Experimental verification of a phenomenological approach, previously introduced in order to analyze possible bifurcation of the Kirkendall plane within a diffusion-grown compound layer, was described. A reaction couple, in which a single-phase layer of β-NiAl grew during interdiffusion from its adjacent phases, was used as a model system. The corresponding Kirkendall velocity diagram was constructed on the basis of interdiffusion and intrinsic diffusion data; obtained using the diffusion couple technique. Agreement between the predicted and experimentally determined positions of the marker planes was good; within the range of uncertainty of the experimental results, thus demonstrating the validity of the model. It was observed that the position of a stable Kirkendall plane was characterized not only by the presence of inert markers, but also by a different crystal morphology on each side of this plane. The bifurcation of the Kirkendall plane within the product layer of β-NiAl was directly related to the growth of grains of this phase at a location between, and not at, the interfaces with the starting materials.

Bifurcation of the Kirkendall Plane during Interdiffusion in the Intermetallic Compound β-NiAl. A.Paul, A.A.Kodentsov, F.J.J.van Loo: Acta Materialia, 2004, 52[13], 4041-8