JP4742843B2 - Core wire for Nb3Sn superconducting wire, Nb3Sn superconducting wire, and manufacturing method thereof - Google Patents

Description

The present invention relates to Nb 3 _Sn superconducting wire core, Nb 3 _Sn superconducting wire and a manufacturing method thereof for use in a superconducting magnet or the like for generating a high magnetic field of more than 9T.

The Nb ₃ Sn superconducting wire is a typical superconducting wire used in almost all superconducting magnets that generate a magnetic field of 9 T or more.

As typical production methods nb 3 _Sn superconducting wire includes the following four methods.

(1) Bronze method In this method, Nb or an Nb alloy core and a Cu—Sn (bronze) matrix are combined to form an ultrafine multi-core, and heat treatment is performed to diffuse Sn in the bronze to the Nb core to form Nb ₃ Sn. It is also possible to make the final filament diameter a uniform submicron order, which is advantageous in reducing AC loss (for example, see Patent Document 1).

(2) Sn internal diffusion method A number of ultrafine Nb cores are arranged in the Cu matrix, and the Sn cores are arranged dispersed in the center of the wire or a plurality of wires, and heat treatment is performed to diffuse Sn into the Nb cores through the Cu matrix. This is a manufacturing method of Nb ₃ Sn. A wire having a high critical current density (Jc) can be produced at low cost (for example, see Patent Document 2).

(3) Powder method Nb powder and Sn powder are mixed, filled into an Nb pipe or the like to form a single core wire, a plurality of bundles are combined into a multi-core wire, and then heat treatment is performed to react Sn and Nb to form Nb ₃ The manufacturing method is Sn (see, for example, Patent Document 3). In addition, as a related manufacturing method, Ta-Sn intermetallic compound powder is filled in an Nb pipe to form a single core wire, a plurality of bundles are combined into a multi-core wire, and then heat treatment is performed to diffuse Sn into Nb. There is also a manufacturing method using ₃ Sn. This method has an advantage that Jc is high in a high magnetic field of 15 T or more.

(4) Nb tube method An Sn rod coated with Cu is accommodated in the Nb tube, and the outer surface of the Nb tube is coated with a Cu tube to form a single-core wire. Is diffused to Nb through a Cu matrix to form Nb ₃ Sn. There is an advantage that a wire having a high critical current density ( _Jc ) can be manufactured at low cost (for example, see Patent Document 4).
JP 2004-342561 A JP 2004-171829 A JP 2005-32631 A JP 2005-93235 A

However, the method described above has the following problems.
First, in the bronze method of (1), when the bronze is repeatedly drawn, it is work hardened to cause disconnection and the like, and the wire drawing becomes impossible. Accordingly, it is necessary to perform an intermediate heat treatment every several passes in the middle of wire drawing to remove and soften the bronze processing distortion, which increases the manufacturing cost and the manufacturing time. In order to achieve a high critical current density (Jc), it is necessary to increase the Sn concentration in the bronze to near the solid solution limit (15.8 wt%) or higher. As a result, the number of intermediate heat treatments is further increased, which further increases the cost and the risk of disconnection.

  Next, the Sn internal diffusion method (2) does not require an intermediate heat treatment like the bronze method, and thus can be manufactured at low cost, and the amount of Sn can be adjusted relatively easily. It is also advantageous for Jc conversion. However, since it is disadvantageous for making the filament extremely thin so that the filament diameter is about 50 μm or less, it is difficult to reduce the AC loss. Moreover, since the position where Sn originally existed after Sn diffusion becomes a gap, the mechanical strength of the wire may be lowered depending on the cross-sectional configuration. Moreover, since Sn having a melting point of 232 ° C. is included, if the extrusion ratio is excessively high (that is, if it is pressed too thinly) in extrusion or the like, even if cold extrusion, Sn melts due to processing heat, resulting in uneven processing. There is a possibility of becoming.

