JPH087682A - Method for producing Nb3Sn compound superconducting wire - Google Patents

Abstract

(57) [Summary] [Purpose] To produce Nb ₃ Sn-based compound superconducting wire with excellent superconducting properties. [Structure] A Sn layer 5 and Sn are formed on a composite element wire in which a large number of Nb filaments are arranged in a Cu-Sn alloy substrate.
A metal wire layer having a higher melting point and non-reactive with Sn is sequentially formed to form a composite wire, and the composite wire is subjected to thermal diffusion treatment to form C
During u-Sn-based alloy substrate to produce Nb ₃ Sn filaments. [Effect] Since the metal material layer 6 having a high melting point and not reacting with Sn holds the molten Sn on the composite wire, the thermal diffusion treatment of Sn can be performed at a high temperature in a short time. Therefore, voids are not formed in the substrate, and an Nb ₃ Sn-based compound superconducting wire having excellent superconducting properties can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has excellent superconducting properties,
The present invention relates to a method for producing a Nb ₃ Sn-based compound superconducting wire.

[0002]

2. Description of the Related Art A compound superconducting wire is a superconducting wire in which a large number of superconducting filaments such as Nb ₃ Sn, Nb ₃ Al and V ₃ Ga are compounded in a Cu or Cu alloy substrate. This compound superconducting wire is manufactured as follows because the superconductor phase such as Nb ₃ Sn is fragile. That is, a large number of Nb metal rods are embedded in a Cu-Sn alloy substrate to assemble a primary billet, which is then annealed and reduced in diameter to form a linear body having a predetermined shape. A large number of Cu-Sn alloy pipes are aligned and filled to assemble a secondary billet, which is then annealed and reduced in diameter to produce a composite element wire in which Nb filaments are compounded in a Cu-Sn alloy substrate. To do. Next, this composite wire is subjected to thermal diffusion treatment at a temperature of 700 to 800 ° C,
The Nb filaments are reacted with Sn in the substrate and pipe to form Nb ₃ Sn filaments.

[0003] In the above manufacturing method, the higher the Sn concentration of the Cu-Sn-based alloy constituting the substrate or pipe, resulting Nb ₃ Sn compound is close to the stoichiometric composition, superconducting properties of the resulting superconducting wire improves. However, the Cu-
When the Sn concentration of the Sn-based alloy is increased, the work hardening of the billet becomes large, and especially when Sn is contained in excess of the solid solution limit, cracking occurred during wire drawing even if the intermediate annealing was performed many times. For this reason, the amount of Sn in the Cu-Sn alloy has to be suppressed below the solid solution limit. Therefore, the amount of Sn is insufficient and a sufficiently high superconducting property cannot be obtained. In addition, the intermediate annealing is Nb ₃ Sn
Since it was applied at a low temperature at which no phase was formed, it took a long time and markedly impaired the productivity.

[0004]

Therefore, the number of intermediate annealings is reduced by using a Cu-Sn type alloy having a low Sn concentration with good workability for the substrate and the pipe. An outdiffusion method has been developed to plate and replenish. In this external diffusion method, the thermal diffusion process is suddenly performed at 700 ° C.
When applied at the above high temperature, Sn plating layer and Sn rich Cu
The -Sn-based compound was burned out and insufficient, and desired superconducting properties were not obtained. Therefore, a thermal diffusion treatment is carried out by first diffusing the Sn layer in the Cu—Sn alloy base at a temperature lower than the melting point of Sn, and then promoting the diffusion of Sn at a temperature of around 300 ° C.
Finally, a method in which the Nb ₃ Sn phase is formed by reaction at a high temperature of 700 ° C or higher in three steps (Japanese Patent Publication No. 62-62003).
Was proposed. However, in such a method in which the thermal diffusion treatment is gradually performed from a low temperature, since the diffusion rates of Cu and Sn atoms are different, holes in the Cu—Sn alloy substrate due to the Kirkendall effect (hereinafter abbreviated as Kirkendall holes). Do)
Occurred. These vacancies increased the strain sensitivity of the superconducting wire, deteriorating the superconducting property and making it unstable. As a measure for preventing the occurrence of Kirkendall pores, a method has been proposed in which the composite wire is thinned to 0.3 mm or less to shorten the Sn diffusion time. According to this method, it takes a great deal of time to align and fill the thin composite wire rod when assembling the secondary billet.

