Concentration Of Hydrogen Atoms Research Articles

Laser Powder Bed Fusion Printing of CoCrFeMnNi High Entropy Alloy: Processing, Microstructure, and Mechanical Properties

Equiatomic CoCrFeMnNi high entropy alloy (HEA) powder was processed by laser powder bed fusion (LPBF) additive manufacturing (AM). The properties of the spherical pre-alloyed CoCrFeMnNi powder were characterized and its processability using LPBF AM was systematically investigated through the volumetric energy density (VED) based on the surface roughness, defects (micro-cracks and porosity) and densification. After optimization, LPBF processing at a VED of 104 J/mm3 achieved highly dense and crack-free vertical and horizontal test specimens with a porosity fraction lower than 0.01% and micro-pores having a mean size of, respectively, 25.9 μm and 13.4 μm, as determined from X-ray micro-computed tomography (μCT) inspection. Scanning electron microscope (SEM) analysis of the as-built (AB) CoCrFeMnNi processed at a VED of 104 J/mm3 showed a heterogeneous solidification microstructure, consisting of columnar grains with a cellular subgrain structure, and electron backscattered diffraction (EBSD) revealed a crystallographic texture mainly along the < 100 > direction. Post treatment with hot isostatic pressing (HIP) was effective in closing the remnant micro-pores in the bulk volume of the AB CoCrFeMnNi. Also, the cellular sub-grain structure in the AB CoCrFeMnNi completely disappeared after HIP and the resulting microstructure consisted of recrystallized equiaxed grains with annealing twins. The room temperature tensile response was anisotropic for AB CoCrFeMnNi with horizontally built specimens exhibiting higher strength and fracture strains (global and local) compared to vertically built ones; HIP reduced the anisotropy in the tensile properties and led to similar tensile strength with elongation values that were ~ 50% higher than in the AB condition. The HIPed CoCrFeMnNi also displayed higher Charpy impact toughness and absorbed energy at both room and liquid nitrogen temperatures compared to the AB material. Examination of the fracture surfaces after tensile and Charpy impact testing revealed ductile features with characteristic dimpled appearance and pointed to the important role of the remnant micro-pores on failure in the AB CoCrFeMnNi. Tribological assessments pointed to the superior low-stress abrasion resistance of AB and HIPed CoCrFeMnNi compared to 316L stainless steel (SS), which was included in this study to reinforce the analysis. SEM observations revealed that scratching and micro-fracture are the dominant wear mechanisms for the CoCrFeMnNi HEA, whereas ploughing and cutting parallel to the abrasive flow direction are the dominant mechanisms for 316L SS. To the authors’ knowledge, this study is the first to evaluate and report the low-stress abrasion resistance of any high entropy alloy. To understand the corrosion behavior, polarization curves of AB and HIPed CoCrFeMnNi were measured in 3.5 wt% NaCl and 1N H2SO4 solutions, and the results were compared to those of 316L SS. The findings indicate that AB and HIPed CoCrFeMnNi outperform 316L SS in a chloride-containing environment, but not in an acid-containing environment. Additionally, observations of hydrogen permeability revealed that AB CoCrFeMnNi permeates a lower volume of hydrogen atoms (by ~ 5 times) compared to 316L SS, despite its higher (by nearly 3 times) diffusion coefficient. Electrochemical hydrogen permeation data showed that the concentration of atomic hydrogen in the sub-surface of AB and HIPed CoCrFeMnNi was, respectively, about 32 and 26 times lower than in 316L SS. This study provides important material–structure–property data and indicates a promising outlook for LPBF of the CoCrFeMnNi HEA with high-performance.

Hydrogen interaction with vacancy defects in tungsten: Unraveling the influence on diffusion mechanisms and mechanical properties

