A method for improving deformation uniformity of NbTi superconducting wire core

Abstract

The present invention discloses a method for improving the uniformity of deformation of the core wire of a NbTi superconducting wire, belonging to the technical field of superconducting wire processing. The method comprises: deep-hole drilling an oxygen-free copper ingot rod, assembling it with a single core rod, welding it, and extruding it to obtain a composite rod, and then drawing the composite rod multiple times to obtain a high-performance, low-loss, high-N value NbTi superconducting wire. The NbTi superconducting wire prepared by the present invention J c 2880~3120A / mm 2 , loss is 450~550mJ / cm 3 , N value is 70~95. Compared with the superconducting wire prepared by conventional process, N value is significantly improved, loss is significantly reduced, and critical current density is increased. The NbTi superconducting wire of the present invention has broad application prospects in MRI magnets.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting wire processing and relates to a method for improving the deformation uniformity of a core wire of a NbTi superconducting wire. Background Art

[0002] With the development of the MRI market, MRI equipment requires high-performance MRI magnets to ensure stability and accuracy. To achieve higher-performance and lower-cost MRI magnets, researchers have continuously optimized magnet structures and key superconducting wire materials used in superconducting magnets, resulting in the development of a variety of new magnets, such as cryogenic helium-free superconducting MRI, low-cryogenic helium MRI, high-field MRI, and ultra-high-field whole-body MRI. NbTi / Cu superconducting wire has been widely used in MRI equipment due to its excellent superconducting properties, good mechanical properties, and processability. Compared to conventional MRI magnets, current MRI magnets of different types and magnetic field gradients place even higher demands on the performance of the NbTi / Cu superconducting wire used. These wires must possess not only a high critical surface current density, but also low losses and a high "N value." The N value reflects the voltage response of a superconductor to a current change and measures the rate at which a superconductor transitions from a superconducting state to a normal state. A higher value indicates a faster transition rate and better performance.

[0003] Currently, methods for improving the N value of superconducting wires primarily include optimizing material selection, wire structure, and fabrication processes. Selecting superconducting materials with high critical temperature, high critical current density, and high stability, such as NbTi and Nb3Sn, can significantly improve the wire's N value. A multi-core design can increase the wire's current transmission channels and improve the uniformity of current distribution, thereby increasing the N value. Through sophisticated processing and heat treatment, the wire's lattice structure and grain size can be controlled to optimize its superconducting properties. Currently, hexagonal core rods are often used as intermediate products in the processing of NbTi / Cu superconducting wires, which are then composited with oxygen-free copper to form a multi-core structure. However, with subsequent extrusion and drawing during processing, the shape of the NbTi core wires in the multi-core superconducting wire becomes increasingly irregular, resulting in higher superconducting wire losses and lower N values. Therefore, providing a high-performance, low-loss, and high-N value superconducting wire is of great significance. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for improving the deformation uniformity of the core wire of NbTi superconducting wire. After deep hole drilling, oxygen-free copper ingot rod is assembled, welded and extruded with a single core rod to obtain a composite rod. After multiple passes of drawing the composite rod, a high-performance, low-loss, high-N value NbTi superconducting wire is obtained. The NbTi superconducting wire prepared by the present invention J c 2880~3120A / mm 2, loss is 450~550mJ / cm 3 , N value is 70~95. Compared with the superconducting wire prepared by conventional process, the N value of the superconducting wire of the present invention is significantly improved, the loss is significantly reduced, and the critical current density is increased. The NbTi superconducting wire of the present invention has broad application prospects in MRI magnets.

[0005] To achieve the technical objectives of the present invention, on the one hand, the present invention provides a method for improving the deformation uniformity of a NbTi superconducting wire core wire, which specifically comprises the following steps:

[0006] S1: The NbTi ingot, Nb tube, CuNi alloy tube or CuMnSi alloy tube, upper cover and lower cover are cleaned, assembled and welded to obtain NbTi / CuNi or NbTi / CuMnSi single core ingot, and then extruded and multi-pass drawn to obtain NbTi / CuNi single core rod or NbTi / CuMnSi single core rod.

