Multihlamentary Nb3Al Wires Reacted at high Temperature for Short Time

An attempt was made to do a high-temperature/short-time heat treatment for the Nb tube processed multifilamentary wires. Heating was carried out by passing a large alternative current for 0.1 sec through the 0.74 mm0 Nb/Al composite wires or by irradiating the composite wires with a 50 kV, 22-34 mA electron beam at a scanning rate 83 mm/sec. Superconducting properties and microstructural aspects did not show significant differences between the two techniques. With increasing heat treatment temperatures, Tc and Jc increase first, reach a maximum and then decrease. They were optimized when the single-core Nb/Al filaments in the first stack were completely reacted and becomes indistinguishable from each other. The highest Tc obtained just after the high temperature heat treatment was 17 K, and the peak height was further increased by 1 K after a subsequent heat treatment at 700 °C for 48 h. The peak effect appeared in the Jc-B characteristics, and the peak Jc of 2 x 108 A/m2 at 17 T, 4.2 K was shifted toward higher magnetic field with the subsequent heat treatment.