Tribological Properties of Electrodeposited Ni–Co₃O₄ Nanocomposite Coating on Steel Substrate

Uniform nanoparticles of cobalt oxide precursors were prepared by the chemical precipitation in which the headspace vapors of ammonium hydroxide solution of known concentration were allowed to bubble through the aqueous solutions of cobalt sulfate, containing appropriate amount of the nonionic surfactant, octylphenoxy poly ethoxy ethanol. Scanning electron microscope (SEM) images showed that uniformity in particle size was dependent upon the applied precipitation conditions. Extensive optimization was therefore performed for the attainment of uniformity in particle size and shape. The amorphous precursor was transformed into crystalline Co₃O₄ as confirmed by X-ray diffractometry. These particles, with isoelectric point (IEP) at pH ∼ 8.4, were then employed as reinforcement additive for strengthening the electrodeposited nickel matrix. Effect of various parameters, i.e., stirring rate, applied current density, and temperature, was studied on the amount of the codeposited Co₃O₄ particles in the nanocomposite coatings (Ni–Co₃O₄) during the electrodeposition process. pH of the coating mixtures was kept below IEP value of Co₃O₄ so that the latter particles carried net positive surface charge. The coated surfaces were subjected to various tests, i.e., microhardness, wear/friction, and corrosion. Results revealed that irrespective of the amount of the embedded Co₃O₄ particles, nanocomposite coatings demonstrated superior performance as compared to pure nickel coatings.