The electrochemical deposition of a nickel–iron alloy from a plating solution based on a deep eutectic solvent (a eutectic mixture of ethylene glycol and choline chloride) in the presence of water ...additives (up to 15 wt.%) has been investigated. It is shown that the codeposition of Ni and Fe is accompanied by an acceleration of the discharge of iron(II) ions (a more electronegative component). A “normal” codeposition behavior is observed in a solution without extra water, whereas an “anomalous” codeposition occurs in a deep eutectic solvent with added water (preferential deposition of iron as a less noble component). The addition of ascorbic acid to the plating solution based on a deep eutectic solvent not only prevents the oxidation of iron(II) ions by atmospheric oxygen but also inhibits the partial reaction of nickel electrodeposition. The iron content in the coating increases both with an increase in the contents of Fe(II) ions and water in the plating bath and with an increase in the cathodic current density. The deep eutectic solvent-based solution allows fabricating uniform nanocrystalline deposits of a nickel–iron alloy with an iron content of up to 10–15 wt.%. The electrocatalytic properties of Ni, Fe, and Ni–Fe coatings are evaluated with respect to the hydrogen evolution reaction in an alkaline medium. It is shown that even at a low iron content in the alloy (~ 2–7 wt.%), a significant increase in electrocatalytic activity is observed (an increase in the exchange current density).
It is well known that metals are strengthened by alloying additions or finely dispersed precipitates of a second phase. Here we show that alloying pristine, defect-free single crystalline nickel ...nanoparticles with iron results in a counter-intuitive softening due to randomly distributed solute (Fe) atoms and nano-size precipitates of the ordered Ni3Fe or Fe-rich phases. The Ni-Fe particles with Fe concentration of 0-50 at.% were synthesized by solid-state dewetting of Ni-Fe bilayer thin films deposited on a sapphire substrate. Ni-27Fe and Ni-50Fe particles exhibited a bimodal size distribution with small (111) and large (100) oriented particles. The solid solution softening was observed in all particles. The precipitation softening was observed in (100) oriented Ni-27Fe particles with uniformly distributed ordered Ni3Fe (L12) precipitates. Fe-rich precipitates were found on the surfaces and near the edges of the highly alloyed Ni-50Fe particles, leading to even greater softening. Molecular dynamic simulations of particle deformation have demonstrated that the softening effect is associated with premature dislocation nucleation at sites with a local stress concentration caused by the randomly distributed solute atoms. This work illustrates how the classical hardening mechanisms operating in bulk materials can be manipulated and even reversed in defect-free single-crystalline metal nanoparticles whose plastic deformation is controlled by dislocation nucleation.
Display omitted
Our current understanding of Earth's core formation is limited by the fact that this profound event is far removed from us physically and temporally. The composition of the iron metal in the core was ...a result of the conditions of its formation, which has important implications for our planet's geochemical evolution and physical history. We present experimental and theoretical evidence for the effect of pressure on iron isotopic composition, which we found to vary according to the alloy tested (FeO, FeHx, or Fe₃C versus pure Fe). These results suggest that hydrogen or carbon is not the major light-element component in the core. The pressure dependence of iron isotopic composition provides an independent constraint on Earth's core composition.
The elemental distributions among various phases in vanadium-bearing slags have been quantified toward high-efficiency separation and extraction by calcium roasting using electron probe X-ray ...microanalysis. The roles of the roasting conditions were clarified, including roasting temperature, roasting time, and calcium amount. It was found that, with increasing roasting temperature, the V2O5 concentration in the target vanadium-enriched phase, predominantly in a form of 2(Ca,Mn)OV205, decreased along with more Si02 and Fe203 in this phase; while, with increasing roasting time, the V205 concentration in the vanadium-enriched phase increased due to a more complete reaction. However, a higher calcium addition induced a lower V2O5 concentration in the vanadium-enriched phase and, therefore, a CaO/V^Os weight ratio of 0.6 was employed. In addition to the vanadium-enriched phase, the solubilities, especially V205 in the Si02 and Fe203 solid solutions under varying roasting conditions, were also identified for a reduction of vanadium loss. Based on those quantitative results, the main principles to target to adjust the elemental distributions among various phases during the calcium roasting of vanadium-bearing slags are discussed toward a low-cost and high-efficiency vanadium extraction.
This study presents the experimental results of structural analysis of the phase composition, grain size, plasticity, and hardness of the elinvar Ni-span-C alloy 902 after various heat treatment ...modes (quenching and quenching with subsequent aging). A thermal treatment mode has been selected to obtain higher physical and mechanical properties of the elinvar alloy. It is shown that the improvement of the alloy structure under thermal treatment occurs due to the thermal stresses, as well as the formation and dissolution of intermetallides. Keywords: elinvar alloy, strength, hardness, heat treatment, microstructure, structural analysis
Display omitted
•We study oxygen interaction with Cr/Ni and vacancy in dilute fcc Fe alloys.•Interstitial O prefer the O-sites in the Cr rich region to form Cr-O complexes.•A vacancy can stably trap ...6 O atoms and Cr enhances vacancy trapping ability.•Cr reduces O migration barrier while Ni increases O migration barrier.
