Nano-crystallization-Driven High Temperature Self-lubricating Properties of Magnetron-Sputtered WS_2 Coatings

摘要

In consideration of high temperature conditions, this paper focuses on the self-lubricating properties of WS_2 coatings at high temperature. A low coefficient of friction (CoF) about 0.07-0.2 for WS_2 coatings can be attained at temperatures of 100-400°C. The chemical stability, mechanical and tribological properties were investigated by energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy(SEM), nano-indentation tester and ball-on-disk tribometer, respectively. According to XRD and XPS spectra, the as-sputtered WS_2 coatings existed as 2 h-WS_2 structure. The crystal transition of WS_2 coatings from amorphous to (002) basal plane-oriented lubricating film, which was obtained by the synergistic effect of load and friction, and provided anti-friction performance at 100-400°C. At 500°C, the WO_3 formed by oxidation of WS_2 on the sample surface with lower hardness reduces the CoF and improves wear resistance. The wear resistance and anti-friction performance are discussed in terms of morphology of the wear scars, anti-oxidation capability of the coating and tribochemical reaction product of the friction pair.