Exudation of Ag and Cu in internally oxidized Ag-Sn-In-(Cu) alloys

Growth and structure of pure Ag layers are investigated on the surface and at grain boundaries of Ag alloys that have been internally oxidized. Two Ag-Sn-In and an Ag-Sn-In-Cu alloy were studied by ion polishing, field emission scanning electron microscopy and optical microscopy. As already known from previous studies Ag atoms diffuse towards the surface. In the present study it is shown that grain boundaries can act as a sink for diffusing Ag atoms in competition with the surface. In the quaternary alloy Ag and Cu diffuse towards the surface simultaneously. The Cu diffusion is confined by the nucleation of CuO particles. The progress of the internal oxidation front is discussed in conjunction with the nucleation of pure Ag crystallites and CuO particles at grain boundaries.