A method for preparing Nb3Sn superconducting wire

Abstract

This invention relates to the field of superconducting material processing technology, specifically to a method for preparing Nb3Sn superconducting wires. The invention mainly involves inserting an Nb-Zr alloy into the exterior and / or center of a Sn-Cu single-core rod, filling the space between the Nb-Zr alloy and the Sn-Cu single-core rod with oxide powder, and then inserting it into a copper substrate. After multiple passes of stretching, forming, and length-cutting, Nb3Sn sub-components are obtained. These Nb3Sn sub-components are then uniformly arranged circumferentially within a copper tube to form a bundle, followed by multiple passes of stretching, heat treatment, and cutting to obtain the Nb3Sn superconducting wire. This invention enhances the critical current density of the Nb3Sn superconducting wire under high magnetic fields of 8T–16T by introducing an artificially pinned array with a density gradient distribution. This solves the problem of the matching effect produced by existing uniform artificially pinned center schemes, which limits the practical application of superconducting wires, and alleviates the decrease in critical current density of Nb3Sn superconducting wires under high fields.

Description

Technical Field

[0001] This invention relates to the field of superconducting material processing technology, specifically to a method for preparing Nb3Sn superconducting wires. Background Technology

[0002] Superconducting materials, due to their unhindered high current-carrying capacity, are of great significance in scientific research and engineering applications. As scientific research and engineering increasingly demand higher magnetic fields, the electromagnetic properties of traditional NbTi superconducting wires can no longer meet these requirements. High-temperature superconducting materials are gradually being used due to their superior electromagnetic properties, but their poor mechanical properties, difficulties in quench protection, and strong anisotropy prevent their large-scale application.

[0003] Nb3Sn is the first superconducting material discovered that can carry a large current without loss under a strong magnetic field. It has a high critical magnetic field, filling the gap between traditional NbTi superconducting wires and expensive and immature high-temperature superconducting materials. The critical temperature of Nb3Sn can reach 18.2K; and at a temperature of 4.2K and a magnetic field of 15T, the critical current density of Nb3Sn can reach 1000 A / mm². 2 Therefore, Nb3Sn is one of the important materials for preparing high-field superconducting magnets and has good development prospects.

[0004] In superconducting magnet applications, critical current density is a key performance indicator. Many high-power electrical devices use superconducting magnets to generate strong magnetic fields, which places high demands on the current-carrying capacity of superconducting materials under strong magnetic fields. For example, the Future Circular Collider (FCC) magnet requires superconducting materials to achieve a critical current density of 2300 A / mm² at a temperature of 1.9 K and a magnetic field of 16 T. 2 The above is an overview. However, the performance of existing Nb3Sn superconducting materials, according to the qualified product specifications determined by CERN and the US accelerator program, still falls short of the requirements for FCC superconducting materials. Furthermore, the critical current density of existing Nb3Sn superconducting materials exhibits rapid decay under high magnetic fields of 8T–16T. Therefore, further increasing the critical current density of Nb3Sn superconducting materials is essential to meeting the engineering requirements of future accelerators and other projects, and is also significant for reducing the size of magnets and lowering construction and operating costs. Summary of the Invention

[0005] To address the gap between the performance of existing Nb3Sn superconducting materials and the requirements of FCC superconducting materials, as well as the problem of rapid decay of the critical current density of existing Nb3Sn superconducting materials under high magnetic fields of 8T to 16T, this invention provides a method for preparing Nb3Sn superconducting wires.

[0006] This invention introduces an artificial pinning array with a density gradient distribution to microscopically control the movement path and arrangement of magnetic flux vortices within the Nb3Sn superconducting wire, thereby enhancing the magnetic flux pinning effect and ultimately increasing the critical current density of the Nb3Sn superconducting wire under high magnetic fields of 8T to 16T. This solves the problem of matching effect caused by existing uniform artificial pinning center schemes, which limits the practical application of superconducting wires, alleviates the decrease in critical current density of Nb3Sn superconducting wires under high fields, and improves the electromagnetic performance of Nb3Sn superconducting wires.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] This invention provides a method for preparing Nb3Sn superconducting wires, comprising the following steps:

[0009] Using a Sn-Cu layer or an Nb-Zr alloy layer as the core layer, alternating Sn-Cu and Nb-Zr alloy layers are arranged outside the core layer to obtain a structural component. A gap exists between the Sn-Cu and Nb-Zr alloy layers, which is filled with oxide powder. The filled structural component is then installed in a copper-based tube and subjected to multiple stretching, forming, and length-cutting processes to obtain Nb3Sn sub-components. The Nb3Sn sub-components are then evenly arranged circumferentially along a copper core rod to form a bundle, which is then installed in a copper tube. After multiple stretching processes, heat treatment and cutting are performed to obtain Nb3Sn superconducting wires. The heat treatment process involves a first heat treatment at 500℃~550℃ to react the Nb-Zr alloy with the oxide powder to form ZrO2 particles, followed by a second heat treatment at 630℃~680℃ to create a density gradient distribution of the ZrO2 particles along the radial direction of the Nb3Sn sub-components.

