It was recalled that more than one interface velocity could exist for planar interfaces in infinite 2-phase ternary diffusion couples. A description was given here of multiple degeneracies which were features of both mode and wave-number selection problems. The present demonstrations were based upon a class of linear phase diagrams, with constant coefficients in the 4 parabolic Fick equations which were involved. For a given set of coefficients, it was found that the terminal couple compositions that might lead to multiple velocities were confined to a zone that was close to the 2-phase domain in the Gibbs isotherm. When the composition of one terminal point was fixed, a map could be drawn for the position of the other terminal point. This permitted the prediction of the multiplicity of the solution: that is, whether it was single, double or triple. It was shown that this map was related to an interface instability map. Multiple paths in the Zn-Ni-Cu system were predicted and compared with experiment, and the problem of removing degeneracies was considered.

P.Maugis, W.D.Hopfe, J.E.Morral, J.S.Kirkaldy: Acta Materialia, 1997, 45[5], 1941-54