Preparation method of Nb3Sn superconducting wire

Abstract

The invention relates to the technical field of superconducting material processing, in particular to a preparation method of an Nb3Sn superconducting wire. The method mainly comprises the steps that Nb-Zr alloy is loaded into the exterior and / or the center of a Sn-Cu single-core rod, oxide powder is filled between the Nb-Zr alloy and the Sn-Cu single-core rod, then the Sn-Cu single-core rod and the Nb-Zr alloy are loaded into a copper substrate, and Nb3Sn subcomponents are obtained after multi-pass stretching, forming and fixed-length cutting; and uniformly arranging the Nb3Sn sub-components in the copper pipe along the circumferential direction to form a bundle, and after multi-pass stretching, carrying out heat treatment and cutting to obtain the Nb3Sn superconducting wire. By introducing the artificial point pinning array in density gradient distribution, the critical current density of the Nb3Sn superconducting wire in a high magnetic field of 8T-16T is enhanced, the problems that an existing uniform artificial point pinning center scheme generates a matching effect and limits the actual application of the superconducting wire are solved, and the decline degree of the critical current density of the Nb3Sn superconducting wire in the high field is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting material processing, and in particular to a method for preparing a Nb3Sn superconducting wire. Background Art

[0002] Superconducting materials, due to their unimpeded high current carrying capacity, are of great significance in scientific research and engineering applications. As research and engineering continue to demand higher magnetic fields, the electromagnetic performance of traditional NbTi superconducting wires is no longer sufficient. High-temperature superconducting materials are gaining application due to their superior electromagnetic properties, but their shortcomings, such as poor mechanical properties, difficulty in quench protection, and strong anisotropy, have hindered their widespread adoption.

[0003] Nb3Sn is the first superconducting material discovered so far that can carry large currents without loss in strong magnetic fields. Its high critical magnetic field fills 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 1000A / mm 2 Therefore, Nb3Sn is one of the important materials for preparing high-field superconducting magnets and has good development prospects.

[0004] In the application of superconducting magnets, critical current density is a key performance indicator. Many devices in the field of strong electricity 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, whose full English name is Future Circular Collider, abbreviated as FCC. For the magnets of the Future Circular Collider, the critical current density of the superconducting material is required to reach 2300A / mm at a temperature of 1.9K and a magnetic field of 16T. 2 However, the performance of existing Nb3Sn superconducting materials, as determined by the qualified product specifications of the European Organization for Nuclear Research and the US accelerator program, still lags behind the requirements of FCC superconducting materials. Furthermore, the critical current density of existing Nb3Sn superconducting materials rapidly decays at high magnetic fields of 8T to 16T. Therefore, further increasing the critical current density of Nb3Sn superconducting materials is essential to meeting the requirements of future accelerator projects and is also crucial for reducing the size of magnets and lowering construction and operating costs. Summary of the Invention

[0005] In order to solve the problem that the performance of existing Nb3Sn superconducting materials still has a gap with the requirements of FCC superconducting materials and the critical current density of existing Nb3Sn superconducting materials rapidly decays under high magnetic fields of 8T to 16T, the present invention provides a method for preparing Nb3Sn superconducting wire.

[0006] The present invention introduces an artificial point pinning array with a density gradient distribution to regulate the movement path and arrangement of magnetic flux vortices inside the Nb3Sn superconducting wire from a microscopic perspective, thereby enhancing the magnetic flux pinning effect of the Nb3Sn superconducting wire and further enhancing the critical current density of the Nb3Sn superconducting wire under a high magnetic field of 8T to 16T. This solves the problem that the existing uniform artificial point pinning center scheme produces a matching effect, which limits the practical application of the superconducting wire, alleviates the decrease in the critical current density of the Nb3Sn superconducting wire under high fields, and improves the electromagnetic performance of the Nb3Sn superconducting wire.

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

[0008] The present invention provides a method for preparing a Nb3Sn superconducting wire, comprising the following steps: A Sn-Cu layer or a Nb-Zr alloy layer is used as a core layer, and Sn-Cu layers and Nb-Zr alloy layers are alternately arranged outside the core layer to obtain a structural component; a gap is provided between the Sn-Cu layer and the Nb-Zr alloy layer, and oxide powder is filled in the gap. The filled structural component is installed in a copper-based tube, and after multiple stretching, forming and cutting to length, Nb3Sn subcomponents are obtained; the Nb3Sn subcomponents are evenly arranged along the circumference of a copper core rod to form a bundle, which is then installed in a copper tube, and after multiple stretching, heat treatment and cutting are performed to obtain Nb3Sn superconducting wire; the heat treatment process is: a first heat treatment is performed at 500°C to 550°C to react the Nb-Zr alloy with the oxide powder to form ZrO2 particles, and then a second heat treatment is performed at 630°C to 680°C to form a density gradient distribution of the formed ZrO2 particles along the radial direction of the Nb3Sn subcomponent.