Further, in the powder method (3), because of powder filling, it is difficult to make a very large number of filaments extremely fine in both the cross section and the length direction. In particular, since it is difficult to reduce the filament diameter to about 50 μm or less, the filament diameter becomes large and it is difficult to reduce AC loss. In addition, when the filament diameter is not uniform in the length direction, the current attenuation in the permanent current mode when the magnet is used is increased, which is disadvantageous for a magnet that generates a uniform magnetic field such as NMR. Moreover, since the filament is thick, the wire after the Nb ₃ Sn generation heat treatment is vulnerable to strain such as bending.

Furthermore, in the Nb tube method of (4), the final filament diameter is limited to about 10 to 20 μm and cannot be made as thin as the bronze method, but it is not as thick as the internal diffusion method and powder method, so the AC loss is relatively reduced. Is possible. However, if the amount of Sn in the Nb tube is increased to further increase the Jc, the workability deteriorates and it becomes impossible to process, so it becomes difficult to increase the Jc due to the workability. Moreover, since Sn having a low melting point is compounded as in the case of the internal diffusion method, it cannot be extruded at a large extrusion ratio. In addition, voids may occur at the position where Sn originally exists inside the Nb ₃ Sn filament generated in a ring shape, and there is a problem in the mechanical strength of the wire.

Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, can be manufactured at low cost using conventional superconducting wire processing equipment, can achieve a high critical current density, is resistant to strain, and has high mechanical strength. excellent _Nb 3 Sn superconducting wire core also is to provide a _Nb 3 Sn superconducting wire and a manufacturing method thereof.

To achieve the above object, Nb ₃ Sn superconducting wire core of the present invention, the inside of the Nb tube or Nb alloy tube, have a Cu coating or Cu-based alloy coating and, Zn concentration is more than 12 wt% 40 wt% A Sn-Zn alloy rod having a total concentration of Sn and Zn of 95 wt% or more is accommodated while a Cu layer or a Cu base alloy layer is formed on the outside of the Nb tube or Nb alloy tube. It is characterized by that.

  A plurality of the single core wires may be dispersed between a Cu tube or a Cu base alloy tube and a Cu core or a Cu base alloy core to form a multi-core wire.

  In the Nb alloy tube, it is preferable that Nb includes one or more of Ti, Ta, Zr, V, and Hf in a total concentration of 5 at% or less.

In order to achieve the above object, Nb ₃ Sn superconducting wire of the present invention, the inside of the Nb tube or Nb alloy tube, have a Cu coating or Cu-based alloy coating and, Zn concentration is more than 12 wt% 40 wt% While containing a Sn—Zn alloy rod in which the total concentration of Sn and Zn is 95 wt% or more, a single core wire in which a Cu layer or a Cu base alloy layer is formed outside the Nb tube or Nb alloy tube Nb ₃ Sn is generated in the region of the Nb tube or the Nb alloy tube .

A multi-core wire in which a plurality of the single-core wires are dispersed between a Cu tube or a Cu-based alloy tube and a Cu core or a Cu-based alloy core, and Nb in the region of the Nb tube or Nb alloy tube in the single-core wire. ₃ Sn may be generated .

  The Nb alloy tube preferably contains one or more of Ti, Ta, Zr, V, and Hf in Nb in a total concentration of 5 at% or less.

In order to achieve the above object, a manufacturing method of Nb ₃ Sn superconducting wire of the present invention, the inside of the Nb tube or Nb alloy tube, have a Cu coating or Cu-based alloy coating and, Zn concentration 12 wt% While containing a Sn—Zn alloy rod having a total concentration of Sn and Zn of 95 wt% or more, a Cu layer or a Cu base alloy layer is formed outside the Nb tube or Nb alloy tube. A single core wire is prepared, and the single core wire is thinned and cut into a fixed length, and then a plurality of the single core wires are dispersed between the Cu tube or the Cu base alloy tube and the Cu core or the Cu base alloy core. It is characterized in that it is combined to form a multi-core wire, and after thinning, heat treatment is performed to react Sn and Nb to generate Nb ₃ Sn.

