JP2742437B2 - Method for producing compound superconducting stranded wire - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a compound superconducting stranded superconducting wire suitable for use as a field winding of a superconducting generator.

"Conventional technology" In a superconducting wire, heat may be generated due to the movement of quantum flux lines, and in such a case, normal conduction buds are partially generated in the superconducting wire, and the entire superconducting wire becomes There is a risk of dislocation to the normal conduction state. Therefore, in order to stabilize the superconducting wire by preventing such magnetic instability, normal conduction dislocation, and the like, conventionally, the following technology has been adopted.

A superconductor is buried inside a stable base material of good conductivity such as copper. In particular, the stabilizing matrix is formed from high-purity copper.

The superconductor is made extremely thin into a filament having a diameter of several μm to several tens μm.

Twist multi-core wire.

Adopt a braided or formed stranded wire structure.

When a superconducting wire is used for alternating current, a stabilizing base material is formed from a high-resistance metal material such as a Cu-Ni alloy to suppress a coupling current generated between superconducting filaments.

Intermetallic compound superconductors are extremely hard and brittle,
When the mechanical strain is applied, the superconductivity tends to deteriorate. Therefore, a reinforcing material is added to the superconducting wire to prevent the mechanical strain from being applied.

`` Problems to be Solved by the Invention '' From the background described above, conventionally, as a structural example of a superconducting wire for AC, a method of twisting a wire material such as an Nb-Ti wire has been adopted, Since compound-based superconducting wires such as Nb ₃ Sn have weak defects in mechanical strain, there are few applications as conductors for superconducting generators for AC and the like.

Therefore, when examining the application of the compound superconducting wire for a superconducting generator, the biggest problems are to countermeasure mechanical distortion in coil processing and to reduce AC loss during energization.

Here, in order to reduce the distortion characteristics at the time of coil processing, if a structure in which the Nb ₃ Sn superconductor is arranged at the center side of the conductor and the stabilizing conductor is arranged outside is adopted, if the superconductor at the time of coil processing is adopted, Since the amount of bending can be minimized, distortion can be reduced.However, when this structure is adopted, the AC loss is lower than that of a superconducting wire in which a stabilizing conductor is placed on the center side and a superconductor is placed on the outside. There is a problem that increases.

The compound superconducting wire contains a plurality of elements constituting the superconducting intermetallic compound, and is subjected to diffusion heat treatment to form a workable composite wire that becomes a superconducting wire. There is known a method of producing a superconducting stranded wire by performing diffusion heat treatment after forming a stranded wire.

Therefore, application of this method to a method of manufacturing a superconducting stranded wire for a superconducting generator has been studied. However, as described above, in the case of a superconducting wire formed in a stranded shape, a break per one superconducting wire is required. Since the area is formed extremely small, even in the state of a composite wire that can be processed before performing diffusion heat treatment,
The outer periphery of the stranded wire has irregularities, and the outer periphery of the stranded wire is liable to be damaged when repeating the stranded wire. May occur. In addition, the superconducting wire in a state where the stranded wire is processed has a problem that there is a gap between the stranded wires, the stability is poor, and the rigidity is insufficient.

The present invention has been made to solve the above problems,
It is an object of the present invention to provide a method for producing a compound superconducting stranded wire having high rigidity, a small gap between stranded wires, excellent workability, and an excellent structure for alternating current such as for a superconducting generator.

"Means for Solving the Problems" In order to solve the above problems, the present invention includes a plurality of elements constituting a superconducting intermetallic compound, and prepares a composite element wire which becomes a superconducting conductor by performing a diffusion heat treatment. Preparing a stabilizing conductor of good conductivity, forming a composite conductor in which the composite element wire is stranded on the outer periphery of the stabilizing conductor and a stranded conductor portion is provided outside the stabilizing conductor, and thereafter The composite conductor is subjected to plastic working to deform the stranded conductor, forming a consolidated stranded conductor by closing the gap between the composite wires, and then performing diffusion heat treatment to superconduct the stranded conductor. It forms an intermetallic compound.

