On the Effect of Pressurizing of Pure Copper

Abstract

The effect of pressurizing on the flow stress of copper up to 15000 kg/cm² has been studied by tensile testing at atmospheric pressure and room temperature on polycrystalline specimens of two kinds of tough pitch copper (O₂: 0.06 wt% and 0.03 wt%), low oxygen copper (O₂: 0.004 wt%) and OFHC copper which contain various amounts of impurity oxygen. The results obtained are as follows: (1) For OFHC copper no change in the stress-strain relation is observed after pressurizing up to 15000 kg/cm². (2) For the other materials which contain oxygen, pressurizing increases their flow stress at atmospheric pressure. There exist critical pressures, below which no effect of pressurizing is observed. The critical pressure for the low oxygen copper is higher than that for tough pitch copper. (3) The amount of the pressurizing effect increases with increasing oxygen content and pressure. (4) The increase of flow stress is very large at the beginning of deformation, but it decreases rapidly with increasing strain and becomes almost zero at large strains. (5) The above experimental results are explained by the following mechanism: The copper which contains oxygen shows a large amount of spherical inclusions of Cu₂O. Hydrostatic pressure generates shear stress components around the inclusions and plastic deformation is induced at pressures higher than the critical pressure. Consequently, the work-hardened regions are formed around the inclusions and act as obstacles against the motion of dislocations resulting in the increase in yield stress and flow stress.