AVS 51st International Symposium
    Surface Science Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM8
In Situ Studies of Interfacial Rheology of MoS2 and Most Solid Lubricating Coatings

Thursday, November 18, 2004, 10:40 am, Room 210C

Session: Tribology, Adhesion, and Friction
Presenter: K.J. Wahl, Naval Research Laboratory
Authors: G.Y. Lee, Naval Research Laboratory
I.L. Singer, Naval Research Laboratory
K.J. Wahl, Naval Research Laboratory
Correspondent: Click to Email
Materials properties (e.g. composition, microstructure, and mechanics) of both solid lubricant coatings and their interfacial transfer films have long been recognized as important to tribological performance. These properties are generally evaluated ex situ, before and after sliding have occurred. However, in situ observations of contacts have shown that interfacial rheology - the deformation and flow of matter within the contact - plays a significant role in controlling friction, wear and endurance of solid lubricants. In this paper, we will present real-time observations of interfacial rheology of MoS2 and MoST@footnote 1@ (Ti-Mo-S) coatings using in situ tribometery. The coatings were deposited by closed field unbalanced magnetron sputtering and contained between 0 and 20% titanium. Reciprocating tests were performed in both dry (<1%) and ambient air (45-60% RH) at 1-4 mm/s and under 1.1 GPa mean contact stress. The interface rheology was studied quantitatively using optical microscopy techniques. Transfer film buildup and depletion were monitored quantitatively using interference fringes, while interfacial dynamics (locus of sliding, stability, and strain rate) were evaluated through video microscopy. The interfacial rheology of MoS2 coatings was strongly influenced by environment (dry vs. humid). In contrast, interfacial rheology of MoST coatings was far less sensitive to humidity, but was strongly influenced by evolution of wear track surface composition and morphology. We will demonstrate how these quantitative measures of interfacial rheology can be used to help us interpret how transfer films influence friction, wear and endurance of MoS2-based solid lubricant coatings. @FootnoteText@ @footnote 1@ D.G. Teer, Wear 251 (2001) 1068-1074.