Magnesium diboride superconducting flat wire and preparation method thereof

Abstract

The invention belongs to the technical field of superconducting wires, and discloses a magnesium diboride superconducting flat wire and a preparation method thereof. Comprising the following steps: S1, selecting a copper slot wire and an MgB2 round wire machined part; s2, tin plating is conducted on the copper slot line, then the copper slot line passes through a U-shaped slot mold, and a soft thin-wall copper slot line is obtained; s3, the soft-state thin-wall copper slot line and the MgB2 round line pass through a rectangular mold at the same time, cold machining combination is conducted, and the MgB2 tinned flat wire of the nested structure is obtained; s4, respectively carrying out surface polishing and tin stripping links on the MgB2 tin-plated flat wire with the nested structure, and only reserving a tin-plated layer in a groove to obtain an MgB2 tin-stripped flat wire; and S5, winding the MgB2 tin-removed flat wire on a steel wheel, and carrying out heat treatment in a heat treatment furnace to obtain the MgB2 superconducting flat wire. The problem that an MgB2 superconducting flat wire is not resistant to bending and poor in mechanical property is effectively solved, and good current-carrying performance can still be kept after repeated winding.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting wires and relates to a magnesium diboride superconducting flat wire and a preparation method thereof. Background Art

[0002] Magnesium diboride (MgB2) is a high-temperature superconductor discovered in 2001. It has the advantages of high critical temperature (39K), simple chemical composition and structure, no weak connection at grain boundaries, low material cost, and excellent processing performance. Based on the refrigeration cost and raw material cost of MgB2 superconducting wire, it is found that it has obvious price advantages in the refrigerator and liquid hydrogen temperature range (10~20K) and low field (1~5T) conditions. It is mainly used in nuclear magnetic resonance imaging systems (MRI), special cables, wind turbines, superconducting energy storage and other fields.

[0003] Since MgB2 superconducting wire is a ceramic structural material, manufacturing a bendable and durable MgB2 superconducting wire faces great challenges. At the same time, MgB2 superconducting wire has poor mechanical properties and is easily affected by external forces in practical applications, resulting in unstable mechanical properties.

[0004] In view of the problem that MgB2 superconducting wire is not resistant to bending and has poor mechanical properties, MgB2 superconducting wire usually uses high-strength and high-toughness CuNi alloy as the matrix to reduce the risk of fracture during stretching and bending. On this basis, if we refer to the nested structure of Wire in channel NbTi superconducting wire (WIC wire for short) used in MRI, and add a copper protective layer to the outside of MgB2 superconducting wire and then perform reaction heat treatment, the obtained MgB2 superconducting wire is a flat wire. Without turning over and passing through a small-diameter guide wheel, the brittle MgB2 superconducting phase will not be broken during the winding process, and then the MgB2 superconducting flat wire can be subjected to eddy current flaw detection, insulation braiding and other links after reaction heat treatment, ensuring the reliable quality of the wire used to wind the magnet.

[0005] However, in the above process, the MgB2 superconducting flat wire is a CuNi alloy matrix. When the Ni content is high, the chemical affinity between the CuB2 superconducting flat wire and the tin is poor. If the traditional dip soldering process is used, there are many cold soldering defects and the solder filling is poor, so the dip soldering method cannot be used for production. Therefore, it is necessary to improve the technical defects of the process and prepare a MgB2 superconducting flat wire with good bending resistance and mechanical properties. Summary of the invention

[0006] In order to produce a MgB2 superconducting flat wire that is resistant to bending and has excellent mechanical properties, the present invention uses a copper slot wire that is tinned and then combined with a MgB2 round wire by cold working, and then removes the surface tin layer by tin stripping, leaving only the tin layer in the slot. During the reaction heat treatment process, the soft thin-walled copper slot wire and the CuNi matrix in the MgB2 round wire diffuse with each other, and the surface tin layer of the soft thin-walled copper slot wire is used as a diffusing agent to achieve a stable combination of the two, thereby obtaining a MgB2 superconducting flat wire. Based on this technical route, the present invention provides the following technical solutions: The present invention provides a method for preparing a MgB2 superconducting flat wire, the method comprising: S1. Select copper slot wire and MgB2 round wire processing parts; S2. The copper slot wire is tinned and then passed through a U-shaped slot die to obtain a soft thin-walled copper slot wire; S3. The soft thin-walled copper slot wire and the MgB2 round wire are simultaneously passed through a rectangular die and cold worked to obtain a nested structure MgB2 tinned flat wire; S4. The nested structure MgB2 tinned flat wire is subjected to surface polishing and tin stripping steps, respectively, leaving only the tinned layer in the groove to obtain MgB2 tin stripping flat wire; S5. Winding the MgB2 detinned flat wire on a steel wheel, placing it in a heat treatment furnace for heat treatment, and obtaining a MgB2 superconducting flat wire.

