JPH08180752A - Nb3sn superconductive wire and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a superconductive wire with excellent properties. CONSTITUTION: A secondary compounded composite billet 8 is produced by putting hexagonal wires 6 with 1.5-2.2 bronze ratio as a single core and hexagonal rods 7 in an oxygen-free copper pipe 4 while putting a Ta tube between the copper pipe and the wires and rods. The bronze ratio of the whole of the composite billet 8 is set to be 2.2-4.0. A composite wire produced by drawing the composite billet is heated to produce a Nb3 Sn superconductive wire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Nb ₃ Sn superconducting wire having excellent characteristics and workability, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, Nb ₃ Sn is Nb ₃ Al, V ₃
Similar to Ga and the like, it is usually called an A ₃ B type compound superconductor (also called an A15 type compound superconductor). Since these are intermetallic compounds and are extremely difficult to process, it is necessary to manufacture a superconducting wire. The composite billet composed of the high melting point metal A and the low melting point metal B constituting the A ₃ B type compound superconductor is stretched to obtain a composite wire, and then the low melting point metal A is placed inside the high melting point metal A. A manufacturing method of reacting and producing the above A ₃ B type compound superconductor by diffusion heat treatment for diffusing and reacting B is adopted.

A typical bronze method will be described below as a method of manufacturing an Nb ₃ Sn superconducting wire. First, prepare the wires. The method for producing the strands is usually performed by forming a hole in a rod made of a Cu-Sn alloy (hereinafter referred to as bronze) as a matrix and inserting an Nb core material into the rod to form a primary composite billet. Then, it is stretched to be manufactured. Next, this strand is filled in a stabilizing metal sheath (tubular body) or a bronze sheath to form a secondary composite billet. This secondary composite billet is stretched to produce a composite wire. The composite wire may be used as an elemental wire and the above steps may be repeated to form a higher-order composite billet.

By the way, the above composite wire has N in the matrix.
It has a structure in which b filaments are embedded. When this composite wire is subjected to heat treatment at about 500 ° C to 750 ° C, Sn in the bronze reacts with the Nb filaments and N
b ₃ Sn is generated. In this way, the Nb filament becomes a superconducting filament, Nb ₃ Sn filament,
A multifilamentary superconducting wire can be obtained. Depending on the heat treatment conditions, unreacted Nb remains inside the superconducting filament. There is also a method of coating the outer periphery of the composite wire with Sn and then performing diffusion heat treatment (called an external diffusion method).

Further, without using bronze, which has poor workability, C
A manufacturing method of assembling a composite billet using a simple substance such as u, Sn, and Nb, stretching the composite billet, and subjecting the composite billet to diffusion heat treatment is also under study. These manufacturing methods can be similarly applied to the case of an A ₃ B type compound superconductor other than Nb ₃ Sn.

As a method for obtaining a superconducting wire having high characteristics, a method of producing a large amount of Nb ₃ Sn, which is a superconductor, and a method of making a superconducting filament ultrafine are known. In the bronze method, it is relatively easy to make the diameter of the Nb filament to a few μm, so that a superconducting wire with less AC loss can be obtained, and mass production technology such as extrusion is established faster than other methods. It has advantages such as that it is widely used in practice.

However, the bronze method has a drawback of using a Cu--Sn alloy. In the heat treatment after the drawing process, if a Cu—Sn based alloy having a high Sn content is used in order to generate a large amount of Nb ₃ Sn which is a superconductor, the workability deteriorates. At present, Cu with Sn added up to about 15 wt%
In some cases, a --Sn alloy is used, but addition of more than this becomes impractical in terms of workability.

Therefore, a method of increasing the bronze ratio of the composite wire is adopted. In order to increase the bronze ratio of the composite wire, it is usually sufficient to assemble the composite billet by using a wire having a high bronze ratio. This will increase the local bronze ratio.
That is, the manufactured composite wire has a structure in which Nb filaments are sparsely arranged in bronze. The bronze ratio is a value obtained by dividing the volume of the Cu—Sn alloy-based matrix by the volume of the filament in the Nb ₃ Sn superconducting wire, the composite wire, or the composite element wire. In the manufacturing process,
It is calculated by the value of the total volume of bronze / the total volume of Nb core material at the stage of the composite billet.

