(1), 60–72 (2006) 64. Oka, Y.I., Okamura, K., Yoshida, T.: Practical estimation of erosion damage caused by solid particle impact: part 1: effects of impact parameters on a predictive equation. Wear 259(1–6), 95–101 (2005) 65. Notomi, A.: High temperature erosion and wear resistant material. Mater. Jpn. (Japan) 36(7), 697–702 (1997) 66. Isomoto, Y., Kawanishi, T., Kawahara, Y., Yosihara, M.: Characteristics and damage mechanisms of sand erosion for self-fluxing alloy coatings. J. Jpn. Inst. Met. 77, 231–236 (2013)

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion Coupled Environments Dongming Yan

and Hao Qian

Abstract In some special cases, steel substrates may suffer the coupled threats of chloride corrosion and elevated temperature, requiring both high-temperature and corrosion protection. Enamel coating has been utilized to protect metallic substrates against corrosion and has proven to be effective. Recently, silicon carbide and silicon nitride were added to pure enamel coating and the composite enamel coatings were developed. Results showed that the composite enamel coatings had excellent thermal shock resistance, good corrosion resistance, and sufficient cracking resistances. Due to these improvements, the composite enamel coating became a candidate material for applications in thermal shock and chloride corrosion coupled environments. Keywords Composite enamel · High-temperature coating · Corrosion protection · Thermal shock · Residual stress · Corrosion mechanism · Microstructure

1 Introduction Corrosion, a pervasive challenge in civil engineering, industry, and daily life, induces significant structural damage and substantial economic costs. Particularly, some distinctive scenarios, like offshore launch towers and related facilities, boilers, chimneys, ship engines, etc., expose steel structures to the combined hazards of chloride corrosion and elevated temperature. Enamel coatings have been employed to mitigate corrosion of metallic substrates, exhibiting commendable efficacy. However, the conventional enamel coatings exhibit constrained resistance to thermal shock and insufficient damage tolerance due to the presence of rigid covalent or ionic bonds. Consequently, these limitations significantly undermine the anti-corrosion performance of such coatings and restrict their practicality in engineering applications subjected to environments featuring both thermal shock and chloride corrosion. Composite coatings have usually been considered to be an attractive option for improving some technical properties of coatings. Recently, silicon carbide or silicon D. Yan (B) · H. Qian College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_3

53

54

D. Yan and H. Qian

nitride was added to pure enamel and the composite enamel coating was developed for applications in thermal shock and chloride corrosion coupled environments. In the present chapter, silicon nitride/enamel composite coatings with 0, 1.5, 2.5, 3.5, 5, and 7.5 wt.% silicon nitride content (N0, N1.5, N2.5, N3.5, N5, and N7.5, respectively) and silicon carbide/enamel composite coatings with 0, 2.5, 5, and 7.5 wt.% silicon nitride content (S0, S2.5, S5, and S7.5, respectively) were investigated, and their microstructure, mechanical properties, thermal shock tolerance, and corrosion resistance were reviewed in detail.

2 Surface and Microstructural Characterization of Composite Enamel Coatings 2.1 Silicon Nitride/Enamel Composite Coatings 2.1.1

Surface Morphology and Contact Angle

Figure 1 shows the surface morphology and the water contact angles of the different composite coatings. From Fig. 1a, with increasing silicon nitride content, there is a noticeable color change from dark blue of N0 to gray of N7.5. For micro view, however, it should be noted that the images exhibited unrealistic colors due to the lighting conditions of digital microscope. N0 presents microcracks on its surface, resulting from the thermal damage when cooling. Silicon nitride not only helps mitigate the microcracks’ formation but also introduces significant porosity as well as visible open pores when redundancy, as observed for N7.5 (Fig. 1a). Figure 1b presents the 3D surface morphologies and corresponding surface roughness data of different samples. Evidently, the incorporation of silicon nitride significantly reduces surface smoothness. Quantitatively, the average surface roughness (Ra) of N0 is 1.51 μm, which undergoes an increase to 4.07 μm, 6.22 μm, and 10.36 μm for N2.5, N5, and N7.5, respectively. This observed rise in roughness can be attributed to the elevated viscosity of the molten enamel caused by the presence of silicon nitride, which hampers effective leveling [1]. Physically, such an increase in roughness contributes to enhanced hydrophobicity of the material [2–4]. Indeed, our findings demonstrate an escalation in the contact angle, which is 55.7° for N0 and progresses to 67.6°, 77.6°, and 76.8° for N2.5, N5, and N7.5, respectively (Fig. 1c). Enamel coatings that have higher contact angles offer improved resistance against water penetration, thus proving advantageous for corrosion protection [5].

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion …

55

Fig. 1 Surface morphology and contact angle of different enamel coatings: a Macro and micro images of N0, N1.5, N2.5, N3.5, N5, and N7.5; and 3D morphologies b and contact angles c of N0, N2.5, N5, and N7.5 [1]

2.1.2

Phase Structure

Figure 2 gives the X-ray diffraction (XRD) patterns obtained for samples. The XRD pattern of all samples exhibits a characteristic hump in the range of 20°–40°, indicating the presence of amorphous phases within the enamel. The diffraction peaks primarily correspond to apatite (Ca5 (PO4 )3 [F, OH]), which is an inorganic component found in the hard tissue of human. Apatite possesses favorable attributes such as low solubility and excellent acid resistance [6, 7], contributing to the capabilities of the enamel coating for corrosion prevention. Despite the inclusion of a bit of silicon nitride (1.5 wt.%, N1.5), distinct diffraction peaks attributable to silicon nitride are evident in the XRD patterns. Notably, the XRD signals’ intensity of the silicon nitride progressively intensifies as the silicon nitride content increases (Fig. 2). There is no indication that the silicon nitride underwent any chemical reactions during the sintering process at 530 °C, as evidenced by the XRD patterns.

56

D. Yan and H. Qian

Fig. 2 XRD results of Si3 N4 , N0, N1.5, N2.5, N3.5, N5, and N7.5 [1]

2.1.3

Microstructure

Figure 3 displays the cross-sectional morphologies of the enamel coatings with varying silicon nitride contents, along with the extracted pore phase. The powder electrostatic spraying ensures a uniform coating thickness of approximately 200 μm for all samples. All coating phases exhibit complete sintering. Notably, the incorporation of CoO and NiO as adhesion promoters facilitates a strong adhesion at enamel/ steel substrate interface [8, 9]. XRD analysis (Fig. 2) confirms pore formation in enamels attributed to the physical effect that silicon nitride makes molten enamel more viscous [1]. Consequently, the escape of sintering-induced gases (H2 , H2 O, CO2 , CO, etc.) is limited [1, 9]. Figure 4 shows the distribution of porosity for all coatings. The incorporation of silicon nitride induces significant alterations in the pore distribution. The total porosity and the maximum pore size both exhibit notable increases with the augmentation of silicon nitride amount. For instance, the initial total porosity of N0 is 6.04%, which raised to 26.14%, 39.75%, 44.80%, 59.42%, and 55.75% for N1.5, N2.5, N3.5, N5, and N7.5, respectively. The dominant pore size is 0–20 μm for N0, which enlarges to 20–40 μm, 20–40 μm, 40–60 μm, 60–80 μm, and 60–80 μm for N1.5, N2.5, N3.5, N5, and N7.5, respectively. Similarly, the maximum pore size is 20– 40 μm for N0, which enlarges to 40–60 μm, 40–60 μm, 60–80 μm, 100–120 μm, and 100–120 μm in N1.5, N2.5, N3.5, N5, and N7.5, respectively. Notably, pores with a diameter greater than 100 μm demonstrate a higher likelihood of interconnection (Fig. 3e, f), which can be detrimental to corrosion protection efforts.

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion …

57

Fig. 3 Cross-sectional view of SEM and pore images of different samples: a N0, b N1.5, c N2.5, d N3.5, e N5, and f N7.5 [1] Fig. 4 Porosity distribution against equivalent pore diameter for different coatings [1]

2.2 Silicon Carbide/Enamel Composite Coatings 2.2.1

Phase Composition

Figure 5 presents the XRD results of silicon carbide and all enamel coatings. All diffraction peaks observed for silicon carbide only corresponded to the characteristic peaks of Moissanite-6H (α-SiC), indicating high purity. In contrast, the enamel coatings displayed an amorphous phase between 20° and 40°. The diffraction peaks observed in S0 can be indexed to CaF2 and Ca5 (PO4 )3 [F, OH]. Besides the same diffraction peaks observed in S0, the diffraction peaks corresponding to silicon

58

D. Yan and H. Qian

Fig. 5 XRD patterns of silicon carbide, S0, S2.5, S5, and S7.5 [13]

carbide were clearly present for S2.5, S5, and S7.5, and the intensity of these silicon carbide diffraction peaks exhibited a gradual increase as the silicon carbide content increased. In addition, not any new phases were detected. These findings indicate that as results of the excellent thermal and chemical stability [10–12], silicon carbide never underwent any chemical reaction throughout the entire sintering.

2.2.2

Surface Morphology

The surface morphologies of coated samples are shown in Fig. 6. Clearly, S0 exhibits significant microcracks on its surface, with approximately 4 μm in width (Fig. 6a). These microcracks have been previously identified as potential pathways for aggressive ions, leading to reduced corrosion resistance during early immersion stages [1]. The presence of microcracks is attributed to that the enamel and steel had a mismatched coefficient of thermal expansion (CTE), which results in considerable residual stress within the coating matrix. Notably in Fig. 6b, the addition of 2.5 wt.% silicon carbide in S2.5 demonstrates marked improvements, with decreased the width ( f c,t , the coating will fail in tension. Noted that the following equation must be satisfied to prevent shear failure between coating and substrate: F = τ I bl > f c tc b

(7)

where τ I denotes the interface shear strength. For a specific material, thinner coating can easily meet the requirements. τI >

tc fc l

(8)

The determination of Young’s modulus for composite coatings involved two steps, first the silicon carbide strengthening and subsequently the pore weakening. To investigate the influence of second particles on Young’s modulus, the Halpin–Tsai model [31] was used, as shown in Eqs. (9) and (10). E dc =

E m 1 + 2sq V pa 1 − q V pa

q=

E pa Em E pa Em

(9)

−1 + 2s

(10)

where E dc denotes the Young’s modulus of composite when dense; E m denotes Young’s modulus of the pure enamel matrix, which was 87.7 GPa in this study, calculated using the Oliver–Pharr method [20]; E pa denotes the Young’s modulus of SiC, assumed to be 447 GPa [21]; V pa and s denotes the volume fraction and the aspect ratio of SiC, respectively. As for the influence of pores on Young’s modulus, pores were considered to be a second phase with zero Young’s modulus. Equations (9) and (10) can be converted to Eq. (11).

72

D. Yan and H. Qian

Ec =

E dc 1 − V po 1+

1 V 2s po

(11)

where E c and V po denote Young’s modulus and volume porosity of porous composite coatings, respectively. Young’s modulus of pure and composite enamel coatings was determined using Eqs. (9)–(11), as shown in Table 1. The results clearly show a decrease in Young’s modulus as follows: S0 has a value of 79.78 GPa, while S2.5, S5, and S7.5 have values of 66.49 GPa, 63.08 GPa, and 57.11 GPa, respectively. This decrease suggests that the weakening impact caused by porosity plays a significant role in determining Young’s modulus, owing to its higher change proportion. The coating’s residual stress plays a crucial role in determining its susceptibility to cracking during the cooling process. To calculate the residual stress, a simplified form Eq. (12), consistent with the approach reported in reference [30], was employed. T2

σc =

Ec 1 − vc

(αs (T ) − αc (T ))dT

(12)

T1

where αs and αc are the CTEs of substrate and coating, respectively; vc is the Poisson’s ratio of the coating, as reported to be 0.27 for enamel [30]. Table 1 shows the obtained residual stress values for all coatings. It is evident that the silicon carbide results in a significant decrease in residual stress. The values decrease from 98.14 MPa for S0 to 80.63 MPa, 62.38 MPa, and 35.19 MPa for S2.5, S5, and S7.5, respectively. For S0, where the residual stress exceeded its tensile strength, presents numerous microcracks (Fig. 6a). With silicon carbide addition, the residual stress decreased, and microcracks’ number and width decreased for S2.5 and S5, eventually no microcracks for S7.5 (Fig. 6b–d). As discussed in Sect. 2.3, a transition layer, consisting of a mixture of enamel and iron oxides, occurs due to the interdiffusion at the enamel/steel interface. This transition layer possesses an intermediate CTE between the enamel and steel, facilitating thermal deformation compatibility. Additionally, the temperature-dependent nature of the enamel coating’s Young’s modulus, as indicated by Wachtman’s equation [32], suggests a potential decrease in actual residual stress at high temperatures. Therefore, the actual residual stress is even lower than the calculated values for composite coatings.

4.4 Microstructure-Dependent Thermal Shock Resistance The addition of silicon nitride in this study has demonstrated several benefits for enamels, including a decrease in the possibility of cracking, reduction in crack length, and increased tolerance to impacts and thermal shocks. These improvements can be attributed to alterations in the microstructure, particularly the pores, which play

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion …

73

a significant role. For crack initiation and propagation, the driving force is typically external loads or thermal stresses. When this driving force exceeds a certain threshold, initial cracks nucleate. If the elastic energy at the fracture tips of initial cracks is adequate to provide the needed surface energy, these nucleated cracks will keep propagating and dissipating energy [33, 34]. The presence of pores has a considerable effect on the mechanical behavior of enamels. Pores can significantly decrease the elastic modulus (E) [35], thereby reducing the elastic energy stored at the fracture site [33]. Additionally, pores have advantages in terms of energy release, passivation of the crack tip, and reduction of stress concentration [36, 37]. Consequently, enamels with increased porosity exhibit shorter indentation crack lengths (Fig. 12c). Moreover, crack length reduction and hardness decrease (Fig. 12a and c) both indicate an increase in fracture toughness (K I c ), as described in the formula [38]. Due to the critical indentation load being directly proportional and inversely proportional to the fourth power of fracture toughness and the third power of material’s hardness, respectively, it also raises with porosity (Fig. 12b) [39]. Furthermore, the porous enamels exhibit the ability to absorb a greater amount of thermal shock energy and can release more thermal stress induced by the mismatch of enamel and steel [40, 41]. In addition, the presence of a porous structure is typically related to a lower global in-plane elastic modulus, that enhances the material’s strain tolerance and, consequently, improves its thermal shock resistance (Fig. 14) [42].

5 Corrosion Resistance of Composite Enamel Coatings 5.1 Corrosion Morphology Evolution Figure 17 shows the corrosion evolution of composite enamel coatings. Upon initial immersion (1 day), no corrosion is observed, although microcracks are evident in N0 and open pores are present in N7.5. After 30 days of immersion, rust spots begin to appear in the cracks of N0 and pores of N7.5 (Fig. 17). In contrast, the other samples still exhibit no noticeable signs of corrosion. At 105 days, clear rust spots are visible for N0, N5, and N7.5, whereas a significant portion of N2.5 remains unaffected by the corrosive effects of the 3.5 wt.% NaCl solution.

5.2 Electrochemical Study Figure 18 illustrates the corrosion behaviors of coated and bare steels at an immersion age of 1 and 105 days (3.5 wt.% NaCl solution). The saturated calomel electrode (SCE) was used as a reference electrode. After 1 day of immersion, noticeable differences in cathodic and anodic behavior were found between the coated and uncoated samples, as well as among the different composite coatings. For anodic polarization,

74

D. Yan and H. Qian

Fig. 17 Corrosion surface of composite coatings after 1, 30, and 105 days immersing in 3.5 wt.% NaCl solution [1]

bare steel exhibits a distinct passivation from −0.9 to −0.7 V versus SCE, followed by the onset of pitting higher than −0.7 V versus SCE (Fig. 18a). In contrast, the samples coated with enamels demonstrate an increase in corrosion potential (E corr ) and a reduction of current density (I corr ) compared to the bare sample, indicating an enhanced corrosion resistance [43]. Notably, N0 presents an I corr value that is roughly one magnitude smaller than bare steel. Moreover, the I corr values of the silicon nitride-modified samples exhibit a reduction of around 5–10 times compared to N0. For 105 days’ immersion tests, bare steel as well as N0, N2.5, N5, and N7.5 were investigated, as presented in Fig. 18b. It was observed that the Icorr values for all coated samples converged to a similar value of approximately 10–6 A/cm2 . This value is nearly one order of magnitude smaller than the bare steel (10–5 A/cm2 ). Furthermore, the slopes of the anodic polarization curves exhibited a decreasing trend with increasing silicon nitride content, indicating an expansion in the defect area [44]. Tafel extrapolation [45, 46] was employed to obtain the Icorr for a quantitative comparison. The extracted E corr and I corr are shown in Fig. 18c, d, respectively. For

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion …

75

Fig. 18 Polarization curves of coated and uncoated samples, at 1 day a and 105 days, b immersing in 3.5 wt.% NaCl solution; extracted, c corrosion potential and d corrosion current density [1]

N0, the E corr increased and I corr decreased after 105 days’ immersion, indicating that the pure enamel coating provides continuous corrosion resistance enhancement. By contrast, though N5 and N7.5 presented best at 1 day, they had the largest degeneration (E corr decreases and I corr increases) at 105 days. The N2.5, which has a low silicon nitride concentration, only showed a slight degeneration. This suggests that the enamel coating’s corrosion barrier properties were dominated by its microstructure, with great pore size and amount (N5 and N7.5) resulting in severe deterioration, whereas individual microcracks (N0) exhibiting enhanced corrosion protection with prolonged time (discussed in Sect. 5.4). Figure 19 presents the electrochemical curves of UC, S0, S2.5, S5, and S7.5 at 1 day’s immersion. From Fig. 19a, the OCP value of S0 (−0.680 V versus SCE) was more positive compared to UC (−0.750 V versus SCE). For composite coatings, the OCP values further shifted to −0.635, −0.609, and −0.568 V versus SCE for S2.5, S5, and S7.5, respectively. This indicates that the amount of electrolyte solution entering the coating/steel interface has decreased [47]. Figure 8b–d shows the EIS results for all samples, with both Nyquist and Bode plots. From Fig. 8d, with silicon carbide increasing, the high-frequency phase angle rose and the lowfrequency phase angle decreased. In addition, when composite coatings contained more silicon carbide, the capacitive arc expanded, and the impedance rose (Fig. 8b,

76

D. Yan and H. Qian

Fig. 19 Electrochemical data of different samples, immersing in 3.5 wt.% NaCl solution for 1 day: a OCP; b nyquist plots; c modulus; d phase angle; and e |Z|0.01 versus Rp [13]

c), suggesting an improved corrosion resistance. Figure 8e compares the EIS (|Z|0.01 ) and LPR (Rp ) data. It can be seen that the average |Z|0.01 of UC was 1.9 × 103 cm2 , and it increased to 8.9 × 103 , 1.0 × 105 , 1.1 × 105 , and 6.8 × 105 cm2 for S0, S2.5, S5, and S7.5, respectively. Additionally, the Rp of UC was 2.7 × 103 cm2 , which rose to 4.1 × 104 , 1.9 × 105 , 1.8 × 105 , and 8.1 × 105 cm2 for S0, S2.5, S5, and S7.5 respectively, suggesting that silicon carbide improved the enamel coating’s corrosion protection. Though |Z|0.01 was a bit lower than Rp , they

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion …

77

had similar trends. Therefore, |Z|0.01 may be utilized to undertake a semi-quantitative evaluation of corrosion protection behavior [48–50]. Composite coatings’ corrosion behavior was found to be closely associated with their microstructure, particularly the presence of surface microcracks. In the case of S0, the observed microcracks (Fig. 6a) served as pathways for the corrosive electrolyte to penetrate, resulting in a relatively low Rp value, which was only around 15 times compared to UC. However, with the silicon carbide addition (S2.5 and S5), the number and width of microcracks reduced (Fig. 6b and c), leading to an increase in the Rp value and an enhancement in corrosion protection. Remarkably, S7.5 was free of any microcracks (Fig. 6d) because of its thermal expansion matched with steel. Consequently, S7.5 exhibited the best corrosion protection, surpassing the UC by around 300 times and the S0 by 20 times in terms of Rp .

5.3 Salt-Spray Test A neutral salt-spray test was conducted to investigate the anti-corrosion behavior of all coated rebars. Figure 20 shows the optical corrosion morphology evolutions of PE, S2.5, S5, and S7.5 with exposure time. The UC sample suffered severe corrosion with the corrosion products thoroughly covering the surface within 8 days, therefore not shown here. Overall, all coatings provided adequate corrosion protection for steel rebars. For PE, S2.5, and S5, slight signs of corrosion located at the defects were observed at 8 days, and the corrosion area gradually enlarged with the exposure time. However, they suffered different extents of corrosion and S5 was still superior to PE and S2.5. For S7.5, corrosion signs appeared as late as 60 days, and the corrosion was almost located at the edge, which was probably due to the undesirable sealing. According to the weight changes shown in Fig. 20b, the UC sample generally followed a linear weight increase trend with the rate of 2.99 mg/(cm2 d). For all coated samples, the weight rapidly increased before 30 days due to the water uptake of enamel coatings and not sufficiently dried before weighing. Following that, the coated samples showed slow weight increase trends with rates of 0.18–0.25 mg/ (cm2 d), which was approximately 10–15 times lower than that of the UC sample. Overall, significant improvements could be seen for coatings with higher silicon carbide addition, which was consistent with the morphology observations.

5.4 Corrosion Evolution Mechanism For coated steel in a 3.5 wt.% NaCl solution, the anodic and cathodic reactions involve the oxidation of iron and the reduction of oxygen, respectively. Corrosion occurs if a corrosive medium penetrates the steel surface, and the corrosion is primarily driven by the localized active dissolution of iron. It is evident that the corrosion protection

78

D. Yan and H. Qian

Fig. 20 Optical corrosion morphology evolutions (a) and weight changes (b) of UC, PE, S2.5, S5, and S7.5, with increasing exposure time under 35 °C and 5 wt.% NaCl neutral salt-spray condition

of the enamel coating is significantly affected by the defects, particularly through defects that serve as pathways for the penetration of corrosive ions [44, 51]. Figure 21 illustrates the corrosion evolution process for enamel coatings with cracks and pores. For N0, initial microcracks were present on its surface (Fig. 1). These microcracks act as pathways for corrosive medium’s penetration, leading to the poor corrosion resistance during the early immersion, despite having the smallest

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion …

79

porosity (Fig. 4). As corrosion progressed (Fig. 21), corrosion products accumulated within microcracks and expanded in both directions, exerting compressive forces on the coating. However, for N0, because of the high hardness and compressive strength (Fig. 12a), and relatively small crack spacing, the expansion forces of corrosion products were insufficient to cause coating damage. Instead, the corrosion products compacted within the crack, obstructing the penetration of corrosive ions. Consequently, an improvement in corrosion resistance of N0 was observed after immersing for 105 days (Fig. 18d). For N5 and N7.5 with pores, their superior hydrophobicity (Fig. 1c) made them more resistant to infiltration. Therefore, during the initial stage of immersion, they remained unwetted with pores in the form of air chambers (Fig. 21), enhancing the physical barrier performance. However, with immersing, corrosive ions penetrated across the coating arriving at the steel surface, leading to corrosion reactions and the accumulation of rust within the pores. Unlike the corrosion products in microcracks, the corrosion products within the pores exerted radial expansion forces, resulting in the coating in tension. This expansion stress exceeds the tensile strength ( f t ) easily, as f t is significantly lower than f c for brittle enamel materials [52]. Additionally, large porosity of coating reduces its entire hardness and apparent strength, indicating the presence of connecting pores. Consequently, the porous coating was more susceptible to destruction caused by the expansion of corrosion products, and the corrosion products were more prone to diffusion. This explains why N5 and N7.5 initially

Fig. 21 Corrosion process for enamel coatings with cracks and pores: at early, middle, and late stages immersing in 3.5 wt.% NaCl solution [1]

80

D. Yan and H. Qian

exhibited the best physical barrier but experienced the most significant deterioration over time. Notably, N2.5 only suffered minimal degradation due to its less pores, smaller pore diameter (Fig. 3), and greater strength and hardness (Fig. 12a) when compares to N5 and N7.5.

6 Summary Engineering structures such as offshore launch towers and industrial facilities such as boilers and chimneys are susceptible to the coupled threats of chloride corrosion and high temperature. The silicon carbide/enamel and silicon nitride/enamel composite coatings were developed, and the results showed that (i) the coating’s cracking resistances against indentation and impact loads were greatly improved; (ii) the composite enamel coatings can withstand more than 100 thermal shocks cycles; and (iii) the composite enamel coated steel kept at least 10 times lower corrosion rate compared to the uncoated one. Due to these improvements, the composite enamel coating became a candidate material for applications in thermal shock and chloride corrosion coupled environments. Acknowledgements Financial support to complete this chapter by the National Key Research and Development Program of China (No. 2022YFE0109200), the National Natural Science Foundation of China (Nos. 51522905, 51778570, and 51879230), and China Postdoctoral Science Foundation (No. 2022M722789) are greatly appreciated.

References 1. Qian, H., Chen, S., Wang, T., Cheng, G., Chen, X., Xu, Z.: Silicon nitride modified enamel coatings enable high thermal shock and corrosion resistances for steel protection. Surf. Coat. Technol. 421, 127474 (2021) 2. Gateman, S.M., Page, K., Halimi, I., Nascimento, A.R.C., Savoie, S., Schulz, R., et al.: Corrosion of one-step superhydrophobic stainless-steel thermal spray coatings. ACS Appl. Mater. Interfaces 12(1), 1523–1532 (2019) 3. Liu, G., Xia, H., Zhang, W., Lang, L., Geng, H., Song, L., Niu, Y.: Photocatalytic superamphiphobic coatings and the effect of surface microstructures on superamphiphobicity. ACS Appl. Mater. Interfaces 13(10), 12509–12520 (2021) 4. Luo, S., Zheng, L., Luo, H., Luo, C.: A ceramic coating on carbon steel and its superhydrophobicity. Appl. Surf. Sci. 486, 371–375 (2019) 5. Lu, H., Zhang, S., Li, W., Cui, Y., Yang, T.: Synthesis of graphene oxide-based sulfonated oligoanilines coatings for synergistically enhanced corrosion protection in 3.5% NaCl solution. ACS Appl. Mater. Interfaces 9(4), 4034–4043 (2017) 6. Pan, H.B., Darvell, B.W.: Solubility of calcium fluoride and fluorapatite by solid titration. Arch. Oral Biol. 52(9), 861–868 (2007) 7. Bhadang, K.A., Gross, K.A.: Influence of fluorapatite on the properties of thermally sprayed hydroxyapatite coatings. Biomaterials 25(20), 4935–4945 (2004) 8. Samiee, L., Sarpoolaky, H., Mirhabibi, A.: Microstructure and adherence of cobalt containing and cobalt free enamels to low carbon steel. Mater. Sci. Eng. A 458(1–2), 88–95 (2007)

Composite Enamel Coatings for Thermal Shock and Chloride Corrosion …

81

9. Yang, X., Jha, A., Brydson, R., Cochrane, R.C.: An analysis of the microstructure and interfacial chemistry of steel–enamel interface. Thin Solid Films 443(1–2), 33–45 (2003) 10. Roy, J., Chandra, S., Das, S., Maitra, S.: Oxidation behaviour of silicon carbide-a review. Rev. Adv. Mater. Sci. 38(1), 29–39 (2014) 11. Krawiec, P., Kaskel, S.: Thermal stability of high surface area silicon carbide materials. J. Solid State Chem. 179(8), 2281–2289 (2006) 12. Singhal, S.C.: Thermodynamic analysis of the high-temperature stability of silicon nitride and silicon carbide. Ceramurg. Int. 2(3), 123–130 (1976) 13. Qian, H., Xu, Z., Chen, S., Liu, Y., Yan, D.: Silicon carbide/enamel composite coatings for steel corrosion protection: Microstructure, thermal expansion behavior, and anti-corrosion performance. Surf. Coat. Technol. 434, 128172 (2022) 14. Fu, C., Guo, R., Lin, Z., Xia, H., Yang, Y., Ma, Q.: Effect of nanosilica and silica fume on the mechanical properties and microstructure of lightweight engineered cementitious composites. Constr. Build. Mater. 298, 123788 (2021) 15. Mur, A., Purcell, C., Soong, Y., Crandall, D., McLendon, T.R., Haljasma, I.V., et al.: Integration of core sample velocity measurements into a 4D seismic survey and analysis of SEM and CT images to obtain pore scale properties. Energy Procedia 4, 3676–3683 (2011) 16. Yan, D., Qian, H., Huang, Z., Tang, F., Chen, G., Deng, J., Liu, Y.: Study of lower temperaturesintered enamel coating on steel bars: effect of coating cycles. J. Mater. Civ. Eng. 32(9), 04020262 (2020) 17. Yamashita, T., Hayes, P.: Analysis of XPS spectra of Fe2+ and Fe3+ ions in oxide materials. Appl. Surf. Sci. 254(8), 2441–2449 (2008) 18. Grosvenor, A.P., Kobe, B.A., Biesinger, M.C., McIntyre, N.S.: Investigation of multiplet splitting of Fe 2p XPS spectra and bonding in iron compounds. Surf. Interface Anal.: Int. J. Dev. Dev. Appl. Tech. Anal. Surf. Interfaces Thin Films 36(12), 1564–1574 (2004) 19. Lupescu, M.B., Zaharescu, M., Andrei, A.: Electron spectroscopy studies of the steel/enamel interface. Mater. Sci. Eng. A 232(1–2), 73–79 (1997) 20. Oliver, W.C., Pharr, G.M.: Measurement of hardness and elastic modulus by instrumented indentation: advances in understanding and refinements to methodology. J. Mater. Res. 19(1), 3–20 (2004) 21. Qian, J., Daemen, L.L., Zhao, Y.: Hardness and fracture toughness of moissanite. Diam. Relat. Mater. 14(10), 1669–1672 (2005) 22. Liao, Y., Zhang, B., Chen, M., Feng, M., Wang, J., Zhu, S., Wang, F.: Self-healing metal-enamel composite coating and its protection for TiAl alloy against oxidation under thermal shock in NaCl solution. Corros. Sci. 167, 108526 (2020) 23. Li, X.C., Meng, M., Li, D., Wei, R., He, L., Zhang, S.F.: Strengthening and toughening of a multi-component lithium disilicate glass-ceramic by ion-exchange. J. Eur. Ceram. Soc. 40(13), 4635–4646 (2020) 24. ISO 6872 (2015) Dentistry–Ceramic Materials, International Organization for Standardization 25. Droste, D.H., Dibenedetto, A.T.: The glass transition temperature of filled polymers and its effect on their physical properties. J. Appl. Polym. Sci. 13(10), 2149–2168 (1969) 26. Fahmy, A.A., Ragai, A.N.: Thermal-expansion behavior of two-phase solids. J. Appl. Phys. 41(13), 5108–5111 (1970) 27. Laplanche, G., Gadaud, P., Horst, O., Otto, F., Eggeler, G., George, E.P.: Temperature dependencies of the elastic moduli and thermal expansion coefficient of an equiatomic, single-phase CoCrFeMnNi high-entropy alloy. J. Alloy. Compd. 623, 348–353 (2015) 28. Tohei, T., Watanabe, Y., Lee, H.S., Ikuhara, Y.: First principles calculation of thermal expansion coefficients of pure and Cr doped α-alumina crystals. J. Appl. Phys. 120(14), 142106 (2016) 29. Bao, Y., Gawne, D.T., Gao, J., Zhang, T., Cuenca, B.D., Alberdi, A.: Thermal-spray deposition of enamel on aluminium alloys. Surf. Coat. Technol. 232, 150–158 (2013) 30. Yan, G., Liu, W., Yu, W., Shen, S.: Effect of crystallization on the macro and micro residual stress of enamel coating. J. Eur. Ceram. Soc. 41(6), 3643–3654 (2021) 31. Ganesh, V.V., Chawla, N.: Effect of particle orientation anisotropy on the tensile behavior of metal matrix composites: experiments and microstructure-based simulation. Mater. Sci. Eng. A 391(1–2), 342–353 (2005)

82

D. Yan and H. Qian

32. Wachtman, J.B., Jr., Tefft, W.E., Lam, D.G., Jr., Apstein, C.S.: Exponential temperature dependence of Young’s modulus for several oxides. Phys. Rev. 122(6), 1754 (1961) 33. Hasselman, D.P.H.: Elastic energy at fracture and surface energy as design criteria for thermal shock. J. Am. Ceram. Soc. 46(11), 535–540 (1963) 34. Hasselman, D.P.H.: Unified theory of thermal shock fracture initiation and crack propagation in brittle ceramics. J. Am. Ceram. Soc. 52(11), 600–604 (1969) 35. Dorey, R.A., Yeomans, J.A., Smith, P.A.: Effect of pore clustering on the mechanical properties of ceramics. J. Eur. Ceram. Soc. 22(4), 403–409 (2002) 36. Wu, L., Li, C., Li, H., Wang, H., Yu, W., Chen, K., Zhang, X.: Preparation and characteristics of porous anorthite ceramics with high porosity and high-temperature strength. Int. J. Appl. Ceram. Technol. 17(3), 963–973 (2020) 37. Carlsson, J., Isaksson, P.: Crack dynamics and crack tip shielding in a material containing pores analysed by a phase field method. Eng. Fract. Mech. 206, 526–540 (2019) 38. Li, H., Khor, K.A., Cheang, P.: Young’s modulus and fracture toughness determination of high velocity oxy-fuel-sprayed bioceramic coatings. Surf. Coat. Technol. 155(1), 21–32 (2002) 39. Tite, M.S., Kilikoglou, V., Vekinis, G.: Strength, toughness and thermal shock resistance of ancient ceramics, and their influence on technological choice. Archaeometry 43(3), 301–324 (2001) 40. Zhong, Y., Shi, L., Li, M., He, F., He, X.: Characterization and thermal shock behavior of composite ceramic coating doped with ZrO2 particles on TC4 by micro-arc oxidation. Appl. Surf. Sci. 311, 158–163 (2014) 41. Wang, L., Xu, G., Liu, C., Hou, H., Tan, S.: Surface-modified CeO2 coating with excellent thermal shock resistance performance and low infrared emissivity at high-temperature. Surf. Coat. Technol. 357, 559–566 (2019) 42. Curran, J.A., Clyne, T.W.: Thermo-physical properties of plasma electrolytic oxide coatings on aluminium. Surf. Coat. Technol. 199(2–3), 168–176 (2005) 43. Husain, E., Narayanan, T.N., Taha-Tijerina, J.J., Vinod, S., Vajtai, R., Ajayan, P.M.: Marine corrosion protective coatings of hexagonal boron nitride thin films on stainless steel. ACS Appl. Mater. Interfaces 5(10), 4129–4135 (2013) 44. Zhang, S.D., Zhang, W.L., Wang, S.G., Gu, X.J., Wang, J.Q.: Characterisation of threedimensional porosity in an Fe-based amorphous coating and its correlation with corrosion behaviour. Corros. Sci. 93, 211–221 (2015) 45. Khodakarami, S., Zhao, H., Rabbi, K.F., Miljkovic, N.: Scalable corrosion-resistant coatings for thermal applications. ACS Appl. Mater. Interfaces 13(3), 4519–4534 (2021) 46. Li, L., Lu, Z., Pu, J., Hou, B.: Investigating the tribological and corrosive properties of MoS2 / Zr coatings with the continuous evolution of structure for high-humidity application. Appl. Surf. Sci. 541, 148453 (2021) 47. Ramezanzadeh, B., Niroumandrad, S., Ahmadi, A., Mahdavian, M., Moghadam, M.M.: Enhancement of barrier and corrosion protection performance of an epoxy coating through wet transfer of amino functionalized graphene oxide. Corros. Sci. 103, 283–304 (2016) 48. Gu, L., Liu, S., Zhao, H., Yu, H.: Facile preparation of water-dispersible graphene sheets stabilized by carboxylated oligoanilines and their anticorrosion coatings. ACS Appl. Mater. Interfaces 7(32), 17641–17648 (2015) 49. Zhang, D., Qian, H., Wang, L., Li, X.: Comparison of barrier properties for a superhydrophobic epoxy coating under different simulated corrosion environments. Corros. Sci. 103, 230–241 (2016) 50. Haddadi, S.A., SA, A.R., Mahdavian, M., Taheri, P., Mol, J.M.C., Gonzalez-Garcia, Y.: Selfhealing epoxy nanocomposite coatings based on dual-encapsulation of nano-carbon hollow spheres with film-forming resin and curing agent. Compos. Part B: Eng. 175, 107087 (2019) 51. Creus, J., Mazille, H., Idrissi, H.: Porosity evaluation of protective coatings onto steel, through electrochemical techniques. Surf. Coat. Technol. 130(2–3), 224–232 (2000) 52. Danzer, R.: On the relationship between ceramic strength and the requirements for mechanical design. J. Eur. Ceram. Soc. 34(15), 3435–3460 (2014)

Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear Fuel Tubes Against Accidental Temperature Corrosion in Water-Cooled Nuclear Reactors Irena Kratochvílová , Petr Ashcheulov, Jakub Luštinec, Jan Macák, Petr Sajdl, and Radek Škoda

Abstract The chapter proposes a new strategy for protecting Zr alloy nuclear fuel tubes from accidental temperature corrosion in water-cooled nuclear reactors. Protection of the zirconium alloy fuel tubes against accidental temperature corrosion in water-cooled nuclear reactors is important for the safety and efficiency of nuclear power plants, as corrosion in fuel tubes can lead to accidents and reduce the lifespan of the fuel. The new strategy of zirconium alloy fuel tubes from accidental temperature corrosion presented here involves a combination of polycrystalline diamond (PCD) and chromium (Cr) layers. The PCD layer prevents direct interaction between the Zr alloy surface and the hot water environment of the reactor and releases carbon into the underlying Zr material to alter conditions for the penetration of oxygen and hydrogen. The Cr layer helps to reduce corrosion by forming carbides and improving adhesion of the coatings to the Zr alloy substrate. The chapter also discusses the importance of the order of the Cr and PCD layers and the parameters affecting the corrosion of coated ZIRLO tubes. Overall, this new strategy has the potential to significantly improve nuclear safety.

I. Kratochvílová (B) · P. Ashcheulov · J. Luštinec Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Prague, Czech Republic e-mail: [email protected] I. Kratochvílová · J. Luštinec Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Bˇrehová 78/7, 115 19 Prague, Czech Republic J. Macák · P. Sajdl Faculty of Environmental Technology, Department of Power Engineering, University of Chemistry and Technology Prague, Technická 1903/3, 166 28 Prague, Czech Republic R. Škoda Robotics and Cybernetics, Czech Technical University in Prague, Czech Institute of Informatics, Jugoslávských partyzán˚u 1580/3, 160 00 Prague, Czech Republic © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_4

83

84

I. Kratochvílová et al.

Keywords Polycrystalline diamond layer · accident tolerant fuel · Corrosion in water-cooled nuclear reactors · ZIRLO fuel tubes surface corrosion · Plasma enhanced chemical vapor deposition · Magnetron-sputtered Cr

1 Introduction Nuclear energy does not emit carbon dioxide or other greenhouse gases during electricity generation, making it a low-carbon source of energy. Overall, the use of nuclear energy needs to be carefully managed to ensure that its benefits are maximized while minimizing any negative environmental impacts. Nuclear power plants also have the advantage of being able to generate large amounts of electricity from a single unit, which reduces the need for multiple power generation facilities in a single location. However, nuclear energy also has its drawbacks. One of the main concerns is the potential for accidents, which can result in devastating consequences for both human life and the environment. The nuclear industry has implemented numerous safety measures and regulations to minimize the risk of accidents, but accidents such as Chernobyl and Fukushima have highlighted the need for continued improvements in safety procedures [1, 2]. Many countries around the world continue to invest in nuclear energy as a key part of their energy mix. The development of advanced nuclear technologies, such as small modular reactors and fusion reactors, could potentially address some of the concerns associated with traditional nuclear power plants and contribute to a sustainable future energy system. Base-load nuclear power plants operate at maximum capacity for roughly 90% of the time during a given year. This is around two times that of coal or natural gas fossil power plants and almost three times as much as solar or offshore wind power plants. This high load factor can be achieved as nuclear plants require little maintenance and are designed to operate for up to several years between refueling [3–7]. The fuel rods are assembled into fuel assemblies, and these assemblies are loaded into the reactor core. During operation, the uranium dioxide fuel pellets undergo fission, generating heat which is used to produce steam to generate electricity. As the fuel is burned, fission products build up in the fuel and eventually the fuel must be replaced. The zirconium alloy cladding provides both mechanical support for the fuel pellets and acts as a barrier to the release of radioactive fission products into the reactor coolant. The cladding is exposed to high temperatures and corrosive environments during normal operation, and the buildup of corrosion products can limit the heat transfer from the fuel to the coolant. This can lead to overheating of the fuel and ultimately, failure of the fuel rod. Therefore, managing corrosion of the cladding is critical to the safe and efficient operation of nuclear reactors. The majority of commercial nuclear reactors today are light water reactors: either pressurized water reactors (PWRs) or boiling water reactors (BWRs). Because of this important function, cladding integrity during fuel and reactor operation is crucial for nuclear safety. Various degradation processes—including grid-to-rod fretting,

Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear …

85

debris-induced failures, localized corrosion, waterside corrosion, and hydriding— may challenge the integrity of the cladding tube [1, 2, 8–11]. In particular, zirconium alloys are not only used as a material for nuclear fuel tubes but also for other structural elements in fuel assemblies and the core internals of nuclear reactors, such as spacer grids or complete pressure channels. The main reason for their use is the low parasitic absorption of neutrons and high resistance against radiation damage. Zirconium alloys also possess very good mechanical properties, namely high melting temperature, and corrosion stability, which are maintained even during long-term exposure to the extreme conditions produced in nuclear reactors, especially high neutron flux, and high pressures [1, 11–15]. However, there is also a significant disadvantage: during the reaction with Zr alloy fuel rod surface the water molecules are dissociated and both oxygen and hydrogen ions penetrate into the Zr alloy [6, 8]. At temperatures around 850 °C the α phase of zirconium changes to β phase which is more prone to oxygen/hydrogen diffusion. The zirconium alloys changed by oxygen/hydrogen diffusion are less dense and are mechanically weaker than the original material—their formation results in blistering and finally cracking of the cladding. So as zirconium alloys oxidize and zirconium hydrides are formed the ductility of the nuclear rod is decreased. Oxygen and hydrogen uptake into the Zr alloy change the mechanical properties of the core components and are an important criterion for nuclear fuel licensing. In nuclear devices Zr alloys have to serve faultlessly and without maintenance, but even if their environmental parameters can become very extreme. The extensive production of hydrogen gas can result in hydrogen-air chemical explosions. Intense heat and pressure can trigger a reaction between the nuclear fuel Zr cladding and the surrounding water stream causing the production of explosive hydrogen gas resulting in several explosions as happened in Fukushima [2, 16–18]. This resulted in the intensive research and accident-tolerant fuel (ATF) development programs launched all around the world. During high-temperature corrosion of ZIRLO, the ZrO2 phase is formed on the surface of the alloy. ZrO2 is a ceramic material that has high thermal stability and oxidation resistance. The ZrO2 phase can exist in several crystal structures, including the tetragonal, monoclinic, and cubic phases. At high temperatures, ZrO2 can transform from its metastable tetragonal phase to the more stable monoclinic phase. This phase transformation is accompanied by a volume increase, which can lead to cracking and spalling of the ZrO2 layer, exposing the underlying alloy to further oxidation and corrosion [19, 20]. One of the approaches to address the corrosion and oxidation issues with zirconium alloy fuel tubes is to apply a protective coating on their surface. The coating material should have high corrosion resistance and adhere well to the substrate. Thin coatings are expected to have a minimal effect on the behavior of the Zrbased cladding during normal operation, i.e., high neutron irradiation stability and high corrosion resistance. The coating should also have high thermal conductivity to maintain heat transfer from the fuel to the coolant. By applying a protective coating, the chemical reactions and physical interactions that cause corrosion and oxidation of the fuel tube surface can be minimized, improving the overall performance and safety of the fuel.

86

I. Kratochvílová et al.

Various coating materials have been investigated, including pure metals, alloys, ceramics, and MAX phases [21]. Among them, MAX phases such as Zr3 AlC2 , Ti3 SiC2 , and Cr2 AlC have shown promise as protective coatings due to their excellent irradiation damage and corrosion resistance. However, these coatings may not be suitable for use as ATF claddings due to their low oxidation resistance at elevated temperatures. FeCrAl coatings have also been studied as protective coatings, and they are adequate for normal conditions. However, they can undergo rapid degradation in high-temperature steam due to severe inter-diffusion between the coating’s iron element and the zirconium substrate. Therefore, researchers are still exploring various coating materials and designs to find suitable alternatives for use as ATF claddings [17]. Chromium (Cr) coatings have been shown to exhibit high corrosion resistance in supercritical water by forming a stable Cr2 O3 protective scale [15, 17]. However, long-term steam oxidation of Cr coatings can lead to the generation of massive structural defects such as bubbles and cracks due to the significant growth stress caused by the large volume difference between Cr2 O3 and Cr [15, 16, 18]. This can compromise the effectiveness of the coating as a protective barrier. Therefore, researchers are investigating methods to reduce the growth stress and improve the durability of Cr coatings, such as using multilayer coatings or incorporating other materials to buffer the stress [10]. Several studies have shown that coating zirconium alloy surfaces with polycrystalline diamond (PCD) of nanocrystalline structure (NCD) layers grown using a Linear Antenna Microwave Plasma-Enhanced Chemical Vapor Deposition (MWLA-PECVD) apparatus can effectively protect against oxygen and hydrogen uptake in water-cooled nuclear reactor environments, both at normal operating and accident temperatures. Diamond has several desirable properties, such as high thermal conductivity, resistance to chemical degradation, and low neutron absorption cross section, making it an attractive coating material for nuclear fuel cladding. However, more research is needed to optimize the growth processes. The composition of thinlayer polycrystalline diamond (PCD) is not homogeneous, and it typically contains both sp3-hybridized diamond (96%) and sp2-hybridized carbon phases. This composition enables PCD layers to have suitable thermal expansion properties even over a wide range of temperatures, which helps to prevent delamination of the coating from the substrate. The main function of PCD as a corrosion-protective coating is based on the fact that the carbon from PCD can change the surface electrochemistry and semiconductivity of the ZrO2 surface, which can enhance the corrosion resistance of the zirconium alloy substrate [22]. ZIRLO fuel tubes were coated with a new double-layered coating consisting of a technologically easily accessible and inexpensive PCD grown in an MW-LA-PECVD apparatus and magnetron-sputtered Cr. Two double-layered coatings of ZIRLO fuel tubes were used: one with a Cr layer as the bottom and a PCD layer as the top coating and the other with Cr as the top and PCD as the bottom coating. Both protective coatings have different and complementary anti-corrosion functions. The ability of the coating to protect Zr nuclear fuel tubes against emergency temperature corrosion

Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear …

87

has been tested at temperatures above 800 °C at which the so-called high-temperature rapid corrosion occurs.