[0007] Furthermore, in S2 of the above method, the tinning temperature is 400-500° C., and the speed is 70-120 m / min.

[0008] Furthermore, in S2 of the above method, the wall thickness of the soft thin-walled copper slot line is ≥0.25 mm.

[0009] Furthermore, in S3 of the above method, the processing rate of cold working is 10-15%.

[0010] Furthermore, in S4 of the above method, the polishing conditions are: polishing with a copper fiber polishing wheel with a diameter of 50-80 mm and a polishing wheel speed of 15000-20000 r / min.

[0011] Furthermore, in S4 of the above method, the tin stripping conditions are: nitric acid-based tin stripping liquid, the tin stripping liquid temperature is 40-50°C, the wire immersion length in the tin stripping liquid is 30m, and the wire running speed is 60-80m / min.

[0012] Furthermore, in S5 of the above method, the MgB2 detinning flat wire must not turn over when it is wound on the steel wheel, and the diameter of the steel wheel is greater than 200 mm.

[0013] Furthermore, in S5 of the above method, the MgB2 detinning flat wire is heat treated under a protective atmosphere, wherein the protective atmosphere is argon.

[0014] Furthermore, in S5 of the above method, the heat treatment conditions are: heat treatment at 500-700° C. for 5-15 hours.

[0015] The present invention also claims protection for the MgB2 superconducting flat wire obtained by the above preparation method.

[0016] Compared with the prior art, the present invention "a magnesium diboride superconducting flat wire and a preparation method thereof" has at least the following beneficial effects: In the method for preparing the MgB2 superconducting flat wire provided by the present invention, the soft thin-walled copper groove wire described in S2 can ensure that it is fully combined with the MgB2 round wire in S3. The reason is that the MgB2 round wire matrix is ​​a CuNi alloy with a relatively large overall hardness, and the soft thin-walled copper groove wire prepared in S2 reduces the difficulty of cold working the two.

[0017] The present invention provides a method for preparing a MgB2 superconducting flat wire, in which a copper slot wire is tinned so that a thin tinned layer is obtained on its surface, and the tinned layer is used as a diffusant to accelerate the diffusion reaction between the copper slot wire and the CuNi matrix of the MgB2 round wire, thereby facilitating stable bonding of the copper slot wire and the MgB2 round wire within a relatively short reaction heat treatment time (500-700°C, 5-15h).

[0018] In the method for preparing the MgB2 superconducting flat wire provided by the present invention, the nested structure MgB2 tin-plated flat wire is subjected to tin removal treatment in S4, thereby avoiding the problem of mutual adhesion between the wound wires due to tin diffusion during the reaction heat treatment in S5.

[0019] The preparation method of the MgB2 superconducting flat wire provided by the present invention requires that the front and back sides of the wire be oriented in the same direction as that when the magnet is finally wound, without flipping, thereby avoiding the superconducting phase being broken and the performance being reduced due to the need to flip the front and back sides of the wire when rewinding after the brittle MgB2 superconducting phase is formed.

[0020] The invention effectively solves the problem of poor bending resistance and mechanical properties of MgB2 superconducting flat wire, and achieves good current carrying performance after repeated winding, and there is no gap between the soft thin-wall copper slot wire and the MgB2 round wire, and the combination is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A cross-sectional view of a copper slot line.

[0022] Figure 2 This is a cross-sectional view of a nested MgB2 tinned flat wire.

[0023] Figure 3 This is the flat line chart of MgB2 tin stripping.

[0024] Figure 4 This is a cross-sectional view of a MgB2 superconducting flat wire. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The embodiment of the present invention provides a method for preparing a MgB2 superconducting flat wire, the method comprising: S1. Select copper groove wire and MgB2 round wire processing parts; the cross section of the copper groove wire is as follows Figure 1 shown.

[0027] S2. Tinning the copper slot wire and then passing it through a U-shaped slot die to obtain a soft thin-walled copper slot wire.