[0009] The main principle of the present invention is to introduce a non-uniformly distributed artificial point pinning array within the Nb3Sn polycrystalline structure formed by the Nb3Sn subcomponent. Specifically, the ZrO2 particles formed serve as artificial point pinning in a ring-shaped arrangement. Heat treatment is then performed to produce a density gradient along the radial direction of the Nb3Sn subcomponent. These non-uniformly distributed artificial point pinnings control the motion path and arrangement of magnetic flux vortices within the Nb3Sn superconducting wire, thereby enhancing the pinning density within the Nb3Sn superconducting wire and thereby increasing the critical current density of the Nb3Sn superconducting wire. The ZrO2 particles serve as the artificial point pinnings.

[0010] In the present invention, the density gradient distribution is mainly generated by the artificial point pinning arranged in an annular manner, which diffuses along the radial direction of the Nb3Sn subcomponent after heat treatment, so that the initial position concentration of the annular arrangement structure formed by the artificial point pinning is high and the concentration gradually decreases along the radial direction.

[0011] Preferably, the first heat treatment lasts 30 to 60 hours, and the second heat treatment lasts 80 to 120 hours. In the present invention, the first heat treatment is a medium-temperature heat treatment, and the second heat treatment is a high-temperature heat treatment. The present invention controls the reaction temperature and holding time of the heat treatment to control the diffusion of ZrO2, thereby forming a density gradient distribution along the radial direction of the Nb3Sn subcomponent.

[0012] Preferably, the processing method of the structural member with the Sn-Cu layer as the core layer is as follows: A through hole is opened in the axial direction of a Nb-Zr alloy rod to obtain a Nb-Zr alloy tube; a Sn-Cu single core rod is installed in the Nb-Zr alloy tube to form a structural component with a Sn-Cu layer as a core layer.

[0013] Preferably, the processing method of the structural member with the Nb-Zr alloy layer as the core layer is as follows: A through hole is opened in the axial direction of a Nb-Zr alloy rod to obtain a Nb-Zr alloy tube; a through hole is opened in the axial direction of 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 the Nb-Zr alloy rod is inserted into the Sn-Cu tube to obtain a structural component with a Nb-Zr alloy layer as the core layer.

[0014] Preferably, the processing method of the structural member with the Nb-Zr alloy layer as the core layer is as follows: A through hole is opened in the axial direction of a Sn-Cu single core rod to obtain a Sn-Cu tube; a Nb-Zr alloy rod is loaded into the Sn-Cu tube to obtain a structural component with a Nb-Zr alloy layer as a core layer.

[0015] Preferably, the composition of the Nb-Zr alloy rod is Nb-Zr alloy, which is composed of Zr, Ta and Nb, wherein the molar percentage of Zr in the Nb-Zr alloy is 0.5% to 0.6%, and the molar percentage of Ta in the Nb-Zr alloy is 2.8% to 3%.

[0016] Preferably, the Sn-Cu single core rod is obtained by placing a Sn ingot into a copper cladding, sealing both ends with covers, and then performing multiple cold precision forging, stretching, and cutting to a predetermined length.

[0017] Preferably, the copper base tube, the copper tube and the copper core rod are all made of oxygen-free copper.

[0018] Preferably, ZrO2 particles are used as artificial point pinning, and a density gradient distribution of ZrO2 particles is set along the radial direction of the Nb3Sn subcomponent to form a density gradient distribution layer of ZrO2 particles, and the average spacing of the artificial point pinning of the density gradient distribution layer of ZrO2 particles is 17nm to 42nm.

[0019] Preferably, the average spacing of the artificial point pinning of the density gradient distribution layer of ZrO2 particles is 17nm to 26nm.

[0020] Preferably, the oxide powder is SnO2.

[0021] Beneficial effects of the present invention: 1. The present invention introduces an artificial point pinning array with a density gradient distribution to microscopically regulate the movement path and arrangement of magnetic flux vortices inside the Nb3Sn superconducting wire, thereby enhancing the pinning density of the Nb3Sn superconducting wire and further enhancing the critical current density of the Nb3Sn superconducting wire under high magnetic fields of 8T to 16T. This solves the problem that the existing uniform artificial point pinning center solution produces a matching effect, which limits the practical application of superconducting wires. It also alleviates the decrease in the critical current density of the Nb3Sn superconducting wire under high fields and improves the electromagnetic properties of the Nb3Sn superconducting wire.

[0022] 2. The present invention arranges Sn-Cu layers and Nb-Zr alloy layers, and fills the gap between the Sn-Cu layers and the Nb-Zr alloy layers with oxide powder to form Nb3Sn subcomponents. The Nb3Sn subcomponents are arranged into a bundle and then loaded into a copper tube. The Nb-Zr alloy reacts with the oxide powder to form ZrO2 particles through a first heat treatment. The ZrO2 particles are used as artificial point pinning. Through a second heat treatment, the formed artificial point pinnings are diffused along the radial direction of the Nb3Sn subcomponents to produce a density gradient distribution. These non-uniformly distributed artificial point pinnings are used to control the movement path and arrangement of magnetic flux vortices inside the Nb3Sn superconducting wire, thereby enhancing the pinning density inside the Nb3Sn superconducting wire and achieving the purpose of enhancing the critical current density of the Nb3Sn superconducting wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the local structure of the Nb3Sn subcomponent of Example 1.

