A method for preparing a low-loss tin source distributed Nb3Sn wire

Abstract

This invention belongs to the field of superconducting material preparation, specifically relating to a method for preparing low-loss tin-source distributed Nb3Sn wire. The method involves drilling holes in an oxygen-free copper ingot in a hexagonal close-packed or ring-shaped distribution pattern, inserting Nb rods to form a hexagonal CuNb composite rod; simultaneously, SnTi / Cu single-core rods are prepared. Then, the CuNb composite rod and SnTi / Cu single-core rod are assembled into an NbTa alloy tube in a hexagonal close-packed pattern, and externally covered with an oxygen-free copper tube to form the final billet. The final billet is stretched, twisted, and finally stretched again to obtain strands, which are then heat-treated to obtain low-loss tin-source distributed Nb3Sn wire. This invention, by optimizing the tin source distribution and core wire structure, combined with low-temperature long-time heat treatment, achieves Nb3Sn grain refinement, effectively balancing high critical current density and low AC loss, making it suitable for demanding applications such as high-field pulse magnets and poloidal field coils in fusion devices.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material preparation, specifically relating to a method for preparing low-loss tin-source distributed Nb3Sn wire. Background Technology

[0002] Nb3Sn is one of the key materials in the field of high-field superconducting magnets, and it is widely used in high-energy physics devices, controlled nuclear fusion devices, and next-generation high-field scientific instruments. These applications place stringent requirements on superconducting materials, requiring them not only to have high critical current density and upper critical field under high magnetic fields, but also to maintain low AC loss under alternating magnetic field conditions to ensure the stability and energy efficiency of the magnet during pulsed operation.

[0003] Currently, the mainstream methods for preparing Nb3Sn wires include the bronze method and the internal tin method. While the bronze method produces wires with relatively low AC losses, its process is lengthy, tin source is limited, and improving the critical current density faces bottlenecks. The internal tin method, such as RRP, can achieve higher critical current densities, but its uneven tin source distribution and complex barrier layer structure result in larger effective core wire sizes, inhomogeneous superconducting phase grain structures, and numerous grain boundaries and defects. Under alternating magnetic fields, these wires are prone to significant flux jumps and eddy current losses, making it difficult to meet the low-loss requirements of rapid pulsed operation scenarios such as poloidal field coils in fusion devices.

[0004] The existing Nb3Sn wire exhibits a significant contradiction between "high critical current density" and "low AC loss," becoming a key technical challenge restricting its large-scale application in high-field pulsed magnets. Developing a novel Nb3Sn wire fabrication process that can maintain both high critical current density and high upper critical field characteristics while significantly reducing AC loss is a crucial technical bottleneck that urgently needs to be overcome in the field of superconducting materials. Summary of the Invention

[0005] This invention aims to overcome the contradiction between critical current density and AC loss in existing Nb3Sn wires, and provides a novel method for preparing Nb3Sn wires that can maintain a high critical current density while significantly reducing AC loss. To achieve the above objective, this invention adopts the following technical solution.

[0006] On one hand, the present invention provides a method for preparing low-loss tin-source distributed Nb3Sn wire, the method comprising the following steps:

[0007] Step 1: Drill holes in oxygen-free copper ingots in a hexagonal close-packed or ring-shaped pattern to produce porous oxygen-free copper ingots. Insert Nb rods into the porous oxygen-free copper ingots to obtain CuNb composite rods with a copper ratio of 0.55~2.5.

[0008] Step 2: Insert the SnTi alloy rod into an oxygen-free copper tube to obtain a SnTi / Cu single-core rod with a copper ratio of 0.20~0.50;

[0009] Step 3: Assemble the CuNb composite rod obtained in Step 1 and the SnTi / Cu single core rod obtained in Step 2 into the NbTa alloy tube in a hexagonal close-packing manner, and set an oxygen-free copper tube on the outside to obtain the final billet.

