FRICTION AND WEAR OF PLASMA-DEPOSITED DIAMOND FILMS

Reciprocating sliding friction experiments in humid air and in dry nit rogen and unidirectional sliding friction experiments in ultrahigh vac uum were conducted with a natural diamond pin in contact with microwav e-plasma-deposited diamond films. Diamond films with a surface roughne ss (R rms) ranging from 15 to 160 nm were produced by microwave-plasma -assisted chemical vapor deposition. In humid air and in dry nitrogen, abrasion occurred when the diamond pin made grooves in the surfaces o f diamond films, and thus, the initial coefficients of friction increa sed with increasing initial surface roughness. The equilibrium coeffic ients of friction were independent of the initial surface roughness of the diamond films. In vacuum the friction for diamond films contactin g a diamond pin arose primarily from adhesion between the sliding surf aces. In these cases, the initial and equilibrium coefficients of fric tion were independent of the initial surface roughness of the diamond films. The equilibrium coefficients of friction were 0.02-0.04 in humi d air and in dry nitrogen, but 1.5-1.8 in vacuum. The wear factor of t he diamond films depended on the initial surface roughness, regardless of environment; it increased with increasing initial surface roughnes s. The wear factors were considerably higher in vacuum than in humid a ir and in dry nitrogen.