Tribological behavior of nano-undulated surface of diamond-like carbon films

Tribological behavior of nano-undulated diamond-like carbon (DLC) films of the surface roughness ranging from 0.6 to 13.7 nm was investigated in an ambient air of 50% relative humidity. The nano-undulated DLC films were prepared by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) using nanosized Ni dots on a Si (100) substrate. The friction coefficient between the DLC film and the steel ball was characterized by a ball-on-disk type wear rig. Auger and Raman spectroscopy analysis of the debris revealed that the tribochemical reaction with environment was significantly suppressed as the surface roughness increased. Even if the rough surface increased the wear rate of the steel ball and thus the concentration of Fe in the debris, neither the oxidation of Fe nor the graphitization of the carbon in the debris occurred on the rough surface. However, the frictional behavior was affected by several factors: the composition and the size of debris, plowing effect of the rough surface, and the presence of the transfer layer on the wear scar surface.