Study on recrystallization and phase transformation of Ti-43Al-4Nb-1Mo-0.2B alloy during the inter-pass annealing

Abstract

The multi-pass thermomechanical process is a common forming method employed for brittle metallic materials such as TiAl alloys, where complex recrystallization behavior and phase transformation are utilized to promote grain refinement and microstructural evolution. Thermal simulation compression experiments at 1200 °C/0.01 s⁻¹ were performed to investigate the recrystallization and phase transformation during inter-pass annealing. The results showed that a little dynamic recrystallization (DRX) preferentially occurred within the β_o+γ mixed structures and along the boundaries of α₂+γ lamellar colonies. Moreover, the inter-pass annealing had little effect on recrystallization of α₂ phase, but facilitated the α/α₂→β/β_o phase transformation to accelerate the fragmentation of α₂ lamellae. Also, the pre-deformed β_o phase mainly underwent static recrystallization (SRX), which was enhanced with the increasing the proceeding-pass strain and inter-pass annealing duration. The recrystallization mechanisms of α₂ and β_o phase were continuous recrystallizations, where nucleation inoculation or early nucleation induced the weak recrystallization texture similar to deformation texture in local regions, yet insufficient recrystallization eliminated the texture. The extension of annealing time at different strains was favorable for SRX of the γ phase, but meta-recrystallization (MDRX) could only occur in short-time annealing at high strains. Consequently, the design and optimization of multi-pass deformation process were proposed.