Deformation of copper single crystals to large strains at 4.2 K

Transmission electron microscopy (TEM) observations of the dislocation substructure developed in high-purity single crystals of Cu deformed at 4.2 K have been carried out in order to relate the detailed defect structures to the mechanical and electrical properties discussed in part I. The results based on weak-beam TEM show that the dislocation substructure contains a very high density of narrow dislocation dipoles of vacancy character. These dipoles become progressively refined in scale as deformation continues. In-situ annealing experiments carried out in the transmission electron microscope allow the stability of these structures against annealing at room temperature and elevated temperatures to be studied. The observations suggest that fine dislocation dipoles can be annealed by processes such as pipe diffusion and that these defects represent the recoverable component of electrical resistivity. For comparison some studies were undertaken in Cu-5 at.% Ni single crystals which indicate that the recoverable component of resistivity in this alloy is smaller owing to the influence of the Ni on the pipe diffusion process. In addition, TEM studies indicate the complexity of processes occurring at the twin-parent interfaces produced in Cu deformed at 4.2 K. These interfaces have an important role in debris storage and in processes that can occur after large plastic strains at 4.2 K.