Materials based on Ni-Co-Fe alloys, due to their excellent magnetic properties, attract great attention in nanotechnology, especially as candidates for high-density magnetic recording media and other applications from spintronic to consumer electronics. In this study, Ni-Co-Fe nanocrystalline coatings were electrodeposited from citrate-sulfate baths with the Ni²⁺:Co²⁺:Fe²⁺ ion concentration ratios equal to 15:1:1, 15:2:1, and 15:4:1. The effect of the composition of the bath on the morphology, microstructure, chemical composition, microhardness, and magnetic properties of the coatings was examined. Scanning (SEM) and transmission (TEM) electron microscopy, X-ray diffractometry (XRD), and energy dispersive X-ray spectroscopy (EDS) were used to study surface morphology, microstructure, chemical, and phase composition. Isothermal cross-sections of the Ni-Co-Fe ternary equilibrium system for the temperature of 50 °C and 600 °C were generated using the FactSage package. Magnetic properties were analyzed by a superconducting quantum interference device magnetometer (SQUID). All the coatings were composed of a single phase being face-centered cubic (fcc) solid solution. They were characterized by a smooth surface with globular morphology and a nanocrystalline structure of grain diameter below 30 nm. It was determined that Ni-Co-Fe coatings exhibit high hardness above 4.2 GPa. The measurements of hysteresis loops showed a significant value of magnetization saturation and small coercivity. The microstructure and properties of the obtained nanocrystalline coatings are interesting in terms of their future use in micromechanical devices (MEMS).

This study investigates the effect of laser power applied for a remelting scan in the laser powder bed fusion process on the formation of a bimodal microstructure and its impact on the mechanical properties of Ni-based Inconel 625 superalloy. Comparison of primary and remelting scans at similar surface energy densities revealed that the melt pools obtained in the remelting scan are smaller than in the primary scan. To achieve comparable remelted melt pool sizes, the 25 pct increase in energy is required. The shape and size of the remelted melt pools significantly affect the microstructure and material texture. The lower surface energy density in laser powder bed fusion favors the formation of a bimodal microstructure with large columnar grains and fine grain bands. Application of higher energy results in the formation of large columnar grains with Goss texture along build direction and separated by a large amount of low angle grain boundaries. Remelting scan also affects reduction of porosity and increasing of the area fraction of nanometric oxide inclusions. The study revealed that the samples subjected to a remelting laser scan and tensile tested along the direction of columnar grains exhibited higher ductility, which was associated with a slight decrease in the ultimate tensile strength compared to the samples that were not remelted. It was demonstrated that the remelting scan in the laser powder bed fusion process offers the possibility of improving the reliability of additively manufactured Inconel 625 superalloy by reducing porosity and tailoring its microstructure towards single-crystal-like, and thus improving the mechanical properties. Graphical Abstract

In recent years, Ni-Cu alloy coatings obtained by electrolytic deposition have received increasing interest, because of their good anti-corrosive, mechanical, magnetic, electrical, and decorative properties. Further applications of these coatings for electrode materials and catalysts may be possible by developing hierarchical surface morphology, and thus a combination of high surface roughness, high microhardness, and good corrosion resistance. In the present work, four types of Ni-Cu alloy coatings were deposited in a single-step process from electrolytic baths with Cu²⁺:Ni²⁺concentrations equal to 1:30, 1:20, 1:15, and 1:10 using deposition current densities of 2 A/dm²and 4 A/dm². The surface morphology of the coatings was characterized using a scanning electron microscope and an optical profilometer. The coatings exhibited a nodular morphology, which with the change of the Cu²⁺:Ni²ratio and the current parameters changed from smooth and compact to rougher with regularly spaced nodular microprotrusions. Thus, a hierarchical surface morphology was obtained. Transmission electron microscopy investigations revealed that the fine-grained microstructure of the coatings consisted of theγsolid solution, as well as the metastable intermetallic L1₀NiCu phase. The differences in the Cu concentration at the cross-sections demonstrated by quantitative microanalysis of the chemical composition indicated a dendritic growth of the coatings and a preferential reduction of copper ions over nickel ions. The coatings were also characterized by a microhardness greater than 3.71 GPa and good electrochemical corrosion resistance in chloride media. Coatings with hierarchical morphology and high surface roughness showed a higher corrosion current. The study provides a new method for electrodeposition hierarchical Ni-Cu coatings under specific chemical compositions of the electrolytic bath and current conditions, characterized by a combination of promising properties for electrode and catalytic applications.Graphical Abstract

This paper presents the results of the optimization of electrophoretic deposition parameters for manufacturing of nc-TiO₂/chitosan composite coatings on X2CrNiMo17-12-2 steel as well as characterization of their microstructure, electrochemical properties and adhesion to the substrate. The parameters of the deposition, such as composition, pH and zeta potential of suspensions as well as voltage and process time were investigated. The microstructure of the coatings was characterized using scanning and transmission electron microscopy. Obtained coatings were crack-free and uniform. The adhesion strength to the substrate was measured by scratch-test method. The deposited coatings improve corrosion resistance of steel, what was confirmed by the results of the potentiodynamic polarization test in Ringer’s solution.

The aim of this work was to investigate the effect of the microstructure of Inconel 625 additively manufactured by laser powder bed fusion (LPBF) and laser-assisted directed energy deposition (LDED) on the resistance to corrosion in sulfuric acid solution. Corrosion tests lasted 30 days, 90 days and 180 days. Microstructure characterization was performed using light microscopy, scanning and scanning-transmission electron microscopy. Corrosion resistance measurements were conducted using polarization curves and impedance spectroscopy. After immersion in sulfuric acid, the corrosion pits were observed on the surface. The area fraction of corrosion pits increased with prolongation of the test and after 180 days was equal to 9.63% and 4.49% in LPBF and LDED specimens, respectively. The higher density of the pits occurred along the boundaries of the melt pools, grain boundaries and cell walls and next to precipitates. It was determined that higher drop in impedance and increase in corrosion current occurred in LPBF than LDED Inconel 625, which was mainly related to a more intensive propagation of corrosion pits in areas with higher free energy. Furthermore, the weaker corrosion resistance is related to a more refined microstructure with a higher density of the preferential sites of localized corrosion after long-term corrosion in sulfuric acid.