Vol 117, No 3 (2016)

The probabilities of the localization of positrons in monovacancies of Al and Cu have been calculated as functions of the energy and temperature. The vacancy was simulated by a void with a radius equal to the radius of the Wigner—Seitz cell in the model of stable jellium. Using the Fermi—Dirac golden rule for transitions, the formula for the rate of positron trapping by a vacancy has been derived as the function of the positron energy. For the thermalized positrons, the rate of localization near the triple point proved to be, on the order of magnitude, close to the rate of annihilation. Within the framework of our previously proposed models, the contribution of vacancies to the work function of electrons and positrons has been demonstrated based on the example of Al. The physical situations where the vacancy effect can manifest have been considered.

A new alloy intended for single-crystal permanent magnets has been suggested. The new alloy has been designed based on the well-known Fe−Co−Ni−Cu−Al−Ti system and contains to 1 wt % Hf. The alloy demonstrates an enhanced potential ability for single-crystal forming in the course of unidirectional solidification of ingot. Single-crystal permanent magnets manufactured from this alloy are characterized by a high level of magnetic properties. When designing the new alloy, computer simulation of the phase composition and calculations of solidification parameters of complex metallic systems have been performed using the Thermo-Calc software and calculation and experimental procedures based on quantitative metallographic analysis of quenched structures. After the corresponding heat treatment, the content of high-magnetic phase in the alloy is 10% higher than that in available analogous alloys.

In this work, the process of the formation of defects and their clusters in collision cascades has been investigated in molybdenum by the molecular dynamics method. We have obtained results on the number of arising defects, the fraction of defects in clusters, and cluster-size distribution. Their dependence on the energy of primary knocked-on atom and temperature of the material has been studied. A comparison with calculations using the SRIM program and NRT model has been made. The effect of annealing defects after the development of cascades on the number of arising defects has been examined.

The purification of graphene from a lead film by irradiating the target with a beam of Xe₁₃ clusters with an energy of 20 eV at different angles of incidence has been studied. Using the method of statistical geometry, it has been shown that, before the bombardment, the double-layer lead film adsorbed on graphene had an irregular structure. Graphene contained divacancies, the edges of which, as well as the edges of the graphene sheet, were hydrogenated. The complete removal of lead from graphene was achieved at the angle of incidence of Xe₁₃ clusters equal to 45°. A major part of the film was separated from graphene in the form of an island, which, after separation, was transformed into a three-dimensional structure. The stresses present in the graphene sheet changed in the course of bombardment, but the stressed state retained after the bombardment was terminated. The type of the distribution of stresses in graphene indicates the absence of enhancement of the stressed state in the course of bombardment. The bombardment at angles of incidence of clusters less than 75° substantially enhances the roughness of graphene. The bombardments in the entire range of the angles of cluster incidence (0°–90°) have resulted in no significant damages in the hydrogenated edges of the graphene sheet.

The heat-transfer behavior of the interface of Flyer plate (or Base Plate) has great influence on the microcosmic structures, stress distributions, and interface distortion of the welded interface of composite plates by explosive welding. In this paper, the temperature distributions in the combing zone are studied for the case of Cu/Fe composite plate jointed by explosive welding near the lower limit of explosive welding. The results show that Flyer plate (Cu plate) and Base Plate (Fe plate) firstly almost have the same melting rate in the explosive welding process. Then, the melting rate of Cu plate becomes higher than that of Fe plate. Finally, the melt thicknesses of Cu plate and Fe plate trend to be different constants, respectively. Meanwhile, the melting layer of Cu plate is thicker than that of Fe plate. The research could supply some theoretical foundations for calculating the temperature distribution and optimizing the explosive welding parameters of Cu/Fe composite plate to some extent.

Variations in the reduced integral intensities of diffraction maxima in X-ray diffraction patterns taken for the Pd–5.3 at % In–0.5 at % Ru alloy foil, which was subjected to electrolytic saturation with hydrogen and subsequent prolonged relaxation at room temperature and atmospheric pressure, have been analyzed. The degree of texture of the sample has been found to decrease substantially, and first-class defects in the alloy matrix dominate.

The processes of the fracture of 40Kh and U8 steels under cyclic dynamic compression are studied. It has been found that the main cause for the fracture of the cyclically compressed specimens is the propagation of cracks due to the effect of residual tensile stresses, which arise near the tips of the cracks at the stage of the unloading of the specimens. The growth rate of a crack has the maximum value at the initial stage of its propagation in the vicinity of the stress concentrator. As the crack propagates deep into the specimen, its growth rate decreases and depends only slightly on the real cross section of the specimen. The model of the process of the fatigue fracture of the steels under dynamic loading by a cyclically varied compressive force is proposed. It has been found that the high fatigue endurance is provided by tempering at 200°C for the 40Kh steel and at 300°C for the U8 steel.

The effect of boron on the microstructure, microhardness, and kinetics of low-temperature decomposition of martensite in the 40Kh and 30KhRA steels quenched at different cooling rates has been studied. It has been shown that the low-temperature decomposition of martensite in the boron-containing steel after quenching from 1050°C at a high cooling rate is strongly decelerated at the initial stage of decomposition. At low quenching cooling rates, the martensite decomposition in the steels under investigation is characterized by a similar kinetics.

The effect of plastic deformation that occurs in the zone of the sliding friction contact on structural transformations in the 12Kh18N9T austenitic steel subjected to subsequent 1-h oxidation in air at temperatures of 300–800°C, as well as on its wear resistance, has been studied. It has been shown that severe deformation induced by dry sliding friction produces the two-phase nanocrystalline γ + α structure in the surface layer of the steel ~10 μm thick. This structure has the microhardness of 5.2 GPa. Subsequent oxidation of steel at temperatures of 300–500°C leads to an additional increase in the microhardness of its deformed surface layer to the value of 7.0 GPa. This is due to the active saturation of the austenite and the strain-assisted martensite (α′) with the oxygen atoms, which diffuse deep into the metal over the boundaries of the γ and α′ nanocrystals with an increased rate. The concentration of oxygen in the surface layer of the steel and in wear products reaches 8 wt %. The atoms of the dissolved oxygen efficiently pin dislocations in the γ and α′ phases, which enhances the strength and wear resistance of the surface of the 12Kh18N9T steel. The oxidation of steel at temperatures of 550–800°C under a light normal load (98 N) results in the formation of a large number of Fe₃O₄ (magnetite) nanoparticles, which increase the resistance of the steel to thermal softening and its wear resistance during dry sliding friction in a pair with 40Kh13 steel. Under a heavy normal load (196 N), the toughness of 12Kh18N9T steel and, therefore, the wear resistance of its surface layer decrease due to the presence of the brittle oxide phase.