JP2001357734A - Nb3Sn SUPERCONDUCTIVE WIRE MATERIAL AND SUPERCONDUCTIVE MAGNET USING IT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Nb3Sn superconductive wire material which is useful as a raw material of a superconductive magnet which is used in a perpetual current mode movement for NMR analysis use or the like by realizing a high overall critical current density and an n value in a high ferromagnetic field, and provide such a superconductive magnet. SOLUTION: This is the Nb3Sn superconductive wire material which is produced by a bronze process, and the ratio of cross-sectional area of Cu-Sn base alloy to the total cross-sectional area of Nb3Sn and Nb is 1.8 to 3.0, and the average area rate of Nb to the total cross-sectional area of Nb3Sn and Nb is constituted to become 5 to 20%.

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 and a superconducting magnet made of such a wire, and more particularly to a superconducting magnet used for a high performance nuclear magnetic resonance (NMR) analyzer and the like. N which is useful for constructing such a superconducting magnet
The present invention relates to a b ₃ Sn superconducting wire.

[0002]

2. Description of the Related Art A superconducting magnet that uses a persistent current phenomenon realized by a superconducting material to flow a large current without consuming power and to generate a magnetic field by coiling a superconducting wire is a nuclear magnetic resonance (NMR). In addition to various physical property measuring devices such as devices, applications to magnetic field levitation trains and nuclear fusion devices are being promoted. As a constituent material of the above-described superconducting magnet, an Nb ₃ Sn superconducting wire has been widely used as a typical material.

As a method for producing the above-described Nb ₃ Sn superconducting wire, an internal diffusion method, a tube method, an in-situ method, a powder method, a bronze method, and the like are known. The most typical method is a composite processing method called a so-called bronze method.

[0004] FIG. 1 is a cross-sectional view of N produced by the bronze method.
b ₃ Sn is the cross-sectional structure of the superconducting wire an explanatory view schematically showing the drawing, 1 is Nb wire, 2 is Cu-Sn based alloy linear base material, 3 diffusion barrier layer, 4 stabilization copper 5 is Nb ₃
The Sn superconducting wires are respectively shown.

First, as shown in FIG. 1, a plurality of (19 in this figure) Nb wires 1 are embedded in a linear preform 2 made of a Cu—Sn based alloy, Are cut into a cross-section and then bundled into a wire group, inserted into the cylindrical diffusion barrier layer 3, and the stabilizing copper 4 is further disposed outside this.
The diffusion barrier layer 3 has a function of suppressing the outward diffusion of Sn during a diffusion heat treatment for generating Nb ₃ Sn, and is made of, for example, Nb or Ta. The stabilizing copper 4 is disposed as a stabilizing material of the Nb ₃ Sn superconducting wire, and is made of, for example, oxygen-free copper.

A material (stack material) configured as shown in FIG. 1 is subjected to wire drawing and heat treatment to obtain the Cu—Sn
By reacting Sn in the linear base material 2 made of the base alloy with the Nb wire 1, the vicinity of the surface of the Nb wire 1 (in this case, Cu
Nb _{3 is applied to} the interface between the Sn-based alloy linear base material 2 and the Nb wire 1).
Sn is generated.

In the structure shown in FIG. 1, a plurality of Nb wires 1 are directly embedded in a Cu-Sn base alloy linear base material 2 to form a material, and a plurality of these are bundled to form a wire group. Although the case where this is inserted into the cylindrical diffusion barrier layer 3 has been described, the configuration of the material is not limited to that shown in FIG.
One Nb wire 1 is buried in a u-Sn base alloy tube, and the Nb wire 1 is reduced in section to produce a single core wire. , And the material may be configured in the same manner. When the material thus configured is subjected to wire drawing and heat treatment, Nb ₃ Sn is formed at the interface between the Cu—Sn base alloy tube and the Nb wire 1.
Is generated.

