Effects of Co contents on the microstructures and properties of electrodeposited NiCo–Al composite coatings

Abstract

In this work, the NiCo–Al composite coatings with different Co contents were prepared by electrodeposition from the modified Watt baths containing different Co2+ concentrations. The effects of Co contents on the composition, crystal structure, texture, grain size, microstrain, surface morphology, microhardness, residual stress and corrosion resistance of the NiCo–Al composite coatings were investigated in detail. The composite coatings exhibited the solid solution NiCo crystal structure with the Co contents in the range of 18.3wt% to 43wt%. Further increasing the Co content to 60.5wt% resulted in the formation of hexagonal (hcp) Co. As the Co contents increased, the NiCo–Al composite coatings exhibited the texture evolution from the (200) preferred orientations to the random orientations or slight (111) preferred orientations. The grain size decreased, while the microstrain and residual stress increased with increasing Co contents. The hardness of the composite coating attained the maximum at the Co content of 43wt%. However, the increasing Co contents decreased the corrosion resistance of the NiCo–Al composite coatings.