JPH0714439A - Nbti superconducting wire - Google Patents

Abstract

PURPOSE:To obtain an NbTi superconducting wire with an excellent critical current vs. density characteristic in a magnetic field. CONSTITUTION:The sectional form of artifical pins 7 compounded continuously in the longitudinal direction in an NbTi superconductor 6 is made in a rectangular form, an elliptical form, or a zigzag form making the rectangular form as the standard unit. And the aspect ratio (the ratio of the vertical size and the lateral size in the section) of the rectangular form, the elliptical form, or the rectangular form of the standard unit of the zigzag form, is limited to 1.5 to 30. Consequently, the probability for quantized magnetic flux lines encountering the artificial pins, and the mean pinning force of the artificial pins 7 are balanced with high precision, so as to improve the superconductivity under a high magnetid field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a NbTi-based superconducting wire having excellent superconducting critical current characteristics.

[0002]

2. Description of the Related Art NbTi-based superconducting wires are excellent in workability and superconducting characteristics such as critical current density (Jc), and are used in magnetic levitation trains, high-energy particle accelerators, nuclear magnetic resonance imaging devices for medical diagnosis, etc. It is being put to practical use in products. The NbTi-based superconducting wire is a stabilized metal material such as copper or aluminum, or a large number of NbTi-based superconducting filaments embedded in a copper alloy or the like.
A process for drawing a billet filled with Ti-based superconducting rod material by drawing it to form a single-core superconducting wire, and again filling a large number of this single-core superconducting wire into a copper tube to form a billet Repeated as many times as desired.

By the way, the quantized magnetic flux lines penetrating into the NbTi-based superconductor by applying an external magnetic field are
Although it is pinned to inhomogeneous parts such as precipitates, lattice defects, and grain boundaries in the Ti-based superconductor, if the pinning force is weak, the quantized magnetic flux lines move in the superconductor to generate a voltage,
Joule loss occurs and the superconductor is transformed into a normal conductor. Therefore, various pinning methods have been developed. Among them, the method of precipitating the α-Ti phase by performing heat treatment during processing is high because the α-Ti phase is deformed into a ribbon shape during processing. Pinning effect can be obtained (eg C. Meingast
et al. J. Appl. Phys. 66 5962 1989), which has been put to practical use. The Jc value of NbTi-based superconducting wire pinned by this method is 3700 to 3800A / mm ² (at 5T, 4.2K) at maximum.
Is. However, with this α-Ti phase precipitation method, Jc
To increase the value to 4000A / mm ² (at 5T, 4.2K) or more, 100
Long-term heat treatment requires heat treatment for 0 hours or more, and brittle intermetallic compounds of Cu and Ti are generated at the interface between the NbTi-based superconductor layer and the stabilized copper layer by long-time heat treatment, resulting in workability of NbTi-based superconducting wire. And the shape, size, and distribution of the α-Ti phase are difficult to control.

[0004]

From such a background,
A method of artificially forming pinning points has been proposed. This method is a method of artificially compounding Nb metal or the like as a pinning point in the NbTi-based superconducting rod material of the billet in which a copper tube is filled with the NbTi-based superconducting rod material.
With this artificial pin method, 3800A / mm ² (at 5T, 4.2K, K.
Matsumoto et al. IEEE Trans.Appl.Supercond. 3 1362
1993) and 3400 A / mm ² (at 5T, 4.2K, HC Kanichi et al.
Adv.Cryog.Eng .38B 675 1992) and the like, Jc values comparable to the α-Ti phase precipitation method have been obtained. Further, in this artificial pin method, the type of the substance serving as the pinning point, and its shape, distribution, amount, etc. can be arbitrarily selected or controlled, so that further improvement of the Jc value is expected.

[0005]

In view of such a situation, the present invention has conducted intensive studies on the artificial pinning method and has found that the Jc value is remarkably influenced by the sectional shape of the composite artificial pinning point. The present invention has been completed through repeated research. That is, according to the present invention, in the NbTi-based superconductor, a substance which is a non-superconductor in a use environment of the NbTi-based superconductor or a substance having a weaker Bc ₂ (upper critical magnetic field) than the NbTi-based superconductor is used as a pinning point in the longitudinal direction. In the NbTi-based superconducting wire rod that is continuously compounded in the above, the cross-sectional shape of the substance that is continuously compounded in the longitudinal direction as the pinning point is a rectangle, an ellipse, or a zigzag shape having a rectangle as a basic unit, and the rectangle The elliptical or zigzag basic unit has a rectangular aspect ratio (aspect ratio of cross section) of 1.5 to 30, which is an NbTi-based superconducting wire.

