Structure, mechanical and tribological properties of TaCx composite films with different graphite powers

Abstract In this study, the TaCx composite films consisted of amorphous carbon and nanocrystalline TaC were synthesized with varying sputtering powers of graphite by DC magnetron sputtering, and studied their microstructure, mechanical and tribological behaviors. The film exhibits a Ta2C phase and high content a-C composite structure at a graphite power of 30 W, then a new composite structure with a lower a-C content and TaC nanocrystalline was formed, as increasing the graphite power, their hardness and toughness was increased at first and then decreased. The TaC110 film obtained the highest hardness (42.8 GPa), H/E (0.12) and elastic recovery (80.5%), this is due to the hard TaCx grains with high carbon vacancy are encompassed by suitable amorphous carbon phase, that the formed strengthening TaCx phase and nanocomposite structure greatly enhanced the mechanical properties. Nevertheless, the TaC50 film with a relatively low hardness and toughness exhibits the lowest average COF of 0.18 and wear rate of 1.44 × 10−6 mm3/N·m, which is attributed to the lubrications of partial tantalum oxide oxides and highly graphitized transfer layer on the frictional interface.