Effect of current density and cobalt concentration on the characteristics of Ni[sbnd]Co coatings prepared by electrodesposition with a supergravity field

Abstract

A supergravity field offers several advantages during electrodeposition. Electrodeposition assisted by a supergravity field was employed to produce nickel–cobalt (NiCo) alloy coatings. The grain size, surface morphology, preferred crystal orientation, microhardness and wear resistance of the deposited NiCo coatings were studied systematically, and all were found to be dependent on the Co concentration in the plating bath and current density. Under a supergravity field, the surface morphology was found to be smoother than that obtained in a normal gravity field. Grain sizes of the as-prepared NiCo coatings were refined, and an average grain size of 15 nm was obtained. A Co content of 40.56 wt% was obtained using a low Co concentration in the bath. NiCo alloy coatings with a maximum microhardness of 660 HV were prepared, and the hardness value was significantly higher than that for coatings prepared by conventional electrodeposition. A minimum friction coefficient of 0.14 and a very low wear weight loss of 2.5 mg were achieved in our experiments.