[0010] The main principle of this invention is to introduce a non-uniformly distributed artificial pinning array within the Nb3Sn polycrystalline structure formed by the Nb3Sn subunits. This array uses ZrO2 particles as artificial pins, arranged in a ring. Through heat treatment, a density gradient is generated along the radial direction of the Nb3Sn subunits. These non-uniformly distributed artificial pins control the movement path and arrangement of the magnetic flux vortices within the Nb3Sn superconductor, thereby increasing the pinning density and ultimately enhancing the critical current density of the Nb3Sn superconductor. The ZrO2 particles are used as artificial pins.

[0011] In this invention, the density gradient distribution is mainly generated by the diffusion of the artificially pinned rings along the radial direction of the Nb3Sn subunit after heat treatment. This results in a high initial concentration in the ring structure formed by the artificially pinned rings, and a gradual decrease in concentration along the radial direction.

[0012] Preferably, the first heat treatment lasts for 30 to 60 hours, and the second heat treatment lasts for 80 to 120 hours. In this invention, the first heat treatment is a medium-temperature heat treatment, and the second heat treatment is a high-temperature heat treatment. This invention controls the diffusion of ZrO2 by controlling the reaction temperature and holding time of the heat treatment, thereby forming a density gradient distribution along the radial direction of the Nb3Sn subcomponent.

[0013] The preferred method for fabricating structural components with a Sn-Cu layer as the core layer is as follows:

[0014] A through hole is made in the Nb-Zr alloy rod along the axial direction to obtain an Nb-Zr alloy tube; a Sn-Cu single core rod is inserted into the Nb-Zr alloy tube to form a structural component with a Sn-Cu layer as the core layer.

[0015] The preferred method for processing structural components with an Nb-Zr alloy layer as the core layer is as follows:

[0016] An axial through-hole is made in an Nb-Zr alloy rod to obtain an Nb-Zr alloy tube; an axial through-hole is made in a Sn-Cu single-core rod to obtain a Sn-Cu tube; the Sn-Cu tube is inserted into the Nb-Zr alloy tube, and then an Nb-Zr alloy rod is inserted into the Sn-Cu tube to obtain a structural component with an Nb-Zr alloy layer as the core layer.

[0017] The preferred method for processing structural components with an Nb-Zr alloy layer as the core layer is as follows:

[0018] A Sn-Cu tube is obtained by opening a through hole along the axial direction on a Sn-Cu single core rod; an Nb-Zr alloy rod is then inserted into the Sn-Cu tube to obtain a structural component with an Nb-Zr alloy layer as the core layer.

[0019] Preferably, the Nb-Zr alloy rod is composed of Nb-Zr alloy, which is composed of Zr, Ta and Nb, wherein Zr accounts for 0.5% to 0.6% of the molar percentage of the Nb-Zr alloy and Ta accounts for 2.8% to 3% of the molar percentage of the Nb-Zr alloy.

[0020] Preferably, the Sn-Cu single mandrel is obtained by inserting Sn ingots into a copper cladding, sealing both ends, and then performing multiple cold precision forging, stretching, and length cutting.

[0021] Preferably, the copper base tube, the copper tube, and the copper core rod are all made of oxygen-free copper.

[0022] Preferably, ZrO2 particles are used as artificial pinning points, and a density gradient distribution layer of ZrO2 particles is formed by generating a density gradient distribution along the radial direction of the Nb3Sn subunit. The average spacing of the artificial pinning points of the density gradient distribution layer of ZrO2 particles is 17nm to 42nm.

[0023] Preferably, the average spacing of the artificially pinned points in the density gradient distribution layer of the ZrO2 particles is 17 nm to 26 nm.

[0024] Preferably, the oxide powder is SnO2.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention introduces an artificial pinning array with a density gradient distribution to microscopically control the motion path and arrangement of magnetic flux vortices inside the Nb3Sn superconducting wire, thereby enhancing the pinning density of the Nb3Sn superconducting wire and thus increasing the critical current density of the Nb3Sn superconducting wire under high magnetic fields of 8T to 16T. This solves the problem of the matching effect produced by the existing uniform artificial pinning center scheme, which limits the practical application of superconducting wires, alleviates the decrease in critical current density of Nb3Sn superconducting wires under high fields, and improves the electromagnetic performance of Nb3Sn superconducting wires.

[0027] 2. This invention arranges Sn-Cu layers and Nb-Zr alloy layers, and fills the gap between the Sn-Cu layers and Nb-Zr alloy layers with oxide powder to form Nb3Sn subunits. After the Nb3Sn subunits are bundled together, they are inserted into a copper tube. A first heat treatment causes the Nb-Zr alloy and oxide powder to react and form ZrO2 particles. The ZrO2 particles are used as artificial pinning points. A second heat treatment causes the artificial pinning points to diffuse along the radial direction of the Nb3Sn subunits, generating a density gradient distribution. These non-uniformly distributed artificial pinning points are used to control the movement path and arrangement of the magnetic flux vortices inside the Nb3Sn superconducting wire, thereby increasing the pinning density inside the Nb3Sn superconducting wire and achieving the purpose of increasing the critical current density of the Nb3Sn superconducting wire. Attached Figure Description

[0028] Figure 1 This is a partial structural diagram of the Nb3Sn subunit in Example 1.

