Russian Physics Journal最新文献

The paper presents models for a prediction of the Vickers microhardness in the indentation load range of 100 to 500 gf. Machine learning methods (random decision forest and adaptive boosting) are used to develop these models for ceramic materials based on hydroxyapatite with the addition of reinforcing multi-walled carbon nanotubes in the amount of 0.1 and 0.5 wt.%. The input data for the model development include the sample type, test load and indenter diameter. A comparative analysis of training quality metrics such as the mean absolute, root mean square, and mean absolute percentage errors and the determination coefficient help to identify the method providing the lowest prediction error. The results of the regression analysis show that the adaptive boosting model with the high (0.918) determination coefficient and low (10.135) mean absolute error demonstrate the highest training accuracy. The proposed predictive models allow to determine the best machine learning method for predicting the Vickers microhardness of ceramic materials based on hydroxyapatite with regard the obtained nonlinear dependencies.

A nanocomposite-filled slot antenna is designed to improve the radiation of a triple band radiator which consists of two rigid radiating elements united to the central strip of a coplanar waveguide (CPW) antenna. The longer strip resonates at the lower resonance frequency and the shorter strip—at the middle resonance frequency. The upper band of the triple band radiator is formed by the L slot on the left CPW ground. The gain and bandwidth of the proposed radiator are improved by a nanocomposite-filled slot. A better cross polarization of the radiator is achieved by decreasing the coupling of rigid radiating elements by spacing them properly. The compact structure is attained by uniting the radiating strips to the 5.00 mm wide signal-generating strip. The proposed radiator bandwidth is within 3.08–3.80 GHz for the lower band, 4.57–5.56 GHz for the middle band and 5.95–7.51 GHz for the upper band, which covers WLAN, WiMAX, 5G and Wi-Fi with an enhanced gain. The proposed radiator is suitable for practical wireless applications due its good radiation characteristics.

Mesoporous nanosized titania with a high specific surface area is synthesized by titanium carbide oxidation with nitric acid followed by a heat treatment of the product. The effect of heating temperature on the structural characteristics of TiO₂ and its activity in the photodecomposition reaction of the dye (rhodamine B) is studied. It is shown that compared with the well-known photocatalyst, Degussa P25, the photocatalytic activity of the samples heat-treated at 200°C and 400 °C is improved, when exposed to visible and UV radiation, respectively. The high photoactivity of the TiO₂ sample (200°C) under exposure to visible light is due to a high specific surface area, the presence of CO_x and NO_x groups on the surface, and the structure of the anatase phase with a trace of rutile phase. Under exposure to the UV radiation, the TiO₂ sample (400°C) is characterized by high photoactivity attributed to a high specific surface area and oxygen structure defects (O⁻).

The paper investigates the microstructure and properties of composite materials based on aluminum-manganese bronze and stainless steel. It is demonstrated that the microstructure has an effect on the tribological behavior of aluminum-manganese bronze–steel composites under dry friction and boundary lubrication conditions. The tribology testing results indicate a catastrophic wear of composites. The increased steel content in the bronze matrix leads to a dramatic growth in the wear intensity during the dry friction due to the enhanced adhesive interaction between the counter body and the sample. Tribology testing at the boundary lubrication shows an acceptable tribological performance and a moderate wear rate for the composite materials.

The effect of cyclic tensile deformation in the loading/unloading mode in the superelastic loop region on the deformation structure of a nanocrystalline aging superelastic Ti-50.9 at.% Ni alloy is studied. It is shown that the initial stage (from 0 to 5–10 cycles) corresponds to the accumulation of dislocations with the formation of a three-dimensional network with the nodes pinned by Ti₃Ni₄ particles, which inhibits the dislocation activity. After 10 loading cycles, there develop additional accommodative deformation mechanisms in the strengthened dislocation structure. It is found out that the relaxation of high internal stresses results in the formation of the reorientation mesobands, which ensure effective stress relaxation due to a local lattice reorientation.

The paper investigates the artificial aging effect on the tensile behaviour of friction stir welding of the aluminum 2219-T87 material, focusing on the impact of different thermal cycles and soaking times. It is shown that artificial aging enhances the ultimate tensile strength (UTS) and yield strength (YS). Aging at 165 °C for 12 h increases the YS by 14.2% due to precipitation hardening. However, aging at 175 °C for 12 h reduces both the UTS and YS due to an excessive precipitation. Ductility decreases with the precipitation hardening, but aging at 165 °C for 12 h retains 9% elongation. In contrast, aging at 175 °C for the same period reduces elongation to 7.4%. Prolonged aging at 165 °C for 18 h further reduces the material ductility.

The effect of high-temperature annealing on the microstructure and microhardness of a V–Cr–Zr–W alloy subjected to a combined treatment, involving a modified thermomechanical treatment and a chemical-heat treatment by the method of internal oxidation, is investigated. It is shown that as a result of this combined treatment the alloy thermal stability increases by a few hundred degrees. It is expected that the high structural-phase inhomogeneity of this alloy after its combined treatment is a consequence of the inhomogeneity of highly defective states and the specific features of introducing oxygen in the internal-oxidation stage.

A technology for producing porous oxide ceramics by irradiating the crucible with an electron beam with an electron energy of 1.4 MeV and a power density of 2.8–55 kW/cm² is described. The effect of the rate of the powder charge irradiation on the efficiency of the radiation synthesis—conversion of a mixture of the precursor powders into a ceramic material—is studied. It is found out that increasing the speed of the crucible irradiation with the electron beam from 0.125 to 2.5 cm/s, given an equal absorbed radiation dose, leads to an increase in the efficiency from 70 to 98%. The role of electron beam energy losses in the powder volume as a result of irradiation is discussed.

This paper studies the mechanoluminescence (ML) behavior of natural calcite under varying impact velocities to assess its potential use in passive mechanical sensing. Calcite samples obtained from Byrnihat, Meghalaya (26°03′03.8″N 91°52′11.0″E), were analyzed using X‑ray diffraction, field emission scanning electron microscopy, energy-dispersive X‑ray spectroscopy, and Fourier-transform infrared spectroscopy. The analysis confirms the formation of the nanocrystalline hexagonal phase with minor impurities that affect its luminescent properties. When subjected to the mechanical impact, the calcite consistently produces a sharp ML peak around 17 ms, regardless of the impact speed. The emitted light intensity shows a linear dependence on the impact velocity, suggesting a reliable correlation between the mechanical input and optical response. The emission decay follows a first-order exponential pattern, supporting its usefulness for identifying short-duration force events. A plot of time against the logarithm of intensity displays a clear negative slope, supporting this kinetic model. These research findings highlight the potential of natural calcite as a reliable and environmentally friendly material for mechanical sensor applications.

The Y₃Al_5–xGa_xO₁₂:Ce ceramic samples are synthesized by the radiation method. The influence of precursors on the radiation synthesis process is studied. The influence of the Al/Ga ratio on the spectral and kinetic properties of luminescence of Y₃Al_5–xGa_xO₁₂:Ce ceramics manufactured by radiation synthesis is investigated. The luminescence spectra of the samples are measured using the optical spectrometry technique with a time resolution of 7 ns. It is shown that gallium shifts the spectrum to the high-energy region due to the appearance of a new emission band at 2.49 eV and decreases the luminescence intensity in the low-energy region of the spectrum and the contribution from the relatively slow processes to the luminescence decay.