Studies on development of electroless Ni–B bath for corrosion resistance and wear resistance applications

Abstract

Electroless deposition process has undergone numerous changes to meet the challenging needs for a variety of industrial applications ever since the invention of the process during 1947. Among the various metals that can be electrolessly plated, electroless nickel has proved its supremacy for producing coatings with high corrosion resistance, hardness, wear resistance and uniformity. Electroless nickel can be deposited from a variety of baths and the coating properties depends upon the type of reducing agents and other deposition conditions. Electroless nickel–boron coatings have received considerable interest nowadays because of the superior hardness, corrosion and wear resistance characteristics. In this paper, the authors have reported on the development of a biodegradable electroless Ni–B bath and evaluated its characteristic properties. The influence of bath constituents, temperature and pH on the rate of deposition was studied. Scanning electron microscopy, X-ray diffraction, X-ray fluorescence spectroscopy and atomic absorption spectroscopy techniques were employed to find out the deposit morphology and boron content in the deposits. The hardness and wear resistance of the deposits were evaluated in the as deposited and heat treated conditions. The influence of sodium hypophosphite as reducing agent on the Ni–B deposit has also been studied. The use of nickel methane sulphonate as the metal ion source increases the bath lifetime without adversely affecting the deposit qualities. Annealing the Ni–B deposit at 400°C for one hour resulted in an increase in the hardness and thereby the wear resistance. The corrosion resistance of as plated electroless Ni–B deposit is higher than the heat treated deposits. Also, the corrosion resistance is highly enhanced by the incorporation of phosphorous to the nickel–boron alloy coating.