Thin foils of deformed superficial layers in 18-8 stainless steel produced by ultrasonic machining were prepared by electropolishing and their structure was examined by transmission electron microscopy. The main results obtained are as follows:
1) Deformed superficial layers changed their structure from the surface to the interior successively; fracture, crystallites, plastic deformation, elastic deformation, matrix.
2) In crystallites, dislocations were densely tangled and α-phase martensite was formed by transformation due to high-temperature plastic deformation. Though cracks found in crystallites had no preferred orientation, sometimes microcracks along the planes {111} were observed in a plastically deformed region.
3) Some lattice defects, such as pile-ups and tangle of dislocations, stacking faults, stacking fault tetrahedra, were observed in a plastically deformed region. ε-phase martensite was also recognized.
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