STRONGLY ENHANCED CRITICAL CURRENT-DENSITY IN NB-47-WT-PERCENT-TI HAVING A HIGHLY ALIGNED MICROSTRUCTURE

The transport critical current density increased from 2610 to 5200 A/mm2 at 5 T, 4.2 K, when a round monofilament Nb 47 wt. % Ti composite was rolled to an aspect ratio of 9.7 and was tested with the broad face of the tape parallel to the field. This value exceeds the previous maximum of 3700 A/mm2 by about 50%. Transmission electron micrographs show that more than 90% of the alpha-Ti precipitates in the optimum-rolled filament are aligned within 10-degrees of the broad face of the tape, whereas the precipitates had a random azimuthal orientation prior to rolling. The strong alignment caused the elementary pinning force to be greatly enhanced in the parallel-field orientation; however, in the orthogonal orientation the J(c) fell to low values characteristic of conventional wires having no alpha-Ti flux pinning centers.