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.