Superconducting properties depending on the processing parameters of Nb3Al wires by the clad-chip extrusion method and the rapid-heating, quenching and transformation treatment

Superconducting properties depending on the processing parameters of Nb₃Al wire fabrication are presented. The adopted process consists of the clad-chip extrusion (CCE) method and the rapid-heating, quenching, and transformation (RHQT) treatment. The former (CCE) is a fabrication method for Nb/Al composite wire. It is characterized by the extrusion of thin chips of Nb/Al clad-rolled sheet. The latter (RHQT) is a heat-treatment method to transform the CCE-processed Nb/Al composite wire into the Nb₃Al intermetallic compound. The focused processing parameters are the chemical composition and the thickness of Nb/Al layers in the composite, and the cold working of the bcc supersaturated solid solution Nb(Al)_ss wire after the rapid-heating and quenching treatment. The results are as follows. A nearly stoichiometric composition of the CCE-processed precursor wire is optimum for enhancing the critical transition temperature T_c and the critical current density J_c of the Nb₃Al wire after the RHQT treatment. The thinner the Nb/Al layers in the CCE-processed wire, the higher the J_c and T_c of the RHQT-treated Nb₃Al wire. The as-quenched Nb(Al)_ss wire can be drawn to nearly 50% reduction at room temperature. Such cold working of the Nb(Al)_ss wire before transformation is an effective operation to improve J_c-B property of the transformed Nb₃Al wire by the following treatment.