Environmental embrittlement of γ titanium aluminide

The environmental embrittlement for the nearly stoichiometric TiAl compound, the microstructure of which consists of monophase γ with equiaxed grains, was evaluated by tensile tests, to determine the effects of the atmospheres used (vacuum, O₂ gas, air, and H₂ gas) and the testing temperatures (R.T. to 1173 K). At room temperature, the highest elongation and UTS values were observed in the samples tested in vacuum, while the worst values were observed in the samples tested in H₂ gas. Transgranular cleavage fracture was dominant and primarily independent of the environmental media. At intermediate temperatures, the samples tested in vacuum exhibited higher elongation and UTS values than those tested in air. Intergranular fracture became more dominant as temperature increased but was insensitive to the environmental media. Based on these results, the mechanism responsible for the observed environmental embrittlement and the implications were discussed.