High-temperature oxidation of Ti-48Al-2Nb-2Cr and Ti-25Al-10Nb-3V-1Mo

The short-term oxidation behavior of a γ-TiAl alloy (Ti-48Al-2Nb-2Cr) was compared and contrasted to that of an α₂-Ti₃Al base (Ti-25Al-19Nb-3V-1Mo) alloy. Oxidation of Ti-25Al-10Nb-3V-1Mo was found to occur at a moderate rate at 800°C, in a N₂+20% O₂ environment. A large increase in the oxidation rate occurred above this temperature. This large weight increase was attributed to a breakdown in the protective oxide scale on the surface of the α₂ intermetallic alloy, thereby permitting rapid diffusion of oxygen and nitrogen to the surface of the intermetallic. The oxidation rate of this alloy at 1200°C was not significantly higher than the oxidation rate at 1000°C. In contrast, the oxidation rate of Ti-48Al-2Nb-2Cr remained low up to 1200°C. At this temperature, a significant increase in oxidation was observed and was attributed to accelerated oxygen diffusion through the α₂ phase and increased solubility of oxygen in the y phase of the intermetallic microstructure. This weight increase occurred despite the fact that at 1200°C, the integrity of the oxide layer formed on the surface of this alloy was maintained. The results of this study illustrate the need for developing protective environmental coatings tailored to the individual intermetallic alloy.