Achieving superlubricity and high adhesion strength of hydrogenated amorphous carbon film with Al/Cr/Si-doping

Excellent tribological properties of hydrogenated amorphous carbon films make it an important candidate for friction reduction in industry. However, the great challenge of achieving both high adhesion strength and super-low friction limits its wide applications. In this work, a novel Al, Cr and Si co-doped hydrogenated amorphous carbon (AlCrSi/a-C:H) film was prepared by high-power impulse magnetron sputtering (HiPIMS) method. The AlCrSi/a-C:H film showed favorable mechanical performance and high adhesion (∼80 N), which was attributed to the controlled elements doping and special transition layers produced by HiPIMS method. Meanwhile, superlubricity was obtained with coefficient of friction 0.0014. Detailed characterizations suggested that doping elements played significant roles in tribo-chemical reactions during friction. On one hand, doping elements can promote shear-induced graphitization and formation of graphite-like layers at the friction interface. On the other hand, the preferential oxidation of doping elements can protect the formed graphite-like layers from oxidation and the formed oxides nanoparticles can also be wrapped by carbon layers to prevent abrasive wear. It was the synergistic effects of graphitization and oxidation actions that led to superlubricity state of the film. The proposed AlCrSi/a-C:H film architecture with strong adhesion and superlubricity properties provides design criteria of superlubricious films for industrial applications.