Superlow friction behavior of diamond-like carbon coatings: Time and speedeffects

The friction behavior of a diamond-like carbon coating was studied in recip rocating sliding contact at speeds from 0.01 to 5 mm/s, in dry nitrogen. "S uperlow" friction coefficients of 0.003-0.008 were obtained in continuous s liding at the higher speeds (>1 mm/s). However, friction coefficients rose to values typical of diamond-like carbon in dry and ambient air (0.01-0.1) at lower speeds (<0.5 mm/s) as well as in time-delayed, higher speed tests. The rise of the friction coefficients in both speed and time-delay tests w as in good quantitative agreement with gas adsorption kinetics predicted by the Elovich equation for adsorption onto carbon. More generally, superlow friction could be sustained, suppressed, and recovered as a function of exp osure time, demonstrating that duty cycle cannot be ignored when predicting performance of superlow friction coatings in devices. (C) 2001 American In stitute of Physics.