Superconducting Properties of<tex>$rm Sn$</tex>Added RHQT-<tex>$rm Nb_3rm Al$</tex>Wires Through the Clad-Chip Extrusion Method

Abstract

Fabrication and superconducting properties of Sn added Nb3 Al wires are presented. The wire fabrication process consists of the clad-chip extrusion (CCE) method and the rapid-heating, quenching, and transformation (RHQT) treatment. The former (CCE) is a metal-composite fabrication method and characterized by the extrusion of thin chips of Nb/Al clad-rolled sheet. It can produce the Sn-adding Nb/Al microcomposite precursor with the intended chemical composition. The latter (RHQT) is a heat-treatment method to transform the precursor to the Nb3Al wire by way of the bcc-structured supersaturated solid solution, Nb(Al)ss. It can produce not only the nearly stoichiometric composition but also fine grain of Nb3Al, which is favorable for upgrading the superconducting properties. The combined process of the CCE method and the RHQT treatment successfully fabricated the Sn added Nb3Al wires with Sn-addition from 0.25 to 5 atomic percent (at%). Sn-addition to Nb/Al composite wires affected the phase transformation at RHQT treatment. With increasing Sn-addition, the Nb(Al)ss became unstable and A15 phase was dominant at the stage of rapid-heating and quenching. The RHQT-treated Nb3Al wire with nearly 2 at% Sn-addition showed the maximum transition temperature Tc but the more addition decreased Tc. The small Sn-addition within 2 at% improved both of the critical field and the critical current density, although the more addition decreased them drastically