急冷法による高性能超電導材料の作製

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Recent researches on the development of practical and emerging superconducting materials are reviewed. Nb-Ti conductors with sub-micron filaments show promising properties for AC applications because of the reduced magnetization loss. Appreciable improvements in high-field performance have been achieved for multifilamentary Nb3Sn by the Ti-dopping, and for V3Ga tape by the two stage heat treatment. Using these improved conductors, a new superconducting magnet generating fields over 18T has been successfully constructed. Superconducting compounds such as Nb3Al and Nb3(Al, Ge) having superior performance to those of Nb3Sn and V3Ga are being developed as the next generation superconductors. The liquid quenching is one of the useful techniques to form stoichiometric A15 phase. Nb-Al base supersaturated bcc solid solution alloys are obtained by the quenching on a hot Cu substrate. The A15 phase converted from the bcc phase by annealing has an extremely small grain size, which leads to a large Jc. Continuous irradiation of electron beam or laser beam onto a moving tape enables a rapid quenching from high-temperature throughout the tape, which leads to the retension of stoichiometric A15 phase and suppression of grain coarsening. The irradiation was carried out on the powder metallurgy processed Nb-Al and Nb-(Al, Ge) composite tapes, and excellent Tc and Jc in high fields have been obtained.
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