PLASTIC-DEFORMATION OF SINGLE GLIDE ORIENTED CU-2 TO 15AT-PERCENT-AL CRYSTALS AT ELEVATED-TEMPERATURES

Single glide oriented Cu-2 to 15at.%Al single crystals were deformed in tension at temperatures between 300 and 1000 K with repeated strain rate changes and stress relaxations. On several crystals the development of slip bands was observed during deformation through an optical microscope and recorded by video. The gradual transition from smooth to serrated (Portevin-Le Chatelier, PLC) slip was examined by determining the load fluctuations in correlation with the number of active slip band bundles and their evolution. Rapid data recording permitted the evaluation of load drops in the PLC regime similar to stress relaxations with respect to the apparent activation volumes. The results are discussed in terms of breakaway of a source dislocation from its solute atmosphere, rapid multiplication of dislocations during the load drop, and their recapture by diffusing solutes. The transition from PLC serrations to smooth deformation at higher temperatures, where beyond the maximum of the critical resolved shear stress and the strain rate sensitivity the slip lines disappear completely, was investigated by comparison of the measured strain rate sensitivity with the concepts of the formation of solute atmospheres at gliding dislocations and their viscous drag.