Enhanced tribological and corrosion properties of multilayer ta-C films via alternating sp3 content

Abstract

Multilayer tetrahedral amorphous carbon (ta-C) films comprising alternating layers of different sp3 contents have been fabricated by periodically adjusting the bias voltage of filtered cathodic vacuum arc (FCVA) system. The microstructure, tribological and corrosion behaviors of the multilayer ta-C films deposited on YG6 cemented carbide were systematically investigated. Results showed that the multilayer structure effectively reduced the residual stress and restrained spalling of ta-C film, which frequently occurred in single-layer structure. The hardness and Young's modulus of multilayer ta-C films decreased with diminishing sp3 content of soft sublayer. Compared to the YG6 substrate, multilayer ta-C films exhibited much lower friction coefficient between 0.06 and 0.08 and effectively reduced the wear rate. Multilayer ta-C film deposited at bias voltage alternating between −50 V and –150 V (M-1 film) had the lowest friction coefficient of 0.06 and the lowest wear rate of 2.87 × 10−7 mm3/N m. The difference in anti-wear performance among the multilayer ta-C films was associated with the ratio of hardness to elastic modulus (H/E ratio). The electrochemical corrosion test confirmed the effective corrosion protection provided by the multilayer ta-C films, and the M-1 film obtained the highest polarization resistance. Judging from electrochemical impedance tests, the existence of some extent of microdefects could be the main factor limiting the electrochemical corrosion performance of the multilayer ta-C films.