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The temperature of the heater, which can be used to join a plate of limited dimensions, to a shell of unlimited dimensions by brazing, in the general case is determined by melting temperature of the filler metal and characteristics of heat transfer in the plate contact zone. In the case of a low heat transfer in the contact zone, its heating to the temperature required for brazing is complicated, as a result of spreading of the heat coming into the shell. The work is an experimental study of the impact of nonideal thermal contacts between the aluminium plates on their heating, using a flat heater, which is in contact with one of the plates. It turned out that the force of pressing the contacting plates to each other has a greater effect on heat transfer in the contact zone that the surface roughness. Here, the value of the coefficient of effective heat transfer changes jump like during heating of the plates, which is associated with microplastic deformation of their surface layers under the impact of a compressive load. A computational-experimental method of self-consistent determination of the values of the coefficient of effective heat transfer for different temperatures was proposed, which is based on comparison of experimentally measured and calculated thermograms of plate heating. 11 Ref., 6 Fig. [ABSTRACT FROM AUTHOR]

The possibility of manufacturing thin foils of high-entropy alloys (HEA) of Co‒Cr‒Fe‒Ni‒Si system by the method of highspeed (up to 10 μm/min) electron beam physical-vapour deposition (EB-PVD) is shown in the work. It was established that silicon content in the alloy composition of approximately 5 wt.% improves the values of high-temperature resistance of basic CoCrFeNi HEA. It is shown that at soaking in air for 28 h at the temperature of 1000 °C the specific change in the weight of CoCrFeNiSi0.2 sample is not more than 0.9 mg/cm². A technological scheme was proposed of manufacturing by welding three-layer thermal protection honeycomb panels with a low specific weight based on thin foils of high-entropy CoCrFeNiSi0.2 alloy. It was found that the produced by the proposed scheme three-layer thermal protection panels can stand multiple thermal cycling from 25 to 1000 °C in air without the structure failure. The derived results can be the base for development of the technology of manufacturing lightweight honeycomb structures, capable of ensuring thermal protection of aerospace equipment elements at their interaction with the atmosphere. [ABSTRACT FROM AUTHOR]

High-entropy alloys are characterized by a complex of mechanical properties, which allows them to be considered promising structural materials. Given that the phase composition of high-entropy alloys remains stable with increasing temperature, it is assumed that they can be used to manufacture structural elements of aerospace equipment operated at elevated temperatures. Electron beam technology makes it possible to obtain thin-sheet material based on these alloys, which greatly simplifies the technology of manufacturing thin-walled elements, such as light heat-shielding honeycomb panels for thermal protection of aircraft. In this regard, the paper investigated the heat resistance of thin-sheet materials based on the Cr–Fe–Co–Ni–Cu system, depending on the copper content in the alloy. It is shown that the content of copper in the composition of high-entropy alloys significantly affects the heat resistance of the material: in the case of CrFeCoNiCu alloy foils, the increase in specific mass at a temperature of 900 °С occurs 8 times more intensively than in CrFeCoNi foils, due to the activation of the diffusion of copper atoms, its release to the surface of the foil and scale formation based on CuO and NiO oxides with a significant number of defects in the structure. CrFeCoNi alloy foils are characterized by higher heat resistance due to the formation of scale on the surface based on Cr2 O3 oxide with fewer defects and greater integrity. The average mass growth rate of the CrFeCoNi alloy sample is about 0.041 mg/(cm2 ∙h). [ABSTRACT FROM AUTHOR]

The regularities of joint structure formation in diffusion pressure welding through multilayer interlayers based on AL-Si and Al-Cu aluminum systems with eutectic, obtained by electron beam deposition in vacuum, were studied, using SiCp-AMg5 aluminum composite, as an example. It is shown that the intermediate multilayer layers of eutectic ‘composition provide permanent joints without degradation of the properties of the base material at a temperature of 500 °C, which corresponds to the beginning of intensive plastic deformation of the interlayer under pressure. It is established that the nature of the diffusion interaction of the components of the interlayer and the composite and the phase composition of the eutectic affect the structure and the chemical composition of the joint. Conditions that prevent the formation of barrier layers at the interlayer/composite interface, namely layer alloying or intermetallic particle formation in it before the welding process, promote intensive mass transfer of interlayer and composite components, ensuring homogeneity of the structure and microhardness of the joint. Mechanisms for forming SiCp-AMg5 composite joint through multilayer intermediate layers based on aluminum systems with eutectic of different types — simple, consisting of system components (for example AI-Si) and one containing an intermetallic based on components (for example AL-Cu) are proposed. [ABSTRACT FROM AUTHOR]

