Studies on filamentary Nb3Sn wires fabricated by the infiltration method

Superconducting wires containing a network, of Nb3Sn filaments are produced by powder metallurgy techniques. The fabrication involves achieving a controlled porosity in compacts of sintered niobium followed by tin infiltration and mechanical reduction. The Nb3Sn filaments, typically 1-5 μm in size, are formed by a short heat treatment. The effects of heat treatment on critical current and transition temperature are presented for reaction temperatures in the range of 700-1200°C and for lengths of time varying from 1 min to several hours. The dependence of Jcon filament size is studied. The conductor evaluation includes measurements of Tc, of Jcup to 170 kG, and mechanical bend tests. Efforts are made to explain the results, wherever possible, by means of microstructural observations such as the Nb3Sn grain size and the microvoids formed as a result of diffusion treatment. In view of the high values of Jcobtained- 1.1×10⁵A/cm²at 100 kG and 7.5×10⁴A/cm²at 150 kG (computed on the basis of the Nb3Sn-Nb core)-these filamentary wires appear to have a potential especially for applications in high field superconducting magnets.