JPH07249328A - Oxide superconductive wire and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture long wires having high critical current density by controlling the relative deviation of cross-section surface area of filaments to be 50% or less of average cross-section surface area. CONSTITUTION:The relative deviation of cross-section surface area of oxide superconductive fillaments 2 buried in a matrix of silver 1 is controlled to be 50%. In the case that the relative deviation exceeds 50%, rupture and cracking occur easily at the time of drawing or rolling after extruding process and the critical current density is lowered. In the case the relative deviation is 50% or less, a long wire having excellent processibility and critical current density as high as 10<4>A/cm<2> or more at 77K and under zero outer magnetic field can be obtained easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting wire and a method for producing the same, and more particularly to a multicore oxide superconducting wire having an oxide superconductor coated with a metal and a method for producing the same. is there.

[0002]

2. Description of the Related Art In recent years, as a superconducting material exhibiting a higher critical temperature, a ceramic material, that is, an oxide superconducting material has been attracting attention. Among them, 90 for yttrium
K, bismuth-based materials have a high critical temperature of about 110K and thallium-based materials have a high critical temperature of about 120K, and their practical application is expected as a high-temperature superconducting material using liquid nitrogen as a refrigerant.

An example of a method for producing a long superconducting multifilamentary wire using this oxide superconducting material will be described below.

First, a superconducting powder or its raw material powder is filled in a metal container, which is then plastically processed and heat-treated to convert the raw material powder into a superconductor to produce an oxide superconducting element wire. Next, this oxide superconducting element wire is formed into a hexagonal cross section through a die, and then a required number of pieces are collectively packed in a metal container to prepare a multi-core billet. continue,
This multi-core billet is subjected to plastic working such as wire drawing and rolling, and then heat treatment.

Thus, an oxide superconducting multifilamentary wire having a high critical current density has heretofore been obtained.

Further, in the production of such an oxide superconducting wire, by applying hydrostatic extrusion to the billet,
It is disclosed in Japanese Patent Application No. 3-56685 (JP-A-4-292811) that an oxide superconducting wire having uniform and excellent characteristics over a long length can be obtained.

Further, it is known that in the production of the above oxide superconducting multifilamentary wire, an oxide superconducting wire having a higher critical current density can be obtained by repeating plastic working and heat treatment a plurality of times.

[0008]

However, the oxide superconducting wire obtained by the above method has room for further improvement in terms of critical current density. This is because, in order to apply the oxide superconducting wire to cables and magnets, it is necessary to have a higher critical current density in addition to a high critical temperature.

The present invention solves the above problems and provides a long oxide superconducting wire having a high critical current density and a method for efficiently producing the same.

[0010]

The oxide superconducting wire according to the present invention is a multi-core oxide superconducting wire in which a plurality of filaments made of an oxide superconductor are embedded in a matrix made of a metal. It is characterized in that the relative deviation of the cross-sectional area of the filament is 50% or less of the average cross-sectional area. Here, the metal means one used as a stabilizer, and for example, silver or silver alloy is preferable.

Further, in the method for producing an oxide superconducting wire according to the present invention, a multi-core billet is produced by filling a plurality of metal wires coated with an oxide superconductor or powder of a raw material thereof into a metal container. , This multi-core billet is subjected to plastic working to obtain a wire, and the obtained wire is heat-treated to form a multi-core oxide superconductor in which a plurality of filaments made of an oxide superconductor are embedded in a matrix made of a metal. In the method of manufacturing a wire rod, the plastic working comprises hydrostatic extrusion,
Further, it is characterized in that the occurrence of sausage of the filament is suppressed in the hydrostatic extrusion.

Here, "sausaging" means that the cross-sectional area of the superconducting filaments in the superconducting wire varies along the longitudinal direction due to the extrusion process.

In order to suppress the occurrence of sausage of the filament, it is preferable that the relative deviation of the cross-sectional area of the filament after hydrostatic extrusion be 50% or less of the average cross-sectional area.

