JP2926774B2 - Nb for AC (3) Sn multi-core superconducting wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wire for an Nb ₃ Sn superconducting magnet in a transformer, a generator, a current limiter, and the like, which are used, for example, in pulse applications and commercial frequency applications. .

[Prior art] Nb ₃ Sn wire has been used as a compound superconducting magnet wire in the past, but most of it is used for direct current, and currently used for pulse and commercial frequency applications. Not. When an Nb ₃ Sn wire is used for a superconducting generator or an AC device, it is necessary to reduce the AC loss as in the case of the NbTi wire. As described above, in order to reduce the AC loss, it is necessary to reduce the AC loss, that is, the hysteresis loss and the coupling loss.

To reduce the hysteresis loss, it is necessary to reduce the Nb ₃ Sn filament to 1 micron or less, that is, to submicron, and to reduce the coupling loss, it is necessary to increase the resistance of the matrix. In the case of Nb ₃ Sn wire, Cu
A -Sn alloy is used, which has as high a resistance as a Cu-Ni alloy. For this reason, the first problem of reducing the AC loss in the Nb ₃ Sn wire rod is to make the filament submicron.

For the Nb ₃ Sn wire rod, various production methods such as a bronze method, an in-situ method, an external diffusion method, an internal diffusion method, an Nb tube method, and a powder method have been developed. In any of the manufacturing methods, it is necessary to perform a heat treatment for generating Nb ₃ Sn at the final wire diameter. Therefore,
Nb ₃ Sn submicron filaments before heat treatment Nb
It is assumed that the filament is submicronized.

[Problems to be Solved by the Invention] However, the conventional manufacturing method has the following problems.

In other words, in the bronze method, intermediate annealing is required in the processing step, but during this intermediate annealing, a compound of Nb and Sn is formed and the filament is deformed inhomogeneously, so that it is difficult to reduce the diameter to submicron. Was.

In the in-situ method and the powder method, since the filaments are not essentially separated from each other, the actual electromagnetic filament diameter, that is, the effective filament diameter, is larger than the designed filament diameter, so that submicronization cannot be achieved. was there.

Further, in the internal diffusion method and the external diffusion method, there is a problem that the filaments come into contact with each other at the time of heat treatment for forming Nb ₃ Sn, so that the effective filament diameter becomes large and submicronization cannot be achieved.

Furthermore, in the Nb tube method, Sn is required to be submicron because of the structure in which Sn is arranged in Nb.However, it is not possible to essentially achieve submicron due to poor workability of Sn. There was a problem.

Therefore, an object of the present invention is to reduce the AC loss by reducing the filament diameter to a submicron Nb ₃ S for AC.
Means for Solving the Problems The Nb ₃ Sn multi-core superconducting wire of the present invention is a primary stack in which a plurality of Nb filaments are embedded in Cu or a Cu alloy. To
A secondary stack is produced by arranging a plurality of the secondary stacks around the Sn or Sn alloy part in the Cu or Cu alloy matrix, further having a structure in which a plurality of the secondary stacks are arranged in the Cu or Cu alloy matrix, In an alternating current Nb ₃ Sn multi-core superconducting wire in which Sn is diffused into Nb filaments by heat treatment to form Nb ₃ Sn, the Sn concentration with respect to Cu in the matrix is 10 wt% or less, and Sn or Sn
The diameter of the alloy part is 30 μm or less, and Nb filament and Sn
Or the distance to the Sn alloy part is 50 μm or less, the Nb filament diameter is 0.3 μm or more and 1 μm or less, and the interval between the Nb filaments is の or more of the diameter of the Nb filament,
1, and the heat treatment temperature for forming Nb ₃ Sn is 700 ° C.
It is characterized as follows.

[Effects of the Invention] In the multi-core Nb ₃ Sn superconducting wire for AC of the present invention, the diameter of the Nb filament is 0.3 μm or more and 1 μm or less, so that the AC loss is low and the interval between the Nb filaments is Nb.
Since the diameter is not less than 1/2 and not more than 1 of the diameter of the filament, electromagnetic coupling between Nb filaments can be prevented and the effective filament diameter can be reduced. Also, set the heat treatment temperature
Since the temperature is 700 ° C or less, a large critical current density is exhibited.

In the present invention, for Cu in the matrix
The reason why the Sn concentration is set to 10% by weight or less is that when the Sn concentration exceeds 10% by weight, the effective filament diameter tends to rapidly increase.

