JPS6226709A - Annealing of superconductor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for annealing superconducting wire, and in particular makes it possible to anneal superconducting wire plated with a low melting point metal or soldered.

Conventional technology Superconducting wires using copper as the stabilizing metal are usually cold-worked into the final shape and then annealed in an atmosphere at 300°C for about 2 hours, or high-temperature (400°C to 400°C to completely remove processing strain). On the other hand, in the case of superconducting wire plated with a low melting point metal such as Sn or soldered, the melting point of Sn and solder is around 200°C.
Since Sn plating and soldering cannot be annealed afterwards, the superconducting wire is generally annealed before Sn plating and soldering.

Problems to be Solved by the Invention In superconducting wires in which a stabilized copper wire is integrated with a superconducting wire by PB-8N soldering, soldering is sometimes done by passing through a drawing die to reduce the area. Annealing to remove is not possible due to the low melting point of pb-8n solder. In addition, in forming stranded superconducting wires for accelerators, multiple superconducting wires are plated with Ag-3n solder and then stranded.
This is not possible due to the low melting point of g-8n solder. Furthermore, if a large amount of superconducting wire is wound around a spool and then annealed, adhesion will occur between the wires, resulting in surface defects, and in severe cases, it may become impossible to unwind the wire. Further, depending on the annealing conditions, the superconducting critical current characteristics may deteriorate under conventional annealing conditions.

Means for Solving the Problems In view of this, and as a result of various studies, the present invention has developed a superconductor that eliminates the cold working strain of superconducting wires plated with low melting point metals or soldered, and that does not deteriorate the critical current characteristics of the superconducting wires. A wire annealing method has been developed, and 50% of the stabilizing metal for superconducting wire is
The superconducting wire is in a cold worked condition of 120-20% or more.
It is characterized by heat treatment at a temperature of 0° C. for 10 hours or more.

That is, in the present invention, in annealing a superconducting wire using copper as a stabilizing metal or a superconducting wire in which a stabilizing metal wire is combined with the superconducting wire, a total of 50 or more stabilized metals of the superconducting wire are subjected to strong cold working, and this is It is heated at a temperature of ~200°C for 10 hours or more. For example, in a stranded superconducting wire made by plating Ag-8n solder on a multi-core superconducting wire using copper as a stabilizing metal and twisting together multiple wires, 50%
After adding the above cold working, solder plating with Ag-8N, twisting a plurality of strands together and molding them.
Heat treatment at ℃ for 10 hours or more. In addition, centering on the above multicore superconducting wire, multiple stabilized copper wires are twisted together and the superconducting wire is semi-concaved, and the multicore superconducting wire and stabilized copper wire are subjected to cold working of 50% or more. After that, they are twisted together, soldered, and then heat treated at 120 to 200°C for 10 hours or more.

Effect of the present invention As described above, by subjecting the stabilizing metal of the superconducting wire to a 50% or more cold-worked state, it is possible to perform annealing at a temperature below the melting point of solder or low-melting point metal, thereby reducing the superconducting critical current of the superconducting wire. It is possible to remove cold working strain without deterioration. As for the cold working state of the stabilized metal, the higher the degree of working, the lower the annealing temperature and the shorter the heating time.

Therefore, according to the present invention, PB is added to superconducting wires and stabilized metal wires.
It is possible to attach low melting point solder such as -8n or Ag-8n and annealing in good condition, and cold working strain after solder attachment can be recovered by annealing. Furthermore, since the annealing is performed at a low temperature, no adhesion occurs even when a large amount of wire is wound around one spool and annealed.

Example (1) Stabilization of superconducting wires Copper wires were cold-worked at various working degrees and then heat-treated at various temperatures to determine the residual resistance ratio (
The ratio of the electrical resistance at 300K to the electrical resistance at 10K was determined. An example of this is shown in FIG.

The figure shows the residual resistance ratio on the vertical axis and the heating temperature on the horizontal axis, and shows the cases where cold-worked samples with a degree of cold working of 50%, 90%, and 95% were heat-treated for 48 hours, and as can be seen from the figure, they were stabilized. It can be seen that the more intensely cold-worked the copper wire is, the lower the temperature it anneals. On the other hand, the stabilized copper wire used in superconducting wires has a residual resistance of 100 or more, and the melting point of solder such as PB-8N used in superconducting wires is around 200°C. It can be seen that if it is 50% or more, preferably around 90%, sufficient annealing is possible even at a low temperature of 200° C. or less by heating for a long time.

Example (2) A NbTi multicore superconducting wire with copper as a stabilizing metal was prepared with a diameter of 2.
Aging heat treatment was performed at 320° C. for 120 hours at 2■, and this was cold worked to a diameter of 0.7 mm (working rate 90%).

As shown in Figure 2, 5n is applied to the circumferential surface of the superconducting wire (1).
Nine pieces of -5% Ag alloy (2) hot-dipped to a thickness of about 1 μm were twisted together and formed as shown in the figure to form a stranded wire with a rectangular cross section for a dipole magnet for an elementary particle accelerator.

When this was annealed at 160° C. for 48 hours in a N2 gas atmosphere, the residual resistance and resistance ratio were 120. Further, no discoloration, no evidence of melting of the 5n-5% Ag alloy, and no adhesion between the strands was observed in the annealed strands. Furthermore, when measuring the superconducting critical current characteristics before and after annealing, there was a difference of only ±1%, and considering the measurement accuracy, it seems that there was no deterioration in the characteristics due to this annealing. The residual resistance ratio of the formed stranded wire before annealing was 55.

Example (3) After performing aging heat treatment at 320°C for 120 hours with a diameter of 3.1 mm, cold working to a diameter of 0.7 wn (processing rate of 95%)
] NbTi multicore superconducting wire using copper as a stabilizing metal,
After annealing at 500℃ for 1 hour with a diameter of 3.1 mm,
Using oxygen-free copper wire that has been cold-worked to a diameter of 0.7 mm (processing rate 95%), as shown in Figure 3, the superconducting wire (1) is centered and the oxygen-free copper wire (3) is placed around it. A completely stabilized superconducting wire was produced by twisting 6 wires together and passing them through a Pb-50wt%Sn solder bath and hot-dip plating while passing through a drawing die with a diameter of 1.8 mm.This was annealed at 150°C for 60 hours. As a result, the residual resistance ratio recovered from 50 before annealing to 125.The superconducting wire after annealing was coated with PB-8.
No evidence of melting of the solder was observed.

Effects of the Invention As described above, according to the present invention, it is possible to perform annealing that removes cold working strain after solder adhesion, which was previously impossible, and also has the remarkable effect that the superconducting critical current characteristics of the superconducting wire do not deteriorate due to annealing. It is something to play.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the influence of cold working rate on the recovery of residual resistance ratio by annealing of stabilized copper wire of superconducting wire, Fig. 2 is a sectional view showing an example of a superconducting stranded wire with a rectangular cross section, Third
The figure is a cross-sectional view showing an example of a fully stabilized superconducting wire. 1 Superconducting wire 2 Sn-Ag alloy layer 2 Oxygen-free copper wire Figure 1

Claims (1)

[Claims] A method for annealing a superconducting wire, the method comprising heating the superconducting wire at a temperature of 120 to 200° C. for 10 hours or more while bringing the stabilizing metal of the superconducting wire into a 50% or more cold-worked state.