In the heat treatment, a holding time including a temperature rising time in a temperature range of 230 ° C. or more and 520 ° C. or less is set to 10 hours or more, and a subsequent Nb ₃ Sn generation heat treatment temperature is set to 550 ° C. or more and 750 ° C. or less. preferable.

According to the present invention, a high critical current density can be achieved as compared with a conventional Nb tube method using a pure Sn core. Also, excellent strength of the wire after Nb 3 _Sn generation, a strong Nb 3 _Sn in the strain can be manufactured at low cost.

  Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows an example of a single core wire obtained by the production process of the Nb 3 _Sn superconducting wire according to the present invention.
This single-core wire accommodates a Sn—Zn alloy rod 3 having a Cu coating 2 inside the Nb tube 1, while forming a Cu layer 4 on the outside of the Nb tube 2.

(Nb tube)
The material of the Nb pipe 1 is preferably not only pure Nb but also an Nb alloy containing one or more of Ti, Ta, Zr, V, and Hf in a total concentration of 5 at% or less.
This is because the addition of Ti, Ta, etc. to Nb improves Jc, and the addition of Ta, Zr, V, Hf, etc. makes the Nb alloy crystal grains uniformly finer, so compared to pure Nb. This is because the shape of the filament can be maintained uniformly. However, if the added concentration exceeds 5 at%, the hardness of the alloy becomes hard, and the difference in hardness (mismatch) with the Sn—Zn alloy compounded in the Nb alloy tube becomes large, which causes uneven processing. .

(Sn—Zn alloy rod)
By adding Zn to Sn, the diffusion reaction of Sn into Nb can be promoted, which is advantageous from the viewpoint of increasing Jc.

  In the Sn—Zn alloy rod 3, the Zn concentration of the Sn—Zn alloy containing Sn and Zn as main components is preferably 12 wt% or more and 40 wt% or less, and the total concentration of Sn and Zn is 95 wt% or more. It is desirable.

The Zn concentration is set to 12 wt% or more when Sn is added to pure Sn having a melting point of 232 ° C. in the phase diagram of Sn and Zn shown in FIG. 2 (phase diagram). This is because the melting point becomes 198.5 ° C. which is the lowest, but if further added, the melting point becomes higher than the melting point of pure Sn at about 12 wt%. Further, the Zn concentration is set to 40 wt% or less, considering the molar ratio of Nb and Sn (3: 1), if Zn is added in a large amount exceeding 40 wt%, the Sn concentration decreases, so that Nb ₃ Sn formation This is because the amount of Sn necessary for the process becomes insufficient.

  As other additive elements, Bi, Al, Cu, Ag, and the like are conceivable from the condition that they are easily dissolved and do not extremely lower the melting point of the alloy. However, since there is a possibility that a compound having poor ductility is formed with either one of the main components, Sn and Zn, the addition concentration is preferably less than 5 wt%. Accordingly, the Sn—Zn alloy concentration is desirably 95 wt% or more.

(Nb ₃ Sn generation heat treatment process)
The single core wire is later subjected to heat treatment, and Nb ₃ Sn is generated by a reaction between Sn of the Sn—Zn alloy rod 3 and Nb of the Nb tube 1 in the single core wire.

In this Nb ₃ Sn generation heat treatment process, the holding time including the temperature rising time in the temperature range of 230 ° C. or more and 520 ° C. or less is 10 hours or more, and the subsequent Nb ₃ Sn generation heat treatment temperature is 550 ° C. or more. It is preferable to set it as 750 degrees C or less.

The reason for this is that a general Nb ₃ Sn generation heat treatment temperature is 600 ° C. or higher, but if the temperature is suddenly increased from room temperature to 600 ° C. or higher in a shorter time than the above time, the Sn—Zn portion becomes liquefied and the wire This is because there is a possibility of leakage from both terminals.
Furthermore, as a result of Nb diffusing into the liquefied Sn—Zn portion inside the cylindrical Nb or Nb alloy filament, Nb ₃ Sn is generated in an island shape and discontinuous in the wire length direction and the radial direction of the filament cross section. And the superconducting properties such as critical current values are degraded.

