Applied Mechanics and Materials Vol. 756

Abstract: The results of the analysis of influence of the phase composition of corundum-zirconium ceramic on its properties are presented in this paper. It was established that the most perspective ceramic has composition 0,6 (ZrО₂ + 3M% Y₂O₃) – 0,4 Аl₂О₃. High strength properties of this composition are determined by the presence of compressive stresses and the opportunity of retaining of tetragonal grains ZrО₂ in a metastable condition at low temperatures.

Abstract: This work presents the characteristic properties of powdered materials sintering under conditions of liquid-phase sintering. It has been established that to implement the liquid-phase sintering advantages it is necessary to do temperature research when the liquid-phase concentration does not exceed the critical one. The implementation of this condition provides the sintering temperature reduction by 150 – 200 °С.

Abstract: This work presents the characteristic properties of powdered materials sintering under conditions of liquid-phase sintering. It has been established that to implement the liquid-phase sintering advantages it is necessary to do temperature research when the liquid-phase concentration does not exceed the critical one. Impact strength is the highest for the bronze, casted in a chill mould at 1220°С, and the lowest for the bronze, casted in aluminum-chromium-phosphate moulds at the same temperature.

Abstract: The paper is devoted to the study of the multicomponent lead-tin bronzes. The data on the influence of rotational velocity of a casting mould and the temperature of melt pouring on the structure and mechanical properties are presented in the article. The results of mechanical tests and studies of the microstructure allowed determining the optimal conditions of obtaining the castings with high strength characteristics. The conducted researches show that the maximum values of strength (σ_V=280–290 MPa) and impact strength (КС=2.7–3.2 KJ/cm²) are provided at the pouring temperature of 1150–1200 ̊С and rotational velocity of a casting mould equal to 1200 rpm.

Abstract: Glass-ceramic composite materials based on lead-borate glass and eucryptite – a compound with a negative coefficient of linear thermal expansion (CTE), along with the conditions for their production are studied in this paper. Effects of the amount and granulometric composition of the eucryptite as well as time/temperature processing conditions on the change of the linear thermal expansion coefficient of the sintered samples are also examined.

Abstract: In the present the results of research of structure, phase composition and microhardness measurement of the surface layers of the Cr/Ti system treated by short-pulsed high intensity ion beams (HPIB) are presented. It was shown that the HPIB impact on a “coating/substrate” system can serve as an affective way to produce near-surface alloys in the metals. In particular, in the Cr/Ti system the formation of solid solution β-Ti (Cr) as well as titanium carbide TiC_x was revealed. The found changes in structure and phase composition of titanium caused by the HPIB impact allow to increase its microhardness in 2 times.

Abstract: The paper shows the iron oxide powder production in the hypersonic jet of electro discharge plasma generated by a coaxial magnetoplasma accelerator with steel electrodes. The influence of gaseous atmosphere parameters has been investigated by carrying out experiments in normal atmospheric conditions and with the introduction of additional oxidant into the plasma discharge. Studies of the structure of synthesized powders and their magnetic properties have been carried out. It has been found that by introducing of additional oxidant it is possible to regulate the phase composition in the direction of increasing the yield of magnetite phase. Specific saturation magnetization decreases with decreasing of the magnetic nanoparticle sizes.

Abstract: The article investigates the counter-vortex flow, one of the most complex spatial nonuniform liquid and gas flows. Counter-vortex phenomenon implies an interaction of two or more wake coaxial circular-longitudinal lines twisted in opposite directions. The relevance of the research issue has determined the desirability of further research and application of unique hydraulic devices in the new situation based on the effect of the interaction of coaxial oppositely swirling flows of water in a circular pipe.

Abstract: Specific features of formation of gas hydrates due to injection of a gas into a porous medium initially filled by a gas and water are considered. Self-similar solutions to the planar one-dimensional problem are constructed, which give the distribution of main bed characteristics. The influence of the initial parameters of the porous medium and the intensity of the gas injection on the dynamics of the processes of hydrate formation is studied. The existence of solutions is demonstrated, which predict gas hydrate formation both on the frontal surface and in the volume zone. The critical conditions that separate the different modes of hydrate formation are found.

Abstract: During the experimental study we examined the ignition of the litter of hardwood species by the particle heated up to high temperatures. Our study involved conducting tests, using a carbonic particle and samples of typical forest fuels, formed of birch leaves. We determined a mechanism for litter ignition by a local heating source, and obtained the dependence of ignition delay of birch leaves on the particle's initial temperature.