JP2002093248A - Oxide superconductive compound multicore wire and manufacturing method for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide superconductive compound multicore wire showing excellent characteristics such as small matrix ratio, small AC loss, and large critical current density and a manufacturing method for it. SOLUTION: This oxide superconductive compound multicore wire is characterized in that it has a structure in which plural compound strands formed by embedding an oxide super-conductive material in a metal matrix are bound, and a metal diffusion layer is formed between the compound strands. This oxide super-conductive compound multi-core wire material is manufactured by bundling plural compound strands, binding the outside thereof by a metal tape or a metal wire material, compressing the bound strands, heat-treating the same, and forming a metal diffusion layer between the compound strands.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an oxide superconducting composite multifilamentary wire and a method for producing the same.

[0002]

2. Description of the Related Art An oxide superconducting wire, for example, a Bi-based superconducting wire is made of an Ag sheath or an Ag alloy sheath in order to secure oxygen permeability, workability, and orientation of the superconducting material required for producing the superconducting material. In general, a raw material powder of a superconducting substance is sealed in the substrate and then subjected to a surface reduction process and a rolling process, which is a so-called powder-in-tube method.

[0003] The superconductor portion embedded in the matrix is provided with multiple cores in order to prevent mechanical deterioration of superconductivity and to reduce AC loss. The method of multifilamentation is to first fill a metal tube with a raw material powder to make a single core wire, reduce the surface area, process it to a certain wire diameter, and bundle multiple tubes to fill the metal tube. The way to do is widespread. As the metal tube, an alloy pipe such as a silver alloy is used in addition to a pure metal tube in order to increase the strength of the wire rod 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 superconducting wire (filament) before rolling and using a method of twisting the superconducting portion (filament) is used. By performing such processing, the coupling loop between the filaments can be reduced, and the AC loss can be reduced.

[0005]

When a multifilamentary wire is manufactured by the above-mentioned powder-in-tube method, a metal such as silver for filling a plurality of single core wires is used in the second assembly (single core wire is bundled and processed). You need a tube. Further, in order to prevent the metal tube from being broken at the time of diameter reduction such as subsequent drawing, the metal tube made of silver or the like used in the second assembly needs a certain thickness.

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, the larger the superconducting portion (the smaller the metal portion), the larger the current flowing through the entire wire can be, which is more practical. However, as described above, the ordinary powder-in-tube method has a limit in reducing the matrix ratio.

Further, in the ordinary powder-in-tube method, since rolling is performed from a round wire state, it is impossible to apply even pressure to filaments dispersed in a matrix during rolling. Therefore, the powder density and the thickness of the filament become non-uniform, and the critical current density Jc per filament tends to be non-uniform. For this reason, there is a problem that Jc of the whole wire becomes smaller than an ideal state in which Jc of all filaments is equal.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an oxide superconducting composite multifilamentary wire exhibiting excellent characteristics of a small matrix ratio, a small AC loss, and a large critical current density, and a method for producing the same. The purpose is to provide.

[0009]

Means for Solving the Problems To solve the above problems, the present invention has a structure in which a plurality of composite strands each having an oxide superconducting material embedded in a metal matrix are bundled,
An oxide superconducting composite multifilamentary wire is provided, wherein a metal diffusion layer is formed between the composite strands.

In the oxide superconducting composite multifilamentary wire of the present invention, the metal constituting the metal matrix is silver, gold,
Platinum, palladium, rhodium, copper, iron or an alloy containing them can be used. The metal matrix can be constituted by a metal tube made of such a metal or a metal tube whose surface is coated with such a metal.

The 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 the AC loss by using a transposed structure in which the composite wires are twisted or transposed.

The present invention also provides a step of filling a metal tube with an oxide superconducting substance or a raw material powder for oxide superconductivity to form a composite strand, bundling a plurality of the composite strands, and using a metal tape or Binding with a metal wire, compressing the composite wire bundle bound with the metal tape or metal wire, and heat treating the composite wire bundle subjected to the compression, A method for producing an oxide superconducting composite multifilamentary wire, comprising a step of forming a metal diffusion layer between composite strands.

In the method for producing a multifilamentary oxide superconducting wire of the present invention, the temperature of the heat treatment is in the range of the melting point of the metal constituting the surface of the composite wire minus 250 ° C. to the superconducting substance forming temperature minus 50 ° C. Is desirable.

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,
Before or after the heat treatment, the metal tape or the metal wire can be removed.

In addition, 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 between the metals constituting the surface of the composite strand.