[0007] Furthermore, the NbTi ingot is in a highly uniform state with uniform structure and composition, with a grain size greater than level 5, a Ti content of 46~48wt%, a carbon content less than 100ppm, a nitrogen content less than 100ppm, a hydrogen content less than 30ppm, and an oxygen content less than 500ppm; the Ni content of the CuNi alloy tube is 5~30wt%; the Mn content of the CuMnSi alloy tube is 1~3wt%, and the Si content is 0.3~0.6wt%.

[0008] Furthermore, the upper cover is made of a CuNi alloy or CuMnSi alloy, the same material as the alloy tube, and has a buckle structure. The lower cover is made of red copper and has a raised structure. Welding is performed using vacuum electron beam welding, with a welding current of 150-200A and a welding speed of 150-160° / min. Extrusion is performed using reverse hot extrusion, with an extrusion temperature of 750-850°C, an extrusion speed of 15-25 mm / s, and an extrusion ratio of 10-15. This reverse hot extrusion ensures uniform deformation of the NbTi core in the NbTi / CuNi or NbTi / CuMnSi single-core rods. After reverse hot extrusion, the surface oxide scale of the NbTi / CuNi or NbTi / CuMnSi single-core rods is removed using centerless turning. The processing rate of each multi-pass drawing pass is controlled at 10-30%, the copper excess ratio of the single-core rod is 0.15-1.0, and the diameter of the single-core rod is 10-40 mm.

[0009] S2: The oxygen-free copper ingot is machined, and both ends are processed into a convex shape. The upper cover and the lower cover of the oxygen-free copper ingot are processed into a buckle shape. The upper cover and the lower cover are both made of oxygen-free copper.

[0010] Furthermore, the oxygen content of the oxygen-free copper ingot is lower than 5ppm, the end faces of the oxygen-free copper ingot and the upper and lower covers after machining need to be chamfered, and the surface roughness of the oxygen-free copper ingot is less than 3.2μm.

[0011] S3: Deep-drill the oxygen-free copper ingot rod that has been machined in S2. The number of holes can be adjusted according to the design requirements. At the same time, in order to facilitate subsequent lifting, lifting holes need to be machined at both ends.

[0012] Furthermore, the holes are arranged in a hexagonal pattern. Each hole undergoes honing after deep-hole drilling to ensure an inner wall roughness of less than 1.6μm. Burrs on both ends are polished to a surface roughness of less than 3.2μm to prevent scratches on the single mandrel surface during subsequent assembly. Three lifting holes are machined on the end face, distributed at 120°. The sizes range from M15 to M20.

[0013] S4: Clean, assemble and weld the NbTi / CuNi single core rod or the NbTi / CuMnSi single core rod, the drilled oxygen-free copper ingot rod, and the upper cover and lower cover of the oxygen-free copper ingot to obtain a NbTi / CuNi / Cu composite ingot or a NbTi / CuMnSi / Cu composite ingot, and extrude to obtain a NbTi / CuNi / Cu composite rod or a NbTi / CuMnSi / Cu composite rod.

[0014] Furthermore, the welding is performed by vacuum electron beam welding, with a welding current of 180-230A and a welding speed of 160-170° / min. The extrusion is performed by reverse hot extrusion, with an extrusion temperature of 650-750°C, an extrusion speed of 10-20 mm / s, and an extrusion ratio of 8-12.

[0015] S5: The NbTi / CuNi / Cu composite rod or the NbTi / CuMnSi / Cu composite rod is subjected to multiple drawing passes, combined with multiple aging heat treatments in the middle, to finally obtain a high-performance, low-loss and high-N value NbTi / CuNi / Cu composite wire or NbTi / CuMnSi / Cu composite wire.

[0016] Furthermore, the black oxide scale on the surface of the NbTi / CuNi / Cu composite rod or NbTi / CuMnSi / Cu composite rod is peeled using a peeling die, with the peeling thickness being 3-4 mm. The multi-pass drawing die is processed using a small-angle die, and the number of aging heat treatments is 1-5. The small-angle die has an angle of 4°-10°, and the aging heat treatment temperature is 300-500°C for 5-60 hours. The diameter of the composite wire is 0.8 mm.

[0017] On the other hand, the present invention claims protection for a NbTi superconducting wire produced by the above method.

