Ｔｉ-44Aｌ-6Ｎb-2Fe 合金低温超塑性及高温拉伸组织演

n order to improve the hot deformation processing capability of high-Nb TiAl based alloys,this study used the Fe element to partly replace the Nb element in high-Nb TiAl based alloys to prepare the new-type high-Nb and Fe-contained Ti-44Al-6Nb-2Fe alloy. The alloy ingot was firstly isothermally package forged,and then the high-temperature tensile testing was carried out on this forged alloy at the initial strain rate of 1×10^-4 s^-1 and temperatures of 800—1 000 ℃,and the high-temperature tensile deformation behavior and microstructure evolution behavior of the alloy were studied. The results show that the alloy contains more B2 phases(30%—40%). With the increasing of temperature,the dynamic recrystallization effect increases,dislocation decreases,grain size increases,and aspect ratio of grains decreases,all of which correspond to the stress-strain state and enhancement of hot deformation processing capability of the alloy. When the tensile testing is at 800 ℃ and 850 ℃,B2 phase is a brittle phase,and the stress concentration in the regions of B2 phase and B2 / γ phase interface leads to the formation of a large number of cracks and holes (14. 5% cavity at 800 ℃),resulting in a low elongation (123. 1% elongation at 800 ℃),even the early fracture,and the neck shrinkage is obvious. When the tensile testing is at 900 ℃,the strain-rate sensitive exponent m is 0. 284,the elongation is significantly increased (163. 0%), and the neck shrinkage still exists. When the tensile testing is at 950 ℃ and 1 000 ℃,B2 phase has transformed into a ‘soft’phase that plays a good role in stress-strain coordination effect,and extensive grain boundary sliding between B2 phase and γ phase can be found. There are almost no cracks and holes in the microstructure,and the elongation increases sharply (307. 9% at 950 ℃)without neck shrinkage. The alloy has superplasticity at 950 ℃ and 1 000 ℃,which belongs to low-temperature superplasticity for TiAl based alloys. The higher content of B2 phase and its excellent stress-strain coordination effect are the important reasons and characteristics for the alloy yielding the low-temperature superplasticity.