In the present invention, the non-superconductor material serving as an artificial pinning point (hereinafter abbreviated as an artificial pin) is Nb.
It is a substance that is in a non-superconducting state under the usage environment of the Ti-based superconductor, that is, under the condition that the NbTi-based superconductor exhibits superconductivity. A material having a lower Bc ₂ (upper critical magnetic field) than the NbTi-based superconductor is also applied to the artificial pinning point. As these substances, Nb metal, Nb alloy, and the like are preferable because they do not deteriorate the NbTi-based superconductor. Other than Nb, Ti,
Ta, Al, Mg, Fe, Hf, Cu, Ge, Ni, Z
Metals such as r and Cr, alloys in which these are appropriately combined, and those in which these metals are appropriately laminated are used.

In the present invention, the cross-sectional shape of the artificial pin which is continuously compounded in the longitudinal direction is a rectangle, an ellipse, or a zigzag shape whose basic unit is a rectangle, and the rectangle of the rectangular, elliptical or zigzag basic unit. The reason for limiting the aspect ratio (aspect ratio of cross section) to 1.5 to 30 is that a high Jc value cannot be obtained even if the aspect ratio of the artificial pin cross section is below or above the above limit value. .

The reason why a high Jc value is obtained when the aspect ratio is in the range of 1.5 to 30 is considered as follows. That is, the pinning force of the quantized magnetic flux line depends on the surface area of the artificial pin with which the quantized magnetic flux line meets, and when the angle θ between the wide surface of the artificial pin and the quantized magnetic flux line is 0, that is, both are parallel. When, the quantized flux lines are most strongly pinned. The pinning force sharply decreases as θ increases, and the rate of decrease increases as the aspect ratio increases. Therefore, the average pinning force at θ of 0 to 90 degrees decreases as the aspect ratio increases. On the other hand, the probability that the quantized magnetic flux line meets the surface of the artificial pin increases as the aspect ratio of the artificial pin decreases. As described above, when the aspect ratio is large, the average pinning force of the artificial pin is reduced, and when the aspect ratio is small, the probability of encountering the artificial pin of the quantized magnetic flux line is increased. It is considered that the balanced aspect ratio of the encounter probability and the pinning force is between 1.5 and 30.

[0009]

In the present invention, the cross-sectional shape of the artificial pin continuously compounded in the longitudinal direction is rectangular, elliptical, or zigzag with the rectangular unit as a basic unit, and the rectangular, elliptical, or zigzag basic shape is used. Since the aspect ratio of the unit rectangle (the aspect ratio of the cross section) is limited to 1.5 to 30, the probability that the quantized magnetic flux line encounters the artificial pin and the average pinning force of the artificial pin balance well Pinning efficiency is improved, and superconducting characteristics in a magnetic field are improved.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 A plate-shaped Nb-50 wt% Ti alloy material having a thickness of 3.3 mm and a plate-shaped Nb material having a thickness of 1.3 mm and an aspect ratio of maximum 30 and minimum 18 were alternately laminated on a copper tube. Were filled to prepare a primary billet. Next, this primary billet is processed into a wire rod by hot extrusion and wire drawing, and the wire rod is immersed in an aqueous nitric acid solution to remove the copper layer on the outer periphery to form a laminated wire rod of 2.5 mmφ NbTi and Nb. A copper tube was filled with 200 wires to form a secondary billet. Next, this was compounded by hot extrusion and further processed into a wire rod of 1.3 mmφ by wire drawing. Next, 750 copper pipes were filled with this wire rod to form a tertiary billet, which was integrated by hot extrusion and further drawn to form a 0.2 mmφ NbTi-based superconducting wire rod. As the copper tube, a copper tube having an outer diameter of 45 mmφ and an inner diameter of 40 mmφ was used.

Example 2 A copper pipe was provided with a plate-shaped Nb-50 wt% Ti alloy material having a thickness of 6 mm,
A plate-shaped Nb material having a thickness of 2.4 mm, an aspect ratio of 16 at the maximum, and a minimum of 13 was alternately laminated and filled to prepare a primary billet. Next, this primary billet is processed into a wire rod by hot extrusion and wire drawing, and this wire rod is immersed in a nitric acid aqueous solution to remove the copper layer on the outer periphery to form a laminated wire rod of 1.3 mmφ NbTi and Nb. 0.2 mmφ was obtained in the same manner as in Example 1 except that 700 wires were filled in a copper tube to form a secondary billet.
Of NbTi-based superconducting wire.

