Plastic deformation of thin copper single crystals. I. The separate roles of edge and screw dislocations in stage I of work hardening

Abstract

Thin copper single crystals with a common axial orientation but with two different surface orientations are deformed in tension. The surface orientations were chosen so that in the one case the maximum glide path length of edge dislocations is reduced-fey thinning the specimen by electrolytic jet polishing of the surface while in the other the glide path length of screw dislocations is reduced. The extent of strain (ϵ₁₁) in Stage I of the stress-strain curve is found to depend strongly on the glide path length of edge dislocations, while it depends only slightly on the glide path length of screw dislocations. Thin crystals with edge dislocation glide path lengths of about 50 microns can sustain the Stage I mode of deformation at applied stress levels three to four times that of crystals of normal thicknesses, while the rate of hardening (θ₁) shows no systematic variation with thickness. It is concluded that the extent of strain in Stage I depends on the rate of accumulation of a primary dislocation array giving rise to an internal stress, while the rate of hardening depends on the rate of increase in the density of forest dislocations.