"Action" Since the composite strand provided by twisting outside the stabilizing conductor is compacted by plastic working, the gap existing between the twisted composite strands is closed, and the rigidity of the twisted part is reduced. In addition, the unevenness of the outer peripheral portion of the twisted composite strand is smoothed, so that the workability is also improved. In addition, since the stranded wire processing is performed before the composite element wire diffusion heat treatment, the stranded wire processing can be easily performed.

 Hereinafter, the present invention will be described in more detail.

FIGS. 1 to 7 are for explaining an example in which the method of the present invention is applied to the case of manufacturing an Nb ₃ Sn-based superconducting stranded twisted wire for alternating current. A stabilizing conductor 1 shown in FIG. 1 is prepared.

The stabilizing conductor 1 is provided by covering a core conductor 2 made of pure copper, an anti-diffusion layer 3 provided to cover the outer peripheral surface of the core conductor 2, and an outer peripheral surface of the anti-diffusion layer 3. And an alloy layer 4. The diffusion preventing layer 3 is a material that does not generate an unnecessary compound or the like between the pure copper constituting the core conductor 2 and is made of a metal material such as Ta or Nb having a high melting point. Is provided to prevent unnecessary elements from diffusing from the outside. The alloy layer 4 is made of a Cu--Ni alloy or a Cu--Sn alloy having a high electric resistance.

In order to form the diffusion preventing layer 3 and the alloy layer 4 outside the core conductor 2, plating is performed on the outside of the core conductor 1, or the material is formed on the outside of the core conductor 1. It can be easily formed by means such as drawing with a tape or foil.

Next, a composite element wire which is provided by twisting outside the stabilizing conductor 1 is prepared. In this example, an in-situ wire plated with Sn is used as the composite wire. To obtain an in-situ wire, a Cu-Nb alloy or Cu-Nb-
The in-situ ingot 6 shown in FIG. 2 is prepared by melting a Sn alloy or the like, and the in-situ ingot 6 is formed by drawing. The in-situ ingot 6 has a structure in which a myriad of dendrites composed of Nb are dispersed inside a metal base made of Cu or Cu-Sn, and is formed by drawing the in-situ ingot 6. An in-situ wire 7 shown in FIG. 3 having a structure in which fibrous Nb filaments are dispersed in a metal matrix can be obtained.

Next, a coating layer of Sn is formed on the outer peripheral surface of the in-situ wire 7 by plating to form a plated in-situ wire (composite strand) 8 shown in FIG. When the plating in-situ wire 8 is prepared, a plurality of plating in-situ wires 8 are prepared, and these are provided by twisting outside the stabilizing conductor 1, as shown in FIG.
A primary composite conductor 10 having a stranded conductor portion 9 provided outside the stabilized conductor 1 is obtained.

Once the primary composite conductor 10 has been created,
10 is subjected to a low-temperature heat treatment at a temperature of 180 to 450 ° C. for a predetermined time, so that Sn of the coating layer formed on the outer surface of the plating in-situ wire 8 is diffused into the plating in-situ wire 8. In this low-temperature heat treatment, the melting point of Sn (231.9
° C) or more from the beginning, the coating layer of Sn melts off from the in-situ wire 7, so in the low-temperature heat treatment, the temperature is lower than the melting point of Sn, and the temperature at which the diffusion of Sn is easy to proceed, that is, It is preferable to perform primary heat treatment at a temperature of about 180 to 220 ° C. for several hours to several tens of hours to sufficiently diffuse Sn of the coating layer into the inside of the in-situ wire 7 so that the coating layer disappears. Thereafter, heat treatment is performed at a temperature of about 300 to 450 ° C. for several hours to several tens of hours to further promote the diffusion of Sn and to suppress the generation of unnecessary compound phases of Cu and Sn in the in-situ wire 7. The metal matrix of the in-situ wire 7 is a stable Cu-Sn alloy phase. When the heat treatment is performed at a temperature higher than 450 ° C. in the low-temperature heat treatment, Sn and Nb
The diffusion reaction of Nb ₃ Sn proceeds to generate Nb ₃ Sn, and the workability of the in-situ wire 7 deteriorates, which is not preferable.

