Formation mechanism of typical microstructural characteristics and microstructure quantification of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si alloy with initial lamellar structure during hot deformation

The microstructure evolution of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si alloy with initial lamellar structure during isothermal compression in α+ β phase field was investigated via scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction techniques. Special attention was paid to the evolutionary mechanisms of typical microstructure features including necklace-like structure, kinking lamellar α with convex and concave morphology, sub-grain boundary parallel or perpendicular to the longitudinal lamellar axis, stable straight lamellar α with hard orientation generating under different deformation conditions. Furthermore, the distributions of recrystallized grain and crystallographic texture corresponding to different deformation parameters were analyzed quantitatively. The results showed that strain rate plays a more significant role in the dynamic globularization of lamellar α and grain coarsening of equiaxed α than deformation temperature, and it is beneficial for accelerating the progression of lamellar kinking and globularization to appropriately reduce the deformation temperature in the high-temperature region of α+ β phase field.