Diffusion Reaction Behavior in Internal Tin Nb₃Sn Wire Using Nb/Cu-Ti/Sn-Zn Diffusion Configuration

Microstructural control of Nb ₃ Sn wire is quite important for improving the critical current density (J _c ). Elemental doping is an effective method to improve the microstructure. In previous work, we have shown that Zn doping of Nb ₃ Sn wire suppresses Kirkendall voids formation, and promotes the Nb ₃ Sn layer formation. As an effective method to dope with Zn, we have previously proposed a Nb/Cu-Ti/Sn-Zn diffusion-pair structural internal tin Nb ₃ Sn wire. In this study, we investigated the effect of Zn doping on the microstructure and the superconducting characteristics of this system, using a single Nb/Cu-Ti/Sn-Zn structural diffusion couple. The Sn composition in the Nb ₃ Sn layer of the Zn doped specimen is slightly slower than that of the non-Zn doped one. The microstructural analysis was carried out by Electron Back Scattered Diffraction (EBSD), Energy Dispersive X-ray Spectroscopy (EDX) and digital image analysis. The average grain size was decreased with Zn doping, leading to an improvement in layer J _c in a low magnetic field. The thickness of the Nb ₃ Sn layer in the Zn doped specimen is also thinner than that in the non-Zn doped one. In the diffusion-pair structure used in this work, increasing of the Zn content in the Sn-Zn core sacrifices the Sn content in the core. A decrease of the Sn content would account for the smaller Nb ₃ Sn thickness in the Zn-doped specimen.