JPS6041710A - Compound superconductive wire material - 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 (1) Background and Objectives of the Invention The present invention relates to an ultrafine multicore compound superconducting wire with improved strain resistance.

Nb3 Sn, (NbTi)3 Sn, V3
Compound-based superconducting wires such as Ga have been widely used in recent years because of their good superconducting properties in high magnetic fields. On the other hand, these compound-based superconducting materials have very mechanically brittle properties, so there are restrictions when using them, such as the need to suppress strain to 0.8% or less. Conventionally, methods such as reducing the wire size to match the superconducting coil winding diameter have been adopted. However, such countermeasures cannot be said to be fundamental countermeasures, and it is considered that the most important thing is to increase the distortion resistance, that is, the usable distortion limit.

By the way, the method of manufacturing compound-based superconducting wires is mainly to perform compound processing on the compound components in a state that is easy to process, and then perform heat treatment to prevent the formation of the compound, causing a diffusion reaction at the interface of each component to generate a compound phase. be. This method will be specifically explained using the example of Nb3Sn'i. As shown in FIG.
An alloy matrix 2, a diffusion barrier 3, and a configuration embedded in stabilized Cu4 are fabricated. At this stage, NI)
The core wire, the Cu5n alloy, the diffusion barrier, the stabilized Cu, and the like are all components that are easy to process and can withstand processing sufficiently if intermediate annealing is performed to remove work hardening. Composite wires with such a configuration are subjected to area reduction and molding processing to the final use shape, and in order to obtain superconducting properties, for example,
Nb
and Sn in Cu5n undergo a diffusion reaction to form a superconducting compound Nb,+Sn layer on the surface of the Nb core wire. As is clear from Figure 2, which shows the cross section of the wire after the heat treatment for compound formation, the diffusion reaction takes place on the surface of the Nb core wire, so that Nb3
The Sn layer is generated only on the surface of the Nb core, and unreacted Nb remains in the center of the core. When the superconducting critical current is measured while applying tensile strain to the Nb3Sn compound superconducting wire produced in this way, as shown in Figure 3, the critical current value increases as the strain is applied, and after reaching a very thick value, it suddenly decreases. decreases to The reason why the critical current value shows a maximum value due to strain is thought to be due to the difference in the coefficient of thermal expansion of each constituent material.

That is, Cu, Cu5 than the N b B S n layer
Since the coefficient of thermal expansion of the n-alloy is large, compressive strain is applied to the N b 3 S n layer during cooling from the compound formation heat treatment temperature to the superconducting wire utilization temperature of 42 K (-269.8 °C), resulting in tensile stress. By applying strain, the compressive strain is relaxed and the critical current value increases (recovers to its original value). As the tensile strain increases further, the critical current value deteriorates. A strain of 0.80i) causes the critical current value to be almost the same as the value of the target for applying strain, which is the value considered to be the limit of use of the Nl)3Sn wire.

The present invention has been made in view of the above points, and aims to provide an ultrafine multi-core compound superconducting wire that eliminates the drawbacks of the prior art described above and improves the strain resistance of the compound superconducting wire. It is.

(2) Summary of the Invention In other words, the gist of the present invention resides in that the core material of a compound-based superconducting wire is composited with a metal material having a large coefficient of thermal expansion. Here, it is preferable that the coefficient of thermal expansion of the composite metal material is larger than that of the superconducting compound, and it is preferable that the metal material is composited inside each core wire.

As mentioned above, by using a metal material with a large coefficient of thermal expansion for the core material, the compound layer is subjected to compressive strain from the inside and outside during cooling from the compound generation heat treatment θ1j to the temperature used as a superconducting wire, so that it can be uniformly strained. And it becomes more distorted. Therefore, when a tensile strain is applied to this wire, it can withstand a tensile size corresponding to a larger compressive strain than a conventional compound wire rod.

(3) Example Hereinafter, an example according to the present invention will be described with reference to FIGS. 4 to 6. FIG. 4 is a cross-sectional view of the compound-based superconducting wire according to the present invention before heat treatment for compound formation. Sn matrix 2,
It is embedded in Nb Nonoria 3 and stabilizing material 4. FIG. 5 shows a cross section of the wire after heat treatment for compound formation at 750°C for 100 hours.
A diffusion reaction occurs with Sn in n to form an NbB Snn layer. The Nb3Sn layer 8 is formed only on the surface of the Nb core, and its thickness is constant depending on the diameter of the Nb core, the cross-sectional area ratio of Cu5n and Nb, and the heat treatment conditions. Therefore, the inside of the core wire with a little unreacted Nb layer 6 remaining becomes Cu7.
The thickness of b can be determined in advance.

In the example of the present invention, the Nb core wire before heat treatment for compound formation was 5
μm, with 2 μm of oxygen-free copper in the center, and after heat treatment at 750°C for 100 hours to form a compound,
An Nb3Sn layer with a thickness of 08-1 μm is formed on the surface of the Nb core wire, but an unreacted Nb layer (05-07 μm thick) remains between the Nb3Sn layer and the oxygen-free copper. did. As a result of measuring the superconducting critical current by applying tensile strain to such a wire, as shown in Fig. 6, the strain resistance was 11 times higher than that of the conventional Nb3Sn structure, and the resistance up to 088 was half that. Ivy.

Although the present invention has been explained using Nb3Sn as an example in order to facilitate understanding of the present invention, the present invention applies to V3Ga.

Of course, it can also be applied to ultrafine multi-core compound-based superelectric Q-rays such as (NbTi)3sn, which exhibits a large coefficient of thermal expansion as a metal moon phase placed in a thin core wire (rf, 'Cu.

It is not limited to pure metals such as At, but also Cu alloys.

A4 alloy or the like may also be used.

(4) Effects of the Invention As mentioned above, according to the present invention, 1) a large compressive strain is applied to the superconducting compound during cooling by compounding metal 4A with a large coefficient of thermal expansion into each core wire; Therefore, it is possible to provide an ultra-fine multi-core compound superconducting wire that can withstand the corresponding tensile strain when twisted.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional compound-based superconducting wire before heat treatment, Figure 2 is a cross-sectional view of it after heat treatment, and Figure 3 shows the relationship between tensile strain and critical current value in a conventional compound-based superconducting wire. Graph, FIG. 4 is a cross-sectional view of the compound-based superconducting wire according to the present invention before heat treatment, FIG. 5 is a cross-sectional view after heat treatment, and FIG. 6 is the tensile strain and critical current value in the compound-based superconducting wire according to the present invention. It is a graph showing the relationship between. 1...Nb core wire, 2...Cu5n matrix, 3...Nb barrier, 4...Cu
, 5...Nb3Sn layer, 6...Nb,
7...Cu, 8...Nb3S
n. Mathematics 30 3rd Picture Garden 411 Children 6121

Claims (3)

[Claims] (1) An ultra-fine multi-core compound superconducting wire material, which is characterized in that each core wire is made of a composite of a metal material with a coefficient of thermal expansion that is extremely high. (2) The ultrafine multicore compound-based superconducting wire according to item (1) above, wherein the thermal expansion coefficient of the composite metal material is larger than that of the superconducting compound. (3) The ultra-fine multicore compound conductive wire according to item (1) or (2) above, wherein the metal material is composited inside each core wire.