Superplastic behavior of a TiAl-based alloy

Superplastic behavior under the conditions of a temperature range from 850 to 1075 degrees C and strain rates varying from 8x10(-5) to 1 x 10(-3) s(-1) was investigated for Ti-33Al-3Cr-0.5Mo (wt%) alloy with a very fine grain size obtained by the multi-step thermal mechanical treatment. The results show that the TiAl-based alloy with a hot-deformed fine grain size possesses good superplasticity. It exhibits a strain rate sensitivity coefficient of 0.9 at a strain rate of 3 x 10(-5) s(-1) and temperature from 1000 to 1075 degrees C. Moreover, the strain rate sensitivity coefficient is stable during the hot deformation, and a tensile elongation of 517% was obtained at 1075 degrees C and a strain rate of 8 x 10(-5) s(-1). The superplastic behavior of the present fine-grained TiAl-based alloy can be explained by the local strain hardening and high m value during the tensile deformation. Microstructure evolution in the superplastic deformation was also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.