First Trial to Fabricate Nb3(Al, Si) Multifilamentary Superconductors by Rapid-Heating and Quenching (RHQ) Process.

Aiming at further improvement of high-field critical current density, Jc, in the Nb3Al conductors, Si addition was attempted. To fabricate the Nb3(Al,Si) conductors, we used two times the rapid-heating and quenching (RHQ) technique. First, drawability of the Nb/Al-Si composite wire has been improved by specially using the RHQ technique at an early stage of the precursor fabrication, where only the Al-alloy core is rapidly solidified from the molten state to form a fine microstructure of the core without any reaction with the Nb. This process makes the subsequent restacking and drawing process easier. Using this technique, multifilamentary Nb/Al-Si precursors with piece length of 30 m have been successfully fabricated at our laboratory workshop. For the prepared precursors, another RHQ was attempted for the formation of the high stoichiometric A15 phase. With increasing Si content, the upper critical field was enhanced, while providing the high Jc property in high magnetic fields such as 150 A/mm2 at 25 T, 4.2 K. Meanwhile, with Si additions of 2 at% to the core, metastable BCC Nb(Al,Si)ss phase was formed by the second RHQ process. This phase can be transformed to the A15 phase by a subsequent annealing around 800°C. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]