[0029] Figure 2 This is a schematic diagram of the Nb3Sn subunit structure in Example 2.

[0030] Figure 3 This is a schematic diagram of the cross-sectional structure of the Nb3Sn superconducting wire in Examples 1 to 3.

[0031] Figure 4 This is a schematic diagram of the Nb3Sn subunit structure in Example 3.

[0032] Figure 5 This is a schematic diagram of the Nb3Sn subunit structure in Comparative Example 1.

[0033] Figure 6 This is a schematic diagram of the electromagnetic model of the grain boundaries of Nb3Sn grains with artificially pinned points of gradient distribution introduced inside the Nb3Sn polycrystalline structure in Example 1.

[0034] Figure 7 This is a schematic diagram of the electromagnetic model of the grain boundaries of Nb3Sn grains with uniformly arranged triangular artificial points pinned inside the Nb3Sn polycrystalline structure, as shown in Comparative Example 1.

[0035] Figure 8 This is a schematic diagram of the electromagnetic model of the grain boundaries of Nb3Sn grains without artificial pinning inside the Nb3Sn polycrystalline structure, as shown in Comparative Example 2.

[0036] Figure 9 The figure shows a comparison between the numerical simulation and scaling law fitting curves of the electromagnetic model of the Nb3Sn grain boundaries without artificial pinning in Comparative Example 2.

[0037] Figure 10 This is a schematic diagram of the critical current density-magnetic field of Nb3Sn superconducting wires with different arrangements of artificially pinned points as shown in Example 1, Comparative Examples 1 and 2.

[0038] Figure 11 A schematic diagram showing the relationship between the average density variation of artificially pinned points with gradient distribution and the critical current density-magnetic field in the Nb3Sn grain boundary electromagnetic model.

[0039] Figure 12 A schematic diagram showing the relationship between the density ratio variation of artificially pinned points with gradient distribution and the critical current density-magnetic field in the Nb3Sn grain boundary electromagnetic model.

[0040] Explanation of reference numerals in the attached figures:

[0041] 10. Sn core; 11. Cu layer; 12. SnO2 powder layer; 13. Nb-Zr alloy layer; 14. Cu base tube; 15. Sn layer; 16. Nb-Zr core; 17. SnO2 powder packed column; 20. Nb3Sn superconducting wire; 21. Oxygen-free copper core rod; 22. Nb3Sn subcomponent; 23. Oxygen-free copper tube. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] In the following embodiments, T c Indicates the critical temperature; J c Indicates the critical current density; H c1 Indicates the lower critical magnetic field; H c2 This indicates the upper critical magnetic field.

[0045] For Nb3Sn type II superconductors, when the external magnetic field is between its lower and upper critical magnetic fields, magnetic flux vortices will enter the interior of the Nb3Sn type II superconductor and undergo vortex motion. At this time, the grain boundaries, dislocations, and defects within the Nb3Sn type II superconductor will exert a pinning effect, hindering the vortex motion and affecting the critical current density of the Nb3Sn type II superconductor.

[0046] In recent years, researchers have made some progress in improving the critical current density of Nb3Sn superconducting wires by modifying the fabrication process. For example, by lowering the heat treatment temperature of Nb3Sn superconducting wires, the grain size of Nb3Sn can be reduced, thereby increasing the internal pinning density of Nb3Sn and thus increasing the critical current density of the superconducting wire. However, a lower heat treatment temperature will reduce the stoichiometry of Nb3Sn, which is detrimental to the upper critical magnetic field of the Nb3Sn superconducting wire. In addition, Nb3Sn superconducting wires prepared by internal oxidation can affect the grain formation pattern of Nb3Sn and reduce the grain size by introducing SnO2 oxide particles inside. However, this method can only refine the average grain size to 50 nm to 60 nm, and it is difficult to further improve the pinning density of Nb3Sn superconducting wires.

[0047] Currently, introducing artificial pinning centers has become one of the core strategies for improving the pinning density of Nb3Sn superconducting wires, thereby enhancing the critical current density. For example, when preparing Nb3Sn superconducting wires using the internal oxidation method, an Nb-Zr alloy can be introduced into the Nb metal layer. The ZrO2 particles generated after heat treatment can serve as artificial pinning centers, significantly increasing the ability to confine magnetic flux vortices. However, in existing technologies, the arrangement of artificial pinning centers often adopts periodic regular arrays such as triangles and rectangles. Although this design can achieve optimized matching between vortices and pinning centers under specific magnetic field conditions—for example, when the number of magnetic flux vortices is an integer multiple of the number of artificial pinning centers, the vortices will be precisely locked at the pinning points, allowing the critical current density to reach its peak—this performance improvement is significantly magnetic field dependent. Once the magnetic field strength deviates from the matching condition, some vortices will escape pinning control, causing the critical current density to drop sharply within a narrow magnetic field range. The performance fluctuations caused by this matching effect severely limit the actual performance of Nb3Sn superconducting wires in wide magnetic field applications, such as high-energy accelerator magnets and nuclear fusion devices.

