Superplastic behaviors of TiAl based alloy with initial grain size of about 2?μm obtained by multistep forging were investigated at 800 ～ 1?075?℃ with strain rates of 8×10 -5 s -1 ～2×10 -3 s -1 . The results show that the material exhibits excellent low temperature superplasticity. Flow softing resulting from dynamic recrystallization is observed at relatively low temperatures (≤ 1?000?℃) or at higher strain rates (≥2×10 -4 s -1 ). Continuous strain hardening resulting from strain enhanced grain growth occurs at higher temperatures or at lower strain rates. A maximum elongation of 533% is obtained at 800?℃ with strain rate of 2×10 -5 s -1 , and at 1?050?℃, a maximum elongation of 570% is obtained at strain rate of 8×10 -5 s -1 . At a fixed strain rate of 2×10 -4 s -1 , when the alloy is deformed at 850?℃, the microstructure is refined, however at 1?050?℃, is coarsened. The as deformed microstructure shows relatively high strain rate sensitivity value and it keeps nearly stable during deformation. The activation energy is calculated to be 290?kJ/mol at 950 ～ 1?075?℃, with the grain size exponent, p =2, and 224?kJ/mol at 800 ～ 900?℃ with p =3. Therefore, it is suggested that the dominant mechanism during superplastic deformation at 800 ～ 900?℃ is grain boundary sliding controlled by grain boundary diffusion; however at 950 ～ 1?075?℃ is grain boundary sliding controlled by lattice diffusion.
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