[0018] Furthermore, the present invention seeks protection for use of the above-mentioned NbTi superconducting wire in an MRI magnet.

[0019] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0020] (1) The present invention uses NbTi ingots, Nb tubes, CuNi alloy tubes or CuMnSi alloy tubes, and oxygen-free copper ingots as raw materials, and selects superconducting materials with high critical temperature, high critical current density, and high stability to improve the N value of the wire. At the same time, the present invention performs deep hole drilling on the oxygen-free copper ingot, the number of holes drilled can be flexibly adjusted, and the hole positions are hexagonally distributed. Subsequently, the single core rod and the deep-drilled oxygen-free copper ingot are assembled, welded, extruded, and drawn to obtain a high-performance, low-loss, high-N-value composite wire. The method provided by the present invention for improving the deformation uniformity of the NbTi core wire in the superconducting wire has good roundness after processing, low superconducting wire loss, and high N value. Superconducting wire prepared by the present invention J c 2880~3120A / mm 2 , loss Qh is 450~550mJ / cm 3 , N value is 70~95, compared with the superconducting wire prepared by conventional process J c 2750~3050A / mm 2 , loss Qh is 790~850mJ / cm 3 The N value is 48-55, the N value of the superconducting wire is significantly improved, the loss is significantly reduced, and the critical current density is increased. The superconducting wire of the present invention has excellent performance when applied to MRI magnets.

[0021] (2) The present invention uses a centerless turning method to remove the oxidized black skin on the surface of the single core rod. Compared with the conventional peeling die, a large number of pits appear on the surface after peeling, and there is a risk of inclusion in the subsequent drawing process, which may cause the composite wire to break. The method of the present invention does not have the above defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention.

[0023] Figure 1 Schematic diagram of the single-core ingot assembly structure. 1 is the upper cover of the single-core ingot package, 2 is the single-core ingot package cylinder, and 3 is the lower cover of the single-core ingot package.

[0024] Figure 2 This is a cross-sectional view of a drilled oxygen-free copper ingot.

[0025] Figure 3 This is a schematic diagram of the composite ingot assembly structure. 1 is the upper cover of the oxygen-free copper ingot, 2 is the drilled oxygen-free copper ingot cylinder, and 3 is the lower cover of the oxygen-free copper ingot.

[0026] Figure 4 This is the actual cross-section diagram of the composite line. DETAILED DESCRIPTION

[0027] The technical solutions of the present invention are described below with reference to the following examples. However, the present invention is not limited to the following examples. The experimental methods and detection methods described in each example are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0028] The NbTi ingot is in a highly uniform state with uniform structure and composition. Its grain size is greater than level 5, the Ti content is 46~48wt%, the carbon content is less than 100ppm, the nitrogen content is less than 100ppm, the hydrogen content is less than 30ppm, and the oxygen content is less than 500ppm.

[0029] The Ni content of the CuNi alloy tube is 5~30wt%.

[0030] The Mn content of the CuMnSi alloy tube is 1~3wt%, and the Si content is 0.3~0.6wt%.

[0031] The oxygen content of oxygen-free copper ingots is less than 5ppm.

[0032] A method for improving the deformation uniformity of a NbTi superconducting wire core wire comprises the following steps:

[0033] S1: Clean, assemble and weld the NbTi ingot, Nb tube, CuNi alloy tube or CuMnSi alloy tube, upper cover and lower cover to obtain NbTi / CuNi single core ingot or NbTi / CuMnSi single core ingot ( Figure 1 ), after extrusion and multi-pass drawing, NbTi / CuNi single-core rod or NbTi / CuMnSi single-core rod is obtained.

[0034] Specifically, the upper cover is made of CuNi alloy or CuMnSi alloy, the same material as the alloy tube, and has a buckle structure. The lower cover is made of red copper and has a raised structure. Welding is performed using vacuum electron beam welding, with a welding current of 150-200A and a welding speed of 150-160° / min. Extrusion is performed using reverse hot extrusion, with an extrusion temperature of 750-850°C, an extrusion speed of 15-25mm / s, and an extrusion ratio of 10-15. After reverse hot extrusion, centerless turning is used to remove the black oxide scale on the surface of the NbTi / CuNi single-core rod or NbTi / CuMnSi single-core rod, followed by multi-pass drawing. The processing rate of each multi-pass drawing is controlled at 10-30%. After multi-pass drawing, a NbTi / CuNi single-core rod or NbTi / CuMnSi single-core rod with a copper overhang ratio of 0.15-1.0 and a diameter of 10mm-40mm is obtained.

