Russian Physics Journal最新文献

This article presents a detailed study of the variation of secondary electron emission as a function of the primary energy. This study is performed with a dedicated scanning electron microscope on the electrical property evolution of the magnesium oxide (100) single crystal. It is shown that the crystalline orientation has a significant influence on the intrinsic secondary electron emission at low energies below 7 keV, but for high energies, the loss function of the secondary energy extending more deeply, disperses before its release. As the incidence angle of the primary beam energy differs from the normal and takes important values, the secondary electron yield increases. The increase in the incidence angle has a similar and complementary effect on the current density growth.

The fatigue crack kinetics in the residual stress field is investigated in the specimens of TC4 titanium alloy after their laser shock peening (LSP). Following this treatment, the fatigue tests are carried out. The fatigue life of the specimens after LSP is found to increase. The maximum applied force in the fatigue cycle, which compensates for the residual stress effect, is determined by a numerical simulation. This determines the range of applied forces within which the compressive residual stress field generated by LSP remains effective.

A molecular dynamics model of a five-component coating based on the TiAlTaSiN system is proposed. A superposition of interatomic potentials is chosen to describe the interaction between the atoms of the system. The superposition includes both the available interatomic potentials and those calculated on the basis of the electron density functional theory. A molecular dynamics simulation is used to analyze the resistance of the developed coating model to thermal and mechanical loading. The influence of the concentration of alloying inclusions and the crystallographic orientation of the grains of this multi-component coating with respect to the applied load on its strength and deformation properties is investigated. A qualitative agreement between the simulation results and the experimental data is demonstrated.

In this paper, an isothermal diagram of the second phase formation in the Hastelloy G35 alloy was constructed to understand possible phase transformations during welding. A welded joint has been studied in three areas: fusion zone (FZ), the heat affected zone (HAZ), and the base metal (BM). The FZ is represented by a dendritic structure; in addition, σ-phase intermetallic compounds are present in the FZ and HAZ. Furthermore, the FZ and BM present similar hardness values, while the hardness increases in the HAZ. It has been established that thermal effects for different areas are characterized by different rates of increase up to 650°C.

It is found out that the HR-GaAs:Cr material is formed when the conductivity of n-GaAs is compensated by N_Cr chromium atoms, resulting in highly localized acceptor states at the mid of the bandgap. Such a structure is characterized by both the extremely high resistivity (ρ_max), exceeding the resistance (ρ_i) of its own semiconductor (ρ_max ≥ ρ_i), and the prolonged lifetime (τ_n) of non-equilibrium electrons, determining its high photosensitivity. Thus, it can be implemented in various basic electronic components for functional devices.

Forging of sintered Al–Fe–Sn samples was carried out in a closed die at different temperatures. The flow of the material under the influence of frictional forces was non-uniform, and the sample was fractured. It has been established that in order to maintain the integrity of the two-phase material, forging must be carried out with the application of back pressure. It is recommended to forge the composites at elevated temperatures.

The most significant and protracted phase of the installation of a dental prosthesis is osseointegration of a metal implant with bone tissue. It is important to accelerate this process, for example, by the use of extracorporeal shock wave therapy. The objective of this study is to investigate numerically the conditions for osseointegration of the implant in the dental region employing a poroelastic model implemented in the movable cellular automaton method. The mandibular segment under consideration includes a spongy tissue covered with a cortical layer 600 μm thick and a gum 400 μm thick. Additionally, the second premolar and second molar exhibited periodontal membranes of their roots, while the implant of the first molar was situated within a shell of soft fibrous tissue. The obtained fields of hydrostatic pressure and interstitial fluid pressure were analyzed according to the mechanobiological principles. The results obtained have indicated that shock wave therapy has a beneficial impact on the creation of conditions conducive to the differentiation and transfer of bone tissue cells along the main volume of the fibrous tissue surrounding the implant during the initial osseointegration stage.

The paper deals with transparent MgAl₂O₄ ceramics reinforced with 0.1 vol.% Al₂O₃ nanofibers and manufactured by spark plasma sintering at 1400°C and 100 MPa. The microstructure of MgAl₂O₄ ceramic samples is studied by the X-ray phase analysis and scanning electron microscopy. The optical properties are investigated in 190 to 8000 nm wavelength range. The influence of Al₂O₃ nanofibers on optical and mechanical properties of ceramics is discussed herein.

An analysis of the photoluminescence (PL) and thermoluminescence (TL) glow curves from the calcite sample collected from the Meghalaya basin is reported. The as-collected sample is thoroughly ground with an agate pestle-and-mortar set for 4 h and is annealed at 400°C for 2 h. An X-ray diffraction (XRD) analysis of the sample reveals cubic crystal structure. The collected sample morphology shows the presence of agglomeration. The bending and stretching of bonds inside the calcite in the fingerprint region is determined by the Fourier transform infrared (FTIR) spectroscopy. The photoluminescence excitation and emission spectra are monitored; they show well resolved peaks at 252 nm (absorption band), 395 nm and 509 nm (emission bands). An analysis of the thermoluminescence (TL) glow curve of calcite is performed using UV excitation for different UV exposure times (5 and 15 minutes), showing a linear response with the UV dose. The corresponding kinetic parameters, like order of kinetics, activation energy and frequency factor, are calculated using the computerized glow curve deconvolution (CGCD) technique. The collected calcite sample shows a good response with the dose, which may be useful for the environmental UV monitoring systems.

The paper examines the structuel formation and its impact on the mechanical properties of cobalt-based superalloy samples, namely Stellite 6 and Stellite 12, produced via wire-feed electron beam additive manufacturing (EBAM). It is demonstrated that this method enables the product fabrication from cobalt superalloys without macroscopic defects. It is shown that the primary phase and structural components of the EBAM-processed samples are dendrite arms comprising a cobalt-based solid solution, two types of carbides (M₇C₃ and MC), and eutectics distributed in the interdendritic space. The mechanical properties of the Stellite 6 alloy sample are superior to those of the Stellite 12 sample due to the martensitic γ-Co → ε-Co transformation in the former.