Role of Cu2O during hot compression of 99.9% pure copper

Several authors have noticed that relatively pure coppers with different oxygen levels present a higher hot flow stress as the oxygen content increases. This work attempts to demonstrate that a large contribution to the observed increase of stress is due to precipitation of fine Cu2O particles during hot working. Three fire-refined 99.9% pure coppers with different oxygen levels (26 ppm, 46 ppm, and 62 ppm) were hot compressed at temperatures 600-950 deg. C and at a strain rate range 0.001-0.3 s-1. A comparison of transmission electron micrographs prepared from coppers compressed at 750 deg. C and 900 deg. C was performed to characterize the possible precipitates. Fine Cu2O precipitates were found only in the two coppers with higher oxygen and at the lower temperature, where stress differences were larger. Precipitation-hardening theories were adapted for higher temperature and used to iteratively determine if the precipitate sizes and calculated volume fractions could be indeed causing an increase of stress