MoSx-Ta composite coatings on steel by d.c magnetron sputtering

Sputter-deposited MoS2 films have been often used as dry lubricant in various industrial fields, such as space application and much attention has been paid to reduction of friction coefficient and improvement of mechanical properties in recent decades. One way to achieve this is to deposit a MoS2 film doped with another metal. The MoSx-metal films were found to be denser, more adhesive and more oxidation-resistant than pure MoS2. In this study, MoSx-Ta composite films were synthesized by Electron Cyclotron Resonance microwave source enhanced DC sputtering with different target powers. The effects of doping Ta on mechanical properties of MoSx-Ta films were investigated. The morphology and structure of films were investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The microhardness was evaluated using microhardness test instrument, and the adhesion strengths were obtained using a scratch tester. The results showed that the S/Mo ratio was influenced by the dc sputtering target power. Typical MoS2 (100) (103) (002) orientations were present in pure MoSx films, but disappeared with the increase in doped Ta, with the S/Mo content ratios decreasing from 1.52 to 0.84, and the hardness increasing from 3.55 to 15.23 GPa. The roughness and surface topography, friction coefficient and adhesion were significantly affected by the Ta, Mo and S content. The content of doped Ta plays a dominant role on the change in the Mo/S ratio, thereby influencing the mechanical and tribological properties of the MoSx-Ta composite films.