Example 3 A copper tube was coated with a Nb-50 wt% Ti alloy material having a thickness of 10.5 mm and a thickness of
A plate-shaped Nb material having a thickness of 4.2 mm and an aspect ratio of 9 was alternately laminated and filled to prepare a primary billet. Next, this primary billet is processed into a wire rod by hot extrusion and wire drawing, and the wire rod is immersed in an aqueous nitric acid solution to remove the copper layer on the outer periphery.
A 0.2 mmφ NbTi-based superconducting wire was manufactured in the same manner as in Example 1 except that a laminated wire rod of 8 mmφ NbTi and Nb was used, and 2000 pieces of this wire rod were filled into a copper tube to form a secondary billet. .

EXAMPLE 4 A copper tube was filled with a 15.5 mm thick Nb-50 wt% Ti alloy material sandwiching an 8 mm thick Nb material having an aspect ratio of 5 to prepare a primary billet. Next, this primary billet is processed into a wire rod by hot extrusion and wire drawing, and this wire rod is immersed in an aqueous nitric acid solution to remove the outer copper layer to form a laminated wire rod of 3.0 mmφ NbTi and Nb. A copper tube was filled with 140 wires to form a secondary billet. Next, after reducing the diameter by hot extrusion, it is immersed again in a nitric acid aqueous solution to remove the outer copper layer to form a laminated wire rod of NbTi and Nb, and 55 copper pipes are filled with this wire rod to form a tertiary wire. A billet was formed, which was compounded by hot extrusion, and further drawn into a 1.3 mmφ wire rod. Next, 750 copper pipes were filled with this wire rod to form a quaternary billet, which was integrated by hot extrusion and further drawn to form a 0.2 mmφ superconducting wire rod.
As the copper tube, a copper tube having an outer diameter of 45 mmφ and an inner diameter of 40 mmφ was used.

Example 5 A hollow round bar made of Nb-50 wt% Ti alloy has a thickness of 1
A Nb square rod having an aspect ratio of 4.5 mm was inserted into the copper tube and the copper tube was filled with the rod to prepare a primary billet. Next, this primary billet is processed into a wire rod by hot extrusion and wire drawing, and this wire rod is immersed in an aqueous nitric acid solution to remove the copper layer on the outer periphery to form a wire rod composed of Nb in a 1.6 mmφ NbTi alloy. A 0.2 mmφ superconducting wire was manufactured in the same manner as in Example 4 except that 470 copper tubes were filled with this wire to form a secondary billet.

Example 6 N pieces of N formed by forming one or both surfaces in a zigzag shape on a copper tube
A 0.2 mmφ NbTi superconducting wire was prepared in the same manner as in Example 2 except that b-50 wt% Ti alloy material and eight Nb materials (thickness: 1.3 mm) bent in a zigzag shape were alternately laminated and filled. Manufactured. The aspect ratio of the rectangle of the basic unit of the zigzag Nb material was set to 5.

Comparative Example 1 A copper tube having a plate-like Nb-50 wt% Ti alloy material having a thickness of 2 mm was used.
A NbT of 0.2 mmφ was prepared in the same manner as in Example 1 except that a plate-shaped Nb material having a thickness of 0.8 mm, an aspect ratio of 40 at the maximum and a minimum of 19 was alternately laminated and filled.
An i-based superconducting wire was manufactured.

Comparative Example 2 A cross section of a hollow round bar of Nb-50 wt% Ti alloy has a cross section of 18
Example 4 except that a Nb material having a size of 18 mm × 18 mm (aspect ratio of 1) was fitted and the copper tube was filled with the Nb material to produce a primary billet.
A 0.2 mmφ NbTi-based superconducting wire was manufactured by the same method as described above. The volume ratio of the Nb material to the NbTi material in the primary billets of the above Examples and Comparative Examples was unified to 1: 3 (the space factor of the Nb material was 25%).

