A method for fabricating Nb3Sn superconducting wires using a die-stretching method with internal tin.

Abstract

This invention belongs to the field of superconducting wire processing technology, specifically relating to a method for preparing Nb3Sn superconducting wire using the internal tin method with a dieless stretching process. The method involves continuously passing the Nb3Sn superconducting base wire prepared by the internal tin method through an integrated processing zone, where preheating, reaction initiation, main reaction, and heat preservation treatments are performed sequentially. During the main reaction treatment, the wire undergoes in-line induction heating while simultaneously experiencing axial dieless stretching. Finally, the integrated processing steps are repeated at least once to control the wire's dimensions and properties, resulting in the finished Nb3Sn superconducting wire. This invention couples dieless stretching deformation with in-situ partitioned induction heating, achieving simultaneous Nb3Sn phase formation and microstructure control, significantly shortening the processing cycle and effectively improving the consistency and mechanical stability of the wire's properties.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire processing technology, specifically relating to a method for preparing Nb3Sn superconducting wires by internal tin method without mold stretching. Background Technology

[0002] Nb3Sn superconducting wires possess high critical current densities, making them an important raw material for manufacturing high-field magnets. The internal tin method is one of the main methods for preparing Nb3Sn superconducting wires. Currently, the highest-performing and most widely used Nb3Sn superconducting wires internationally are all prepared using the internal tin method. Existing technologies primarily involve a three-stage assembly process: inserting Nb rods into porous copper ingots to assemble an internal tin-based Nb3Sn CuNb composite sheath; inserting SnTi alloy rods into CuNb composite tubes to assemble internal tin-based Nb3Sn subcomponents; and finally assembling the composite wire (subcomponents, Ta tube, copper tube). This process is followed by high-temperature heat treatment to prepare the internal tin-based Nb3Sn composite wire.

[0003] Currently, the preparation method of Nb3Sn composite wire using the internal tin method requires a process of (drawing-forming-magnet winding-heat treatment-phase formation), which has a long processing cycle and can take up to 30-40 days. Furthermore, the heat-treated Nb3Sn is highly brittle, making further processing impossible using the "reaction-then-drawing" method; while the "drawing-then-reaction" method easily introduces microcracks during processing. In addition, heat treatment relies on large tube furnaces or box furnaces, with static heating of the entire coil, resulting in low thermal efficiency and high energy consumption per unit product. The temperature gradient within the furnace causes uneven axial and radial thermal fields, leading to significant differences in the thickness and distribution of the Nb3Sn phase, affecting the consistency of current-carrying performance. Therefore, there is an urgent need to develop a method for preparing Nb3Sn superconducting wires that can significantly improve processing efficiency, shorten processing time, and maintain Nb3Sn performance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing Nb3Sn superconducting wires by online heat treatment via dieless stretching using the internal tin method, in order to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] On the one hand, a method for preparing a die-stretched, internally tin-based Nb3Sn superconducting wire is provided, the method comprising the following steps:

[0007] S1. Provide Nb3Sn superconducting base wires using the internal tin method;

[0008] S2. The base wire is continuously passed through an integrated processing zone, in which the base wire sequentially undergoes preheating treatment, reaction initiation treatment, main reaction treatment, and heat preservation treatment.

[0009] In the main reaction process, the base wire is subjected to axial moldless tension while undergoing online induction heating.

[0010] S3. Repeat step S2 at least once to adjust the wire size and performance to obtain the finished Nb3Sn superconducting wire.

[0011] Furthermore, in the preparation method, the temperature of the main reaction treatment is 660℃-670℃.

[0012] Furthermore, in the preparation method, the temperature of the heat preservation treatment is 660℃-670℃.

[0013] Furthermore, in the preparation method, the true strain ε of the axial dieless stretching is 0.1-0.5.

[0014] Furthermore, in the preparation method, the axial tensile stress applied during the axial dieless stretching process is 150 MPa-250 MPa.

