Russian Metallurgy (Metally)最新文献

The report presents the results of heat-resistance tests of single-crystal samples made of a rhenium–ruthenium VZhM10 nickel superalloy with a two-layer heat-resistant condensation–diffusion ion–plasma SDP-41 + VSDP-16 coating in the temperature range 1150–1300°C. The ion–plasma coating is shown to ensure the protection of the alloy from catastrophic oxidation at temperatures up to 1300°C for a short time of 10–25 h. The loss rates of the specific mass of VZhM10 alloy samples with the coating and without it are determined in the temperature range 1150–1300°C using tests for up to 100 h. The influence of the coating on the long-term strength of the 〈001〉 VZhM10 alloy single crystals has been estimated at temperatures of 1150, 1200, 1250, and 1300°C.

Abstract—The melting diagram of the diphenyl oxide–n-nonadecane system is calculated by the Schroeder, UNIFAC, and UNIFAC Dortmund methods and is shown to belong to the eutectic type. Individual substances and their mixtures are studied experimentally using a differential scanning microcalorimeter. Two endoeffects corresponding to the polymorphic transition of n-nonadecane and eutectic melting are observed on the DTA curve of eutectic alloy heating. The eutectic coordinates calculated by these methods are compared with the experimental data. The specific enthalpy of melting, molar entropy and enthalpy of melting, volume specific enthalpy of melting, and density are calculated for the eutectic alloy under standard conditions. The eutectic mixture can be recommended for using as a heat carrier and a working fluid of a heat accumulator.

The features of studying the stress distribution in an axisymmetric maximum-interference joint, in which the inner part of the joint transforms into a plastic state, are described. The distributions of the circumferential and radial stress tensor components over the insert and bushing of an interference sample are analytically estimated. The calibration coefficients are adjusted with allowance for the stress gradient over the surface in order to calculate the stresses by drilling holes to detect strains by a strain-gage rosette. This made it possible to obtain a more uniform depth distribution of stresses: the coefficient of variation of circumferential stresses decreased from almost 10 to 3%, and the coefficient of variation of radial stresses, from 32 to 14%. The radial and circumferential stresses in the drilling zone of a probing hole are estimated and compared using strain gages and optical speckle interferometry.

The microstructure and microhardness of the surface layer of the gearwheels produced by laser cutting of 6-mm-thick 30KhGS sheet steel disks at a laser power of 1200 W and a cutting speed of 20 mm/s are studied. The structure of the heat-affected zone is found to have the following structure: a 6-μm-thick white layer forms on the cutting surface; under it, a structure consisting of martensite and a small amount of retained austenite forms at the side facing a gas jet; at the side facing laser radiation, the structure consists of a sorbite–troostite mixture with spheroidized carbide inclusions. Below, the structure is represented by a sorbite–troostite mixture and martensite grains. The modified layer thickness is 100–250 μm, and the hardness of the layer can reach 500–716 HV.

Abstract—The possibility of improving the performance characteristics of Kh12MF die steel using gas–powder laser cladding and a nickel-based powder alloy containing 60% tungsten carbide as a cladding material is investigated. Laser cladding is carried out using a domestic SVAROG-1-5DR laser installation equipped with a 5-kW fiber diode laser. Laser cladding conditions have been experimentally selected. The microstructure, microhardness, and chemical composition of the deposited layer and the substrate are studied on transverse metallographic sections. Laser cladding is found to provide reliable melting of a carbide-containing powder material to the substrate and to significantly increase the surface hardness of Kh12MF steel. The hardness of the Kh12MF steel increases to 75.3 HRC upon cladding at P = 5 kW, V = 7 mm/s, and F = 30 mm.

The previously considered composition of the powder mixture in the ZrSi₂–MoSi₂–ZrB₂–Si system is corrected toward decreasing the content of the relatively low-melting phases ZrSi₂ and MoSi₂ and increasing the fraction of the refractory phase ZrB₂. A heat-resistant coating is formed on the C/C–SiC composite by the firing facing of the powder mixture at 1750°C under an argon expansion pressure of 150–200 Pa. The phase composition of the coating includes (mol %): 23.2 ZrSi₂, 16.8 MoSi₂, 46.0 ZrB₂, and 14.0 ZrC. The synthesis of the secondary phase ZrC is carried out in situ by the reaction in the ZrSi₂–C system. Oxidation and ablation resistance tests are carried out under flow at surface and surface heating conditions in a T_w temperature range of 1300–2350°C with an air plasma flow at a speed of 4.7–4.8 km/s and a stagnation enthalpy of 48–50 MJ/kg. The performed correction of the composition is shown to provide an enhancement of the protective ability of the coating at T_w = 2200°C by 2.5 times (up to 170 s), as well as an increase in the maximum permissible level of working temperatures from T_w = 2200 to 2350°C. At the same time, the average values of the specific mass loss and mass removal rate of the coating decrease by 23 and 14% and amount to 3.9 mg/cm² and 13.1 mg cm^–2 h^–1, respectively. The rate constants of heterogeneous recombination of air plasma atoms and ions on the coating surface are estimated: K_w = 2 ± 1, 5 ± 2, 9 ± 3, 14 ± 3, and 19 ± 2 m/s at T_w = 1300–1450, 1500–1750, 1800–1950, 2000–2150, and 2200–2350°C, respectively. The spectral emissivity of the coating ε_λ is found to decrease from 0.69 ± 0.02 in the initial state to 0.41 ± 0.02 after the fire tests in the wavelength range λ = 600–900 nm at room temperature. The main factors limiting the protection effect resource of the coating are shown to be the through oxidation of the ZrSi₂ matrix and evaporation of the zirconium-modified borosilicate glass leading to an increase in the fraction of the ZrO₂ phase with high anionic conductivity and catalytic activity in the oxide film.