In addition, as a measure for preventing the occurrence of Kirkendall vacancies, a method has been proposed in which an Sn layer and a Cu layer are sequentially formed on a composite wire (Japanese Patent Laid-Open No. 1-261313). In this method, a molten Sn layer is held on the outer Cu layer and a thermal diffusion process is performed at a high temperature to shorten the thermal diffusion process time. But,
In this method, Sn is solid-dissolved in the Cu layer and consumed, so that the Sn layer is plated thicker by that amount, resulting in a longer thermal diffusion treatment time and Kirkendall vacancies. I had the same problem.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been earnestly studied under such circumstances, and an object thereof is to provide a method for producing an Nb ₃ Sn compound superconducting wire having excellent superconducting properties. To do. That is, according to the present invention, a Sn layer and a metal material layer having a higher melting point than Sn and non-reactive with Sn are sequentially formed on a composite wire in which a large number of Nb filaments are arranged in a Cu—Sn alloy base. The composite wire is formed into a composite wire, and the composite wire is subjected to a heat diffusion treatment to form Nb _{3 in the} Cu—Sn alloy substrate.
It is characterized by producing Sn filaments.

In the present invention, the metal material layer having a higher melting point than Sn and non-reactive with Sn is subjected to the thermal diffusion treatment by the melting point of Sn (232
Even if the temperature is higher than (.degree. C.), it is a metal material layer that keeps the molten Sn inside the uniform shape and does not consume Sn due to solid solution or compound formation. Specifically, Cr, Ni, Zn, A
Pure metal materials such as g, Co, Fe, Pd, Pt, Au, Ag
-Pd system, Ag-Sb system, Ag-Se system, Au-Ni
System, Au-Co system, Cu-Zn system, Cu-Sn system, Zn
It is an alloy material such as -Sn system, Ni-Sn system, Co-Sn system. When the metal material layer is combined with a Cu—Sn based alloy substrate in which Nb filaments are arranged with the Sn layer interposed therebetween,
Cu-Sn in which Sn of Sn layer has Nb filaments arranged
The metal material layer preferentially diffuses toward the base alloy base. When the metal material layer is a Cu-Sn alloy or the like, Sn is contained in a saturated state or in an amount close to the saturated state. The metal material layer is
Since the melting point is high, the molten Sn layer can be maintained in a uniform shape and Sn
And the Sn layer can be made thin because it is non-reactive, and therefore the thermal diffusion treatment time is shortened and Kirkendall vacancies are not formed. In the present invention, in order to form the Sn layer and the metal material layer on the composite wire, any method capable of forming a uniform thickness such as electroplating, electroless plating, and hot dipping can be applied. The Sn
Since the contained alloy material allows Sn to diffuse and pass therethrough, it can be formed in multiple layers alternately with the Sn layers. When Cr is used for the metal material layer, the Cr layer also has a function as an insulating coating layer because it is electrically insulating. Therefore, the superconducting wire can be twisted without the need for enamel coating or the like.

The structure before and after the thermal diffusion treatment of the composite wire produced in the intermediate step of the method of the present invention will be described below with reference to the drawings. FIG. 1A is a transverse cross-sectional view of a composite wire using Ni for the metal material layer before the thermal diffusion treatment. Nb around the stabilized copper wire 1
Of the diffusion barrier, and the Nb / bronze (Cu—Sn alloy) composite layer 3, the bronze sheath (pipe) layer 4, the Sn layer 5, and the Ni metal material layer 6 are sequentially formed around the diffusion barrier. FIG. 1B is a cross-sectional view of the composite wire after the thermal diffusion treatment. In FIG. 7, Nb filaments of the Nb / bronze composite layer 3 are Nb ₃ Sn filaments formed into Nb ₃ Sn filaments.
₃ Sn-containing bronze layer. Around the Nb ₃ Sn-containing bronze layer 7, a united layer 8 of the bronze sheath layer 4 and the Sn layer 5 having a low Sn content is formed, and a Ni metal layer 6 is located around the united layer 8.

FIG. 2A is a cross-sectional view of a composite wire using bronze as a metal material layer before heat diffusion treatment. It is the same as that shown in FIG. 1A except that the bronze metal material layer 9 is formed on the outermost layer. FIG. 2B is a cross-sectional view after the thermal diffusion process. It is the same as that shown in FIG. 1B except that the bronze metal material layer 9 is formed on the outermost layer.