[0035] S2: The oxygen-free copper ingot is machined, and both ends are processed into a convex shape. The upper cover and the lower cover of the oxygen-free copper ingot are processed into a buckle shape. The upper cover and the lower cover are both made of oxygen-free copper.

[0036] Specifically, the machined oxygen-free copper ingot rod and the end faces of the upper and lower covers all need to be chamfered, and the surface roughness must be less than 3.2 μm.

[0037] S3: Deep-drill the oxygen-free copper ingot rod that has been machined in S2. The number of holes can be adjusted according to the design requirements. Then, lift holes are machined at both ends.

[0038] Specifically, deep drilling results in a hexagonal hole pattern. Each hole undergoes honing after completion to ensure an inner wall roughness of less than 1.6μm and a surface roughness of less than 3.2μm. Three lifting holes are machined on the end face, distributed at 120°. The sizes range from M15 to M20.

[0039] S4: Combine NbTi / CuNi single core rod or NbTi / CuMnSi single core rod with drilled oxygen-free copper ingot rod ( Figure 2 ), the upper cover and the lower cover of the oxygen-free copper ingot are cleaned, assembled and welded to obtain a NbTi / CuNi / Cu composite ingot or a NbTi / CuMnSi / Cu composite ingot ( Figure 3 ), after extrusion, NbTi / CuNi / Cu composite rods or NbTi / CuMnSi / Cu composite rods are obtained.

[0040] Specifically, the welding is vacuum electron beam welding, the welding current is 180-230A, and the welding speed is 160-170° / min. The extrusion is reverse hot extrusion, the extrusion temperature is 650-750°C, the extrusion speed is 10-20mm / s, and the extrusion ratio is controlled at 8-12.

[0041] S5: Use a peeling die to remove the black oxide scale on the surface of the NbTi / CuNi / Cu composite rod or NbTi / CuMnSi / Cu composite rod, then perform multiple drawing passes, combined with multiple aging heat treatments in the middle, and finally obtain high-performance, low-loss and high-N value NbTi / CuNi / Cu composite wire or NbTi / CuMnSi / Cu composite wire ( Figure 4 ), the lifting holes are filled with copper after hot extrusion.

[0042] Specifically, the multi-pass drawing die uses a small-angle die, which is a die with an angle of 4° to 10°. The number of aging heat treatments is 1 to 5 times, the aging heat treatment temperature is 300 to 500°C, and the time is 5 hours to 60 hours.

[0043] Example 1

[0044] This embodiment provides a method for improving the deformation uniformity of a core filament of a NbTi superconducting wire, which specifically includes the following steps:

[0045] S1: A Nb47Ti ingot (Ti content of 46-48wt%) with uniform structure and composition of Φ115mm in diameter, a Cu15Ni alloy tube with an outer diameter of Φ150mm and an inner diameter of Φ120mm, a Nb cylinder with a diameter of Φ118mm, an upper cover (made of Cu15Ni), and a lower cover (made of copper) were cleaned and assembled. A NbTi / Cu15Ni single-core ingot (the structure of the single-core ingot from the outside to the inside is Cu15Ni alloy tube, Nb cylinder, and Nb47Ti ingot) was obtained by vacuum electron beam welding at a welding current of 150A and a welding speed of 150° / min. The single-core ingot was reversely hot-extruded to Φ40mm to obtain a NbTi / Cu15Ni single-core rod. The extrusion temperature was 750℃, the extrusion speed was 25mm / s, and the extrusion ratio was 15. The single core rod is mechanically straightened, and after straightening, the black skin on the surface is removed by a centerless lathe to obtain a single core rod with a diameter of Φ37mm. It is then drawn to Φ20mm through multiple passes. The processing rate of each pass of the multiple drawing is controlled at 10%, and the copper excess ratio is 0.15.

