JPH0358123B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to improvements in ultrafine multicore compound superconducting conductors. [Prior Art and Problems] Ultrafine multicore compound superconducting conductors are generally classified into the following types. (1) Bronze process continuous multicore wire. (2) Internal and external diffusion method continuous line. (3) In-Situ method and Powder method discontinuous line. However, each of the above-mentioned superconducting conductors had the following problems. In the compound superconducting wire of (1), the compound filament is continuous from one end of the wire to the other, so there is no electrical discontinuity and the material is free of current loss. However, since there is a manufacturing limit to the number of filaments included per unit cross-sectional area of the wire, it has the disadvantage of low current density. In the case of this wire (for example, Nb ₃ Sn wire), it is obtained by composite processing of bronze and niobium, and even if the area reduction processing rate is increased by performing multiple intermediate annealing, it will continue without breaking. In order to maintain the condition of the filament, the diameter of the filament is limited to a minimum of about 3 μm, and if it is processed to be thinner, it will break. Also, by solid diffusion of bronze and niobium
In order to form Nb ₃ Sn, a high concentration of Sn or a diffusion heat treatment at high temperature is required. However, the upper limit of the Sn concentration in bronze is 14.0 wt%. For this reason, the entire 3μm filament
To create a Nb ₃ Sn layer, high temperature heat treatment must be selected. On the other hand, diffusion heat treatment at high temperatures coarsens the crystal grain size of the Nb ₃ Sn layer, reducing the effective pinning force (one of the factors governing critical current density), making it difficult to increase the current density. It is something that cannot be done. The compound superconducting wire in (2) above is continuous like the compound filament in (1) above, and it is possible to increase the Sn concentration to about 30 wt% higher than in the bronze method, so it is possible to increase the current density. It is something that can be done. However, the biggest drawback common to the compound superconducting wires mentioned in (1) and (2) is that the compound filament is continuous from one end of the wire to the other, so it does not add to the wire during handling or winding during the manufacturing process. Bending strain is directly applied to the compound filament. As a result, 0.2~
It breaks down at a strain rate of 0.5% and becomes unable to function as a superconducting wire. Therefore, (1) and (2) above
Compound superconducting wire is unsuitable for applications where strain of 0.2% or more is applied. In the compound superconducting wire (3), since the compound filament is discontinuous, most of the strain applied from the outside is absorbed by the matrix material, which can be sufficiently deformed at the discontinuous portions of the filament. As a result, only a small amount of the strain is transmitted to the filament, thereby reducing its sensitivity to strain. Furthermore, the current density can also be increased. The reason for this is that the diameter of the filament is relatively thin with a height of 1.5 μm, which makes it possible to perform diffusion heat treatment at low temperatures based on a reduction in the diffusion distance, and that the Sn concentration can be freely adjusted, resulting in high Sn content.
This is to make it possible to increase the concentration. However, the biggest drawback of the compound superconducting wire is that the length of the filament cannot be controlled at all. The length of the filament in the In-Sutu method and the Powder method is usually distributed over a wide range of 10 mm to 1000 mm, but the length of the filament is related to the outer diameter of the wire (outer diameter of the matrix material) and depends on the current density. This has a major impact. That is, when the length of the compound filament is shorter than the outer diameter of the wire, a large amount of current loss occurs in current transfer between the filaments, significantly reducing the current density of the wire. Therefore,
