TRIBOLOGY OF CERAMICS AND COMPOSITES
TRIBOLOGY OF CERAMICS AND COMPOSITES
A Materials Science Perspective
BIKRAMJIT BASU Department of Materials Science and Engineering Indian Institute of Technology Kanpur, India Materials Research Center Indian Institute of Science Bangalore, India
MITJAN KALIN Faculty of Mechanical Engineering University of Ljubljana Ljubljana, Slovenia
A JOHN WILEY & SONS, INC., PUBLICATION
Copyright © 2011 by The American Ceramic Society. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/ permissions. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com. Library of Congress Cataloging-in-Publication Data: Basu, Bikramjit. â•… Tribology of ceramics and composites : a materials science perspective / Bikramjit Basu and Mitjan Kalin. â•…â•…â•… p. cm. â•… Includes index. â•… ISBN 978-0-470-52263-9 (cloth) 1.╇ Ceramic materials–Mechanical properties.â•… 2.╇ Ceramic materials–Fatigue.â•… 3.╇ Mechanical wear.â•… 4.╇ Friction.â•… 5.╇ Tribology.â•… I.╇ Kalin, Mitjan.â•… II.╇ Title. â•… TA455.C43B38 2011 â•… 621.8'9–dc22 2010045250 oBook ISBN: 978-1-118-02166-8 ePDF ISBN: 978-1-118-02164-4 ePub ISBN: 978-1-118-02165-1 Printed in the United States of America. 10â•… 9â•… 8â•… 7â•… 6â•… 5â•… 4â•… 3â•… 2â•… 1
Bikramjit Basu dedicates this book with a great sense of gratitude to his parents, Mr. Manoj Mohan Basu and Mrs. Chitra Basu
Mitjan Kalin would like to dedicate this book to Matija, his inspiration, pride, and happiness; and to Janja, for her understanding and support
CONTENTS
PREFACE
xvii
FOREWORD BY PROF. IAN HUTCHINGS
xxi
FOREWORD BY PROF. KARL-HEINZ ZUM GAHR
xxiii
ABOUT THE AUTHORS SECTION Iâ•… CHAPTER 1â•…
2.1 2.2 2.3 2.4 2.5
3.4 3.5
INTRODUCTION
3
6
OVERVIEW: TRIBOLOGICAL MATERIALS
Introductionâ•… 7 Definition and Classification of Ceramicsâ•… Properties of Structural Ceramicsâ•… 9 Applications of Structural Ceramicsâ•… 11 Closing Remarksâ•… 14 Referencesâ•… 16
CHAPTER 3â•…
3.1 3.2 3.3
FUNDAMENTALS
Referencesâ•…
CHAPTER 2â•…
xxv
7
8
OVERVIEW: MECHANICAL PROPERTIES OF CERAMICS
Theory of Brittle Fractureâ•… 18 Cracking in Brittle Materialsâ•… 23 Definition and Measurement of Basic Mechanical Propertiesâ•… 3.3.1 Hardnessâ•… 24 3.3.2 Compressive Strengthâ•… 27 3.3.3 Flexural Strengthâ•… 28 3.3.4 Elastic Modulusâ•… 30 3.3.5 Fracture Toughnessâ•… 31 Toughening Mechanismsâ•… 33 Closing Remarksâ•… 37 Referencesâ•… 37
18
24
vii
viiiâ•…
CONTENTS
CHAPTER 4â•…
4.1 4.2 4.3 4.4 4.5
CHAPTER 5â•…
5.1 5.2 5.3 5.4 5.5
44
49
54
FRICTIONAL HEATING AND CONTACT TEMPERATURE
Tribological Process and Contact Temperatureâ•… 60 Concept of “Bulk” and “Flash” Temperatureâ•… 61 Importance and Relevance of Some Ready-to-Use Analytical Modelsâ•… Review of Some Frequently Employed Ready-to-Use Modelsâ•… 64 6.4.1 Assumptions in Various Modelsâ•… 65 6.4.2 Model Descriptions and Implicationsâ•… 65 6.4.2.1 Archard Modelâ•… 66 6.4.2.2 Kong–Ashby Modelâ•… 67 Referencesâ•… 68
CHAPTER 7â•…
7.1 7.2
39
FRICTION
Introductionâ•… 49 Laws of Frictionâ•… 49 Friction Mechanismsâ•… 51 Friction of Common Engineering Materialsâ•… Closing Remarksâ•… 58 Referencesâ•… 59
CHAPTER 6â•…
6.1 6.2 6.3 6.4
SURFACES AND CONTACTS
Surface Roughnessâ•… 39 Surface Topography and Asperitiesâ•… 41 Real Contact Areaâ•… 42 Contact Load Distribution and Hertzian Stressesâ•… Closing Remarksâ•… 47 Referencesâ•… 48
60
63
WEAR MECHANISMS
Introductionâ•… 70 Classification of Wear Mechanismsâ•… 72 7.2.1 Adhesive Wearâ•… 73 7.2.2 Abrasive Wearâ•… 75 7.2.2.1 Abrasion of Compositesâ•… 77 7.2.3 Fatigue Wearâ•… 78 7.2.4 Oxidation and Tribochemical Wearâ•… 80 7.2.5 Fretting Wearâ•… 81 7.2.5.1 Fretting Modesâ•… 82 7.2.5.2 Mechanics of Elastic Contacts under Fretting Conditionsâ•… 7.2.5.3 Mechanics of Elastic–Plastic Contacts under Fretting Conditionsâ•… 86 7.2.5.4 Fretting Regimesâ•… 86 7.2.5.5 Determination of Fretting Regimesâ•… 89 7.2.5.6 Fretting Mapsâ•… 89 7.2.5.7 Velocity Accommodation in Frettingâ•… 91 7.2.5.8 Friction Logsâ•… 92 7.2.6 Solid Particle Erosionâ•… 92 7.2.6.1 Erosion of Ductile Materialsâ•… 94 7.2.6.2 Erosion of Brittle Materialsâ•… 96
70
84
â•… ix
CONTENTS
7.3
Closing Remarksâ•… Referencesâ•… 99
CHAPTER 8â•…
8.1 8.2
LUBRICATION
Lubrication Regimesâ•… Stribeck Curveâ•… 107 Referencesâ•… 109
SECTION IIâ•… CHAPTER 9â•…
9.1 9.2 9.3 9.4 9.5
9.6 9.7 9.8 9.9 9.10
FRICTION AND WEAR OF STRUCTURAL CERAMICS
OVERVIEW: STRUCTURAL CERAMICS
113
CASE STUDY: TRANSFORMATION-TOUGHENED ZIRCONIA
Backgroundâ•… 142 Wear Resistanceâ•… 144 Morphological Characterization of the Worn Surfacesâ•… 146 Zirconia Phase Transformation and Wear Behaviorâ•… 149 Wear Mechanismsâ•… 152 Relationship among Microstructure, Toughness, and Wearâ•… 154 Influence of Humidity on Tribological Properties of Self-Mated Zirconiaâ•… Wear Mechanisms in Different Humidityâ•… 157 Tribochemical Wear in High Humidityâ•… 160 Closing Remarksâ•… 163 Referencesâ•… 164
CHAPTER 11â•…
11.1 11.2 11.3 11.4
101 101
Introductionâ•… 113 Zirconia Crystal Structures and Transformation Characteristics of Tetragonal Zirconiaâ•… 114 Transformation Tougheningâ•… 116 9.3.1 Micromechanical Modelingâ•… 116 Stabilization of Tetragonal Zirconiaâ•… 117 Different Factors Influencing Transformation Tougheningâ•… 118 9.5.1 Grain Sizeâ•… 119 9.5.2 Yttria Contentâ•… 121 9.5.3 Yttria Distributionâ•… 122 Stress-Induced Microcrackingâ•… 125 Development of SiAlON Ceramicsâ•… 126 Microstructure of S-sialon Ceramicsâ•… 127 Mechanical Properties and Crack Bridging of SiAlON Ceramicâ•… 129 Properties of Titanium Diboride Ceramicsâ•… 132 Referencesâ•… 138
CHAPTER 10â•…
10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10
98
142
156
CASE STUDY: SIALON CERAMICS
Introductionâ•… 167 Materials and Experimentsâ•… 168 Tribological Properties of Compositionally Tailored Sialon versus β-Sialonâ•… Tribological Properties of S-Sialon Ceramicâ•… 179
167
172
xâ•…
CONTENTS
11.5
Concluding Remarksâ•… Referencesâ•… 183
CHAPTER 12â•…
12.1 12.2 12.3 12.4 12.5 12.6
182
CASE STUDY: MAX PHASE—TI3SIC2
Backgroundâ•… 185 Frictional Behaviorâ•… 188 Wear Resistance and Wear Mechanismsâ•… 188 Raman Spectroscopy and Atomic Force Microscopy Analysisâ•… Transition in Wear Mechanismsâ•… 193 Summaryâ•… 194 Referencesâ•… 195
185
190
CHAPTER 13â•…
CASE STUDY: TITANIUM DIBORIDE CERAMICS AND COMPOSITES 13.1 13.2 13.3
13.4 13.5
197
Introductionâ•… 197 Materials and Experimentsâ•… 198 Tribological Properties of TiB2–MoSi2 Ceramicsâ•… 200 13.3.1 Friction and Wearâ•… 200 13.3.2 Wear and Dissipated Energyâ•… 202 13.3.3 Wear and Abrasion Parameterâ•… 203 13.3.4 Material Removal Mechanismsâ•… 204 Tribological Properties of TiB2–TiSi2 Ceramicsâ•… 204 Closing Remarksâ•… 206 Referencesâ•… 208
SECTION IIIâ•…
FRICTION AND WEAR OF BIOCERAMICS AND BIOCOMPOSITES CHAPTER 14â•…
14.1 14.2
14.3 14.4 14.5 14.6 14.7
14.8
213
