It was recalled that the presence of 2 Kirkendall planes had been identified in solid-state diffusion couples in various binary metallic systems. Here, 3 Kirkendall marker planes were found in a Ti/TiAl3 couple. The bifurcation and trifurcation of the Kirkendall plane could be quantitatively described by using classical diffusion theory in terms of a Kirkendall velocity construction. The position of a Kirkendall plane was revealed in the reaction zone; not only by inert markers, but also by a different crystal morphology on either side of the plane. A physico-chemical approach was developed which elucidated the role of the Kirkendall effect in the morphogenesis of interdiffusion systems. The occurrence of one or more Kirkendall planes, characterized by morphology changes in the reaction layers, was found to be related to different nucleation sites of the product grains. The model was demonstrated by using experimental results on the Co-Si system. It was shown that predictions made by using the physico-chemical approach were in good agreement with experimentally observed positions of the Kirkendall planes. The presence or absence of inert markers at the Kirkendall planes provided some insight into the initial stages of reactive phase formation.

The Kirkendall Effect in Multiphase Diffusion. A.Paul, M.J.H.van Dal, A.A.Kodentsov, F.J.J.van Loo: Acta Materialia, 2004, 52[3], 623-30