[0015] Furthermore, in the preparation method, the preheating temperature is 250℃-300℃, and the reaction initiation temperature is 450℃-500℃.

[0016] Furthermore, in the preparation method, during the heat preservation process, the winding tension is 20 MPa-50 MPa throughout, and / or the diameter of the winding device reel is φ0.5m-2.0m.

[0017] Furthermore, in the preparation method, the linear velocity of the base wire passing through the integrated processing zone is 0.1 m / min-2.0 m / min.

[0018] Furthermore, in the preparation method, step S1, the method of providing the basic wire includes: assembling a composite structure containing an Nb3Sn superconducting core, a Ta barrier layer, and a copper stabilizing layer through a tube, and cold-drawing it to a diameter of φ1.0mm-φ35.0mm to obtain the basic wire; and after the cold drawing and before step S2, the method further includes an intermediate annealing step of the basic wire under an inert atmosphere, wherein the intermediate annealing temperature is 400℃-600℃ and the holding time is 1h-5h.

[0019] Finally, Nb3Sn superconducting wires prepared by the method described in this invention are also provided.

[0020] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0021] (1) The present invention adopts continuous online induction heat treatment to replace the traditional static batch furnace heat treatment, realizes dynamic continuous processing of wire, greatly improves production efficiency and shortens the processing cycle.

[0022] (2) Online induction heating has the characteristics of being fast, precise and localized. Combined with continuous transmission, it effectively avoids the problem of uneven axial and radial thermal fields caused by temperature gradient and static heating in traditional tube furnaces or box furnaces, thus making the Nb3Sn phase reaction more uniform and the wire current carrying capacity more consistent.

[0023] (3) Simultaneous axial dieless stretching is applied in the main reaction zone, causing plastic rheology to occur in the wire while the Nb3Sn phase is generated at high temperature. This process can refine the grains, densify the structure, and promote uniform stress distribution, effectively suppressing the generation and propagation of microcracks, thereby improving the mechanical properties of brittle Nb3Sn wire and making it better able to meet the mechanical load-bearing requirements of high-field magnet winding.

[0024] (4) Through single or multiple repeated integrated processing, the final size and superconducting properties of the wire can be flexibly and precisely controlled, realizing the integrated manufacturing of shape and properties. Attached Figure Description

[0025] Figure 1 A schematic diagram of an integrated continuous production system that combines moldless stretching and induction heating.

[0026] Explanation of reference numerals in the attached diagram: 1. Paying-out device; 2. Tension control system; 3. Electromagnetic induction heating zone; 3a. Preheating zone; 3b. Reaction initiation zone; 3c. Main reaction zone; 3d. Heat preservation zone; 4. Water-cooled rapid cooling zone; 5. Taking-up device. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Example 1

[0031] This example demonstrates the construction of a continuous production system incorporating a moldless stretching and induction heating system.

[0032] A continuous production system incorporating a moldless stretching and induction heating system is constructed. This system mainly includes: a wire feeding device 1, a tension control system 2, an electromagnetic induction heating zone 3, a water-cooled rapid cooling zone 4, and a wire take-up device 5. A schematic diagram of the system is shown below. Figure 1 As shown, the electromagnetic induction heating zone 3 includes a preheating zone 3a, a reaction initiation zone 3b, a main reaction zone 3c, and a heat preservation zone 3d.

[0033] The zoned electromagnetic induction heating system is configured with four independent temperature control zones along the wire transmission direction, and the functions of each zone are as follows:

[0034] Preheating zone: Used to remove adsorbates from the wire surface and activate atomic lattice diffusion energy.

[0035] Reaction initiation region: Sn begins to diffuse towards the Nb interface, forming the initial Nb-Sn reaction layer.

[0036] Main reaction zone: Nb and Sn react fully at this temperature to generate Nb3Sn superconducting phase. The moldless stretching process is started simultaneously in this zone. By controlling the speed difference between the wire feeding device and the wire taking-up device, effective plastic rheological control of the thick wire is achieved.

