Transmission electron microscopy observations of debris structure in deformed copper single crystals

The debris component of the dislocation substructure in copper single crystals deformed at 78 K was studied by weak-beam transmission electron microscopy. The following defects were identified: primary unfaulted dipoles, faulted dipoles, stacking-fault tetrahedra and defect clusters. It is shown that all these defects can be derived from primary dislocations. The distribution of dipole sizes as a function of flow stress suggests that they are refined by chopping as deformation proceeds; so just before fracture their lengths vary from 30 nm down to vanishingly small loops. The size distribution of stacking-fault tetrahedra shows a small dependence upon the degree of deformation and suggests that some equilibrium size of these defects is established in the presence of the other elements of the substructure. Small dot-like clusters of dimension below 2 nm are most probably the remains of larger entities that have shrunk during warm-up to room temperature. Rearrangement of the structure, which occurs between 78 K and room temperature, may to a large degree explain the observed changes in electrical resistivity described in previous work by Niewczas et al.