基于无铅焊料的Y0.5Gd0.5Ba2Cu3O7-z超导带材搭接接头的电学和力学性能研究

Electromechanical properties study on lapped joints of Y0.5Gd0.5Ba2Cu3O7-z coated conductors joining with lead-free solders

摘要:

由于单根Y0.5Gd0.5Ba2Cu3O7-z(YGdBCO)超导带材的长度有限,因此在制造高温超导(HTS)器件时不可避免地需要接头。HTS设备的稳定运行在很大程度上取决于接头的品质,因为接头的机电性能通常低于母材。本研究应用Sn42Bi58焊料制作YGdBCO带材搭接接头。与传统的Sn60Pb40焊料相比,无铅Sn42Bi58焊料对环境友好,且熔点降低了40℃,因此可在低于150℃的低温下进行焊接操作,有助于抑制超导带材在连接过程中的性能下降。通过测量自场和液氮温度下的电压-电流曲线,研究了加载压力,增压速度和搭接长度对YGdBCO接头临界电流,电阻和n值的影响。通过优化焊接技术,可在12.5 MPa的压强和50 N/s的加压速度下重复获得与母材临界电流相当的25 cm长的低阻接头,其电阻为4.35～5.58 nΩ。本文还对轴向拉伸作用下接头的力学行为进行了研究,单根带材和接头部分的临界轴向拉伸力分别为213 N和212 N。 上述结果表明,与传统焊接技术相比,采用优化的无铅Sn42Bi58焊料的连接技术制备低电阻、高拉伸特性的焊接接头的稳定性和重复性明显提升,为YGdBCO超导带材大规模运用的接头连接提供了一种有前景的选择。

Abstract:

Due to the limited available piece length of Y_0.5Gd_0.5Ba₂Cu₃O_7-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.