2 PCD Coating on ZIRLO Substrate: History of Application Due to its exceptional electrical, thermal, and optical properties, diamond is a very attractive material for radiation detection [23, 24]. In [23] a device based on detectorgrade polycrystalline CVD diamond plate with graphite electrical contacts was presented. In [22, 25–27], a new polycrystalline diamond layer application was presented: the composite thin polycrystalline/nanocrystalline diamond (PCD/NCD) coating significantly reduced corrosion of Zr alloy nuclear fuel tube surfaces [28]. Tests have shown that PCD coatings reduce oxidation and penetration of H into Zr alloy both with shortterm elevated emergency temperatures up to 1100 °C and long-term maintenance temperatures (autoclave at 360 °C, resulting in 40% lower oxidation in PCD-coated samples). This prolongs the use of fuel that is removed from the reactor mainly due to surface corrosion rather than sufficient burning and thus improves nuclear safety. The PCD layer is quasi-elastic and can withstand thermal loads, preventing direct contact of the Zr alloys with the corrosive environment of the reactor. In addition, carbon from the PCD layer penetrates the underlying Zr material, changing it to significantly slow the corrosion process. The specific technology of PCD formation results in high-layer adhesion to the surface. Fuel cells covered by PCD are being tested for long-term use in the Halden Norwegian reactor and have been selected by Westinghouse as fuel-resistant [28]. The study in [28] discusses the behavior of PCD-coated Zr alloys in a neutron flux environment, which was simulated using Fe ion beam irradiation. The results show that the NCD films grown using the MW-LA-PECVD method exhibit structural integrity after Fe2+ beam irradiation and hot steam processing. The effects of neutron irradiation on chemical vapor-deposited diamonds were also investigated, and despite an increase in unit-cell volume, the crystalline structure remained stable. The PCD layers grown using the MW-LA-PECVD method consist of diamond and inclusions of anisotropic graphite. The study [29] shows that PCD layers of different thicknesses (300–700 nm) can decrease oxygen and hydrogen uptake into ZIRLO fuel tubes and plates processed in hot water at 360 °C for more than 100 days under primary circuit conditions in Pressurized Water Reactors (PWR) according to ASTM standard procedures. The protective performance of PCD layers was also evaluated in hot steam at 400 °C for 4 days and at extremely high hot steam temperatures of 900– 1100 °C for 1 h and at 1200 °C for 30 min [25, 27, 29]. It was explained that the carbon from the PCD layer enters into the underlying Zr alloy, resulting in a significant change in its structural, chemical, and physical parameters, leading to a lower uptake of hydrogen and oxygen into the material and resulting in a lower degradation of

88

I. Kratochvílová et al.

ZIRLO fuel tubes and ZIRLO plates in hot steam or water environments. Overall, the study suggests that protective PCD layers can prolong nuclear cladding lifetime and enhance nuclear fuel burnup.

3 Growth of PCD Layer on ZIRLO Substrate As the number of possible applications for polycrystalline increases, there is constant development and enhancement of the film properties. Polycrystalline diamond has further advantages if in the form of a thin film (compared to a thicker polycrystalline layer), such as a smoother surface, less deposition time, and less light absorption. PCD thin films can have tailored properties, including controlled grain size and orientation, and can be synthesized with other materials to form composites with enhanced properties. PCD thin films are also highly resistant to wear and chemical corrosion, making them suitable for various applications in harsh environments. Overall, the development of PCD thin film technology has greatly expanded the potential applications of diamond in various fields, including electronics, biomedicine, energy, and aerospace [30, 31]. PCD films can be synthesized using a chemical vapor deposition (CVD) technique. In this method, a substrate is placed in a reactor chamber and heated to a high temperature. A gas mixture containing a carbon source, such as methane, and a hydrogen carrier gas is then introduced into the chamber. RF energy or a microwave discharge is used to dissociate the gas mixture and create a plasma. The carbon atoms in the plasma then deposit onto the substrate surface and form diamond crystals. By controlling the deposition conditions, such as gas composition, pressure, temperature, and deposition time, the microstructure, morphology, and properties of the PCD films can be tailored to meet specific requirements for various applications [32, 33]. The suitability of PCD for various applications depends on material parameters like substrate nature, substrate dimensions, the possibility of nonplanar geometries, surface morphology, electrical conductivity, the capability of device fabrication, electrochemical properties (given by the sp3 /sp2 ratio) and favorable cost. PCD diamond films have advantages compared to single-crystalline forms (like low-cost and large area) thus a variety of applications were meanwhile expanded beyond the classical mechanical use of diamond. These applications include PCD polycrystalline diamonds for optical, electronic, and electrochemical applications, PCD diamond grades for thermal management, and PCD films for a number of further advanced applications [33]. Industrial applications of the polycrystalline diamond grown on large area substrates, 3D shapes, at low substrate temperatures, and on standard engineering substrate materials require novel plasma concepts. One of them is the application of the non-MW-LA-PECVD apparatus for polycrystalline diamond growth (see Fig. 1). The MW-LA-PECVD apparatus consists of a vacuum system, a growth chamber, a pressure control system, a process gas delivery control system, a microwave power controller and delivery system, a water cooling system and an air cooling system. The

Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear …

89

MW-LA-PECVD apparatus is capable of producing both continuous wave and pulsed microwaves, with maximum powers of 3 kW and 10 kW, respectively. Microwave power is controlled by the use of a pulse generator, magnetron heads, rectangular tunable waveguides, and coaxial power distributors. Microwaves are delivered into the growth chamber in a linear form by four pairs of antennas enclosed in quartz envelopes. The linear microwave plasma sources are arranged parallelly to one another above the substrate holder. Temperature of the samples can be estimated during the diamond deposition by a Williamson Pro 92-38 infrared thermometer capable of measurements in the 400– 1000 °C range. The samples (e.g., Zr alloy tubes/rods) are usually immersed/spincoated in a dispersion containing nanodiamond particles, which act as seeds and therefore induce nucleation sites for PCD growth. The samples are then mounted on a substrate or on a specially designed sample holder to ensure that the whole circumference of the sample/tube is exposed to plasma, and placed into the reactor chamber. The MW-LA-PECVD apparatus chamber allows for the deposition of PCD on substrates with sizes as large as 50 × 30 cm2 using a gas mixture of H2 + CH4 + CO2 at low process pressures (95% of the diamond phase, the corrosion was reduced by 25% after a 60 min exposition in 1000 °C hot steam [38].

5.2 Corrosion of ZIRLO Coated by Magnetron-Sputtered Cr The Cr coating on the ZIRLO surface provides protection against hot steam corrosion by forming a dense layer of Cr2 O3 , which acts as a diffusion barrier for oxygen and reduces the oxidation rate in high-temperature steam environments. The interaction between Cr and Zr produces a Cr–Zr interdiffusion layer that improves the adhesion between the coating and the Zr substrate. When the chromium oxide layer grows to a certain extent, Zr diffuses upward, reducing the Cr2 O3 oxide and creating monoclinic ZrO2 , which creates paths for further oxygen uptake into the Zr alloy substrate. In our study, the Cr-coated Zr alloy surface had a layered phase structure, with a Cr-rich sublayer on the surface, followed by chromium oxide (Cr2 O3 ), residual metallic Cr, and the Zr–Cr intermetallic phase and oxidized Zr-αZr(O) in the inward direction. The characterization of the coated surface was performed using techniques such as SEM, Raman spectroscopy/optical microscopy, and electrochemical impedance spectroscopy (EDS). The results indicate that the Cr coating provides effective protection against hot steam corrosion of ZIRLO.

5.3 Hot Steam Oxidation of PCD and Cr-Coated ZIRLO Additionally, in the results of accidental-temperature water/steam tests, ZIRLO/PCD were also compared to ZIRLO/Cr and double coated of ZIRLO: ZIRLO/PCD/Cr and

Polycrystalline Diamond and Cr Double Coatings Protect Zr Nuclear …

97

ZIRLO/Cr/PCD (Fig. 6). Coated and bare ZIRLO fuel cladding tubes were placed for 30 min in a 900 °C hot steam furnace followed by 40 min in a 1000 °C hot steam furnace. The measured weight gains were caused by oxidation and hydrogen uptake into the hot steam-tested samples. The hot steam oxidation kinetics of different coatings on ZIRLO fuel cladding tubes were measured using a hot steam furnace. The initial oxidation stage (1 to ≤120

(>9.807 to ≤1176.800 N)

ISO 4545

1–1

(0.0098 to ≤9.807 N)

ASTM E 384

1–1

(0.0098 to ≤9.807 N)

Brinell Vickers

Knoop

indent’s diagonals to establish the hardness. Generally speaking, the material behind the indent during the hardness test should be indicative of the whole microstructure. Therefore, a larger impression is advised than for a homogeneous material if the microstructure is rather coarse and heterogeneous. The following primary factors should be taken into account when choosing the hardness test method: the type of material to be tested, whether compliance with a standard is required, the tested material’s typical hardness, the homogeneity or heterogeneity of the testing material, sample size and shape, mounting circumstances, the number of tested samples, and the degree of result accuracy. There are specific requirements for the different hardness tests (Table 11).

4.7 Measurement of Enthalpy An approach called calorimetry is typically used to assess enthalpy. By monitoring the temperature variations, the heat evolved during the operation is typically computed using the known heat capacities of the liquid and the calorimeter. Two different situations are used to conduct these measurements: It is important to remember that enthalpy and internal energy can be calculated using two different methods: constant volume, which is referred to as internal energy, and constant pressure, which is referred to as enthalpy. – At constant pressure, qp – At constant volume, qv . Enthalpy is defined as the energy released at constant pressure. Mathematically, it is the sum of internal energy with the product of pressure and volume. H = U + PV

(4)

152

T. D. Duy and V. Duong

where H U P V

is th enthalpy is the internal energy is the pressure of the system is the volume of the system.

Directly calculating a system’s absolute enthalpy is rather challenging. So, it is possible to determine the enthalpy around a reference point. As a result, it is used to calculate enthalpy change. Enthalpy change, or ∆H, is positive for endothermic processes, whereas it is negative for exothermic ones. Calorimetry methods are used to measure the change in enthalpy under laboratory circumstances. Enthalpy change is understood to be the heat change at constant pressure, or ∆H = qp . This approach involves partially filling the system with a specified amount of water and inserting a thermometer to gauge the temperature change. The heat generated by a chemical reaction is absorbed by the water. The quantity of heat that has been absorbed or developed is determined by the change in water temperature. In this procedure, the energy change or enthalpy change is computed as ∆H = q p = m · c p · ∆T

(5)

where m cp ∆T

mass of water specific heat capacity of water at constant pressure temperature difference.

4.8 Determination of the Velocity of Particles in Plasma Spraying A high-speed imaging camera can capture fast-moving events at high frame rates and replay the recorded pictures as a slow-motion movie. When choosing a highspeed camera for your study, there are a number of factors to take into account. This, of course, has an impact on the intended resolution, so a powerful system is often required if a particular resolution and frame are desired. Your image’s duration is determined by the frames per second; a longer movie will be produced at a higher frame rate. The image size, object velocity, and temporal resolution must all be taken into consideration when calculating the frame rate. The determination of the frame rate is greatly influenced by the image size. Because bigger events (events with larger picture sizes) often last longer throughout the full field of vision, they tend to have lower frame rates than those recorded at a higher magnification. The frame rate must be raised to capture a shorter period of time (within a narrower field of vision). The resolution is the number of pixels for a specific field of vision. The image resolution determines which features of your image can be resolved. A photograph with a greater resolution will really be of “better quality.” The greatest

A New Solution to Save Production Costs in the Deposition …

153

resolution and required frame rate cannot, however, be obtained with all cameras. It is necessary to first determine the frame rate and then assess the resolution of potential cameras in order to choose one that will deliver the proper frame rate and a suitable resolution. The amount of time that a camera’s film (or digital sensor) is exposed to light is known as exposure time (also known as shutter speed). Motion blur, also known as the sharpness or blurriness of a picture, is influenced by exposure duration. A little bit of blurriness in a photograph is usually accepted, but if there is a lot of motion blur, the subject’s edges look blurry, and it is hard to measure and distinguish the subject without a clear outline. Due to their high frame rates, highspeed imaging cameras often have short exposure durations. A shorter exposure time indicates that less time is needed for light to reach the camera’s sensor. Some cameras require a manual trigger, which means we must wait for the event to happen before activating the camera system to start taking pictures. The electronic shutter may be precisely timed to operate in phase with a timing signal through synchronization. The Inter-Range Instrumentation Group (IRIG-B) time code with or without phase shift, the internal camera clock (crystal frequency oscillator), the external clock source (f-sync signal from a second camera or any source that generates a TTL pulse), and the video signal are all synchronization instruments (f-sync pulses generated by the video raster generator). Multiple cameras may be present. A good lens is a crucial component of a successful photographic setup. There are several factors that need to be taken into account while choosing lenses. This comprises the following: sensor size, flange focal distance, field of vision, depth of field, and lens mount. The lens mount serves as the mechanical (and occasionally electronic) link between the camera body and the lens. The focal length is the separation between the lens’s nodal plane and the point at which light waves converge. The opening in the lens through which light passes is called the aperture (also known as the f-stop). The aperture controls both the amount of light the camera receives and the angle at which different wavelengths focus on the picture plane. As was already noted, the image size is essentially determined by the field of vision. The area of the image that seems to be reasonably crisp is called the “depth of field” (as opposed to softer portions of the image, which may appear as a background). The actual dimensions of the image sensor’s active area make up the sensor’s size. The distance between the picture plane and the front face of the image camera’s front mount is known as the “flange focal distance.” The sort of photographs that are needed and the topic that has to be shot will eventually choose the proper lens, which will deliver a clear and accurate image of its subject. The price variations between lenses often correspond to the variations in their speeds. Fast lenses are more expensive and lighter, and they allow us to photograph in low light with faster shutter speeds. Depending on the application, choosing between monochrome and color systems is a crucial choice. Color masks are used in polychrome systems to lower sensitivity by two to three times. As a result, a polychrome system needs two to three times more light to produce a picture with the same exposure as a monochrome system. While the ability to discern between hues may be useful in some applications, it is not always essential in laboratory research because the drawback of decreased light sensitivity is frequently noticeable. For the

154

T. D. Duy and V. Duong

examination of photographs, a variety of tools are available. Manufacturers of highspeed cameras typically sell their own packages of analysis software. This program may be used to obtain quantitative quantities, including the subject’s velocity, as well as to edit pictures and videos. Additionally, there are various free picture analysis apps that should be taken into consideration.

5 Conclusions – Spray thermal coatings are used to deposit heated powder droplets onto a substrate’s surface, creating a coating and giving it a certain surface quality that it did not have before. As a result, the substrate provides the component’s bonding and cohesive strength, while coatings improve the surface’s superior properties, including wear resistance, corrosion resistance, and heat resistance. The main benefit of thermal spray coatings is that they may provide certain surface characteristics that are only possible by thermal spraying and operate well in high-temperature environments. Therefore, for new and reconditioned sections and components for jet engines and gas turbines, compressors, and pumps, thermal spray coatings are widely utilized in the aerospace, automotive, and power generation industries. – The most commonly used thermal spray technology for coatings is plasma spraying, which can apply coatings through both inert gases and their mixtures as well as through regular air. In order to ensure the resourcefulness of the electrodes and the quality of the coatings, particularly the Fe-based amorphous powder, the construction of this type of plasma torch and the entire system requires some specific design. This helps to lower production costs and improve some coating properties, depending on the working conditions. – The modernization and creative design of the plasma torch’s construction can help increase the efficiency of the thermal spray process. These improved solutions focus on stabilizing the plasma stream, which raises the temperature and velocity of the particle stream. This topic has been the subject of various fascinating investigations, such as those on better laminar or cascaded plasma torches with swirling units. The internal shape of the anode nozzle, in particular, has a significant impact on the kinetic and thermal characteristics of the in-flight particles, which in turn affect the coating quality. – A unique annular input unit for supplying powder material that coincides with the Laval inner contour of the anode in the plasma torch was installed in the cascaded plasma torch to modernize the supersonic plasma jet outflow. A swirl unit’s vortex movement enhances gas mixing in the arc stream, isolates it from the plasma channel walls, and raises the voltage of the plasma jet. The plasma torch will operate more favorably with a longer jet length because the axial temperature gradient will be improved, the cathode’s lifespan will be increased by a reduction in plasma current, and the voltage drop may be increased thanks to the changeable length of the plasma jet.

A New Solution to Save Production Costs in the Deposition …

155

– Surface engineering and matrix strengthening are the main avenues for enhancing wear resistance in coatings. This issue can also be taken into account in close connection to the composition, grain size, and spraying process parameters, particularly the velocity and temperature of the particle stream. Fe-based amorphous coatings and other nanocomposite coatings with higher wear resistance can be found in high-temperature environments. The modern wear resistance capabilities of the surface in a heavy operating environment are made possible by the right design of the surface coating layer. It is generally acknowledged that a key factor in determining how resistant a material is to wear is its hardness. However, depending on the macro- and microscale domains, as well as the lubrication conditions, the stiffness of the surface layer in the substrate plays a variety of roles in the wear resistance. – The porosity has advantages and disadvantages depending on how the coating was applied. The porosity has a beneficial function in thermal-barrier coatings, but depending on the loading and lubrication conditions, it has a variable impact on wear- or corrosion-resistant coatings. The thermal insulation of thermal-barrier coatings is greatly influenced by the size, shape, and distribution of the pores. The spraying parameters, the physical, mechanical, and chemical interactions between the in-flight particle and the spraying jet, as well as the substrate contact process, can control these features. – It is obviously challenging to suggest a general approach for all coating types given their diverse uses and operational environments. The most often drawn conclusion from this chapter is how to enhance everything, including the engineering surface, the substrate layer’s matrix, and the plasma torch’s unique construction, with the right technological processes and feedstock materials. The quality of the coatings and the cost of manufacturing are heavily dependent on the managers’ and investors’ wise and prudent decisions.

References 1. Vardelle, A., et al.: The 2016 thermal spray roadmap (review). J. Therm. Spray Technol. 25(8), 1376–1433 (2016). https://doi.org/10.1007/s11666-016-0473-x 2. Schinder, B., Garling, A., Mayer, U., Grabs, R., Lampke, T.: Advanced corrosion resistant cylinder—Bore coatings. IOP Conf. Ser.: Mater. Sci. Eng. 1147(2021), 012034 (2021). https:// doi.org/10.1088/1757-899X/1147/1/012034 3. Shukla, V.N., Gupta, D., Misra, V.: Advantage of advanced erosion-corrosion resistant nanostructured coatings: a review. Int. J. Adv. Res. Sci. Eng. 06(02), 552–559 (2017). ISSN:23198354 4. Joshi, S., Nylen, P.: Advanced coatings by thermal spray processes. Technologies 7(79) (2019). https://doi.org/10.3390/technologies7040079 5. Mondal, K., Nu˜nez III, L., Downey, C.M., Van Rooyen, I.J.: Thermal barrier coatings overview: design, manufacturing and applications in high-temperature industry. Ind. Eng. Chem. Res. 60, 176061–6067 (2021). https://doi.org/10.1021/asc.iecr.1c00788 6. Hussainova, I., Antonov, M.: Assessment of cermet performance in erosive media. Int. J. Mater. Prod. Technol. 28(3–4), 361–376 (2007). https://doi.org/10.1504/IJMPT.2007.013085

156

T. D. Duy and V. Duong

7. De la Obra, A.G., Aviles, M.A., Torres, Y., Chicardi, E.: A new family of cermets: chemically complex but microstructurally simply. Int. J. Refract. Metals Hard Metar. 63, 17–25 (2016). https://doi.org/10.1016/j.ijrmhm.2016.04.011 8. Jose, S.A., John, M., Menezes, P.L.: Cermet system: synthesis, properties and applications. Ceramics 5(2), 210–236 (2022). https://doi.org/10.3390/ceramics5020018 9. Moraes, C.G.P., et al.: Investigating the correlation between the microstructure and electrical properties of FeSbO4 ceramics. Materials 15(19), 6555 (2022). https://doi.org/10.3390/ma1 5196555 10. Trelka, A., et al.: The effect of the substrate on the microstructure and tribological properties of cold sprayed (Cr3 C2 –25(Ni20Cr))-(Ni-Graphite) cermet coatings. Materials 15(3), 994 (2022). https://doi.org/10.3390/ma15040994 11. Kolnes, M., et al.: Performance of ceramic-metal composites as potential tool materials for friction stir welding of aluminium. Coper Stain. Steel. Mater. 13(8), 1994 (2022). https://doi. org/10.3390/ma13081994 12. Heydari, L., et al.: Ti (C, N) and WC-based cermets: a review of synthesis, properties and applications in additive manufacturing. Materials 14(22), 6786 (2021). https://doi.org/10.3390/ ma14226786 13. Wang, G., Huang, Z., Xiao, P., Zhu, X.: Spraying of Fe-based amorphous coatings with high corrosion resistance by HVAF. J. Manuf. Process. 22, 34–38 (2016). https://doi.org/10.1016/j. jmapro.2016.01.009 14. Zhang, S., Li, W., Hu, Y., Jiang, T., Guo, L., Zhang, Y., Zhao, Y.: Effect of spraying power on the microtructure and wear behavior of the plasma-sprayed FeCoCrNiMo0.2 coatings. AIP Adv. 11(11), 115110 (2021). https://doi.org/10.1063/5.0074776 15. Report on Carcinogens-Background Document for Cobalt—Tungsten Carbide: Powder and Hard Metal. National Toxicology Program, U.S. Department of Health and Human Services, Public Health Service, Research Triangle Park, NC 27709, 180 pp (2009). https://ntp.niehs. nih.gov/ntp/roc/twelfth/2010/finalbds/hardmetalsbd20100408_508.pdf 16. Li, Y., Li, C.J., Yang, G.J., Xing, L.K.: Thermal fatigue behavior of thermal barrier coatings with the McrAlY bond coasts by cold spraying and low-pressure plasma spraying. Surf. Coat. Technol. 205, 2225–2233 (2010). https://doi.org/10.1016/j.surfcoat.2010.08.144 17. Eden, T.J., Wolfe, D.E., Champagne, V., Widener, C.: Chapter 9-Cold spray applications in the defense industry (2016). https://doi.org/10.31399/asm.tb.hpcspa.t54460227 18. Tan, K., Markovych, S., Hu, W., Wang, Y., Shorinov, O., Wang, Y.: On the characteristics of cold spray technology and its application in aerospace industry. In: The 7th international conference on environmental science and civil engineering. IOP Conf. Ser.: Earth Eviron. Sci. 719, 032023 (2021). https://doi.org/10.1088/1755-1315/719/3/032023 19. Kumar, S., Kumar, M., Jindal, N.: Overview of cold spray coating applications and comparisons: a critical review. World J. Eng. 17(1), 27–51 (2021). https://doi.org/10.1108/WJE-01-20190021 20. Lee, C., et al.: Applicability of aerosol deposition process for flexible electronic device and determining the film formation mechanism with cushioning effect. Sci. Rep. 9, 2166 (2019). https://doi.org/10.1038/s41598-019-38477-y 21. Hanft, D., Exner, J., Schbert, M., Stocker, T., Fuierer, P., Moss, R.: An overview of aerosol deposition method: process fundamentals and new trends in material applications. J. Ceram. Sci. Technol. 6(3), 147–182(2015). https://doi.org/10.4416/JCST2015-00018 22. Li, C., Singh, N., Andrews, A., Olson, B.A., Schwartzentruber, T.E., Hogan Jr, C.J.: Mass, momentum and energy transfer in supersonic aerosol deposition processes. Int. J. Heat Mass Transf. 129, 1161–1171 (2019). https://doi.org/10.1016/j.ijheatmasstransfer.2018.10.028 23. Jami, H., Jabbarzadeh, A.: Ultrafast thermodynamical effects in aerosol deposition of hydroxyapatite nanoparticles on a titanium substrate. Surf. Coat. Technol. 382, 125173 (2020). https:// doi.org/10.1016/j.surfcoat.2019.125173 24. Smith, M.F., Hall, A.C., Fleetwood, J.D., Meyer, P.: Very low pressure plasma spray-a review of an emerging technology in the thermal spray community. Coatings 1, 117–132 (2011). https:// doi.org/10.3390/coatings1020117

A New Solution to Save Production Costs in the Deposition …

157

25. Aghasibeig, M., Tarasi, F., Lima, R.S., Dolatabadi, A., Moreau, C.: A review on suspension thermal spray patented technology evolution. J. Thermal Spray Technol. 28, 1579–1605 (2019). https://doi.org/10.1007/s11666-019-00904-x 26. Joshi, S.: Advances in thermal spray technology. Materials 13, 3521 (2020). https://doi.org/10. 3390/ma13163521 27. Pawlowski, L.: Suspension and solution thermal spray coatings. Surf. Coat. Technol. 203, 2807–2829 (2009). https://doi.org/10.1016/j.surfcoat.2009.03.005 28. Killinger, A., Gadow, R., Mauer, G., Guignard, A., Vasen, R., Stover, D.: Review of new developments in suspension and solution precusor thermal spray processes. JTTEE 5(20), 677–695 (2011). https://doi.org/10.1007/s11666-011-9639-8 29. Ghorui, S., Das, A.K.: Arc plasma devices: evolving mechanical design from numerical simulation. Pranama J. Phys. Indian Acad. Sci. 80(4), 685–699 (2013). https://doi.org/10.1007/s12 043-012-0491-2 30. Kuzmin, V., Gulyaev, I., Sergachev, D., Vashchenko, S., Lysakov, A., Palagushkin, B.: Supersonic air-plasma spraying of carbide ceramic coatings. Mater.: Proc. 38(4), 1974–1979 (2021). https://doi.org/10.1016/j.matpr.2020.09.150 31. Brardwaj, R.L., Lahirl, S., Shukla, R., Mascarenhas, M.R., Sharma, A.: Design and development of indigenous 100 kW plasma torch. BARC Newsl. Res. Dev. 381, 30–32 (2022), 0976–2108 32. Caliari, F.R., Miranda, F.S., Reis, D.A.P., Filho, G.P., Charakhovski, L.I., Essiptchouk, A.: Plasma torch for supersonic plasma spray at atmospheric pressure. J. Mater. Process. Technol. 237, 351–360 (2016). https://doi.org/10.1016/j.jmatprotec.2016.06.027 33. Rotundo, F., et al.: Design and optimization of components and processes for plasma sources in advanced material treatments. Dotoratto di Ricerca in Maccanica e Scienze Avanzate dell’Ingegneria, Ciclo XXIV, Settore Concorsuale: 09/A3 (2012) 34. Sun, Q., Liu, Y., Zhu, Y., Han, Y.: Experimental Investigation into the anode erosion phenomenon in DC non-transferred arc plasma torch. Preprint from Research Square PPR: PPR239050 (2020). https://doi.org/10.21203/re.3.rs/106433/v1 35. Wen, K., Liu, M., Zhou, K., Liu, X., Huang, R., Mao, J., Yang, K., Zhang, X., Deng, C., Deng, C.: The influence of anode inner contour on atmospheric DC plasma spraying process. Adv. Mater. Sci. Eng. 1–12 (2017). https://doi.org/10.1155/2017/2084363 36. Kittaka, S., Satto, T., Vakida, S., Miyashita, M.: Twin-torch type tundish plasma heater “NSPlasma II” for continuous caster. Nippon Steel Technical Report, 2 (2005). UDC 621.746.27: 621.36 37. Gros, P., Kurekova, E.: Advanced experiments designs for three torch plasma cutter testing. Meas. Sci. Rev. 5(3), 67–70 (2005). https://www.measurement.sk/2005/S3/Gros.pdf 38. Yu, N., Jourdain, R., Gourma, M., Xu, F., Bennett, A., Fang, F.: Power dissipation of an inductively coupled plasma torch under E mode dominated regime. Micromachine 12(7), 834 (2021). https://doi.org/10.3390/mi12070834 39. Marques, J.-L., Forster, G., Schein, J.: Multi-electrode plasma torch: motivation for development and current state-of-the art. Open Plasma Phys. J. 2, 89–98, 1876–5343 (2009). https:// benthamopen.com/contents/pdf/TOPPJ/TOPPJ-2-89.pdf 40. Safronov, A.A., Kuznetsov, V.E., Vasilieva, O.B., Dudnik, Y.D., Shiryaev, V.N.: AC Plasma torch. Arc initiation system. Design feature and applications. Instru. Exp. Tech. 62(2), 193–200 (2019). https://link.springer.com/journal/10786/volumes-and-issues/62-2 41. Surov, A.V., Popov, S.D., Serba, E.O., Pavlov, A.V., Nakonechny, G.V., Spodobin, V.A., Nikonov, A.V., Borovskoy, A.M.: High voltage AC plasma torches with long electric arcs for plasma-chemical applications. In: 14th High-Tech Plasma Processes Conference. IOP Conf. Series: J. Phys.: Conf. Ser. (825), 012016 (2017). https://doi.org/10.1088/1742-6596/825/1/ 012016 42. Safronov, A., Shiryaev, V., Popov, S., Surov, A.: Poweful alternating current plasma torches for plasma technologies (2015). https://www.researchgate.net/publication/267261674 43. Global Thermal Spray Coatings Market: Report ID: GMI 1347 (2018). https://www.gminsi ghts.com/industry-analysis/thermal-spray-coating-market

158

T. D. Duy and V. Duong

44. Kuzmin, V., Gulyaev, I., Sergachev, D., Vashchenko, S., Lysakov, A., Palagushkin, B.: Supersonic air-plasma spraying of carbide ceramic coatings. Mater. Today: Proc. xxx(xxxx), 2214–7853 (2020) (Elsevier Ltd.). https://doi.org/10.1016/j.matpr.2020.09.150 45. Kuzmin, V., Gulyaev, I., Sergachev, D., Vaschenko, S., Kornienko, E., Tokarev, A.: Equipment and technologies of air-plasma spraying of functional coatings. MATEC Web of conference 129, 01052 (2017). https://doi.org/10.1051/matecconf/201712901052 46. Zhai, J., Li, C., Tian, L., Lu, Y., Kou, S.: A review of corrosion resistance of Fe-based amorphous coatings: influencing factors and enhancing methods. Mater. Rep. 35(3), 03129–03140 (2021). https://doi.org/10.11896/cldb.20040058 47. Iqbal, A., Siddique, S., Maqsood, M., Rehman, M.A.U., Yasir, M.: Comparative analysis on the structure and properties of iron-based amorphous coating sprayed with the thermal spraying techniques. Coatings 10, 1006 (2020). https://doi.org/10.3390/coatings10101006 48. Xu, Y., Wang, Y., Xu, Y., Li, M., Hu, Z.: Microscopic characteristics and properties of Fe-based amorphous alloy compound reinforced WC–Co-based coatings via plasma spray welding. Processes 9, 6 (2021). https://www.mdpi.com/journal/processes 49. Li, G., Gan, Y., Liu, C., Shi, Y., Zhao, Y., Kou, S.: Corrosion and wear resistance of Fe-based amorphous coatings. Coatings 10(1), 73 (2020). https://doi.org/10.3390/coatings10010073 50. Priyan, M.S., Hariharan, P.: Wear and corrosion resistance of Fe based coatings by HVOF sprayed on gray cast-iron for automotive application. Tribol. Ind. 35(4), 394–405 (2014). www.tribology.fink.rs 51. Zhang, C., Shen, X., Wang, J., Xu, C., He, J., Bai, X. Improving surface properties of Fe-based laser cladding coating deposited on a carbon steel by heat assisted ultrasonic burnishing. J. Mater. Res. Technol. 12, 110–116 (2021). https://doi.org/10.1016/j.jmrt.2021.02.076 52. Ma, H., Li, D., Li, J.: Effect of spraying power on microstructure, corrosion and wear resistance of fe-based amorphous coatings. J. Thermal Spray Technol 31, 1683–1694 (2022). https://doi. org/10.1007/s11666-022-01403-2 53. Ma, H.R., Chen, X.Y., Li, J.W., Chang, C.T., Wang, G., Li, H., Wang, X.M., Li, R.W.: Fe-based amorphous coating with high corrosion and wear resistance. Surf. Eng. 33(1), 56–62 (2017). https://doi.org/10.1080/02670844.2016.1176718 54. Arizmendi-Morquecho, A., Campa-Castilla, A., Leyva-Porras, C., Aguilar Martinez, J.A., Vargas Gutiérrez, G., Moreno Bello, K.J. and López López, L.: Microstructural characterization and wear properties of Fe-based amorphous-crystalline coating deposited by twin wire arc spraying. Adv. Mater. Sci. Eng. 2014, 11, article ID 836739 (2014). https://doi.org/10.1155/ 2014/836739 55. Vu, D., Le Thu, Q.: The bilateral influence of main parameters in plasma spray using the air as primary gas on tribology of Fe-based amorphous coatings. In: Proceedings of the second International Conference on Advanced Mechanical Engineering, Automation, and Sustainable Development (AMAS) (2021). ISBN 978-3-030-99665-9 56. Kumar, A., Kumar, R., Bijalwan, P., Dutta, M., Banerjee, A., Laha, T., Fe-based amorphous/ nanocrystalline composite coating by plasma spraying: effect of heat input on morphology, phase evolution and mechnical properties. J. Alloy Comps. 771, 827–837(2019). https://doi. org/10.1016/j.jallcom.2018.09.024 57. Chen, L.Y., Xu, T., Lu, S., Wang, Z.X., Chen, S., Zhang, L.C.: Improved hardness and wear resistance of plasma sprayed nanostructured NiCrBSi coatings via short-time heat treatment. Surf. Coat. Technol. 350, 436–444 (2018). https://doi.org/10.1016/j.surfcoat.2018.07.037 58. Lee, J.-H., Kim, Y.-S.: Effect of post heat treatment on wear characteristics of thermal sprayed Co-based self-flux alloy coatings. J. Power Syst. Eng. 18(1) (2014). https://doi.org/10.9726/ kspse.2014.18.1.106 59. Liu, L., Xu, H., Xiao, J., Wei, X., Zhang, G., Zhang, C.: Effect of heat treatment on structure and property evolutions of atmospheric plasma sprayed NiCrBSi coatings. Surf. Coat. Technol. 326, 548–554 (2017). https://doi.org/10.1016/J.SURFCOAT.2017.07.011 60. Pakseresht, A.H., Rahimipour, M.R., Vaezi, M.R., Salehi, M.: Effect of heat treatment on the microstructure and dielectric properties of plasma—Sprayed barium titanate films. Int. J. Mater. Res. 107, 28–34 (2016). https://doi.org/10.3139/146.111314

A New Solution to Save Production Costs in the Deposition …

159

61. ASTM E2109-01.: Standard test methods for determining area percentage porosity in thermal sprayed coatings. ASTM International, West Conshohocken, PA (2014).www.astm.org 62. Wang, H., Gee, M., Qiu, Q., Zhang, H., Liu, X., Nie, H., Song, X., Nie, Z.: Grain size effect on wear resistance of WC–Co cemented carbides under different tribological conditions. J. Mater. Sci. Technol. 35, 2435–2446 (2019). https://doi.org/10.1016/j.jmst.2019.07.016 63. Manjunatha, S.S., Basavarajappa, S.: Effect of powder particle size on wear resistance of plasma sprayed molipdenum coating. Proc. Imech E Part J: J. Eng. Tribol. 228(7), 789–796 (2014). https://doi.org/10.1177/1350650114531744 64. Movahedi, B.: Mechanical investigation approach to optimize the high-velocity oxygen fuel Fe-based amorphous coatings reinforced by B4 C nanoparticles. Int. J. Mater. Metall. Eng. 12(9) (2018). ISNI:0000000091950263 65. Konyashin, I., Ries, B., Hlawatscheck, D., Zhuk, Y., Mazilkin, A., Strauman, B., Dorn, F., Park, D.: Wear-resistance and hardness: are they directly related for nanostructured hard materials? Int. J. Refract Metal Hard Mater. 49, 203–211 (2015). https://doi.org/10.1016/j.ijrmhm.2014. 06.017 66. Rao, D.S., Sivakumar, G., Sen, D., Joshi, S.V.: Detonation sprayed coatings and their tribological performance. Chapter, 294–327 (2015). https://doi.org/10.4018/978-1-4666-7489-9. ch010 67. Xie, L., Wang, Y.-M., Xiong, X., Chen, Z.-K.: Comparison of microstructure and tribological properties of plasma, high velocity oxygen-fuel and detonation sprayed coatings form an iron— Based powders. Mater. Trans. 59(10), 1591–1595 (2018). https://doi.org/10.2320/matertrans. M2018141 68. Rus, D., Capitanu, L., Badita, L.-L.: A qualitative correlation between friction coefficient and steel surface wear in linear dry sliding contact to polymer with SGF. Friction 2(1), 47–57 (2014). https://doi.org/10.1007/s40544-014-0038-2 69. Ran, X., Shang, J., Wang, L., Zhang, X.: Effect of porosity on wear behavior of remanufacturing Cr3 C2 –NiCr coatings under oil lubrications. Procedia Manuf. 43, 487–494 (2020) (Elsevier B.V.) 70. Curry, N., Leitner, M., Körner, K.: High—Porosity thermal barrier coatings from high— Power plasma spray equipment—Processing, performance and economics. Coatings 10(10), 957 (2020). https://doi.org/10.3390/coatings10100957 71. Curry, N., Leitner, M., Körner, K.: Improved corrosion behavior and biocompatibility of porous titanium samples coated with bioactive chitosan-based nanocomposites. Materials 14, 6322 (2021). https://doi.org/10.3390/ma14216322 72. Odhiambo, J.G., Li, W., Zhao, Y., Li, C.: Porosity and its significance in plasma-sprayed coatings. Coatings 9(7), 460 (2019). https://doi.org/10.3390/coatings9070460 73. Cheppudira Thimmaiah, P., Panda, A.K., Pandey, U.K., McCague, C., Dutta, P., Bahrami, M.: A new approach to compute the porosity and surface roughness of porous coated capillaryassisted low pressure evaporators. Sci. Rep. 8,11708 (2018). https://doi.org/10.1038/s41598018-30090-9

Duong Vu received a Ph.D. in mechanical engineering from Saint Petersburg University, Russia, in 1993. He graduated from the university in 1980 (Eastern Ukrainian University). His diploma is in Equipment and Technology of Welding Production. He is currently the vice dean of the School of Engineering Technology at Duy Tan University in Danang, Vietnam. His interests are in welding technology, plasma spraying technology, surface treatment, materials science, manufacturing processes, applied mechatronics, entrepreneurship, professional starter education, and engineering technology education. He published about 40 works (papers, proceedings of international conferences, books, and book chapters) and taught courses such as Applied Strength of Materials, Materials and Manufacturing, Machine Design, Machine Element, and Production Drawing and CAD.

Wear/Erosion Resistant High-Temperature Coatings S. Arulvel, D. Dsilva Winfred Rufuss, Jayakrishna Kandasamy, P. Kumaravelu, R. Prayer Riju, and P. U. Premsuryakanth

Abstract Numerous mechanical parts, including, rotary vanes, emission and intake blowers, rotor rings, boiler tubes, steam turbines, gas turbines, pulverized fuel supply lines, nozzles, and gun barrels, are susceptible to erosive wear. Due to the simultaneous effects of various factors such as particle size, velocity, hardness, and impact angle, this erosive wear phenomenon is extremely complex. To alleviate the problems caused by erosion, several technical solutions have been proposed. Amongst these coatings are one such solution. The application of high-temperature coatings was found to be an efficient technique to reduce erosive wear in extreme environments. In recent years, many ceramic and metal coatings have both advantages and drawbacks. Therefore, it is crucial to discuss how different high-temperature coatings might enhance the erosive wear resistance. The technology development, influencing variables, properties, and failures of high-temperature erosion-resistant coatings are therefore highlighted in the current chapter. This could open up new opportunities for research into cutting-edge high-temperature erosive wear resistance coatings. Keywords Erosion · Wear · Coatings · High temperature · Failures

Nomenclature Ti–6Al–4V Al2 O3 Al AISI ASTM APS B C

Alpha-beta titanium alloy Alumina Aluminium American Iron and Steel Institute American Society for Testing and Materials Atmospheric plasma spray Boron Carbon

S. Arulvel (B) · D. Dsilva Winfred Rufuss · J. Kandasamy · P. Kumaravelu · R. Prayer Riju · P. U. Premsuryakanth School of Mechanical Engineering, Vellore Institute of Technology, Vellore 632014, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_7

161

162

CNTs CVD Cr Cr3 C2 Co °C DC g/g HVOF HEA h HfC K Kg kW LZO Q345 µm mm Mg min NASA Ni NiAl IN625 NiCr PVD RF Gr SEM SA210 s Si SiC SiO2 SPE SS TaC TBCs Ti TiN MDN321 WC UV V

S. Arulvel et al.

Carbon nanotubes Chemical vapour deposition Chromium Chromium carbide Cobalt Degree Celsius Direct current Gramme per gramme High Velocity Oxygen Fuel High-entropy alloys Hour Hydrofluorocarbon kelvin Kilogramme kilowatt Lanthanum zirconium oxide low alloy steel Micro metre Millimetre Milligramme Minutes National Aeronautics and Space Administration Nickel Nickel aluminide Nickel-based superalloy Nickel-Chromium Alloys Physical vapour deposition Radio frequency Roentgenium Scanning electron microscope Seamless medium carbon steel Second Silicon Silicon carbide Silicon dioxide Solid particle erosion Stainless steel Tantalum carbide Thermal barrier coatings Titanium Titanium nitride Titanium stabilized austenitic stainless steel Tungsten carbide Ultraviolet Vanadium

Wear/Erosion Resistant High-Temperature Coatings

YSZ Y ZrC ZrO2

163

Yttria stabilized-zirconia Yttrium Zirconium carbide Zirconium dioxide

1 Introduction Solid particle erosion (SPE) and high-temperature erosion wear are the major issues in many of the engineering components. This type of erosions has a wider impact on the failures of components in various applications such as steam turbines, gas turbines, wind turbines, hydroelectric power plants, and boiler tubes, which leads to plant shut down and resulting in large economic losses through maintenance and replacement [1]. The gas turbine engine is a critical part of the aircraft, which often subjects to the SPE damage. This leads to high maintenance costs, high fuel consumption, and high emissions problems [2]. In addition, the mission completion rates, readiness, and safety decrease could produce the catastrophic accidents of the turbine engines [3]. The wind turbines are also subjects to SPE damage, which can result in higher cost with decrement in the annual energy production. In other application like hydroelectric power plants, the corrosion and SPE are the challenging problems and can result in increased maintenance costs and production losses. So, it is clear that the erosion wear was the serious drawbacks in the components of engineering applications [4]. Hence, to enhance the life of the components with low maintenance costs, an extensive effort has been put up to improve the surface properties of the materials [5], which is briefly discussed in this chapter. Materials like titanium, stainless steel, and nickel-based alloys were often used in the aerospace, automobile, and energy sectors, where the erosive wear is predominant. So, researchers studied the erosive wear behaviour of titanium, stainless steel, and nickel alloys at various parameters [6]. Ti6 Al4 V is a commonly used alloy in the aerospace field, and different authors have studied its solid particle erosion properties at varying temperatures. Generally, the rate of erosion decreases with the temperature for all angles of impingement. Accordingly, the similar findings were observed for the Inconel and SS304 alloys, both of which are used in the aerospace sector. However, in 1989, Tabakoff reported an increase in erosion rate for both Inconel alloys and Ti6 Al4 V alloy with the increase in the temperature. This may be due to the fact that Tabakoff only tested the alloys at 204 and 371 °C for Ti6 Al4 V and Inconel, respectively, which did not allow for the observation of a downtrend in the erosion rate [7]. In the case of SS410 alloy, the erosion rate decreased for lower angle impingements and increased for normal impingement angle (30°) with high temperature. A similar trend was observed for the Al2024 alloy, with decreased erosion rates for a 20° impinging angle and increased erosion rates for 60°. Here, the rate of material removal depends on the hardness of the material, as well as the erodent

164

S. Arulvel et al.

[8]. Therefore, the hardness of the material plays a vital role in the improvement of erosion resistance. During SPE, the particles with the size ranging from 10 to 300 µm collide with the substrate and transfer their energy to it. This kinetic energy leads to break the bonds and initiates the cracking process in the brittle substrates or plastic deformation in the metallic substrates [9]. Furthermore, different material clearance techniques, including brittle fracture, cutting, and melting, fatigue, might erosive wear even worse. So in addition to the hardness, the properties like ductility, thermal expansion, and oxidation resistance are important to control the erosive wear [10]. The machinery components such as turbines, propellers, pumps, and valves are often subjects to surface degradation like erosion and wear with a significant economic impact. To address this issue, more advanced materials with superior surface characteristics are necessary. So, researchers have proposed a wide range of coatings on the materials to prevent the erosion. These can be categorized as titanium-based, ferrous, cobalt-based, bulk metallic glass, and nickel-based materials In the case of ductile ferrous materials (SS304), the erosion increases with the impact velocity and reaches a critical value. To reduce the impact caused by the erosion, several surface treatment methods and coatings have been used to improve surface hardness. The advanced coating technology such as oxy-fuel powder process, laser surface alloying, wire arc spraying, physical vapour deposition, detonation-gun spray plasma, high-velocity oxy-fuel process, and flame spray methods (thermal sprayed coatings) were used to deposit the erosion-resistant coatings. Other protective coatings, such as polyurethane-based coatings, are frequently used to protect against SPE damage due to their thermal stability, elasticity, long-term damping, mechanical strength, excellent UV stability, low toxicity, and chemical resistivity. Besides that, ceramic coating is environmentally friendly and provides benefits such as affordability, thermal stability, mechanical endurance, corrosion, and wear resistance. In comparison, the ceramic coatings are frequently employed in a variety of industrial applications [11] due to their substantial wear resistance, chemical resistance, and thermal properties. From the literatures, it is evidenced that the coatings were majorly used to prevent the high-temperature erosion and wear. However, there is no article or chapter which focused on the technological advancements, parametrical influence, and failures of recent high-temperature erosion-resistant coatings. Therefore, the present chapter elaborates on the advanced coatings and technology developed in recent years, as well as the failures of the coatings.

