Minimization of Through Thickness Flaws in Tungsten-Doped Diamond Like Carbon Thin Film

Tungsten-doped diamond-like carbon (DLC) coatings have been magnetron sputtered onto 52100 steel with chromium and chromium/tungsten carbide dual interlayers. The surface finish (Ra) of the substrate before deposition was 0.102 to 0.203 μm for a set of blocks and 0.05 to 0.10 μm for another set of samples, called buttons. SEM and TEM analyses revealed that this substrate finish as well as surface contaminants resulted in the formation of significant size flaws that develop during the deposition process through the film thickness. On the other hand a perfect flawless film was seen with the smooth substrate in the coupons. It was also observed that the film amplifies the substrate roughness. These two findings impact the tribological performance of the film. Current efforts attempted to determine an optimum set of deposition parameters, such as temperature and buffering gas pressure that would minimize or eliminate the formation of such flaws, and consequently minimize the roughness of the film surface.