Russian Metallurgy (Metally)最新文献

Electrochemical co-deposition of Mo and Ni from NaCl–KCl–MoCl₃–NiCl₂ melt at 720°C is studied. The results of studying Ni and Ni–Mo cathodic deposits obtained by electrolysis in the cathodic current density range of 0.01–0.05 A/cm² are presented. The conditions of electrolysis of NaCl–KCl–MoCl₃–NiCl₂ melt providing production of nickel-molybdenum coatings on MPG-8, AISI 316 L, CrNi₈₀MoTiAl substrates in an argon atmosphere are revealed. It is found that compact deposits of Mo–Ni alloys can be obtained at a cathodic current density of up to 0.03 A/cm². It is shown that at cathodic current densities above 0.03 A/cm², dendritic deposits are deposited. Dendritic formation was observed at the three-phase boundary MPG-8/electrolyte/argon. The chemical composition of Mo–Ni precipitates corresponds to the compounds Ni₄Mo, Ni₃Mo, which is consistent with the Ni–Mo phase diagram.

Modern industry is known to require cost reduction in production and an increase in the service life of manufactured products. This drives a constantly growing demand for the development and production of materials with improved properties. The different crystal structures and limited solubility of Cu and Fe strictly restrict the alloying of Cu with iron and vice versa. However, the immiscibility of Cu and Fe allows for the creation of surfaces with completely different chemical compositions and physical properties within a single product. The addition of Al to a Cu–Fe alloy causes an fcc–bcc phase transformation and a transition to a B2 phase. The alloy is also alloyed with zinc to increase its corrosion resistance and ductility. Using the HEAPS software package, we have shown that the Al_0.25Cu_0.25Zn_0.25Fe_0.25 system does not have Laves phases and the alloy has an fcc lattice. The FactSage 8.0 thermodynamic modeling software package is used for a more detailed study of the phase transformations that occur during solidification in the alloys Al_0.33Cu_0.33Fe_0.33, Al_0.32Cu_0.32Zn_0.03Fe_0.32, Al_0.31Cu_0.31Zn_0.06Fe_0.31, and Al_0.25Cu_0.25Zn_0.25Fe_0.25. Alloy samples are prepared in an 18-kW induction furnace in an alumina crucible. The temperature was monitored using a tungsten–rhenium thermocouple. The sequence of loading materials for alloy production is different. The synthesized alloys are analyzed by X-ray diffraction. X-ray diffraction patterns are recorded on a Shimadzu XRD diffractometer at a counting time of 2 s per point in the angle range 2θ = 10°–90° at a step of 0.02°. AlCuZnFe alloy samples are analyzed on a Carl Zeiss EVO 40 scanning electron microscope at magnifications of 500, 1000, and 1200 in the SE mode. AlCuZnFe alloys have a significant potential for further investigations due to the presence of a favorable phase distribution; however, the development of a technology for producing an alloy of a specified composition presents some difficulty.

An aluminum–graphene composite material is produced using direct chemical interaction of two carbon-containing precursors (glucose, boron carbide) with a molten Al–Mn aluminum alloy matrix containing 1.22 wt % manganese in molten alkali metal halides. The structure and number of graphene layers in the Al–Mn alloy matrix are shown to depend on the type of precursor. Specifically, synthesis with glucose yields bilayer graphene, whereas synthesis with boron carbide yields trilayer graphene in the Al–Mn–graphene composite. According to X-ray photoelectron spectroscopy data, the oxide film thickness on the Al–Mn–graphene composite material is 3.3 nm. X-ray diffraction and X-ray photoelectron spectroscopy studies of the aluminum alloy–graphene system have revealed the formation of double aluminum–manganese carbide AlMn₃C for the first time.

Molten FLiBe-based mixtures are promising technological media for molten-salt nuclear reactors (MSRs) due to their physicochemical properties. There is no structural material resistant to fluoride melts due to their high aggressiveness. It is purposeful to search for and develop new method of protecting structural materials, including the deposition of corrosion-resistant protective coatings. The corrosion behavior of laser-surfaced coatings made of STELLITE 6 alloy, WC–Ni/Cr composite material, metallic nickel, and NiCrSiBFe alloy on a 12Kh18N10T steel substrate is studied. Corrosion tests for 100 h have been carried out in the 73 LiF–27 BeF₂ (mol %) salt melt at a temperature of 700°C. Quantitative and qualitative corrosion characteristics demonstrate that the coatings made of metallic nickel and STELLITE 6 alloy are most resistant. Samples with NiCrSiBFe and WC–Ni/Cr coatings have substantial defects (cracks) after deposition, and they are the main cause of their degradation during corrosion tests.

The results of fundamental investigations of the physicochemical properties of the slags in the CaO–SiO₂–FeO–MnO–P₂O₅–MgO and CaO–SiO₂–B₂O₃–Al₂O₃–MgO systems are presented. They are the basis of a technology developed to melt semifinished steel products in oxygen converters and modern electric arc furnaces (EAFs) under magnesia-based slags. This technology provides a high-durability refractory lining in EAFs and a guaranteed low phosphorus content. Moreover, it includes innovative technological solutions for deep desulfurization and direct boron microalloying of structural steels in ladle furnaces (LFs) using environmentally friendly basic boron-containing slags. The introduction of these technological solutions has allowed for the production of next-generation low-carbon low-manganese-alloy boron-containing structural steels. These steels have a low sulfur content and enhanced mechanical properties, making them ideal for large-diameter strength class X80 pipes.

