Some consequences of surface and size effects in plastically deformed copper single crystals

Abstract

AbstractThe dislocation behaviour in deformed copper single crystals was previously shown to correspond to a lower local flow stress in the surface region than in the interior and the primary glide plane was found to undergo a characteristic bending in the surface region, reflecting a local excess density of unpaired edge dislocations. The detailed features of this “profile” are explained by a dislocation model which takes into account both surface and inner dislocation sources. It is shown that, as a result of the surface effects, dislocation glide paths in stage II as determined from slip lines are about 2.5 times larger than those in the interior. The rate of work‐hardening in stage II above a certain stress level, however, is found to be fairly constant over the cross‐section inspite of surface effects. It is concluded from Seeger's stage II work‐hardening theory that the number of dislocations per group should therefore decrease in the same way as the glide paths from the surface towards the interior. This prediction is in line with available experimental data. The shape of the macroscopic stress‐strain curve is explained by the local microscopic behaviour. Our results are consistent with Fourie's concept of preferential core‐hardening. The possibility of preferential near‐surface‐hardening is indicated.