Formation and Structural Characterization of Electroless Ni-B-P Ternary Alloy Coatings

Abstract

The aim of the present investigation is to study the formation of electroless Ni-B-P alloy coatings and structural and morphological characterization of various coatings with different boron and phosphorous content. An alkaline plating bath with nickel chloride hexahydrate as the source of nickel ions and sodium borohydride and sodium hypophosphite as reducing agents were used for the formation of electroless Ni-B-P alloy coatings. The influence of changes in the concentrations of the reducing agents in the electroless plating bath on the chemical composition, structural and morphological characteristics of the coatings were studied. Scanning electron microscopic studies revealed that the surface morphology of Ni-B-P alloy coatings changed from corn cob-like structure to cauliflower-like structure with increasing borohydride concentration in electroless plating bath, whereas increase in hypophosphite concentration favoured sideway growth, thereby decreased the surface roughness of the Ni-B-P alloy coatings. The peak broadening in the X-Ray Diffraction profiles indicates the large reduction in the crystallite size of the electroless Ni-B-P alloy coatings with increasing boron content in the coating (i.e. for higher borohydride concentration in the plating bath).