In the present invention, when the total amount of Sn contained in the composite wire is 16 wt% or more, a sufficient amount of Sn is supplied, and the stoichiometry (Nb-25) is excellent in superconducting properties.
A Nb ₃ Sn phase close to at% Sn) is formed. Therefore,
The amount of Sn contained in the entire composite wire is preferably 16 wt% or more.

If the ratio [t / T] of the thickness t of the Sn layer formed on the composite wire to the thickness T of the metal material layer having a higher melting point than Sn and not reacting with Sn is less than 1, the metal material layer is It becomes uneconomical because it becomes excessively thick. On the other hand, if it exceeds 10, the effect of retaining the molten Sn of the metal material layer decreases. Therefore, it is preferable that the ratio [t / T] of the thickness t of the Sn layer of the composite wire and the thickness T of the metal material layer having a higher melting point than Sn and not reacting with Sn is 1 or more and 10 or less.

The present invention is based on a Cu--Sn alloy substrate or Nb.
Similar effects can be obtained when the filament contains a trace amount of elements such as Ti, Ta, Ha, and Ga. The stabilizing material of Nb and Ta same effect by applying a barrier layer to Nb ₃ Sn compound superconducting wire in complex with the interposition of such as Cu or Al can be obtained in the center.

In the present invention, the thermal diffusion treatment is usually S
The n layer and low-temperature treatment to diffuse into the Cu-Sn-based alloy substrate of Sn in the substrate is reacted with Nb is performed by dividing into high-temperature treatment for forming a Nb ₃ Sn phase. Generation of Kirkendall vacancies can be suppressed by performing low-temperature treatment for a short time at a temperature equal to or higher than the melting point of Sn. If Kirkendall vacancies occur, the amount is small and can be eliminated by light rolling before the high temperature treatment.

[0014]

In the present invention, when the Nb ₃ Sn compound superconducting wire is manufactured by the external diffusion method, the molten Sn on the composite wire is held by the metal material layer having a high melting point and not reacting with Sn.
The heat diffusion treatment can be performed at high temperature in a short time. Therefore, no pores are formed in the substrate, and N having excellent superconducting properties is obtained.
A b ₃ Sn-based compound superconducting wire can be manufactured.

[0015]

The present invention will be described below in detail with reference to examples. (Example 1) Bronze with an outer diameter of 45.3 mmφ (Cu-14.3 wt%
Sn-0.2 wt% Ti-based alloy) 19 holes with 6.0 mmφ through holes at regular intervals, insert Nb wire with 5.8 mmφ outside diameter into these holes, and bronze lids at the front and rear ends of the bronze rod. Was vacuum-sealed by electron beam welding and covered to prepare a primary billet. Next, this primary billet was hot extruded, and this extruded material was repeatedly subjected to wire drawing and intermediate annealing to produce a hexagonal wire having an opposite side length of 1 mm. This hexagonal wire was filled into a bronze pipe having the same composition as the primary billet and having an outer diameter of 45 mmφ and an inner diameter of 38 mmφ to produce a secondary billet. At the center of the bronze pipe, an oxygen-free copper rod having a diameter of 20 mm, which serves as a stabilizing material, was arranged by winding Nb foil on the outer circumference. This secondary billet was processed into a composite wire of 0.7 mmφ by the same method as the primary billet. Next, a Sn layer and a Ni layer were sequentially electroplated on this composite wire to prepare a composite wire. The thicknesses of the Sn layer and the Ni layer were variously changed. Next, this composite wire was subjected to the first thermal diffusion treatment at 450 ° C. for 50 hours. After thermal diffusion treatment,
The tissue was observed. Sn of Sn layer is 100 in the bronze substrate.
It was diffused uniformly by about μm. There was no burnout of the Sn layer. The Nb filaments were linearly positioned in the bronze substrate at equal intervals, and no turbulence was observed. A small amount of Kirkendall pores were observed in the bronze substrate. Next, this wire rod was subjected to wire drawing at a cross-section reduction rate of 5% to adjust the outer diameter of the wire rod and eliminate Kirkendall pores inside the wire rod. Then, the second thermal diffusion treatment was performed at 695 ° C for 40 hours to obtain Nb ₃ S.
An n-based compound superconducting wire was manufactured.

Example 2 Nb ₃ Sn was prepared by the same method as in Example 1 except that the Sn layer and the Cu-10 wt% Sn alloy layer were sequentially electroplated on the composite wire to form a composite wire. A compound superconducting wire was manufactured.

