卷 62, 编号 8 (2019)

Using the methods of transmission electron microscopy, new aspects of formation of reorientation nanobands with partial involvement of nondislocational deformation mechanisms are investigated in nickel nanocrystals under the conditions of its severe plastic deformation by high-pressure torsion in Bridgman anvils: local reversible (FCC→BCC→FCC) transformations of the martensitic type and quasi-viscous mass transfer by the flows of nonequilibrium point defects in the fields of high local pressure gradients. The features of disclinational structure and elastically stressed state at the nanoband propagation front are studied. A theoretical analysis of the rate of plastic deformation via the mechanisms of quasi-viscous mass transfer by the flows of nonequilibrium point defects is performed. A possibility of simultaneous realization of the martensitic and quasi-viscous deformation modes at the front of nanoband propagation is established. An analysis of the conditions and mechanisms where these modes are involved is performed as a function of the type of point defects (vacancies and interstitial atoms), deformation temperature, and peculiarities of disclination structure and elastically stressed state.

Studies of the evolution of the structural-phase state and changes in the mechanical properties of the ultrafine-grained alloy VТ22 after annealing in the temperature interval 773–1073 K have been carried out. It has been shown that after annealing at 773 K practically no decrease in the density of deformation defects and practically no changes in the average size of the elements of the grain-subgrain structure and the mechanical properties of the alloy are observed. However, the structural-phase state of the alloy under these conditions is thermally unstable. There take place a generation of new grains with sizes less than 0.1 μm and growth of individual grains up to sizes on the order of 1 μm, and also a change in the volume fractions of the α- and β-phases. At higher annealing temperatures, there is observed a decrease in the density of deformation defects, growth of existing grains, a transition of the grain boundaries to a more equilibrium state, and, as a consequence, a substantial deterioration of the mechanical properties at room temperature. Under these conditions, α–β-phase transformations actively develop, leading to an increase in the volume fraction of the β-phase with increasing temperature. Estimates of the activation energy of grain growth were performed. It is shown that its value is 145 kJ/mol.

The regularities in the inhomogeneous development of plastic deformation at the front of the Lüders band at the yield plateau in Hadfield steel single crystals are considered. It has been established that the Lüders front moves in jumps under these conditions. This character of motion is associated with the rearrangement of the inhomogeneous distributions of the components of the plastic distortion tensor components at the deformation front. A plausible estimate of the frequency of oscillations in the development of the Lüders front has been obtained.

The stage-like character of the stress-strain curves and microstructure in the fracture zone of coarse-grained and ultrafine-grained specimens of the VT1-0 and Zr–1Nb alloy specimens under quasistatic loading are investigated using the temperature curves obtained by the method of IR-imaging. New experimental data are obtained, which provide evidence on a considerable influence of the ultrafine-grained state on the evolution of plastic deformation and fracture in the VT1-0 and Zr–1Nb alloys.

The paper considers the current state of the problem of choosing methods for surface hardening of metallic materials aimed at ensuring advanced tribological characteristics of friction pairs. Several technological processes of surface engineering are analyzed in the paper. The information on the macro- and microstructure of coatings, obtained by ion beam doping, thermochemical treatment, and vapor and gas deposition of coatings by PVD and CVD technique, is considered. The data on the wear characteristics of modified layers obtained by various techniques under dry and boundary friction conditions are presented.

The influence of the characteristics of particle inclusions and the surface microgeometry of the substrate on the conditions of formation of a stable transfer film under friction of a polymer nanocomposite are analyzed. The investigations have been performed with the help of cellular automata, within the framework of which the profile of the counterbody surface, the adhesion properties of the matrix material, and the size of the nanofiller particles are taken into account. It is shown that to endow a hybrid polymer nanocomposite with low-friction properties, it is preferable that the nanofiller consist of particles whose sizes are comparable to the characteristic size of the microprofile of the substrate. Estimates are made of the shape and size of cavities in the surface of the counterbody facilitating the conditions of formation of a stable transfer film of SiO₂ particles.

The paper deals with heat-reflecting ZrB₂–20% SiC ceramic composite and heat-reflecting ZrB₂–20% SiC composite laminate with ZrO₂ addition, the amount of which varies from 0 to 100%. Their properties and behavior are studied under the conditions of three-point bending and diametral compressive tests. The increased amount of ZrO₂ in the composite layers notably reduces the elastic modulus and increases the thermal-expansion coefficient. It is found that in the composite laminate layer adjacent to that with lower thermal-expansion coefficient and in the layer adjacent to that with higher thermal-expansion coefficient, compressive and tensile residual stresses appear, respectively. The hardness in the region of compressive stress is higher than in the region of tensile stress. The texture of the broken specimen surface indicates that the main crack bifurcation occurs at the interface of the layers with 30 and 70% ZrO₂ content and the greater difference in the thermal-expansion coefficient, regardless of the loading conditions of three-point bending. The fracture energy of ZrB₂–SiC–ZrO₂ composite laminate significantly exceeds that of ZrB₂–20% SiC ceramic composite.

