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

The microstructures of electroless plated and thermally aged nanocrystalline nickel-3.6 at.% phosphorus layers were investigated on an atomic scale with a tomographic atom probe (TAP). After heat treatments at 250 and 400 degrees C, a continuous P-segregation in the grain boundaries of the nanocrystalline structure was directly proved for the first rime. This segregation effect explains the comparatively high thermal stability of the material. Assuming the existence of a metastable equilibrium, a simple mass balance calculation, which uses experimentally determined data exclusively, makes it possible to predict grain sizes of other NiP alloys within the thermal stability region. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.