Thermomechanical Processing of Nb for Improved Superconductor Applications

72559B03-I For Nb-based superconductor applications, prior work has indicated that if the starting Nb configuration (rod, plate, sheet, or tube) has large grain size, a nonuniform grain size, or significant texture gradients, then the resulting multi-filamentary conductors will have a lower critical current due to fabrication limitations (such as filament size) or such difficulties as filament sausaging. Recent experiments on one-square-inch-cross-section bars have shown that equal channel angular extrusion (ECAE) can be effective not only in reducing the grain sizes but also in homogenizing the micro structure of re-melted Nb. This project will demonstrate that the same technology is effective in processing large diameter (up to 8-inch diameter) commercially fabricated billets. Phase I will demonstrate the scale-up of ECAE processing technology on four-square-inch-cross-section re-melted Nb billets with existing equipment. The scale-up will be assessed by comparing micro-hardness, recrystallized grain size, and microstructural uniformity results on 0.56 , 1, and 4 square-inch-cross-section billets. Commercial Applications and Other Benefits as described by awardee: The ECAE technology should lead to the preparation of better starting pure Nb for Nb3Sn superconductors.