Pulse diffusion welding of female joints

Abstract

Special feature of operation of electrovacuum tubes, in particular the cathode assembly, is constant heating due to bombardment of its surface with electrons. Stable characteristics and durability of the cathode assembly depend on high-quality connection (welding) of the core surfaces with the emitter over the entire area of the overlapped conjugation. The use of diffusion welding for joining a cathode assembly made of dissimilar materials is not possible due to the occurrence of poor welding fusion due to the presence of gaps in the ring sectors of the equipment, and, consequently, a decrease in the service life of the cathode assembly. The authors proposed to implement the process by combining magnetic pulse welding with diffusion welding. The originality of the work is the possibility of remote action on the joint through a dielectric quartz cup, which is a part of the technological vacuum chamber. The inductor system is outside the quartz cup, which allows heating the assembled unit without heating the tool – an inductor made of dissimilar materials – to a temperature of 700 ° C and higher. The authors determined the main parameters of the process of pulse diffusion welding in vacuum: pressure in the working chamber is В=0.66•10−2 Pa (5•10−5 mm Hg); preheating temperature is T=700–1250 °C; magnetic field pulse energy is W=5÷17 kJ; operating frequency of current pulse discharge is fd=5–15 kHz; magnetic pressure is Pm>∙107 N/m2. In this way, cathode assemblies of a wide range of metal pair combinations with a base diameter of d=20 mm and a sample length of L=40 mm were produced. The proposed technology has been successfully implemented and introduced at Tantal (Open Joint Stock company). The economic effect consists in reducing labor intensity and obtaining joints of stable quality.

Keywords

• pulse diffusion welding
• welding of female joints
• magnetic pulse welding
• inductor
• magnetic pressure
• input energy
• dissimilar alloys