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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。
The fracture morphology and microstructure evolution of fine-grained Ti-6Al-4V alloy were investigated by optical microscopy and scanning electron microscopy. The results show that the fracture mode of the fine grained Ti-6Al-4V alloy is quasi-cleavage fracture at room temperature and the main fracture mode of the sample is dimple-void accumulation fracture in superplastic stretching. With the initial strain rate unchanged, the α-phase grain size increases, the β-phase number increases, and the number of voids decreases with the increase of the stretching temperature. When stretched at 840 ℃ to 930 ℃, The grains remained isosceles, but the α-phase grains were elongated at higher temperature (960 ℃), and the baskets appeared in some areas. When the stretching temperature is constant, as the initial strain rate decreases, the α-phase grain size increases, the β phase increases, and the number of voids decreases. The β phase particles have good plasticity and low hardness when stretched at high temperature (above 960 ℃). The rich β phase is conducive to the coordinated sliding of the grain boundaries and has an inhibitory effect on the cavitation.