[0009]

However, when a composite billet is assembled by using a wire having a high bronze ratio and the composite billet is stretched to produce a composite wire, an Nb core material and a Cu-Sn alloy are produced. Since there is a large difference in workability between the Nb core material and the Nb core material, abnormal deformation may occur. This abnormal deformation is usually called sausaging, and it means that the cross-sectional area of the Nb filaments (and thus of the superconducting filaments after the heat treatment) becomes non-uniform in the longitudinal direction of the produced composite wire. This sausaging mainly occurs in the hot extrusion of the composite billet and is not eliminated even in the subsequent wire drawing. In the manufacturing process of superconducting wire, Nb filament (Nb core material) may cause problems such as disconnection to some extent due to various causes, but this sausage is one of the causes of disconnection of Nb core material (Nb filament). It is considered. Therefore, such Nb
It is considered that the sausage of the filament and the disconnection thereof cause the deterioration of the characteristics of the manufactured superconducting wire, and the improvement thereof has been desired.

[0010]

SUMMARY OF THE INVENTION The present invention is in view of such circumstances, has been made result of intense study, its purpose is to suppress the sausaging of Nb filaments, Nb ₃ realizes the excellent characteristics Sn It is to provide a superconducting wire and a manufacturing method thereof.

That is, according to the present invention, the local bronze ratio is 1.5 to.
2.2 includes a filament embedded portion filament is embedded in the Cu-Sn based the alloy matrix, the overall bronze ratio provides a Nb ₃ Sn superconducting wire is 2.2 to 4.0. In addition, as a method of manufacturing this superconducting wire, Cu-
A bronze ratio of 2.2 containing a single-core composite element wire having a bronze ratio of 1.5 to 2.2 containing an Sn-based alloy matrix member and an Nb core material and a Cu-Sn alloy matrix member.
Provided is a method for producing a composite wire rod by subjecting a 4.0 composite billet to a stretching process, and subjecting the composite wire rod to heat treatment.

Generally, in the field of Nb ₃ Sn superconducting wire, what is called a matrix is a bronze part,
A stabilizing metal part and the like. In addition, a diffusion barrier material for preventing Sn or the like from diffusing into the stabilizing metal portion may also be referred to as a matrix. In the present invention, the Nb ₃ Sn superconducting wire overall bronze ratio of the superconducting wire Cu-Sn
It is calculated as the volume of the alloy-based matrix divided by the volume of the filament. The local bronze ratio is the volume ratio of each filament and its surrounding bronze.
At the stage of the composite billet, considering the entire billet, the volume of the arranged bronze part (Cu-Sn alloy-based matrix material) divided by the volume of the arranged Nb core material is the entire bronze of the composite billet. Call it the ratio. The local bronze ratio at the stage of the composite billet is one Nb core material 1
The ratio of the bronze between the book and its surroundings.

In the method for producing an Nb ₃ Sn superconducting wire of the present invention, a single core composite wire is used as a composite element wire containing a Cu-Sn alloy matrix member having a bronze ratio of 1.5 to 2.2 and an Nb core material. The wire is used. When a composite billet is assembled using this wire, the bronze of the composite wire corresponds to the local bronze ratio of the composite billet. When such a single-core composite element wire is used, the bronze ratio (that is, the local bronze ratio) is locally observed around the Nb core material (Nb filament) at the stage of the composite billet or during the drawing process. This is because it is easy to adjust it to a substantially constant value.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In designing a Nb ₃ Sn superconducting wire, a stabilizing metal portion is often arranged in the outermost layer or the central portion of the superconducting wire. In order to prevent the stabilizing metal part from being contaminated by impurities such as Sn during the manufacture of the superconducting wire, it is usual to arrange the stabilizing metal member via a diffusion barrier during assembly of the composite billet. ing. Ta or Nb is often used as the diffusion barrier. By the way, the Cu-Sn alloy-based matrix exists in the superconducting filament embedded portion in which the superconducting filament is embedded, and in the portion where the superconducting filament is not embedded. There is. The Cu-Sn alloy-based matrix portion may be arranged in the central portion of the superconducting wire, the outer peripheral portion of the superconducting filament embedded portion, or the superconducting filament embedded portion.