In the present invention, the diameter of the Sn or Sn alloy portion is
The reason why the diameter is 30 μm or less is that the diameter of the Sn or Sn alloy portion is
If it exceeds 30 μm, the workability as a wire material will deteriorate, and the diffusion distance of Sn to the Nb filament will be long, and it will be uniform.
This is because it becomes difficult to disperse Sn.

Further, in the present invention, the distance between the Nb filament and the Sn or Sn alloy portion is set to 50 μm or less because the distance
If the thickness exceeds μm, the diffusion of Sn in Cu or Cu alloy may be insufficient.

Therefore, the Nb ₃ Sn multi-core superconducting wire according to the present invention,
It is effective as a superconducting magnet wire for pulse applications and commercial frequency applications.

Embodiment FIG. 1 is a sectional view showing an entire Nb ₃ Sn multi-core superconducting wire according to an embodiment of the present invention. Referring to FIG. 1, Nb ₃ Sn multifilamentary superconducting wire 1 has Cu or Cu alloy matrix 2
It is configured by arranging a secondary stack 3 of books.

FIG. 2 is a sectional view showing a secondary stack in the Nb ₃ Sn multicore superconducting wire of FIG. Referring to FIG. 2, the secondary stack 3 is formed in a Cu or Cu alloy matrix 4 by
It is constituted by disposing six primary stacks 5 around the Sn or Sn alloy portion 6.

FIG. 3 is a sectional view showing a primary stack in the secondary stack of FIG. Referring to FIG. 3, primary stack 5
Is constituted by arranging a large number of Nb filaments 8 in a Cu or Cu alloy matrix 7.

When the wire thus configured is heat-treated, Sn diffuses through the matrix and causes a diffusion reaction with the Nb filament 8 to form Nb ₃ Sn.

In this example, as shown in Table 1, two types of A and B Nb ₃ Sn multicore superconducting wires were roughly divided. In the sample A, the primary stack having 169 Nb filaments was arranged around the Sn or Sn alloy to form a secondary stack. A further seven bundles of this secondary stack were used as the element wires as they were, and a second bundle was prepared by twisting seven strands. As a matrix, Cu-6.
Using 2 wt% Sn, the interval between Nb filaments was set to be half of the Nb filament diameter.

On the other hand, in the sample B, the primary stack in which 169 Nb filaments were also arranged was arranged around the Sn or Sn alloy portion to constitute a secondary stack. A further seven bundles of this secondary stack were used as the element wires as they were, and a second bundle was prepared by twisting seven strands. Cu-5.8wt% Sn was used as the matrix, and the interval between Nb filaments was set to 1 with respect to the Nb filament diameter.

As shown in Table 1, depending on whether a strand having a wire diameter of 0.1 mm is used as seven stranded wires or a strand having a wire diameter of 0.2 mm is used as it is as a strand, a sample symbol A for each of A and B is used. -1, A-2 and four types of sample symbols B-1, B-2 were prepared.

In sample symbol A-1, the Nb filament diameter was 0.4 μm,
The primary stack was configured so that the filament interval was 0.2 μm. In the secondary stack, six primary stacks were considered around a Sn or Sn alloy portion having a Sn core diameter of 7 μm. In addition, seven secondary stacks are bundled to make strands,
After drawing to 0.1 mm, a twisted wire having a wire diameter of 0.1 mm is formed so as to have a twist pitch of 1.0 mm, and the seven wires are twisted to have a twist pitch of 3.0 mm.

Similarly, in sample symbol B-1, the Nb filament diameter is 0.3 μm.
The primary stack was configured so that the spacing between the m and Nb filaments was 0.3 μm. In the secondary stack, the six primary stacks were arranged around a Sn or Sn alloy portion having a Sn core diameter of 7 μm. Further, a bundle of seven secondary stacks is bundled to produce a wire, and after drawing to 0.1 mm, a wire having a wire diameter of 0.1 mm is twisted so that a twist pitch becomes 1.0 mm. The books are twisted at a twist pitch of 3.0 mm.

In sample symbol A-2, the Nb filament diameter was 0.8 μm,
The primary stack was configured so that the filament interval was 0.4 μm. In the secondary stack, this 6 primary stacks
It was arranged around a Sn or Sn alloy part having a Sn core diameter of 14 μm. In addition, seven secondary stacks are bundled to produce strands,
After drawing to 2 mm, a twisted wire having a wire diameter of 0.2 mm was formed so as to have a twist pitch of 2.0 mm, and the wire was evaluated as it was.

