Russian Physics Journal最新文献

Metal matrix composites with intermetallic strengthening phases have high mechanical strength, wear resistance and thermal stability, but their application is limited due to brittleness and complexity of processing. In this paper, the effect of friction stir processing (FSP) on the tribological characteristics of bronze-steel composites fabricated by electron beam additive manufacturing (EBAM) is investigated. It has been found that FSP leads to the formation of a finely dispersed structure with a uniform distribution of strengthening phases, which increases the microhardness from 2.0 to 2.8 GPa. Tribological tests show a decrease in the specific wear rate by 39% after three FSP passes compared to the initial material, despite a slight increase in the friction coefficient. Acoustic emission and vibration analysis reveals a change in wear mechanisms associated with the formation of a gradient structure. The results obtained demonstrate the promise of a combined approach (EBAM + FSP) for fabricating wear-resistant materials with improved performance properties.

Organic solar cells (OSCs), fabricated by solution process, have attracted renewed attention from the scientific society because of their low-cost and environmentally friendly characteristics along with their flexibility and simplicity in processing. In the present work, an attempt is made to enhance the photovoltaic performance of polymer solar cells based on poly(3-hexylthiophene) (P3HT) by incorporating silver nanoparticles (AgNPs). The nanocomposite is made by the solution mixing of P3HT and AgNPs in chloroform, followed by the formation of a spin coating on a conductive glass substrate. The resulting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite is subsequently deposited on the active layer to aid in the charge collection and improve the contact between layers. The effects of the AgNPs doping are studied using several characterization methods. The photoluminescence (PL) measurements show that the light emission is highly decreased, demonstrating that excitons are more easily dissociated, and their recombination becomes less effective. According to the atomic force microscopy (AFM) data, the surface becomes slightly rougher at the optimal concentration, although nanoparticles are well-distributed. The AgNPs are revealed by scanning electron microscopy (SEM); they are well dispersed in some areas at low concentrations but are aggregated in other regions at high concentrations. The current and voltage measurements demonstrate a noticeable enhancement in the short-circuit current density and the power conversion efficiency of the device with the AgNPs relative to the standard cells. This suggests that integrating the silver NPs with the P3HT material, in combination with an appropriate layer structure, could enhance the performance of organic solar cells and promote their application in a flexible renewable energy technology.

The paper presents the numerical simulation of and experiments with the dynamics of wave patterns in isotropic and anisotropic materials under the dynamic load. In experiments, manganese sensors are used to record pressure profiles for samples. The finite element modeling is used for three-dimensional formulation within the phenomenological approach to mechanics of deformable solids using the proposed software. It is shown that the influence of anisotropy of properties on the plate resistance to shock waves reduces with increasing interaction velocity.

The paper investigates the phase composition and microstructure of sintered cylindrical samples made of 12% chromium ferritic-martensitic steel, fabricated from elemental powders. The experimental characterization involves optical metallography, X‑ray diffraction (XRD), scanning and transmission electron microscopies. The investigation shows the formation of the typical highly defective lamellar martensitic structure. This matrix incorporates finely dispersed particles of cementite-type M₃C carbides. The identified regions with retained austenite predominantly locate as thin interlayers along the prior austenite grain boundaries. Severely deformed localized zones are observed in the material with increased dislocation density and refined (sub-microcrystalline) grain-subgrain structure. According to the XRD microanalysis, a notable heterogeneity is observed in the elemental distribution across different structural regions. Specifically, Cr and Ni demonstrate significant changes in their concentration, which is likely attributed to micro-segregation during sintering and subsequent cooling. Regarding mechanical properties, the microhardness distribution across both the diameter and height of the cylindrical sample is relatively uniform, indicating to homogeneous overall processing. However, the observed localized spread in the microhardness values probably correlates with the chemical and microstructural heterogeneity.

The structure and properties of composite materials with a metal matrix based on titanium Grade 2 alloy and a pure copper powder are studied. It is found out that at the constant processing parameter values an excessive penetration of the tool into the workpiece surface is possible with the formation of beading or flash on the edges of the contact zone between the tool arms and the material. There is also stirring of the substrate material in the stir zone with the formation of a coarse dispersed macroscopically inhomogeneous structure. At high copper contents, the sample structure inhomogeneity increases, and in a number of experiments the formation of macroscopic defects is observed. After 1–4 passes of the tool there is an increase in the homogeneity of the powder particle distribution in the stir zone.

This work presents the latest developments of the pre-compound model and nuclear relaxation module simulated in Geant4 toolkit in view of the future experiments with the high-energy large hadron collider and the nuclotron-based ion collider facility in the moderate energy region. These processes have a significant impact on spectra of low energy neutrons, protons, and ions in nuclear interactions, which affect various application domains. The paper presents the model modifications and validation. Updated hadronic models created in Geant4 are included in the public release of Geant4 11.4.

Four samples of Inconel 718 superalloy are produced by wire-feed electron beam additive manufacturing (EBAM). The samples are formed under different heat input conditions by varying the additive printing speed and the electron beam current. It is shown that the macrostructure has several characteristic zones differing significantly throughout the entire height of the additively produced samples. The microstructure, consisting of dendritic arms and carbides located between them, varies for each selected process parameter set. With a decrease in the resulting energy input, the dendritic core is mainly refined. The formation of strengthening phases and carbides is uneven throughout the height of the additively produced samples, leading to unstable mechanical properties.

In this work, bimetallic samples based on steels 13Mn6 and SS321 are produced using wire-feed electron beam additive manufacturing (EBAM). Each material is deposited in 50 mm layers on top of each other, forming a sharp transition boundary without defects such as lack of fusion, discontinuities, or pores. The microstructure and mechanical properties of the bimetallic steel samples are studied. It is established that the bimetallic sample is characterized by a clear interface between the two materials, which has a macroscopically heterogeneous structure with two-phase transition zones on both sides of the boundary. As the bimetallic sample grows (moving away from the sharp transition boundary), an anisotropic grain structure begins to form under the conditions of non-stationary local metallurgy. The heterogeneous grain structure affects the macroscopic deformation behavior, likely due to the influence of the orientation and density of grain boundaries formed during the additive bimetallic material growth. The fracture occurs through the base metal, bypassing the junction zone between the different steel grades. The samples with the boundary strength not lower than that of the base metal are successfully manufactured.

Complex permittivity is the main parameter of ground-penetrating radar (GPR), a method to determine the probing depth of the geological environment. At the same time, a diversity of rocks provides an extremely wide range in complex permittivity, which significantly complicates interpretation of the data obtained. High-frequency coaxial measuring cells are used for the laboratory measurement of complex permittivity of rock samples. However, most of these cells are used exclusively for loose rocks, which means that complex permittivity of crystalline rocks remains essentially unstudied. To solve this problem, a waveguide cell is proposed and manufactured for operation with solid samples. Complex permittivity of some types of rocks is investigated in the GPR frequency range using this cell.

The results of a study on the sensitivity of sensors fabricated from single-crystal sapphire and bulk undoped silicon carbide to X‑ray radiation with photon energies in the range of 10–80 keV are presented. The photocurrent is measured experimentally and the carrier lifetime is estimated. The photocurrent dependence on the X‑ray intensity and the sensor voltage is determined experimentally and via modeling.