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Solute segregation can profoundly affect the thermodynamic stability and cohesive properties of the grain boundaries (GBs) in Fe-based alloys. In the present work, first-principles ...calculations based on density functional theory (DFT) are performed to understand the atomistic mechanisms of the solute-GB interactions under the dilute limit condition. The segregation effects of six transition metal elements (Cr, Ni, Cu, Zr, Ta, and W) on the Σ3 11111-0 tilt boundary in BCC Fe are systematically studied by examining GB energy, solute segregation energy, and GB cohesion. The solute segregation energy is verified to be composed of a combination of the strain and electronic contributions rather than either of them alone, even for the solute elements with large atomic volume. The potential effects of the FCC/BCC polymorphic phase transformations on the solute segregation behaviors are also discussed. The dynamic change in atomic and electronic structures with straining are investigated to provide physical insights into the effects of solute segregation on the properties of the GB cohesion.
The densities of liquid copper, cobalt, and iron, their binary and ternary alloys have been measured over a temperature range including the undercooled regime. A non-contact technique was used, ...consisting of electromagnetic levitation combined with optical dilatometry.
For all samples, the density was a linear function of temperature. The concentration dependence was studied by means of the excess volume which was negligible for Co– Fe and positive for Cu– Fe, Cu– Co, and Cu–Co – Fe.
The density of the ternary alloy could be predicted from the excess volumes of the binary phases without the need to introduce any ternary interactions.
Density and surface tension of liquid Ni –Cu –Fe alloys have been measured over a wide temperature range, including the undercooled regime. A non-contact technique was used, consisting of an ...electromagnetic levitator, an optical densitometer, and an oscillating drop tensiometer.
At temperatures above and below the liquidus point, density and surface tension are linear functions of temperature. The concentration dependence of the density is significantly influenced by a third-order (ternary) parameter in the volume, while the surface tensions can be derived from the thermodynamic potentials
of the binary phases alone.
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This work investigates solute transport due to self-interstitial defects and radiation induced segregation tendencies in dilute ferritic alloys, by computing the transport ...coefficients of each system based on ab initio calculations of binding energies, migration rates, as well as formation and migration vibrational entropies. The implementation of the self-consistent mean field method in the KineCluE code allows for the calculation of transport coefficients extended to arbitrary interaction ranges, crystal structures, and diffusion mechanisms. In addition, the code gives access to the diffusion and dissociation rates of small solute-defect clusters – in this case, vacancy- and dumbbell-solute pairs. The results show that the diffusivity of P, Mn, and Cr solute atoms is dominated by the dumbbell mechanism, that of Cu by vacancies, while the two mechanisms might be in competition for Ni and Si, despite the fact that the corresponding mixed dumbbells are not stable. Systematic positive radiation-induced segregation (RIS) at defect sinks is expected for P and Mn solutes due to dumbbell diffusion, and for Si due mainly to vacancy drag. Vacancy drag is also responsible for Cu and Ni enrichment at sinks below 1085 K. The RIS behavior of Cr is the outcome of a fine balance between enrichment due to the dumbbell diffusion mechanism and depletion due to the vacancy one. Therefore, for dilute Cr concentrations global enrichment occurs below 540 K, and depletion above. This threshold temperature grows with solute concentration. The findings are in qualitative agreement with experimental observations of RIS and clustering phenomena, and confirm that solute-defect kinetic coupling plays an important role in the formation of solute clusters in reactor pressure vessel steels and other alloys.
This paper deals with the experimental study of the iron losses under real operating conditions of a permanent magnet synchronous machine. The latter is a high frequency (>1 kHz) and high ...power-to-weight ratio (4 kW/kg) motor intended for an aerospace application. The measurements were carried out on different laminated stator cores based on classical commercial grades, namely, the NO20 and M270-35A for the silicon-iron alloy and the Vacodur49 (0.2 mm) for the cobalt-iron alloy. The lamination sheets stemmed from different manufacturing processes: insulation (bonding varnish and C5 varnish), cutting (laser and electrical discharge machining), and thermal treatment (fully processed only and fully processed + thermal re-treatment after cutting). We measured the iron losses at no load and over a wide range of frequency (speed) until around 1400 Hz, and then we compared them to the estimations yielded by the finite-element model under ANSYS Maxwell. Hence, this allowed us to accurately assess the iron loss add-on factor (<inline-formula> <tex-math notation="LaTeX">K_{\mathrm {add}} </tex-math></inline-formula>), which takes into account the extra magnetic loss caused by a complex magneto-thermo-mechanical coupling within the ferromagnetic material. This coupling occurs during the manufacturing and the assembly phase (cutting, welding, stacking, shrink fitting, ...) and also during the real running conditions of an electrical machine (elliptic field, local saturation, high frequency, and harmonics).
