Influence of oxygen on the processing maps for hot working of electrolytic tough pitch copper

Abstract

Processing maps for the hot deformation of electrolytic tough pitch (ETP) copper (100 ppm oxygen) have been developed in the temperature range 600-950°C and strain rate range 0.001-100 s^-1, and compared with those published earlier on ETP copper with higher oxygen contents (180, 220 and 260 ppm). These reveal that dynamic recrystallization (DRX) occurs over a wide temperature and strain rate range and is controlled by different diffusion mechanisms. In ETP copper with 100 and 180 ppm oxygen, the apparent activation energy in the DRX domain occurring in the strain rate range 0.001-10 s^-1 and temperature range 600–900°C is about 198 kJ/mol which suggests lattice self-diffusion to be the rate-controlling mechanism. This DRX domain has moved to higher temperatures and lower strain rates in ETP copper with higher oxygen content. In the second domain occurring at strain rates in the range 10-100 s^-1 and temperatures >700°C, the apparent activation energy is 91 kJ/mol and DRX is controlled by grain boundary self-diffusion. This domain is absent in the maps of ETP copper with oxygen content higher than 180 ppm and this is attributed to the pinning of the grain boundaries by the oxide particles preventing their migration.