Ti-5Al-2.5Sn合金绝热剪切带的形成机制

Formation Mechanism of Adiabatic Shear Band of Ti-5Al-2.5Sn Alloy

利用分离式Hopkinson Bar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.

Using the technology of split Hopkinson Bar, the dynamic shearing experimentation on Ti-5Al-2.5Sn alloy has been conducted. The specimens are hat-shaped. Formation mechanism of adiabatic shear band of Ti-5Al-2.5Sn alloy has been studied by optical microscope and transmission electron microscopy (TEM). Results show that twins play a key role in the formation process of adiabatic shear band of Ti-5Al-2.5Sn alloy. The formation process of the adiabatic shear band can be divided into three stages. In the first stage, the plastic deformation of the forced shear zone is accomplished by dislocation slip and twining shear under impacting loading. A great deal of twins are formed in the deformed area. In the second stage, the local crystal orientation is adjusted due to the formation of deformed twins so that the dislocation that is at a disadvantage orientation of slipping formerly starts up, resulting in formation of the elongated sub-grains in the shear area. In the last stage, owing to interacting of the mobile dislocation and the twins, the fine equiaxial grains are formed by fracture of the twins under dynamic loading. At the same time, the fine equiaxial orthoscopic dynamic-recrystallized grains with fewer dislocations are formed in local areas of the shear band center. Size of the fine equiaxial grains formed in the shear band of Ti-5Al-2.5Sn alloy is approximately 0.1-0.3 mu m.