A double-serpentine diffusion path for a ternary diffusion couple Original Research Article

A double-serpentine diffusion path that crosses the straight line joining the terminal alloy compositions twice on a ternary isotherm is reported for a diffusion couple assembled with two β (B2) Fe–Ni–Al alloys and annealed at 1000°C for 2 days. The couple developed a Ni concentration profile 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 coefficients were determined at the composition of intersection. Also, average values of the ternary interdiffusion coefficients, D̃̄ijFe (i, j=Al, Ni), were determined over selected composition ranges of the couple and employed to model the concentration profiles. The cross D̃̄NiAlFe coefficient was negative and comparable in magnitude to the main D̃̄NiNiFe coefficient. The double-serpentine diffusion path was characterized by large diffusional interactions among the components and appreciable variations in the interdiffusion coefficients over different compositional ranges.