The development of advanced generation IV technologies, such as a molten salt reactor-burner nuclear power plant (MSR-B NPP), requires progressive and innovative solutions. The implementation of the MSR-B NPP necessitates a final resolution to the problem of selecting structural materials capable of maintaining corrosion resistance under reactor operating conditions, namely, under the influence of high temperatures, aggressive media, and inherent neutron irradiation. Corrosion-resistant steels are considered as promising candidate structural materials. In this work, ampule-type corrosion tests of austenitic 12Kh18N10T and SS 316L steels and an iron-nickel-based 06KhN28MDT alloy are performed. The corrosion tests are carried out in a melt based on the LiF–KF–NaF (FLiNaK) eutectic mixture with a uranium tetrafluoride addition, FLiNaK + UF₄ (5 wt % UF₄), in the temperature range 650–750°C for 100 h under isothermal conditions (static mode, implying no melt movement in the working space). The aim of this study is to analyze and compare the corrosion properties of the chosen materials in the FLiNaK + UF₄ (5 wt %) melt and to determine the mechanisms of the observed corrosion processes.

The corrosion processes that occur in structural materials in high-temperature apparatuses with a significant volume of molten salt mixtures are caused by the complex hydrodynamic conditions induced by the temperature gradients in different parts of an installation, the presence of gaseous reaction products, and other technological factors that set a molten salt electrolyte in motion, along with chemical and electrochemical factors. It is advisable to conduct both static and dynamic corrosion experiments to substantiate the choice of structural materials for the apparatuses used in the pyrochemical processing of spent nuclear fuel from fast neutron reactors. This work investigates the influence of forced convection of the LiCl–2 wt % Li₂O melt with a specified linear velocity from 4 to 16 mm/s on the degradation of 12Kh18N10T steel. Corrosion tests for 100 and 1000 h are performed at a temperature of 650°C in an inert argon gas atmosphere with a water content of less than 0.1 ppm and an oxygen content of less than 10 ppm. When the rotation speed of a sample increases, the degradation rate is found to increase significantly (from 0.018 to 0.094 g/(m² h)). When the rotation speed of steel samples increases, a Cr–Fe phase and FeO form on their surface, and LiFeO₂ and LiCrO₂, which form as a result of corrosion exposure under natural convection and at a speed of up to 8 mm/s, have not been detected. Corrosion tests for 1000 h under forced convection conditions (medium movement speed is 16 mm/s) do not lead to a significant increase in the corrosion rate (0.059 g/(m² h)) compared to the values obtained in a static isothermal medium (0.052 g/(m² h)). Electron probe microanalysis analysis indicates the presence of a near-surface layer with a predominant content of oxygen and chromium.

Ba_0.5Sr_0.5Fe_12 – xCr_xO₁₉ (x = 0.5–3) hexaferrites are synthesized by a solid-phase reaction method. The influence of substitution of chromium ions (Cr³⁺) for iron ions (Fe³⁺) on the structure and morphology of the materials is studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). All synthesized samples are found to be single-phase and to have a magnetoplumbite structure. When the chromium content increases, the unit cell parameters (a, c, V) decrease monotonically, which is explained by the smaller ionic radius of Cr³⁺ compared to Fe³⁺. The substitution is found to decrease the Curie temperature (T_C) due to a weakening of the superexchange interaction. The investigation of dielectric properties demonstrates that chromium doping improves dielectric characteristics: the permittivity increases in the low-frequency region and the dielectric losses decrease significantly.

Transition metal silicides are widely used in various fields of science and technology; available methods for their production are expensive and characterized by the relatively low productivity. In the present study, the possibility of synthesis of nickel silicides by electrolysis of the KCl–K₂SiF₆ melt at a temperature of 790°C is investigated. For this purpose, the melt electrolysis parameters are determined using a nickel cathode and cyclic voltammetry, and a series of experiments on the electrolysis of the melt under study are carried out in the galvanostatic mode at a cathode current density of 50 mA/cm² and in the potentiostatic mode at a cathode potential of 0.15 to –0.15 V relative to a silicon quasi-reference electrode. The morphology and element composition of the deposits formed after separation of the electrolyte residues are studied by scanning electron microscopy and energy dispersive spectral analysis. As the cathodic overvoltage increases, the number of nuclei is shown to increase and, therefore, the deposit sizes decrease. The adhesion of the samples prepared during galvanostatic electrolysis is assumed to be poor. The voltammetry measurements performed at various potential sweep rates suggest that the electroreduction of silicon ions on nickel is irreversible and is accompanied by a chemical reaction.

The review considers published works devoted to the use of the carbothermic reduction method in an inert carrier gas flow for the quantitative determination of the oxygen content in metals and oxides, which is widely applied in metallurgy and semiconductor industry. The scientific foundations of the method, the reduction fusion mechanism, principal features, and the influence of various parameters on analysis accuracy are described. Specimens of diverse materials (oxides as an example) differ substantially in physicochemical properties: melting and boiling points and the thermal decomposition mechanism. Therefore, the methodical approach to the procedure for the determination of the oxygen content in different specimens can differ significantly. Capsules and metallic baths (Sn, Ni, Fe, and Pt) decreasing the reduction temperature and preventing specimen losses are used to enhance accuracy. A specimen weight, a correct blank experiment, and the choice of standards are important factors. A significant attention is given to the hardware: LECO, Horiba, and ELTRA gas analyzers and domestic analogues (METAVAK-K and METEK-600). Modifications of instruments, including the use of boxes with an inert atmosphere for analysis of hygroscopic material, additional filters and traps for volatiles, as well as systems for CO additional oxidation, are considered. These improvements make it possible to diminish inaccuracies, especially for the determination of oxygen at the ppm level.