分步变形条件对TC4-DT合金超塑性的影响

Effects of Multi-Step Tension on the Superplasticity of TC4-DT Alloy

采用分步超塑成形法研究了未经特殊细化的TC4-DT钛合金的超塑性。结果表明,在温度为860~950℃,应变速率为3.3×10^(-4)～1.0×10^(-2) s^(-1),预应变量为20%～80%,间隙保温时间为5～30min条件下,TC4-DT合金均表现出良好的超塑性(305.93%～506.67%)。变形温度为890℃,预应变量为50%,间隙保温时间为10min,第1步和第2步应变速率均为3.3×10-4 s^(-1)时,TC4-DT合金表现出最佳超塑性,伸长率为506.67%。真应力-真应变曲线表明,第2步开始时的应力明显小于第1步结束时的应力,第1步变形对该合金产生一定的软化作用。TC4-DT显微组织显示,动态再结晶一直伴随着整个分步超塑性变形过程,静态再结晶发生在间隙保温时间。再结晶行为的发生,为塑性变形提供了细小等轴组织,有利于该合金超塑性的提高。

The superplasticity of TC4-DT alloy without any special refinement was investigated through a multi-step superplasticity deformation method.The results indicate that the TC4-DT alloy exhibits the satisfied superplasticity（305.93%~506.67%）at 860 ~ 950 ℃ with strain rate from 3..3×10^-4 to 1.0×10^-2 s^-1,pre-tensile elongation from 20%to 80% and clearance holding time from 5to 30 min.TC4-DT alloy possesses the satisfied superplasticity with an elongation of 506.67% with deformation at 890℃ and pre-tensile elongation of 50%,the clearance holding time of 10 min as well as the both steps strain rates of 3.3×10^-4 s^-1.The true stress-strain curves reveal that the stress at the beginning of the second step is the smaller obviously than that at the end of the first step,and the deformation at first step can soften the alloy to some degree.The microstructure of the TC4-DT alloy shows that dynamic recrystallization accompany the whole process of the multi-step superplasticity deformation,and static recrystallization occurs in the clearance holding time of two steps.The occurrence of recrystallization behavior,which provides fine equiaxed microstructure for the superplastic deformation,is beneficial to the improvement of the superplasticity of the alloy.