JP3884222B2 - Manufacturing method of oxide superconducting composite multi-core wire - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an oxide superconducting composite multifilamentary wire.
[0002]
[Prior art]
An oxide superconducting wire, for example, a Bi-based superconducting wire, is a raw material of a superconducting material in an Ag sheath or an Ag alloy sheath in order to ensure oxygen permeability, workability, and orientation of the superconducting material necessary for generating the superconducting material. In general, it is produced by a so-called powder-in-tube method in which powder is encapsulated and then subjected to surface reduction and rolling.
[0003]
The superconductor portion embedded in the matrix is multi-core to prevent mechanical deterioration of superconducting characteristics and to reduce AC loss. The multi-core method is to first fill the metal tube with raw material powder to make a single core wire, reduce the surface area, process it to a certain diameter, and bundle it into a metal tube. The way to do it is widespread. As the metal pipe, an alloy pipe such as a silver alloy is used in addition to a pure metal pipe or the like in order to increase the wire strength after the heat treatment.
[0004]
On the other hand, in order to reduce the AC loss of these superconducting wires, a method of twisting the entire wire before rolling and twisting the superconducting portion (filament) is used. By performing such processing, it becomes possible to reduce the coupling loop between the filaments and reduce the AC loss.
[0005]
[Problems to be solved by the invention]
When a multi-core wire is manufactured by the above-described powder-in-tube method, a metal tube made of silver or the like for filling a plurality of single-core wires is required at the second assembly (bundling single-core wires). Further, in order to prevent the metal tube from cracking during subsequent diameter reduction processing such as drawing, the metal tube made of silver or the like used for the second assembly requires a certain thickness.
[0006]
For this reason, there is a problem that the area ratio (matrix ratio) between the superconducting portion and the metal portion such as silver can be reduced only to a certain extent. In the case of superconducting wires having the same cross-sectional area, a larger number of superconducting portions (a smaller number of metal portions) can increase the current flowing through the entire wire and is more practical.
However, as described above, the normal powder-in-tube method has a limit in reducing the matrix ratio.
[0007]
Further, in the normal powder-in-tube method, since rolling is performed from a round line state, it is impossible to apply pressure evenly to the filaments dispersed in the matrix during rolling. Therefore, the powder density and the thickness of the filament are not uniform, and the critical current density Jc per filament tends to be non-uniform. For this reason, there exists a problem that Jc of the whole wire will become smaller than the ideal state in which Jc of all the filaments is equal.
[0008]
The present invention has been made in view of such circumstances, the matrix ratio is small, AC loss is small and to provide a method of manufacturing an oxide superconducting composite multifilamentary wire exhibits excellent characteristics that the critical current density is large Objective.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a step of forming a composite strand by filling a metal tube with an oxide superconducting material or oxide superconducting raw material powder, bundling a plurality of the composite strands, and placing the outer side of a metal A step of binding with a tape or a metal wire, a step of compressing the bundle of composite wires bound with the metal tape or metal wire, and a heat treatment of the bundle of composite wires subjected to the compression processing The present invention provides a method for producing an oxide superconducting composite multi-core wire comprising a step of forming a metal diffusion layer between the composite wires .
[0010]
In the method for producing an oxide superconducting composite multifilamentary wire according to the present invention, silver, gold, platinum, palladium, rhodium, copper, iron, or an alloy containing them can be used as the metal constituting the metal matrix. The metal matrix can be composed of a metal tube made of such a metal or a metal tube whose surface is coated with such a metal.
[0011]
A structure in which a plurality of composite wires are bundled can be a structure in which a plurality of composite wires are transposed. That is, it is possible to reduce AC loss by adopting a transposed structure in which composite strands are twisted or dislocated.
[0013]
In the method for producing an oxide superconducting composite multifilamentary wire according to the present invention, the temperature of the heat treatment is desirably in the range of the melting point of the metal constituting the surface of the composite strand minus 250 ° C. to the superconducting substance generation temperature minus 50 ° C.
