High critical current density with low current sharing in a multifilament Nb55w/oTi superconductor

The Ti-rich NbTi-multifilament superconductor with a high current density at low fields and low current sharing properties is particularly well suited for application in NMR-magnets. In order to improve the performance of this kind of superconductors a number of Cu-billets with 54 filaments Nb55w/oTi have been extruded in a 1.4 GPa hydrostatic extrusion press. By subsequent cold area reduction and final precipitation heat treatment high critical current densities at low fields are obtained with very low current sharing (Jc= 5.8 * 10⁹A/m²at 2T). TEM-investigations reveal a high density of small disc-like ω-Ti precipitates (Ptt. density m^-3). The ω-Ti precipitates with a special orientation relationship relative to the β-matrix are situated on specific crystallographic planes inside the subbands. This is different from the α-Ti precipitation in subband walls observed by other investigators in conventionally extruded and optimized NbTi-superconductors.