Diffusion in Bimetal Vapor-Solid Couples

The intrinsic diffusivities of individual components in several binary systems have been determined with vapor-solid type diffusion couples. In this type of couple a high vapor-pressure component is diffused from the vapor phase into a slab of lower vapor pressure initially containing inert markers on its surface. Diffusivities may then be calculated from marker movement and diffusion-penetration curve data. Equations necessary for analysis of such couples are developed. The alpha brass, copper-nickel, and silver-gold systems were investigated. Observations of polygonization during diffusion and dimensional changes normal to the diffusion direction were also made. Porosity formation, which occurred only in the vapor-solid silver-gold couples, was investigated in detail and was compared to porosity formation in corresponding sandwich couples. The general use and limitations of such couples in diffusion studies are discussed.