In the Nb ₃ Sn superconducting wire manufactured as described above, an intermetallic compound that causes inconvenience such as disconnection during wire processing is replaced with a Cu—Sn base alloy wire base material 2.
(Or a Cu—Sn based alloy tube), the Sn content in the Cu—Sn based alloy used must be suppressed to 15% by mass or less. Due to such restrictions, as described above, Nb
In order to form b ₃ Sn, the Sn content tends to be insufficient. When the Sn content is insufficient, Nb
₃ Sn core critical current density is an important requirement of a superconducting wire (divided by the cross-sectional area of the Nb wire before the heat treatment the critical current) will occur is lowered.

From the viewpoint of avoiding the inconvenience of lowering the core critical current density as described above, in the conventional bronze method, as a measure for increasing the supply amount of Sn to the Nb wire 1, Nb ₃ Sn after heat treatment and Nb (hereinafter, referred to as
One cross-sectional area of the Cu-Sn-based alloy with respect to the total cross-sectional area of the "remaining Nb core" (the cross-sectional area of the Cu-Sn-based alloy base material 2 or one tube of the Cu-Sn-based alloy) (Hereinafter referred to as the "bronze ratio") in some cases when the Nb wire is embedded in the structure and the ratio is the total cross-sectional area of the Cu-Sn-based alloy linear base material 2 and the Cu-Sn-based alloy tube. ) Is made as large as possible and all the Nb lines 1 are transformed into Nb ₃ Sn. As such a method, for example, JP-A-62-93355 discloses that the above bronze ratio is 3.1.
To 4.5 and N remaining after Nb ₃ Sn formation.
A technique has been proposed in which the area ratio of the b-core is set to 0%.

However, increasing the bronze ratio has a problem in that the critical current density of the overall obtained by dividing the critical current by the cross-sectional area of the wire is rather reduced. Further, in order to reduce the residual ratio of the remaining Nb core after forming Nb ₃ Sn to 0%, it is necessary to perform a full annealing heat treatment. However, if such a heat treatment is performed, large growth occurs in the Nb ₃ Sn crystal grains. Things appear and broaden the particle size distribution.

Since the critical current density depends on the size of the crystal grains of Nb ₃ Sn, in such a state, Nb ₃
A variation in the core current density occurs in the longitudinal direction of the Sn core. When such variations occur, the n value, which is important in a wire for a superconducting magnet operated in a permanent current mode, such as nuclear magnetic resonance (NMR), remains small.

As described above, the Nb ₃ Sn superconducting wire manufactured by the bronze method cannot increase the critical current density and the n value of the overall.
A high-performance Nb ₃ Sn superconducting wire used for a superconducting magnet used in a permanent current mode operation for NMR analysis or the like could not be obtained.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems in the prior art as described above, and has as its object to provide a high overall critical current density and n in a strong magnetic field. realized value, useful Nb ₃ Sn superconducting wire as the superconducting magnet of the material used in the persistent current mode operation, such as for NMR analysis, and is to provide such superconducting magnet.

[0014]

The Nb ₃ Sn superconducting wire of the present invention that has solved the above problems SUMMARY OF THE INVENTION, a Nb ₃ Sn superconducting wire produced by the bronze process,
Cu—Sn with respect to the total cross-sectional area of Nb ₃ Sn and Nb
The ratio of the cross-sectional area of the base alloy (that is, the bronze ratio) is 1.8 to
It is 3.0, and the average area ratio of Nb (residual Nb cores) to the total cross-sectional area of the Nb ₃ Sn and Nb is 5-20%
The point is that it is configured to be as follows.

[0015] The "cross-sectional area of the Cu-Sn base alloy" means
As described above, in the configuration shown in FIG.
The cross-sectional area of the linear base material 2 made of a base alloy, and when a superconducting material is formed by embedding one Nb wire in a tube made of a Cu-Sn base alloy, a linear base material made of a Cu-Sn base alloy And the total cross-sectional area of the Cu-Sn base alloy pipe.

