A NbTi superconducting wire and its preparation method

Abstract

This invention belongs to the field of superconducting wire technology and relates to an NbTi superconducting wire and its preparation method. The preparation steps are as follows: multiple NbTi / Cu single-core round rods are tightly arranged and loaded into an oxygen-free copper tube. The spaces between adjacent single-core round rods are filled with first-insertion rods containing 30%–40% Ta and the remainder Nb. The spaces between the single-core round rods and the copper cladding are filled with second-insertion rods containing 0.1%–1% Nb and the remainder Cu. The oxygen-free copper tube is then sealed to obtain an NbTi / Cu composite cladding. An NbTi / Cu superconducting multi-core composite wire is obtained through extrusion, drawing, and multiple aging heat treatments. This composite wire is then combined with a U-shaped copper channel wire, tin-plated, and inlaid to obtain the NbTi superconducting wire. This method can effectively improve the critical current and RRR value of the NbTi superconducting wire under high fields.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire technology, and relates to an NbTi superconducting wire and its preparation method. Background Technology

[0002] Niobium-titanium (NbTi) superconducting wires, as one of the most widely used low-temperature superconducting materials, occupy more than 90% of the global superconducting materials market share due to their excellent machinability, stable superconducting properties, and high cost-effectiveness. They have become the core conductor material for critical equipment such as nuclear magnetic resonance imaging (MRI), nuclear magnetic resonance spectrometers (NMR), the International Thermonuclear Experimental Reactor (ITER), and large particle accelerators. Their core superconducting mechanism is achieved through the synergistic effect of cold working plastic deformation and aging heat treatment, transforming the NbTi alloy from a β single-phase structure to an α+β two-phase structure. The finely grained α phase forms a flux pinning center, thereby increasing the critical current density (Jc). Currently, the mainstream manufacturing process for NbTi superconducting wires includes key steps such as NbTi alloy melting, single-core round bar preparation, copper sheathing, bundle stretching, and multi-pass aging heat treatment. To optimize the wire cross-sectional structure, some processes have attempted to use single-component slotted rods to fill the gap between the single-core round bar and the copper sheath, but existing technologies still face significant bottlenecks. Existing superconducting wires perform poorly in high-field environments, failing to meet the demands of high-field MRI and other equipment for high current-carrying capacity and efficient quench protection, further hindering the synergistic improvement of superconducting performance and thermal and electrical conductivity. While other superconducting materials offer performance advantages at higher magnetic fields, they suffer from difficulties in processing, high costs, and significant brittleness, preventing them from replacing NbTi superconducting wires in medium-to-high field applications. With the increasing demands for magnetic field strength and operational stability from large scientific facilities and high-end medical equipment, there is an urgent need to develop an NbTi superconducting wire fabrication technology that can simultaneously address the issues of structural compactness, high-field superconductivity, and tissue homogeneity. Through structural design and process optimization, this technology can overcome existing technological bottlenecks and meet the engineering application requirements of high-end superconducting equipment. Summary of the Invention

[0003] The purpose of this invention is to provide an NbTi superconducting wire that effectively improves its critical current and RRR value under high field by adding a slotted rod of a specific material.

[0004] To address this need, the present invention provides an NbTi superconducting wire and a method for preparing the same, which meets the requirements of the art.

[0005] On one hand, the present invention relates to a method for preparing NbTi superconducting wire, which includes: arranging multiple NbTi / Cu single-core round rods closely and then loading them into an oxygen-free copper tube, filling the gaps between adjacent NbTi / Cu single-core round rods with a first insert rod, filling the gaps between the NbTi / Cu single-core round rods and the oxygen-free copper tube with a second insert rod, and sealing the oxygen-free copper tube to obtain an NbTi / Cu composite sheath;

[0006] The NbTi / Cu composite sheath is subjected to extrusion, drawing and multiple aging heat treatments to obtain an NbTi / Cu superconducting multi-core composite wire.

[0007] The NbTi / Cu superconducting multi-core composite wire and the U-shaped copper groove wire are combined and then tin-plated and inlaid to obtain NbTi superconducting wire.

[0008] The chemical composition of the first insert rod is 30%–40% Ta and the balance Nb by weight percentage;

[0009] The second insert rod has a chemical composition of 0.1% to 1% Nb and the balance Cu by weight percentage.

[0010] Furthermore, in the method for preparing NbTi superconducting wire provided by the present invention, the diameter of the NbTi / Cu single-core round rod is 3-30 mm, the diameter of the first slotted rod is 1-2 mm, and the diameter of the second slotted rod is 2-3 mm.

[0011] Furthermore, in the method for preparing NbTi superconducting wire provided by the present invention, the copper ratio of the NbTi / Cu single-core round bar is 0.3 to 1.0.

