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No 4 (2023)
Articles
MULTICOMPONENT ALLOYS AND LAYERED COMPOSITE NANOMATERIALS FOR HYDROGEN TECHNOLOGIES
Abstract
The stability of high entropy alloys (HEA) is of great importance for various applications in many areas. This review covers one of the most topical areas in this area – the creation of stable multicomponent membrane alloys with improved performance. The review presents an analysis of the results of studies of equiatomic and non-equiatomic four- and five-component alloys, which are successfully used as membrane alloys for hydrogen technologies. An effective method for increasing the strength of membrane alloys is a special heat treatment, as a result of which secondary strengthening phases are precipitated and superlattices are formed. In addition, an unusual morphology of micrograins is formed in the form of cuboid blocks with rounded tops, spheroidal and ellipsoidal grains, consisting of hardening thermodynamically stable γ' and γ-phases isolated during heat treatment. Alloying is an important factor in strengthening HEAs. The influence of alloying with Ni or Cr on the mechanical properties of a number of multicomponent compositions has been analyzed. It is shown that Al + Ti or Al + Nb alloying pairs, structured into matrices of solid solutions of membrane alloys, increase their strength, thermal stability, hydrogen kinetics, and resistance to hydrogen embrittlement. Within the framework of molecular dynamics, the effect of strain hardening of membrane HEAs by multiple deformation has been studied and the mechanism for creating a synergistic effect has been established. The review also presents relatively recently obtained hexa- and pentagonal two-dimensional structures with ultrahigh strength and increased thermal stability and excellent photocatalytic properties, such as MX2 dichalcogenides and their pentagonal configurations, as well as two-dimensional alloys Cu1 – xNix, Ti1 – xNix and compounds Bi1 – xSbx. All these materials are effective catalysts for water dissociation and hydrogen concentration. Particular attention is paid to neural network prediction of interatomic potentials as an effective method of theoretical research for the search for new membrane HEAs.
333-376
CORROSION BEHAVIOR OF 12Cr18Ni10Ti STEEL IN LiCl–KCl MELT CONTAINING ADDITIVES OF f-ELEMENT CHLORIDES
Abstract
When reprocessing spent nuclear fuel, it is supposed to use LiCl–KCl melt (0.49:0.51) in an inert atmosphere, all metal materials in this salt melt are extremely susceptible to corrosion, besides, during the processing of spent fuel, both the liquid (melt) and the gas phase are saturated with decay products that can act as additional oxidizing agents, increasing the aggressiveness of the environment. The pyrochemical technology of SNF includes operations such as soft chlorination, electrofining and metallization, implying the presence in the melt of compounds of chlorides of rare earth metals lanthanum, cerium and neodymium, as well as uranium(III, IV) chlorides. In this work, the corrosion behavior of 12CR18NI10TI steel in LiCl–KCl melt containing NdCl3, CeCl3, LaCl3, UCl3 and UCl4 additives up to 2 wt % was investigated. Corrosion tests lasting 100 hours were performed at a temperature of 500°C in an inert argon atmosphere. It was found that the presence of REM chlorides significantly reduces the degradation of the steel under study. The addition of (REM)Cl3 leads to the formation of a compound (REM) on the surface of the samples OCl, the thickness and continuity of which increases in the following row: LaCl3 < NdCl3 < CeCl3. The formation of such a compound leads to the inhibition of the corrosion process of steel 12CR18NI10TI due to salt passivation of the surface. The addition of UF4 to the melt causes significant corrosion of 12CR18NI10TI intercrystalline steel. The introduction of UF3 into the melt leads to a decrease in the corrosion rate, which is associated with the predominant interaction of trivalent uranium chloride with dissolved molecular oxygen contained in the melt, and the formation of a non-stoichiometric compound with the crystal chemical formula U3O7 on the surface of samples according to microrentgenospectral analysis.
