JPH09120721A - Nb3sn compound superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the critical current characteristics and lower the trait of hysteresis loss by forming continuous fibers from an Nb-Ta alloy containing 0.5-1.5at.%, and turning them into ultra-thin fibers without degrading the easiness in processing the conductor. SOLUTION: An Nb3 Sn compound superconductor is structured so that sub- element wires 1 in which a number of continuous Nb-Ta alloy fibers are embedded, are gathered in a matrix 2 made of Cu-Sn alloy, and a diffusive barrier of Ta 3 and a stabilizer of Cu 4 are formed one over another on the periphery of the gathering of sub-element wires. The continuous fibers in these sub-element wires 1 consist of Nb-Ta alloy containing 0.5-1.5at.% Ta, and the diameter prior to the final heat treatment is 1-4μm. Besides Sn, the matrix of Cu-Sn alloy contains at least one of the Ti, Ni, Ga, Si, Al, Zn, Ta, and B in a total content of no more than 5at.%. This ensures that the critical current characteristics are enhanced and the trait of hysteresis loss is lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Nb ₃ Sn-based compound superconducting conductor, and more particularly, to improving the critical current characteristics and the history loss characteristics by making it possible to make the continuous fibers extremely fine without deteriorating the workability of the conductor. The present invention relates to a Nb ₃ Sn-based compound superconducting conductor for reducing

[0002]

2. Description of the Related Art As a compound superconducting conductor, for example, Cu
-Nb formed by bronze method using Sn alloy
₃ There are Sn-based superconducting conductors.

Conventionally, this type of Nb ₃ Sn-based compound superconducting conductor has a large number of Nb in a matrix containing Sn.
Of the continuous fiber are embedded and subjected to predetermined processing (for example, heat treatment) to form an Nb ₃ Sn compound layer.

Further, in the production of Nb ₃ Sn-based compound superconducting conductors, the Cu-Sn alloy matrix is generally significantly hardened by cold surface-reduction processing, which makes it difficult to process the conductors. As an intermediate heat treatment for recovering the workability of the Sn alloy matrix, annealing at 600 ° C. or higher is performed many times during cold working.

[0005]

However, the conventional Nb ₃
According to the Sn-based compound superconducting conductor, Cu-Sn described above is used.
Due to the intermediate heat treatment of the alloy matrix, a trace amount of Nb ₃ Sn is formed at the interface between the Cu-Sn alloy matrix and the Nb continuous fiber.
A system compound is produced. This Nb ₃ Sn-based compound is Nb
If the diameter of the continuous fiber is large, it does not hinder the workability of the conductor at all. However, if the diameter of the continuous Nb fiber is in the order of micron, necking or breakage occurs in the continuous Nb fiber, and the number of disconnection increases. This causes inconvenience that workability is lowered and critical current characteristics are lowered.
Therefore, the diameter of the Nb continuous fiber could not be reduced to 4 μm or less.

It is therefore an object of the present invention Hakare ultrafine of continuous fibers without reducing the processability of the conductor, it is possible to reduce the increase and history loss characteristics of critical current characteristic Nb ₃ Sn
An object is to provide a compound superconductor.

[0007]

In view of the above-mentioned problems, the present invention is capable of achieving ultrafine continuous fibers without deteriorating the workability of the conductor, improving the critical current characteristics and reducing the hysteresis loss characteristics. there is provided a continuous fiber is constituted by Nb-Ta alloy containing 0.5～1.5At% of Ta Nb ₃ Sn compound superconducting conductors.

The continuous fiber has a structure in which the diameter before the final heat treatment for producing the Nb ₃ Sn type compound is 1 μm or more and 4 μm or less.

The matrix containing Sn is composed of a Cu-Sn alloy, and the Cu-Sn alloy contains Sn, Ti, Ni, Ga, Si, Al, Zn,
It has a configuration in which at least one of Ta and B is contained in a total amount of 5 at% or less.

The reason why the Ta content of the Nb-Ta alloy constituting the continuous fiber is 0.5 to 1.5 at% is that the content of 0.5 at% or less is less than that of pure Nb. The compound production inhibitory effect does not appear, and the content is 1.5
This is because, when the content is at% or more, on the contrary, a compound production promoting effect occurs and the compound production amount increases.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The Nb ₃ Sn compound superconductor of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows the sectional structure of the Nb ₃ Sn compound superconductor of the present invention before the final heat treatment. This Nb ₃ Sn-based compound superconducting conductor contains 5 continuous fibers of Nb-Ta alloy in a matrix 2 of Cu-Sn-based alloy.
Assembling 361 sub-element wires 1 embedded 5
A diffusion barrier 3 of Ta and a stabilizing material 4 of Cu are sequentially formed on the outer circumference of the barrier.

The continuous fibers in the sub-element wire 1 have a density of 0.
It is composed of an Nb-Ta alloy containing 5 to 1.5 at% Ta. This continuous fiber has a diameter of 1 before the final heat treatment.
It is about 4 μm.

The embodiments of the present invention will be described in more detail below. First, the above configuration, that is, Nb-T of continuous fibers
a and a 1st and 2nd embodiment which has a structure whose Ta content is 0.5-1.5 at%, the comparative example 1 whose continuous fiber is pure Nb, and the Nb-Ta alloy of continuous fiber. Comparative Example 4 having a Ta content of 1.5 at% or more was prepared based on the conditions shown in Table 1. That is, the conductor diameter is 0.9 mm,
The number of fibers was 19,855, the continuous fiber diameter before the final heat treatment was about 1.90 μm, and the cross-sectional area ratio of copper to non-copper portion was 1.6: 1.

