Dry sliding behaviour of non-hydrogenated DLC coatings against Al, Cu and Ti in ambient air and argon

Abstract

Magnetron sputtered non-hydrogenated diamond-like carbon (DLC) coatings were tested against Al, Cu and Ti pins using a vacuum pin-on-disc tribometer. The objective was to investigate the effect of counterface material on the tribological behaviour of the non-hydrogenated DLC coatings in air (29% RH) and an inert atmosphere (argon). In argon, a significant amount of adhesion and material transfer occurred from the Al and Ti pins to the DLC coating surfaces, increasing the coefficient of friction (COF) and inflicting severe damage to the coatings. Wear and material transfer between DLC coating and Cu were negligible in argon. Compared to the tests in argon, the tribological performance of DLC coatings against Al and Ti significantly improved in ambient air. In contrast, the wear rate of DLC coatings against Cu was higher in ambient air and its COF was similar under both conditions. In ambient air, carbonaceous layers were generated on Al and Ti but not on Cu. The adsorption of water vapour on the DLC coating surface and the formation of an easy-to-shear carbonaceous material at the sliding interface reduced the COFs and wear rates of non-hydrogenated DLC coatings in air with humidity.