(Comparative Example 1) Nb ₃ was prepared in the same manner as in Example 1 except that a Sn layer was plated on the composite wire to a thickness of 8 μm and a Cu layer was plated thereon to a thickness of 1.5 μm.
An Sn-based compound superconducting wire was manufactured.

(Comparative Example 2) In Example 1, an Sn layer was plated on the composite wire to a thickness of 14 μm, and a Cu layer was plated thereon to a thickness of 2.5 μm, and the first thermal diffusion treatment was performed at 450 ° C. for 100 minutes. An Nb ₃ Sn-based compound superconducting wire was manufactured by the same method as in Example 1 except that the time was applied.

(Comparative Example 3) A Nb ₃ Sn-based compound superconducting wire was manufactured in the same manner as in Example 1, except that only the Sn layer was formed to a thickness of 8 μm on the composite element wire.

(Comparative Example 4) In Example 1, only a Sn layer was formed on the composite wire to a thickness of 8 μm to form a composite wire.
This composite wire is heated at a temperature of 200 ° C below the melting point of Sn for 60 hours, then at 300 ° C for 50 hours, and finally at 695 ° C.
Example 1 except that the heat diffusion treatment was performed under heating conditions for 40 hours
A Nb ₃ Sn-based compound superconducting wire was manufactured by the same method as described above.

The critical current (Ic) was measured for each of the obtained Nb ₃ Sn-based compound superconducting wires. Also, the cross section was observed to examine the presence or absence of Sn burn-out and the presence or absence of Kirkendall pores. The results are shown in Table 1.

[0022]

[Table 1]

As is clear from Table 1, all the products of the method of the present invention (Nos. 1 to 10) had high Ic, no Sn burn-through, excellent cross-sectional shape, and small or few Kirkendall pores. . Incidentally, in No. 2, the average Sn concentration was below 16 wt%, so that Ic was slightly lowered. No. 6 was uneconomical because the metal material layer (Ni layer) was slightly thicker than the Sn layer thickness,
There was no problem in terms of characteristics. In No. 7, the metal material layer (Ni layer) was thin, the coercive force of the Sn layer was weakened, the cross-section was slightly deformed, and Ic was also slightly lowered. However, there was no problem in practical use.

On the other hand, in No. 11 of the comparative example, since the Cu layer was formed on the Sn layer, the Sn layer was consumed by the Cu layer and S
n was insufficient and Ic was lowered. In No. 12, since the Sn layer was formed thickly, the heat diffusion treatment time became long, a large number of Kirkendall vacancies were generated, and it remained even after light pressure reduction to lower Ic. In No. 13, the high melting point metal material layer was not used, and since the thermal diffusion treatment was performed at a temperature of 450 ° C. from the beginning, the Sn layer was burned out, the Nb ₃ Sn filament was exposed, and the Ic was significantly lowered. In No. 14, the thermal diffusion treatment was started at a temperature lower than the melting point of Sn, so the burnout of the Sn layer could be prevented, but a large number of Kirkendall vacancies were generated and the Ic was reduced even after the pressure was reduced. .

[0025]

As described above, according to the present invention, since the metal material layer having a high melting point and non-reactive with Sn holds the molten Sn on the composite wire, the thermal diffusion treatment of Sn can be performed at high temperature in a short time. It can be carried out. Further, since the thermal diffusion treatment is carried out at a high temperature in a short time, the growth of holes in the substrate can be suppressed, and N having excellent superconducting characteristics can be obtained.
A b ₃ Sn-based compound superconducting wire is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing aspects of a composite wire according to the present invention before and after thermal diffusion treatment.

FIG. 2 is a cross-sectional view showing another embodiment before and after the thermal diffusion treatment of the composite wire according to the present invention.

[Explanation of symbols]

1--Stabilized copper wire 2 --Nb foil 3 --Nb / bronze composite layer 4 --Bronze sheath layer 5 --Sn layer 6 --Ni metal material layer 7 --Nb ₃ Sn-containing bronze layer 8- -Bronze sheath layer and Sn layer combined layer 9 --- Bronze metal material layer

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 24, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Method for producing Nb ₃ Sn compound superconducting wire

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has excellent superconducting properties,
The present invention relates to a method for producing a Nb ₃ Sn-based compound superconducting wire.

