Nb-Ti superconducting wire and method for manufacturing the same

Abstract

The application belongs to the technical field of superconducting wires and relates to a niobium-titanium superconducting wire and a preparation method thereof. The preparation method comprises the following steps: mixing, sintering, smelting and forging Nb powder, Ti powder and Ta powder to obtain an NbTiTa rod; electroplating an Nb layer on the surface of the NbTiTa rod to obtain an NbTiTa / Nb rod; loading the NbTiTa / Nb rod into a Cu tube to obtain an NbTiTa / Nb / Cu primary single-core ingot; loading multiple NbTiTa / Nb / Cu primary single-core ingots into a Cu tube to obtain an NbTiTa / Nb / Cu secondary composite wire; and twisting and stretching the NbTiTa / Nb / Cu secondary composite wire to obtain the niobium-titanium superconducting wire. The application solves the technical problem that the magnet is not stable and the critical current density is low when the niobium-titanium superconducting wire is in a high field (≥9T).

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire technology, and relates to a niobium-titanium superconducting wire and its preparation method. Background Technology

[0002] NbTi superconducting wires possess advantages such as good processing characteristics, stable superconducting properties, and relatively low price, making them widely used in low-field (<9T) superconducting magnets. With the advancement of magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) technologies, the demand for high-field (≥9T) superconducting materials with high critical current density is continuously increasing. Traditional fabrication processes for niobium-titanium superconducting wires are more suitable for preparing low-field (<9T) niobium-titanium superconducting materials. However, the critical current density of high-field (≥9T) niobium-titanium superconducting materials prepared using these processes is relatively low and cannot meet the requirements for magnet applications. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problem that niobium-titanium superconducting wires have insufficient magnet stability and low critical current density at high fields (≥9T).

[0004] To achieve the above objectives, the present invention provides a niobium-titanium superconducting wire and a method for preparing the same to meet this need in the art.

[0005] On one hand, the present invention relates to a method for preparing niobium-titanium superconducting wire, which includes: mixing, sintering, melting, and forging Nb powder, Ti powder and Ta powder to obtain NbTiTa rod;

[0006] An Nb layer is electroplated on the surface of the NbTiTa rod to obtain an NbTiTa / Nb rod;

[0007] The NbTiTa / Nb rod is inserted into a Cu tube, and after vacuuming, the upper and lower covers are sealed and welded to form a primary NbTiTa / Nb / Cu single-core ingot. The primary NbTiTa / Nb / Cu single-core ingot is then extruded, stretched, and peeled to obtain an NbTiTa / Nb / Cu single-core rod.

[0008] Multiple NbTiTa / Nb / Cu single-core ingots are loaded into a Cu tube, and the gaps are filled with copper inserts to prepare NbTiTa / Nb / Cu secondary composite ingots. NbTiTa / Nb / Cu secondary composite wires are obtained by extrusion, stretching and heat treatment.

[0009] The niobium-titanium superconducting wire was obtained by twisting and stretching the NbTiTa / Nb / Cu secondary composite wire.

[0010] When preparing NbTiTa rods, those skilled in the art can select appropriate parameters and use powder metallurgy to mix and sinter Nb powder, Ti powder and Ta powder to prepare electrode blocks. Then, they can select reasonable melting and forging processes, control the heating temperature, holding time and cooling method of the material melting and forging process, and select appropriate forging ratio and deformation amount to make the deformation relatively uniform during upsetting and drawing, so as to obtain suitable NbTiTa rods.

[0011] Specifically, the preparation method of niobium-titanium superconducting wire provided by this invention includes the following steps: cleaning NbTiTa / Nb rods and Cu tubes; after cleaning, inserting the NbTiTa rods into the Cu tubes; evacuating and sealing the upper and lower covers to form a primary NbTiTa / Nb / Cu single-core ingot; extruding, stretching, and peeling the NbTiTa / Nb / Cu primary single-core ingots to obtain NbTiTa / Nb / Cu single-core rods; cutting and straightening the NbTiTa / Nb / Cu single-core rods to a fixed length; inserting multiple NbTiTa / Nb / Cu single-core rods into the cleaned Cu tubes and filling the gaps with copper inserts to prepare a secondary NbTiTa / Nb / Cu composite ingot; obtaining a secondary NbTiTa / Nb / Cu composite wire from the secondary NbTiTa / Nb / Cu composite ingot through extrusion, stretching, and heat treatment processes; twisting the NbTiTa / Nb / Cu composite wire and stretching it to the required specifications.

