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Dr. Kathryn J. Wahl
Tribology Section, Code 6176
U.S. Naval Research Laboratory
Washington DC 20375-5342
Wednesday March 5, 4 pm
Thirkield Hall (Physics), room 103
In situ tribology: What's really happening in the buried sliding interface?
Tribological processes that influence friction and wear involve a complex combination of materials science, physics, chemistry, and rheology. Our understanding of these sliding contact phenomena is limited by the fact that all the action takes place in a buried interface. Most often the only evaluation of these interfaces is accomplished through ex situ means after separating the contacts. In situ approaches to studying friction and wear processes are challenging because most engineering surfaces are metals or ceramics that have no optical transparency at visible wavelengths. For this reason, most of what is known about interfacial processes occurring during sliding has been learned through optical probes of bearing interfaces.
In this talk, I will present examples of the kinds of physical and chemical processes occurring in buried sliding interfaces. Film thickness, chemistry/phase, rheology, morphology, and contact pressure are readily determined by optical methods. These real- time, in situ methods show a rich variety of physics and materials processing phenomena occurring during sliding. In situ experiments have demonstrated that steady state friction values often correlate with interface chemistry, while dynamic instabilities are associated with morphology and film thickness changes. I will give examples of how in situ measurements have helped us understand a variety of low friction materials (MoS2, diamond-like carbon, etc.). I will conclude by outlining scientific issues and opportunities for advancing our understanding of interfacial phenomena in tribology.
Refreshments will be served at 3:40pm