INFLUENCE OF OXYGEN ON DYNAMIC RECRYSTALLIZATION DURING HOT-WORKING OF POLYCRYSTALLINE COPPER

The characteristics of dynamic recrystallization (DRX) during hot working of copper containing various amounts of oxygen are studied in the temperature range 650-950-degrees-C and strain-rate range 0.001-100 s-1. Using the dynamic materials model, the efficiency of power dissipation given by [2 m(m + 1)], where m is the strain-rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. One of the domains in the processing map has been correlated with DRX, and in the DRX domain the temperature and strain rate for the efficiency peak depended on the oxygen content. Up to about 150 ppm of oxygen, the DRX strain rate and temperature decrease; at higher oxygen contents, a steep decrease in DRX strain rate and an increase in DRX temperature have been recorded. The results are qualitatively explained on the basis of a simple DRX model where the rate of nucleation of a recrystallized grain boundary and the rate of its migration are considered. Oxygen present both as interstitial atoms and as oxide particles increases the rate of dislocation generation and hence the rate of nucleation of DRX This results in lowering of the DRX strain rate. The large back stress caused by the presence of the oxide particles is responsible for the increase in DRX temperature.