[0037] Insulation zone: Maintain high temperature to ensure sufficient Nb3Sn phase transformation and complete homogenization.

[0038] Example 2

[0039] This embodiment describes an integrated, continuous fabrication method for Nb3Sn superconducting wires. By combining moldless stretching with zoned induction heating technology, deformation is controlled simultaneously with Nb3Sn phase formation, resulting in high-performance finished superconducting wires. The specific fabrication steps are as follows:

[0040] Step 1: Basic wire assembly and processing

[0041] The ITER-type Nb3Sn superconducting wire is assembled using the classic structure. From the inside out, the components are: an Nb3Sn superconducting core (to carry the superconducting current), a Ta barrier layer (covering the outer periphery of the Nb3Sn superconducting core to prevent Sn from diffusing into the copper stabilizing layer), and a copper stabilizing layer (covering the outer periphery of the Ta barrier layer to provide a current shunt path when the superconducting state loses its superconductivity). The assembled ITER-type Nb3Sn superconducting wire is then cold-drawn to a target diameter of φ1.0mm to obtain the ITER-type Nb3Sn superconducting base wire.

[0042] Step 2: Intermediate Annealing

[0043] The ITER-type Nb3Sn superconducting base wire obtained in step one was subjected to intermediate annealing to eliminate stress accumulated during cold working. The annealing process parameters were: 400℃ for 5 hours under an Ar protective atmosphere. After treatment, the wire regained its plasticity, which is beneficial for subsequent processing.

[0044] Step 3: Process Setting for Integrated Continuous Production System

[0045] Set the process parameters for the integrated continuous production system constructed in Example 1.

[0046] The zoned electromagnetic induction heating system is configured with four independent temperature control zones along the wire transmission direction. The functions and temperature settings of each zone are as follows:

[0047] Preheating zone (250±5℃): Used to remove adsorbates from the wire surface and activate atomic lattice diffusion energy.

[0048] Reaction initiation zone (450±5℃): Sn begins to diffuse towards the Nb interface, forming the initial Nb-Sn reaction layer.

[0049] Main reaction zone (660±5℃): Nb and Sn react fully at this temperature to generate Nb3Sn superconducting phase. The dieless stretching process is started simultaneously in this zone. By controlling the speed difference between the wire feeding device and the wire taking-up device, the wire is subjected to a true strain ε=0.1 of axial dieless stretching at high temperature, and the corresponding applied axial tensile stress is 150MPa.

[0050] Insulation zone (660±5℃): Maintains high temperature to ensure complete Nb3Sn phase transformation and homogenization. The entire take-up tension is 20MPa, and the take-up reel diameter is φ0.5m.

[0051] Step 4: Continuous heat treatment and deformation

[0052] The ITER-type Nb3Sn superconducting base wire obtained in step two and subjected to intermediate annealing is continuously passed through the integrated continuous production system with process parameters set in step three at a constant speed of 0.1 m / min. The superconducting base wire successively undergoes the preheating, reaction initiation, main reaction (accompanied by stretching) and heat preservation stages to complete the Nb3Sn phase generation and crystal grain structure regulation.

[0053] Step 5: Repeated Processing and Post-processing

[0054] The coiled wire is then processed again using the integration process described in step four to obtain a finished ITER-type Nb3Sn superconducting wire with a diameter of 0.818mm. The finished wire is then subjected to surface cleaning and insulation coating.

[0055] Performance measurement and characterization results:

[0056] The critical current Ic of the Nb3Sn superconducting wire prepared in this embodiment was tested to be 310A (12T@4.2K). Morphological characterization revealed that the Nb3Sn grain size was 130nm, comparable to the 150nm grain size of Nb3Sn wire prepared by conventional processes. The residual resistivity ratio (RRR) of the wire tested at 273K / 20K was 150~170, meeting the superconducting wire delivery standards, indicating good purity and conductivity of the copper stabilizing layer. Mechanical properties were tested using GB / T 38841—2020 "Relative Tensile Strength Test Method for Reacted Nb3Sn Composite Superconducting Wires at Room Temperature," with the following results: tensile strength (UTS) was 865MPa, and yield strength (Rp) was... 0.2 The strength of the elastic modulus (E) is 610 MPa, the elastic modulus (E) is 132 GPa, and the elongation (A) is... 50 The result was 0.48%. The results showed that although the Nb3Sn phase was fully formed and the material as a whole was brittle, the uniform distribution of the stress field during the moldless stretching process effectively suppressed the propagation of microcracks, thus ensuring the stability of the mechanical properties. The mechanical properties met the strict requirements for the mechanical load-bearing capacity of superconducting wires when winding high-field magnets.

[0057] Example 3

[0058] This embodiment describes an integrated, continuous fabrication method for Nb3Sn superconducting wires. By combining moldless stretching with zoned induction heating technology, deformation is controlled simultaneously with Nb3Sn phase formation, resulting in high-performance finished superconducting wires. The specific fabrication steps are as follows:

[0059] Step 1: Basic wire assembly and processing

[0060] The ITER-type Nb3Sn superconducting wire is assembled using the classic structure. From the inside out, the components are: an Nb3Sn superconducting core (to carry the superconducting current), a Ta barrier layer (covering the outer periphery of the Nb3Sn superconducting core to prevent Sn from diffusing into the copper stabilizing layer), and a copper stabilizing layer (covering the outer periphery of the Ta barrier layer to provide a current shunt path when the superconducting state loses its superconductivity). The assembled ITER-type Nb3Sn superconducting wire is then cold-drawn to a target diameter of φ35.0mm to obtain the ITER-type Nb3Sn superconducting base wire.

[0061] Step 2: Intermediate Annealing

[0062] The ITER-type Nb3Sn superconducting base wire obtained in step one was subjected to intermediate annealing to eliminate stress accumulated during cold working. The annealing process parameters were: holding at 600℃ for 1 hour under an Ar protective atmosphere. After treatment, the wire regained its plasticity, which is beneficial for subsequent processing.

[0063] Step 3: Process Setting for Integrated Continuous Production System

[0064] Set the process parameters for the integrated continuous production system constructed in Example 1.

[0065] The zoned electromagnetic induction heating system is configured with four independent temperature control zones along the wire transmission direction. The functions and temperature settings of each zone are as follows:

[0066] Preheating zone (300±5℃): Used to remove adsorbates from the wire surface and activate atomic lattice diffusion energy.

[0067] Reaction initiation zone (500±5℃): Sn begins to diffuse towards the Nb interface, forming the initial Nb-Sn reaction layer.

[0068] Main reaction zone (670±5℃): Nb and Sn react fully at this temperature to generate Nb3Sn superconducting phase. The dieless stretching process is started simultaneously in this zone. By controlling the speed difference between the wire feeding device and the wire taking-up device, the wire is subjected to a true strain ε=0.5 of axial dieless stretching at high temperature, and the corresponding applied axial tensile stress is 250MPa.

[0069] Insulation zone (670±5℃): Maintains high temperature to ensure complete Nb3Sn phase transformation and homogenization. The entire take-up tension is 50MPa, and the take-up reel diameter is φ2.0m.

[0070] Step 4: Continuous heat treatment and deformation

[0071] The ITER-type Nb3Sn superconducting base wire obtained in step two and subjected to intermediate annealing is continuously passed through the integrated continuous production system with process parameters set in step three at a constant speed of 2.0 m / min. The superconducting base wire sequentially undergoes preheating, reaction initiation, main reaction (accompanied by stretching) and heat preservation stages to complete the formation of Nb3Sn phase and control of crystal grain structure.

[0072] Step 5: Repeated Processing and Post-processing

[0073] The coiled wire is then processed again using the integration process described in step four to obtain a finished ITER-type Nb3Sn superconducting wire with a diameter of 0.818mm. The finished wire is then subjected to surface cleaning and insulation coating.

