Friction and wear behaviour of modified diamondlike carbon films

Hydrogen-free amorphous carbon films can be produced by sputtering or vacuum-arc discharge from a solid graphite source. Depending on the energy of the evaporated carbon atoms the growing film structure is more graphite-like (sp(exp 2)) or more diamond-like (sp(exp 3)), as the subplantation of impinging carbon atoms is the prerequisite for forming diamond bonds. Carbon atoms with sufficient high energy are formed by arc evaporation of graphite. Hence, tetrahedral amorphous carbon (ta-C) films with about 70% sp(exp 3)-bonds can be deposited. These ta-C films are known to have superhardness and an extremely low wear coefficient. In this contribution standard ta-C-filrns are compared to modified (t)a- C:X-films, deposited by using different gases and doped graphite targets. The first kind of modified ta-C was produced by using argon gas in order to moderate the carbon ion energy. The second modification was made by using nitrogen gas to deposit (t)a-C:N films. Finally, metal- containing (t)a-C:Me films were deposited from metal-doped graphite target. The different film types were analyzed with respect to structural constitution, mechanical and tribological properties. The friction and wear behaviour was measured in ball-disk arrangement under dry and lubricated conditions. The results are evaluated against the background of different sp3-contents and the chemical influence of doping elements. From these investigations important conclusions can be drawn for designing of ta-C based coating systems. It is shown, that coatings can be optimized by multilayering for demanding tribological conditions.