[0028] S3. The soft thin-walled copper groove wire and the MgB2 round wire are simultaneously passed through a rectangular die and cold worked to obtain a nested structure MgB2 tinned flat wire; the nested structure MgB2 tinned flat wire cross section is as Figure 2 shown.

[0029] S4. The nested structure MgB2 tinned flat wire is subjected to surface polishing and tin stripping steps, respectively, and only the tinned layer in the groove is retained to obtain MgB2 tin stripping flat wire; the MgB2 tin stripping flat wire is as Figure 3 shown.

[0030] S5. The MgB2 flat wire is wound on a steel wheel and placed in a heat treatment furnace for heat treatment to obtain a MgB2 superconducting flat wire; the cross section of the MgB2 superconducting flat wire is as follows. Figure 4 shown.

[0031] Illustratively, in S2 of the above method, the tinning temperature is 400-500° C., and the speed is 70-120 m / min.

[0032] Exemplarily, in S2 of the above method, the wall thickness of the soft thin-walled copper slot line is ≥0.25 mm.

[0033] Exemplarily, in S3 of the above method, the processing rate of cold working combination is 10-15%.

[0034] Illustratively, in S4 of the above method, the polishing conditions are: polishing with a copper fiber polishing wheel with a diameter of 50-80 mm and a polishing wheel speed of 15000-20000 r / min.

[0035] Exemplarily, in S4 of the above method, the tin stripping conditions are: nitric acid-based tin stripping liquid, the tin stripping liquid temperature is 40-50° C., the wire immersion length in the tin stripping liquid is 30 m, and the wire running speed is 60-80 m / min.

[0036] For example, in S5 of the above method, the MgB2 detinning flat wire must not turn over when it is wound on the steel wheel, and the diameter of the steel wheel is greater than 200 mm.

[0037] Illustratively, in S5 of the above method, the heat treatment is performed under a protective atmosphere, and the protective atmosphere is argon.

[0038] Illustratively, in S5 of the above method, the heat treatment conditions are: heat treatment at 500-700° C. for 5-15 hours.

[0039] Example 1 This embodiment provides a method for preparing a MgB2 superconducting flat wire.

[0040] S1. Select copper groove wire and MgB2 round wire processing parts; in this embodiment, the copper groove wire width is 2.6mm, height is 2.0mm, and groove width is 1.4mm; the diameter of MgB2 round wire is 1.45mm.

[0041] S2. The copper slot wire selected in S1 is first passed through flux, then immersed in a 500°C tin bath for tinning at a tinning speed of 120m / min, and then passed through a U-shaped slot mold with a width of 2.4mm, a height of 1.85mm, and a slot width of 1.5mm to obtain a soft thin-walled copper slot wire with a wall thickness of 0.35mm.

[0042] S3. The soft thin-walled copper slot wire and the MgB2 round wire are simultaneously passed through a rectangular die with a width of 2.24 mm and a height of 1.73 mm for cold working and combining. The cold working and combining processing rate is 14.5%, and a nested structure MgB2 tinned flat wire is obtained.

[0043] S4. The nested structure MgB2 tinned flat wire is subjected to surface polishing and tin stripping steps respectively, so that the surface of the wire is completely stripped of tin, and only the tinned layer in the groove is retained to obtain the MgB2 tin stripped flat wire. In this step, the polishing conditions are: polishing with a copper fiber polishing wheel with a diameter of 80 mm, and the polishing wheel speed is 20000r / min. Tin stripping conditions: nitric acid-based tin stripping liquid, the tin stripping liquid temperature is 50°C, the wire is immersed in the tin stripping liquid for 30m, and the wire running speed is 80m / min.

[0044] S5. The MgB2 detinning flat wire is wound on a steel wheel with a diameter of 350 mm, and the MgB2 detinning flat wire is not turned over during the winding process; then placed in a heat treatment furnace, and heat treated under an argon protective atmosphere. The treatment conditions are: heat treatment at 700°C for 15 hours to obtain the MgB2 superconducting flat wire.

[0045] Example 2 This embodiment provides a method for preparing a MgB2 superconducting flat wire.

[0046] S1. Select copper groove wire and MgB2 round wire processing parts; in this embodiment, the copper groove wire width is 1.65mm, height is 1.25mm, and groove width is 0.82mm; the diameter of MgB2 round wire is 0.88mm.

