A novel cross-lamellar deformation mechanism through α2 ↔ γ bidirectional phase transformation in a γ-TiAl alloy

Cross-lamellar deformation is hard to be activated because of the obstruction of α₂/γ interface to dislocations in the lamellar TiAl alloy. In the present work, continuous shear across the lamellar interface was achieved through twinning and α₂ ↔ γ bidirectional phase transformation during high-temperature tensile deformation. The {20$\bar{2}$1} α₂ twins were induced by the stress concentration at the tips of γ twins in adjacent lamellae and propagated through the nanoscale (α₂ + γ) lamellae (γ → ${\alpha }_2^T$), followed by the nucleation and growth of γ phase inside α₂ twins (${\alpha }_2^T$ → γ). The existence of Blackburn orientation relationship between α₂ twin and γ inside it, as well as the Al-rich stacking faults in α₂ twins, provide strong evidence for this bidirectional phase transformation. These findings offer an innovative understanding for the coordinated deformation of (α₂ + γ) lamellar structures and provide a new sight for improving the deformation capacity of TiAl alloys.