Further, preferably, the suppression of the occurrence of sausaging of the filament is included in the die angle during hydrostatic extrusion, the temperature during hydrostatic extrusion, the extrusion ratio during hydrostatic extrusion, and the strands. It may be carried out by adjusting at least one condition selected from the group consisting of the relative density of the powder, the particle size of the powder, and the hardness ratio between the powder and the coating metal.

The adjustment of the die angle at the time of hydrostatic extrusion is preferably characterized by setting the die angle in all angles to 30 ° or more and 90 ° or less.

The temperature adjustment during hydrostatic extrusion includes:
The billet heating temperature is preferably set to 600 ° C. or lower.

The adjustment of the extrusion ratio during the hydrostatic extrusion is preferably characterized by setting the extrusion ratio to 5 or more and 20 or less. Here, “extrusion ratio” means A / where the cross-sectional area of the wire material before extrusion is A and the cross-sectional area of the wire material after extrusion is a
A value represented by a.

In order to adjust the relative density of the powder contained in the wire, it is preferable to set the relative density to 40% or more and 95% or less.

The particle size of the powder may be adjusted by setting the average particle size to 4 μm or less.

The hardness ratio of the powder and the coating metal may be adjusted by setting the hardness ratio to 4 or less.

Preferably, the metal coating the oxide superconductor powder is a gold or silver alloy.

Preferably, the metal container filled with the oxide superconducting element wire is made of silver or a silver alloy.

Further, preferably, the suppression of the sausaging of the filaments is performed by setting the extrusion ratio in the hydrostatic extrusion to 5 or more and 7 or less and the average particle diameter of the powder to be 1 μm.
It is recommended to do the following.

[0024]

The present inventors have noticed that one of the reasons why the conventional multi-core oxide superconducting wire cannot obtain a high critical current density is the occurrence of sausage due to extrusion. Then, it was confirmed that an oxide superconducting wire having a high critical current density can be obtained by suppressing the occurrence of this sausaging.

Further, conventionally, there has been a problem that, when the wire diameter is reduced to about ⅛ at a time by isostatic pressing, the critical current density is greatly reduced. Therefore, if the rate of reducing the wire diameter at a time is reduced, the critical current density can be prevented from lowering, but the process becomes complicated and the production cost increases. That is, considering the simplification of the manufacturing process and the cost reduction, it is preferable to increase the ratio of reducing the wire diameter at one time as much as possible.

Therefore, the inventors conducted an original experiment in order to investigate the relationship between the extrusion ratio and the critical current density during hydrostatic extrusion at room temperature. As a result, the particle size of the oxide superconductor powder for producing the oxide superconducting wire, the extrusion ratio at the time of hydrostatic extrusion, and the critical current density of the resulting oxide superconducting wire rod have a correlation. Found that there is.

Further, as a result of repeated experiments, the inventors have found that
Occurrence of sausage, die angle during hydrostatic extrusion, temperature during hydrostatic extrusion, extrusion ratio during hydrostatic extrusion, relative density of powder contained in the wire, powder particle size and powder It has been found that the hardness ratio of the coating to the coating metal has an interrelated effect.

That is, according to the present invention, the relative deviation of the cross-sectional area of the filament is 50% or less. If the relative deviation exceeds 50%, during wire drawing or rolling after extrusion,
This is because breakage and cracks are likely to occur and the critical current density is reduced. If it is 50% or less, the workability is excellent,
A long wire having a high critical current density of 10 ⁴ A / cm ² or more (77 K, zero external magnetic field) can be easily obtained.

According to the present invention, hydrostatic extrusion is used. Therefore, it is possible to manufacture a wire having a uniform cross section. Moreover, since a large extrusion ratio can be taken, the manufacturing process is simplified.

Further, according to the present invention, the die angle is 3
It is set to 0 ° or more and 90 ° or less. If the angle is smaller than 30 °, the billet tip portion becomes long and the yield is lowered. On the other hand, if the angle is larger than 90 °, it is difficult to manufacture a wire having a cross section with a uniform relative deviation of filaments, and the metal flow is likely to be non-uniform. In particular, when the extrusion ratio is as high as 8 or more, it is preferably set to 30 ° or more and 60 ° or less.

