Role of refractory metal elements addition on the early oxidation behavior of TiN coatings

In this work, the early oxidation behaviors of TiN coatings incorporating V, Ta, W were comparatively studied at 500 degrees C for 30 min. It was found that O penetrates the TiN and TiVN coatings entirely, whereas the oxidation depths of TiTaN and TiWN coatings only occupy 10-20 % of their total thicknesses. The phase diagrams and XPS measurements suggest that all of V, Ta, W with the valence states higher than Ti4+ are present in TiO2 layers, which is advantageous to reduce the vacancy concentration as per the valence control rule. From the perspectives of thermodynamics and kinetics, however, the decreases in formation energy of O vacancy and diffusion coef-ficient of O, originating from the doping of Ta and W (rather than V) in TiO2 layers, should be responsible for the enhanced oxidation resistance.