[0002]

2. Description of the Related Art A compound superconducting wire is a superconducting wire in which a large number of superconducting filaments such as Nb ₃ Sn, Nb ₃ Al and V ₃ Ga are compounded in a Cu or Cu alloy substrate. This compound superconducting wire is manufactured as follows because the superconductor phase such as Nb ₃ Sn is fragile. That is, a large number of Nb metal rods are embedded in a Cu-Sn alloy substrate to assemble a primary billet, which is then annealed and reduced in diameter to form a linear body having a predetermined shape. A large number of Cu-Sn alloy pipes are aligned and filled to assemble a secondary billet, which is then annealed and reduced in diameter to produce a composite element wire in which Nb filaments are compounded in a Cu-Sn alloy substrate. To do. Next, this composite wire is subjected to thermal diffusion treatment at a temperature of 700 to 800 ° C,
The Nb filaments are reacted with Sn in the substrate and pipe to form Nb ₃ Sn filaments.

[0003] In the above manufacturing method, the higher the Sn concentration of the Cu-Sn-based alloy constituting the substrate or pipe, resulting Nb ₃ Sn compound is close to the stoichiometric composition, superconducting properties of the resulting superconducting wire improves. However, the Cu-
When the Sn concentration of the Sn-based alloy is increased, the work hardening of the billet becomes large, and especially when Sn is contained in excess of the solid solution limit, cracking occurred during wire drawing even if the intermediate annealing was performed many times. For this reason, the amount of Sn in the Cu-Sn alloy has to be suppressed below the solid solution limit. Therefore, the amount of Sn is insufficient and a sufficiently high superconducting property cannot be obtained. In addition, the intermediate annealing is Nb ₃ Sn
Since it was applied at a low temperature at which no phase was formed, it took a long time and markedly impaired the productivity.

[0004]

Therefore, the number of intermediate annealings is reduced by using a Cu-Sn type alloy having a low Sn concentration with good workability for the substrate and the pipe. An outdiffusion method has been developed to plate and replenish. In this external diffusion method, the thermal diffusion process is suddenly performed at 700 ° C.
When applied at the above high temperature, Sn plating layer and Sn rich Cu
The -Sn-based compound was burned out and insufficient, and desired superconducting properties were not obtained. Therefore, a thermal diffusion treatment is carried out by first diffusing the Sn layer in the Cu—Sn alloy base at a temperature lower than the melting point of Sn, and then promoting the diffusion of Sn at a temperature of around 300 ° C.
Finally, a method in which the Nb ₃ Sn phase is formed by reaction at a high temperature of 700 ° C or higher in three steps (Japanese Patent Publication No. 62-62003).
Was proposed. However, in such a method in which the thermal diffusion treatment is gradually performed from a low temperature, since the diffusion rates of Cu and Sn atoms are different, holes in the Cu—Sn alloy substrate due to the Kirkendall effect (hereinafter abbreviated as Kirkendall holes). Do)
Occurred. These vacancies increased the strain sensitivity of the superconducting wire, deteriorating the superconducting property and making it unstable. As a measure for preventing the occurrence of Kirkendall pores, a method has been proposed in which the composite wire is thinned to 0.3 mm or less to shorten the Sn diffusion time. According to this method, it takes a great deal of time to align and fill the thin composite wire rod when assembling the secondary billet.

In addition, as a measure for preventing the occurrence of Kirkendall vacancies, a method has been proposed in which an Sn layer and a Cu layer are sequentially formed on a composite wire (Japanese Patent Laid-Open No. 1-261313). In this method, a molten Sn layer is held on the outer Cu layer and a thermal diffusion process is performed at a high temperature to shorten the thermal diffusion process time. But,
In this method, Sn is solid-dissolved in the Cu layer and consumed, so that the Sn layer is plated thicker by that amount, resulting in a longer thermal diffusion treatment time and Kirkendall vacancies. I had the same problem.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been earnestly studied under such circumstances, and an object thereof is to provide a method for producing an Nb ₃ Sn compound superconducting wire having excellent superconducting properties. To do. That is, according to the present invention, a Sn wire and a metal material layer having a higher melting point than Sn are sequentially formed on a composite wire in which a large number of Nb filaments are arranged in a Cu-Sn alloy base to form a composite wire. a method of manufacturing a composite wire in Nb ₃ Sn compound superconducting wire to produce Nb ₃ Sn filaments is subjected to thermal diffusion treatment in the Cu-Sn-based alloy substrate, the metal material layer, Sn of the Sn layer is Nb a method for producing a Nb ₃ Sn compound superconducting wire which is a metal material layer to diffuse preferentially towards the Cu-Sn-based alloy substrate having an array of filaments.