[0010] Step 4: The final billet obtained in Step 3 is stretched, twisted, and stretched again to obtain Nb3Sn strands.

[0011] Step 5: Heat-treat the Nb3Sn strands obtained in Step 4. The heat treatment includes holding at 610~630℃ for 150~250h to generate the Nb3Sn phase.

[0012] Furthermore, in the method for preparing the low-loss tin-source distributed Nb3Sn wire, the diameter of the hole in step one is 5.0~15.0mm, and the spacing between the holes is 1.0~5.0mm.

[0013] Furthermore, in the preparation method of the low-loss tin-source distributed Nb3Sn wire, the mass percentage of Ti in the SnTi alloy rod is 1.5~2.5%, and the balance is Sn.

[0014] Furthermore, in the preparation method of the low-loss tin-source distributed Nb3Sn wire, in step three, in the final blank, except for the edges, each SnTi / Cu single core rod is surrounded by 6 CuNb composite rods, and each CuNb composite rod is adjacent to 3 SnTi / Cu single core rods and 3 CuNb composite rods. The edge SnTi / Cu single core rods are fan-shaped or hexagonal, and the edge SnTi / Cu single core rods can be replaced with CuNb composite rods.

[0015] Secondly, this invention also provides a low-loss tin-source distributed Nb3Sn wire prepared by the method described in this invention, wherein the critical current density of the low-loss tin-source distributed Nb3Sn wire under conditions of 4.2K and 12T is not less than 1514A / mm². 2 The AC loss under a magnetic field variation of ±3T is no higher than 554 mJ / cm. 3 .

[0016] Thirdly, a CuNb composite rod is also provided, which is made by embedding Nb rods in an oxygen-free copper ingot. The cross-section is hexagonal and the copper ratio is 0.55~2.5. The Nb rods are embedded in holes drilled in the oxygen-free copper ingot in a hexagonal close-packed or annular distribution manner. The diameter of the holes is 5.0~15.0 mm and the spacing between the holes is 1.0~5.0 mm.

[0017] Fourthly, a final blank for preparing the low-loss tin-source distributed Nb3Sn wire of the present invention is also provided. The final blank includes an NbTa alloy tube, a CuNb composite rod and a SnTi / Cu single core rod arranged in a hexagonal close-packed manner in the NbTa alloy tube, and an external oxygen-free copper tube.

[0018] Finally, the invention also provides the application of the low-loss tin-source distributed Nb3Sn wire described in this invention in high-field pulse magnets, poloidal field coils of fusion devices, or magnets of high-energy physics detectors.

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

[0020] (1) This invention creates a large number of independent, small-scale Nb-Sn diffusion reaction units by distributing tin sources (SnTi / Cu single core rods) into an array of Nb sources (CuNb composite rods) in a discrete and regular manner. After heat treatment, this structure can form fine and uniformly distributed Nb3Sn core wires, which not only provide abundant current transmission channels to obtain a high critical current density Jc, but also significantly reduce hysteresis loss and eddy current loss in alternating magnetic fields due to the small size of the core wires, controllable spacing and weakened coupling.

[0021] (2) The method of first preparing CuNb composite rods and SnTi / Cu single core rods and then assembling them in a hexagonal manner avoids the wire breakage problem caused by the large difference in material hardness and the complex processing in the traditional inner tin method or bronze method, thereby improving the stability and yield of wire preparation.

[0022] (3) By adjusting the diameter and spacing of the drill holes and the copper ratio of CuNb composite rods and SnTi / Cu single core rods, the size, spacing and copper-to-non-copper ratio of Nb core wires in the final wire can be flexibly and precisely controlled, thereby enabling customized design for different application magnetic fields and loss requirements.

[0023] (4) A low-temperature, long-term heat treatment process of 610~630℃ is adopted to avoid rapid coarsening of Nb3Sn grains at high temperatures. This process is conducive to the formation of fine Nb3Sn grains, increasing grain boundary density and improving the critical current density of the wire under high field.

