Том 54, № 15 (2018)

The temperature dependences of the specific resistance and Hall coefficient of high-quality synthetic boron-doped diamond single crystals grown via a high-pressure high-temperature method are studied. The concentration of acceptors in the (001) cut plates was varied in a range of 2 × 10¹⁵–3 × 10¹⁷ cm^–3 by varying the concentration of boron in the growth mixture (0.0004–0.04 at %). Thin rectangular plates with the uniform concentration of boron and free from extended structural defects are cut out by a laser after the X-ray topography and mapping of UV luminescence. The concentrations of donors and acceptors in the samples are calculated from the data of the Hall effect and capacitance–voltage characteristics. The obtained results correlate with the concentration of boron in the growth mixture. The minimum compensation ratio of acceptors with donors (below 1%) is observed in the crystals grown with the concentration of boron in the growth mixture of 0.002 at %. The ratio increases when the amount of boron is increased or decreased. The samples grown at such a concentration of boron have the maximum mobility of charge carriers (2200 cm²/(V s) at T = 300 K and 7200 cm²/(V s) at T = 180 K). The phonon scattering of holes dominates throughout the range of temperatures (180–800 K), while the scattering by point defects (neutral and ionized atoms of the impurity) is insignificant. The diamond crystals which are grown from a mixture containing 0.0005–0.002 at % boron and have perfect quality and a lattice mechanism of scattering can be considered as a reference semiconductor.

Film samples of poly(vinylidene fluoride-trifluoroethylene) copolymer containing 2% of carbon nanotubes were synthesized. The temperatures of the ferroelectric phase transition and the value of permittivity at the frequency of 1 MHz were determined. The surface was visualized using scanning probe microscopy; the values of the effective piezoelectric coefficient were obtained. It was shown that incorporation of carbon nanotubes into the polymer matrix improves the values of the permittivity and piezoelectric coefficient of the polymer.

Advantages of fabricating precision optical coatings by magnetron sputtering with a gas discharge powered from a medium-frequency current-variation supply unit are considered. The significance of selecting optimal characteristics and operating modes of the power supply sources of the magnetron sputtering system (MSS) for fabrication of high-quality optical coatings is justified. Using the developed magnetron sputtering facility that comprises a multimode power supply unit of the MSS, samples with thin TiO₂ films were fabricated at different recurrence frequencies f_mag of the current pulses transmitted to the MSS and under other identical sputtering conditions. The samples were tested by laser ellipsometry, atomic force microscopy, X-ray diffractometry, and X-ray reflectometry. The influence of  f_mag on the functional properties of the TiO₂ films, namely, the refractive index, density, and roughness, is shown.

A brief review of the methods for the study of residual process stresses (RSs) in the elements of structures and specimens is given. The possibilities and the fields of the application of nondestructive testing of RSs are indicated. Destructive experimental and calculation methods for the study of two-dimensional and three-dimensional nonuniform fields of RSs in spatial structures, which are based on the interpretation of experimental data as an inverse problem of elasticity theory, are particularly noted. It is recommended to use optical-digital methods for the recording of displacement fields in order to obtain significant collections of experimental information necessary in this case, which are caused by the formation of the cuts of various configurations in the object under study.

In this paper, we studied the distribution of stresses and deformations in a deformed metal under the indents obtained by indentation of a spherical indenter with a different degree of loading. For this purpose, the hardness method and the finite element method are used. These methods are shown to complement each other and their combined use gives more complete information on the values of stresses and strains in various zones of the deformed metal volume.

Special features of the quantitative assessment of the Bauschinger effect in magnesium alloys with asymmetrical deformation behavior are considered. It is found that the Bauschinger effect is associated with the different contribution of detwinning to the overall deformation, and calculation of the quantitative parameters of this effect by stress and deformation criteria gives close results. In this case, the asymmetrical behavior of the magnesium alloys at strain and compression exerts similar influence both on stress of the initial plastic deformation (compressional yield strength) and on the contribution of the deformation detwinning to the overall plastic deformation. Parameters of the Bauschinger effect during condensation of the magnesium alloys are close to zero; i.e., in this case, the effect is hardly evident; and inelasticity, responsible for that, is associated with the special features of detwinning just under strain. Comparison of the Bauschinger effect for two alloys—industrial ZK30 and advanced ZE10 with the rare earth elements—counts in favor of the latter in all cases.

The damage accumulation patterns under one- and two-frequency loading modes were studied on the basis of deformation and energy failure criteria under elastoplastic cyclic deformation. It is demonstrated that the change in fatigue life upon applying a high-frequency component of strains (deformations) to the basic low-cycle process can be determined from the sum of fatigue damage components from basic and applied deformation or the observed coefficient of breaking cycle number decrease, depending on the relations between frequencies and amplitudes of interacting cyclic processes. With regard to this, the components of damage due to cyclic deformations are related to the energy characteristics of the deformation processes studied, including the mechanical energy expended on the deformation process, the thermal energy released (determined by measuring the self-heating temperature change), and also the energy absorbed before the fracture.

In this paper, we studied the microstructure and mechanical properties of thin-sheet TRIP steel VNS9-Sh obtained by cold rolling of a hot rolled sheet for several transitions with intermediate heat treatment and supplied in the form of a strip with a thickness of 250–260 μm. The structure of the TRIP steel is deformation martensite and metastable hardened austenite. On the basis of the average grain size (35 μm) and the strip thickness, the optimum loading of the Vickers pyramid equal to 1 kgf (9.81 N) was determined when determining the hardness. Under this load, the indent covers several grains of steel and the ratio of the tape thickness to the indent depth is at least 20, which excludes the influence of the substrate (the instrument stage or other equipment) on the hardness values. To evaluate other mechanical properties, a kinetic (instrumental) indentation by a spherical diamond indenter with a radius of 0.2 mm was used. A methodolgy for determining the normal elastic modulus, yield stress, and time resistance is proposed. It is shown that the maximum deviation of the values of the indicated mechanical characteristics found by instrumented indentation from the values of these characteristics determined by the sample tension test did not exceed ±7%.

Known methods for assessing the crack resistance of very hard or strengthened surface layers of materials by using a pyramid indenter are intended for the cases of the formation of radial cracks around the indent. However, at indentation of a pyramid into some types of hardening coatings, for example, made of titanium nitride, annular rather than radial cracks are formed around the indent. For this case of crack formation, we proposed to use the kinetic diagram of indentation for determination of the specific energy of elastoplastic deformation that is needed for the formation of the first visible crack. This energy can be used to compare the ability of the coating to resist crack formation of any kind.