[0048] This invention enhances the critical current density of Nb3Sn materials at the microscopic level without altering the main structure and fabrication cost of existing, relatively mature Nb3Sn superconducting wires. Specifically:

[0049] By introducing an artificial pinning array with a density gradient distribution, the motion path and arrangement of the magnetic flux vortices inside the Nb3Sn superconductor are controlled from a microscopic perspective, thereby enhancing the pinning density of the Nb3Sn superconductor and thus increasing the critical current density of the Nb3Sn superconductor under high magnetic fields of 8T to 16T. This solves the problem of the matching effect generated by the existing uniform artificial pinning center scheme, which limits the practical application of superconductors, alleviates the decrease in critical current density of Nb3Sn superconductors under high fields, and improves the electromagnetic performance of Nb3Sn superconductors.

[0050] Compared to existing uniformly arranged artificial pinning, this invention fills the gap between the Sn-Cu layer and the Nb-Zr alloy layer with oxide powder, and combines it with a heat treatment process to make the formed ZrO2 particles act as artificial pinning particles. These particles diffuse along the radial direction of the Nb3Sn subcomponent, generating a density gradient distribution. This solves the problem of rapid decay of the critical current density of existing Nb3Sn superconducting materials under high magnetic fields of 8T to 16T.

[0051] The main principle of this invention is to introduce a non-uniformly distributed artificial pinning array inside the Nb3Sn polycrystalline structure, and use these artificial pinning arrays to control the movement path and arrangement of the magnetic flux vortices inside the Nb3Sn superconductor, thereby increasing the pinning density inside the Nb3Sn superconductor and achieving the purpose of increasing the critical current density of Nb3Sn.

[0052] The technical solution of the present invention will be further described below through specific embodiments.

[0053] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0054] In the following embodiments, the elemental composition of the Nb-Zr alloy tube is: Nb-0.6%Zr-3%Ta. The copper substrate is an oxygen-free copper tube.

[0055] In the following embodiments, multi-pass stretching, forming, and length cutting are conventional fabrication processes in the preparation of Nb3Sn superconducting wires.

[0056] Example 1

[0057] A method for preparing Nb3Sn superconducting wire includes the following steps:

[0058] Sn ingots are placed in copper cladding, and after being sealed by electron beam welding with caps at both ends, Sn-Cu single-core rods are obtained through multiple cold precision forging, stretching, and length cutting.

[0059] The Nb-Zr alloy rod is composed of Nb-Zr alloy, which is composed of Zr, Ta and Nb. Zr accounts for 0.6% of the molar percentage of the Nb-Zr alloy, and Ta accounts for 3% of the molar percentage of the Nb-Zr alloy.

[0060] An axial through-hole is drilled in an Nb-Zr alloy rod to obtain an Nb-Zr alloy tube. A Sn-Cu single-core rod is inserted into the Nb-Zr alloy tube to form a structure with a Sn-Cu layer as the core and an Nb-Zr alloy layer as the outermost layer. A gap exists between the Sn-Cu single-core rod and the Nb-Zr alloy layer; SnO2 powder is filled into this gap. The filled structure is then inserted into an oxygen-free copper tube to obtain an Nb3Sn subcomponent blank. After multiple stretching, forming, and length-cutting processes, the Nb3Sn subcomponent is obtained, as shown below. Figure 1 As shown. The Nb3Sn subunit 22 includes, from the inside out, a Sn core 10, a Cu layer 11, a SnO2 powder layer 12, an Nb-Zr alloy layer 13, and a Cu substrate 14.

[0061] Oxygen-free copper core rods are obtained by stretching, shaping, and cutting copper rods to length.

[0062] Multiple Nb3Sn subunits are uniformly arranged along the circumference of an oxygen-free copper core rod to form a bundle, such as... Figure 3Nb3Sn superconducting wire blanks were obtained by packing the wires into an oxygen-free copper tube with a hexagonal close packing pattern on the outside and a hexagonal inside. After multiple stretching passes, the blanks underwent heat treatment and were cut. The heat treatment process involved a first heat treatment at 500℃–550℃ for 50 hours, followed by a second heat treatment at 630℃–680℃ for 100 hours. This resulted in the Nb3Sn superconducting wire, as shown below. Figure 3 As shown. Figure 3 In the Nb3Sn superconducting wire, it is mainly formed by a copper tube with an outer circle and an inner hexagonal shape, and multiple Nb3Sn sub-components evenly arranged along the circumferential direction inside the copper tube. The Nb3Sn superconducting wire 20 includes, from the inside out, an oxygen-free copper core rod 21, an Nb3Sn sub-component 22, and an oxygen-free copper tube 23.

[0063] Example 2

[0064] A method for preparing Nb3Sn superconducting wire includes the following steps:

[0065] Sn ingots are placed in copper cladding, and after being sealed by electron beam welding with caps at both ends, Sn-Cu single-core rods are obtained through multiple cold precision forging, stretching, and length cutting.

