Approaching the theoretical strength in ductile copper

The process of dislocation accumulation in both polycrystals and [100] single crystals of high purity copper has been investigated at 4.2 K using both the mechanical response and electrical resistivity. The results indicate that in fine grained polycrystals in the early stages of deformation dislocations are accumulated faster than in multislip single crystals due to storage at the grain boundaries. A salient feature of the results is that just prior to failure the materials accumulate dislocation densities of the order of 1013cm−2 resulting in fracture stresses in the range 1.4 to 2.6 GPa. This strength levels are of the order of one third of theoretical strength and are similar in magnitude to the level observed in dislocation free whiskers.