Further, after the composite multifilamentary wire integrated by forming the metal diffusion layer is subjected to processing for reducing the cross section, heat treatment for generating a superconductor or improving superconductivity is performed. By performing rolling,
An oxide superconducting composite multifilamentary wire can be obtained.

Hereinafter, the method for producing the oxide superconducting wire of the present invention will be described in more detail. First, the surface is silver,
A metal tube made of gold, platinum, palladium, copper, or iron is filled with an oxide superconducting substance or an oxide superconducting raw material powder. Next, this is reduced in diameter and processed into a round or square cross section to obtain a composite strand. The steps so far are the same as the method generally called the powder-in-tube method. In addition, it is effective to process the composite strand into a tape from the viewpoint that a bonding area during diffusion heat treatment described later can be increased.

Next, the surface of the composite element wire is roughened by polishing it with coarse abrasive grains or the like, and washed. Then, a plurality of roughened composite strands are bundled, and the outside is bound with a metal tape or the like. The metal tape used at this time is of the same quality as the metal constituting the metal tube of the composite wire, for example, if the metal tube is silver, silver tape is used, but in order to integrate the composite wire and the metal tape, desirable.

When the surface of the composite wire is made of a silver-magnesium alloy in order to improve the mechanical strength of the composite wire, magnesium oxide is generated on the surface during heat treatment, which inhibits the diffusion reaction. It is also effective to interpose a material such as a pure silver sheet between the composite strands to facilitate diffusion bonding later.

Instead of the pure silver sheet, it is also possible to use a composite, for example, a sheet having a stronger strength than a pure silver sheet such as a Ni tape, coated with pure silver or the like on the surface by plating or the like.

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 tape is removed after the diffusion heat treatment, so that the space factor of the superconductor portion can be further increased. So effective. For example, if the metal constituting the surface of the composite strand is silver, a nickel tape can be used as the binding tape.

Thereafter, the surface of the composite wire is reduced by several percent to several tens percent using a four-sided roll, a hole die, a two-high rolling mill, a swager, or the like, so that the composite strands are brought into close contact. Before this step,
It is also effective to perform a preliminary heat treatment at about several hundred degrees Celsius to physically adhere the composite wires and the binding tape.

Thereafter, a temperature lower than the melting point of the metal constituting the metal tube and which does not inhibit the superconducting material formation reaction, that is, the melting point of the metal tube minus 250 ° C. or more, and the superconducting material forming temperature minus 50 By performing heat treatment in a temperature range of not more than ° C for several minutes to several tens minutes, a diffusion layer having a thickness of several nm or more is formed at the interface between the composite strands.

Here, the reason why the temperature at which the generation of the superconducting material is not hindered is set to the superconducting material generation temperature minus 50 ° C. or less will be described. The generation temperature of the superconducting material is, for example, about 840 ° C. in the case of Bi-2223 type, but actually the reaction of the phase constituting the raw material powder starts around 810 ° C. Therefore, it is not preferable to perform a diffusion heat treatment at a temperature close to the superconducting substance generation temperature, because the oxide superconducting substance powder or the raw material powder is melted or deteriorated.

On the other hand, if the diffusion heat treatment temperature is too low, it takes a long time for the diffusion between the composite strands, or the diffusion is insufficient, resulting in poor adhesion. Therefore, it is necessary to select the temperature and time according to the material. is important. When the matrix metal portion is silver and the superconducting material to be filled is a Bi-2223-based superconducting material, it is preferable to perform a heat treatment at 750 to 800 ° C. for about 10 minutes.

After integrating the composite wires in this manner, a desired superconducting wire can be obtained by combining plastic working such as rolling and drawing with heat treatment. Specifically, the composite wire rod integrated by the above-described method is rolled so that the total draft is 70% or more, and then the first heat treatment for generating a superconducting material is performed. The heat treatment temperature for generating the superconducting material depends on the heat treatment atmosphere,
Depending on the production conditions such as the raw material powder composition, when the oxide superconducting raw material powder is Bi-2223-based,
About 0 hours is desirable.

Thereafter, rolling for promoting the orientation of the superconducting material is performed at a rolling reduction of about 15%, and heat treatment is performed again at 840 ° C. for about 150 hours to sufficiently generate a Bi-2223 phase. Thus, an oxide superconducting composite multifilamentary wire having a high critical current density can be obtained.

Unlike the above-described method of the present invention, if the layers are simply laminated without performing the diffusion heat treatment, the composite strands are disaggregated in the rolling process, or the composite strands are displaced from each other and the entire strand is uniformly formed. It is not processed.

