Vol 124, No 3 (2023)

In this paper, we present the calculation results of the electronic structure and optical spectrum
and an experimental study of the optical properties of Heusler alloys Mn2 – xFe1 + xAl (x = –0.5, 0, 0.5, 1).
An anomalous for metallic systems behavior of the optical conductivity of alloys in the IR region of the spectrum
was found: the absence of Drude growth and a high level of interband absorption. This behavior is shown
to be determined by the features of the electronic structure: the Fermi level is located in the region of high
density of states that is formed by the d states of Mn and Fe.

The results of the application of a combination of several surfactants in preparing submicron hard magnetic Sm2Fe17N3 powders by milling in a centrifugal mill are reported. Along with methyl caproate, to protect the powder against oxidation, the efficiency of siloxane has been studied. The application of the combined surfactants allowed us to increase both the (BH)max of the Sm2Fe17N3 powder to 23.6 MG Oe and its corrosion resistance. The effect of milling kinetics on the angular dependence of the coercive force Hc has been determined. Information on the primary mechanism of magnetization reversal of the powders has been
obtained.

The effect of the action of temperature on the structure and phase composition of an
Fe3C/Fe7C3/P-phase/Cam composite obtained by mechanosynthesis of Fe–75 at % C has been studied by the methods of X-ray diffraction, Mössbauer spectroscopy, thermogravimetric analysis, and differential
scanning calorimetry. It is shown that the structural and phase changes at heating have a multistage character.
In the temperature range 315–400°C crystallization of the paramagnetic P-phase with generation of Fe3C
and/or Fe7C3 occur. In the course of heating to higher temperatures, complete decomposition of carbide
Fe7C3 (in the range 450–550°C) and partial decomposition of Fe3C (at 600°C and above) are observed. After
cooling from 800–1000°C the mechanocomposite consists of α-Fe, cementite Fe3C, and graphite. The phase
transformations are accompanied by the processes of composite oxidation with the formation of Fe3O4 oxide and its subsequent reduction. The P-phase is a disorded amorphous carbide Fe1 – xCx, which is characterized by magnetic ordering at the temperature of liquid nitrogen.

The grain-boundary diffusion of Co in Nb has been studied by a layer-by-layer radiometric analysis in the temperature range of 723–873 K. The diffusion annealing modes corresponded to the kinetic C mode, which implies that the diffusion proceeds only along grain boundaries. The coefficients of grain-boundary diffusion of Co in Nb have been determined for several temperatures from diffusion profiles. An expression for the Arrhenius dependence of Co diffusion coefficient along the grain boundaries of Nb has been determined. The temperature dependence of coefficient of grain-boundary segregation of Co in Nb is constructed
based on the temperature dependence of coefficient of grain-boundary diffusion of Co in Nb and the data in the literature on the temperature dependence of the triple product.

Diffusion along a network of the triple junctions of grains has been considered under the conditions of negligibly small diffusion along all other diffusion paths. The conditions have been found where such a network acts similar to a homogeneous medium. For this case, the effective diffusion coefficient in the absence of texture has been found.

Cast Nb–14 at % Si–9 at % Al alloys fabricated by self-propagating high-temperature synthesis (SHS) and by SHS followed by electric arc remelting have been investigated. A structure consisting of a solid solution of silicon and aluminum in niobium (NbSS), a Nb3Al intermetallic compound, and a β-Nb5(Si,Al)3
silicide formed in the alloy fabricated by SHS. Electric arc remelting suppressed the formation of the Nb3Al
phase and resulted in the formation of a dispersed two-phase NbSS and β-Nb5(Si, Al)3 structure in the alloy.
The increased volume fraction of NbSS and the dispersed structure formed after electric arc remelting in the
alloy increase its fracture toughness to 14.8 ± 0.8 MPa m1/2 compared to 7.7 ± 0.8 MPa m1/2 for the SHSprepared
alloy.

Based on the measured physical properties of the Fe–Ga alloy, it was found that a decrease in the material thickness to 0.3 mm leads to an acceptable level of eddy current losses at high-frequency magnetization reversal (20 kHz). Recommendations have been developed on the choice of rolling modes to achieve the required thickness. The modeling of rolling according to the proposed mode is implemented, the distributions of deformation, stresses, and temperature for each pass were obtained. The results obtained are analyzed
in the context of the relation between the features of deformation and the processes of crystallographic texture
formation.