JP2742436B2 - 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.

From the above background, conventionally, in the case of manufacturing a stranded superconducting wire in a compound-based superconducting wire for alternating current, a wire containing at least one of the elements constituting the superconducting intermetallic compound is superconducting. Of the elements that constitute the intermetallic compound, a covering layer containing the remaining elements is formed to form a workable composite wire, twisting is performed at the stage of this composite wire, and diffusion heat treatment is performed after twisting. To produce a superconducting twisted wire.

[Problems to be Solved by the Invention] By the way, in the superconducting wire for AC, a secondary stranded wire constituted by assembling a plurality of once-twisted wires and then re-twisting them for the purpose of improving stability. Attempts have been made to adopt a structure.

In such a case, conventionally, a plurality of the composite strands are assembled into a primary stranded wire, and subsequently, a plurality of the primary stranded wires are assembled into a secondary stranded wire, and then a winding process is performed. , Followed by a diffusion heat treatment to generate a superconducting intermetallic compound,
A superconducting stranded wire for AC is obtained.

However, as described above, in the superconducting wire for alternating current formed in a stranded form, the cross-sectional area per superconducting wire is formed extremely small for stabilization. Even in the state of a possible composite strand, there has been a problem that troubles such as disconnection are likely to occur during a plurality of times of twisting.

On the other hand, conventionally, as an example of the structure of the superconducting wire for a superconducting generator, but a method of stranded wire of the wire of Nb-Ti wire and the like is employed, the compound superconducting wire, such as Nb ₃ Sn is Because of the weakness of mechanical strain, there were few applications as conductors for AC superconducting generators.

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 during coil processing, if a structure in which the Nb ₃ Sn superconductor is arranged on the center side of the conductor and the stabilizing conductor is arranged on the outer side is adopted, if the superconductor during 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 present invention has been made to solve the above problems,
To provide a superconducting stranded wire suitable for AC such as for a superconducting generator, and even if a superconducting stranded wire is manufactured by performing stranded wire processing a plurality of times, so as not to cause disconnection during manufacturing. It is an object of the present invention to provide a method for producing a compound superconducting stranded wire that can be used.

"Means for Solving the Problem" In order to solve the problem, the invention described in claim 1 includes, among a plurality of elements constituting a superconducting intermetallic compound,
A composite wire is prepared by forming a coating layer containing the remaining elements of the plurality of elements constituting the superconducting intermetallic compound on a wire containing at least one element, and twisting the composite wire. The necessary operation is repeated as many times as necessary to form a stranded conductor, and then a stranded conductor is formed.
A method for producing a superconducting stranded wire by performing a diffusion heat treatment for generating a superconducting intermetallic compound, comprising: adding a superconducting metal to the composite element wire before the stranded wire processing or the stranded wire conductor before performing the second or subsequent stranded wire processing. A low-temperature heat treatment is performed at a temperature lower than the diffusion heat treatment temperature at which the compound is generated, and a low-temperature heat treatment is performed to diffuse the elements of the coating layer into the inside of the strand. After this low-temperature heat treatment, further twisting is performed, followed by a diffusion heat treatment Things.

[Operation] On the other hand, the element of the coating layer diffuses into the strand by low-temperature heat treatment performed before the twisting processing, and the strand and the coating layer are integrated. Disconnection during processing is prevented. Further, the diffusion preventing layer formed on the stabilized conductor prevents unnecessary elements from diffusing into the core conductor during heat treatment.

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

FIGS. 1 to ₃ 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. The in-situ wire is formed by drawing an in-situ ingot 6 shown in FIG. 2 obtained by melting a predetermined component of a Cu-Nb alloy or a Cu-Nb-Sn alloy. The in-situ ingot 6 has a structure in which a myriad of dendrites made of Nb are dispersed inside a metal base made of Cu or Cu-Sn.
The 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 by wire drawing.

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 plated in-situ wire 8 is prepared, a plurality of plated in-situ wires 8 are prepared, and these are provided in a twisted form outside the stabilizing conductor 1 to provide a cross-sectional structure as shown in FIG. To obtain the primary stranded conductor 10.

Once the primary stranded conductor 10 has been created,
10 is subjected to a low-temperature heat treatment of heating to a temperature of 180 to 450 ° C. for a predetermined time to diffuse the elements of the coating layer into the in-situ wire 7. 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 promote the diffusion of Sn, and to suppress the generation of unnecessary compound phases of Cu and Sn in the in-situ wire 7 to perform in-situ heating. The metal matrix of the Chu wire 7 is a stable Cu-Sn alloy phase. In the low-temperature heat treatment, if the heat treatment is performed at a temperature higher than 450 ° C., the diffusion reaction between Sn and Nb proceeds, and Nb ₃ Sn starts to be generated, which undesirably lowers the workability of the in-situ wire 7.