  Therefore, in order to prevent the above phenomenon, the time required for temperature rise (temperature rise time) at 230 ° C. or more near the melting point of Sn and 520 ° C. or less at which the ε phase in the Cu—Sn alloy is generated, or 230˜ By setting the holding time including the temperature rising time to 10 hours or more within the range of 530 ° C., a Cu—Sn—Zn alloy that does not liquefy even at around 600 ° C. can be obtained.

(Manufacturing process)
3 shows an example of a manufacturing process of the Nb 3 _Sn superconducting wire according to the present embodiment.
First, in order to produce the single core billet shown in FIG. 4, a Cu coating 12 having a diameter of 15 mm is placed in an Nb—Ta alloy tube 11 made of Nb-1 at% Ta having an inner diameter of 15.1 mm, an outer diameter of 22 mm, and a length of 150 mm. The applied Sn—Zn alloy rod 13 (the diameter of the Sn—Zn alloy rod 13 is 10.3 mm) is accommodated, and the outer periphery of the Nb—Ta alloy tube 11 is covered with a Cu tube 14 having an inner diameter of 22.1 mm and an outer diameter of 28 mm. Thus, a single-core billet 10 is obtained (step a in FIG. 3).

  After this single-core billet is hydrostatically extruded to a diameter of 12 mm at room temperature (step b), the wire drawing process is repeated (step c) to form a hexagonal cross-section single wire 20 having an opposite side distance of 1.1 mm as shown in FIG. (Step d).

After this single wire is straightened (step e), it is cut into a length of 150 mm to obtain a hexagonal cross-section single core wire (step f).
Next, as shown in FIG. 6, 85 Cu hexagonal wires 31 of the same size are bundled, 276 hexagonal cross-section single core wires 33 are bundled around it, and then placed in a Cu tube 35 having an inner diameter of 24 mm and an outer diameter of 28 mm. The multi billet 30 is stored (step g).

  This multi billet is extruded at a room temperature to a diameter of 12 mm by hydrostatic pressure (step h), and then the wire drawing is repeated (step i) to obtain a multi wire having a diameter of 1 mm (step j).

FIG. 7 shows a schematic structural diagram of this multi-line.
In this multi-wire 40, a hexagonal cross-section composite group 45 is formed between the Cu tube 41 and the Cu core 43, and the hexagonal cross-section composite group 45 is formed in order from the Sn-Zn alloy rod 51 to the Cu layer 53, A plurality of hexagonal bodies on which the Nb—Ta alloy layer 55 is formed are dispersed in the Cu matrix 47.

The multi-wire 40 is heated in multiple stages in an Ar atmosphere under the conditions of (415 ° C. × 10 h) + (515 ° C. × 5 h), and then heat-treated at 600 ° C. for 100 hours to generate Nb ₃ Sn (Step k).

