Tribological performances of non-hydrogenated amorphous carbon coupling with different coating counterparts in ambient air and water

The tribological performances of non-hydrogenated amorphous carbon (a-C) coating sliding against different coating counterparts including a-C:H, CrN, CrSiN, TiN, TiCN and itself in ambient air and water were comparatively studied. Results showed that the a-C coating coupling with these different coatings exhibited similar low friction coefficients in ambient air, and the friction coefficients would decrease further in water if the a-C coating could survive. The wear rates of a-C coating sliding against transition metal nitride coatings were higher than those sliding against carbon-based coatings in ambient air. Water could reduce the wear rate of a-C coating drastically if there was a stable wear, while the unstable wear with rupture and delamination of the coupled coating in water would result in the wear rate increase or rupture of the a-C coating as well. The a-C coating coupling with itself exhibited the optimum tribological performances in water.

► The a-C coating shows low friction and wear to various coatings in ambient air.
► Friction between a-C and coatings without ruptures in water are reduced by water.
► Wear of a-C against coatings without ruptures in water are alleviated by water.
► Ruptures of the coupled coatings in water would lead to the wear increase of a-C.
► The a-C coupling with itself exhibits optimum tribological performances in water.