AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Monday Sessions
       Session NS1-MoA

Paper NS1-MoA1
Scaling Effects in Tribology: Micro- and Macroscale Studies of Diamond Like Carbon Nanocomposite Coatings

Monday, October 31, 2005, 2:00 pm, Room 204

Session: Nanotribology
Presenter: K.J. Wahl, Naval Research Laboratory
Authors: R.R. Chromik, North Carolina State University
K.J. Wahl, Naval Research Laboratory
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The formation of a transfer film is a key part of how solid lubricant and protective coatings provide low friction and resist wear. These interfacial films, or "third bodies," are found to be chemically and mechanically different from the original mating surfaces, and the evolution of contact behavior is tied intimately with their dynamic nature.@footnote 1,2@ While the role of transfer films in macroscopic contacts has received considerable study, the effects of scaling on friction, transfer film formation and dynamics remains largely uninvestigated. To this end, we have studied the microtribology of DLC nanocomposite coatings using a commercially available nanoindentation system. Reciprocating sliding tests at speeds of 1-4 µm/s were conducted using diamond and sapphire counterfaces having radii of 10 and 150 µm, respectively. These geometries resulted in two regimes of contact stresses: 0.25 to 0.85 GPa for sapphire and 1.5 to 5.5 GPa for diamond. The friction behavior as a function of contact stress was explored in the elastic regime. Microcontact friction behavior fit a Hertzian contact model over a broad load range. Diamond vs. DLC gave shear stress similar to macroscopic values@footnote 1@, while sapphire vs. DLC showed lower interfacial shear strength but higher friction overall. Ex situ optical microscopy, atomic force microscopy and micro-Raman spectroscopy suggest that friction response is correlated with formation of transfer films on the counterface. @FootnoteText@ @footnote 1@ T.W. Scharf and I.L. Singer, Tribology Letters 14, 3 (2003).@footnote 2@ I.L. Singer, S.D. Dvorak, K.J. Wahl and T.W. Scharf, J. Vac. Sci. Technol. A21, S232 (2003).