A double-serpentine diffusion path for a ternary diffusion couple

A double-serpentine diffusion path that crosses the straight line joining t he terminal alloy compositions twice on a ternary isotherm is reported for a diffusion couple assembled with two beta (B-2) Fe-Ni-Al alloys and anneal ed at 1000 degrees C for 2 days. The couple developed a Ni concentration pr ofile that exhibited two regions of mass loss separated by a region of mass gain on one side of the Matano plane. With an additional couple whose path intersected the double serpentine path, ternary interdiffusion coefficient s were determined at the composition of intersection. Also, average values of the ternary interdiffusion coefficients (D) over tilde(y)(-Fe) (i, j = A l, Ni), were determined over selected composition ranges of the couple and employed ra model the concentration profiles. The cross (D) over tilde(NiAl )(-Fe) coefficient was negative and comparable in magnitude to the main (D) over tilde(NiNi)(-Fe) coefficient. The double-serpentine diffusion path wa s characterized by large diffusional interactions among the components and appreciable variations in the interdiffusion coefficients over different co mpositional ranges. (C) 2000 Acta Metallurgica Inc. Published by Elsevier S cience Lid. All rights reserved.