Dynamic recrystallization of copper polycrystals with different purities

The hot deformation behaviour and associated structural changes were studied by means of compression tests and metallographic observations of polycrystalline copper with three different purities of 99.99 (4N), 99.9999 (6N) and 99.99999 (7N) mass percent of copper. The samples were strained up to 1.2 at temperatures ranged from 523 to 773 K under various true strain rates of 10−4–10−1 s−1. The deformation behaviours are characterised by multiple peaks or a single peak flow, followed by a steady state flow stress and a new grain evolution by dynamic recrystallization (DRX) at high strains. The steady state stresses and their temperature and strain rate dependencies for 6N and 7NCu are almost the same, but clearly lower and higher than those for 4NCu, respectively. The activation energy for hot deformation is affected by materials purity, i.e. about 210 kJ mol−1 for 6N or 7NCu and 245 kJ mol−1 for 4NCu. On the other hand, the DRX grain sizes, represented by a unique function of steady state flow stress, strongly depend on the solute concentration for all of samples studied. The effect of impurity atoms on the deformation and DRX grains is discussed in such high purity materials.