[0012] Furthermore, in the method for preparing NbTi superconducting wires provided by the present invention, the extrusion ratio is 15-20, the extrusion temperature is 600-700℃, and the extrusion speed is 5-8 mm / min.

[0013] Furthermore, in the method for preparing NbTi superconducting wire provided by the present invention, the number of drawing passes is 5-10%, and the die angle is 6°-8°.

[0014] Furthermore, in the method for preparing NbTi superconducting wire provided by the present invention, the temperature of the aging heat treatment is 300-500℃, the time is 5-40h, and the strain between each two aging heat treatments is controlled at 0.2-0.5.

[0015] Furthermore, in the method for preparing NbTi superconducting wires provided by the present invention, the temperature of the tin plating and inlay welding is 250–450°C.

[0016] Furthermore, in the method for preparing NbTi superconducting wire provided by the present invention, the line width of the U-shaped copper groove wire is 1-5 mm, the height is 1-3 mm, and the groove width is 0.5-2 mm.

[0017] On the other hand, the present invention relates to an NbTi superconducting wire, which is prepared by the aforementioned method for preparing NbTi superconducting wire.

[0018] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0019] This invention provides an NbTi superconducting wire and its preparation method. By introducing two specific insert rods into the traditional NbTi / Cu multi-core composite wire assembly process, the material structure, interface bonding, and heat treatment behavior are systematically optimized, thereby significantly improving the overall performance of the wire without substantially increasing the process complexity. The first insert rod (Ta...) A Nb alloy is filled between the superconducting cores to suppress grain growth, refine the microstructure, and enhance flux pinning ability under high fields. A second insert rod (a Cu alloy containing Nb) is filled between the superconducting core and the Cu cladding, which helps to form a denser and better-bonded interface in subsequent processing, and may also strengthen the copper matrix through fine second-phase particles, improving bonding strength and conductivity. Overall, this invention utilizes materials... structure The collaborative design of the process achieves a dual breakthrough in high-field current carrying capacity and conductivity stability of NbTi superconducting wires while maintaining process feasibility, making them suitable for fields with stringent requirements for superconducting performance, such as high-field magnets, accelerators, and nuclear magnetic resonance. Detailed Implementation

[0020] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentages. Unless otherwise specified, all proportions in the following embodiments refer to mass ratios.

[0021] Example 1

[0022] This embodiment provides a process for preparing NbTi superconducting wires.

[0023] NbTi / Cu single-core round bars with a copper ratio of 0.3 were selected and stretched into round bars with a diameter of 3 mm. After cutting and straightening, the straightness deviation was ≤1 / 1000, and the maximum outer diameter was no more than 0.3 mm larger than before straightening. The first insert bar had a chemical composition of 30%Ta + 70%Nb, a diameter of 1 mm, and a straightness deviation of ≤1 / 1000. The second insert bar had a chemical composition of 0.1%Nb + 99.9%Cu, a diameter of 2 mm, and a straightness deviation of ≤1 / 1000. The U-shaped copper groove had a line width of 1 mm, a height of 1 mm, and a groove width of 0.5 mm, with no oxide layer on the surface. A matching oxygen-free copper cladding with a wall thickness of 10 mm and matching upper and lower covers were machined. 1000 NbTi / Cu single-core round bars were tightly arranged and placed into the copper cladding. The triangular gaps between adjacent round bars were filled with the first insert bar, and the gaps between the round bars and the inner wall of the copper cladding were filled with the second insert bar. The upper and lower covers were sealed using a vacuum electron beam welder to obtain the NbTi / Cu composite cladding. A 5000t extrusion press was used with an extrusion ratio of 15, an extrusion temperature of 600℃, and an extrusion speed of 5mm / min. The composite sheath was preheated for 2 hours (preheating temperature 580℃) before extrusion, resulting in no cracks or peeling defects on the wire surface after extrusion. The wire was then repeatedly reduced in diameter using a broaching machine, a coil drawing machine, and a multi-die drawing machine, employing a 6° die with a processing rate of 5% per pass, ultimately reaching the target wire diameter of Φ0.8mm. Three aging treatments were performed in a muffle furnace at 300℃, each lasting 5 hours. A strain of 0.2 was applied between each aging process using the drawing machine, followed by natural cooling to room temperature. U-shaped copper grooves with groove width and depth matching the dimensions of the superconducting round wire were machined. The NbTi / Cu superconducting multi-core composite wire was embedded into the grooves of the U-shaped copper grooves and tin-plated and inlaid at 250℃ for 10 minutes. The solder spread was uniform, with no incomplete or missing solder joints. Its critical current density (Jc @ 4.2K, 9.8T) was measured to be 352 A / mm². 2 The RRR value is 184.