[0012] Furthermore, in the method for preparing niobium-titanium superconducting wire provided by the present invention, the content of Ti in the NbTiTa rod is 30-80%, the content of Ta is 0.05-15%, and the balance is Nb, based on atomic ratio.

[0013] Furthermore, in the method for preparing niobium-titanium superconducting wires provided by the present invention, the particle size of the Ta powder is smaller than that of the Nb powder and / or the Ti powder.

[0014] Furthermore, in the preparation method of niobium-titanium superconducting wire provided by the present invention, the particle size of the Nb powder is 50-200 μm, the particle size of the Ti powder is 50-200 μm, and the particle size of the Ta powder is 5-40 μm.

[0015] Furthermore, in the method for preparing niobium-titanium superconducting wire provided by the present invention, an Nb layer is electroplated on the surface of the NbTiTa rod, and the thickness of the Nb layer is 100-1000 μm.

[0016] On the other hand, the present invention relates to a niobium-titanium superconducting wire, which is prepared by the above-described preparation method.

[0017] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects or advantages:

[0018] (1) The particle size of Ta powder selected in this invention is smaller than that of Nb powder and Ti powder. This results in NbTiTa rods with uniform composition and consistent size, and the process is uninterrupted, which is beneficial for subsequent processing.

[0019] (2) The Nb layer can prevent the chemical reaction between NbTiTa and Cu, playing an important role in the preparation of niobium-titanium superconducting wires. Traditional niobium-titanium superconducting wires use Nb foil or Nb plates, which overlap, resulting in large gaps that lead to uneven core wire deformation and reduce the area of ​​the NbTiTa superconductor. This invention uses electroplating to deposit a layer of Nb on the surface of the NbTiTa rod, with a thickness of 100–1000 μm. This ensures the composition and smoothness of the NbTiTa rod surface while maximizing the area of ​​the NbTiTa superconductor, thereby increasing the critical current density of the niobium-titanium superconducting wire at high fields.

[0020] (3) The method for preparing niobium-titanium superconducting wires provided by this invention, by adding Ta, can increase the upper critical magnetic field and the critical current density at high fields (≥9T). Electroplating the Nb layer can eliminate the area and unevenness at the Nb plate overlap in the original preparation method. Electroplating the Nb layer can both increase the area of ​​the superconductor and ensure the symmetry of the structure, thus allowing for better deformation of the core wire. Therefore, this method can greatly improve the critical current density of niobium-titanium superconducting wires at high fields (≥9T), meeting the requirements of high-field (≥9T) magnets, and can be applied to superconducting magnets such as those used in MRI and NMR with high magnetic fields. Detailed Implementation

[0021] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0022] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0023] Example 1

[0024] This embodiment provides a method for preparing niobium-titanium superconducting wires.

[0025] First, the particle size of Nb powder is 50–60 μm, the particle size of Ti powder is 50–60 μm, and the particle size of Ta powder is 5–10 μm. The atomic percentage content of Ti is 30%, that of Ta is 0.05%, and that of Nb is 69.95%. Electrode blocks are prepared by mixing and sintering Nb, Ti, and Ta powders using powder metallurgy, followed by melting and forging to obtain NbTiTa rods. The vacuum degree is less than 10. -4The sintering process was carried out at a temperature of 800 degrees Celsius, a pressure of 20 MPa, and a holding time of 2 hours. Ingots were obtained through two vacuum melting processes. These ingots were then heated to 300 degrees Celsius and held for at least two hours before forging. The forging process was repeated five times to obtain NbTiTa rods with a diameter of 90 mm.

[0026] Next, the NbTiTa rod is cleaned, and Nb is electroplated on its surface to form an NbTiTa / Nb rod. The thickness of the electroplated Nb layer is 100 μm.

[0027] Next, clean the NbTiTa / Nb rod and Cu tube. After cleaning, insert the NbTiTa rod into the Cu tube, evacuate the vacuum, and then seal the top and bottom caps to form a single-core NbTiTa / Nb / Cu ingot. The outer diameter of the Cu tube is 100 mm, and the inner diameter is 90.6 mm.

[0028] The NbTiTa / Nb / Cu single-core ingot was extruded, stretched, and peeled to obtain NbTiTa / Nb / Cu single-core rods. These rods were then cut to length and straightened. The extrusion temperature was 700°C, the holding time was 4 hours, and the diameter after extrusion was 80 mm. The stretching rate was 15%.

