Studies on filamentary Nb3Sn wires fabricated by the infiltration method

Superconducting wires containing a network of Nb3Sn filaments are produced by 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 700-12000C and for lengths of time varying from 1 min to several hours. The dependence of J/sub c/ on filament size is studied. The conductor evaluation includes measurements of T/sub c/, of J/sub c/ up 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 J/sub c/ obtained (1.1 x 105 A/cm2 at 100 kG and 7.5 x 104 A/cm2 at 150 kG), these filamentary wires appear suitable for high field superconducting magnets. 9 fig