Interdiffusion in two-phase ternary solid systems

Abstract

The pseudobinary approach to diffusion in two-phase ternary systems is discussed. In particular, the circumstances under which virtual diffusion paths arise are highlighted. Despite the imprecision inherent in virtual paths, it is recognized that they have an adavantage over so-called real paths (which simply run along phase boundaries) in that they include information about the relative proportions of the phases present in two-phase regions. The term ‘composite diffusion path’ is introduced, which retains this advantage of a virtual path, but avoids its shortcomings by not being based on the assumption of pseudobinary behaviour. The composite diffusion paths are derived from first principles of two model diffusion couples, each comprising a single-phase (α) alloy annealed in contact with a two-phase (α+β) alloy. Comments are also made on the interrelationship between diffusion coefficient data and the shapes of phase boundaries in ternary systems; results being presented which suggest that conclusions about one can be made on the basis of information about the other.