[0029] Multiple NbTiTa / Nb / Cu single-core rods were inserted into a cleaned Cu tube, and the gaps were filled with copper inserts to prepare an NbTiTa / Nb / Cu secondary composite ingot. The NbTiTa / Nb / Cu secondary composite wire was obtained through extrusion, stretching, and heat treatment. The outer diameter of the Cu tube was 230 mm. The extrusion temperature was 700 degrees Celsius, the holding time was 2 hours, and the diameter after extrusion was 100 mm. The stretching rate was 15%. The heat treatment temperature was 200 degrees Celsius.

[0030] The NbTiTa / Nb / Cu composite wire was twisted in a right-hand direction with a torque of 45 mm. After twisting, it was stretched to the required specification of φ0.85 mm, resulting in a high-field, high-performance NbTiTa / Nb / Cu composite wire with an Ic (4.2K, 9T) of 69 A / mm. 2 Ic (4.2K, 9.5T) reaches 52A / mm 2 Ic (4.2K, 10T) reaches 37A / mm 2 .

[0031] Example 2

[0032] This embodiment provides a method for preparing niobium-titanium superconducting wires.

[0033] First, the particle size of Nb powder is 100–110 μm, the particle size of Ti powder is 100–110 μm, and the particle size of Ta powder is 15–20 μm. The atomic percentage content of Ti is 50%, that of Ta is 5%, and that of Nb is 45%. Nb, Ti, and Ta powders are mixed and sintered using powder metallurgy to prepare electrode blocks, which are then smelted and forged to obtain NbTiTa rods. The vacuum degree is less than 10. -4 The sintering temperature was 790 degrees Celsius, the pressure was 20 MPa, and the holding time was 3 hours. Ingots were obtained through two vacuum melting processes. These ingots were then heated to 300 degrees Celsius and held for more than two hours before forging. The forging process was repeated four times to obtain NbTiTa rods with a diameter of 120 mm.

[0034] Next, the NbTiTa rod is cleaned, and Nb is electroplated on its surface to form an NbTiTa / Nb rod. The thickness of the electroplated Nb layer is 500 μm.

[0035] Next, clean the NbTiTa / Nb rod and Cu tube. After cleaning, insert the NbTiTa rod into the Cu tube, evacuate the vacuum, and then seal the top and bottom caps to form a single-core NbTiTa / Nb / Cu ingot. The outer diameter of the Cu tube is 138 mm, and the inner diameter is 121.1 mm.

[0036] The NbTiTa / Nb / Cu single-core ingot was extruded, stretched, and peeled to obtain NbTiTa / Nb / Cu single-core rods. These rods were then cut to length and straightened. The extrusion temperature was 800°C, the holding time was 4 hours, and the diameter after extrusion was 100 mm. The stretching rate was 15%.

[0037] Multiple NbTiTa / Nb / Cu single-core rods were inserted into a cleaned Cu tube, and the gaps were filled with copper inserts to prepare an NbTiTa / Nb / Cu secondary composite ingot. The NbTiTa / Nb / Cu secondary composite wire was obtained through extrusion, stretching, and heat treatment. The outer diameter of the Cu tube was 230 mm. The extrusion temperature was 670 degrees Celsius, the holding time was 4 hours, and the diameter after extrusion was 100 mm. The stretching rate was 15%. The heat treatment temperature was 300 degrees Celsius.

[0038] The NbTiTa / Nb / Cu composite wire was twisted in a right-hand direction with a torque of 50 mm. After twisting, it was stretched to the required specification of φ1.00 mm, resulting in a high-field, high-performance NbTiTa / Nb / Cu composite wire with an Ic (4.2K, 9T) of 170 A / mm. 2 Ic (4.2K, 9.5T) reaches 133A / mm 2 Ic (4.2K, 10T) reaches 94A / mm 2.

[0039] Example 3

[0040] This embodiment provides a method for preparing niobium-titanium superconducting wires.

[0041] First, the particle size of Nb powder is 180–190 μm, the particle size of Ti powder is 180–190 μm, and the particle size of Ta powder is 35–40 μm. The atomic content of Ti is 70%, the atomic content of Ta is 8%, and the atomic content of Nb is 22%. Electrode blocks are prepared by mixing and sintering Nb, Ti, and Ta powders using powder metallurgy, followed by melting and forging to obtain NbTiTa rods. The vacuum degree is less than 10. -4 The sintering temperature was 780 degrees Celsius, the pressure was 20 MPa, and the holding time was 2 hours. Ingots were obtained through two vacuum melting processes. These ingots were then heated to 300 degrees Celsius and held for more than two hours before forging. The forging process was repeated three times to obtain NbTiTa rods with a diameter of 140 mm.

