Microstructure, mechanical and tribological properties of Ti doped ta-C films deposited by a hybrid coating system

Abstract

Ti doped ta-C films were deposited by a hybrid coating system with filtered cathodic vacuum arc and pulsed DC magnetron sputtering. The microstructure, mechanical and tribological properties of ta-C: Ti films were investigated. Results showed that the Ti content in the films linearly increased from 0 to 19.9 at. % by increasing the Ti target current from 0 to 2 A. Without and with small amount of Ti doing, ta-C films presented typical amorphous characteristic. TiC phase was formed in the film at Ti content of 5.5 at. %, and as the Ti content further increased, the microstructure of the films gradually transformed to nanocomposite structure, where TiC nanocrystalls were embedded in amorphous carbon matrix. The sp3 bonding fraction was decreased with increasing Ti content, accordingly, the hardness and residual stress of films also decreased with diminishing sp3 content. In addition, the Ti doping had a positive impact on the adhesion force between films and substrates. ta-C film with Ti doping content of 5.5 at. % had the lowest friction coefficient and the lowest wear rate under different friction temperatures, corresponding to 0.09 and 3.6 × 10−8 mm3/N·m at room temperature, and 0.25 and 22.5 × 10−8 mm3/N·m at 400 °C, respectively, which was mainly attributed to the relative high hardness, lower residual stress, good adhesion of the film.