Phase transformation and dynamic recrystallization behavior of a β-solidifying γ-TiAl alloy and its wrought microstructure control

摘要

This study deals with phase transformation and dynamic recrystallization (DRX) behavior of a β-solidifying alloy Ti-45Al-4Nb-2Mo-B (at.%). Its phase transformation and DRX modes strongly depended on temperature/specific phase field. At low forging temperature within α/α_2 + γ + B2/β phase field, decomposition of lamellar structures via L(α/β) → γ + β along with DRX of γ and B2/β grains prevailed around prior α/γ colony boundaries. Conversely, when forging close to α-transus (T_α), closely following quick transition of γ + B2/β → α, DRX was totally localized within a grains. All these processes could be promoted greatly by lowering strain rate. Based on this study, large-scale forging and its microstructural design were realized successfully. Besides an-isotropic flow behavior of prior lamellar structures, insufficient decomposition time was also considered as the reason of remnant lamellar structures. Finally, post-forging annealing and an alternative superplastic straining within α_2 + B2/β + γ phase field were proposed to entirely eliminate the remnant lamellar structures, in order to produce full fine-grained B2/β + γ microstructure.