[0014]
The metal tape or metal wire used in the method of the present invention can be made of a metal that does not react with the metal constituting the surface of the composite strand. In this case, the metal tape or the metal wire can be removed before or after the heat treatment.
[0015]
Further, a metal sheet that easily causes a diffusion reaction with the metal constituting the surface of the composite strand can be interposed between the composite strands rather than the metals constituting the surface of the composite strand.
[0016]
Furthermore, the composite multi-core wire integrated by the formation of the metal diffusion layer is subjected to processing for reducing the cross section, and then heat treatment and rolling are performed to generate a superconductor or improve superconducting characteristics. Thus, an oxide superconducting composite multicore wire can be obtained.
[0017]
Hereinafter, the method for producing the oxide superconducting wire of the present invention will be described in more detail.
First, a metal tube whose surface is made of silver, gold, platinum, palladium, copper, or iron is filled with an oxide superconducting material or oxide superconducting raw material powder. Next, this is diameter-reduced and processed into a round or square cross section to obtain a composite strand. The steps up to here are the same as a method generally called a powder-in-tube method. In addition, it is effective to process the composite wire into a tape shape from the viewpoint of obtaining a large bonding area at the time of diffusion heat treatment described later.
[0018]
Next, the surface of the composite strand is roughened by polishing with rough abrasive grains and washed. Then, a plurality of roughened composite wires are bundled, and the outside is bound with a metal tape or the like. The metal tape used at this time is the same as the metal constituting the metal tube of the composite strand, for example, if the metal tube is silver, silver tape is used in order to integrate the composite strand and the metal tape. desirable.
[0019]
Further, in order to improve the mechanical strength of the composite wire, when the surface of the composite wire is a silver-magnesium alloy, magnesium oxide is generated on the surface during the heat treatment and inhibits the diffusion reaction. It is also effective to make a subsequent diffusion bonding easy by interposing a pure silver sheet between the wires.
[0020]
Instead of the pure silver sheet, it is also possible to use a composite, for example, a material having a higher strength than the pure silver sheet such as Ni tape and having a surface coated with pure silver by plating or the like.
[0021]
On the other hand, if a tape that does not react with the metal on the surface of the composite strand is selected as the outer binding tape, the space factor of the superconductor portion can be increased by removing it after diffusion heat treatment. It is. For example, if the metal constituting the surface of the composite strand is silver, a nickel tape can be used as the binding tape.
[0022]
Thereafter, surface reduction of several to several tens of percent is performed by a four-sided roll, a hole die, a two-high mill, a swager, etc., and the composite strands are brought into close contact with each other. Prior to this step, it is also effective to perform a preliminary heat treatment at about several hundreds of degrees Celsius so that the composite strands and the binding tape are physically brought into close contact with each other.
[0023]
Thereafter, the temperature is lower than the melting point of the metal constituting the metal tube, and does not inhibit the superconducting substance formation reaction, that is, the melting point of the metal pipe is minus 250 ° C. or more and the superconducting substance production temperature is minus 50 ° C. or less. By performing heat treatment for several minutes to several tens of minutes in the temperature range, a diffusion layer having a thickness of several nm or more is formed at the interface between the composite strands.
[0024]
Here, the reason why the superconducting material generation temperature minus 50 ° C. or less is set as the temperature that does not inhibit the generation of the superconducting material will be described.
For example, in the case of the Bi-2223 system, the superconducting material is formed at a temperature of about 840 ° C., but actually, the reaction of the phase constituting the raw material powder starts from around 810 ° C. Therefore, it is not preferable to perform diffusion heat treatment near the superconducting material generation temperature because the oxide superconducting material powder or the raw material powder melts or deteriorates.
[0025]
On the other hand, if the diffusion heat treatment temperature is too low, it takes a long time to diffuse between the composite strands, or the diffusion is insufficient, resulting in poor adhesion. Therefore, it is important to select the temperature and time according to the material. . When the matrix metal portion is silver and the superconducting material to be filled is a Bi-2223 series superconducting material, it is desirable to perform heat treatment at 750 to 800 ° C. for about 10 minutes.
