Temperature and water vapor pressure effects on the friction coefficient of hydrogenated diamondlike carbon films

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 [H.sub.2]O and [O.sub.2]. 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. [DOI: 10.1115/1.3139047] Keywords: gas-surface interactions, humidity, DLC, environment, ultra low friction, adsorption