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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.
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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Here, mechanical property-microstructure relationships of an X70 pipeline steel were evaluated at temperatures up to 400 °C using tensile testing, scanning and transmission electron microscopy, and ...synchrotron wide-angle X-ray scattering characterization techniques. The X70 steel had a bainitic microstructure consisting of quasi-polygonal ferrite, retained austenite, martensite-austenite islands, and carbide/nitride microconstituents. Results are compared to an X52 steel with a ferrite-pearlite microstructure. Both steels exhibited dynamic strain aging (DSA) as evidenced by serrated yielding, reductions in strain rate sensitivity, increased strengths, and reduced dutilities in the approximate temperature ranges of 100–250 °C. For temperatures above the DSA range, the X70 steel exhibited unique properties of an increase in strength simultaneously with an increase in uniform strain, both features interpreted due to microstructural changes during testing due to dynamic tempering, indicated by decomposition of the retained austenite and associated cementite and transition carbide nucleation and coarsening, i.e. microstructural changes normally associated with static tempering at temperatures above 400 °C. However, if the X70 steel was tempered at the test temperature prior to testing, dynamic microstructural changes were absent and the steel exhibited behavior similar to that observed for the X52 steel, i.e. a decrease in strength and increase in ductility at temperatures above the DSA range. New alloying strategies are suggested to improve microstructure stability during isothermal holds at elevated temperature, while maintaining the strength benefits from strain assisted bainitic tempering during plastic deformation.
The etching of iron alloy items in a Hsub.3POsub.4 solution is used in various human activities (gas and oil production, metalworking, transport, utilities, etc.). The etching of iron alloys is ...associated with significant material losses due to their corrosion. It has been found that an efficient way to prevent the corrosion of iron alloys in a Hsub.3POsub.4 solution involves the formation of thin complex compound films consisting of the corrosion inhibitor molecules of a triazole derivative (TrzD) on their surface. It has been shown that the protection of iron alloys with a mixture of TrzD + KNCS in a Hsub.3POsub.4 solution is accompanied by the formation of a thin film of coordination polymer compounds thicker than 4 nm consisting of TrzD molecules, Fesup.2+ cations and NCSsup.−. The layer of the complex compound immediately adjacent to the iron alloy surface is chemisorbed on it. The efficiency of this composition as an inhibitor of iron alloy corrosion and hydrogen bulk sorption by iron alloys is determined by its ability to form a coordination polymer compound layer, as experimentally confirmed by electrochemical, AFM and XPS data. The efficiency values of inhibitor compositions 5 mM TrzD + 0.5 mM KNCS and 5 mM TrzD + 0.5 mM KNCS + 200 mM Csub.6Hsub.12Nsub.4 at a temperature of 20 ± 1 °C are 97% and 98%, respectively. The kinetic parameters of the limiting processes of hydrogen evolution and permeation into an iron alloy in a Hsub.3POsub.4 solution were determined. A significant decrease in both the reaction rate of hydrogen evolution and the rate of hydrogen permeation into the iron alloy by the TrzD and its mixtures in question was noted. The inhibitor compositions 5 mM TrzD + 0.5 mM KNCS and 5 mM TrzD + 0.5 mM KNCS + 200 mM Csub.6Hsub.12Nsub.4 decreased the total hydrogen concentration in the iron alloy up to 9.3- and 11-fold, respectively. The preservation of the iron alloy plasticity in the corrosive environment containing the inhibitor under study was determined by a decrease in the hydrogen content in the alloy bulk.
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