Similarly, the sample symbol B-2 has an Nb filament diameter of 0.6.
The primary stack was configured so that the spacing between the Nb filaments was 0.6 μm. In the secondary stack, the six primary stacks were arranged around a Sn or Sn alloy portion having a Sn core diameter of 14 μm. Furthermore, a bundle of seven secondary stacks is bundled to produce a strand, and after drawing to 0.2 mm, a strand having a diameter of 0.2 mm is twisted so as to have a twist pitch of 2.0 mm. It was evaluated as it was.

Evaluation by atomic ratio In order to quantitatively examine the Nb ₃ Sn formation reaction, Nb ₃ Sn after heat treatment was applied to each composition of Samples A-2 and B-2.
EDX analysis was performed on the filament. FIG.
FIG. 4 is a diagram showing the results of this EDX analysis. In this analysis, the atomic ratio is quantitatively analyzed assuming that it is composed of 100% of Nb and Sn. The filaments analyzed were those at the center of the 169 primary stack.

As is apparent from FIG. 4, at 500 ° C., Nb is 90 to 100.
% And Sn are 0 to 10%, but as the heat treatment temperature increases, the ratio of Nb decreases and the ratio of Sn increases. 70
By the heat treatment at 0 ° C., Nb: Sn = 3: 1, and it is considered that the Nb ₃ Sn filament is almost completely formed at 700 ° C. From this, it was found that in the case of the Nb ₃ Sn wire having a submicron filament diameter, the heat treatment at 700 ° C. was sufficient, and there was an optimum value at a temperature lower than the heat treatment temperature conventionally performed.

Critical current characteristics For samples A-1, A-2, B-1 and B-2,
Critical current densities were measured for wires obtained by heat treatment at different heat treatment temperatures, and the dependence of the critical current density on the treatment temperature was examined. Heat treatment temperature is 500 ℃, 550 ℃,
Changed to 600 ° C, 650 ° C, 700 ° C, and 750 ° C. The measurement of the critical current density was performed in liquid helium by a four-terminal method. The sample was made into a spiral shape, and the direction of the 0.5 T magnetic field was set to the vertical direction. The critical current density was calculated assuming that the area of the Nb filament became Nb ₃ Sn, and the portions of Cu and Sn were used as a matrix. The definition of the critical current value was determined at 1 μv / cm per wire.

FIG. 5 is a diagram showing the heat treatment temperature dependence of the critical current density in samples A-1 and A-2. As shown in FIG. 5, in both samples A-1 and A-2, the critical current density increases as the heat treatment temperature increases. In sample A-1, it decreases after it takes the maximum value at 650 ° C. On the other hand, sample A-
In 2, the value is kept almost constant from 650 ° C to 750 ° C.

FIG. 6 is a diagram showing the heat treatment dependency of the critical current densities of samples B-1 and B-2. As shown in FIG. 6, the tendency was almost the same as that of Samples A-1 and A-2. Sample B-1 decreased after having reached the maximum value at 650 ° C., whereas Sample B- 2 increases slightly from 650 ° C to 700 ° C.

As is clear from the above results, it was found that the optimal heat treatment condition was 650 ° C. to 700 ° C.

AC Loss Characteristics The heat treatment temperature was changed for each of the samples A-1, A-2, B-1 and B-2, and the dependency of the heat treatment temperature on the AC loss was examined. FIG. 7 is a graph showing the heat treatment temperature dependence of the AC loss obtained in this manner. The loss value indicates a value per cycle.

In the case of sample A-2, the loss value increases as the heat treatment temperature increases, and increases to 750 ° C. In sample A-1, after the maximum value of 40 kJ / m ³ was obtained at 600 ° C., the value was kept almost constant up to 750 ° C.

The loss value of the sample B-2 is saturated at 650 ° C. and that of the sample B-1 at 750 ° C., but increases again as the heat treatment temperature increases. However, the absolute value of the loss was the same as in Sample B-1.
And B-2 are smaller than Samples A-1 and A-2, and in particular, Sample B-2 shows a value which is one digit lower.

From the above results, it is understood that there is a correlation between the loss value, the filament diameter, and the filament interval, and the loss value increases as the filament interval decreases. The increase in the loss value is thought to be mainly due to the increase in the Nb ₃ Sn phase as seen in the increase in the critical current density.
As described above, although the critical current density is almost saturated, the loss values of the samples A-2, B-1, and B-2 are increasing. This is considered to be due to an increase in the effective filament diameter due to close contact between the filaments.

