Local-structure-affected behavior during self-driven grain boundary migration
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Local-structure-affected behavior during self-driven grain boundary migration X. M. Luo, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, People’s Republic of China B. Zhang, Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, School of Materials Science and Engineering, Northeastern University, 3-11 Wenhua Road, Shenyang 110819, People’s Republic of China X. F. Zhu, and Y. T. Zhou, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, People’s Republic of China T. Y. Xiao, Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, School of Materials Science and Engineering, Northeastern University, 3-11 Wenhua Road, Shenyang 110819, People’s Republic of China G. P. Zhang, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, People’s Republic of China Address all correspondence to G. P. Zhang at [email protected] (Received 29 November 2015; accepted 25 February 2016)
Abstract In nanocrystalline (nc) metals, it is still not clear how local grain boundary (GB) structures accommodate GB migration at atomic scales and what dominates the motion of atoms at the inherently unstable GB front. Here, we report the adjustment of the local GB structures at atomic scales during self-driven GB migration, simultaneously involving GB dissociation, partial dislocation emission from GB, and faceting/defaceting in the nc Cu. Furthermore, we reveal that the fundamental of GB migration ability is closely related to the local structure, i.e. the GB segment consisting of “hybrid” structural units and delocalized GB dislocations is relatively unstable.
Nanocrystalline (nc) materials, showing unusual mechanical properties (dramatically increased strength and hardness,[1,2] and even greatly enhanced ductility[3]), have great technological attraction. However, grain boundaries (GBs) usually become unstable, and GB-related deformation takes over in nc materials.[2,4] The GB-related behaviors are found to operate by three main processes: GB migration,[4,5] dislocation nucleation from GB,[6] and GB dislocation (GBD) motion.[7] GB migration may happen simultaneously accompanying with other GB-related behaviors. Molecular dynamics simulations[8] and experimental observations[9] suggest that twin lamella can form via GB migration or dissociation. GBs containing GBDs can emit a partial dislocation during deformation by local atomic shuffling and stress-assisted free volume migration.[10,11] Simultaneously, GB-related behaviors also greatly change the local GB environment. GB ledges were observed to form by the glide motion of dislocations in the GB plane.[12] GB migration would form periodic facets.[13] Obviously, the interaction among different GB-related behaviors is a very complex process, which needs to be gotten
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