Deformation of copper and low stacking-fault energy,copperbase alloys

The effects of deformation on the structure of copper and its low stacking-fault energy alloys are reviewed and it is shown that these may be classified according to the method of examination used. In rolled low stacking-fault energy alloys the deformation sequence involves the formation of stacking faults, mechanical twins, and shear bands that are at first restricted to individual grains but subsequently extend from one surface to the opposite surface. Shear bands form at ∼35° to the trace of the rolling plane in longitudinal sections and are composed of very small, slightly elongated crystallites. The twin thickness and crystallite spacing are determined by the stacking-fault energy and decrease as that parameter decreases. In copper the deformation sequence involves the formation of equiaxed cells of dislocations, microbands, clustering of microbands, and shear-band formation. It is shown that measurements of cell thickness as a function of strain in copper are meaningless. Replication and other techniques are used to establish the relationships between the various features of the optical microstructure and the structure seen in transmission electron microscopy. Although there is considerable uncertainty about the nature of shear bands in copper, it is pointed out that shear bands are a common deformation feature in metals and that both shear bands and microbands are manifestations of instability.