Achievement of Low-Resistivity Diffusion Joint of REBCO Coated Conductors by Improving the Interface Connection of Ag Stabilizer

Abstract

The achievement of low-resistance connection in REB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-z</sub> (REBCO, RE = Y, Gd) coated conductors (CCs) has become one of the strategic factors for magnet applications. In this letter, we fabricated low-resistivity (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sj</sub> = 4.9 nΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) Ag-diffusion joints of REBCO CC by improving the interface connection of the Ag stabilizer. The effective contact area at the interface between two Ag stabilizers can be increased by polishing the surface of the Ag stabilizers, which can reduce joint resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> ). Compared with a traditional diffusion temperature (400 °C), diffusion bonding of the Ag stabilizers at higher temperatures (800 or 850 °C, typical connection temperatures for superconducting joint) can promote interface connection between two Ag stabilizers. The oxygen content in REBCO will be reduced due to diffusion bonding at higher temperatures. Therefore, we etched some microchannels that serve as the fast oxygen diffusion paths on the surface of the Ag stabilizers to help restore the oxygen content, thereby recovering critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and reducing R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> . The connection mechanism of the interface between two Ag stabilizers was investigated through the cross-sectional analysis and delamination of the joint part. In addition, the REBCO layer can be completely peeled off and almost retain the original I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> by diffusion bonding of the Ag stabilizers at higher temperatures. This fabrication technique is a unique practicable solution to reduce the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> for the CC with thin Ag stabilizers and improve the peeling quality of the REBCO layer for efficiently fabricating the superconducting joint.