[0024] Example 2

[0025] This embodiment provides a process for preparing NbTi superconducting wires.

[0026] NbTi / Cu single-core round bars with a copper ratio of 0.6 were selected, stretched into round bars with a diameter of 10mm, and after cutting and straightening, the straightness deviation was ≤1 / 1000, and the maximum outer diameter deviation was ≤0.3mm. The first insert bar had a chemical composition of 35%Ta + 65%Nb, a diameter of 1.5mm, and a straightness deviation of ≤1 / 1000. The second insert bar had a chemical composition of 0.5%Nb + 99.5%Cu, a diameter of 2.5mm, and a straightness deviation of ≤1 / 1000. The U-shaped copper groove had a line width of 3mm, a height of 2mm, a groove width of 1.2mm, and a groove wall thickness uniformity deviation of ≤±0.1mm. A matching oxygen-free copper cladding with a wall thickness of 15mm and upper and lower covers were machined. 630 NbTi / Cu single-core round bars were tightly arranged and loaded into the cladding. The spaces between adjacent round bars were filled with the first insert bar, and the gaps between the round bars and the cladding were filled with the second insert bar. Vacuum electron beam sealing was then performed to obtain the composite cladding. Processed using a 5000t extrusion press, with an extrusion ratio of 17, an extrusion temperature of 650℃, and an extrusion speed of 6.5mm / min, preheating and holding for 3 hours (preheating temperature 630℃), the extruded wire cross-section is free of pores and inclusions. A broaching machine, a coil drawing machine, and a multi-die drawing machine are used, with a 6° die, achieving a processing rate of 7.5% per pass, resulting in a final wire diameter of Φ1.2mm. Four aging treatments are performed in a muffle furnace at 400℃, with each treatment holding for 20 hours; the strain between each aging period is controlled at 0.35, and the wire is naturally cooled to room temperature after aging. U-shaped copper groove wires with groove width and depth matching the dimensions of the superconducting round wire are machined. After assembling the composite wire with the U-shaped copper groove wire, tin plating and soldering are performed at 350℃ for 20 minutes. The critical current density (Jc @ 4.2K, 9.8T) is measured to be 385A / mm². 2 The RRR value is 203.

[0027] Example 3

[0028] This embodiment provides a process for preparing NbTi superconducting wires.

[0029] NbTi / Cu single-core round bars with a copper ratio of 0.8 are drawn into 20mm diameter round bars. After cutting and straightening, the straightness deviation is ≤1 / 1000, and the outer diameter deviation is ≤0.3mm. The first slotted bar has a chemical composition of 40%Ta + 60%Nb, a diameter of 2mm, and a straightness deviation of ≤1 / 1000. The second slotted bar has a chemical composition of 1%Nb + 99%Cu, a diameter of 3mm. The U-shaped copper groove has a line width of 4mm, a height of 2.5mm, a groove width of 1.5mm, and a surface roughness Ra≤0.8μm. Matching oxygen-free copper cladding and upper and lower covers with an inner diameter and wall thickness of 20mm are machined. 144 single-core round bars are tightly arranged and loaded, with the first slotted bar filling the gaps between adjacent round bars and the second slotted bar filling the gaps between the round bars and the cladding. Vacuum electron beam sealing is used to ensure the composite cladding is leak-free. A 5000t extrusion press was used, with an extrusion ratio of 18, an extrusion temperature of 680℃, and an extrusion speed of 7mm / min. Preheating and holding for 3.5 hours (preheating temperature 660℃) resulted in a surface finish of Ra≤1.2μm for the extruded wire. A 6° die was used, along with a broaching machine, a coil drawing machine, and a multi-die drawing machine. The processing rate was 8% per pass, resulting in a final wire diameter of Φ1.5mm. Three aging processes were performed at 450℃, with each holding time of 30 hours. The strain was 0.4 between each aging process, and the wire was cooled to below 100℃ after aging before being removed from the furnace. U-shaped copper groove wires with groove width and depth matching the dimensions of the superconducting round wire were machined and embedded into the superconducting round wire using a die. The wires were then immersed in a tin bath for soldering at 400℃ for 25 minutes. The critical current density (Jc @ 4.2K, 9.8T) was measured to be 392A / mm². 2 The RRR value is 210.

[0030] Example 4

[0031] This embodiment provides a process for preparing NbTi superconducting wires.

