Volume 126, Nº 5 (2025)

The magnetization curves of nanocomposites with LiCoPO₄, LiNiPO₄ and LiNi_0.5Co_0.5PO₄ orthophosphate particles have been studied in the low temperature range. The measurements were performed both on direct current and in alternating fields. The dependence of the magnetic susceptibility on the magnetic field in alternating fields and the susceptibility measured at direct current is compared. An anomalous maximum of susceptibility is observed in a field with a strength of about ~ 32 kOe, which can be interpreted as a consequence of an additional reversal of magnetic moments. A formula is proposed to describe the field dependence of magnetic susceptibility in alternating fields.

Longitudinal and transverse magnetotransport effects were investigated in a monocrystalline HgSe sample (electron concentration n = 4 × 10¹⁶ cm⁻³, electron mobility µ = 1.2 × 10⁵ cm² V⁻¹ s⁻¹) under a planar electric and magnetic field configuration. Analysis of Shubnikov-de Haas oscillations in both longitudinal and transverse magnetoresistance yielded data on the half-filling of the zeroth Landau level and revealed a nontrivial Berry phase. These signatures of the relativistic nature of the HgSe electronic spectrum are complemented by two key magnetotransport signatures of the chiral anomaly: the chiral magnetic effect and the planar Hall effect. Collectively, these findings indicate the existence of a Weyl semimetal electronic topological phase in HgSe — an isotropic, nonmagnetic material characterized by strong spin-orbit coupling.

Based on experimental data on the surface tension (σ) of indium–tin–lead, thallium–lead–bismuth and indium–tin–gallium melts, the features of σ changes with composition changes were revealed. The boundary binary systems indium–tin and thallium–lead are characterized by the presence of a minimum on the σ isotherm of the melts. It is shown that in the studied ternary systems, the characteristic minimum on the σ isotherms along the sections of the triangle of compositions with a constant content of the third component is preserved. With an increase in the content of the 3rd component in the section, the depth of the minimum, (“depression” on the isothermal surface σ), decreases and the “depression” disappears at the following values of the molar fractions of the third component: 0.1 mole fractions of lead (in the indium–tin–lead system); 0.1 mole fractions of bismuth (in the thallium–lead–bismuth system); 0.3 mole fractions of gallium (in the indium–tin–gallium system). It was found that in the studied ternary systems, the concentration of the third component, at which the “dip” on the isothermal surface σ disappears, is directly related to the surface activity of this component in the melts, which determines its content in the surface layer. Based on the σ isotherms, within the framework of the ideal monomolecular surface layer model, the composition of the surface layer of ternary melts was calculated. The results showed that the "dip" on the isothermal surface σ of all studied ternary systems disappears at 0.25±0.03 mole fractions of the third component in the surface layer.

Crystallization kinetics of Fe₄₀Ni₄₀P₁₄B₆ and Fe₄₈Co₃₂P₁₄B₆ glasses at isothermal conditions was investigated in the temperature ranges of 617–662 and 683–714 K, respectively. The onset crystallization times were used as indicators of thermal stability. The transient behavior of crystal nucleation was established in the framework of the Kolmogorov–Johnson–Mehl–Avrami model and the combined Kolmogorov–Kashchiev model and both the degrees of non-stationarity and the times characterizing crystallization kinetics at steady-state and transient nucleation were determined. The temperature dependencies of the effective diffusivity governing transfer atoms across the interfaces and steady-state nucleation rates were calculated using the characteristic steady-state crystallization times and values of the crystal growth rates known from the literature. From these data the temperature dependencies of both the work of critical nucleation formation and the specific free energy of nucleus/matrix interface were found in the framework of the classical equation of homogeneous nucleation rate. From comparison between the experimentally measured and calculated for steady-state nucleation onset crystallization times it was established that the enhanced thermal stability of Fe₄₈Co₃₂P₁₄B₆ compared with that of Fe₄₀Ni₄₀P₁₄B₆ was caused by the lowered diffusion mobility and the higher degree of deviation of nucleation rate from its steady-state value.

The deformation behavior and changes in the microstructure of manganese brass Cu–40%Zn–2%Mn (wt%) during multidirectional isothermal forging (MDF) at temperatures of 400°C and 500°C, which is ~ 50°C lower and higher than the temperature of the β→β' transition, were studied. It has been shown that MDF at both temperatures promotes the formation of a homogeneous and fine-grained structure with an average grain size of α- and β'-phases of ~ 5 and ~ 12 microns, respectively, increasing the hardness by 2.5 times from 130 HV in the initial state to ~ 310 HV after the total true deformation ∑e = 7.2. An increase in the true strain to ∑e = 14.4 did not have an additional strengthening effect. In the case of MDF at 400°C, an increase in the true deformation was accompanied by a slight grinding of the grains of the α and β' phases to 3.6 and 9.2 microns, respectively, and in the case of deformation at 500°C, it led to an increase in their sizes to 7.1 and 17.5 microns, respectively.

This study developed modes of surface modification of a niobium-molybdenum alloy by nitrogen ion implantation to investigate the effect of treatment on the alloy's protective properties during high-temperature oxidation. The chemical and phase composition of the modified surfaces was analyzed by X-ray spectral microanalysis and X-ray diffraction. The thickness of the implanted layer was determined by transmission electron microscopy. The results of the modulus of elasticity, microhardness, and nanohardness measurements of the alloy samples in their initial and nitrogen-implanted states are presented. The implanted and initial alloys were evaluated for resistance to high-temperature oxidation in air for 15, 30, and 60 minutes at a temperature of 900°C. The surface structure was examined, and the thickness of the oxide layer was determined after high-temperature oxidation tests using scanning electron microscopy. The specific weight gain of the samples was measured during the testing process. The results show that, in the ion implantation modes used, nitrogen concentrations of up to 39.3 at% are achieved at a depth of approximately 100 nm in the surface layer, with the formation of niobium nitrides. Moreover, the treatment enhances the alloy's mechanical properties, including an increase in the modulus of elasticity, microhardness, and nanohardness as well as improve the alloy's resistance to high-temperature oxidation, as evidenced by the formation of thinner oxide layers and a lower weight gain compared to the untreated alloy.

Alumina-matrix composites reinforced with multi-walled carbon nanotubes (MWCNTs) in the cast state were obtained by introducing powders of different compositions containing MWCNTs, Cu and/or Mg metals, and SiC ceramic particles into the Al melt. The structure of the composites was studied using light and scanning electron microscopy. It was found that the powder composition affects the effect of modifying the structure of aluminum matrix composites. The most dispersed structure (grain size 200 μm) is found in composites reinforced with MWCNTs with a microadditive of Mg. The hardness and mechanical properties of the composites were measured in a wide range of deformation rates (έ = 10^–2 – 10⁵ s^–1). Experiments on loading aluminum matrix composites with plane shock waves were performed for the first time. From these data it follows that with an increase in the deformation rate, a gradual increase in the yield strength of composites up to 100 MPa is observed. A comparison of the strength characteristics of aluminum matrix composites with the corresponding characteristics of unreinforced Al shows that the strengthening effect of MWCNTs is more pronounced at higher deformation rates and reaches 60% at the maximum deformation rate.