INFLUENCE OF WELDING PARAMETERS ON THE PERFORMANCE CHARACTERISTICS OF THE THERMOCATODES
The paper considers materials for the manufacture of a hot cathode based on lanthanum and niobium hexaboride. Lanthanum hexaboride has high emission properties; therefore, it is used in many fields of technology for the manufacture of cathodes for direct and indirect heating. Comparisons of the activation energies of the processes of interaction of metals with boron during diffusion welding in vacuum, and the assessment of the efficiency of diffusion protection of the interaction surface due to the use of an intermediate layer are carried out. Based on the data, titanium was selected as an intermediate layer. Analysis of the state diagram of lanthanum-boron made it possible to determine the optimal welding temperature. The selected welding temperature is 1473 K, which promotes the intensification of the diffusion process. The diffusion interaction of layered compositions of lanthanum hexaboride, a niobium substrate, and a titanium barrier layer has been studied. The influence of the welding parameters on the length of the phase layers and the quality of the hot cathode for low-thrust ion engines is investigated. It has been established that the relationship between the development of diffusion layers and the quality of the welded joint using microstructural methods of analysis does not give reliable results. The microhardness measurement provides an approximate estimate of the total width of the transition layer. Qualitative micro-X-ray spectral analysis made it possible to graphically determine the length of each phase layer on the concentration scanning curve. Thus, the methodology of using physical research methods made it possible to determine the reliability of the scientific substantiation of the developed technological process for manufacturing welded structures and to assess their performance under operating conditions. The general requirements for the material of the hot cathode are determined: metals must have simple state diagrams; the system of metals to be welded must have at least two heat-resistant intermetallics; the system should form significant areas of solid solutions. The mechanism of formation of a diffusion compound of lanthanum hexaboride with titanium due to boron diffusion into titanium, in order to avoid recrystallization grain growth in the titanium interlayer and the formation of titanium borides, which provide an increase in the thermal stability of the compound, has been established. The use of the above research scheme and assessment of the relationship between phase formation and the quality of welded joints based on lanthanum hexaboride makes it possible to effectively select the material of the intermediate layers and welding modes for obtaining cathode devices.
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Пути повышения производительности процесса диффузионной сварки в вакууме: https://cyberleninka.ru/article/n/puti-povysheniya-pr.