[0066] The Nb-Zr alloy rod is composed of Nb-Zr alloy, which is composed of Zr, Ta and Nb. Zr accounts for 0.6% of the molar percentage of the Nb-Zr alloy, and Ta accounts for 3% of the molar percentage of the Nb-Zr alloy.

[0067] An axial through-hole is drilled in an Nb-Zr alloy rod to obtain an Nb-Zr alloy tube; an axial through-hole is drilled in a Sn-Cu single-core rod to obtain a Sn-Cu tube; the Sn-Cu tube is inserted into the Nb-Zr alloy tube, and then an Nb-Zr alloy rod is inserted into the Sn-Cu tube, resulting in a structural component with an Nb-Zr alloy layer as the core layer, an Nb-Zr alloy layer as the outermost layer, and alternating Sn-Cu and Nb-Zr alloy layers. SnO2 powder is filled into the gap between the Sn-Cu tube and the Nb-Zr alloy tube, and simultaneously, SnO2 powder is filled into the gap between the Nb-Zr alloy rod and the Sn-Cu tube. The filled structural component is then inserted into an oxygen-free copper tube to obtain an Nb3Sn subcomponent blank. After multiple stretching, forming, and length-cutting processes, the Nb3Sn subcomponent is obtained, as shown below. Figure 2 As shown. The Nb3Sn subunit 22 includes, from the inside out, an Nb-Zr core 16, a SnO2 powder layer 12, a Sn layer 15, a Cu layer 11, a SnO2 powder layer 12, an Nb-Zr alloy layer 13, and a Cu base tube 14.

[0068] Multiple Nb3Sn subunits are uniformly arranged along the circumference of an oxygen-free copper core rod to form a bundle, such as... Figure 3Nb3Sn superconducting wire blanks were obtained by packing the wires into an oxygen-free copper tube with a hexagonal close packing pattern on the outside and a hexagonal inside. After multiple stretching passes, the blanks underwent heat treatment and were cut. The heat treatment process involved a first heat treatment at 500℃–550℃ for 60 hours, followed by a second heat treatment at 630℃–680℃ for 120 hours. This resulted in the Nb3Sn superconducting wire, as shown below. Figure 3 As shown.

[0069] Example 3

[0070] A method for preparing Nb3Sn superconducting wire includes the following steps:

[0071] Sn ingots are placed in copper cladding, and after being sealed by electron beam welding with caps at both ends, Sn-Cu single-core rods are obtained through multiple cold precision forging, stretching, and length cutting.

[0072] The Nb-Zr alloy rod is composed of Nb-Zr alloy, which is composed of Zr, Ta and Nb. Zr accounts for 0.6% of the molar percentage of the Nb-Zr alloy, and Ta accounts for 3% of the molar percentage of the Nb-Zr alloy.

[0073] A Sn-Cu tube is obtained by drilling a through hole along the axial direction into a Sn-Cu single-core rod. An Nb-Zr alloy rod is then inserted into the Sn-Cu tube to create a structural component with an Nb-Zr alloy layer as the core layer and a Sn-Cu layer as the outermost layer, with the Sn-Cu and Nb-Zr alloy layers arranged alternately. A gap exists between the Nb-Zr alloy rod and the Sn-Cu tube. SnO2 powder is filled into this gap. The filled structural component is then inserted into an oxygen-free copper tube to obtain an Nb3Sn subcomponent blank. After multiple stretching, forming, and length-cutting processes, the Nb3Sn subcomponent is obtained, as shown below. Figure 4 As shown. The Nb3Sn subunit 22 includes, from the inside out, an Nb-Zr core 16, a SnO2 powder layer 12, a Sn layer 15, a Cu layer 11, and a Cu substrate 14.

[0074] Multiple Nb3Sn subunits are uniformly arranged along the circumference of an oxygen-free copper core rod to form a bundle, such as... Figure 3 Nb3Sn superconducting wire blanks were obtained by packing the wires into an oxygen-free copper tube with a hexagonal close packing pattern on the outside and a hexagonal inside. After multiple stretching passes, the blanks underwent heat treatment and were cut. The heat treatment process involved a first heat treatment at 500℃–550℃ for 30 hours, followed by a second heat treatment at 630℃–680℃ for 80 hours. This resulted in the Nb3Sn superconducting wire, as shown below. Figure 3 As shown, the Nb3Sn superconducting wire contains 54 Nb3Sn subunits and 7 oxygen-free copper core rods.

[0075] Comparative Example 1

[0076] A method for preparing Nb3Sn superconducting wire includes the following steps:

[0077] Sn ingots are placed in copper cladding, and after being sealed by electron beam welding with caps at both ends, Sn-Cu single-core rods are obtained through multiple cold precision forging, stretching, and length cutting.

[0078] The Nb-Zr alloy rod is composed of Nb-Zr alloy, which is composed of Zr, Ta and Nb. Zr accounts for 0.6% of the molar percentage of the Nb-Zr alloy, and Ta accounts for 3% of the molar percentage of the Nb-Zr alloy.