[0024] Figure 2 Schematic diagram of the structure of the Nb3Sn subcomponent of Example 2.

[0025] Figure 3 Schematic diagram of the cross-sectional structure of the Nb3Sn superconducting wire in Examples 1 to 3.

[0026] Figure 4 Schematic diagram of the structure of the Nb3Sn subcomponent of Example 3.

[0027] Figure 5 Schematic diagram of the structure of the Nb3Sn subcomponent of Comparative Example 1.

[0028] Figure 6Schematic diagram of the electromagnetic model of Nb3Sn grain boundaries in which gradient-distributed artificial point pinning is introduced into the Nb3Sn polycrystalline structure in Example 1.

[0029] Figure 7 Schematic diagram of the electromagnetic model of the Nb3Sn grain boundary in which artificial points with uniform triangular arrangement are introduced into the Nb3Sn polycrystalline structure for comparative example 1.

[0030] Figure 8 Schematic diagram of the electromagnetic model of the Nb3Sn grain boundary without artificial point pinning in the Nb3Sn polycrystalline structure of Comparative Example 2.

[0031] Figure 9 This is a comparison chart of the numerical simulation and scaling law fitting curve of the electromagnetic model of the Nb3Sn grain boundary without artificial point pinning in Comparative Example 2.

[0032] Figure 10 Schematic diagram of critical current density-magnetic field of Nb3Sn superconducting wire with artificial point pinning of different arrangements introduced in Example 1 and Comparative Examples 1 and 2.

[0033] Figure 11 Schematic diagram of the relationship between the average density change of artificial point pinning with gradient distribution and the critical current density-magnetic field in the electromagnetic model of Nb3Sn grain boundaries.

[0034] Figure 12 Schematic diagram of the relationship between the density ratio change of artificial point pinning with gradient distribution and the critical current density-magnetic field in the electromagnetic model of Nb3Sn grain boundaries.

[0035] Description of reference numerals: 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 filling column; 20. Nb3Sn superconducting wire; 21. Oxygen-free copper core rod; 22. Nb3Sn subcomponent; 23. Oxygen-free copper tube. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0038] In the following embodiments, Tc represents the critical temperature; J c represents the critical current density; H c1 represents the lower critical magnetic field; H c2 represents the upper critical magnetic field.

[0039] For Nb3Sn type II superconductors, when the external magnetic field is between its lower critical magnetic field and upper critical magnetic field, magnetic flux vortices enter the Nb3Sn type II superconductor and initiate vortex motion. At this point, the grain boundaries, dislocations, and defects within the Nb3Sn type II superconductor create a pinning effect that hinders vortex motion, affecting the critical current density of the Nb3Sn type II superconductor.

[0040] In recent years, researchers have made progress in improving the critical current density of Nb3Sn superconducting wires by modifying their preparation processes. 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, in turn, the critical current density of the superconducting wire. However, lower heat treatment temperatures reduce the stoichiometric ratio of Nb3Sn, which is detrimental to the upper critical magnetic field of the Nb3Sn superconducting wire. Furthermore, by introducing SnO2 oxide particles into Nb3Sn superconducting wires prepared by internal oxidation, the formation pattern of Nb3Sn grains can be influenced, reducing the grain size. However, this method can only refine the average grain size to 50nm-60nm, making it difficult to further improve the pinning density of Nb3Sn superconducting wires.

[0041] At present, the introduction of artificial pinning centers has become one of the core strategies for improving the pinning density of Nb3Sn superconducting wires and thus enhancing the critical current density. For example, when preparing Nb3Sn superconducting wires by the internal oxidation method, 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 binding capacity of magnetic flux vortices. However, in the prior art, the arrangement of artificial pinning centers mostly adopts periodic regular arrays such as triangles and rectangles. Although this design can achieve optimal 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 on the pinning sites, causing the critical current density to reach its peak value. However, this performance improvement has significant magnetic field dependence. Once the magnetic field strength deviates from the matching condition, some vortices will break away from the pinning control, causing the critical current density to drop sharply within a narrow magnetic field range. The performance fluctuations caused by this matching effect seriously restrict the actual effectiveness of Nb3Sn superconducting wires in wide magnetic field application scenarios, such as high-energy accelerator magnets and nuclear fusion devices.