Wear/Erosion Resistant High-Temperature Coatings

165

2 Technology Advancement in High-Temperature Erosive Wear Resistance The history of TBCs for high-temperature erosion resistance application (gas turbine engines) dates back to 1987. TBCs are advanced coatings that are usually applied to metallic surfaces operating at higher temperatures, such as gas turbine engines. The main purpose of TBCs is to shield the surfaces from high-temperature environments and to enhance their performance. Figure 1 illustrates the gradual increase in the use of coating technologies for depositing various coatings on material surfaces to withstand high-temperature erosion, between 1990 and 2023. Different coating techniques such as PVD, CVD, and electroless coating were utilized between 1990 and 2000s. Each technique has benefits and drawbacks; for example, electroless NiP coating needs lower temperatures to deposit metals onto high-temperature wear resistance material surfaces, whereas CVD and PVD need a temperature of 250 °C and above to begin the deposition process. From 2001 to 2010, HVOF and thermal spray were commonly used to deposit high-temperature-resistant coatings like Inconel and titanium. In recent years, plasma spray and laser cladding techniques have become popular for controlling the erosive wear at high temperatures. Overall, the advancements of these coating technologies over the years have contributed the development of more durable and efficient coatings, thereby enhancing the performance of components operated at high-temperature conditions.

Fig. 1 Technological road map of high-temperature erosive wear resistance

166

S. Arulvel et al.

3 Parameters Influencing Erosive Wear The parameters that influence the erosive wear are mainly divided into three main categories: the first one is related to fluid velocity conditions (temperature of liquid, concentration of particles, flow speed, density of liquid, particle impingement angle, liquid chemical activity), the second associated with solid particles (their hardness, size, strength, shape), and the third related to the target material [12] (surface topography, toughness, fatigue, yield and ultimate tensile strength, size of the defects, and microstructure.). Moreover, the material stiffness and hardness have a significant impact on the rate of material erosion. The higher rate of erosion occurs at a normal impact angle for brittle materials and at higher impact angle for the ductile materials. Importantly, the hardness of the eroded particles can also have an impact on the erosion rate, regardless of the hardness of the material [13].

4 Advance Coating Techniques 4.1 Thermal Spray Techniques Thermal spray techniques (TSP) are coating processes that deposit various coatings (metals, ceramics, and polymeric materials) on the surface by using a spray gun that operates at extremely high temperatures (900–1600 °C range) [14]. TSP are used to prevent the surfaces from the erosion, corrosion, and wear and can also provide an electrical insulation or thermal insulation to the surface [15]. The coatings are applied in layers, and each layer is typically between 0.051 and 0.127 mm thick. In this process, the TSP material is heated to a very high temperature and sprayed onto the surface of the substrate through a spray gun. During the coating process, the particle melts on the surface of the substrate, which allows the coating to strongly adhere to the substrate. The coating material is then cooled and solidified, forming a uniform protective layer over the substrate [16]. TSP can be applied to different materials like metals, plastics, ceramics, and composites. The type of coating material chosen will depend on the application and the environment in which it will be used. For example, some coatings may be more resistant to corrosion and wear in wet or salty environments, while the others may be better suited for use in dry or hot environments. Thermal spray coatings are generally used to protect the surfaces from erosion caused by wear and tear. The coating acts as a barrier between the surface of the substrate and the outer atmosphere, protecting it from the elements and reducing the rate of erosion. The coatings are also hard and durable layers, which can provide a high resistance to abrasive wear and erosion. The type of coating, thickness, and the substrate hardness are some of the important factors that affect the erosive wear resistance of the surface coatings [17]. The various types of thermal spray coating are as follows: Cold Sprayed Coatings, Flame Sprayed Coatings, Plasma Sprayed Coatings, High Velocity Oxy-Fuel

Wear/Erosion Resistant High-Temperature Coatings

167

Sprayed Coatings, Arc Sprayed Coatings, Detonation Gun Sprayed Coatings, Laser Cladding Coatings, Robotic Thermal Spray Coatings, Combustion Powder Flame Spraying, and Electron Beam Physical Vapour Deposition Coatings. Through the use of the atmospheric plasma spraying (APS) and high-velocity oxygen fuel (HVOF), the coatings can offer excellent mechanical properties like hardness, fracture toughness, and cohesive strength. In recent years, the WC–Cr3 C2 –Ni coating has shown exceptional properties than the other WC-based coatings. However, the WC–Cr3 C2 – Ni coating lost its ability at temperatures above 500 °C due to catastrophic oxidation. This coating is known to have superior high-temperature wear and oxidation resistance than other WC compositions, and further, the HVOF process parameters have been optimized to maximize its bond strength. WC–Cr3 C2 –Ni coating has higher corrosion, hot corrosion, and high-temperature wear resistance than other WC-based coatings and hard chrome plating [18]. However, the further research on improving the high-temperature erosion resistance of WC–Cr3 C2 –Ni coatings could be a great benefit to the extend the performance of components used in the aerospace, oil-gas, and power generation industries.

4.1.1

High-Velocity Oxygen Fuel (HVOF)

In HVOF process, the oxygen and fuel are injected into the combustion chamber along with the coating powder. This creates a high-temperature, high-pressure environment in the chamber, then propelling the gases through the nozzle at supersonic speeds. The powder particles are then exposed in the chamber between the temperature range from 2500 to 3200 °C, depending on the fuel, fuel gas/oxygen ratio, and gas pressure [19]. Depending on the various factors like flame temperature, the time spent by the particles, the material’s melting point, and thermal conductivity, the particles could fully or partly melt. The supersonic jet used in the HVOF process sets it apart from conventional flame spraying and is responsible for the higher speed of particle impact on the substrate, leading to improved coating characteristics. The jet expansion and vaporization of the coating particles at the exit of the gun further distinguishes the HVOF process (Fig. 2) from flame spraying [20]. The HVOF process is an attractive method of applying coatings due to its high particle velocity on impact and reasonable process temperature. The coatings produced are generally dense, adherent, and contain few oxides, making them well-suited for spraying highquality metallic coatings and cermets. Further, its high kinetic energy and low thermal energy have a beneficial impact on coating properties, making it suitable for spraying tungsten carbide coatings [21]. This makes the HVOF process ideal for applications such as bond coats within thermal barrier coating systems. The main advantage of the HVOF process is its ability to produce coatings with high hardness and wear resistance. Several studies have been conducted to assess the wear resistance of HVOF coatings, and it has been observed that the wear resistance of HVOF is better than the other thermal spray coatings [22]. The studies compared the wear resistance of an HVOF coating (WC–Co–Cr) with an electroplated (WC–Co–Cr) coating and found that the HVOF had a minimum wear rate

168

S. Arulvel et al.

Fig. 2 Schematic illustration of HVOF coating

under erosive wear conditions. The authors also concluded that the increases in wear resistance of the HVOF were due to its high hardness and better adhesion [23]. Under simulated turbine circumstances, S. Matthews examined the high-temperature erosion-oxidation of Cr3 C2 –Ni Cr thermal spray coatings. The Cr3 C2 phase was highly susceptible to internal oxidation, and the Cr3 C2 –Ni Cr phase boundary served as a preferred path for oxygen diffusion and oxidation. Additionally, the depth of internal oxidation increases with the temperature [24]. After repeated re-oxidation and erosion trials, a similar internal oxidized layer was found, and the depth of oxidation remained constant after 20, 40, and 60 days of testing. This indicates the achievement of a steady state, where the internal oxidation has moved into the HVOF composite coating ahead of the least erosive mass loss. In other studies, the CrNiAlCY metal powder is coated on AISI401 through HVOF coating. The higher oxygen flow rate during thermal spraying has allowed the dendritic chromium carbide grains to embed in an intermetallic aluminium nitride matrix. This results in a reduced porosity and increased micro-hardness of the coatings, which further improved the high-temperature wear resistance without any phase segregation, oxidation, or decarburization [25]. Table 1 debits the summary of HVOF Coated material with erosive rate with failure mechanism.

4.1.2

Plasma Spray Coating Process

The plasma spraying process melts the feedstock at a very high temperature, typically with a primary carrier gas such as argon or argon–hydrogen mixture. The generated plasma stream can reach temperatures of up to 7720 °C at atmospheric pressure,

Wear/Erosion Resistant High-Temperature Coatings

169

Table 1 Summary of HVOF Coated material with erosive rate with failure mechanism S.no

Base material

Coatings

Erosive wear rate

Erosive failure mechanism

References

1

Steel C45

Cr3 C2 –Ni

2.5 mm3

• Tensile residual stresses • Fatigue cracks • Detachment of material during erosion

[26]

2

SS304

WC–Co

0.00043 g/g

• Ductile mode of erosion • Micro-cutting • Ploughing

[27]

3

Cast iron

Inconel-718, Al2 O3

0.00043 g/g

• Brittle erosion mode • Lip formation • Micro-cutting • Abrasion

[28]

4

SS 316L

WC–Cr3 C2 –Ni

0.39 × 10–3 g/g

• • • •

5

Mild steel

Ni–20Cr2 O3

49 mg

• Micro-cutting • Ductile erosion mechanism • Lip formation • Ploughing

Ploughing [29] Spalling pits Abrasive grooving Mixed erosion mechanisms [30]

which is enough to melt refractory materials or materials with high melting points. It is also possible to customize the process for high-value coatings in atmospheric air or a more controlled environment. This process utilizes either direct current (DC) arcs or radio frequency (RF) discharges to generate plasma [31]. The structure of a plasma-sprayed coating (Fig. 3) is determined by the temperature, velocity, and size distribution of the incident particles. Direct measurements of these factors in a plasma torch have been linked to the formation of the coating. The particles that strike the substrate may not be completely molten, which can affect the deposition efficiency and the microstructure of the deposit. When a spherical liquid droplet hits a flat surface at high velocity, it will flatten and the thin sheet of liquid at the edges will disintegrate into small droplets [32]. In the case of plasma spraying, the substrate is below the melting point of the droplet, so solidification interrupts the spreading and breakup. Then the individual particles are splat quenched with a cooling rate of around 106 K s−1 . Heat treatments suggest that the interface structure is determined by distributed contact points within an effectively non-conducting film arising from entrapped gas. The microstructure of plasma-sprayed coatings is thus linked to the

170

S. Arulvel et al.

Fig. 3 Schematic illustration of plasma spray coating

mechanism, including the interfaces between lamellae and the internal structure created by rapid solidification [33]. Digvijay G. Bhosale investigated the high-temperature solid particle erosion behaviour of SS 316L with WC–Cr3 C2 –Ni coatings. The coated specimens showed a variety of erosion processes, while uncoated ones experienced more malleable effects. At lower angles of impact, the wear of coated samples was mainly caused by ploughing and cutting caused by the erodent. However, at a direct angle, intense wear mechanisms such as splintering and delamination were observed in the case of an APS coating. Table 2 debits the summary of plasma spray coated material with erosive rate with failure mechanism.

4.1.3

Laser Cladding Process

Laser cladding is a popular technique used for hard facing or surfacing in industrial applications that applies a layer of powder coating onto the substrate surface (base metal) using a laser beam or arc as a source of heat (Fig. 4). In this process, a laser beam of different shapes is consistently emitted through different nozzles, while also combining various powder combinations. These powder combinations then melt upon contact with the laser beam, resulting in the creation of a coating layer [39]. Laser cladding offers many advantages over traditional coating methods and its performance is significantly higher. Firstly, laser cladding allows for precise control over the coating thickness, resulting in a more uniform and consistent deposition. Secondly, it enables the use of a wide range of materials, including dissimilar metals, alloys, and ceramics, offering flexibility in coating selection [40]. Additionally, laser

Wear/Erosion Resistant High-Temperature Coatings

171

Table 2 Summary of plasma spray coated material with erosive rate with failure mechanism S.no

Base material

Coating material

Erosive wear rate

Erosive failure mechanism

References

1

SS316l

WC

0.71 × 10–3 g/g

• Splat delamination • Ploughing • WC pull-outs • Micro-cutting

[34]

2

AISI 304

NiCrSiB/Al2 O3 0.4 × 10–3 g/g

• Micro ploughing [35] • Splat removal and detachment of Al2 O3 hard particles • Ni softer phases • Micro-cutting

3

Al

Fly as + Al2 O3

17 mg/kg

• • • •

Local scratching Cracks Crater formation Plastic deformation • Micro-cutting • Extrusion and chipping of the coating

[36]

4

SA210 GrA1

IN625-bimodal Al2 O3

0.21 × 10–3 g/g

• Ploughing • Micro-cutting • Brittle erosion mode • Detached splats • Fracture and cracks

[37]

5

MDN321

NiCrBSiFe and NiCr

0.5 × 10–3 g/g

• Wrinkles • Pitting • Ductile mode

[38]

cladding minimizes heat-affected zones, reducing the risk of distortion or damage to the substrate. Moreover, it provides excellent metallurgical bonding between the coating and the substrate, enhancing overall coating integrity. Lastly, laser cladding offers high deposition rates, enabling efficient and cost-effective coating application [41]. It is also an efficient way to repair mechanical parts, as opposed to other approaches that require more time and energy. Various process parameters are involved in laser cladding, such as laser energy, the diameter of the laser beam spot, scanning velocity of the laser, thickness of the pre-powder layer, rate of powder feed, nozzle angle, and stand-off distance [42]. The effectiveness of the laser cladding process is largely determined by its scanning speed, which can affect the thickness, width, and height of the clad layer. If the scanning speed is appropriate, the clad layer can exhibit desirable properties such as

172

S. Arulvel et al.

Fig. 4 Schematic illustration of laser cladding process

a strong metallurgical bond with the base material, small crystals, and no cracks or gas cavities. A higher scanning speed generally results in a thinner clad layer, while a lower scanning speed leads to a thicker layer. Similarly, a higher scanning speed typically results in a narrower clad width, whereas a lower scanning speed produces a wider width. These factors are important in laser cladding for several reasons. First, the thickness of the clad layer determines the desired material properties, such as hardness or corrosion resistance. Controlling the thickness ensures the coating meets specific requirements. The width of the clad layer affects the coverage and area being treated. A wider clad width can cover a larger surface area in a single pass, increasing the efficiency and reducing the processing time. The height of the clad layer is crucial for achieving the desired geometry or restoring worn or damaged parts. Precise control over the height ensures dimensional accuracy and proper fit with the surrounding components. Optimizing the scanning speed to control these factors is vital in achieving the desired coating quality, dimensional accuracy, and overall performance of the laser-cladded component [43]. In one study, the impact of laser cladding speed on SS 431 was examined, but it was found that increasing the speed did not improve the hardness and wear properties of the stainless steel coatings. Other researchers have also investigated the effects of scanning and cladding speed on the microstructure and hardness of these coatings [44]. The laser power used in the process is also crucial, as it can cause micro-cracks if too low or reduce wear resistance if too high. An experiment showed that increasing the laser power from 1.8 to 3.0 kW led to deeper laser melted pools and some micro-cracks, with the best wear resistance achieved at 2.5 kW. The powder feed rate is another important parameter that affects the cladding thickness, with an increase in feed rate leading to a proportional increase in coating thickness until a certain limit is reached [45]. Additionally, research has shown that the hardness and wear resistance of the coating also increase

Wear/Erosion Resistant High-Temperature Coatings

173

with a rise in powder feed rate [46]. Several other parameters, such as overlap clad, direction of clad, preheating, nozzle distance, injection angle, and particle size shape, have also been studied, but their impact is less significant than the main parameters discussed above. Nonetheless, their interaction with the quality of the clad surface should not be disregarded [47]. In the past, steel was the most commonly used material for erosion wear, but composite materials and alloys are now being used as replacements. As a result, researchers have studied a variety of materials for erosion wear, including steel, copper alloys, magnesium alloy, Ti–6Al–4V and its alloys [48]. However, these materials can be expensive, so researchers have developed erosion-resistant coatings using low-cost materials such as steel through laser cladding techniques. Different types of powder materials, such as nickel and cobalt base, tungsten carbide, titanium and its composite, high chromium cast iron, and some iron base alloys, have been used to improve corrosion and erosion wear resistance. In a recent study, Stellite 6 clad layers were used on stainless steel as a base material, and the results showed that the clad surface improved erosion wear resistance by five times compared to bare stainless steel [49]. Table 3 debits the summary of the laser cladding process coated material with the erosive rate with failure mechanism.

5 Erosive Wear Resistance of Ceramic Coatings Ceramic coatings can be effective at controlling high-temperature erosive wear, as they offer several benefits such as high hardness, thermal stability, thermal shock resistance, surface seals, erosion resistance, diffusion barriers, sealants, corrosion resistance, and resistance to chemical and mechanical degradation. These properties make them suitable for use in high-temperature environments, such as gas turbines and other combustion engines. Ceramic coatings are the most frequently applied metallic components to withstand high-temperature environments [54]. Ceramic coatings exhibit exceptional resistance to the erosive effects of solid particles, such as abrasion and impact. The erosive wear resistance of ceramic coatings stems from their inherent properties, including high hardness, high-temperature stability, and chemical inertness. These properties enable ceramic coatings to withstand the erosive forces and prevent material loss or degradation. Additionally, the microstructure of ceramic coatings plays a crucial role in their erosive wear resistance. Fine-grained ceramics with a dense and uniform structure exhibit enhanced resistance to erosive wear, as they effectively resist the penetration and removal of material by abrasive particles. These coatings have demonstrated significant improvements in reducing erosive wear and extending the service life of components in industries such as mining, power generation, oil and gas, and aerospace [55]. One of the most commonly used ceramic coatings for controlling hightemperature erosive wear is thermal barrier coatings (TBCs). TBCs are designed to protect metal components from the high temperatures generated during combustion and to reduce the transfer of heat to the underlying substrate. This can help to prevent

174

S. Arulvel et al.

Table 3 Summary of laser cladding process Coated material with erosive rate with failure mechanism S.no

Base material

Coating material

Erosive wear rate Inference

References

1

SS410

NiCrSiBC + WC

0.02 from 0.16 mg

• Plastic [50] deformation • Worn-out marks • Micro-cutting • Minute ploughing sites • Lip structures • Ploughing mark • Tiny craters

2

Martensitic stainless steel

Ni + 50% Cr3 C2

26.5 g m−2 h−1

• Impact craters • Deformed lips • Plastic deformation

[51]

3

Martensitic stainless steel

Ni + 50% WC

43.8

• Little micro-cracks • Ropping holes • Plastic deformation

[51]

4

AISI 304 plate

Inconel Cr3 C2

0.10

• Microcracks • Transgranular crack

[52]

5

Q345 steel

Alx CoCrFeNiTi0.5

0.04 mg/min

• Ductile erosion mode • Micro-cutting • Ploughing

[53]

thermal fatigue and cracking, which can lead to erosive wear [56]. Other types of ceramic coatings that can be effective at controlling high-temperature erosive wear include oxide and carbide coatings. Oxide coatings, such as alumina or zirconia, can provide excellent resistance to high-temperature corrosion and wear. Carbide coatings, such as titanium carbide or tungsten carbide, are also highly resistant to wear and can provide excellent protection against erosive wear. Cermet-based coatings can also be employed in extreme temperatures. Understanding the microstructure and behaviour of ceramic coatings is critical for optimizing their performance in controlling high-temperature erosive wear [57]. Furthermore, there is no uniform testing method that can determine which material is best for varied wear or wearcorrosion. Numerous studies have also been investigated to find the effectiveness of ceramic coatings such as ZrO2 , Al2 O3 , SiC, SiO2 , HfC, TaC, and ZrC in hightemperature environments. These coatings have been explored for their ability to withstand high temperatures, resist wear and corrosion, and provide thermal insulation to protect underlying materials. Researchers have conducted experiments and analysed data to determine the properties and performance of these coatings in various

Wear/Erosion Resistant High-Temperature Coatings

175

high-temperature conditions, such as in gas turbines, engines, and industrial applications [58]. When selecting a ceramic coating for controlling high-temperature erosive wear, it is important to consider factors such as the type of substrate material, the operating environment, and the specific wear mechanisms that are likely to be encountered. Proper surface preparation, including cleaning and roughening, is also critical to ensure good adhesion and performance of these ceramic coating [59]. Based on recent literature it is found that ceramic coatings are effective in controlling high-temperature erosive wear by creating a protective layer on metallic components. This layer can mitigate or prevent the effects of high-velocity particle impact, which leads to erosive wear. Microscopic analysis is used to study the formation of voids in the coating and to understand the impact of temperature on its erosion resistance. Studies have shown that ceramic coatings with 80% ceramic powder exhibit greater cavitation erosion resistance compared to aluminium alloy references [60]. Fe-based coatings, on the other hand, form oxide scales to protect against oxidation and corrosion in high-temperature environments. The formation of voids and pores is one of the major challenges in ceramic coating. The formation of voids in ceramic coatings is influenced by temperature, void formation increases as the temperature is raised and as a result it will end up in oxide formation. To understand this effect, oxidation studies have been performed on cast Co–22Cr–11Al (CoCrAl) coating alloy at temperatures ranging from 700 to 1000 °C [61]. However, warm-pressing above 180 °C can produce transparent and void-free monoliths, suggesting that lower temperatures may reduce void formation [62]. The properties of ceramic layers are also linked to processing technology, such as sintering temperature and method of coating. Overall, temperature is a crucial factor affecting the formation of voids in ceramic coatings, with higher temperatures promoting increased void formation. Ceramic coatings offer a reliable solution for protecting components from hightemperature erosive wear by forming a protective layer that reduces the impact of high-velocity particles [63].

6 Erosive Wear Resistance of Metallic Coatings Metallic coatings are a viable option for controlling high-temperature erosive wear in aerospace applications [1]. NiCr-based coatings, such as nimonic coatings, are commonly used for high-temperature applications to minimize oxidation [64]. Other metallic coatings, including aluminide, chromide, and MCrAlY, are effective in protecting superalloys against high-temperature environmental factors. These coatings are applied using either a diffusion or conversion process in which the deposited material is diffused and/or reacted with the substrate to create a gradual change in composition. To achieve effective erosion-resistant coatings, thicker coatings with good mechanical properties are required. The use of cost-effective precursor materials and innovative coating designs can help achieve the desired coating thickness with low production costs [65]. Metallic coatings have the ability to manage high-temperature erosive wear through various mechanisms. For instance, Fe-based

176

S. Arulvel et al.

coatings form oxide scales to prevent corrosion and oxidation in high-temperature conditions [60]. Metallic coatings like High Velocity Oxygen Fuel (HVOF) sprayed coatings have been developed to shield against solid particle erosion [64]. The study also investigates high-temperature erosion-oxidation mechanisms to understand how ductile materials undergo material loss due to erosive wear conditions [66]. The temperature range at which metallic coatings can endure high-temperature erosive wear is determined by several factors, including the coating type and its specific use. The temperature range also varies depending on the compressor stage, whereas turbine blades undergo extreme temperatures of 1000 °C and above [1]. The study of HVOF sprayed coatings’ erosion behaviour was conducted at a temperature of 900 °C [1]. Cermet compositions are well known for their wear resistance, high-temperature oxidation resistance, hardness, and abrasion properties. Fe-based coatings have been found to exhibit wear behaviour, corrosion analysis, and high-temperature resistance properties [60]. An increase in temperature results in a decrease in the volume loss of coated samples, and some coatings can perform well even at temperatures as high as 700 °C [67]. In general, the temperature range at which metallic coatings can resist high-temperature erosive wear varies depending on multiple factors, but in some cases, it can be as high as 1000 °C or more. To assess the effectiveness of metallic coatings in controlling high-temperature erosive wear, researchers use microstructure studies, micro-hardness tests, and high-temperature oxidation and erosion tests. When it comes to ceramic coatings, the main obstacle is the formation of pores, while with metallic coatings, the major hurdle is oxidation [1]. Dervis Ozkan examined how oxidation and wear affect the Cr3 C2 –NiCr hard metal coatings on stainless steel substrates under various temperature and time conditions. In recent research, efforts have been made to understand the elevated temperature erosion behaviour of metals and alloys and to develop new erosion-resistant coatings which have low erosion–oxidation ratio [68]. NASA worked together with the Allison Advanced Development Company to enhance erosion coatings for gas turbine fan and compressor applications. Six different erosion coating systems were tested to determine their ability to endure intense thermal cycling without spalling. All six coating systems were able to survive the tests [69].

7 Erosive Wear Resistance of Composite Coatings Composite coatings are effective in controlling high-temperature erosive wear due to their high resistance to wear and corrosion, surface toughness, hardness, adhesive strength, and temperature resistance [70, 71]. They have the ability to withstand high temperatures and provide erosion resistance to metallic coating [72]. The composite surface-coating can be made using various coating techniques, such as chemical vapour deposition, physical vapour deposition, and thermal spray coating [70]. These coatings provide a protective surface layer that can withstand wear, corrosion, and erosion problems, while it also increases the mechanical strength

Wear/Erosion Resistant High-Temperature Coatings

177

[67]. According to recent studies, composite coatings containing higher amounts of carbon nanotubes (CNTs) have demonstrated the best resistance to erosive wear [73]. Moreover, research has found that CNT-reinforced Cr2 O3 coatings on ASTM-A36 steel and NiCr coatings on turbine steel exhibit high resistance to hot corrosion and slurry erosion, respectively [74]. Additionally, CNTs have been shown to enhance the hardness, corrosion, and wear resistance of coatings [75]. CNTs possess unique properties, including high strength, stiffness, thermal conductivity, and chemical stability, making them useful in various industries [76]. Overall, the use of composite coatings containing higher amounts of CNTs can provide superior erosion resistance and better protection against high-temperature erosive wear. In aviation turbines, thermal barrier coatings (TBCs) made of composites are frequently utilized to safeguard nickel-based superalloys against both melting and thermal cycling. The addition of cool air flow enables TBCs to raise the maximum gas temperature beyond the melting point of the superal compared to single-phase thermal barrier coatings (TBCs), phase composite TBCs have shown superior coating durability, thermal conductivity, and solid particle erosion resistance. Studies on the erosive wear resistance of LZO and YSZ coatings have found that the coating density and content significantly affect the coatings’ erosion resistance [77]. Researchers have investigated the impact of heat treatment on the erosion resistance of composite coatings and found that when treated at 600 °C and 90°, erosion was reduced. This reduction in erosion was attributed to the removal of porosity, improved coherence of the nickel matrix, and decreased hardness. Composite fibre materials are employed in a wide range of applications, from everyday appliances to high-tech uses, in order to reduce wear rates. Extensive research has been conducted on the anti-erosive anti-wear properties of polymers and their composites [77]. Recent advancements in understanding the methods for controlling erosive wear have been made for composite coating with the creation of erosion-corrosion maps showing transitions. In many industrial conditions, composite coating experiences solid particle erosion in corrosive environments leading to degradation, and controlling the damage can depend entirely on empirical experience.

8 Erosive Wear Resistance of Super Alloy Coatings Superalloy coatings have been found to exhibit good temperature stability in addition to their high resistance to wear and erosion. To control high-temperature erosive wear, super alloy coatings are utilized. Because of the work hardening and temperature stability of their constituents, these coatings have a high hardness, resulting in lower volume loss due to erosion and as a result it can withstand extreme heat environment [67]. There are a variety of erosion-resistant superalloy coatings available, and their performance is temperature dependent. NiAl super alloy coating is a type of high-performance coating that is made from a superalloy consisting of nickel and aluminium. This coating is designed to provide excellent protection against high-temperature corrosion, oxidation, and wear. It is

178

S. Arulvel et al.

commonly used in high-temperature applications, such as gas turbines, power plants, and aerospace components. NiAl super alloy coatings are known for their outstanding oxidation resistance, as the aluminium content in the alloy forms a protective oxide layer at high temperatures, which prevents further oxidation of the substrate material. Additionally, these coatings offer excellent wear resistance due to their high hardness and low coefficient of friction. NiAl intermetallic super alloy coatings can carburize the super alloy coated substrate at high temperatures as a result increases the hardness and weight of the component and thereby making the coating substance brittle; hence, it leads to crack formation resulting in failure [78]. Some common materials used in superalloy coatings include nickel–chromium alloys, titanium alloys, cobalt-chromium alloys, and stainless steels. These materials offer a range of properties that make them suitable for different applications, including high strength, corrosion resistance, and thermal stability [79]. The application of superalloy coatings can be achieved using various techniques, including thermal spray, electroplating, and chemical vapour deposition. The selection of a coating technique is determined by the application’s particular requirements and the coating material’s characteristics. Thermal spray coating is a significant method amongst them. Researchers have developed thermal spray high-entropy alloy (HEA) coatings to enhance the erosion resistance of Ni-base superalloys under extreme temperatures. These HEA coatings possess excellent tribological properties, such as porosity, hardness, and wear resistance. AlSiCrFeCoNi alloys with the HEA coating process have gained popularity chiefly due to their resistance to high-temperature oxidation [80].

9 Coatings Failure at High-Temperature Conditions There are four important coating failures in high-temperature applications, which include oxidation, hot corrosion, mechanical distress, and solid-state diffusion. In addition to these failure modes, the cyclic and thermal loads of the component can also cause the thermomechanical fatigue in the coatings. In advanced turbine engines, the thermomechanical stress cracking was frequently observed around film-cooling holes. Later, this is controlled through the application of TBC. The brief discussion on the different types of failure modes in the coatings is provided below.

9.1 High-Temperature Oxidation The coatings have been introduced in order to produce a barrier between the substrate material and the high-temperature gases. The coatings could prevent the formation of oxide scale at higher temperatures. For example, the chromia scale tends to sublimate

Wear/Erosion Resistant High-Temperature Coatings

179

to CrO3 above the higher temperatures (840–870 °C), which provides a low protection compared to the alumina. The coating and ultimately the substrate are quickly attacked without the shielding scale. So, recent research has shown the improvement of oxide layer adhesion, which can further improve the properties of the coatings at higher temperature. To increase the adherence of the oxide layer, the coatings are frequently supplemented with oxygen-active materials like hafnium and yttria. Nonetheless, a solid quantitative knowledge of these consequences is lacking in controlling the high-temperature oxidation.

9.2 Hot Corrosion Hot corrosion refers to the attack of molten salts, usually sodium and potassium sulphates, which enter the turbine hot section as impurities from the air and fuel and can cause a rapid material loss in the components. It is not quite obvious what function secondary elements with impurities like chlorine, calcium, and iron from the local environment serve. Once the scale is lost or penetrated, both the protective covering and the metal substrate beneath it will quickly deteriorate. This requirement is for petroleum-based fuels, and either chromia or alumina can typically meet it. However, alumina coating was better at greater operating temperatures compared to the chromia.

9.2.1

Mechanical Distress

The impact damage and mechanically induced erosion are two related failure mechanisms that require specific attention. Particles in the air stream cause erosion when they abrade the coating. When a heavy object contacts the coating, the impact could cause the damages. These failure modes will, however, become more significant as substrate materials are used in situations where they provide no built-in defence against the oxidation or other severe failure modes. Even, the retention of TBCs is heavily influenced by these failure mechanisms. Compared to the metallic coatings, these ceramic coatings are naturally more susceptible to impact damage and erosion.

9.3 Solid-State Diffusion The diffusion of the coating with the base metal is another significant degradation pathway for the coating’s failure at high-temperature conditions. For example, the concentration of aluminium that is available to produce alumina in the coating is reduced by the diffusion of aluminium into the base metal. Once the aluminium concentrations fall below a particular threshold, a protective oxide can no longer

180

S. Arulvel et al.

sustain the spallation failure. Hence for better high-temperature coating properties, the fundamental principles of diffusion should be clear and in control.

10 Summary and Future Scope The present chapter elaborates on the erosion and wear resistant of high-temperature coatings with various failure modes. And, also discussed how the coatings overcome the failures to reduce the erosive wear. Comparatively, the thermal barrier coatings are frequently used to increase the performance of the turbine and also to reduce the thermomechanical fatigue cracking in high-temperature operating conditions. Ceramic coatings are found better than the metallic coatings towards the damage and erosion resistance. The alumina was better at high operating temperatures compared to the chromia because of the reduced scaling effects. For an efficient diffusion process, the optimum quantity of the coating should be used, because the oxide layer will not prevent the spallation failure if the weight fraction of oxidizing elements falls below the certain threshold. It is also concluded that the developed coatings should be more durable and able to withstand the intense heat of the environment. Also, the coating can be developed that is more resistant to chemical and environmental damage. Still, there is a scope for the research in analysing the high-temperature resistance coatings with various phase constituents. So, in the future, the high-temperature coatings could be developed with various phase constituents to provide a better protection from the extreme temperatures. This could uplift the coated materials in various high-temperature applications like boilers, turbine blades, steam lines, spacecraft nozzles, and gun barrels, where the erosive wear is predominant.

References 1. Bonu, V., Barshilia, H.C.: High-temperature solid particle erosion of aerospace components: its mitigation using advanced nanostructured coating technologies. Coatings 12, 1979 (2022). https://doi.org/10.3390/coatings12121979 2. Szczepankowski, A., Przysowa, R.: Thermal degradation of turbine components in a military turbofan. Eng. Fail. Anal. 134, 106088 (2022). https://doi.org/10.1016/j.engfailanal.2022. 106088 3. Yildirim, M.T., Kurt, B.: Aircraft gas turbine engine health monitoring system by real flight data. Int. J. Aerosp. Eng. 2018, 1–12 (2018). https://doi.org/10.1155/2018/9570873 4. Chhetry, B., Rana, K.: Effect of sand erosion on turbine components: a case study of Kali Gandaki “A” hydroelectric project (144 MW), Nepal, Hydro Nepal. J. Water Energy Environ. 17, 24–33 (2015). https://doi.org/10.3126/hn.v17i0.13270 5. Xue, L., Wang, J., Li, L., Chen, G., Sun, L., Yu, S.: Enhancement of wear and erosion-corrosion resistance of Inconel 718 alloy by liquid nitriding. Mater. Res. Express 7, 096510 (2020). https:// doi.org/10.1088/2053-1591/abb426

Wear/Erosion Resistant High-Temperature Coatings

181

6. Tshephe, T.S., Akinwamide, S.O., Olevsky, E., Olubambi, P.A.: Additive manufacturing of titanium-based alloys-A review of methods, properties, challenges, and prospects. Heliyon 8, e09041 (2022). https://doi.org/10.1016/j.heliyon.2022.e09041 7. Reviewed, P., Berkeley, L., Cancer, B.: Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory, pp. 35–43 (2010) 8. Aribo, S., Fakorede, A., Ige, O., Olubambi, P.: Erosion-corrosion behaviour of aluminum alloy 6063 hybrid composite. Wear 376–377, 608–614 (2017). https://doi.org/10.1016/j.wear.2017. 01.034 9. Bousser, E., Martinu, L., Klemberg-Sapieha, J.E.: Solid particle erosion mechanisms of protective coatings for aerospace applications. Surf. Coat. Technol. 257, 165–181 (2014). https://doi. org/10.1016/j.surfcoat.2014.08.037 10. Buszko, M.H., Krella, A.K.: An influence of factors of flow condition, particle and material properties on slurry erosion resistance. Adv. Mater. Sci. 19, 28–53 (2019). https://doi.org/10. 2478/adms-2019-0010 11. Zang, D., Xun, X.: Ceramics coated metallic materials: methods, properties and applications. In: Advanced Ceramic Materials. IntechOpen (2021). https://doi.org/10.5772/intechopen.93814 12. Rasse, C., Mary, N., Abe, H., Watanabe, Y., Normand, B.: Role of the jet angle, particle size, and particle concentration in the degradation behavior of carbon steel under slow slurry erosion-corrosion conditions. Metals (Basel) 11, 1152 (2021). https://doi.org/10.3390/met110 81152 13. Javaheri, V., Porter, D., Kuokkala, V.-T.: Slurry erosion of steel—Review of tests, mechanisms and materials. Wear 408–409, 248–273 (2018). https://doi.org/10.1016/j.wear.2018.05.010 14. Araguás-Rodríguez, S., Ferran-Marqués, M., Pilgrim, C.C., Kamnis, S., Feist, J.P., Nicholls, J.R.: Thermal history coatings: Part I—Influence of atmospheric plasma spray parameters on performance. In: Volume 3 Ceramic Coal, Biomass and Hydrogen, and Alternative Fuels, American Society of Mechanical Engineers (2020). https://doi.org/10.1115/GT2020-16004 15. Keshavamurthy, R., Naveena, B.E., Sekhar, N.: Thermal spray coatings for erosion-corrosion protection, pp. 246–267 (2018). https://doi.org/10.4018/978-1-5225-4194-3.ch010 16. Chen, X., He, M.Y., Spitsberg, I., Fleck, N.A., Hutchinson, J.W., Evans, A.G.: Mechanisms governing the high temperature erosion of thermal barrier coatings. Wear 256, 735–746 (2004). https://doi.org/10.1016/S0043-1648(03)00446-0 17. Tavana, S.M.: Thermal spray coating of carbon reinforcement composites for wear and erosion resistance applications (2020) 18. Poirier, D., Legoux, J.-G., Lima, R.S.: Engineering HVOF-sprayed Cr3C2–NiCr coatings: the effect of particle morphology and spraying parameters on the microstructure, properties, and high temperature wear performance. J. Therm. Spray Technol. 22, 280–289 (2013). https://doi. org/10.1007/s11666-012-9833-3 19. Oksa, M., Turunen, E., Suhonen, T., Varis, T., Hannula, S.-P.: Optimization and characterization of high velocity oxy-fuel sprayed coatings: techniques. Mater. Appl. Coat. 1, 17–52 (2011). https://doi.org/10.3390/coatings1010017 20. Jadidi, M., Moghtadernejad, S., Dolatabadi, A.: A comprehensive review on fluid dynamics and transport of suspension/liquid droplets and particles in high-velocity oxygen-fuel (HVOF) thermal spray. Coatings 5, 576–645 (2015). https://doi.org/10.3390/coatings5040576 21. Picas, J.A., Rupérez, E., Punset, M., Forn, A.: Influence of HVOF spraying parameters on the corrosion resistance of WC–CoCr coatings in strong acidic environment. Surf. Coat. Technol. 225, 47–57 (2013). https://doi.org/10.1016/j.surfcoat.2013.03.015 22. Priyan, M.S., Azad, A., Araffath, S.Y.: Influence of HVOF parameters on the wear resistance of Cr3C2–NiCr coating. J. Mater. Sci. Surf. Eng. 4, 355–359 (2016) 23. Song, B., Murray, J.W., Wellman, R.G., Pala, Z., Hussain, T.: Dry sliding wear behaviour of HVOF thermal sprayed WC–Co–Cr and WC–CrxCy–Ni coatings. Wear 442–443, 203114 (2020). https://doi.org/10.1016/j.wear.2019.203114 24. Matthews, S., James, B., Hyland, M.: High temperature erosion–oxidation of Cr3C2–NiCr thermal spray coatings under simulated turbine conditions. Corros. Sci. 70, 203–211 (2013). https://doi.org/10.1016/j.corsci.2013.01.030

182

S. Arulvel et al.

25. Garfias Bulnes, A., Albaladejo Fuentes, V., Garcia Cano, I., Dosta, S.: Understanding the influence of high velocity thermal spray techniques on the properties of different anti-wear WC-based coatings. Coatings 10, 1157 (2020). https://doi.org/10.3390/coatings10121157 26. Surzhenkov, A., Goljandin, D., Traksmaa, R., Viljus, M., Talviste, K., Aruniit, A., Latokartano, J., Kulu, P.: High temperature erosion wear of cermet particles reinforced self-fluxing alloy matrix HVOF sprayed coatings. Mater. Sci. 21 (2015). https://doi.org/10.5755/j01.ms.21.3. 7617 27. Praveen, A.S., Arjunan, A.: High-temperature oxidation and erosion of HVOF sprayed NiCrSiB/Al2O3 and NiCrSiB/WC Co coatings. Appl. Surf. Sci. Adv. 7, 100191 (2022). https:// doi.org/10.1016/j.apsadv.2021.100191 28. Vasudev, H., Thakur, L., Singh, H., Bansal, A.: Effect of addition of Al2O3 on the hightemperature solid particle erosion behaviour of HVOF sprayed Inconel-718 coatings. Mater. Today Commun. 30, 103017 (2022). https://doi.org/10.1016/j.mtcomm.2021.103017 29. Bhosale, D.G., Prabhu, T.R., Rathod, W.S.: Sliding and erosion wear behaviour of thermal sprayed WC-Cr3C2-Ni coatings. Surf. Coat. Technol. 400, 126192 (2020). https://doi.org/10. 1016/j.surfcoat.2020.126192 30. Bansal, A., Goyal, D.K., Singh, P., Singla, A.K., Gupta, M.K., Bala, N., Kolte, J., Setia, G.: Erosive wear behaviour of HVOF-sprayed Ni-20Cr2O3 coating on pipeline materials. Int. J. Refract. Met. Hard Mater. 92, 105332 (2020). https://doi.org/10.1016/j.ijrmhm.2020.105332 31. Odhiambo, J.G., Li, W., Zhao, Y., Li, C.: Porosity and its significance in plasma-sprayed coatings. Coatings 9, 460 (2019). https://doi.org/10.3390/coatings9070460 32. Caliari, F.R., Miranda, F.S., Reis, D.A.P., Filho, G.P., Charakhovski, L.I., Essiptchouk, A.: Plasma torch for supersonic plasma spray at atmospheric pressure. J. Mater. Process. Technol. 237, 351–360 (2016). https://doi.org/10.1016/j.jmatprotec.2016.06.027 33. Li, L., Vaidya, A., Sampath, S., Xiong, H., Zheng, L.: Particle characterization and splat formation of plasma sprayed zirconia. J. Therm. Spray Technol. 15, 97–105 (2006). https://doi.org/ 10.1361/105996306X92668 34. Bhosale, D.G., Prabhu, T.R., Rathod, W.S., Patil, M.A., Rukhande, S.W.: High temperature solid particle erosion behaviour of SS 316L and thermal sprayed WC-Cr3C2-Ni coatings. Wear 462–463, 203520 (2020). https://doi.org/10.1016/j.wear.2020.203520 35. Praveen, A.S., Sarangan, J., Suresh, Siva Subramanian, S.: Erosion wear behaviour of plasma sprayed NiCrSiB/Al2O3 composite coating. Int. J. Refract. Met. Hard Mater. 52, 209–218 (2015). https://doi.org/10.1016/j.ijrmhm.2015.06.005 36. Sahu, S.P., Satapathy, A., Patnaik, A., Sreekumar, K.P., Ananthapadmanabhan, P.V.: Development, characterization and erosion wear response of plasma sprayed fly ash–aluminum coatings. Mater. Des. 31, 1165–1173 (2010). https://doi.org/10.1016/j.matdes.2009.09.039 37. Prashar, G., Vasudev, H.: Structure-property correlation and high-temperature erosion performance of Inconel625-Al2O3 plasma-sprayed bimodal composite coatings. Surf. Coat. Technol. 439, 128450 (2022). https://doi.org/10.1016/j.surfcoat.2022.128450 38. Medabalimi, S.R., Ramesh, M.R., Kadoli, R.: High-temperature solid particle erosion behavior of partially oxidized NiCrBSiFe/NiCr plasma spray coatings. J. Therm. Spray Technol. 30, 1638–1652 (2021). https://doi.org/10.1007/s11666-021-01225-8 39. John, M., Kuruveri, U.B., Menezes, P.L.: Laser cladding-based surface modification of carbon steel and high-alloy steel for extreme condition applications. Coatings 12, 1444 (2022). https:// doi.org/10.3390/coatings12101444 40. Zhang, H., Li, W., Xu, H., Chen, L., Zeng, J., Ding, Z., Guo, W., Liu, B.: Microstructure and corrosion behavior of laser cladding FeCoNiCrBSi based high-entropy alloy coatings. Coatings 12, 628 (2022). https://doi.org/10.3390/coatings12050628 41. Lu, K., Zhu, J., Guo, D., Yang, M., Sun, H., Wang, Z., Hui, X., Wu, Y.: Microstructures, corrosion resistance and wear resistance of high-entropy alloys coatings with various compositions prepared by laser cladding: a review. Coatings 12, 1023 (2022). https://doi.org/10.3390/coatin gs12071023 42. Singh, S., Goyal, D.K., Kumar, P., Bansal, A.: Laser cladding technique for erosive wear applications: a review. Mater. Res. Express. 7, 012007 (2020). https://doi.org/10.1088/20531591/ab6894

