Effect of pressure on the evolution of copper microstructure upon large plastic deformation

Copper of 99.99% purity has been deformed by shear under pressure of 2, 6, or 9 GPa at room temperature. The structural changes observed correspond to the temperature and strain-rate conditions of deformation and occur as a result of three processes, namely, dynamic recovery, dynamic recrystallization, and post-dynamic recrystallization, relationship between which depends on the pressure applied. At a pressure of 2 GPa, the dynamic recovery plays a significant role, showing up in the absence of deformation-induced hardening and in a low driving force for grain growth upon the post-dynamic recrystallization. As the pressure rises to 6 GPa, the recovery is hampered and the post-dynamic recrystallization leads to growth of some coarse grains. Grains of more uniform size are retained after deformation at a pressure of 9 GPa.