Reducing joint resistance by heat treatment during fabrication of a mechanical joint of high-temperature superconducting conductors
Reducing joint resistance by heat treatment during fabrication of a mechanical joint of high-temperature superconducting conductors
复制标题
高温超导导体机械接头制造过程中通过热处理降低接头电阻
DOI：
10.1109/tasc.2016.2521891
复制
发表时间：
2016
影响因子：
1.8
通讯作者：
H. Hashizume
中科院分区：
文献类型：
--
作者：
T. Nishio;S. Ito;N. Yusa;H. Hashizume
为未来聚变反应堆高温超导磁体的分段制造，对高温超导(HTS)导体的机械连接进行了研究。在先前的研究中，采用桥式机械搭接并在接头表面插入铟箔的大规模简单叠层GdBCO(GdBCO)导体的接头电阻在100kA时达到1.8。然而，获得的接头电阻率(接头电阻与接触面积的乘积)比以往研究中获得的单个机械搭接接头的电阻率大10倍，这可能是由于接触压力分布不均匀造成的。因此，为了减小这种接头的电阻，我们提出了一种在接头制作过程中引入热处理的新方法。采用该方法后，接头电阻在75℃~90℃的加热温度范围内最小，为未经热处理时的60%。接头电阻的降低是由于插入的铟的厚度减少和接触表面的真实面积增加所致。另一方面，当加热温度超过120℃时，X射线计算机断层扫描在铟中观察到较大的空洞，空洞是由带材和金属箔中吸收的气体排放造成的，热处理前通过烘烤导电带和铟箔可以减少空洞。对大型导体接头进行热处理后，由于温度超过120℃，大接头的温度控制变得更加困难，容易产生空洞。因此，在接头制造和热处理之前进行烘烤工艺是避免空洞形成的选择之一。
A mechanical joint of high-temperature superconducting (HTS) conductors has been investigated for segmented fabrication of HTS magnets proposed for a future fusion reactor. In a previous study, joint resistance of 1.8at 100 kA was achieved for a large-scale simple-stacked gadolinium barium copper oxide (GdBCO) conductor having a bridge-type mechanical lap joint with indium foils inserted between joint surfaces. The obtained joint resistivity (the product of joint resistance and contact area) was, however, ten times larger than that of a single mechanical lap joint achieved in previous studies, which may be caused by nonuniform distribution of contact pressure. In order to reduce this joint resistance, therefore, we propose a new method by introducing heat treatment in fabricating process of the joint. By applying the method, the joint resistance became the lowest at heating temperatures of 75 °C–90 °C, which was reduced to 60% of the value obtained without heat treatment. The reduction of joint resistance was due to a decrease in thickness of the inserted indium and an increase in true area of the contact surface. On the other hand, relatively large voids were observed in the indium by X-ray computed tomography when the heating temperature exceeds 120 °C. The voids were caused by emission of the gases absorbed in the tape and foil, and the voids decreased by baking the conductor tapes and indium foil before the heat treatment. Applying the heat treatment to a large conductor joint, the voids can be formed due to the temperature exceeding 120 °C since the temperature control in the large joint becomes more difficult. Therefore, the baking process before the joint fabrication with heat treatment is one of the options to avoid the void formation.