Further, according to the present invention, the billet heating temperature (extrusion temperature) is set to 600 ° C. or lower. In general,
The higher the heating temperature, the more preferable the pressure during extrusion can be suppressed to be low. However, if the heating temperature is too high,
This is because the strength difference between the coating metal and the oxide powder becomes large, and uneven deformation is likely to occur. More preferably, 2
The temperature is preferably 00 ° C or lower. When using silver for the coating metal,
This is because at 200 ° C. or lower, silver does not recrystallize and the extrusion pressure is lowered because it is in the warm working region, but no significant strength difference occurs with the oxide powder.

According to the present invention, the extrusion ratio is 5 or more and 20 or less. If it is less than 5, the powder portion will not be densified, the critical current density will be low, and the productivity will be poor. On the other hand, if it is larger than 20, even if combined with other conditions,
This is because the relative deviation increases, the workability deteriorates, and the critical current density decreases.

Further, according to the present invention, the relative density (ratio of apparent packing density and true density) of the powder in the wire is 40%.
It should be 95% or less. If it is less than 40%, the hydrostatic pressure at the time of extrusion cannot be endured, and the extrusion itself is difficult such as the extruded material breaking, and even if it is extruded, non-uniform deformation easily occurs. Normally, if tap filling and wire drawing are performed, 60
%, It is possible to control the relative density by adjusting the degree of wire drawing and applying hydrostatic extrusion to manufacture the wire.

According to the present invention, the average particle size of the powder is 4 μm or less. When it is larger than 4 μm, the fluidity of the powder is deteriorated and the powder is liable to be unevenly deformed. Also, since the average particle size is considered, there are also particles larger than this, and if the particles are non-superconducting layers, the particle size of the finally remaining non-superconducting layer will also increase, and the critical current density Is reduced.

Further, according to the present invention, the hardness difference between the powder and the coating metal is 4 or less. Although it is related to the density of powder, whether the coating metal is an alloy, the processing history of the coating metal, etc., the hardness difference and the strength difference are in an equivalent relationship, and the smaller the hardness difference, the greater the extrusion ratio. This is because uniform deformation is unlikely to occur.

According to the present invention, the coating metal is silver or silver alloy. This is because silver or a silver alloy does not react with the powder and can maintain a high critical current density.
Further, it is possible to arbitrarily control the hardness difference (strength difference) with the powder by alloying, and it is possible to arrange the alloy at any position in the cross section, such as the entire matrix, only the outermost circumference, only around the filament. .

[0037]

【Example】

(Example 1) First, the experimental results of examining the relationship between the extrusion ratio and the critical current density during hydrostatic extrusion at room temperature will be shown.

First, Bi ₂ O ₃ , PbO, SrCO ₂ ,
Using CaCO ₂ and CuO as raw material powders, Bi: P
b: Sr: Ca: Cu = 1.80: 0.40: 2.0
Powders of these raw materials were blended so as to have a composition of 1: 2.21: 3.02. Next, this mixed powder is heated to 700 ° C.
After heat treatment for 12 hours and 800 ° C. for 8 hours, heat treatment was performed at 850 ° C. for 4 hours. After each heat treatment, the powder was ground with a ball mill. At this time, by adjusting the grinding time by the ball mill,
Powders of various particle sizes were obtained. This powder in air at 800 ℃
After degassing by heat treatment for 15 minutes, the average particle size was measured and found to be 0.8 μm, 1 μm, 2 μm.
And four powders of 3 μm were obtained.

Next, each of the above-mentioned four kinds of powders has an outer diameter of 24
A silver pipe having a thickness of 2 mm and a thickness of 2 mm was filled, and the lid was covered with a silver jig provided with a groove. After vacuuming at 2 × 10 ⁻⁵ Torr for 10 hours, both ends were electron beam welded. 6.54 diameter
After wire drawing to mm, wire drawing was carried out with a regular hexagonal die having opposite side length of 5.50 mm to prepare a silver-coated oxide superconducting element wire.

61 pieces of the respective superconducting wires obtained in this manner were used, having an outer diameter of 68 mm, an inner diameter of 57 mm and a length of 27.
It was filled in a 0 mm silver container and capped.

