Study on High-Temperature Flow Behavior and Substructure and Texture Evolution of TA15 Titanium Alloy

The hot deformation behaviors of TA15 titanium alloy were investigated by isothermal compression experiments on Gleeble-3500 thermal simulation machine. The results indicate that the flow stress curves of TA15 titanium alloy in the two-phase region are dynamic recrystallization (DRX) type while in the β single-phase region are main dynamic recovery (DRV) type. The evolution of microstructure and substructure (grain boundary misorientation and dislocation) under different process parameters were studied by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). Microstructure analysis shows that a large number of recrystallized α grains and martensite α′ phase appear as the strain rate decreases under the condition of two-phase region. However, lath martensite microstructure is replaced by lamellar martensite microstructure at low strain rate in β single-phase region. Grain boundary misorientation analysis indicates that low angle boundaries (LABs) transform into high angle boundaries (HABs) sufficiently by reducing strain rate or increasing deformation temperature. Texture evolution analysis shows that the degree of preferred orientation after deformation weakens and the intensity of texture decreases with strain rate increasing in the two-phase region. However, more potential slip systems are activated in the β single-phase region. TEM analysis suggests that microscopic deformation bands with high density of parallel arrangement dislocations evolve into subboundaries or boundaries. As the deformation continues, dislocations are accumulated around the subboundaries, and they promote the transformation of subgrains with LABs into new grains with HABs.