If you want to increase the outer diameter of the wire, it is necessary to increase the length of the filament, but there are restrictions on the outer diameter of the quenched ingot and the powder particle size in the In-Situ method, regardless of the thickness of the final wire. Only filament lengths suitable for the final wire diameter can be produced. For this reason, the compound superconducting wire described in (3) above has a considerably high electrical resistance as a wire in a superconducting state, especially when the outer diameter of the wire is increased, and it is difficult to use with high-precision magnets, precision equipment, and AC operating conditions. It is unsuitable for this purpose. The present invention was made in order to solve the above-mentioned conventional problems, and has a structure in which the equivalent diameter of the compound filament, the length of the filament, and the outer diameter of the wire are limited, so that the current density is high and the strain is low. The object of the present invention is to provide a compound superconducting conductor that can suppress a decrease in critical current density even when the current density is increased. [Means for Solving the Problems] The present invention provides a compound superconducting conductor in which a large number of discontinuous ultrafine compound superconducting filaments are embedded in a matrix metal material, in which the equivalent diameter of the compound superconducting filaments is 0.1 to 1.0 μm. The compound superconducting conductor is characterized in that the length of the filaments located between the discontinuous portions on the same filament is 70 times or more the equivalent diameter of the matrix material. As the matrix metal material, for example, Cu
Or Cu-Sn, Cu-Ga, Cu-Ga-Sn, Cu-Sn
-Copper-based alloys such as Ti, Sn-based alloys such as Sn-Cu,
Examples include Ga-based alloys, Al-based alloys, and silver-based alloys. The compound superconductor includes Nb ₃ Sn, V ₃ Ga,
All compound superconductors formed by composite processing methods such as Nb ₃ Ga, Nb ₃ Al, and V ₃ Si and diffusion heat treatment. The term "equivalent diameter" means the diameter of a circle having an area equal to the cross-sectional area of the filament or matrix material in the final wire. [Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. As shown in Figures 1A and 1B, a large number of
A Nb ₃ Sn compound superconducting filament 1 is embedded in a bronze matrix 2, and the outside thereof is coated with stabilizing copper 4 via a diffusion barrier 3.
Experiments described below (Experimental Examples 1 and 2) were conducted on Nb ₃ Sn compound superconducting wires. Experimental Example 1 In Experimental Example 1, we investigated how the length of the filament affects the Jc value. First, the filament diameter (Df) is kept constant (Df
~0.3 μm), and the filament discontinuity 5,
Various samples were prepared in which the length (lf) of the filament transmitting between The critical current from ρ=
Measured under resistances of 10 ^-10 Ωcm, ρ = 10 ^-11 Ωcm and ρ = 10 ^-12 Ωcm, and based on the measured values, divided by the cross-sectional area of the wire excluding barrier material 3 and stabilizing copper 4.
The Jc value was determined. The results are shown in FIG. As is clear from Figure 2, the filament length is
When lf<70Db, the Jc value decreases for any resistance. This is considered to be mainly due to the phenomenon of current transfer between discontinuous filaments. That is, if lf is short, resistance occurs during current transfer. Therefore, it was confirmed that the length of the filament must be lf≧70Db. However, the upper limit of the length of the filament is infinite, that is, it does not need to be continuous.
It has also become clear that lf ~ 100Db is sufficient for practical use. Experimental Example 2 In Experimental Example 2, the relationship between the filament diameter and the Jc value was investigated. As shown in Figure 3, the filament length lf is constant (30Db) and the filament diameter Df is 0.01 to 100μm.
We fabricated various Nb ₃ Sn compound superconducting wires with varying values. In addition, the filament lengths are lf = 70Db and lf
=90Db, various superconducting wires with different filament diameters were produced in the same manner as above. Each superconducting wire is 4.2〓, ε=0.9%, ρ=-
The current density was measured under the condition of 10 ¹¹ Ωcm. The results are shown in FIG. As is clear from Figure 3, the filament diameter Df
=0.1~1.0μm, filament length lf=70Db and lf=
A high current density one was obtained at 90Db. However, it was observed that the Jc value decreased when Df<0.1 μm or obtained f<70Db. Therefore, the equivalent diameter of the filament is 0.1~1.0μ
The range is limited to m. Next, specific examples will be described based on the experimental examples described above. Example First, a Cu-13.5wt%Sn alloy with an outer diameter of 45mm was
After drilling 37 through holes of 3.1 mm and inserting pure Nb rods of 3 mm in diameter into each of the through holes, the temperature was heated to approximately 500°C.
While performing intermediate annealing, the wire was subjected to area reduction processing to an outer diameter of 0.2 mm to produce a wire. In addition, an outer diameter of 38mm is inserted into a Cu tube with an outer diameter of 45mm and an inner diameter of 38.1mm.
