Effect of Mo addition on the oxidation behavior of TiAl intermetallic compound

Abstract

The oxidation behavior of the Mo-modified Ti-34.5 mass% Al intermetallic compound in air at 1073, 1173 and 1273 K was investigated by comparing with that of a binary Ti-34.5 mass% Al. The oxidation mass gain of the Mo-modified TiAls isothermally oxidized below 1273 K decreased with increasing Mo content. At 1273 K, however, a minimum in a mass gain-Mo content curve was observed at 2 mass% Mo content. For the Mo-modified TiAls parabolic oxidation curves obtained under the cyclic oxidation condition at 1173 K, in contrast to a linear curve for the binary TiAl. As a result of SEM-EPMA observation, the scales on the Mo-modified TiAls were found to have a layered structure in the following order from the outer side; TiO2/Al2O3/TiO2 + Al2O3/Ti3Al (Mo-enriched phase)/TiAl(matrix). Al2O3 in the scale/metal interface zone formed along the Mo-enriched phases. The second Al2O3 layer from outer and the Al2O3 in the inner layer were much more continuous and must have acted as protective layers. The oxygen solid solubility decreased in the Mo-modified TiAl and further in the Mo-enriched phase region, which must be the cause for the Al2O3 formation in the external oxidation manner.