JP2931020B2 - Cu or Al stabilized superconducting wire and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a Cu or Al-stabilized superconducting wire in which a pinning center in an Nb-Ti filament is artificially introduced, and a method for producing the same.

[Conventional technology]

Nb-Ti superconducting wires are required to have different superconducting properties depending on the application, and are manufactured. As a method for controlling the critical current density characteristics of the Nb-Ti superconducting wire, generally, a working strain is added by cold working the Nb-Ti superconducting wire after hot extrusion, and successive multi-stage aging heat treatment is performed. In addition, fine α-
A method of precipitating Ti has been adopted, and a method of controlling a critical current density characteristic obtained by the cold working ratio and the aging heat treatment condition has been performed. According to this method,
It is clear that a higher critical working density can be obtained by increasing the cold working ratio and increasing the number of times of the multi-stage aging heat treatment or lengthening the time, but since the workability of Nb-Ti itself is significantly reduced, It is not uncommon for the Nb-Ti filament to break, resulting in deterioration of superconducting characteristics or even breakage of the wire itself. In particular, in the case of ultra-fine multi-core Nb-Ti superconducting wires that are required to cope with high magnetic fields, such as large magnets for particle accelerators, there has been a problem that workability is remarkably reduced and disconnection occurs frequently.

From the above problems, as a method of improving the pinning force without the need for severe cold working and aging heat treatment,
A method of artificially introducing a pinning center has been studied. In this method, a normal conducting material having good workability to some extent in the Nb-Ti filament is introduced in advance at the stage of element wire formation, and is reduced to about several to several tens of nm by subsequent surface reduction processing to form a pinning center. Is what you do. For example, a bundle of a plurality of Nb-Ti thin rods wound with a sheet of pure Cu having a predetermined thickness is inserted and fitted into a Cu or Cu alloy tube,
When a multi-filamentary superconducting wire is formed by using a hot-extruded composite material as a strand, Cu serves as a pinning center. Since Cu is a normal conductor even at liquid He temperature, it functions as a pinning center. According to this method, pinning centers can be generated without the need for severe cold working or aging heat treatment, and the number of pinning centers can be freely controlled by the design of the strands. There is an advantage that characteristics can be controlled more accurately, and different superconducting wires can be designed and manufactured depending on required characteristics.

[Problems to be solved by the invention]

However, as described above, when Cu is used as an artificial pinning center, there is a problem in composite workability due to a large difference in deformation resistance from Nb-Ti, and an interface between Nb-Ti and Cu due to intermediate heat treatment or the like. In addition, since a Cu-Ti compound with extremely poor workability is generated, breakage of the filament occurs during the surface reduction processing and the superconductivity is significantly deteriorated, and in the worst case, the wire itself breaks There was such a problem.

[Means for solving the problem]

In view of the above, the present invention has been made as a result of diligent studies, and its purpose is to provide an Nb-Ti superconducting wire in which a pinning center is artificially introduced into an Nb-Ti filament. Cu or Al-stabilized superconducting wire with good workability without artificially introducing a pinning center to produce secondary reaction products that are harmful in practical use and not deteriorating superconducting characteristics. , And a method of manufacturing the same.

That is, the superconducting wire in the present invention, each of a plurality of Nb-Ti filaments embedded on the stabilizing material, practically,
A superconducting wire coated with a material B that does not generate a reaction product with a stabilizer or Nb-Ti, wherein the Nb-Ti filament is
Practically, it has a cross-sectional structure in which a plurality of materials A that do not generate an intermetallic compound with Nb-Ti or material B have a cross-sectional structure, and the Nb-Ti
The material A scattered in the Ti filament is a Cu or Al stabilized superconducting wire, which is a pinning center of magnetic flux in the Nb-Ti filament, and the material A is Nb or Ta, Nb or Ta is suitable as the material B. In addition, the manufacturing method refers to Nb-Ti
In the alloy rod, a plurality of through holes are provided in parallel with the longitudinal direction,
After inserting a rod of Nb or Ta into it, coating the periphery of the Nb-Ti alloy rod with Nb or Ta, and then sealing this in a pure Cu tube to obtain a hot-extruded composite material as a strand, One or several through-holes are provided in the Nb-Ti alloy rod in parallel with the longitudinal direction, Nb or Ta rods are inserted in the through-holes, and a plurality of bundles are bundled, and the periphery is covered with Nb or Ta. And then clean this
When sealed in a Cu tube and hot-extruded as a strand, Nb
-Ti alloy rods and Nb or Ta rods are bundled together so that Nb or Ta rods do not contact each other,
The surrounding area is coated with Nb or Ta, and then sealed in a pure Cu tube. For each of the cases where the composite material obtained by hot extrusion is used as a strand, a plurality of the strands are bundled to form a pure Cu pipe or a pure Al pipe. A method for producing a Cu or Al-stabilized superconducting wire, characterized in that the superconducting wire is subjected to hot extrusion after being inserted into and sealed in a wire.