FIG. 6 shows a sectional view of this silver container. Note that FIG. 6 shows the dimensions (unit: mm) of this silver container.

Next, the silver container filled with the superconducting element wire is
After vacuuming at 2 × 10 ⁻⁵ Torr for 10 hours, both ends were electron beam welded to produce a multi-core billet.

Six silver billets were produced in this way, and the extruding force was 400 tons using a hydrostatic extruder.
It was extruded at room temperature into 6 different diameters as shown in Tables 1 to 4. Tables 1 to 4 also show the calculated extrusion ratios. All the samples had a straightness of 5 mm / m or less, and could be satisfactorily extruded without any abnormal appearance.

The straightness is a value obtained by dividing the maximum displacement of the sample by the length with reference to FIG. 7, that is, X _max / L.

The cross-sectional area of each superconductor filament was measured by image processing on the cross-section of all samples,
A value obtained by dividing the deviation of the filament cross-sectional area by the average filament cross-sectional area (hereinafter referred to as "relative deviation") was calculated. The results are also shown in Tables 1 to 4.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

FIG. 2 is a cross-sectional view showing a cross section of the multi-core billet of Sample No. 4 after extrusion.

FIG. 3 is a view showing a cross section of the extruded multi-core billet of sample No. 4 shown in FIG. 2 cut into quarters along the longitudinal direction. It is the central part of the core billet, and the lower end of the figure is the outer peripheral part of the multi-core billet.

Referring to FIG. 2, in this extruded multi-core billet, superconductor filaments 2 embedded in silver 1 are regularly arranged while maintaining a hexagonal cross section. Recognize.

Further, referring to FIG. 3, in this multi-core billet, there is no variation in the cross-sectional area of the superconductor filament 2 embedded in the silver 1 along the longitudinal direction, and the sausage is performed. You can see that not.

On the other hand, FIG. 4 is a view showing a cross section of the multi-core billet of Sample No. 6 after extrusion.

FIG. 5 is a view showing a cross section of the extruded multi-core billet of sample No. 6 shown in FIG. 4 cut into quarters along the longitudinal direction. It is the central part of the core billet, and the lower end of the figure is the outer peripheral part of the multi-core billet.

Referring to FIG. 4, in this extruded multi-core billet, the superconducting filament 2 embedded in silver 1 has a hexagonal cross-section that is broken, and the cross-sectional area of each filament varies. You can see that

Further, referring to FIG. 5, in this multi-core billet, the cross-sectional area of the superconductor filament 2 embedded in the silver 1 varies along the longitudinal direction,
You can see that it is sausage.

Next, the extruded multi-core billet obtained up to the above step was heat-treated at 800 ° C. for 10 hours in the air to diffusion-bond the superconducting wire silver and the silver billet. . After that, cross-section reduction rate of about 20.7%
Then, wire drawing was performed up to a diameter of 1.02 mm. that time,
There was no breakage on the way and the workability was good.

Subsequently, the drawn wire rod was processed into a tape having a thickness of 0.255 mm by one flat roll rolling operation, and then heat-treated at 845 ° C. for 50 hours in the atmosphere.
After that, 0.222m in one further flat roll rolling operation
It was processed into a tape having a thickness of m. The width of the tape-shaped wire is
It was 2.70 mm. Then, in the air at 840 ° C for 5
After performing heat treatment for 0 hours, the critical current of the entire length is measured in the state of being immersed in liquid nitrogen, and the obtained sample is embedded in epoxy resin to measure the cross-sectional area of the superconductor by image processing. Critical current density Jc (specific resistance 1
0 ⁻¹³ Ω · m definition) was calculated. The values of the critical current density Jc calculated in this way are shown in Tables 1 to 4.

The relationship between the extrusion ratio and the critical current density at each average particle size of the superconductor powder obtained by the above experiment is shown in FIG. In FIG. 1, the horizontal axis represents the extrusion ratio at the time of hydrostatic extrusion, and the vertical axis represents the critical current density Jc (10 ⁴ A / cm ² ) of the obtained superconducting wire.

