Microstructure evolution and softening mechanism of Ti-55511 alloy with equiaxed structure during sub β-transus hot deformation

Microstructure evolution behavior and softening mechanism of Ti-55511 alloy during sub beta-transus hot deformation were systematically investigated. The results show that the deformation parameters greatly affect the dynamic softening behavior of alpha and beta. Among them, either increasing the temperature or significantly increasing the strain rate favor the DRX of the alpha phase. The aspect ratio of the equiaxed alpha gradually increases during early stages of hot deformation, and the alpha phase is elongated to form the lamellar-like structure. Subsequently, its inner interface gradually migrate and transform, which is accompanied by the wedging of the beta phase and dynamic globalization of the alpha phase, leading to the refinement of alpha grains. For beta, the main softening mechanism is DRV. However, increasing the deformation temperature and decreasing the strain rate can promote DRX of the beta phase. Its DRX is accomplished by the progressive sub-grains rotation, which increases their misorientation and thus facilitates the LAGB to HAGB transition, a typical CDRX. The equiaxed alpha grains promote nucleation of beta recrystallized grains at the alpha/beta phase interface.