TEM study on oxidized TiCrN coatings ion-plated on a steel substrate

Coatings of TiCrN having compositions of (TiCr0.7)N, (TiCr1.2)N and (TiCr3.6)N were ion-plated on a steel substrate. The coatings were oxidized at 800 °C for 50 h in air, and the resultant morphology and compositional variance were studied utilizing transmission electron microscopy. The scales consisted of fine TiO2 and Cr2O3 grains, of which forming-tendency, size and the location in the oxide scale strongly depended on the Ti/Cr ratio of the coatings. During oxidation, not only the coating elements (Ti and Cr) but also the substrate element (iron) predominantly diffused outwards. At the same time, inward diffusion of oxygen from the atmosphere occurred. A detailed oxidation mechanism of TiCrN coatings is presented.