Structure and tribological properties of WSe x, WSe x/TiN, WSe x/TiCN and WSe x/TiSiN coatings

Abstract

WSe x coatings were obtained by pulsed laser deposition (PLD) and ion-assisted PLD. The films were studied by means of X-ray diffraction, scanning and transmission electron microscopy, Auger electron spectroscopy and energy-dispersive X-ray spectroscopy. The WSe x films were also characterized in terms of their hardness, elastic modulus, surface topography and wear performance. The structure of WSe x films was shown to consist of various nanocrystalline mixtures of WSe 2 and W 3O phases in an amorphous WSe x matrix. Depending on deposition conditions, the WSe 2 crystallites were oriented with their basal planes either parallel or perpendicular to the substrate surface. A correlation between an amount of W 3O phase and c-axis-oriented WSe 2 phase was outlined. The incorporation of oxygen atoms between the basal planes was shown to cause lattice distortion and resulted in anisotropy of the lattice parameter. Improved endurance of WSe x coatings was due to their composite structure. The presence of hard underlayer, such as TiC, TiCN or TiSiN, was shown to be essential for extremely low friction coefficients down to 0.015–0.03. The WSe x /TiC films showed low friction from the very start of the tests without initial maximum. The superior performance of WSe x /TiSiN coatings both in air and under water suggests that the double-layer coatings are suitable for use in terrestrial tribological applications.