This study investigates hydrogen diffusion in tungsten at high temperatures using molecular dynamics simulations. It explores the effect of different hydrogen concentrations on diffusion mechanisms, the interaction of hydrogen atoms with vacancy defects, and their impact on the mechanical properties of tungsten. The activation energy for hydrogen diffusion in perfect bulk tungsten with 0.1 % hydrogen concentration is calculated as 0.235 eV, with a diffusion pre-exponential factor of 5.336 × 10-8 m2/s at temperatures ranging from 1000 to 3000 K. The investigation reveals two factors contributing to the increase in activation energy with temperature: migration paths involving TIS-TIS and TIS-OIS-TIS pathways, and an increase in migration energy. Three diffusion regimes are identified, with trapping effects dominating at temperatures below 1500 K, TIS-TIS pathway dominating at intermediate temperatures, and TIS-OIS-TIS pathway becoming more prominent at higher temperatures. Increasing hydrogen concentration up to 2 % (H/W concentrations in fusion environments) has minimal effect on diffusion in perfect tungsten. However, in a W-H-V system with a 1 % vacancy defect, increasing hydrogen concentration increases the effective diffusion coefficient and activation energy. The presence of hydrogen atoms and vacancy defects reduces the tensile strength and elastic modulus of tungsten, with hydrogen atoms having a greater impact on mechanical properties compared to vacancies. The degree of reduction in mechanical properties is proportional to the concentration of hydrogen atoms and vacancy defects.

Effect of impurities on radical formation in gibbsite radiolysis.

The generation and stabilization of gamma radiation-induced hydrogen atoms in gibbsite (Al(OH)3) nanoplates is directly related to the nature of residual ions from synthetic precursors used, whether nitrates or chlorides. The concentration of hydrogen atoms trapped in the interstitial layers of gibbsite is lower and decays faster in comparison to boehmite (AlOOH), which could affect the management of these materials in radioactive waste.

Experimental study of graphene synthesis by different gas-doped plasma

Plasma gas phase synthesis of graphene method is one-step synthesis, without catalyst, acid, solvent and substrate materials. In this paper, plasma pyrolysis of C2H4 for the preparation of graphene was carried out to investigate the effect of doping H2, CO2, and N2 on the morphology characteristics and chemical reaction properties of the synthesized products at different reaction temperatures ranging from 1500 to 4500 K. It was found that an increase in temperature leads to flatter morphology, less agglomeration, and a decrease in defect density and oxygen content in graphene. The addition of H2, CO2, and N2 gases affected the morphology and defect density of the products. In addition, the high temperature conditions increase the hydrogen atom concentration and etch the edges of graphene, while CO2 slows down the etching process and decreases the defect density. Doping with high enthalpy N2 favors the improvement of crystallinity and defect density at low temperatures, but increases the defect density at high temperatures. These findings contribute to further understanding of the application and optimization of the method of plasma gas phase synthesis of graphene.

On the role of vacancy-hydrogen complexes on dislocation nucleation and propagation in metals

New insights are provided into the role of vacancy-hydrogen (VaH) complexes, compared to the hydrogen atoms alone, on hydrogen embrittlement of nickel. The effect of the concentration of hydrogen atoms and VaH complexes is investigated in different crystal orientations on dislocation emission and propagation in single crystal of nickel using atomistic simulations. At first, embrittlement is studied on the basis of unstable and stable stacking fault energies as well as fracture energy to quantify the embrittlement ratio (unstable stacking fault energy/fracture energy). It is found that VaH complexes lead to high embrittlement compared to H atoms alone. Next, dislocation emission and propagation at pre-cracked single crystal crack-tip are investigated under Mode-I loading. Depending upon the elastic interaction energy and misfit volume, high local concentrations at the crack front lead to the formation of nickel-hydride and nickel-hydride with vacancies phases. These phases are shown to cause softening due to earlier and increased dislocation emission from the interface region. On the other hand, dislocation propagation under the random distribution of hydrogen atoms and VaH complexes at the crack front or along the slip plane shows that VaH complexes lead to hardening that corroborates well with the increased shear stresses observed along the slip plane. Further, VaH complexes lead to the disintegration of partial dislocation and a decrease in dislocation travel distance with respect to time. The softening during emission and hardening during propagation and disintegration of partial dislocation loops due to VaH complexes fit the experimental observations of various dislocation structures on fractured surfaces in the presence of hydrogen, as reported in literature.

