Brass を母材とした新しい内部拡散法 Nb₃Sn 線材の研究

抄録

 Bronze processed and internal Sn processed Nb₃Sn wires with a small amount of Ti additive are being widely used for ITER, NMR and other applications. However, heat treatment for Nb₃Sn synthesis reduces the Sn concentration in the matrix to a few %. The wires then become mechanically delicate and must be handled carefully. As an alternative method to improve the mechanical properties of the wires, we choose gold brass (Cu-15 wt% Zn) as the matrix, which exhibits attractive mechanical performances. Two different processes have been applied to fabricate the wires, and then the diffusion behavior of each element in the wires has been investigated. EPMA results indicate good inter diffusion between brass matrix and Sn during heat treatment. Zn does not penetrate into Nb₃Sn, and remains homogeneously in the matrix after the Nb₃Sn synthesis, improving the mechanical tolerance of the wire. Moreover, Zn seems to be effective in accelerating the Nb₃Sn synthesis. A J_c (without sheath) of 350 A/mm² at 16 T and Bc₂ of 25.5 T have been obtained at 4.2 K for the wire. The J_c of the wire may be improved by the optimization of filament configuration in future. React and wind process may be hopeful in the present new wires, which may extend the application area of Nb₃Sn wires.

Fig. 9

Local EPMA mappings of Sn on the cross section of inside of Nb sheath after the heat treatment at 700℃ for 200 h. (a) 0.6φ GB matrix composite-processed wire, and (b) 0.6φCu matrix composite-processed wire.