[0079] A central through hole and three peripheral through holes are made along the axial direction of the Nb-Zr alloy rod. The three peripheral through holes are evenly spaced along the circumference with the axis of the Nb-Zr alloy tube as the center.

[0080] A Sn-Cu tube is inserted into a central through-hole, and SnO2 powder is filled into three peripheral through-holes. The filled structural component is then inserted into an oxygen-free copper tube to obtain an Nb3Sn subcomponent blank. After multiple stretching, forming, and length-cutting processes, the Nb3Sn subcomponent is obtained. For example... Figure 5 As shown. The Nb3Sn subunit 22 includes, from the inside out, a Sn core 10, a Cu layer 11, an Nb-Zr alloy layer 13, a SnO2 powder-filled pillar 17, and a Cu base tube 14; the SnO2 powder-filled pillar 17 is located in the three peripheral through holes of the Nb-Zr alloy layer 13.

[0081] Multiple Nb3Sn subunits are uniformly arranged along the circumference of an oxygen-free copper core rod to form a bundle, such as... Figure 3 Nb3Sn superconducting wire blanks were obtained by packing the wires into an oxygen-free copper tube with a hexagonal close packing pattern on the outside and a hexagonal inside. After multiple stretching passes, the blanks underwent heat treatment and were cut. The heat treatment process involved a first heat treatment at 500℃–550℃ for 50 hours, followed by a second heat treatment at 630℃–680℃ for 100 hours. This resulted in the Nb3Sn superconducting wire, as shown below. Figure 3 As shown.

[0082] Comparative Example 2

[0083] A method for preparing Nb3Sn superconducting wires, differing from Example 1 in that SnO2 powder is not used as a filler. The specific preparation method includes the following steps:

[0084] Sn ingots are placed in copper cladding, and after being sealed by electron beam welding with caps at both ends, Sn-Cu single-core rods are obtained through multiple cold precision forging, stretching, and length cutting.

[0085] The Nb-Zr alloy rod is composed of Nb-Zr alloy, which is composed of Zr, Ta and Nb. Zr accounts for 0.6% of the molar percentage of the Nb-Zr alloy, and Ta accounts for 3% of the molar percentage of the Nb-Zr alloy.

[0086] An axial through-hole is drilled into an Nb-Zr alloy rod to obtain an Nb-Zr alloy tube. A Sn-Cu single-core rod is then inserted into the Nb-Zr alloy tube to form a structure with a Sn-Cu layer as the core and an Nb-Zr alloy layer as the outermost layer. This structure is then inserted into an oxygen-free copper tube to obtain an Nb3Sn subunit. The Nb3Sn subunit, from the inside out, consists of a Sn core, a Cu layer, an Nb-Zr alloy layer, and a Cu base tube.

[0087] Oxygen-free copper core rods are obtained by stretching, shaping, and cutting copper rods to length.

[0088] Multiple Nb3Sn subunits are uniformly arranged along the circumference of an oxygen-free copper core rod to form a bundle, such as... Figure 3 Nb3Sn superconducting wire blanks were obtained by packing the wires into an oxygen-free copper tube with a hexagonal close packing pattern on the outside and a hexagonal inside. After multiple stretching passes, the blanks underwent heat treatment and were cut. The heat treatment process involved a first heat treatment at 500℃–550℃ for 50 hours, followed by a second heat treatment at 630℃–680℃ for 100 hours. This resulted in the Nb3Sn superconducting wire, as shown below. Figure 3 As shown.

[0089] In Examples 1 to 3 of this invention, Nb-Zr alloy and SnO2 oxide powder are introduced during the preparation of the Nb3Sn superconducting wire. During heat treatment, SnO2 provides oxygen to the Nb-Zr layer, generating ZrO2 particles. These particles exist as defects in the superconductor within the superconducting wire, pinning magnetic flux. By arranging the distribution of SnO2 powder, the diffusion of ZrO2 particles can be guided during heat treatment, creating an artificial pinning array with a density gradient distribution. By controlling the heat treatment time, the ZrO2 particles can be controlled to be distributed in Nb3Sn with different concentration gradients. Figure 2 As shown, introducing SnO2 and Nb-Zr layers into the Nb3Sn subunit can generate multilayer ZrO2 particles in Nb3Sn.

[0090] To verify the feasibility of the methods in Examples 1 to 3 of this invention, artificial point pinning with gradient distributions of different average densities was introduced into the Nb3Sn polycrystalline structure using numerical simulation, and the critical current density of Nb3Sn was calculated. During the simulation, an electromagnetic model of the Nb3Sn grain boundaries with artificial point pinning was established according to the actual internal structure, material, and size of the Nb3Sn superconducting wire. Then, current was applied to the Nb3Sn grain boundary electromagnetic model under different external magnetic field environments to obtain the critical current density of the Nb3Sn grain boundary electromagnetic model.

[0091] The results show that introducing artificial point pinning with a gradient distribution of a certain average density within the Nb3Sn grain boundary electromagnetic model can maximize the enhancement of 9T≤ H a Critical current density at ≤16T.

