Coordinated grain boundary deformation governed nanograin annihilation in shear cycling
YB Chen and QS Huang and Q Zhu and KX Song and YJ Zhou and HF Zhou and JW Wang, JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 86, 180-191 (2021).
Grain growth and shrinkage are essential to the thermal and mechanical stability of nanocrystalline metals, which are assumed to be governed by the coordinated deformation between neighboring grain boundaries (GBs) in the nanosized grains. However, the dynamics of such coordination has rarely been reported, especially in experiments. In this work, we systematically investigate the atomistic mechanism of coordinated GB deformation during grain shrinkage in an Au nanocrystal film through combined state-of-the-art in situ shear testing and atomistic simulations. We demonstrate that an embedded nanograin experiences shrinkage and eventually annihilation during a typical shear loading cycle. The continuous grain shrinkage is accommodated by the coordinated evolution of the surrounding GB network via dislocation-mediated migration, while the final grain annihilation proceeds through the sequential dislocation-annihilation-induced grain rotation and merging of opposite GBs. Both experiments and simulations show that stress distribution and GB structure play important roles in the coordinated deformation of different GBs and control the grain shrinkage/annihilation under shear loading. Our findings establish a mechanistic relation between coordinated GB deformation and grain shrinkage, which reveals a general deformation phenomenon in nanocrystalline metals and enriches our understanding on the atomistic origin of structural stability in nanocrystalline metals under mechanical loading. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
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