Work hardening and deformation sub-structure in iron single crystals deformed in tension at 298°k

Abstract

Single crystal strips of Ferrovac E iron with various orientations were grown by a strain anneal method then strained various amounts in tension at room temperature. Slip lines on the polished surfaces were examined by light and electron microscopy. Distribution of dislocations within the strained crystals was determined by transmission electron microscopy. It was found that the shape of the stress-strain curves depends very much on the orientation. For crystals which favour single slip, the stress-strain curve is characterized by three stages of hardening. For crystals of symmetric orientations, stage I hardening was absent and the initial work hardening rate is higher. Non-uniform distribution of dislocations was observed in early stages of deformation. This was followed by the alignment of dislocations and clusters of loops along the traces of primary slip planes. Cell formation was completed in stage III. The dislocation density of all crystals after various stages of deformation depends on the flow stress. The proportion of secondary to primary dislocations was estimated from diffraction contrast experiments for several crystals after various amounts of deformation, and was correlated with the work hardening rates at various stages.