Nickel-cobalt alloy coatings prepared by electrodeposition Part II: Morphology, structure, microhardness, and electrochemical studies

Abstract

A study was carried out to synthesize Ni-Co alloy coatings electrochemically from complex acidic glycine (gly) bath. The impacts of some operating parameters such as Co2+ to Ni2+ concentration ratios in the bath, gly concentrations, pH, applied current, plating time and temperature on the morphology of Ni-Co alloy were investigated. The microstructure, microhardness, and electrochemical studies were also investigated. The electrochemical studies utilized cyclic voltammetry, anodic linear stripping voltammetry, and potentiostatic current-time transient techniques. It was realized that gly lowers the cathodic overvoltage for the Co2+ deposition while promoting cathodic overvoltage of Ni2+ deposition. Accordingly, the concurrent codeposition of Co2+ and Ni2+ ions was simplified. The morphology of Ni-Co alloy is significantly dependent on the operating parameters rather than on the bath composition. Moreover, increasing either pH or bath temperature produces Ni-Co deposits free from cracking. The roughness of the alloy is decreased in the presence of gly as shown by the atomic force microscope (AFM) study. In the presence of gly, the microhardness increases from 387 to 970 kg f mm−2, i.e., it increased more than two-and-a-half times. On the other hand, X-ray diffraction analysis (XRD) data show that the crystallinity decreases with enhancing the percentage of cobalt in the deposits.