Development of Ag-Added InSn Solders for ReBCO Joints

This study explores ternary Ag-added InSn solders to develop low-resistance, reliable, and mechanically robust joints between YBCO tapes, an essential requirement for superconducting magnets, including the magnets in the fusion industry. To investigate the impact of Ag addition to the widely used SnIn solder, several solders were made by adding small amounts of Ag (1-5wt.% ) to the eutectic In-Sn solder. Lap joints were fabricated between YBCO tapes using these solders and were characterized for electrical resistivity, microstructure, and mechanical properties. According to the results, Ag addition changes the solder bulk structure with minimum impact on the interface and mainly dissolves in the In-rich phase of the solder. The joints made with Ag-added solders show significantly higher mechanical strength and ductility, with fracture shifting from the joint to the tape outside the joint region, and reasonably low electrical resistance. The optimized 5wt.% Ag addition to the binary In-Sn solder showed the best compromised joining performance as a result of a homogenous joint microstructure, offering a promising approach towards more reliable joints for superconducting magnet applications.