Abstract:Due to the limited available piece length of Y0.5Gd0.5Ba2Cu3O7-z (YGdBCO) coated conductors (CCs), joints are inevitable for manufacturing high temperature superconducting (HTS) devices. The stable operation of HTS devices is largely determined by the quality of joints, because the electromechanical performance of joints is usually lower than that of original tapes. In this work, lead-free Sn42Bi58 solder was applied to make the lap joints for YGdBCO CCs. Compared with conventional Sn60Pb40 solder, lead-free Sn42Bi58 solder is environmentally friendly and soldering operation at lower temperatures below 150℃ because of about 40℃ lower melting point further reduces the CCs deterioration in joining process. The influence of loading pressure, pressurization speed and lapped length on the critical current, resistance and n values of the YGdBCO joints were investigated by measurement of voltage-current curve at self-field and liquid nitrogen temperature. By optimizing soldering technique, the 25 cm-long joints with quite low resistance of 4.35~5.58 nΩ and comparable critical current with virgin CCs were repeatedly achieved with pressure of 12.5 MPa and pressurization speed of 50 N/s. The mechanical behaviors of the joints under axial tension were studied and the critical axial tension force of single CCs and joint portion is 213 N and 212 N, respectively. The above results show that compared with traditional soldering techniques, the robustness and reproducibility have been significantly improved for the soldering joints with low resistance and high tension performance by the joining technique based on this lead-free Sn42Bi58 solder, which offers another promising choice for joints manufacturing in the large scale applications of YGdBCO CCs.