Study and Manufacture of Nb3Sn Strands by Bronze Route

Three kinds of Nb3Sn strands with different designs were made by bronze route. Studies were carried out on bronzeto-NbTa-volume ratio, filament diameter, annealing, hot isostatic pressure process, diffusion barrier, and heat treatment. It is important for strand designs to achieve a good performance. Moreover, bronze-to-NbTa-volume ratios of 2.4 and 2.8 were applied in the strand designs. Strands with lower bronze ratio means that more Nb3Sn layer fraction formed, while, at the same time, it is provided with a high critical current density (J
_c
). J
_c
increases with the reduction of filament diameter, when there is the same bronze ratio. In addition, Nb and Ta were used as diffusion barrier materials. A strand that used Nb barrier has several times hysteresis loss to a strand that used Ta barrier. When it comes to the intermediate processes, such as annealing and hot isostatic pressure, they could affect the homogeneous deformation and properties of strands. It is important to keep a low annealing temperature to realize a high J
_c
and n-value. As for the hot isostatic pressure process, it is helpful for uniform cross section. Furthermore, different heat treatments were also carried out, while analysis was also conducted on the microstructure.microstructure.