[Action]

In the present invention, since a plurality of materials A scattered in the cross section of one Nb-Ti filament do not produce Nb-Ti and an intermetallic compound for practical use, a pinning center is artificially introduced. Secondary reaction products that are harmful to plastic working are not generated, and processing can be performed soundly. Further, it is preferable to use a material having a small difference in deformation resistance from Nb-Ti, such as Nb or Ta, for example, as the material A, since the composite workability is improved. Here at the artificial pinning center
When Nb or Ta is used, they also show superconductivity at liquid He temperature, but since the superconductivity of Nb-Ti is superior to these, in practice, it is necessary to use these materials under conditions above their critical magnetic field and critical current density. Under these conditions, the superconductivity of Nb or Ta is broken and the state of normal conduction is obtained, so that the pinning effect can be obtained without any practical problem. In addition, each Nb-Ti filament introduced with an artificial pinning center can be used as a stabilizer or Nb-
By coating with Ti, material A and material B that does not produce a reaction product, it is possible to prevent the stabilizing material from reacting with Nb-Ti and / or material A, and to make secondary work harmful to plastic working. Since no natural reaction product is produced, it can be processed soundly.

〔Example〕

Open 220 through holes parallel to the longitudinal direction of the Nb-Ti rod,
After inserting and filling the Nb rod into it, the periphery of the Nb-Ti rod is
A composite material coated with an Nb sheet and then inserted and fitted into a Cu-0.5 wt% Mn tube was hot-extruded at an extrusion temperature of 900 ° C.
After drawing and shaping into the final hexagonal shape, straightening and cutting the material into a primary strand, bundle the 130 primary strands neatly into pure Cu
After inserting into a tube and extruding the composite material with both ends sealed with a pure Cu lid at an extrusion temperature of 500 ° C., the wire was drawn, formed into a final hexagonal shape, straightened and cut to form a secondary element wire. 22 secondary wires
Two cables were neatly bundled and inserted into a pure Cu tube, and both ends were sealed with a pure Cu lid to produce a cable billet of 100 mmφ × 500 mml. This cable billet is hot-extruded to a diameter of 15 mm at an extrusion temperature of 500 ° C, and then subjected to an aging heat treatment every 380% of the total processing rate.
3.44mmφ (as
−annealed) and then 0.520mmφ without annealing
Wire, and finally, annealing at 500 ° C. × 20 m / min was performed with an annealer. At this time, the diameter per Nb-Ti filament is about 1.065 μm, and the filament has a cross-sectional structure in which Nb having a thickness of about 5.8 nmφ is scattered at an interval of about 64.9 nm. . The wires of this 0.520mmφ cooled by liquid He, the critical current value in a magnetic field of 5T · I _C (A)
Was measured, and the critical current density, J _C (A / mm ² ), was determined by calculation. The measurement was performed for n = 20 arbitrarily sampled from a long line of 0.520 mmφ. As a result, 3080-3220
(A / mm ² ), indicating that a high critical current density was obtained stably. As a comparative material, a Nb-Ti rod wrapped with an Nb sheet was inserted into and fitted with a Cu-0.5wt% Mn tube, and the composite material was hot-extruded at an extrusion temperature of 900 ° C, drawn to a final hexagonal shape. The molded, straightened and cut pieces are used as primary strands to produce a cable billet (number of strands: 28860) of 100 mmφ × 500 mml with the same configuration as above, and 0.5 mm under the same processing conditions.
Wire drawing to 20mmφ, and finally 500 ℃ × 20m with annealer
/ min running annealing was performed. At this time, the diameter per one Nb-Ti filament was about 1.065 μm, and nothing was buried in the cross section. I _C (A) was measured for this 0.520 mmφ wire according to the same measurement method and measurement conditions as above, and J _C (A / mm ² ) was calculated.
~2680 (A / mm ²⁾ and although there was a high J _C values became slightly inferior result than in the example of the introduction of Nb artificial pinning center. Also, as another kind of comparative material,
A wire rod with a configuration in which the artificial pinning center of Nb was introduced was replaced with pure Cu, that is, a configuration in which Cu was considered as an artificial pinning center, was manufactured. However, in this case, before the diameter was reduced to 0.520 mmφ in the final processing step, constriction was observed on the surface of the wire rod, and disconnection occurred frequently. Cu portion was dissolved and removed disconnection of the wire was immersed in HNO _3, were examined scanning electron microscope excised Nb-Ti filaments, and an electron beam microanalyzer, Nb-Ti filaments surface or internal It is considered that grains of the Cu-Ti compound were generated everywhere, and this led to disconnection.

