Codeposition of Nickel-Phosphorus Alloys Reinforced with Boron Carbide Microparticles: Direct and Pulse Plating

Abstract

Hard chromium coatings are widely used nowadays due to their remarkable properties such as good corrosion and wear resistance, low friction coefficient and high hardness. The main problem associated however with hard chromium plating is that during the deposition of the coating hexavalent chromium ions may be released. These are extremely dangerous for human health, as they are carcinogenic. For this reason its use has been limited by European Union Restriction of Hazardous Substances Directive. For these reasons researchers are looking for a suitable alternative with characteristics comparable to those of Cr. Nickel-phosphorus alloys were codeposited with boron carbide particles. Two compositions of nickel-phosphorus, one presenting a low phosphorus content in the order of 4 % wt. and another one presenting a high phosphorus content of about 12% wt., were deposited from modified nickel Watt’s electrolytes using both direct and pulse plating. A strong influence of the deposition method was observed on the phosphorus content in the matrix and on the quantity of codeposited particles. Pulse plating was found to significantly increase both of them. Nucleation of the pure nickel-phosphorus alloy and the codeposit were studied using chronoamperometry and AFM in potentiostatic mode. An instantaneous nucleation mechanism was evidenced on iron and gold. Microhardness was measured and connected to the phosphorous and particle contents.