Russian Metallurgy (Metally)最新文献

Abstract—The high-temperature corrosion in molten salts is studied to consider the problems of estimating the characteristics of corrosion failure of structural materials. At present, the corrosion resistance of materials is described using such quantitative indicators as the corrosion rate estimated by a gravimetric method, the corrosion damage depth, and the number of corrosion products. However, these characteristics often do not allow one to fully determine the corrosion resistance of materials; therefore, such qualitative subjective characteristics as the type and mechanism of corrosion damage are also used. In this work, we propose additional quantitative characteristics, which are responsible for the intergranular damage intensity (k-parameter) and the uniformity of continuous corrosion (η-parameter), in order to quantify the contribution of various corrosion mechanisms to the generalized estimation of the resistance of structural materials and to predict their service resource. The results of the developed techniques for estimation of the proposed parameters are presented, and their applicability in real corrosion tests is approved and shown.

The processing of primary aluminum with boric acid in a ladle is subjected to thermodynamic analysis. The HSC Chemistry 9.0 (Outotec Technologies) software was used for calculations. The temperature range investigated in the calculations (650–950°C) corresponds to the production conditions of the Kazakhstan Electrolysis Plant. The pressure range is determined using the technological conditions of flux treatment of aluminum in a crane ladle with a working height of 2 m and ranged from 101.33 to 148.99 kPa. The presence of a solid phase and low process kinetics are characterized by the lower limit of the temperature range. The upper limit of temperatures demonstrates the conditions closest to the actual working conditions during electrolysis. The pressure at the metal melt surface is represented by the lower limit in the pressure range, and the pressure at the depth of flux immersion equivalent to 2 m is represented by the upper limit. The depth of the suspension immersion in the calculations is varied in the range 0.5–2 m. The thermodynamic analysis in the investigated range of temperatures and pressures unequivocally indicates that vanadium borides are more stable compared to aluminum borides; therefore, they will predominantly form in this temperature range. The stability order also suggests that vanadium can be easily removed from aluminum melts by adding boron.

Abstract—Nitriding is the oxidation of UN-based nitride fuel by nitrogen at elevated temperatures. In this case, uranium mononitride UN is oxidized to sesquinitride U₂N₃, and the fcc structure of UN changes into a less dense bcc structure of U₂N₃, which is accompanied by an increase in mass by about 4% and an increase in fuel volume by more than 30%. The replacing one crystal structure with another and increasing the fuel volume lead to fuel fragmentation and the expansion of fuel-element cladding. The next operation is to remove part of nitrogen and to perform the reverse U₂N₃ → UN transformation (denitriding). Higher uranium nitrides are known to be unstable upon heating in an inert medium. The transformation from U₂N₃ to UN, which is again accompanied by a change in the crystal structure and a decrease in the fuel volume, occurs at elevated temperatures in an argon atmosphere. This process further contributes to the dispersion of fuel and its separation from fuel-element cladding fragments, the diameter of which was increased at the nitriding stage. Crushing of the fuel and a twofold change in its structure promotes the release of volatile fission products, such as inert gases, Cs, CsI, and Cd. Another advantage of this method is that nitrogen does not interact with the cladding and, hence, the cladding components do not pollute the fuel. In this work, the theoretical aspects of nitriding and denitriding are considered and thermodynamic modeling is performed. The next work in this series will present the results of an experimental test of the proposed method.

Abstract—Cyclic and square-wave voltammetry and open-circuit chronopotentiometry (on/off curves) are used to study the cooperative electroreduction of cerium and nickel ions at a tungsten electrode in the equimolar KCl–NaCl melt at 973 K. Analysis of cyclic voltammetry curves of the KCl–NaCl–СеCl₃–NiCl₂ molten system and results obtained by open-circuit chronopotentiometry (on/off curves) and square-wave voltammetry allow us to conclude that the electrochemical synthesis of cerium intermetallics with nickel can be fulfilled only in a kinetic mode, i.e., by electroreduction of [CeCl₆]^3– ions on metallic nickel preliminary deposited on the tungsten electrode, which is accompanied by the formation of Ce_xNi_y intermetallics as a result of reactive diffusion. Based on the data obtained by different physicochemical methods, electrochemical synthesis of the Ce_xNi_y intermetallics is performed. The synthesized intermetallics are studied by X-ray diffraction using a D2Phaser diffractometer and a VEGA 3LMN (Tescan) scanning electron microscope.

Abstract—We are the first to analyze the immiscibility in Bi–Ga melts by molecular dynamics simulation. Interatomic interaction is specified using ab initio data parameterized neural network potential (DeePMD model). The DeePMD potential is parameterized using an active machine learning algorithm. In the course of molecular dynamics simulation, melts of the Ga_xBi_{100 – x} (x = 0, 10, …, 90, 100) compositions are cooled from 800 to 300 K. Separation is detected using a changes in the temperature behavior of the partial radial distribution function of the Ga–Bi pair. The DeePMD potential, the initial training set of which has no configurations corresponding to a separated state, is still able to reproduce the miscibility gap in the Bi–Ga system. The concentration range of the miscibility gap determined by molecular dynamics simulation with the DeePMD potential coincides with the experimental data. The shift in the maximum of the immiscibility dome toward melts rich in gallium is also correctly described. Nevertheless, the maximum of the immiscibility dome is not determined correctly enough, specifically, Ga₈₀Bi₂₀ instead of experimental Ga₇₀Bi₃₀. In addition, the determined temperature range of the immiscibility dome is wider than the experimental one. Nevertheless, the use of neural network potentials in atomistic simulation is shown to be effectively used to predict a miscibility gap in binary metal systems.