[0024] (5) The Nb3Sn wire prepared by the preparation method provided by the present invention has both high critical current density (up to 2580A / mm² at 4.2K and 12T) and low AC loss (down to 389 mJ / cm³ under ±3T magnetic field change). This wire meets the requirements of high field pulse magnets, poloidal field coils of fusion devices, and magnets of high energy physics detectors, which have stringent performance requirements. It can meet the requirements of stable and efficient operation in rapidly changing magnetic fields and has broad application prospects. Attached Figure Description

[0025] Figure 1 This is a cross-sectional view of the CuNb composite ingot prepared in Example 1.

[0026] Figure 2 The images show the final cross-sectional views of the billets prepared in Examples 1-3.

[0027] Figure 3 This is a cross-sectional view of the CuNb composite ingot prepared in Example 2.

[0028] Figure 4 This is a cross-sectional view of the final billet prepared in Example 4.

[0029] Explanation of reference numerals in the attached figures: 1. Porous copper ingot; 2. Nb rod; 3. CuNb composite rod; 4. SnTi / Cu single-core rod; 5. NbTa alloy tube; 6. Oxygen-free copper tube. Detailed Implementation

[0030] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0031] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0032] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0033] In this invention, "copper ratio" refers to the ratio of the volume of copper to the volume of non-copper.

[0034] Example 1

[0035] This example provides a method for preparing low-loss tin-source distributed Nb3Sn wire, the specific steps of which are as follows:

[0036] Step 1: Drill holes in the oxygen-free copper ingot using a hexagonal close-packing method. The spacing between adjacent holes in the oxygen-free copper ingot is 2.0mm, the size of the hole is Φ10.0mm, and the number of holes is 253, thus producing a porous oxygen-free copper ingot.

[0037] Step 2: Insert the cleaned Nb rod into the holes of a cleaned porous oxygen-free copper ingot to obtain a CuNb composite ingot. Perform degassing, welding, extrusion, stretching, peeling, forming, cutting, and straightening processes on the obtained CuNb composite ingot to produce hexagonal CuNb composite rods. The copper ratio (copper volume: non-copper volume) of the hexagonal CuNb composite rod is 1.5. The cross-section of the CuNb composite ingot is shown below. Figure 1 As shown;

[0038] Step 3: Tin and tin-titanium alloy are melted, turned and extruded to obtain Sn2Ti (wt.%) alloy rods. The Sn2Ti alloy rods are peeled and cleaned, and then put into clean oxygen-free copper tubes. After stretching, hexagonal forming and cutting, hexagonal and fan-shaped SnTi / Cu single core rods with a copper ratio of 0.35 are obtained.

[0039] Step 4: Assemble the hexagonal CuNb composite rods obtained in Step 2 and the SnTi / Cu single-core rods obtained in Step 3 in a hexagonal close-packed manner within an NbTa alloy tube. Except for the edge portions, each SnTi / Cu single-core rod is surrounded by 6 CuNb composite rods, and each CuNb composite rod is adjacent to 3 SnTi / Cu single-core rods and 3 CuNb composite rods. The areas where the edges cannot be completely filled with hexagonal SnTi / Cu single-core rods are designated as fan-shaped SnTi / Cu single-core rods. Then, insert an oxygen-free copper tube to obtain the final billet. A cross-sectional diagram of the final billet is shown below. Figure 2 As shown. The final billet is stretched, twisted, and finally stretched to obtain Nb3Sn strands.

[0040] Step 5: Staged heat treatment. The Nb3Sn strands obtained in Step 4 are first heated at a low temperature of 210±10℃ for 50 hours to allow Sn-Cu to slowly interdiffuse. Then, the temperature is raised to 400±10℃ and held for 50 hours to fully alloy Sn-Cu. Finally, the temperature is raised to 620℃ and held for 200 hours to generate the Nb3Sn phase, thus obtaining the low-loss tin-source distributed Nb3Sn wire.

