The effect of trace solute Au atoms on the phase structure, mechanical and self-lubricating properties of MoSi2 films

To overcome the high friction coefficient and low toughness bottleneck of MoSi2 used as protective films for moving parts, a novel strategy of doping and alloying through magnetron sputtering to build self-lubricating Mo-Si-Au solid solution film has been proposed. Herein, a series of MoSi2 films with different Au contents were prepared, and their phase structure, mechanical and tribological properties were investigated. The results indicate that when Au/Mo atomic ratio R = 0.10, Au atoms tend to replace Si atoms to form Mo-Si-Au solid solution film. Nevertheless, the Au atom would segregate to form a nanocomposite at R = 0.20. The nanoindentation test shows that the Mo-Si-Au solid solution film possesses the largest hardness, which is mainly attributed to the solid solution strengthening. The result of tribological testing exhibits that Au doping can significantly reduce the friction coefficient of MoSi2. More importantly, Mo-Si-Au solid solution film is realized with a lower coefficient of friction (∼0.08), which is ascribed to the formation of MoSiOx lubricating phase during the sliding induced solute Au atoms. Accordingly, the research would provide a considerable theoretical and technical foundation for the development of novel self-lubricating films with excellent mechanical properties.