Welding of Cu-Nb microcomposites for pulsed power applications

Abstract

Compact pulsed magnetic systems up to 100 T become more popular in the different fields of science and industry [1]. One of the most important parts of these systems are magnetic coils, which are winded from Cu-Nb microcomposite wire. When the magnetic systems are installed, the conductor’s connections are unavoidable [2]. Nowadays, for this purpose are used only soldered and screwed joints, which don‘t have the reliability and strength, that withstand strong dynamic and cyclic thermal loads [3-4]. Therefore, one of the most important and unsolved problems in the field of pulsed power applications is the reliability of nondestructive joints. This problem can be theoretically solved using the special methods of welding. Therefore, the main purpose of this work was experimental investigations of Cu-Nb conductors EBW (electron beam welding) welding joints. The evaluation of welded joints properties was carried out according to the methodology [5-6], which is applied to contact electrical connections. The major electrical and mechanical properties of welded joints were established. Moreover, the microscopic examination showed, that EBW joints of Cu-Nb conductors in comparison with samples welded with other processes have minimal thermal effect on the structure of the conductor and propagation of welding defects thanks to the welding in a vacuum. The difference of electrical resistance of conductor and conductor with welded joint doesn‘t exceed the requirements for electrical contact connections according to standards [5-6]. The heating effect, when the electric current flow through the welded joint, was fixed using thermovisor. It was found, that the difference of temperature of welding joint and conductor don‘t exceed the recommendations for electrical contact connections. The results of tensile testing of samples showed, that the strength of the welded joint exceeds the minimum recommended strength for electrical contact connections. The analogous 350 MPa tensile strength has the brazed joints of Cu-Nb conductors [3]. However, the brazed joints are very brittle (elongation at break is 0.34 %). Meanwhile, the EBW welded joints are considerably elastic (elongation at break is 4 %). Taking into account the results of the investigations we can conclude, that the used welding technology and characteristics of joint are better in comparison with other popular in practice methods. Therefore, EBW welding is promising technology, which can be used for nondestructive joining of conductors of pulsed magnetic systems.