Optimization of Mechanical Properties of Nickel-Cobalt Coatings from Sulphamate Baths

Abstract

Nickel-cobalt alloys are important coating materials due to their magnetic properties [1-2],wear resistance [3-4] and electrocatalytic properties [5]. Their deposition from sulfamateelectrolytes has many advantages including low internal stress, homogenous deposition athigh current densities, high current efficiencies and higher hardness as compared to theconventional Watts electrolyte [6]. A statistical experimental design was used to study theeffects of boric acid and nickel chloride concentrations, bath temperature and applied currentdensity on nickel coatings in sulphamate baths. After the optimization of the electrolytecomposition, effects of pH and Co additions to the electrolyte were investigated. The coatingthickness and its distribution were measured by XRF techniques. Microhardness, surfacemorphology and internal stress of coatings were also determined. It was found that Coaddition to the electrolyte and operation at higher pH yielded deposits of higher Co contentand enhanced hardness up to a certain point.