超塑成形工艺对TC21合金超塑性的影响

Effect of superplastic forming process on superplastic of TC21 alloy

分析对比了一步与两步超塑成形法对未经特殊细化的TC21钛合金超塑性和显微组织的影响。研究结果表明:在变形温度为870~930℃范围内,两步超塑成形伸长率明显好于一步超塑成形。在变形温度为870℃,第1步和第2步应变速率均为3.3×10-4s-1,预应变量为50%,间隙保温时间为20 min时,两步超塑成形的伸长率达到最大值为438.60%,和恒应变速率的一步超塑成形相比,伸长率提高了74.72%。真应力-应变曲线表明:两步超塑成形时,第2步开始时的应力明显小于第1步结束时的应力,第1步变形对金属产生了一定的软化作用。显微组织显示:动态再结晶一直伴随着整个两步超塑性变形过程,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 superplastic and microstructure of one-steps and two-steps superplastic forming without any special refinement for TC21 ti- tanium alloy were analyzed and contrasted. The results indicate that the elongation of two-steps superplastic forming is better than that of the one-step superplastie forming significantly when the deformation temperature in the range of 870 -930 ℃. The maximum elongation of 438. 60% for two-steps superplastic forming is obtained under the temperature of 870 ℃ , the pre-tensile elongation of 50% , the clear- ance holding time of 20 min, and the strain rates of 3.3 × 10-4 s- 1 for both steps, which increases by 74. 72% compared with that under the constant strain rate of one-step. The true stress-strain curves show that the stress at the beginning of the secoml step is smaller than the stress at the end of the first step obviously, the deformation in the first step softens the alloy in some degree. The microstructure shows that dynamic recrystallization accompanies the whole process of the two-steps superplastic forming, and the occurrence of dynamic recrystallization behavior provides fine microstrueture for the superplastic deformation and is beneficial to the improvement of the superplastieity of the alloy.