Microstructure evolution and recrystallization of Ti-44.5Al-3.8Nb-1Mo-0.2B alloy with different initial microstructure during hot pack rolling

Ti-44.5Al-3.8Nb-1Mo-0.2B alloy (TNM) sheets were prepared by hot rolling, and the effect of the initial microstructure on the process was discussed in this work. The as-received TNM alloy billets with nearly and fully lamellar structures were prepared by forging and casting processes (named M1 and M2), respectively. For the as-rolled sheets from M1, the fraction of recrystallization increased gradually with the decrease of reduction per pass based on GOS analysis. Compared with M1, M2 required a larger deformation to achieve complete recrystallization. Meanwhile, the as-rolled sheets from M2 possessed a smaller grain size than that from M1. In addition, the γ-DRX behavior during the multi-pass hot rolling was discussed, and the DDRX was found to play the dominant role in this process. The phase transformation of β/β₀ → α occurred in the 1200 °C rolling process. It was presumed that this transformation was promoted by increasing the rolling temperature, therefore, the volume fraction of the β₀ phase decreased. The α₂ lath decomposed gradually with the increasing of rolling temperature from 1200 °C to 1250 °C, simultaneously, the combination of the adjacent γ laths resulted in the coarsening of γ lath.