Revealing abnormal coarse grain growth mechanisms of Ti-10V-2Fe-3Al alloy die forging during solid solution treatment in α plus β two-phase region

Anomalous macrostructure was observed in the local areas of Ti-10V-2Fe-3Al alloy die forging during solid solution in alpha+(3 two-phase region. Such specific structure corresponds to the formation of abnormal coarse (3 grains (ACGs), which mainly depends on the degree of dynamic recrystallization (DRX) under different hot deformation conditions (temperature, strain, and strain rate). Electron back scatter diffraction (EBSD) analysis shows that discontinuous dynamic recrystallization (DDRX) of (3 dominates the flow softening during overall deformation. In the case of low degree of DDRX, the abnormal grain growth which is reflected by a fact that the subgrain with high angle grain boundary rapidly expands to its adjacent unrecrystallized grain characterized by low angle grain boundary, can be triggered upon subsequent solid solution treatment due to accelerated release of the accumulated stored energy. This is mainly responsible for the formation of ACGs. Instead, in the case of high degree of DDRX, a significant increase in both number and size of subgrains and recrystallized grains reduces the space available for abnormal grain growth of subgrains, whereby the ACGs can be rarely observed. Moreover, the initial texture of (3 phase plays an important role in the degree of DDRX, giving rise to the different size of ACGs.