[0042] The present invention enhances the critical current density of Nb3Sn material from a microscopic level without changing the main structure and preparation cost of the existing relatively mature Nb3Sn superconducting wire. Specifically: By introducing an artificial point pinning array with a density gradient distribution, the movement path and arrangement of the magnetic flux vortex inside the Nb3Sn superconducting wire are regulated from a microscopic perspective, thereby enhancing the pinning density of the Nb3Sn superconducting wire and further enhancing the critical current density of the Nb3Sn superconducting wire under a high magnetic field of 8T to 16T. This solves the problem that the existing uniform artificial point pinning center scheme produces a matching effect, which limits the practical application of superconducting wires, alleviates the decrease in the critical current density of the Nb3Sn superconducting wire under high fields, and improves the electromagnetic properties of the Nb3Sn superconducting wire.

[0043] Compared with the existing uniformly arranged artificial point pinning, the present 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 point pinning, diffuse along the radial direction of the Nb3Sn subcomponent, and produce a density gradient distribution, thereby solving the problem of rapid decay of the critical current density of the existing Nb3Sn superconducting material under a high magnetic field of 8T to 16T.

[0044] The main principle of the present invention is to introduce a non-uniformly distributed artificial point pinning array inside the Nb3Sn polycrystalline structure, use this artificial point pinning array to control the movement path and arrangement of the magnetic flux vortex inside the Nb3Sn superconducting wire, enhance the pinning density inside the Nb3Sn superconducting wire, and achieve the purpose of enhancing the critical current density of Nb3Sn.

[0045] The technical solution of the present invention is further described below through specific embodiments.

[0046] In the following examples, the methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0047] In the following embodiments, the element composition of the Nb-Zr alloy tube is: Nb-0.6% Zr-3% Ta. The copper substrate is an oxygen-free copper tube.

[0048] In the following embodiments, multi-pass stretching, forming and cutting to length are conventional processes for preparing Nb3Sn superconducting wires.

[0049] Example 1 A method for preparing a Nb3Sn superconducting wire comprises the following steps: The Sn ingot is placed in a copper cladding, and after the two ends are covered and sealed by electron beam welding, it is subjected to multiple passes of cold precision forging, stretching and cutting to a fixed length to obtain a Sn-Cu single core rod.

[0050] The composition of the Nb-Zr alloy rod is Nb-Zr alloy, which is composed of Zr, Ta and Nb. The molar percentage of Zr in the Nb-Zr alloy is 0.6%, and the molar percentage of Ta in the Nb-Zr alloy is 3%.

[0051] A through hole is opened in the axial direction of the Nb-Zr alloy rod to obtain a Nb-Zr alloy tube; a Sn-Cu single core rod is placed in the Nb-Zr alloy tube to form a structural component with a Sn-Cu layer as the core layer and a Nb-Zr alloy layer as the outermost layer. There is a gap between the Sn-Cu single core rod and the Nb-Zr alloy layer, and SnO2 powder is filled in the gap between the Sn-Cu single core rod and the Nb-Zr alloy tube; then the filled structural component is placed in an oxygen-free copper tube to obtain a Nb3Sn subcomponent blank. After multiple stretching, forming and cutting to size, the Nb3Sn subcomponent is obtained, such as Figure 1 The Nb3Sn subcomponent 22 includes, from the inside out, a Sn core 10, a Cu layer 11, a SnO2 powder layer 12, a Nb-Zr alloy layer 13 and a Cu base tube 14.

[0052] The copper rod is stretched, formed and cut to length to obtain the oxygen-free copper core rod.

[0053] Multiple Nb3Sn subcomponents are evenly arranged along the circumference of the oxygen-free copper core rod to form a cluster, such as Figure 3 , according to the hexagonal close packing, they are packed into an oxygen-free copper tube with an outer circle and an inner hexagonal shape to obtain Nb3Sn superconducting wire blanks, which are then subjected to heat treatment and cutting after multiple stretching. During the heat treatment process, the first heat treatment is carried out at a temperature of 500℃~550℃ for 50h, and then the second heat treatment is carried out at a temperature of 630℃~680℃ for 100h. The Nb3Sn superconducting wire is obtained, such as Figure 3 shown. Figure 3 In the example, the Nb3Sn superconducting wire is primarily composed of a copper tube with a circular outer surface and a hexagonal inner surface, and multiple Nb3Sn subcomponents uniformly arranged along the inner circumference of the copper tube. From the inside out, the Nb3Sn superconducting wire 20 comprises an oxygen-free copper core rod 21, Nb3Sn subcomponents 22, and an oxygen-free copper tube 23.

[0054] Example 2 A method for preparing a Nb3Sn superconducting wire comprises the following steps: The Sn ingot is placed in a copper cladding, and after the two ends are covered and sealed by electron beam welding, it is subjected to multiple passes of cold precision forging, stretching and cutting to a fixed length to obtain a Sn-Cu single core rod.

[0055] The composition of the Nb-Zr alloy rod is Nb-Zr alloy, which is composed of Zr, Ta and Nb. The molar percentage of Zr in the Nb-Zr alloy is 0.6%, and the molar percentage of Ta in the Nb-Zr alloy is 3%.