〔The invention's effect〕

As described above, according to the present invention, when artificially introducing a pinning center into Nb-Ti filaments, Nb-Ti and secondary reaction products that are harmful to plastic working do not practically occur. By using an artificial pinning center as the material, the target wire can be processed without deteriorating the workability, and by introducing the artificial pinning center, the industrially superior effect of improving superconductivity can be achieved. is there.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the structure of a Cu or Al stabilized superconducting wire of the present invention. In FIG. 1, (a) gathers and (b)
And (b) gathers to become (c). 1 ... Nb-Ti, 2 ... Material A, 3 ... Material B, 4 ... Stabilizer, 5 ... Strand, 6 ... Cable.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kinya Ogawa 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Examiner at Furukawa Electric Co., Ltd. Mitsuru Koyama (56) Reference JP-A-63-124310 (JP, A JP, A 60-100307 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01B 12/10 H01B 13/00 563

Claims (6)

(57) [Claims] A plurality of Nb-Ti filaments embedded in a stabilizing material are superconducting wires coated with a material B that does not generate a reaction product with the stabilizing material or Nb-Ti in practical use. The Nb-Ti filament has, in practice, a cross-sectional structure in which a plurality of materials A that do not generate an intermetallic compound with Nb-Ti or material B are scattered, and the material A that is scattered in the Nb-Ti filament Is a pinning center for magnetic flux in the Nb-Ti filament, wherein the Cu or Al-stabilized superconducting wire is provided. 2. The Cu or Al stabilized superconducting wire according to claim 1, wherein the material A is Nb or Ta. 3. The Cu or Al stabilized superconducting wire according to claim 1, wherein the material B is Nb or Ta. 4. An Nb-Ti alloy rod is provided with a plurality of through-holes parallel to the longitudinal direction thereof, and a Nb or Ta rod is inserted therein. Then, the periphery of the Nb-Ti alloy rod is Nb or Ti. Coating with Ta, then sealing this in a pure Cu tube, making the extruded composite material a strand, bundling a plurality of these strands, inserting into a pure Cu pipe or a pure Al pipe, sealing and extruding hot A method for producing a Cu or Al-stabilized superconducting wire, characterized in that: 5. An Nb-Ti alloy rod is attached to a rod in parallel with its longitudinal direction.
Or a plurality of through-holes into which a plurality of Nb or Ta rods are inserted are bundled, and the surrounding area is Nb or Ti
The composite material was sealed in a pure Cu tube and extruded by hot extrusion to obtain a strand.
A method for producing a Cu or Al-stabilized superconducting wire, characterized in that it is inserted into a tube, sealed and then extruded hot. 6. A plurality of Nb-Ti alloy rods and a plurality of Nb or Ta rods are bundled so that the Nb or Ta rods do not contact each other, and the periphery is covered with Nb or Ta. Next, a composite material obtained by sealing this in a pure Cu tube and hot extruding is used as a strand, and a plurality of the strands are bundled, inserted into a pure Cu tube or a pure Al tube, sealed, and then hot-extruded, Cu or Manufacturing method of Al-stabilized superconducting wire.