Исследована структура медно-цинкового покрытия, нанесенного на сталь 40Х при 450 °C методом газодинамического напыления при смещении сопла распылителя на 2 мм с использованием механической смеси частиц меди, цинка и корунда. Проведена термическая обработка образцов с покрытием в печи при 420 – 430 °C в течение не более 180 мин. Исследована структура и химический состав покрытия методами рентгеноструктурного фазового и микроспектрального анализов. Показано, что в процессе напыления происходят процессы диффузии меди в цинк и образуется твердый раствор электронного типа на базе Cu5Zn8 (g-фаза). После термической обработки при 420 – 430 °C в течение 180 мин в покрытии наблюдается твердый раствор цинка в меди (a-фаза) и твердый раствор электронного типа на базе CuZn (b¢-фаза). Покрытие по химическому и фазовому составу соответствует двойной латуни Л65.

The structure of a copper–zinc coating deposited onto steel 40Kh at 450°C by the method of gas-dynamic spraying of a mechanical mixture of copper, zinc and corundum particles with 2-mm displacement of the sprayer nozzle is studied. The coated specimens are heat treated in a furnace at 420 – 430°C for at most 180 min. The structure and the chemical composition of the coating are studied by the methods of x-ray diffraction phase analysis and microscopic spectrum analysis. It is shown that the spraying is accompanied by diffusion of copper into zinc, which yields an electron-type solid solution based on Cu 5 Zn 8 (a γ-phase). After the heat treatment at 420 – 430°C for 180 min the coating contains a solid solution of zinc in copper (an α-phase) and an electron-type solid solution based on CuZn (a γ ′ -phase). The chemical and phase compositions of the coating correspond to duplex brass L65.

The problems of changes in the coating structure depending on the composition of the sprayed mechanical mixture using copper particles and mixture of copper and zinc particles (" brass") and the effect of structural factors on the tribological properties of the deposited metal layer are considered. The results of X-ray structural, phase, chemical and durometric analyzes, as well as tribological testing of coatings are presented. It is found that structure with hardness of ≈102.7 HV is formed in the coating from mechanical mixture of particles of copper and aluminum oxide (corundum). Numerous pores are observed in the structure of the deposited metal layer, the main size of which does not exceed 2 μm. In the coating from mechanical mixture of particles copper, zinc and aluminum oxide (corundum), structure is formed based on copper with hardness of ≈106.5 HV, zinc — ≈49.7 HV, intermetallic compounds (γ- and ε-phases) — ≈168.7 HV, the mass fraction of which is 62.0, 7.9 and 24.2 %, respectively. Both coatings can be used in sliding friction pairs.

The structure of a coating based on a mixture of particles of Cu and Zn deposited by the method of gas dynamic spraying is studied. An x-ray diffraction analysis and a microscopic spectrum analysis are used to determine the structure and the elemental composition of the coating. Development of diffusion after the formation of the coating is shown to yield a solid solution of copper and zinc in it. The phase composition of the coating after the heat treatment (a hold at 405 – 415°C) is shown to change for intermetallic compounds and a solid solution of zinc in copper.

One of the predicted disruptions in the normal functioning of steam generators in a lead-cooled reactor over a long period of operation is depressurization of the heat-exchange tubes. The most likely tube failure sites are the tube–spacer comb interfacing zones. The oscillatory motion of the tubes in the lead coolant makes it necessary to study the fretting of the tube material. We describe the structural features of the setup modeling the interaction of the heat-exchange tubes and the spacer comb provided that the heatengineering properties of the lead coolant are the same and the material and structure features of the interfacings are the same. The experimental data on the wear of heat-exchange tubes that serve as the basis for theoretical modeling of their fretting are presented.

The results of effect of deposition temperature and the overlap coefficient on the formation of the phase composition of coating based on Cu, Zn and Al2O3 particles mixture applied by cold gas-dynamic deposition are presented. Using X-ray diffraction and X-ray spectral analysis, it is shown that when using the 55 % overlap coefficient electron-type compound based on CuZn3 (ε-phase) is formed in the coating, the mass fraction of which increases to 11.4 % with increase in the deposition temperature. Deposition with 64 % overlap coefficient is accompanied by the formation not only of the ε-phase, but of electron-type compound based on Cu5Zn8 (γ-phase), the mass fraction of which increases to 33 % at temperature of 450 °C. In the process of coating deposition, the predominant diffusion copper into zinc takes place; the calculations show high value of the diffusion coefficient copper — 1,56•10–13 m2 /s.

Adenine phosphoribosyltransferase (APRT) belongs to the type I phosphoribosyltransferase family and catalyzes the formation of adenosine monophosphate via transfer of the 5-phosphoribosyl group from phosphoribosyl pyrophosphate to the nitrogen atom N9 of the adenine base. Proteins of this family are involved in a salvage pathway of nucleotide synthesis, thus providing purine base utilization and maintaining the optimal level of purine bases in the body. Adenine phosphoribosyltransferase from the extremely thermophilic Thermus thermophilus strain HB27 was produced using a highly efficient E. coli producer strain and was then purified by affinity and gel-filtration chromatography. This enzyme was successfully employed as a catalyst for the cascade biosynthesis of biologically important nucleotides. The screening of crystallization conditions for recombinant APRT from T. thermophilus HB27 was performed in order to determine the enzyme structure by X-ray diffraction. The crystallization conditions, which were found by the vapor-diffusion technique, were then optimized to apply the counter-diffusion technique. The crystals of the enzyme were grown by the capillary counter-diffusion method. The crystals belong to sp. gr. P12 1 1 and have the following unitcell parameters: a = 69.86 Å, b = 82.16 Å, c = 91.39 Å, α = γ = 90°, β = 102.58°. The X-ray diffraction data set suitable for the determination of the APRT structure at 2.6 Å resolution was collected from the crystals at the SPring-8 synchrotron facility (Japan).

The research results of experimental aluminum alloys intended for the possible replacement of costly bronzes in the friction units of railway transport have been presented. The preliminary selection of alloys was carried out by the sclerometry technique on the criterion of relative shear strength as more informative compared with microcutting contact stress. The tribotechnical tests of selected alloys were performed by the three-finger scheme, which simulates the work of supporting the sliding bearing. In principle, the test results confirmed the possibility of using these alloys as substitutes for bronze. The structure and chemical composition of surface both the original samples and the samples after testing was studied. The influence of the alloy’s chemical composition on the tribological properties of investigated alloys has been revealed.