[0056] A through hole is opened in the axial direction of the Nb-Zr alloy rod to obtain a Nb-Zr alloy tube; a through hole is opened in the axial direction of the Sn-Cu single core rod to obtain a Sn-Cu tube; the Sn-Cu tube is loaded into the Nb-Zr alloy tube, and then the Nb-Zr alloy rod is loaded into the Sn-Cu tube to obtain a structural component with the Nb-Zr alloy layer as the core layer, the Nb-Zr alloy layer as the outermost layer, and the Sn-Cu layer and the Nb-Zr alloy layer arranged alternately. SnO2 powder is filled into the gap between the Sn-Cu tube and the Nb-Zr alloy tube. At the same time, SnO2 powder is filled into the gap between the Nb-Zr alloy rod and the Sn-Cu tube. The filled structural component is then loaded into an oxygen-free copper tube to obtain a Nb3Sn subcomponent blank. After multiple stretching, forming and cutting to length, the Nb3Sn subcomponent is obtained, such as Figure 2 The Nb3Sn subcomponent 22 includes, from the inside out, a Nb-Zr core 16, a SnO2 powder layer 12, a Sn layer 15, a Cu layer 11, a SnO2 powder layer 12, a Nb-Zr alloy layer 13, and a Cu base tube 14.

[0057] Multiple Nb3Sn subcomponents are evenly arranged along the circumference of the oxygen-free copper core rod to form a cluster, such as Figure 3 , according to the hexagonal close packing, they are packed into an oxygen-free copper tube with an outer circle and an inner hexagonal shape to obtain Nb3Sn superconducting wire blanks, which are then subjected to heat treatment and cutting after multiple stretching. During the heat treatment process, the first heat treatment is carried out at a temperature of 500℃~550℃ and kept warm for 60h, and then the second heat treatment is carried out at a temperature of 630℃~680℃ and kept warm for 120h. The Nb3Sn superconducting wire is obtained, such as Figure 3 shown.

[0058] Example 3 A method for preparing a Nb3Sn superconducting wire comprises the following steps: The Sn ingot is placed in a copper cladding, and after the two ends are covered and sealed by electron beam welding, it is subjected to multiple passes of cold precision forging, stretching and cutting to a fixed length to obtain a Sn-Cu single core rod.

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

[0060] A Sn-Cu single core rod is axially opened with a through hole to obtain a Sn-Cu tube; a Nb-Zr alloy rod is placed into the Sn-Cu tube to obtain a structural component with a Nb-Zr alloy layer as the core layer, a Sn-Cu layer as the outermost layer, and the Sn-Cu layer and the Nb-Zr alloy layer arranged alternately. There is a gap between the Nb-Zr alloy rod and the Sn-Cu tube, and the gap between the Nb-Zr alloy rod and the Sn-Cu tube is filled with SnO2 powder. The filled structural component is then placed in an oxygen-free copper tube to obtain a Nb3Sn subcomponent blank. After multiple stretching, forming and cutting to size, the Nb3Sn subcomponent is obtained, such as Figure 4 The Nb3Sn subcomponent 22 includes, from the inside out, a Nb-Zr core 16, a SnO2 powder layer 12, a Sn layer 15, a Cu layer 11, and a Cu base tube 14.

[0061] Multiple Nb3Sn subcomponents are evenly arranged along the circumference of the oxygen-free copper core rod to form a cluster, such as Figure 3 , according to the hexagonal close packing, they are packed into an oxygen-free copper tube with an outer circle and an inner hexagonal shape to obtain Nb3Sn superconducting wire blanks, which are then subjected to heat treatment and cutting after multiple stretching. During the heat treatment process, the first heat treatment is carried out at a temperature of 500℃~550℃ for 30h, and then the second heat treatment is carried out at a temperature of 630℃~680℃ for 80h. The Nb3Sn superconducting wire is obtained, such as Figure 3 As shown in Figure 2, the Nb3Sn superconducting wire contains 54 Nb3Sn subcomponents and 7 oxygen-free copper core rods.

[0062] Comparative Example 1 A method for preparing a Nb3Sn superconducting wire comprises the following steps: The Sn ingot is placed in a copper cladding, and after the two ends are covered and sealed by electron beam welding, it is subjected to multiple passes of cold precision forging, stretching and cutting to a fixed length to obtain a Sn-Cu single core rod.

[0063] The composition of the Nb-Zr alloy rod is Nb-Zr alloy, which is composed of Zr, Ta and Nb. The molar percentage of Zr in the Nb-Zr alloy is 0.6%, and the molar percentage of Ta in the Nb-Zr alloy is 3%.

[0064] A central through hole and three peripheral through holes arranged around the central through hole are formed in the Nb-Zr alloy rod along the axial direction. The three peripheral through holes are evenly spaced along the circumferential direction with the axis of the Nb-Zr alloy tube as the center.