[0026]
After integrating the composite strands in this way, a desired superconducting wire can be obtained by combining plastic processing such as rolling or drawing and heat treatment. Specifically, the composite wire integrated by the above-described method is rolled so that the total rolling reduction is 70% or more, and then heat treatment for generating the first superconducting material is performed. The heat treatment temperature for generating the superconducting material depends on the heat treatment atmosphere and the production conditions such as the raw material powder composition, but when the oxide superconducting raw material powder is Bi-2223, it is preferably about 840 ° C. for about 20 hours.
[0027]
Thereafter, rolling for promoting the orientation of the superconducting material is performed at a reduction rate of about 15%, and heat treatment is again performed at about 840 ° C. for about 150 hours to sufficiently generate the Bi-2223 phase. In this way, a high critical current density oxide superconducting composite multicore wire can be obtained.
[0028]
Note that, unlike the method of the present invention described above, simply by laminating without performing diffusion heat treatment, the composite strands are scattered during the rolling process, or the composite strands are shifted from each other and the whole is not processed uniformly. I will.
[0029]
On the other hand, if a plurality of composite strands are integrated by diffusion heat treatment as in the method of the present invention, the integration is maintained even if the outer binding tape is removed. There is no hindrance. Therefore, the space factor of the superconducting portion can be increased by removing the binding tape, which is extremely effective in practical use.
[0030]
Also, if the composite strands are assembled in a tape shape, and finally formed into a tape shape, the composite strand and the assembly can be processed in a similar shape, which reduces the abnormal deformation of the filament, It is also possible to improve Jc due to the effect of reducing the variation in powder density.
[0031]
In addition, when assembling composite strands, not just aligning them in parallel, but also transposing the strands by dislocation or twisting them, and applying the filament twist that is done with ordinary superconducting wires Can do. By performing such processing, there is also an effect of bonding the composite strands more firmly as a whole in the diffusion heat treatment.
[0032]
If the bundle of composite strands is not subjected to diffusion heat treatment and is simply rolled after assembly, the composite strands may be separated from each other, or the gap between the composite strands may be increased and integrated. It does not become a wire.
[0033]
In order to reduce the AC loss, the twist pitch of the filament is preferably several tens of times or less the filament diameter. In a method of producing a composite wire in which filaments are pre-twisted by a conventional powder-in-tube method and rolling the composite wire in a metal tube, the twist pitch can be used even in the reduction process until the composite wire is manufactured. Is elongated in the longitudinal direction, resulting in a very long pitch in the finished stage, which does not contribute to a reduction in AC loss.
[0034]
On the other hand, according to the method of the present invention, an arbitrary pitch can be obtained immediately before the final rolling, which is effective in reducing AC loss. The composite wire obtained in this manner can be made into a desired superconducting wire by repeating rolling and heat treatment in the same manner as the above-described parallel lamination.
[0035]
As described above, according to the present invention, since the outer metal tube is not required at the time of the second assembly, the space factor of the superconductor portion is higher than that in the case of making a multi-core wire by a normal powder-in-tube method. Can be increased. Therefore, if the total cross-sectional area of the wire is the same and Jc is equal, the critical current can be increased.
[0036]
In the case of a silver sheath Bi-based wire, the silver ratio is 2 to 3 using a normal powder-in-tube method, but according to the present invention, the silver ratio can be reduced to about 1. A wire having a silver ratio of 1 can obtain Ic twice as much as a wire having a silver ratio of 3 if Jc is equal, and is useful for applications such as large-capacity energization.
[0037]
In addition, since the amount of expensive precious metals such as silver and gold can be reduced, there is a great cost advantage.
Furthermore, by setting the diffusion heat treatment temperature to the melting point of the metal constituting the surface of the composite strand minus 200 ° C. or more and the superconducting material generation temperature minus 50 ° C. or less, an effective diffusion phase can be obtained without hindering the production of the superconducting material. Can be obtained.
