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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 12    No. 4    August 2002

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Superplastic behavior of TiAl based alloy at
 relatively low temperatures ranging from
800℃ to 1075℃
HUANG Bai-yun(黄伯云)1, ZHANG Jun-hong(张俊红)1,
HE Yue-hui(贺跃辉)1, LIU Yong(刘  咏)1, SUN Jian(孙  坚)2,
WU Jian-sheng(吴建生)

1. State Key Laboratory for Powder Metallurgy,
Central South University, Changsha 410083, China;
2. Shanghai Jiaotong University, Shanghai 200030, China

Abstract:Superplastic behaviors of TiAl based alloy with initial grain size of about 2μm obtained by multistep forging were investigated at 800~1075℃  with strain rates of 8×10-5s-1~2×10-3s-1. The results show that the material exhibits excellent low temperature superplasticity. Flow softing resulting from dynamic recrystallization is observed at relatively low temperatures (≤1000℃) or at higher strain rates (≥2×10-4s-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 2×10-5s-1, and at 1050℃, a maximum elongation of 570% is obtained at strain rate of 8×10-5s-1. At a fixed strain rate of 2×10-4s-1, when the alloy is deformed at 850℃, the microstructure is refined, however at 1050℃, 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 290kJ/mol at 950~1075℃, with the grain size exponent, p=2, and 224kJ/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 950~1075℃ is grain boundary sliding controlled by lattice diffusion.

 

Key words: TiAl based alloy; superplasticity; activation energy; grain size exponent

ISSN 1672-7029
CN 43-1423/U

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