The effects of the surface roughness of hydrogenated diamond-like carbon (DLC) films on friction and wearproperties have been studied using a ball-on-disk type tribometer in air and water environments. RoughDLC films were formed by depositing DLC with the plasma-enhanced chemical vapor deposition methodon roughened stainless steel substrate prepared by argon plasma sputter etching. DLC films deposited ona smooth stainless steel substrate showed unstable friction behavior in both air and water environments.The final friction coefficient values ranged from 0.10 to 0.15 in air and 0.15 to 0.20 in water. Line-shapedlarge-scale delamination of DLC film from stainless steel substrate was observed for smooth DLC filmsrubbed in water. In an air environment, large-scale delamination was not observed, but wear of the DLCfilm could be seen. The wear scar formed on the stainless steel ball under water lubrication was larger thanthat formed in air environment. In contrast to smooth DLC film, DLC films having a rough surface showedstable frictional behavior. The friction coefficients in water and air environments were approximately 0.1and 0.2, respectively. No large-scale delamination of DLC film was observed for rough DLC films. Althoughfriction characteristics were improved by roughing the surface of the DLC films, the wear scars formingon the ball surface became larger with increases in the surface roughness of the DLC film. From the resultsof the tribotest in n-decane, which has almost the same viscosity as water, it was suggested that not onlythe hydrodynamic effect but also the interaction between DLC films and water affect the friction andwear behavior. DLC films changed from hydrophobic to hydrophilic by tribochemical reaction in waterenvironment. The low friction and wear of DLC films under water lubrication is considered to be causedby hydrophilication of the DLC films.
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