Dislocation microstructure evolution in cyclically twisted microsamples: a discrete dislocation dynamics simulation

Abstract

Miniaturization in technical devices has increased interest in the investigation of the deformation and fatigue behaviour of metals in the micrometre regime. Due to the small dimensions of these devices, mechanical properties depend on the motion of a marginal number of dislocations. In this paper, the evolution of dislocation microstructure in torsion loaded single crystalline aluminium wires is analysed by three-dimensional discrete dislocation dynamics simulations. It is shown that the size of pile-ups and the number of the active slip systems is significantly influenced by cross-slip events independent of the crystallographic orientation. Dislocations are driven by the stress gradient from the applied loading to move into the centre of the sample. These dislocations cannot escape through the surface because of the reversal of the sign of the stress in the centre of the sample. If the micrometre-sized specimens are untwisted, the remaining dislocation microstructure in these samples depends on the maximum torsion angle reached before unloading. The larger the torsion angle, the higher is the remaining dislocation density in the unloaded specimens. These results are discussed with respect to cyclic deformation mechanisms at small scale.