In添加したCu合金Nb₃Sn超伝導線材における熱処理温度とミクロ組織変化

抄録

The critical current density （J_c） of Nb₃Sn wires tends to degrade under thermal and mechanical stress or strain during operation. The addition of indium （In） to the Cu–Sn matrix has been proposed as a way to improve stress and strain tolerance, thereby helping to maintain J_c under operating conditions. Because Nb₃Sn superconducting wires are used in the International Thermonuclear Experimental Reactor (ITER) as coils to confine fusion plasma with high J_c, I_c, and mechanical properties as superconducting wires for magnetic fields in future DEMO reactors and fusion power plants. Although this approach shows promise, the microstructural effects of In addition are still not well understood. In particular, how heat treatment and different In contents influence the microstructure has not been sufficiently clarified. In this study, we investigated the effect of heat treatment on the microstructure of Nb/Cu–Sn–In–Ti wires with different Sn and In contents using scanning and transmission electron microscopy. As a result, it was found that indium remained in the Cu matrix even after heat treatment and Nb₃Sn formation. Furthermore, in wires with higher In content, the Nb_₃Sn grains became coarser.