Mechanisms of microstructural evolution and their synergistic evolutionary behavior of a near (3 Ti alloy with lamellar structure during sub (3-transus hot deformation

Understanding microstructural evolution and its interactions is essential for designing hot working processes of near (3 Ti alloys. Dynamic globularization of lamellar alpha phase and DRX of (3 phase in Ti-55511 alloy during sub (3-transus compression were systematically investigated. The results show that these microstructural evolutions are closely related to the process parameters and evolve synergistically. The globularization fraction of lamellar alpha phase increases with decreasing strain rate and increasing deformation temperature. The lamellar alpha phase first forms an alpha/alpha internal interface through dislocation substructure or twin boundary evolution, and then the (3 matrix wedges into alpha phase along the interface to form thermally etched grooves. The centripetal force on the alpha/(3 interface surface induces the migration and diffusion of the alpha/(3 phase interface, and the lamellar alpha phase ultimately separates and globularizes along the internal interface. The (3 phase undergoes significant CDRX, mainly characterized by gradual sub-grain rotation and grain boundary migration. Its softening mechanism transitions from DRV to CDRX with increasing height reduction. The DRX fraction in (3 matrix initially increases then decreases with increasing deformation temperature due to competitive effects between nucleation and growth. Conversely, it shows a decreasing-then-increasing trend with increasing strain rate, attributed to the coupling effects of dynamic phase transition, alpha/(3 orientation evolution and dislocation proliferation rate on the DRX at different strain rates. Notably, preferentially activated (3 phase slip systems promotes columnar and conical slip initiation in alpha phase, thereby facilitating interfacial evolution and dynamic globularization of alpha phase. The globularized alpha grains also promote DRX nucleation of the (3 phase at alpha/(3 phase interface.