A comprehensive study on the synthesis, characteristics, and catalytic applications of submerged hydrogen-mixed argon plasma-synthesized silver nanoparticles

This research studied the effects of hydrogen addition on the structural, optical, and catalytic properties of silver nanoparticles (AgNPs) synthesized by an atmospheric-pressure argon plasma jets with a submerged nozzle. A 3% hydrogen-mixed argon (H2–Ar) plasma jet rapidly and efficiently produced more AgNPs than a pure argon (Ar) plasma jet. Moreover, a submerged plasma jet enhanced the synthesis of AgNPs compared to an atmospheric-pressure plasma jet with its nozzle above the solution. Electrical conductivity, acidity, and hydrogen emission measurements suggested that the efficient and rapid synthesis of AgNPs was due to an increase in the aqua-electron and atomic-hydrogen concentrations caused by the interaction between the H2–Ar plasma and the silver precursor solution. The H2–Ar plasma jet-synthesized AgNPs exhibited strong catalytic effects for rhodamine-B dye and Saccharomyces cerevisiae cells. The H2–Ar plasma synthesis of AgNPs is rapid, low cost, and environmentally friendly. We hope that this research will promote the broader use of metal nanoparticles.

Hydrogen-induced cracking of X70 steel affected by sulfate-reducing bacteria and cathodic potential: experiment and density functional theory study

Submarine pipeline are often exposed to the risk of hydrogen embrittlement from the dual action of marine sulfate-reducing bacteria (SRB) and cathodic protection (CP). In this work, hydrogen permeation test, slow strain rate tensile (SSRT) experiments, and density functional theory (DFT) were used to explain the hydrogen embrittlement (HE) mechanism of subsea pipeline steel under the action of SRB and CP. When the applied CP potential is increased from −850 mV to −1200 mV, the hydrogen seepage current increases 1.8 times. And the tensile specimens pre-charged with hydrogen exhibit significant hydrogen embrittlement behavior. DFT calculations show that the increased concentration of hydrogen atoms on the material surface decreases the diffusion potential barrier, leading to a larger hydrogen seepage current. In addition, the aggregation of hydrogen atoms in the steel weakens the chemical bonds between Fe atoms, leading to hydrogen embrittlement.

Numerical analysis of hydrogen atom diffusion and trapping at an unconstrained dent on pipelines

In this work, a three-dimensional finite element-based mechanics-diffusion coupling model is developed to determine the stress/strain distribution and hydrogen (H) atom concentration at an unconstrained dent on an X52 steel pipe which is to be used for transport of high-pressure hydrogen gas. Both von Mises stress and equivalent plastic strain concentrations and a high hydrostatic stress gradient exist at the dent. The distribution of H atom concentration coincides with that of the hydrostatic stress. The maximum H atom concentration in the steel lattice locates at the dent bottom, while the distribution of the H atom concentration at metallurgical traps is consistent with that of the equivalent plastic strain. A competitive effect exists between the hydrostatic stress and the plastic strain on the H atom distribution. At low initial H atom concentrations (e.g., 0.001 mol/m3), the equivalent plastic strain dominates the distribution of H atoms. At high initial H atom concentrations (e.g., 0.1 and 1 mol/m3), the hydrostatic stress is more important to determine the distribution of H atom concentration. As the dent depth increases, both the von Mises stress and plastic strain at the dent increases, while the total H atom concentration decreases due to decreased hydrostatic stress. When the internal pressure increases from 5 MPa to 15 MPa, there are slightly increases in von Mises stress, equivalent plastic strain and the total H atom concentration.

Study by finite element modeling of hydrogen atom diffusion and distribution at a dent on existing pipelines for hydrogen transport

