Microstructure and tribological properties of Cu-doped VCN films: The role of Cu

Element doping has been proved to be an effective method to improve the tribological property of hard films. In this work, C and Cu element co-doping are applied to reduce the room-temperature friction coefficient of VN film and the effect of Cu content on microstructure and tribological property of Cu-doped VCN films are discussed in detail. As expected, owing to the catalytic action of Cu, there is a transformation from sp(3) C-C to sp(2) C-C, which greatly affects the tribological property of Cu-doped VCN films, and with the increase of Cu content, the surface roughness and film thickness accordingly increase, and the nano-hardness has a gradual downward trend, however, the average grain size has an unexpected order: VCN-1Cu < VCN-2Cu < VCN-3Cu < VCN. Among these Cu-doped VCN films, the VCN-3Cu film with a higher sp(2) C-C content has the lowest friction coefficient, while the VCN-1Cu film with a higher sp(3) C-C content and a minimum grain size has the minimum wear rate of (0.36 +/- 0.03) x 10(-14) m(3)/N.m. Anyhow, the wear mechanism of these Cu-doped VCN films are all oxidation wear and adhesive wear