Wear/Erosion Resistant High-Temperature Coatings

183

43. Shi, B., Li, T., Guo, Z., Zhang, X., Zhang, H.: Selecting process parameters of crack-free Ni60A alloy coating prepared by coaxial laser cladding. Opt. Laser Technol. 149, 107805 (2022). https://doi.org/10.1016/j.optlastec.2021.107805 44. Hemmati, I., Ocelík, V., De Hosson, J.T.M.: The effect of cladding speed on phase constitution and properties of AISI 431 stainless steel laser deposited coatings. Surf. Coat. Technol. 205, 5235–5239 (2011). https://doi.org/10.1016/j.surfcoat.2011.05.035 45. Chowdhury, S., Yadaiah, N., Prakash, C., Ramakrishna, S., Dixit, S., Gupta, L.R., Buddhi, D.: Laser powder bed fusion: a state-of-the-art review of the technology, materials, properties & defects, and numerical modelling. J. Mater. Res. Technol. 20, 2109–2172 (2022). https://doi. org/10.1016/j.jmrt.2022.07.121 46. Yan, Q., Yang, K., Wang, Z., Chen, M., Sun, G., Ni, Z.: Surface roughness optimization and high-temperature wear performance of H13 coating fabricated by extreme high-speed laser cladding. Opt. Laser Technol. 149, 107823 (2022). https://doi.org/10.1016/j.optlastec.2021. 107823 47. Lusquiños, F., Comesaña, R., Riveiro, A., Quintero, F., Pou, J.: Fibre laser micro-cladding of Co-based alloys on stainless steel. Surf. Coat. Technol. 203, 1933–1940 (2009). https://doi.org/ 10.1016/j.surfcoat.2009.01.020 48. Mishra, S.K., Biswas, S., Satapathy, A.: A study on processing, characterization and erosion wear behavior of silicon carbide particle filled ZA-27 metal matrix composites. Mater. Des. 55, 958–965 (2014). https://doi.org/10.1016/j.matdes.2013.10.069 49. Jeyaprakash, N., Yang, C.-H., Sivasankaran, S.: Laser cladding process of Cobalt and Nickel based hard-micron-layers on 316L-stainless-steel-substrate. Mater. Manuf. Process. 35, 142– 151 (2020). https://doi.org/10.1080/10426914.2019.1692354 50. Singh, S., Goyal, D.K., Kumar, P., Bansal, A.: Influence of laser cladding parameters on slurry erosion performance of NiCrSiBC + 50WC claddings. Int. J. Refract. Met. Hard Mater. 105, 105825 (2022). https://doi.org/10.1016/j.ijrmhm.2022.105825 51. Zhang, D., Zhang, X.: Laser cladding of stainless steel with Ni–Cr3C2 and Ni–WC for improving erosive–corrosive wear performance. Surf. Coat. Technol. 190, 212–217 (2005). https://doi.org/10.1016/j.surfcoat.2004.03.018 52. Janicki, D.: Laser cladding of Inconel 625-based composite coatings reinforced by porous chromium carbide particles. Opt. Laser Technol. 94, 6–14 (2017). https://doi.org/10.1016/j.opt lastec.2017.03.007 53. Zhao, J., Ma, A., Ji, X., Jiang, J., Bao, Y.: Slurry erosion behavior of AlxCoCrFeNiTi0.5 highentropy alloy coatings fabricated by laser cladding. Metals (Basel) 8, 126 (2018). https://doi. org/10.3390/met8020126 54. Petrova, V., Schmauder, S., Georgiadis, A.: Thermal fracture of functionally graded coatings with systems of cracks: application of a model based on the rule of mixtures. Ceramics 6, 255–264 (2023). https://doi.org/10.3390/ceramics6010015 55. Gupta, A., Kumar, D.: Development of Al2O3-based hybrid ceramic matrix composite coating to mitigate the erosive wear of advanced steel. Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl. 235, 752–762 (2021). https://doi.org/10.1177/1464420720978676 56. Liu, G., Shen, Z., He, L., Mu, R., Huang, G.: LaYZrO/YSZ double ceramic layer thermal barrier coatings by EB-PVD: thermal performance, morphology and failure behavior. Materialia 27, 101661 (2023). https://doi.org/10.1016/j.mtla.2022.101661 57. Chavana, N., Bhajantri, F.V., Jambagi, S.C.: Improvement in slurry erosion and corrosion resistance of plasma-sprayed fly ash coatings for marine applications. ACS Omega 7, 32369– 32382 (2022). https://doi.org/10.1021/acsomega.2c03800 58. Yang, S., Wang, J., Wang, G., Tong, S., Wang, Z., Zhang, M., Lin, Z., Feng, Z., Xiong, Y.: Study on high-temperature erosion resistance of precursor ceramic coatings. IOP Conf. Ser. Earth Environ. Sci. 474, 052082 (2020). https://doi.org/10.1088/1755-1315/474/5/052082 59. Medvedovski, E.: Advanced ceramics and coatings for erosion-related applications in mineral and oil and gas production: a technical review. Int. J. Appl. Ceram. Technol. 20, 612–659 (2023). https://doi.org/10.1111/ijac.14240

184

S. Arulvel et al.

60. Ndumia, J.N., Kang, M., Gbenontin, B.V., Lin, J., Nyambura, S.M.: A review on the wear, corrosion and high-temperature resistant properties of wire arc-sprayed Fe-based coatings. Nanomaterials 11, 2527 (2021). https://doi.org/10.3390/nano11102527 61. Provenzano, V., Sadananda, K., Louat, N.P., Reed, J.R.: Void formation and suppression during high temperature oxidation of MCrAlY-type coatings. Surf. Coatings Technol. 36, 61–74 (1988). https://doi.org/10.1016/0257-8972(88)90136-3 62. Brimhall, J.L., Kissinger, H.E., Kulcinski, G.L.: Effect of temperature on void formation in irradiated pure and impure metals. Richland, WA (United States) (1971). https://doi.org/10. 2172/4722271 63. Guillon, O., Dash, A., Lenser, C., Uhlenbruck, S., Mauer, G.: Tuning the microstructure and thickness of ceramic layers with advanced coating technologies using zirconia as an example. Adv. Eng. Mater. 22, 2000529 (2020). https://doi.org/10.1002/adem.202000529 64. Vasudev, H., Thakur, L., Bansal, A., Singh, H., Zafar, S.: High temperature oxidation and erosion behaviour of HVOF sprayed bi-layer Alloy-718/NiCrAlY coating. Surf. Coat. Technol. 362, 366–380 (2019). https://doi.org/10.1016/j.surfcoat.2019.02.012 65. Uusitalo, M.A., Vuoristo, P.M.J., Mäntylä, T.A.: Elevated temperature erosion–corrosion of thermal sprayed coatings in chlorine containing environments. Wear 252, 586–594 (2002). https://doi.org/10.1016/S0043-1648(02)00014-5 66. Wellman, R., Nicholls, J.: High temperature erosion–oxidation mechanisms, maps and models. Wear 256, 907–917 (2004). https://doi.org/10.1016/j.wear.2003.04.003 67. Padmini, B., Mathapati, M., Niranjan, H., Sampathkumaran, P., Anand Kumar, S., Padmavathi, G.: Elevated temperature erosive wear behavior of superalloy coatings deposited using cold spray technology. Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl. 146442072110370 (2021). https://doi.org/10.1177/14644207211037010 68. Roy, M.: Elevated temperature erosive wear of metallic materials. J. Phys. D Appl. Phys. 39, R101–R124 (2006). https://doi.org/10.1088/0022-3727/39/6/R01 69. Erosion coatings for high-temperature polymer composites: a collaborative project with Allison advanced development company, pp. 2–4 (n.d.) 70. Nisa, Z.U., Chuan, L.K., Guan, B.H., Ayub, S., Ahmad, F.: Anti-wear and anti-erosive properties of polymers and their hybrid composites: a critical review of findings and needs. Nanomaterials 12, 2194 (2022). https://doi.org/10.3390/nano12132194 71. Kazasidis, M., Verna, E., Yin, S., Lupoi, R.: The effect of heat treatment and impact angle on the erosion behavior of nickel-tungsten carbide cold spray coating using response surface methodology. Emerg. Mater. 4, 1605–1618 (2021). https://doi.org/10.1007/s42247-021-002 74-7 72. Ivosevic, M., Knight, R., Kalidindi, S.R., Palmese, G.R., Sutter, J.K.: Erosion/oxidation resistant coatings for high temperature polymer composites. High Perform. Polym. 15, 503–517 (2003). https://doi.org/10.1177/0954008303015004007 73. Manjunatha, K., Giridhara, G., Shivalingappa, D.: High temperature erosion behaviour of high-velocity oxy-fuel sprayed CNT/NiCr–Cr3C2 composite coatings. Surf. Coat. Technol. 448, 128900 (2022). https://doi.org/10.1016/j.surfcoat.2022.128900 74. Goyal, K., Singh, H., Bhatia, R.: Hot corrosion behaviour of carbon nanotubes reinforced chromium oxide composite coatings at elevated temperature. Mater. Res. Express. 5, 116408 (2018). https://doi.org/10.1088/2053-1591/aadc34 75. Kuruba, M., Gaikwad, G., Natarajan, J., Koppad, P.G.: Effect of carbon nanotubes on microhardness and adhesion strength of high-velocity oxy-fuel sprayed NiCr–Cr3C2 coatings. Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl. 236, 86–96 (2022). https://doi.org/10.1177/146 44207211040922 76. Choudhary, M., Sharma, A., Aravind Raj, S., Sultan, M.T.H., Hui, D., Shah, A.U.M.: Contemporary review on carbon nanotube (CNT) composites and their impact on multifarious applications. Nanotechnol. Rev. 11, 2632–2660 (2022). https://doi.org/10.1515/ntrev-20220146 77. Ma, X., Rivellini, K., Ruggiero, P., Wildridge, G.: Novel thermal barrier coatings with phase composite structures for extreme environment applications: concept, process, evaluation and performance. Coatings 13 (2023). https://doi.org/10.3390/coatings13010210

Wear/Erosion Resistant High-Temperature Coatings

185

78. Wang, Y., Chen, W.: Microstructures, properties and high-temperature carburization resistances of HVOF thermal sprayed NiAl intermetallic-based alloy coatings. Surf. Coat. Technol. 183, 18–28 (2004). https://doi.org/10.1016/j.surfcoat.2003.08.080 79. Superalloys.: In: Alloying, pp. 290–307. ASM International (2001). https://doi.org/10.31399/ asm.tb.aub.t61170290 80. Meghwal, A., Anupam, A., Murty, B.S., Berndt, C.C., Kottada, R.S., Ang, A.S.M.: Thermal spray high-entropy alloy coatings: a review. J. Therm. Spray Technol. 29, 857–893 (2020). https://doi.org/10.1007/s11666-020-01047-0

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni High Entropy Alloys Coatings Prepared by Laser Cladding Jin Zhang and Minyu Ma

Abstract Oxidation and wear have been confirmed to be a great threat to the metals at high temperatures, for instance, in the fields of power, petrochemical industry, weapon, and aerospace. A novel Co–Cr–Fe–Nb–Ni high-entropy alloy coating was designed and manufactured by laser cladding, which was composed of toughness FCC and hardness Laves phase. The Cr atoms dissolved into the FCC phase, while the Si atoms doped into the Laves phase by replacing the Nb atoms. In the oxidation process, the coating experienced mainly the selective oxidation of the Cr and Nb. The oxidation of Si in the Laves phase replaced the Nb, producing a more stable (Cr, Si)Ox at the interface and delaying the internal diffusion of oxygen. The addition of Ce improved the compactness and bonding strength of the Cr2 O3 oxide film. The hardness of Co–Cr–Fe–Nb–Ni coatings was determined by the Laves phase and the MC phase, which precipitated by the diffusion of Nb and C and decreased the Laves content. The wear mechanism changed from abrasive wear to oxidation wear as temperature increased. The Co–Cr–Fe–Nb–Ni HEAs coatings exhibited superior performance of anti-oxidation and wear resistance compared to electroplated hard Cr coating at high temperature. Keywords High-entropy alloys · Laser cladding · Thermal growth oxides · Wear · Corrosion

J. Zhang (B) University of Science and Technology Beijing, Beijing, China e-mail: [email protected] M. Ma Chongqing University of Technology, Chongqing, China e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_8

187

188

J. Zhang and M. Ma

1 Introduction 1.1 Protection Requirement for Oxidation/Wear Resistance at High Temperature Thermal power generation is one of the world’s primary forms of electricity production. The enhanced efficiency and reduced emissions technology pertaining to thermal power generation help power plants burn less coal while reducing CO2 emissions. Supercritical steam generator works at supercritical pressure and temperature of water, which is commonly employed in power production. When the water work enters the generator’s condenser at the temperature and pressure below the critical point, it results in slightly less fuel consumption. Unlike traditional boilers, supercritical steam generators operate above the critical temperature of 374 °C and pressure of 22 MPa. The density of liquid water decreases smoothly without any phase change and becomes indistinguishable from steam. The thermodynamic efficiency of power plants using supercritical steam generators improved significantly. From Carnot’s theorem, the conversion of higher temperature steam in the turbine is more efficient at supercritical pressure. Nowadays, the supercritical power plants can reach efficiencies of 42–45%. The Rheinhafen-Dampfkraftwerk Block 8 unit in Germany achieved the record-breaking net efficiency of 47.5% by utilizing the superheated and reheated steam temperatures of 600/620 °C and pressures of 27.5 MPa [1]. It has been confirmed that the advanced ultra-supercritical (AUSC) power plants can improve the power generation efficiency to 50% by improving the temperatures and pressures of steam over 700 °C and 35 MPa, which are anticipated to commence operations within the next 10 years [2, 3]. As the temperature further increased in AUSC power plants, the heated components become subject to more demanding requirements for high-temperature oxidation resistance, which is one of the primary factors in the failure of these components [4, 5]. The CO2 and H2 O mixture gas has a great corrosion damage on the structural alloys of heated components. Also, the high-temperature flue gas with ash particles impacts on the surface of heat components at high speed, causing erosion and wear [6]. The erosion resistance of the metals used in boilers in the high-temperature corrosive atmosphere is an important parameter to ensure the stable operation of power plants. Currently, with the 700 °C AUSC power plants are expected to be operated, the oxidation resistance and mechanical properties of the heated components’ materials are more severely desired. Also in the automatic weapon, the erosion resistance of the metals used in the barrel is expected to be improved. The bore surface heated by combustion gas may reach 1000 °C and decline to half this value in a few milliseconds. The combustion products by propellants can severely erode and oxidize material surfaces. In addition, projectiles move forward and gradually squeeze into the rifling, the friction force produced by the projectiles causes mechanical wear on the bore surface.

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

189

In the above combustion process, the coupling effect of high-temperature oxidation and wear will result in serious damage to the heated components. The mixture atmosphere can seriously affect the surface condition of the materials. Electroplated hard Cr coatings provide excellent corrosion and mechanical properties for protecting the heated components in many industries; however, the viability of the electroplating process is at risk due to the toxic hexavalent chromium baths. Currently, the materials with an environmentally friendly, anti-oxidation, and excellent mechanical properties at high temperature are more severely desired to improve the reliability and service life of heated structural components.

1.2 High-Entropy Alloy Properties High-entropy alloys (HEAs) have received a great deal of attention for their unique mechanisms and excellent properties in challenging service conditions. Unlike conventional alloys, which contain one and rarely two base elements, HEAs consisting of four or more elements in an equimolar or near-equimolar composition to form a solid solution alloy and stimulating significant interest in the field of material science and engineering [7, 8]. The high mixing entropy effect makes HEAs exhibit a series of properties different from conventional materials, such as lattice distortion, slow diffusion, and high-temperature phase stability. According to Gibbs free energy, the mixing entropy competes with the mixing enthalpy, and the high mixing entropy plays a dominant role in the free energy of the system, especially at the high temperature. In the random intercalation state, the high mixing entropy of the HEAs can greatly reduce the free energy of the system, thus making it exhibit perfect high-temperature stability. Therefore, HEAs have full potential as a high-temperature protective material. CoCrFeNi is one of the most common HEAs with face-centered cubic, exhibiting high ductility and relatively low strength. The performance of the alloy can be substantially improved by additional elements. For example, Al can promote the phase transition of FCC changed to BCC, improving the hardness of HEAs. Additionally, Al can inhibit the impact of supercooling on grain morphology [9]. Chen [10] revealed that Ti and Al play a crucial role in the formation of L12 precipitates and enhance the phase stability in CoCrFeNi HEAs. Yang [11] reported that the multicomponent Ni3 (Al, Ti)-type nanoparticles have attractive features for strengthening HEAs without compromising ductility. The precipitation of multicomponent Ni3 (Al, Ti)-type nanoparticles provides appealing characteristics for enhancing the strength of 1.5 GPa without sacrificing the ductility as high as 50% of HEAs. The addition of the Nb element can form the Laves phase which effectively improving the wear resistance of FCC HEAs at high temperature [12, 13]. Chromium (Cr) is one of the most important elements for improving high-temperature properties, as it can play a role in solid solution strengthening and produce short-range ordered strengthening. Additionally, the chromium oxide (Cr2 O3 ) film formed by the Cr element has excellent high-temperature oxidation resistance.

190

J. Zhang and M. Ma

1.3 Laser Cladding High-Entropy Alloys Coatings From the economic aspect, the high cost of bulk HEAs is due to the high content of expensive alloying elements. The surface coatings technologies can achieve a judicious combination of costs and properties. Moreover, it was reported that HEA coating performed even better properties compared to the bulk material, which might be due to the homogeneous microstructure by more precise shaping control [14]. Li [15] deposited AlCoCrFeNi coatings onto AISI 1045 carbon steel. In contrast to the bulk HEA material, no discernible Cr-rich interdendritic segregation or nano-sized precipitates were detected within the dendrites of the HEA coating. The corrosion current of the HEA-coated specimen was significantly lower than that of the bulk HEA material. It takes the advantage of fine microstructure, metallurgical bonding, and less intermixing with the substrate. Furthermore, the rapid solidification rate of 104 –106 K/s can lead to significant effect of non-equilibrium solute trapping, reduce the nucleation and growth rate of the brittle intermetallic compound, and improve solubility limitation. In this work, the Co–Cr–Fe–Nb–Ni HEAs coatings were prepared by laser cladding. The Cr, Si, C, and Ce were used to improve the high-temperature oxidation and wear resistance of coatings. A N2 –44CO2 –6H2 O (vol. %) mixture gas at 800 °C was generated to evaluate the high-temperature oxidation resistance of the HEAs coatings. The wear tests of HEAs coatings were carried out in dry sliding condition using a ball-on-disc wear from room temperature (RT) to 800 °C. The 5 mm diameter grinding balls are made of Si3 N4 . The cylindrical discs dimensions with a diameter of 20 mm and a height of 10 mm were machined from HEAs coatings. The disc samples’ surface was ground with 400–2000 grit silicon carbide papers. Wear tests were carried out with loads of 100 N and sliding velocity of 1 m/s. The role of each element on oxidation and wear resistance was elaborated. The HEAs coatings were produced by laser cladding on the surface of Cr–Mo–V steel. Each specimen was abraded via silicon carbide papers up to 800 #, cleaned with alcohol, and dried subsequently before cladding. The cladding powders consisted of Fe, Cr, Co, Ni and Nb, CeO2 particles with a purity >99.5 wt.% and size of 75–150 μm. The Si, C, and Ce were added into the coatings by FeSi, FeCrC, and CeO2 with the same particle size for reducing the sparks during laser cladding. The powders were weighed according to the ratio of elements and mixed by a ball mill for 8 h. The mixed powders were dried over 2 h at 120 °C, then pre-placed on the substrate steel. The thickness of the pre-placed layer was about 1 mm. A 1.5 kw fiber laser processing system with a 1.5 mm spot diameter was employed for manufacturing the HEAs coatings. The laser cladding parameters: 800 W of power, 7 mm/s of the scanning speed, and an overlapping ratio of 30%. The Argon gas was used to protect the molten pool during the laser cladding process with a flux of 8 L/min.

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

191

2 The Microstructure Co–Cr–Fe–Nb–Ni Coating 2.1 Effect of Cr Content on the Microstructure Cr is a crucial element in ensuring high-temperature oxidation resistance of metal due to its dense and stable thermal growth oxides of Cr2 O3 . In the CoCrx FeNb0.5 Ni HEAs coatings, the coating microstructure mainly consists of FCC and Laves phase, when the Cr content x from 0.5 increases to 2 (Fig. 1). The Co, Cr, Fe, and Ni have similar atomic radius and can form FCC solid solutions [16–18]. The atomic radius ratio of Nb to other atoms concentrated within the range of 1.1–1.3, promoting the formation of Laves phase [19]. As shown in the XRD patterns, all the diffraction peak positions of the Laves and FCC phase shift to the lower angle, meaning the crystal spacing for both phases crystal becomes larger according to Bragg’s Law. The solution of Cr atoms in both phases results in the lattice distortion. The microstructure of coatings was observed by scanning electron microscope (SEM) (Fig. 2) The CoCrx FeNb0.5 Ni HEAs coatings all show a dendritic structure along the solidification direction, wherein the interdendritic structure becomes more obvious with the Cr content increased. Additionally, the growth of the dendritic structures was inhibited in CoCr0.5 FeNb0.5 Ni and CoCrFeNb0.5 Ni coatings. The typical lamellar eutectic microstructure consists of gray FCC phase and white Laves phase can be observed in the above two coatings. As the Cr content increased, the granular microstructure of Laves phase formed in CoCrFeNb0.5 Ni coatings (x = 1.5 and 2). The precipitation of granular structure Laves phases owing to the growth drive decreased as the consumption of Nb in the molten pool. The chemical composition of the FCC and Laves phase in CoCr2 FeNb0.5 Ni coating were detected by EDS

Fig. 1 The XRD patterns of CoCrx FeNbNi HEAs coatings. a The diffraction peak of CoCrx FeNbNi coatings. b The diffraction peak of (200) in the FCC phase. c The diffraction peak of (110) in Laves phase

192

J. Zhang and M. Ma

(Table 1). The gray region consists of only 4.09 at.% Nb and 44.86 at.% Cr. The Nb content of the white region reaches 29.27 at.%, implying the white region is the Laves phase. Additionally, the atomic content of Cr in the FCC phase is much higher than in the Laves phase, meaning the Cr atoms prefer to dissolve in the FCC phase. The FCC and Laves phases in the CoCr2 FeNb0.5 Ni coating were further observed via TEM (Fig. 3). The lamellar structure as well as the granular structure of the Laves phase can be clearly observed. Due to the fast-cooling rate of the laser cladding and the “sluggish diffusion effect” of the HEAs, the Laves phases are mostly nanosized thickness with a lamellar structure. The diffraction pattern of the FCC phase ¯ ¯ crystalline band axis) and the Laves structure (along the [21¯ 10] (along the [112] crystalline band axis) further confirm the structure of CoCr2 FeNb0.5 Ni coating. An inverse Fourier transform of the high-resolution photograph of the FCC phase in the coating shows a large number of non-parallel white lines, indicating that the lattice deformation of the FCC phases is caused by distortion. This is consistent with the results of XRD and electron microscopy energy spectra result.

2.2 Effect of Si Addition on the Microstructure Si is an important element in the laser cladding process for its strong deoxidation effect. Also, the SiO2 film formed by Si at high temperature has a protective effect. The phases of CoCr2 FeNb0.5 NiSix depend on the addition of Si. The XRD result reveals little change in phase constitution when x is no more than 0.2. The diffraction peaks of Cr15 Co9 Si6 (M24 Si6 ) were detected with more Si addition. The metal silicide formed when too much Si was added due to the limited solution of Si in the FCC and Laves phase. Noteworthy, the diffraction peaks in the FCC phase keep at the same 2θ position, while those of the Laves phase are significantly shifted to a higher angle in CoCr2 FeNb0.5 NiSi0.2 , meaning the Si dissolved into the Laves phase and affected the structure of the Laves phase (Fig. 4). The Laves phase in CoCr2 FeNb0.5 Ni coatings is a hexagonal structure of type A2 B. Wherein, the Co, Cr, Fe, and Ni atoms randomly occupy A-sites and Nb atoms mainly occupy the B-sites. The stability of the Laves phase is related to the ratio of B–A atomic radius. The ideal atomic radius ratio of DB /DA is 1.225, for the tightest stacks result in the most stable structure [20]. In the CoCr2 FeNb0.5 Ni coatings, the atomic radius ratio of B–A is close to Cr2 Nb owing to the higher Cr content, which is smaller than the ideal ratio. The Si will occupy the A-sites, and some of the Nb at the sites of B will be replaced by Cr, Ni, Co, or Fe when the Si dissolved into the Laves phase. The DB /DA is closer to 1.225 due to the average atomic radius of A rises and that of B decreases (Fig. 5). The interplanar spacing of Laves phases becomes smaller with Si-doped having a more stable structure [21, 22]. The CoCr2 FeNb0.5 NiSi0.2 coating has the similar microstructure compared to CoCr2 FeNb0.5 Ni. With the increase of Si content, a feathery-like microstructure appears in the coating, concomitant with the precipitated of fine phases. The eutectic structure disappeared and more pores defects appear in the coating in laser processing

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

193

Fig. 2 Microstructure of CoCrx FeNb0.5 Ni coatings was observed by scanning electron microscope. a–a1 x = 0.5, b–b1 x = 1, c–c1 x = 1.5, d–d1 x = 2

194

J. Zhang and M. Ma

Table 1 The chemical composition of different regions in CoCr2 FeNb0.5 Ni HEAs coatings in Fig. 2 (at.%) Region

Phase

Co

Cr

Fe

Nb

Ni

A

FCC

17.17

44.86

17.48

4.09

16.40

B

Laves

15.88

23.99

15.97

29.27

14.89

Fig. 3 TEM of CoCr2 FeNb0.5 Ni coating. a Microstructure at the bright field and diffraction spot of FCC and Laves phase. b High-resolution morphology and inverse Fourier transformation

when the Si atom ratio is above 0.2 (Fig. 6). Pores always be caused by the entrapment of gas released from the powders. The metal with better fluidity eutectic structure in the melting process is conducive to the escape of gas. However, the gas in the molten poor cannot escape in time during the laser cladding process due to the poor melt fluidity with excessive Si addition [23]. The quality of the coating can be guaranteed when the Si atomic ratio is less than 0.2.

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

195

Fig. 4 The XRD patterns of CoCr2 FeNb0.5 NiSix HEAs coatings. a The diffraction peak of Co– Cr2 FeNb0.5 NiSix coatings. b The diffraction peak of (110) in the Laves phase

Fig. 5 The structure schematic diagram of A2 B Laves without and with Si-doped in Cr2 FeNb0.5 Ni coating. a Without Si-doped, b with Si-doped

The chemical composition of FCC and Laves phase in CoCr2 FeNb0.5 Ni and CoCr2 FeNb0.5 NiSi0.2 were detected (Table 2). It is obvious that Si dissolved in the Laves phase and the Nb content of Laves phase decreased. The mixing entropy ∆Hmix AB of Fe, Co, Cr, Ni, and Nb between Si are −35 kJ/mol, −38 kJ/mol, −37 kJ/mol, −40 kJ/mol, and −56 kJ/mol, respectively [24]. Si can preferentially combine with Nb, forming the Laves during the solidification due to the stronger affinity of Si and Nb atoms. Therefore, the Si atoms can occupy the A-sites in Laves

196

J. Zhang and M. Ma

Fig. 6 The microstructure of CoCr2 FeNbNiSix HEAs coatings. a x = 0, b x = 0.2, c x = 0.4 and d x = 0.6

Table 2 The chemical composition of different regions in CoCr2 FeNb0.5 NiSix HEAs coatings in Fig. 6 (at.%) Coatings

Region

Phase

Co

Cr

Fe

CoCr2 FeNb0.5 Ni

A

FCC

17.17

44.86

17.48

B

Laves

15.88

23.99

15.97

A

FCC

17.01

45.38

17.43

B

Laves

17.70

20.98

18.04

CoCr2 FeNb0.5 NiSi0.2

Nb

Ni

Si

4.09

16.40

–

29.27

14.89

–

3.76

15.71

0.71

21.22

17.65

3.59

phase and the Co, Cr, Fe, or Ni can replace the Nb atoms at B site. This results in a tighter occupation of the atoms, decreasing the interplanar spacing. The interplanar spacing of the Laves phase decreases from 0.797 to 0.768 nm in CoCr2 FeNb0.5 Ni and CoCr2 FeNb0.5 NiSi0.2 coatings are observed by inverse Fourier transform (Fig. 7). The Nb content in the Laves phase also decreases from ~30 to ~20 at.% with the Si addition. More Nb atoms can expelled in the melt pool, promoting the formation of Laves phases which results in a higher content of Laves phases in the coating.

2.3 Effect of C Addition on the Microstructure The addition of Si leads to an increase in defects of the coatings, making it difficult to improve its mechanical properties. C is a type of interstitial atom often used to enhance the strength of metallic materials. In the CoCr2 FeNb0.5 NiSi0.2 coatings, the diffraction peaks of MC can be clearly observed after the addition of C, indicating that in-situ reaction during solidification produced a reinforced phase of MC (Fig. 8). The C in the melt pool reacted with the strong carbide-forming element Nb to form

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

Fig. 7 Transmission electron microscopy and inverse Fourier transformation CoCr2 FeNb0.5 NiSix coating prepared by laser cladding. a x = 0 and b x = 0.2

197

of

MC phase. The high content of Nb elements in the high-entropy alloys inhibited the separate reaction of Cr and C, and no other structure carbides were observed. The typical eutectic structure can still be observed in the dendritic. After the C addition, some fine spherical phases can be considered as MC are observed in the interdendritic. Also, the MC phase size grows larger significantly with more C addition (Fig. 9). Another interesting phenomenon, the edges of the MC phase are very smooth when the C-atom ratio is 0.1, while the burr structure appears on the surface of MC phase when the C-atom ratio is 0.3. Also, it is obvious from the distribution of elements that the MC particles mainly consist of Nb and C in CoCr2 FeNb0.5 NiSi0.2 C0.3 (Fig. 10). In the TEM pictures of CoCr2 FeNb0.5 NiSi0.2 C0.1 coatings, diffusely distributed phases with ~100 nm were clearly observed. The selected area electron diffraction ¯ and (2¯ 42) ¯ crystal plane can be identified as NbC (Fig. 11). In (SAED) with (3¯ 31) traditional metallic materials, the NbC strengthened phase is mostly irregular such as granular, petal-like, and polyhedral, mainly because the difference in interfacial energy of NbC can lead to different growth direction of the crystal plane during solidification [25, 26]. In the HEAs coatings of this study, the mechanism of NbC phase growth based on diffusion reactions can be explained by the Oswald ripening. The high concentration of Nb provides sufficient growth drive for NbC, which does not undergo oriented growth during the growth process, forming a spherical phase with minimal surface area for the lowest energy eventually [27, 28]. As the C addition

198

J. Zhang and M. Ma

Fig. 8 The XRD patterns of CoCr2 FeNb0.5 NiSi0.2 HEAs coatings with and without C addition

Fig. 9 The microstructure of CoCr2 FeNb0.5 NiSi0.2 HEAs coatings with and without C addition. a x = 0, b x = 0.1, c x = 0.2, d x = 0.3

increases, selective orientational growth of the NbC phases since the concentration of free Nb atoms decreases, therefore burr edges appear on the surface.

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

199

Fig. 10 The elements distribution of CoCr2 FeNb0.5 NiSi0.2 C0.3 HEAs coatings

Fig. 11 TEM pictures of CoCr2 FeNb0.5 NiSi0.2 C0.1 coatings. a Microstructure of CoCr2 Fe– Nb0.5 NiSi0.2 C0.1 coatings. b Microstructure, diffraction spot, and chemical composition of MC particle

2.4 Effect of CeO2 Addition on the Microstructure Rare earth elements can purify the molten pool and refine grains, which is an effective way for enhancing the mechanical properties of laser cladding coatings [29, 30]. Also, the Ce can decrease the defects at the oxide/metal interface, improving the adhesion of the thermal growth oxide film. The denser and well adherently oxide film is a benefit to high-temperature oxidation resistance of metal [31, 32]. Ce is difficult to exist in the form of elemental powder, therefore, the CeO2 powders with 75 μm particle size were added into the CoCr2 FeNb0.5 NiSi0.2 C0.1 mixture powders. In the CoCr2 FeNb0.5 NiSi0.2 C0.1 laser clad coating, the diffraction peaks positions of FCC, Laves, and NbC phases have little shift after the addition of CeO2 , which implies that the CeO2 is not participated in the phase solidification reaction. Also, no diffraction peaks of CeO2 can be observed even when the CeO2 content reaches 3 wt.% (Fig. 12).

200

J. Zhang and M. Ma

Fig. 12 The XRD patterns of CoCr2 FeNb0.5 NiSi0.2 C0.1 HEAs coatings with CeO2 addition

The microstructure of the coatings after the addition of CeO2 shows a clear refinement (Fig. 13). The flower-like morphology consisted of lamellar structure becoming smaller and more uniform and dispersible. The CeO2 particles had not been found in the coating, indicating that they absorbed the energy of the laser beam and melted. During the laser cladding process, CeO2 with a high laser absorption rate significantly increased the absorption rate of the powders and promoted the fluidity of the molten pool [33]. CeO2 melted in the molten pool, and the Ce atoms could be easily trapped by defects at the interface. The Ce atoms adsorbed at the grain boundaries formed new fine CeOx particles with O in the melt pool. The difference between the surface energy of the interfaces was reduced, and the growth of interfaces with maximum surface tension was suppressed. The CeOx increased the nucleation sites of the Laves phase. The growth of the lamellar structure was suppressed due to the pinning effect of the CeOx , resulting in a finer eutectic structure.

Fig. 13 Microstructure of CoCr2 FeNbNiSi0.2 C0.1 coatings with CeO2 addition. a 0 wt.%, b 0.5 wt.%, c 1 wt.%, d 2 wt.% and f 3 wt.%

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

201

3 The Oxidation Behavior of Co–Cr–Fe–Nb–Ni Coatings 3.1 The Role of Cr on Wet Mixture Gas Oxidation H2 O and CO2 have a significant influence on the oxidation kinetics of coatings. They are the main atmospheres for high-temperature oxidation in AUSC boilers. The oxidation test was carried out in a quartz tube furnace filled with mixture gas. The specimens were cut into 10 × 10 × 1 mm and all the surfaces were polished to 1 μm. Hereafter, the specimens were ultrasonically washed with absolute ethanol and placed in a corundum crucible, which was used to record weight change. The quartz tube furnace was pumped into 10 Pa and subsequently filled with the N2 –44CO2 – 6H2 O (vol. %) mixture gas at a flux of 300 mL/min. The furnace was stabilized at 800 °C by heating rate of 20 °C /min. The total exposure time was 320 h and weighted the specimen every 40 h. The oxidation kinetic curves clearly show that the oxidation weight gain of the coating is divided into two main stages (Fig. 14). In the first 100 h, the oxidation curves grew rapidly for the initial stage of the oxide film growth. The oxidizing gases reached the surface of the coating, reacting with the epilayer atoms. The rate of weight gain decreased after 100 h. The surface of the coatings was covered with a complete oxide film, preventing oxidizing gases from contacting the coating directly. The diffusion is the main way for oxygen ions to reach the interface between the coating and the oxide film. At this time, the metal ions in the coating could only diffuse outwards through the oxide film and further oxidated. The process of oxidation weight gain is controlled by the reaction to diffusion. The oxidation weight gain curves of CoCrx FeNb0.5 Ni can be approximated as parabolic laws, which can be fitted using the equation: (∆m)2 = K p × t, where ∆m is the weight gain per unit area of coating oxidation, K p is the parabolic rate constant, and t is the oxidation time. The K p of CoCrx FeNb0.5 Ni is 0.203 mg2 /(cm4 h), 0.174 mg2 /(cm4 h), 0.133 mg2 /(cm4 h), and 0.086 mg2 /(cm4 h), respectively. The addition of Cr significantly improves the oxidation resistance of the coating. The oxidation products on the surface consist of fine-grain and blade oxides (Fig. 15). In CoCr0.5 FeNb0.5 Ni coating, the oxidized surface morphology is relatively rough. The clustered spherical structure is composed of fine-grain and blade oxidation products. With the content of Cr increased, the surface of the oxidation products becomes relatively flat and the spherical clusters disappear. The blade oxides are randomly distributed among the fine-grain oxides. The main oxidation products of CoCrx FeNb0.5 Ni coatings are Cr2 O3 due to the XRD result (Fig. 16). Also, a few Cr3 O diffraction peaks are also observed, which could form due to the oxidation of Cr at low oxygen partial pressure [34, 35]. Some diffraction peaks of NbO2 could be detected in the oxidized CoCr0.5 FeNb0.5 Ni coating. The interface cross section of oxidized high-entropy alloys coatings can be divided into four main regions (Fig. 17). The elements composition of these regions was detected (Table 3). The outer surface (Region A) is a Cr2 O3 oxide film composed of Cr and O. The region B is the inner oxidation zone (IOZ) at the interface between the

202

J. Zhang and M. Ma

Fig. 14 The oxidation kinetic curves of CoCrx FeNb0.5 Ni HEAs coatings at 800 °C in wet mixture gas oxidation

Fig. 15 The oxidized surface morphology of CoCrx FeNb0.5 Ni HEAs coatings at 800 °C in wet mixture gas oxidation after 320 h. a x = 0.5, b x = 1, c x = 1.5 and d x = 2

coating and the oxide film, which consists of Cr, Nb, and O. Combined with the NbO2 and Cr3 O diffraction peaks found in the XRD results, this region can be considered as mixed oxides of Nb and Cr. The Laves phase and FCC phase existed in the regions C and D, respectively. The NbO2 is produced by the oxidized Laves phase for the

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

203

Fig. 16 X-ray diffraction spectra of oxidized CoCrx FeNb0.5 Ni HEAs coating in mixture gases of HEAs coatings at 800 °C in wet mixture gas oxidation after 320 h

Nb mainly presents in this phase in the coating. Kirkendall voids can also be clearly observed at the interface after oxidation. At the later stage of oxidation, the coating surface was covered by a complete oxide film. At this time, the metal cations in the coating diffused outward, and the oxygen ions diffused inward. Since the diffusion rate of cations outward was faster than the diffusion rate of anions inward, Kirkendall voids were left at the interface [36]. In the N2 –44CO2 –6H2 O (vol.%) mixture gas, N2 is a relatively stable gas. As no N-containing products were found after exposing to the mixed gas, it can be assumed that N2 in the atmosphere does not participate in the reaction. The oxidation reaction of oxygen comes from CO2 and H2 O, and the mainly reaction can be described as follows [37]: 1 CO2 ⇌ CO + O2 2 2CO ⇌ CO2 + C

Fig. 17 The interface cross section of CoCrx FeNb0.5 Ni HEAs coating at 800 °C in wet mixture gas oxidation for 320 h. a, e x = 0.5, b, f x = 1, c, g x = 1.5 and d, h x = 2

204

J. Zhang and M. Ma

Table 3 The elements composition of different regions in oxidized CoCrx FeNb0.5 Ni coatings in Fig. 17 (wt.%) Coatings

Region

O

Cr

Nb

Fe

Co

Ni

CoCr0.5 FeNb0.5 Ni

A

64.86

35.14

–

–

–

–

B

60.86

11.97

27.17

–

–

–

C

–

5.59

22.42

26.27

22.18

23.54

CoCrFeNb0.5 Ni

CoCr1.5 FeNb0.5 Ni

CoCr2 FeNb0.5 Ni

D

–

5.32

30.16

27.15

27.81

A

62.47

37.53

9.56

–

–

–

–

B

61.97

12.89

25.14

–

–

–

C

–

5.12

23.20

26.13

23.31

22.24

D

–

6.98

5.13

30.75

28.38

28.76

A

64.46

35.54

–

–

–

–

B

58.37

15.53

26.10

–

–

–

C

–

10.24

32.28

21.46

17.82

18.21

D

–

14.13

4.77

28.13

26.39

26.58

A

61.15

38.85

–

–

–

–

C

–

12.15

33.17

19.26

19.81

15.61

D

–

22.89

5.00

25.84

23.11

23.16

1 H2 O ⇌ H2 + O2 2 CO + H2 ⇌ H2 O + C The mixed atmosphere can provide free O and C at the surface of the coating. At equilibrium in the 800 °C environment, the pO2 (partial pressure of oxygen) in the atmosphere is 2.6 × 10–7 atm, while the ac (carbon potential) is 1.66 × 10–40 . The Cr and Nb are the elements that preferentially oxidize in the coating at 800 °C according to the Ellingham diagram. Carbides of Nb or Cr had not been found, for the carbide reactions could hardly occur for the extremely low carbon potential [38]. Therefore, the coating reacts preferentially as follows: 4 Cr + O2 ⇌ Cr2 O3 3

∆ f GΘ = − 746840 + 170.29T

2Nb + O2 ⇌ 2NbO2

∆ f GΘ = − 786590 + 149.79T

At 800 °C, the free energy of Cr2 O3 and NbO2 is −564.12 and −625.86 kJ/mol. The NbO2 with more negative free energy is easier to grow in this environment. However, in the cross-sectional observation of the coating after high-temperature oxidation, it is obvious that the Cr2 O3 appeared at the outer of the coating, while NbO2 is observed only in the inner oxidation zone. The high concentration of Cr

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

205

enhances the selective oxidation of chromium and Cr2 O3 preferentially formed on the surface.

3.2 The Role of Si on Wet Mixture Gas Oxidation The Si was added into the CoCr2 FeNb0.5 Ni coating to improve the quality of lase clad coating. Also, its oxides contribute to the high-temperature oxidation resistance. The oxidation kinetics for these samples with and without Si can be approximately fitted by the parabolic law. The oxidation weight gain of CoCr2 FeNb0.5 NiSi0.2 decreased compared to CoCr2 FeNb0.5 Ni. It can be found that the weight gain of the above two coatings is similar at the early stage of oxidation, while decreasing after 200 h with the Si addition. The effect of Si in improving the oxidation resistance is mainly demonstrated in the late stage of oxidation. The excessive Si addition decreases the oxidation resistance of the coatings (Fig. 18). Similar to the CoCr2 FeNb0.5 Ni coating, the oxides on the surface of the coating with Si addition are still consisted of finegrain and blade oxides. Excessive Si addition results in more defects in the coating (Fig. 19). The difference between the CoCr2 FeNb0.5 Ni and CoCr2 FeNb0.5 NiSi0.2 oxide layer is mainly at the interface after 320 h oxidation, which can be observed from the examined cross section (Fig. 20). The complete outside oxide layer can be identified as Cr2 O3 , while the interface between coating and oxidation layer is quite different. Minor oxides at the interface seem different from the Cr2 O3 . The aggregation of Nb disappeared at the interface when Si was added to the coating. Instead, the aggregation of Si at the interface becomes obvious, indicating the Si diffused to the interface and reacted with O. The Fe, Co, and Ni are still concentrated in the coatings. The selective oxidation and the delayed diffusion effect of the high-entropy alloys inhibited the oxidation of these elements. The interface of CoCr2 FeNb0.5 NiSi0.2 coating after oxidation was observed more carefully by TEM (Fig. 21). The corresponding SAED patterns are FCC (red dot) Fig. 18 The oxidation kinetic curves of CoCr2 FeNb0.5 NiSix HEAs coatings at 800 °C in wet mixture gas oxidation

206

J. Zhang and M. Ma

Fig. 19 The oxidized surface morphology of CoCr2 FeNbNiSix HEAs coatings at 800 °C in wet mixture gas oxidation after 320 h. a x = 0, b x = 0.2, c x = 0.4 and d x = 0.6

Fig. 20 The elements distribution mapping of cross-sectional morphology of a CoCr2 FeNb0.5 Ni and b CoCr2 FeNb0.5 NiSi0.2 HEAs coating after oxidation [39]. Authorized by Elsevier

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

207

and the Laves (yellow dot) phases, respectively. The outer oxide layer of SADE with ¯ crystal plane can be judged as Cr2 O3 . The IOZ (green dot) can be (001) and (021) ¯ and (2¯ 10) ¯ crystal plane. recognized as the Cr3 O via the SAED pattern with (02¯ 1) However, the chemical composition of this zone is mainly 24.71 at.% Cr, 3.63 at.% Si, 60.91 at.% O and 11.47 at.% Cu. The detected Cu might be polluted during the focused ion beam (FIB) preparation. The samples were welded to the copper column after the cut. The Si in both the inner oxide zone and the Laves phases implies that Si had diffused from the Laves phase to the inner oxide zone. The HRTEM images of the inner oxide zone shows that the path of internal oxidation is mainly along the boundary between the Laves and FCC phase (Fig. 22). Broadened diffraction rings were observed around the Laves phase at the internal oxidation zone by Fourier transform. Amorphous products were generated by the oxidation of Si and Cr, which are mainly (Cr, Si)Ox amorphous oxides [40]. SiO2 has a more negative free energy (−717.28 kJ/mol) compared with that of NbO2 and Cr2 O3 . In the early stage of high-temperature oxidation, oxygen atoms reached the coating surface and reacted with Cr atoms due to the selective oxidation. The high concentration of Cr promoted the growth of Cr2 O3 film on the coatings’ surface. After the oxide film completely covers the coating surface, oxygen ions must diffuse through the oxide film to contact the coating, meanwhile the Cr ions diffused outward through the film. Kirkendall voids were formed at the interface owing to the Fig. 21 The elements distribution mapping of cross-sectional morphology of CoCr2 FeNb0.5 NiSi0.2 HEAs coating after oxidation [39]. Authorized by Elsevier

208

J. Zhang and M. Ma

Fig. 22 High-resolution transmission electron microscope image of the interface between IOZ and HEAs matrix [39]. Authorized by Elsevier

difference in diffusion rates between anions and cations. The oxygen ions reached the coating surface and then diffused inward along the interface between the FCC and the Laves phases, both two phases oxidated slowly. The oxygen partial pressure at IOZ is low, contributing to the formation of Cr3 O. The Si replaced the oxidation of Nb since the Laves phase was doped with Si. An extremely thin amorphous (Cr, Si)Ox oxide layer was formed to cover the Laves phase. It could effectively prevent the contact between oxygen ions and the Laves phase, since the higher stability of (Cr, Si)Ox and no grain boundaries of amorphous structure [40]. The reducing the oxidation rate of the Laves phase helped to improve the high-temperature oxidation resistance of the coating.