Pipelines, especially existing natural gas pipelines, provide an efficient and economical means for hydrogen transport, accelerating realization of a full-scale hydrogen economy. However, the existing aged pipelines usually contain dents, which serve as effective traps to accumulate hydrogen atoms, potentially causing hydrogen embrittlement and pipeline failures. To date, there has been a strong interest in development techniques for assessment of hydrogen atom distribution at a dent on pipelines. In this work, a three-dimensional nonlinear finite element-based model was developed to investigate the hydrogen atom diffusion and distribution at a constrained dent on an X52 steel pipe. Parametric effects, including dent depth and internal pressure, were determined. The presence of a dent on pipelines drastically changes the local stress and strain distributions, facilitating diffusion and accumulation of hydrogen atoms at the dent. The minimum hydrogen atom concentration at the crystalline lattice sites, (i.e., 3.8 mol/m3) is located on the outer surface of the dent center, and the maximum hydrogen atom concentration (i.e., 12.1 mol/m3) is found on both sides of the dent with 103 mm from the dent center in the circumferential direction. The hydrogen atom concentration at trap sites at the dent is much lower than that at the lattice sites. The diffusion and accumulation of hydrogen atoms at the dent area is affected by two competitive mechanisms, i.e., hydrostatic stress and plastic strain, depending on the initial concentration of hydrogen atoms entering the interior of the pipe steel. At a low initial concentration such as 0.001 mol/m3, the equivalent plastic strain dominates the distribution of hydrogen atoms at the dent, and the hydrogen atom concentration at the lattice sites is much lower than the concentration at the trap sites. At high initial hydrogen atom concentrations such as 0.1 and 1 mol/m3, the hydrostatic stress is the dominant factor to determine the distribution of hydrogen atoms, which mainly accumulate at the lattice sites. With an increased depth of the dent, both the von Mises stress and plastic strain concentrations increase, and so is the hydrogen atom concentration. The increase of internal pressure from 5 MPa to 15 MPa only slightly elevates the von Mises stress, equivalent plastic strain and the hydrogen atom concentration.

Ground-Based Microwave Measurements of Mesospheric Ozone Variations over Moscow Region during the Solar Eclipses of 20 March 2015 and 25 October 2022

An increase in the ozone content in the mesosphere over the Moscow region during the solar eclipses of 20 March 2015 and 25 October 2022 was observed by means of a ground-based microwave radiometer operated at frequencies of the ozone spectral line of 142.175 GHz. Changes in ozone mixing ratio (OMR) at altitudes of 90 km and 65 km were estimated and compared with diurnal ozone variations measured on the dates closest to the events. It was found that the observed increase in the OMR at 90 km during the 20 March 2015 eclipse was almost two times greater than during the 25 October 2022 eclipse, although the maximum Sun’s obscurations of these eclipses were close to each other (0.625 and 0.646). Most likely, this difference can be explained by the difference in concentration of atomic hydrogen, which plays an important role in ozone destruction at altitudes of around 90 km and above.

Hijacking the hydrogen atoms in photo-splitting of H2O2 for efficient reduction of CO2 to CH3OH

Photo-splitting of H2O2 in visible light is achieved by Cu-MOFs of Cu nodes and 1, 3, 5-benzene tricarboxylic acid (BTC) organic linkers (CuM) decorated with CdS (C) at varying concentrations of CdS in the CuMC composite. This process produces abundant nascent hydrogen atoms to promote the efficient catalytic reduction of CO2 to methanol (CH3OH) in visible light. The slow rate of recombination of the nascent hydrogen atoms produced by the H2O2 photo-splitting on the surface of the CdS quantum dots ensures a high steady-state concentration of hydrogen atoms with significantly reduced production of the less reactive hydrogen gas. With slow recombination of the photo-generated charges and the large surface areas for CO2 adsorption by the MOF, one of the CuMC composites is capable of convertingCO2 into CH3OH with a quantum efficiency approaching 80 %. A mechanism for the selective conversion of CO2 into CH3OH is proposed.

Diffusion flames and a semi-empirical method for estimating the distribution of hydrogen molecules in propane flames

Relevance. The greatest effectiveness in determining the main characteristics in gas burning was shown by optical methods due to their high speed and accuracy. Despite all the advantages of these methods, their main disadvantage is the price and folding of implementation. Therefore, today it is necessary to improve approaches to solve this problem. Purpose. The research is devoted to the study of diffusion flame by a semi-empirical method. Methods. The data of the experimental study of the diffusion flame of hydrocarbons on the example of propane are presented. To visualize the invisible part of the structure of this flame, namely, the afterburning zone of hydrogen molecules formed in the flames in nonequilibrium quantities and, due to the large value of the diffusion coefficient, leaving the flame zone and creating a new combustion zone, molecules containing atoms of alkali metals (NaCl and Na2CO3) are vaporized in the flame zone. Results. The method of delivery of molecules of alkali metal salts from outside was applied for the first time, which allowed the investigation of this phenomenon more thoroughly. Based on the research results, a method for determining the concentration of hydrogen atoms and the relative distribution of the concentration of hydrogen molecules along the axis of propagation of the flame after the burning zone was proposed. The research method combines experiments with mathematical modeling. The application of the method described in the article makes it possible to determine the distribution of hydrogen molecules over the glow zone of the main fuel. Conclusions. The results obtained will help to better understand the phenomena of hydrocarbon combustion under diffusion flame conditions, as well as to search for new ways of obtaining hydrogen fuel from domestic waste treatment

