Deposition and characterisation of nanostructured nickel-cobalt alloys

Abstract

Nanostructured nickel and cobalt alloy disperse deposits were obtained galvanostati-cally on Cu substrates from ammonium sulfate chloride electrolytes. The influence of current density and the Ni2+/Co2+ ratio in the bath on the microstructure and phase composition of the Ni-Co deposits were studied. It was shown that both bath composition and current density influence strongly the deposit growth mechanism as well as the deposit composition, microstructure, grain size and surface morphology. When electrodeposition was performed at high overpotentials, far from equilibrium conditions, face-centered cubic (FCC) mixtures of Ni and Co were generated while at low overpotentials, as well as at higher content of cobalt in the electrolyte, hexagonal close packed (HCP) Co was formed with a lower rate of hydrogen evolution. The increase in the concentration of HCP phase in the nanocrystalline deposits was caused by increasing the overall Co content in the materials prepared as well as by decreasing deposition current density. The effects of structural changes on magnetic properties of the electrochemically obtained nanocrystalline deposits were studied in the temperature interval from room temperature to 600 °C. It was shown that each stage of the structural changes caused corresponding changes in the magnetic permeability for the alloys prepared.