| Voids are revealed by transmission electron microscopy on high angle and high Σ CSL grain boundaries in Ag-20 at.% Au dealloyed 100 mV above the critical potential, Ec in I M perchloric acid. Voids are present at a depth at least 5 times the thickness of the dealloyed layer. Voids are absent on low Σ boundaries. Void size and separation follow a simple mass balance model based on grain boundary diffusion of vacancies. In the vicinity of Ec vacancies diffuse along grain boundaries as base metal atoms are extracted, in competition with Au surface diffusion and shallow bulk interdiffusion. The complete absence of voids on low Σ boundaries is attributed to the combination of low surface energy and low diffusivity of these boundaries. Implications to stress corrosion cracking, including transitions between intergranular and transgranular cracking and methods of improving material resistance to stress corrosion cracking are discussed. |