Hydrogen production from ammonia decomposition catalyzed by Ru nano-particles in alkaline molecular sieves under photothermal conditions

Because the high electron cloud density around Ru is favorable for ammonia decomposition, gallium addition to it resulted in an alkaline molecular sieve carrier with a large specific surface area. It was revealed that GaOH not only elevated the electron cloud density near the active center of Ru but also encouraged NH bond breaking and hydrogen atoms’ binding on the catalyst surface. Furthermore, the molecular sieve's regular pore structure strongly inhibited the growth of Ru particles within it, resulting in a high degree of mono-dispersion of Ru nanoparticles and a reduction in the average particle size of the Ru active center to < 3 nm. For TOF >1, the above two factors combined to decrease the ammonia decomposition temperature to < 450 °C. Furthermore, under photothermal synergistic catalysis, the hydrogen production rate via ammonia decomposition was further elevated, and the reaction temperature was further decreased to < 380 °C with TOF > 1. In situ UV photoelectron spectroscopy clarified that the hydrogen atom concentration on Ru increased during photothermal catalysis. According to the FT-IR analysis of the surface intermediate of NH/NH2 formed by ammonia decomposition, photothermal synergistic catalysis can weaken the NH bond compared with pure heating, making it easier for H atoms to combine and form H2. The test results of the correlation between activation energy, reaction rate, and ammonia partial pressure show that, when compared to pure thermal catalysis, photothermal catalysis does not substantially alter the reaction path. The primary reason behind the increased hydrogen production rate of ammonia decomposition by photothermal catalysis was the thermal effect of the light source.

In-situ visualization of hydrogen atom distribution at micro-indentation in a carbon steel by scanning Kelvin probe force microscopy

Abstract In this work, a scanning Kelvin probe force microscope was used to in-situ visualize distribution of hydrogen atoms at micro-indentation and metallurgical phases contained in a carbon steel. Topographic profiles and Volta potentials of the steel upon various times of hydrogen-charging were measured. The hydrogen atom distribution at the micro-indentation was analyzed. Results demonstrate that the micro-indentation can serve as a preferential site to accumulate hydrogen atoms. Particularly, the vertex of the indention shows the greatest hydrogen atom enrichment, while the indentation bottom possesses a slightly lower hydrogen atom concentration. More hydrogen atoms accumulate in ferrite than in pearlite in the steel.

Effects of proton irradiation-induced point defects on Shockley–Read–Hall recombination lifetimes in homoepitaxial GaN p–n junctions

This work examined the intentional generation of recombination centers in GaN p–n junctions on freestanding GaN substrates. Irradiation with a 4.2 MeV proton beam was used to create a uniform distribution of vacancies and interstitials across GaN p+/n− and p−/n+ junctions through anode electrodes. With increasing proton dose, the effective doping concentrations were found to be reduced. Because the reduction in the doping concentration was much higher than the hydrogen atom concentration, this decrease could not be attributed solely to carrier compensation resulting from interstitial hydrogen atoms. In fact, more than half of the electron and hole compensation was caused by the presence of point defects. These defects evidently served as Shockley–Read–Hall (SRH) recombination centers such that the SRH lifetimes were reduced to several picoseconds from several hundred picoseconds prior to irradiation. The compensation for holes in the p−/n+ junctions was almost double that for electrons in the p+/n− junctions. Furthermore, the SRH lifetimes associated with p−/n+ junctions were shorter than those for p+/n− junctions for a given proton dose. These differences can be explained by variations in the charge state and/or the formation energy of intrinsic point defects in the p-type and n-type GaN layers. The results of the present work indicate the asymmetry of defect formation in GaN based on the fact that intrinsic point defects in p-type GaN readily compensate for holes.

Hydrogen-induced cracking of welded X80 steel studies by experimental testing and molecular dynamics modeling

Impact and slow strain rate tensile tests, as well as molecular dynamics modeling, were used to study hydrogen-induced cracking (HIC) of a welded X80 pipeline steel. There is the highest HIC susceptibility at the coarse-grained heat-affected zone, showing an obvious intergranular brittle fracture upon hydrogen-charging. Hydrogen atoms delay dislocation emissions, and the accumulated energy is released mainly through crack initiation. The hydrogen atoms decrease the elasticity of grain boundaries. The locations to initiate cracks in the polycrystalline system are not necessarily the sites with the highest hydrogen atom concentration, but are always at the multi-node grain boundaries.