In evaluating the "average area ratio of Nb to the total cross-sectional area of Nb ₃ Sn and Nb", the diffusion barrier layer 3 and the stabilizing copper 4 are arranged outside the superconducting wire. (FIG. 1 described above), it is necessary to calculate by excluding the area of these parts. And these diffusion barrier layers 3 and stabilized copper 4
Assuming that the distance from the center point of the cross section of the wire to the surface of the wire is L, the wire generally exists outside 0.80 L. Further, in a portion inside of 0.20 L, a reinforcing material such as Ta may be disposed in some cases. Therefore, when actually calculating this average area ratio, for example, as shown in FIG. 2, a region having an area of at least 0.5% or more of the total cross-sectional area of the wire in a region of 0.20 L to 0.80 L is used. Then, an optical microscope photograph or an electron microscope photograph of the portion may be taken and measured.

In the above-mentioned Nb ₃ Sn superconducting wire of the present invention, the Cu-Sn based alloy contains at least one selected from the group consisting of Ta, Zr, Ti and Hf in addition to Cu and Sn. Some things are also useful.

Further, by forming a superconducting magnet using the above-described Nb ₃ Sn superconducting wire as a material,
A superconducting magnet useful for realizing a high-resolution NMR analyzer or the like can be realized.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have studied from various angles to achieve the above object. As a result, it has been found that the above object can be achieved satisfactorily if the bronze ratio defined as described above and the average area ratio of the remaining Nb core are adjusted to fall within a predetermined range. completed. The reasons for defining each requirement in the Nb ₃ Sn superconducting wire of the present invention are as follows.

The above bronze ratio is determined as described above by Nb ₃ Sn
Is defined as the ratio of the cross-sectional area of the Cu-Sn-based alloy to the total cross-sectional area of Nb and Nb.
_{In a} 3Sn superconducting wire, this bronze ratio is set to 1.8 to
It is necessary to be 3.0, and by setting it within this range, a high overall critical current density is basically achieved. That is, if the bronze ratio is less than 1.8, the amount of Sn that can be supplied becomes insufficient, so that the Nb ₃ Sn crystal is coarsened in a state where Sn is missing from the stoichiometric composition, and the core critical current density is reduced. Will decrease. In particular, in the case of an Nb ₃ Sn superconducting wire, since the pinning center for pinning the magnetic flux is a crystal grain boundary, when a large crystal grain grows, the grain boundary decreases and the critical current density decreases. On the other hand, when the bronze ratio is larger than 3.0, the supply amount of Sn increases and the core current density increases, but the ratio of the bronze portion increases, so that the overall critical current increases. The density will be reduced.

In the Nb ₃ Sn superconducting wire of the present invention, it is also an important requirement that the average area ratio of the remaining Nb core to the total cross-sectional area of Nb ₃ Sn and Nb (remaining Nb core) is 5 to 20%. By satisfying these requirements, the n value can be basically kept high. That is, when the average area ratio is less than 5%, some of the remaining Nb cores are fully annealed, and as described above, some of the Nb ₃ Sn crystal grains that grow large appear and become grainy. The diameter distribution is widened and the value of n decreases. On the other hand, when the average area ratio is larger than 20%, the thickness of the Nb ₃ Sn generation layer becomes thin, and the remaining N due to the variation in the thickness of the Nb ₃ Sn generation layer in the longitudinal direction of the wire.
The variation in the area ratio of the b-core increases, and as a result, the n value decreases.

The area ratio of the remaining Nb core can be controlled by adjusting the Nb wire diameter at the material stage or by changing the heat treatment temperature. Is preferred since the method of adjusting the value can be more easily realized.

