Microstructure and tribological properties of WSx/a-C multilayer films with various layer thickness ratios in different environments

Abstract

WSx/a-C multilayer films with different layer thickness ratios and the modulation period of ~50nm were prepared on monocrystalline silicon substrate by magnetron sputtering method. The morphology, microstructure and composition of the films were characterized by using scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. The surface chemical states under different etching conditions were investigated by X-ray photoelectron spectroscopy (XPS) depth profile technique. The hardness, the adhesion to the substrate and the tribological properties of the films under various test environments were evaluated by means of nano-indentation, scratching tester and ball-on-disk tribometer. The results showed that a WS2 phase with (101) preferential orientation was formed in WSx sublayer and the WC phase was not present at the WSx/a-C interface. The effects of La-C/LWSx ratio on the microstructure of as-prepared films were negligible while the effects on the mechanical and tribological properties of the film were significant. An increased hardness (the maximum of ~2.2GPa) and a decreased adhesion were found in the multilayer films. The WSx/a-C multilayer films were of the best wear resistance in vacuum (the minimum of 5.7×10−15m3N−1m−1) and exhibited much better tribological properties than a single WSx film in various test environments.