In order to develop Fe-based nanocrystalline soft magnetic alloys with high saturation magnetic flux density (B s) and good manufacturability, the effect of the Nb content on the thermal stability, ...microstructural evolution and soft magnetic properties of Fe78-xSi13B8NbxCu1 (x = 0, 1, 2 and 3) alloys were investigated. It is found that proper Nb addition is effective in widening the optimum annealing temperature range and refining the alpha-Fe grain in addition to enhancing the soft magnetic properties. For the representative Fe76 Si13B8Nb2Cu1 alloy, the effective annealing time can be over 60 min in the optimal temperature range of 500-600°C. FeSiBNbCu nanocrystalline soft magnetic alloys with desirable soft magnetic properties including high B s of 1.39 T, low coercivity (H c) of 1.5 A/m and high effective permeability (mu e) of 21,500 at 1 kHz have been developed. The enhanced soft magnetic performance and manufacturability of the FeSiBNbCu nanocrystalline alloys are attributed to the high activated energy for the precipitation of alpha-Fe(Si) and the second phase. These alloys with excellent performance have promising applications in electromagnetic fields like inductors.
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•Amorphous phase formation was confirmed in Fe–Cu–Nb–B immiscible alloys.•Fe-based amorphous phase with emulsion type structure was obtained.•A prediction method for Fe–Cu-based ...immiscible alloys with an amorphous phase formation was suggested.
The microstructure of arc-melted ingots and rapidly solidified melt-spun ribbons of quaternary Fe–Cu–Nb–B immiscible alloys was investigated, with a focus on amorphous-phase formation and solidification structure. A continuous melt-spun ribbon with an Fe–Nb–B-based amorphous matrix and 10–100nm diameter fcc-Cu crystalline globules was obtained for the (Fe0.75Nb0.10B0.15)80Cu20 alloy.
We examined the density, bulk sound (compressional) velocity, and Grüneisen parameter of liquid pure Fe, Fe100H28 (0.50 wt % H), Fe88H40 (0.81 wt % H), and Fe76H52 (1.22 wt % H) at Earth's outer core ...pressure and temperature (P‐T) conditions (~100 to 350 GPa, 4000 to 7000 K) based on first‐principles molecular dynamics calculations. The results demonstrate that the thermodynamic Grüneisen parameter of liquid iron alloy decreases with increasing pressure, temperature, and hydrogen concentration, indicating a relatively small temperature gradient in the outer core when hydrogen is present. Along such temperature profile, both the density and compressional velocity of liquid iron containing ~1 wt % hydrogen match seismological observations. It suggests that hydrogen could be a primary light element in the core, although the shear velocity of the inner core is not reconciled with solid Fe‐H alloy and thus requires another impurity element.
Key Points
Liquid Fe‐H alloys under the outer core conditions are calculated by first principles
Approximately 1 wt % hydrogen concentration is found to reproduce density and bulk sound velocity of PREM
Gruneisen parameter depends on hydrogen concentration
Fe-Cr ferritic-martensitic (FM) steels are promising structural material candidates for fusion and advanced fission reactors due to their attractive mechanical properties and volumetric swelling ...resistance. However, significant discrepancies exist regarding the effect of solutes and irradiation temperature on cavity swelling under ion versus neutron irradiation conditions. In this study, simultaneous dual ion irradiations (8 MeV Ni3+ ions and energy-degraded 3.5 MeV He2+ ions) were used to quantify the cavity swelling behavior in ultra-high purity Fe and Fe-Cr alloys (3-14 wt.% Cr), Fe-10 wt.% Cr-780 wt.ppm C, and Eurofer97 FM steel. The irradiations were conducted over a wide temperature range (400-550°C) with a mid-range dose of ~30 displacements per atom (dpa) and 0.1 appm/dpa He implantation rate. Using state-of-the-art transmission electron microscopy (TEM), we reveal that pure Fe has a ~50°C lower peak swelling temperature difference than Fe-Cr alloys, which is attributed to higher vacancy mobility in pure Fe. Chromium solute appears to strongly suppress cavity swelling in Fe-Cr alloys for temperatures below ~470°C, but seems to have little effect or slightly enhances swelling above ~470°C. Cavities were observed in all the irradiated samples between 400-550°C. This indicates that the narrow temperature range of observable cavities reported in prior ion irradiated Fe-Cr ferritic alloy studies is likely an artifact associated with the use of low ion energies (<5 MeV), which leads to pronounced near-surface and implanted ion effects that suppress cavity swelling even at midrange depths (particularly at high temperatures).
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The discovery of high-temperature superconductivity in a layered iron arsenide has led to an intensive search to optimize the superconducting properties of iron-based superconductors by changing the ...chemical composition of the spacer layer between adjacent anionic iron arsenide layers. Superconductivity has been found in iron arsenides with cationic spacer layers consisting of metal ions (for example, Li(+), Na(+), K(+), Ba(2+)) or PbO- or perovskite-type oxide layers, and also in Fe(1.01)Se (ref. 8) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Li(x)(NH(2))(y)(NH(3))(1-y)Fe(2)Se(2) (x~0.6; y~0.2), with lithium ions, lithium amide and ammonia acting as the spacer layer between FeSe layers, which exhibits superconductivity at 43(1) K, higher than in any FeSe-derived compound reported so far. We have determined the crystal structure using neutron powder diffraction and used magnetometry and muon-spin rotation data to determine the superconducting properties. This new synthetic route opens up the possibility of further exploitation of related molecular intercalations in this and other systems to greatly optimize the superconducting properties in this family.