[0047] S2. The copper slot wire selected in S1 is first passed through flux, then immersed in a 400°C tin bath for tinning at a tinning speed of 70m / min, and then passed through a U-shaped slot mold with a width of 1.55mm, a height of 1.15mm, and a slot width of 0.9mm to obtain a soft thin-walled copper slot wire with a wall thickness of 0.25mm.

[0048] S3. The soft thin-walled copper slot wire and the MgB2 round wire are simultaneously passed through a rectangular die with a width of 1.45 mm and a height of 1.08 mm for cold working and bonding. The cold working bonding processing rate is 13.8%, and a nested structure MgB2 tinned flat wire is obtained.

[0049] S4. The nested structure MgB2 tinned flat wire is subjected to surface polishing and tin stripping steps respectively, so that the surface of the wire is completely stripped of tin, and only the tinned layer in the groove is retained to obtain the MgB2 tin stripped flat wire. In this step, the polishing conditions are: polishing with a copper fiber polishing wheel with a diameter of 50 mm, and the polishing wheel speed is 15000r / min. Tin stripping conditions: nitric acid-based tin stripping liquid, the tin stripping liquid temperature is 40°C, the wire is immersed in the tin stripping liquid for 30m, and the wire running speed is 60m / min.

[0050] S5. Wind the MgB2 detinning flat wire on a steel wheel with a diameter of 200 mm, and the MgB2 detinning flat wire does not turn over during the winding process; then place it in a heat treatment furnace and perform heat treatment under an argon protective atmosphere. The treatment conditions are: heat treatment at 550°C for 5 hours to obtain the MgB2 superconducting flat wire.

[0051] Example 3 This embodiment provides a method for preparing a MgB2 superconducting flat wire.

[0052] S1. Select copper groove wire and MgB2 round wire processing parts; in this embodiment, the copper groove wire width is 2.05mm, height is 1.52mm, and groove width is 1.03mm; the diameter of the MgB2 round wire is 1.08mm.

[0053] S2. The copper slot wire selected in S1 is first passed through flux, then immersed in a 450°C tin bath for tinning at a tinning speed of 100 m / min, and then passed through a U-shaped slot mold with a width of 1.9 mm, a height of 1.4 mm, and a slot width of 1.12 mm to obtain a soft thin-walled copper slot wire with a wall thickness of 0.28 mm.

[0054] S3. The soft thin-walled copper slot wire and the MgB2 round wire are simultaneously passed through a rectangular die with a width of 1.78 mm and a height of 1.32 mm for cold working and combining. The processing rate of the cold working and combining is 13.2%, and a nested structure MgB2 tinned flat wire is obtained.

[0055] S4. The nested structure MgB2 tinned flat wire is subjected to surface polishing and tin stripping steps respectively, so that the surface of the wire is completely stripped of tin, and only the tinned layer in the groove is retained to obtain the MgB2 tin stripped flat wire. In this step, the polishing conditions are: polishing with a copper fiber polishing wheel with a diameter of 65mm, and the polishing wheel speed is 18000r / min. Tin stripping conditions: nitric acid-based tin stripping liquid, the tin stripping liquid temperature is 50°C, the wire is immersed in the tin stripping liquid for 30m, and the wire running speed is 75m / min.

[0056] S5. Wind the MgB2 detinning flat wire on a steel wheel with a diameter of 300 mm, and the MgB2 detinning flat wire does not turn over during the winding process; then place it in a heat treatment furnace and perform heat treatment under an argon protective atmosphere. The treatment conditions are: heat treatment at 630°C for 12 hours to obtain the MgB2 superconducting flat wire.

[0057] Example 4 This example describes the performance test of the MgB2 superconducting flat wires prepared in Examples 1 to 3, including critical current (Ic value) and cross-sectional observation.

[0058] 1.Ic value The Ic value test of the MgB2 superconducting flat wire prepared in Examples 1 to 3 is as follows: 1) Take the MgB2 superconducting flat wire obtained in S5 and name it "superconducting wire-1"; 2) Take the MgB2 superconducting flat wire obtained from S5 and repeat winding it on the steel wheel twice before sampling. The wire is not turned over during the winding process. The diameter of the winding steel wheel is the same as that of S5 and is named "superconducting wire-2". 3) The "superconducting wire-2" sample was wound twice more and then sampled without turning over during the winding process. The diameter of the winding steel wheel was the same as S5 and it was named "superconducting wire-3".

[0059] 4) The Ic values ​​(4.2K, 3T) of the “superconducting wire-1”, “superconducting wire-2” and “superconducting wire-3” samples were measured respectively. The results are shown in Table 1.