In the present invention, the overall superconducting wire has a bronze ratio of 2.2 to 4.0. When it is less than 2.2, Sn tends to be insufficient in the generation of Nb ₃ Sn during heat treatment. Therefore, the bronze ratio is preferably 2.2 or more. On the other hand, the bronze ratio is 4.
When it exceeds 0, the occupied cross-sectional area of the superconducting filament becomes smaller than the cross-sectional area of the superconducting wire. Therefore, it is practically desirable to set the upper limit of the bronze ratio to 4.0. In the present invention, the local bronze ratio of the filament-embedded portion in which the filament is embedded is set to 1.5 to 2.2.

When the local bronze ratio is larger than 2.2, it is advantageous from the viewpoint of supplying Sn in the formation of Nb ₃ Sn during heat treatment, but from the viewpoint of processing, especially in the hot extrusion step, the sausage of the filaments. It is easy to cause a ring. However, if the local bronze ratio is set to a too low value, Sn will be in short supply.

As a result of intensive studies, the inventors of the present invention set the local bronze ratio to 1.5 to 2.2 to enhance the binding force between adjacent Nb cores and suppress the occurrence of sausage. , And the bronze ratio of the superconducting wire is 2.2 to 4.0.
It has been found that, by satisfying the above conditions, the Sn supply can be sufficiently maintained and excellent characteristics can be realized. That is, by setting the bronze ratio of the superconducting wire to 2.2 to 4.0 and at the same time setting the local bronze ratio to 1.5 to 2.2,
The characteristics and workability are compatible, and it is possible to suppress abnormal deformation of the filament and to supply sufficient Sn in the heat treatment.

With respect to the superconducting wire as described above, a preferable method for manufacturing the superconducting wire is a wire made of a Cu--Sn alloy and one Nb core material, that is, a single core wire. By doing so, it is possible to make the local bronze ratio of the manufactured superconducting wire substantially uniform, and abnormal deformation of the filament is further suppressed, and sausage hardly occurs.

[0019]

EXAMPLES Next, examples will be described with reference to FIGS. Sn: 14.5 wt%, Ti: 0.2 wt%, the balance substantially consisting of Cu bronze round bar (diameter 210 mm,
A bronze tube was prepared by concentrically forming a through hole having a diameter of 106 mm in a length of 600 mm). Then, the diameter 105
After inserting an Nb rod of mm, oxygen-free copper disks were welded to both ends, the interior was evacuated, and then sealed to produce a primary composite billet. After this is subjected to hot isostatic pressing, the outer diameter is cut to 200 mm, then hot extruded at 750 ° C. to a diameter of 40 mm, and then wire drawing, peeling wire drawing, annealing, etc. Then, a hexagonal element wire having a distance between opposite sides of 1.2 mm was manufactured. In addition, 6 manufactured by the above-mentioned peeling wire drawing process
The bronze ratio of the square wire (corresponding to the local bronze ratio in the superconducting wire after production) was adjusted to the value shown in Table 1. FIG. 1 shows an example of a cross section of a hexagonal element wire.
And Cu-Sn alloy 2. The cross-sectional area of the Cu—Sn alloy 2 / the cross-sectional area of the Nb core material 1 is the bronze ratio of the hexagonal wire 3. In FIG. 1, the Nb core material 1 is drawn in a circular shape for the sake of simplicity, but in reality, it is slightly distorted.

Next, a secondary composite billet was assembled using the above hexagonal wire 3. FIG. 2 is an explanatory view showing a part of the cross section of the secondary composite billet. Outer diameter 128 mm, inner diameter 122
mm Ta tube 5 is inserted into an oxygen-free copper tube 4 (stable metal sheath) having an outer diameter of 220 mm and an inner diameter of 130 mm, and a hexagonal wire 6 and the same size as the hexagonal wire 6 are provided inside the Ta tube 5. A hexagonal rod 7 (Sn: 14.5 wt%, Ti: 0.2 wt%, the balance being substantially Cu) was filled to produce a secondary composite billet 8. As shown in the figure, a predetermined number of hexagonal rods 7 are arranged and filled in the central portion of the oxygen-free copper pipe 4 and around the inner wall thereof. However, if this number is changed, the overall bronze ratio can be adjusted. Also, the hexagonal bar 7 is used in addition to the central portion and the inner wall periphery,
For example, they can be arranged in the intermediate portion or the like. In FIG. 2, the hexagonal wires 6 and the hexagonal bars 7 are drawn in a large size for easy viewing.