377-384
LOW-TEMPERATURE ELECTROLYTIC PRODUCTION OF Al-REM ALLOYS IN CRYOLITE MELTS
Abstract
The process of electrolytic production of Al–Y and Al–Sc alloys in an electrolyte based on potassium cryolite KF–NaF(10 wt %)–AlF3 with a cryolite ratio (CR) of 1.5, containing Al2O3, Sc2O3, or Y2O3 oxides, in a cell with vertical electrodes has been studied. The Fe–Ni–Cu alloy served as an inert anode. The wetted cathode was a graphite plate coated with the aluminum diboride. The electrolysis was carried out at a cathode current density of 0.2 A/cm2 and a temperature of 830°C. The Al2O3 mass was calculated based on the value of the current efficiency of 60%. The Sc2O3 additive was introduced into the melt in an amount of 1 wt %. The mass of the Y2O3 additive was chosen based on its solubility in the melt under study. For this, the influence of Y2O3 additives on the liquidus temperature of the quasi-binary mixture [KF–NaF(10 wt %)–AlF3 (KO = 1.5)]–Y2O3 was determined and it was found that, in contrast to Sc2O3 additives, which lower the liquidus temperature of the cryolite melt, small additions of Y2O3 lead to its sharp increase. It has been found that the efficiency of the electrolytic reduction of Y2O3 is 10 times higher than that of the aluminothermic reduction. Other things being equal, the efficiency of the electrolytic reduction of Y2O3 is higher than that of Sc2O3. Alloys Al–Y and Al–Sc with a REM content of 0.6 wt % have been obtained. However, the time to reach the maximum recovery of yttrium significantly exceeds the time to recover scandium. Metallographic studies of the obtained alloys indicated the presence of Al3Sc and Al2Y intermetallic compounds. A conclusion is made about the fundamental possibility of low-temperature electrolytic production of Al-REM alloys in cryolite melts based on potassium cryolite in vertical cells with an inert metal anode and a wettable cathode.
385-395
PRODUCING METHOD OF HIGH ENTROPY CARBIDE IN AN IONIC MELT
Abstract
Refractory metal carbides TiC, ZrC, HfC, NbC and TaC have excellent physical, chemical and mechanical properties as materials for ultra-high temperature ceramics. Of these, the most refractory are TaC and HfC, whose melting points approach 4000°C. It should be noted the high hardness, strength and wear resistance of refractory carbides. Hence, there is a natural interest in high-entropy carbides based on them, which are becoming an important class of new ceramic materials, since they potentially have more advanced applied properties. However, obtaining such materials by classical metallurgical methods is a difficult task. In modern research, samples of high-entropy carbides are most often synthesized using expensive special equipment (methods of plasma-spark sintering, high-energy planetary mills, etc.) and a relatively long preparation of precursors for sample production. This paper describes a new approach to the synthesis of multicomponent carbide (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C using an electrochemical process at a temperature not exceeding 1173 K. The method is based on the phenomenon of currentless metal transfer in molten salts. After the step-by-step transfer of metals, the sample was washed from the electrolyte, then sintered in a vacuum furnace. According to X-ray phase analysis, the resulting high-entropy carbide is a single-phase solid solution with an FCC structure. The diffraction pattern of the synthesized sample is in good agreement with the calculated diffraction pattern obtained by the Debye formula for a supercell of 64 000 atoms. A compact sample of high-entropy carbide was produced by pressing a tablet 10 mm in diameter with the addition of cobalt as a matrix metal. After vacuum sintering, the sample was ground to prepare for examination on a scanning electron microscope. Elemental mapping of the sample surface was performed, which showed a satisfactory distribution of metals that make up the high-entropy carbide. The measured microhardness of the sample turned out to be less than the values found in the publications of other authors, which may be due to some residual sample porosity.
