Effect of Oxygen Content on the Processing Maps for Hot Deformation of OFHC Copper

Abstract

Processing map for the hot deformation of high purity oxygen free high conductivity (OFHC) copper (2ppm oxygen) has been developed in the temperature range 600–950°C and strain rate range 0.001–100s−1. The map is compared with those published earlier on OFHC copper with higher oxygen contents (11ppm and 30ppm) with a view to evaluating the effect of oxygen content on the dynamic behavior of OFHC copper and the mechanism of hot deformation. The maps reveal that dynamic recrystallization (DRX) occurs over a wide temperature and strain rate range and is controlled by different diffusion mechanisms. In OFHC copper with 2ppm oxygen, the apparent activation energy for the DRX domain in the strain rate range 0.01–10s−1 and temperature range 600–900°C is estimated to be about 137kJ∕mole which suggests dislocation core diffusion to be the rate controlling mechanism. However, this domain is absent in the maps for OFHC copper with higher oxygen content due to the “clogging” of dislocation pipes by the oxygen atoms thereby preventing this short circuit diffusion process. At strain rates in the range 1–100s−1 and temperatures >700°C, the apparent activation energy is 73kJ∕mole suggesting that DRX is controlled by grain boundary self diffusion, and this domain expands with higher oxygen content in OFHC copper. At strain rates <0.01s−1 and temperatures >750°C, lattice self-diffusion is the rate controlling mechanism and this lower strain rate domain moves to lower temperatures with increasing oxygen content.