THE EFFECT OF ROUGHNESS ON THE FRICTION AND WEAR OF DIAMOND THIN-FILMS

The friction and wear properties of polycrystalline diamond thin films depend on both the counterface material and the properties of the diamond layer. The roughness of the diamond is critical because it controls the amount of abrasive damage to the counterface. Reducing the surface roughness by polishing or control of the diamond growth process leads to reductions in both friction and the wear of the counterface. For low friction, the smoothest polished films or those which consist of microcrystalline diamond give the best performance and lead to only small amounts of counterface wear. When diamond slides against other materials a transfer layer forms which controls friction. Very little diamond debris is found in this layer for smooth films, but some debris from the fracture of the highest asperities is embedded in the transferred material for rougher films. There is no evidence for reaction between the diamond debris and the transferred material from a sapphire counterface.