Russian Physics Journal最新文献

The paper focuses on the formation of high-intensity submillisecond chromium ion beams with a high power density. The ion-induced electron emission at the energy reaching 70 keV affects the neutralization of space charge and determination accuracy of the ion beam parameters. It is shown that at high ion energies, the virtual anode effect does not appear, and the formation of ion beams of a high pulse duration occurs. It is found that at 170 A discharge current, the maximum current density averaged over 16 pulses, reaches 2.8 A/cm². The maximum power density in the ion beam at 35 kV accelerating voltage approaches to 100 kW/cm². Instability of the ion-induced electron emission from the vacuum arc plasma improves the power density of pulses by more than 2 times.

Corrosion-resistant nickel-based alloys are of interest because of their potential applications in various industries, where the operations involve aggressive environments, including high temperature conditions. The results of measuring the modulus of elasticity under isothermal exposure of various durations in the temperature range of 350–650°C are presented. It is shown that two simultaneous processes are observed in the alloy under study: the formation of an ordered phase and the austenite lattice compression.

The paper investigates the structure and properties of the surface layers of AA5056 and AA2024 aluminum alloy plates 35 to 40 mm thick after reverse-polarity plasma cutting. It is shown that for alloys with varied parameters of the heat capacity, plasma cutting conditions are the same. At the best plasma cutting parameters, the cut geometry shows the lowest distortion. It is found that the cutting surface distortion occurs in exceeding the optimum heat input of the plasma arc. Conversely, at the reduced heat input, the alloy plate cannot be cut to its full thickness. Most of cutting modes provide the higher surface roughness, while the roughness of the upper edge cut reduces relative to the central and lower areas.

The microstructure and impact toughness of high-strength low-alloy steels joined by friction stir welding are studied. The hardened steel samples are tempered at a temperature of 600–650°C for 1 hour, followed by warm rolling to a total strain of 1.5 at the same temperature. The resulting steels are characterized by an ultrafine-grained lamella-type microstructure. The as-processed steel plates are joined by friction stir welding. A martensitic microstructure is formed in the stir zone. The steel samples with a carbon content of 0.15% show high impact toughness of 68 J/cm² at room temperature with a gradual decrease to 16 J/cm² at a temperature of –196°C, while the steel samples with a carbon content of 0.36% exhibit an impact toughness of 10 J/cm² at room temperature. The 0.36% carbon steel joints are tempered at a temperature of 650°C for 1 hour, which increases their room-temperature impact toughness to 67 J/cm².

The paper proposes the model describing the initial stage of skin electrical explosion of cylindrical conductors. The model considers the magnetic field diffusion, skin effect, Joule heating, conducting material dynamics under the action of the Ampere force and thermoelastic stresses, material transition to the plastic state and plastic flow, phase transition from solid to liquid at the melting point, and transition from liquid to vapor (vaporization). The analysis is given to the nature of thermoelastic stresses and elastoplastic deformations of the material in states preceding its melting. Discussed is the probability of the material fracture and/or deformation of its surface. The dynamics of the outer boundary is calculated for both solid and liquid states of the material. The analysis is presented for the decrement of the perturbation growth on the molten surface, and ways of improving the stability of the external surface of exploding conductors are discussed.

The results of experimental studies on the formation of an ultrafine-grained structure in aluminum bronzes printed using multi-wire electron beam additive manufacturing technology are presented. Based on the mechanical tests, the influence of the filament and heat treatment on the printed sample properties is established. A possibility of forming an ultrafine-grained structure in the studied alloys by multi-sided forging and rolling is demonstrated.

Comprehensive mechanical testing of steels provides important information about the possibilities of their use under different processing and operating conditions. Comparison of test methods with each other, taking into account the development of plastic deformation and fracture analysis, is an urgent task for materials certification. The present work is devoted to the study of the characteristics of the response to deformation of high-manganese steels (13 and 22 wt.% Mn steels) in comparison with the behavior of high-entropy Cantor alloy during scratching, tensile, and microhardness tests. The plasticity of the materials and the nature of their destruction were assessed by the surface deformation relief and fractography. Analysis of the structure during scratch testing made it possible to assess the degree of plasticity of the materials and relate it to the results of tensile tests and the nature of destruction. The steel with 13 wt.% Mn (Hadfield steel) the destruction of which occurs by the quasi-viscous mechanism has the lowest ductility. The highest ductility has the Cantor alloy characterized by the viscous fracture mechanism. The Hadfield steel has the highest hardness of all materials studied, while the Cantor alloy has the least hardness. The research results lay the basis for the possibility of recalculating the mechanical characteristics from different tests, taking into account the implemented stress state scheme and processes of structural changes during deformation.

The structure and phase composition of powder materials of the Ti–Al–B system formed in the process of vacuum sintering and synthesis in the mode of high temperature self-propagating synthesis (SHS) are considered depending on the combination of components in the form of elementary powders (Ti, Al and B) and using the finished titanium diboride (TiB₂) compound. The proportions of the components were calculated in such a way that the number of interacting elements was sufficient to form a two-phase TiAl₃ + TiB₂ composition. When sintering the Ti + Al + TiB₂ mixture, the diboride is retained, but the presence of TiB is noted as a result of the redistribution of boron due to its migration into free titanium. It was discovered that sintering of compacts from the mixture based on elemental powders (Ti, Al and B) occurs under conditions of high exothermic effect, as a result of which the samples were destroyed. This made it possible to use this mixture under conditions of high-temperature synthesis in combustion mode. As a result of both vacuum sintering and SHS compacting, aluminide TiAl₃ and titanium diboride (TiB₂) are mainly formed from a mixture of elemental powders (Ti, Al and B). In this case, some transition phases can be observed. It is shown that after the synthesis of the Ti + Al + B mixture, it is possible to obtain a powder product from which compacts are well sintered while maintaining their shape with a slight shrinkage.

The paper focuses on plasma cutting of AA5056 and AA2024 aluminum alloy sheets. It is shown that at the minimum thicknesses, the upper edge of the sheet tends to undercut when using reverse polarity. This phenomenon considerably diminishes when using the best cutting conditions. In the case of the AA2024 alloy, most of the material remains in the cutting zone, adhering to the surface and forming a substantial zone of melting or beading. The AA2024 alloy demonstrates a greater oxidation and hardening of the cutting surface. Degraded material layers and surface roughness reduce when using the best cutting conditions. The upper edge of both alloys is more homogeneous and exhibits less roughness than the lower edge. This is attributed to a more complex displacement of the metal relative to the lower edge undercut.

The paper studies the regularities of wave propagation in an inhomogeneous elastic layer with gradient properties varying along the layer thickness. The laws of change in elastic parameters are established at which the waves propagating in the direction of parameter change are harmonic. The waves propagating in the layer with a linear law of change in the elastic parameters are noт-harmonic. Analytical solutions obtained for a monochromatic wave defined on the boundary of a plane layer with a rigidly fixed second boundary are represented by special functions. In the case of gradient variation of the layer density, the solution is determined by a superposition of the Airy functions, in the case of equal relative variations of the density and elastic moduli, they are expressed through the modified Bessel functions, and in the case of arbitrary linear laws of variation in the elastic parameters, they are expressed through the confluent hypergeometric functions. Based on the analytical solution obtained for a layer with inhomogeneous density, the conditions for extreme values of displacements and strains are determined, and their distributions over the layer thickness are calculated and analyzed.