JPH04133215A - Manufacture of nb3(al, ge) super conductive wire - Google Patents

Abstract

PURPOSE:To enable industrial production of super ultrafine multicore wires being essential for alternating current in a Nb3(Al, Ge) super conductor by using an Al-Ge alloy of a specified composition as a core material. CONSTITUTION:By substituting Al-38-62wt.% Ge alloys for a core material, presently used cold extrusion method or hydrostatic extrusion method can be applied as it is, and extremely short Nb/AlGe alloy diffusion pairs of submicron order can be easily manufactured, and diffusion treatment at a low temperature and for a shorter time becomes effective. Namely, super ultrafine multicore wires suitable for low alternating current loss in which filaments of submicron diameter are neatly isolated from each other at submicron spacings, can be industrially produced.

Description

[Detailed description of the invention] [Field of industrial application] Research and development of superconducting applied equipment 1 For example, in superconducting coil conductors for nuclear fusion reactors, power generators, transformers, etc., high magnetic fields, bipulse and alternating current Large capacity Nb that can be expected for
, relates to an industrial manufacturing method of (Al, Ge) superconducting wire.

[-Conventional technology]

Nb is attracting attention as the next generation material for high magnetic fields.

Al and Nb, (Al; Ge) A15 type compound superconductors can be obtained by diffusing or dissolving metal elements whose exact stoichiometry is equal to theirs, but the stable production temperature is Since the temperature is higher than 1300°C and 1900°C or higher for NbaGe, the crystal grains of the generated compound become coarse.

As a result, the critical electromagnetic density Jc (2
00A/- or more) can be obtained. For this reason.

Co-deposition and rapid cooling on the tape surface using plasma spraying sputtering, PVD, (ion coating), etc., powder metallurgy method in which Nb powder and Al powder are packed into a Cu pipe and rolled, or Nb and Al A thin plate is wrapped around a Cu core rod.

By inserting this into a Cu pipe, reducing its diameter, and drawing it using the Dieliroll method, we are able to increase the diffusion interface, promote the formation of compounds, suppress grain coarsening, and achieve the critical temperature TC=
17° or more (Nb, Al) or 20”K or more (Nb
j Ge); Upper critical magnetic field Hc, = 207' (Tesla) or more or 40 T or more has been achieved.

However, it is a well-known fact that these manufacturing methods have many drawbacks due to their mechanisms that prevent them from being adopted as a means of producing large-capacity practical conductors.

In order to prevent the crystal grains of the generated compound from becoming coarse and to enable industrial production, the diffusion distance between Nb and Al or Ge must be made shorter than in the case of other Nb+Sn or VxGa superconducting wires. do.

In addition, diffusion pairs can be stably obtained, that is, Nb+ Al, Nb, (A4°Ge
), , or NbaGe phase must be able to be generated by diffusion.

Conventional methods for obtaining short diffusion pairs 9 For example, in Nb5Sn superconductors, a bronze (Cu-Sn alloy) rod is inserted into an Nb tube, or conversely, a Nb rod is inserted into a bronze tube, or There is a composite method/diffusion method in which a two- or three-layer composite billet inserted into an oxygen-free Cu tube is linearized by repeated processing and intermediate annealing, and then subjected to diffusion heat treatment to obtain a Nb5Sn superconducting material. However, Nb,
Regarding Al-based materials, since Al is of high purity (4N or higher), its deformation resistance during cold working is too different from that of Nb or Cu alloys, and cold working is rarely applied to composites. It is known that this is impossible. Ge is also more fragile, and in the end, it is impossible to realize an ultrashort diffusion pair. For this reason, recently, Mg + Zn or Cu, etc. are added to A2 to make it into an Al alloy, and then age hardening is performed to increase the deformation resistance, improve the workability of the composite, and produce ultrashort diffusion pairs. A new manufacturing method has been reported.

