Phosphorus segregation in nanocrystalline Ni-3.6 at.% P alloy investigatedwith the tomographic atom probe (TAP)

The microstructures of electroless plated and thermally aged nanocrystallin e nickel-3.6 at.% phosphorus layers were investigated on an atomic scale wi th a tomographic atom probe (TAP). After heat treatments at 250 and 400 deg rees C, a continuous P-segregation in the grain boundaries of the nanocryst alline structure was directly proved for the first rime. This segregation e ffect explains the comparatively high thermal stability of the material. As suming the existence of a metastable equilibrium, a simple mass balance cal culation, which uses experimentally determined data exclusively, makes it p ossible to predict grain sizes of other NiP alloys within the thermal stabi lity region. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.