[0074] Performance measurement and characterization results:

[0075] The critical current Ic of the Nb3Sn superconducting wire prepared in this embodiment was tested to be 305A (12T@4.2K). Morphological characterization revealed that the Nb3Sn grain size was 140nm, comparable to the 150nm grain size of Nb3Sn wire prepared by conventional processes. The residual resistivity ratio (RRR) of the wire tested at 273K / 20K was 160~170, meeting the superconducting wire delivery standards, indicating good purity and conductivity of the copper stabilizing layer. Mechanical properties were tested using GB / T 38841—2020 "Relative Tensile Strength Test Method for Reacted Nb3Sn Composite Superconducting Wires at Room Temperature," and the results are as follows: tensile strength (UTS) was 840MPa, and yield strength (Rp) was... 0.2 The strength of the elastic modulus (E) is 600 MPa, the elastic modulus (E) is 130 GPa, and the elongation (A) is... 50 The result is 0.47%. The results show that although the Nb3Sn phase has been fully formed and the material as a whole is brittle, the uniform distribution of stress field during the moldless stretching process effectively suppresses the propagation of microcracks, thus ensuring the stability of mechanical properties. This mechanical property index meets the strict requirements for the mechanical load-bearing capacity of superconducting wires when winding high-field magnets.

[0076] Example 4

[0077] This embodiment describes an integrated, continuous fabrication method for Nb3Sn superconducting wires. By combining moldless stretching with zoned induction heating technology, deformation is controlled simultaneously with Nb3Sn phase formation, resulting in high-performance finished superconducting wires. The specific fabrication steps are as follows:

[0078] Step 1: Basic wire assembly and processing

[0079] The ITER-type Nb3Sn superconducting wire is assembled using the classic structure. From the inside out, the components are: an Nb3Sn superconducting core (to carry the superconducting current), a Ta barrier layer (covering the outer periphery of the Nb3Sn superconducting core to prevent Sn from diffusing into the copper stabilizing layer), and a copper stabilizing layer (covering the outer periphery of the Ta barrier layer to provide a current shunt path when the superconducting state loses its quench). The assembled ITER-type Nb3Sn superconducting wire is then cold-drawn to a target diameter of φ3.0mm to obtain the ITER-type Nb3Sn superconducting base wire.

[0080] Step 2: Intermediate Annealing

[0081] The ITER-type Nb3Sn superconducting base wire obtained in step one was subjected to intermediate annealing to eliminate the stress accumulated during cold working. The annealing process parameters were: 500℃ for 3 hours under an Ar protective atmosphere. After treatment, the wire regained its plasticity, which is beneficial for subsequent processing.

[0082] Step 3: Process Setting for Integrated Continuous Production System

[0083] Set the process parameters for the integrated continuous production system constructed in Example 1.

[0084] The zoned electromagnetic induction heating system is configured with four independent temperature control zones along the wire transmission direction. The functions and temperature settings of each zone are as follows:

[0085] Preheating zone (280±5℃): Used to remove adsorbates from the wire surface and activate atomic lattice diffusion energy.

[0086] Reaction initiation zone (470±5℃): Sn begins to diffuse towards the Nb interface, forming the initial Nb-Sn reaction layer.

[0087] Main reaction zone (665±5℃): Nb and Sn react fully at this temperature to form Nb3Sn superconducting phase. The dieless stretching process is started simultaneously in this zone. By controlling the speed difference between the wire feeding device and the wire taking-up device, the wire is subjected to a true strain ε=0.3 of axial dieless stretching at high temperature, and the corresponding applied axial tensile stress is 200MPa.

[0088] Insulation zone (665±5℃): Maintains high temperature to ensure sufficient Nb3Sn phase transformation and homogenization. The entire take-up tension is 30MPa, and the take-up reel diameter is φ1.0m.

[0089] Step 4: Continuous heat treatment and deformation

[0090] The ITER-type Nb3Sn superconducting base wire obtained in step two and subjected to intermediate annealing is continuously passed through the integrated continuous production system with process parameters set in step three at a constant speed of 1.0 m / min. The superconducting base wire successively undergoes the preheating, reaction initiation, main reaction (accompanied by stretching) and heat preservation stages to complete the Nb3Sn phase generation and crystal grain structure regulation.

