The role of Si on the structure and tribological properties of a-C:H:Ni soft films at elevated temperatures

Si was doped into a-C:H:Ni film by radio frequency magnetron sputtering to improve its tribological properties at elevated temperatures from 25 to 300 °C. The structure, morphology, mechanical and tribological properties were investigated. The results showed that doped Si facilitated sp2-to-sp3 rehybridization, decreased H content, improved hardness, adhesion strength, higher structural stability and tribological properties. Notably, the a-C:H:Ni:Si-2 film (with Si content of 5.92 at.%) showed relatively better mechanical and tribological properties. The wear mechanism changed from ploughing accompanied by abrasive wear at 25 °C to adhesive wear at higher temperatures, which was closely related to increased sp3-to-sp2 rehybridization in the film and changes in the existing form of Si from Si-OH to SixOy at the counterface.