Vol 124, No 5 (2023)

The effect of a magnetic field on the phase transitions of a two-dimensional frustrated Potts model with the number of spin states q = 4 on a hexagonal lattice was studied by the Monte Carlo method. The studies were carried out for a wide range of magnetic field strength. The magnetic structures of the ground state in this range have been obtained. The dependence of the magnetization on the magnetic field has been constructed. It has been found that an external magnetic field leads to a first-order phase transition. It is shown that a strong magnetic field removes the degeneracy of the ground state and suppresses the phase transition in the system

A theoretical and experimental study of the dependence of the magnetoresistance for two spin-tunnel junctions (STJs) of ellipsoidal shape has been made. The one-sided homogeneous magnetization reversal mode of an ellipsoidal STJ with different aspect ratios has been experimentally selected. Despite the reverse
inhomogeneous remagnetization, this selection has allowed for the calculation of the magnetic parameters of these elements by developing the Stoner-Wohlfarth theory.

Electrodynamic, quasi-static magnetic hysteresis loops and the form of the domain texture of a single-crystal plate have been experimentally obtained. Using mathematical modeling, the change in the dynamic magnetic hysteresis (the magnetic loss energy per unit volume per magnetization reversal cycle) depending on the frequency of the magnetic field is shown. This dependence is due to the inertia of the magnetization of the sample. With a change in frequency, the dynamic magnetic hysteresis can differ significantly from the hysteresis in the case of quasi-static magnetization reversal.

The results of a theoretical study of the structural and dynamical parameters of surface phases (adsorption phase and surface alloy phase) formed upon the adsorption of 0.33 Pb monolayer on the Ni(111) plane surface are discussed. Calculations were performed using interatomic potentials obtained within the framework of the embedded atom method. The stability of the surface phases was analyzed on the basis of data on the equilibrium atomic configuration, phonon spectra, local density of phonon states, and polarization of localized vibration modes. It is shown that the Pb–Ni surface alloy has the highest dynamic stability among the two possible surface phases.

Metastable solid solutions of metals have been obtained using nano- and subnanoparticles. This study shows the effect of the size of atoms of a second element on the multiple increase in solubility and limiting concentration in the solvent, independently of the type of crystal lattice. As an example, the limiting solubility of lead (rPb = 0.935 nm) in niobium (rNb = 0.625 nm) is 23.0 at % and that of cadmium (rCd = 0.1727 nm)
in niobium is 64.0 at %. Further, amorphization of the matrix metal occurs. Compared to metastable solid solutions with the equilibrium systems for which the Hume–Rothery rules work, alloys are formed from metals with different types of crystal lattices. In many cases, a 15% limit of the difference of the sizes of metal atoms is observed. There is a strong discrepancy in the valences of atoms and, in rare cases, in electronegativity. Using analysis of the attributes of the alloys prepared by sputtering of ultradisperse particles, the possibility of expanding the boundaries of the Hume–Rothery criteria should be noted for metastable alloys, in comparison to their equilibrium analogs, which indicates the possibility of deviation from the traditional forecasting the routine of preparation of the material.

The features of the structure and phase composition of corrosion-resistant austenitic chromium–nickel steel (16.80 wt % Cr, 8.44 wt % Ni) subjected to carburizing in electron beam plasma at temperatures of 350 and 500°C, frictional treatment with a sliding indenter, and a combination of frictional treatment and plasma carburizing have been considered. It has been established that plasma carburizing results in the formation of a modified surface layer consisting of carbon-saturated austenite and carbides (Cr23C6, Fe3C); in this case, the formation of γC-phase occurs only at a temperature of 350°C. The depth of a modified layer increases with an increase in the carburizing temperature. It has been shown that it is useful to perform combined frictional treatment and plasma carburizing at a carburizing temperature of 350°C, since in this case the deformation-induced structure formed as a result of frictional treatment is preserved, and the precipitated carbides remain highly dispersed. In this case, frictional treatment should provide the formation of the deepest
possible diffusion-active layer with a dispersed structure.

The precipitation of Ω-phase {111}α plates in the Al–Cu–Mg alloy has been investigated at a Cu/Mg ratio > 10 and low Si content. Unlike Al–Cu–Mg alloys containing Ag, nanoscale plates with an {111}α habit plane has been found for the first time to precipitate in the alloy according to a heterogeneous mechanism, namely, along low-angle boundaries, dislocation lines, and at the θ′-phase/Al-matrix interphase
boundary.

A neutron diffraction method has been used to study residual stresses in corrosion-resistant martensitic steel AISI 410 plates of the composition (wt %): 0.15 С, 13 Cr, < 1 Mn, < 1 Si, and Fe for balance obtained by direct laser deposition. The plates are deposited on rigid substrates, which are commonly used in practice in the production of large parts. It has been shown that in plates of different thicknesses (2.2 and 7.4 mm) and the same length and width (70 × 30 mm), the patterns of the stress distribution curves are very close, however, the stresses in a 7.4-mm-thick plate are lower than in a 2.2-mm-thick plate. In both plates (2.2/7.4 mm), the maximum normal tensile stresses (~450/350 MPa) are induced near lateral edges of the substrate. The maximum tensile longitudinal stresses (~400/250 MPa) are induced in the middle section of the plate near the upper edge. In the middle section of a 7.4-mm-thick plate, a stress distribution over the thickness is observed: the stresses near the side surfaces are higher than in the middle section. The thickness distribution becomes more uniform by approaching the plate edges. The stress distribution pattern in plates obtained by direct laser deposition strongly depends on the rigidity of the substrate and, to a lesser extent, on the material and deposition technology.