Systematic analysis of the softening mechanism and texture evolution of Ti–6Cr–5Mo–5V–4Al alloy during hot compression in α+β phase region

Abstract

Ti–6Cr–5Mo–5V–4Al (Ti-6554) alloy has wide applications for large load-bearing components in the aerospace field. However, during the hot forming process of the alloy in the α+β phase region, there are a variety of interaction and restriction softening mechanisms and complex texture evolution behaviors, which jointly affect the microstructure and mechanical properties. This paper systematically studies the softening mechanism and texture evolution of Ti-6554 alloy in the α+β phase region using electron backscatter diffraction (EBSD), including dynamic phase transformation (DPT) and dynamic spheroidization of α phase and dynamic recrystallization (DRX) of β phase. Firstly, the effect of deformation parameters on the DPT is studied, and it is found that the volume fraction of α phase declines gradually with raising the strain rate, deformation temperature and deformation amount. The yield stress and the driving force for DPT increase with raising the strain rate and decreasing the deformation temperature. The equiaxed α phase will gradually transform into the lamellar α phase during the spheroidization process, accompanied by the wedging of the β phase. The combined effect of DPT and dynamic spheroidization leads to α grain refinement. Furthermore, the effect of deformation parameters on the DRX process of β phase is also investigated. The DRX degree only increases gradually with increasing the strain. Increasing the deformation temperature and decreasing the strain rate do not significantly increase the DRX volume fraction. Meantime, the DRX process of the β phase is heavily dependent on the α phase. The higher proportion of the α phase is capable of promoting continuous dynamic recrystallization (CDRX) process of β phase, while the lower proportion of the α phase will promote the transformation of CDRX into dynamic recrystallization (DDRX), but can not effectively increase the DRX degree of β phase. Further, the texture evolution shows that due to the combined effect of DPT and dynamic spheroidization, the effect of deformation parameters on the texture strength of α phase is very complicated. For the β phase, <001> and <111> fiber textures are easily formed during the deformation process.