Fig. 1. Ultra-high plasticity of a hetero-grain-sized nanocrystalline Au NW. (a-f) Series of TEM images showing the tensile deformation of the Au NW. The references are indicated by short red lines. The symbol ε represents the total strain during each tensile stage. The scale bar is 5 nm. (g) Grain size distribution of the hetero-grain-sized Au NW. (h) Curve of elongation strain vs. diameter reduction.

Fig. 2. GB migration-induced grain growth in a hetero-grain-sized nanocrystalline Au NW. (a, b) HRTEM images showing grain boundary plasticity leading to grain growth in the heterogeneous- structured nanocrystalline Au NW subjected to strain. The scale bar is 5nm. (c-f) Enlarged HRTEM images of the white framed regions in (a) and (b) show the GB migration and grain growth more clearly. The scale bar is 2 nm.

Fig. 3. (a) Four grains labeled G1-G4. Their GBs are indicated by a white dotted line. (b, c) With further loading, the orientation angle between G2 and G4 increased from ～9.1° to ～ 14.2°. Simultaneously, the GB also migrated. (d-f) Movement of the GB of G1-2 toward the surface of the NW, GBs of G2-3 and G1-3 simultaneously changed dramatically.

Fig. 4. In situ atomic-scale observation of full dislocation activities in a large grain. (a) Full dislocation D1 (labeled “T”) with a Burgers vector of $b=\frac{1}{2}[011](11\bar{1})$ was observed in the large grain. (b) With continued strain, two full dislocations, D2 and D3, nucleated near D1. (c) With further loading, D3 disappeared and a new dislocation, D4, nucleated. (d) With further loading, D2 disappeared and a new dislocation, D5, nucleated. (e-h) Enlarged HRTEM images corresponding to the red-framed regions in (a-d). These are in situ atomic-scale observation of the LD lock generation and destruction processes.

Fig. 5. In situ atomic-scale observation of full dislocation activities in a large grain near the NW surface. (a-c) Three HRTEM images captured ～1 s apart showing full dislocation activities: nucleation and a slide toward the surface. (d-f) Another typical example of dislocation. The dislocation labeled D8 remained in the same region and another full dislocation, D9, slipped toward the surface and disappeared.

Fig. 6. (a) Statistical data of dislocation density vs. uniform elongation. At first, dislocation density increased as the strain increased. Then it remained high as deformation continued. (b) Statistical data show the proportion of full dislocations, partial dislocations resulting in stacking faults, and dislocation locks at different strains.

Fig. 7. In situ atomic-scale observation of surface diffusion during tensile deformation of a hetero-grain-sized NW. The surface of the NW displayed steps with different lengths and heights. The steps are indicated by the white zigzag line, and each step's length is represented numerically. During straining, diffusion of the surface atoms led to changes in the lengths and heights of the steps.

Fig. 12. (a) Statistical data for elastic strain and stress vs. uniform elongation. (b) Properties (elongation and the product of strength and ductility) of heterogeneously structured nanocrystalline Au NW compared with those of other high-performing materials, including different metals and alloys. The materials represented by the statistical data are divided into nine categories [2,3,[7], [8],[10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24],[30], [31], [32], [33], [34], [35],[55], [56], [57], [58], [59], [60], [61], [62], [63], [64], [65], [66], [67], [68], [69], [70], [71], [72], [73], [74], [75], [76], [77], [78], [79]]: Metallic NWs (dark yellow), GNS Metals (red), Entropy Alloys (wine), BCC Metals (orange), Steels (olive), Al/Al Alloys (blue), Cu/Cu Alloys (magenta), HCP Metals (black), and This Work (stars).

Fig. 8. Tensile deformation of a heterogeneously structured nanocrystalline Au sample in a MD simulation. MD result of the sample subjected to a tensile strain of 0 to ～29.6%. The nanocrystalline structure was subjected to tension. Small grains tended to fuse via GB plastic deformation to form large grains.

Fig. 9. Typical example of GB migration promoting grain growth in small grains in the MD simulation.

Fig. 10. Dynamic grain growth is dominated by GB migration and grain rotation. The GB position is indicated by the red dotted line. The grain boundary angles G1-4 and G4-5 decreased from 14° to 8.7° and from 16° to 5.5°, respectively.

Fig. 11. Typical example showing surface diffusion both parallel to and vertical to the tensile direction.