Introductionâ•… 213 Some Useful Definitions and Their Implicationsâ•… 215 14.2.1â•… Biomaterialsâ•… 215 14.2.2 Biocompatibilityâ•… 216 14.2.3 Host Responseâ•… 216 Experimental Evaluation of Biocompatibilityâ•… 217 Wear of Implantsâ•… 221 Coating on Metalsâ•… 223 Glass-Ceramicsâ•… 224 Biocompatible Ceramicsâ•… 226 14.7.1 Bioinert Ceramicsâ•… 226 14.7.2 Calcium Phosphate-Based Biomaterialsâ•… 226 Outlookâ•… 228 Referencesâ•… 229
CHAPTER 15â•…
15.1 15.2
OVERVIEW: BIOCERAMICS AND BIOCOMPOSITES
CASE STUDY: POLYMER-CERAMIC BIOCOMPOSITES
Introductionâ•… 233 Materials and Experimentsâ•…
235
233
â•… xi
CONTENTS
15.3 15.4 15.5 15.6 15.7
Frictional Behaviorâ•… 237 Wear-Resistance Propertiesâ•… 240 Wear Mechanismsâ•… 242 Correlation among Wear Resistance, Wear Mechanisms, Material Properties, and Contact Pressureâ•… 247 Concluding Remarksâ•… 248 Referencesâ•… 249
CHAPTER 16â•…
CASE STUDY: NATURAL TOOTH AND DENTAL RESTORATIVE
MATERIALS
251
16.1 16.2
Introductionâ•… 251 Materials and Methodsâ•… 254 16.2.1 Preparation of Human Tooth Materialâ•… 254 16.3 Tribological Tests on Tooth Materialâ•… 255 16.4 Production and Characterization of Glass-Ceramicsâ•… 255 16.5 Wear Experiments on Glass-Ceramicsâ•… 256 16.6 Microstructure and Hardness of Human Tooth Materialâ•… 257 16.7 Tribological Properties of Human Tooth Materialâ•… 260 16.7.1 Friction Behaviorâ•… 260 16.7.2 Wear Mechanismsâ•… 262 16.8 Wear Properties of Glass-Ceramicsâ•… 262 16.9 Discussion of Wear Mechanisms of Glass-Ceramicsâ•… 266 16.10 Comparison with Existing Glass-Ceramic Materialsâ•… 271 16.11 Concluding Remarksâ•… 273 Referencesâ•… 274 CHAPTER 17â•…
17.1 17.2 17.3 17.4 17.5 17.6 17.7
276
Introductionâ•… 276 Materials and Experimentsâ•… 277 Frictional Propertiesâ•… 278 Wear Resistance and Wear Mechanismsâ•… 278 Wear Debris Analysis and Tribochemical Reactionsâ•… 282 Influence of Glass Infiltration on Wear Propertiesâ•… 283 Concluding Remarksâ•… 284 Referencesâ•… 285
CHAPTER 18â•…
18.1 18.2 18.3
CASE STUDY: GLASS-INFILTRATED ALUMINA
TRIBOLOGICAL PROPERTIES OF CERAMIC BIOCOMPOSITES
287
Backgroundâ•… 287 Tribological Properties of Mullite-Reinforced Hydroxyapatiteâ•… 288 Friction and Wear Rateâ•… 288 18.3.1 Effect of Simulated-Body-Fluid Medium on Wear of Mullite-Reinforced Hydroxyapatiteâ•… 289 18.3.2 Surface Topography of Mullite-Reinforced Hydroxyapatite after Fretting Wearâ•… 293 18.3.3 Frictional Behaviorâ•… 293 18.3.4 Wear Micromechanisms of Hydroxyapatite-Based Materials in Simulated Body Fluidâ•… 296
xiiâ•… 18.4
CONTENTS
Concluding Remarksâ•… Referencesâ•… 302
SECTION IVâ•… CHAPTER 19â•…
19.1 19.2 19.3
19.4 19.5
298
FRICTION AND WEAR OF NANOCERAMICS
OVERVIEW: NANOCERAMIC COMPOSITES
307
Introductionâ•… 307 Processing of Bulk Nanocrystalline Ceramicsâ•… 309 Overview of Developed Nanoceramics and Ceramic Nanocompositesâ•… 19.3.1 Monolithic Nanoceramicsâ•… 311 19.3.2 Alumina-Based Nanocompositesâ•… 313 19.3.3 Tungsten Carbide-Based Nanocompositesâ•… 314 19.3.4 Zirconia-Based Nanocompositesâ•… 317 Overview of Tribological Properties of Ceramic Nanocompositesâ•… 318 Concluding Remarksâ•… 320 Referencesâ•… 322
309
CHAPTER 20â•…
CASE STUDY: NANOCRYSTALLINE YTTRIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTALLINE CERAMICS 20.1 20.2 20.3 20.4 20.5 20.6
325
Introductionâ•… 325 Materials and Experimentsâ•… 327 Tribological Propertiesâ•… 329 Tribomechanical Wear of Yttria-Stabilized Zirconia Nanoceramic with Varying Yttria Dopantâ•… 330 Comparison with Other Stabilized Zirconia Ceramicsâ•… 335 Concluding Remarksâ•… 335 Referencesâ•… 336
CHAPTER 21â•…
CASE STUDY: NANOSTRUCTURED TUNGSTEN CARBIDE–ZIRCONIA NANOCOMPOSITES 21.1 21.2 21.3 21.4 21.5 21.6
Introductionâ•… 338 Materials and Experimentsâ•… 339 Friction and Wear Characteristicsâ•… 340 Wear Mechanismsâ•… 345 Explanation of High Wear Resistance of Ceramic Nanocompositesâ•… Concluding Remarksâ•… 349 Referencesâ•… 349
SECTION Vâ•… CHAPTER 22â•…
347
LIGHTWEIGHT COMPOSITES AND CERMETS
OVERVIEW: LIGHTWEIGHT METAL MATRIX COMPOSITES AND
CERMETS 22.1 22.2
338
Development of Metal Matrix Compositesâ•… Development of Cermetsâ•… 356 Referencesâ•… 358
353 353
CONTENTS
â•… xiii
CHAPTER 23â•…
CASE STUDY: MAGNESIUM–SILICON CARBIDE PARTICULATEREINFORCED COMPOSITES 23.1 23.2 23.3 23.4 23.5 23.6
362
Introductionâ•… 362 Materials and Experimentsâ•… 363 Load-Dependent Friction and Wear Propertiesâ•… 363 Fretting-Duration-Dependent Tribological Propertiesâ•… 366 Tribochemical Wear of Magnesium–Silicon Carbide Particulate-Reinforced Compositesâ•… 371 Concluding Remarksâ•… 375 Referencesâ•… 376
CHAPTER 24â•…
CASE STUDY: TITANIUM CARBONITRIDE–NICKELBASED CERMETS 24.1 24.2 24.3 24.4
24.5 24.6 24.7
24.8
Introductionâ•… 377 Materials and Experimentsâ•… 379 Energy Dissipation and Abrasion at Low Loadâ•… 381 Influence of Type of Secondary Carbides on Sliding Wear of Titanium Carbonitride–Nickel Cermetsâ•… 386 24.4.1 Wear Mechanismsâ•… 387 Tribochemical Wear of Titanium Carbonitride–Based Cermetsâ•… 387 24.5.1 Evolution of Tribochemistry and Contact Temperatureâ•… 387 Influence of Tungsten Carbide Content on Load-Dependent Sliding Wear Propertiesâ•… 393 High Temperature Wear of Titanium Carbonitride–Nickel Cermetsâ•… 397 24.7.1 Wear Mechanismsâ•… 398 24.7.2 Discussion of High-Temperature Oxidation and Its Relation to Material Removalâ•… 401 24.7.3 Thermal Oxidationâ•… 402 24.7.4 Influence of Different Secondary Carbide Additionâ•… 403 Summary of Key Resultsâ•… 403 Referencesâ•… 404
CHAPTER 25â•…
25.1 25.2 25.3 25.4 25.5 25.6
377
CASE STUDY: (W,Ti)C–CO CERMETS
407
Introductionâ•… 407 Materials and Experimentsâ•… 408 Microstructure and Mechanical Propertiesâ•… 409 Wear Propertiesâ•… 410 Correlation between Mechanical Properties and Wear Resistanceâ•… Concluding Remarksâ•… 418 Referencesâ•… 419
413
SECTION VIâ•…
FRICTION AND WEAR OF CERAMICS IN A CRYOGENIC ENVIRONMENT CHAPTER 26â•…
26.1 26.2
OVERVIEW: CRYOGENIC WEAR PROPERTIES OF MATERIALS
Backgroundâ•… 423 Designing a High-Speed Cryogenic Wear Testerâ•…
425
423
xivâ•… 26.3
26.4
CONTENTS
Summary of Results Obtained with Ductile Metalsâ•… 26.3.1 Self-Mated Steelâ•… 427 26.3.2 Titanium/Steel Coupleâ•… 430 26.3.3 Copper/Steel Sliding Systemâ•… 433 Summaryâ•… 437 Referencesâ•… 437
427
CHAPTER 27â•…
CASE STUDY: SLIDING WEAR OF ALUMINA IN A CRYOGENIC ENVIRONMENT 27.1 27.2 27.3 27.4
27.5
439
Backgroundâ•… 439 Materials and Experimentsâ•… 440 Tribological Properties of Self-Mated Aluminaâ•… 442 Genesis of Tribological Behavior in a Cryogenic Environmentâ•… 449 27.4.1 Friction of Self-Mated Alumina in LN2â•… 449 27.4.2 Brittle Fracture and Wear of Self-Mated Alumina in LN2â•… 450 Concluding Remarksâ•… 452 Referencesâ•… 452
CHAPTER 28â•…
CASE STUDY: SLIDING WEAR OF SELF-MATED TETRAGONAL ZIRCONIA CERAMICS IN LIQUID NITROGEN 28.1 28.2 28.3 28.4 28.5 28.6 28.7
Introductionâ•… 454 Materials and Experimentsâ•… 456 Friction of Self-Mated Y-TZP Material in LN2â•… 456 Cryogenic Wear of Zirconiaâ•… 459 Cryogenic Sliding-Induced Zirconia Phase Transformationâ•… Wear Mechanisms of Zirconia in LN2â•… 464 Concluding Remarksâ•… 466 Referencesâ•… 467
454
460
CHAPTER 29â•…
