Investigation on the Recrystallization and Nb3Sn Microstructure of Nb Alloys With Large Deformation During Heat Treatment

At fields of greater than 10 T, Nb₃Sn wires with high critical current density are commercially available and has been used to manufacture high field magnets. In such wires, Nb or Nb alloys are drawn with a large reduction to micrometer scale, resulting in high work hardening, and the Nb₃Sn A15 phase is produced by a heat treatment. After the heat treatment, Nb₃Sn A15 phase was generated within Nb or Nb alloys. In this study Nb and Nb-Ta-Zr alloys were used to process Nb₃Sn wire. The microstructure and the hardness were investigated during wire drawing process. After large deformation the grains of Nb filaments were elongated to fiber texture. The heat treatments of Nb₃Sn wires were used to study the recrystallization and Nb₃Sn phase formation within Nb alloys. The results showed that with high deformation the hardness of Nb-Ta-Zr alloy increased more and higher than the pure Nb about 70∼90 Hv with the same strain. During the high temperature heat treatment smaller grains about 100 nm in diameter of Nb₃Sn were produced within Nb-Ta-Zr alloy. Recrystallization proceeded less readily for Nb-Ta-Zr than pure Nb, and at the heat treatment temperature pure Nb grains coarsen to micrometer scale.