[0038]
Furthermore, even when the surface of the composite strand is made of an alloy that hardly forms a diffusion phase, an effective diffusion phase can be obtained by interposing a pure metal or the like that promotes a diffusion reaction between the composite strands. Can be obtained.
[0039]
Also, by transposing the composite wire immediately before rolling, and then adhering it by diffusion heat treatment, a plurality of composite wires can be integrated more firmly as a whole. It is possible to obtain a wire material with a filament twist at an arbitrary pitch. By doing in this way, the effect similar to the filament twist of the multicore wire material generally performed can be acquired, and alternating current loss can also be reduced.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, various examples will be described as embodiments of the present invention.
Example 1
Bi-2223 oxide superconducting raw material powder was compacted into a rod shape of φ15 mm × L500 mm, and this was fitted and filled in a pure silver pipe having an inner diameter of φ15.1 mm and an outer diameter of 18 φmm. Subsequently, the pure silver pipe filled with the Bi-2223 oxide superconducting raw material powder was subjected to diameter reduction processing to obtain a single core wire of φ1.5 mm.
[0041]
Next, this single core wire was rolled and processed into a tape having a thickness of 0.3 mm and a width of 2 mm to obtain a strand. And the surface of this strand was grind | polished with the abrasive paper, and the surface was roughened. Thereafter, the surface-roughened strands were degreased and washed with alcohol, and 10 pieces of these were laminated in parallel, and a pure silver tape having a thickness of 0.05 mm and a width of 5 mm was spirally wound around this laminate. 1 was obtained as an integrated laminate.
[0042]
In FIG. 1, each of the ten strands 2 laminated is composed of Bi-2223 raw material powder 3 and a silver matrix (silver pipe) 4 surrounding the periphery thereof, and a pure silver tape 5 is surrounded around them. It is wound in a spiral.
[0043]
Next, the laminated body 1 around which the pure silver tape 5 was wound was processed with a four-sided roll with a surface reduction rate of 10% to obtain a thickness of 2.85 mm and a width of 1.99 mm. Thereafter, diffusion heat treatment is performed at 770 ° C. for 10 minutes, and as shown in FIG. 1, a diffusion layer 6 having a thickness of several hundreds of nanometers is formed at the interface between the strands 2, and the whole is integrated. And finished into a tape shape having a thickness of 0.3 mm and a width of 4 mm.
[0044]
Next, the tape was subjected to a heat treatment for generating a superconductor (hereinafter referred to as SC generation heat treatment) (first time) at 825 to 840 ° C. for 50 hours, and then rolled at a reduction rate of 15%. SC generation heat treatment (second time) was performed at 825 to 840 ° C. for 200 hours to obtain a superconducting wire.
[0045]
The critical current Ic of the superconducting wire thus obtained under liquid nitrogen temperature was 120 A, and the silver ratio was 2. Using this value, the critical current density Je per total cross-sectional area of the wire was calculated and found to be 10,000 A / cm2.
[0046]
Example 2
A single core wire was produced in the same manner as in Example 1, processed to φ0.7 mm, rolled, and processed into a tape shape having a thickness of 0.3 mm and a width of 1 mm to form a strand. The surface of this strand was polished with abrasive paper to roughen the surface.
[0047]
As shown in FIG. 2, the strands 12 are arranged in two rows and four stages and subjected to dislocation processing at a pitch of 20 mm, and then a pure silver tape 15 having a thickness of 0.07 mm and a width of 7 mm is spirally wound and integrated. . In the figure, reference numeral 13 denotes Bi-2223 raw material powders 3 and 14 denotes a silver matrix (silver pipe).
[0048]
A set of the strands 12 around which the silver tape 15 was wound was processed with a four-sided roll with a surface reduction rate of 20% to obtain a thickness of 0.8 mm and a width of 1.95 mm. Thereafter, a diffusion heat treatment is performed at 790 ° C. for 5 minutes to form a diffusion layer having a thickness of several hundreds of nanometers at the interface between the strands 12, and the whole is integrated and rolled to a thickness of 0.3 mm. And finished in a tape shape with a width of 4 mm.
