Effects of titanium addition to the Nb3Sn wires fabricated by the internal tin diffusion process

The titanium-doped Nb3Sn wires have been successfuly fabricated by the internal tin diffusion process (IDP). These wires consist of a Sn-4.8 at%Ti alloy core at the center and 99 pure niobium and/or Nb-1.9at%Ti alloy filaments placed in three layers around the Sn-Ti core. These wires were easily drawn to the final sizes without any intermediate annealing, and were heat treated at 650-750°C for 30 - 300 hr. The Electron Probe Micro Analysis analysis (EPMA) has revealed that, when the titanium is added only to the tin core, the titanium content in Nb3Sn filaments decreases with increasing distance from the center of the wire. On the other hand, the simultaneous titanium addition to the tin core and two outer layers of niobium filaments has attained the uniformity of the titanium content; ∼ 0.8at%Ti is incorporated in all Nb3Sn filaments. The overall Jcof A/cm²at 15 T and the improved Bc2have been obtained for the Nb3Sn wires with the simultaneous titanium addition. These results indicate that the IDP Nb3Sn wires with simultaneous titanium addition to the tin core and niobium filaments are the most promising candidate materials for high field magnets.