Nanostructured WS2–Ni composite films for improved oxidation, resistance and tribological performance

Abstract

WS2 films were prepared by radio frequency sputtering. In order to improve its mechanical properties and oxidation resistance, Ni was used as the dopant and the effect of Ni content on the microstructure, anti-oxidation capability, mechanical and tribological properties of composite films were studied by energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), high resolution transmission electron microscope (HRTEM), field emission scanning electron microscopy (FESEM), nano-indentation tester, scratch tester and ball-on-disk tribometer. WS2 existed in nanocrystalline 2H–WS2 structure and Ni an amorphous phase. Increasing the Ni content resulted in a microstructural change from columnar platelet structure of pure WS2 film to a fiber-like structure of the composite film at low Ni content (5.0at%), and to a featureless structure at high Ni content (>10at%). Meanwhile, the films became more and more compact and showed improved anti-oxidation capability. The films represented an increase in hardness with Ni content ranging from 0 to 10.3at% due to the microstructure being densified, but exhibited high brittleness as the Ni content higher than 10at%. The composite film at low Ni content of about 5.0at% showed much better wear resistance than pure WS2 film, but became brittle and had poor wear resistances at high Ni content of above 10.3at%. The WS2–5.0at% Ni composite film exhibited the longest wear life of 5.8×105 cycles about sevenfold better than that of pure WS2 film in humid air. The wear mechanism was discussed in terms of the anti-oxidation capability of the films, morphology of the wear track and formation of transfer film.