3.3 The Influence of C and CeO2 on High-Temperature Oxidation The addition of C can form MC-reinforced particles. However, the high diffusion rate at high temperature is detrimental to the oxidation resistance of the coating [41]. The oxidation kinetic curve of the CoCr2 FeNb0.5 NiSi0.2 Cx coating reveals that the addition of C weakens the high-temperature oxidation resistance (Fig. 23). Even the oxidation products are still Cr2 O3 . The growth drive of Cr2 O3 becomes weaker since the Cr atoms are immobilized in MC. The oxidation resistance of the coatings shows a significant decrease, especially at the C-atom ratio of 0.3. The fine-grain and blade Cr2 O3 can still be observed on the oxidized surface of the coating (Fig. 24). The blade Cr2 O3 oxides grew with the increase of C content. The oxidized surface became rather rough when the C-atom ratio reached 0.3. The cross sections clearly show the differences in the oxide layer. The interface of the coating surface remains flat, which is different from the previous rough oxide surface. The blade oxides growth with C addition, leading to more voids between oxide films (Fig. 25). The Cr atoms could diffuse outward and oxidate more easily since the denseness of the

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

209

oxide film decreases. The growth of blade oxides would produce a rough surface and decrease the oxidation resistance. The CeO2 was added to the coatings to improve the denseness of the oxide layer. A significant decrease in oxidation weight gain of the coatings after the addition of CeO2 (Fig. 26). The surface of the oxidation layer had changed significantly. The blade oxides disappeared, replaced by whisker-like oxides (Fig. 27). The cross section of the oxide further illustrates the difference in coating oxidation after CeO2 addition. With the addition of CeO2 , the denseness of the oxide film was significantly improved. Kirkendall voids at the interface disappeared, and the bonding ability of the thermal growth oxides layer was enhanced. The diffusion path of ions became more tortuous since the grain of the coating was refined after CeO2 addition. During oxidation, Ce ions were released from the CeOx nanoparticles that were enveloped by the inward-growing oxides from the scale/metal interface. The pegging effect of intergranular CeOx , which was preferentially formed at the grain boundaries, reduced the outward diffusion rate of Cr ions. The growth Fig. 23 The oxidation kinetic curves of CoCr2 FeNb0.5 NiSi0.2 HEAs coatings with C addition in wet mixture gas oxidation at 800 °C

Fig. 24 The oxidized surface morphology of CoCr2 FeNb0.5 NiSi0.2 Cx HEAs coatings at 800 °C in wet mixture gas oxidation after 320 h. a x = 0, b x = 0.1, c x = 0.2 and d x = 0.3

210

J. Zhang and M. Ma

Fig. 25 The cross-sectional morphology of CoCr2 FeNb0.5 NiSi0.2 Cx HEAs coatings at 800 °C in wet mixture gas oxidation after 320 h. a x = 0, b x = 0.1, c x = 0.2, and d x = 0.3

Fig. 26 The oxidation weight gain of CoCr2 FeNb0.5 NiSi0.2 C0.1 HEAs coatings at 800 °C in wet mixture gas

Fig. 27 The cross section and surface morphology of CoCr2 FeNb0.5 NiSi0.2 C0.1 HEAs coatings with CeO2 addition in wet mixture gas at 800 °C. a, e 0.5 wt.%, b, f 1 wt.%, c, g 2 wt.% and d, h 3 wt.%

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

211

process of the thermal oxidation film controlled was changed from Cr ions to oxygen ions, which inhibited the growth of Cr2 O3 orientation [31, 41–43]. The process of inward diffusion of oxygen ions through the oxide film became difficult due to the denser oxide film. The CeOx aggregated at the scale/metal interface, inhibiting the vacancy aggregation, and Kirkendall voids disappeared. The consumption of Cr ions for oxidation was reduced as the diffusion of ions became difficult. The oxide film was more tightly bonded to the coating, and the adhesion was improved. Meanwhile, the Cr2 O3 film would be further vaporization and redeposition in the wet environment following the reaction [44]: Cr2 O3 (s) + 2H2 O(g) + 3/2O2 (g) = 2CrO2 (OH)2 (g) Further oxidation of Cr2 O3 produced CrO2 (OH)2 vapor by H2 O, which molecule at the tip of the blades had faster dissociation, favoring the whiskers form [45].

4 The Wear Mechanisms of Co–Cr–Fe–Nb–Ni Coatings 4.1 The Influence of C Addition on Hardness Hardness is an important indicator of wear resistance. The Laves and MC phases are important strengthening phases in CoCr2 FeNb0.5 NiSi0.2 with C addition, both dependent on the content of Nb. The hardness of the coating increases and then decreases with the addition of carbon. The highest hardness of the coatings can be obtained at a C-atom ratio of 0.1, reaching 851 HV0.3 (Fig. 28). The content of FCC, Laves, and MC phase were counted through numerous microstructures. The content of MC increased, while the Laves decreased with more addition of C. When the C atomic ratio was 0.3, the increment of the MC phase was only ~5%, while the reduction of the Laves phase was almost ~10%. (Fig. 29). It illustrates that the process of MC formation leads to a serious decrease of the Laves phase. NbC precipitated preferentially by diffusion reaction during solidification because of the strongest affinity between Nb and C atoms and the high melting point of NbC. When adding a few C, the little Nb in the melt pool can be captured by the C to form the NbC reinforced phase without causing a serious drop in the Laves phase. NbC has a stronger reinforcement effect due to its hardness is ~20 GPa, much higher than that of the Laves phase (~8 GPa) [46, 47]. The synergistic reinforcement of NbC and Laves phase improves the hardness of the coating. With more NbC precipitated, the free Nb atoms in the melt pool were insufficient for the formation of the Laves phase, and its content decreased. The increased concentration of Fe, Co, Cr, and Ni resulted in an increase in the FCC phase. The hardness of the coatings decreased because the strengthening effect of NbC could not compensate for the decrease of the Laves phase.

212

J. Zhang and M. Ma

Fig. 28 The hardness of CoCr2 FeNb0.5 NiSi0.2 coatings with C addition

Fig. 29 The phase content of CoCr2 FeNb0.5 NiSi0.2 coatings with C addition

4.2 The Wear Mechanisms of HEAs Coatings at Elevated Temperature Besides the erosion of the high-temperature atmosphere, the heated components also receive the impact of ash and other particles, which wear out the materials’ surface. The wear rate was calculated by profile measurement after test [48]. The wear rate of CoCr2 FeNb0.5 NiSi0.2 coatings with a C addition atom ratio of 0.1 reveals the optimize wear resistance, which is consistent with the hardness trend of the coatings (Fig. 30). The wear rates 3.43 × 10–5 (mm/(N m)) and 2.56 × 10–5 (mm/(N m)) increased by 1.25 times and 1.24 times, respectively, compared to the coating without C addition at RT and 800 °C. The hardness plays a significant effect on the wear resistance of the coatings at elevated temperatures. The relationship between the wear rate and hardness of CoCr2 FeNb0.5 NiSi0.2 C0.1 coating was compared at different temperatures (Fig. 31). The wear rate of the coating increases with the decline of

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

213

hardness when the temperature is below 400 °C, indicating that hardness has a direct effect on the wear resistance. When the temperature exceeds 400 °C, the wear rate begins to decrease, implying that hardness is no longer the only factor. Noteworthy, the CoCr2 FeNb0.5 NiSi0.2 C0.1 maintained a hardness higher than 600 HV3 even at 800 °C, thanks to the NbC phase retaining a high hardness at high temperatures [41]. A significant difference can be observed when comparing the wear morphology of HEAs coatings at different temperatures (Fig. 32). At RT and 200 °C, parallel grooves along the sliding direction on the surface, which is a typical type of abrasive wear. The brittle phase of the Laves fractured and became debris, which continuously micro-cut the coating surface. When C was added to the coating, the MC particles acted as debris in the wear process. The size of MC particles was small and had a nearly spherical structure when the C content was low. The cutting effect of debris on the coating surface was weak, and the grooves were relatively shallow. The grooves Fig. 30 The wear rate of CoCr2 FeNb0.5 NiSi0.2 coatings with different C addition at an evolved temperature

Fig. 31 The wear rate and hardness of CoCr2 FeNb0.5 NiSi0.2 C0.1 coating at different temperatures

214

J. Zhang and M. Ma

became deeper as the NbC grew larger. The wear mechanism is mainly abrasive wear at RT and 200 °C. At 400 °C, some oxides were found on the grooves, showing a certain oxidative wear and abrasive wear. When the temperature reached 600 °C, oxide layer delamination could be observed on the worn surface except the grooves. The wear mechanism is abrasive wear and oxidative wear. With the temperature further improved to 800 °C, the worn surface becomes flat and only a little debris is observed. Some slight grooves are observed on the surface of the oxide layer. The wear mechanism is oxidative wear and slight abrasive wear. The surface morphology of the C0.1 CoCr2 FeNb0.5 NiSi0.2 coatings before wear at elevated temperature was observed (Fig. 33). At 400 °C, visible processing evidence on the surface of the coating means that oxidation has not occurred. Some oxides were found after the wear test mainly originated from the heat resulting from friction during the wear process [49]. At 600°C, the fine granular oxides do not fully cover the coating surface due to minimal oxidation. During subsequent friction, the coating undergoes further oxidation. At 800°C, the coating surface is nearly entirely covered with oxides. Throughout the wear process, the oxide layer cyclically experiences squeezing, delamination, peeling, and compaction. The complete oxide film Cr2 O3 may played a protective role for the coating [50].

Fig. 32 The wear morphology of the CoCr2 FeNb0.5 NiSi0.2 Cx coatings at different temperatures. a1–a5 x = 0, b1–b5 x = 0.1, c1–c5 x = 0.2 and d1–d5 x = 0.3

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

215

Fig. 33 The surface morphology of the CoCr2 FeNb0.5 NiSi0.2 C0.1 coating before wear at hightemperature environment. a 400 °C, b 600 °C and c 800 °C

5 Comparison of HEAs Coatings to Electroplated Hard Cr 5.1 The Oxidation Behavior of Two Coatings Electroplated hard Cr is often used in a high-temperature environment as a wear and oxidation-resistant coating in industrial and decorative fields [51]. To realize the Co– Cr–Fe–Nb–Ni coatings real performance of high-temperature wear and oxidation at 800 °C, the electroplated hard Cr coatings with 50 μm thickness were compared. The high-temperature oxidation in mixture gas of two coatings was also tested, and the cross section of the oxide layers was observed. The oxide film thickness of the HEAs coating is only 2.21 μm, while that of electroplated hard Cr is 20.26 μm, almost 10 times (Fig. 34). Noteworthy, there are numerous voids inside the oxide film of hard Cr coatings. The oxide film of HEAs coating was denser for better protection. Also, the weight gain per unit area of electroplated hard Cr was 6.77 mg/cm2 , and that of the HEAs coating was only 0.43 mg/cm2 , with a decrease of 93%. Some microcracks were observed in the electroplated hard Cr. In the electroplating process, the unstable intermediate chromium hydride of β-Cr decomposes to stable pure chromium of αCr, and the hard chromium layers generally crack relieved the internal stresses of coatings [52]. In high-temperature oxidation, oxidizing gases could travel deeper into the coating through the cracks, resulting in more oxidation.

Fig. 34 The oxide layer thickness of hard Cr compared to HEAs coating at 800 °C. a HEAs coating and b electroplated hard Cr

216

J. Zhang and M. Ma

Fig. 35 The wear of the electroplated hard Cr compared to HEAs coating at 800 °C. a The wear profile of two coatings, 3D wear profile of b HEAs coating and c hard Cr

5.2 The Wear Behavior of Two Coatings The high-temperature stability of electroplated hard Cr reduces to 600 HV at 600 °C, which is weaker than that of high-entropy alloys [53]. The wear profile of hard Cr is almost 60 μm, much deeper than that of the HEAs coating, which is only 15 μm (Fig. 35). The depth of the wear trace exceeded the thickness of the electroplated hard Cr coating itself, indicating that the plated hard Cr only has a protective effect in the early stage of wear. At the later stage of the wear process, the electroplated hard Cr was worn through and loses the protective effect. The base material was abraded in the later stage of the wear test. The wear rate of hard Cr was 14.54 × 10–5 mm3 / (N m). The HEAs coating was 1.47 × 10–5 mm3 /(N m), with 89% reduction relative to hard Cr. Due to the special effects of HEAs coatings, the stability of HEAs coatings and thin oxide film might be beneficial to wear resistance at high temperature. HEAs exhibited superior performance to electroplated hard Cr, both in oxidation and wear resistance at high temperature.

6 Conclusion The Co–Cr–Fe–Nb–Ni HEAs coatings prepared by laser cladding show a superior oxidation and wear resistance at elevated temperature. The Co–Cr–Fe–Nb–Ni HEAs coatings have eutectic microstructure composed of FCC and Laves phases. Cr can dissolve into the FCC phase, causing lattice distortion of the FCC phase without changing the phase composition of the coating. The increment of the Cr can significantly improve the high-temperature oxidation resistance of the HEAs coatings. High Cr content enhances the selective oxidation of Cr, and protective Cr2 O3 oxide film on the surface inhibits the oxidation of the Laves phase. A drop of Si can form a

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

217

more compact dimension in the Laves phase with higher stability. In addition, the Si in the Laves phase replaces the oxidation of Nb, producing a more stable (Cr, Si)Ox internal oxide layer, which effectively inhibits further internal diffusion of oxygen ions. The C added in the melt pool can react with the Nb, generating a fine NbC reinforcing phase in-situ. The content of NbC and Laves strongly influenced the HEAs coatings’ hardness, and high hardness benefits the wear resistance. The protective oxide film may play more impactful on wear resistance at the temperature above 400 °C. The CeO2 melted in the molten pool, and new CeOx adsorbs at the boundary can effectively inhibit the growth of lamellar structure and refine the coatings. The active element effect of Ce speeds the short-range diffusion of Cr ions, promoting the formation of denser Cr2 O3 film. Whether in oxidation or wear at high temperature, Co–Cr–Fe–Nb–Ni HEAs coatings exhibit more excellent performance compared to electroplated hard Cr. In complex mixed atmosphere working conditions, the HEAs coatings with Cr2 O3 protective film seem to be insufficient for it can be further reacted by H2 O above 600 °C. Ion diffusion at phase and grain boundaries is also an important factor in high-temperature oxidation. The thermal growth oxides should be considered in the design of HEAs. Also, the coherent, semi-coherent interface and twin crystals may be introduced into the HEAs coatings to inhibit ion diffusion. In conclusion, the lase clad HEAs coatings have potential prospects for high-temperature applications. More HEAs coatings need to be systematically researched in the future. HEAs coatings with attractive properties are worthy of development from both academic and application viewpoints. Acknowledgements This research was supported by the National Natural Science Foundation of China (Grant No. 51901016), the Fundamental Research Funds for the Central Universities (FRF-TP-18-031A2, FRF-GF-18-024B), University Innovation Research Group of Chongqing (CXQT20023), and Scientific Research Foundation of Chongqing University of Technology (2023ZDZ004).

References 1. Tramošljika, B., Blecich, P., Bonefaˇci´c, I., Glažar, V.: Advanced ultra-supercritical coal-fired power plant with post-combustion carbon capture: analysis of electricity penalty and CO2 emission reduction. Sustainability 13, 801 (2021). https://doi.org/10.3390/su13020801 2. Wang, Y.X., Feng, W.Z.: Efficient and clean coal-fired technology: 700 °C ultra-supercritical coal-fired power generation technology. In: 7th International Symposium on Advances in Electrical, Electronics, and Computer Engineering, pp. 286–290. SPIE (2022). https://doi.org/10. 1117/12.2641016 3. Zhang, Z., Zhou, R., Ge, X., Zhang, J., Wu, X.: Perspectives for 700 °C ultra-supercritical power generation: thermal safety of high-temperature heating surfaces. Energy 190, 116411 (2020). https://doi.org/10.1016/j.energy.2019.116411 4. Yeo, W.H., Fry, A.T., Purbolaksono, J., Ramesh, S., Inayat-Hussain, J.I., Liew, H.L., Hamdi, M.: Oxide scale growth and presumed exfoliation in a 700 °C or higher steam condition: a simulation study for future operations of ultra-supercritical power plants. J. Supercrit. Fluids 92, 215–222 (2014). https://doi.org/10.1016/j.supflu.2014.06.002

218

J. Zhang and M. Ma

5. Zhong, X., Wu, X., Han, E.-H.: The characteristic of oxide scales on T91 tube after long-term service in an ultra-supercritical coal power plant. J. Supercrit. Fluids 72, 68–77 (2012). https:// doi.org/10.1016/j.supflu.2012.08.015 6. El Kanzaoui, M., Ennawaoui, C., Eladaoui, S., Hajjaji, A., Guenbour, A., Boussen, R.: Study of the physical behavior of a new composite material based on fly ash from the combustion of coal in an ultra-supercritical thermal power plant. J. Compos. Sci. 5, 151 (2021). https://doi. org/10.3390/jcs5060151 7. Ye, Y.F., Wang, Q., Lu, J., Liu, C.T., Yang, Y.: High-entropy alloy: challenges and prospects. Mater. Today 19, 349–362 (2016). https://doi.org/10.1016/j.mattod.2015.11.026 8. Zhang, W., Liaw, P.K., Zhang, Y.: Science and technology in high-entropy alloys. Sci. China Mater. 61, 2–22 (2018). https://doi.org/10.1007/s40843-017-9195-8 9. Cai, Y., Li, X., Xia, H., Cui, Y., Manladan, S.M., Zhu, L., Shan, M., Sun, D., Wang, T., Lv, X., Han, J.: Fabrication of laminated high entropy alloys using differences in laser melting deposition characteristics of FeCoCrNi and FeCoCrNiAl. J. Manuf. Process. 72, 294–308 (2021). https://doi.org/10.1016/j.jmapro.2021.10.022 10. Chen, D., He, F., Han, B., Wu, Q., Tong, Y., Zhao, Y., Wang, Z., Wang, J., Kai, J.: Synergistic effect of Ti and Al on L12-phase design in CoCrFeNi-based high entropy alloys. Intermetallics 110, 106476 (2019). https://doi.org/10.1016/j.intermet.2019.106476 11. Yang, T., Zhao, Y.L., Tong, Y., Jiao, Z.B., Wei, J., Cai, J.X., Han, X.D., Chen, D., Hu, A., Kai, J.J., Lu, K., Liu, Y., Liu, C.T.: Multicomponent intermetallic nanoparticles and superb mechanical behaviors of complex alloys. Science 362, 933–937 (2018). https://doi.org/10. 1126/science.aas8815 12. He, F., Wang, Z., Cheng, P., Wang, Q., Li, J., Dang, Y., Wang, J., Liu, C.T.: Designing eutectic high entropy alloys of CoCrFeNiNbx. J. Alloy. Compd. 656, 284–289 (2016). https://doi.org/ 10.1016/j.jallcom.2015.09.153 13. He, F., Wang, Z., Shang, X., Leng, C., Li, J., Wang, J.: Stability of lamellar structures in CoCrFeNiNbx eutectic high entropy alloys at elevated temperatures. Mater. Des. 104, 259–264 (2016). https://doi.org/10.1016/j.matdes.2016.05.044 14. Li, W., Liu, P., Liaw, P.K.: Microstructures and properties of high-entropy alloy films and coatings: a review. Mater. Res. Lett. 6, 199–229 (2018). https://doi.org/10.1080/21663831. 2018.1434248 15. Li, Q.H., Yue, T.M., Guo, Z.N., Lin, X.: Microstructure and corrosion properties of AlCoCrFeNi high entropy alloy coatings deposited on AISI 1045 steel by the electrospark process. Metall. and Mater. Trans. A. 44, 1767–1778 (2013). https://doi.org/10.1007/s11661-012-1535-4 16. Wang, Y., Liu, B., Yan, K., Wang, M., Kabra, S., Chiu, Y.-L., Dye, D., Lee, P.D., Liu, Y., Cai, B.: Probing deformation mechanisms of a FeCoCrNi high-entropy alloy at 293 and 77 K using in situ neutron diffraction. Acta Mater. 154, 79–89 (2018). https://doi.org/10.1016/j.actamat. 2018.05.013 17. Liu, B., Wang, J., Liu, Y., Fang, Q., Wu, Y., Chen, S., Liu, C.T.: Microstructure and mechanical properties of equimolar FeCoCrNi high entropy alloy prepared via powder extrusion. Intermetallics 75, 25–30 (2016). https://doi.org/10.1016/j.intermet.2016.05.006 18. Cai, B., Liu, B., Kabra, S., Wang, Y., Yan, K., Lee, P.D., Liu, Y.: Deformation mechanisms of Mo alloyed FeCoCrNi high entropy alloy: in situ neutron diffraction. Acta Mater. 127, 471–480 (2017). https://doi.org/10.1016/j.actamat.2017.01.034 19. Šlapáková, M., Zendegani, A., Liebscher, C.H., Hickel, T., Neugebauer, J., Hammerschmidt, T., Ormeci, A., Grin, J., Dehm, G., Kumar, K.S., Stein, F.: Atomic scale configuration of planar defects in the Nb-rich C14 Laves phase NbFe2. Acta Mater. 183, 362–376 (2020). https://doi. org/10.1016/j.actamat.2019.11.004 20. Alonso, P.R., Gargano, P.H., Rubiolo, G.H.: Stability of the C14 Laves phase (Fe, Si)2Mo from ab initio calculations. Calphad 35, 492–498 (2011). https://doi.org/10.1016/j.calphad. 2011.08.006 21. Mittal, R.C., Si, S.K., Gupta, K.P.: Si-Stabilised C14 laves phases in the transition metal systems. J. Less Common Metals 60, 75–82 (1978). https://doi.org/10.1016/0022-5088(78)900 91-7

Research on Anti-Oxidation and Wear-Resistance Co–Cr–Fe–Nb–Ni …

219

22. Peng, L., Takizawa, S., Ikeda, K., Horiuchi, T., Miura, S.: Effect of Si on the stability of NbCr2 Laves phase in Cr–Mo–Nb system. Intermetallics 110, 106457 (2019). https://doi.org/10.1016/ j.intermet.2019.03.020 23. Yang, F., Wang, L., Wang, Z., Wu, Q., Zhou, K., Lin, X., Huang, W.: Ultra strong and ductile eutectic high entropy alloy fabricated by selective laser melting. J. Mater. Sci. Technol. 106, 128–132 (2022). https://doi.org/10.1016/j.jmst.2021.08.015 24. Takeuchi, A., Inoue, A.: Classification of bulk metallic glasses by atomic size difference, heat of mixing and period of constituent elements and its application to characterization of the main alloying element. Mater. Trans. 46, 2817–2829 (2005) 25. Li, Q., Lei, Y., Fu, H.: Laser cladding in-situ NbC particle reinforced Fe-based composite coatings with rare earth oxide addition. Surf. Coat. Technol. 239, 102–107 (2014). https://doi. org/10.1016/j.surfcoat.2013.11.026 26. Cao, Y., Zhi, S., Gao, Q., Tian, X., Geng, T., Guan, X., Qin, C.: Formation behavior of in-situ NbC in Fe-based laser cladding coatings. Mater. Charact. 119, 159–165 (2016). https://doi.org/ 10.1016/j.matchar.2016.08.005 27. Vance, J.E.: Growth and perfection of crystals. J. Am. Chem. Soc. 81, 3489–3490 (1959). https://doi.org/10.1021/ja01522a099 28. Frank, F.C.: On the kinematic theory of crystal growth and dissolution processes. II. Zeitschrift für Physikalische Chemie 77, 84–92 (1972). https://doi.org/10.1524/zpch.1972.77.1-6.084 29. Liu, L., Qiao, Y., Xu, P.: Effect of La2O3 on microstructure and properties of laser cladding SMA coating on AISI 304 stainless steel. Coatings 12, 1004 (2022). https://doi.org/10.3390/ coatings12071004 30. Balaram, V.: Rare earth elements: a review of applications, occurrence, exploration, analysis, recycling, and environmental impact. Geosci. Front. 10, 1285–1303 (2019) 31. Du, X., Ma, X., Ding, X., Zhang, W., He, Y.: Enhanced high-temperature oxidation resistance of low-cost Fe–Cr–Ni medium entropy alloy by Ce-adulterated. J. Market. Res. 16, 1466–1477 (2022). https://doi.org/10.1016/j.jmrt.2021.12.087 32. Wei, L., Zheng, J., Chen, L., Misra, R.D.K.: High temperature oxidation behavior of ferritic stainless steel containing W and Ce. Corros. Sci. 142, 79–92 (2018). https://doi.org/10.1016/j. corsci.2018.07.017 33. Yuling, G., Meiping, W., Xiaojin, M., Chen, C.: Effect of CeO2 on crack sensitivity and tribological properties of Ni60A coatings prepared by laser cladding. Adv. Mech. Eng. 13, 16878140211013124 (2021). https://doi.org/10.1177/16878140211013125 34. Schoenberg, N.: X-ray studies on vanadium and chromium oxides with low oxygen content. Acta Chem. Scand. 8, 221–225 (1954). https://doi.org/10.3891/acta.chem.scand.08-0221 35. Lawrence, R.V.: Phase equilibria studies of Cr3O-type structures in the vanadium-rhodiumsilicon and niobium-rhodium-silicon ternary systems (1964) 36. Yu, X., Gulec, A., Andolina, C.M., Zeitchick, E.J., Gusieva, K., Yang, J.C., Scully, J.R., Perepezko, J.H., Marks, L.D.: In situ observations of early stage oxidation of Ni–Cr and Ni–Cr–Mo alloys. Corrosion 74, 939–946 (2018). https://doi.org/10.5006/2807 37. Zhao, X., Li, X., Li, M., Zhou, C.: Comparison of the corrosion resistance of Ni2Al3 coating with and without Ni–Re interlayer in dry and wet CO2 gas. Corros. Sci. 159, 108121 (2019). https://doi.org/10.1016/j.corsci.2019.108121 38. Shatynski, S.R.: The thermochemistry of transition metal carbides. Oxid. Met. 13, 105–118 (1979). https://doi.org/10.1007/BF00611975 39. Ma, M., Han, A., Zhang, Z., Lian, Y., Zhao, C., Zhang, J.: The role of Si on microstructure and high-temperature oxidation of CoCr2FeNb0.5Ni high-entropy alloy coating. Corros. Sci. 185, 109417 (2021). https://doi.org/10.1016/j.corsci.2021.109417 40. Aye, K.K., Nguyen, T.D., Zhang, J., Young, D.J.: Effect of silicon on corrosion of Fe–20Cr and Fe–20Cr–20Ni alloys in wet CO2 with and without HCl at 650 °C. Corros. Sci. 179, 109096 (2021). https://doi.org/10.1016/j.corsci.2020.109096 41. Thibaux, P., Métenier, A., Xhoffer, C.: Carbon diffusion measurement in austenite in the temperature range 500–900 °C. Metall. Mater. Trans. A 38, 1169–1176 (2007). https://doi.org/10.1007/ s11661-007-9150-5

220

J. Zhang and M. Ma

42. Amano, T., Yajima, S., Saito, Y.: High-temperature oxidation behavior of Fe–20Cr–4Al alloys with small additions of cerium. Trans. Jpn Inst. Metals 20, 431–441 (1979). https://doi.org/10. 2320/matertrans1960.20.431 43. Peng, X., Guan, Y., Dong, Z., Xu, C., Wang, F.: A fundamental aspect of the growth process of alumina scale on a metal with dispersion of CeO2 nanoparticles. Corros. Sci. 53, 1954–1959 (2011). https://doi.org/10.1016/j.corsci.2011.02.014 44. Nguyen, T.D., Zhang, J., Young, D.J.: Growth of Cr2O3 blades during alloy scaling in wet CO2 gas. Corros. Sci. 133, 432–442 (2018). https://doi.org/10.1016/j.corsci.2018.01.045 45. Raynaud, G.M., Rapp, R.A.: In situ observation of whiskers, pyramids and pits during the high-temperature oxidation of metals. Oxid. Met. 21, 89–102 (1984). https://doi.org/10.1007/ BF00659470 46. Woydt, M., Mohrbacher, H., Vleugels, J., Huang, S.: Niobium carbide for wear protection— Tailoring its properties by processing and stoichiometry. Met. Powder Rep. 71, 265–272 (2016). https://doi.org/10.1016/j.mprp.2015.12.010 47. Takeyama, M., Liu, C.T.: Microstructure and mechanical properties of Laves-phase alloys based on Cr2Nb. Mater. Sci. Eng. A 132, 61–66 (1991). https://doi.org/10.1016/0921-5093(91)903 61-P 48. Wu, J.-M., Lin, S.-J., Yeh, J.-W., Chen, S.-K., Huang, Y.-S., Chen, H.-C.: Adhesive wear behavior of AlxCoCrCuFeNi high-entropy alloys as a function of aluminum content. Wear 261, 513–519 (2006). https://doi.org/10.1016/j.wear.2005.12.008 49. Stott, F.H.: The role of oxidation in the wear of alloys. Tribol. Int. 31, 61–71 (1998). https:// doi.org/10.1016/S0301-679X(98)00008-5 50. Cheng, X., Jiang, Z., Wei, D., Wu, H., Jiang, L.: Adhesion, friction and wear analysis of a chromium oxide scale on a ferritic stainless steel. Wear 426–427, 1212–1221 (2019). https:// doi.org/10.1016/j.wear.2019.01.045 51. Huang, C.A., Li, K.C., Lin, W., Liao, M.C.: The behavior of electroplated hard-chromium on Cr–Mo steel subject to long-term annealing at 250 °C. Mater. Sci. Eng. A 403, 222–226 (2005). https://doi.org/10.1016/j.msea.2005.05.007 52. Sarraf, S.H., Soltanieh, M., Aghajani, H.: Repairing the cracks network of hard chromium electroplated layers using plasma nitriding technique. Vacuum 127, 1–9 (2016). https://doi. org/10.1016/j.vacuum.2016.02.001 53. Wang, L., Gao, Y., Xue, Q., Liu, H., Xu, T.: A novel electrodeposited Ni–P gradient deposit for replacement of conventional hard chromium. Surf. Coat. Technol. 200, 3719–3726 (2006). https://doi.org/10.1016/j.surfcoat.2004.10.016

The Boriding Process for Enhancing the Surface Properties of High-Temperature Metallic Materials I. E. Campos Silva, A. Günen, M. Serdar Karaka¸s, and A. M. Delgado Brito

Abstract High-temperature metallic materials operate in environments with a broad spectrum of mechanical and chemical conditions, originating typical failures such as steam oxidation, hot corrosion, and wear-corrosion; the service life of the metallic component is reduced with severe economic losses. The ever-increasing demands for enhanced component performance require continuous improvements in existing material systems. In this sense, boriding is a promising thermochemical process used to increase the surface properties of metallic materials for high-temperature applications. The resulting boride coating has excellent wear resistance at high temperatures due to its high hardness, thermal, and chemical stability, and adhesion to the substrate material. In addition, the boride coating is resistant to corrosion in acidic, alkaline, and salt media, suitable for use in harsh environments. The mechanical and chemical properties of the boride coating are preserved at high temperatures (up to 1000 °C); the probability of the boride coating cracking or spalling at high temperature is negligible. This chapter reviews the various boriding methods as adopted for the formation of boride coating on high-temperature metallic materials to improve its performance for diverse high-temperature applications. Wear, practical adhesion, oxidation, corrosion, and tribocorrosion properties of borided materials are explained in terms of the boride coating-substrate system behavior. Keywords Boriding · High-temperature materials · Boride coatings · Mechanical properties · Oxidation resistance · Wear-corrosion resistance I. E. Campos Silva (B) Instituto Politécnico Nacional, SEPI ESIME Zacatenco, Grupo Ingeniería de Superficies, U.P. Adolfo López Mateos, 07738 Ciudad de México, Mexico e-mail: [email protected] A. Günen Department of Metallurgy and Materials Engineering, Faculty of Engineering and Natural Sciences, Iskenderun Technical University, 31200 Hatay, Turkey M. Serdar Karaka¸s Department of Metallurgical and Materials Engineering, Faculty of Engineering and Natural Sciences, Konya Technical University, 42130 Konya, Turkey A. M. Delgado Brito TecNM/Tecnológico de Estudios Superiores de Jocotitlán, 50700 Estado de México, Mexico © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_9

221

222

I. E. Campos Silva et al.

1 The Boriding Process The reactivity of B toward metals leads to various boron compounds widely used for a variety of tribological and corrosion applications. Introducing boron into metallic materials is an efficient method to increase physical and chemical properties such as hardness, wear resistance, corrosion resistance, and oxidation resistance due to the formation of metal borides on the material’s surface. Usually, the metal borides are characterized by the combination of covalent, metallic, or ionic bonds, leading to the development of materials with outstanding properties [1]. Boriding is a thermochemical diffusion-based surface-hardening process applied to various ferrous, nonferrous, and cermet materials for extending the lifespan of metal components for high-temperature applications. The resulting boride coating on the metallic material has high hardness (between 10 GPa and 33 GPa) in combination with high thermal and chemical stability of the constituent boron compounds, which make it resistant to wear and corrosion. In fact, the hardness of boride coating produced on different metallic materials is much greater than those produced by any other conventional surface hardening treatments and is equivalent to that of tungsten carbide and many hard PVD coatings [2–4]. The boride coating is stable at high temperatures due to its high melting point, which allows it to maintain its hardness and oxidation resistance up to 1000 °C, with the possibility to increase the high-temperature wear resistance of metallic materials. Also, two key factors contribute to the high-temperature wear resistance of the boride coating: (i) the formation of a protective oxide layer (H3 BO3 ) over the borided surface that acts as a solid lubricant during sliding and (ii) the boride coating has a high Young’s modulus (or stiffness), which increases its deformation resistance under stress [5]. On the other hand, the boride coating can withstand corrosive environments such as strong acids, salts, and water steam, even in the presence of corrosive gases at elevated temperatures and pressures. Notably, when the boride coating is exposed to high-temperature industrial applications, a stable B2 O3 protective layer is developed on the borided surface due to the reaction of the coating with O or other oxidizing agents in the environment, preventing corrosion of the underlying metallic material [6]. On most engineering alloys and metals used for high-temperature applications, the boriding process is usually carried out at 700 °C – 1000 °C for 0.5 h –12 h, forming 10 μm – 150 μm thick coatings. The thickness and the microstructure of the formed boride coating affect the mechanical and chemical properties of borided materials. They depend on the boriding temperature, the exposure time, the amount of B atoms surrounding the surface sample, and the chemical composition of the material. Therefore, selecting the optimum process parameters is vital to obtain boride coatings with adequate thicknesses for their intended practical applications [7]. Some microstructures of boride coatings on materials used for high-temperature applications are presented in Fig. 1.

The Boriding Process for Enhancing the Surface Properties …

223

Fig. 1 Cross-sectional views of boride coating microstructures: a Fe2 B on low-carbon steel; b Fe2 B coating with isolated FeB on high-alloy steel; c FeB–Fe2 B on low-alloy steel; d FeB–Fe2 B on stainless steel; e FeB–Fe2 B combined with borocementite; f cobalt boride coating on Co-base alloy; g nickel boride coating on Ni-base alloy; h titanium boride coating on Ti-base alloy. Courtesy of Grupo Ingeniería de Superficies, Instituto Politécnico Nacional

The boriding of low-carbon, low-alloy, and high-alloy steels results in the formation of a saw-toothed coating consisting of three types of microstructures: (i) Fe2 B with a tetragonal crystalline structure (Fig. 1a), (ii) tetragonal Fe2 B with an isolated orthorhombic FeB (Fig. 1b), or (iii) FeB–Fe2 B coating (Fig. 1c). The saw-toothed microstructure of both FeB and Fe2 B can be explained by dendrite “side-arm” growth like that observed during the solidification of many metallic systems [8]. Also, Brackman et al. [9] establish that the preferential direction growth of borides into the substrate exhibits orientations close to or with [001] perpendicular to the surface. The substrate’s alloying elements influence the boride coating’s growth and microstructure. The saw-toothed microstructure of the boride coating becomes less pronounced as the proportion of alloying elements in the substrate increases (Fig. 1b and d). The saw-toothed microstructure of the boride coating is reduced due to the concentration of the alloying elements on the tips of the boride columns, decreasing the active boron flux in these regions, and inhibiting the growth of the boride coating. Alloying elements such as C, Si, and Al are insoluble in the boride coating. They are displaced ahead of the coating, forming a well-defined zone of precipitates that denominate the diffusion zone. Figure 1e depicts the cross-sectional view of borided 1018 steel. The boride coating microstructure consists of a FeB–Fe2 B coating

224

I. E. Campos Silva et al.

combined with borocementite that develops into the columns of the jagged structure. The formation of borocementite is associated with the diffusion of C that is displaced by the boride coating to the bulk material [10]. In contrast, for the variety of borided high-alloy materials (i.e., steels, nickel alloys, and cobalt alloys), alloying elements such as Cr, Ni, Mo, V, and W tend to dissolve in the boride coating and form interstitial compounds with B. In addition, these alloying elements’ presence restricts the boride coating’s growth, developing a semi-flat boride coating microstructure. The microstructure of the boride coating on stainless steel (Fig. 1d) involves the FeB (outer coating) and the Fe2 B (inner coating) combined with CrB and Cr2 B phases due to Cr substituting Fe to form complex borides. The presence of CrB and Cr2 B increases the hardness on the outer zone of the borided surface [11]. Underneath the coating, the diffusion zone is constituted by two zones: a Cr-rich layer (beneath the boride coating) that enhances the diffusion across the grain boundaries, in addition to the appearance of a Ni-rich layer between the Cr-rich layer and the substrate [12, 13]. The boriding of Co-base and Ni-base high-temperature alloys develops a flat, uniform boride coating microstructure with a well-defined diffusion zone under the coating. The microstructure of the cobalt boride coating mainly consists of CoBCo2 B (orthorhombic and tetragonal crystalline structures, respectively) combined with CrB, Cr2 B, and Mo2 B compounds (Fig. 1f). The formation of the diffusion zone is related by the primary precipitation of Cr-rich products along the grain boundaries of the substrate [14, 15]. The coating of borided nickel-base alloys (Fig. 1g) is mainly composed of nickel borides (orthorhombic Ni4 B3 and tetragonal Ni2 B), iron borides (FeB, Fe2 B), and chromium borides (CrB, Cr2 B). The diffusion zone is an intermixture of Ni–B, Fe–B, and Cr–B phases, acting as a diffusion barrier to restrict the growth of the nickel boride coating [16–19]. Titanium and its alloys are attracting considerable attention because of their potential use as low-density and high-temperature structural materials. Their inadequate oxidation resistance (at elevated temperatures >800 °C) and poor tribological performance limit their practical applications. Boriding is also applicable to titanium alloys to improve their mechanical and chemical properties by the formation of a compact, uniform coating composed of hexagonal TiB2 and orthorhombic TiB compounds according to the Ti–B phase diagram [20–23]. The coating is characterized by a TiB2 outer coating with a TiB coating containing distributed TiB whiskers mixed with the microstructure of the base metal, as shown in Fig. 1h. The whiskers growth has been primarily attributed to the one-way diffusion of B along [010] crystal direction. Some mechanical properties of boride coatings on high-temperature metallic materials are presented in Table 1. The mechanical properties of the boride coating are anisotropic, varying along the depth of the coating/substrate system. In addition, the properties depend on the coating microstructure, the substrate’s chemical composition, the boriding techniques used to produce the coatings (temperatures, exposure time, the boron potential surrounds the material surface, etc.), and the heat treatments employed after boriding.

The Boriding Process for Enhancing the Surface Properties …

225

Table 1 Mechanical properties of boride coatings on high-temperature metallic materials Borided material

Microstructure Hardness of boride (H) (GPa) coating

AISI 4140 steel*

FeB, Fe2 B, CrB

FeB–Fe2 B FeB–Fe2 B (~313) (14–19)

AISI 8620 steel*

FeB, Fe2 B

FeB (~23) Fe2 B (~19)

FeB–Fe2 B (~ 292) FeB (2.2–3.6) Fe2 B (2.6–3.9)

FeB (+0.6) Fe2 B (–2.7)

[27–29]

AISI H13 steel

FeB, Fe2 B, CrB

FeB (17–22) Fe2 B (10–18)

FeB (350–379) Fe2 B (320–334)

FeB (1.3–1.4) Fe2 B (5.0–5.2)

FeB (+0.7 to +0.9) Fe2 B (–0.2 to –0.5)

[30, 31]

316L steel

FeB, Fe2 B, CrB, Cr2 B, Mo2 B, Ni3 B

FeB rich zone (18–22) Fe2 B rich zone (16–18)

FeB rich zone (338–341) Fe2 B rich zone (256–299)

FeB (1.2–1.6) Fe2 B (2.2–3.0)

Outer [32–34] zone of the coating (+1.1 to + 1.6) Inner zone of the coating (–1.2 to –1.4)

Co-base alloys

CoB, Co2 B, Mo2 B, CrB, Cr2 B

CoB rich zone (18–20) Co2 B rich zone (16–17)

CoB rich zone (300–320) Co2 B rich zone (260–290)

CoB rich zone (0.5–0.8) Co2 B rich zone (2.7–4.6)

CoB rich [35–37] zone (+1.1 to +1.2) Co2 B rich zone (–1.2 to –0.6)

Nickel-base Ni3 B, Ni2 B, alloys NiB, Ni4 B3 , Cr2 B, CrB

Outer zone of the coating (21–24) Inner zone of the coating (15–19)

Outer zone of the coating (370–390) Inner zone of the coating (340–360)

Outer zone of the coating (~0.6) Inner zone of the coating (~4.4)

Outer [38, 39] zone of the coating (+1.2 to + 1.3) Inner zone of the coating (–0.25 to –1.2)

Ti-base alloy

TiB2 (~32) TiB2 (~343) TiB (23–27)

TiB2 –TiB (0.8–4.4)

[40–42]

TiB2 , TiB

Young’s modulus (E) (GPa)

Fracture toughness (KIC ) (MPa m1/2 )

Residual References stresses (σr ) (GPa)

FeB–Fe2 B FeB–Fe2 B [24–26] (2.9–3.5) (0 to –0.3)

* Low-alloy steels are often used up to about 650 °C. The prolonged exposure at temperatures above 370 °C may result in graphitization and weakening of the steel

226

I. E. Campos Silva et al.

1.1 The Boriding Techniques The boriding techniques are classified into two groups: chemical and physical, which are discussed in detail by Kulka [17]. The techniques are divided based on the formation mechanism of free B atoms diffusing into the metallic substrate. Surface alloying with B, thermal spraying, detonation spraying, and cladding with B are examples of physical boriding techniques. The chemical boriding techniques include solid, liquid, and gaseous media. They need an activator (reducing agent) and a boriding agent that supplies the B atoms during the process; the activator and boriding agent react to derive elemental B, which diffuses into the metal surface, forming the boride coating. In this section, a greater focus is placed on boriding chemical techniques; a brief overview of some of them is presented in Table 2. The concept of “hybrid” boriding (chemical-physical) techniques was used during the last years, such as ultra-fast boriding, fluidized bed boriding, plasma-paste boriding, and the pulsed-DC powder-pack boriding [17, 43, 46–50]. The “hybrid” techniques offer, principally, the reduction of temperature and boriding time (in most cases, the temperature ranges are between 700 °C and 950 °C with exposure times around 0.25 h – 4 h), relatively low energy consumption, and they are friendly to the environment. In addition, the use of plasma and electricity, increases the growth kinetics of boride coatings on the material’s surface. For example, the fluidized bed boriding contains a bed of SiC particles, a powder boriding agent, and an N2 –H2 gas mixture. The technique can employ electricity as the heat source. Thus, the bed serves as a faster heat-transfer medium; the high rates of heating and flow, as well as direct withdrawal of the parts, provide shorter operating cycle times [4]. On the other hand, ultra-fast boriding involves the preparation of a molten electrolyte consisting of about 90 wt.% borax and ~10 wt.% carbonates of alkaline and alkaline-earth elements (sodium and/or calcium carbonate) or sodium chloride. A high-frequency induction furnace containing a graphite crucible gives external agitation and mixing of electrolytes. In addition, it helps overcome diffusion barriers in the electrochemical process, developing fast boriding and thick boride coatings in short processing times (less than an hour). The induction furnace has a positively charged cathode (to which the samples are attached) and a negatively charged anode; the furnace is connected to a power source, and ions flow from the anode to the cathode, depositing B on the cathode and attached samples [46, 51, 52]. Based on the enhancement effect of the direct current field on powder-pack boriding [53–55], a novel technique called pulsed-DC powder-pack boriding (PDCPB) was developed [50]. This technique was carried out by generating a direct current field between two electrodes in the powder mixture (the material to be borided is collocated among the electrodes). The direct current field promotes an electromigration effect, increasing the B diffusion over the surface of materials. A schematic diagram of the main parts of the experimental apparatus is shown in Fig. 2a. In this apparatus, two electrodes with a distance of 10 mm are placed in the powder mixture in a metallic container and heated in a conventional muffle. The PDCPB employs a

The Boriding Process for Enhancing the Surface Properties …

227

Table 2 Various boriding techniques in solid, liquid, and gas media Technique

Media

Powder-pack Solid

Examples of the boriding mixture components’

Brief description

Some advantages and disadvantages

References

Boron source: boron carbide, ferroboron, and amorphous boron Activator: NaBF4 , KBF4, Na2 CO3 , BaF2 and Na2 B4 O Diluent: SiC, Al2 O3

The specimens are introduced in a container (heat-resisting steel or similar) and embedded into the powder mixture. The sealed container is heated to the required temperature with or without an inert atmosphere. The thickness and microstructure of the boride coating depend on the process parameters (temperature, holding time, and so on) and the composition of the boriding mixture. After boriding, the sealed container is cooled to room temperature

Easy handling, [17, 43] low-cost requirements, simplicity of the equipment, and the possibility of changing the composition of the boriding mixture. The powder mixture can be reused about 5–6 times by blending in 20–50% with the new boriding mixture However, the technique is limited to only small-sized products and requires high labor costs in packing and removing powder after boriding

(continued)

228

I. E. Campos Silva et al.

Table 2 (continued) Technique

Media

Examples of the boriding mixture components’

Brief description

Some advantages and disadvantages

Paste

Solid

Water-base paste containing B4 C (boron source), and Na3 AlF6 (activator). The ratio of the water to the mixture of B4 C and Na3 AlF6 is around 1:5. In some cases, a paste composition of B4 C, KBF4 , and SiC is used, combined with a binder media, employed for long-term stability of the paste

The paste is applied by spraying, brushing, or dipping. The paste thickness over the material’s surface is controlled using a mold. After boriding, the material is quenched (in different media) to room temperature

Used in [17, 44, 45] high-volume production, also for partial boriding applied locally on parts of the work pieces. The manual work involved when boriding in powder can be drastically reduced. Nevertheless, a protective atmosphere, or in a vacuum, is necessary to avoid oxidation during the process. The boron supply by the atmosphere is limited compared to the powder-pack

Electroless salt-bath

Liquid The bath usually contains 70% Na2 B4 O7 and 30% B4 C (by weight)—the B4 C content up to 20 wt.% is replaced by ferroaluminum to increase the number of B atoms in the bath. A mixture of 55% Na2 B4 O7 , 45% ferroboron, and 5% ferroaluminum is also used

The material is immersed in the salt bath at temperatures above 900 °C. After boriding, the material is retired from the bath and cooled to room temperature

Boriding is simple and economical to operate. After boriding, excess salt must be removed, increasing the cost and time consuming. Maintenance cost is high for the technique since it requires regular recharging with salt due to increased bath viscosity

References

[10, 17, 43]

(continued)

The Boriding Process for Enhancing the Surface Properties …

229

Table 2 (continued) Technique

Media

Examples of the boriding mixture components’

Brief description

Some advantages and disadvantages

Gaseous

Gas

Boron halide/ hydrogen mixture combined with organic compounds ((CH3 )3 B and (C2 H5 )3 B)

The material is put into a chamber or cylindrical retort of a muffle under a protective atmosphere. When the boriding temperature is achieved, the gas mixture is activated for the desired exposure time. After boriding, the material is cooled under a protective atmosphere to room temperature

The gas mixture [17, 43] is supplied continuously to the furnace retort. A constant boriding atmosphere is maintained constant on the material’s surface, compared to solid and liquid, in which the boron source is exhausted during boriding. However, gases such as B2 H6 , BCl3 , and BF3 are highly toxic, cancerogenous, and explosive/ corrosive

References

DC power supply coupled with a programmable electronic control device (PECD) to generate polarity changes in the flux of B+ ions. The pulsed-DC field provides a uniform B+ ions diffusion, causing the formation of similar boride coating thicknesses on both surfaces (anode and cathode) exposed to the current field. Notably, the PDCPB develops uniform and compact boride coatings (~15 μm) for the boriding conditions of 700 °C and 0.25 h of exposure.

