NIST rPUBLfCATIONS ERCE /-II Nation 1 IVJ^C700D<£I and Technology Richard S/Ceramic triboloqy QC100 .U57 N0.758 1988 V1988 £ 2 NIST-PU (formerly tandards) NIST Special Publication 758 Ceramic Tribology: Methodology and Mechanisms of Alumina Wear Richard S. Gates, Stephen M. Hsu, and E, Erwin Klaus will f ? T T T NIST Special Publication 758 Ceramic Tribology: Methodology and Mechanisms of Alumina Wear Richard S. Gates and Stephen M. Hsu Ceramics Division Institute for Materials Science and Engineering National Institute of Standards and Technology (formerly National Bureau of Standards) Gaithersburg, MD 20899 E. Erwin Klaus Department of Chemical Engineering The Pennsylvania State University University Park, PA 16802 NOTE: As of 23 August 1988, the National Bureau of Standards (NBS) became the National Institute of Standards and Technology (NIST) when President Reagan signed into law the Omnibus Trade and Competitiveness Act September 1988 U.S. Department of Commerce C. William Verity, Secretary National Institute of Standards and Technology (formerly National Bureau of Standards) Ernest Ambler, Director Library of Congress U.S. Government Printing Office For sale by the Superintendent Catalog Card Number: 88-600582 Washington: 1988 of Documents, National Institute of Standards U.S. Government Printing Office, and Technology Washington, DC 20402 Special Publication 758 229 pages (Sept. 1988) CODEN: XNBSAV For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 FOREWORD This report is born out of a cooperative effort between the Chemical Engineering Department, at the Pennsylvania State University (PSU) , the Tribology Group of the National Bureau of Standards, and the partial support of the DOE ECUT Tribology Program. For years, the NBS has encouraged and sponsored graduate cooperative programs in which promising young scientists (some of them NBS staff members) come to NBS to conduct research, part of which often becomes the graduate's thesis. While it is not the objective of NBS to teach and train graduate students, such a program often furthers NBS programmatic goals by attracting high caliber scientists working on areas where NBS mission lies. Many excellent research papers have resulted and many students, upon graduation, have chosen to stay at NBS to continue their research careers. Such programs also draw many first rate university professors to NBS through the participation of these students in NBS research programs and projects, thus fostering NBS -university interactions and enhancing the scientific caliber of the work and reputation at NBS and the participating university. At the same time, through the frequent contacts that NBS has with industries, a natural university/government lab/industry relationship evolves, bringing a team focus on many research projects of significant economic and technological impact. In 1984, primarily through the interactions of Dr. Stephen M. Hsu of NBS and Professors Elmer Klaus and Larry Duda of PSU, a cooperative program in Tribology was started. Three graduate students: Mr. Richard Gates ( a NBS staff member), Mr. Jeffrey Yellets, and Mr. Douglas Deckman were enrolled at the Chemical Engineering Department at PSU. Three reports have been prepared to describe the fruit of their relentless efforts in the last three years. These studies were conducted at NBS under the guidance of Dr. Stephen Hsu with the close participation of Prof. Elmer Klaus who visited NBS frequently. Dr. James Eberhardt, Mrs. Terry Levinson, and Mr. David Mello of the DOE ECUT Tribology Program have at the same time sponsored a major Tribology program at NBS. That program also benefited from the studies conducted by Mr. Gates, Mr. Yellets, and Mr. Deckman. These students, while not working on sponsored projects directly, enabled NBS to explore some high risk, high pay off projects parallel to ECUT projects. When appropriate, the students were supported by ECUT for some time. To this, we gratefully acknowledge the generous support of DOE ECUT, without whose support many ideas would not be explored. Stephen M. Hsu Chief, Ceramics Division iii . ABSTRACT This report describes a systematic study that has been conducted to develop methods for measuring the tribological properties of ceramic materials under concentrated contacts. Step- loading four-ball and ball-on- three-flat wear tests were developed to provide friction and wear characteristics of ceramic/lubricant combinations under various lubrication conditions. These measurement techniques now enable one to study the effect of different materials processing parameters, material microstructures , and different lubricants on