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利用分离式HopkinsonBar技术,采用帽形试样,对Ti-5Al-2.5Sn合金进行动态剪切实验,通过光学显微镜、透射电镜研究了其绝热剪切带的形成机制。结果表明:孪晶在Ti-5Al-2.5Sn合金绝热剪切带的形成过程中起到了非常关键的作用;Ti-5Al-2.5Sn合金绝热剪切带的形成过程可分为3个阶段:第1阶段,在冲击载荷作用下,强迫剪切区的塑性变形由位错滑移与孪生切变共同完成,并形成大量孪晶;第2阶段,由于孪晶的形成,调整了局部晶体的位向,原来不动的位错启动,形成长条状的亚晶结构;第3阶段,在外加动态载荷下,运动位错与孪晶作用,使孪晶片发生断裂,形成细小等轴晶粒;同时,剪切带中心区域局部形成了等轴、畸变小、位错少的细小动态再结晶晶粒。Ti-5Al-2.5Sn合金绝热剪切带内的细小等轴晶粒尺寸为0.1~0.3μm。
The dynamic shearing experiment of Ti-5Al-2.5Sn alloy was carried out by using the split HopkinsonBar technique. The formation mechanism of adiabatic shear band was studied by optical microscope and transmission electron microscope. The results show that the twins play a key role in the formation of adiabatic shear band of Ti-5Al-2.5Sn alloy. The formation of adiabatic shear band in Ti-5Al-2.5Sn alloy can be divided into three stages: In the first stage, the plastic deformation of the forced shearing zone was completed by the dislocation slip and twin shear under the action of impact load, and a large number of twins were formed. In the second stage, due to the formation of twins, the local crystal position In the third stage, under dynamic loading, motion dislocations and twins cause the twins to break to form fine equiaxed grains. In the third stage, At the same time, small dynamic recrystallization grains with equiaxed, small distortion and few dislocations are formed locally in the center of the shear zone. The fine equiaxed grain size in the adiabatic shear band of Ti-5Al-2.5Sn alloy is 0.1 ~ 0.3μm.