Effect of atomic interaction on grain boundary diffusion in the B regime

Atomic interaction in grain boundaries that leads to complex formation in two-component solid solutions A–B and the effect of such complexes on grain boundary diffusion are discussed. Two particular types of complex are considered: AB, for systems with restricted solubility and intermediate phases of the AB type, and B2, for systems with restricted solubility without intermediate phases. A thermodynamic description of the complex formation is discussed in the framework of a model of ideal associated solution. Assuming that the complexes are immobile in grain boundaries but that atoms within the complexes are involved in the leakage to the bulk, a new numerical solution of Fisher’s model of grain boundary diffusion is obtained. The solution shows that the complex formation leads to a decrease in diffusion flux along a grain boundary. The theory is in good agreement with several experimental results found in the literature.