[0060] Table 1. Ic values ​​of MgB2 superconducting flat wires prepared in Examples 1 to 3 (4.2K, 3T)

[0061] It can be seen from Table 1 that in Examples 1 to 3, the Ic values ​​of the samples "superconducting wire-1", "superconducting wire-2" and "superconducting wire-3" are basically the same, indicating that the current carrying capacity of the MgB2 superconducting flat wire is stable, and it can still maintain good wire performance after repeated winding, and it is resistant to bending and has good mechanical properties.

[0062] 2. Cross-sectional observation In addition, the cross sections of the samples of each embodiment were cut to observe whether there was no gap between the soft thin-walled copper groove wire and the MgB2 round wire. By observing the cross sections of the MgB2 superconducting flat wires prepared in Examples 1 to 3, it was confirmed that there was no gap between the soft thin-walled copper groove wire and the MgB2 round wire, and the combination was stable.

[0063] In summary, the preparation method of the MgB2 superconducting flat wire provided by the present invention is to tin the copper slot wire and then cold-process and combine it with the MgB2 round wire, and then remove the surface tin layer by tin stripping, leaving only the tin layer in the slot. In the subsequent reaction heat treatment process, the soft thin-walled copper slot wire and the CuNi matrix in the MgB2 round wire diffuse with each other. Since the Ni content in the CuNi matrix is ​​high and the reaction time is short (500~700℃, 5~15h), the surface tin layer of the soft thin-walled copper slot wire is used as a diffusant, which can achieve a stable combination of the two and obtain a MgB2 superconducting flat wire with stable current-carrying performance. It has been verified that the present invention effectively solves the problems of the MgB2 superconducting flat wire's poor bending resistance and mechanical properties, and achieves that it can still maintain good current-carrying performance after repeated winding, and there is no gap between the soft thin-walled copper slot wire and the MgB2 round wire, and the combination is stable.

[0064] The embodiments described above are only some embodiments of the present invention, not all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but only represents selected embodiments of the present invention. All other embodiments obtained without creative work and related deductions and substitutions made by ordinary technicians in the field under the conditions of the concept of the present invention belong to the scope of protection of the present invention.

Claims

1. A method for preparing a MgB2 superconducting flat wire, characterized in that: The method comprises: S1. Select copper slot wire and MgB2 round wire processing parts; S2. The copper slot wire is tinned and then passed through a U-shaped slot die to obtain a soft thin-walled copper slot wire; S3. The soft thin-walled copper slot wire and the MgB2 round wire are simultaneously passed through a rectangular die and cold worked to obtain a nested structure MgB2 tinned flat wire; S4. The nested structure MgB2 tinned flat wire is subjected to surface polishing and tin stripping steps, respectively, leaving only the tinned layer in the groove to obtain MgB2 tin stripping flat wire; S5. Winding the MgB2 detinned flat wire on a steel wheel, placing it in a heat treatment furnace for heat treatment, and obtaining a MgB2 superconducting flat wire.

2. The preparation method according to claim 1, characterized in that: In S2, the tinning temperature is 400~500℃ and the speed is 70~120m / min.

3. The preparation method according to claim 1, characterized in that: In S2, the wall thickness of the soft thin-walled copper slot line is ≥0.25 mm.

4. The preparation method according to claim 1, characterized in that: In S3, the processing rate of cold working is 10~15%.

5. The preparation method according to claim 1, characterized in that: In S4, the polishing conditions are: polishing with a copper fiber polishing wheel with a diameter of 50~80mm and a polishing wheel speed of 15000~20000r / min.

6. The preparation method according to claim 1, characterized in that: In S4, the tin stripping conditions are: nitric acid-based tin stripping solution, the tin stripping solution temperature is 40~50℃, the wire immersion length in the tin stripping solution is 30m, and the wire running speed is 60~80m / min.

7. The preparation method according to claim 1, characterized in that: In S5, the MgB2 detinning flat wire must not turn over when it is wound on the steel wheel, and the diameter of the steel wheel is greater than 200 mm.

8. The preparation method according to claim 1, characterized in that: In S5, the MgB2 detinned flat wire is heat treated under a protective atmosphere, wherein the protective atmosphere is argon.

9. The preparation method according to claim 1, characterized in that: In S5, heat treatment conditions: heat treatment at 500~700℃ for 5~15h.

10. MgB2 superconducting flat wire prepared by the preparation method according to claim 1.

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