Fundamental’nye problemy sovremennogo materialovedenia / Basic Problems of Material Science

MAGNETIC PROPERTIES OF NANOCOMPOSITES BASED ON NANOTUBULAR SODIUM TRITITANATE

Tue, 01 Apr 2025 00:00:00 +0000

Recently, nanostructured Na₂Ti₃O₇ has attracted increasing attention of researchers as a promising material for gas sensors, photocatalysts, orthopedic devices, batteries, supercapacitors, etc. In some cases, the usage of such materials requires magnetic properties, e.g., for separation of nanoparticles from aqueous media or for targeted drug delivery. In this work, a method for preparing composite nanomaterials based on Na₂Ti₃O₇ and Fe₂O₃ (α-phase) multi-walled nanotubes has been developed. The outer diameter of multi-walled nanotubes is 7–10 nm, the inner diameter is 3.5–4 nm, and the distance between walls is 1–2 Å. Na₂Ti₃O₇–Fe₂O₃ nanocomposites were synthesized by a one-step hydrothermal method due to the simultaneous treatment of titanium dioxide and iron trichloride in a concentrated sodium hydroxide solution. Compared to sodium trititanate, Na₂Ti₃O₇–Fe₂O₃ nanocomposites have improved optical activity, especially in the visible region, and a reduced band gap (from 3.29 to 2.85 eV) due to the formation of a heterojunction between two semiconductors. Nanocomposites Na₂Ti₃O₇–Fe₂O₃ exhibit superparamagnetic properties at room temperature, their magnetization increases with increasing Fe₂O₃ phase content, and the coercive force reaches 965 Oe (at 3 K).

OPERATION ON OVERHEAD TRANSMISSION LINES

Tue, 01 Apr 2025 00:00:00 +0000

The mechanical properties of the AC50 aluminum steel wire of an overhead power line after 52 years of operation were investigated. Characteristics such as Young's modulus, attenuation decrement, X-ray and integral mass densities of aluminum and steel wires were measured. The measured characteristics were compared with those for a new wire that had not been used. The dependences of these values on the position in the span between adjacent supports are presented. It is shown that the dependence of the Young's modulus and the integral mass density on a part of the span length has a Λ- and W-shaped character for steel and aluminum wire, respectively. The dependence of the attenuation decrement for them has a Λ and V-shaped character, and the dependence of the mass density in the near-surface layer is M-shaped. These dependencies are associated with the formation of micro-gaps in the wire material during its deformation during operation on a power line under the influence of wind, ice and other influences. The increased operating temperature creates conditions for the return or recrystallization of the aluminum part of the wire. The change in the attenuation decrement is associated with the transformation of grain boundaries in the process of such deformation. The change in surface mass density is explained by the formation and healing of micro-pores and microcracks, as well as with a change in the chemical composition of the surface layers, in particular, the formation of aluminum oxide.

TWO VERSIONS OF 3D COMPUTER MODEL OF THE AG-SB-SN PHASE DIAGRAM, DETERMINED BY THE THERMAL STABILITY OF SB3SN4

Vera P. Vorob’eva, Anna E. Zelenaya, Vasily I. Lutsyk, Maria D. Parfenova — Tue, 01 Apr 2025 00:00:00 +0000

The Ag-Sb-Sn system is of interest to microelectronics and is a promising material used in high temperature soldering. The analysis of phase equilibria in the system is difficult because of the lack of an agreed opinion on its structure: various versions are due to an ambiguous description of the formed compounds and the conditions for their existence. Thus, compound Sb3Sn4 is either considered stable up to room temperature or exists in a limited of 323-242^oC temperature range.

The purpose of the work was to analyze phase equilibria in the Ag-Sb-Sn system depending on the method of formation and the temperature boundaries of the existence of the binary compound Sb3Sn4. For this, two versions of a three-dimensional (3D) computer model of the Ag-Sb-Sn phase diagram were constructed. The technology of assembling a phase diagram from surfaces and/or phase regions was used. Iso- and polythermal sections were calculated for both versions of the 3D model. The resulting versions provide a complete geometric description of the phase diagram, including in solid regions. In addition, the model can be adjusted when new experimental information is obtained and even a radical change in the understanding of the properties of compounds formed in the system. Both versions of 3D models expand the predictive functions of the phase diagram, and in the future will help to understand the structure of phase diagrams of other ternary systems formed on the basis of the binary Sb-Sn system.