[Problem to be solved by the invention]

+Cu/Cu-Ni alloy/N as a superconductor for AC
NbTi ultrafine multicore wires with a three-layer bTi alloy structure are generally manufactured, but in order to further reduce AC loss,
By reducing the diameter of superconducting filaments to submicrons,
It is necessary to shorten the twist pitch by making the wire diameter as small as possible. Of course, the above-mentioned improvements are required in the case of the N bs S n compound superconductor for the same reason, but in addition, the superconducting filaments in bronze and the stabilized Cu are replaced by a Cu-Ni alloy with high electrical resistance. It is necessary to adopt a structure divided and shielded by a (cupronickel) matrix and a Nb diffusion barrier layer. In this way, in the production of ultra-fine multifilamentary wires with complex cross-sectional structures using compound systems,
Improves workability and adhesion between dissimilar metals that make up the cross section.

It is essential to perform uniform extrusion and drawing processes.

When considering mass production of Nb and Al compound superconducting wires.

The difference in hardness and tensile strength, which corresponds to the difference in deformation resistance between Al and Nb and Cu-Ni alloys, is too large as shown in Figure 2, so there is a problem that conventional processing methods for manufacturing conductors cannot be applied. be.

In FIG. 2, although the hardness 2 of Nb is high, the work hardening relative to the working rate is small and the workability is good. Tensile strength 31#
The hardness 3 of the Cu-Cu-2O%Ni alloy with f/- is N
Although the hardness is lower than that of b, the work hardening relative to the working rate is large and exceeds that of Nb at working rates of 60 inches or more.

The hardness 1 of the Al-47wt-1pGe alloy is located between the above two hardnesses. Note that the two-dot line indicates the hardness when cracking occurs due to the Noog hardness indentation, making it impossible to measure the true hardness. For these,
Hardness 4 of Al is very low and no work hardening is observed. Therefore, it is necessary to improve either the processing method or the deformation resistance, but the former is much more difficult and impractical than the latter.

Therefore, regarding the latter, we focused on modifying the material. In addition, the development of new technology that does not impair the inherent superconducting properties of Nb, Al, and Nb3Ga has become an issue.

[Means to solve the problem]

As for the manufacturing method of Nb, Al superconductor, + The manufacturing method of Nb3Si compound conductor (embedding Nb in a bronze matrix and performing diffusion heat treatment after thinning) is similar to y, a core in which an Al rod is inserted into an Nb tube that becomes a filament. The rod is Cu-10 or 20wt which becomes the matrix.

The material inserted into the %N1 alloy tube is extruded into a single-core composite, which is further bundled into several tens to hundreds of pieces, wrapped in a Cu-Ni alloy tube again, and processed to form a multi-core composite, or further processed into a multi-core composite. It is conceivable to repeat the processing and extrude and draw the superconducting strands to the diameter. Therefore, we changed the Al or Ge core material to a hard and brittle Al-47wt-%Ge binary eutectic alloy to enable extrusion processing, and also to prevent the crushed granules from penetrating the inner wall of the surrounding Nb pipe. This creates a relatively wide two-layer mixed zone at the boundary (tube/core), improving adhesion, and at the same time eliminating short diffusion pairs that rely only on conventional crimping processes that do not cause powdering. We considered that it is possible to obtain an extremely short diffusive pair by further shortening .

FIG. 1 shows a conceptual diagram of the powder mechanism of Al-47Ge alloy produced by extrusion processing. Note that this also applies to the subsequent drawing process. In the figure, 5 is a three-layer single-core composite billet before processing.

6 is the core material, 7 is a pure Nb tube, 8 is a Cu=2ONi alloy tube that will later become the base material of the wire, 9 is a single-core composite billet, and the inside of the billet is evacuated. A Cu-2ONi alloy lid is electron beam welded at both ends to give the billet a similar deformation, 10 is an extrusion container, 12 is an extrusion die, and 13 is a core material fracture area (cracks and 14 is a core material pulverization area (fine grain/atomization part) 15 is a single-core composite, and a mixed zone is formed at the boundary between 6 and 7 in Steps 3 and 4. Also,
Al-47wt, %Ge alloy is Nb,
This corresponds to the composition of the (AlO,75GeO,25) compound, and the superconducting properties are considered to be considerably superior to Nb and Al and close to pNbmGe.

[Effect]

For Nb, (A4Ge) superconductors, Al-38~
62wt.