We investigate oxygen (O) interaction with alloying elements (Cr/Ni) and vacancies and O migration property in dilute austenitic iron alloys to understand the stability of oxygen-related clusters by first-principles calculations. First, O prefers to occupy the octahedral interstitial sites in the Cr-rich region, the O-Cr interaction is attractive with the binding energy of 0.24 eV, while the O-Ni (−0.16 eV) and O-O (−0.25 eV) interactions are repulsive. The stability and atomic configurations of small CrmOn clusters are determined for m,n = 1−4. The O-vacancy interaction is strong attraction with the binding energy of 1.16 eV, while the Cr-vacancy and Ni-vacancy interactions are weak attraction. Furthermore, we compare multi-O trapping in a vacancy, Cr-vacancy and Ni-vacancy and determined the stability of vacancy-On and Cr/Ni-vacancy-On complexes for n = 1−7. A Cr-vacancy/ Ni-vacancy can stably trap 6 O atoms as the same as those of alone vacancy and Cr presence enhances the trapping ability of vacancy. Finally, O prefers to migrate between two octahedral sites by passing a tetrahedral site, the presence of Cr reduces O migration barrier while Ni increases it.
We examined the compression behavior of hexagonal‐close‐packed (hcp) (Fe0.88Si0.12)1H0.61 and (Fe0.88Si0.12)1H0.79 (in atomic ratio) alloys up to 138 GPa in a diamond anvil cell (DAC). While ...contradicting experimental results were previously reported on the compression curve of double‐hcp (dhcp) FeHx (x ≈ 1), our data show that the compressibility of hcp Fe0.88Si0.12Hx alloys is very similar to those of hcp Fe and Fe0.88Si0.12, indicating that the incorporation of hydrogen into iron does not change its compression behavior remarkably. The present experiments suggest that the inner core may contain up to 0.47 wt % hydrogen (FeH0.26) if temperature is 5000 K. The calculated density profile of Fe0.88Si0.12H0.17 alloy containing 0.32 wt % hydrogen in addition to geochemically required 6.5 wt % silicon matches the seismological observations of the outer core, supporting that hydrogen is an important core light element.
Key Points
Compressibility of hcp Fe0.88Si0.12Hx (x = 0.61 and 0.79) was examined up to 138 GPa
Compression behavior of Fe0.88Si0.12Hx is similar to that of hcp pure Fe and Fe0.88Si0.12
Density profile of Fe0.88Si0.12H0.17 matches the PREM for the outer core
Display omitted
The coercivity of hot-deformed Nd–Fe–B magnet was substantially enhanced from 1.0T to 2.6T by the grain boundary diffusion process using Pr–Cu alloy. However, the temperature ...dependence of coercivity is larger compared to the sample diffusion processed with Nd–Cu. Microstructure studies showed a good isolation of platelet shaped Nd2Fe14B grains by Pr-rich intergranular phase, which explains pronounced coercivity at room temperature. Small portions of Nd2Fe14B become (Nd,Pr)2Fe14B phase, which has a higher anisotropy field compared to that of the Nd2Fe14B phase at room temperature, while it becomes lower than that of the Nd2Fe14B phase above ∼110°C. Co is depleted from the (Nd,Pr)2Fe14B phase, which is considered to cause a slight decrease in Curie temperature. Micromagnetic simulations with the magnetically isolated grains including (Nd,Pr)2Fe14B regions showed that the degradation of thermal stability of coercivity in the Pr–Cu diffusion processed sample is due to the large temperature dependence of anisotropy field in the (Nd,Pr)2Fe14B regions.
Manipulating structure, defects and composition of a material at the atomic scale for enhancing its physical or mechanical properties is referred to as nanostructuring. Here, by combining advanced ...microscopy techniques, we unveil how formation of highly regular nano-arrays of nanoparticles doubles the strength of an Fe-based alloy, doped with Ti, Mo, and V, from 500 MPa to 1 GPa, upon prolonged heat treatment. The nanoparticles form at moving heterophase interfaces during cooling from the high-temperature face-centered cubic austenite to the body-centered cubic ferrite phase. We observe MoC and TiC nanoparticles at early precipitation stages as well as core-shell nanoparticles with a Ti-C rich core and a Mo-V rich shell at later precipitation stages. The core-shell structure hampers particle coarsening, enhancing the material's strength. Designing such highly organized metallic core-shell nanoparticle arrays provides a new pathway for developing a wide range of stable nano-architectured engineering metallic alloys with drastically enhanced properties.
PDF