CASE STUDY: SLIDING WEAR OF SILICON CARBIDE IN A CRYOGENIC ENVIRONMENT 29.1 29.2 29.3 29.4 29.5 29.6 29.7
469
Introductionâ•… 469 Materials and Experimentsâ•… 470 Friction and Wear Propertiesâ•… 470 Thermal Aspect and Limited Tribochemical Wearâ•… 473 Tribomechanical Stress-Assisted Deformation and Damageâ•… 479 Comparison with Sliding Wear Properties of Oxide Ceramicsâ•… 481 Concluding Remarksâ•… 482 Referencesâ•… 483
SECTION VIIâ•…
WATER-LUBRICATED WEAR OF CERAMICS
CHAPTER 30â•…
FRICTION AND WEAR OF OXIDE CERAMICS IN AN AQUEOUS ENVIRONMENT 30.1 30.2
Backgroundâ•… 487 Tribological Behavior of Alumina in an Aqueous Solutionâ•…
488
487
â•… xv
CONTENTS
30.3
30.4
30.2.1 Electrochemical Properties and Wear Characterization of Self-Mated Aluminaâ•… 491 30.2.2 Surface Roughness and Frictional Behaviorâ•… 492 Tribological Behavior of Self-Mated Zirconia in an Aqueous Environmentâ•… 493 30.3.1 Zirconia Transformation and Wearâ•… 497 30.3.2 Electrochemical Aspect of Wearâ•… 498 Concluding Remarksâ•… 499 Referencesâ•… 500
SECTION VIIIâ•…
CLOSURE
CHAPTER 31â•…
PERSPECTIVE FOR DESIGNING MATERIALS FOR TRIBOLOGICAL APPLICATIONS
505
INDEX
509
PREFACE
Tribology, by definition, is the science and technology of interacting surfaces in relative motion. Such scientific understanding has significant technological relevance for various engineering industries. Broadly, tribology deals with the concepts of friction, wear, and lubrication. Over the last few decades, it has been widely recognized that tribology, being an interdisciplinary area, involves the interaction of concepts drawn from multiple disciplines, including mechanical engineering, materials science, physics, and chemistry. The development of new materials (bulk or coating) with better friction and wear resistance, as well as the progress in tribology research, clearly requires an improved understanding in multiple disciplines as well as the development of new design methodologies in order to obtain better properties in relation to tribological performance. Even though tribology is still not broadly known as a research field to many in industry or academia, we are all intrigued by the topic in everyday life, as well as in almost every engineering application. Across the world, very few universities teach this subject; however, the subject is gaining importance. There are many books on tribology written from different perspectives, such as materials science, mechanics, mechanical engineering, lubrication and additives, physics, and chemistry. This book is intended to cover mostly the materials science aspects applicable to tribology science. Researchers interested in automotive, aerospace, biomaterials, hardmetals, and related applications would look for a complete set of possible materials for those applications, as well as wear and friction mechanisms. On the other hand, people from the materials science community would look for details of mechanisms, effect of microstructure, working conditions, lubrication, environment, and so on, which again are covered here due to very broad materials selection. This book places the utmost importance on the microstructure–material-properties–tribological-properties relationship for the range of advanced materials that are covered herein. The description of the wear micromechanisms of the various materials will provide a strong background to readers on how to design and develop new tribological materials. From the aforementioned perspective, this book is structured into various thematic sections, and each section contains a number of chapters. This book was designed to motivate students and young researchers as well as to provide experts in the area with a healthy balance of topics for teaching and academic purposes, primarily for two disciplines: materials science/metallurgy and mechanical engineering. It is expected that this book, if used as a text, would strongly benefit senior undergraduate and postgraduate students. xvii
xviii
Preface
Section I of this book is designed to provide the readers with a background in the area of tribology and basic materials science. Characteristics of material surfaces in terms of surface roughness and various material properties are discussed, as well as the fundamentals of the friction, wear mechanism, and lubrication. This is followed by Section II, where the tribological properties of structural ceramics, which include zirconia, sialon, ternary carbides, and high-temperature ceramics, such as borides, are discussed. This selection of materials also represents a class of technologically important and emerging ceramics. It is shown how the microstructure and mechanical properties both determine the wear resistance of these materials. One area in which ceramics and polymers are increasingly important is biomedical applications. In Section III, the tribological properties of hydroxyapatitebased bioceramic composites are discussed first. Polymers are known for their poor wear resistance; it is shown how the development of hybrid polymer-ceramic biocomposites can lead to higher wear resistance while retaining good frictional properties of the polymer matrix. This is followed by a discussion on the wear properties of some of the stabilized zirconia ceramics. The two chapters in this section deal with the materials that are important in dental restoration. A rather recent development in the materials world is the synthesis of nanoÂ� ceramic composites. In view of this, Section IV discusses the friction and wear properties of zirconia and WC-based nanocomposites, which are processed using the advanced processing technique of spark plasma sintering. A summary of the literature on the tribological properties of various nanoceramics is also included. In the last decade, lightweight composites have been considered for use in automotive and other applications requiring good wear resistance. Similarly, new generation cermets, based on TiCN as well as mixed carbide cermets, are also being developed as a replacement for widely used WC-Co cemented carbides. Hence, Section V demonstrates how these new–generation materials will behave at tribological contacts. While our understanding of the dry, unlubricated tribological properties of various materials is extensive, such understanding in a cryogenic environment and under high speed sliding conditions is rather limited. In view of this, Section VI discusses the tribological properties of oxide and non-oxide ceramics in liquid nitrogen with reference to similar properties under ambient and room temperature sliding conditions. In Section VII, the tribological properties of various ceramics in aqueous environments are discussed, with reference to regimes and pH regions and their effect on performance. The book concludes with Section VIII, which covers the various issues to be investigated in the near future in the design and development of materials with better tribological properties. This section summarizes the information provided in the book and gives an insight into the broader knowledge of these materials and advice on how to use them in various applications. The above-described structure of this book as well as the succession of various sections and chapters is expected to be useful in helping both students and experts pursuing the area of tribology of advanced materials to gradually build up knowledge
