Optimization of process parameters for electroless Ni–Co–P coating deposition to maximize micro-hardness

Abstract

The present study investigates optimisation of microhardness of electroless Ni–Co–P alloy coating over copper substrate. The microhardness of the coating was significantly higher compared to the substrate. Three different design factors i.e., the concentration of cobalt sulphate, concentration of sodium hypophosphite and bath temperatures were used as the process parameters which were optimised by using Box Behnken Design (BBD) and coating micro hardness was taken as a response factor. Vickers’ hardness test was conducted to obtain the micro hardness values of the coated samples. From the model analysis results, it was found 15 g L−1 of cobalt sulphate, 25 g L−1 of sodium hypophosphite and a bath temperature of 85 °C were the optimum conditions for the coating deposition in order to obtain the hardness value of 1921 HV10g. After annealing at 350 °C the hardness value was further enhanced to 1990 HV10g. Analysis of variance (ANOVA) was carried out to find the graphical relationship between the different process parameters. The detail surface morphology of the Ni–Co–P coating was studied by using an optical microscope and a Scanning Electron Microscope (SEM). The phase and elemental compositions were determined by x-ray Diffraction (XRD) analysis and Energy Dispersive x-ray analysis (EDX).