MORPHOLOGY AND COMPOSITION OF BORON-CONTAINING PEO-COATINGS ON MG ALLOY MA8

Tue, 01 Apr 2025 00:00:00 +0000

The paper presents the results of a study of the morphology and composition of coatings on magnesium alloy MA8 obtained by plasma electrolytic oxidation (PEO) in boron-containing electrolytes. The effect of electrolyte composition and PEO modes on the elemental and phase composition, morphology and structure of heteroxide coatings has been established. It was found that with PEO in electrolytes containing boron particles, the surface of the formed coatings contains up to 2.3 at. % of boron in the bound state. It is also shown that during oxidation in electrolytes containing a dispersed phase in the form of a boron-containing suspension, inert incorporation of boron particles into the coating structure occurs.

STRUCTURE AND PHASE COMPOSITION OF MULTILAYER METAL MATRIX COMPOSITE PRODUCED BY HIGH PRESSURE TORSION OF ALUMINUM AND COPPER PLATES

Valeriy N. Danilenko, Leila U. Kiekkuzhina, Yuryi A. Lebedev, Vill D. Sitdikov — Tue, 01 Apr 2025 00:00:00 +0000

The structure and phase composition of metal matrix composites obtained by high-pressure torsion of Al and Cu plates with different layer arrangements: 6Cu-5Al and 6Al-5Cu were studied using scanning electron microscopy, X-ray diffraction and energy dispersive analysis. The samples were deformed by high-pressure torsion of 6 GPa for 5 revolutions at a speed of 1 rpm. It was shown that the sample with the 6Al-5Cu plate arrangement has a more uniform structure than the sample with the 6Cu-5Al arrangement. The mixing process in the 6Al-5Cu sample occurs more intensively throughout the entire volume of the sample, while in the 6Cu–5Al sample it occurs only at the edge. X-ray diffraction and energy dispersive analysis showed that the phase composition of the studied samples differs significantly. Intermetallic phases AlCu, Al₂Cu, Al₄Cu₉, as well as a solid solution of aluminum in copper are present in the 6Al-5Cu sample, the basis is aluminum and copper. Similar intermetallic phases are also observed in the 6Cu-5Al sample, and the basis is copper and a solid solution of aluminum in copper. The microhardness of the studied samples, measured in the cross section, is significantly higher than the microhardness of the original metals. Microhardness is formed depending on the obtained structure and phase composition of the studied samples.

LAYER-BY-LAYER TOOL INDENTATION OF AA7075 ALLOY PRODUCED BY ADDITIVE TECHNOLOGY METHOD

Tue, 01 Apr 2025 00:00:00 +0000

Aluminum alloys are widely used in various industries, including aviation, electronics, automotive and military industries. Nanohardness and Young's modulus of aluminum alloys play a significant role in their study and optimization, since the measurement results provide more accurate information on the mechanical properties of materials at the nanolevel, which is especially important when developing new parts and improving the characteris-tics of existing alloys. Studying the nanohardness of aluminum alloy 7075 allows us to study the effect of various additives and alloying components on their mechanical properties. The data obtained are used to optimize the modes of obtaining alloys, by additive manufacturing and the formation of new materials with improved properties.
The use of instrumental indentation methods made it possible to establish the presence of phases in the upper region that affect the nanohardness of the part. The formation of secondary phases with poor solubility in the metal matrix is due to a higher temperature gradient due to interlayer cooling. Secondary phases hinder the movement of grain boundaries, which contributes to an increase in nanohardness and elastic modulus to 2.3±3.27 GPa and 100.1±0.6 GPa, respectively. SEM methods have shown that in layers near the substrate, where the cooling rate of the part becomes lower with increasing height of the deposited sample, the average grain size is from 10 to 15 μm, and in areas with a higher temperature gradient, due to interlayer cooling, the grain size decreases to 5-10 μm

TWO-DIMENSIONAL BREATHERS AND THEIR INFLUENCE ON MACROSCOPIC PROPERTIES OF ALUMINUM MONOCRYSTAL

Olga V. Bachurina, Ramil T. Murzaev, Dmitry V. Bachurin — Tue, 01 Apr 2025 00:00:00 +0000

