Improvement on oxidation resistance of titanium aluminide intermetallics by coatings

TiAl intermetallics are emerging as a revolutionary engineering material for high temperature structural applications. However, it's poor oxidation resistance must be overcome before it may be used in practice above 800 degrees C. In this paper, the effect of MCrAlY overlay coatings, reactively-sputtered Al2O3 films and TiAlCr coatings on the oxidation resistance of TiAl alloy was investigated. CoCrAlY and NiCrAlY coatings could remarkably decrease the oxidation rate of TiAl. However, due to the inward diffusion of Co and Ni into the substrate, two brittle and hard diffusion layers formed at the coating/substrate interface. Reactively-sputtered Al2O3 films were very effective to improve the isothermal oxidation resistance of TiAl at 900 degrees C. However, the thermal expansion mismatch resulted in the poor cyclic oxidation resistance. TiAlCr coatings not only effectively improved the isothermal and cyclic oxidation resistance of TiAl due to the formation of adherent Al2O3 scale, but also exhibited a good compatibility with the substrate. This coating may become a realistic protective coating for engineering gamma-TiAl.