Dynamic recrystallization under warm deformation of polycrystalline copper

Structural changes taking place under warm deformation of pure copper were studied in compression at temperatures ranging from 473 to 673 K (0.35 to 0.50 T-m) under strain rates of 10(-3)-10(-1) s(-1). Dynamic recrystallization (DRX) takes place fully or partly at temperatures higher than 523 K, while no fine grains are evolved in the pan-caked original grains with serrated boundaries even after high strains at 473 K. The new grains are evolved by bulging mechanism associated with local migration of the original grain boundaries and the evolution of twins and dislocation boundaries. The relationship of peak flow stress to the new grain size evolved under warm deformation can be expressed by a power law function with a grain size exponent of about -0.35, which is different from that for DRX taking place under hot deformation (i.e. -0.75). The correlation between the mechanisms of plastic deformation and the structural evolution, such as dislocation densities, cell sizes, and DRX grain sizes, and the mechanisms of low and high temperature DRX are discussed in combination with the analysis of deformation behaviour at moderate temperatures.