Abstract: The necessity and urgency of studying plastic deformation of metals is determined by both scientific significance of the problem and requirements of practice. So the objective of this work is investigation of aluminum alloy creep under action of static magnetic fields. This subject matter is of practical importance for engineering since the parts of engineering constructions are subject to various loads which may lead to their damage or even creep rupture. Based on the experiments performed by us, it is found that creeping increases under stable magnetic field; the main features appear at the first creep stage. Investigation of these processes will help to predict time dependence of creep strain and its rate as well as durability and plasticity at destruction.
Abstract: It was achieved a visual representation of information about the crystallization process in the multidimensional space, which creates prerequisites for the development of software systems to solve a wide class of problems. With the geometric interpretation Minkowski space-time, quasi-Lorentz and Einstein's concept concerning the concept of giving time physical sense, simulated the process of formation of crystals in the four-dimensional space. The 4D model space combines the physical three-dimensional space of the factors affecting the formation of crystals, and time. Visualization of the crystallization process in spacetime plays an important role, as having great cognitive and probative value, and contributes to a better understanding of crystallization processes, creates conditions to control the properties of materials in the process of crystallization.
Abstract: The authors present the results of investigations of degradation processes that occur in the structure of heat-resistant coating of the Si-TiSi2-MoSi2-B-Y system in hypersonic flows of air plasma. It is found that coating operating capacity at surface temperatures Tw ≤ 1820÷1830°C is provided by the structural-phase state of its microcomposite main layer and formation on the coating surface of a heterogeneous passivating protective film. It is based on borosilicate glass reinforced by rutile microneedles. The mechanism of coating destruction at Tw ≥ 1850÷1860°C is erosion loss of oxide film as well as generation and growth of gas-filled cavities at the "coating main layer–oxide film" interface. As the pressure of saturated vapor of gaseous oxidation products (SiO, CO, MoO3 and B2O3) exceeds that of the ambient, the oxide film integrity is disrupted and oxidation process becomes active. The rates of erosion loss and sublimation grow as operating temperature increases and ambient pressure decreases.
Abstract: The substances move in conductors owing to drift of ions that occurs due to momentum exchange at collisions between the conductive carriers and atomic lattice. This effect is substantial at high-density direct currents, e.g., in power electronics. Therefore, the assigned subject matter is topical. The aim of this work is investigation of the effect of magnetic fields on electromigration processes of liquid inclusions in aluminum. We performed an analysis of formation and electromigration of molten Al-Si inclusions in silicon and aluminum crystals. It was found that molten inclusions 50-800 μm in size are formed in the studied system by contact melting in the 850-920 K temperature range. The electro-stimulated migration of inclusions along the electric lines of force at current densities j 4106 A/m2 was also established. From the dimensional dependence of specific velocity of travel w/j of molten Al-Si regions in silicon and aluminum, we made a conclusion concerning mechanisms of molten regions travelling. These are melting and crystallization at interphase boundaries due to thermoelectric phenomena and electromigration of atoms in the inclusion bulk. The numerical values of effective charges of Al and Si atoms in Al-Si melts as well as Peltier coefficients of the crystal-melt system were determined experimentally. It was found that preexposure of aluminum alloy (with iron concentration of ~0.6%) in a static magnetic field (В = 0.7 T) leads to changing of dimensional dependence of migration velocity of inclusions (i.e., it is magneto-sensing).
Abstract: This article presents the results of the binder jetting technology application for the silicon nitride ceramics production. A modified version of the Plan-B 3D printer with an epoxy-based binder was used for silicon green bodies preforming. Silicon powder was pre-coated with epoxy resin, and the curing agent was added during 3-D printing of green bodies using a standard cartridge. Curing and removal of organics was carried out during the high-temperature vacuum drying of the printed preforms. Reaction-bonded silicon nitride was obtained by using pressureless sintering. An additional compaction of green bodies is proposed to reduce the porosity of green bodies and sintered ceramics. It is shown that the proposed methods allows to improve the mechanical properties of sintered specimens.
Abstract: In this paper the authors present the methodology and results of computational studies of the stress state and the evaluation of the construction durability with multipoint welded joints in the event of random vibration. A special feature of the technique is a detailed simulation of the stress state in the most stressed connection junctions, taking into account the change in the properties of the base material during welding. The empirical equations between the microhardness and the material yield point in the local zone of the welded point are used for this. The developed technique for numerical simulation of the dynamic stressed state of a construction with a point-welded joints can be used to assess the vibration strength of such constructions under conditions of random loading.
Abstract: The paper is devoted to the study of the nonlinearity of the output signal of the pressure sensor on the silicon on sapphire structure (SOS). The authors constructed a mathematical model of the strain-gauge and carried out numerical simulation by using the ANSYS 12.1 software. For comparative analysis, the problem was solved both in a geometrically nonlinear and in a geometrically linear formulation. To account for the elastic-plastic properties of the silver solder PSR72, the Prandtl diagram was used. As a result, the maximum stresses and deformations in the sapphire crystal, solder, and titanium membrane under which the design successfully works were determined, and also the nonlinearity of the output signal was estimated in depending of the applied pressure. According to calculations, the nonlinearity of the output signal is 11.3%. The received value is unacceptable for this type of sensor, and requires further tuning, which negatively affects the accuracy of the product and its cost.
Abstract: The study is devoted to the study of the mechanical properties of penodiatomite ceramics. Dynamics of changes in the dynamic moduli of elasticity of highly porous (up to 70%) diatomite ceramics from the annealing time at temperatures of 800-1000 °С has been experimentally studied. The values of the activation energies of the change in the modulus of elasticity (Wa = 0.22-0.24 eV) were measured for high-temperature annealing (800-1000 °С). The change in the phase composition of the samples under the influence of annealing is demonstrated.
Abstract: The paper is devoted to the study of the magnetostimulated dynamics of dislocations in silicon and the influence of electric current on this process. As a result of the conducted studies, it was found that preliminary exposure of n-and p-type silicon single crystals in a constant magnetic field (B = 1 T, exposure time up to 30 minutes) leads to an increase in mobility of dislocation segments in them during plastic deformation of samples (Т=675 оС, σ=60–100 MPa, t=45–60 minutes). The quadratic dependence of the dislocation ranges on the induction of a constant magnetic field was found on the samples studied. A decrease in the activation characteristics of the process of displacement of linear defects during the flow of electric current during deformation is also detected: the transmission of electric current helps to reduce the activation energy of the process from 2.2± 0.2 eV to 0.7±0.1 eV. The observed changes are attributed to a decrease in the interaction energy of linear defects with dislocation stoppers based on the dopant.