The transformation of edge dislocation dipoles in aluminium

The transformations of dipoles of dissociated edge dislocations in aluminium are investigated using molecular dynamics for dipole heights ranging from one to ten {1 1 1} interplanar distances and at temperatures up to 900 K. Three types of configurations, hollow, vertical compact and inclined dipoles, are considered and their relative stabilities compared. Hollows are unstable at finite temperature. Dipoles neither annihilate nor form stable hollow cores but transform into height- and temperature-dependent layouts including cores containing ordered free volumes, zigzag faulted dipoles and agglomerated truncated stacking fault tetrahedra (SFT). Small individual SFT are formed at the highest temperatures, attesting to short-range pipe diffusion. These rearranged configurations are strong obstacles to mobile dislocations, thence potential nucleation sites for dislocation entanglement and self-patterning under single slip. A new thermally activated mechanism of SFT formation directly from vacancy clusters resulting from local dipole pinching-off is reported.