Preparation of Co-Ni alloy coating with stable composition by jet-electrodeposition

Abstract

Cobalt-Nickel (Co-Ni) alloy coatings were prepared by jet electrodeposition on brass substrate under different Co2+/Ni2+ ratio contents (M = 2:1, 1:1, 1:2 and 1:3) and solution flow rates (from 2.0 to 4.5 L/min). The surface morphology, element content, and phase structure of the coating were observed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffractometer (XRD). The hardness and wear resistance of the coatings were also measured. The results showed that the Co content in coatings was greater than 70%, no matter at what flow rate and concentration. With an increase of the flow rate, the Co content in the coating increases, and the grain size on the surface of the coating decreases, which leads to increased hardness of the coating. However, the flow rate of the plating solution has little effect on the grain growth orientation, and the phase structure is dominated by the elemental content of the coating. The coatings are in a single phase of hexagonal close-packed (HCP) when the Co content is more than 80%, while the coatings are in dual phases of the HCP and face-centered cubic (FCC) when the Co content is less than 80%. With an increase in the Co content, the grain size decreases, and consequently, the hardness and wear resistance of the alloy increase. A Co-Ni alloy coating with stable composition can be obtained when the ratio of Co2+ to Ni2+ is 2:1.