Nb3Al conductor fabricated by DRHQ (Double Rapidly-Heating/Quenching) process

For Nb₃Al 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°C, resulting in a 2-5 times higher J_c(4.2 K) than those of commercial (Nb,Ti)₃Sn wires. However, the best values of T_c=17.8 K and H_c2=26 T are rather lower than those of stoichiometric Nb₃Al, 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°C) heat treatment to obtain near-stoichiometric Nb₃Al. Without any additional elements, the Nb₃Al compounds synthesized by the DRHQ (Double Rapid Heating/Quenching) process show T_c and H_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/mm² at 25 T, 270 A/mm² at 24 T and 330 A/mm² at 23 T