A Nb pipe with an inner diameter of 35 mm was set. Next, about 21,000 strands obtained by cutting the 0.2 mm diameter strands into lengths of 100 mm were incorporated into the Nb tube set in the Cu tube. In this assembly process, one wire per 50 of the plurality of wires is
Two parts of the main wire were cut to a length of 1 mm, and the plurality of wires were assembled into the Nb tube so that the cut portions were sequentially shifted. The composite thus assembled is subjected to intermediate annealing while the outer diameter is
The surface was reduced to 2.7mm. This wire was heated at 600°C for 20 hours to produce a Nb ₃ Sn superconducting wire. It takes
The filament of the Nb ₃ Sn superconducting wire was approximately 0.8 μm. Further, the filament length (lf), which is the length between the cut parts, was about 278 mm. Comparative Example 1 (Bronze method) First, a Cu-13.5wt%Sn alloy with an outer diameter of 45mm was
After drilling 37 through holes of 3.1 mm and inserting pure Nb rods of 3 mm in diameter into each of the through holes, the temperature was heated to approximately 500°C.
While performing intermediate annealing, the wire was subjected to area reduction processing to an outer diameter of 1.5 mm to produce a wire. In addition, an outer diameter of 38mm is inserted into a Cu tube with an outer diameter of 45mm and an inner diameter of 38.1mm.
A Nb pipe with an inner diameter of 35 mm was set. Next, approximately 380 strands obtained by cutting the 1.5 mm diameter strands into lengths of 100 mm were assembled into an Nb tube set in the same Cu tube as in the example. The thus assembled composite was subjected to intermediate annealing while reducing its outer diameter to 2.7 mm. 600 pieces of this wire
℃ for 20 hours to produce a Nb ₃ Sn superconducting wire. Comparative example 2 (In-situ method) First, Cu-40wt%Nb with an outer diameter of 35 mm and a length of 250 mm.
The composite was melted as an electrode in a consumable arc furnace and solidified in a water-cooled copper mold with an internal diameter of 45 mm. The ingot with an outer diameter of 45 mm taken out from the mold was made of Cu.
Nb dendrites of approximately 0.18 to 1.8 mm were dispersed inside. Next, the outer diameter of the ingot is
After reducing the area to 2.7 mm and applying Sn plating to a thickness of approximately 150 μm, Sn was diffused inside by step heating at 200°C, 400°C, and 600°C to produce Nb ₃ Sn superconducting wire. . However, in this example and comparative examples 1 and 2,
The critical current density (Jc) of the Nb ₃ Sn superconducting wire in the strain-free state was measured in magnetic fields of 10T and 12T. The results are shown in Table 1 below.

[Table] In addition, the Nb ₃ Sn superconducting wires of Examples and Comparative Examples 1 and 2 were strained by bending, and the critical current density in the unstrained state was used as a reference, and the relative value of the critical current density when strain was applied was calculated. The value was measured. The results are shown in FIG. In addition, if the product was manufactured using the conventional internal diffusion method,
The Nb ₃ Sn superconducting wire exhibits similar characteristics to the Nb ₃ Sn superconducting wire manufactured by the bronze method of Comparative Example 1. As is clear from Table 1 and FIG. 4, the compound superconducting wire made of discontinuous filaments of this example has the same absolute value of critical current density as that of Comparative Example 1 using the bronze method, and the in-situ method. It can be seen that this is significantly higher than that of Comparative Example 2. In addition, it can be seen that in this example, the degree of decrease in the relative value of critical current density when strain is applied is the same as Comparative Example 2, which is an in-situ method, and is smaller than Comparative Example 1, which is a bronze method. . Thus, it can be seen that the compound superconducting conductor of the present invention has a high absolute value of critical current density and is extremely little affected by strain, that is, it is not strain sensitive. In addition, in the present invention, the filament diameter is
Df is 0.1 to 1.0μm and filament length lf is 70Db
