Oxidation behavior of sulfidation processed TiAl–2 at.%X (X=Si, Mn, Ni, Ge, Y, Zr, La, and Ta) alloys at 1173 K in air

The oxidation behavior of sulfidation processed TiAl–2 at.%X (X=Si, Mn, Ni, Ge, Y, Zr, La, and Ta) alloys was investigated at 1173 K in air for up to 630 ks under a heat-cycle condition between 1173 K and room temperature. During the sulfidation processing the TiAl–2 at.%Ta alloy formed Ta-aluminides on the TiAl3 layer, while the alloys containing Mn, Ni, Y, and Zr formed a TiAl3 (TiAl2 included) layer including a small amount of the third element, like the TiAl binary alloy. The cross-sectional microstructure of the TiAl–2 at.%Ta alloy shows the sequence: oxide scale/TiAlTa/TiAl2/alloy substrate; and the cross sections of the alloys containing Mn, Ni, Y, and Zr are: oxide scale/Ti3Al/alloy substrate. The TiAl–2 at.%Ta alloy showed some scale exfoliation at the initial stage of oxidation, but very little exfoliation after long oxidation times, whereas alloys containing other third elements such as Si and Ge showed little exfoliation at the first several cycles and then tended to exfoliate significantly, resulting in very rapid oxidation. The TiAlTa/TiAl2 layers formed by the reaction between the Ta-aluminide and TiAl3 improve the oxidation properties of the TiAl–2 at.%Ta alloy.