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

• Published in: Nature materials 2024-01, Vol.23 (1), p.47-51
• Main Authors: Proville, Laurent, Choudhury, Anshuman
• Format: Article
• Language: English
• Subjects: 639/301/1034/1035; 639/301/119/1002; Alpha iron; Biomaterials; Chemistry and Materials Science; Condensed Matter Physics; Crystal defects; Crystal dislocations; Crystals; Deformation; Foils; Letter; Low temperature; Materials Science; Nanotechnology; Nucleation; Optical and Electronic Materials; Plastic deformation; Screw dislocations; Spikes (lattice defects)
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-023-01728-5

In situ straining tests in high purity α-Fe thin foils at low temperatures 1 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. Plastic deformation requires the propagation of a kinked profile along dislocations. It is shown that each kink acts as a set of travelling thermal spikes, favouring the nucleation of supplementary kinks and long dislocation jumps that are observed experimentally.