Phase constitution-dependent deformation mechanisms and texture evolution in a β-solidifying γ-TiAl alloy during hot extrusion

Hot extrusion across the α-transus temperature (T_α) produces a strong basal texture in β-solidifying γ-TiAl alloys; however, the underlying mechanisms remain contentious owing to the disparate deformation behaviors of the constituent phases. This study employs a multi-scale characterization approach to examine the texture and microstructural evolution of a Ti-43.25Al-3.91Nb-0.98Mo-0.13B (at.%) alloy during hot extrusion across 1230–1290 °C. Microtextural decoupling via electron backscatter diffraction (EBSD) reveals that texture development follows two distinct pathways dictated by phase constitution. Below T_α, within the (α + β + γ) regime, the strong basal texture in un-recrystallized regions originates not from classical dislocation slip but from a coordinated rotation of (α/γ) lamellar colonies mediated by semi-coherent interfaces, a mechanism which, though qualitatively suggested previously, is directly validated in this work via transmission electron microscopy observations of shear strain localization at the α/γ interfaces. Above T_α, γ phase dissolution triggers a fundamental mechanistic shift: deformation becomes dominated by α-phase plastic anisotropy, and the texture is dramatically sharpened via orientation-selective continuous dynamic recrystallization (CDRX). Consequently, extrusion at 1290 °C results in superior microhardness (421.6 ± 12.1 HV), coupled with microstructural homogeneity and an exceptionally strong basal texture (7.17 m.r.d.). These findings establish a unified mechanistic framework that resolves the long-standing debate on texture correlation and provides a basis for tailoring properties in advanced TiAl alloys.