THE COUPLED EFFECTS OF ENVIRONMENTAL COMPOSITION, TEMPERATURE AND CONTACT SIZE-SCALE ON THE TRIBOLOGY OF MOLYBDENUM DISULFIDE by Harmandeep S. Khare A dissertation submitted to the Faculty of the University of Delaware in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering Spring 2014 © 2014 Harmandeep S. Khare All Rights Reserved UMI Number: 3631183 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI 3631183 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, MI 48106 - 1346 THE COUPLED EFFECTS OF ENVIRONMENTAL COMPOSITION, TEMPERATURE AND CONTACT SIZE-SCALE ON THE TRIBOLOGY OF MOLYBDENUM DISULFIDE by Harmandeep S. Khare Approved: __________________________________________________________ Suresh G. Advani, Ph.D. Chair of the Department of Mechanical Engineering Approved: __________________________________________________________ Babatunde Ogunnaike, Ph.D. Dean of the College of Engineering Approved: __________________________________________________________ James G. Richards, Ph.D. Vice Provost for Graduate and Professional Education I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ David L. Burris, Ph.D. Professor in charge of dissertation I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ Joshua L. Hertz, Ph.D. Member of dissertation committee I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ Chaoying Ni, Ph.D. Member of dissertation committee I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ Michael H. Santare, Ph.D. Member of dissertation committee This dissertation is dedicated to my parents ACKNOWLEDGMENTS I thank the Air Force Office of Scientific Research (AFOSR), the University of Delaware Office of Graduate and Professional Education, and the University of Delaware Department of Mechanical Engineering for financial support of this work. I thank my dissertation committee, Dr. Joshua Hertz, Dr. Chaoying Ni and Dr. Michael Santare, for their support and contributions to this research and my graduate training. I thank the staff and members of the Keck Advanced Microscopy Facility, especially Dr. Fei Deng and Dr. Laurel Kegel for their time and effort in making available the microscopy instrumentation. I also thank the administrative staff at the Department of Mechanical Engineering, especially Lisa Katzmire and Lita Toto for all their work and support during the past six years. A very special thank you to Steve Beard for helping me mill and lathe all those doozies, for being accommodating of my incessant demands of the shop, for the music and trivia, conversations and friendship. I thank Andy Korenyi-Both for valuable discussions and for providing the MoS2 coatings used in this study, and to Alan Ponder for all his efforts and support to keep our AFM on its feet. A special thanks to the tribology community for the camaraderie, and for inciting, critiquing and facilitating research ideas over the years. I extend a very special thanks to all current and former members of the Materials Tribology Laboratory, for the invaluable discussions, collaborations, 80s music and above all, friendship. I thank all my friends here at Delaware, especially Ananth and Tulasi for their friendship through the years of graduate school. v I owe a debt of gratitude to my parents for their selflessness, sacrifice and support through the years. They have been an inspiration to me since before I knew what the word meant. I owe an equal measure of gratitude to my sisters, especially Baldeep, for her love, humor and steadfast support. I thank Shannen for all the love, laughter and optimism. Finally, I would like to express my heartfelt gratitude to my graduate mentor, Dr. David Burris for his unfaltering support, patience and encouragement of my graduate research and training during the last five years. His enthusiasm and dedication to tribology research is an inspiration which will remain a hallmark of my time in graduate school. vi TABLE OF CONTENTS LIST OF TABLES ........................................................................................................ ix LIST OF FIGURES ........................................................................................................ x LIST OF ABBREVIATIONS ..................................................................................... xvi ABSTRACT .............................................................................................................. xviii Chapter 1 INTRODUCTION .............................................................................................. 1 Tribology and the Importance of Lubrication .................................................... 1 Introduction to Solid Lubricants ......................................................................... 3 Solid Lubricants in Extraterrestrial Environments ............................................. 5 2 MOLYBDENUM DISULFIDE AS A SOLID LUBRICANT ........................... 7 Tribofilms and Interfacial Friction ..................................................................... 9 Effect of Water on MoS2 Tribology ................................................................. 11 Effect of Temperature on MoS2 Tribology ...................................................... 14 Lubrication Mechanisms: Motivation for Current Studies ............................... 15 3 FRICTION AND WEAR IN MATERIALS .................................................... 17 Background: Adhesive Theory of Friction ....................................................... 17 Elastic Contact Mechanics ............................................................................... 22 Single and Multi-Asperity Contact ................................................................... 23 Tribological Characterization ........................................................................... 24 Single asperity contacts .............................................................................. 24 Multiasperity contact .................................................................................. 27 Multi-Scale Tribometry of Molybdenum Disulfide ......................................... 29 4 EXPERIMENTAL MATERIALS AND METHODS ...................................... 30 Materials ........................................................................................................... 30 Macroscale Tribometry .................................................................................... 32 High temperature tribometry ...................................................................... 32 vii In-situ wear measurement ........................................................................... 34 Nanoscale Tribometry ...................................................................................... 38 Lateral force calibration: Background and challenges ............................... 38 Lateral force calibration: Method development ......................................... 42 Lateral force calibration: Experimental validation ..................................... 53 LFM measurements .................................................................................... 57 Environmental Control ..................................................................................... 58 Energy Dispersive X-Ray Spectroscopy .......................................................... 60 5 RESULTS ......................................................................................................... 62 Effects of Environment and Temperature on MoS2 Friction ............................ 62 Role of Oriented Nanoscale Tribofilms ........................................................... 82 6 DISCUSSION ................................................................................................... 88 7 CLOSING REMARKS .................................................................................... 99 Design Considerations .................................................................................... 101 REFERENCES ........................................................................................................... 102 Appendix A EXTENDED WEDGE METHOD VALIDATION DATA ..........................