Deformation of copper in easy glide

Abstract

In the pre-yield region of large copper crystals deformed in a single slip orientation it is confirmed that below the multiplication stress some dislocations are displaced on all slip planes distances comparable to the forest spacing of 25 × 10⁻⁴ cm. Above the multiplication stress, as the stress is raised, the dislocation activity increases preferentially on the primary slip system where larger numbers of dislocations move increasingly large distances until in easy glide the distances of motion become comparable with the crystal size (0·5 cm). In the pre-yield region the curvatures of the microstress-strain curves decrease steadily until they become zero in easy glide. Dipolar associations of retained dislocations begin in the pre-yield region and become dominant in easy glide. All dislocation configurations can be resolved into dipolar groupings. When the stress is removed, only isolated individual dislocations displace backward: there is no sign of any expansion of trains of dislocations. Therefore, there is no evidence for the presence of an internal stress with range longer than dislocation spacings in dipoles. While no reproducible correlation between the flow stress and the primary dislocation density was found, a reproducible relation between the flow stress and the square root of the forest dislocation density was observed—suggesting that the velocity of mobile dislocations remains constant during easy glide.