Abstract
Surface diffusion layer produced by oxynitridation under glow discharge on Ti-6Al-4V alloy was analysed with respect to its microstructure, phase composition and selected mechanical as well as tribological properties. The microstructure and phase chemical composition have been examined by analytical transmission electron microscopy (TEM). By combining direct imaging/spectroscopy (eg. STEM-EDS) and selected area electron diffraction (SAED), it was possible to obtain detailed information about microstructure and phase chemical composition of both, substrate and surface layer. The as-received and oxynitrided alloy have the bimodal microstructure. TEM investigations of cross-sectional thin foils revealed a graded character of the surface layer consisting of three different sublayers: outermost TiO sublayer followed by ε-Ti₂N sublayer and a nitrogen-rich α (N) solid solution.
Selected micromechanical (microhardness, Young�s modulus) and tribological properties were measured. The results show that oxynitridation significantly improved microhardness and wear resistance of the Ti-6Al-4V alloy. Oxynitrided diffusion layers exhibit a good adhesion to the alloy substrate.

Key words
microstructure, oxynitrided layer, titanium alloy, wear resistance

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