2 The Adhesion Resistance of Boride Coating on Metallic Substrates Adhesion is one of the most critical factors contributing to boride coatings’ reliability. The adhesion of the boride coating to the metallic substrate is of great importance in the design, functionality, and performance of the borided metallic materials. In this sense, the wear and the corrosion are intimately related to the extent of adhesion of the boride coating to the substrate: (i) the boride coating should firmly

230

I. E. Campos Silva et al.

Fig. 2 a Schematic representation of the thermoelectrical system used in PDCPB: 1 Power supply, 2 PECD, 3 Container, 4 Electric furnace, 5 Electrodes, 6 Material. Representation of boron diffusion through several stages: b B atoms dissociation from the boriding media, c transport of B+ ions through the electric field, d nucleation of borides, and e growth of boride coating

adhere to the substrate to avoid or retard the infiltration of corroding species at the coating/substrate interface, (ii) scratches produced by abrasive and erosive environments constantly wear away the borided surface. Both phenomena progressively compromise the integrity of the surface and may lead to its failure. The adhesion of boride coating to the metallic substrate is measured in terms of the force, defining the force of adhesion as the maximum force per unit area exerted when the coating and substrate are separated; the Daimler-Benz Rockwell C and scratch tests are the most widely tests used for evaluating the adhesion of boride coating-substrate system [39, 56–65]. Notably, in the scratch test, a diamond indenter with a spherical tip (typically a radius = 200 μm, angle of 120°) is scratched over the surface of the specimen under investigation with the application of a specific load and speed. The load is often progressively increased during the test, resulting in flaking or chipping of the coating. After the scratch test, different failure modes (cohesive and adhesive) are subsequently expressed in terms of critical loads (LC ) and are defined as the minimum loads under which a certain failure mode occurs. Critical loads are either obtained by visually inspecting of the specimen either during or after the test, by monitoring an acoustic emission signal (AE) [66, 67]. Usually, the onset of AE and the microscopical observations of the first damage occurring in the coating correlate quite well. In the same manner, the coefficient of friction (CoF) and residual indenter

The Boriding Process for Enhancing the Surface Properties …

231

depth (Rd) are measured during the scratch test as shown in Fig. 3 On the other hand, typical failure mechanisms (cohesive and/or adhesive) developed by the scratch test at the surface of borided materials are presented in Fig. 4. The scratch resistance of the boride coating is a complex phenomenon because there are many factors involved, including coating parameters (i.e., boriding technique, boriding temperature, the microstructure of the boride coating, hardness and Young’s modulus along the depth of the coating, boride coating thickness, distribution of residual stresses in the coating, and fracture toughness of the boride coating), scratching conditions (shape and radius size of the indenter, applied load, and scratching speed), and substrate properties such as hardness and Young’s modulus. Scratch tests on XC38 borided steel were performed in the work of Allaoui et al. [57]. This steel is employed in pressure vessels, turbine fasteners, boiler support rods, and machine tools. The steel was exposed to molten salts of borax (Na2 B4 O7 ) with different reducing agents (B4 C, Al, and SiC), producing two types of boride coating microstructures on the surface: the Al and B4 C agents propitiated the formation of FeB–Fe2 B coating, whereas SiC led to the development of a Fe2 B coating. The scratch tests revealed that the best adhesion performance was obtained in the steel

Fig. 3 The scratch profile on the surface of borided Inconel 718 obtained during a progressive load. The scratch properties such as CoF, Rd, and AE were plotted as a function of the indenter displacement, while LC1 , LC2 , and LC3 correspond to the development of failures at specific points of the scratch track. Courtesy of Grupo Ingeniería de Superficies, Instituto Politécnico Nacional

232

I. E. Campos Silva et al.

Fig. 4 Scratch failure mechanisms on the surface of borided metallic materials: cohesive (tensile and Hertzian cracks) and adhesive (lateral cracks, spalling and gross spallation). Courtesy of Grupo Ingeniería de Superficies, Instituto Politécnico Nacional

exposed to boriding with the mixture containing SiC (critical load > 200 N). The XC38 steel exposed to boriding with the reducing agent of Al revealed fewer effective results (critical load ~80 N). The practical adhesion resistance of the boride coating to the substrate can be modified by post-heat treatments [68]. When a FeB–Fe2 B coating on an AISI 316 L steel is exposed to a diffusion annealing process (DAP), the amount of FeB can be limited or dissolved completely, increasing the Fe2 B coating thickness. The DAP leads to a relaxation of residual stresses accompanying both the dissolution of the FeB and changes in the boride coating-substrate bonding. The scratch test results

The Boriding Process for Enhancing the Surface Properties …

233

demonstrated that the critical load for the detachment of the coating to the substrate was increased around 3 times for the borided AISI 316 L steel exposed to DAP (cohesive failure was the predominant mechanism) compared to the borided steel non-exposed to the post-heat treatment that exhibited an adhesive failure. The scratch test evaluated the influence of boride coating thicknesses and the distribution of residual stresses on the practical adhesion resistance of nickel boride coating to the Inconel 718 [39]. The presence of high tensile stresses at the outer zone of the boride coating caused the layer to fail on low loads. However, on the inner zone of the nickel boride coating and for deeper coating thickness, the presence of compressive residual stresses produced an opposite effect, increasing the critical loads of the nickel boride coating-substrate system. Bull and Rickerby [69] established that, in real tribological systems, the working loads are smaller than the critical load determined by the single-pass scratch test. Thus, several passes over the same scratch track are needed before cumulative damage results in film or coating failure. Rodríguez-Castro et al. [70] studied the multi-pass scratch behavior of Fe2 B coating and FeB–Fe2 B coating on the borided AISI 316 L steel. Boride coatings, in the thickness range from 4 μm to 18 μm, were formed by the powder-pack method, employing the interrupted boriding procedure proposed by Gopalakrishnan et al. [71] to achieve the single (Fe2 B) coating. First, single-pass scratch tests with a Rockwell C indenter were carried out and critical chipping load was determined (51 N). Next, 100 unidirectional scratch passes with the 20%, 30%, and 40% of the critical load were performed. After the multipass-scratch tests, they found a lower coefficient of friction in the borided samples compared to the untreated AISI 316 L steel; at the highest load employed, the Fe2 B coating presented the lowest friction. The boriding process, regardless of single (Fe2 B) or dual-phase (FeB–Fe2 B) coatings, improved up to five times in wear resistance than that of the untreated AISI 316 L steel. It was also observed that the substrate contributed significantly when the boride coating was thin (96 wt.% Sn. The presence of a FeB– Fe2 B coating on the steel surfaces increased the corrosion resistance after 40 days of continuous immersion testing, with no change in the microstructure or the thickness of the boride coating and inhibiting the formation of reaction products on the borided surfaces. Similar corrosion behaviors of the borided Inconel 718 alloy and borided Hastelloy C276 alloy were obtained when immersed at 800 °C in a molten KCl–MgCl2 –NaCl salt. The formation of a uniform and compact boride coating on both alloys revealed a superior corrosion resistance compared to their untreated counterparts. Particularly, the boride coating microstructures consisted of an outermost silicide’s coating and metal borides, an intermediate metal borides’ “compound” coating, and beneath the coating, a diffusion zone intermixed with metal borides. Medvedovski [6] tested the high-temperature corrosion of borided low-carbon steels (J55 and A36/44 both with C contents ranging between 0.2% and 0.3%) and compared them to untreated AISI 304 and AISI 316L stainless steels immersed in two acidic solutions: one consisting of 15% HCl and the other consisting of 70% H2 SO4 , both held at 100 °C, with a total test duration of 168 h. The corrosion behavior of the stainless steels in the acids was complicated: in HCl, the corrosion of both steels was intensive in the first 24 h – 36 h, after which the corrosion rate decreased significantly; in H2 SO4 , corrosion was very intensive during the first 72 h – 96 h during which the protective chromium oxide scale was dissolved entirely, increasing the corrosion rate significantly. The untreated stainless steels lost between 6.5% and 23.5% of their masses after 168 h. However, the borided low carbon steels lost less than 1% of their masses within the entire duration of the corrosion test. The boride coating did not show evidence of delamination, pitting, bubble formation, or cracking. Petrova et al. [114] showed similar corrosion results in seven borided metallic materials exposed to H2 SO4 solution: AISI 1018 steel, AISI 4340 steel, AISI 304 steel, Inconel 625 alloy, Inconel 718 alloy, and Ti–6Al–4V alloy. In all the circumstances, the presence of boride coatings on metallic materials improved corrosion performance compared to untreated materials.

244

I. E. Campos Silva et al.

Moreover, the effects of selective boriding (i.e., where only part of the material’s surface is subjected to boriding) and full boriding in the corrosion performance of Nimonic 80A alloy were evaluated by Makuch et al. [127]. For the immersion corrosion tests conducted at 145 °C in H2 O, H2 SO4 , and Fe2 (SO4 )3 solutions, the mm ), and untreated Nimonic 80A alloy depicted the lowest corrosion rate (~0.555 year mm . The the fully borided Nimonic 80A alloy revealed a corrosion rate around 1.352 year mm highest corrosion rate (~515.92 year ) measured for the selectively borided Nimonic 80A alloy was associated with the significant differences in electrochemical potential between the coated (borided) and uncoated regions, which in turn aggravated the corrosion of the base material. The results of the abovementioned studies demonstrate the potential of boriding in improving the corrosion resistance of various alloys, intermetallics, and composites. In general, the boride coating produced on the surfaces appears to be highly resistant to a variety of corrosive environments, especially in acidic and oxidative (hightemperature oxidation) environments. However, the surface of the borided X12CrNiMoV12-3 stainless steel becomes more susceptible to corrosive attack when it is immersed in a NaCl + Na2 SO4 solution. The solution simulates the corrosive environment created by the combustion reaction of Na, S, and O when the X12CrNiMoV12-3 stainless steel is used as turbine blades. As turbine blades operate, Na and S might be present as fuel impurities, whereas NaCl and sulfates might enter the air needed for combustion, reacting with S in the fuel to become Na2 SO4 (an alkaline metal sulfate layer is formed at the surface of gas turbine blades). The latter causes hot corrosion, reducing load-carrying capacity, and might lead to a catastrophic failure of the component. Mejía-Caballero et al. [128] performed potentiodynamic polarization tests at room temperature on the borided X12CrNiMoV12-3 steel and the untreated stainless steel immersed for 5 days in a 0.1 M NaCl + 0.04 M Na2 SO4 solution. After 5 days of immersion in the neutral solution, the polarization resistance of the borided stainless steel was around 8 kΩ cm2 compared to the value of ~579 kΩ cm2 obtained in the untreated stainless steel. The corrosion performance of the borided X12CrNiMoV123 steel was explained by the presence of {020}//ND, {021}//ND texture components of the FeB coating; the corrosion process started in the grains associated with the texture components, as they were the more susceptible sites. In addition, the polarization resistance was affected by the formation of corrosion products (Fe2 O3 and B2 S3 ) in a crystal cluster form over the borided surface (Fig. 8), resulting from the interaction of the chloride-sulfate solution and the FeB–Fe2 B coating.

5 Tribocorrosion of Borided Metallic Materials Tribocorrosion is a form of surface degradation that leads to the progressive removal of material resulting from the simultaneous interaction of tribological effects caused by the relative movement between two or more surfaces in contact and the

The Boriding Process for Enhancing the Surface Properties …

245

Fig. 8 a SEM image on the borided X12CrNiMoV12-3 surface after 5 days of immersion in a NaCl + Na2 SO4 solution. b Crystal clusters on the borided surface after the 5th day of immersion in a NaCl + Na2 SO4 solution. c, d High resolution XPS spectra of B1s and O1s over the borided X12CrNiMoV12-3 surface after 5 days of immersion in a NaCl + Na2 SO4 solution. Courtesy of Grupo Ingeniería de Superficies, Instituto Politécnico Nacional

electrochemical action due to the exposition with a corrosive environment. This phenomenon, also called wear-corrosion synergism, where a worn surface interacts with a corrosive medium, can occur in various engineering systems such as in power generation, marine devices, chemical pumps and pipelines, biomedical implants, etc. [129–131]. The synergy between wear and corrosion causes a significant increase in material loss than the damage generated by each effect acting separately. Therefore, the material loss due to tribocorrosion can be greater than the sum of the individual contributions and is expressed as follows: [ T = W +C +S

mm3 mm2 year

] (1)

T is the total material loss, W is the material loss due to wear, C is the material loss due to corrosion, and S is the synergy between wear and corrosion. From Fig. 9, the synergy between wear and corrosion (S) occurs as follows: the physical interaction of the surfaces in relative motion (which generates phenomena of adhesion, abrasion, erosion, etc.) can provide particle and passive film detachment due to wear loss material. The active material surface (zone I) is exposed to the corrosive environment,

246

I. E. Campos Silva et al.

through electrochemical dissolution causing an “accelerated wear corrosion” until the passive film is formed again (repassivation process). The corrosion products, in combination with wear debris, can act as abrasive particles, generating a “wear accelerated corrosion”. The combined effects of wear and corrosion can significantly increase the material’s degradation exposed to tribocorrosion [129, 130, 132]. Conventionally, the parameters recorded in a tribocorrosion test are the friction coefficient, the material loss rate, the electrochemical potential of the contact surfaces exposed to a corrosive medium during sliding, and/or the corrosion current. The sliding or relative movement between the contacting surfaces may be continuous, discontinuous, unidirectional, or reciprocating [130, 131]. Some metallic materials are used in high-temperature applications (up to 370 °C) in fossil-fired power-generating plants, aircraft power plants, chemical processing plants, petroleum-processing plants, and aircraft components such as critical rotating parts, airfoils, supporting structures, and pressure vessels. Under these conditions, the degradation by high-temperature oxidation (hot-corrosion) is a typical components’ failure mode in hot sections, reducing the load-carrying capacity and might lead to a catastrophic failure [133–136]. Furthermore, the metallic materials are exposed to aggressive corrosive environments and oxidizing atmospheres. In different environments, the inherent corrosion resistance of a material usually depends on its ability to form a thin protective, and stable oxide film on the material’s surface, i.e., stainless steels, Ni-base alloys, Co-base alloys, and Ti-base alloys [129, 137–139]. However, the erosion-corrosion phenomenon occurs in applications subjected to multiphase flow conditions. In this way, the behavior of a material under erosioncorrosion conditions (e.g., the exposition to the continuous impingement of hard particles or detached debris from the passive film) is related to the materials’ passivation rate and the impact resistance of the passive film. When the metallic materials

Fig. 9 Schematic representation of tribological contact involving simultaneous mechanical and chemical effects

The Boriding Process for Enhancing the Surface Properties …

247

are exposed to specific mechanical effects, the passive film can break down, and the material enters a transpassive state, accelerating the material loss [102, 138, 140]. Tribocorrosion studies have been conducted on different borided metallic materials exposed to various environments, including saltwater, acidic solutions (HCl, H2 SO4 , HNO3 , etc.), and biological fluids, among others. For all the circumstances, the boride coatings showed a superior tribocorrosion resistance that can enhance the metallic material’s performance and service life for high-temperature applications. Low-carbon steels are employed in petroleum production applications. The contact of low-carbon steels with corrosive petroleum products causes severe damage to machine parts. In this sense, Medvedovski et al. [141] applied thermal diffusion based on the CVD process on A36/44W low-carbon steel. The tribocorrosion tests were performed using the rod-on-flat reciprocating sliding on the borided A36/44W steel and the untreated A36/44W steel immersed in water and oil solution (SAE30) combined with 0.02 M NaCl and 0.001 M H2 SO4 . In addition, another set of triboabrasive-corrosion experiments was performed by adding 5% of silica sand (diameter size of 38 μm – 53 μm) to simulate the abrasive effect. In both types of tests, the boride coating exhibited significantly lower wear-corrosion losses without delamination and fragmentation failures. For the tribocorrosion tests, the borided A36/44W reduced the wear-corrosion effect roughly by 76 times compared to the untreated steel, while for the tribo-abrasive-corrosion, the wear rate was decreased by around 194 times. The superior tribocorrosion performance of borided A36/44W was related to the boride coating’s high hardness and chemical inertness. Therefore, Medvedovski and Antonov [142] evaluated the erosion-corrosion resistance of a FeB–Fe2 B coating (total coating thickness of ~200 μm) on J55 carbon steel. The slurry erosion-corrosion tests were conducted in a mixture of 10% SiC and 3% NaCl with a centrifugal erosion device at 20 m s−1 impact velocity. The erosioncorrosion performance of the boride coating showed a 25% – 57% reduction of the volume loss than that of the untreated steel, attributed to its high hardness, chemical inertness, coating thickness, and coating adhesion to the substrate. The latter reduced the microcrack propagation at erosion impacts. The untreated steel exhibited plastic deformation and plowing erosion mechanisms, while the boride coating revealed microcracking, commonly observed for many advanced ceramics. Similarly, da Costa Aichholz et al. [26] evaluated the influence of the boriding process on the tribocorrosion behavior of an AISI 4140 steel. This steel is commonly used in petroleum and natural gas applications. The borided AISI 4140 steel (with a Fe2 B coating) was subjected to dry sliding and wet (3.5% NaCl solution) sliding conditions, respectively. The boride coating depicted lower wear rates in both dry and wet conditions as compared to the untreated AISI 4140 steel. During the dry condition, the boride coating exhibited higher friction coefficient values than the untreated steel; an opposite behavior was observed for the wet sliding conditions. Notably, the low friction coefficient of the boride coating (in wet conditions) was attributed to the surface formation of an H3 BO3 thin film due to the exposition of the NaCl solution. Before the wet sliding tests, the open circuit potential (OCP) was measured in both borided and untreated steels immersed in the NaCl solution. The untreated AISI 4140 steel showed more positive OCP values regarding the borided

248

I. E. Campos Silva et al.

steel. In contrast, during sliding, the borided AISI 4140 revealed the most positive OCP values, associated with the protective H3 BO3 film developed on the surface, decreasing the influence of the wear effect and enhancing the corrosion resistance than that of untreated AISI 4140 steel. In another study, Panda et al. [143] established the tribocorrosion behavior of a boride coating + BN-based layer on A36/44W low-carbon steel, and the results were compared with the untreated AISI 316 L and A36/44W steels. The boride coating + BN-based layer was evaluated under ball-on-flat technique in dry conditions and exposed to a 0.5 M NaCl solution. The multi-component coating had a lower friction coefficient, wear rate, and surface damage as compared to the untreated A36/44W and 316L steels in both dry and NaCl environments. The better performance of the borided low-carbon steel was regarded as the higher hardness and chemical inertness of the FeB–Fe2 B coating. In addition, the top BN-based layer reduced the boride coating susceptibility to crack propagation and decreased the friction coefficient because of its high lubricating property. Moreover, the accumulation of soft debris (from the top BN-based layer) on the boride coating achieved reduced material detachment, while the plowing effect on the untreated steels promoted debris accumulation on the worn surface. This accelerated the wear rate (at least 10 times), enhancing the friction coefficient (between 2 and 6 times) by three body abrasion wear. For all the circumstances, an adverse effect of the wear-corrosion synergy on the material surfaces was observed, increasing the wear rates in the NaCl environment. For the boride coating + BN-based layer, a tribofilm based on the partial oxidation of BN was developed on the borided surface. The tribofilm reduced the probability of the micro-crack formation, limiting the penetration of abraded microparticles and corrosive liquid through the coating microdefects compared to the common boride coating’s wear and corrosion mechanisms at least until the total detachment of the top BN-based layer. The tribocorrosion behavior of the borided AISI 321 steel, borided AISI 431 steel, and borided 30NiCrMo16 (FDMA) steel was evaluated by Chilali et al. [144]. The borided steels were exposed to 3.5 wt.% NaCl solution and reciprocating sliding wear. Under tribocorrosion conditions, the borided steels showed lower corrosion resistance than the untreated steels due to the porosity and microcracks within the boride coatings and the chemical reaction between the boron species and the corrosive environment. Although the borided steels showed lower corrosion resistance, the synergistic effect between wear and corrosion resulted in a decreased material loss (17% – 27%) with respect untreated steels. The latter was regarded as the boride coating’s high hardness.

The Boriding Process for Enhancing the Surface Properties …

249

On the other hand, turbine blades are one of the significant applications for Nibased superalloys, which are exposed to a corrosive environment produced by the combustion reaction of Na, S, and O. By simulating these demanding conditions in accordance with ASTM G119-09 procedure (Standard Guide for Determining Synergism between Wear and Corrosion), Morón et al. [145] exposed the borided Inconel 718 alloy to a sodium sulfate (0.04 M Na2 SO4 ) and sodium chloride (0.1 M NaCl) solution to evaluate the tribocorrosion behavior under ball-on-flat wear test. The boride coating (~50 μm thicker) consisted of a Ni4 B3 –Ni2 B–Ni3 B microstructure with a high superficial hardness around of 25 GPa. The results revealed a weardominant regime for the untreated alloy affected by the passive film removal and high contact pressure at the tribopair, increasing the total material loss rate by wear. The nickel boride layer on the Inconel 718 superalloy displayed a wear-corrosion regime due to boride layer debris that increased the corroded area. The contribution of wear-corrosion synergism to the total material loss (T) was around 73% for the untreated alloy and about 64% for the borided Inconel 718 alloy. Under these experimental conditions, the presence of the nickel boride layer on the Inconel 718 alloy improved tribocorrosion resistance by approximately three times. Figure 10 shows the wear tracks developed during tribocorrosion on the surface of borided Inconel 718 alloy and untreated alloy, both immersed in a Na2 SO4 + NaCl solution. Gunen et al. [146] proposed using Fe-based superalloys instead of high-cost Nibased superalloys in tribocorrosion applications. However, the strength and hardness of the Fe-based superalloys limit their use in tribological applications. For this reason, the A-286 superalloy was subjected to different boriding conditions (temperature and exposure times) to develop a FeB, Fe2 B, NiB, Ni3 B4 , and CrB coating microstructure and then exposed to sliding wear in a 3.5% NaCl solution. The results of the borided A-286 superalloy showed lower friction coefficients (around 18% – 67%) and higher wear resistance (6 – 35 times) compared with the untreated material. These values were attributed to both high hardness and Young’s modulus of the boride coatings. On the other hand, the wear resistance results were not proportional to the boride coating thicknesses (20 μm – 130 μm), regarding factors such as porosity, residual stresses, fracture toughness, and the Kirkendall effect. In the worn surface of untreated A286 superalloy, the presence of grooving-type micro-scratching wear was observed, while the worn borided surface displayed a fracture-type wear mechanism assisted by oxidative effect. Currently, two studies are related to the tribocorrosion behavior of a boride coating on High Entropy Alloys (HEAs). In both studies, the boride coatings demonstrated the potential for expanding the use of HEAs in tribocorrosion applications. The boriding process was applied to Co1.19 Cr1.86 Fe1.30 Mn1.39 Ni1.05 Al0.17 B0.04 HEA at different temperatures, obtaining a boride coating microstructure of Cr2 Ni3 B6 , Fe0.4 Mn0.6 B, Cr0.4 Mn0.6 B and CrFeB2 [147]. The tribocorrosion resistance of borided HEA and untreated HEA was evaluated by ball-on disk wear tests immersed in a 5% HCl solution. The friction coefficient values and the wear losses on the borided HEA were reduced (6 – 30 times) compared to the untreated HEA.

250

I. E. Campos Silva et al.

Fig. 10 Worn surfaces after tribocorrosion tests: a Borided Inconel 718 alloy and b Inconel 718 alloy. The counterpart was Al2 O3 ball that applied 20 N for a sliding distance of 100 m. The solution was Na2 SO4 + NaCl. Courtesy of Grupo Ingeniería de Superficies, Instituto Politécnico Nacional

The tribocorrosion effect was more pronounced for a thicker boride coating, as determined by increased hardness and Young’s modulus on the borided surface. The wear mechanism on the borided HEA was abrasive, accompanied by oxidation and pitting, while abrasive combined with pitting was observed on the untreated HEA surface. Similar tribocorrosion results were obtained on the borided Al0.07 Co1.2 6Cr1.80 Fe1.42 Mn1.35 Ni1.10 HEA [148]. The boriding process was conducted at diverse conditions (temperature and exposure time) to obtain different boride coating thicknesses with a (Cr0.4 Mn0.6 )B, (CoFe)B2, and Cr2 Ni3 B6 microstructure. The borided and untreated HEA were evaluated under sliding conditions and exposed to 3.5% NaCl and 5% H2 SO4 solutions, respectively. The boride coating on the HEA reduced the material loss (up to 30 times) and the friction coefficients in both corrosive environments more effectively than on untreated HEA, associated with the high hardness on the surface and the influence of the coating’s thickness. However, for all the circumstances, the H2 SO4 solution was more aggressive in relation to the NaCl solution, causing an increase in wear loss. Finally, during the exposition of the NaCl solution, the worn borided surface was smoothened by a polishing mechanism. Meanwhile polishing and flaking wear mechanisms were observed on the borided surface exposed to H2 SO4 solution.

The Boriding Process for Enhancing the Surface Properties …

251

Acknowledgements The authors gratefully acknowledge the members of the Grupo Ingeniería de Superficies (Instituto Politécnico Nacional) A. D. Contla-Pacheco, L. E. Castillo-Vela, K. D. Chaparro-Pérez, M. Olivares Luna, J. L. Rosales-López, and J. Escobar-Hernández for their important contribution to this Chapter. A. D. Delgado-Brito thanks Consejo Nacional de Humanidades Ciencia y Tecnologia (CONAHCyT) in Mexico. I. E. Campos-Silva would like to thank Tammy Williams Abram for her valuable assistance in the chapter revision.

References 1. Shah, F.U., Glavatskih, S., Antzutkin, O.N.: Boron in tribology: from borates to ionic liquids. Tribol. Lett. 51, 281–301 (2013). https://doi.org/10.1007/s11249-013-0181-3 2. Davis, J.R.: Surface Hardening of Steels. ASM International, Ohio (2002) 3. Sinha, A.K.: Boriding (Boronizing) of steels. In: ASM Handbook Committee (ed.) Heat Treating. ASM Handbook, vol. 4, pp. 437–447. ASM International, Ohio (1991) 4. Zimmerman, C.: Boriding (Boronizing) of metals. In: Dossett, J.L., Totten, G.E. (eds.) Steel Heat Treating Fundamentals and Processes. ASM Handbook, vol. 4A, pp. 709–724. ASM International, Ohio (2013) 5. Cimenoglu, H., Atar, E., Motallebzadeh, A.: High temperature tribological behaviour of borided surfaces based on the phase structure of the boride layer. Wear 309, 152–158 (2014). https://doi.org/10.1016/j.wear.2013.10.012 6. Medvedovski, E.: Advanced iron boride coatings to enhance corrosion resistance of steels in geothermal power generation. Adv. Appl. Ceram. 119, 462–481 (2020). https://doi.org/10. 1080/17436753.2020.1830359 7. Campos-Silva, I., Tadeo-Rosas, R., Santos-Medina, H.D., López-García, C.: Boride layers: growth kinetics and mechanical characterization. In: Colás, R., Totten, G.E. (eds.) Encyclopedia of Iron, Steel and Their Alloys, vol. 1, pp. 331–345. CRC Press, New York (2016) 8. Ninham, A.J., Hutchings, I.M.: On the morphology of thermochemically produced Fe2 B/Fe interfaces. J. Vac. Sci. Technol. A 4, 2827–2831 (1986). https://doi.org/10.1116/1.573686 9. Brakman, C.M., Gommers, A.W.J., Mittemeijer, E.J.: Boriding of Fe and Fe–C, Fe–Cr, and Fe–Ni alloys; boride-layer growth kinetics. J. Mater. Res. 4, 1354–1370 (1989). https://doi. org/10.1557/JMR.1989.1354 10. Dearnley, P.A., Bell, T.: Engineering the surface with boron based materials. Surf. Eng. 1, 203–217 (1985). https://doi.org/10.1179/sur.1985.1.3.203 11. Dybkov, V.I., Lengauer, W., Gas, P.: Formation of boride layers at the Fe-25% Cr alloy-boron interface. J. Mater. Sci. 41, 4948–4960 (2006). https://doi.org/10.1007/s10853-006-0032-9 12. Rus, J., Luis De Leal, C., Tsipas, D.N.: Boronizing of 304 steel. J. Mater. Sci. Lett. 4, 558–560 (1985). https://doi.org/10.1007/BF00720032 13. Campos-Silva, I., Ortiz-Domínguez, M., Bravo-Bárcenas, O., Doñu-Ruiz, M.A., BravoBárcenas, D., Tapia-Quintero, C., Jiménez-Reyes, M.Y.: Formation and kinetics of FeB/Fe2 B layers and diffusion zone at the surface of AISI 316 borided steels. Surf. Coat. Technol. 205, 403–412 (2010). https://doi.org/10.1016/j.surfcoat.2010.06.068 14. Mu, D., Shen, B.-L., Zhao, X.: Effects of boronizing on mechanical and dry-sliding wear properties of CoCrMo alloy. Mater. Des. 31, 3933–3936 (2010). https://doi.org/10.1016/j.mat des.2010.03.024 15. Campos-Silva, I., Bravo-Bárcenas, D., Meneses-Amador, A., Ortiz-Dominguez, M., Cimenoglu, H., Figueroa-López, U., Andraca-Adame, J.: Growth kinetics and mechanical properties of boride layers formed at the surface of the ASTM F-75 biomedical alloy. Surf. Coat. Technol. 237, 402–414 (2013). https://doi.org/10.1016/j.surfcoat.2013.06.083

252

I. E. Campos Silva et al.

16. Ueda, N., Mizukoshi, T., Demizu, K., Sone, T., Ikenaga, A., Kawamoto, M.: Boriding of nickel by the powder-pack method. Surf. Coat. Technol. 126, 25–30 (2000). https://doi.org/ 10.1016/S0257-8972(00)00517-X 17. Kulka, M.: Current Trends in Boriding. Springer Nature, Cham (2019) 18. D’Souza, B., Leong, A., Yang, Q., Zhang, J.: Corrosion behavior of boronized nickel-based alloys in the molten chloride salt. Corros. Sci. 182, 109285 (2021). https://doi.org/10.1016/j. corsci.2021.109285 19. Contla-Pacheco, A.D., Keddam, M., Lartundo-Rojas, L., Ortega-Avilés, M., Mejía-Caballero, I., Campos-Silva, I.: Application of the heat balance integral method to the growth kinetics of nickel boride layers on an Inconel 718 superalloy. Surf. Coat. Technol. 420, 127355 (2021). https://doi.org/10.1016/j.surfcoat.2021.127355 20. Anthymidis, K.G., Tsipas, D.N.: Boriding of titanium alloys in a fluidized bed reactor. J. Mater. Sci. Lett. 20, 2067–2069 (2001). https://doi.org/10.1023/A:1013510629005 21. Atar, E., Kayali, E.S., Cimenoglu, H.: Characteristics and wear performance of borided Ti6Al4V alloy. Surf. Coat. Technol. 202, 4583–4590 (2008). https://doi.org/10.1016/j.sur fcoat.2008.03.011 22. Sarma, B., Ravi Chandran, K.S.: Accelerated kinetics of surface hardening by diffusion near phase transition temperature: mechanism of growth of boride layers on titanium. Acta Mater. 59, 4216–4228 (2011). https://doi.org/10.1016/j.actamat.2011.03.046 23. Kara, G., Purcek, G.: Boriding behaviour of titanium alloys with different crystalline structures. Surf. Eng. 35, 611–617 (2019). https://doi.org/10.1080/02670844.2018.1552646 24. Campos-Silva, I., Ortiz-Domínguez, M., López-Perrusquia, N., Meneses-Amador, A., Escobar-Galindo, R., Martínez-Trinidad, J.: Characterization of AISI 4140 borided steels. Appl. Surf. Sci. 256, 2372–2379 (2010). https://doi.org/10.1016/j.apsusc.2009.10.070 25. Sen, S., Sen, U., Bindal, C.: Tribological properties of oxidised boride coatings grown on AISI 4140 steel. Mater. Lett. 60, 3481–3486 (2006). https://doi.org/10.1016/j.matlet.2006. 03.036 26. da Costa Aichholz, S.A., Sostag Meruvia, M., Soares Júnior, P.C., Torres, R.D.: Tribocorrosion behavior of boronized AISI 4140 steel. Surf. Coat. Technol. 352, 265–272 (2018). https://doi. org/10.1016/j.surfcoat.2018.07.101 27. Gunes, I.: Wear behaviour of plasma paste boronized of AISI 8620 steel with borax and B2 O3 paste mixtures. J. Mater. Sci. Technol. 29, 662–668 (2013). https://doi.org/10.1016/j.jmst. 2013.04.005 28. Doñu Ruiz, M.A., López Perrusquia, N., Sánchez Huerta, D., Torres San Miguel, C.R., Cortés Suárez, V.: Characterization and fracture toughness on AISI 8620 with hard coatings. Defect Diffus. Forum. 369, 89–94 (2016). https://doi.org/10.4028/www.scientific.net/DDF.369.89 29. Olivares-Luna, M.: Estudio de la adhesión mediante la prueba de rasgado del sistema capasubstrato formado en un acero borocarburizado AISI 8620. Dissertation. Instituto Politécnico Nacional (in Spanish) (2021) 30. Erdo˘gan, A.: Investigation of high temperature dry sliding behavior of borided H13 hot work tool steel with nanoboron powder. Surf. Coat. Technol. 357, 886–895 (2019). https://doi.org/ 10.1016/j.surfcoat.2018.10.066 31. Morón, R.C., Hernández-Onofre, I., Contla-Pacheco, A.D., Bravo-Bárcenas, D., CamposSilva, I.: Friction and reciprocating wear behavior of borided AISI H13 steel under dry and lubricated conditions. J. Mater. Eng. Perform. 29, 4529–4540 (2020). https://doi.org/10.1007/ s11665-020-04957-w 32. Hernández-Sánchez, E., Domínguez-Galicia, Y.M., Orozco-Álvarez, C., Carrera-Espinoza, R., Herrera-Hernández, H., Velázquez, J.C.: A study on the effect of the boron potential on the mechanical properties of the borided layers obtained by boron diffusion at the surface of AISI 316L steel. Adv. Mater. Sci. Eng. 2014, 249174 (2014). https://doi.org/10.1155/2014/ 249174 33. Ruiz-Rios, A., López-García, C., Campos-Silva, I.: The solid particle erosion on borided X12CrNiMoV12-3 stainless steel. Mater. Lett. 277, 128381 (2020). https://doi.org/10.1016/ j.matlet.2020.128381

The Boriding Process for Enhancing the Surface Properties …

253

34. García-Léon, R.A., Martínez-Trinidad, J., Campos-Silva, I., Wong-Angel, W.: Mechanical characterization of the AISI 316L alloy exposed to boriding process. DYNA. 87, 34–41 (2020). https://doi.org/10.15446/dyna.v87n213.82924 35. Campos-Silva, I., Bravo-Bárcenas, D., Flores-Jiménez, M., Arzate-Vázquez, I., López-García, C., Bernabé-Molina, S.: Diffusion boride coatings in CoCrMo alloy and some indentation properties. Metallogr. Microstruct. Anal. 4, 158–168 (2015). https://doi.org/10.1007/s13632015-0200-x 36. Delgado-Brito, A.M., López-Suero, D., Ruiz-Ríos, A., García-León, R.A., Martínez-Trinidad, J., Oseguera-Peña, J., Campos-Silva, I.: Effect of the diffusion annealing process in the indentation properties of cobalt boride layer. Ceram. Int. 45, 7767–7777 (2019). https://doi.org/10. 1016/j.ceramint.2019.01.081 37. Delgado-Brito, A.M., Contla-Pacheco, A.D., Castrejón-Sánchez, V.H., López-Suero, D., Oseguera-Peña, J., Campos-Silva, I.: Effect of the diffusion annealing process on the sliding wear resistance of cobalt boride layer. J. Mater. Eng. Perform. 29, 109–125 (2020). https:// doi.org/10.1007/s11665-019-04538-6 38. Makuch, N., Kulka, M.: Fracture toughness of hard ceramic phases produced on Nimonic 80A-alloy by gas boriding. Ceram. Int. 42, 3275–3289 (2016). https://doi.org/10.1016/j.cer amint.2015.10.119 39. Campos-Silva, I., Contla-Pacheco, A.D., Ruiz-Rios, A., Martínez-Trinidad, J., RodríguezCastro, G., Meneses-Amador, A., Wong-Angel, W.D.: Effects of scratch tests on the adhesive and cohesive properties of borided Inconel 718 superalloy. Surf. Coat. Technol. 349, 917–927 (2018). https://doi.org/10.1016/j.surfcoat.2018.05.086 40. Khater, M.A., Bouaziz, S.A., Garrido, M.A., Poza, P.: Mechanical and tribological behaviour of titanium boride coatings processed by thermochemicals treatments. Surf. Eng. 37, 101–110 (2021). https://doi.org/10.1080/02670844.2020.1763765 41. Chen, T., Koyama, S., Yu, L.: Improvement of mechanical, tribological, and fricative reduction properties of pure titanium by boriding. Appl. Sci. 11, 4862 (2021). https://doi.org/10.3390/ app11114862 42. Kaouka, A., Keddam, M., Zoukel, A.: Niobized layers produced on Ti–6Al–4V alloy and their mechanical properties. J. Chem. Technol. Metall. 57, 1060–1070 (2022) 43. Tsipas, D.N., Tsipas, S.A.: Boronizing of iron-based alloys. In: Colás, R., Totten, G.E. (eds.) Encyclopedia of Iron, Steel and Their Alloys, vol. 1, pp. 376–400. CRC Press, New York (2016) 44. Campos, I., Oseguera, J., Figueroa, U., García, J.A., Bautista, O., Kelemenis, G.: Kinetic study of boron diffusion in the paste boriding process. Mater. Sci. Eng. A 352, 261–265 (2003). https://doi.org/10.1016/S0921-5093(02)00910-3 45. Campos, I., Ramírez, G., Figueroa, U., Velázquez, C.V.: Paste boriding process: evaluation of boron mobility on borided steels. Surf. Eng. 23, 216–222 (2007). https://doi.org/10.1179/ 174329407X174416 46. Kahvecioglu, O., Sista, V., Eryilmaz, O.L., Erdemir, A., Timur, S.: Ultra-fast boriding of nickel aluminide. Thin Solid Films 520, 1575–1581 (2011). https://doi.org/10.1016/j.tsf.2011. 08.077 47. Dziarski, P., Makuch, N.: The importance of plasma paste boriding parameters for thickness, nanomechanical properties, residual stress distribution and fracture toughness of layers produced on Nimonic 80A-alloy. Eng. Fract. Mech. 275, 108842 (2022). https://doi.org/10. 1016/j.engfracmech.2022.108842 48. Tsipas, D.N., Anthymidis, K.G., Flitris, Y.: Deposition of hard and/or corrosion resistant, single and multielement coatings on ferrous and nonferrous alloys in a fluidized bed reactor. J. Mater. Process. Technol. 134, 145–152 (2003). https://doi.org/10.1016/S0924-0136(02)004 34-X 49. Anthymidis, K.G., Stergioudis, E., Tsipas, D.N.: Boriding in a fluidized bed reactor. Mater. Lett. 51, 156–160 (2001). https://doi.org/10.1016/S0167-577X(01)00283-X 50. Campos-Silva, I., Hernández-Ramirez, E.J., Contreras-Hernández, A., Rosales-Lopez, J.L., Valdez-Zayas, E., Mejía-Caballero, I., Martínez-Trinidad, J.: Pulsed-DC powder-pack

254

51.

52.

53. 54.

55.

56.

57.

58.

59.

60.

61.

62.

63.

64.

65.

66.

