Influence of Final Drawing Strain on the Jc of NbTi Superconductor

The optimization of critical current density in NbTi superconductors involves a complex schedule of heat-treatments, which precipitate normal conducting alfa-Ti precipitates and reduce the dimensions of these precipitates to the optimum size for flux pinning. Final drawing strain is the most important parameter for the optimization of the critical current density. In this paper, high homogeneity Nb47Ti alloy was applied for the fabrication of the NbTi superconductors. The NbTi samples were having the same intermediate stage heat-treatment schedule just varied in the final drawing strain ranging between 4 to 5.5. The critical current of these samples were tested at 4.2 K under different magnetic fields ranging between 2 to 8 Tesla. Based on the results, it was found that the optimal final strain for the NbTi/Cu samples was about 4.8. Jc decreased abruptly after the maximum value has been passed. The effect of the final drawing strain on the Jc in the low magnetic field region was more significant than which in the high magnetic fields.