Next, the primary composite conductor 10 after the low-temperature heat treatment is compacted by a plastic working method such as die drawing or groove roll processing, and the stranded conductor part 9 is deformed into a substantially rectangular cross section to form a void existing in the stranded conductor part 9. To form a wire rod 12 having a consolidated stranded conductor portion 11 as shown in FIG. This wire rod 12
In the case of forming the in-situ wire 7, the Sn in the coating layer in the plated in-situ wire 8 has already disappeared and diffused into the in-situ wire 7 by the low-temperature heat treatment, and the in-situ wire 7 has been strengthened. Even when a small in-situ wire 7 is used, there is no breakage during plastic working.

Next, a plurality of wires 12 are further assembled and twisted to form a secondary stranded conductor 13 shown in FIG. In the case where the secondary stranded conductor 13 is formed, the stranded conductor portion 9 has already been consolidated and becomes the consolidated stranded conductor portion 11 and the rigidity is improved.
This part does not break during processing.

Next, the secondary stranded conductor 13 is subjected to a diffusion heat treatment of heating to 500 to 700 ° C. for several tens to several hundreds hours, and the Sn and the Nb filament diffused into the inside of the in-situ wire 7 react with each other, and Nb ₃ Sn
By generating a filament of the superconducting intermetallic compound, a superconducting stranded wire having a secondary stranded structure shown in FIG. 7 can be obtained.
At the time of the diffusion heat treatment, Sn or Ni contained in the alloy layer 4 attempts to diffuse into the inside of the stabilized conductor 1, but the diffusion prevention layer 3 prevents the diffusion into the inside. In addition, the pure copper core conductor 2 is not contaminated with unnecessary elements such as Sn. If the core conductor 2 is contaminated with an element such as Sn, the electric resistance of the core conductor 2 at an extremely low temperature is increased, and the performance of the core conductor 2 as a stabilized conductor is undesirably reduced.

The superconducting stranded wire manufactured as described above has high rigidity because the stranded wire portion is compacted by plastic working, and the outer peripheral portion of the stranded wire portion is smooth. Furthermore, because of the secondary stranded structure, it has high stability for AC use. Further, since the superconducting conductor portion formed from the in-situ wire 7 and the core conductor 2 are interrupted by the alloy layer 4 having a high electric resistance, an eddy current loss that tends to occur between the superconducting conductor portion and the core conductor 2 Can be reduced. In addition, since the superconducting conductor portion is manufactured from the in-situ wire 7, it is excellent in critical current characteristics, and is excellent in mechanical strength such that the superconducting characteristics are less deteriorated even when subjected to mechanical strain.

Therefore, the superconducting stranded wire having the above-described structure is suitable for alternating current with a field winding of a superconducting generator.

In the above-described example, the superconducting conductor portion was formed using the in-situ wire 7. However, a composite multi-core wire manufactured by performing a plurality of operations of reducing the diameter by covering an Nb core material with a Sn pipe is performed in an in-situ manner. Of course, it may be used as a substitute for the chewing wire 7.

In the above example, the secondary stranded conductor 13 is subjected to diffusion heat treatment to form a superconducting stranded wire, but the primary stranded conductor 10 may be subjected to diffusion heat treatment to form a superconducting stranded wire.

Furthermore, in the above example, an example was described in which the method of the present invention was applied to a method for producing a superconducting stranded Nb ₃ Sn-based wire, but the method of the present invention was applied to V ₃ Ga-based, Nb ₃ Ge, NB ₃ Al, etc. Of course, it can be applied as a method for producing a compound superconducting stranded wire.