As the Cu-Sn base alloy used in the present invention, an alloy containing about 13 to 15% of Sn in Cu is basically used. If necessary, Ta, Ti, Z may be used.
It is also useful to contain one or more selected from the group consisting of r and Hf, and by including such an element, the core critical current density in a strong magnetic field can be further improved. These effects increase as the content increases, but from the viewpoint that if the content is too large, a non-superconducting intermetallic compound is generated and the workability for forming a wire is reduced. Should be less than 5%.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples do not limit the present invention, and any design change based on the above and following points is not limited to the present invention. It is included in the technical range of. For example, the cross section of the wire is not limited to a rectangular shape as shown in FIG. 2 but may be a square or a circle.

[0025]

EXAMPLE 1 Using bronze of Cu-14.5% Sn, the bronze ratio was 2.5, the number of Nb lines was about 25,000, and the cross-sectional shape was 1.5.
It was processed into a rectangular wire (material) of 0 × 2.50 (mm).
At this time, the average diameter of the Nb line was 3.8 μm.

A wire having an average area ratio of residual Nb cores (average Nb residual core ratio) of 0 to 28% was produced by heat-treating such a material at 700 ° C. for 30 to 200 hours. After the heat treatment, the overall current density based on the electric field of 0.1 μV / cm and the n value in the range of 0.1 to 1.0 μV / cm were evaluated at a temperature of 4.2 K and an external magnetic field of 19 T. FIG. 3 shows the evaluation results.

The n value is an amount indicating the sharpness of the transition from the superconducting state to the normal conducting state. This value reflects the degree of uniform processing of the filament (Nb core), and the larger the value, the better the characteristic. It is said to be excellent. That is, when a current flows through a superconducting wire, a resistance is generated at a certain current value (critical current) or more, and a voltage is generated. The relationship between the current and the voltage at this time is empirically determined by the following (1).
The value of n in this equation (1) is called an "n value". V = V ₀ (I / Ic) ⁿ (1) where V: generated voltage V ₀ : constant Ic: critical current

As is apparent from FIG. 3, when the average Nb residual core ratio is 5 to 20%, the n value maintains a practical level of 30 or more, and a high value of 42 is obtained at the maximum. You can see that. Also, the overall critical current density exceeded 60 A / mm ² in a wide range of the average Nb residual core rate, and a value as high as 110 A / mm ² was obtained.

Comparative Example 1 An Nb ₃ Sn rectangular wire was produced under the same conditions as in Example 1 except that the bronze ratio was 3.5. By changing the time at which this wire is kept at 700 ° C. in the range of 30 to 200 hours, the average Nb residual core ratio is 0 to 28.
% Of a wire rod was produced. After the heat treatment, the n value and the critical current were evaluated under the same conditions as in Example 1.

FIG. 4 shows the evaluation results. This figure 4
As is apparent from FIG.
% Wire has an overall critical current density of 60 A /
mm ^TwoIs obtained, but the n value is as very low as 12.
Stayed at the value. Further, the average Nb residual core ratio is 5 to 20%.
In the case of, the n value is improved to a practical level of 30 or more.
But overall critical current density was fully annealed
60A / mm which is the value of the wire^TwoIs less than
Call

COMPARATIVE EXAMPLE 2 Except that the bronze ratio was 1.4,
Under the same conditions as described above, an Nb ₃ Sn rectangular wire was produced. By changing the time at which this wire is held at 700 ° C. in the range of 30 to 200 hours, the average Nb residual core ratio is 8 to 2 hours.
An 8% wire rod was produced. In this case, since the supply amount of Sn is insufficient (because the bronze ratio is small), the average N
(b) A wire rod having a residual core ratio of less than 8% could not be produced. After the heat treatment, the n value and the critical current were evaluated under the same conditions as in Example 1.

FIG. 5 shows the evaluation results. As is clear from FIG. 5, it can be seen that the overall critical current density of all the evaluated wires is lower than 60 A / mm ² .

