Electrodeposition of nanocrystalline Ni-Fe alloys

Investigation of the Enhancement Mechanism of Electrochemically Deposited Ni-Co-W Coatings via Laser Irradiation: Effect of W Contents on Corrosion Resistance

Ni-Co-W is an alloy with excellent overall performance and wide application prospects. Electrochemical deposition of Ni-Co-W alloys is currently the most promising process for replacing hexavalent chromium plating. Variations in the W content of the Ni-Co-W coating significantly affect its surface morphology, internal structure, and mechanical properties. Considering the numerous defects with conventional electrochemical deposition, a laser was introduced to enhance the quality and rate of deposition. Using a multienergy composite field, the deposition technique enhanced various properties at room temperature. Ni-Co-W alloy coatings were fabricated through electrochemical deposition and laser electrochemical deposition using electrolytes containing Na₂WO₄·2H₂O at concentrations of 12, 15, 18, and 24 g/L in this investigation. This study aimed to examine how laser irradiation strengthens the corrosion resistance of the coatings. The corrosion resistance could be enhanced with an initial W content increase, but the corrosion resistance did not depend entirely on the W content. Variations in the W content of the electrochemically deposited coatings affected the surface morphology, residual internal stresses, and crystal structure, changing the corrosion resistance. In contrast, the laser electrochemical deposition coating was caused by the combined effect of the W content and laser irradiation (concentration of <18 g/L). Laser electrochemical deposition of the Ni-Co-W coating resulted in a higher W content than electrochemical deposition (≥3.5%), improved the residual internal stresses, and refined the grain size of the coating, resulting in better corrosion resistance (corrosion rate decreased by 74% and R_ct increased by 109.1% at most).

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

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.

Microstructure and Properties of Electrodeposited Nanocrystalline Ni-Co-Fe Coatings

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).

Microstructural heterogeneity in the electrodeposited Ni: insights from growth modes

Microstructures of electrodeposited Ni were studied from the perspective of growth modes during electrodeposition. The electrodeposited Ni had a heterogeneous microstructure composed of nanocrystalline- and microcrystalline-grains. Electron backscatter diffraction analyses showed that nanocrystalline- and microcrystalline-grains were preferentially oriented to specific planes. Secondary ion mass spectrometry also revealed that coarse-grained regions had higher S content than that of finer-grained regions. Hence, microstructural heterogeneity in electrodeposited Ni is reflected by the overlap of inhibited and free growth modes. Our discussion surrounding microstructural heterogeneity also provides insight into other electrodeposited nanocrystalline systems.

Achieving Ultrahigh Hardness in Electrodeposited Nanograined Ni-Based Binary Alloys

Annealing hardening has recently been found in nanograined (ng) metals and alloys, which is ascribed to the promotion of grain boundary (GB) stability through GB relaxation and solute atom GB segregation. Annealing hardening is of great significance in extremely fine ng metals since it allows the hardness to keep increasing with a decreasing grain size which would otherwise be softened. Consequently, to synthesize extremely fine ng metals with a stable structure is crucial in achieving an ultrahigh hardness in ng metals. In the present work, direct current electrodeposition was employed to synthesize extremely fine ng Ni-Mo and Ni-P alloys with a grain size of down to a few nanometers. It is demonstrated that the grain size of the as-synthesized extremely fine ng Ni-Mo and Ni-P alloys can be as small as about 3 nm with a homogeneous structure and chemical composition. Grain size strongly depends upon the content of solute atoms (Mo and P). Most importantly, appropriate annealing induces significant hardening as high as 11 GPa in both ng Ni-Mo and Ni-P alloys, while the peak hardening temperature achieved in ng Ni-Mo is much higher than that in ng Ni-P. Electrodeposition is efficient in the synthesis of ultrahard bulk metals or coatings.

A simple robust method of synthesis of copper-silver core-shell nano-particle: evaluation of its structural and chemical properties with anticancer potency

A simple method of synthesis of a stable bimetallic copper-silver nano-particle (CuAg-NP) was developed by successive reduction of Cu(NO₃)₂ and AgNO₃, using hydrazine hydrate as the reducing agent and gelatin and poly-vinyl pyrrolidone (PVP) as the capping agents. The round-shaped particles were of a core-shell structure with a core of Cu⁰ atoms surrounded by a shell of Ag⁰ atoms. The size and the mol. wt. of the NPs were (100 ± 10) nm and (820 ± 157) Kd, respectively; the particles were crystalline in nature and 90% of the precursors Cu(NO₃)₂ and AgNO₃ were converted to the NPs. The particles were more toxic to cancer cells than normal cells; the dose of the NPs (4-5 μg ml^-1), that killed about 75% of the different human cancer cell lines viz, HepG2 (liver cancer), A549 (lung cancer) and AGS (stomach cancer), killed only about 22.5% of the normal cell lines viz, WRL68 (liver) and WI38 (lung). Therefore, the NP may be developed as a potent anticancer drug in future. The more detailed study on the cytotoxicity of the CuAg-NP on the HepG2 cell line revealed that the particles caused cell cycle arrest in a G2/M phase, depolarization of mitochondrial membrane potential, translocation of phosphatidylserine residues from inner to outer leaflets of cell membrane and DNA degradation; these phenomena confirmed that the NP-induced cell death was apoptotic in nature.

