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

Experimental investigations are reported on mechanisms by which disloc ation 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 th at the plastic strain became localized in PSBs. The spacings of the di slocation walls in these PSBs are about 1.4 mum. After the temperature had been lowered to 77 K, cyclic deformation was continued with uncha nged 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 obvi ously inactive. In the state of cyclic saturation reattained at 77 K 5 0% of the PSBs, which had been formed at 300 K, show the dislocation p attern characteristic of 77 K. It is concluded that the amplitude of t he 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 expe riments crystals were cyclically deformed at constant temperatures of 430 K, 300 K, 190 K, and 77 K. In the temperature range covered by the se experiments, the amplitude of the saturation flow stress, tau(S), a ppears to be proportional to the intrinsic amplitude of the PSBs, gamm a(PSB).