Evaluation of Effective Filament Diameter The effective filament diameter at each heat treatment temperature was calculated for four types of samples A-1, A-2, B-1, and B-2. The effective filament diameter (deff) is In the above, Bm was obtained in the case where the amplitude of the triangular wave was ± 0.5T. Jc (B) was approximated by the following equation based on the measured value of the magnetic field dependence of Jc at each of the heat treatment temperatures of 0.5T and 1.0T.

FIG. 8 shows the results of Samples A-2 and B-2, and FIG. 9 shows the results of Samples A-1 and B-1.
As is clear from FIG. 9, in the sample A-1, the effective filament diameter became constant at about 9 μm in the heat treatment at 550 ° C. or more. On the other hand, in sample B-1, it increased with the heat treatment temperature and became about 5 μm by the heat treatment at 750 ° C. The value of 9 μm is approximately 25 times the 0.4 μm of the filament design value of the sample A-1, and is substantially equal to the diameter of the primary stack. This indicates that the primary stack was already electromagnetically coupled in the low-temperature heat treatment at 550 ° C. or higher because the filament interval was small. Further, in sample B-1, it is considered that the electromagnetic coupling gradually occurred with an increase in the heat treatment temperature because the filament interval was wide.

On the other hand, as is clear from FIG. 8, in sample A-2, the effective filament diameter increased with an increase in the heat treatment temperature, and significantly increased from the design value. In sample B-2, the saturation occurred at about 1 μm, and the value was about twice the designed filament diameter.

As is clear from the above results, it was found that in the samples other than the sample B-2, the electromagnetic coupling between the filaments occurred with the heat treatment, and the loss value increased due to the increase in the effective filament diameter. In particular, when the filament interval is narrow, the loss increases even in the low-temperature heat treatment at 550 ° C. to 600 ° C. In sample B-2, it was found that the effective filament diameter almost coincided with the design filament diameter. From this, it became clear that it is effective to reduce the effective filament diameter and to approach the design value by setting the filament interval to at least 1/2 the filament diameter, preferably the same size.

As is clear from the above experimental results, the diameter of the Nb filament should be 0.3 μm or more and 1 μm or less, the interval between the Nb filaments should be 1/2 or more and 1 or less of the Nb filament diameter, and the heat treatment temperature should be 700 ° C. or less. Nb ₃ Sn for AC with small effective filament diameter and low AC loss
It can be a multi-core superconducting wire.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an entire Nb ₃ Sn multi-core superconducting wire according to an embodiment of the present invention. FIG. 2 is a sectional view showing a secondary stack in the Nb ₃ Sn multicore superconducting wire of FIG. FIG. 3 is a sectional view showing a primary stack in the secondary stack of FIG. FIG. 4 is a view showing an EDX analysis result of the Nb ₃ Sn filament. FIG. 5 is a diagram showing the heat treatment temperature dependence of the critical current density in samples A-1 and A-2. FIG. 6 is a view showing the heat treatment temperature dependence of the critical current density in samples B-1 and B-2. FIG. 7 is a diagram showing the heat treatment temperature dependence of AC loss. FIG. 8 is a diagram showing the heat treatment temperature dependence of the effective filament diameter in samples A-2 and B-2. FIG. 9 is a diagram showing the heat treatment temperature dependence of the effective filament diameter in samples A-1 and B-1. In the figure, 1 is Nb ₃ Sn multi-core superconducting wire, 2 is Cu or Cu
Alloy matrix, 3 for secondary stack, 4 for Cu or Cu
Alloy matrix, 5 for primary stack, 6 for Sn or Sn
The alloy part, 7 indicates a Cu or Cu alloy matrix, and 8 indicates an Nb filament.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01B 12/10

Claims (1)

(57) [Claims] A secondary stack is formed by arranging a plurality of primary stacks in which a plurality of Nb filaments are embedded in Cu or Cu alloy around a Sn or Sn alloy portion in a Cu or Cu alloy matrix. Produced, and this 2
In the alternating current Nb ₃ Sn multi-core superconducting wire having a structure in which a plurality of the next stacks are arranged in a Cu or Cu alloy matrix and diffusing Sn into the Nb filament by heat treatment to form Nb ₃ Sn, Sn concentration is 10 wt% or less, Sn or Sn alloy part diameter is 30 μm or less, Nb
The distance between the filament and the Sn or Sn alloy part is 50 μm or less, and the Nb filament diameter is 0.3 μm or more and 1 μm.
Less and, and the Nb spacing between filaments Nb filaments diameter 1/2 or more, is 1 or less, when the temperature of the heat treatment for Nb ₃ Sn formed to 700 ° C. or less, AC Nb ₃
Sn multi-core superconducting wire.