Fabrication of superconducting composite tapes by a newly developed liquid quenching technique

Abstract

A new liquid quenching technique for preparing composite tapes composed of superconducting compound and copper substrate has been developed. In this technique, the alloy melted by r.f. levitation-melting is ejected through a nozzle as a molten alloy jet onto a high-speed moving copper tape heated at a proper temperature. The heating of the substrate improves quenching effect and the resulting composite has good bonding between the alloy layer and the copper substrate, which may enable the use of copper as a stabilizing material. Using this technique, composite tapes of V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</inf> (Hf.Zr)60 amorphous alloy layer and copper substrate were successfully prepared at tape speeds of 10-20m/sec. The amorphous layer was then transformed by annealing into a veryfine crystalline mixture of α + Laves phases, having a critical current density J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5 \times10^{4}</tex> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 10 T and 4.2 K. Preliminary experiment for applying this technique to Nh <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Al.Ge) has been also carried out. The composite tape of bcc-Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Al.Ge) and copper substrate was successfully formed, and the bcc-Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Al.Ge) was then transformed into Al5 structure having a J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> exceeding 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 16 T and 4.2 K.