As is clear from FIG. 1, the value of the extrusion ratio at which the critical current density Jc reaches a peak shifts to the high extrusion ratio side as the average particle size decreases, and the wire drawing process after extrusion is simplified. I understand that In particular, when the average particle diameter is 1 μm or less, the increase tendency of the critical current density with the increase of the extrusion ratio becomes large, and it can be seen that an oxide superconducting wire having excellent characteristics can be obtained by a simple process.

From the above experiments, the relationship between the extrusion ratio at room temperature and the critical current density was clarified. Further, the experimental results at temperatures other than room temperature are shown below.

(Example 2) Bi ₂ O ₃ , PbO, SrC
Using O ₃ , CaCO ₃ and CuO, Bi: Pb: S
Powders having a composition ratio of r: Ca: Cu: O = 1.8: 0.4: 2: 2: 3 were mixed. This powder was heat treated at 700 ° C. for 12 hours and 800 ° C. for 8 hours, and then 850
Heat treatment was carried out at 8 ° C. for 8 hours. After each heat treatment, the powder was ground with a ball mill. This powder, 800
The filling powder was prepared by degassing by heat treatment at 15 ° C. for 15 minutes. The particle size of the powder was adjusted by changing the crushing time of the ball mill.

Next, the powder was filled in a silver pipe, the lid was covered with a grooved silver jig, and then 1 at 2 × 10 ^-5 Torr.
After vacuum drawing for 0 hour, electron beam welding was performed, and wire drawing was performed into a regular hexagonal shape with opposite sides of 5.5 mm to prepare a silver-coated oxide superconducting element wire. The relative density of the powder contained in the wire was adjusted by changing the filling pipe size and the wire drawing workability. 61 superconducting wires obtained in this way were used, with an outer diameter of 68 mm, an inner diameter of 57 mm and a length of 270 m.
It was filled in a silver container of m and capped.

Next, the silver container in which the superconducting element wire was coated with silver was evacuated at 2 × 10 ^-5 Torr for 10 hours, and then electron beam welding was performed to produce a multi-core billet.

This billet was hydrostatically extruded under the conditions shown in Table 5 and the relative deviation of the filament cross-sectional area of all samples was measured. The results are shown in Table 5.

[0067]

[Table 5]

The extruded material was drawn to a diameter of 1.15 mm, rolled to a thickness of 0.24 mm, heat-treated in the atmosphere at 840 ° C. for 50 hours, and then immersed in liquid nitrogen. The critical current density was calculated by measuring the 100 m long critical current and measuring the cross-sectional area of the filament portion of the sample. The results are shown in Table 6.

[0069]

[Table 6]

Example 3 Using the powder having an average particle size of 3 μm prepared in Example 2, Ag having a diameter of 24 mm and a wall thickness of 2 mm was used.
A 10% Au alloy pipe was filled with powder to prepare a multi-core billet similar to that in Example 2. At this time, the container for multi-core also used Ag-10% Au alloy. At this time, the difference in hardness between the metal part and the powder part was metal part: powder part = 1: 2. The Vickers hardness at this time is 9 in the metal part.
0 kg / mm ^2, was 180 kg / mm ² in powder unit.

When this multi-core billet was hydrostatically extruded under the conditions of a die angle of 60 °, an extrusion temperature of 100 ° C. and an extrusion ratio of 15, the relative deviation of the filament was 5%. Furthermore, when the extruded material was drawn and rolled under the same conditions as in Example 2, there was no breakage, no cracking, and good workability.
Also, the critical current density was as high as 33,000 A / cm ² .

It should be noted that the disclosure of the above embodiments is merely specific examples of the present invention and does not limit the technical scope of the present invention. That is, the application of the present invention is not limited to the production of bismuth-based oxide superconducting wires, but can be applied to the production of thallium-based and yttrium-based oxide superconducting wires.

[0073]

As described above, according to the present invention, it is possible to efficiently manufacture an oxide superconducting multifilamentary wire having uniform characteristics over a long length and a high critical current density.

