Plastic enhancement mechanism of γ-TiAl//α₂-Ti₃Al lamellar structure via Al_Ti antisite defect

Polysynthetically twinned (PST) TiAl consisting of a two-phase (γ and α₂) lamellar structure is an effective microstructural strategy for enhancing mechanical properties, and Al-rich composition is a common phenomenon. However, the effect of the Al_Ti antisite defect on the deformation mechanism of the γ-TiAl//α₂-Ti₃Al lamellar structure remains unclear. The deformation mechanisms of the γ//α₂ lamellar structure under pure shear mainly involve three sequential stages: (i) The weaker Ti–Ti and Al–Al metallic bonds induce the “phase boundary (PB) transition”. (ii) The stronger Ti–Ti and Al–Al metallic bonds induce the “orientation transition” in γ-TiAl. (iii) The strongest Ti–Al covalent bonds induce the “phase transition” in α₂-Ti₃Al. Introducing an Al_Ti antisite defect can weaken the original Ti–Al covalent bonds while generating new Al–Al metallic bonds, which provides an additional slip path and results in excellent enhancement of plasticity. The competition mechanisms between these plastic behaviors can be well explained through generalized stacking fault energy (GSFE) calculations.