(Effect in this embodiment)
(1) In the conventional manufacturing method, when processing is repeated, only Sn is softened, and other composites such as Nb and Cu are work-hardened, so that the difference in hardness becomes remarkable and non-uniform processing occurs. In this manufacturing method, the melting point of the Sn—Zn alloy is made higher than that of pure Sn by adjusting the Zn concentration, so that the melting and softening phenomenon of Sn due to the processing heat can be prevented, and uniform processing becomes possible. .
(2) In the conventional manufacturing method, there is a limit value in the amount of Sn that can be accommodated in the Nb pipe from the viewpoint of workability, and Sn required for Nb: Sn = 3: 1 could not be supplied. Even if a part of Sn becomes Zn, the amount of Sn · Zn itself can be increased, and as a result, more Sn can be supplied compared to pure Sn.
(3) Since a core made of a Cu—Zn alloy (brass) having a relatively high Zn concentration remains inside the ring-shaped Nb ₃ Sn layer after the heat treatment, it is effective as a reinforcing material for the ring-shaped Nb ₃ Sn filament. As a result of the function and increased mechanical strength, a high-strength Nb ₃ Sn wire that can withstand electromagnetic force even when wound on a magnet is obtained.
(4) In terms of cost, both Sn and Zn are inexpensive metals, and it is possible to manufacture a wire with a filament diameter of 10 μm without increasing the cost compared to the conventional internal diffusion method or the like. In addition, no intermediate heat treatment like the bronze method is necessary.
(5) A high critical current density can be achieved as compared with the Nb tube method using a conventional pure Sn core. In addition, the strength of the wire after the generation of Nb ₃ Sn can also be increased by the Cu—Zn alloy inside the Nb ₃ Sn filament, and Nb ₃ Sn that is resistant to strain can be manufactured at low cost.

Nb ₃ Sn superconducting wires were prepared according to the process diagram shown in FIG. 3 with the Zn concentration of the Cu-coated Sn—Zn alloy rods set to five types of 0 (pure Sn), 10, 20, 30, and 40 wt%.

The surface temperature of the extruded material immediately after hydrostatic pressure extrusion processing of the multi billet (step h) was increased to about 150 ° C. by the processing heat. It is considered that the temperature inside the extruded material is further increased. Thereafter, the wire drawing process (step i) was repeated to obtain a multi-wire having a diameter of 1 mm. FIG. 8 shows a cross-sectional photograph of this multi-line.
According to this production method, work hardening does not occur even when processing is repeated as in the bronzing method, and therefore, wire drawing can be performed to φ1 mm without intermediate heat treatment.

  Table 1 shows the measurement results of critical current (Ic) and n value at 12T of five types of wire rods with Sn concentration of Sn—Zn alloy rod (core) being 0 (pure Sn), 10, 20, 30, 40 wt%. Show. The n value corresponds to the slope of the log (I) -log (I) graph plotted logarithmically when a finite resistance occurs in the current (I) -voltage (V) characteristics of the superconducting wire, and the filament uniformity There is a correlation. A higher n value indicates that the filament is more uniform in the wire length direction, and a wire material having a higher n value can prevent the permanent current from being attenuated in the superconducting magnet operated in the permanent current mode.

  From the results of Table 1, Ic and n value have a correlation, and both are Sn-20, 30, 40, 10, 0 wt% in descending order, and the Sn-20 wt% Zn core showed the highest value. In the Sn-40 wt% Zn core wire, the Sn concentration was lowered, so that Ic was lowered. Further, the Sn-10, 0 wt% Zn core wire has a low Ic and n value, and it was found from the cross-sectional photograph observation that the non-uniform deformation and size of the filaments are not constant. As a result of the non-uniform cross section, the characteristics are considered to have deteriorated. The reason for this is that the processing heat at the time of extrusion reached around 200 ° C., so Sn or Sn-10 wt% Zn was softened, and the difference in hardness from NbTa became significant. It is thought that uniformity was further promoted.

  Next, Table 2 shows the results of a tensile test of the heat treated wire at room temperature.

From the results in Table 2, the breaking strength was Sn-40, 30, 20, 10, 0 wt% in descending order, and the tensile strength was also increasing in the descending order of Zn concentration. This is because the tensile strength of _Nb 3 Sn after generation in a ring shape _Nb 3 Cu-Zn alloy produced in Sn (brass) is presumably a result of increased with increasing Zn concentration.

It is sectional drawing which shows the single core wire which concerns on this embodiment. It is a phase diagram (phase diagram) of Sn and Zn. It is a manufacturing process diagram of the Nb 3 _Sn superconducting wire according to the present embodiment. It is sectional drawing which shows the single core billet which concerns on this embodiment. It is sectional drawing which shows the hexagonal cross-section single line which concerns on this embodiment. It is sectional drawing which shows the multi billet which concerns on this embodiment. It is a typical structure figure showing a multi line concerning this embodiment. It is a cross-sectional photograph of the multi-line | wire based on this embodiment, (a) is a whole photograph, (b) is a partial enlarged photograph.

