Effect of yttrium doping on the structure and tribological properties of MoSx coatings in humid atmosphere

MoS₂ is prone to oxidation and moisture-induced decomposition in humid environments, leading to a sharp decline in its frictional properties. This significantly restricts the application scope of MoS₂. Therefore, modifying MoS₂ to enhance its frictional performance in humid conditions is of great necessity. To this end, MoS_x-Y composite coatings with varying yttrium contents were fabricated by direct current magnetron sputtering. The effects of Y doping and its concentration on the structural characteristics, mechanical properties, and tribological performance of MoS_x coatings were systematically investigated using SEM, XPS, XRD, nanoindentation, and friction tests. The results indicate that the doped Y element mainly existed in the form of Y₂O₃ within the coating. As the Y element content increased, the hardness and elastic modulus of the MoS_x-Y composite coating gradually increased. The tribological properties of the coatings with different Y contents under a humid atmosphere (RH=60 %) were comprehensively evaluated through rotary friction experiments. The experimental results reveal that the introduction of appropriate Y contents can effectively reduce the friction coefficient of the MoS_x coating in a humid environment to approximately 0.1, and significantly enhance its friction life. The doping of the Y element inhibits the growth of the (100) and (110) planes of MoS_x, causing the coating to grow preferentially along the (002) plane, which is an important factor contributing to the enhancement of the tribological properties of the MoS_x coating by yttrium doping. This work demonstrates the controllability and potential of the tribological properties of the MoS_x coating.