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Microstructure and fracture appearance of nanoporous Au shown at different magnifications. (a) Low-magnification SEM micrograph revealing a combination of transgranular (featureless region I) and intergranular brittle fracture (rock candy region II). (b) Boundary region between transgranular (region I) and intergranular fracture (region II) at higher magnification. (c) A close-up of the outlined area in (b) reveals the ductile nature of the fracture: the ligaments fail by necking due to overloading. (d) Region I (transgranular) and region II (intergranular) are separated by two-dimensional, void-like defects (marked by arrows) that serve as crack nucleation sites.
SEM micrographs showing crack formation during high-load Vickers indents . (a) High magnification micrograph from a crack tip region showing highly strained ligaments bridging a microcrack. Elongations in the order of 100% have been observed. (b) Detail of a larger crack revealing pronounced necking prior to failure.
Fracture surface of a np-Au sample that had been heat treated for at prior to fracture at room temperature. The heat treatment increases the pore size/ligament diameter from . (a) Extensive plastic deformation is observed in a larger region around cracks: cell collapse in regions of compressive stress (cs), and elongation of the cell structure in regions of tensile stress (ts). (b) A higher magnification view of the area within the rectangle reveals plastic deformation of individual ligaments by slip (sb).
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