[0041] Testing revealed that the loss of this low-loss tin-source distributed Nb3Sn wire was 456 mJ / cm². 3 (±3T), critical current density is 2187A / mm 2 (@4.2K, 12T).

[0042] Example 2

[0043] Step 1: Drill holes in the oxygen-free copper ingot in a ring-shaped pattern. The spacing between adjacent holes in the oxygen-free copper ingot is 5.0 mm, the size of the hole is Φ15.0 mm, and the number of holes is 19, thus producing a porous oxygen-free copper ingot (the holes on the oxygen-free copper ingot are distributed in a ring).

[0044] Step 2: The cleaned Nb rods are inserted into the holes of a cleaned porous oxygen-free copper ingot (the holes on the oxygen-free copper ingot are distributed in a ring) to obtain a CuNb composite ingot. The obtained CuNb composite ingot is then subjected to degassing, welding, extrusion, stretching, peeling, forming, cutting, and straightening processes to produce hexagonal CuNb composite rods. The copper ratio (copper volume: non-copper volume) of the hexagonal CuNb composite rods is 2.5. The cross-section of the CuNb composite ingot is shown below. Figure 3 As shown;

[0045] Step 3: Tin and tin-titanium alloy are melted, turned and extruded to obtain Sn1.5Ti (wt.%) alloy rods. The Sn1.5Ti alloy rods are peeled and cleaned, and then put into clean oxygen-free copper tubes. After stretching, hexagonal forming and cutting, hexagonal and fan-shaped SnTi / Cu single core rods with a copper ratio of 0.5 are obtained.

[0046] Step 4: Assemble the CuNb composite rods obtained in Step 2 and the SnTi / Cu single-core rods obtained in Step 3 in a hexagonal close-packed manner within an NbTa alloy tube. Except for the edge portions, each SnTi / Cu single-core rod is surrounded by 6 CuNb composite rods, and each CuNb composite rod is adjacent to 3 SnTi / Cu single-core rods and 3 CuNb composite rods. The areas where the edges cannot be completely filled with hexagonal SnTi / Cu single-core rods are designated as fan-shaped SnTi / Cu single-core rods. Then, insert an oxygen-free copper tube to obtain the final billet. A cross-sectional diagram of the final billet is shown below. Figure 2 As shown. The final billet is stretched, twisted, and finally stretched to obtain Nb3Sn strands.

[0047] Step 5: Staged heat treatment. The Nb3Sn strands obtained in Step 4 are first held at a low temperature of 210±10℃ for 50 hours, during which Sn-Cu undergoes slow interdiffusion. Then, the temperature is increased to 400±10℃ and held for another 50 hours, during which Sn-Cu is fully alloyed. Finally, the temperature is increased to 630℃ and held for 150 hours to generate the Nb3Sn phase. This yields a low-loss tin-source distributed Nb3Sn wire.

[0048] Testing revealed that the loss of this low-loss tin-source distributed Nb3Sn wire was 389 mJ / cm². 3 (±3T), critical current density 1514A / mm 2 (@4.2K, 12T).

[0049] Example 3

[0050] This example provides a method for preparing low-loss tin-source distributed Nb3Sn wire, the specific steps of which are as follows:

[0051] Step 1: Drill holes in the oxygen-free copper ingot using a hexagonal close-packing method. The spacing between adjacent holes in the oxygen-free copper ingot is 1.0mm, the size of the hole is Φ5.0mm, and the number of holes is 379, thus producing a porous oxygen-free copper ingot.

[0052] Step 2: Insert the cleaned Nb rod into the hole of the cleaned porous oxygen-free copper ingot to obtain CuNb composite ingot. Perform degassing, welding, extrusion, stretching, peeling, forming, cutting and straightening processes on the obtained CuNb composite ingot to make hexagonal CuNb composite rod. The copper ratio (copper volume: non-copper volume) of the CuNb composite rod is 0.85.

