DISLOCATION SUBSTRUCTURE EVOLUTION IN TORSION OF PURE COPPER

The evolution of dislocation substructures in pure copper during torsion deformation at strains ranging from 0 to 440 pct has been investigated using transmission electron microscopy. The study reveals that checkerboard patterns have formed and shrunk in size at strains ranging from 10 to 60 pct. This was followed by the development of laminar dislocation structures consisting of paired sheets which evolved from short double walls delineating the checkerboard patterns. Linear strain hardening was found to be maintained in the paired sheets at strains from 120 to 330 pct. Dislocation wall annihilation and microbands located along the wall of paired sheets were observed in stage IV of the work-hardening curve. At higher strains, another set of wall formation intersects with the paired sheets. The strain hardening of copper under torsional loading from the checkerboard pattern to the laminar structure is described by the mesh length theory of dislocation structures.