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.
Fe-based alloy coating was laser cladded on gray cast iron using Ni-Cu alloy as an intermediate layer. The cross section of the laser cladded coating was characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and a Vickers hardness tester. A microdimple texture was created by reciprocating an electrolyte jet with prefabricated mask (REJP) machining on an Fe-based alloy coating. The tribological performances of untextured and textured coatings were examined through interrupted wear tests using an in-house developed reciprocating ball-on-plate tribotester under dry sliding and starved lubricated conditions. The results show that the presence of microdimple edges in the nonconformal contact region has a detrimental effect on the friction performance under dry sliding. However, the microdimples can be beneficial for trapping debris to preserve a smoother contacting surface and thus a lower volume wear track compared to untextured coatings. Due to its role in oil reservoirs and debris entrapment, the microdimple textured coating can maintain a low friction coefficient for a long time period after lubricant oil cutoff and results in a lower volume wear track under starved lubrication.
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