Numerical and Experimental Investigation of the Effect of Current Density on the Anomalous Codeposition of Ternary Fe-Co-Ni Alloy Coatings

Abstract

Gradient-structured ternary Fe-Co-Ni alloy coatings electrodeposited on steel substrates at various current densities from chloride baths were numerically and experimentally investigated. The electrodeposition process, considering hydrogen evolution and hydrolysis reaction, was modelled using the finite element method (FEM) and was based on the tertiary current distribution. The experimentally tested coating thickness and elemental contents were used to verify the simulation model. Although there was a deviation between the simulation and experiments, the numerical model was still able to predict the variation trend of the coating thickness and elemental contents. The influence of the current density on the coating characterization was experimentally studied. Due to hydrogen evolution, the coating surface exhibited microcracks. The crack density on the coating surface appeared smaller with increasing applied current density. The XRD patterns showed that the deposited coatings consisted of solid-solution phases α-Fe and γ (Fe, Ni) and the metallic compound Co3Fe7; the current density in the present studied range had a small influence on the phase composition. The grain sizes on the coating surface varied from 15 nm to 20 nm. The microhardness of the deposited coatings ranged from 625 HV to 655 HV. Meanwhile, the average microhardness increased slightly as the current density increased from 5 A/dm2 to 10 A/dm2 and then decreased as the current density further increased. Finally, the degree of anomaly along with the metal ion and hydrogen atom concentrations in the vicinity of the cathodic surface were calculated to investigate the anomalous codeposition behaviour.

Electrolyte pH dependence of composition, roughness parameters, particle diameter and magnetic features of nanostructured Fe‐Co‐Ni/ITO deposits prepared by electrochemical deposition method

“…During the ECD process at low electrolyte pH, the penetration of H 2 gas bubbles into the deposit by cling to the cathode surface leads to the formation of some pinholes on the deposit surface. 24,[41][42][43][44][45] The H 2 gas bubbles that penetrate into the deposit can also cause the formation of some cracks due to the high tensile stress. [42][43][44]46 The films are composed of nano-sized particles with different diameters.…”

“…24,[41][42][43][44][45] The H 2 gas bubbles that penetrate into the deposit can also cause the formation of some cracks due to the high tensile stress. [42][43][44]46 The films are composed of nano-sized particles with different diameters. The particle diameter distribution images obtained from the AFM micrographs are presented in Figure 6.…”

“…In addition, some pinholes and cracks are clearly visible on the film surface at low electrolyte pH of 3.2 (Figure 5C). During the ECD process at low electrolyte pH, the penetration of H 2 gas bubbles into the deposit by cling to the cathode surface leads to the formation of some pinholes on the deposit surface 24,41–45 . The H 2 gas bubbles that penetrate into the deposit can also cause the formation of some cracks due to the high tensile stress 42–44,46 …”