Plastic deformation of copper crystals under alternating tension and compression

Abstract

The strain hardening of high purity copper single crystals during cycles of reversed plastic strain has been studied and shown to depend markedly on the orientation of the crystal. Crystals oriented near [100] or [111] show a high rate of strain hardening, while those in the middle of the stereographic triangle or near [110] show a very low rate of strain hardening, i.e., “easy glide”; in crystals oriented near the [100]–[111] and [100]–[110] boundaries, the rate of strain hardening is low at first and later increases, while in those oriented near the [110]–[111] boundary the rate of strain hardening is more uniform. Similar behaviour was shown in tensile tests, but the easy glide was not as extensive. The importance of small diameter and the unimportance of mishandling of the specimens are discussed in connection with the conditions for the occurrence of easy glide. Easy glide is shown to be accompanied by very uniform distribution of slip lines, while in crystals oriented nearer [111] or [100] and showing rapid strain hardening the slip lines are strongly clustered and sometimes traces of slip on other systems appear between the clusters of main slip lines. X-ray Laue photographs show no asterisms for any crystals after reversed deformation; however, the crystals of high strain hardening give faint Kossel lines while those showing easy glide do not. An explanation of the observed strain-hardening behaviour in terms of the interaction of dislocations on intersecting planes is proposed. The Bauschinger effect is clearly demonstrated in the copper single crystals.