Atomic-scale investigation on the interface structure of {2(2)over-bar01} alpha(2)-Ti3Al deformation twins in polysynthetically twinned TiAl single crystals

The interface structure of {2 (2) over bar 01} alpha(2)-Ti3Al deformation twins formed during tensile deformation of poly synthetically twinned (PST) TiAl single crystals at 900 degrees C has been studied systematically by aberration-corrected scanning transmission electron microscopy. Numerous superlattice intrinsic stacking faults (SISFs) are formed on the (0001) basal plane of alpha(2) twins, thereby resulting in the formation of steps on the twin boundaries. The height of steps equals to the spacing of the (2 (2) over bar 01) twinning plane. The basal-plane SISFs formed in alpha(2) twins can't be attributed to the glide of Shockley superpartial dislocations. Lattice correspondence analyses based on classical twinning theory reveal that complex atomic shuffle and interchange shuffling are responsible for the formation of twinning and basal-plane SISFs in alpha(2) twins. In addition, basal-plane antiphase boundaries (APB) are formed at the vicinity of alpha(2) twin tips to relieve the stress concentration imposed by misfit dislocations.