[0032] NbTi / Cu single-core round bars with a copper ratio of 1.0 are drawn into 15mm diameter round bars. After cutting and straightening, the straightness deviation is ≤1 / 1000, and the outer diameter deviation is ≤0.3mm. The first slotted bar has a chemical composition of 38%Ta + 62%Nb, a diameter of 1.8mm, and a straightness deviation of ≤1 / 1000. The second slotted bar has a chemical composition of 0.8%Nb + 99.2%Cu, and a diameter of 2.8mm. The U-shaped copper groove has a line width of 2mm, a height of 1.5mm, and a groove width of 0.8mm, with a dimensional tolerance of ≤±0.05mm. A matching oxygen-free copper cladding with a wall thickness of 12mm and upper and lower covers are machined. 360 single-core round bars are tightly arranged and loaded, with the first slotted bar filling the gaps between adjacent round bars and the second slotted bar filling the gaps between the round bars and the cladding. Vacuum electron beam sealing is performed, and the composite cladding is free from deformation. A 5000t extrusion press, extrusion ratio 16, extrusion temperature 620℃, extrusion speed 5.5mm / min, preheating and holding for 2.5h (preheating temperature 600℃), resulted in no significant segregation in the extruded wire. Using a 6° die, broaching machine, coil drawing machine, and multi-die drawing machine, the processing rate per pass was 6%, resulting in a final wire diameter of Φ1.0mm. Four aging processes were performed at 350℃, with each holding time 15h; the strain was 0.3 between each aging process, followed by natural cooling, resulting in fine and uniform core wire grains. U-shaped copper groove wires with groove width and depth matching the dimensions of the superconducting round wire were machined, embedded into the superconducting round wire using a die, and then immersed in a tin bath for soldering at 300℃ for 15min. The critical current density (Jc @ 4.2K, 9.8T) was measured to be 375A / mm². 2 The RRR value is 191.

[0033] Comparative Example 1

[0034] This comparative example is the same as Example 1, except that both the first and second insertion rods are oxygen-free copper rods. The measured critical current density (Jc @ 4.2K, 9.8T) is 153 A / mm². 2 The RRR value is 152.

[0035] Comparative Example 2

[0036] This comparative example is the same as Example 1, except that both the first and second insertion rods are Nb rods. The measured critical current density (Jc @ 4.2K, 9.8T) is 186 A / mm². 2 The RRR value is 134.

[0037] Comparative Example 3

[0038] This comparative example is the same as Example 1, except that it does not have a slotted rod. Its critical current density (Jc @ 4.2K, 9.8T) was measured to be 10² A / mm². 2 The RRR value is 107.

[0039] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for preparing NbTi superconducting wires with improved critical current and RRR value under high field, characterized in that, The high field is 9.8T, which includes: arranging multiple NbTi / Cu single-core round bars closely and then inserting them into an oxygen-free copper tube; filling the gaps between adjacent NbTi / Cu single-core round bars with a first insert bar; filling the gaps between the NbTi / Cu single-core round bars and the oxygen-free copper tube with a second insert bar; and sealing the oxygen-free copper tube to obtain an NbTi / Cu composite cladding. The NbTi / Cu composite sheath is subjected to extrusion, drawing and multiple aging heat treatments to obtain an NbTi / Cu superconducting multi-core composite wire. The NbTi / Cu superconducting multi-core composite wire and the U-shaped copper groove wire are combined and then tin-plated and inlaid to obtain NbTi superconducting wire. The chemical composition of the first insert rod is 30%–40% Ta and the balance Nb by weight percentage; The chemical composition of the second insert rod, by weight percentage, is 0.1% to 1% Nb and the balance Cu; The extrusion ratio is 15-20, the extrusion temperature is 600-700℃, and the extrusion speed is 5-8 mm / min; The drawing pass rate is 5-10%, and the die angle is 6°-8°; The aging heat treatment is performed at a temperature of 300–500℃ for 5–40 hours, with the strain controlled between each two aging heat treatments at 0.2–0.

5.

2. The method for preparing NbTi superconducting wires with improved critical current and RRR value under high field according to claim 1, characterized in that, The diameter of the NbTi / Cu single-core round bar is 3-30 mm, the diameter of the first insertion bar is 1-2 mm, and the diameter of the second insertion bar is 2-3 mm.

3. The method for preparing NbTi superconducting wires with improved critical current and RRR value under high field according to claim 1, characterized in that, The copper ratio of the NbTi / Cu single-core round bar is 0.3 to 1.

0.

4. The method for preparing NbTi superconducting wires with improved critical current and RRR value under high field according to claim 1, characterized in that, The temperature for the tin plating and inlay soldering is 250–450°C.

5. The method for preparing NbTi superconducting wires with improved critical current and RRR value under high field according to claim 1, characterized in that, The U-shaped copper channel wire has a line width of 1-5mm, a height of 1-3mm, and a channel width of 0.5-2mm.

6. An NbTi superconducting wire, characterized in that, The method described in any one of claims 1 to 5 for preparing NbTi superconducting wires to improve critical current and RRR value under high field is used.