Achieving stable hot forging of a γ-TiAl alloy with limited hot deformability through dynamic recrystallization and twin-associated phase transformation

The limited hot deformability of γ-TiAl alloys caused by limited slip systems, strong anisotropy, and insufficient strain accommodation remains a major challenge for their thermomechanical processing. In this study, the hot deformation behavior and associated microstructural evolution of a heat-treated Ti48Al5Nb2Cr0.6Re0.1C alloy were systematically investigated through compression tests, processing-map analysis, EBSD, TEM, and first-principles calculations. The results reveal that deformation stability is strongly dependent on the balance between strain accumulation and microstructural restoration. The instability at 1150 °C-0.1 s -1 condition originates from heterogeneous deformation, where localized strain accumulation competes with incomplete dynamic recrystallization, resulting in flow localization and lamellar distortion. In contrast, decreasing the strain rate promotes dislocation rearrangement, dynamic recrystallization, and the formation of high-angle grain boundaries, leading to stable deformation. At 1200 °C and above, additional phase transformation is observed in close association with twin-related interfaces. The deformation-related 57°–73° boundaries, particularly the 70°/<110> twin-related interfaces, are spatially associated with the transformed regions and exhibit crystallographic compatibility with the γ→α 2 transformation. First-principles calculations further demonstrate that the increased thermal expansion mismatch between γ and α 2 phases and the enhanced thermodynamic driving force at high temperatures promote γ → α 2 transformation. Based on the combined processing-map and microstructural analysis, a stable deformation window of 1200–1250 °C and 0.001–0.01 s -1 is identified for the investigated alloy. These results provide a fundamental basis for selecting appropriate hot-working parameters and controlling deformation-induced microstructural evolution in γ-TiAl alloys.