Multifilamentary Nb/sub 3/Al wires reacted at high temperature for short time

An attempt was made to carry out a high-temperature/short-time heat treatment of Nb tube-processed multifilamentary wires. The wires were heated passing a large alternative current for 0.1 s through the 0.74-mm-diameter Nb/Al composite wires or by irradiating the composite wires with a 50-kV, 22-34-mA electron beam at a scanning rate of 83 mm/s. Superconducting properties and microstructural aspects did not show significant differences for the two techniques. With increasing heat treatment temperatures, critical temperature, T/sub c/, and critical current density, J/sub c/, increased at first, reached a maximum, and then decreased. They were optimized when the single-core Nb/Al filaments in the first stack had completely reacted and become indistinguishable from each other. The highest T/sub c/, 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 degrees C for 48 h. The peak effect appeared in the J/sub c/-B characteristics, and the peak J/sub c/ of 2*10/sup 8/ A/m/sup 2/ at 17 T at 4.2 K was shifted toward higher magnetic field with the subsequent heat treatment.<
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