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Research Papers: Mixed and Boundary Lubrication

Temperature and Water Vapor Pressure Effects on the Friction Coefficient of Hydrogenated Diamondlike Carbon Films

[+] Author and Article Information
Pamela L. Dickrell, N. Argibay, W. Gregory Sawyer

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611

Osman L. Eryilmaz, Ali Erdemir

Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439

J. Tribol 131(3), 032102 (May 27, 2009) (5 pages) doi:10.1115/1.3139047 History: Received April 27, 2007; Revised April 24, 2009; Published May 27, 2009

Microtribological measurements of a hydrogenated diamondlike carbon film in controlled gaseous environments show that water vapor plays a significant role in the friction coefficient. These experiments reveal an initial high friction transient behavior that does not reoccur even after extended periods of exposure to low partial pressures of H2O and O2. Experiments varying both water vapor pressure and sample temperature show trends of a decreasing friction coefficient as a function of both the decreasing water vapor pressure and the increasing substrate temperature. Theses trends are examined with regard to first order gas-surface interactions. Model fits give activation energies on the order of 40 kJ/mol, which is consistent with water vapor desorption.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the contact region of the low contact pressure tribometer

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Figure 2

Initial run-in of two as-deposited self-mated NFC samples in a dry argon environment

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Figure 3

Friction coefficients for repeated sliding at the same location after separating the surface for specified periods of time in a dry argon environment

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Figure 4

Friction coefficients over a single experiment ramping the water vapor concentration while holding the oxygen partial pressure below 20 ppm. Under a contact load of 200 mN and a sliding speed of 4 mm/s.

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Figure 5

Experimental results of friction coefficient (μ) as a function of counterface surface temperature and water vapor pressure

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Figure 6

Model fit of Eq. 5 to experimental data with (a) a universally fit value for τ0 and Ea and (b) a universally fit value of τ0 and a variable fit of Ea

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Figure 7

Plot of the friction coefficient versus the relative humidity at the heated sample surface

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