"Example" A rod-shaped in-situ ingot having a composition of Cu-40w% Nb was melted, forged, extruded, and drawn, and an Sn plating layer having a thickness of 8 µm was formed on the outer peripheral surface thereof. Coating yielded a 0.2 mm diameter in-situ wire. Also,
Nb layer and Cu- around the 99.9% pure oxygen-free copper core conductor
A stabilized conductor having a diameter of 1.3 mm, which was coated with a Ni alloy layer, was prepared, and the in-situ wire was formed and twisted around the stabilized conductor to form a primary composite conductor.

Thereafter, a low-temperature heat treatment of heating at 180 ° C. for 96 hours and then heating at 400 ° C. for 48 hours in an N ₂ gas atmosphere was performed to diffuse Sn into the in-situ wires to integrate the in-situ wires. Subsequently, the primary composite conductor is subjected to plastic working by wire drawing using a dice to consolidate the stranded wire portion formed on the outer periphery to form a consolidated conductor portion. At this time, no disconnection of the in-situ wire occurred.

Thereafter, as shown in FIG. 7, seven primary composite conductors were used to form a secondary stranded wire to obtain a secondary stranded conductor having a thickness of 3 mm and a width of 5 mm. In this secondary stranded conductor, winding processing could be easily performed.

After the winding process, heat to 500-550 ° C for 150-200 hours
Diffusion heat treatment for Nb ₃ Sn generation was performed, and a Nb ₃ Sn superconducting stranded wire for high flow was obtained.

[Effects of the Invention] As described above, the method of the present invention closes the voids existing in the stranded wire conductor portion by plasticizing the stranded wire portion provided by twisting the outside of the stabilized conductor. The rigidity of the stranded wire portion can be improved, and the unevenness existing on the outer peripheral portion of the stranded wire conductor can be smoothed, so that the workability can be improved. Further, since the composite wire is subjected to the stranded wire processing before the diffusion heat treatment, the stranded wire processing can be easily performed without causing trouble such as disconnection.

Therefore, according to the method of the present invention, a superconducting stranded wire excellent for alternating current, such as a field winding of a superconducting generator, can be manufactured.

[Brief description of the drawings]

FIGS. 1 to 7 are diagrams for explaining an example in which the present invention is applied to a method for manufacturing a superconducting stranded wire having an Nb ₃ Sn diameter.
The figure is a sectional view of the stabilizing conductor, FIG. 2 is a sectional view of the in-situ ingot, FIG. 3 is a sectional view of the in-situ line,
FIG. 4 is a cross-sectional view of the plating in-situ wire, and FIG.
Fig. 6 is a cross-sectional view of a consolidated stranded conductor,
FIG. 7 is a sectional view of the secondary stranded conductor. 1 stabilizing conductor, 2 core conductor, 3 anti-diffusion layer, 4 alloy layer, 6 in-situ ingot, 7
... in-situ wire, 8 ... plated in-situ wire (composite strand), 9 ... stranded conductor, 10 ... primary composite conductor, 11 ... consolidated stranded conductor, 12 ... wire, 13 ... ... Secondary stranded conductor.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Masayoshi Tange 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd. (72) Inventor Satoshi Kono 1-1-1, Kiba, Koto-ku, Tokyo Fujikura Electric Wire (56) References JP-A-60-39705 (JP, A) JP-A-54-119681 (JP, A) JP-A-55-100611 (JP, A)

Claims (1)

(57) [Claims] 1. A composite element wire comprising a plurality of elements constituting a superconducting intermetallic compound and being subjected to a diffusion heat treatment to prepare a superconducting conductor, and a stabilizing conductor having good conductivity being prepared. The composite strand is twisted around the outer periphery of the conductor to form a composite conductor having a stranded conductor outside the stabilized conductor, and thereafter, the composite conductor is subjected to plastic working to deform the stranded conductor. And forming a consolidated stranded conductor by closing a gap between the composite strands, and thereafter performing a diffusion heat treatment to generate a superconducting intermetallic compound in the consolidated stranded conductor. Manufacturing method of stranded wire.