Nb/sub 3/Al conductor fabricated by DRHQ (Double Rapidly-Heating/Quenching) process

Abstract

For Nb/sub 3/Al compound, extremely high temperatures are required to obtain the stoichiometric A15 phase, so that the rapidly-heating/quenching process has been developed. In the process the Nb/Al composite filaments change into Nb-Al supersaturated bcc solid solution filaments with rapid-heating/quenching. The Nb-Al solid solutions are transformed into A15 phases with post-annealing at 800/spl deg/C, resulting in a 2-5 times higher J/sub c/(4.2 K) than those of commercial (Nb,Ti)/sub 3/Sn wires. However, the best values of T/sub c/=17.8 K and H/sub c2/=26 T are rather lower than those of stoichiometric Nb/sub 3/Al, which is due to its off-stoichiometry. Therefore, we tried a 2nd rapid-heating/quenching to the 1st rapidly-heated/quenched wires having Nb-Al solid solution filaments. The phase transformation was performed with the 2nd rapid-heating/quenching, which is a very-short high-temperature (about 1900/spl deg/C) heat treatment to obtain near-stoichiometric Nb/sub 3/Al. Without any additional elements, the Nb/sub 3/Al compounds synthesized by the DRHQ (Double Rapid Heating/Quenching) process show T/sub c/ and H/sub c2/(4.2 K) of about 18.4 K and 30 T, respectively. The most interesting result is its excellent J,(4.2 K)-B performance, e.g., 2nd A/mm/sup 2/ at 25 T, 270 A/mm/sup 2/ at 24 T and 330 A/mm/sup 2/ at 23 T.