TEMPERATURE-INDUCED REARRANGEMENT OF THE DISLOCATION PATTERN OF PERSISTENT SLIP BANDS IN COPPER SINGLE-CRYSTALS

Experimental investigations are reported on mechanisms by which dislocation arrangements of Persistent Slip Bands (PSBs) respond to changes of the deformation temperature. Copper single crystals orientated for single slip were cyclically deformed well into saturation at 300 K at an applied resolved plastic shear-strain amplitude, gamma(pl), such that the plastic strain became localized in PSBs. The spacings of the dislocation walls in these PSBs are about 1.4 mum. After the temperature had been lowered to 77 K, cyclic deformation was continued with unchanged gamma(pl). A transformation of the dislocation pattern started. A certain fraction of the PSBs produced at 300 K finally showed a mean wall spacing of about 0.7 mum which is typical for PSBs formed at 77 K. The remaining PSBs did not finish the transformation and became obviously inactive. In the state of cyclic saturation reattained at 77 K 50% of the PSBs, which had been formed at 300 K, show the dislocation pattern characteristic of 77 K. It is concluded that the amplitude of the resolved plastic shear strain localized in a PSB, gamma(PSB), MUSt be twice as large at 77 K as at 300 K. In an additional series of experiments crystals were cyclically deformed at constant temperatures of 430 K, 300 K, 190 K, and 77 K. In the temperature range covered by these experiments, the amplitude of the saturation flow stress, tau(S), appears to be proportional to the intrinsic amplitude of the PSBs, gamma(PSB).