396-405
MOLECULAR DYNAMICS SIMULATION OF STRATIFICATION IN Bi–Ga MELTS
Abstract
In present work, the process of stratification in melts of the Bi–Ga system was simulated using molecular dynamics method. The interaction between atoms was specified using a neural network potential parameterized on ab initio data (DeePMD model). The parameterization of the DeePMD potential was performed using an active machine learning algorithm. During molecular dynamics simulation, melts with the compositions GaxBi100 – x where x = 0, 10, …, 90, 100 were cooled from 800 to 300 K. The phase separation was registered by changes in the temperature behavior of the partial radial distribution function for the Ga–Bi pair. It has been established that the DeePMD potential, in the initial training set of which no configurations corresponding to the phase separated state were introduced, is still able to reproduce the stratification in the Bi-Ga system. The concentration range of separation determined by molecular dynamics modeling with the DeePMD potential coincides with the experiment. It was also possible to correctly determine the shift of the maximum of the stratification dome towards melts rich in gallium. However, the stratification dome maximum was incorrectly defined as Ga80Bi20 instead of the experimental Ga70Bi30. In addition, a certain temperature range of the delamination dome is wider than in the experiment. Despite this, the use of neural network potentials in atomistic simulations, as shown in present work, can be effectively used to predict delamination in binary metallic systems.
406-413
THERMOCHEMICAL STUDY OF THE FORMATION OF SILICIDES, BORIDES, CARBIDES IN Fe–Ni–Cr–Cu–Si–B–C ALLOY
Abstract
To determine thermochemical characteristics: enthalpy, molar heat capacity and Gibbs energy of formation of silicides, borides and carbides in an alloy of a given composition (40Fe–31Ni–16Cr–5Cu–5Si–2B–1C) calculation methods were used using mixed GGA and GGA + U schemes (semi-empirically tuned generalized gradient approximations). Three modules of the HSC Chemistry 6.0 software package (Metso Outotec, version 6.0, Espoo, Finland) were used in the study. First, the “Reaction Equation” module was used to calculate the change in Gibbs free energy at different temperatures. Secondly, to calculate the composition of each chemical in the equilibrium state, the module “Equilibrium Composition” was used (“Equilibrium compositions” – calculation of equilibrium compositions of phases in the presence of reversible chemical reactions). Thirdly, the module “H, S, C and G diagrams” (“Graphs of thermodynamic functions” – plotting thermodynamic functions) was used to determine the relative phase stability of compounds depending on temperature in the form of Ellingham diagrams. The results of thermochemical modeling showed that the temperature dependences of the heat capacity of the formation of hardening compounds in the alloy increase with increasing temperature. Thermodynamic calculations of the enthalpies of the hardening phases in the alloy showed that at temperatures >1400°C, silicides, borides, and carbides are formed. ∆G(T) of silicides, there is an increase in the values of the Gibbs energy and a tendency towards stability with increasing temperature. During the formation of borides in the alloy, one can see a strong absorption of heat, an increase in the Gibbs energy in the studied temperature range. The results of calculating the Gibbs energy as a function of temperature showed the formation of carbides Ni3C, Fe3C, SiC, B4C, Cr3C2, Cr4C, Cr7C3. The formation of phases occurs with a decrease in the values of the Gibbs energy to a temperature of ~1500°C. A further increase in temperature indicates the absorption of heat, which is associated with a high ordering temperature of the carbide structures. Thus, the thermochemical study justified the formation of silicides, borides, carbides in the alloy 40Fe–31Ni–16Cr–5Cu–5Si–2B–1C.
414-425
THE INFLUENCE OF COBALT ON DENSITY AND ELECTRICAL RESISTIVITY OF Al–Ni–Co–Ce ALLOYS IN CRYSTALLINE AND LIQUID STATES
Abstract
In this work were studied density (by gamma-absorption method) and electrical resistivity (by contactless method in rotating magnetic field) of Al–Ni–Co–Ce glass-forming alloys with different ratios of transition metals. It was found the existence of a wide two-phase zone was established and jump-like changes in properties at solidus and liquidus temperatures. Increasing of cobalt content from 2 to 4 at % leads to 2% decrease of density and 3% increase of electrical resistivity in crystalline and liquid states. Temperature coefficients of change in properties were calculated. Density hysteresis was detected, which occurs when melts are overheated above 1350 K. This fact is related to the disintegration of large-scale microheterogeneities that exist in melts during heating. It is shown that these results can be used to optimize the process of obtaining rapidly hardened alloys.
426-436
Ремпелю Андрею Андреевичу – 65 лет
437-438
Архипову Павлу Александровичу – 65 лет
439-440