The interest in discrete breathers (DB), i.e. time-periodic and spatially localized vibrational modes in a defect-free nonlinear lattice, is related to their ability to localize vibrational energy of the order of several eV per atom. In this paper, the molecular dynamics method is used for the first time to study the effect of a two-dimensional DB on the macroscopic properties (heat capacity and thermal expansion) of a defect-free fcc aluminum single crystal. The standard embedded atom method interatomic potential was applied. All calculations were carried out at zero absolute temperature. The DBs were excited by displacing the atoms from their equilibrium lattice sites corresponding to three delocalized nonlinear vibrational modes (DNVMs) previously discovered for a two-dimensional triangular lattice. It was found that the compressive stress increases with increasing initial amplitude, i.e., excitation of a two-dimensional DB leads to thermal expansion of the crystal. The two-dimensional DB is characterized by a decrease in heat capacity with increasing amplitude. At high amplitudes, the vibrational energy can reach values in the range of 0.6-1.1 eV per atom. All studied DBs are characterized by a hard type of nonlinearity, i.e. an increase in frequency with increasing vibration amplitude.

PHYSICAL AND MECHANICAL PROPERTIES OF NANOSTRUCTURED CERAMICS BASED ON AL2O3 TOUGHENED YSZ

Egor D. Kuzmenko, Sergey V. Matrenin — Tue, 01 Apr 2025 00:00:00 +0000

In the conducted work, the physical and mechanical properties of ceramics based on corundum reinforced with zirconium dioxide stabilized with yttrium oxide were investigated. The studied material was obtained on the basis of mechanically activated nanodispersed powders of these components. The following pressing pressures were used in the work: 50, 100, 200 and 300 MPa. The obtained blanks were sintered in a high-temperature furnace at a temperature of 1700 ℃ in an air environment. When conducting scanning electron microscopy with mapping of elements, the presence of a corundum matrix with a uniformly distributed phase of a solid solution of zirconium dioxide and yttrium oxide in it was established. After sintering, a fine-grained structure with a predominant particle size of 1-9 μm was observed in the studied materials. It was found that a pressure of 300 MPa is the limiting pressure for pressing these ceramic batches, above which pressing defects may occur. At this pressure, the highest relative density of the material among those studied was achieved – 85.12%. It was found that by changing the pressing pressure, it becomes possible to achieve the properties of materials in a wide range and adapt them to the required operating conditions. Thus, it was found that when sintering the blanks obtained in the specified range of pressing pressures, Young's moduli varied within the range from 126 to 297 GPa, and the indentation hardness from 2.25 to 7.95 GPa.

SIMULATION OF ULTRASONIC WELDING OF NANOCRYSTALLINE COPPER

Ramil T. Murzaev, Maryam A. Idrisova, Ayrat A. Nazarov — Tue, 01 Apr 2025 00:00:00 +0000

Using the molecular dynamics (MD) method, we simulated the joining of two nanocrystalline copper blocks by alternating mutual displacements under the action of applied pressure, simulating the process of ultrasonic welding (USW) of metals. The computational cell for the simulation consisted of two copper blocks with columnar grains 6.26 nm in size, having a common column axis [112] and a cross-section in the form of a regular hexagon. The surfaces of the blocks contained irregularities described by a sinusoid with an amplitude of 10 Å. The system was initially relaxed under a given pressure from 0.25 to 2 GPa until equilibrium was reached at a temperature of 300 K, then sinusoidal displacements with an amplitude of 5 nm in opposite directions were imparted to the blocks. The simulation showed that the joint was formed by expanding the contact area of the blocks during mutual shifts of the latter, and the initial cavity is transformed into a pore, the size of which decreases with increasing pressure. At a certain critical pressure, the pore is completely healed and a continuous joint is formed. The nanocrystal formed as a result of joining has an increased atomic volume, which is associated with the relaxation of the pore under the action of shear deformations and tensile stress. The alternating shear deformation occurring during the simulated USW leads to grain growth, including the coalescence of grains that originally belonged to two different blocks. This is an important factor leading to the formation of a defect-free joint during USW.

