抄録
Microstructures of fractured surfaces of metals are observed by electron microscope. Fractured surfaces of polycrystalline ductile metals accompanied with considerable plastic deformation, consist of domains of the sizes comparable to those of crystal grains. In the cases of tempered steel and age-hardened duralumin the sizes of these domains are very small as compared with those of the normalized metals. On the stereo electron micrographs of the fractured surfaces it is observed that the interiors of these domains are dented. Fracture of ductile polycrystalline metals is regarded to proceed by the following steps:
(1) As the plastic deformation progresses, large concentration of stress is produced in the grain boundaries or in the neighbourhood of precipitates.
(2) Therefore at these positions microcracks are induced.
(3) But around the crack, it is yet ductile enough to continue plastic deformation. Therefore the stress concentration at the crack apexes is relieved and cavities are formed.
(4) This plastic flow continues until the rupture and the fractured surface appears with dented domains.
Fractured surfaces of brittle metals also show the domain structures of the sizes comparable to those of the crystal grains. In the interior of these domains, glass like fracture is observed
