Crystallization and phase transformation behaviour of electroless nickel-phosphorus deposits with low and medium phosphorus contents under continuous heating

Abstract

Electroless nickel-phosphorus deposits with 5–8 wt% P and 3–5 wt% P were analysed for the effects of continuous heating on the crystallization kinetics and phase transformation behaviour of the deposits. The as-deposited coatings consist of a mixture of amorphous and microcrystalline nickel phases, featuring in their X-ray diffraction patterns. Continuous heating processes to 300°C–800°C at 20°C/min were carried out on the deposits in a differential scanning calorimetric apparatus. The subsequent X-ray diffraction analyses show that the sequence of phase transformation process was: amorphous phase + microcrystalline nickel → f.c.c. nickel + Ni3P stable phases. Preferred orientation of nickel (200) plane developed in the deposits after the heating processes. Differential scanning calorimetry of the deposits indicates that the crystallization temperatures increased with decreasing phosphorus content, and increasing heating rate. Crystallization activation energies of the deposits (230 and 322 kJ/mol, respectively) were calculated using the peak temperatures of crystallization process, from the differential scanning calorimetric curves at the heating rates ranging from 5 to 50°C/min. It was found that the deposit with lower phosphorus content has higher activation energy.