the friction and wear performance of ceramics. Water was found to react with alumina in a wearing contact to produce lubricous products. A combination of x-ray diffraction and thermogravimetric analysis techniques were used to investigate the kinetics of alumina-water reactions. These experiments determined that transition (gamma) alumina reacts with water at =200°C to form aluminum oxide hydroxide (boehmite - AlO(OH)), while reactions at -100°C produce aluminum trihydroxide (bayerite - Al(0H)3). A mechanism for lubrication of alumina with water is proposed whereby stresses in the contact junction cause a phase transformation from alpha to gamma alumina. The gamma alumina subsequently reacts with water to form a lubricous, layer lattice, hydroxide V CONTENTS Page FOREWORD iii ABSTRACT v LIST OF TABLES xi LIST OF FIGURES xiii Chapter I. INTRODUCTION AND SCOPE 1 II. CERAMIC WEAR TEST METHODOLOGIES: BACKGROUND AND LITERATURE SURVEY A. Basic Types of Tribological Studies .... 5 B. Current Efforts in Fundamental Ceramic Tribological Studies 8 C. Key Differences Between Ceramics and Metals 12 D. Approach to Evaluation of Ceramic Wear Used in This Report 18 III. EXPERIMENTAL APPARATUS AND OPERATING PROCEDURES A. Wear Tester Selection 19 B. Specimen Material Selection 25 C. Lubricant Selection 25 D. Specimen Characterization Methods 27 E. Friction and Wear Measurement 38 F. Specimen Preparation 40 G. Operating Procedure Descriptions 42 IV. RESULTS AND DISCUSSION A. Constant Condition Four-Ball Wear Testing Study 1. Base Conditions 45 2. Explanation of Severity Differences Between Steel and Ceramic Tests Conducted at the Same Operating Conditions 46 3. Four-Ball Constant Condition Test: Effect of Test Duration 50 4. Four-Ball Constant Condition Test: Effect of Load 55 B. Wear Test Severity Overlay 61 C. Analysis of Wear Scars 64 D. Four-Ball Constant Condition Test: Effect of Batch to Batch Variations in Specimen Material 78 vii E. Step-Loading Four-Ball Wear Testing Study 1 . Base Conditions 81 2. Step-Loading Test: Effect of Speed 86 3. Step-Loading Test: Effect of Specimen Material 86 F. Ball-on-Three-Flat Testing 89 1. Comparison of Results to Four-Ball Tests .... 89 2. Ball-on-Three-Flat Test: Interpretation of Friction Data 93 3. Ball-on-Three-Flat Test: Effect of Specimen Material 96 G. Summary 99 V. ALUMINA/WATER TRIBOSYSTEM: INTRODUCTION AND LITERATURE SURVEY A. Preliminary Explanation of Lubrication Mechanisms for Alumina With Water 100 B. Structures and Nomenclature of Aluminum Oxides and Hydroxides 103 C. Approach 112 VI. ALUMINA/WATER TRIBOSYSTEM: EXPERIMENTAL APPARATUS AND OPERATING PROCEDURES A. Test Approaches 113 1. Static Kinetic Tests 114 2. Powder Friction Tests 119 3. Dynamic Wear Tests 119 B. Reference Powders 120 C. Analytical Techniques 129 1. The rmogravime trie Analysis (TGA) 131 2. Differential Scanning Calorimetry (DSC) 141 3. X-Ray Powder Diffraction (XRPD) 141 4. Fourier Transform Infrared (FTIR) Analysis . 144 5. Scanning Electron Microscopy (SEM) 145 VII. ALUMINA/WATER TRIBOSYSTEM: RESULTS AND DISCUSSION A. Kinetic Experiments on Powders 146 B. Powder Friction Tests 158 C. Wear Debris Analysis 162 VIII. SUMMARY AND CONCLUSIONS 175 IX. RECOMMENDATIONS FOR FUTURE WORK 179 REFERENCES 180 APPENDIX A - Selected Bulk Properties of Cer 006 and Cer 021 Alumina 184 viii APPENDIX B - Coefficient of Friction Calculation for the Four-Ball Apparatus 185 APPENDIX C - Equivalent Wear Scar Diameter Concept 187 APPENDIX D - Specimen Cleaning Procedure 190 APPENDIX E - Pressure-Temperature Relationship for the Alumina/Water Bomb Reactor 192 APPENDIX F - X-Ray Powder Diffraction Patterns for Reference Powders ALl through AL6 195 APPENDIX G - Interplaner Spacings, 2 Thetas, and Relative Line Intensities for X-Ray Powder Diffraction Patterns of Alumina's, Alixminum Oxide Hydroxides and Aluminum Trihydroxides 201 APPENDIX H - An Estimate of the Hertzian Contact Diameter, Mean Pressure, and Maximum Pressure for 52100 Steel, and Alumina Specimens, in the Four-Ball Apparatus 205 APPENDIX I - Derivation of a Pseudo First Order Dependence for the Gamma Alumina/Water Reaction at 194°C . 210 APPENDIX J - Mean Pressure Test Severity Plot for Wear Scar Diameter vs Load (psi) 213 APPENDIX K - Mean Pressure Test Severity Plot for Wear Scar Diameter vs Load (MPa) 214 NOTE: Certain commercial equipment, instruments, or materials are identified in this report to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. ix LIST OF TABLES Table Title Page 1 Wear Test Design Philosophies 6 2 ASTM Wear Test Methods Applicable to Ceramic Materials 11 3 Comparison of Physical and Mechanical Properties of Selected