Ti-6Al-4V合金超塑性变形时的组织演化

利用光学显微镜和扫描电镜对超塑性拉伸后的细晶Ti-6Al-4V合金分别进行了断口形貌分析和组织演化规律研究。结果表明:细晶Ti-6Al-4V合金室温拉伸时,断裂方式为准解理断裂;超塑性拉伸时,试样断裂的主要形式是韧窝-空洞聚集型断裂。在初始应变速率不变的条件下,随着拉伸温度的升高,α相晶粒尺寸增大,β相数量增多,空洞数量减少,且在840℃至930℃拉伸时,α相晶粒仍保持等轴状态,但在较高温度(960℃)拉伸时,α相晶粒被拉长,部分区域出现网篮组织。在拉伸温度不变时,随着初始应变速率的降低,α相晶粒尺寸增大,β相增多,空洞数量减少。高温(960℃以上)拉伸时,β相颗粒具有良好的塑性和较低的硬度,丰富的β相有利于晶界协调滑动,并对空洞的产生具有抑制作用。

Microstructure Evolution of Ti-6Al-4V Alloy during Superplastic Deformation

The microstructure evolution and morphologies of Ti-6Al-4V alloy fracture after superplastic tensile testing were investigated by the optical microscope and the scanning electron microscope. The results show that, the ultrafine-grained Ti-6Al-4V alloy displays quasi ductile fracture in room temperature testing, while the ductile dimples-voids gathered type fracture in the superplastic tensile testing. In the same initial strain-rate, the grains dimension and β phase contents increase, and the voids decrease with increasing of the tensile temperature. From 840 °C to 930 °C, the grains still retain in equiaxed state. At the higher temperature (960 °C), the grains are coarsed and exhibit lamellar crystal at some sections. At the same tensile temperature, the grains dimension and β phase contents increase and the voids decrease with decreasing of the initial strain-rate. At elevated temperature (above 960 °C), β phases have good plasticity and low hardness. More β phase contents are favorable to the grain boundary sliding and the voids are difficult to generate.