The effect of heat treatment on corrosion behaviour of Ni–P–3 gr/lit Cu nano-composite coating

In this investigation, the effect of heat treatment on corrosion behaviour of Ni–P–Cu nano-composite coating was studied. Initially, an Ni–P–(3?g?l^?1) Cu nano-composite coating was produced under the bath condition of pH?=?4.5–5, RPM?=?400. The coatings were then heat treated at 400°C for 1?h. Scanning electron microscope (SEM), electron dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed to analyse the coating characteristics. As well, corrosion resistance of the coatings in a solution of 1?M HCl was explored by potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Results show that heat treatment for 1?h at 400°C crystallised the Ni–P–Cu coating and changed the amorphous morphology of the coating. This crystallisation also decreased corrosion resistance mainly due to P content reduction of the nano-composite coating. Finally, heat treatment reduced the P content of the coating as it formed different phases such as Cu₃P, Ni₈P₃, Ni₅P₂ and CuP₂.