The oxidation resistance and degradation process were investigated in air at 1173K for up to 1.44 Ms for the TiAl alloy, which has been pre-sulfidized at 1173 K in a H_2-H_2S gas mixture to form a TiAl_3 (+ TiAl_2) layer with 20 micron thickness on the alloy surface. And the reaction diffusion process of the TiAl_3-TiAl_2-TiAl system was computer-simulated.The TiAl_3 layer with very good oxidation resistance changed quickly into a TiAl_2 at 80 ks, which agreed well with the calculated one. The TiAl_2 layer transformed slowly to a TiAl, indicating good oxidation resistance for up to 810 ks, while with further oxidation it degraded significantly at 1.44 Ms, in contrast to the calculated time of 4 Ms. This is due to a localized oxidation along alloy grain boundaries, and the degradation mechanism was proposed.
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