The paper presents the fabrication of Ti–6Al–4V alloy specimens using two operating modes of the electron beam additive manufacturing (EBAM). The structure, phase composition and microhardness of the obtained alloy specimens are investigated. The EBAM process includes a deposition of Ti–6Al–4V wire onto a substrate comprising of VT1-0 (grade 2) titanium alloy and 12Kh18N10 (AISI 321) stainless steel. It is shown that at a high electron beam current, the height and width of the β-phase columnar grains are lower than at a low electron beam current. This phenomenon is discussed in terms of stabilization of the temperature gradient and the increased cooling rate during the building process. This phenomenon is caused by the formation of Fe₂Ti, FeTi and Cr₂Ti intermetallic phases in the diffusion bonding appeared between the titanium and stainless steel plates.

The data on the influence of thermomechanical treatment modes on characteristics of the short-term strength and plasticity of vanadium alloys of different systems (V–Ti–Cr, V–Zr–C, V–Cr–Zr, V–Cr–W–Zr, V–Cr–Ta–Zr) are generalized. It is shown that an application of a modified mode ensures an appreciable increase in the short-term strength at room temperature and elevated temperatures, while maintaining an acceptable plasticity. The principal mechanisms of metastable carbide transformations into oxicarbonitride phase particles with phase-forming elements participation and the conditions of their realization are discussed.

The paper considers the controlled bulk synthesis of composite in a cylindrical reactor with regard to the main control parameters, including the temperature distribution over the reactor volume, different properties of reagent and reactor, and two combined synthesis stages. The first stage is exothermal synthesis of oxide inclusions and the second is the matrix formation. It is shown that for special cases of the controlled synthesis, nearly adiabatic conditions can be created as well as a standard thermal explosion in the conditions of heat exchange with the environment, the dynamic initiation of reaction at various heat rates, and a synthesis in cooling conditions with the formation of a non-uniform composition. The synthesis process is implemented in the experimental conditions.

The deformation and thermal action on the microstructure and mechanical properties of a stable austenitic Cr-Ni stainless steel is investigated. It is shown that under deformation conditions packets of microtwins and bands of localized deformation with the inner fragmented structure are formed, where the fragments are of the submicro- and nanocrystaalline scales with low- and high-angle misorientation boundaries. These features of microstructure ensure high yield-point values ≈1100 MPa at a relative elongation of ≈6–7%. Short-term (to 150 s) high-temperature (850°С) annealing of the deformed structure gives rise to a local development of the processes of polygonization and recrystallization in the regions of strain localization bands. As a result of such annealing, packets of microtwins, strain localization bands, polygonized subgrains and recrystallized grains of primarily submicron dimensions are observed in the steel structure. The resulting structural states ensure the yield strength values up to 740 MPa at the relative elongations ≈20–28%. The physical processes taking place in the steel under the experimental deformation and annealing conditions are discussed.

Nanocolloids, obtained by pulsed laser ablation (Nd:YAG laser, 1064 nm, 7 ns, 150 mJ) of metallic Sn in distilled water and also in solutions of hydrogen peroxide and nitric acid, were dried and subjected to heat treatment at different temperatures up to 800°С. It has been shown that addition of H₂O₂ or HNO₃ has an effect not only on the size characteristics and structure of the initial nanoparticles, but also on the process of formation and the final characteristics of SnO₂ under annealing. By the method of powder x-ray diffraction it was established that in the case of pulsed laser ablation in water and in a solution of nitric acid, the initial particles contain the phase SnO, but for annealed sample obtained by ablation in HNO₃, an intermediate orthorhombic phase of SnO₂ is formed. Additional studies using Raman spectroscopy and thermal analysis made it possible to determine the presence of tin hydroxide in the initial samples and formation of intermediate forms of its oxides, SnO_x, upon annealing.

As a rule, a discussion of physical properties of crystals is accompanied by far from simple mathematical calculations based on algebraic expressions in tensor and matrix notations. Such an approach caused by the nature and uniform presentation of properties of crystalline materials makes practical calculations of their specific characteristics and parameters very difficult. By an example of the titanium nickelide crystals, it is shown that the anisotropy coefficient of elastic properties of the cubic syngony crystals, which is equal to the ratio of the extreme values (minimum and maximum) of the shear modulus, is close to the ratio of the extreme values of Young's modulus. Some variants of describing the elastic anisotropy of cubic crystals using a series of dimensional and dimensionless independent indicators are considered. It is shown on a concrete example that they can give significantly different results. Methods of visual interpretation of the elastic properties anisotropy using the corresponding characteristic surfaces and their cross sections are discussed. It is noted that the characteristic surface of the Young's modulus of normal elasticity is the most accessible for construction, although it is not a complete characteristic of the anisotropy of elastic properties of cubic crystals. A method is proposed for visualizing matrices of elastic constants of crystals using the MatLab application package, which provides visual information on the ratio of the values of matrix elements. Single crystals of titanium nickelide TiNi, widely used in various fields of science, technology, and medicine and often discussed in the literature, are considered as an example of calculating the extreme values and parameters of anisotropy, as well as constructing characteristic surfaces and their cross sections.