Dislocation self-interaction in TiAl: Evolution of super-dislocation dipoles revealed by atomistic simulations

Abstract

As one of the fundamental outcomes of dislocation self-interaction, dislocation dipoles have an important influence on the plastic deformation of materials, especially on fatigue and creep. In this work, super-dislocation dipoles in γ-TiAl and α2-Ti3Al were systematically investigated by atomistic simulations, with a variety of dipole heights, orientations and annealing temperatures. The results indicate that non-screw super-dipoles transform into locally stable dipolar or reconstructed cores at low temperature, while into isolated or interconnected point defect clusters and stacking fault tetrahedra at high temperature via short-range diffusion. Non-screw super-dipoles in γ-TiAl and α2-Ti3Al exhibit similar features as fcc and hcp metals, respectively. Generally, over long-term annealing where diffusion is significant, 60° super-dipoles in γ-TiAl are stable, whereas the stability of super-dipoles in α2-Ti3Al increases with dipole height and orientation angle. The influence on mechanical properties can be well evaluated by integrating these results into mesoscale or constitutive models.