Characterisation of crystallisation behaviour of electroless Ni-P plating during heating

Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis were used to study the crystallisation and phase transformation behaviour in the electroless Ni-P platings with 3∼5 wt% (NiP4) or 6∼9 wt% (NiP75) phosphorus contents. X-ray line broadening technique was used to estimate the grain size and microstrain, with the aid of the software PROFIT to separate the reflections of crystalline nickel from the amorphous phase. Results showed that in both Ni-P platings the grain size increases when temperature increases, with sharp increase at temperatures above 400°C. The microstrain in the platings decreases with increasing temperature. The crystalline nickel formed is largely randomly orientated, with possible preferential orientation {220}. It was also shown that the NiP4 specimen heated up to the termination point of the DSC peak at 40°C/min has larger grain size and microstrain than that at 5°C/min. The amount of Ni₃P phase formed at this point is the same regardless of the heating rate. The increase of grain size may contribute to the exothermal peak in the DSC curve.