Ammonia decomposition in a dielectric barrier discharge plasma: Insights from experiments and kinetic modeling

Utilizing ammonia as a storage medium for hydrogen is currently receiving increased attention. A possible method to retrieve the hydrogen is by plasma-catalytic decomposition. In this work, we combined an experimental study, using a dielectric barrier discharge plasma reactor, with a plasma kinetic model, to get insights into the decomposition mechanism. The experimental results revealed a similar effect on the ammonia conversion when changing the flow rate and power, where increasing the specific energy input (higher power or lower flow rate) gave an increased conversion. A conversion as high as 82 % was achieved at a specific energy input of 18 kJ/Nl. Furthermore, when changing the discharge volume from 31 to 10 cm3, a change in the plasma distribution factor from 0.2 to 0.1 was needed in the model to best describe the conversions of the experiments. This means that a smaller plasma volume caused a higher transfer of energy through micro-discharges (non-uniform plasma), which was found to promote the decomposition of ammonia. These results indicate that it is the collisions between NH3 and the high-energy electrons that initiate the decomposition. Moreover, the rate of ammonia destruction was found by the model to be in the order of 1022 molecules/(cm3 s) during the micro-discharges, which is 5 to 6 orders of magnitude higher than in the afterglows. A considerable re-formation of ammonia was found to take place in the afterglows, limiting the overall conversion. In addition, the model revealed that implementation of packing material in the plasma introduced high concentrations of surface-bound hydrogen atoms, which introduced an additional ammonia re-formation pathway through an Eley-Rideal reaction with gas phase NH2. Furthermore, a more uniform plasma is predicted in the presence of MgAl2O4, which leads to a lower average electron energy during micro-discharges and a lower conversion (37 %) at a comparable residence time for the plasma alone (51 %).

Diffusion and redistribution of hydrogen atoms in the vicinity of localized deformation zones

The presence of hydrogen atoms in the lattice of polycrystalline metals can lead to hydrogen embrittlement. The diffusion of hydrogen atoms and formation of hydrides depend on several parameters such as the microstructure of the metal alloy, the presence of stress risers, and the applied loading condition. In this study, a non-local crystal plasticity finite element model is coupled with hydrogen diffusion equations to study the effects of such parameters on the stress-assisted diffusion of hydrogen atoms in zirconium polycrystals. The concentrations of hydrogen atoms in the lattice and dislocation trap sites under different scenarios are studied to deconvolute the effects of texture, microstructure, and applied strain on hydrogen diffusion. It is shown that the concentration of hydrogen in the lattice peaks in the vicinity of grain boundaries and most importantly, at the triple-junction points. It is further shown that in localized deformation zones, such as twin or notch tips where dislocations concentrate, the effects of trapped hydrogen content can be significant.

Elemental carbon and hydrogen concentrations as the main factors in gas-phase graphene synthesis: Quantitative fourier-transform infrared spectroscopy study

Gas-phase microwave plasma-assisted synthesis of freestanding graphene is a promising route to produce high-quality graphene flakes. However, a comprehensive understanding of the gas-phase kinetics that is required to advance production rates and yields is still lacking. Here, we use line-of-sight Fourier-transform infrared (FTIR) absorption spectroscopy as an in situ diagnostic to measure gaseous species formed during graphene synthesis, thereby elucidating the chemical kinetics mechanism. Different carbonaceous precursors that lead to the formation of either few-layer graphene flakes or soot-like particles are examined, and the results are compared with numerical simulations and mass spectrometry measurements. Quantitative FTIR measurements show a correlation between concentration of atomic carbon and hydrogen in the post-plasma region and particle morphology. Lower carbon and higher hydrogen concentrations lead to graphene formation, while higher carbon and lower hydrogen concentrations shift the reaction toward soot-like particles. We also investigate how the precursor chemical composition, precursor flowrate, and delivered microwave power affect the carbon concentration in the post-plasma region, thus enabling to control particle morphology.

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.