%Ge composition is observed to exhibit the highest Jc and HC2. The solid solubility limit of Ge in Al is 7.2
wt, %, and the solid solubility limit of Al in Ge is Q, 5wt
, %, fi, 1-38 to 62 wt, % It can be seen from the phase diagram that the occupation rate of the eutectic structure is still low in the alloy having the Ge composition. The average composition of water droplets is Nb5 (Al0.
75GeO, 25) is selected, and Al-47wt, %Ge alloy is used as a representative value for the core material composition. Although the above-mentioned eutectic is hard, it exhibits a lamellar (layer) shape and is brittle.

For example, as mentioned above, the hardness of Al is about Hv20. The bow strength is about 4#f/-, while Al-2.5wt
, %Ge alloy has a hardness of Hv36. Tensile strength is 12#f
/d.

And in Al-47wt, %Ge alloy, the hardness is Hv 7
Although the tensile strength is high at 9-83, the tensile strength is 13-14 f/-, which is low compared to the improvement in hardness. However, Nb and Cu-Ni
It has properties that do not impede cold working of composites and the like using an alloy as a mating material, and is rather considered to be a suitable core material that can be expected to have the following effects.

(1) The hardness of this alloy is mainly to achieve the deformation resistance required in the initial processing, and also to achieve the ultrafine grain (0.01 μm) in the fine wire process.
m level), and because of its high density, sausaging (
No abnormal deformation) or wire breakage.

(2) The eutectic spheroidized by intermediate annealing progresses to grain refinement and crushing within the Nb tubular layer during processing.

The fine particles invade the surrounding Nb tube and improve the adhesion.

(3) Improved hardness and adhesion improve uniform processing of the composite and reduce heat generation due to friction with the die.

(4) At the stage where the diameter is reduced to 10-' or less, the particles become submicro/sized (0.1 μm or less) fine particles.

Contributes to the formation of submicron ultrashort diffusion pairs.

(5) Due to the diffusion heat treatment, the compact of the diffusion pair melts and diffuses with Nb. The technical conditions for mass production are established by one or more core material properties and mechanisms.

By replacing the core material with Al-38~62wt%Ge alloy, the current cold extrusion and hydrostatic extrusion methods can be applied as is, and extremely short Nb/Al-Ge alloy diffusion on the submicron order can be achieved. The pair is easily manufactured, and low-temperature, short-time diffusion treatment is effective. That is, it becomes possible to industrially manufacture an ultra-fine multifilamentary wire suitable for low AC loss in which filaments of submicron diameter are neatly separated with submicron spacing.

〔Example〕

In order to confirm the practicality of the production method of the present invention, the scale of the experiment,
The specifications of the primary conductor were planned in consideration of the technology, etc., and the conductor strand was prototyped, the cross-sectional structure was observed, and T c + Hc x and Jc were measured.

(1) Elements of conductor wire? fM (strand) diameter 0.15+m, Nb, (
Al, Ge) superconductor filament diameter 0.40 μm
, number of filaments 7686. spacing 0.20
μml Cu stabilizing material diameter and number 6.70 μm, 61 pieces, wire sheath (Cu-2ON1 alloy) thickness 23 μm,
Spacing of Cu stabilizer (Nb diffusion barrier) 0.0
2 μm or more, Nb.

(AlO,75Ge0.25):Cu:Cu-2ONi
The volume occupancy of the alloy is 1:2.2:14.4. The volume occupancy of the filament and Cu stabilizing material gathering area is 1.0
: 2.2 : 5.4', filament twist pitch 1.5W+.