Explanation of symbols

1 Nb tube 2, 12, 22 Cu coating 3, 13, 23 Sn-Zn alloy rod 4 Cu layer 10 Single core billet 11, 21 Nb-Ta alloy tube 14, 24, 35 Cu tube 20 Hexagonal cross section single wire 30 Multi billet 31 Cu hexagonal wire 33 Hexagonal cross-section single core wire 40 Multi-wire 41 Cu tube 43 Cu core 45 Hexagonal cross-section composite group 47 Cu matrix 51 Sn-Zn alloy rod 53 Cu layer 55 Nb-Ta alloy layer

Claims (8)

Inside the Nb tube or Nb alloy tube, it has a Cu coating or Cu-based alloy coating and, Zn concentration is less 12 wt% or more 40 wt%, the total concentration of Sn and Zn is more than 95 wt% Sn-Zn A core wire for a Nb ₃ Sn superconducting wire, wherein a single core wire is formed by forming a Cu layer or a Cu-based alloy layer outside the Nb tube or the Nb alloy tube while accommodating an alloy rod. The core wire for Nb ₃ Sn superconducting wire according to claim 1, wherein a plurality of the single core wires are dispersed between a Cu tube or a Cu base alloy tube and a Cu core or a Cu base alloy core. . _3. The Nb ₃ Sn superconductivity according to claim 1, wherein the Nb alloy tube contains one or more of Ti, Ta, Zr, V, and Hf in Nb in a total concentration of 5 at% or less. Wire core wire. Inside the Nb tube or Nb alloy tube, it has a Cu coating or Cu-based alloy coating and, Zn concentration is less 12 wt% or more 40 wt%, the total concentration of Sn and Zn is more than 95 wt% Sn-Zn While the alloy rod is accommodated , Nb ₃ Sn is generated in the region of the Nb tube or the Nb alloy tube in the single core wire in which the Cu layer or the Cu base alloy layer is formed outside the Nb tube or the Nb alloy tube. A Nb ₃ Sn superconducting wire, characterized in that A multi-core wire in which a plurality of the single-core wires are dispersed between a Cu tube or a Cu-based alloy tube and a Cu core or a Cu-based alloy core, and Nb in the region of the Nb tube or Nb alloy tube in the single-core wire. 5. The Nb ₃ Sn superconducting wire according to claim 4, wherein ₃ Sn is generated. 6. The Nb ₃ Sn superconductivity according to claim 4 , wherein the Nb alloy tube contains one or more of Ti, Ta, Zr, V, and Hf in Nb in a total concentration of 5 at% or less. line. Inside the Nb tube or Nb alloy tube, it has a Cu coating or Cu-based alloy coating and, Zn concentration is less 12 wt% or more 40 wt%, the total concentration of Sn and Zn is more than 95 wt% Sn-Zn While accommodating the alloy rod, on the outside of the Nb tube or Nb alloy tube, a Cu layer or a Cu-based alloy layer is formed to produce a single core wire, and the single core wire is thinned and cut into a standard length, then Cu A plurality of single core wires are dispersed and combined between a tube or a Cu-based alloy tube and a Cu core or a Cu-based alloy core to form a multi-core wire, and after thinning, heat treatment is performed to react Sn and Nb. _A method for producing a Nb ₃ Sn superconducting wire, characterized in that ₃ Sn is generated. In the heat treatment, a holding time including a temperature rising time in a temperature range of 230 ° C. or more and 520 ° C. or less is set to 10 hours or more, and a subsequent Nb ₃ Sn generation heat treatment temperature is set to 550 ° C. or more and 750 ° C. or less. The method for producing a Nb ₃ Sn superconducting wire according to claim 7,

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