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 in the processing, and the space factor of the superconducting portion can be increased by removing the binding tape, so that it is practically extremely effective.

Further, if the composite wires are assembled in a tape shape and finally formed into a tape shape, the composite wires and the aggregate thereof can be processed in a similar shape, so that abnormal deformation of the filament is reduced. Also, Jc can be improved by the effect of reducing the variation in the powder density of the filament.

Further, when assembling the composite wires, the wires are transposed not only by simply aligning them but also by transposition or twisting, so that the filament twist which is performed by a normal superconducting wire is used. Can be applied. By performing such processing, there is also an effect of bonding the composite strands more firmly as a whole in the diffusion heat treatment.

If the bundle of composite wires is not subjected to diffusion heat treatment and is simply rolled after assembly, the composite wires may be separated from each other or the gap between the composite wires may be increased. It does not become a converted wire.

Further, in order to reduce the AC loss, it is desirable that the twist pitch of the filament is several tens or less times the filament diameter. In the conventional method of preparing a composite wire with twisted filaments by the powder-in-tube method, storing a plurality of this composite wire in a metal tube and rolling it, the twist pitch can be used even in the warping process until the composite wire is manufactured. Is elongated in the longitudinal direction, so that the pitch becomes very long in the finishing stage, and does not contribute to a reduction in AC loss.

On the other hand, according to the method of the present invention, an arbitrary pitch can be obtained immediately before final rolling, which is effective in reducing AC loss. The composite wire thus obtained can be made into a desired superconducting wire by repeating rolling and heat treatment in the same manner as the above-described parallel-laminated one.

As described above, according to the present invention, the outer metal tube is not required at the time of the second assembling. The space factor can be increased. for that reason,
If the total cross-sectional area of the wires is the same and Jc is equal, the critical current can be increased.

In the case of a silver sheath Bi-based wire, when a normal powder-in-tube method is used, the silver ratio is 2-3,
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 long as a wire having a silver ratio of 3 if Jc is equal, and is useful for applications such as large-capacity energization.

In addition, since the amount of expensive noble metals such as silver and gold can be reduced, there is a great cost advantage. Further, by setting the diffusion heat treatment temperature to a melting point of the metal constituting the surface of the composite wire minus 200 ° C. or more and a superconducting material forming temperature minus 50 ° C. or less, an effective diffusion phase can be formed without hindering the production of the superconducting material. It is possible to obtain.

Furthermore, even when the surface of the composite strand is made of an alloy which is unlikely to form a diffusion phase, it is effective to interpose a pure metal or the like which promotes a diffusion reaction between the composite strands. A suitable diffusion phase can be obtained.

Further, by transposing the composite wire immediately before rolling and then bringing the composite wire into close contact by diffusion heat treatment, a plurality of composite wires can be more firmly integrated as a whole. Without twisting, it is possible to obtain a wire having a filament twisted at an arbitrary pitch. By doing so, the same effect as that of a generally used filament twist of a multifilamentary wire can be obtained, and the AC loss can be reduced.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below. Example 1 Bi-2223 oxide superconducting raw material powder was
The powder is pressed into a rod shape of L500 mm and the inner diameter is 15.1 m.
m, and fitted and filled in a pure silver pipe having an outer diameter of 18 mm. Next, the pure silver pipe filled with the Bi-2223 oxide superconducting raw material powder was subjected to diameter reduction processing,
A single core wire of φ1.5 mm was obtained.

Next, this single core wire was subjected to rolling, and processed into a tape shape having a thickness of 0.3 mm and a width of 2 mm to obtain a strand. Then, the surface of the wire was polished with abrasive paper to roughen the surface. Thereafter, the element wires whose surfaces were roughened were degreased and washed with alcohol, and ten sheets were laminated in parallel. A pure silver tape having a thickness of 0.05 mm and a width of 5 mm was spirally wound around the laminate, and FIG. As a result, an integrated laminated body 1 was obtained.

In FIG. 1, ten laminated element wires 2
Are composed of Bi-2223 raw material powder 3 and a silver matrix (silver pipe) 4 surrounding the powder, and a pure silver tape 5 is spirally wound therearound.

Next, the laminated body 1 around which the pure silver tape 5 was wound was processed with a four-sided roll at a reduction in area of 10% to a thickness of 2.85 mm and a width of 1.99 mm. Then 770
Diffusion heat treatment at 10 ° C. for 10 minutes, as shown in FIG.
A diffusion layer 6 having a thickness of several hundred nm was formed at the interface between the strands 2, and the whole was integrated, and then rolled to finish into a tape shape having a thickness of 0.3 mm and a width of 4 mm.

