Effects of plating parameters on the Ni–P–Al2O3 composite coatings prepared by pulse and direct current plating

In this study, Al2O3 nanoparticles were incorporated into Ni–P alloy matrix by pulse current (PC) and direct current (DC) plating. The effects of bath composition and operating conditions of electrodeposited Ni–P–Al2O3 composite coatings were studied, and the micro-hardness of the deposits was determined. The results showed that with increasing current density as well as Al2O3 content in the bath for DC plating, the embedding volume percentage of Al2O3 of coating increased and the phosphorus content decreased. The incorporation percentage of Al2O3 particles in the composite coatings prepared by PC plating was significantly affected by pulse plating parameters such as average current density, duty cycle and frequency as well as the bath composition. It is also found that PC plating leads to higher embedding percentages and more homogeneous distribution of Al2O3 particles in the Ni–P matrices compared with deposits prepared under DC conditions. The incorporation percentage of Al2O3 particles in PC plated composite coatings increased when high duty cycles and high frequencies were used. The hardness of the composite coatings deposited with a pulse current increased as the duty cycle increases from 0.2 to 0.7.