In situ atomistic observation of disconnection-mediated grain boundary migration

Abstract

Shear-coupled grain boundary (GB) migration is of general significance in the deformation of nanocrystalline and polycrystalline materials, but comprehensive understanding of the migration mechanism at the atomic scale remains largely lacking. Here, we systematically investigate the atomistic migration of Σ11(113) coherent GBs in gold bicrystals using a state-of-art in situ shear testing technique combined with molecular dynamic simulations. We show that shear-coupled GB migration can be realised by the lateral motion of layer-by-layer nucleated GB disconnections, where both single-layer and double-layer disconnections have important contributions to the GB migration through their frequent composition and decomposition. We further demonstrate that the disconnection-mediated GB migration is fully reversible in shear loading cycles. Such disconnection-mediated GB migration should represent a general deformation phenomenon in GBs with different structures in polycrystalline and nanocrystalline materials, where the triple junctions can act as effective nucleation sites of GB disconnections.

Metallic nanocrystals with low angle grain boundary for controllable plastic reversibility

“…Moreover, asymmetrical twinning/detwinning shear 21 and the associated huge surface kinks 19 inevitably lead to deformation instability and irreversible structural damage in metallic nanocrystals, which compromises their long-time plastic deformability. Additional investigations suggest that grain boundary (GB)-mediated deformation may contribute to the recovery of plastic strain in nanostructured metals [22][23][24] . Likewise, in bulk polycrystalline metals, high densities of internal interfaces, such as GBs 25 and nanoscale twin boundaries (TBs) 26 , have been widely adopted to alleviate damage accumulation in loading cycles.…”

Phase diagram of grain boundary facet and line junctions in silicon

“…Generally, they have both step and dislocation character and play a crucial role on the shear coupled migration [29]. Recent TEM investigations on Au bicrystals revealed the lack of lattice defects at the core of disconnections with a height of two lattice spacings at 11(113) coherent GBs [30]. These boundaries showed a layer by layer migration.…”

Building on Gleiter: The Foundations and Future of Deformation Processing of Nanocrystalline Metals

“…A number of theories and simulations point to the critical role of disconnections in strain-induced environments where, in the absence of dislocation-controlled plasticity, collective grain boundary mechanisms determine grain boundary mobility. [153][154][155] In parallel with advances in theory and simulation, in-situ microscopy studies [64,147,156,157] at ambient and elevated temperatures will reveal the fundamental disconnection and disclination deformation physics associated with alloys processed and engineered for thermally stability. These would be valuable, not just for knowledge of the retention of grain size in applications, but critically, to appropriately model [158] and to assess the stability of the microstructures formed during elevated temperatures SPD processing, but also during the thermomechanical manufacturing processing conditions needed to fabricate end products.…”