Next, this tape was heat-treated at 825 to 840 ° C. for 50 hours to form a superconductor (hereinafter referred to as S).
C heat treatment) (first time), and then a reduction ratio of 1
5%, and further at 825-840 ° C. for 200 hours,
SC generation heat treatment (second time) was performed to obtain a superconducting wire.

The superconducting wire thus obtained has a critical current Ic at liquid nitrogen temperature of 120 A and a silver ratio of 2
Met. When this value was used to calculate the critical current density Je per total cross-sectional area of the wire, it was 10,000 A / cm 2.

Example 2 A single core wire was prepared in the same manner as in Example 1, processed to a diameter of 0.7 mm, and then rolled to a thickness of 0.3 mm and a width of 1 mm.
To form a strand. The surface of the wire was polished with abrasive paper to roughen the surface.

As shown in FIG. 2, the wires 12 are
After arranging them in steps and performing dislocation processing at a pitch of 20 mm,
A pure silver tape 15 having a thickness of 0.07 mm and a width of 7 mm was spirally wound and integrated. In the drawings, reference numeral 13 denotes Bi-2223 raw material powders 3, and 14 denotes a silver matrix (silver pipe).

The wire 1 around which the silver tape 15 is wound
The assembly of No. 2 was processed with a four-sided roll at a surface reduction rate of 20% to a thickness of 0.8 mm and a width of 1.95 mm. Then 790 ° C
For 5 minutes, a diffusion layer having a thickness of several hundred nm is formed at the interface between the strands 12, and the whole is integrated, and then rolled to have a thickness of 0.3 mm and a width of 4 mm. Finished in tape shape.

After subjecting the tape to a heat treatment for SC generation (first time) at 825 to 840 ° C. for 50 hours, a reduction ratio of 20% was obtained.
%, And at 825-840 ° C. for 200 hours,
C generation heat treatment (second time) was performed.

The thus obtained wire had a critical current density Ic at a liquid nitrogen temperature of 180 A and a silver ratio of 1. When Je is calculated using this value, 15,000 A
/ Cm ² . The AC loss of this wire by the magnetizing method was 200 J / m ³ , which was の of the AC loss of the wire of Example 1 of 400 J / m ³ .

Example 3 A single core wire was prepared in the same manner as in Example 1, and the surface of the wire obtained by reducing the diameter to 1 mm was rubbed with abrasive paper to roughen the surface. Then, it was degreased and washed with alcohol, and then stranded together.

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 denotes a Bi-2223 raw material powder, and 24 denotes a silver matrix (silver pipe).

This was drawn out with a φ2.8 hole die to make the surface of the stranded wire smooth, and then at 770 ° C. for 10 minutes.
Diffusion heat treatment was performed to form a diffusion layer 26 having a thickness of several hundred nm, and the whole was integrated. And rolled, 0.3m thick
m, 4 mm width tape.

This was treated at 825-840 ° C. for 50 hours with S
After performing the C generation heat treatment (first time), rolling was performed at a rolling reduction of 15%, and further, the SC generation heat treatment (second time) was performed at 825 to 840 ° C. for 200 hours. The critical current Ic at a liquid nitrogen temperature of this wire was 120 A and the silver ratio was 2. When Je was calculated using this value, it was 10000 A / cm ² .

Example 4 In Example 1, after assembling wires having been reduced in diameter by a four-way roll, as shown in FIG.
A pure silver tape 35 was spirally wound from the outside and integrated. This was further subjected to compression processing using a four-sided roll at a surface reduction rate of 5%, followed by diffusion heat treatment at 770 ° C. for 10 minutes. In the figure, reference numeral 33 denotes Bi-2223 raw material powder, 34
Indicates a silver matrix (silver pipe), and 36 indicates a diffusion layer.

This was pulled out using a die to a thickness of 1 m.
m and a width of 2.5 mm. In addition, rolling
It processed to thickness 0.25mm and width 4mm. This is 82
After performing SC generation heat treatment (first time) at 5 to 840 ° C. for 50 hours, rolling was performed at a rolling reduction of 15%.
SC generation heat treatment (second time) was performed at 0 ° C. for 200 hours.

The superconducting composite wire thus obtained has a critical current Ic at liquid nitrogen temperature of 160 A and a silver ratio of 2.
It was 5. When Je is calculated using this value, 160
It was 00 A / cm ² .