In the present invention, the metallic material layer means that even if the thermal diffusion treatment is carried out at a temperature higher than the melting point of Sn (232 ° C.), the inner molten Sn is kept in a uniform shape and is formed by solid solution or compound formation. Is a metal material layer that does not consume. Specifically, C
r, Ni, Zn, Ag, Co, Fe, Pd, Pt, Au
Pure metal materials such as Ag-Pd system, Ag-Sb system, Ag-S
e type, Au-Ni type, Au-Co type, Cu-Zn type, C
u-Sn system, Zn-Sn system, Ni-Sn system, Co-Sn
It is an alloy material such as series. When the metal material layer is combined with a Cu—Sn based alloy base body in which Nb filaments are arranged with the Sn layer interposed therebetween, Sn in the Sn layer is preferentially directed to the Cu—Sn base alloy base body in which Nb filaments are arranged. It is a metal material layer that diffuses into the. When the metal material layer is a Cu-Sn alloy or the like, Sn is contained in a saturated state or in an amount close to the saturated state. Since the metal material layer has a high melting point, the molten Sn layer can be held in a uniform shape, and the Sn layer is not consumed.
Is preferentially diffused toward the Cu-Sn based alloy substrate in which Nb filaments are arranged, so that the Sn layer can be thinned. Therefore, the thermal diffusion treatment time is shortened and Kirkendall vacancies are not formed. In the present invention, in order to form the Sn layer and the metal material layer on the composite wire, any method capable of forming a uniform thickness such as electroplating, electroless plating, and hot dipping can be applied. Since the Sn-containing alloy material allows Sn to diffuse and pass therethrough, it can be formed in multiple layers alternately with the Sn layers. When Cr is used for the metal material layer, the Cr layer also has a function as an insulating coating layer because it is electrically insulating. Therefore, the superconducting wire can be twisted without the need for enamel coating or the like.

The structure before and after the thermal diffusion treatment of the composite wire produced in the intermediate step of the method of the present invention will be described below with reference to the drawings. FIG. 1A is a transverse cross-sectional view of a composite wire using Ni for the metal material layer before the thermal diffusion treatment. Nb around the stabilized copper wire 1
Of the diffusion barrier, and the Nb / bronze (Cu—Sn alloy) composite layer 3, the bronze sheath (pipe) layer 4, the Sn layer 5, and the Ni metal material layer 6 are sequentially formed around the diffusion barrier. FIG. 1B is a cross-sectional view of the composite wire after the thermal diffusion treatment. In FIG. 7, Nb filaments of the Nb / bronze composite layer 3 are Nb ₃ Sn filaments formed into Nb ₃ Sn filaments.
₃ Sn-containing bronze layer. Around the Nb ₃ Sn-containing bronze layer 7, a united layer 8 of the bronze sheath layer 4 and the Sn layer 5 having a low Sn content is formed, and a Ni metal layer 6 is located around the united layer 8.

FIG. 2A is a cross-sectional view of a composite wire using bronze as a metal material layer before heat diffusion treatment. It is the same as that shown in FIG. 1A except that the bronze metal material layer 9 is formed on the outermost layer. FIG. 2B is a cross-sectional view after the thermal diffusion process. It is the same as that shown in FIG. 1B except that the bronze metal material layer 9 is formed on the outermost layer.

In the present invention, when the total amount of Sn contained in the composite wire is 16 wt% or more, a sufficient amount of Sn is supplied, and the stoichiometry (Nb-25) is excellent in superconducting properties.
A Nb ₃ Sn phase close to at% Sn) is formed. Therefore,
The amount of Sn contained in the entire composite wire is preferably 16 wt% or more.

If the ratio [t / T] of the thickness t of the Sn layer formed on the composite wire and the thickness T of the metal material layer is less than 1, the metal material layer becomes excessively thick, which is uneconomical. On the other hand, if it exceeds 10, the effect of retaining the molten Sn of the metal material layer decreases. Therefore,
The ratio [t / T] of the thickness t of the Sn layer of the composite wire and the thickness T of the metal layer is preferably 1 or more and 10 or less.

