FRICTIONAL BEHAVIOR OF DIAMOND-LIKE CARBON AND DIAMOND COATINGS IN OSCILLATING SLIDING

It is generally accepted that diamond-like carbon and diamond coatings have good frictional properties. Here it is shown that the frictional behaviour of diamond-like carbon coatings is strongly dependent on the actual deposition process used and that the frictional behaviour of diamond coatings is markedly different, depending on the counterbody material. An arc-ion-plated amorphous carbon (a-C) coating in oscillating sliding against a corundum counterbody has self-lubricating properties, owing to the formation of debris with characteristics of a defected graphitic phase. However, a plasma-assisted, chemical vapour deposition (CVD) hydrogenated a-C coating in oscillating sliding against a corundum counterbody does not give rise to measurable debris formation and, in comparison with the a-C coating, has a higher coefficient of friction. Brittle, non-metallic counterbody materials, such as corundum and diamond, in oscillating sliding contact with hot filament CVD diamond coatings result in a low coefficient of friction, whereas metallic materials, such as WC-C and Cr steel, form transfer layers on the diamond coatings, resulting in high friction.