Effect of HfO2 target sputtering power on mechanical and tribological properties of WS2 coatings

Abstract

To enhance the wear resistance and load-bearing capacity of WS₂ coatings, this study, leveraging the excellent mechanical properties of HfO₂, prepared HfO₂/WS₂ composite coatings via unbalanced magnetron sputtering by regulating the sputtering power of the HfO₂ target. The results show that within the low sputtering power range, as the sputtering power of the HfO₂ target increases, the surface density and hardness of the coating are improved, while the friction coefficient and wear loss are significantly reduced. The main mechanism is as follows: The increase in HfO₂ content promotes the amorphous transformation of the WS₂ matrix, and the dispersedly distributed HfO₂ particles can passivate the contact interface between the steel ball and the coating, achieving a low friction coefficient by inhibiting adhesive wear. However, within the high sputtering power range, as the power continues to increase, although the coating hardness keeps rising, the friction coefficient and wear loss increase significantly. This phenomenon stems from the coating oxidation caused by the formation of W–O bonds induced by excessive HfO₂, ultimately leading to the degradation of tribological properties. When the sputtering power is 80 W, the lubricating phase of amorphous WS₂ and the hard phase of HfO₂ reach the optimal synergistic balance, and the tribological properties of the coating are the best at this point (with an average friction coefficient of 0.062 and a wear rate of 1.571 × 10⁻⁸ mm³ N⁻¹ m⁻¹). The research indicates that HfO₂ doping can effectively improve the hardness and wear resistance of bearing surface coatings, providing a new method and idea for the development of novel hard lubricating coatings.