The present invention is based on a Cu--Sn alloy substrate or Nb.
Similar effects can be obtained when the filament contains a trace amount of elements such as Ti, Ta, Ha, and Ga. The stabilizing material of Nb and Ta same effect by applying a barrier layer to Nb ₃ Sn compound superconducting wire in complex with the interposition of such as Cu or Al can be obtained in the center.

In the present invention, the thermal diffusion treatment is usually S
The n layer and low-temperature treatment to diffuse into the Cu-Sn-based alloy substrate of Sn in the substrate is reacted with Nb is performed by dividing into high-temperature treatment for forming a Nb ₃ Sn phase. Generation of Kirkendall vacancies can be suppressed by performing low-temperature treatment for a short time at a temperature equal to or higher than the melting point of Sn. If Kirkendall vacancies occur, the amount is small and can be eliminated by light rolling before the high temperature treatment.

[0014]

In the present invention, when the Nb ₃ Sn compound superconducting wire is produced by the external diffusion method, the molten Sn on the composite wire is
The melting point is higher than n, Sn is not consumed, and Sn in the Sn layer is Nb.
Since the metal material layer preferentially diffuses toward the Cu—Sn alloy base body in which the filaments are arranged, the thermal diffusion treatment of Sn can be performed at high temperature in a short time. Therefore, no holes are formed in the substrate, and Nb ₃ Sn excellent in superconducting properties is obtained.
A system compound superconducting wire can be manufactured.

[0015]

The present invention will be described below in detail with reference to examples. (Example 1) Bronze with an outer diameter of 45.3 mmφ (Cu-14.3 wt%
Sn-0.2 wt% Ti-based alloy) 19 holes with 6.0 mmφ through holes at regular intervals, insert Nb wire with 5.8 mmφ outside diameter into these holes, and bronze lids at the front and rear ends of the bronze rod. Was vacuum-sealed by electron beam welding and covered to prepare a primary billet. Next, this primary billet was hot extruded, and this extruded material was repeatedly subjected to wire drawing and intermediate annealing to produce a hexagonal wire having an opposite side length of 1 mm. This hexagonal wire was filled into a bronze pipe having the same composition as the primary billet and having an outer diameter of 45 mmφ and an inner diameter of 38 mmφ to produce a secondary billet. At the center of the bronze pipe, an oxygen-free copper rod having a diameter of 20 mm, which serves as a stabilizing material, was arranged by winding Nb foil on the outer circumference. This secondary billet was processed into a composite wire of 0.7 mmφ by the same method as the primary billet. Next, a Sn layer and a Ni layer were sequentially electroplated on this composite wire to prepare a composite wire. The thicknesses of the Sn layer and the Ni layer were variously changed. Next, this composite wire was subjected to the first thermal diffusion treatment at 450 ° C. for 50 hours. After thermal diffusion treatment,
The tissue was observed. Sn of Sn layer is 100 in the bronze substrate.
It was diffused uniformly by about μm. There was no burnout of the Sn layer. The Nb filaments were linearly positioned in the bronze substrate at equal intervals, and no turbulence was observed. A small amount of Kirkendall pores were observed in the bronze substrate. Next, this wire rod was subjected to wire drawing at a cross-section reduction rate of 5% to adjust the outer diameter of the wire rod and eliminate Kirkendall pores inside the wire rod. Then, the second thermal diffusion treatment was performed at 695 ° C for 40 hours to obtain Nb ₃ S.
An n-based compound superconducting wire was manufactured.

Example 2 Nb ₃ Sn was prepared by the same method as in Example 1 except that the Sn layer and the Cu-10 wt% Sn alloy layer were sequentially electroplated on the composite wire to form a composite wire. A compound superconducting wire was manufactured.

(Comparative Example 1) Nb ₃ was prepared in the same manner as in Example 1 except that a Sn layer was plated on the composite wire to a thickness of 8 μm and a Cu layer was plated thereon to a thickness of 1.5 μm.
An Sn-based compound superconducting wire was manufactured.

(Comparative Example 2) In Example 1, an Sn layer was plated on the composite wire to a thickness of 14 μm, and a Cu layer was plated thereon to a thickness of 2.5 μm, and the first thermal diffusion treatment was performed at 450 ° C. for 100 minutes. An Nb ₃ Sn-based compound superconducting wire was manufactured by the same method as in Example 1 except that the time was applied.

(Comparative Example 3) A Nb ₃ Sn-based compound superconducting wire was manufactured in the same manner as in Example 1, except that only the Sn layer was formed to a thickness of 8 μm on the composite element wire.

