Fabrication of Nb3Al wires by the clad-chip extrusion method and the rapid-heating, quenching and transformation treatment and their superconducting properties

This paper describes a fabrication process of Nb3Al intermetallic compound wires and measurements of their superconducting properties. Nb3Al superconducting wires are successfully fabricated by the combined process of the clad-chip extrusion (CCE) method and the rapid-heating, quenching and transformation (RHQT) treatment. The CCE method is a processing of Nb/Al composite wire with fine-layered structure, which is characterized by the extrusion of thin chips of clad-rolled Nb/Al sheet. Its chemical composition is controlled by the thickness ratio of the Nb-layer to the Al-layer at clad-rolling. The RHQT treatment is a heat-treatment to convert the Nb/Al composite into Nb3Al, which can produce fine grain structure of Nb3Al intermetallic compound with nearly stoichiometric composition. It is favorable for upgrading the superconducting properties. The critical transition temperature and the critical current density are enhanced by optimizing the microstructure of the CCE-processed precursor wire and the transformation condition in the RHQT process. Plastic working of the bcc supersaturated solid solution wire after rapid-heating and quenching is found to be effective for enhancing the critical current density in high magnetic field.