Experimental study of tribological and scratch properties of a-C:H films

Diamond-like-carbon coatings (DLC or a-C:H films) were prepared on Ti alloy substrate by rfplasma enhanced chemical vapor deposition. The surface morphology, surface roughness, hardness, critical load and frictional properties of the films were analyzed and evaluated by atomic force microscopy, nano-indentation, scratch test, friction test and fretting wear test. It was found that with the increase of film thickness, the surface roughness sharply increases and then significantly decreases, and it finally comes to a constant. The hardness and critical load determined by scratch test increase with the increase of film thickness, while the friction coefficient decreases with the decrease of surface roughness and the increase of hardness at ambient environment in air. After sliding for 5000 cycles, no evident wear trace was found on the film surface and the friction coefficient of DLC coating against corundum determined by fretting wear test decreases with the increase of relative humidity.