[0092] Figure 9 This is a comparison of the numerical simulation and scaling law fitting curves of the electromagnetic model of the Nb3Sn grain boundaries without artificial pinning in Comparative Example 2. Figure 9 The image shows the critical current density-magnetic field curves in the electromagnetic model of Nb3Sn grain boundaries without artificial pinning. The solid line represents the continuous function fitted according to the scaling law, and the dashed line represents the numerical simulation results. It can be seen that the numerical simulation results fit the scaling law curve well, demonstrating the reliability of the numerical simulation method.

[0093] Figure 6 This is a schematic diagram of the Nb3Sn polycrystalline structure with artificially pinned gradient distribution introduced in Example 1. Figure 7 This is a schematic diagram of the Nb3Sn polycrystalline structure with artificially pinned points arranged in a uniform triangle pattern, as shown in Comparative Example 1. Figure 8 This is a schematic diagram of the Nb3Sn polycrystalline structure without artificial pinning in Comparative Example 2.

[0094] The electromagnetic model of Nb3Sn grain boundaries with uniformly arranged and gradient-distributed artificial point pinning within the Nb3Sn polycrystalline structure was simulated using this numerical simulation method. The simulation results were compared with those of the Nb3Sn grain boundary electromagnetic model without artificial point pinning. A schematic diagram of the Nb3Sn grain boundary electromagnetic model with gradient-distributed artificial point pinning within the Nb3Sn polycrystalline structure in Example 1 is shown below. Figure 6 As shown, the white areas represent superconducting materials, the black lines represent grain boundaries, and the black dots represent artificially pinned grains. A schematic diagram of the electromagnetic model of the Nb3Sn grain boundaries with uniformly arranged triangular artificially pinned grains, as illustrated in Comparative Example 1, is shown below. Figure 7 As shown. A schematic diagram of the electromagnetic model of the grain boundaries of Nb3Sn grains without artificial pinning within the Nb3Sn polycrystalline structure in Comparative Example 2, as shown. Figure 8 As shown, it serves as a contrast.

[0095] Figure 10 This study demonstrates the effect of introducing different arrangements of artificial point pinning on the critical current density of Nb3Sn superconducting wires. From... Figure 10 As can be seen, artificial point pinning with gradient distribution can significantly improve the performance of Nb3Sn superconductors at high fields of 0.3. H c2 ≤ H a ≤0.5 H c2 The critical current density of Nb3Sn superconducting wires under high fields can be increased to some extent by artificially pinning the wires in a uniformly arranged triangular pattern. However, its critical current density under the same magnetic field is still relatively low.

[0096] pass Figures 4-8 contrast and combination Figure 10 It was found that the artificial point pinning with a gradient distribution introduced inside the Nb3Sn polycrystalline structure in Example 1 can effectively enhance the critical current density in the Nb3Sn grain boundary electromagnetic model. This indicates that the artificial point pinning with a gradient distribution introduced inside the Nb3Sn polycrystalline structure can effectively enhance the critical current density of the Nb3Sn superconductor.

[0097] Figure 11 This paper demonstrates the effect of the average density variation of gradient-distributed artificial point pinning on the critical current density-magnetic field relationship in the Nb3Sn grain boundary electromagnetic model. Gradient-distributed artificial point pinning was introduced into the Nb3Sn grain boundary electromagnetic model, and the number of pinnings in the gradient-distributed Nb3Sn grain boundary electromagnetic model was counted. The average density in the gradient-distributed Nb3Sn grain boundary electromagnetic model was obtained by calculating the average of the spacing between all adjacent artificial point pinnings. Additionally, uniformly distributed artificial point pinning was introduced into the Nb3Sn grain boundary electromagnetic model, and the number of artificial point pinnings in the uniformly distributed Nb3Sn grain boundary electromagnetic model was counted.

[0098] Artificial point pinning with gradient distributions of different average densities was introduced into the electromagnetic model of Nb3Sn grain boundaries, and its critical current density was simulated under different magnetic fields. Figure 11 As can be seen, when the average spacing of the artificial pinning is 17 nm, the critical current density value reaches its maximum under high field in the Nb3Sn grain boundary electromagnetic model. This demonstrates that introducing gradient-distributed artificial pinning can effectively improve the critical current density level of Nb3Sn superconductors under high field.

[0099] Figure 12This study demonstrates the effect of the density ratio variation of gradient-distributed artificial pinning on the critical current density-magnetic field relationship in the Nb3Sn grain boundary electromagnetic model. Gradient-distributed artificial pinning is introduced into the Nb3Sn grain boundary electromagnetic model. The ratio of the number of artificial pins at both the dense and sparse ends of the Nb3Sn grain boundary electromagnetic model is statistically analyzed to obtain the density ratio parameter, which expresses the degree of non-uniformity of the artificial pinning distribution. Dense indicates high density, and sparse indicates low density.