For each 0.2 mmφ NbTi-based superconducting wire obtained in Examples 1 to 6 and Comparative Examples 1 and 2, N
The distribution state of the b material (artificial pin) was observed, and its cross section is shown in FIGS. 1 to 6 and FIGS. For reference, the arrangement of the Nb material of the primary billet is also shown. The primary billet of Example 1 has Nb inside the copper tube 1 as shown in the cross section of FIG.
The Ti material 2 and the Nb material 3 are filled in layers. The aspect ratio of the Nb material 3 differs between the center and the end of the cross section. The NbTi-based superconducting wire 5 obtained based on the primary billet 4 has an artificial pin 7 of Nb material in a unit of 8 layers in the NbTi-based superconductor 6, as shown in the cross section of FIG. 1B. As it is distributed in various directions. Primary billet N
The aspect ratio of the b material and the aspect ratio of the Nb material (artificial pin) of the NbTi superconducting wire material were extremely well matched. Hereinafter, the cross sections of the primary billets and NbTi superconducting wires of Examples 2 to 6 and Comparative Examples 1 and 2 are shown in FIG.
6 and FIGS. 8 and 9, the description is omitted. still,
The rectangle of the zigzag basic unit of Example 6 is a linear portion of the zigzag artificial pin 7 as shown in FIG. 7, and its aspect ratio is length (length) to thickness (width). It is the value divided by.

Next, each of the obtained 0.2 mmφ NbTi
System superconducting wire, the critical current density (Jc) 5T, 4.
It was measured under the condition of 2K. For measurement, wire diameter 0.2 mmφ
The maximum Jc value was obtained by shaking the sample before and after. The results are shown in Table 1.

[0020]

[Table 1]

As is clear from Table 1, the products of the present invention (No.
1 to 6) all showed high Jc values. This is because the aspect ratio of the artificial pin was in the range of 1.5 to 30, so that the probability that the quantized magnetic flux line encounters the artificial pin and the average pinning force of the artificial pin are well balanced. On the other hand, in the comparative example No. 7, the aspect ratio of the artificial pin exceeded 30, so the average pinning force and the probability of encounter between the artificial pin and the quantized magnetic flux line decreased, and No. 8 had an aspect ratio of 1 Therefore, the probability of encounter between the artificial pin and the quantized magnetic flux line increased, but the Jc value decreased in each case because the individual pinning force decreased. Although the case where Nb metal is used for the artificial pin has been described above, the present invention has the same effect when the Nb alloy or other substance is used for the artificial pin.

[0022]

[Effect] As described above, the NbTi-based superconducting wire of the present invention is a composite of artificial pins having an aspect ratio (aspect ratio of cross section) of 1.5 to 30, so that the probability that the quantized magnetic flux line meets the artificial pin and the artificial pin The average pinning force of the pins is balanced to a high level, and the Jc value under a high magnetic field is improved, resulting in a remarkable industrial effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a primary billet and a superconducting wire according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a primary billet and a superconducting wire according to a second embodiment of the present invention.

FIG. 3 is a transverse sectional view of a primary billet and a superconducting wire according to a third embodiment of the present invention.

FIG. 4 is a transverse sectional view of a primary billet and a superconducting wire according to a fourth embodiment of the present invention.

FIG. 5 is a transverse sectional view of a primary billet and a superconducting wire according to a fifth embodiment of the present invention.

FIG. 6 is a transverse sectional view of a primary billet and a superconducting wire according to a sixth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a rectangle and an aspect ratio of a basic unit of a zigzag artificial pin.

FIG. 8 is a transverse cross-sectional view of a primary billet and a superconducting wire in Comparative Example 1.

FIG. 9 is a cross-sectional view of a primary billet and a superconducting wire according to Comparative Example 2.

[Explanation of symbols]

 1 Copper Tube 2 NbTi Material 3 Nb Material 4 Primary Billet 5 NbTi Superconducting Wire Material 6 NbTi Superconductor 7 Artificial Pin

Claims (1)

[Claims] 1. A NbTi-based superconductor in which NbTi-based superconductor is used as a non-superconductor material or NbT in an environment where the NbTi-based superconductor is used.
NbTi, which is a compound with a lower Bc ₂ (upper critical magnetic field) lower than that of the i-based superconductor, is continuously compounded in the longitudinal direction with a pinning point.
In the system superconducting wire rod, the cross-sectional shape of the substance continuously compounded in the longitudinal direction as the pinning point is a rectangle, an ellipse, or a zigzag shape having a rectangle as a basic unit, and the rectangle, an ellipse, or a zigzag shape. An NbTi-based superconducting wire rod characterized in that the rectangular aspect ratio (the aspect ratio of the cross section) of the basic unit is 1.5 to 30.