[0042] Next, the NbTiTa rod is cleaned, and Nb is electroplated on its surface to form an NbTiTa / Nb rod. The thickness of the electroplated Nb layer is 1000 μm.

[0043] Next, clean the NbTiTa / Nb rod and Cu tube. After cleaning, insert the NbTiTa rod into the Cu tube, evacuate the vacuum, and then seal the top and bottom caps to form a single-core NbTiTa / Nb / Cu ingot. The outer diameter of the Cu tube is 180 mm, and the inner diameter is 141.7 mm.

[0044] The NbTiTa / Nb / Cu single-core ingot was extruded, stretched, and peeled to obtain NbTiTa / Nb / Cu single-core rods. These rods were then cut to length and straightened. The extrusion temperature was 800°C, the holding time was 5 hours, and the diameter after extrusion was 120 mm. The stretching rate was 15%.

[0045] Multiple NbTiTa / Nb / Cu single-core rods were inserted into a cleaned Cu tube, and the gaps were filled with copper inserts to prepare an NbTiTa / Nb / Cu secondary composite ingot. The NbTiTa / Nb / Cu secondary composite wire was obtained through extrusion, stretching, and heat treatment. The outer diameter of the Cu tube was 230 mm. The extrusion temperature was 640 degrees Celsius, the holding time was 5 hours, and the diameter after extrusion was 100 mm. The stretching rate was 15%. The heat treatment temperature was 400 degrees Celsius.

[0046] The NbTiTa / Nb / Cu composite wire was twisted in a right-hand direction with a torque of 55 mm. After twisting, it was stretched to the required specification of φ1.20 mm, resulting in a high-field, high-performance NbTiTa / Nb / Cu composite wire with an Ic (4.2K, 9T) of 288 A / mm. 2 Ic (4.2K, 9.5T) reaches 229A / mm 2 Ic (4.2K, 10T) reaches 161A / mm 2 .

[0047] Comparative Example 1

[0048] Same as Example 1, except that the particle size of Ta powder is 50-60 μm.

[0049] Comparative Example 2

[0050] Same as Example 2, except that Nb foil is used for coating instead of electroplating.

[0051] The niobium-titanium superconducting wires prepared in the above embodiments were tested, and the experimental results are shown in Table 1.

[0052] Table 1 Critical Current Density of Niobium-Titanium Superconducting Wires

[0053]

[0054] The wires prepared using the niobium-titanium superconducting wire preparation method provided by this invention in Examples 1-3 exhibit significantly higher critical current densities at high fields (9T, 9.5T, 10T) than those in Comparative Example 1, and the number of wire breaks in Comparative Example 1 is also significantly higher than in Examples 1-3. Because Comparative Example 2 uses Nb foil coating instead of electroplating, its deformation is poor, and its critical current density at high fields (9T, 9.5T, 10T) is lower than that in Examples 1-3.

[0055] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a niobium-titanium superconducting wire, characterized in that, include: Nb powder, Ti powder and Ta powder are mixed, sintered, melted and forged to obtain NbTiTa rods; An Nb layer with a thickness of 100~1000μm is electroplated on the surface of the NbTiTa rod to obtain an NbTiTa / Nb rod; The NbTiTa / Nb rod is inserted into a Cu tube, and after vacuuming, the upper and lower covers are sealed and welded to form a primary NbTiTa / Nb / Cu single-core ingot. The primary NbTiTa / Nb / Cu single-core ingot is then extruded, stretched, and peeled to obtain an NbTiTa / Nb / Cu single-core rod. Multiple NbTiTa / Nb / Cu single-core ingots are loaded into a Cu tube, and the gaps are filled with copper inserts to prepare NbTiTa / Nb / Cu secondary composite ingots. NbTiTa / Nb / Cu secondary composite wires are obtained by extrusion, stretching and heat treatment. The NbTiTa / Nb / Cu secondary composite wire was twisted and stretched to obtain niobium-titanium superconducting wire. The particle size of the Nb powder is 50~200μm, the particle size of the Ti powder is 50~200μm, and the particle size of the Ta powder is 5~40μm, and the particle size of the Ta powder is smaller than that of the Nb powder and / or the Ti powder.

2. The method for preparing niobium-titanium superconducting wire according to claim 1, characterized in that, In terms of atomic ratio, the NbTiTa rod contains 30-80% Ti, 0.05-15% Ta, and the balance is Nb.

3. A niobium-titanium superconducting wire, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 2.

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