(Comparative Example 4) In Example 1, only a Sn layer was formed on the composite wire to a thickness of 8 μm to form a composite wire.
This composite wire is heated at a temperature of 200 ° C below the melting point of Sn for 60 hours, then at 300 ° C for 50 hours, and finally at 695 ° C.
Example 1 except that the heat diffusion treatment was performed under heating conditions for 40 hours
A Nb ₃ Sn-based compound superconducting wire was manufactured by the same method as described above.

The critical current (Ic) was measured for each of the obtained Nb ₃ Sn-based compound superconducting wires. Also, the cross section was observed to examine the presence or absence of Sn burn-out and the presence or absence of Kirkendall pores. The results are shown in Table 1.

[0022]

[Table 1]

As is clear from Table 1, all the products of the method of the present invention (Nos. 1 to 10) had high Ic, no Sn burn-through, excellent cross-sectional shape, and small or few Kirkendall pores. . Incidentally, in No. 2, the average Sn concentration was below 16 wt%, so that Ic was slightly lowered. No. 6 was uneconomical because the metal material layer (Ni layer) was slightly thicker than the Sn layer thickness,
There was no problem in terms of characteristics. In No. 7, the metal material layer (Ni layer) was thin, the coercive force of the Sn layer was weakened, the cross-section was slightly deformed, and Ic was also slightly lowered. However, there was no problem in practical use.

On the other hand, in No. 11 of the comparative example, since the Cu layer was formed on the Sn layer, the Sn layer was consumed by the Cu layer and S
n was insufficient and Ic was lowered. In No. 12, since the Sn layer was formed thickly, the heat diffusion treatment time became long, a large number of Kirkendall vacancies were generated, and it remained even after light pressure reduction to lower Ic. In No. 13, the high melting point metal material layer was not used, and since the thermal diffusion treatment was performed at a temperature of 450 ° C. from the beginning, the Sn layer was burned out, the Nb ₃ Sn filament was exposed, and the Ic was significantly lowered. In No. 14, the thermal diffusion treatment was started at a temperature lower than the melting point of Sn, so the burnout of the Sn layer could be prevented, but a large number of Kirkendall vacancies were generated and the Ic was reduced even after the pressure was reduced. .

[0025]

As described above, according to the present invention, the melting point of Sn is higher than Sn, Sn is not consumed, and Sn in the Sn layer is N.
Since the metal material layer preferentially diffusing toward the Cu—Sn alloy base body in which the b filaments are arranged holds the molten Sn on the composite wire, the thermal diffusion treatment of Sn can be performed at a high temperature in a short time. Further, since the thermal diffusion treatment is carried out at a high temperature in a short time, the growth of holes in the substrate can be suppressed, and N having excellent superconducting characteristics can be obtained.
A b ₃ Sn-based compound superconducting wire is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing aspects of a composite wire according to the present invention before and after thermal diffusion treatment.

FIG. 2 is a cross-sectional view showing another embodiment before and after the thermal diffusion treatment of the composite wire according to the present invention.

[Explanation of Codes] 1--Stabilized copper wire 2 --Nb foil 3 --Nb / bronze composite layer 4 --Bronze sheath layer 5 --Sn layer 6 --Ni metal material layer 7 --Nb ₃ Sn Contained bronze layer 8 --- Coalescing layer of bronze sheath layer and Sn layer 9 --- Metal material layer of bronze

Claims (2)

[Claims] 1. An Sn layer and an S layer are formed on a composite element wire in which a large number of Nb filaments are arranged in a Cu—Sn based alloy substrate.
A metal wire layer having a melting point higher than n and non-reactive with Sn is sequentially formed to form a composite wire, and the composite wire is subjected to a thermal diffusion treatment to form an Nb ₃ Sn filament in a Cu-Sn alloy base. A method for producing a Nb ₃ Sn-based compound superconducting wire, comprising: 2. A metal material layer having a higher melting point than Sn and not reacting with Sn is Cr, Ni, Zn, Ag, Co, Fe, Pd, P.
Pure metal materials such as t and Au, or Ag-Pd-based, Ag-Sb
System, Ag-Se system, Au-Ni system, Au-Co system, Cu
-Zn system, Cu-Sn system, Zn-Sn system, Ni-Sn
System, method according to claim 1 Nb ₃ Sn compound superconducting wire according to, characterized in that it is composed of an alloy material of Co-Sn system, etc..