xix
Preface
of the fundamentals and, subsequently, to understand the most recent advances. In particular, this book has the following major important features: (1) the fundamental science of tribology is presented, thus allowing the book to be used as a textbook for teaching, academic, or research purposes; (2) a broad range of materials is covered, such as advanced tough ceramics, high-temperature ceramics, biomaterials, and nanoceramics, to illustrate how the materials science aspect can be realized while analyzing the tribological results; and (3) the book will appeal to a large number of active researchers from various disciplines of metallurgy and materials science, ceramics, and mechanical engineering. This book is an outcome of several years of teaching undergraduate and postgraduate courses in the area of tribology of materials, advanced ceramics, composite materials, and biomaterials, and other related fundamental courses in materials science, which were offered to students of the Indian Institute of Technology (IIT) Kanpur, India, as well as at the Faculty of Mechanical Engineering at the University of Ljubljana, Slovenia. More important, the research results of many of the postgraduate students from our groups are also summarized in some chapters. B. Basu would like to specifically acknowledge some of his past and present students, B. V. Manoj Kumar, G. B. Raju, Shekhar Nath, P. Suresh Babu, Amartya Mukhopadhyay, K. Madhav Reddy, Animesh Choubey, M. Surender, S. Bajaj, N. Sinha, Tufan Kumar Guha, P. Maji, Rohit Khanna, Subhodip Bodhak, Srimanta Das Bakshi, D. Sarkar, Manisha Taneja, Ravi Kumar, A. Tewari, T. Venkateswaran, U. Raghunandan, Divya Jain, Nitish Kumar, Amit S. Sharma, Ashutosh K. Dubey, Alok Kumar, Sushma Kalmodia, Shilpee Jain, Neha Gupta, Indu Bajpai, Garima Tripathi, Prafulla K. Mallik, Anup Patel, Rajeev Kumar, and Atiar R. Molla. The dedication of these students to understanding the tribological properties of a range of ceramics and composites is reflected in the research work summarized in many of the chapters of this book. With gratitude, B. Basu appreciates the past and present research collaboration with a number of researchers and academicians, including Drs. Omer Van Der Biest, Jozef Vleugels, R. K. Bordia, G. Sundararajan, S. K. Mishra, A. K. Suri, R. Mitra, I. Manna, A. Basumallick, J. Ramkumar, B. Subramonian, Manoj Gupta, K. C. Hari Kumar, R. G. Vitchev, Hasan Mondal, Ferhat Kara, Nurcan Kalis Ackibas, P. Gilman, S. C. Koria, R. K. Dube, M. Karanjai, D. Roy, M. C. Chu, S. J. Cho, Doh-Yeon Kim, Jo Wook, and S. Kang. The encouragement and collaboration with two of his colleagues, the late Prof. R. Balasubramaniam and the late Prof. V. S. R. Murty, is also remembered. B. Basu also expresses sincere thanks to his long-term friend and mentor, Dr. Jaydeep Sarkar, for his constant encouragement during the writing of this book. B. Basu also remembers the constant inspiration of a number of colleagues and former teachers, including Profs./Drs. S. Ranganathan, K. Chattopadhyay, Sanjay K. Biswas, Ashutosh Sharma, N. K. Mukhopadhyay, Indranil Manna, D. Basu, Anoop K. Mukhopadhyay, Brian Lawn, M. V. Swain, M. Hoffman, Vikram Jayaram, Goutam Biswas, D. Mazumdar, Dipankar Banerjee, Atul Chokshi, and B. S. Murty. M. Kalin acknowledges cooperation related to tribology of ceramics from J. Vižintin and F. Kopacˇ from his group at the Faculty of Mechanical Engineering, and S. Novak and G. Dražicˇ from the Jožef Stefan Institute in Ljubljana, Slovenia. M. Kalin would like to acknowledge help from M. Polajnar and J. Kogovšek for
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Preface
assistance in final technical revisions of this book. He would also like to express particular thanks to S. Jahanmir (MiTi Heart Corp, USA) and K. Kato (Tohoku University, Japan) for their mentoring, scientific, and personal advice during their joint work at the Ceramics Department at the National Institute of Standards and Technology (NIST, Gaithersburg, MD), and Tohoku University (Japan), respectively, as well as for the remarkable support and kind friendship over many years. The authors would like to thank Drs. Ian Hutchings, Said Jahanmir, Koji Kato, and Karl-Heinz Zum Gahr for writing the comments on and forewords to this book. The authors would like to take this opportunity to acknowledge the financial support, of various governmental agencies of India, including the Indian Space Research Organisation (ISRO), Department of Atomic Energy (DAE), Department of Biotechnology (DBT), Defense Research and Development Organization (DRDO), Council of Scientific and Industrial Research (CSIR), Department of Science and Technology (DST), UK-India Education and Research Initiative (UKIERI), and Indo-US Science and Technology Forum (IUSSTF) in the last two decades, which facilitated research in the area of tribology of advanced materials at IIT Kanpur. B. Basu also expresses gratitude to Mr. N. M. Dube and his colleagues at DUCOM, Bangalore, for designing and fabricating custom-made fretting and high-speed cryogenic tribotesters. B. Basu expressed sincere thanks to Mr. Divakar Tiwari and his present students (Amit, Ashutosh, Anup, Neha, Indu, Shilpee, and Alok) for their untiring efforts and effective assistance during various stages of the manuscript preparation. We would also like to thank IIT Kanpur for extending financial and other support during the writing this book. The continuous financial support from the Ministry of Higher Education, Science and Technology of Slovenia, as well as the Slovenian Research Agency, over the years is also greatly appreciated. Finally, we would like to acknowledge the continuous support extended by our parents, in-laws, and family members, Pritha and Prithvijit and Janja and Matija, during the course of the writing of this book. IIT Kanpur, India, and IISc, Bangalore, India Ljubljana, Slovenia July 2011
Bikramjit Basu Mitjan Kalin
