选区电子束熔炼Ti-6Al-4V钛合金的绝热剪切各向异性

使用分离式霍普金森压杆对选区电子束熔炼的Ti-6Al-4V合金棒材进行动态加载,通过动态加载曲线对比、X射线衍射及金相观察,分析了晶界和hcp-α相取向对纵/径向试样绝热剪切行为的影响。结果表明,纵向试样的临界应变和绝热剪切形成能均比径向试样的小,即绝热剪切敏感性比径向试样的高,因此试样在纵/径方向上存在绝热剪切各向异性。在同一加载方向下,晶界与hcp-α相取向对材料流变应力的影响相反,而且hcp-α相取向的作用更强。当hcp-α相的c轴平行于加载方向时(纵向试样),材料的流变应力更大、变形做功更多、热软化效应更强,因此纵向试样更易发生绝热剪切。

Anisotropic Behavior of Adiabatic Shear Band in Ti-6Al-4V Titanium Alloy Fabricated by Selected Electron Beam Melting

Ti-6Al-4V bar fabricated by selected electron beam melting was dynamically loaded by using a split Hopkinson pressure bar. The influences of grain boundaries and hcp-α phase orientation on adiabatic shearing behavior of the longitudinal/radial samples were analyzed by comparison of dynamic loading curves, X-ray diffraction and metallographic observation. The results show that compared to the radial sample, the longitudinal sample has smaller critical strain and formation energy of adiabatic shear, that is, its adiabatic shear susceptibility is higher than that of the radial sample, so there exists anisotropic behavior of adiabatic shear in the longitudinal/radial samples. With the same loading direction, not only the grain boundary and hcp-α phase orientation have opposite effects on the flow stress, but also the hcp-α phase orientation brings greater effect to the flow stress. When the c-axis of the hcp-α phase is parallel to the loading direction (longitudinal sample), the flow stress of the material is greater, the deformation process does more work, and the thermal softening effect is also greater. As a result, adiabatic shear phenomenon is more prone to occur in the longitudinal sample.