Revealing shear-coupled migration mechanism of a mixed tilt-twist grain boundary at atomic scale

ZW Fang and BY Li and SS Tan and ST Mao and GF Wang, ACTA MATERIALIA, 258, 119237 (2023).

DOI: 10.1016/j.actamat.2023.119237

Shear-coupled grain boundary (GB) migration greatly influences the plasticity and creep resistance of nanocrystalline materials. However, the atomistic mechanisms underlying the shear-coupled migration of general mixed tilt-twist GBs (MGBs) remain largely elusive to date. Here, using in-situ high-resolution transmission electron microscopy and molecular dynamics simulations, we uncover the atomic-scale migration behavior of a typical MGB, i.e., < 001 >200/ < 0 (1) over bar1 >(1) over bar 11 GB, during the room-temperature shear deformation of Au nanobicrystals. Two distinct migration patterns showing the opposite signs of shear-coupling factor were observed and further revealed to be mediated by the motion of GB disconnections with different crystallographic parameters and exhibit different lattice correspondence relations, i.e., < 001 > 020-to-< 0 (1) over bar1 >200 and < 001 >020-to- < 0 (1) over bar1 >111. Simulation results confirm that the two distinct migration patterns could be activated under different stress/strain states. Moreover, excess GB sliding and GB plane reorientation were found to accommodate the GB migration in both experiments and simulations, likely due to the necessity of establishing a point-to-point lattice correspondence during GB migration. These findings provide atomic-scale experimental evidence on the disconnection-mediated migration of MGBs and elaborate on the hitherto unreported complex shear response of MGBs, which have valuable implications for optimizing the ductility of metallic nanocrystals through controlling GB migration.

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