Evidence for an early softening behavior in pure copper processed by high-pressure torsion

Pure copper of 99.99 % purity was processed by high-pressure torsion under a pressure of 6.0 GPa at room temperature through various numbers of turns from 1/4 to 10. Microhardness measurements show that the hardness initially increases to a maximum value at a strain of ~5.6, decreases to a strain of ~8.4, and then increases slowly to a saturation condition at strains at and above ~80. These data are interpreted in terms of the advent of dynamic recrystallization. The results have similarities and differences to the softening with recovery that is well established in high-purity aluminum.