[0046] S2: The oxygen-free copper ingot rod with a diameter of Φ220 mm is machined. Both ends of the oxygen-free copper ingot rod are machined into a convex shape. The upper cover and lower cover of the oxygen-free copper ingot (both the upper cover and the lower cover are made of oxygen-free copper) are machined into a buckle shape. The end faces of the oxygen-free copper ingot rod and the upper and lower covers after machining need to be chamfered. The surface roughness of the copper ingot is less than 3.2 μm.

[0047] S3: The oxygen-free copper ingot processed in S2 is deep-hole drilled. The number of holes drilled is 55, the hole diameter is Φ20.5mm, the distance between two adjacent holes is 3mm, the surface roughness is less than 3.2μm, and the roughness of the inner wall of the hole is less than 1.6μm. Three M15 lifting holes distributed at 120° are selected at one end of the drilled copper ingot.

[0048] S4: The NbTi / Cu15Ni single core rod and the upper and lower covers of the 55-hole drilled copper ingot and the oxygen-free copper ingot were cleaned and assembled, and vacuum electron beam welded at a welding current of 180A and a welding speed of 160° / min. After reverse hot extrusion, a NbTi / Cu15Ni / Cu composite rod with a diameter of Φ60 mm was obtained. The extrusion temperature was 650°C, the extrusion speed was 10 mm / s, and the extrusion ratio was 8.

[0049] S5: The composite rod is mechanically straightened and stripped with a stripping die to Φ56 mm, and then drawn with a 4° small angle die to Φ0.8 mm. During the drawing process, it is subjected to five aging heat treatments at 300°C for 60 hours. Finally, a high-performance, low-loss, high-N value NbTi / Cu15Ni / Cu composite wire with uniform core wire deformation is obtained.

[0050] 55-core NbTi / Cu composite wire prepared by conventional method (using oxygen-free copper as the matrix, assembly method) J c (4.2K, 5T) is 3050A / mm 2 , loss Qh (4.2K, ±3T) is 850mJ / cm 3 , N value is 50. The NbTi / Cu15Ni / Cu composite wire prepared by the method of this embodiment J c (4.2K, 5T) is 3120A / mm 2 , loss Qh (4.2K, ±3T) is 540mJ / cm 3 , the N value is 70.

[0051] Example 2

[0052] This embodiment provides a method for improving the deformation uniformity of a core filament of a NbTi superconducting wire, which specifically includes the following steps:

[0053] S1: A Nb47Ti ingot with uniform structure and composition of Φ150mm in diameter, a Cu2Mn0.5Si alloy tube with an outer diameter of Φ190mm and an inner diameter of 155mm, a Nb cylinder with a diameter of Φ153mm, an upper cover (made of Cu2Mn0.5Si), and a lower cover (made of red copper) were cleaned and assembled. A NbTi / Cu2Mn0.5Si single-core ingot was obtained by vacuum electron beam welding at a welding current of 180A and a welding speed of 155° / min. The single-core ingot was reversely hot-extruded to Φ60mm to obtain a NbTi / Cu2Mn0.5Si single-core rod. The extrusion temperature was 800℃, the extrusion speed was 15mm / s, and the extrusion ratio was 10. The single core rod is mechanically straightened, and after straightening, the black skin on the surface is removed by a centerless lathe to obtain a single core rod with a diameter of Φ57mm. It is then drawn to Φ25mm through multiple passes. The processing rate of each pass of the multiple drawing is controlled at 20%, and the copper excess ratio is 0.5.

[0054] S2: The oxygen-free copper ingot rod with a diameter of Φ270 mm is machined. Both ends of the oxygen-free copper ingot rod are machined into a convex shape. The upper cover and lower cover of the oxygen-free copper ingot (both the upper cover and the lower cover are made of oxygen-free copper) are machined into a buckle shape. The end faces of the oxygen-free copper ingot rod and the upper and lower covers after machining need to be chamfered. The surface roughness of the copper ingot is less than 3.2 μm.

[0055] S3: The oxygen-free copper ingot processed in S2 is deep-hole drilled. The number of holes drilled is 55, the hole diameter is Φ25.5mm, the distance between two adjacent holes is 4mm, the surface roughness is less than 3.2μm, and the roughness of the inner wall of the hole is less than 1.6μm. Three M15 lifting holes distributed at 120° are selected at one end of the drilled copper ingot.