Example 5 In Example 1, the tape for binding the strands was a nickel tape instead of a silver tape, and after diffusion heat treatment at 770 ° C. for 10 minutes, the nickel tape was removed. Thereafter, processing was performed in the same manner as in Example 1, the tape was finished into a tape shape having a thickness of 0.3 mm and a width of 4 mm, and the same SC generation heat treatment as in Example 1 was performed.

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 .

Example 6 Instead of the pure silver pipe used in Example 1, a composite pipe having the same outer diameter and inner diameter as in Example 1 but having a surface of 1 mm thick copper and an inner side made of a silver-magnesium alloy Using the same process as in Example 1, a wire rod having similar characteristics was obtained.

The superconducting composite wire obtained in this way has excellent mechanical strength, and the superconducting composite wire obtained in Example 1 has an Ic
Starts to deteriorate with a tensile stress of 30 MPa,
In the superconducting composite wire obtained in this example, Ic did not deteriorate even with a tensile stress of 200 MPa.

Example 7 A silver-magnesium pipe was used instead of a pure silver pipe.
Example 1 except that a pure silver sheet was interposed between the strands
In the same manner as in the above, a superconducting composite wire was obtained. The resulting superconducting composite wire had the same excellent properties as in Example 16.

Comparative Example 1 A powder of Bi-2223 oxide superconducting raw material was φ15 mm × L
A powder compacted into a 500 mm rod shape has an inner diameter of 15.1 m.
m, and fitted to a pure silver pipe with an outer diameter of φ17 mm to reduce the diameter to produce a single core wire of φ2 mm. This is 16m inside diameter
m, outer diameter 20 mm, length 550 mm, fitted with a pure silver pipe, reduced in diameter and rolled, thickness 0.2 mm, width 3
mm. Further, 825 to 84
A superconducting material generation heat treatment was performed at 0 ° C.

The critical current Ic of this superconducting composite wire at liquid nitrogen temperature was 35 A, and the silver ratio was 3. When Je was calculated using this value, it was 5800 A / cm 2.

[0065]

As described in detail above, according to the present invention, the space factor of the superconductor portion can be increased, so that if the total cross-sectional area of the wires is the same and Jc is equal, the critical current is reduced. Can be bigger. In addition, since the amount of expensive precious metals such as silver and gold can be reduced, there is a great cost advantage.

Further, by transposing the strands, the AC loss can be reduced.

[Brief description of the drawings]

FIG. 1 is a 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 multifilamentary wire manufactured according to Example 2.

FIG. 3 is a sectional view showing an oxide superconducting composite multifilamentary wire manufactured according to Example 3.

FIG. 4 is a sectional view showing an oxide superconducting composite multifilamentary wire manufactured according to Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oxide superconducting composite multifilamentary 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 (7)

[Claims] The present invention has a structure in which a plurality of composite wires each having an oxide superconducting substance embedded in a metal matrix are bundled, and a metal diffusion layer is formed between the composite wires. Oxide superconducting composite multifilamentary wire. 2. An oxide superconducting composite multifilamentary wire according to claim 1, wherein said plurality of composite strands have a transposed structure. 3. A step of filling a metal tube with an oxide superconducting substance or a raw material powder for oxide superconductivity to form a composite strand, bundling a plurality of the composite strands, and binding the outside thereof with a metal tape or a metal wire. Performing a compression process on the composite wire bundle bound by the metal tape or metal wire, and heat-treating the compression-processed composite wire bundle to form a wire between the composite wires. A method of forming a metal diffusion layer on a multi-core oxide superconducting composite wire. 4. The oxidation according to claim 3, wherein the temperature of the heat treatment is in the range of the melting point of the metal constituting the surface of the composite wire minus 250 ° C. to the superconducting material formation temperature minus 50 ° C. For manufacturing multi-core superconducting composite wire. 5. A step of removing the metal tape or the metal wire before or after the heat treatment, wherein the metal tape or the metal wire is made of a metal that does not react with the metal constituting the surface of the composite strand. The method for producing an oxide superconducting composite multifilamentary wire according to claim 3, further comprising: 6. A metal sheet that causes a diffusion reaction with the metal constituting the surface of the composite strand more easily than the metal constituting the surface of the composite strand, between the composite strands. The method for producing an oxide superconducting composite multifilamentary wire according to claim 3. 7. A heat treatment for producing a superconductor or improving superconducting properties after subjecting a composite multifilamentary wire integrated by forming the metal diffusion layer to processing for reducing a cross section. The method for producing an oxide superconducting composite multifilamentary wire according to claim 3, wherein rolling and rolling are performed.