Next, a plurality of primary stranded conductors 10 that have been subjected to a low-temperature heat treatment are further assembled and stranded to form a secondary stranded conductor 11 shown in FIG. When the secondary stranded conductor 11 is formed, the Sn coating layer in the primary stranded conductor 9 is lost by the low-temperature heat treatment, and Sn is diffused into the in-situ wire 7 to strengthen the in-situ wire 7. Therefore, even when the in-situ wire 7 having a small diameter is used, the wire is not broken during the twisting process.

Next, the secondary stranded conductor 11 is subjected to a diffusion heat treatment of heating to 500 to 700 ° C. for several tens to several hundred hours, and the Sn and the Nb filament diffused into the inside of the in-situ wire 7 are reacted with each other.
By forming the in-situ wire 7 as the superconducting conductor 9 by generating a filament of the ₃ Sn superconducting intermetallic compound, a secondary stranded superconducting conductor having a cross-sectional structure equivalent to that of the secondary stranded conductor 11 shown in FIG. A stranded wire 12 can be obtained. In addition, it is contained in the alloy layer 4 during the diffusion heat treatment.
Although Sn, Ni, or Sn contained in the coating layer attempts to diffuse into the inside of the stabilizing conductor 1, the diffusion to the inside is prevented by the diffusion preventing layer 3. The core conductor 2 is not contaminated with unnecessary elements such as Sn. If the core conductor 2 is contaminated with Sn, the electric resistance of the core conductor 2 at an extremely low temperature increases, and the performance of the core conductor 2 as a stabilizing conductor is deteriorated.

Since the superconducting stranded wire manufactured as described above has a 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. Furthermore, since the superconducting conductor portion is manufactured from the in-situ wire 7,
It has excellent critical current characteristics and is excellent in mechanical strength, such as little deterioration of superconductivity 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.

By the way, in the above example, the secondary stranded conductor 11 is subjected to diffusion heat treatment, but the primary stranded conductor 10 may be subjected to diffusion heat treatment to generate a superconducting intermetallic compound, thereby producing a superconducting stranded wire. Of course.

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.

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 Nb ₃ Sn-based superconducting stranded 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-40wt% Nb was melted, forged, extruded, and drawn, and an Sn plating layer having a thickness of 8 µm was further 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 into a twist around the stabilized conductor to prepare a primary stranded conductor.

Thereafter, after heating at 180 ° C. for 96 hours in an N ₂ gas atmosphere, a low-temperature heat treatment of heating at 400 ° C. for 48 hours was performed to diffuse Sn into the in-situ wires to integrate the in-situ wires.

Thereafter, as shown in FIG. 3, five 1-time stranded 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 the case of manufacturing this two-hour stranded conductor, no breakage of the in-situ wire occurred. Moreover, 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, according to the invention described in claim 1, in the case where the composite wire composed of the wire and the coating layer is twisted, or the composite wire in which the composite wire is twisted is formed. When the conductor is further twisted, the composite strand and the coating layer are integrated and strengthened by low-temperature heat treatment before stranding, and then the strand is processed, so that the composite strand or the twisted conductor is broken. It can be processed without twisting.

Therefore, a superconducting stranded wire excellent for AC use, such as a field winding of a superconducting generator, can be manufactured without breaking during manufacturing.

[Brief description of the drawings]

1 to 6 are diagrams for explaining an example in which the method of the present invention is applied to a method for producing a superconducting stranded wire having an Nb ₃ Sn diameter.
1 is a cross-sectional view of a stabilizing conductor, FIG. 2 is a cross-sectional view of an in-situ ingot, FIG. 3 is a cross-sectional view of an in-situ wire, FIG. 4 is a cross-sectional view of a plated in-situ wire, and FIG. FIG. 6 is a sectional view of a secondary stranded conductor, and FIG. 6 is a sectional view of a secondary stranded conductor. 1 stabilizing conductor, 2 core conductor, 3 diffusion preventing layer, 4 alloy layer, 6 in-situ ingot,
7 ... in-situ wire, 8 ... plated in-situ wire (composite strand), 9 ... superconducting conductor, 10 ... primary stranded conductor, 11 ... 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-60-250506 (JP, A) JP-A-60-62011 (JP, A A)

Claims (1)

(57) [Claims] 1. A wire containing at least one of a plurality of elements constituting a superconducting intermetallic compound, on a wire rod comprising a coating layer containing the remaining elements among the elements constituting the superconducting intermetallic compound. A composite strand is prepared, and the operation of twisting the composite strand is further performed as necessary to produce a stranded conductor, and then a stranded conductor is formed on the stranded conductor. A method for producing a superconducting stranded wire by performing a diffusion heat treatment for producing a compound, comprising: forming a superconducting intermetallic compound on the composite element wire before the stranded wire processing or on the stranded wire conductor before the second or subsequent stranded wire processing. Perform a low-temperature heat treatment at a lower temperature than the diffusion heat treatment to diffuse the elements of the coating layer inside the strand,
A method for producing a compound superconducting stranded wire, characterized by further performing a twisting process after the low-temperature heat treatment and then performing a diffusion heat treatment.