[0053] Step 3: Tin and tin-titanium alloy are melted, turned and extruded to obtain Sn2.5Ti (wt.%) alloy rods. The Sn2.5Ti alloy rods are peeled and cleaned, and then placed into clean oxygen-free copper tubes. After stretching, hexagonal forming and cutting, hexagonal and fan-shaped SnTi / Cu single core rods with a copper ratio of 0.3 are obtained.

[0054] Step 4: Assemble the hexagonal CuNb composite rods obtained in Step 2 and the SnTi / Cu single-core rods obtained in Step 3 in a hexagonal close-packed manner within an NbTa alloy tube. Except for the edge portions, each SnTi / Cu single-core rod is surrounded by 6 CuNb composite rods, and each CuNb composite rod is adjacent to 3 SnTi / Cu single-core rods. The areas where the edges cannot be completely filled with hexagonal SnTi / Cu single-core rods are designated as fan-shaped SnTi / Cu single-core rods. Then, insert an oxygen-free copper tube to obtain the final billet. A cross-sectional diagram of the final billet is shown below. Figure 2 As shown. The final billet is stretched, twisted, and finally stretched to obtain Nb3Sn strands.

[0055] Step 5: Staged heat treatment. The Nb3Sn strands obtained in Step 4 are first held at a low temperature of 210±10℃ for 50 hours, during which Sn-Cu undergoes slow interdiffusion. Then, the temperature is raised to 400±10℃ and held for 50 hours, during which Sn-Cu is fully alloyed. Finally, the temperature is raised to 610℃ and held for 250 hours to generate the Nb3Sn phase, thus obtaining the low-loss tin-source distributed Nb3Sn wire.

[0056] Testing revealed that the loss of this low-loss tin-source distributed Nb3Sn wire was 452 mJ / cm². 3 (±3T), critical current density 2340A / mm 2 (@4.2K, 12T).

[0057] Example 4

[0058] This example provides a method for preparing low-loss tin-source distributed Nb3Sn wire, the specific steps of which are as follows:

[0059] Step 1: Drill holes in the oxygen-free copper ingot using a hexagonal close-packing method. The spacing between adjacent holes in the oxygen-free copper ingot is 1.0mm, the size of the hole is Φ12.2mm, and the number of holes is 85, thus producing a porous oxygen-free copper ingot.

[0060] Step 2: Insert the cleaned Nb rod into the hole of the cleaned porous oxygen-free copper ingot to obtain CuNb composite ingot. Perform degassing, welding, extrusion, stretching, peeling, forming, cutting and straightening processes on the obtained CuNb composite ingot to make hexagonal CuNb composite rod. The copper ratio (copper volume: non-copper volume) of the CuNb composite rod is 0.55.

[0061] Step 3: Tin (Sn) and tin-titanium alloy are melted, turned and extruded to obtain Sn2Ti (wt.%) alloy rods. The Sn2Ti alloy rods are peeled and cleaned, and then put into clean oxygen-free copper tubes. After stretching, hexagonal forming and cutting, hexagonal and fan-shaped SnTi / Cu single core rods with a copper ratio of 0.20 are obtained.

[0062] Step 4: Assemble the hexagonal CuNb composite rods obtained in Step 2 and the SnTi / Cu single-core rods obtained in Step 3 in a hexagonal close-packed manner within an NbTa alloy tube. Except for the edge portions, each SnTi / Cu single-core rod is surrounded by 6 CuNb composite rods, and each CuNb composite rod is adjacent to 3 SnTi / Cu single-core rods and 3 CuNb composite rods. To further increase the Nb content in the wire, in this example, the edges that should have been occupied by hexagonal or fan-shaped SnTi / Cu single-core rods are replaced with CuNb composite rods. Then, insert an oxygen-free copper tube to obtain the final billet. A cross-sectional diagram of the final billet is shown below. Figure 4 As shown. The final billet is stretched, twisted, and finally stretched to obtain Nb3Sn strands.