Abstract—When the growth of an ensemble of crystals from metastable melts is modeled, it is important to take into account the shape of growing particles. As experimental data show, the shape of evolving crystals can often be considered ellipsoidal, since it allows us to describe the deviations in the shape of particles from spherical geometry in the first approximation. In this work, we theoretically study the evolution of a polydisperse ensemble of elongated and oblate ellipsoidal crystals in a supercooled single-component melt. The volume growth rates of elongated and oblate ellipsoids with the same supercooling of the melt are analytically found and compared. Elongated crystals are shown to evolve faster than oblate ones, and the difference in their growth rates increases with the supercooling of the melt. These volume growth rates are taken into account to formulate a model describing the evolution of an ensemble of elongated/oblate ellipsoidal particles. An analytical solution to this integro-differential model has been found for two particle nucleation mechanisms in a parametric form for elongated and oblate ellipsoids using the saddle point method. A particle volume distribution function and the time and supercooling of the system are determined depending on the maximum crystal volume, which plays the role of a solution parameter. The constructed solution shows that an ensemble of elongated particles grows and removes the supercooling of the melt faster than an ensemble of oblate particles. As a result, the particle volume distribution function of elongated crystals shifts toward larger crystal sizes than the same distribution for oblate crystals. Considering this behavior, we can conclude that the crystal shape plays a crucial role in the melt supercooling removal dynamics and the volume distribution of particles during crystallization.

Abstract—The possibilities of confocal laser scanning microscopy (CLSM) methods for estimating the parameters of crevice and pitting corrosion of austenitic chromium–nickel AISI 316L steel after corrosion tests in aqueous media with various chlorine ion contents are estimated. Saturated and diluted artificial seawater with various chlorine ion contents in the range from ~100 to ~29 000 ppm is used as a corrosive medium, and the corrosion test time ranges from ~1000 to ~4200 h at temperatures of 25 and 70°C. Corrosion tests and CLSM studies have found that the foci of crevice corrosion form at a chlorine ion content of more than 7300 ppm in water at both test temperatures and all exposure times, and the formation of corrosion sites with metastable pittings is only detected after the maximum test time at 70°C and the maximum Cl^– content of ~29 000 ppm.

Abstract—The adsorption activity of the iridium electrode in molten sodium, potassium, and cesium bromides is studied by the capacitance and electrochemical impedance methods in a temperature range of 1033–1123 K and at the alternating signal frequency from 3 × 10⁰ to 1 × 10⁴ Hz in the whole available range of electric polarization. Two main minima on the capacitance curves corresponding to the ranges of increasing cathodic and anodic currents are observed in all systems under study for both the direct measurement of the electrode capacitance and calculation from the impedance spectra. The calculated capacitances obtained by the equivalent-circuit method in the potential range more positive than the cathodic capacitance minimum coincide with the iridium electrode capacitance obtained for the potential sweep rate at an alternating signal frequency of 10 kHz for the capacitance of the electric double layer and 10 Hz for the adsorption capacitance, respectively. An additional (intermediate) minimum that disappears with increasing temperature is observed in molten sodium bromide at the lowest temperature of the temperature range under study. In molten potassium and cesium bromides, this intermediate minimum is observed at all temperatures under study, and its position on the capacitance curve depends on the alternating signal frequency. An increase in the cation radius in the NaBr–KBr–CsBr series results in the narrowing of the potential range in which the behavior of the system in the anodic range is described by the Gouy–Chapman–Stern model. A decrease in the alternating signal frequency and an increase in the experimental temperature also lead to this range narrowing. The narrowing is assumed to be associated with the enhancement of halide ion adsorption from the melt on the iridium electrode surface upon the potential shift to the positive values from the point of the cathodic capacitance minimum.

The electrical conductivity of (LiCl–KCl)_eut–ZrCl₄ molten mixtures has been studied for the first time as a function of ZrCl₄ concentrations (0–30 mol %) with the increment of ~5 mol % in a wide temperature range (764–1075 K). A conductometric cell of an original construction has been used. The electrical conductivity of these mixtures ranges from 0.9 to 2.8 S/cm. An increase in the temperature was found to increase the electrical conductivity, whereas an increase in the ZrCl₄ concentration was found to decrease the electrical conductivity of the melt. Our new results on the electrical conductivity are compared with those previously obtained for other zirconium-containing molten systems and discussed on the basis of the available data on the structure of such melts. For the first time, the liquidus line was constructed for the (LiCl–KCl)_eut–ZrCl₄ quasi-binary system at the concentrations of zirconium tetrachloride up to 30 mol %.

The influence of the crystallographic texture and phase composition of 1441, V-1461, and V-1469 alloy sheets of the Al–Cu–Li system on the anisotropy of Young’s modulus is studied. The {110}(leftlangle {112} rightrangle ) brass-type texture is shown to form in the sheets and to cause the same anisotropy of the elastic modulus of the alloys: the maximum value in the direction transverse to the rolling direction and the minimum value in the direction at an angle of 45°. This corresponds to the peculiarities of elastic anisotropy of aluminum. The quantitative ratios of the δ' (Al₃Li) and T₁ (Al₂CuLi) phases are determined using a unique procedure of phase analysis, and their elastic moduli are estimated. Young’s modulus averaged over three chosen directions (along and across the rolling direction and at an angle of 45°) is found to be proportional to the total content of intermetallic compounds.