编号 1 (2024)

The influence of heat treatment and deformation on the change in the structure of amorphous alloys Co₆₇Fe₇Si₁₂B₉Nb₅, Al₈₇Ni₈Y₅, Al₈₈Ni₆Y₆, Al₈₇Ni₈Gd₅, Al₈₇Ni₈La₅, Zr₅₀Cu₁₅Ti₁₆Ni₁₉ obtained by melt quen-ching has been studied. It has been established that both heat treatment and deformation lead to the for-mation of a heterogeneous structure, while structure inhomogeneities can be due to formation the regions both with different concentrations of components (during heat treatment) or/and with different density (free volume concentration). At the early stages of crystallization, the phase composition of the emerging struc-ture depends on the type of impact on the amorphous structure and processing parameters (temperature, type and degree of deformation). The sizes of nanocrystals and the fraction of the nanocrystalline component depend on the prehistory of the sample.

The results of a comprehensive experimental study of the influence of the pulsed magnetic field of the amplitude strength on the properties and characteristics of an Al–Si–Cu–Fe aluminum alloy during aging are presented. Data are presented on the modes of thermomagnetic treatment and the results of measurements of the microhardness, lattice parameter, and fine structure parameters of the alloy aged at a temperature of 175°С for 4 h in a pulsed magnetic field with a strength amplitude of 79.6–557.2 kA/m and in its absence. The main regularities of changes in the structure and properties of the metal alloy during annealing are formulated.

The processes of evolution of the structure and surface morphology of Al₈₇Ni₈La₅ and Fe₇₆Si₁₃B₁₁ amorphous alloys under deformation have been studied. It is shown that the deformation occurs through the formation and propagation of shear bands, which form steps when they reach the surface. The formation of nanocrystals in shear bands was noted. It is shown that steps on the surface are formed under the combined action of several elementary shear bands. Shear bands have a variable thickness in the range from 5 to 20 nm. An elementary step has a thickness of about 15 nm. Shear bands can be combined into zones. The transverse size of the zones is about 1 μm. The formation of nanocrystals in zones can lead to anisotropy in the orientational position of nanocrystals in an amorphous matrix. With an increase in the degree of deformation, nanocrystals are formed not only in shear bands, but also in areas adjacent to them. There is a difference in the kinetics of the formation of nanocrystals in an alloy based on aluminum and iron.

Perlite is one of the main structural constituents of carbon and low-alloy steels. In it, between the bcc ferritic and orthoboric cementite phases of Fe₃C, the orientational relation (OR) of Bagaryatskii, Isaichev, and Pitch can be observed. The first two, which are close to each other and are not always, repeated in the experiment, predominate in low-temperature pearlite, which has the highest strength. In this study, the simulation "from first principles" by the DFT method in the WIEN2k software package of the structure and energy of coherent α-Fe/Fe₃C interfaces was carried out. The supercells were subjected to structural and volume optimization. Calculations of the surface energy of the interphase boundaries gave the values of 0.383 J/m² for the Bagaryatskii OR and 0.594 J/m² for the Isaichev OR. This agrees well with the existing experimental values and the results of other molecular dynamics and first-principles calculations. The difference in surface energy can play a significant role for low-temperature pearlite with a small thickness of ferrite and cementite plates and a large area of interfacial boundaries per unit volume.

The effect of post-growth isothermal annealing in vacuum and in air on the optical properties of Ca₃TaGa₃Si₂O₁₄ crystal samples of Z and X-cuts has been studied. Spectral dependences of transmission coefficients were measured in the wavelength range (240–700) nm taking into account anisotropy and dichroism. On the Z-cut samples in the initial state an absorption band at λ = 360 nm in the ultraviolet range is observed, in the visible region – two absorption bands at λ = 460 nm and λ = 605 nm. Additionally, a band at λ = 290 nm was observed on the X-cut samples. When the sample was rotated around the direction of the light beam by 90 degrees, a change in the intensity of the absorption bands was observed. Annealing in vacuum leads to a decrease in the intensity of the absorption bands in the near ultraviolet and visible range, except for the absorption band at λ = 605 nm. Annealing in air leads to the opposite effect – an increase in the intensity of the absorption bands, except for the band λ = 605 nm. The value of the anomalous birefringence of the samples was estimated by the Mallard method. The degree of linear dichroism is calculated. It is shown that the degree of dichroism decreases as a result of annealing in vacuum, and increases during annealing in air.

The influence of size effects on the properties of a hexagonal boron nitride (h-BN) monolayer containing C_BV_N, N_BV_N, and O_BO_BV_N defects has been studied by first principles methods. These defects are potentially capable of generating single photons in quantum optics and quantum information devices. Size effects here mean the dependence of the studied model properties on the simulated fragment size of the 2D structure under periodic boundary conditions. Physically, this means that the properties of a monolayer depend on the distance between defects. This dependence allows us to judge how strongly the defects interact with each other and whether they interact at all. For technical applications, the characteristics of the band structure (band gap, spectrum and density of electron states induced by the defect in the band gap) and the atomic structure of the defect (defect formation energy, geometry in the equilibrium configuration), which form this band pattern, are important. In this work, these properties are studied by using the density functional theory with the basis of atom-like functions (SIESTA package) and plane waves (VASP package). The results obtained using both packages are consistent with each other. It has been established that the defects can be considered non-interacting, when the distance between them is ten unit cell parameters.

The formation of misoriented substructures in plastically deformable metal materials has been theoretically studied. Expressions are obtained for the intensity of accumulation of low-angle and high-angle misorientation boundaries. Within the framework of a mathematical model of shear plastic deformation and hardening, numerical calculations of the dependences of the average characteristics of a defective medium on the degree of deformation under conditions of uniaxial compression with a constant strain rate at room temperature are performed. It is shown that the intensity of generation of low-angle tilt walls depends significantly on the scenario of changes in the density of jogs on the screw segments of dislocation loops emitted by dislocation sources. The main mechanism for the formation of low-angle walls is the rearrangement of clusters of edge segments of dislocation loops into tilt dislocation walls under the influence of flows of interstitial atoms generated by moving screw segments. It is assumed that low-angle walls merge into one until the total misorientation angle of the merged walls reaches a critical value of about 10°, after which the distance between dislocations in the wall decreases to the corresponding critical value and further penetration of individual dislocations into the wall becomes impossible. The expression for the intensity of the formation of high-angle boundaries was obtained as a consequence of the continuation of the work of dislocation sources and the formation of clusters of low-angle walls, the total energy of which is higher than the energy of an equilibrium high-angle boundary at the same misorientation.

The effect of bending of reflection planes in crystals on the propagation of an anomalous wave in X-ray diffraction has been studied by numerical simulation methods. The bending sign of the reflection planes was found to affect radically the propagation of the X-ray wave field in the crystal. The Bormann effect was shown to be suppressed at certain bending parameters.