[0065] The Sn-Cu tube is filled with a central through hole, and the three peripheral through holes are filled with SnO2 powder. The filled structural parts are then placed into an oxygen-free copper tube to obtain a Nb3Sn subcomponent blank. After multiple stretching, forming and cutting to size, the Nb3Sn subcomponent is obtained. Figure 5The Nb3Sn subcomponent 22 includes, from the inside out, a Sn core 10, a Cu layer 11, a Nb-Zr alloy layer 13, SnO2 powder filled columns 17, and a Cu base tube 14; the SnO2 powder filled columns 17 are located in the three peripheral through holes of the Nb-Zr alloy layer 13.

[0066] Multiple Nb3Sn subcomponents are evenly arranged along the circumference of the oxygen-free copper core rod to form a cluster, such as Figure 3 , according to the hexagonal close packing, they are packed into an oxygen-free copper tube with an outer circle and an inner hexagonal shape to obtain Nb3Sn superconducting wire blanks, which are then subjected to heat treatment and cutting after multiple stretching. During the heat treatment process, the first heat treatment is carried out at a temperature of 500℃~550℃ for 50h, and then the second heat treatment is carried out at a temperature of 630℃~680℃ for 100h. The Nb3Sn superconducting wire is obtained, such as Figure 3 shown.

[0067] Comparative Example 2 A method for preparing a Nb3Sn superconducting wire, which differs from Example 1 in that no SnO2 powder is added. The specific preparation method includes the following steps: The Sn ingot is placed in a copper cladding, and after the two ends are covered and sealed by electron beam welding, it is subjected to multiple passes of cold precision forging, stretching and cutting to a fixed length to obtain a Sn-Cu single core rod.

[0068] The composition of the Nb-Zr alloy rod is Nb-Zr alloy, which is composed of Zr, Ta and Nb. The molar percentage of Zr in the Nb-Zr alloy is 0.6%, and the molar percentage of Ta in the Nb-Zr alloy is 3%.

[0069] A Nb-Zr alloy rod is axially bored to create a Nb-Zr alloy tube. A single Sn-Cu core rod is then inserted into the Nb-Zr alloy tube, forming a structural component with a Sn-Cu core layer and a Nb-Zr alloy layer as the outermost layer. The structural component is then inserted into an oxygen-free copper tube to create a Nb3Sn subcomponent. The Nb3Sn subcomponent consists, from the inside out, of a Sn core, a Cu layer, a Nb-Zr alloy layer, and a Cu base tube.

[0070] The oxygen-free copper core rod is obtained by stretching, forming and cutting the copper rod to a predetermined length.

[0071] Multiple Nb3Sn subcomponents are evenly arranged along the circumference of the oxygen-free copper core rod to form a cluster, such as Figure 3 , according to the hexagonal close packing, they are packed into an oxygen-free copper tube with an outer circle and an inner hexagonal shape to obtain Nb3Sn superconducting wire blanks, which are then subjected to heat treatment and cutting after multiple stretching. During the heat treatment process, the first heat treatment is carried out at a temperature of 500℃~550℃ for 50h, and then the second heat treatment is carried out at a temperature of 630℃~680℃ for 100h. The Nb3Sn superconducting wire is obtained, such as Figure 3 shown.

[0072] In Examples 1 to 3 of the present invention, Nb-Zr alloy and SnO2 oxide powder are introduced during the preparation of Nb3Sn superconducting wire. During the heat treatment process, SnO2 provides oxygen elements to the Nb-Zr layer to generate ZrO2 particles. These particles exist as defects in the superconductor in the superconductor, and have a pinning effect on the movement of magnetic flux. By arranging the distribution position of SnO2 powder and guiding the diffusion of ZrO2 particles during the heat treatment process, an artificial point pinning array with a density gradient distribution can be generated. By controlling the heat treatment time, the ZrO2 particles can be controlled to be distributed in Nb3Sn with different concentration gradients. As Figure 2 As shown in Figure 3, the introduction of SnO2 and Nb-Zr layers inside the Nb3Sn subcomponent can produce multilayer ZrO2 particles in Nb3Sn.

[0073] To verify the feasibility of the methods of Examples 1 to 3 of the present invention, numerical simulations were performed to introduce artificial point pinning with a gradient distribution of varying average densities within the Nb3Sn polycrystalline structure, and the critical current density of the Nb3Sn was calculated. During the simulation, an electromagnetic model of the Nb3Sn grain boundaries with artificial point pinning was established based on the internal structure, material, and dimensions of a realistic Nb3Sn superconducting wire. Current was then applied to the electromagnetic model under different external magnetic fields to determine the critical current density of the Nb3Sn grain boundary electromagnetic model.

[0074] The results show that the introduction of artificial point pinning with a gradient distribution of a certain average density inside the electromagnetic model of the Nb3Sn grain boundary can maximize the enhancement of 9T≤ H a Critical current density at ≤16T.