At heating of multilayer Al/Ni foil the component interdiffusion is accompanied by phase transformations, which can be occur by a two-channel multistage or single-channel single-stage schemes. It is shown that the type of the scheme by which the phase transformations develop in the studied multilayer foils, is related to the process of formation of a metastable Al9 Ni2 -phase on the layer interfaces. The work is a study of the influence of multilayer foil microstructure on formation of a metastable Al9 Ni2 -phase. It is found that the thickness of Al9 Ni2 -phase layers is determined by the thickness of aluminium layers in the initial multilayer foil. At the thickness of Al layers of 70…80 nm and greater, the thickness of Al9 Ni2 -phase layers practically does not change, and is equal to approximately 30..35 nm; at reduction of Al layer thickness, the thickness of Al9 Ni2-phase layers decreases abruptly, and at Al thickness less than 10…12 nm, the layers of metastable Al9 Ni2 -phase do not form. The process of formation of metastable Al9 Ni2-phase layers is characterized by a high rate and incubation time. Proceeding from the obtained results, a structural-kinetic diagram was proposed, which allows determination of the conditions for prevention of the multistage process of achievement of the foil equilibrium state during its heating. Ref. 15, Table 1, Fig. 8. [ABSTRACT FROM AUTHOR]

In this work mechanical and dissipative properties of vacuum condensates of high-entropy alloys (HEAs) of Cr–Fe–Co– Ni–Cu system produced by high-rate electron beam vapor deposition in a vacuum are investigated, depending on their structural-phase state. It is shown that a transition from a single-phase (FCC) structure of the condensate to the dual-FCC phase state (FCC1 + FCC2) occurs in the temperature range of 923…1025 K. It was found that the mechanical properties of CrFeCoNiCu vacuum condensates produced by EBPVD method, significantly depend on their structural and phase states. Two-phase condensates exhibit a lower microhardness (3.0 GPa) and higher plasticity (δA = 0.90) against those of single-phase condensates (5.5 GPa and δA = 0.83) due to the presence of plastic Cu-rich precipitates at grain boundaries of CrFeCoNiCu0.5 solid solution. It is shown that transition from the single-phase FCC structure to a two-phase structure (FCC1 + FCC2) in CrFeCoNiCu coatings leads to increase of the damping capacity by 1.5…1.7 times in the temperature range of 293…693 K, and by 3…4 times, compared with an uncoated sample. Ref. 20, Tabl. 2, Fig. 8. [ABSTRACT FROM AUTHOR]

The impact of technological measures in vacuum diffusion welding on formation of the structure and mechanical properties of joints of TiAlNb intermetallic alloy was studied in the work. It is shown that welding of intermetallic alloy by the method of vacuum diffusion welding at temperature Tw = 1050 °C, pressure Pw = 10 MPa, for 20 min does not ensure producing sound joints. After welding, the joint line is visible in the butt, along which there is a considerable number of defects in the form of pore lines. Increase of welding parameters up to the temperature Tw = 1200 C, pressure Pw = 30 MPa, welding time of 30 min, as well as application of a ductile interlayer from NbTi alloy 1 mm thick allows improving the conditions of welded joint formation and greatly reducing the number of defects in the butt joint. During welding, common grains and diffusion zone 25 - 35 ~m thick form between the interlayer material and intermetallic alloy. Application of nanolayered interlayer of Al-Ti system of the total thickness of 25 ~m in welding of TiAlNb intermetallic alloy, combined with cyclic loading in the form of 3 cycles of loading-unloading leads to a change of the nature of the structure in the joint zone. In the microstructures of welded joints obtained by optical metallography, the joint line is not visible. Application of electron microscopy allows detecting in the butt joint a diffusion zone 15 to 20 ~m thick, close by its chemical composition to that of the intermetallic alloy. Investigation of the compressive strength of welded joints demonstrated that the average strength of joints of TiAlNb intermetallic alloy, produced using an interlayer from NbTi alloy, is equal to 988.2 MPa, and application of a nanolayered insert of Al-Ti system in welding allows increasing the average strength of the samples up to 1279.8 MPa. [ABSTRACT FROM AUTHOR]

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Investigations allowing obtaining of 82Sr isotopes upon irradiation of target RbCl by internal proton beam in the cyclotron U-240 were performed. The facility, providing long exposure of the target RbCl upon internal proton beam with the intensity of 150 mA and with energy not less than 70 MeV, was constructed. [ABSTRACT FROM AUTHOR]