APPLICATION OF FAST JOULE HEATING FOR SYNTHESIS OF CARBON NANOFILMS

Aisen R. Prokopev, Efim P. Neustroev — Tue, 01 Apr 2025 00:00:00 +0000

The paper presents a two-step synthesis of carbon nanofilms containing graphene flakes in their structure. In the first stage, amorphous a-C:H films were obtained in low-temperature plasma deposition of methane on Si/SiO2 substrates. Fast Joule heating of the samples was carried out by electric discharge of 180 mF capacitors charged to a voltage of 100 to 300 V. The studies involved the methods of Raman spectroscopy, scanning electron microscopy, X-ray energy-dispersive spectroscopy and current-voltage characteristics. It was found that heating leads to a significant increase in electrical conductivity and an increase in the hydrophobicity of the material. The maximum results were obtained when discharging a capacitor block charged to a voltage of 160 V. Also, at this discharge voltage, a high degree of structural ordering of carbon films is observed in relation to samples obtained with other parameters of fast Joule heating. The obtained results are explained by the transition of the initial amorphous carbon film into a crystalline structure with a predominance of sp²-hybridized bonds, which has low electrical resistance. The reason for the emergence of water-repellent properties may be the "lotus effect" caused by the formation of spherical particles up to 1 μm in size and their conglomerates on the surface of the film.

STRUCTURAL PHASE TRANSFORMATIONS IN INTERMETALLIC NiAl UNDER UNIAXIAL HIGH-SPEED DEFORMATIONS IN THE ABSENCE OF ENERGY DISSIPATION

Tue, 01 Apr 2025 00:00:00 +0000

Using a computer experiment, the structural and phase transformations possible in the intermetallic compound NiAl 50% (at.) Al and 50% (at.) Ni under conditions of high-speed deformation at speeds exceeding the speed of sound of 5∙10⁹ s^-1 and 5∙10¹⁰ s^-1 were studied. The experimental conditions were set in such a way that no energy dissipation occurred in the unloading waves. The interactions between atoms in the alloy were specified in the approximation of the many-particle potential of Mishin et al. The single crystal was represented as a cube with an edge length of 57.6 Å with the orientation of the axes [100], [010], [001]. It is shown that uniaxial tension is accompanied by two phase transformations: BCC – BCC+FCC and BCC+FCC – FCC. During uniaxial compression, phase transformations BCC – BCC+HCP and BCC+HCP – HCP occur. Compression at 300 K at the last front, manufacturing defects with FCC interlayers. At higher temperatures, such defects do not form. As the deformation rate increases, the yield strength of the material increases. At all stages, deformation occurs according to a quasi-elastic mechanism. At transition stages, areas of plastic deformation are observed, but the movement of dislocations is carried out due to the applied external stress without the contribution of thermal vibrations of the lattice. At transition stages, areas of plastic deformation are observed, but the movement of dislocations is carried out due to the applied external stress without the contribution of thermal vibrations of the lattice.

THE STRUCTURAL STATE OF THIN SILICON FILMS AND THEIR LOCAL CONDUCTIVITY

Vladimir A. Plotnikov , Anna A. Maltseva, Sergei V. Makarov — Tue, 01 Apr 2025 00:00:00 +0000

Thin silicon films on silicium glass substrates with a copper sublayer were produced by condensation from the vapor-gas phase obtained by resistive evaporation of silicon in vacuum. The structural state of the films was studied by scanning probe microscopy using a conductive probe. The analysis of the surface relief indicates the high quality of the film, the average deviation of the z-component of the film on the copper sublayer is about 7 nm. And on silicium glass substrates – 1.34 nm. Thin silicon films can have a different structural state depending on the method of their preparation and the conditions under which their formation occurs. In our case, the structural state of both silicon films and the copper sublayer is cluster-like, which follows from the size distribution of the structural components

Clusters consist of a small number of atoms and usually have sizes from fractions to several nanometers, which leads to a significant change in the electronic subsystem associated with the localization of electrons and the appearance of energy levels in both the valence and conduction bands and the expansion of the energy gap between them. Such changes in the electronic subsystem significantly affect the electrophysical and optical properties of films, for example, there is an increase in the energy of electrons to transition from one level to another, which leads to electron tunneling.

Electron tunneling affects their transport properties. The study of local conductivity was carried out using scanning probe microscopy. It is established that nonlinear volt-ampere dependences with a pronounced section of the so-called "zero current" are observed in the copper sublayer and in the Cu/Si hybrid structure. The presence of such a section on the volt-ampere dependence indicates electron tunneling, and the width of this section characterizes the energy for making a tunnel transition both in the cluster itself and between adjacent ones. The conductivity of the silicon film on the glass substrate is absent, which may indicate the dielectric properties of the film.