Therefore, the oxide superconducting wire obtained by the present invention can be advantageously applied to power cables, magnets, bus bars, current leads and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an extrusion ratio and a critical current density at each average particle diameter of superconductor powder.

FIG. 2 is a view showing a cross section of a multi-core billet according to an embodiment of the present invention.

FIG. 3 is a plan view of the multi-core billet shown in FIG.
It is a figure which shows the cross section when it cut | disconnects in one-half.

FIG. 4 is a view showing a cross section of a multi-core billet according to another embodiment of the present invention.

5 is a cross-sectional view of the multi-core billet shown in FIG.
It is a figure which shows the cross section when it cut | disconnects in one-half.

FIG. 6 is a sectional view showing a silver container used in an embodiment of the present invention.

FIG. 7 is a diagram for explaining straightness.

[Explanation of symbols]

 1 silver 2 superconductor filament In each figure, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Sato 1-3-3 Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industries, Ltd. Osaka Works

Claims (13)

[Claims] 1. A multi-core oxide superconducting wire in which a plurality of filaments made of an oxide superconductor are embedded in a matrix made of a metal, and the relative deviation of the cross sectional areas of the filaments is an average cross sectional area. 50% or less of the oxide superconducting wire. 2. A multifilament billet is prepared by filling a plurality of metal wires coated with an oxide superconductor or a powder of a raw material thereof into a metal container, and the multifilament billet is subjected to plastic working to obtain a wire rod. In the method for producing a multi-core oxide superconducting wire in which a plurality of filaments made of an oxide superconductor are embedded in a matrix made of a metal by heat treating the obtained wire, the plastic working is A method for producing an oxide superconducting wire, comprising hydroextrusion, and suppressing generation of sausage of the filament in the hydrostatic extrusion. 3. The suppression of the occurrence of sausaging of the filament is to make the relative deviation of the cross-sectional area of the filament after the hydrostatic extrusion be 50% or less of the average cross-sectional area. Manufacturing method of oxide superconducting wire. 4. The suppression of the occurrence of sausaging of the filament is performed by a die angle during the hydrostatic extrusion, a temperature during the hydrostatic extrusion, an extrusion ratio during the hydrostatic extrusion, and The relative density of the powder contained, the particle size of the powder, and at least one condition selected from the group consisting of the hardness ratio of the powder and the coating metal are adjusted to adjust the temperature. A method for producing the oxide superconducting wire described. 5. The method for producing an oxide superconducting wire according to claim 4, wherein the die angle in the hydrostatic extrusion is adjusted such that the die angle is 30 ° or more and 90 ° or less in full angle. . 6. The method for producing an oxide superconducting wire according to claim 4, wherein the temperature at the time of the hydrostatic extrusion is adjusted by setting a billet heating temperature to 600 ° C. or lower. 7. The adjustment of the extrusion ratio during the hydrostatic extrusion is performed by adjusting the extrusion ratio to 5 or more and 20 or less.
The manufacturing method of the oxide superconducting wire in any one of Claims 4-6. 8. The adjustment of the relative density of the powder contained in the strands is performed by adjusting the relative density to 40% or more and 95% or less, according to any one of claims 4 to 7. A method for producing the oxide superconducting wire described. 9. The adjustment of the particle size of the powder is characterized in that the average of the particle size is 4 μm or less.
A method for manufacturing the oxide superconducting wire according to any one of claims 4 to 8. 10. The hardness ratio of the powder and the coating metal is adjusted by setting the hardness ratio to 4 or less.
~ A method for producing an oxide superconducting wire according to any one of claims 9 to 10. 11. The method for producing an oxide superconducting wire according to claim 2, wherein the metal coating the oxide superconductor powder is silver or a silver alloy. 12. The method for producing an oxide superconducting wire according to claim 2, wherein the metal container filled with the oxide superconducting element wire is a gold or silver alloy. . 13. The suppression of the occurrence of sausaging of the filament is performed by setting the extrusion ratio during the hydrostatic extrusion to 5 or more and 7 or less and the average particle diameter of the powder to 1 μm or less. The method for producing the oxide superconducting wire according to claim 2.