Development of superconducting soldered joints between Bi-2212/Ag wires

Journal article

Bi-2212/Ag superconducting wires are being considered as key conductor candidates for the development of high field magnets (up to 25 T), but it is recognised that a reliable joining process between these wires is a critical challenge for most high-field applications. This work focuses on the design and testing of jointing processes between multifilamentary Bi-2212 wires to make persistent mode joints using soldering techniques. The ability of several different superconducting solder alloys from the PbBi and SnInBi systems to remove and replace the Ag matrix in fully reacted Bi-2212 wires has been explored. The SnInBi leadfree solder was found to be relatively effective at removing the Ag matrix, but does not make good contact with the Bi-2212 filaments. PbBi solder wets the Bi-2212 filaments more effectively, but is slower at removing the Ag matrix. Therefore, a two-stage process has been developed using molten Sn to first remove the Ag matrix followed by PbBi to replace the non-superconducting Sn. Joints made using this two-stage process have higher critical currents (133 A in self-field and 4 K) than joints made using PbBi alone (120 A in self-field 4 K).

Authors: Mousavi, T; Davies, T; Melhem, Z; Grovenor, C; Speller, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IEEE
• Journal: IEEE Transactions on Applied Superconductivity
• Volume: 28
• Issue: 4
• Article number: 6400303
• Publication date: 2018-03-22
• Acceptance date: 2018-03-15
• DOI: 10.1109/TASC.2018.2817260
• ISSN: 1051-8223
• Keywords: multifilamentary superconductors; superconducting filaments and wires; lead-free solder; joints