FOREWORD Engineering ceramics form a diverse and important class of materials, with a wide range of properties and applications, from rolling bearings to dental implants, and from high-performance cutting tools to artificial hip joints. In these applications and many more, the tribological behavior of the ceramic is paramount, but the properties by which the material is specified are often “standard” and easily measured ones such as density, hardness, Young’s modulus, modulus of rupture, and perhaps fracture toughness. As we now know from extensive research, these properties are often poor predictors of tribological performance. Better understanding of the behavior of ceramics in tribological applications, and of the detailed influence of microstructural features such as porosity, phase, and grain size distributions, as well as the tribochemical processes that occur at the material’s surface, will benefit all manufacturers and users of these materials and will enable their properties and value to be optimized. A deep appreciation of materials science and engineering, coupled with both the chemical and mechanical influences which act on the ceramic in use, is needed to understand the wear and friction of these materials. Fracture, plastic flow, and tribochemical processes can all play key roles in the wear and friction of ceramics. It can be argued that their tribological behavior is even more complex than that of metals. This book, which focuses on the subject from a materials science perspective, forms a valuable contribution to the literature on the tribology of engineering ceramics and their composites, and the authors are to be congratulated on its comprehensive scope. Prof. Ian Hutchings Cambridge, UK
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FOREWORD Microstructures of structural ceramics and their composites have been developed during the last decades mainly for applications under static and dynamic mechanical, thermal, or corrosive loads. Among others, the aim was to improve fracture toughness to overcome the inherent brittleness and increase the reliability of ceramic components in high-loaded applications by optimizing microstructural features, such as size and shape of grains or reinforcing phases, as well as processing technologies. However, to use the potential of ceramic materials in components under high tribological loading, materials microstructures have to be adjusted based on a competent knowledge of tribological mechanisms involved and the structure–property relationships. Using case studies, this book contributes to filling the gap in our understanding of the effects of structures of ceramic materials on tribological behavior. Beginning with fundamental aspects of structure and properties of ceramic materials as well as an introduction to tribology, it covers the tribological behavior of a wide range of materials from structural ceramics through bioceramics, biocomposites, and nanocomposites to cermets. This book can be very useful for newcomers, such as students, in the field of ceramics and tribology, as well as for readers with an interest in utilizing the high potential of ceramic materials in tribological applications. Prof. Karl-Heinz Zum Gahr Karlsruhe Institute of Technology (KIT), Germany
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ABOUT THE AUTHORS
Bikramjit Basu, PhD Associate Professor, Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, India; E-mail: bikram@ iitk.ac.in; currently at Materials Research Center, Indian Institute of Science, Bangalore, India Dr. Bikramjit Basu is currently an Associate Professor at the Indian Institute of Science, Bangalore, and is on leave from the Indian Institute of Technology (IIT), Kanpur, India. Bikramjit obtained his undergraduate and postgraduate degrees, both in Metallurgical Engineering, from the National Institute of Technology (NIT), Durgapur, and the Indian Institute of Science, Bangalore, in 1995 and 1997, respectively. He earned his PhD in Ceramics at Katholieke Universiteit Leuven, Belgium, in March 2001. He returned to India to join IIT Kanpur in November 2001 as Assistant Professor after a brief postdoctoral research experience at the University of California, Santa Barbara. He held visiting positions at the University of Warwick (U.K.), Seoul National University (South Korea), and University Polytechnic Catalonia (Spain). Dr. Basu has authored or co-authored more than 140 peer-reviewed research papers with 20 papers in the Journal of American Ceramic Society. He is the principal editor of the book Advanced Biomaterials: Fundamentals, Processing and Applications (John Wiley & Sons Inc., in association with American Ceramic Society), which was published in September 2009. He is on the editorial boards of five international journals and serves as a reviewer of more than 20 SCI journals in the area of ceramics and biomaterials. He has edited a number of special issues of various journals, including Journal of Materials Science, International Journal of Applied Ceramics Technology, and Journal of Biomedical Materials Research: Part B. At IIT Kanpur, Dr. Basu established a vibrant research program in the area of tribology, structural ceramics, and biomaterials. His research spans the interdisciplinary areas of ceramics, tribology, and biomaterials. In developing interdisciplinary research programs in tribology and ceramics, he has collaborated with the xxv
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About the Authors
materials scientists of the International Advanced Research Center for Powder Metallurgy and New Materials (ARCI), Defense Metallurgical Research Laboratory (DMRL), National Metallurgical Laboratory (NML), Central Glass and Ceramics Research Institute (CGCRI), Indian Space Research Organization (ISRO), and Bhabha Atomic Research Center (BARC). In the area of tribology, he has made significant contributions in establishing the correlation between wear micromechanisms and material properties for a large number of ceramics/composites, including toughened ceramics, such as yttriastabilized tetragonal zirconia polycrystals (Y-TZP), Ti3SiC2, sialon, and other materials, such as (W,Ti)C-Co, TiB2-based ceramics, and TiCN-Ni-XC(X=Nb/W/Ta/Hf). Using a self-designed high-speed cryo-tribometer, Dr. Basu and his co-workers performed a critical set of experiments to understand friction and wear mechanisms of high-purity metals and ceramic bearings. Such a study has relevance for space applications. His research mostly focused on developing microstructure-based understanding of wear mechanisms for various ultra-fine grained ceramics, nanocomposites, and biomaterials, as well as critically analyzing wear resistance properties in the light of the mechanics-based models. His fundamental contribution is the development of analytical models to predict the tribochemical and tribomechanical wear of ceramics. In recognition of his contributions to the field of ceramics, tribology, and biomaterials, Dr. Basu received noteworthy awards from the Indian Ceramic Society (2003), Indian National Academy of Engineering (2004), and Indian National Science Academy (2005), and was awarded the “Metallurgist of the Year” (2010), by the Ministry of Steels, Government of India. He is the first Indian from India to receive the prestigious “Coble Award for Young Scholars” from the American Ceramic Society in 2008. In 2010, he received the NASI (National Academy of Science, India)–SCOPUS Young Scientist award.
