Compositional design of diamond-like carbon film for tribological performance at elevated temperature: Si and W co-doping

Abstract Silicon and tungsten co-doped diamond-like carbon (Si-W-DLC) films with W gradually increased from the top surface to the internal layer were deposited via reactive megnetron sputtering. The mechanical and high-temperature tribological properties of the films were investigated by nanoindentation tester and reciprocating sliding tribometer, respectively. The structures, surface bonding states of the wear tracks were examined by Raman and X-ray photoelectron spectroscopy (XPS), respectively. The results reveal that the gradual W incorporation increases the hardness and elastic modulus from 19.8 ± 0.5 GPa and 183.3 ± 2.8 GPa GPa for the Si-DLC film to 21.6 ± 0.6 GPa and 192.6 ± 3.0 GPa for the Si-W-DLC film, respectively. The Si-W-DLC film maintains a coefficient of friction (COF) below 0.1 and a wear rate of 6.4 × 10−7 mm3/N•m at 500 °C, while the Si-DLC film is worn out. The graphitization of the Si-W-DLC film confirmed by the increment of the ID/IG ratio from 2.26 at room temperature to 3.44 at 500 °C is beneficial to reduce the coefficient of friction (COF). WO3, WO2, WC and silicon oxides are detected on the wear track tested at 500 °C. It is proposed that the synergistic effect of film graphitization, WO3, WO2, WC and silicon oxides formed on the wear track and the improved mechanical properties attributed to the gradual W distribution are responsible for the well high-temperature tribological properties.