Structure and tribological properties of WSex, WSex/TiN, WSex/TiCN and WSex/TiSiN coatings

WSex 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 WSex films were also characterized in terms of their hardness, elastic modulus, surface topography and wear performance. The structure of WSex films was shown to consist of various nanocrystalline mixtures of WSe2 and W3O phases in an amorphous WSex matrix. Depending on deposition conditions, the WSe2 crystallites were oriented with their basal planes either parallel or perpendicular to the substrate surface. A correlation between an amount of W3O phase and c-axis-oriented WSe2 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 WSex 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 WSex/TiC films showed low friction from the very start of the tests without initial maximum. The superior performance of WSex/TiSiN coatings both in air and under water suggests that the double-layer coatings are suitable for use in terrestrial tribological applications.