Investigation of oxidation behaviors of the γ-TiAl substrate and plasma grown Mo-Si-Ti coating at 750 °C

Abstract

The oxidation behaviors of γ-TiAl and Mo-Si-Ti coating at 750 °C were investigated through controlling oxidation duration. Growth of Al2O3 and TiO2 divided the oxidation process of substrate into four stages with increasing duration. (i) Al2O3 oxide film caused low initial oxidation weight gain. (ii) TiO2 rod-like oxide particles destroyed the oxide film, causing increase of oxidation weight gain. (iii) Plate-like oxide particles caused by preferred orientation growth of Al2O3, hindered the rapid increase of oxidation weight gain. (ⅳ) Growth of TiO2 rod-like oxide particles and flaking of oxide film led to rapid increase of oxidation weight gain. Mo-Si-Ti coating mainly composed of (Ti, Mo)5Si3 showed a gradient structure. A diffusion layer allowed the coating to show a compositional gradient. Grain size gradually decreased from substrate to coating, with equiaxed grains near substrate and columnar grains near coating surface. Columnar grains accelerated initial oxidation as well as the production and volatilization of MoO3, causing holes in TiO2/SiO2 oxide film and higher initial oxidation weight gain than substrate. As the duration increased, oxide film became dense and fine grains and gradient structure prevented its flaking, accompanied by low oxidation weight gain. Mo-Si-Ti coating could enhance the oxidation resistance of substrate effectively.