GRAIN-BOUNDARIES AS DISLOCATION SOURCES IN THE PRE-MACROYIELD STRAIN REGION

The early stages of yielding in high purity copper (plastic strains of 1-10 × 10-4) have been studied by both quantitative transmission electron microscopy (TEM) and tensile data analysis. The TEM observations, in the form of comparative lattice defect densities, and the tensile data, in the form of stress vs square root of plastic strain plots, both indicate a two stage deformation process separated by a transition region. Each stage is characterized by a dominant deformation mode. In the first stage, this mode is the generation of lattice dislocations at grain boundaries, with the dislocations remaining at or near the boundaries. In the second stage, these dislocations are emitted into the grain interiors, where the grownin dislocations are moving and multiplying as well. These two stages are separated by a transition region where both modes are competitive. © 1979.