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

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 gamma twins from alpha(2)-platelets within beta(0) areas was analyzed at atomic-scale by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM). The growth faults (ABABCBC) were formed in alpha(2)-platelets, yielding a local D0(19)-> L1(0) (alpha(2) -> gamma) phase transformation. During the annealing process, the growth faults can be rearranged into gamma (ABCABC) and gamma(T) (ACBACB) platelets via the slipping of Shockley partial dislocations 1/3[(1) over bar 010] and 1/3[10 (1) over bar0], respectively. The gamma and gamma(T) can merge into y twins by accident during growing. The interface steps between alpha(2) and gamma platelets implied that this transformation is a diffusion-controlled defect migration process. The present work provides profound insight towards the formation mechanism of gamma twins, contributing to microstructure controlling and performance improving for TiAl alloys. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

In this study, the formation mechanism of gamma twins in TiAl alloys was analyzed at the atomic scale using HADDF-STEM. The results revealed the process of growth defects in alpha(2)-platelets transforming into the gamma phase, as well as the rearrangement of defects into gamma and gamma(T) platelets during annealing. This provides significant insights for microstructure control and performance improvement in TiAl alloys.