The friction and wear properties of polycrystalline diamond thin films
depend on both the counterface material and the properties of the dia
mond layer. The roughness of the diamond is critical because it contro
ls the amount of abrasive damage to the counterface. Reducing the surf
ace roughness by polishing or control of the diamond growth process le
ads to reductions in both friction and the wear of the counterface. Fo
r low friction, the smoothest polished films or those which consist of
microcrystalline diamond give the best performance and lead to only s
mall amounts of counterface wear. When diamond slides against other ma
terials a transfer layer forms which controls friction. Very little di
amond debris is found in this layer for smooth films, but some debris
from the fracture of the highest asperities is embedded in the transfe
rred material for rougher films. There is no evidence for reaction bet
ween the diamond debris and the transferred material from a sapphire c
ounterface.