图3. 由过剩体积通过瞬态拓扑转变(TTT)引发晶界塑性变形的示意图、高分辨TEM (HRTEM)像及晶格应变图^[66]

Fig.3. Schematics (a, b) and high-resolution TEM (HRTEM) images (c-i) of GB plastic deformation initiated by excess volume through transient topological transition (TTT) (Scale bar: 2 nm)^[66]
(a) uniform lattice straining in response to external load in crystalline solid
(b) plastic deformation initiated preferentially at the GB through excess-volume-assisted TTT (The red and blue circles denote atoms with excess volume above and below that of the perfect lattice (black circles), respectively. G1 and G2—grain 1 and grain 2)
(c-e) in situ HRTEM images showing TTT at general high-angle grain boundaries in Au with increasing compressive loading (Insets in Figs.3d and e are lattice strain images)
(c) atomic structure of a 24° [\mathrm{1}\overline{\mathrm{1}}\mathrm{0}] asymmetrical tilt GB in Au (Two alternate types of facets are delineated by the white and yellow dashed lines)
(d) TTT of the originally faceted GB into an orthogonal configuration (yellow area) under compressive loading (σ) (TTT mainly occurs at the upper edge of GB)
(e) continuous expansion of the TTT region along the GB with limited thickening into G2
(f-i) TTT at a curved GB in polycrystalline Au
(f, g) atomic structures of the flat and curved segments of the initial 32° [\mathrm{1}\overline{\mathrm{1}}\mathrm{0}] tilt GB
(h, i) TTT at the flat and curved GB segments under [112]_G1-compression (indicated by the black arrow)