Nanocrystalline Ni–3.6 at.% P and its transformation sequence studied by atom-probe field-ion microscopy

Abstract The transformation sequence of electroless plated nanocrystalline Ni–3.6 at.% P layers upon different heat treatments is studied by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and atom-probe field-ion microscopy (APFIM). APFIM reveals P segregation at the grain boundaries in the as-plated nanocrystalline alloy. DSC shows two heat releases upon isochronic heat treatment. During the first heat release, starting at about 136°C for a heating rate of 20°C/min, structural relaxation occurs first, followed by slight crystal growth and segregation enhancement, as shown by XRD and APFIM. Nucleation of the equilibrium phase Ni 3 P starts in the transition to the second heat release. This second heat release, with a sharp onset at 417°C for heating at a rate of 20°C/min, is related to the major part of Ni 3 P-phase formation and substantial grain growth. The transformation sequence is compared with the one observed on amorphous Ni–P alloys and discussed in terms of a thermodynamic model.