On diffusion paths with "horns" and the formation of single phase layers in multiphase diffusion couples

The current study using DICTRA finite difference software predicts sharp deviations from the linear zigzag diffusion paths predicted by an error function model for multiphase diffusion couples. The deviations appear as "horns" that protrude from the linear paths. It was found that the horn length is proportional to the composition vector component along the major eigenvector of the effective diffusivity matrix. Applying these results to a study on Ni-Cr-Al diffusion couples prepared from (gamma) + (beta) alloys, it was also found that the formation of single phase (beta) layers could be attributed to the horns pointing away from each other, in which case the diffusion path could intersect the single phase (beta) region of the phase diagram.