[0063] Step 5: Staged heat treatment. The Nb3Sn strands obtained in Step 4 are first held at a low temperature of 210±10℃ for 50 hours, during which Sn-Cu undergoes slow interdiffusion. Then, the temperature is raised to 400±10℃ and held for 50 hours, during which Sn-Cu is fully alloyed. Finally, the temperature is raised to 610℃ and held for 250 hours to generate the Nb3Sn phase, thus obtaining the low-loss tin-source distributed Nb3Sn wire.

[0064] Testing revealed that the loss of this low-loss tin-source distributed Nb3Sn wire was 554 mJ / cm. 3 (±3T), critical current density 2580A / mm 2 (@4.2K, 12T).

[0065] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a low-loss tin-source distributed Nb3Sn wire, characterized in that, Includes the following steps: Step 1: Drill holes in oxygen-free copper ingots in a hexagonal close-packed or ring-shaped pattern to produce porous oxygen-free copper ingots. Insert Nb rods into the porous oxygen-free copper ingots to produce CuNb composite rods with a hexagonal cross-section and a copper ratio of 0.85~2.

5. The diameter of the holes is 5.0~15.0 mm and the spacing between the holes is 1.0~5.0 mm. Step 2: Insert the SnTi alloy rod into an oxygen-free copper tube to obtain a SnTi / Cu single-core rod with a hexagonal or fan-shaped cross-section and a copper ratio of 0.20~0.

50. The mass percentage of Ti in the SnTi alloy rod is 1.5~2.5%, and the balance is Sn. Step 3: Assemble the CuNb composite rods obtained in Step 1 and the SnTi / Cu single core rods obtained in Step 2 into the NbTa alloy tube in a hexagonal close-packed manner, and set the oxygen-free copper tube on the outside to obtain the final billet. Except for the edge, each SnTi / Cu single core rod is surrounded by 6 CuNb composite rods, and each CuNb composite rod is adjacent to 3 SnTi / Cu single core rods and 3 CuNb composite rods. Step 4: The final billet obtained in Step 3 is stretched, twisted, and stretched again to obtain Nb3Sn strands. Step 5: Heat-treat the Nb3Sn strands obtained in Step 4. First, keep them at 210±10℃ for 40~60 hours, then keep them at 400±10℃ for 40~60 hours, and finally keep them at 610~630℃ for 150~250 hours to generate the Nb3Sn phase.

2. A low-loss tin-source distributed Nb3Sn wire prepared by the preparation method described in claim 1, characterized in that, The wire has a fine-scale Nb3Sn filament array derived from discretely distributed SnTi / Cu single-core rods, and the Nb3Sn filament array is isolated by a copper substrate; the critical current density of the low-loss tin-source distributed Nb3Sn wire at 4.2K and 12T is not less than 1514A / mm². 2 The AC loss under a magnetic field variation of ±3T is no higher than 456mJ / cm. 3 .

3. A CuNb composite rod for preparing the low-loss tin-source distributed Nb3Sn wire of claim 2, characterized in that, The CuNb composite rod is made by embedding Nb rods into an oxygen-free copper ingot. The cross-section is hexagonal and the copper ratio is 0.85~2.

5. The Nb rods are embedded in holes drilled in the oxygen-free copper ingot in a hexagonal close-packed or ring-shaped manner. The diameter of the holes is 5.0~15.0 mm and the spacing between the holes is 1.0~5.0 mm.

4. A final blank for preparing the low-loss tin-source distributed Nb3Sn wire as described in claim 2, characterized in that, The final billet includes an NbTa alloy tube, a CuNb composite rod and a SnTi / Cu single core rod arranged in a hexagonal close-packed manner within the NbTa alloy tube, and an external oxygen-free copper tube.

5. The application of the low-loss tin-source distributed Nb3Sn wire as described in claim 2 in high-field pulse magnets, poloidal field coils of fusion devices, or magnets of high-energy physics detectors.

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