Effect of Substrate Bias Voltage and Ti Doping on the Tribological Properties of DC Magnetron Sputtered MoSx Coatings

Molybdenum disulfide (MoS2) is one of the most widely used solid lubricants. In this work, composite MoSx/Ti coatings were deposited by direct-current magnetron sputter ion plating onto plain carbon steel substrates. The MoSx/Ti ratio in the coatings was controlled by sputtering the composite targets. The composition, microstructure, and mechanical properties of the coatings were explored using an energy dispersive analysis of X-ray (EDX), Xray diffraction (XRD), and nano indentation and scratch techniques. The tribological behavior of the coatings was investigated using the pin-on-disc test at room temperature. With the increase of doped titanium content, the crystallization degree of the MoSx/Ti composite coatings decreased. The MoSx/Ti coatings showed a maximum hardness of 13 GPa at a dopant content of 5 at% Ti and the MoSx/Ti composite films outperformed the MoSx films. Moreover, the films exhibited a steady state friction coefficient from 0.13 to 0.19 and the main wear mechanisms of the MoSx/Ti coating in air were abrasive, adhesive, and oxidation wear.