Transmission electron microscopy and energy dispersive X-ray spectroscopy on the worn surface of nano-structured TiAlN/VN multilayer coating

Nano-structured TiAlN/VN multilayer hard coatings grown by cathodic arc metal ion etching and unbalanced magnetron sputtering deposition have repeatedly shown low coefficients of friction and wear. In this paper, we employed the combined methods of cross-sectional ion beam milling sample preparation, conventional transmission electron microscopy, energy dispersive X-ray spectroscopy and quantitative spectrum analysis to give a comprehensive characterization of wear induced tribofilm, worn TiAlN/VN surface as well as wear debris. The major wear mechanism operating in the TiAlN/VN coating is the tribo-oxidation wear. A 20–50 nm thick tribofilm was observed on the TiAlN/VN worn surface, having inhomogeneous density, amorphous structure and multicomponent V–Al–Ti–O composition. Therefore the real sliding contact during the ball-on-disk test was a three-body sliding system including the tribofilm, in which the self-sintering and shearing deformation of the multicomponent oxide film played a significant role in determining the low friction coefficient. Owing to the low friction and high hardness, the TiAlN/VN worn surface retained good structural integrity without any crack, delamination or detectable deformation, resulting in minimized mechanical wear.