Plasticity of nanocrystalline alloys with chemical order: on the strength and ductility of nanocrystalline Ni-Fe

Plastic deformation and alloying of nanocrystalline Ni-Fe is studied by means of atomic scale computer simulations. By using a combination of Monte-Carlo and molecular dynamics methods we find that solutes have an ordering tendency even if grain sizes are in the nanometer regime, where the phase field of the ordered state is widened as compared to larger grain sizes. Tensile testing of disordered structures with various elemental distributions and the simultaneous analysis of intragranular defects reveal that solid solution strengthening is absent for the studied grain sizes. The composition and relaxation state of the grain boundary control the strength of the material, which is also found for ordered structures (L12), where dislocation activity is suppressed.

AN INVESTIGATION ON THE EFFECT OF ELECTROCHEMICAL ADSORBATES ON PROPERTIES OF ELECTRODEPOSITED NANOCRYSTALLINE Fe–Ni ALLOYS

Iron–Nickel nanocrystalline alloys were electrodeposited from a simple chloride bath using different current densities. The composition and grain size of deposited alloys were in the range of 29–42% Ni and 8–11 nm, respectively. The alloy deposited at lower current density showed higher microhardness, which is most probably due to its higher Fe content and lower grain size. EIS measurements showed that the iron hydroxide species can be formed and adsorbed onto the cathode surface during the deposition. Such species showed an inhibitive effect not only on Ni ion reduction but also on grain growth. By increasing the deposition current density, the adsorption tendency of iron hydroxide was reduced which caused an increase in grain size and Ni percentage of the alloy produced.

Dispersion of Strengthening Particles on the Nickel-Iron-Silicon Nitride Nanocomposite Coating

Nickel-iron-silicon nitride nanocomposite coatings were prepared by electrodeposition technique. The deposition was performed at current density of 11.5 A dm-2. Nano-size silicon nitride was mixed in the electrolyte bath as dispersed phase. The effects of silicon nitride nanoparticulates in the nickel-iron nanocomposite coating were investigated in relation to the concentration of silicon nitride in the plating bath. X-ray diffraction (XRD) analysis showed that the deposited nickel iron alloy coating has face-centered cubic structure (FCC). However, a mixture of body-centered cubic (BCC) and face-centered cubic (FCC) phases were observed for nickel iron-silicon nitride nanocomposite coatings. . The change of crystal structure to FCC + BCC is due to the higher Fe content in the deposit. The crystallite size of Ni-Fe nanocomposite coating decreased with increasing concentration of silicon nitride in the coating. An increase of silicone nitride in electrolyte solution leads to the increase in surface roughness of the nickel-iron-silicon nitride nanocomposite.

Grain Growth in Nanocrystalline Nickel

In this study, the effect of grain size distribution on the thermal stability of electrodeposited nanocrystalline nickel was investigated by pre-annealing material such that a limited amount of abnormal grain growth was introduced. This work was done in an effort to understand the previously reported, unexpected effect, of increasing thermal stability with decreasing grain size seen in some nanocrystalline systems. Pre-annealing produced a range of grain size distributions in materials with relatively unchanged crystallographic texture and total solute content. Subsequent thermal analysis of the pre-annealed samples by differential scanning calorimetry showed that the activation energy of further grain growth was unchanged from the as-deposited nanocrystalline nickel.

Electrochemical Deposition of Nanostructured Metals and Alloys from Ionic Liquids

Metals like aluminium, magnesium, tungsten or their alloys cannot be electrodeposited from aqueous electrolytes. We have developed a procedure using AlCl3-based ionic liquids for the deposition of nanostructured metals and alloys. The ionic liquids (IL) employed for these studies consist of mixtures of an inorganic (e.g., AlCl3) and an organic component (e.g., 1-butyl-3-methyl-imidazoliumchloride or [BMIm]Cl). In our contribution we describe the electrochemical deposition of less noble metals like Al or Fe and alloys like Al x Mn1−x with a controlled nanostructure. The variation of physical and chemical process parameters allows the deposition of samples with crystallite sizes from 10 up to several hundred nm. Deposits prepared from IL's show remarkable properties. Based on nanoindentation measurements we observe crystallite size dependent microhardness for nanostructured aluminium (from 1.44 GPa (100 nm) to 3.40 GPa (14 nm)). The thermal stability of the deposits was measured by high temperature X-ray diffraction. The deposits show a thermal stability up to 350 °C resulting from oxide impurities in the grain boundaries. An activiation energy of 41 kJ/mol can be determined for the crystallite growth process. The magnetization curves of nanostructurd iron exhibit soft magnetic behavior; the coercivity is inverse proportional to the crystallite size.

Electrodeposition of nanostructured coatings and their characterization-A review

Nanostructured materials have gained importance in recent years due to their significantly enhanced properties. In particular, electrochemistry has a special role in producing a variety of nanostructured materials. In the current review, we discuss the superiority of electrochemical deposition techniques in synthesizing various nanomaterials that exhibit improved characteristics compared with materials produced by conventional techniques, as well as their classification, synthesis routes, properties and applications. The superior properties of a nanostructured nickel coating produced by electrochemical deposition are outlined. The properties of various nanostructured coating materials produced by electrochemical techniques are also described. Finally, the importance of nanostructured coatings in industrial applications as well as their potential in future technologies is emphasized.

Strain-dependent deformation behavior in nanocrystalline metals

The deformation behavior as a function of applied strain was studied in a nanostructured Ni-Fe alloy using the in situ synchrotron diffraction technique. It was found that the plastic deformation process consists of two stages, undergoing a transition with applied strain. At low strains, the deformation is mainly accommodated at grain boundaries, while at large strains, the dislocation motion becomes probable and eventually dominates. In addition, current results revealed that, at small grain sizes, the 0.2% offset criterion cannot be used to define the macroscopic yield strength any more. The present study also explained the controversial observations in the literature.