The above compound superconducting filaments may be arranged, and conventional compound superconducting continuous filaments may be arranged in other parts. That is, as shown in FIG. 5A, a compound superconducting filament 1 having a filament diameter and a filament length that define the present invention is placed in a matrix material 2 in the periphery of the wire where the strain rate applied to the wire is relatively large. A continuous filament 6, which is sensitive to strain, is arranged in the matrix material in the central part, where the ratio is small, or a continuous filament 6 and a foil-like compound superconductor 6' are arranged as shown in Fig. 5B to provide a diffusion barrier to the outside. Stabilized copper 4 through 3
A compound superconducting wire may also be used. Also,
The cross-sectional shape can be applied to conductors of any shape, such as a round wire as shown in FIG. 5A or a tape as shown in FIG. 5B. Furthermore, the method for manufacturing the compound superconducting conductor of the present invention is not particularly limited. For example, as shown in FIG. 6A, an strand in which an Nb filament 9 having a filament length and filament diameter specified in the present invention is embedded in copper 10 produced by a powder method, a rapid casting method, a composite processing method, etc. By using S as a stranded wire, plating it with Sn11 from the outside, and then performing diffusion heat treatment,
A structure as shown in FIG. 6B in which the Nb ₃ Sn filament 1 is embedded in the bronze 2 may also be used. Further, as shown in FIG. 7A, an Nb continuous filament 60 is embedded in the copper 10, and around the strand, an Nb filament having a filament length and filament diameter specified in the present invention is placed in the copper 10. Six element wires 9 with many built-in wires 9 are arranged.
Solidified by Sn11, with Nb barrier 3 on the outside.
By performing a diffusion heat treatment on the composite plate on which stabilized copper 4 is arranged through the Nb ₃ Sn
A structure as shown in FIG. 7B in which the filament 1 and the central thick Nb ₃ Sn filament 6 are embedded together in the bronze matrix 2 may be used. Furthermore, as shown in FIG. 8A, a composite wire in which Sn 11 was embedded in the center of the wire S according to the provisions of the present invention and stabilized copper 4 was arranged on the outside through a diffusion barrier 3 was subjected to diffusion heat treatment. , according to the present invention
Nb ₃ Sn filament 1 to bronze matrix 2
It may also have a structure embedded therein as shown in FIG. 8B. [Effects of the Invention] As detailed above, the compound superconducting conductor of the present invention has a high absolute value of critical current density, and even when strain is applied, the critical current density decreases very little, so it is suitable for wire rods in winding processes, etc. It has remarkable effects such as being extremely stable against bending applied to it.

[Brief explanation of drawings]

FIG. 1A is a longitudinal cross-sectional view of a compound superconducting conductor according to the present invention, FIG. B is a side cross-sectional view of FIG. A, FIG. 2 is a characteristic diagram showing the relationship between filament length and critical current density, and FIG. Figure 4 is a characteristic diagram showing the relationship between filament diameter and critical current density, Figure 4 is a characteristic diagram showing the relationship between strain rate and critical current density (relative value to the non-strain state), and Figure 5 A and B are respectively Cross-sectional view showing another example of the compound superconducting conductor according to the present invention, No. 6
FIGS. 6 to 8 show steps of one example of the compound superconducting conductor according to the present invention, and FIGS.
A in the figure is a cross-sectional view before constructing the compound superconducting conductor of the present invention, and B in FIGS. 6 to 8 is a cross-sectional view of the compound superconducting conductor of the present invention obtained by diffusion heat-treating the constituent composite of A. DESCRIPTION OF SYMBOLS 1... Compound superconducting filament, 2... Bronze matrix, 3... Barrier, 4... Stabilized copper, 5,5'... Discontinuous part of filament, 6
...Continuous filament.

Claims (1)

[Claims] 1. In a compound superconducting wire in which a large number of discontinuous ultrafine compound superconducting filaments are embedded in a matrix metal material, the equivalent diameter of the compound superconducting filaments is 0.1 to 1.0 μm, and there is no space between the discontinuous parts on the same filament. A compound superconducting conductor characterized in that the length of the filament located thereon is 70 times or more the equivalent diameter of the matrix material.