In-situ resistance measurements of RHQT processed Nb3Al superconductors

The bcc supersaturated solid solution, Nb(Al)_ss obtained by rapid heating and quenching of a multifilamentary Nb/Al composite wire has shown a change from a disordered to an ordered structure before finally transforming to the A15 Nb₃Al phase. It is believed that such ordering is responsible for suppressing the critical temperature, T_c, the upper critical magnetic field, B_c2, and the critical current density, J_c. The ordering of the bcc phase can be suppressed by increasing the heating rate, and therefore this should improve the superconducting properties of the resulting Nb₃Al wires. Enhancement of J_c can also be achieved if the Nb(Al)_ss phase is mechanically deformed before transformation. The transformation process was studied in as-quenched and mechanically deformed Nb/Nb(Al)_ss wires by in-situ resistance measurement under heating at two different rates, 200°C/h and 800°C/h. The electrical resistivities of the wires decrease abruptly during the transformation from bcc to A15 phases and the process is much faster for mechanically deformed wires. Also, the heating rate affects the onset temperature of the A15 transformation. The results also show that the J_c of the transformed Nb₃Al wires increases with increasing reduction in area.