[0100] With an average spacing of 12 nm for the artificial pinning, gradient distributions of artificial pinning with different density ratios were introduced into the Nb3Sn grain boundary electromagnetic model, and the critical current density was simulated under different magnetic fields. Figure 12 As can be seen, the higher the density ratio of the artificially pinned points in the gradient distribution, the better the Nb3Sn grain boundary electromagnetic model behaves in the high magnetic field range of 0.3. H c2 ≤ H a ≤0.5 H c2 The higher the critical current density within the field, the better. This shows that a higher density of artificially pinned points in the gradient distribution can effectively increase the critical current density of the Nb3Sn superconducting wire under high field conditions.

[0101] Compared with existing technologies, the method of this invention has the advantage of lower cost. This invention introduces gradient-distributed artificial point pinning within the Nb3Sn polycrystalline structure without altering the main structure of existing Nb3Sn conductors. After introducing a certain density of gradient-distributed artificial point pinning into the Nb3Sn polycrystalline structure, this invention significantly improves the critical current density of the Nb3Sn superconductor under high fields, and the gradient-distributed artificial point pinning is effective in high magnetic field ranges of 0.3. H c2 ≤ H a ≤0.5 H c2 Both methods can effectively enhance the critical current density of Nb3Sn superconducting wires, solving the matching effect problem of uniformly arranged artificial point pinning models.

[0102] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing Nb3Sn superconducting wire, characterized in that, Includes the following steps: Using Sn-Cu or Nb-Zr alloy layers as the core layer, alternating Sn-Cu and Nb-Zr alloy layers are arranged outside the core layer to obtain a structural component; there is a gap between the Sn-Cu and Nb-Zr alloy layers, and oxide powder is filled into the gap. The filled structural component is then installed in a copper-based tube, and after multiple stretching, forming and length cutting, Nb3Sn sub-components are obtained; The Nb3Sn subunits are evenly arranged around the circumference of the copper core rod to form a bundle, which is then inserted into a copper tube. After multiple stretching passes, heat treatment and cutting are performed to obtain the Nb3Sn superconducting wire. The heat treatment process is as follows: a first heat treatment is performed at 500℃~550℃ to react the Nb-Zr alloy with the oxide powder to form ZrO2 particles, and then a second heat treatment is performed at 630℃~680℃ to generate a density gradient distribution of the ZrO2 particles along the radial direction of the Nb3Sn subunit.

2. The method for preparing Nb3Sn superconducting wire according to claim 1, characterized in that, The first heat treatment lasts for 30 to 60 hours; the second heat treatment lasts for 80 to 120 hours.

3. The method for preparing Nb3Sn superconducting wire according to claim 1, characterized in that, The fabrication method for structural components with a Sn-Cu layer as the core layer is as follows: A through hole is made in the Nb-Zr alloy rod along the axial direction to obtain an Nb-Zr alloy tube; a Sn-Cu single core rod is inserted into the Nb-Zr alloy tube to form a structural component with a Sn-Cu layer as the core layer.

4. The method for preparing Nb3Sn superconducting wire according to claim 1, characterized in that, The processing method for structural components with Nb-Zr alloy layers as the core layer is as follows: An axial through-hole is made in an Nb-Zr alloy rod to obtain an Nb-Zr alloy tube; an axial through-hole is made in a Sn-Cu single-core rod to obtain a Sn-Cu tube; the Sn-Cu tube is inserted into the Nb-Zr alloy tube, and then an Nb-Zr alloy rod is inserted into the Sn-Cu tube to obtain a structural component with an Nb-Zr alloy layer as the core layer.

5. The method for preparing Nb3Sn superconducting wire according to claim 1, characterized in that, The processing method for structural components with Nb-Zr alloy layers as the core layer is as follows: A Sn-Cu tube is obtained by opening a through hole along the axial direction on a Sn-Cu single core rod; an Nb-Zr alloy rod is then inserted into the Sn-Cu tube to obtain a structural component with an Nb-Zr alloy layer as the core layer.

6. The method for preparing Nb3Sn superconducting wire according to any one of claims 3 to 5, characterized in that, The Nb-Zr alloy rod is composed of Nb-Zr alloy, which is composed of Zr, Ta and Nb. Among them, Zr accounts for 0.5% to 0.6% of the molar percentage of Nb-Zr alloy, and Ta accounts for 2.8% to 3% of the molar percentage of Nb-Zr alloy.

7. The method for preparing Nb3Sn superconducting wire according to any one of claims 3 to 5, characterized in that, Sn-Cu single-core rods are obtained by inserting Sn ingots into copper sheaths, sealing both ends, and then performing multiple cold precision forging, stretching, and length cutting.

8. The method for preparing Nb3Sn superconducting wire according to claim 1, characterized in that, Using ZrO2 particles as artificial anchors, a density gradient distribution layer of ZrO2 particles is formed by creating a density gradient distribution along the radial direction of the Nb3Sn subunit. The average spacing of the artificial anchors in the density gradient distribution layer of ZrO2 particles is 17nm to 42nm.

9. The method for preparing Nb3Sn superconducting wire according to claim 8, characterized in that, The average spacing of the artificially pinned points in the density gradient distribution layer of the ZrO2 particles is 17 nm to 26 nm.

10. The method for preparing Nb3Sn superconducting wire according to claim 1, characterized in that, The oxide powder is SnO2.

Images