Ag and Cu Whisker Formation in Ag-Cu-Te Alloys

Long Ag and Cu whiskers are found in Ag-Cu-Te alloys annealed at 400°C and 600°C. Depending upon the nominal compositions of the alloys, there are three kinds of whiskers, Ag, Cu, and Ag+Cu whiskers. For the first time, two different kinds of whiskers grown simultaneously from the same substrate are observed. These whiskers are all polycrystalline, and the grain sizes of the Ag are larger than those of Cu. The whiskers are grown in the solid state pushed out by stress, as indicated by their continuous connection with the substrate, many shear bands in the whiskers, and low-angle grain boundaries piling up near the grain boundaries. The Ag-Cu-Te liquidus projection is calculated using the Calphad method. It is found the compositional regimes of whisker growth overlap with the regions of the liquid miscibility gaps. The stress developed following solidification originated from the two regions of different compositions is the main driving force of whisker formation. The rapid growth rates of the whiskers are a result of the rapid liquid-like diffusion behaviors of the Ag and Cu atoms in the Ag-Cu-Te alloys of the cage-like structures.