Enhanced Grain Refining Efficiency Assisted by Martensitic Transformation in Metastable β-Titanium Alloy

摘要:

利用重复冲击变形技术对比研究了α钛合金Ti-2Al-2.5Zr和亚稳β钛合金Ti-10V-2Fe-3Al变形过程中的微观组织演化及纳米晶的形成机制。金相形貌、X射线衍射及透射电镜观察显示，对于Ti-2Al-2.5Zr合金，塑性变形先后经历了形变孪生、位错活动、剪切等3个过程。与之相反，对于Ti-10V-2Fe-3Al合金，马氏体相变主导着合金的变形。相变分割、剪切及逆向马氏体相变持续贡献于合金的晶粒细化。同时发现，尽管变形到应变量1.2时两类合金组织内均出现纳米晶，但是大量的透射形貌观察显示Ti-10V-2Fe-3Al合金中生成的纳米晶晶粒尺寸更小，纳米晶区域更大。这表明，变形过程中激活马氏体相变可加速材料的晶粒细化。

Abstract:

The microstructural evolution and formation mechanism of nanograins in Ti-2Al-2.5Zr α-titanium alloys and Ti-10V-2Fe-3Al metastable β-titanium alloys subjected to multi-impact process at ambient temperature were investigated using optical microscopy, X-ray diffraction and transmission electron microscopy. The results show that deformation twinning, dislocation activities and shear banding successively dominate plastic deformation in Ti-2Al-2.5Zr alloy. In contrast, deformation-induced martensitic phase transformation becomes prevalent in Ti-10V-2Fe-3Al alloy. Martensitic subdivision, shear banding and reverse martensitic transformation contribute to grain refinement. Moreover, nanograins are finally achieved in both titanium alloys at a strain of 1.2, but grain refining efficiency is more significant in Ti-10V-2Fe-3Al alloy. The accelerated grain refinement could be attributed to the assistance of martensitic phase transformation.