I. E. Campos Silva et al. boriding: growth kinetics of boride layers on an AISI 316 L stainless steel and Inconel 718 superalloy. Surf. Coat. Technol. 421, 127404 (2021). https://doi.org/10.1016/j.surfcoat.2021. 127404 Kartal, G., Timur, S., Eryilmaz, O.L., Erdemir, A.: Influence of process duration on structure and chemistry of borided low carbon steel. Surf. Coat. Technol. 205, 1578–1583 (2010). https://doi.org/10.1016/j.surfcoat.2010.08.050 Sista, V., Kahvecioglu, O., Kartal, G., Zeng, Q.Z., Kim, J.H., Eryilmaz, O.L., Erdemir, A.: Evaluation of electrochemical boriding of Inconel 600. Surf. Coat. Technol. 215, 452–459 (2013). https://doi.org/10.1016/j.surfcoat.2012.08.083 Xie, F., Zhu, Q.H., Lu, J.J.: Influence of direct current field on powder-pack boriding. Solid State Phenom. 118, 167–172 (2006). https://doi.org/10.4028/www.scientific.net/SSP.118.167 Xie, F., Sun, L., Pan, J.: Characteristics and mechanisms of accelerating pack boriding by direct current field at low and moderate temperatures. Surf. Coat. Technol. 206, 2839–2844 (2012). https://doi.org/10.1016/j.surfcoat.2011.12.003 Angkurarach, L., Juijerm, P.: Effects of direct current field on powder-packed boriding process on martensitic stainless steel AISI 420. Arch. Metall. Mater. 57, 799–804 (2015). https://doi. org/10.2478/v10172-012-0087-3 Taktak, S., Tasgetiren, S.: Identification of delamination failure of boride layer on common Cr-based steels. J. Mater. Eng. Perform. 15, 570–574 (2006). https://doi.org/10.1361/105994 906X124587 Allaoui, O., Bouaouadja, N., Saindernan, G.: Characterization of boronized layers on a XC38 steel. Surf. Coat. Technol. 201, 3475–3482 (2006). https://doi.org/10.1016/j.surfcoat.2006. 07.238 Qin, L., Liu, C., Yang, K., Tang, B.: Characteristics and wear performance of borided Ti6Al4V alloy prepared by double glow plasma surface alloying. Surf. Coat. Technol. 225, 92–96 (2013). https://doi.org/10.1016/j.surfcoat.2013.02.053 Kayali, Y., Taktak, S.: Characterization and Rockwell-C adhesion properties of chromiumbased borided steels. J. Adhes. Sci. Technol. 29, 2065–2075 (2015). https://doi.org/10.1080/ 01694243.2015.1052617 Rodríguez-Castro, G.A., Jiménez-Tinoco, L.F., Méndez-Méndez, J.V., Arzate-Vázquez, I., Meneses-Amador, A., Martínez-Gutiérrez, H., Campos-Silva, I.: Damage mechanisms in AISI 304 borided steel: scratch and Daimler-Benz adhesion tests. Mater. Res. 18, 1346–1353 (2015). https://doi.org/10.1590/1516-1439.025515 Meneses-Amador, A., Jiménez-Tinoco, L.F., Reséndiz-Calderon, C.D., Mouftiez, A., Rodríguez-Castro, G.A., Campos-Silva, I.: Numerical evaluation of scratch tests on boride layers. Surf. Coat. Technol. 284, 182–191 (2015). https://doi.org/10.1016/j.surfcoat.2015. 06.088 Bravo-Bárcenas, D., Campos-Silva, I., Cimenoglu, H., Martínez-Trinidad, J., Flores-Jiménez, M., Martinez-Gutiérrez, H.: Characterisation of CoB–Co2 B coatings by the scratch test. Surf. Eng. 32, 570–577 (2016). https://doi.org/10.1080/02670844.2015.1121315 Johnston, J.M., Catledge, S.A.: Metal-boride phase formation on tungsten carbide (WC-Co) during microwave plasma chemical vapor deposition. Appl. Surf. Sci. 364, 315–321 (2016). https://doi.org/10.1016/j.apsusc.2015.12.156 Meneses-Amador, A., Blancas-Pérez, D., Corpus-Mejía, R., Rodríguez-Castro, G.A., Martínez-Trinidad, J., Jiménez-Tinoco, L.F.: Adhesive and cohesive strength in FeB/Fe2 B systems. J. Mater. Eng. Perform. 27, 2089–2098 (2018). https://doi.org/10.1007/s11665-0183150-z Reyes-Carcaño, O., Martínez-Trinidad, J., Meneses-Amador, A., Rodríguez-Castro, G.A., Campos-Silva, I., Figueroa-López, U.: Scratch test in boride layers: Influence of indenter tip radius on failure mechanisms. Mater. Lett. 315, 131918 (2022). https://doi.org/10.1016/j.mat let.2022.131918 Perry, A.J.: Scratch adhesion testing of hard coatings. Thin Solid Films 107, 167–180 (1983). https://doi.org/10.1016/0040-6090(83)90019-6

The Boriding Process for Enhancing the Surface Properties …

255

67. Bull, S.J., Berasetegui, E.G.: An overview of the potential of quantitative coating adhesion measurement by scratch testing. Tribol. Int. 39, 99–114 (2006). https://doi.org/10.1016/j.tri boint.2005.04.013 68. Campos-Silva, I., Bernabé-Molina, S., Bravo-Bárcenas, D., Martínez-Trinidad, J., RodríguezCastro, G., Meneses-Amador, A.: Improving the adhesion resistance of the boride coatings to AISI 316L steel substrate by diffusion annealing. J. Mater. Eng. Perform. 25, 3852–3862 (2016). https://doi.org/10.1007/s11665-016-2201-6 69. Bull, S.J., Rickerby, D.S.: Multi-pass scratch testing as a model for abrasive wear. Thin Solid Films 181, 545–553 (1989). https://doi.org/10.1016/0040-6090(89)90523-3 70. Rodríguez-Castro, G.A., Vega-Morón, R.C., Meneses-Amador, A., Jiménez-Díaz, H.W., Andraca-Adame, J.A., Campos-Silva, I.E., Pardavé, M.E.P.: Multi-pass scratch test behavior of AISI 316L borided steel. Surf. Coat. Technol. 307, 491–499 (2016). https://doi.org/10. 1016/j.surfcoat.2016.09.017 71. Gopalakrishnan, P., Shankar, P., Palaniappa, M., Ramakrishnan, S.S.: Interrupted boriding of medium-carbon steels. Metall. Mater. Trans. A 33, 1475–1485 (2002). https://doi.org/10. 1007/s11661-002-0070-0 72. Vega-Morón, R.C., Rodríguez-Castro, G.A., Jiménez-Tinoco, L.F., Meneses-Amador, A., Méndez-Méndez, J.V., Escobar-Hernández, J., Reséndiz-Calderón, C.D., Nava-Sánchez, J.L.: Multipass scratch behavior of borided and nitrided H13 steel. J. Mater. Eng. Perform. 27, 3886–3899 (2018). https://doi.org/10.1007/s11665-018-3410-y 73. Archard, J.F., Hirst, W.: The wear of metals under unlubricated conditions. Proc. Math. Phys. Sci. Eng. 236, 397–410 (1956). https://doi.org/10.1098/rspa.1956.0144 74. Liu, Y., Liskiewicz, T.W., Beake, B.D.: Dynamic changes of mechanical properties induced by friction in the Archard wear model. Wear 428–429, 366–375 (2019). https://doi.org/10. 1016/j.wear.2019.04.004 75. Tabrizi, A.T., Aghajani, H., Saghafian, H., Laleh, F.F.: Correction of Archard equation for wear behavior of modified pure titanium. Tribol. Int. 155, 106772 (2021). https://doi.org/10. 1016/j.triboint.2020.106772 76. Leyland, A., Matthews, A.: On the significance of the H/E ratio in wear control: a nanocomposite coating approach to optimised tribological behaviour. Wear 246, 1–11 (2000). https:// doi.org/10.1016/S0043-1648(00)00488-9 77. Rebholz, C., Monclus, M.A., Baker, M.A., Mayrhofer, P.H., Gibson, P.N., Leyland, A., Matthews, A.: Hard and superhard TiAlBN coatings deposited by twin electron-beam evaporation. Surf. Coat. Technol. 201, 6078–6083 (2007). https://doi.org/10.1016/j.surfcoat.2006. 08.121 78. Beake, B.D.: The influence of the H/E ratio on wear resistance of coating systems—Insights from small-scale testing. Surf. Coat. Technol. 442, 128272 (2022). https://doi.org/10.1016/j. surfcoat.2022.128272 79. Inman, I.A., Datta, P.K., Du, H.L., Burnell-Gray, J.S., Pierzgalski, S., Luo, Q.: Studies of high temperature sliding wear of metallic dissimilar interfaces. Tribol. Int. 38, 812–823 (2005). https://doi.org/10.1016/j.triboint.2005.02.007 80. Li, J.L., Xiong, D.S., Huo, M.F.: Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena. Wear 265, 566–575 (2008). https:// doi.org/10.1016/j.wear.2007.11.024 81. Newcomb, T., Sparrow, M., Ciupak, B.: Glaze analysis of friction plates. SAE Tech. Pap. 200601-3244 (2006). https://doi.org/10.4271/2006-01-3244 82. Dreano, A., Fouvry, S., Sao-Joao, S., Galipaud, J., Guillonneau, G.: The formation of a cobaltbased glaze layer at high temperature: a layered structure. Wear 440–441, 203101 (2019). https://doi.org/10.1016/j.wear.2019.203101 83. Xin, B., Zhang, A., Han, J., Su, B., Meng, J.: Tuning composition and microstructure by doping Ti and C for enhancing mechanical property and wear resistance of Al0.2 Co1.5 CrFeNi1.5 Ti0.5 high entropy alloy matrix composites. J. Alloys Compd. 836, 155273 (2020). https://doi.org/ 10.1016/j.jallcom.2020.155273

256

I. E. Campos Silva et al.

84. Stott, F.H., Wood, G.C., Glascott, J.: Models for the generation of oxides during sliding wear. Proc. R. Soc. Lond. 402, 167–186 (1985). https://doi.org/10.1098/rspa.1985.0113 85. Stott, F.H.: High-temperature sliding wear of metals. Tribol. Int. 35, 489–495 (2002). https:// doi.org/10.1016/S0301-679X(02)00041-5 86. Kato, K.: Abrasive wear of metals. Tribol. Int. 30, 333–338 (1997). https://doi.org/10.1016/ S0301-679X(96)00063-1 87. Günen, A., Kanca, E., Karaka¸s, M.S., Koç, V., Gök, M.S., Kanca, Y., Çürük, A., Demir, M.: High temperature wear behavior of the surface-modified externally cooled rolls. Surf. Coat. Technol. 348, 130–141 (2018). https://doi.org/10.1016/j.surfcoat.2018.04.071 88. Ren, X., Fu, H., Xing, J., Yi, Y.: Research on high-temperature dry sliding friction wear behavior of Ca–Ti modified high boron high speed steel. Tribol. Int. 132, 165–176 (2019). https://doi.org/10.1016/j.triboint.2018.12.009 89. Garcia-Bustos, E., Figueroa-Guadarrama, M.A., Rodríguez-Castro, G.A., Gómez-Vargas, O.A., Gallardo-Hernández, E.A., Campos-Silva, I.: The wear resistance of boride layers measured by the four-ball test. Surf. Coat. Technol. 215, 241–246 (2013). https://doi.org/ 10.1016/j.surfcoat.2012.08.090 90. Piasecki, A., Kotkowiak, M., Makuch, N., Kulka, M.: Wear behavior of self-lubricating boride layers produced on Inconel 600-alloy by laser alloying. Wear 426–427, 919–933 (2019). https://doi.org/10.1016/j.wear.2018.12.026 91. Chien, H., Diaz-Jimenez, C., Rohrer, G.S., Ban, Z., Prichard, P., Liu, Y.: The influence of residual thermal stresses on the mechanical properties of multilayer α-Al2 O3 /TiCx N1−x coatings on WC/Co cutting tools. Surf. Coat. Technol. 215, 119–126 (2013). https://doi.org/10. 1016/j.surfcoat.2012.07.088 92. Alias, S.K., Abdullah, B., Jaffar, A., Latip, S.A., Kasolang, S., Izham, M.F., Ghani, M.A.A.: Mechanical properties of paste carburized ASTM A516 steel. Procedia Eng. 68, 525–530 (2013). https://doi.org/10.1016/j.proeng.2013.12.216 93. Mindivan, H.: High-temperature wear and oxidation behavior of electrochemically borided low carbon steel. J. Fac. Eng. Archit. Gazi Univ. 38, 937–946 (2022). https://doi.org/10.17341/ gazimmfd.1063321 94. Campos-Silva, I.E., Rodríguez-Castro, G.A.: Boriding to improve the mechanical properties and corrosion resistance of steels. In: Mittemeijer, E.J., Somers, M.A.J. (eds.) Thermochemical Surface Engineering of Steels, pp. 651–702. Woodhead Publishing, Cambridge (2015) 95. Taktak, S.: Tribological behaviour of borided bearing steels at elevated temperatures. Surf. Coat. Technol. 201, 2230–2239 (2006). https://doi.org/10.1016/j.surfcoat.2006.03.032 96. Carbucicchio, M., Reverberi, R., Palombarini, G., Sambogna, G.: On the early stages of oxidation of iron borides. Hyperfine Interact 46, 473–479 (1989). https://doi.org/10.1007/ BF02398233 97. Motallebzadeh, A., Dilektasli, E., Baydogan, M., Atar, E., Cimenoglu, H.: Evaluation of the effect of boride layer structure on the high temperature wear behavior of borided steels. Wear 328–329, 110–114 (2015). https://doi.org/10.1016/j.wear.2015.01.029 98. Yang, H., Wu, X., Cao, G., Yang, Z.: Enhanced boronizing kinetics and high temperature wear resistance of H13 steel with boriding treatment assisted by air blast shot peening. Surf. Coat. Technol. 307, 506–516 (2016). https://doi.org/10.1016/j.surfcoat.2016.09.029 99. Pu, S., Yang, H., Wang, H., Wu, X.: Effect of rare earth Ce on high temperature friction and wear property of pack boronized H13 steel. Chin. J. Mater. Res. 29, 481–488 (2017) 100. Smith, W.F.: Structure and Properties of Engineering Alloys. McGraw-Hill, New York (1993) 101. Pollock, T.M., Tin, S.: Nickel-based superalloys for advanced turbine engines: chemistry, microstructure, and properties. J. Propuls. Power 22, 361–374 (2006). https://doi.org/10.2514/ 1.18239 102. Chen, X.M., Lin, Y.C., Wen, D.X., Zhang, J.L., He, M.: Dynamic recrystallization behavior of a typical nickel-based superalloy during hot deformation. Mater. Des. 57, 568–577 (2014). https://doi.org/10.1016/j.matdes.2013.12.072

The Boriding Process for Enhancing the Surface Properties …

257

103. Günen, A., Döleker, K.M., Korkmaz, M.E., Gök, M.S., Erdogan, A.: Characteristics, high temperature wear and oxidation behavior of boride layer grown on nimonic 80A Ni-based superalloy. Surf. Coat. Technol. 409, 126906 (2021). https://doi.org/10.1016/j.surfcoat.2021. 126906 104. Gheisari, R., Polycarpou, A.A.: Tribology of selected hard coatings for oil and gas applications up to 450 °C. Tribol. Lett. 67, 51 (2019). https://doi.org/10.1007/s11249-019-1159-6 105. Günen, A.: Properties and high temperature dry sliding wear behavior of boronized Inconel 718. Metall. Mater. Trans. A 51, 927–939 (2020). https://doi.org/10.1007/s11661-019-055 77-3 106. Kayali, Y., Kanca, E., Günen, A.: Effect of boronizing on microstructure, high-temperature wear and corrosion behavior of additive manufactured Inconel 718. Mater. Charact. 191, 112155 (2022). https://doi.org/10.1016/j.matchar.2022.112155 107. Günen, A., Bölükba¸sı, Ö.S., Özgürlük, Y., Özkan, D., Odaba¸s, O., Somunkıran, ˙I: Effect of Cr addition on properties and tribological behavior at elevated temperature of boride layers grown on borosintered powder metallurgy alloys. Met. Mater. Int. 29, 748–766 (2023). https:// doi.org/10.1007/s12540-022-01251-3 108. Fichtl, W.: Boronizing and its practical applications. Mater. Des. 2, 276–286 (1981). https:// doi.org/10.1016/0261-3069(81)90034-0 109. Joshi, R., Ningthoujam, R.S.: Synthesis, characterization, physical properties and applications of metal borides. In: Tyagi, A.K., Ningthoujam, R.S., (eds.) Handbook on Synthesis Strategies for Advanced Materials, vol. III, pp. 251–306. Springer Nature, Singapore (2021) 110. Matuschka, A.G.: Boronizing. Hanser, Philadelphia (1980) 111. Kane, K.A., Pint, B.A., Mitchell, D., Haynes, J.A.: Oxidation of ultrahigh temperature ceramics: kinetics, mechanisms, and applications. J. Eur. Ceram. Soc. 41, 6130–6150 (2021). https://doi.org/10.1016/j.jeurceramsoc.2021.05.055 112. Golla, B.R., Mukhopadhyay, A., Basu, B., Thimmappa, S.K.: Review on ultra-high temperature boride ceramics. Prog. Mater. Sci. 111, 100651 (2020). https://doi.org/10.1016/j.pma tsci.2020.100651 113. Tsipas, D.N., Noguera, H., Rus, J.: Corrosion behaviour of boronized low carbon steel. Mater. Chem. Phys. 18, 295–303 (1987). https://doi.org/10.1016/0254-0584(87)90143-X 114. Petrova, R.S., Suwattananont, N., Samardzic, V.: The effect of boronizing on metallic alloys for automotive applications. J. Mater. Eng. Perform. 17, 340–345 (2008). https://doi.org/10. 1007/s11665-008-9228-2 115. Caillet, M., Galerie, A., Pons, M.: Influence of laser surface boronizing on the hightemperature oxidation of nickel. Mater. Lett. 4, 102–106 (1986). https://doi.org/10.1016/0167577X(86)90059-5 116. Makuch, N., Dziarski, P.: The importance of phase composition for corrosion resistance and thermal oxidation behavior of gas-borided layer produced on nickel alloy. Corros. Rev. 39, 269–277 (2021). https://doi.org/10.1515/corrrev-2020-0081 117. Lu, X.P., Xiang, H.M., Han, P., Li, M.S., Zhou, Y.C.: Effect of boronizing treatment on the oxidation resistance of Zr2 (AlSi)4 C5 /SiC composite. Corros. Sci. 162, 108201 (2020). https:// doi.org/10.1016/j.corsci.2019.108201 118. Yokota, H., Kudoh, T., Suzuki, T.: Oxidation resistance of boronized MoSi2 . Surf. Coat. Technol. 169–170, 171–173 (2003). https://doi.org/10.1016/S0257-8972(03)00221-4 119. Yokota, H., Suzuki, T.: Improvement in the oxidation of TiAl by molten salt boronizing. J. Stage News 91, 217–223 (2004). https://doi.org/10.2355/tetsutohagane1955.91.1_217 120. Qiao, Y., Kong, J., Zhou, R., Guo, X.: Boronizing of the silicide coating on a multicomponent Nb–Ti–Si based alloy as protection against corrosion at high temperatures. Vacuum 161, 314–323 (2019). https://doi.org/10.1016/j.vacuum.2018.12.054 121. Swad´zba, R.: High temperature oxidation behavior of C103 alloy with boronized and siliconized coatings during 1000 h at 1100 °C in air. Surf. Coat. Technol. 370, 331–339 (2019). https://doi.org/10.1016/j.surfcoat.2019.04.019 122. Mu, D., Shen, B.-L.: Oxidation resistance of boronized CoCrMo alloy. Int. J. Refract. Met. Hard Mater. 28, 424–428 (2010). https://doi.org/10.1016/j.ijrmhm.2010.01.003

258

I. E. Campos Silva et al.

123. Dokumaci, E., Özkan, I., Önay, B.: Effect of boronizing on the cyclic oxidation of stainless steel. Surf. Coat. Technol. 232, 22–25 (2013). https://doi.org/10.1016/j.surfcoat.2013.04.047 ˇ cka, R., Kusý, M., Hudáková, M.: Oxidation 124. Ptaˇcinová, J., Drienovský, M., Palcut, M., Ciˇ stability of boride coatings. Kov. Mater. 53, 175–186 (2015). https://doi.org/10.4149/km_ 2015_3_175 125. Medvedovski, E., Chinski, F.A., Stewart, J.: Wear- and corrosion-resistant boride-based coatings obtained through thermal diffusion CVD processing. Adv. Eng. Mater. 16, 713–728 (2014). https://doi.org/10.1002/adem.201400090 126. Salyi, Z., Kaptay, G., Koncz-Horvath, D., Somlyai-Sipos, L., Kovacs, P.Z., Lukacs, A., Benke, M.: Boride coatings on steel protecting it against corrosion by a liquid lead-free solder alloy. Metall. Mater. Trans. B 53, 730–743 (2022). https://doi.org/10.1007/s11663-021-02412-2 127. Makuch, N., Kulka, M., Mikołajczak, D.: Corrosion behavior of hard boride layer produced on Nimonic 80A-alloy by gas boriding. Trans. Indian Inst. Met. 70, 2509–2527 (2017). https:// doi.org/10.1007/s12666-017-1113-y 128. Mejía-Caballero, I., Escobar-Martínez, C., Palomar-Pardavé, M., Le Manh, T., Romero-Romo, M., Rodríguez-Clemente, E., Lartundo-Rojas, L., Campos-Silva, I.: On the corrosion mechanism of borided X12CrNiMoV12-3 steel immersed in a neutral aqueous solution containing chloride and sulfate ions. Metall. Mater. Trans. A 51, 4868–4879 (2020). https://doi.org/10. 1007/s11661-020-05869-z 129. Ponthiaux, P., Wenger, F., Celis, J.P.: Tribocorrosion: material behavior under combined conditions of corrosion and mechanical loading. In: Shih, H., (ed.) Corrosion Resistance, pp. 81–106. Intech, Rijeka (2012) 130. Mischler, S.: Sliding tribo-corrosion of passive metals: mechanisms and modeling. In: Blau, P.J., Celis, J.P., Drees, D., (eds.) Tribo-Corrosion: Research, Testing, and Applications, pp. 1– 18. ASTM International, Pennsylvania (2013) 131. Celis, J.P., Ponthiaux, P. (eds.): Testing Tribocorrosion of Passivating Materials Supporting Research and Industrial Innovation: a Handbook. Maney Publishing, Wakefield (2012) 132. Batchelor, A.W., Lampman, S.: Chemically assisted and environmentally controlled wear. In: Totten, G.E. (ed.) Friction, Lubrication, and Wear Technology. ASM Handbook, vol. 18, pp. 351–359. ASM International, Ohio (2017) 133. Viswanathan, R.: Damage Mechanisms and Life Assessment of High-Temperature Components. ASM International, Ohio (1989) 134. Davis, J.R., (ed.): Metals Handbook Desk Edition. ASM International, Ohio (1998) 135. Kamal, S., Jayaganthan, R., Prakash, S.: High temperature cyclic oxidation and hot corrosion behaviours of superalloys at 900 °C. Bull. Mater. Sci. 33, 299–306 (2010). https://doi.org/10. 1007/s12034-010-0046-4 136. Geddes, B., Leon, H., Huang, X.: Superalloys: alloying and Performance. ASM International, Ohio (2010) 137. López, A., Bayón, R., Pagano, F., Igartua, A., Arredondo, A., Arana, J.L., González, J.J.: Tribocorrosion behaviour of mooring high strength low alloy steels in synthetic seawater. Wear 338–339, 1–10 (2015). https://doi.org/10.1016/j.wear.2015.05.004 138. Sun, Y., Rana, V.: Tribocorrosion behaviour of AISI 304 stainless steel in 0.5 M NaCl solution. Mater. Chem. Phys. 129, 138–147 (2011). https://doi.org/10.1016/j.matchemphys.2011. 03.063 139. Chen, J., Zhang, Q., Li, Q.A., Fu, S.L., Wang, J.Z.: Corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys in artificial seawater. Trans. Nonferrous Met. Soc. China 24, 1022–1031 (2014). https://doi.org/10.1016/S1003-6326(14)63157-5 140. Yi, J.Z., Hu, H.X., Wang, Z.B., Zheng, Y.G.: On the critical flow velocity for erosion-corrosion of Ni-based alloys in a saline-sand solution. Wear 458–459, 13–21 (2020). https://doi.org/10. 1016/j.wear.2020.203417 141. Medvedovski, E., Jiang, J., Robertson, M.: Iron boride-based thermal diffusion coatings for tribo-corrosion oil production applications. Ceram. Int. 42, 3190–3211 (2016). https://doi. org/10.1016/j.ceramint.2015.10.109

The Boriding Process for Enhancing the Surface Properties …

259

142. Medvedovski, E., Antonov, M.: Erosion studies of the iron boride coatings for protection of tubing components in oil production, mineral processing and engineering applications. Wear 452–453, 203277 (2020). https://doi.org/10.1016/j.wear.2020.203277 143. Panda, J.N., Wong, B.C., Medvedovski, E., Egberts, P.: Enhancement of tribo-corrosion performance of carbon steel through boronizing and BN-based coatings. Tribol. Int. 153, 106666 (2021). https://doi.org/10.1016/j.triboint.2020.106666 144. Chilali, A., Salhi, H., Abdi, A., Djeghlal, M.E.A., Omar, A., Montagne, A., Mejias, A., Iost, A.: Corrosion and tribocorrosion behaviours of AISI 321, AISI 431 and FDMA borided and non-borided steels. Mater. Res. Express 6, 116448 (2019). https://doi.org/10.1088/2053-1591/ ab4e4b 145. Morón, R.C., Contla-Pacheco, A.D., Castrejón-Sánchez, V.H., Melo-Máximo, L., CamposSilva, I.: Estimation of the wear and corrosion synergism of borided Inconel 718 alloy immersed in a neutral aqueous solution. Ceram. Int. 49, 2495–2505 (2023). https://doi.org/ 10.1016/j.ceramint.2022.09.225 146. Günen, A., Keddam, M., Alkan, S., Erdo˘gan, A., Çetin, M.: Microstructural characterization, boriding kinetics and tribo-wear behavior of borided Fe-based A286 superalloy. Mater. Charact. 186, 111778 (2022). https://doi.org/10.1016/j.matchar.2022.111778 147. Günen, A.: Tribocorrosion behavior of boronized Co1.19 Cr1.86 Fe1.30 Mn1.39 Ni1.05 Al0.17 B0.04 high entropy alloy. Surf. Coat. Technol. 421, 127426 (2021). https://doi.org/10.1016/j.sur fcoat.2021.127426 148. Karaka¸s, M.S., Günen, A., Çarbo˘ga, C., Karaca, Y., Demir, M., Altınay, Y., Erdo˘gan, A.: Microstructure, some mechanical properties and tribocorrosion wear behavior of boronized Al0.07Co1.26Cr1.80Fe1.42Mn1.35Ni1.10 high entropy alloy. J. Alloys Compd. 886, 161222 (2021). https://doi.org/10.1016/j.jallcom.2021.161222

Tribological Characterization of Electroless Nickel Coatings at High Temperatures Arkadeb Mukhopadhyay, Tapan Kumar Barman, and Prasanta Sahoo

Abstract Electroless nickel (EN) coatings are widely applicable in industries. Current trends also present enhanced high-temperature performance of EN-based coatings. The high-temperature tribological behaviour is guided by phase transformations and formation of tribo-oxide layers. The present chapter reports hightemperature tribological characterization of EN coatings. The electroless coatings present a globular morphology. The wear surface at high temperatures consists of oxide glaze. At 100 °C, tribological behaviour is controlled by formation of strainhardened wear debris. Nickel phosphides and nickel borides are formed due to heat accumulation and high flash temperature at the interface. Further, the future scope and possibilities of improvement of wear resistance of the coatings have also been discussed. Keywords Electroless nickel · Wear rate · COF · High temperature · Oxide layer

1 Introduction Surface coatings are applied on a substrate to modify surface properties rather than bulk properties. A thin layer of coating is applied to improve surface performance, which includes low coefficient of friction (COF), hardness, wear, etc. Degradation of any mechanical component initiates at the surface when exposed to harsh conditions. Surface engineering or surface coatings are an effective way to mitigate such damage. There are various methods of surface engineering or application of surface coatings on a surface. This includes laser surface modification [1, 2], physical vapour deposition [3, 4], chemical vapour deposition [5, 6], thermal spray [7, 8], using an aqueous bath [9, 10], friction surface processing [11, 12], etc. Each method has their A. Mukhopadhyay Department of Mechanical Engineering, Birla Institute of Technology, Mesra, Ranchi 835215, India T. K. Barman · P. Sahoo (B) Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India e-mail: [email protected]; [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_10

261

262

A. Mukhopadhyay et al.

own set of advantages and disadvantages [13]. An aqueous bath may be utilized for electroless or electrodeposition. Various functional coatings with desired properties may be deposited by both methods [14, 15]. Electroless method is a novel coating deposition technique, which does not utilize electricity for coating deposition and is an autocatalytic process [16]. As the coatings’ initial layer is deposited, process continues and hence is termed autocatalytic [17]. The advantage of electroless method includes the deposit uniformity wherein a sharp edge, blunt hole or intricate parts can be coated with ease [18–20]. Other functional advantages include smooth surface appearance, corrosion and wear resistance, conductivity, etc. [21, 22]. Various metals may be deposited by electroless process like copper, gold, silver, nickel, cobalt, etc. [23–25]. But the electroless nickel (EN) coatings were primarily utilized for tribological applications [26]. The applicability of EN coatings is summarized in Fig. 1. The electroless nickel coatings require reducing agents, which include either sodium hypophosphite or sodium borohydride. Ni–P or electroless Ni–B (ENB) coatings are formed consequently [27–30]. Better corrosion resistance was seen for Ni–P coatings whereas ENB coatings are associated with high wear resistance and hardness [31–34]. Though pure nickel may be deposited by electroless process, they are not in use due to hazards related to hydrazine in the coating bath [17, 18]. With rising demand from industries and growing challenges/harsh environments, there was a need for the expansion of the EN family. Apart from the pure nickel or binary alloys, further metallic additions may be also carried out to form ternary and quaternary coatings [35–38]. The coating matrix may be dispersion strengthened by forming composite coating by addition of ceramic particles or self-lubricating particles or both [39–45]. EN classification is depicted in Fig. 2. The coating properties

Fig. 1 Applications of electroless nickel coatings

Tribological Characterization of Electroless Nickel Coatings at High …

263

Fig. 2 Classification of EN coatings

may be further enhanced through aid of different heat treatments. The coatings may be heat treated in a furnace in the presence of air, vacuum and nitride [46–50]. Precipitation of hard crystalline phases takes place consequently [46–50]. This improves microhardness and wear resistance. Though, higher heat treatment temperature leads to an increase in grain size and degradation in mechanical properties [46–50]. The EN bath comprises of several chemicals such as nickel, reducing agent, buffer, complexing agent, surfactants, nano/micro-particles, etc. [17, 18]. These chemical composition and deposition conditions may be tailored to produce coatings with varying microstructures, which in turn influences mechanical properties, tribological behaviour and corrosion resistance [17, 18, 22]. The aid of experimental designs, optimization and machine learning has been successfully utilized to optimize the coatings for harsh conditions [27–29, 34]. Recent studies have also found out the usefulness of EN coatings at high temperature. Thus, the present chapter discusses deposition of EN coatings and their high-temperature tribological behaviour along with the recent progress and future prospects.

2 Deposition of EN Coatings The Ni–P coatings can be deposited from alkaline or acidic baths. The acidic bath Ni– P coatings were better than those obtained from alkaline bath. Sodium hypophosphite is a reducing agent and pH lies between 5–6 and 8–9 for the acidic and alkaline baths, respectively. The bath composition of Ni–P-based binary and ternary coatings is represented in Table 1. The Ni–P coatings from acidic baths can be considered as high P (10–14% P), medium P (6–9% P) and low P (3–5% P) [17]. The medium

264

A. Mukhopadhyay et al.

phosphorus coatings are the most popular variants for corrosion and wear protection. The Ni–P coatings obtained from alkaline bath on the other hand have lower adhesion to steel and are difficult to process on substrates such as aluminium. On the other hand, ENB coatings may be also obtained from acidic and alkaline baths. The ENB coatings from acidic bath may be obtained from dimethyl amino borane (DMAB) as reducing agent with a lower bath temperature of 50–60 °C. The coating deposition rate is fairly high and produces coatings with high melting point [16–18]. The alkaline bath ENB coatings are normally found from sodium borohydride as reducing agent. Similar to Ni–P coatings, ENB coatings obtained from alkaline baths may be also categorized as low, mid and high B coatings [51–55]. Different poly-alloys may be also deposited from alkaline baths and the compositions are depicted in Table 2. Therefore, the EN coatings may be deposited from both alkaline and acidic baths. The Ni–P coatings obtained from acidic baths are more popular whereas ENB coatings obtained from alkaline baths are more popular. The ENB coatings obtained from both acidic as well as alkaline baths have high as-deposited hardness with respect to Ni–P coatings and are more suitable for tribological applications [16–18].

3 Coating Characteristics The EN coatings may be characterized in terms of their surface appearance, constituents and structure. A globular morphology is detected for both Ni–P and ENB coatings. Figure 3 shows Ni–P coatings after deposition. The coatings appear greyish and free of porosities. In some cases, bright particles and overgrowths of Ni were seen for EN coating with W [51, 55]. The EN coatings with Cu appear as aggregates and clusters of nodules [51, 55]. The surface of ENB based coatings resemble a typical cauliflower [53]. On observing their cross-sections, it was seen that there are columnar growths, which act as lubricant retainers in adhesive wear situations [54]. Furthermore, inherent selflubricating capability of ENB-based coatings was attributed to these cauliflower-like growths [53]. Furthermore, the columnar growths decrease actual area of contact. Interestingly, for EN coatings, the nodular sizes tend to increase on heat treatment as a sign of occurrence of crystallization. The ENB-based coatings are depicted in Fig. 4 similar to morphology resembles a typical cauliflower especially for ENB-Mo coatings. The coating structure is an important aspect in determining its mechanical properties and tribological behaviour. Generally, the crystal structure is determined from X-ray diffraction (XRD). Immediately after deposition and without any treatment, a broad peak is observed indicating amorphous phase. For Ni–P coatings, low P coatings are a combination of amorphous and nano-crystalline. High P coatings are amorphous [51, 55]. Similarly, the crystallinity of ENB coatings in as-deposited is dependent on B content [53]. The high B coatings are entirely amorphous and the crystallinity increases with a decrease in B content [52]. This is due to the fact

20 15

×

×

20

30

Ni–P–W

Ni–P–Cu Coating time 3h

Bath temperature ( °C) 80 ± 2 90 ± 2 85 ± 2

pH

4.5

7–8

9.5

Ni–P–W

Ni–P–Cu

15

×

30

×

× 35

Ammonium sulphate

Sodium citrate

Coatings

×

×

12

Sodium succinate

Ni–P

Coating deposition parameter

10

30

30

Sodium hypophosphite

Ni–P

Nickel chloride

Nickel sulphate

Coatings

Coating bath formulation (Composition in g/l)

Table 1 Bath composition of Ni–P coatings obtained from alkaline and acidic baths

200 ml

Bath volume

×

5

×

Lactic acid

×

2.5

×

Sodium tungstate

0.5

×

×

Copper sulphate

Tribological Characterization of Electroless Nickel Coatings at High … 265

266 Table 2 Bath composition of ENB-based coatings obtained from alkaline baths

A. Mukhopadhyay et al.

Composition

Values (g/L) Ni–B

Ni–B–W

Ni–B–Mo

Nickel chloride

20

20

20

Sodium borohydride

0.8

0.8

0.8

Ethylenediamine

59

59

59

Lead nitrate

0.0145

0.0145

0.0145

Sodium hydroxide

40

40

40

Sodium tungstate

×

25

×

Sodium molybdate

×

×

25

Coating deposition conditions Deposition condition

Values

pH

12.5

Temperature

90 ± 2 °C

Time of coating

4 h (2 + 2 double bath)

Bath volume

200 ml

Fig. 3 Surface morphology of as-deposited. a Ni–P, b Ni–W–P and c Ni–Cu–P coatings [55]

that higher B content prevents nucleation of Ni. Thus, higher B content leads to ENB coatings exhibiting amorphous nature. Furthermore, the phase transformation temperatures are also dependent on P or B content in EN coatings. For example, high B coatings crystallize at a higher temperature compared to low or mid B coatings

Tribological Characterization of Electroless Nickel Coatings at High …

267

Fig. 4 Morphological images of ENB-based coatings [53]

[52]. Furthermore, the crystallization temperature is also raised on addition of W or Mo in the EN coatings [53]. A typical XRD of Ni–P-based coatings is depicted in Fig. 5. The Ni–P or Ni–P–Cu coatings are amorphous whereas for the Ni–P–W coatings, they are seen to be mixed amorphous and nano-crystalline [55]. The as-deposited ENB coatings’ structure is represented in Fig. 6. They are amorphous. This is manifested as a broad dome in the XRD peak representing disorder in crystal arrangement [53]. The coating structure of ENB coatings is dependent on B segregation as well as the content of the third element such as W or Mo [53]. EN coatings show crystalline structure post-thermal treatments. Crystalline Ni and its phosphides were seen when Ni–P coatings were heat treated while borides were precipitated on heat treatment of ENB coatings. This in turn increased hardness and improved the tribological behaviour.

268

A. Mukhopadhyay et al.

Fig. 5 Structure of as-deposited. a Ni–P, b Ni–P–W and c Ni–P–Cu coatings [55]

4 High-Temperature Tribological Behaviour of EN Coatings Recent studies have shown promising tribological behaviour of EN coatings at high temperature. High-temperature tribological behaviour is dominated by various mechanisms such as abrasive wear, adhesive wear, fracture, oxidation, formation of oxide glazes etc. The tribological behaviour of EN coatings is discussed subsequently.

4.1 Performance of Ni–P Coatings at High Temperatures The Ni-10% P coatings were deposited, and heat treatment was carried out at 600 °C [56]. The as-deposited coatings were found to show improved tribological behaviour at high temperature (550 °C) while heat-treated ones at room temperature (RT). The as-deposited coatings underwent phase transitions due to in-situ heat treatment. The heat-treated coatings’ poor tribological performance was attributed to grain coarsening at the high temperature and crack propagation by Orowan mechanism. The asdeposited coatings showed adhesive wear at RT sliding wear tests with torn patches.

Tribological Characterization of Electroless Nickel Coatings at High …

269

Fig. 6 Coating structure of ENB coatings in as-deposited state [53]

On other hand, heat-treated coatings showed abrasive wear at room temperature. While at high temperature, as-deposited coatings hardness increased post wear test. It was finally concluded that an optimal grain size exists for Ni–P coatings, which allows enough plastic deformation slowing down the crack growth and relax stress concentration. The already crystalline and heat-treated coatings undergo further grain growth and grain coarsening due to high-temperature sliding conditions. The effect of variation of P content with 4, 5, 9 and 12% P on the tribological behaviour at 250 °C was investigated by Ghaderi et al. [57]. All the coatings were heat-treated 400 °C under argon gas for 1 h. The heat-treated coatings were crystalline and also had enhanced hardness compared to as-deposited ones. With rise in P, the wear mass loss declined and highest wear resistance was concluded for 12% P coatings. Formation of oxide layers was also observed using energy dispersive X-ray spectroscopy (EDS). The coating microhardness post wear test for 9% P coatings increased by ~10 Vicker’s hardness due to further crystallization of the coatings. But for low P coatings, a significant variation in microhardness was not detected. The Ni–P coatings with high P were investigated at 100–500 °C [58]. The load and velocity were also varied. Both as-deposited and heat-treated coatings (400 °C for 1 h) were investigated. The COF and wear rate rise with rise in load. This trend was followed at all the test temperatures investigated. On the other hand, wear rate and COF decreased with rise in velocity as shown in Fig. 7. At high temperatures,

270

A. Mukhopadhyay et al.

Fig. 7 COF variation at high temperature for Ni–P in as-deposited state with a load and b speed [58]

especially near phase transformation temperature of Ni–P coatings, the as-deposited variants exhibited enhanced tribological behaviour. This was due to in-situ heat treatment of the coatings and undergoing crystallization. Wear mode was dominated by mixed adhesion and abrasion as well as tribo-oxidation. The Ni–P–B coatings’ tribological behaviour was investigated at room temperature to 500 °C [59]. The Ni–P–B coatings were also heat treated at 400 °C for 1 h. The hardness of as-deposited and heat-treated coatings were larger than Ni–P or ENB coatings. Comparison of wear rate of as-deposited and heat-treated coatings with Ni–P deposits shows enhanced wear resistance of the former than the latter in Fig. 8. Furthermore, here again wear rate was lower at 300 °C with respect to 100 or 500 °C, which was attributed to the sliding of coatings nearer to their phase transformation temperature. The phase transition investigation using X-ray diffraction (XRD) post-wear tests also revealed precipitation of hard phosphide phases and borides. Electroless Ni–P–W coatings with high as-deposited hardness were obtained by Kundu et al. [60]. Heat treatment at 400 °C for 1 h was done. Addition of W enhances thermal stability and crystallinity of coatings. Both as-deposited and heat-treated coatings were exposed to RT and high-temperature tests (100, 300 and 500 °C). The heat-treated coatings show lower wear rate than as-deposited ones at all test temperatures as shown in Fig. 9. This was attributed to creation of oxide layers and coating crystallization during high-temperature tests. Interestingly, a 46% rise in (compared to as-deposited films) microhardness of the coatings was observed after sliding wear tests at 500 °C. Similarly, there was a 12.8% rise in microhardness after the coatings underwent sliding at 300 °C. The rise in hardness of heat-treated coatings was marginal post-sliding wear at all temperatures with respect to as-deposited Ni– P–W coatings.

Tribological Characterization of Electroless Nickel Coatings at High …

271

Fig. 8 The wear rate of Ni–P and Ni–P–B coatings at different temperatures in a as-deposited and b heat-treated state [59]

Fig. 9 The wear rate of Ni–P–W coatings at different temperatures in a as-deposited and b heattreated state [60]

Composite coatings with Ni–P matrix can also be a suitable alternative at high temperature. The composite coatings enhance mechanical and tribological behaviour by dispersion strengthening of coating matrix. The Ni–P–BN (h) coatings were deposited on 310L stainless steel [61]. The tribo-behaviour was studied at 25–400 °C. The wear rate and COF rise with rise in temperature. The coatings were categorized by gross plastic deformation at high temperature. Adhesion and fracture were dominant at high-temperature sliding and coating material transfer to the ball. Finally, it was concluded that the high-temperature tribological response was dependent upon the Ni matrix and not on BN (h) particles.

272

A. Mukhopadhyay et al.

Fig. 10 Wear rate of as-deposited and heat-treated Ni–P–BN(h) at a RT and b 300 °C [62]

In another study, Ni–P–BN(h) heat treated at 400 °C was investigated at RT300 °C [62]. Due to high hardness and less adhesive wear, heat-treated coatings exhibited enhanced wear resistance at RT as represented in Fig. 10. The hardness of as-deposited coatings increased by 40% post-sliding wear at 300 °C. Furthermore, wear resistance changed negligibly post-heat treatment at 300 °C test temperature. Incorporation of Al2 O3 leads to an overall enhancement in hardness and hightemperature wear resistance of Ni–P coatings [63]. High-temperature wear was characterized by microstructural changes and improvements associated with formation of oxide layers at 500 °C. The Ni–P–SiC coatings were deposited on AISI 1020 steel and tribological behaviour was investigated at RT and high temperature of 100 °C and 300 °C [64]. Heat treatment caused an increase in wear resistance by 135% (with respect to asdeposited coatings) at RT. The higher particle size to coating thickness ratio aggravated the wear rate at high temperature. At 100 and 300 °C, wear rate increased by 23 and 116 times, respectively, with respect to RT tests. Franco et al. [65] investigated composite Ni–P–SiC coatings at elevated test temperature of 200 °C. As-deposited and 400 °C heat treated coatings were evaluated. The reinforcing SiC particles were varied from 0 to 42%. The specific wear rate decreases as the reinforcing particles increase as shown in Fig. 11. Heat treatment also enhances the wear resistance. Investigation of sub-surface of coatings after wear test was also carried out. It was seen that micro-cracks were developed in the particle-free coating. While the inclusion of SiC reduced the probability of lengthening of the cracks. Addition of self-lubricating particles in Ni–P coatings may enhance wear resistance and decrease COF at high temperatures. The Ni–P–Ag coatings were developed on medium carbon steel specimens [66]. The as-deposited and heat-treated hardness of Ni–P–Ag coatings were lesser than Ni–P coating. High-temperature tribological tests at 500 °C revealed that heat treated Ni–P–Ag coatings had lesser wear rate than Ni–P coating. At RT, the COF of Ni–P–Ag coating was found to be 0.32 and 0.37 at 500 °C. This was lower compared to Ni–P coating. The enhanced tribological behaviour at high temperature was attributed to entrapment of Ag particles

Tribological Characterization of Electroless Nickel Coatings at High …

273

Fig. 11 Specific wear rate of Ni–P–SiC coatings (A = 0%, B = 14%, C = 24% and F = 42% SiC) [65]

and their nucleation at the surface acting as self-lubricants. The Ag particles also decrease the fluctuations in COF at high temperature. Addition of alumina also leads to enhanced tribological behaviour of Ni–P–Ag coating and there was a ‘chameleon’ like behaviour due to creation of self-lubricating film [67]. The hybrid Ni–P–Ag– Al2 O3 coating provided an optimum combination of enhanced high-temperature tribological behaviour and hardness. Self-lubricating MoS2 particles were incorporated in Ni–P coatings and deposited on AISI 1045 specimens [68]. The coated specimens were heat treated at 300 °C for 2 h. Tribological investigation was done by rising temperature from RT to 600 °C by progressively increasing temperature by 100 °C. The COF was high at RT (0.78) and decreased as the test temperature increased with lowest value of 0.27 at 500 °C. The wear rate firstly increased with a rise in temperature up to 200 °C then started falling with the lowest at 400 °C and then again started increasing up to 600 °C as shown in Fig. 12. A dense and continuous oxide film decreased the COF or wear rate at elevated temperature. The wear mechanism was mild scuffing. Fig. 12 Variation of wear rate of Ni–P–MoS2 coatings at high temperatures [68]

274

A. Mukhopadhyay et al.

The Ni–P coatings with inclusion of MoS2 and CaF2 were deposited and heat treated at 300 °C for 2 h [69]. High-temperature tribological tests were carried out at RT to 570 °C. The friction and wear behaviour are depicted in Fig. 13. The COF declines with a rise in temperature. The wear rate displays a similar trend but increases 570 °C. At 200 °C, the surface was characterized by discontinuous oxide films and micro-scuffing. At 390 °C, the surface was smoother and with a compact film. This consequences in a decrease in COF and wear rate. At 570 °C, surface was fully covered by a compact film along with micro-ploughing and micro-scuffing. The wear rate rises due to a decrease in strength of coating matrix. The coatings also exhibited a stable COF during entire sliding period at RT and high-temperature tribological tests. The self-lubrication at high temperature was due to synergistic effects of the oxides of Ni and Mo, MoS2 , CaF2 , sulphates, phosphates and CaMoO4 , which provides a lubricating effect due to formation of a low shear film at the interface of sliding. Fig. 13 Variation of a COF and b wear rate of Ni–P–MoS2 –CaF2 coatings at high temperatures [69]

Tribological Characterization of Electroless Nickel Coatings at High …

275

4.2 Performance of ENB Coatings at High Temperatures Recent studies have also shown potential of ENB-based coatings at high temperatures. As-deposited ENB coatings in mid-B range were deposited on AISI 1040 steel, and the tribological behaviour was investigated at RT, 100, 300 and 500 °C [70]. The wear rate rises from RT to 100 °C (Fig. 14). Then, wear rate decreased at 300 °C. This was attributed to the existence of phase transition during high-temperature sliding. The phenomenon was supported by XRD results of the coatings post-wear test. At high temperature of 500 °C, there was depletion of B at the surface and possibility of occurrence of the inter-diffusion phenomenon (diffusion of B from the surface towards the substrate at high temperature) was also noted. The COF also decreased at 500 °C. An important phenomenon observed for the coatings was the effect of bi-layered coatings as shown in Fig. 15. The upper layer was deformed and an oxide layer was formed. This oxide layer was supported by a toughened bottom layer. This led to an enhanced tribological behaviour at high temperature. A comparative study of as-deposited ENB binary and ternary alloy coatings at high temperature was done by Mukhopadhyay et al. [71]. The Ni–B–W coatings showed the highest wear resistance as shown in Fig. 16. Ni–B–Mo coatings offered lowered COF. At 100 °C, coatings undergo severe grinding by strain-hardened debris. The debris cut the coating matrix and produce deep grooves. This results in a rise in COF or wear rate at 100 °C. Phase transformation at 500 °C with boride precipitation was detected for all three coating variants in XRD results of worn surface. The coatings

Fig. 14 Wear rates of as-deposited ENB coating at different temperatures [70]

276

A. Mukhopadhyay et al.

Fig. 15 The bi-layered ENB as-deposited coating undergoing wear test at 300 °C [70]

were amorphous before the sliding wear test. While after wear test at 500 °C, XRD of the worn surface revealed coating crystallization with precipitation of Ni, Ni2 B and Ni3 B. The effect of heat treatment on tribological behaviour of ENB-based coatings was also investigated [72–74]. The heat treatment was carried out at 350, 400 and 450 °C for 1 h. It was concluded for the coatings that high heat treatment temperature and high sliding temperature result in grain coarsening and rise in wear rate. Optimal tribological behaviour at high temperature was concluded for ENB and Ni–B–W coatings for a heat treatment temperature of 350 °C for 1 h while for Ni–B–Mo coatings, optimal heat treatment temperature was 450 °C for 1 h. The variation of wear rate can be seen for Ni–B–W coatings in Fig. 17. The wear rate clearly rises with rise in heat treatment at 100 °C. While heat treatment did not cause a noticeable effect at 300 or 500 °C operating temperature. This also reflected the enhanced thermal stability of coatings on addition of W. A similar behaviour was also seen for Ni–B–Mo coatings [74]. A significant change in COF or the wear rate was not detected with rise in heat treatment temperature. Pal et al. [75] investigated the tribological behaviour of ENB coatings for various heat treatment conditions. Completely crystalline ENB coatings were obtained by heat treatment at 385 °C for 4 h. They were investigated at high-temperature tribological tests as shown in Fig. 18. At both 1 N and 5 N loads, COF or wear rate increased with test temperature. Though there was no significant effect on COF, wear rate was affected profoundly. The worn surface was characterized by breakage of oxide film at high temperatures with a dominating effect of plastic ratcheting. The flash temperature was found to increase to almost 1010 at 450 °C test temperature. The inert counterface was supposedly the reason for such high flash temperature occurring at the sliding interface. The effect of load, speed and temperature was also investigated for crystalline ENB, Ni–B–W and Ni–B–Mo coatings by Mukhopadhyay et al. [76–79]. Within 10–50 N, the load was varied. Whereas speed range was 0.25–0.42 m/s. The test

Tribological Characterization of Electroless Nickel Coatings at High …

277

Fig. 16 ENB coatings undergoing wear at a RT and b elevated temperatures [71]

temperature was varied between ambient temperature and 500 C. At 10 N load and ambient temperature, the mass loss was almost steady with an increase in sliding speed [79]. Whereas as the load was increased to 50 N, the mass loss of ENB coatings showed a steep rise. The COF also showed a similar nature. At 100 °C, the wear rate and COF both increased with an increase in load and speed for all the three coating variants. This was attributed to grinding action of strain-hardened wear particles. On the other hand, at 300 °C, there was a curvature in the variation of wear rate and COF with an increase in sliding speed at all loads. Formation of oxide glazes was reported at 500 °C leading to a lowering of wear rate. At all temperatures and load, Ni–B–W coatings show higher wear resistance. At 100 and 300 °C, ENB coatings exhibit an overall lower COF at the aforesaid constraints, i.e., load and sliding speed. At 100 °C, overall COF of Ni–B–Mo coatings was lower [79].

