Том 120, № 11 (2019)

Based on the Mie–Lennard-Jones interatomic pair potential and the Einstein crystal model, the thermal equation of state and the pressure dependences of the thermophysical properties of niobium are obtained. The pressure dependences of the Debye temperature, the first, second, and third Grüneisen parameters, isothermal compression modulus, isochoric and isobaric heat capacity, thermal expansion coefficient, and the pressure derivatives of these parameters along the 300 and 3000 K isotherms are studied. The calculations showed good agreement with experimental data. Based on the results obtained, the pressure dependence of the melting point of niobium and its pressure derivative are calculated.

The absorption of electromagnetic radiation by a composite based on bimetallic nanoparticles with a “core–shell” type of structure has been analyzed using the Maxwell–Garnett theory. Expressions have been obtained for the real and imaginary parts of the dielectric function of a two-layered particle in the limiting cases of “thick” and “thin” shells. It has been established that the presence of two metals in the composition of the inclusions leads to a splitting of the maxima and minima in the frequency dependences of the dielectric function and of the coefficient of absorption of the nanocomposite. The frequency dependences of the real and imaginary parts of the dielectric function and of the coefficient of absorption of the composite with bimetallic nanoparticles of different metals have been calculated. An essential influence of both the geometric characteristics of the particles-inclusions and of their composition on the optical properties of the composite has been revealed.

Features of motion and of the dynamic rearrangement of a domain wall (DW) have been studied in a thin film placed in an external magnetic field perpendicular to the surface of the film. It has been shown that in fields less than some critical magnitude the motion is quasi-stationary, and in overcritical fields the movement becomes periodic. A backward motion effect was observed in some time intervals. Periodic changes of the polarity of the magnetization distribution were detected. The maximum velocities of the forward and backward motion have been shown to be identical. The coincidence of the graphs of the velocities in the half-periods with the opposite polarity was revealed. The magnetization distributions observed upon the forward and backward motion, as well as upon the change of the polarity, were found to be spatially symmetric with respect to one another. The relationship between the graphs of the full energy of the DW and its velocity has been studied. It has been shown that the maximum and minimum of the energy correspond to the zeroes of the velocity.

Using numerical simulation in the CAFÉ module of the ProCast commercial program, a study was performed of the competitive growth of grains in the seeding unit of the setup to obtain single crystal castings of nickel-base heat-resistant alloy in the process of directional crystallization using the Bridgman method. Using the example of a flat crystal selector, the mechanism of selection of a single grain from several grains with a close axial and arbitrary azimuthal orientation has been considered. It has been found that a significant role in the grain selection is played by the position of the grain in the input section of the crystal selector system. The initial growth advantage comes to those grains that lie in the zone of the crystallization front, from which the way for an unimpeded growth along the crystallization channel is opened. The position of this zone changes as the front moves in the curvilinear channel of the crystal selector. The main tool for selecting a single grain from a variety of closely oriented grains is a change in the position of the zone that is favorable for unimpeded growth. The continuous cyclic change of the zone of favorable growth, which occurs while the grain grows in the helicoid crystal selector, leads to a rapid selection of one grain. In a flat zigzag-shaped crystal selector, the zone of the favorable growth changes only a limited number of times, so this crystal selector is less efficient. The described mechanism of grain selection is applicable in the case of crystal selectors with an angle between the channel axis and the vertical axis Z of no more than 45°, i.e., when the primary axes of dendrites are formed in the crystallographic direction [001].

The structure, chemical and phase compositions, and hardness of Fe–Ni–Ti–C–B composites prepared by self-propagating high-temperature synthesis (SHS) were studied. It is shown that, in using Fe, Ni, Ti, C, and B₄C powders as the starting materials, which are charged into a steel tube, an integrated multilayer plate consisting of steel shell and composite forms in the course of SHS and subsequent hot compacting. The solid solution of Ni and Ti in γ-Fe is the composite matrix; the TiC, TiB₂, Fe₂B, Ni₃Ti, and NiTi compounds are the strengthening phases. The hardness of composites reaches 57–62 HRC. The internal surface of steel shell is strongly jointed with the composite at the expense of the diffusion of synthesis products into steel.

The structure of the contact lines and of the thermomechanically affected zone of welded joints of medium-carbon steels obtained by rotary friction welding have been studied using metallography and scanning electron microscopy supplemented with X-ray electron microprobe analysis. The results of the microhardness distribution over the cross section of the welded joint are presented. The phase transformations realized at each stage of the technological process of welding in the regions subjected to the thermodeformation influence have been analyzed. The results of the uniaxial tensile and impact bending tests supplemented by the fractography of the fracture surface are presented.

Radiation and structural-phase transformations in Fe–16% Cr–15% Ni–3% Mo austenitic steel in the initial and the titanium-alloyed states were studied by measuring the residual electrical resistance after irradiation with 5-MeV electrons and isochronous annealing. Vacancies migrate at temperatures below 320 K and form vacancy clusters upon irradiation. Due to the migration of vacancies during irradiation and upon the dissociation of vacancy clusters during isochronous annealing above 400 K, the separation of the solid solution occurs, which is accompanied by an increase in the electrical resistance. At temperatures above 700 K, the state of the steels, non-irradiated among them, approaches equilibrium due to thermal diffusion. In this case, all the dependences of the electrical resistance on temperature for each alloy irradiated at different temperatures or non-irradiated converge to a common dependence in the region of high temperatures. Doping with titanium inhibits ordering. Intermetallic compounds of Ni₃Ti composition were formed thermally upon annealing above 850 K in the alloys doped with titanium, which is accompanied by a decrease in the electrical resistance to below the initial level.

Isothermal hot compression tests were conducted on the 6063 aluminum alloy using a Gleeble-3810 thermal simulator at four different strain rates (0.01, 0.1, 1, and 10 s^–1) and five different temperatures (300, 350, 400, 450, and 500°C). Based on the constitutive relationship to process the experimental data, processing maps were produced to evaluate the efficiency of power dissipation (η) and identify regimes with flow instability. Processing maps were produced for two regions with relatively high η at a strain of 0.6, namely (300–320)°C/(0.01–0.02) s^–1 and (400–500)°C/(0.01–1) s^–1. There were also two unstable regions at (300–325)°C/(0.06–1.5) s^–1 and (350–500)°C/(3–10) s^–1. The microstructures observed by optical microscopy and electron back-scattered diffraction maps indicated that the deformed samples only underwent dynamic recovery under deformation conditions of (300–320)°C/(0.01–0.02) s^–1, while at 500°C/0.01 s^–1 the samples showed a high degree of dynamic recrystallization and then produced new equiaxed fine grains. At high strain rates, the precipitates had a pinning effect on dislocations, leading to stress concentration. Local plastic deformation occurred, resulting in thermoplastic instability. Therefore, the optimum processing conditions for the 6063 aluminum alloy determined from true stress-strain curves, processing maps, and microstructural analysis were 500°C/0.01 s^–1.

An estimate of the vacancy migration energy in alloys is obtained. Since atoms of different substitution elements need different energy to hop to a neighboring vacant site, the vacancy migration energy is usually evaluated using some averaged characteristic. Based on the data of previously conducted dilatometric experiments, the vacancy migration energies of Ni, Fe, and Cr in the ChS68 and EK164 steels are determined and used to calculate the pore growth rate in these steels under neutron irradiation at the beginning of the unsteady swelling stage.