Structure, Morphology and Wear Resistance of Electrodeposited Ni–Co Alloy Deposits

Abstract

Ni–Co alloys with different Co content and microstructures were produced employing Watts-type electrolyte. Effect of high pulse frequency, Co content on the composition, phase structure, surface morphology and wear resistance of the electrodeposited Ni–Co alloy deposit films has been studied. The morphology, composition, wear resistance and phase structure of the Ni–Co alloy deposit were investigated by a magnification of 500× using optical microscope, SEM with an attached energy dispersive X-ray spectroscope and XRD, respectively. Results indicated that the grain size and morphology of alloys are mainly attributed to the Co content. And what's more, the phase structure of Ni–Co alloys dramatically changed from fcc into hcp structure with the increase of Co content. From the optical micrographs, we could clearly observe a change in microstructure from mixed columnar-fibrous to lamellar and finally turn into fibrous with increase in Co content. And the XRD studies showed the crystal structure would be cubic for Co content in the range of 0–50 wt.%, a conversion to hexagonal structure was happened for 70 wt.% and above. A change in preferred orientation was also observed with respect to cobalt addition, simultaneously. When compared with Ni-rich alloys, the Co-rich ones exhibited much higher wear resistance and lower friction coefficient. It has been concluded that hcp crystal structure in Co-rich alloys contributed to the distinguished friction–reduction effect and better anti-wear performance under the dry sliding wear conditions.