双态组织Ti−6Al−2Zr−1Mo−1V合金的热拉伸变形行为与球化机理

摘要

通过等温拉伸实验研究双态组织Ti?6Al?2Zr?1Mo?1V合金的热变形行为、显微组织演变与断裂特征.结果表明:材料的流动软化由双态组织动态球化引起,并导致较高的应力指数和热激活能.结合SEM、EBSD和TEM显微组织观察发现,750和800℃下动态球化由α/α亚晶界的形成与β相的渗透共同导致;而在850℃下由于低角度晶界向高角度晶界转化,生成呈项链状分布的细小晶粒,证明该温度下主要的球化机制为动态再结晶.随着变形温度的升高或应变速率的减小,合金的断裂机制由微孔聚集向沿晶断裂转变.%The hot deformation behavior, microstructure evolution and fracture characteristics of bimodal microstructured Ti?6Al?2Zr?1Mo?1V alloy were investigated by isothermal tensile tests. Results reveal that flow softening is caused by dynamic globularization of the bimodal microstructure, which also results in a relatively high stress exponent and thermal activation energy. The corresponding SEM, EBSD and TEM observations indicate that the dynamic globularization at 750 and 800 ℃ is accomplished by the formation ofα/α sub-grain boundary and penetration of theβ phase. However, dynamic recrystallization (DRX) is the main globularization mechanism at 850 ℃, which was proved by the generation of fine grains with a necklace-like character due to the transformation of low-angle boundaries (LABs) into high-angle boundaries (HABs). With an increase in the deformation temperature or a decrease in the strain rate, the fracture mechanism changes from microvoid coalescence to intergranular fracture.