High temperature oxidation behaviour of (Ti1-xCrx)N coatings

(Ti1-xCrx) N coatings with different Ti/Cr ratios were deposited on polished high speed steel substrates by reactive magnetron sputtering and oxidized in air at temperatures between 350 and 800 degrees C, with reaction times between 10 and 300 min. The oxidized coatings were characterized by sputter depth profiling using Auger Electron Spectroscopy (AES). The oxide layers of all the coatings grow according to an oxygen and chromium diffusion controlled, parabolic time law with activation energies between 98 and 166 kJ mol(-1). Composition of the oxide layers as well as the oxidation rate depend strongly on the chromium content of the Ti1-xCrx) N coatings. A minimum oxidation rate is observed for the (Ti0.6Cr0.4) N coating and is explained by the counterdiffusion effect of oxygen and chromium through the oxide layers.