Friction-induced reconstruction of sliding interface and low friction mechanism of WC/a-C films

Abstract

Tungsten carbide reinforced amorphous carbon (WC/a-C) films exhibit significantly lower coefficient of friction (COF) than typical a-C films in the atmospheric environment; thus, they are promising candidates for use as solid lubricants. However, the low friction mechanism of WC/a-C films remains poorly understood. Here, we revealed that the friction-induced formation of WO3-rich transfer film changed the real sliding interface between the initial friction pair materials into an interface between a WO3-rich transfer film and carbon-rich worn film surface (WO3/C interface). First-principles calculations indicated that the WO3/C interface showed weaker interactions than the C/C interface of the a-C film under the same conditions, particularly when the dangling carbon bonds at the sliding interface were not completely passivated. This resulted in a reduced COF of the WO3/C interface. Thus, friction-induced reconstruction of the sliding interface to an intrinsically weak-interacting interface is proposed as a new path to further improve the tribological performance of a-C-based films.