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 α and β plates whose growth is accompanied by the renucleation event of the new β 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 α lamellae with an equilibrium Sn content at the α/β 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 α and β lamellae. (orig.)