PHOSPHORUS SEGREGATION IN NANOCRYSTALLINE Ni-3.6 at. P ALLOY INVESTIGATED WITH THE TOMOGRAPHIC ATOM PROBE (TAP)

摘要

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℃, a continuous P-segregation in the grain boundaries of the nanocrystalline structure was directly proved for the first time. This segregation effect explains the comparatively high ther- mal 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.