Dr. Mitjan Kalin Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana, Slovenia; E-mail:
[email protected] Since obtaining his PhD in 1999 (University of Ljubljana, Slovenia), Dr. Kalin has focused primarily on the research of wear and friction mechanisms for advanced materials, such as ceramics and coatings, as well as on boundary lubrication, tribochemistry, and nanotribology. In the last 10 years, he has led about 15 single-investigator, bilateral, and multilateral projects, more than half of which were international. He has contributed to about 120 conference proceedings and 70 peer-reviewed papers. He has published eight chapters in interna-
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About the Authors
tional books, as well as eight full-text student-course scripta. He is a co-editor of the book Tribology of Mechanical Systems: A Guide to Present and Future Technologies (ASME Press, 2004). He has delivered over 30 invited lectures and talks at conferences, institutes, universities, and technology-driven companies worldwide. He has also presented about 80 reports and studies made for industrial partners in the area of maintenance, wear, and lubrication. He is author or co-author of eight patents, two of them U.S. patents. Dr. Kalin has received three awards from the Faculty of Mechanical Engineering for scientific and research work, and two awards from the Slovenian Society for Tribology for international recognition. He is also a recipient of the prestigious Burt L. Newkirk Award (ASME, 2006) and the Slovenian state Zois award (2006) for important scientific achievements. Dr. Kalin is a reviewer for over 30 international peer-reviewed journals in various fields of engineering, material science, physics, chemistry, and nanotechnology. Since 2006, he has been Associate Editor of the ASME Journal of Tribology. He is also a member of the editorial boards of the Journal of Industrial Lubrication and Tribology, Emerald (2004– ), Advances in Tribology, Hindawi (2009– ), and ISRN Mechanical Engineering, Hindawi (2010– ), and a member of the publishing council of the SV-JME Journal of Mechanical Engineering (2007– ). He has been Guest Editor of several special issues of Tribology International (Elsevier) and Lubrication Science (Wiley). He has also been recently appointed Editor of Lubrication Science (Wiley, 2012– ). He also reviews various proposals for Wiley, ASME Press, and Springer, over 30 SCI peer-reviewed journals in tribology and several related fields, as well as many proposals for national and international research agencies, such as the European Commission and the European Research Foundation. He is a secretary and member of the Executive Committee (1997– ) of the Slovenian Society for Tribology, and one of its founding members. He also serves as an executive board member (2006– ) of the Slovenian Society for Materials. He is also an active member of the Society of Tribologists and Lubrication Engineers (STLE); since 2001 he has served in various positions in the Ceramics and Composites Committee, and in 2004 he was elected as president of this committee. He has been a member of organizing, international, and/or advisory boards at many international conferences, and in 2009 acted as a chair of the Engineering Conferences International (ECI) conference “Advances in Boundary Lubrication and Surface Boundary Films” (Seville, Spain, 2009). He is currently full professor (2010– ) and Head of the Chair for Tribology, Technical Diagnostics, and Maintenance (2011– ) at the University of Ljubljana, Slovenia. He has also done postdoctoral work at NIST, the Catholic University (Leuven, Belgium), Tohoku University (Japan), and the University of Pisa (Italy). Currently, he holds the position of Vice-Dean for Research and International Affairs at the Faculty of Mechanical Engineering at the University of Ljubljana on his second term.
SECTION
I
FUNDAMENTALS
CHAPTER
1
INTRODUCTION It is imperative to define and introduce various fundamental concepts of tribology in this very first section. After a brief introduction, this chapter provides some general discussion on tribology with a particular emphasis on interdisciplinary aspects. This chapter is followed by a discussion in Chapter 2 on the typical nature and properties of metals, ceramics, and polymers that are used widely for various tribological applications. The material-intrinsic surface properties, such as hardness, strength, ductility, and work hardening, are very important factors for wear resistance. Since this book largely discusses the case studies of ceramics and composites, the mechanical properties of ceramics are reviewed in Chapter 3. However, other factors, such as load, relative speed, lubrication, temperature, and environment (ambient, inert atmosphere, relative humidity), are equally important. Importantly, the chemical nature and compatibility of mating materials with environment and lubricants as well as their interplay—which defines tribochemical reactions—will have a significant influence on friction and wear of ceramics and composites. Therefore, it is very important to understand the performance of engineering materials and to correlate them with their properties. Such correlation should be made in terms of microstructural, physical, electrical, mechanical, and (tribo)chemical properties under different tribological conditions. In the above perspective, Chapter 4 describes the physical characteristics of typical engineering surfaces, while Chapters 5 and 6 discuss the fundamentals of friction as well as origin/quantitative analysis of frictional heating, respectively. The phenomenological and mechanistic description of various wear mechanisms with a particular focus on fretting wear is provided in Chapter 7. The last chapter of this section briefly discusses the fundamentals of lubrication. Tribology is now widely accepted as “the science of interacting surfaces in relative motion and practices related there to.”1 Tribology embraces primarily the study of friction, wear, and lubrication and it is strongly an interdisciplinary field.2 As such, it is much broader in terms of areas that affect it, as well as its having a large effect on many other areas in engineering and sciences. The word “tribology” is derived from the Greek word tribos, which means rubbing.3 It is interesting to observe from a tribologist’s perspective that, although tribology seems to be a fresh field, having enormous potential for fundamental research, the history of this important branch of science has its roots in the early ages of humans.4 Using the friction
Tribology of Ceramics and Composites: A Materials Science Perspective, First Edition. Bikramjit Basu, Mitjan Kalin. © 2011 The American Ceramic Society. Published 2011 by John Wiley & Sons, Inc.
