Formation mechanism of γ twins in β-solidified γ-TiAl alloys

Abstract Defects, such as stacking faults (SF) and twins, play a crucial role in stabilizing the order phase and improving the mechanical properties for engineering alloys. The formation mechanism of the γ twins from α2-platelets within β0 areas was analyzed at atomic-scale by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM). The growth faults (ABA B ˙ CBC) were formed in α2-platelets, yielding a local D019→L10 (α2 → γ) phase transformation. During the annealing process, the growth faults can be rearranged into γ (ABCABC) and γT (ACBACB) platelets via the slipping of Shockley partial dislocations 1 / 3 [ 1 ¯ 01 0] and 1 / 3 [ 10 1 ¯ 0], respectively. The γ and γT can merge into γ twins by accident during growing. The interface steps between α2 and γ platelets implied that this transformation is a diffusion-controlled defect migration process. The present work provides profound insight towards the formation mechanism of γ twins, contributing to microstructure controlling and performance improving for TiAl alloys.