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 atomicscale mechanisms linking defect dynamics to mechanical properties remain elusive. Here, we unveil unprecedented deformation pathways in single-crystal γ-TiAl through largescale 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 hightemperature materials.