[0075] Figure 9 This is a comparison chart of the numerical simulation and scaling law fitting curve of the electromagnetic model of the Nb3Sn grain boundary without artificial point pinning in Comparative Example 2. Figure 9 The image shows the critical current density-magnetic field curve for an electromagnetic model of Nb3Sn grain boundaries without artificial pinning. The solid line is a continuous function fitted according to the scaling law, and the dashed line is the result of numerical simulation. It can be seen that the numerical simulation results fit the scaling law curve well, demonstrating the reliability of the numerical simulation method.

[0076] Figure 6 Schematic diagram of the Nb3Sn polycrystalline structure with artificial point pinning with gradient distribution introduced in Example 1. Figure 7 Schematic diagram of the Nb3Sn polycrystalline structure with artificial point pinning with uniformly arranged triangles introduced in Comparative Example 1. Figure 8Schematic diagram of the Nb3Sn polycrystalline structure without artificial point pinning in Comparative Example 2.

[0077] The numerical simulation method was used to simulate the electromagnetic model of the Nb3Sn grain boundary with artificial pinning points of uniform arrangement and gradient distribution introduced into the Nb3Sn polycrystalline structure, and the simulation results were compared with the electromagnetic model of the Nb3Sn grain boundary without artificial pinning points. The schematic diagram of the electromagnetic model of the Nb3Sn grain boundary with artificial pinning points of gradient distribution introduced into the Nb3Sn polycrystalline structure in Example 1 is shown in FIG. Figure 6 As shown in FIG, the white part is the superconducting material, the black lines are the grain boundaries, and the black dot matrix is ​​the artificial dot pinning. Schematic diagram of the electromagnetic model of the grain boundary of Nb3Sn grains with artificial dot pinning arranged uniformly in triangles in Comparative Example 1, as shown in FIG. Figure 7 Schematic diagram of the electromagnetic model of the Nb3Sn grain boundary without artificial pinning in the Nb3Sn polycrystalline structure in Comparative Example 2, as shown in FIG. Figure 8 As shown, for comparison.

[0078] Figure 10 The effects of introducing artificial pinning with different arrangements on the critical current density of Nb3Sn superconducting wires are demonstrated. Figure 10 It can be seen that the gradient distribution of artificial point pinning can significantly improve the Nb3Sn superconducting wire at high field 0.3 H c2 ≤ H a ≤0.5 H c2 The critical current density at high field is improved to that at 9 T to 16 T. Triangular uniformly arranged artificial pinning can also improve the critical current density of Nb3Sn superconducting wire at high field to a certain extent. However, its critical current density at the same magnetic field is still relatively low.

[0079] pass Figures 4 to 8 Contrast combination Figure 10 It was found that the introduction of gradient-distributed artificial pinning points within the Nb3Sn polycrystalline structure in Example 1 can effectively enhance the critical current density in the Nb3Sn grain boundary electromagnetic model. This shows that the introduction of gradient-distributed artificial pinning points within the Nb3Sn polycrystalline structure can effectively enhance the critical current density of the Nb3Sn superconducting wire.

[0080] Figure 11The effect of varying the average density of gradient-distributed artificial pinning points on the critical current density-magnetic field relationship in an electromagnetic model of Nb3Sn grain boundaries is demonstrated. Gradient-distributed artificial pinning points were introduced into the electromagnetic model of Nb3Sn grain boundaries, and the number of pinning points in the model was counted. The average density in the model of gradient-distributed artificial pinning points was calculated by calculating the spacing between all adjacent artificial pinning points and taking the average value. Furthermore, uniformly distributed artificial pinning points were introduced into the electromagnetic model of Nb3Sn grain boundaries, and the number of artificial pinning points in the model was counted.

[0081] In the electromagnetic model of Nb3Sn grain boundaries, artificial point pinning with gradient distribution of different average densities is introduced, and its critical current density is simulated under different magnetic fields. Figure 11 As can be seen in the figure, when the average spacing of the artificial pinning points is 17nm, the critical current density in the Nb3Sn grain boundary electromagnetic model reaches its highest value under high fields. This shows that introducing gradient-distributed artificial pinning points can effectively improve the critical current density level of Nb3Sn superconducting wires under high fields.

[0082] Figure 12 This study demonstrates the effect of varying the density ratio of gradient-distributed artificial pinning on the critical current density-magnetic field relationship in an electromagnetic model of Nb3Sn grain boundaries. Gradient-distributed artificial pinning was introduced into the Nb3Sn grain boundary electromagnetic model. The density ratio, a parameter representing the unevenness of the artificial pinning distribution, was calculated by counting the ratio of the number of artificial pinning points at the dense and sparse ends of the model. A dense ratio indicates a high density, while a sparse ratio indicates a low density.

