Speaker
Description
The discovery that small amounts of Cu enable the formation of V3Ga, Nb3Sn and other A15 compounds without intermediate Nb-Sn phase formation without needing to go to liquid reactions opened the path to fine A15 grain size and multifilamentary strand and all the applications that followed, from NMR to ITER and beyond. Nb3Sn tape then rapidly disappeared. In order to meet the needs of the next generation of high-field magnets in the 16-18 T range, we need Nb3Sn conductors that not only significantly exceed today’s best critical current properties but also can be produced at reasonable cost. Our own most recent ventures have been with Hf-alloyed Nb4at.%Ta alloys. Kyoji Tachikawa had championed Hf as a potentially beneficial addition to Nb in the early 1980s. With few demands then for ultra-high field properties, the benefits may have been overlooked. We have since returned to examine Hf additions to the Hc2-optimized Nb4at.%Ta alloy. We have found that the Nb4at.%Ta1Hf alloy recrystallizes much less easily than Nb4at.%Ta alloy and forms a much smaller A15 grain size without sacrificing irreversibility field, greatly increasing the high field current density. We look at the history of these developments and what they might suggest for the future development of Nb3Sn conductors.