[0049]
This tape was subjected to SC generation heat treatment (first time) at 825 to 840 ° C. for 50 hours, then rolled at a reduction rate of 20%, and further subjected to SC generation heat treatment (second time) at 825 to 840 ° C. for 200 hours. gave.
[0050]
The critical current density Ic at the liquid nitrogen temperature of the wire thus obtained was 180 A, and the silver ratio was 1. When Je was calculated using this value, it was 15,000 A / cm ² . Further, ac loss by magnetization method of this wire is 200 J / ^{m 3,} it was 1/2 of AC loss 400 J / ^{m 3} of the wire of Example 1.
[0051]
Example 3
A single core wire was produced in the same manner as in Example 1, and the surface of the strand obtained by reducing the diameter to φ1 mm was rubbed with abrasive paper to roughen the surface. Then, it degreased and washed with alcohol and twisted seven pieces.
[0052]
As shown in FIG. 3, a pure silver tape 25 was spirally wound around the stranded wire and integrated. In the figure, reference numeral 23 indicates Bi-2223 raw material powder, and 24 indicates a silver matrix (silver pipe).
[0053]
After drawing this with a φ2.8 hole die and smoothing the surface of the stranded wire, diffusion heat treatment is performed at 770 ° C. for 10 minutes to form a diffusion layer 26 having a thickness of several hundred nm, and the whole is integrated. did. And it rolled and finished in the tape shape of thickness 0.3mm and width 4mm.
[0054]
This was subjected to SC generation heat treatment (first time) at 825 to 840 ° C. for 50 hours, then rolled at a reduction ratio of 15%, and further subjected to SC generation heat treatment (second time) at 825 to 840 ° C. for 200 hours. It was. The critical current Ic at the liquid nitrogen temperature of this wire was 120 A and the silver ratio was 2. Using this value to calculate Je, it was 10000 A / cm ² .
[0055]
Example 4
In Example 1, as shown in FIG. 4, the aggregated wires after the diameter reduction by the four-way roll were further arranged in parallel, and pure silver tape 35 was spirally wound from the outside to be integrated. This was further compressed using a four-sided roll at a surface reduction rate of 5%, and diffusion heat treated at 770 ° C. for 10 minutes. In the figure, reference numeral 33 denotes Bi-2223 raw material powder, 34 denotes a silver matrix (silver pipe), and 36 denotes a diffusion layer.
[0056]
This was processed to a thickness of 1 mm and a width of 2.5 mm using a drawing die. Furthermore, it rolled and processed to thickness 0.25mm and width 4mm. This was subjected to SC generation heat treatment (first time) at 825 to 840 ° C. for 50 hours, then rolled at a reduction ratio of 15%, and further subjected to SC generation heat treatment (second time) at 825 to 840 ° C. for 200 hours. It was.
[0057]
The superconducting composite wire thus obtained had a liquid nitrogen temperature critical current Ic of 160 A and a silver ratio of 2.5. When Je was calculated using this value, it was 16000 A / cm ² .
[0058]
Example 5
In Example 1, the tape for binding the strands was not a silver tape but a nickel tape, and after diffusion heat treatment at 770 ° C. for 10 minutes, the nickel tape was removed. Then, it processed like Example 1, finished in the tape shape of thickness 0.3mm and width 4mm, and performed SC production | generation heat processing similar to Example 1. FIG.
[0059]
The superconducting composite wire thus obtained had a critical current Ic of 130 A and a silver ratio of 1.8. Je was 10800 A / cm ² .
[0060]
Example 6
Instead of the pure silver pipe used in Example 1, the outer diameter and inner diameter were the same as in Example 1, and a composite pipe having a surface of 1 mm thick copper and an inner side made of a silver magnesium alloy was used. By performing the same processing as in Example 1, a wire having the same characteristics was obtained.
