Crystallisation and phase transformation behaviour of electroless nickel phosphorus platings during continuous heating

Abstract

Crystallisation process in electroless nickel phosphorus (Ni–P) platings during continuous heating was investigated using X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC). X-ray line broadening technique was used to estimate the grain size and microstrain, with the aid of PROFIT software to separate the reflections of crystalline nickel from the amorphous phase. Results showed that in the as-deposited condition, platings with 3–5 wt.% (NiP4), 5–8 wt.% (NiP65), and 6–9 wt.% (NiP75) phosphorus are a mixture of amorphous and microcrystalline materials, whereas the plating with 10–14 wt.% (NiP12) phosphorus is fully amorphous. In all the platings after continuous heating the grain size increases sharply when the temperature increases above 400 °C. The microstrain in the platings decreases with increasing temperature. The crystalline nickel formed is largely randomly orientated. It was also shown that the NiP4 specimen heated up to the termination point of the major exothermal DSC peak at 40 °C/min has larger grain size and microstrain than that heated at 5 °C/min. The amount of Ni 3P phase formed at this point is about the same, which indicates that the major DSC peak in the NiP4 plating corresponds to similar transition processes regardless of the heating rate. The processes that contribute to the major exothermal peak in the DSC curve are discussed.