AVS 52nd International Symposium
    Advanced Surface Engineering Tuesday Sessions
       Session SE-TuM

Invited Paper SE-TuM7
The Effects of Water Vapor on the Friction Coefficient of Near Frictionless Carbon

Tuesday, November 1, 2005, 10:20 am, Room 201

Session: Hard Coatings and Wear Mechanisms of Protective Coatings
Presenter: W.G. Sawyer, University of Florida
Authors: W.G. Sawyer, University of Florida
P.L. Dickrell, University of Florida
A. Erdemir, Argonne National Laboratory
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Diamond-like carbon (DLC) films are of tribological interest due to their low friction, low wear rate, high hardness, and chemical inertness. These films can potentially be used in a wide range of applications, such as bearings, cutting tools, submersible parts, and biomedical applications. One class of diamond-like carbon coatings termed near frictionless carbon (NFC) that was developed at Argonne National Laboratory have been shown to sustain superlow coefficients of friction ( µ < 0.003) and wear rates ( K < 3-10 mm3/Nm) in self-mated contacts. The tribological behavior of these films is sensitive to the environment, only realizing their low coefficient of friction and wear rate in inert, dry, or vacuum environments. Using a microtribometer that is enclosed in a controlled environmental chamber the coefficient of friction over a range of surface temperatures and gaseous water vapor pressure was measured. The normal load for these experiments was 100 mN, the reciprocating speed was 18 mm/s, and the reciprocating path length was 0.6 mm. The oxygen partial pressure was measured to be less than 10 ppm for all experiments. The relative humidity varied from nominally dry to approximately 40%. The surface temperatures varied from 35C to 100C. The friction coefficient data will be presented with an accompanying uncertainty analysis. Using the friction coefficient to estimate the fractional coverage of adsorbate or percentage of effected sites, the data set was fit to an adsorption and desorption equation. This curve fitting revealed an activation energy of approximately 50 kJ/mol, which is consistent with the activation barrier for water.