Structure-dependent chemical reaction and nucleation of fracture in Cu 3Au single crystals

Abstract

The associated phenomena of structure-dependent chemical removal of copper from Cu 3Au and the nucleation and growth of fracture have been investigated in single crystals. Copper is selectively removed from Cu 3Au by ferric chloride from imperfections originating during crystal growth. Selective removal of copper also occurs from local areas in slip clusters, apparently unrelated to growth imperfections. Under applied stress, both sites of reaction become nuclei of fracture cracks. Fracture propagates only in the presence of stress and the chemical reagent. The fracture path is normal to the stress axis and independent of crystallography, after initial nucleation occurring in areas of clustered slip bands. The fact that the fracture path is not a rational crystallographic plane indicates that deformation at the leading edge of the crack is highly complex. In accordance with the observed chemical activity localized in slip clusters, possibly at sites of cross slip, it is proposed that fracture occurs as a result of the selective removal of copper from the zone of complex deformation at the leading edge of the crack.