The well-known methods of determining the critical stress intensity factor K_Ic of the surface layers of materials by indentation of a pyramid for the formation of radial cracks propagating from the vertices of an indent are considered. It is noted that the existing methods for estimating the fracture toughness of a material by indentation do not allow one to determine the crack initiation energy. A technique is proposed to determine the specific crack initiation energy and the specific crack propagation energy using the critical points of a pyramid indentation diagram during instrumented indentation. Energy fracture toughness criterion G_Ic is found to be related to specific crack propagation energy ω_p, which is determined using an indentation diagram, for brittle materials and hardening coatings. This finding makes it possible to develop a technique for rapid estimation of critical stress intensity factor K_Ic using an indentation diagram recorded during instrumented indentation without measuring the geometric parameters of formed cracks and regardless of their type.

Abstract—The eutectic LiF–NaF–KF mixture is considered as a fuel salt for molten salt reactors for the transmutation of minor actinides; therefore, information on the solubility of fluorides and oxides in it as both fissile materials and fission products is necessary to substantiate reactor operating conditions and to develop methods for fuel salt refabrication. From this point of view, cerium and neodymium can be considered as both representatives of fission products and imitators of actinides. Cooling curves and isothermal holding are analyzed to determine the temperature dependence of the solubility of a mixture of cerium and neodymium fluorides and cerium and neodymium oxides in the LiF–NaF–KF melt. The total solubility of rare earth trifluorides is found to reach 51 wt % at 550°C and to be in good agreement with the data for individual cerium and neodymium fluorides. The solubility of REM oxides has significant kinetic difficulties, which is associated with the formation of intermediate compounds in the form of cerium and neodymium oxyfluorides and alkali metal oxides or peroxides. The solubility of cerium oxide is significantly lower than that of neodymium oxide, 0.049 and 0.221 wt % at 750°C, respectively.

Abstract—One of the main factors in improving the reliability of individual components and assemblies of machines is the use of new materials with specific properties, which include superelasticity and shape memory effect. For shape memory metals and alloys, heat treatment is used to ensure the required behavior of materials depending on operating conditions. The research purpose of this study is searching for the regularities of changes in the physicomechanical properties of titanium nickelide-based shape memory alloys depending on the thermomechanical effect. The materials used to carry out the planned studies are divided in accordance with their working conditions: the properties of short-term memory is used for the operation of equipment and components under technical working conditions; the nature of the memory effect manifests itself for a long time or is repeated periodically at the operating temperatures of the equipment, that is, under working conditions. The groups of heat treatment of these materials are identified according to the above-mentioned alloy characteristics. Special technological techniques are used to obtain the shape memory necessary for parts that do not correspond to the semifinished product. The necessity of using heat treatment for shape memory has been revealed. It is found that shape memory heat treatment is not performed if plastic deformation during the production of semifinished products is applied at a temperature of at least 400°C and the shape of a workpiece coincides with the configuration of a semifinished product. It has been proved that, in order to stabilize the size of semifinished products during heat treatment, annealing should be carried out at a temperature of 400–450°C. For shape memory alloys, heat treatment influences the provision of the required physicomechanical and thermophysical properties of materials to be used to achieve specific memory effects in certain parts. For the purpose of the efficient operation of shape memory alloys, heat treatment of the given material has been proposed in accordance with the required characteristics and configuration of a part.

Abstract—In the last decade, the diversity of high-entropy materials (HEMs) has increased dramatically, including the expansion of investigations in the field of amorphous, nano-, and heterostructures. Interest in nanoscale HEAs is primarily related to their potential applications in various fields, such as renewable and green energy, catalysis, hydrogen storage, and surface protection. The development of nanotechnologies made it possible to develop an innovative design of nanoscale HEAs with fundamentally new structures having unique physical and chemical properties. The problems of controlled synthesis with precisely specified parameters of chemical composition, microstructure, and morphology are solved. Traditional technologies, such as rapid pyrolysis, mechanical alloying, magnetron sputtering, electrochemical synthesis, etc., are being modified. In addition, innovative synthesis technologies, such as carbothermal shock and controlled hydrogen spillover, have appeared. This review analyzes the methods of synthesizing nanoscale HEAs for various applications that have been developed in the last six–seven years. Most of them result from the modification of traditional methods, and another group of techniques presents innovative solutions stimulated and inspired by the HEA phenomenon.