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4â•…
CHAPTER 1â•… Introduction
Friction at tribological interface Wear of mating solids
Variables/system parameters
Fundamental disciplines
Interactions
Mating materials and surface properties
Metallurgy, materials science and engineering Physics and chemistry
Tribological environment, operating parameters, mechanics at interface
Mechanical engineering
Figure 1.1â•… Concept triangle illustrating the interaction of basic science and engineering disciplines and multiple parameters, as involved in the science of tribology.
between wood and/or stones in inventing fire is considered as the first utilization of the concept of tribology, and it belongs to Stone Age humans. The other important instances of tribology during early ages seem to be in making drills, bearings, sledges for transporting heavy loads, and so on. In particular, the Egyptian civilization has a record of understanding the significance of friction and wear as well as lubrication during construction of giant pyramids. As illustrated in Figure 1.1, the science of tribology can be explained based on synergistic interaction among the concepts and ideas drawn from fundamentals of physics and chemistry, as well as metallurgy, materials science, engineering, and mechanical engineering. It may be noted here that conventional metallurgical engineering principles are commonly used to tailor surface properties, for example, case hardening or nitriding of steels to improve wear resistance. On the other hand, various new materials (e.g., ceramics and polymers as well as their composites) have been developed in last few decades using the processing–structure–property correlation, a fundamental concept used in materials engineering. Many of these materials are now considered as potential replacements for traditional metallic materials. In mechanical engineering, multiple research groups actively contributed to the lubrication aspect of tribology. This has major relevance for ball bearings and various lubricated mechanical joints and bearings. A number of textbooks have dealt largely with the lubrication aspect. In this book, a great emphasis has therefore been placed on obtaining understanding based on the materials science aspect. Overall, the response of any tribocouple depends on the surface properties of two mating materials as well as on the tribological interaction with the environment; such interaction also critically depends on the mechanics at the tribological interface. This will result
â•… 5
CHAPTER 1â•… Introduction
in friction and wear damage of both the mating solids. Therefore, it is important to understand how two mating materials will respond mechanically at a loaded contact experiencing relative motion; equally important is the interaction of the environment and lubrication with the mating couple. These are explained in various chapters throughout this book. Friction, under nonlubricated conditions, is considered as the resistance to motion that arises from the solid surface interactions at the real area of contact.5–7 On the other hand, in the presence of lubricants, their viscous flow components and solid–liquid interactions play a major or a key role. Having low friction is important for certain applications such as hinges, rivets, bearings, and human hip joints, but applications such as brakes, clutches, and tires on roads in contrast require much higher or even “high” friction. In any case, the ability to control the optimal friction for a particular application is the goal of every designer; this ability depends on many of the aforementioned parameters and, in great part, on understanding and the performance of materials and their surface properties. The progressive loss of material due to the tribological interactions at contacting interfaces under relative motion is considered as the definition of the term “wear.” Wear may arise from the contact and relative motion of the solid body against a mating solid, but it often also includes a liquid or gaseous counterbody (water jet, air bubble implosions). Thus, the conditions of wear include several forms (sliding, rolling, erosion, impact, cavitation, etc.) in various atmospheric conditions. Wear is detrimental in many engineering applications, leading to failure of the various components and, finally, requiring repair or replacement. If we consider a technical system that drives a great part of modern economies, such as a car or any other vehicle, we find that most expenses for maintenance and replacement are due to tribological issues and wear. For example, wear of tires, brakes, wheel joints, bearings, and windshield wipers, scratches on paint and glass, and replacement of oil and oil filters are major concerns of end users, and consequently of manufacturers as well. On the other hand, sometimes wear is desirable: high wear rates are required for efficient production in some surface finishing processes such as polishing and grinding. However, like friction, not only the amount, but also, primarily, the control and prediction of wear of materials in every application is important for appropriate use and maintenance and is thus the key to success of every tribological application. It is understood that the extent of friction and wear depends on the system in which the component is utilized.8 Moreover, friction and wear are not intrinsic material properties, but the tribological features need to be considered as an engineeringsystem dependent property.9 Such control over friction and wear can be achieved by proper design, fabrication, and loading of the components. While friction is a direct and momentary response of the tribological components under the contact conditions, wear also includes the loading history of these components. Therefore, understanding and considering materials’ nature and responses are critical and very important for tailoring the properties of the materials and achieving the desirable conditions of friction and wear.10 In this regard, the aim of the material scientist is to control the properties of a specific component by incorporating suitable changes in its composition at the microstructural level during the processing stage, keeping
6â•…
CHAPTER 1â•… Introduction
tribological requirements in mind. Such microstructural modification should be correlated with performance at different tribological conditions in order to understand, design, manufacture, and control conventional and novel materials in a specific application, and to use all their capabilities and advantages. This is particularly important for advanced and heavily engineered materials, such as composites, ceramics, and nanomaterials. In this book, we tend to present the key material properties that are available to a material scientist for designing a material and that have critical influences on the material’s tribological behavior. We also discuss the fundamentals of tribology and related key parameters, finally describing and presenting examples of the microstructural control of advanced ceramic and composite materials for optimal tribological performance. We focus on a specific segment of high-tech materials that have a great potential for use in many applications and that, primarily, give much freedom and possibility for future development and innovative solutions. Although the book mainly focuses on the materials perspective, we would like to stress that response and success of every material, no matter how well designed, will finally depend on the tribological system, and this should therefore be considered in the early stages of materials and system development.
REFERENCES ╇ 1â•… B. Bhushan. Principles and Applications of Tribology. A Wiley-Interscience Publication, John Wiley & Sons, New York, 1999. ╇ 2â•… I. M. Hutchings. Tribology: Friction and Wear of Engineering Materials. Butterworth-Heinemann Publications, Guernsey, UK, 1992. ╇ 3â•… A. D. Sarkar. Friction and Wear. Academic Press, London, 1980. ╇ 4â•… H. Czichos. Tribology. Elsevier, Amsterdam, 1978. ╇ 5â•… J. F. Archard. Contact and rubbing of flat surfaces. J. Appl. Physics. 24 (1953), 981–988. ╇ 6â•… K. L. Johnson. Contact Mechanics, Vol. 26. Cambridge University Press, London, New York, Sydney, 1985, 230. ╇ 7â•… N. P. Suh. Tribophysics. Prentice-Hall, Englewood Cliffs, NJ, 1986. ╇ 8â•… G. W. Stachowaik and A. W. Batchelor. Engineering Tribology. Tribology Series, Vol. 24. Elsevier, Amsterdam, 1993. ╇ 9â•… K.-H. Zum Gahr. Microstructure and Wear of Materials. Elsevier, Oxford, 1987. 10â•… E. Rabinowicz. Friction and Wear of Materials, 2nd ed. Wiley, New York, 1995.
CHAPTER
2
OVERVIEW: TRIBOLOGICAL MATERIALS This chapter discusses the need for development of new materials in the context of tribological applications, followed by general classification of materials. Particular reference is made to the properties and applications of ceramics and their composites.
2.1 INTRODUCTION Materials have dominated technological development, and their importance has been recognized in all industrialized countries. The driving forces behind the development of “advanced materials” are various technological, socioeconomic, and environmental requirements, including the following: 1. improved performance, integrity, and reliability of engineering systems; 2. higher durability of products; 3. higher efficiency and lower energy consumption of engineering systems; 4. lightweight and high-strength structures. There is a general consensus that engineering materials can be classified into three primary classes: metals and alloys, ceramics and glasses, and polymers.1–6 Among these three primary classes, metals, metallic alloys, and polymers are, by far, more widely used than ceramics and glass for various structural and engineering applications. The widespread use of metallic materials is driven by their high tensile strength, high toughness (crack growth resistance), and ability to be manufactured in various sizes and shapes using reproducible fabrication techniques. Similarly, polymers have distinct advantages in terms of their low density, high flexibility, and availability in different shapes and sizes. Nevertheless, polymeric materials have low melting point (less than 400°C) as well as very low strength and elastic modulus. Compared with ceramics, metals have much lower hardness, and many commonly used metallic materials have much lower melting point. From this perspective, ceramics and glasses have advantageous properties, including refractoriness
Tribology of Ceramics and Composites: A Materials Science Perspective, First Edition. Bikramjit Basu, Mitjan Kalin. © 2011 The American Ceramic Society. Published 2011 by John Wiley & Sons, Inc.
