The morphology and chemistry of discontinuous precipitates in a Ni-4 at% Sn alloy

The study of the discontinuous precipitation reaction in a Ni-4 at.% Sn alloy aged at 775 K revealed that the process results in alternating alpha and beta plates whose growth is accompanied by the renucleation event of the new lamellae at the reaction front. Energy dispersive X-ray, analysis of thin foils revealed a step-like change of the Sn content across the reaction Front indicating that the process is governed by boundary diffusion. The parabolic behaviour of the Sn concentration profiles across the alpha lamellae with an equilibrium Sn content it the alpha/beta interface is consistent with the solution of Cahn's diffusion equation. The Cahn parameter C changes by a factor of 2 within the same colony of alpha and beta lamellae.