Fig. 1. Different approaches towards atomistic understanding of GB disconnections. (a) Geometric model of GB disconnection. (b) Atomistic simulation of disconnection on a Σ5[001](013) STGB in Cu. (c) High-resolution TEM image showing the atomic structure of a disconnection core in the Σ41[001](540) tilt GB in high-purity Al bicrystal. (d) Real-time atomistic observation of disconnection motion during shear-coupled migration of a Σ11[1$\bar{1}$0](113) GB in Au bicrystal. (b-d) are reprinted from Refs. [11,16,19], respectively.

Fig. 2. Atomistic dynamics of disconnection nucleation on the Σ11(113) GBs in Au. (a, b) Heterogeneous disconnection nucleation from the surface in an Au bicrystal. The insets show atomic structures of the surface before and after disconnection nucleation. (c, d) Heterogeneous disconnection nucleation from a TJ (shown by the red circle) in nanocrystalline Au. (e, f) MD snapshots showing the homogeneous nucleation of a disconnection dipole in the pristine GB. The hollow arrows indicate the GB migration directions coupled with the subsequent motion of disconnections after nucleation. (g-i) 3D schematics of the respective disconnection nucleation dynamics.

Fig. 3. Quantitative comparison between surface and homogeneous nucleation of disconnections on the Σ11(113) GB. (a, b) Horizontal shear strain (εxz) of the Σ11(113) GB before and after surface nucleation of a single-layer disconnection under shear loading parallel to the GB plane (along the <332> direction). (d, e) Horizontal shear strain evolution associated with the homogeneous nucleation of a double-layer disconnection dipole. (c, f) Atom displacements inside the bicrystal during the surface and homogeneous nucleation of a GB disconnection in (b, e). The displacement vectors have been enlarged by three times in (c, f) for clear demonstration and the black dashed lines delineate the GB planes. (g) Engineering shear stress-strain curves associated with surface and homogeneous disconnection nucleation at 300 K.

Fig. 4. Interaction dynamics of GB disconnections. (a) Dynamic interaction between GB disconnections during the upward migration of Σ11(113) GB (indicated by the hollow arrow). S and D denote single-layer and double-layer disconnections. (b) GB-lattice SF interaction during the downward migration of Σ11(113) GB. (c, d) 3D schematics of the respective dynamic interactions. (e-h) MD simulation snapshots showing the heterogeneous nucleation of disconnections from the GB-dislocation intersection site. An incoming mixed full dislocation b = 1/2<110> was accommodate at the Σ11(113) GB, which triggers the nucleation of single-layer disconnections (bd = 1/22<471>, h = d113) on the GB.

Fig. 5. Quantitative analysis of GB-dislocation interactions at 300 K. (a) Engineering shear stress–strain curves for upward GB migration under [33 $\bar{2}$]-shear loading. (b) Engineering shear stress–strain curves for downward GB migration under [$\bar{3}$ $\bar{3}$2]-shear loading. Pin, Surf, and Acc labels in the plot denote GB pinning, surface nucleation, and dislocation accommodation, respectively. The insets show the final positions of the Σ11(113) GBs in each shear loading, while the dashed lines delineate the initial GB position.

Fig. 6. Disconnection-dominated migration of different GBs in Au. (a) Stress-induced lateral motion of single-layer disconnections on the Σ3 CTB. (b) Lateral motion of a multi-layer disconnection along the Σ3 CTB. (c) Disconnection composition during the migration of a [1$\bar{1}$0]//[001] mixed GB under shear loading.

Fig. 7. Schematic summary of disconnection dynamics. (a) Conceptual map of disconnection-based GB plasticity. (b-d) Schematics of critical disconnection dynamics and their respective contributions to GB plasticity. (b) Disconnection nucleation and propagation. (c) Disconnection interaction. (d) Disconnection-dominated TJ motion in polycrystalline system and the associated GB network evolution.