细晶Ti-6Al-4V合金的超塑性变形行为与组织演变

Superplastic deformation behavior and microstructure evolution of fine-grained Ti-6Al-4V alloy

对不同温度下退火处理后的细晶TC4合金板材进行超塑性拉伸变形，研究该合金在750～850℃，应变速率为3＆#215;10^-4×10^-3 s^-1条件下的超塑性拉伸变形行为，分析晶粒尺寸、变形温度和β相含量对合金性能的影响。结果表明：退火后的（α＋β）型细晶Ti-6Al-4V合金表现出良好的超塑性，并且晶粒越细，最佳超塑性变形温度越低。晶粒直径为2.5μm、β相含量（体积分数）为9.6%的TC4合金在温度为800℃、应变速率为1×10＾-3 s＾-1的变形条件下，伸长率最大，达到862%。不同晶粒度合金的应变速率敏感系数m均随变形温度升高先上升后下降，最高达0.61。β晶粒处于α晶粒三叉晶界处，升温或拉伸变形时聚集并沿α晶界长大，形成细长的β晶粒并逐渐变粗大，因此在900℃以上高温下合金的超塑性变形能力降低。

Superplastic tensile deformation behavior was studied on fine-grained Ti-6Al-4V alloy sheets which are achieved from annealing treatment at temperature of 750～850℃and strain rate range of 3×10-4～1×10-3 s-1. And the effect of the grain size, deformation temperature andβphase volume fraction on the properties of the alloy were analyzed on superplastic deformation capacity. Result shows that fine-grained Ti-6Al-4V alloys has excellent superplasticity. When the Ti-6Al-4V alloy with the average grain size of 2.5 μm and beta volume fraction of 9.6% was deformed at the temperature of 800 ℃ and strain rate of 1×10-3 s-1, the highest elongation of 862% can be obtained. The sensitivity value （m） of the Ti-6Al-4V alloy with different grain size increase first and then decrease as the deformation temperature increases. The largest number of m value reaches 0.61. The beta grains locate at the triple junctions of alpha grains and they will agglomerate and grow along the triple junctions to form slender beta grains and grow coarsen. The optimum superplastic deformation temperature is largely decreased compared to traditional Ti-6Al-4V alloy for commercial use.