[0056] S4: The NbTi / Cu2Mn0.5Si single core rod and the upper and lower covers of the 55-hole drilled copper ingot and the oxygen-free copper ingot were cleaned and assembled, and vacuum electron beam welded at a welding current of 200A and a welding speed of 165° / min. After reverse hot extrusion, a NbTi / Cu2Mn0.5Si / Cu composite rod with a diameter of Φ80mm was obtained. The extrusion temperature was 700℃, the extrusion speed was 15mm / s, and the extrusion ratio was 11.

[0057] S5: The composite rod is mechanically straightened and stripped with a stripping die to Φ76 mm, and then drawn to Φ0.8 mm using an 8° small angle die. During the drawing process, it is subjected to four aging heat treatments at 400°C for 30 hours. Finally, a high-performance, low-loss, high-N value NbTi / Cu2Mn0.5Si / Cu composite wire with uniform core wire deformation is obtained.

[0058] 55-core NbTi / Cu composite wire prepared by conventional method (using oxygen-free copper as the matrix, assembly method) Jc (4.2K, 5T) is 2900A / mm 2 , loss Qh (4.2K, ±3T) is 840mJ / cm 3 , N value is 55. The NbTi / Cu2Mn0.5Si / Cu composite wire prepared by the method of this embodiment J c (4.2K, 5T) is 2980A / mm 2 , loss Qh (4.2K, ±3T) is 550mJ / cm 3 , the N value is 80.

[0059] Example 3

[0060] This embodiment provides a method for improving the deformation uniformity of a core filament of a NbTi superconducting wire, which specifically includes the following steps:

[0061] S1: A Nb47Ti ingot with uniform structure and composition of Φ250mm in diameter, a Cu7Ni alloy tube with an outer diameter of Φ280mm and an inner diameter of 255mm, a Nb tube with a diameter of Φ253mm, an upper cover (made of Cu7Ni), and a lower cover (made of copper) were cleaned and assembled. A NbTi / Cu7Ni single-core ingot was obtained by vacuum electron beam welding at a welding current of 200A and a welding speed of 160° / min. The single-core ingot was reversely hot-extruded to Φ80mm to obtain a NbTi / Cu7Ni single-core rod. The extrusion temperature was 850℃, the extrusion speed was 10mm / s, and the extrusion ratio was 12. The single-core rod was mechanically straightened, and after straightening, the black skin on the surface was removed by centerless turning to obtain a single-core rod with a diameter of Φ77mm. It was then drawn to Φ15mm through multiple passes. The processing rate of each pass of the multi-pass drawing was controlled at 30%, and the copper excess ratio was 1.0.

[0062] S2: The oxygen-free copper ingot rod with a diameter of 160 mm is machined. Both ends of the oxygen-free copper ingot rod are machined into a convex shape. The upper cover and lower cover of the oxygen-free copper ingot (both the upper cover and the lower cover are made of oxygen-free copper) are machined into a buckle shape. The end faces of the oxygen-free copper ingot rod and the upper and lower covers after machining need to be chamfered. The surface roughness of the copper ingot is less than 3.2 μm.

[0063] S3: The oxygen-free copper ingot processed in S2 is deep-hole drilled. The number of holes drilled is 55, the hole diameter is Φ15.5mm, the distance between two adjacent holes is 2mm, the surface roughness is less than 3.2μm, and the roughness of the inner wall of the hole is less than 1.6μm. Three M15 lifting holes distributed at 120° are selected at one end of the drilled copper ingot.

[0064] S4: The NbTi / Cu7Ni single core rod and the upper and lower covers of the 55-hole drilled copper ingot and the oxygen-free copper ingot were cleaned and assembled, and vacuum electron beam welded at a welding current of 230A and a welding speed of 170° / min. After reverse hot extrusion, a NbTi / Cu7Ni / Cu composite rod with a diameter of Φ45mm was obtained. The extrusion temperature was 750℃, the extrusion speed was 20mm / s, and the extrusion ratio was 13.