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CHAPTER 2â•… Overview: Tribological Materials
(capability to withstand high temperatures), strength retention at high temperature, high melting point, and good mechanical properties (hardness, elastic modulus, and compressive strength). In view of such an attractive combination of properties, ceramics are considered as potential materials for high-temperature structural applications and various tribological applications requiring high hardness and wear resistance. To combine various advantageous properties of the three primary material classes, a derived material class (i.e., composites) is being developed. The composites are generally defined as a class of materials that comprise at least two intimately bonded microstructural phases aimed to tailor properties (e.g., elastic modulus, hardness, strength) for specific applications; it is expected that a specific property of a composite should be higher than the simple addition of that property of the constituent phases. Depending on whether metals, ceramics, or polymers comprise more than 50% by volume of a composite, it can be further classified as a metal matrix composite (MMC), a ceramic matrix composite (CMC), or a polymer matrix composite (PMC). From the microstructural point of view, a composite contains a matrix (metal, ceramic, polymer) and a reinforcement phase. The crystalline matrix phase can have an equiaxed or elongated grain structure; the reinforcement phase can have different shapes, for example, particulates, whiskers, and fibers. The reinforcement shapes can be distinguished in terms of aspect ratio: particulates can be spheroidal; whiskers have an aspect ratio greater than 2; fibers have the largest aspect ratio. It is widely recognized now that the use of fibers or whiskers can lead to composites with anisotropic properties (different properties in different directions). As far as nomenclature is concerned, it is a common practice to designate a composite as M-Rp, M-Rw, or M-Rf, where M and R are the matrix and reinforcement, respectively, and the subscripts (p, w, f) essentially indicate the presence of reinforcement as particulates, whiskers, or fibers, respectively. One widely investigated MMC is AlSiCp composite. Also, Mg-SiCp is being developed as a lightweight composite. Several MMCs are used for automotive parts and structural components. Popular examples of CMCs include Al2O3–ZrO2â•›p, Al2O3–SiCw. These CMCs are typically used as wear parts and cutting tool inserts. Various resin-bonded PMCs are used for aerospace applications. While this book largely focuses on the tribological properties of ceramics and CMCs, a few chapters also deal with the friction and wear behavior of MMCs and PMCs that have ceramic reinforcements.
2.2 DEFINITION AND CLASSIFICATION OF CERAMICS A proper and exact definition of ceramics is very difficult. In general, ceramics can be defined as a class of inorganic nonmetallic materials that can be either processed or used at high temperatures and have ionic and/or covalent bonding.6 To the common person in society, the word “ceramic” means a coffee cup, sanitary tiles, and so on, which are traditional ceramic products. Although the major use of ceramics in last few decades was centered on applications such as construction materials, tableware, and sanitary ware, the advancement of ceramic science and technology
2.3 Properties of Structural Ceramics
â•… 9
since the early 1990s has enabled the application of this class of materials to extend from more traditional applications to such cutting-edge technologies as aerospace, nuclear, electronics, and biomedical, among others.1–6 In fact, ceramics are classified as traditional ceramics and engineering ceramics in many textbooks. Traditional ceramics are largely silica or clay based and typically involve low-cost fabrication processes. On the other hand, engineering ceramics are processed from high-purity ceramic powders and their properties can be tailored by varying process parameters and, thereby, microstructures. Also, engineering ceramics are, by far, more expensive than traditional ceramics. A large cross section of people in the developing world is slowly getting to know and realize the applications of engineering ceramics.7 To this end, this book sheds light on how various structural ceramics can be useful in tribological applications. Based on applications, engineering ceramics are usually categorized into two major classes: structural ceramics and functional ceramics. While the development of structural ceramics is mainly driven by the optimization of mechanical strength, hardness, and toughness,3 the performance of functional ceramics is determined by electric, magnetic, dielectric, optical, and other properties. In the ceramics community, structural ceramics can be further classified as (1) oxide ceramics (Al2O3, ZrO2, SiO2, etc.) and (2) non-oxide ceramics (SiC, TiC, B4C, TiB2, Si3N4, TiN, etc.). It needs to be categorically mentioned here that friction and wear properties determine the performance of structural ceramics in various engineering applications. This aspect is discussed in various chapters of this book.
2.3 PROPERTIES OF STRUCTURAL CERAMICS In general, ceramics have many useful properties, such as high hardness, stiffness, and elastic modulus, wear resistance, high strength retention at elevated temperatures, and corrosion resistance associated with chemical inertness.8 These are highlighted in Figure 2.1; the relative comparison among metals, ceramics, and polymers of various aspects in the context of tribological applications is summarized in Tables 2.1 and 2.2. Also, all the relevant mechanical properties are introduced in the next chapter. As is discussed in some of the subsequent chapters, although good hardness is required for resistance against abrasive and adhesive wear, higher elastic modulus is necessary for better resistance against Hertzian contact damage. From Table 2.1, it is clear that many engineering ceramics have better hardness and elastic modulus than steels, and, therefore, they are expected to have better abrasive and adhesive wear resistance. Also, it is known that ceramics can be used at very high temperature (more than 1000°C), where any other material class cannot be used. As far as maximum operating temperature is concerned, Ni-based superalloys are typically used at 1000°C. In contrast, some nitride and some oxide ceramics can be used at temperatures close to 1500°C. In addition to high melting point, ceramics have an advantage over metals in terms of high-temperature strength. High melting point can be very useful in terms of two aspects: (1) high contact temperatures, which are generated at a tribological contact, depending on the friction and operating parameters; and (2) high-temperature machining and tribological
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Excellent hardness and elastic modulus (better contact damage resistance)
High compressive strength (relevant for applications requiring high load at tribocontact)
Structural ceramics Low density (better specific properties than many metals)
High melting and mechanical property retention at elevated temperature (high temperature tribological applications)
Figure 2.1â•… Various properties of relevance to tribological applications of structural ceramics. TABLE 2.1â•… Physical, Mechanical, and Thermal Properties of Some Important Metallic, Polymer, and Ceramic Materials, Which Are Relevant for Various Tribological Applications8
Material
Density (ρ), gm/cm3
Elastic modulus (E), GPa
Fracture toughness (KIc), MPam1/2
Vickers hardness (HV), GPa
Thermal conductivity (K), W/m/K
Steel Cast iron Al-alloy Al2O3 ZrO2 Si3N4 SiC Polyamide (PA) Polyimide (PI) Polytetrafluoroethylene (PTFE) High-density polyethylene (HDPE)
7.8–7.9 7.1–7.4 2.6–2.9 3.9 5.6–6.25 3.2 3.2 1.1–1.14 1.3 2.1–2.3
210 64–181 60–80 210–390 140–210 170 450 2–4 3–5 0.4
50–214 6–20 23–45 3–5 8–10 4–7 4.5 3 —
1–9 1–8.5 0.25–1.40 14–19 12 16–18 25 0.8–1 — 0.12
30–60 30–60 121–237 25–35 2 25–50 90–125 0.25–0.35 0.37–0.52 0.25
0.92
0.2
0.13
0.33–0.57
1–2
TABLE 2.2â•… A Comparison among Three Primary Material Classes in Terms of Relevant Aspects in Relation to Tribological Applications10
Mass forces (F) Hertzian pressures (P) Friction-induced temperature increase (T ) Adhesion energy (Ad) Abrasion (Ab) Tribochemical reactivity (R)
Fpolymer╯
