Surface observation of nickel-plated iron single crystals deformed at 77 K

Abstract

The surface morphology of nickel-plated iron single crystals deformed at 77 K has been investigated to identify the mechanism of surface film softening. Two types of striation were found to form on the specimen surfaces, i.e. cracks approximately perpendicular to the tensile axis on the edge-faces and slip-like lines on the screw-faces. The direction of these lines deviated from the traces of the primary slip planes. Specimens which were electroplated on only one of the edge-faces exhibited a clear correspondence between the cracks on the plated face and the slip steps on the unplated face. Both the cracks and the slip steps were irregularly jogged. The lines connecting the corresponding points on the two faces were parallel to the primary slip direction. The observations indicate that dislocation loops are generated near the cracks below the stress level for screw dislocation motion. As the edge component of these loops can move substantially at the low stress level, the generation of a large number of dislocation loops results in macroscopic deformation. The observed angle of deviation between the direction of the slip-like lines and the trace of the primary slip plane on the screw-face is consistent with this model.