[0065] S5: The composite rod is mechanically straightened and stripped with a stripping die to Φ42 mm, and then drawn with a 10° small angle die to Φ0.8 mm. During the drawing process, it is subjected to three aging heat treatments at 500°C for 5 hours. Finally, a high-performance, low-loss, high-N value NbTi / Cu7Ni / Cu composite wire with uniform core wire deformation is obtained.

[0066] 55-core NbTi / Cu composite wire prepared by conventional method (using oxygen-free copper as the matrix, assembly method) J c (4.2K, 5T) is 2750A / mm 2 , loss Qh (4.2K, ±3T) is 790mJ / cm 3 , N value is 48. The NbTi / Cu2Mn0.5Si / Cu composite wire prepared by the method of this embodiment J c (4.2K, 5T) is 2880A / mm 2 , loss Qh (4.2K, ±3T) is 450mJ / cm 3 , the N value is 95.

[0067] The embodiments described above are some of the embodiments of the present invention, rather than all of them. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments obtained without creative effort and through deduction and substitution by a person of ordinary skill in the art based on the concept of the present invention are within the scope of protection of the present invention.

Claims

1. A method for improving the deformation uniformity of a NbTi superconducting wire core, characterized in that: include: Deep drilling is performed on the oxygen-free copper ingot, and the holes are distributed in a hexagonal pattern to obtain the drilled oxygen-free copper ingot; Assembling, welding, second-extruding, and drawing the drilled oxygen-free copper ingot and the single core rod to obtain a composite superconducting wire; The single core rod is a NbTi / CuNi single core rod or a NbTi / CuMnSi single core rod; The raw materials of the NbTi / CuNi single core rod are NbTi ingot, CuNi alloy tube and Nb tube; The raw materials of the NbTi / CuMnSi single core rod are NbTi ingot, CuMnSi alloy tube and Nb tube; Assembling, welding, first extruding, and drawing the raw materials of the NbTi / CuNi single-core rod or the raw materials of the NbTi / CuMnSi single-core rod to obtain the NbTi / CuNi single-core rod or the NbTi / CuMnSi single-core rod; The NbTi ingot is in a highly uniform state with uniform structure and composition, with a grain size greater than level 5, a Ti content of 46-48 wt%, a carbon content less than 100 ppm, a nitrogen content less than 100 ppm, a hydrogen content less than 30 ppm, and an oxygen content less than 500 ppm. The Ni content of the CuNi alloy tube is 5-30wt%; The CuMnSi alloy tube has a Mn content of 1-3 wt% and a Si content of 0.3-0.6 wt%; The NbTi superconducting wire J c 2880~3120A / mm 2 , loss is 450~550mJ / cm 3 , N value is 70~95.

2. The method according to claim 1, characterized in that The difference between the diameter of the deep drilled hole and the diameter of the single core rod is 0.5 mm; The inner wall roughness of the deep drilled hole is less than 1.6 μm; The surface roughness of the drilled oxygen-free copper ingot is less than 3.2 μm.

3. The method according to claim 1, characterized in that The second extrusion is reverse hot extrusion; The extrusion temperature of the reverse hot extrusion is 650-750° C., the extrusion speed of the reverse hot extrusion is 10-20 mm / s, and the extrusion ratio of the reverse hot extrusion is 8-13.

4. The method according to claim 1, wherein After the second extrusion, the skin is peeled, and the thickness of the peel is 3-4 mm; The drawing is combined with aging heat treatment, and the number of aging heat treatment is 3 to 5 times; The temperature of the aging heat treatment is 300-500° C., and the time of the aging heat treatment is 5-60 hours.

5. The method according to claim 1, wherein The first extrusion is reverse hot extrusion; The extrusion temperature of the reverse hot extrusion is 750-850° C., the extrusion speed of the reverse hot extrusion is 15-25 mm / s, and the extrusion ratio of the reverse hot extrusion is 10-15.

6. The method according to claim 1, wherein After the first extrusion, the skin is peeled using a centerless lathe, and the thickness of the skin is 3 mm.

7. A NbTi superconducting wire, characterized in that: Prepared by the method according to any one of claims 1 to 6.

8. Use of the NbTi superconducting wire according to claim 7 in an MRI magnet.

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