Research of Cu-Nb microcomposite wires welded joints

Abstract

Compact impulse magnet installations can generate record magnetic fields up to 100 T. Impulse magnetic systems are quite simple in their construction and use low electrical power, therefore are popular in various fields of science and industry [1]. The key element of such magnetic systems is the solenoid. The most popular are multi-layer winded solenoids. The materials of conductors of such solenoids must be very strong and have good electrical conductivity. Magnetic fields over 45 T can be generated only in the form of short impulses, therefore the electric cables shall stand extreme impact and cyclic heating. For those purposes presently composite wires of 4 new types are used: Cu-Nb and Cu-Ag microcomposites, GlidCop, GlidCuSS macrocomposites [2, 3, 4]. Cu-Nb microcomposite is presently considered as the best-fit of all above-mentioned types because of the whole set of its unique properties. The strength of such wire is about 1,5 GPa, when electric conductivity is 67-70 % IACS. This material is useful in different magnetic installations, but also in levitation transport, high-voltage power lines, induction welding, industrial equipment of thermal treatment. Presently the construction of solenoids of the most magnetic equipment is sectional, therefore it needs many contact connections [5, 6, 7]. In electrical engineering, wire and cable connections may be destructive (screw) and nondestructive (welded, soldered and pressed). Nondestructive joints are preferable in such case, since microcomposite wires are characterised as of limited capability for deformation. Besides, after magnetic systems are entered into operation, access to all connections is very limited. All contact connections shall not be the weakest chain of systems [8]. So far in practice only the screwed and soldered conductor connections, which do not demonstrate sufficient reliability and long service time in terms of impact and cyclic heating, are used [9, 10]. Therefore, the welded joints are advanced and more reliable. The complexity of selection of welding technologies for those purposes occurs due to the Cu-Nb microcomposites structure and production specifics, as well as conditions of exploitation. The structure of microcomposites Cu-Nb consists of copper matrix where very thin Nb treads are integrated [11, 12, 13]. The technology of Cu-Nb microcomposite production is similar to the process of multi-stage pressure or diffusion bonding, when Cu-Nb wire is obtained by multiple plastic deformations of materials. Fusion welding methods for connection of microcomposite wires may not be used because of inevitable microcomposite melting, overheat of the joined wires and the loss of unique properties. Therefore, one of the most important unsettled problems in the techniques of strong magnetic fields is creation of a reliable welded connection of microcomposite conductors. This problem theoretically may be solved using special methods of welding. In this work we presented the experimental results of Cu-Nb wire joining applying the different technologies and analysis of nondestructive joints properties.