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This paper studies preparation process and its technology of high RRR value of Wire in channel (WIC) NbTi superconductor wires. It is generally accepted that the lower the oxygen content in the oxygen-free copper, the higher RRR value. In this paper, the results show that the RRR of WIC wire also can achieve relatively high levels under the high oxygen content condition.
Three methods were adopted in this article.
The first method is online annealing on medium frequency furnace, cooling, fluxing, and then soldering using C10100 copper channel wire. When the heating power was higher, the RRR value can meet the requirement of more than 175. But the surface quality of WIC wire and inserting effect were poor.
The second method is using C10100 copper channel wire heat in the vacuum furnace, fluxing, and then soldering. The RRR values of WIC wire were 213-256, with the surface quality and inserting effect were good.
The third method is using C11000 copper channel wire to solder directly. The oxygen content of the selected C11000 copper channel wire ranges from 75 to 200 parts per million (PPM). The RRR value of WIC wire can be improved to 240-260.
In order to study the problem, using C11000 and C10100 to heat at 500 ℃ for 2 hours, and then the microstructure was observed. The C10100 still exist dislocation etc. defects. And the C11000 have no dislocation and other defects basically, which increase RRR values. In addition, the second-phase was found in grain boundary of C11000, which was Cu2O phase.
The oxygen content of C11000 can exist in the form of Cu2O, which do not affect the increase of low temperature resistance. If oxygen element exists in the form of gap element, it will greatly increase the low temperature resistance, and reduce lower RRR value.