(2) Conductor prototype Al-47wt0%Ge (hereinafter abbreviated as Al-47Ge) alloy was melted in an Ar (argon) atmosphere and cast into a water-cooled copper mold.The outer periphery of the mold was ground to a diameter of 30 mm as shown in Figure 1. Processed into a 9m round bar, outer diameter 61.4 + m - inner diameter 3
Insert it into a 1.0 m Nb pipe 7, and further extend this pipe with an outer diameter of 89 mm.
．． It is inserted into a Cu-2ONi alloy tube 8 with a diameter of 0 mm and an inner diameter of 51.5W, and finally a Cu-2ONi alloy lid 9 is vacuum electron beam welded to both ends to form a three-layer structure cross section shown in the A-A cross section of Fig. 1. Billet 5 was produced. This is subjected to diameter reduction processing by cold extrusion, and then a third
A regular hexagonal bar with a distance across sides a9 a+:, 05 mm as shown in the figure was used, and a three-layer structure single-core composite consisting of Al-47Ge alloy/Nb/Cu-2ONi alloy was used. 1 in the same figure
6 is AJ! -47Ge alloy powder (stippling part) 19 means a mixed zone of Nb F, 18 means Cu-2ONi alloy tube 8
Compatible with hexagonal molded bodies. Next, the core composite of the same year was cut into a length of f, 120τ, which was corrected in the axial direction, and the 61 cutting rods were cut into an outer diameter of 89.0fi - an inner diameter of 7 as shown in Figure 4.
2. The pipes were bundled in a Cu-2ONi alloy tube 20, and the tube was vacuum welded at both ends to seal the inside of the tube to form the billet for the next multicore composite.

Process this $R [(Cross-sectional area S before processing - Cross-sectional area S of processed edge) /5oX100%] = 1O-5T for every 75%
Intermediate furnace heated at 410°C for 2 hours in a vacuum below orr3.
It was made into a regular hexagonal multicore composite of 46+005 m. Next, add 126 pieces of this method cover, and 9 pieces as shown in Figure 6.
Opposite distance 3.46 + o, os with Nb PVD (ion blating) layer 24 of 6 μm thickness provided on the surface
Separately manufacture the regular hexagonal OFC (oxygen-free steel) rod 23,
As shown in Figure 5, the 61 pieces have an outer diameter of 890 m and an inner diameter of 6.
Inside the 1.5 m Cu-2ONi alloy tube 22, OF
The G rod was arranged in the center and the -order multicore composite 21 was arranged around it, and the mixture was bundled and vacuum sealed to produce a billet for a second order multicore composite.

- The billet was repeatedly extruded, drawn, and softened in the same manner as the billet for method covering, and a pseudo-composite wire rod with a final wire diameter of 0.15a was obtained.

As a result of observing the cross section of the wire rod through the above steps using a scanning electron microscope (SEM), as shown in FIG.
A secondary multicore composite 26 with a diameter of μm is evenly separated into a Cu-2ONi alloy matrix at intervals of 1.2 to 13 μm.

It was observed that they were arranged. In the same figure, 27 is the stabilizing material Cu, 2aji, its Nb coating layer, 29
27 and 28: Cu stabilizing materials provided with different diffusion barriers. FIG. 8 schematically shows a further enlarged observation of the cross section of the secondary composite 26, showing the Al-47Ge alloy 19 and Nb17 with a diameter of 0.4 μm according to the planned specifications.
It was observed that the annular layer was embedded in the rCu-2ONi alloy base material (matrix) with a spacing of about 0.2 μm, and it was confirmed that the cross-sectional structure of the ultrafine multifilamentary wire was maintained.

After confirming the above, he cut the wire to the required length.

He twisted it to 15cm using a wire twisting machine, heated it to 960℃ in a vacuum of 10-' Torr or less using a vacuum furnace, kept it at the same temperature for 24 hours, and then left it in a vacuum at room temperature. Naturally cooled until

(3) Results of another SEM observation of the strands that were subjected to diffusion heat treatment beyond confirmation of superconductivity.

As shown in Figure 9, single-core composite Al-47Ge alloy/
Both the Nb annular layer and the boundary 30 of the single-core composite Mad Vx are dissolved, and Nb, (Al
, Ge) The arrangement of the filament conductors 31, which appears to be a compound, was confirmed.

Next, in order to clarify the superconducting properties of this conductor wire, a wire sample of about 50 cm was cut.

4. Solder the voltage lead and current lead to the sample end.
The critical current Ic at temperatures ranging from 2K to a maximum of 17K was measured by a four-terminal resistance method.

For Ic, increase the sample current in a steady magnetic field applied perpendicular to the wire, chart the current vs. voltage curve, and
l All of the 47Ge alloy is Nb.