[0091] Step 5: Repeated Processing and Post-processing

[0092] The coiled wire is then processed again using the integration process described in step four to obtain a finished ITER-type Nb3Sn superconducting wire with a diameter of 0.818mm. The finished wire is then subjected to surface cleaning and insulation coating.

[0093] Performance measurement and characterization results:

[0094] The critical current Ic of the Nb3Sn superconducting wire prepared in this embodiment was tested to be 315A (12T@4.2K). Morphological characterization revealed that the Nb3Sn grain size was 120nm, comparable to the 150nm grain size of Nb3Sn wire prepared by conventional processes. The residual resistivity ratio (RRR) of the wire tested at 273K / 20K was 160~170, meeting the superconducting wire delivery standards, indicating good purity and conductivity of the copper stabilizing layer. Mechanical properties were tested according to GB / T 38841—2020 "Relative Tensile Strength Test Method for Reacted Nb3Sn Composite Superconducting Wires at Room Temperature," with the following results: tensile strength (UTS) 828MPa, yield strength (Rp0.2) 615MPa, elastic modulus (E) 135GPa, and elongation (A... 50 The result is 0.49%. The results show that although the Nb3Sn phase has been fully formed and the material as a whole is brittle, the uniform distribution of stress field during the moldless stretching process effectively suppresses the propagation of microcracks, thus ensuring the stability of mechanical properties. These mechanical properties meet the strict requirements for the mechanical load-bearing capacity of superconducting wires when winding high-field magnets.

[0095] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in this invention, based on the technical solutions and inventive concepts of the present invention, should be covered within the protection scope of this invention.

Claims

1. A method for preparing Nb3Sn superconducting wire using the internal tin method without mold stretching, characterized in that, The preparation method includes the following steps: S1. Provide Nb3Sn superconducting base wires using the internal tin method; S2. The base wire is continuously passed through an integrated processing zone, in which the base wire sequentially undergoes preheating treatment, reaction initiation treatment, main reaction treatment, and heat preservation treatment. In the main reaction process, the base wire is subjected to axial moldless tension while undergoing online induction heating. S3. Repeat step S2 at least once to adjust the wire size and performance to obtain the finished Nb3Sn superconducting wire.

2. The preparation method according to claim 1, characterized in that, The temperature of the main reaction treatment is 660℃-670℃.

3. The preparation method according to claim 1, characterized in that, The temperature for the heat preservation treatment is 660℃-670℃.

4. The preparation method according to claim 1, characterized in that, The true strain ε of the axial unmodulated tension is 0.1-0.

5.

5. The preparation method according to claim 1, characterized in that, The axial tensile stress applied during the axial dieless stretching process is 150MPa-250MPa.

6. The preparation method according to claim 1, characterized in that, The preheating temperature is 250℃-300℃, and the reaction initiation temperature is 450℃-500℃.

7. The preparation method according to claim 1, characterized in that, During the heat preservation process, the winding tension is 20MPa-50MPa throughout, and / or the diameter of the winding device reel is φ0.5m-2.0m.

8. The preparation method according to claim 1, characterized in that, The linear speed of the base wire passing through the integrated processing area is 0.1m / min-2.0m / min.

9. The preparation method according to claim 1, characterized in that, In step S1, the method for providing the base wire includes: assembling a composite structure containing an Nb3Sn superconducting core, a Ta barrier layer, and a copper stabilizing layer through a tube, and cold-drawing it to a diameter of φ1.0mm-φ35.0mm to obtain the base wire; and after the cold drawing and before step S2, the method further includes an intermediate annealing step of the base wire under an inert atmosphere, wherein the intermediate annealing temperature is 400℃-600℃ and the holding time is 1h-5h.

10. Nb3Sn superconducting wire prepared by the preparation method according to any one of claims 1-9.

Images