Optimization studies for processing Nb3Al by a rapid ohmic-heating and quenching method

Rapid heating to different temperatures in the vicinity of 2000 degreesC followed by quenching to room temperature was used to prepare short samples of jelly-roll-type Nb3Al superconductor, The as quenched material has either a bce or A15 structure depending on the presence or absence of a specific endothermic reaction during the rapid heating, but after a secondary heat treatment at 800 degreesC an A15 structure is obtained for both cases. Significantly higher critical current densities at magnetic fields up to 18T (4.2K) are obtained for samples quenched as bcc, while the A15-quenched material is superior at higher fields due to a larger upper critical field. For the bcc-quenched samples the critical current density is optimized (16T, 4.2K) when they are quenched from temperatures just above or 400 degreesC higher than the temperature of the endothermic reaction, with a noticeable drop in the middle range. A 10 hour secondary heat treatment gives rise to better superconducting properties than a 3 hour heat treatment (both at 800 degreesC). Some of the observed dependencies are explained using SEM microstructure analysis.