Unravelling the jerky glide of dislocations in body-centred cubic crystals.

Abstract

In situ straining tests in high purity α-Fe thin foils at low temperatures1 have demonstrated that crystal line defects, called dislocations, have a jerky type of motion made of intermittent long jumps of several nanometres. This observation conflicts with the standard Peierls mechanism for plastic deformation in body-centred cubic crystals, where the screw dislocation jumps are limited by inter-reticular distances, that is, distances of a few angstroms. Employing atomic-scale simulations, we show that although the short jumps are initially more favourable, their realization requires the propagation of a kinked profile along the dislocation line, which yields coherent atomic vibrations acting as travelling thermal spikes. Such local heat bursts favour the thermally assisted nucleation of new kinks in the wake of primary ones. The accumulation of new kinks leads to long dislocation jumps like those observed experimentally. Our study constitutes an important step towards predictive atomic-scale theory for materials deformation.