Microstructure of cold-rolled copper

Abstract

Optical and electron metallography have been used to examine the substructures developed in OFHC copper after rolling reductions from 50–97%. These structures are related to the displacements observed at free surfaces after deformation. It is shown that deformation occurs in a series of overlapping stages in each of which a single operating mechanism predominates. At low strains >10% reduction), deformation occurs by slip on planes spaced about 0.03 μm apart to produce an elementary structure. In the range 10–65% reduction, the operative mechanism produces microbands. It is shown that these features correspond to surface slip lines and to particular strain markings in metallographic specimens and that their formation involves the cooperative movement of dislocations. on planes that are much more closely spaced (<0.008 μm) than has been thought previously. At higher levels of strain, instabilities develop in the form of shear bands and these gradually replace microband formation as the dominant deformation mechanism. The equiaxed cell structure formed at low strains cannot be related to the microband structure or the surface slip steps and is apparently a relaxation effect.