278

A. Mukhopadhyay et al.

Fig. 17 Effect of heat treatment on wear behaviour of Ni–B–W coatings at high temperatures [73]

Recent developments in ENB coatings include the elimination of heavy metalbased stabilizers from coating bath. In this regard, ENB coatings obtained from a stabilizer-free bath were investigated at high temperatures [80]. The results were quite similar to lead stabilized Ni–B variants. At 100 °C, wear rate was higher with respect to 300 °C. The initiation of phase transformation was also reported. But one of the interesting findings was the formation of a mechanically mixed oxide layer with Fe, which results in an enhanced tribological behaviour comparable to that of lead-stabilized coatings. It was concluded that the coating adhesion was poor for the lead-free coatings, thereby the coatings were delaminated and got mechanically mixed with Fe from substrate.

5 Conclusions and Future Directions With progress of time, industrial demands have become stringent and mechanical components are subjected to harsh environment. There are several coatings methods for surface engineering of such components. But EN coating is a novel technique that can be used to coat complex geometry substrates. Recently, in the last 5 years, a significant progress has been made where the high-temperature tribological behaviour has been reported. The Ni–P coatings perform well at elevated temperature. There exists a critical grain size which arrests cracks and its propagation. Apart from the binary alloy, ternary coatings were also investigated. A significant finding of all studies was improved tribological behaviour of EN coatings near to their phase transformation temperature. This result is also applicable to the Ni–B-based binary and poly-alloys. The high-test temperature and frictional heating may result in the flash temperature rising to almost 1010 °C. This essentially causes microstructural changes and

Tribological Characterization of Electroless Nickel Coatings at High …

279

Fig. 18 The a COF and b wear rate of completely crystalline ENB coatings at high temperatures [75]

280

A. Mukhopadhyay et al.

phase transformations. Therefore, it becomes quite critical to select coating deposition parameters, which would result in coating with appropriate P and B content, which finally would result in achieving optimal grain size during sliding at harsh conditions. This is a challenge and may be addressed in future research works. On the other hand, composite coatings were also investigated. The composite coatings also improve mechanical properties by dispersion strengthening. But at high temperatures, the sustainability essentially depends on the strength of the coating matrix. Furthermore, in a recent development, mechanically mixed layers of coating and substrate and formation of the oxide layer resulted in a significant improvement in wear resistance. Hence, this aspect may be also further investigated with in-depth studies of sub-surface layers of wear track and the oxide layers. Acknowledgements The authors gratefully acknowledge the support of DST-PURSE, PHASE II program of Jadavpur University. The first author also acknowledges the funding of DST-SERB Core Research Grant (File Number: CRG/2022/001441).

References 1. Muthaiah, V.S., Indrakumar, S., Suwas, S., Chatterjee, K.: Surface engineering of additively manufactured titanium alloys for enhanced clinical performance of biomedical implants: a review of recent developments. Bioprinting 25, e00180 (2022). https://doi.org/10.1016/j.bpr int.2021.e00180 2. Yang, Y.W., Cristino, V.A.M., Tam, L.M., Lo, K.H., Kwok, C.T.: Laser surface alloying of copper with Cr/Ti/CNT for enhancing surface properties. J. Mater. Res. Technol. 17, 560–573 (2022). https://doi.org/10.1016/j.jmrt.2021.12.129 3. Dan, A., Bijalwan, P.K., Pathak, A.S., Bhagat, A.N.: A review on physical vapor depositionbased metallic coatings on steel as an alternative to conventional galvanized coatings. J. Coat. Technol. Res. 19(2), 403–438 (2022). https://doi.org/10.1007/s11998-021-00564-z 4. Vengesa, Y., Fattah-alhosseini, A., Elmkhah, H., Imantalab, O.: Influence of post-deposition annealing temperature on morphological, mechanical and electrochemical properties of CrN/ CrAlN multilayer coating deposited by cathodic arc evaporation-physical vapor deposition process. Surf. Coat. Technol. 432, 128090 (2022). https://doi.org/10.1016/j.surfcoat.2022. 128090 5. Arnault, J.C., Saada, S., Ralchenko, V.: Chemical vapor deposition single-crystal diamond: a review. Phys. Status Solidi (RRL). Rapid Res. Lett. 16(1), 2100354 (2022). https://doi.org/10. 1002/pssr.202100354 6. Xu, X., Zhong, T., Zuo, N., Li, Z., Li, D., Pi, L., Zhou, X.: High-TC two-dimensional ferroelectric CuCrS2 grown via chemical vapor deposition. ACS Nano 16(5), 8141–8149 (2022). https://doi.org/10.1021/acsnano.2c01470 7. Govande, A.R., Chandak, A., Sunil, B.R., Dumpala, R.: Carbide-based thermal spray coatings: a review on performance characteristics and post-treatment. Int. J. Refractory Metals Hard Mater. 103, 105772 (2022). https://doi.org/10.1016/j.ijrmhm.2021.105772 8. Prashar, G., Vasudev, H.: A review on the influence of process parameters and heat treatment on the corrosion performance of Ni-based thermal spray coatings. Surf. Rev. Lett. 29(01), 2230001 (2022). https://doi.org/10.1142/S0218625X22300015 9. Li, Y., Cai, X., Zhang, G., Xu, C., Guo, W., An, M.: Optimization of electrodeposition nanocrytalline Ni–Fe alloy coatings for the replacement of Ni coatings. J. Alloys Compd. 903, 163761 (2022). https://doi.org/10.1016/j.jallcom.2022.163761

Tribological Characterization of Electroless Nickel Coatings at High …

281

10. Mukhopadhyay, A., Sahoo, S.: A grey-fuzzy based approach for the optimization of corrosion resistance of rebars coated with ternary electroless nickel coatings. J. Soft Comput. Civil Eng. 6(2), 107–127 (2022). https://doi.org/10.22115/SCCE.2022.326903.1401 11. Butola, R., Pandit, D., Pratap, C., Chandra, P.: Two decades of friction stir processing—A review of advancements in composite fabrication. J. Adhes. Sci. Technol. 36(8), 795–832 (2022). https://doi.org/10.1080/01694243.2021.1938835 12. Farajollahi, R., Aval, H.J., Jamaati, R., Hájovská, Z., Nagy, Š: Effects of pre-and post-friction surfacing heat treatment on microstructure and corrosion behavior of nickel-aluminide reinforced Al–Cu–Mg alloy. J. Alloys Compd. 906, 164211 (2022). https://doi.org/10.1016/j.jal lcom.2022.164211 13. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: High temperature tribology of surface coatings. Recent Adv. Layer. Mater. Struct. 25–48 (2021). https://doi.org/10.1007/978-981-33-455 0-8_2 14. Krishnan, K.H., John, S., Srinivasan, K.N., Praveen, J., Ganesan, M., Kavimani, P.M.: An overall aspect of electroless Ni–P depositions—A review article. Metall. Mater. Trans. A 37, 1917–1926 (2006). https://doi.org/10.1007/s11661-006-0134-7 15. Lee, K.H., Chang, D., Kwon, S.C.: Properties of electrodeposited nanocrystalline Ni–B alloy films. Electrochim. Acta 50(23), 4538–4543 (2005). https://doi.org/10.1016/j.electacta.2004. 03.067 16. Loto, C.A.: Electroless nickel plating—A review. Silicon 8, 177–186 (2016). https://doi.org/ 10.1007/s12633-015-9367-7 17. Sudagar, J., Lian, J., Sha, W.: Electroless nickel, alloy, composite and nano coatings—A critical review. J. Alloys Compd. 571, 183–204 (2013). https://doi.org/10.1016/j.jallcom.2013.03.107 18. Sahoo, P., Das, S.K.: Tribology of electroless nickel coatings—A review. Mater. Des. 32(4), 1760–1775 (2011). https://doi.org/10.1016/j.matdes.2010.11.013 19. Barati, Q., Hadavi, S.M.M.: Electroless Ni–B and composite coatings: a critical review on formation mechanism, properties, applications and future trends. Surf. Interfaces 21, 100702 (2020). https://doi.org/10.1016/j.surfin.2020.100702 20. Chintada, V.B., Koona, R., Raju Bahubalendruni, M.V.A.: State of art review on nickel-based electroless coatings and materials. J. Bio Tribo-Corros. 7(4), 134 (2021). https://doi.org/10. 1007/s40735-021-00568-7 21. Kundu, S., Das, S.K., Sahoo, P.: Properties of electroless nickel at elevated temperature-a review. Procedia Eng. 97, 1698–1706 (2014). https://doi.org/10.1016/j.proeng.2014.12.321 22. Vitry, V., Hastir, J., Mégret, A., Yazdani, S., Yunacti, M., Bonin, L.: Recent advances in electroless nickel-boron coatings. Surf. Coat. Technol. 429, 127937 (2022). https://doi.org/10.1016/ j.surfcoat.2021.127937 23. Agarwala, R.C., Agarwala, V., Sharma, R.: Electroless Ni–P based nanocoating technology— A review. Synth. React. Inorg. Met. Org. Nano Met. Chem. 36(6), 493–515 (2006). https://doi. org/10.1080/15533170600596030 24. Ghosh, S.: Electroless copper deposition: a critical review. Thin Solid Films 669, 641–658 (2019). https://doi.org/10.1016/j.tsf.2018.11.016 25. Barrera, G., Scaglione, F., Celegato, F., Coïsson, M., Tiberto, P., Rizzi, P.: Electroless cobalt deposition on dealloyed nanoporous gold substrate: a versatile technique to control morphological and magnetic properties. Nanomaterials 13(3), 494 (2023). https://doi.org/10.3390/nan o13030494 26. Liu, Y.Y., Yu, J., Huang, H., Xu, B.H., Liu, X.L., Gao, Y., Dong, X.L.: Synthesis and tribological behavior of electroless Ni–P–WC nanocomposite coatings. Surf. Coat. Technol. 201(16–17), 7246–7251 (2007). https://doi.org/10.1016/j.surfcoat.2007.01.035 27. Sahoo, P.: Wear behaviour of electroless Ni–P coatings and optimization of process parameters using Taguchi method. Mater. Des. 30(4), 1341–1349 (2009). https://doi.org/10.1016/j.matdes. 2008.06.031 28. Sahoo, P., Pal, S.K.: Tribological performance optimization of electroless Ni–P coatings using the Taguchi method and grey relational analysis. Tribol. Lett. 28, 191–201 (2007). https://doi. org/10.1007/s11249-007-9264-3

282

A. Mukhopadhyay et al.

29. Das, S.K., Sahoo, P.: Tribological characteristics of electroless Ni–B coating and optimization of coating parameters using Taguchi based grey relational analysis. Mater. Des. 32(4), 2228– 2238 (2011). https://doi.org/10.1016/j.matdes.2010.11.028 30. Miri, T., Seifzadeh, D., Rajabalizadeh, Z.: Electroless Ni–B–MMT nanocomposite on magnesium alloy. Surf. Eng. 37(9), 1194–1205 (2021). https://doi.org/10.1080/02670844.2021.195 9287 31. Shozib, I.A., Ahmad, A., Abdul-Rani, A.M., Beheshti, M., Aliyu, A.A.A.: A review on the corrosion resistance of electroless Ni–P based composite coatings and electrochemical corrosion testing methods. Corros. Rev. 40(1), 1–37 (2022). https://doi.org/10.1515/corrrev-20200091 32. Li, L., Wang, J., Xiao, J., Yan, J., Fan, H., Sun, L., Tang, Z.: Time-dependent corrosion behavior of electroless Ni–P coating in H2S/Cl—Environment. Int. J. Hydrog. Energy 46(21), 11849– 11864 (2021). https://doi.org/10.1016/j.ijhydene.2021.01.053 33. Taha-Tijerina, J., Aviña-Camarena, K., Torres-Sánchez, R., Dominguez-Ríos, C., MaldonadoCortes, D.: Tribological evaluation of electroless Ni–B coating on metal-working tool steel. Int. J. Adv. Manuf. Technol. 103, 1959–1964 (2019). https://doi.org/10.1007/s00170-019-036 84-4 34. Yazdani, S., Vitry, V.: RSM models approach for optimization of the mechanical properties of electroless Ni–B–nanodiamond coating: an experimental and molecular dynamic simulation study. Surf. Coat. Technol. 452, 129133 (2023). https://doi.org/10.1016/j.surfcoat.2022.129133 35. Mukhopadhyay, A., Sahoo, S.: Improving corrosion resistance of reinforcement steel rebars exposed to sulphate attack by the use of electroless nickel coatings. Eur. J. Environ. Civ. Eng. 26(11), 5180–5195 (2022). https://doi.org/10.1080/19648189.2021.1886177 36. Roy, S., Mishra, B.M., Bose, G.K.: Characterization of Ni–P based poly-alloy and composite coatings involving nanoindentation and nanoscratch tests. Mater. Today Commun. 29, 102991 (2021). https://doi.org/10.1016/j.mtcomm.2021.102991 37. Yildiz, R.A., Genel, K., Gulmez, T.: Effect of electroless Ni–B and Ni–W–B coatings on the corrosion-fatigue behaviour of 7075 Al alloy. Int. J. Fatigue 144, 106040 (2021). https://doi. org/10.1016/j.ijfatigue.2020.106040 38. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Corrosion resistance of electroless Ni–B–W– Mo coatings using electrochemical impedance spectroscopy. Port. Electrochim. Acta 37(3), 193–203 (2019) 39. Uppada, S., Koona, R., Chintada, V. B., Koutavarapu, R.: Influence of heat treatment on crystal structure, microhardness and corrosion resistance of bilayer electroless Ni–P–SiC/Ni–P–Al2 O3 coatings. Silicon 1–11 (2022). https://doi.org/10.1007/s12633-022-02042-6 40. León-Patiño, C.A., García-Guerra, J., Aguilar-Reyes, E.A.: Tribological characterization of heat-treated Ni–P and Ni–P–Al2 O3 composite coatings by reciprocating sliding tests. Wear 426, 330–340 (2019). https://doi.org/10.1016/j.wear.2019.02.015 41. Gunduz, H., Karslioglu, R., Ozturk, F.: Microstructural evaluation of graphene-reinforced nickel matrix Ni–P–Gr coating on Ti–6Al–4V alloy by the electroless coating method. Coatings 12(12), 1827 (2022). https://doi.org/10.3390/coatings12121827 42. Chintada, V.B., Gurugubelli, T.R., Koutavarapu, R.: The impact of surfactants on the properties of electroless Ni–P–SiC coatings. Mater. Chem. Phys. 291, 126682 (2022). https://doi.org/10. 1016/j.matchemphys.2022.126682 43. Georgiza, E., Gouda, V., Vassiliou, P.: Production and properties of composite electroless Ni– B–SiC coatings. Surf. Coat. Technol. 325, 46–51 (2017). https://doi.org/10.1016/j.surfcoat. 2017.06.019 44. Ghaderi, M., Rezagholizadeh, M., Heidary, A., Monirvaghefi, S.M.: The effect of Al2 O3 nanoparticles on tribological and corrosion behavior of electroless Ni–B–Al2 O3 composite coating. Prot. Met. Phys. Chem. Surf. 52, 854–858 (2016). https://doi.org/10.1134/S20702051 16050087 45. Yazdani, S., Mahboubi, F., Tima, R., Sharifahmadian, O.: Effect of carbon nanotube concentration on the corrosion behavior of electroless Ni–B–CNT coating. J. Mater. Eng. Perform. 28, 3446–3459 (2019). https://doi.org/10.1007/s11665-019-04155-3

Tribological Characterization of Electroless Nickel Coatings at High …

283

46. Dervos, C.T., Novakovic, J., Vassiliou, P.: Vacuum heat treatment of electroless Ni–B coatings. Mater. Lett. 58(5), 619–623 (2004). https://doi.org/10.1016/S0167-577X(03)00581-0 47. Davoodi, D., Emami, A.H., Vaghefi, S.M.M., Omidi, M., Bakhsheshi-Rad, H.R.: Deposition of electroless Ni–Cu–P coatings on L80 steel substrates and the effects of coatings thickness and heat treatment on the corrosion resistance. Int. J. Press. Vessel. Piping. 200, 104823 (2022). https://doi.org/10.1016/j.ijpvp.2022.104823 48. Tima, R., Mahboubi, F.: Ability of plasma nitriding to improve tribological behavior of medium and high boron electroless nickel coatings. Tribol. Int. 156, 106822 (2021). https://doi.org/10. 1016/j.triboint.2020.106822 49. Mirhosseini, S.S., Mahboubi, F.: Effect of plasma nitriding on tribological properties of nickelboron-nanodiamond electroless coatings. Surf. Coat. Technol. 435, 128216 (2022). https://doi. org/10.1016/j.surfcoat.2022.128216 50. Yazdani, S., Mahboubi, F.: Comparison between microstructure, wear behavior, and corrosion resistance of plasma-nitrided and vacuum heat-treated electroless Ni–B coating. J. Bio TriboCorros. 5, 1–11 (2019). https://doi.org/10.1007/s40735-019-0264-2 51. Duari, S., Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Tribological performance optimization of electroless nickel coatings under lubricated condition. In: Design and Optimization of Mechanical Engineering Products, pp. 250–280 (2018). https://doi.org/10.4018/978-1-52253401-3.ch013 52. Vitry, V., Bonin, L.: Increase of boron content in electroless nickel-boron coating by modification of plating conditions. Surf. Coat. Technol. 311, 164–171 (2017). https://doi.org/10.1016/ j.surfcoat.2017.01.009 53. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Co-deposition of W and Mo in electroless Ni–B coating and its effect on the surface morphology, structure, and tribological behavior. Proc. Inst. Mech. Eng. Part L 235(1), 149–161 (2021). https://doi.org/10.1177/1464420720956270 54. Vitry, V., Sens, A., Kanta, A.F., Delaunois, F.: Experimental study on the formation and growth of electroless nickel–boron coatings from borohydride-reduced bath on mild steel. Appl. Surf. Sci. 263, 640–647 (2012). https://doi.org/10.1016/j.apsusc.2012.09.126 55. Mukhopadhyay, A., Sahoo, S.: Corrosion protection of reinforcement steel rebars by the application of electroless nickel coatings. Eng. Res. Express 1(1), 015021 (2019). https://doi.org/ 10.1088/2631-8695/ab35f0 56. Masoumi, F., Ghasemi, H.R., Ziaei, A.A., Shahriari, D.: Tribological characterization of electroless Ni–10% P coatings at elevated test temperature under dry conditions. Int. J. Adv. Manuf. Technol. 62, 1063–1070 (2012). https://doi.org/10.1007/s00170-011-3832-2 57. Ghaderi, M., Rezagholizadeh, M., Monir Vaghefi, S.M., Heidary, A.: Investigation of high temperature wear resistance of electroless nickel coating with different contents of phosphorous. Prot. Met. Phys. Chem. Surf. 52, 538–542 (2016). https://doi.org/10.1134/S20702051160 30126 58. Kundu, S., Das, S.K., Sahoo, P.: Tribological behaviour of electroless Ni–P deposits under elevated temperature. Silicon 10, 329–342 (2018). https://doi.org/10.1007/s12633-016-9450-8 59. Kundu, S., Das, S.K., Sahoo, P.: Tribological behavior of autocatalytic Ni–P–B coatings at elevated temperatures. Appl. Phys. A: Solids Surf. 125(8), 520 (2019). https://doi.org/10.1007/ s00339-019-2816-1 60. Kundu, S., Das, S.K., Sahoo, P.: Friction and wear behavior of electroless Ni-PW coating exposed to elevated temperature. Surf. Interfaces 14, 192–207 (2019). https://doi.org/10.1016/ j.surfin.2018.12.007 61. León, O.A., Staia, M.H., Hintermann, H.E.: High temperature wear of an electroless Ni–P– BN (h) composite coating. Surf. Coat. Technol. 163, 578–584 (2003). https://doi.org/10.1016/ S0257-8972(02)00663-1 62. Kiran, K.U.V., Arora, A., Sunil, B.R., Dumpala, R.: Effect of heat treatment on the temperature dependent wear characteristics of electroless Ni–P–BN (h) composite coatings. SN Appl. Sci. 2(6), 1101 (2020). https://doi.org/10.1007/s42452-020-2920-z 63. Kundu, S., Das, S.K., Sahoo, P.: Influence of alumina particles on tribology of autocatalytic Ni–P coatings at high temperature. Int. J. Surf. Eng. Interdiscip. Mater. Sci. (IJSEIMS) 9(1), 1–25 (2021). https://doi.org/10.4018/IJSEIMS.2021010101

284

A. Mukhopadhyay et al.

64. Staia, M.H., Conzoño, A., Cruz, M.R., Roman, A., Lesage, J., Chicot, D., Mesmacque, G.: Wear behaviour of silicon carbide/electroless nickel composite coatings at high temperature. Surf. Eng. 18(4), 265–269 (2002). https://doi.org/10.1179/026708401225005359 65. Franco, M., Sha, W., Aldic, G., Malinov, S., Çimeno˘glu, H.: Effect of reinforcement and heat treatment on elevated temperature sliding of electroless Ni–P/SiC composite coatings. Tribol. Int. 97, 265–271 (2016). https://doi.org/10.1016/j.triboint.2016.01.047 66. Alirezaei, S., Monirvaghefi, S.M., Saatchi, A., Ürgen, M., Motallebzadeh, A.: High temperature tribology of nanocrystalline Ni–P–Ag coating. Surf. Eng. 29(4), 306–311 (2013). https://doi. org/10.1179/1743294412Y.0000000085 67. Alirezaei, S., Monirvaghefi, S.M., Saatchi, A., Ürgen, M., Motallebzadeh, A.: High temperature friction and wear behaviour of Ni–P–Ag–Al2 O3 hybrid nanocomposite coating. Trans. IMF 91(4), 207–213 (2013). https://doi.org/10.1179/0020296713Z.000000000105 68. Li, Z., Wang, J., Lu, J., Meng, J.: Tribological characteristics of electroless Ni–P–MoS2 composite coatings at elevated temperatures. Appl. Surf. Sci. 264, 516–521 (2013). https:// doi.org/10.1016/j.apsusc.2012.10.055 69. Du, S., Li, Z., He, Z., Ding, H., Wang, X., Zhang, Y.: Effect of temperature on the friction and wear behavior of electroless Ni–P–MoS2 –CaF2 self-lubricating composite coatings. Tribol. Int. 128, 197–203 (2018). https://doi.org/10.1016/j.triboint.2018.07.026 70. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Effect of operating temperature on tribological behavior of as-plated Ni–B coating deposited by electroless method. Tribol. Trans. 61(1), 41–52 (2018). https://doi.org/10.1016/j.triboint.2018.07.026 71. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Tribological behavior of sodium borohydride reduced electroless nickel alloy coatings at room and elevated temperatures. Surf. Coat. Technol. 321, 464–476 (2017). https://doi.org/10.1016/j.surfcoat.2017.05.015 72. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Effects of heat treatment on tribological behavior of electroless Ni–B coating at elevated temperatures. Surf. Rev. Lett. 24(01), 1850014 (2017). https://doi.org/10.1142/S0218625X18500142 73. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Tribological behavior of electroless Ni–B–W coating at room and elevated temperatures. Proc. Inst. Mech. Eng. Part J 232(11), 1450–1466 (2018). https://doi.org/10.1177/1350650118755781 74. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Effect of heat treatment on tribological behavior of electroless Ni–B–Mo coatings at different operating temperatures. Silicon 10, 1203–1215 (2018). https://doi.org/10.1007/s12633-017-9594-1 75. Pal, S., Sarkar, R., Jayaram, V.: Characterization of thermal stability and high-temperature tribological behavior of electroless Ni–B coating. Metall. Mater. Trans. A 49, 3217–3236 (2018). https://doi.org/10.1007/s11661-018-4599-y 76. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Friction and wear performance of electroless Ni–B coatings at different operating temperatures. Silicon 11, 721–731 (2019). https://doi.org/ 10.1007/s12633-017-9678-y 77. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Wear and friction characteristics of electroless Ni–B–W coatings at different operating temperatures. Mater. Res. Express 5(2), 026526 (2018). https://doi.org/10.1088/2053-1591/aaae5a 78. Mukhopadhyay, A., Barman, T.K., Sahoo, P.: Tribological characteristics of electroless Ni– B–Mo coatings at different operating temperatures. Surf. Rev. Lett. 26(04), 1850175 (2019). https://doi.org/10.1142/S0218625X18501755 79. Mukhopadhyay, A., Barman, T.K., Sahoo, P., Davim, J.P.: Comparative study of tribological behavior of electroless Ni–B, Ni–B–Mo, and Ni–B–W coatings at room and high temperatures. Lubricants 6(3), 67 (2018). https://doi.org/10.3390/lubricants6030067 80. Agrawal, R., Mukhopadhyay, A.: Development of Ni-B electroless coating from stabilizer free bath and characterization of high temperature tribological behaviour, scratch and corrosion resistance. Surf. Topogr. Metrol. Prop. 10(4), 045028 (2022). https://doi.org/10.1088/2051672X/aca784

Heat Resistant Coatings

Thin Chromium-Based Coatings for Internal Combustion Automobile Engine Valve Protection Zbigniew Grzesik and Grzegorz Smoła

Abstract The chapter presents the latest findings concerning the impact of various liquid fuel types on the course of internal combustion engine valve high temperature corrosion, as well as a method to increase the heat-resistance of these elements by applying innovative chromium-based metallic coatings that are only a few micrometers thick. It also presents experimental results confirming the beneficial effect of adding nickel as an alloying element on the functionality of the thin chromium coatings along with an active element—yttrium. The latter significantly improves the heat-resistance of valve steels covered with the aforementioned protective coatings under thermal shock conditions. Finally, examples of potential application areas for chromium-based thin metal coatings outside the automotive industry are indicated. Keywords Valve steels · Thin coatings · Biofuels · High temperature corrosion · Kinetics · Isothermal conditions · Thermal shocks

1 Introduction Nowadays, high temperature corrosion of metallic materials is a cause of significant difficulties in various branches of modern industry [1, 2]. Due to the high rank of this problem, several methods have been elaborated to protect constructive materials against degradation at high temperatures. One of them is the application of protective coatings [1, 3–7]. Thermal barrier coatings (TBCs) are treated as some of the most promising because they exhibit extraordinary protective properties in high temperature aggressive environments [8–14]. However, the relatively high thickness (usually 100 μm–2 mm) of such TBC coatings limits their use in the protection of movable machine parts, due to the danger of their destruction during work. Deposition of TBC coatings on movable well-matched parts requires their redesigning in order to give them smaller dimensions. Unfortunately, it is a rather expensive and time-consuming Z. Grzesik (B) · G. Smoła Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Pakseresht and K. K. Amirtharaj Mosas (eds.), Coatings for High-Temperature Environments, Engineering Materials, https://doi.org/10.1007/978-3-031-45534-6_11

287

288

Z. Grzesik and G. Smoła

process that involves changing the manufacturing method of the parts mentioned above. Consequently, many operating elements are entirely unprotected by coatings against the attack of aggressive gasses at high temperatures. Such a situation occurs, e.g., in the case of engine valves applied in lower and middle-class automobiles, in spite of the fact that car engine valves operate in very aggressive environments containing corrosive exhaust gases at high temperatures reaching 1173 K. The solution to the presented problem may be to elaborate a new generation of thin, cost efficient coatings based on chromium, which would ensure an acceptable high level of anti-corrosion protection for movable elements without the requirement of changing their dimensions. The results of the first systematic research to develop such coatings were presented in 2015 [15]. It should be emphasized that no previous attempts were made to test the effectiveness of the protection provided by coatings with a thickness of the order of one micrometer. Indeed, attention was drawn to the fact that these coatings were too thin to provide a sufficient chromium reservoir over a long period of time. Taking into account the high corrosion rates at high temperatures, it was expected that the chromium contained in such a thin coating would be completely consumed in a short period of time, about a dozen or so hours. Such a short service life of the coating would make their use of no practical value. Nevertheless, the results of preliminary tests on the oxidation rate of one micrometer thick chromium coated steel [15] showed that the effectiveness of the proposed thin coating is much longer than the life-time of the coating itself. This chapter demonstrates that a one micrometer thick chromium layer deposited on valve steels enhances the growth of corrosion products containing chromium-rich oxides (Cr2 O3 , CrMn2 O4 , Cr1.5 Mn1.5 O4 ) that exhibit excellent protective properties and increase the heat-resistance of the steel substrates. This unexpected phenomenon can be explained by the fact that the thin chromium layer only begins the growth of the previously mentioned oxides, after which this layer rapidly disappears and the scale continues to form as a result of outward chromium diffusion from the metallic core. Subsequently, steels protected by thin coatings demonstrate higher oxidation resistance under isothermal conditions in comparison to particular unmodified steels for a considerably longer duration than the lifetime of the deposited coatings. In the following years, the previously mentioned hypothesis was experimentally verified using selected valve steels currently utilized to manufacture engine valves (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) coated with thin chromium-based coatings. This chapter presents the results of these tests with comparison to analogous data received for the same types of unmodified steels.

Thin Chromium-Based Coatings for Internal Combustion Automobile …

289

2 Operating Conditions of the Internal Combustion Automobile Engine Valves Engine valves operate in particularly aggressive conditions, i.e. relatively high temperatures (up to around 1173 K) and rapid temperature changes, which are called thermal shocks in literature. It is common knowledge that during such shocks, high thermal stresses appear at the scale/substrate interface, being the result of different thermal expansion coefficients of these two materials [2, 16]. Thus, during the start and finish of the automobile engine operation, the scale can crack and spall off, consequently significantly lowering the valve steel’s corrosion resistance [2, 16–18]. Under such a situation, the problem of adhesion between the substrate surface and scale is very important and its solution is very significant to considerably increase the corrosion resistance of discussed steels. In recent years, corrosion problems of engine valves became more severe due to an increase in the maximum operation temperature of automobile engines (from about 973 to 1173 K), as well as application of biofuels. Biofuels in automobile applications are standard petroleum or fuel oil with the addition of bio-components. Fatty Acid Methyl Ester (FAME) additions constitute bio-components for fuel oil and on European Union territory ethanol is added to petroleum. Nowadays, the FAME concentration or ethanol content utilized as a bio-component addition to fuel oil and petrol, respectively, in European Union countries is equal to about 5 wt.%. However, it is expected that in the following decade, this content will increase up to 10 wt.% [19]. It should be noted that biofuels seem to be particularly useful in automotive transport, because they can become alternatives to petroleum and fuel oil [19–22]. It should be noted that rapid exhaustion of crude oil is a reason for the continuous increase of its price. Furthermore, the application of conventional fossil fuels leads to major environmental damages, like global climate changes, ozone layer loss and acid rains [23]. Moreover, the widespread use of biofuels may become a significant renewable energy resource, reducing the concentration of carbon dioxide (CO2 ) and other greenhouse gases in Earth’s atmosphere [19, 21, 24, 25]. They have also great economical promise, assuming a future increase in fossil fuel prices. This aspect is particularly relevant today. Unfortunately, in addition to important benefits, biofuels also exhibit several disadvantages, which currently limit their large scale use in the automotive industry [26–31]. From a purely technical point of view, the main reason for these limitations is due to accelerated corrosion of those car engine parts that operate at the highest temperatures and in environments of aggressive exhaust gasses, which are the products of biofuel combustion, i.e., exhaust engine valves. The problem of engine valves corrosion during their exploitation has not yet been solved, due to its high complexity.

290

Z. Grzesik and G. Smoła

3 Methods for Testing the Oxidation Resistance of Materials Used in the Manufacture of Engine Valves Tests performed on individual components of internal combustion engines— including engine valves—are primarily carried out as a result of automotive concerns. Basically, they use two test methods. The first method consists of placing the complete engine on the engine test house and specifying its operation under the given load conditions. In the second method, the engine is placed in the car, which then is operated under strictly defined field conditions for a given period of time. In both cases, after the tests are completed, the engine is disassembled and the wear of individual parts of the engine is analyzed. Unfortunately, such tests are extremely expensive and do not easily lead to conclusions on the kinetics and corrosion mechanism of engine valves. In addition, little can be said concerning the details of individual research results, as these results are usually treated by automotive companies as confidential, which means that their dissemination is limited. Being active in the high temperature corrosion field, studying metallic materials degradation for years, in our laboratory, we undertook systematic corrosion tests of valve steels, both surface-modified and covered with protective coatings, which were performed in both isothermal conditions and thermal shocks. Corrosion rate studies at a constant temperature were conducted using the gravimetric method. This method consists of measuring changes in the mass of the tested sample, suspended in the reaction zone of the microthermogravimetric setup, filled with reaction gases heated to the desired temperature, as a function of time. On the basis of this type of experiment, conclusions can be drawn regarding not only the corrosion rate, but also the kinetics law, according to which the oxidation process takes place. In general, the smaller the mass increments of the test sample, the greater its resistance to oxidation. Since the rate at which valve steels oxidize is low, mass change measurements of the tested samples must be carried out with high precision. This requires the use of an electronic microbalance that records these changes with a high sensitivity of 10–7 g. This equipment should create conditions in which, on the one hand, a strictly defined composition of the atmosphere flowing through the reaction space is ensured, and on the other hand, the space of the electronic microbalance must be protected against aggressive exposure to a corrosive atmosphere with a protective noble gas (helium or argon). Finally, this device must ensure a constant temperature inside the reaction chamber with ±1 °C precision during long-term measurements carried out for hundreds of hours. Corrosion rate tests under thermal shock conditions are performed by heating a given sample starting from room temperature up to the required temperature with high speed. Next, the sample is maintained at this temperature for a specific duration of time (in the case of our investigations: two hours). Subsequently, the sample is rapidly cooled down to room temperature. The approximated heating time in our experiments was 1 min, whereas the cooling (quenching) time was about two minutes. Next, the subsequent heating cycle is started. After a specific amount of such thermal cycles, the mass of a given sample relative to its surface area is measured and recorded as a

Thin Chromium-Based Coatings for Internal Combustion Automobile …

291

function of thermal cycles. The discussed tests are interpreted in the following way. When the oxidized sample systematically loses its mass during consecutive thermal cycles, this effect results in the scale cracking and spalling off from the sample surface, because of thermal stresses. From these experiments, it can be concluded that if the mass losses as a function of thermal shocks number of the investigated material are higher, then the scale adherence is worse and thereby, so are the scale protective properties. Conversely, when the sample mass is virtually constant as the shock number progresses, it denotes that despite thermal stresses present between the scale and metallic core, cracking and spalling of the scale from the substrate surface is not observed. In this case, scale adherence is very good and thus, it satisfactorily provides protection against high temperature corrosion. The corrosion rate tests, the results of which are presented in this chapter, were performed in real combustion gases and air. Tests performed in air do not reflect the conditions prevailing in the atmosphere of real exhaust gases, however, they allow for preliminary identification of the degree of heat-resistance the materials intended for the production of engine valves have. It turned out that valve steels with higher resistance against oxidation are also characterized by higher corrosion resistance in atmospheres of real exhaust gases. This thesis is fully confirmed by the results presented in the next part of this work. In addition, oxidation studies in air are many times less expensive than the tests carried out in real exhaust gas atmosphere. However, a large part of the corrosion studies under thermal shocks was performed in an atmosphere of real combustion gases, obtained from engines placed in an engine test house. A schematic representation of the equipment used in such conditions is illustrated in Fig. 1. It should be noted that, although the apparatuses for testing the oxidation kinetics in isothermal conditions, as well as under thermal shocks are standard and commonly used in many laboratories around the world, such a unique setup has never been used before in corrosion studies of valve steels. More details on the course of measurements both in isothermal and thermal shock conditions can be found in the literature [32–34].

Fig. 1 Schematic representation of the equipment used for thermal shock experiments conducted in an atmosphere of real combustion gases

292

Z. Grzesik and G. Smoła

4 Corrosion Behavior of Popular Automobile Engine Valve Steels at High Temperatures In the automobile industry, four chromium-nickel steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) are currently being utilized in the production of valves intended for automobile engines in low and medium class cars. Valves from these steels constitute about 90% of the total primary market of engine valves in Europe. The nominal chemical compositions of these steels are presented in Table 1. The test specimens presented for the purpose of the discussed investigations were prepared using a standard metallographic procedure. They were obtained from rods of a given valve steel with a ~20 mm diameter by cutting them into flat disks with around 1 mm thickness. In order to obtain mirror-like surfaces of the samples, they were ground with different SiC papers and finally polished using diamond pastes.

4.1 Oxidation in Air Atmosphere The oxidation behavior of the above-mentioned valve steels was studied both in isothermal [35, 36], as well as thermal shock conditions [33]. The tests conducted under isothermal conditions showed that oxidation kinetics of all investigated valve steels at temperatures lower than 1173 K can be described as in accordance with the parabolic oxidation rate law. Only oxidation courses obtained at 1173 and 1273 K for X33CrNiMn23-8 steel firmly follow parabolic kinetics from the initial time of the reaction, indicating that the process is controlled by diffusion. In the case of the three other remaining steels with lower chromium content, the oxidation process is more complex. After a certain incubation period, during which the oxidation rate is relatively low, sample mass increases with reaction time but in agreement with the parabolic oxidation rate law. Figure 2 presents exemplary kinetics obtained at 1173 K (Fig. 2). As illustrated in Fig. 2, X33CrNiMn23-8 steel demonstrates the best oxidation resistance. It should be emphasized that this steel exhibits the best behavior compared to the remaining steels at all temperatures, at which oxidation tests were performed [36]. The difference between the oxidation kinetic rates of studied steels, represented by parabolic rate constants (k p ), increases along with temperature and at 1273 K is more than one hundred times higher. Such results are not unexpected. In accordance with earlier expectations, the chromium concentration in the X33CrNiMn23-8 steel is high enough for its selective oxidation and the growth of a highly protective chromia scale. In addition, the relatively high concentration of nickel in this steel, exceeding 7 wt.% (Table 1), increases selective oxidation of chromium by accelerating outward chromium diffusion in the metallic substrate to the metal-scale interface [37]. The chromium and manganese concentrations in the three remaining

1.50 – 3.50

8.00 – 10.00

0.28 – 0.38

0.45 – 0.50

0.48 – 0.58

0.50 – 0.60

X33CrNiMn23-8

X50CrMnNiNbN21-9

X53CrMnNiN20-8

X55CrMnNiN20-8

7.00 – 10.00

8.00 – 10.00

Mn

C

Grade of steel

Max. 0.25

Max. 0.25

Max. 0.45

0.50 – 1.00

Si

19.50 – 21.50

20.00 – 22.00

20.00 – 22.00

22.00 – 24.00

Cr

1.50 – 2.75

3.25 – 4.50

3.50 – 5.50

7.00 – 9.00

Ni

0.20 – 0.40

0.35 – 0.50

0.40 – 0.60

0.25 – 0.35

N

–

–

0.80 – 1.50

Max. 0.50

W

–

–

1.80 – 2.50

–

Nb

0.030

0.030

0.030

0.030

S

0.045

0.045

0.045

0.045

P

–

–

–

Max. 0.50

Mo

Bal.

Bal.

Bal.

Bal.

Fe

Table 1 The nominal concentrations of elements (wt.%) in X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8 valve steels

Thin Chromium-Based Coatings for Internal Combustion Automobile … 293

294

Z. Grzesik and G. Smoła

Fig. 2 Exemplary oxidation kinetics of discussed valve steels obtained at 1173 K and stable level of oxygen pressure, equal to 2.1 × 104 Pa (∆m/S—mass changes of the oxidized samples per unit surface area)

Fig. 3 Schematic representation of multilayered scale formation on valve steels

steels are practically the same, but greater differences can be seen in nickel concentrations (1.5–5.5 wt.%). Literature data clearly indicates that the nickel existence in chromium-containing steels has a beneficial effect on their oxidation resistance [37]. Manganese, in turn, has the opposite influence [2]. The concentration of nickel and manganese is the lowest in X55CrMnNiN20-8 steel and therefore, it may then be expected that the higher oxidation rate of the X55CrMnNiN20-8 steel compared to those of X50CrMnNiNbN21-9 and X53CrMnNiN20-8 steels is the result of a compromise between manganese and nickel contents in these materials. It can be also highlighted that the oxidation processes of four different valve steels do not depend on the oxygen pressure [36]. Such a situation is rather common in the case of oxidation of a number of commercial chromium-containing steels and alloys. This fact is the result of parabolic rate growth of multilayered scales, the external layer of which is thinner than the thickness of the entire scale, Fig. 3. As a consequence, the change in oxygen pressure in the given reactive atmosphere only affects the formation kinetics of the most external layer of the scale, while the majority

Thin Chromium-Based Coatings for Internal Combustion Automobile …

295

Fig. 4 Comparison of the results obtained during oxidation of investigated steels under thermal shocks (298–1173 K)

of the scale forms at a constant oxygen pressure, being equal to the decomposition pressure of this external oxide. A summary of the valve steels oxidation kinetics investigated under thermal shocks in air atmosphere is presented in Fig. 4. From this diagram it follows that all of the studied materials demonstrate rather good oxidation resistance, but the X33CrNiMn23-8 steel containing the highest chromium concentration, as in the case of the isothermal experiments, exhibits the best oxidation resistance in high temperature conditions. This denotes that the chromia scale cracks and spalls off only fragmentarily and thereby the oxidation products provide relatively good protection for this valve material. The scale growing on the X33CrNiMn23-8 steel, formed after 500 shocks, is mainly built of chromium oxide (Cr2 O3 ), along with islands of iron oxides (Fe3 O4 and Fe2 O3 ) on its surface. On the contrary, the scale grown on the steel with lowest chromium concentration is complex and only consists of iron oxides (Fe3 O4 and Fe2 O3 ).

4.2 Oxidation in Combustion Gasses of Fuels Containing Bio-Additions Corrosion of four valve steel types at high temperature in combustion gasses of bio-additive containing fuels was investigated only under thermal shocks. Results concerning the application of 5 different types of fuels are described in this subsection. In the fuel oil case, 5 and 10 wt.% FAME concentrations were used (fuel oil B5 and B10) as bio-additions [38], while for petrol 5, 10 and 50 wt.% of ethanol concentrations were added (petrol containing 5 wt.% ethanol is designated as 95Al, 10 wt.% ethanol petrol as 90Al and 50 wt.% ethanol petrol as 50Al) [34]. The fuel oil and petrol properties, consisting of different bio-component concentrations are listed in Tables 2 and 3, respectively.

296

Z. Grzesik and G. Smoła

Table 2 Properties of diesel fuels [38] Property

Fuel oil B5

Fuel oil B10

EN standard

Specification limit

Density at 15 °C, kg/m3

832.0

838.0

EN ISO 12185

820–845

Ignition temperature, °C

61.0

69.5

EN ISO 2719

>55

Cetane no.

55.0

51.4

EN ISO 5165

>51

Water content, mg/kg

26

150

EN ISO 12937