In situ atomistic observation of disconnection-mediated grain boundary migration

Qi Zhu,Jiangwei Wang,Chuang Deng,Scott X Mao,Guang Cao,Jixue Li,Ze Zhang

doi:10.1038/s41467-018-08031-x

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.

Highlights

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
By conducting the state-ofart in situ shear testing and molecular dynamic (MD) simulation, we revealed the atomistic migration mechanism of the Σ11(113) coherent GB coupled to the lateral motion of layer-by-layer nucleated GB disconnections with the height of either one or two atomic layers
The mechanism of disconnection-mediated migration still involved contradictory conclusions, especially about the roles of different types of GB disconnections7,27,28. These contradictions may originate from the fact that the frequent composition and decomposition between different types of GB disconnections observed in our experiments were usually neglected in previous theoretical studies due to the unclear disconnection dynamics

Summary

Introduction

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. We systematically investigate the atomistic migration of Σ11(113) coherent GBs in gold bicrystals using a stateof-art in situ shear testing technique combined with molecular dynamic simulations. 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. The atomistic mechanism of disconnection dynamics (including the nucleation, propagation and interaction) and their contribution to the GB deformation remain largely unclear, especially in experiments due to the technical limitations.

Methods

Results

Conclusion