[0061]
The superconducting composite wire thus obtained has excellent mechanical strength, and the Ic of the superconducting composite wire obtained in Example 1 starts to deteriorate due to a tensile stress of 30 MPa, whereas the superconducting composite wire obtained in this example is used. Ic did not deteriorate even at a tensile stress of 200 MPa.
[0062]
Example 7
A superconducting composite wire was obtained in the same manner as in Example 1 except that a silver-magnesium pipe was used instead of the pure silver pipe and a pure silver sheet was interposed between the strands. The obtained superconducting composite wire had excellent characteristics similar to Example 16.
[0063]
Comparative Example 1
A Bi-2223 oxide superconducting raw material powder compacted into a rod shape of φ15 mm × L500 mm was fitted into a pure silver pipe having an inner diameter of φ15.1 mm and an outer diameter of φ17 mm to reduce the diameter to produce a single core wire of φ2 mm. This was fitted into a pure silver pipe having an inner diameter of 16 mm, an outer diameter of 20 mm, and a length of 550 mm, subjected to diameter reduction processing and rolling, and processed into a tape shape having a thickness of 0.2 mm and a width of 3 mm. Further, the superconductor material was heat-treated at 825 to 840 ° C.
[0064]
The superconducting composite wire had a critical current Ic of 35 A at a liquid nitrogen temperature and a silver ratio of 3. Je calculated using this value was 5800 A / cm 2.
[0065]
【The invention's effect】
As described above in detail, according to the present invention, since the space factor of the superconductor portion can be increased, the critical current can be increased if the total cross-sectional area of the wire is the same and Jc is equal. . In addition, since the amount of expensive precious metals such as silver and gold can be reduced, there is a great cost advantage.
[0066]
Furthermore, alternating current loss can be reduced by transposing the strands.
[Brief description of the drawings]
1 is a cross-sectional view showing an oxide superconducting composite multifilamentary wire manufactured according to Example 1. FIG.
2 is a cross-sectional view showing an oxide superconducting composite multi-core wire manufactured according to Example 2. FIG.
3 is a cross-sectional view showing an oxide superconducting composite multi-core wire manufactured according to Example 3. FIG.
4 is a cross-sectional view showing an oxide superconducting composite multifilamentary wire manufactured according to Example 4. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Oxide superconducting composite multi-core wire 2, 12 ... Composite strand 3, 13, 23, 33 ... Bi-2223 raw material powder 4, 14, 24, 34 ... Silver matrix 5, 15, 25, 35 ... Pure silver tape 6 , 26, 36 ... diffusion layer

Claims (5)

A step of forming a composite strand by filling an oxide superconducting material or raw material powder for oxide superconductivity in a metal tube;
Bundling a plurality of the composite strands, binding the outside with a metal tape or a metal wire,
A step of compressing the bundle of composite strands bound with the metal tape or metal wire, and heat-treating the bundle of composite strands subjected to the compression processing to diffuse metal between the composite strands. A method for producing an oxide superconducting composite multifilamentary wire comprising a step of forming a layer. 2. The oxide superconducting composite multicore according to claim 1 , wherein a temperature of the heat treatment is in a range of a melting point of the metal constituting the surface of the composite strand minus 250 ° C. to a superconducting material generation temperature minus 50 ° C. 3. A manufacturing method of a wire. The metal tape or metal wire is made of a metal that does not react with the metal constituting the surface of the composite strand, and further includes a step of removing the metal tape or metal wire before or after the heat treatment. The method for producing an oxide superconducting composite multifilamentary wire according to claim 1 . Wherein between the composite wires, according to claim than said metal that constitute the surface of the composite strand, characterized in that the interposition of the metal sheet resulting readily diffusion reaction with the metal constituting the surface of the composite wire 2. A method for producing an oxide superconducting composite multifilamentary wire according to 1 . The composite multi-core wire integrated by the formation of the metal diffusion layer is processed to reduce the cross section, and then heat treatment and rolling are performed to generate a superconductor or improve superconducting properties. The method for producing an oxide superconducting composite multifilamentary wire according to claim 1 .

Images