Fracture topography of commercial copper

There is an interest in relating the fracture process of metallic materials to the plastic deformation mechanisms which precede fracture. Thus, in many reported cases the fracturing path follows the dislocation cell walls present in the material and hence can be directly correlated to the dislocation cell structures. This study examines this hypothesis for high purity (99.94%) commercial copper containing inclusions. Tensile specimens, having two grain sizes, were pulled to fracture at three different cross-head speeds. The fracture surfaces were examined using scanning electron microscopy. The relative strengths of both grain and grain boundaries were determined from microhardness measurements. The microhardness was also used to obtain the variation in hardness with respect to reduction in area. The dislocation cell structures were observed using transmission electron microscopy. It is shown that, while the plastic deformation preceding fracture is related to dislocation structures, final fracture is dominated by the distribution of inclusions and other impurities in the grains.