[0083] The average spacing of artificial pinning is 12nm, and artificial pinning with gradient distribution of different density ratios is introduced into the electromagnetic model of Nb3Sn grain boundary, and its critical current density is simulated under different magnetic fields. Figure 12 It can be seen that the greater the density of the artificial point pinning with gradient distribution is, the greater the Nb3Sn grain boundary electromagnetic model shows in the high magnetic field range of 0.3 H c2 ≤ H a ≤0.5 H c2 From this, it can be seen that when the density of gradient-distributed artificial point pinning is relatively large, the critical current density of Nb3Sn superconducting wire under high field can be effectively improved.

[0084] Compared with the existing technology, the method of the embodiment of the present invention has a lower cost effect. The embodiment of the present invention introduces gradient-distributed artificial point pinning inside the Nb3Sn polycrystalline structure without changing the main structure of the existing Nb3Sn wire. After the embodiment of the present invention introduces a certain density of gradient-distributed artificial point pinning into the Nb3Sn polycrystalline structure, the critical current density of the Nb3Sn superconducting wire under high field is significantly improved. The gradient-distributed artificial point pinning is effective in the high magnetic field range of 0.3 H c2 ≤ H a ≤0.5 H c2 It can effectively enhance the critical current density of Nb3Sn superconducting wire and solve the matching effect problem of the uniformly arranged artificial point pinning model.

[0085] The above are only 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 in the scope of protection of the present invention.

Claims

1. A method for preparing a Nb3Sn superconducting wire, characterized in that: The following steps are involved: A Sn-Cu layer or a Nb-Zr alloy layer is used as a core layer, and Sn-Cu layers and Nb-Zr alloy layers are arranged alternately outside the core layer to obtain a structural component; a gap is formed between the Sn-Cu layer and the Nb-Zr alloy layer, and the gap is filled with oxide powder. The filled structural component is installed in a copper-based tube, and after multiple stretching, forming and cutting to a predetermined length, the Nb3Sn subcomponent is obtained; The Nb3Sn subcomponents are evenly arranged along the circumference of the copper core rod to form a bundle, which is then loaded into a copper tube. After multiple stretching steps, the Nb3Sn superconducting wire is heat treated and cut to obtain the Nb3Sn superconducting wire. The heat treatment process is: performing a first heat treatment at 500°C to 550°C to react the Nb-Zr alloy with the oxide powder to form ZrO2 particles, and then performing a second heat treatment at 630°C to 680°C to form a density gradient distribution of the formed ZrO2 particles along the radial direction of the Nb3Sn subcomponent.

2. The method for preparing a Nb3Sn superconducting wire according to claim 1, wherein: The time for the first heat treatment is 30h~60h; the time for the second heat treatment is 80h~120h.

3. The method for preparing the Nb3Sn superconducting wire according to claim 1, wherein: The processing method of the structural part with Sn-Cu layer as the core layer is as follows: A through hole is opened in the axial direction of a Nb-Zr alloy rod to obtain a Nb-Zr alloy tube; a Sn-Cu single core rod is installed in the Nb-Zr alloy tube to form a structural component with a Sn-Cu layer as the core layer.

4. The method for preparing the Nb3Sn superconducting wire according to claim 1, wherein: The processing method of the structural part with Nb-Zr alloy layer as the core layer is as follows: A through hole is opened in the axial direction of a Nb-Zr alloy rod to obtain a Nb-Zr alloy tube; a through hole is opened in the axial direction of 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 the Nb-Zr alloy rod is inserted into the Sn-Cu tube to obtain a structural component with a Nb-Zr alloy layer as the core layer.

5. The method for preparing the Nb3Sn superconducting wire according to claim 1, wherein: The processing method of the structural part with Nb-Zr alloy layer as the core layer is as follows: A through hole is opened in the axial direction of a Sn-Cu single core rod to obtain a Sn-Cu tube; a Nb-Zr alloy rod is loaded into the Sn-Cu tube to obtain a structural component with a Nb-Zr alloy layer as a core layer.

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

7. The method for preparing a Nb3Sn superconducting wire according to any one of claims 3 to 5, characterized in that: Sn-Cu single core rod is made by placing Sn ingot into copper cladding, sealing both ends with covers, and then undergoing multiple passes of cold forging, stretching and cutting to length.

8. The method for preparing a Nb3Sn superconducting wire according to claim 1, wherein: Using ZrO2 particles as artificial point pinning, the ZrO2 particles are set to generate a density gradient distribution along the radial direction of the Nb3Sn subcomponent to form a density gradient distribution layer of ZrO2 particles. The average spacing of the artificial point pinning of the density gradient distribution layer of ZrO2 particles is 17nm to 42nm.

9. The method for preparing a Nb3Sn superconducting wire according to claim 8, wherein: The average spacing of artificial point pinning in the density gradient distribution layer of ZrO2 particles is 17nm to 26nm.

10. The method for preparing a Nb3Sn superconducting wire according to claim 1, wherein: The oxide powder is SnO2.

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