Effect of initial grain size on dynamic recrystallization of copper

Abstract

Oxygen free high conductivity (OFHC) and electrolytic tough pitch (ETP) copper specimens of different grain sizes (10–800 μm) were tested at various constant true strain rates in a modified Instron testing machine. The temperature range investigated was 725–1075 K. The effect of initial grain size on the transition from multiple to single peak flow was studied. The dependence of the stable dynamic grain size on the temperature corrected strain rate and the steady state stress was determined, as were the density of twins and of deformation bands. The density of twins decreased as the initial grain size was increased and when the recrystallization mechanism changed from static to dynamic. The density of deformation bands increased markedly with initial grain size. As the deformation bands are preferential nucleation sites for new dynamic grains, the results indicate that the initial effective grain size <mml:math><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mtext>o</mml:mtext><mml:mi>*</mml:mi></mml:msubsup></mml:mrow></mml:math> relevant to the critical grain size condition D _o = 2D _s, where D _o and D _s are the initial and stable dynamic grain size respectively, decreases in the presence of the bands.