(A4 Ge) It is assumed that the phase has transformed into a compound,
The resistivity is 10Ω when converted to the total cross-sectional area S of the filament.
Let the current equal to m be Ic.

The critical current density Jc was the value obtained by dividing Ic by S.

Results of measurements with various temperature T and magnetic field H.

The critical temperature Tc of this conductor is 21. OK, critical magnetic field Hc+ is 41.0T (42K), Jc is 1980A/- (4,
2, l0T) and 205A/-(4,2, 17
T).

As described above, it has been revealed that the prototype wire has sufficient superconducting properties comparable to Nb, Al, or Nb5Ge conductors. At the same time, it was confirmed that this manufacturing method has no problems as a means of mass-producing superconducting wires.

〔Effect of the invention〕

In order to be able to manufacture AC ultrafine multifilamentary wires made of Nb, Al or Nb s Ge compound superconductors using current industrial production methods based on composite/diffusion methods, it is necessary to use Al or Ge as the core material. The deformation resistance, that is, the hardness and tensile strength of
Modified to properties corresponding to those of b and Cu-Ni alloy,
It is necessary to obtain extremely short diffusion pairs. However, when these metal elements are in a highly pure state, it is impossible to modify them by general methods except for special methods such as irradiation.

Therefore, the core material of Al, which is advantageous in terms of cost compared to +Ge, is
- By replacing the core material with 47Ge binary alloy and utilizing its hardness and brittleness, the tensile strength can be increased to 14#f/
- Based on the fact that the hardness can be improved to Hv 80 while maintaining the same, Al-47Ge/Nb/Cu-2ONi
Cold extrusion and wire drawing of a three-layer alloy composite were attempted. As a result, it has become possible to industrially produce ultra-fine multifilamentary wires essential for alternating current applications in Nb=(A4Ge) superconductors.

[Brief explanation of the drawing]

Figure 1 shows Al-
Conceptual diagram of grain refinement mechanism of 47Ge alloy, Figure 2 is Al-4
A diagram showing the relationship between cold working rate and hardness of 7Ge alloy + N b r Cu-20N i alloy and Al, Figure 3 is a single core composite whose diameter was reduced into a regular hexagonal bar using a modified drawing roller die. Fig. 4 is a cross-sectional schematic diagram of a billet for method encasing in which 61 single-core composites are filled in a Cu-2ONi alloy tube, and Fig. 5 is a cross-sectional diagram of a billet for method encasing in which 61 single-core composites are filled in a Cu-2ONi alloy tube.
-A schematic cross-sectional view of a billet for a secondary composite filled with 2ONi alloy tubes, Figure 6 is a cross-sectional view of a regular hexagonal bar Cu stabilizing material before processing into a secondary composite, and Figure 7 is a cross-sectional view of the secondary composite billet. A diagram partially showing the aggregate arrangement of the primary composite and the stabilizing material,
Fig. 8 is a schematic cross-sectional view of a single-core composite in a primary composite embedded in a secondary composite, and Fig. 9 shows that the single-core composite has been converted into an N bs (Al, Ge) compound by diffusion heat treatment. Schematic cross-sectional diagram when changed to a single layer) A3゜ 5... Billet, 6... Core material, 7... Pure Nb tube, 8... Cu 2ONi alloy tube, 9... Lid, 10・
・Container, 11... Stem, 12... Dice, 1
3... Core material crushing area. 14--Crushing area of core material, 15-Al-Ge alloy Nb
/Cu-Ni alloy three-layer structure single-core composite, 21... Multi-core composite with regular hexagonal cross section processed by roller tice drawing. 31...Nb, (Al, Ge) compound-based superconductor.

Claims (1)

[Claims] When producing a three-layer single-core composite composed of Al-Ge alloy/pure Nb/Cu-Ni alloy or a multi-core composite made of these, 62 to 38 Wt. %Al-
38-62Wt. A method for producing a superconducting wire by cold extrusion and drawing with the introduction of an alloy having a composition of %Ge, characterized in that an Al-Ge alloy having the above composition is used as a core material.