Key Engineering Materials Vol. 839

Abstract: The paper discusses application possibilities of nanostructured crystals of partly stabilized zirconium dioxide in greaseless running of plain bearings in order to support normal operation of friction joints at high temperatures and in aggressive conditions. This issue is a burning one in different industries, e.g. circulating pumps in nuclear power engineering, mixing units of crystal synthesizing lines in chemical engineering; motors in space-based targets, rotors of guide blades in axial compressors of airplane engines, supports of high-speed gas centrifuges. Micro-hardness was investigated, and friction surfaces were explored using methods of X-ray, electron-microscopic and element analysis to find a wear mechanism for crystals ZrO₂- Y₂O₃. The paper reports on tribological properties of partly stabilized zirconium dioxide crystals and prospects of their industrial usage.

Abstract: This paper analyzes the effect of SLM parameters on mechanical characteristics and surface roughness of a single-component copper powder. The study reports on appropriate SLM conditions for a single-component copper powder; to form a layer a technique within layer-by-layer selective laser melting is suggested and comprises roughing, semi-finishing and finishing modes. The work establishes a range to vary surface roughness, porosity and ultimate compressive strength of a single-component copper powder by means of laser processing conditions. Rz is variable 332 to 689 μm, porosity ranges approximately 13-39%, and ultimate compressive strength is 8 to 104 МPа.

Abstract: Provides information about the results of the evaluation of anti-icing properties of coatings. It is shown, that the hysteresis of wetting of the superhydrophobic surface based on the developed composition is 3,7 degrees. The critical angle of rolling of a drop of water from an inclined surface is determined. The results of the evaluation of the kinetics of freezing of a water droplet on a superhydrophobic surface are given. It is shown, that in the initial period there is a transfer of heat from the surface to a drop of water. Then there is a movement of the freezing front from the substrate upwards.

Abstract: This paperwork presents the results of a series of experiments on the use of homogenizing annealing, aimed at the possibility to control the structure and properties of steel samples obtained by aluminothermy. This method of processing, in some cases, allows to eliminate the need to use subsequent heat treatment operations due to the achievement of the required properties by the cast blank material. Refractory materials and thermite mixtures used, conditions for the production of castings and their total chemical composition are given. The tensile diagram analysis of the samples before and after heat treatment is presented; the structures and diffraction patterns of the samples’ destruction spots are considered. The material obtained by aluminothermy corresponds in its chemical composition to A1, A2, A3, A4 grade of steels for the rail transport according to GOST 31334-2007 which are used in the manufacture of locomotive axes and other rolling stock.

Abstract: A comparative analysis on structure, mechanical and tribological properties of a multicomponent extrudable polymer composites "UHMWPE + 17 wt. % HDPE-g-SMA + 12 wt. % PP" fabricated by i) FDM (fused deposition modeling) as well as hot pressing of ii) powder mixture, and iii) granules of the same composition has been conducted. It is shown that UHMWPE composites obtained by the 3D–printing over a complex of tribomechanical properties (wear resistance, friction coefficient, elastic modulus, yield point, tensile strength, elongation at break) are comparable with those of composites fabricated by compression sintering of granules (this is associated with formation of more homogeneous permolecular structure, first of all, due to the compounding with the help of a twin-screw extruder) and significantly exceed those for hot pressing of powder mixtures. The obtained results allow one to recommend this composite for manufacturing complex shape products for tribotechnical application at employing 3D-printing technologies.

Abstract: The decay mechanism of silicon particles in silumin in the thermal effect zone of low-energy high-current electron beam is proposed. Its essence consists in the fact that under the effect of the mechanical stresses the interface of silicon inclusion with aluminum matrix becomes instable resulting in the decay of silicon particle. It was supposed that the instability was the analog of Rayleigh-Taylor instability. The mechanical stresses arising due to the discrepancy of the elastic moduli and the linear expansion coefficients of the inclusion and the matrix are the analogs of gravity force. The analysis of the initial stage of instability within the frameworks of the visco-potential approximation has shown that the dependence of the rate of perturbations’ growth has only one maximum which falls on the wave length of the order ≈ 500 nm that is 5-fold higher than that of the experimental data. Such a discrepancy may be explained by the fact that when developing the model the temperature of the silicon inclusion and the aluminum matrix was considered to be constant, similar and being equal to the eutectic temperature of silumin. In fact, the temperatures of the inclusion and the matrix are different. To take into account the influence of these facts on the instability of the interface the new investigations are necessary.

Abstract: The data on obtaining construction compositions for the manufacture of wall products based on industrial waste, such as non-autoclaved foam concrete, dense ash and slag concrete and wood concrete are given. These types of concrete are made of local aggregates - by-products of the fuel and energy and wood processing industry and cementless ash-silica binder. It is shown that the compositions developed according to the main physic-mechanical characteristics comply with the requirements of the regulatory documents and can be recommended for the production of small-piece wall products

Abstract: This article states the results of experimental studies to assess concrete strength in cast-in-situ structures based on a systematic approach, including integrated research methods at all stages of construction of reinforced concrete structures. It was established that the concrete strength of the sample-cubes made on the object simultaneously with the structure and stored under the same conditions was slightly lower than the structures and standard control samples. The decrease in the strength of concrete samples from structures is on average 13,3%. Its value is effected by several factors, one of the main was the maintenance of the structure. The most appropriate is to meet the requirements of achieving 70% of the design strength and higher percentage is required for cast-in-situ construction in terms of winter pouring concrete. At the same time, along with the assessment of the physical and mechanical properties of the structure by non-destructive methods, it is necessary to carry out tests aimed at determining the actual concrete strength based on samples made in the batching plant laboratory and solidified (cured) in permissible humidity conditions (herein after referred as PHC).

Abstract: Since the 1987 Montreal Protocol, chlorinated refrigerants (CFCs and HCFCs) have been pointed out as responsible for the destruction of the ozone layer. The chemical industry has realized suitable replacement for CFC-12 and for HCFC-22 e.g. HFC-134a, HFC-404A, HFC-410A, HFC-507. This generation of refrigerants developed by the chemical industry can be characterized by the no ozone depleting potential and long atmospheric lifetime resulting in global warming potential. The contribution of the HFCs to the global warming brings up to discussion whether the HFCs should be considered as a transitional substance. Historically the use of natural and ecologically safe refrigerants was a strategy to eliminate environmental problems and avoid uncertainties with synthetic replacement fluids. Since ammonia is toxic, carbon dioxide provide high pressure, and the hydrocarbons are flammable, the general conclusion is often drawn that natural fluids gave safety problems. This paper will describe the possibilities of application as working fluids in low-temperature engineering refrigeration, heat pumping and organic Rankine cycles of the hydrofluoroolefins (HFOs) as third generation of synthetic working fluids.