Mechanistic origins of lamellar orientation-dependent strength-ductility duality in polycrystalline γ-TiAl alloys at elevated temperatures

In this study, the critical role of lamellar orientation in controlling the strength-ductility balance of γ-TiAl alloys at elevated temperatures is elucidated through systematic microstructure design and multiscale characterization. The precise tailoring of the parent α-phase texture via hot extrusion (ratios of 2:1 and 4:1) enabled the engineering of two distinct lamellar structures: randomly oriented and strongly textured colonies. Tensile tests at 750 °C revealed an orientation-dependent inverse relationship, where the preferred alignment enhanced yield strength by 29 % but reduced elongation by 47 %. Multiscale analysis demonstrated that this duality originates from competing deformation mechanisms: hard-oriented colonies (<30° to loading axis) strengthen through dislocation blocking at semi-coherent α₂/γ interfaces, yet accumulate stress concentrations at grain boundaries due to limited strain accommodation, while soft-oriented colonies accommodate plasticity via grain boundary-mediated processes and dynamic recrystallization that relieve local stresses. This work establishes the orientation-dependent strength-ductility relationship in γ-TiAl alloys, providing the design principles for optimizing lamellar architectures in high-temperature applications.