Abstract
The pathways by which dislocations, line defects within the lattice structure, overcome microstructural obstacles represent a key aspect in understanding the main mechanisms that control mechanical properties of ductile crystalline materials. While edge dislocations were believed to change their glide plane only by a slow, non-conservative, thermally activated motion, we suggest the existence of a rapid conservative athermal mechanism, by which the arrested edge dislocations split into two other edge dislocations that glide on two different crystallographic planes. This discovered mechanism, for which we coined a term “cross-split of edge dislocations”, is a unique and collective phenomenon, which is triggered by an interaction with another same-sign pre-existing edge dislocation. This mechanism is demonstrated for faceted α-Fe nanoparticles under compression, in which we propose that cross-split of arrested edge dislocations is resulting in a strain burst. The cross-split mechanism provides an efficient pathway for edge dislocations to overcome planar obstacles.
Highlights
The ongoing efforts to improve strength and ductility through miniaturizing specimens1 or by forming sub-micrometer scale microstructure2–4 bring with it the need to deeply understand mechanical properties of nanostructured materials on the atomic level, i.e. identify and relate the effect of dimensionality to properties of dislocations, line defects within the crystal structure5–8
While the nanoparticle hardens as the dislocation nucleation-driven pile-ups develop, the strain burst commences when the front dislocation in the pile-up splits into two edge dislocations on two different slip planes
The hardening stage terminated in a ~1–3% strain burst; this behavior differs from the previously reported stress-strain response of pristine faceted nanoparticles, such as Au15 and Ni3Al16, where the nanoparticles deformed elastically and collapsed plastically after the first dislocation nucleation event with strain burst of almost 100%
Summary
The ongoing efforts to improve strength and ductility through miniaturizing specimens1 or by forming sub-micrometer scale microstructure2–4 bring with it the need to deeply understand mechanical properties of nanostructured materials on the atomic level, i.e. identify and relate the effect of dimensionality to properties of dislocations, line defects within the crystal structure5–8. While the nanoparticle hardens as the dislocation nucleation-driven pile-ups develop, the strain burst commences when the front dislocation in the pile-up splits into two edge dislocations on two different slip planes.
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