[Table 1]

These conductors were manufactured by the double stacking method using hydrostatic extrusion, and the extrusion temperature at the time of production was 400 ° C. which is common to each stage, and the extrusion ratio was 5.3 for the extrusion billet diameter of about 27.5 mm. Carried out. Further, the intermediate heat treatment condition in the drawn wire was 600 ° C. × 30 minutes, and the heat treatment area reduction ratio was 35 to 40%.

Next, Nb produced in the conductors of the first and second embodiments and the comparative examples 1 and 2 by the intermediate heat treatment.
_In order to compare the amount of ₃ Sn compound layer, the temperature change of the magnetization intensity was measured for these conductors before the final heat treatment of Nb ₃ Sn formation, and the Tc (about 9 K) of Nb or Nb-Ta alloy was measured. The strength of magnetization immediately above was measured. The measurement was performed by a high-sensitivity magnetization measuring device equipped with an SQUID capable of measuring the strength of magnetization by changing the temperature. The sample applied magnetic field at this time was 0.01 T, and the measurement temperature was 20 K to 4.5 K.

FIG. 2 shows the measurement result. Here, the strength of magnetization refers to a magnetic moment per unit volume of continuous fibers on the assumption that a compound is not formed in the intermediate heat treatment. As can be seen from this figure, in the first and second embodiments in which the Ta concentration in the Nb-Ta alloy is in the range of 0.5 to 1.5 at%, the amount of compound produced in the intermediate heat treatment is pure N.
It can be reduced by about 50% from that of b. Also, T
On the contrary, when the concentration a increases, the compound production promoting effect appears, and the compound production amount increases.

After that, the conductors of the first and second embodiments and Comparative Examples 1 and 2 were subjected to Nb _{3 at} 650 ° C. for 200 hours.
The critical current characteristics of the conductors subjected to the heat treatment for forming the Sn compound were considered. FIG. 3 shows the result of the consideration. As can be seen from this figure, the critical current in each of the magnetic fields of 10T, 11T, and 12T is closely related to the production amount of the compound produced in the intermediate heat treatment. That is, in the first and second embodiments in which the Ta concentration in the Nb-Ta alloy is in the range of 0.5 to 1.5 at%, the critical current is significantly improved as compared with Comparative Examples 1 and 2. ing.

Finally, the effective fiber diameter at 5T of the conductors of the first and second embodiments and Comparative Examples 1 and 2 was measured. The measurement result is shown in FIG. As can be seen from this figure, the conductors of the first and second embodiments in which the amount of compound produced in the intermediate heat treatment is small have wire diameters that are about 50% smaller than those of the conductors of Comparative Examples 1 and 2. It is considered that this is because the ribbon-shaped deformation of the fiber due to the compound layer, which is one of the causes of the increase in the effective fiber diameter, was difficult to occur.

However, as can be seen from FIG.
Even within the composition range of the b-Ta alloy, compound formation in the intermediate heat treatment cannot be completely prevented. Therefore, the effect of the present invention has a limit in the continuous fiber diameter. Therefore, the conductor of the second embodiment has a wire diameter of 0.4 mm (continuous fiber diameter of 0.84 μm) under the same intermediate heat treatment condition and reduction of surface area during heat treatment.
m), and the relationship between the amount of compound produced in the intermediate heat treatment and the continuous fiber diameter was examined by the above-mentioned method.
The magnetization just above Tc of the Ta alloy was a value at which a sufficient critical current could not be obtained when the continuous fiber diameter was 1 μm or less. Further, it was found from the same measurement that the continuous fiber diameter of 4 μm or more had almost no influence on the characteristics in the compound formation in the intermediate heat treatment. From this, it is most desirable that the continuous fiber diameter is 1 μm or more and 4 μm or less.

[0021]

As described above, the Nb ₃ S of the present invention is used.
According to the n-based compound superconducting conductor, the continuous fiber is 0.5 to
Since it is composed of Nb-Ta alloy containing 1.5 at% of Ta, the continuous fiber can be made extremely fine without deteriorating the workability of the conductor, and the critical current characteristic and the hysteresis loss characteristic can be improved. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a Nb ₃ Sn-based compound superconducting conductor of the present invention before final heat treatment.

FIG. 2 is a graph showing the relationship between the content of Ta in Nb and the strength of magnetization just above Tc of Nb.

FIG. 3 is a graph showing the relationship between the content of Ta in Nb and the critical current.

FIG. 4 is a graph showing the relationship between the content of Ta in Nb and the effective fiber system at 5T.

[Explanation of symbols]

 1 Sub-element line 2 Matrix 3 Diffusion barrier 4 Stabilizer

Claims (3)

[Claims] 1. A Nb ₃ Sn-based compound superconducting conductor obtained by embedding a large number of continuous fibers containing Nb in a matrix containing Sn and subjecting it to heat treatment or the like to form an Nb ₃ Sn-based compound layer. The Nb ₃ Sn based compound superconducting conductor, wherein the continuous fiber is composed of an Nb-Ta alloy containing 0.5 to 1.5 at% Ta. Wherein said continuous fibers, the Nb ₃ diameter before final heat treatment that produces a Sn-based compound is 1μm or more, according to claim 1 of configuration is 4μm or less Nb ₃ Sn compound superconducting conductors. 3. The Sn-containing matrix is C
The Cu-Sn alloy is composed of u-Sn alloy, and the Cu-Sn alloy is Ti, Ni, G in addition to Sn.
Nb ₃ of claim 1, wherein the composition contains at least one of a, Si, Al, Zn, Ta and B in a total content of 5 at% or less.
Sn-based compound superconducting conductor.