Russian Metallurgy (Metally)最新文献

Using a VZh159 superalloy as an example, we consider the formation of the surfaces of the gage portion and the fillet transitions during the selective laser melting synthesis of profiled monolithic cylindrical and flat specimens for mechanical tests. The main defect in the near-surface layer is found to be scattered gas microporosity. After heat treatment, a fine-grained layer forms at the surface of the profiled specimens. When cylindrical synthesized specimens without additional processing of the gage portion surface are tested, their short-term strength characteristics at temperatures of 20, 800, and 1000°C are found to decrease by no more than 3, 4, and 17%, respectively, compared to polished synthesized specimens.

The effect of various hot isostatic pressing and high-temperature treatment conditions (for long-term strength determined based on the time to failure) at the operating temperatures of gas-turbine engine elements on the lattice parameters of the γ' (Ni₃Al-based solid solution) and γ (Ni-based solid solution) phases and the misfit of structural cast Ni-based intermetallic alloy is studied.

The preliminary results of studying the efficiency of using the siloxane low-molecular-weight SKTN-A rubber as a matrix for a thin-film drug coating of implantable stents are presented. A porous film structure is formed by the introduction of intermediate (removable) fillers, such as ethanol, sodium hydrocarbonate, and high-molecular-weight chitosan. The ultimate tensile strength and the relative elongation of the prepared films are studied. The strength of the films formed using ethanol is found to be nearly analogous to that of pure siloxane, but their relative elongation is lower by 10%. The use of sodium hydrocarbonate makes it possible to enhance the strength of the films by 37% (to 0.22 MPa), and the relative elongation increases to 93%. When chitosan is used, the strength of the films increases almost twofold (to 0.28 MPa) and their plasticity is similar to that of pure siloxane and amounts to approximately 40%.

The influence of preliminary cyclic loading on the strength characteristics of additive 316L steel manufactured by selective laser melting, its damage, acoustic emission parameters, and characteristics of deformed state estimated by the digital image correlation is studied. The stages of fracture are analyzed during material tension before and after preliminary cycling taking into account the kinetics of changing acoustic emission parameters and deformation characteristics (maximum principal strains and the plastic zone areas). The fatigue characteristics of the additive 316L steel are found to be substantially lower than those of the 316L steel manufactured by traditional technology. Preliminary cyclic loading causes opening of technological defects in a structure and the formation of small cracks. Tensile tests of such specimens are found to lead to the growth of the residual strength and the fracture energy, and these characteristics decrease sharply at a relative life of 0.7 of the number of cycles to failure. The main fracture mechanism of the additive 316L steel is the opening and growth of small cracks initiated on technological defects. The growth of small cracks during cyclic loading influences the kinetics of acoustic emission parameters estimated during tension of previously cycled specimens, which confirms high informativeness of this method for analyzing the fracture stages of materials.

Abstract—Molten mixtures of sodium and potassium cryolites KF–(10 wt %)NaF–AlF₃ with a cryolite ratio CR = 1.5 are promising electrolytes for the production of aluminum alloys with scandium, yttrium, zirconium, and boron using aluminothermic and electrochemical reduction of alloying component oxides at temperatures of 800–850°C. The viscosity is not only an important technological parameter, but also an information source for the structure and mechanism of viscous flow of a liquid. The dynamic viscosity of the KF–(10 wt %)NaF–AlF₃ (CR = 1.5) melt containing Sc₂O₃ (to 9.9 wt %) and Y₂O₃ (to 6.5 wt %) oxide additives has been measured at a constant shear rate of 12 s^–1 in the temperature range from the liquidus point to 930°C. The viscosity of the KF–(10 wt %)NaF–AlF₃ (CR = 1.5) melt is found to change from 1.8 to 1.3 mPa s in the temperature range 800–930°C, which is substantially lower than the viscosity of the KF–AlF₃ melt (CR = 1.5), which is 1.7–2.4 MPa s, in a lower temperature range of 800–730°C. Sc₂O₃ and Y₂O₃ oxide additives substantially increase the viscosity, which is related to the formation of complex REM ions and oxifluoroaluminates in the melt during dissolution of the oxides.

Functionally organized steel–aluminum laminated compositions are fabricated by friction surfacing. Grade 20 steel is chosen as a substrate material, and ER 1100 and ER 5356 aluminum alloys are chosen as the consumable rotating rod material. The process parameters (axial load, longitudinal displacement velocity, rotation frequency) have been determined to ensure the vertical stability of the consumed rotating rods. The microstructure and phase composition of the diffusive intermetallic layer having formed at the interfaces of the main steel–aluminum composite layers are studied.