Example 2 Several types of Nb ₃ Sn rectangular wire rods having different bronze ratios other than 1.4, 2.5 and 3.5 but under the same conditions as Comparative Example 1 were processed. For these wires, 7
The heat treatment was performed while changing the holding time at 00 ° C. to prepare a wire having an average Nb residual core ratio of 5 to 20%. After the heat treatment, the critical current and the n value were evaluated under the same conditions as in Example 1. FIG. 6 shows the results together with the results of Comparative Examples 1 and 2 and Example 1.

As apparent from FIG. 6, the bronze ratio is 1.
When the value is from 8 to 3.5, the overall critical current density exceeds the value of the fully annealed wire of Comparative Example 1 of 60 A / mm ² , and it can be seen that a practical level of n value of 30 or more is obtained. .

Example 3 An Nb ₃ Sn rectangular wire was produced under the same conditions as in Example 1 except that a Cu-14.5% Sn-0.5% Ti alloy was used. Thereafter, a wire rod having an average Nb residual core ratio of 0 to 28% was produced in the same manner as in Example 1 under the heat treatment conditions. After the heat treatment, the critical current density and the n value were evaluated under the same conditions as in Example 1.

As a result, as in Example 1 (FIG. 3), when the average Nb residual core ratio was 5 to 20%, the n value was 3
A practical level of 0 or more was maintained, and a maximum value of 45 or more in Example 1 was obtained. In addition, the overall critical current density of the fully annealed wire of Comparative Example 1 was 60 A / m in a wide range of the average Nb core content including 5 to 20%.
m ² , and the highest value exceeds the highest value of Example 1 by 12
It was 5 A / mm ² .

[0037]

The present invention is configured as described above, and a high-performance bronze-processed Nb ₃ Sn superconducting wire having both a high overall critical current density and an n value in a strong magnetic field can be realized. By using such a technology, a high-performance superconducting magnet that requires persistent current mode operation in a strong magnetic field, as typified by a superconducting magnet for NMR analysis, is required to produce a magnet that exhibits even better performance than before. This is extremely advantageous in applications of superconducting magnets requiring other permanent current modes.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram schematically showing a cross-sectional structure before heat treatment of an Nb ₃ Sn superconducting wire manufactured by a bronze method.

FIG. 2 is a schematic cross-sectional view showing a region for evaluating an average Nb residual core ratio.

FIG. 3 is a graph showing the evaluation results of the overall critical current density and the n value of the wire manufactured in Example 1.

FIG. 4 is a graph showing the evaluation results of the overall critical current density and the n value of the wire manufactured in Comparative Example 1.

FIG. 5 is a graph showing the results of evaluation of the overall critical current density and n value of the wire manufactured in Comparative Example 2.

FIG. 6 is a graph showing the effect of the Brins ratio on the overall critical current density and the n value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nb wire 2 Cu-Sn base alloy linear base material 3 Diffusion barrier layer 4 Stabilized copper

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Mitsuo Tomonaga 1-5-5 Takatsukadai, Nishi-ku, Kobe F-term in Kobe Steel Research Institute, Kobe Research Institute Co., Ltd. 5G321 AA11 BA03 CA35 CA36 DC09

Claims (3)

[Claims] 1. Nb produced by the bronze method_ThreeS
n superconducting wire, Nb_ThreeTotal breakage of Sn and Nb
The ratio of the cross-sectional area of the Cu-Sn-based alloy to the area is 1.8 to
3.0 and Nb_ThreeTotal cross-sectional area of Sn and Nb
Is configured so that the average area ratio of Nb with respect to
Nb characterized by the fact that _ThreeSn superconducting wire
Wood. 2. The Cu—Sn based alloy is composed of Ta, Zr,
Nb ₃ Sn superconducting wire according to claim 1 from the group consisting of Ti and Hf are those containing at least one selected. 3. A superconducting magnet comprising the Nb ₃ Sn superconducting wire according to claim 1 as a material.