Unlocking anisotropic plasticity in γ-TiAl with an atomic scale simulation: From metastable BCC states to hierarchical twinning

Crystal orientation governs the plasticity of intermetallic alloys, yet the atomic-scale mechanisms linking defect dynamics to mechanical properties remain elusive. Here, we unveil unprecedented deformation pathways in single-crystal γ-TiAl through large-scale molecular dynamics simulations under uniaxial tension across four crystallographic orientations: [100], [112], [110], and [111]. Strikingly, a metastable body-centered cubic (BCC) phase emerges transiently during [100]-oriented stretching, acting as a critical bridge between elastic and plastic regimes—a phenomenon unreported in γ-TiAl. For [110] and [111] orientations, we identify a hierarchical defect evolution cascade (intrinsic stacking faults→extrinsic stacking faults→twin boundary (ISF→ESF→TB)) driven by intersecting stacking faults and Shockley partial dislocation interactions, which govern twin boundary nucleation and growth. In contrast, [112]-oriented deformation adheres to conventional dislocation-mediated plasticity. These findings reveal how crystallographic anisotropy dictates defect dynamics, offering atomic-scale insights into deformation twinning and transient phase transitions. This work bridges atomistic processes to macroscopic properties, advancing the design of next-generation lightweight high-temperature materials.