Optimization of the Direct Diffusion Bonding Process Using Cu Stabilizing Layers of the REBCO Coated Conductors

Low resistivity joint technique for high-temperature superconducting tapes is one of the most indispensable techniques for practical applications. In the present study, we propose solid phase joining technique to make direct joint of REBa2Cu3Oy (REBCO, RE:rare earth elements) tapes, as an alternative to conventional solder joining technique. In this solid phase joining technique, we directly join the copper stabilizing layer and get rid of the soldering material, so that we can expect reduction of joint resistivity. The important points for direct joining technique are to remove the oxide layer on the metal surface and to make the joint surface adhere to each other. It means that, after removing the oxide film on the surface, it is necessary to have an optimum pressure so that sufficient adhesion can be obtained while maintaining a clean surface. First, we examined the type and concentration of the acid used to remove the oxide film. Next, the joining pressure, joining atmosphere, and joining time were optimized, while the joining temperature was fixed at 200 ?. Finally, we have succeeded in joining REBCO tape with this technique. The measured resistivity at liquid nitrogen temperature was about 50-80 nOcm(2).

Automated summary

The study proposes a solid phase joining technique for low resistivity joint of high-temperature superconducting tapes. By directly joining the copper stabilizing layer and eliminating the soldering material, the joint resistivity can be reduced. The key points for this technique include removing the oxide layer on the metal surface and ensuring sufficient adhesion between the joint surfaces. The researchers successfully joined REBCO tape with an measured resistivity of 50-80 nΩcm(2) at liquid nitrogen temperature.