Oxygen-free copper disks (not shown) were attached to both ends of the above-mentioned secondary composite billet 8, and the inside was evacuated,
Welded and sealed. Further, after hot isostatic treatment was performed, the outer diameter was cut to 200 mm. Next, hot extrusion was performed at 680 ° C. to obtain a diameter of 40 mm, and then wire drawing was performed to produce about 25 kg (about 5400 m) of a 0.8 mm composite wire. At this time, the number of disconnection of the superconducting wire due to the filament disconnection was examined. This number is shown in Table 1 as an evaluation of workability. By observing the broken portion of the superconducting wire with a microscope, it can be determined whether or not it is caused by the broken filament.

Next, 650 is applied to the above composite wire in an Ar atmosphere.
A Nb ₃ Sn superconducting wire was manufactured by performing a heat treatment at ℃ × 200 hours. Table 1 also shows the bronze ratio, critical current density (Jc) per non-copper portion, and n value of this superconducting wire. Here, the n value is the rate of change of the voltage value with respect to the current value when a current is applied to both ends of a superconducting wire having a predetermined length and the superconducting state is broken.

As is clear from Table 1, the invention sample No. 1
In all of Nos. 6 to 6, good Jc was obtained, and a high n value, which is an index showing the soundness of the filament, was obtained. Further, there is no disconnection of the superconducting wire due to abnormal deformation of the filament, and excellent workability is obtained. When observing the cross section of these superconducting wires, all are good,
No sausage of the filament was observed.

On the other hand, in Comparative Examples Nos. 7, 10, 12, and 13, as a result of observing the cross section, the sausaging of the filament was not particularly recognized, but sufficient Jc was not obtained. Comparative Example No. 10 has a high local bronze ratio of 1.8, but has a low overall bronze ratio of the superconducting wire, and Comparative Example No.
7, 12 and 13 have a small local bronze ratio, so high J
It is considered that c was not obtained.

In Comparative Examples Nos. 8, 9 and 14, Jc was relatively high, but the n value was considerably low. Also, the number of wire breakages due to abnormal deformation of the filament was large. When observing the cross section of these superconducting wires, sausaging of the filaments was recognized, and it is considered that the Jc, n value and workability were deteriorated due to this. Since Comparative Example No. 11 has more bronze than necessary, it has a low Jc and is not practical.

[0026]

[Table 1]

[0027]

As described above in detail, the Nb ₃ S of the present invention is used.
The n superconducting wire and the method for producing the same provide a superconducting wire having excellent workability and excellent characteristics, and its industrial contribution is remarkable.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a cross section of a hexagonal element wire according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing a part of the secondary composite billet of the embodiment of the present invention.

[Explanation of symbols]

 1 Nb core material 2 Cu-Sn alloy 3 Hexagonal element wire 4 Oxygen-free copper tube 5 Ta tube 6 Hexagonal element wire 7 Hexagonal rod 8 Secondary composite billet

Claims (2)

[Claims] 1. A C having a local bronze ratio of 1.5 to 2.2.
includes a filament embedded portion filament is embedded in the u-Sn system the alloy matrix, the overall bronze ratio Nb ₃ Sn superconducting wire is 2.2 to 4.0. 2. A Cu—Sn alloy matrix member and N
a single-core composite element wire having a bronze ratio of 1.5 to 2.2 including a b-core material, and a Cu-Sn alloy matrix member.
Subjected to stretching the composite billet bronze ratio from 2.2 to 4.0 to prepare a composite wire, a manufacturing method of the heat treatment to the composite wire is subjected Nb ₃ Sn superconducting wire.