Effect of Titanium Content and Doping Method on Phase Formation and Properties of Nb3Sn Strand

Doping with Ti is crucial for enhancing the upper critical field of Nb₃Sn strand produced by internal tin process. This study investigates the effects of different Ti doping methods and concentrations on the low-temperature performance of Nb₃Sn strand. We compare two methods: one replaces Nb cores with NbTi cores, while the other integrates Ti into Sn ingots to form SnTi alloys, with adjustable Ti content. Four Nb₃Sn strand with varying Ti concentrations were produced using these methods. Microstructural and performance tests show that Ti doping refines Nb₃Sn grains. J_c increases with Ti content from 0% to 2%, but decreases beyond 2% due to grain growth from excessive Ti. Additionally, the larger Ti₆Sn₅ phase in the SnTi alloy results in more breakage during processing. Thus, using SnCu alloy as the Sn source and NbTi rods for Ti doping is a more feasible approach for the production of Nb₃Sn strands.