High-temperature X-ray diffraction is used to study the peculiarities of the thermal expansion of VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel; 20Kh15AN3MD2 steel without the TRIP effect (both steels belong to the Fe–Cr–Ni–Mn system), and multiphase heat-resistant coatings with the compositions c-ZrO₂ + α-Al₂O₃ + γ-Al₂O₃, α-Al₂O₃ + γ-Al₂O₃ + t-ZrO₂, and Si + SiC. The studies are performed at temperatures up to 1000°C. VNS9-Sh steel with a larger lattice parameter of the α phase as compared to that of 20Kh15AN3MD2 steel (2.890–2.892 and 2.888 Å, respectively) is shown to have a lower linear thermal expansion coefficient (LTEC): (7.6–7.9) × 10^–6 and (10.3–10.9) × 10^–6 K^–1, respectively. It is confirmed that high-temperature X-ray diffraction is an efficient method for estimating the LTEC of multiphase coatings and that the single-crystal LTEC characteristics of phases with tetragonal and hexagonal lattices can be estimated on polycrystalline objects. For phases with tetragonal and hexagonal structures, we are the first to use LTEC representation in the form of a second-rank tensor, which allows us to increase the accuracy of estimating LTEC.

Abstract—An installation is designed for preliminary electric resistance low-temperature heating of workpieces for stamping complex-profile parts made of carbon and alloy steels on automatic cold upsetters. A schematic diagram of the installation has been developed, and the main technical characteristics of the preliminary electric resistance low-temperature heating installation have been determined. The use of this installation will reduce the deformation forces during stamping by 1.5 times and the loads and will increase the life of the working tool by 1.5–2.5 times.

The working fluid temperature and pressure increase constantly in the process of improving gas turbine engines (GTE) and increasing their service life and performance. Turbine elements are subjected to high thermomechanical loads and a continuous action of an aggressive environment. These actions are especially significant for the working blades of the first stages of a GTE turbine located in a region of the highest temperatures. One of the most serious types of damage in this case is the corrosive effect on a working blade from the combustion gases entering the flow part of the turbine. The TS-1 fuel used in an aircraft contains sulfur compounds, namely, elemental sulfur and mercaptans, which leads to an aggressive effect on the GTE turbine blade material together with sodium and potassium from the air during combustion. To ensure long-term operation of GTE turbine blades at a gas temperature of up to 800–850°C at the turbine inlet, the content of these products in both fuel and air is limited according to regulatory and technical documentation. However, it is not yet possible to completely exclude them. The presence of sulfur compounds on GTE turbine blades causes sulfide corrosion. Therefore, we consider the influence of impurities in the fuel and air on the sulfide corrosion of the GTE turbine blade material and present a mechanism for sulfur dissolution in metal oxides or protective coating and the diffusion of sulfur oxide from the coating surface into depth. The cause of the influence of sodium chloride contained in the air on the corrosion of a nickel alloy or a protective coating applied on it has been established. The influence of vanadium in the fuel on the corrosion rate is presented. To increase the performance of GTE turbine blades under the influence of such an aggressive environment, we propose to use a new coating formed from an aqueous suspension and to introduce chromium into the coating, which provides a longer durability of this coating compared to serial aluminide coatings. The introduction of chromium is ensured due to an exothermic reaction during coating formation in the course of heat treatment.

Abstract—The structures of model analogs of salt melts containing neodymium complexes are subjected to ab initio studies. The importance of this work is mainly determined by the need to develop methods and technologies for recycling electronic and magnetic materials, which are a secondary source of rare earth metals. Quantum-chemical calculations, in turn, are a powerful tool for studying the structural features of model analogs of real high-temperature salt melts. The calculations are performed by the Hartree–Fock and density functional theory methods using the quantum-chemical Firefly 8.20 software package. An approach is proposed to calculate the interaction energies in a three-component model system consisting of a neodymium complex, an outer-sphere (OS) cation shell, and the remaining part of the cluster. The energies of interaction of the neodymium complex with the system fragments are determined. The influence of the number of OS cations on the calculated interaction energies has been studied, and the compositions of the most stable particles consisting of neodymium complex + OS shell have been determined. The data obtained using quantum-chemical calculations are compared with the results available in the world scientific literature, including the results of direct spectroscopic studies of molten salts containing neodymium complexes. The calculated interatomic distances Nd–X (X = F, Cl) are shown to agree well with the available experimental data. Raman spectra are calculated for 18MCl + M₃NdCl₆ (M = Na, K, Rb, Cs) model systems, and the calculated and experimental frequencies of the most intense spectral line are shown to be in good agreement. The results obtained allow us to assert that the model systems studied in this work can be used as the minimum possible ones for studying the structures of molten salts using quantum-chemical methods.