Method for preparing internal tin method Nb3Sn superconducting wire through dieless stretching

Abstract

The invention belongs to the technical field of superconducting wire processing, and particularly relates to a method for preparing an internal tin method Nb3Sn superconducting wire through die-free stretching. According to the method, an Nb3Sn superconducting base wire prepared by an internal tin method continuously passes through an integrated treatment area, and preheating treatment, reaction initial treatment, main reaction treatment and heat preservation treatment are sequentially carried out in the area; wherein in the main reaction treatment, the wire is subjected to on-line induction heating and axial die-free stretching at the same time; and finally, repeating the integrated processing step for at least one time so as to regulate and control the size and the performance of the wire rod and prepare the finished Nb3Sn superconducting wire rod. According to the method, dieless stretching deformation and partition induction heating are coupled in situ, Nb3Sn phase generation and microstructure regulation and control are synchronously carried out, the machining period is greatly shortened, and the performance consistency and mechanical stability of the wire are effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of superconducting wire processing, and particularly relates to a preparation method of an Nb3Sn superconducting wire prepared by a dieless drawing internal tin method. BACKGROUND

[0002] Nb3Sn superconducting wire has a high critical current density and is an important raw material for manufacturing high-field magnets. The internal tin method is one of main methods for preparing Nb3Sn superconducting wire. At present, the Nb3Sn superconducting wire with the highest performance and the widest application is prepared by the internal tin method. The existing technology mainly forms the Nb3Sn composite wire by three assembly methods, i.e. inserting a Nb rod into a porous copper ingot to assemble an internal tin Nb3Sn CuNb composite sheath, inserting a SnTi alloy rod into a CuNb composite tube to assemble an internal tin Nb3Sn subelement, and assembling a composite wire from the subelement, a Ta tube and a copper tube, and then performing high-temperature heat treatment.

[0003] The current internal tin Nb3Sn composite wire preparation method needs to go through a process of (drawing-forming-magnet winding-heat treatment-phase formation), and the processing cycle is long, and the whole process takes 30-40 days. Meanwhile, the Nb3Sn after heat treatment is very brittle, and the "react first and then draw" method cannot continue to be processed, and the "draw first and then react" method is easy to introduce microcracks in the processing. In addition, the heat treatment relies on a large-scale tube furnace or box furnace, and the whole coil is heated statically, so the heat efficiency is low, the energy consumption per product is high, the temperature gradient in the furnace causes the axial and radial thermal field to be uneven, the thickness and distribution of the Nb3Sn phase are greatly different, and the consistency of the current-carrying performance is affected. Therefore, it is urgent to develop a Nb3Sn superconducting wire preparation method which can greatly improve the processing efficiency, shorten the processing time and maintain the performance of Nb3Sn. SUMMARY

[0004] The application aims to provide a method for preparing Nb3Sn superconducting wire by dieless drawing internal tin method on-line heat treatment of Nb3Sn superconducting wire, so as to solve the problems in the background art.

[0005] To achieve the above-mentioned purpose, the application provides the following technical scheme: On the one hand, the application provides a preparation method of an internal tin Nb3Sn superconducting wire by dieless drawing, which comprises the following steps: S1, providing an internal tin Nb3Sn superconducting base wire; S2, making the base wire continuously pass through an integrated processing zone, and the base wire sequentially passes through preheating treatment, reaction initiation treatment, main reaction treatment and holding treatment in the integrated processing zone, In the main reaction treatment, the base wire is subjected to on-line induction heating while being subjected to axial dieless drawing. S3, repeating step S2 at least once to regulate the size and performance of the wire, to obtain a finished Nb3Sn superconducting wire.

[0006] Further, in the preparation method, the temperature of the main reaction treatment is 660-670℃.

[0007] Further, in the preparation method, the temperature of the holding treatment is 660-670℃.

[0008] Further, in the preparation method, the true strain ε of the axial free stretching is 0.1-0.5.

[0009] Further, in the preparation method, the axial tensile stress applied during the axial free stretching is 150-250 MPa.

[0010] Further, in the preparation method, the temperature of the preheating treatment is 250-300℃, and the temperature of the reaction initiation treatment is 450-500℃.

[0011] Further, in the preparation method, during the holding treatment, the take-up tension is 20-50 MPa, and / or the diameter of the wire wheel of the take-up device is φ0.5-2.0 m.

[0012] Further, in the preparation method, the linear velocity of the base wire through the integrated treatment zone is 0.1-2.0 m / min.

[0013] Further, in the preparation method, in step S1, the method for providing the base wire comprises: pipe assembly of a composite structure comprising a Nb3Sn superconducting core, a Ta barrier layer and a copper stabilizing layer, and cold drawing to a diameter of φ1.0-φ35.0 mm to obtain the base wire; and after the cold drawing and before step S2, a step of intermediate annealing the base wire under inert atmosphere protection is further included, the temperature of the intermediate annealing is 400-600℃, and the holding time is 1-5 h.

[0014] Finally, the Nb3Sn superconducting wire prepared by the preparation method is also provided.

[0015] Compared with the prior art, the technical scheme provided by the present application at least has the following beneficial effects or advantages: (1) The present application adopts continuous online induction heat treatment instead of traditional static batch furnace heat treatment, realizes dynamic continuous processing of the wire, greatly improves the production efficiency, and shortens the processing cycle.

[0016] (2) Online induction heating has the characteristics of rapidness, precision and localization, combined with continuous transmission mode, effectively avoiding the problem of axial and radial thermal field unevenness caused by temperature gradient and static heating in traditional tube furnace or box furnace, so as to make the Nb3Sn phase reaction more uniform, and the consistency of wire current carrying performance better.

[0017] (3) Synchronous application of axial dieless drawing in the main reaction zone makes the wire plastic flow at the same time of generating Nb3Sn phase at high temperature. This process can refine the grain, densify the structure, and promote the uniform distribution of stress, effectively inhibiting the generation and expansion of micro-cracks, thereby improving the mechanical properties of brittle Nb3Sn wire, and making it more capable of meeting the mechanical bearing requirements of high-field magnet winding.

[0018] (4) Through single or multiple repeated integrated processing, the final size and superconducting performance of the wire can be flexibly and accurately controlled, realizing the integrated manufacturing of shape and properties. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of an integrated continuous production system of dieless drawing and induction heating integrated system; BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described below in conjunction with examples, but the present application is not limited to the following examples.

[0021] In order to enable those skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific examples and drawings, but the examples are not limiting to the present application.

[0022] The experimental methods and detection methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0023] Example 1 This example is to construct a continuous production system containing a dieless drawing and induction heating system.

[0024] A continuous production system containing a dieless drawing and induction heating system is constructed, which mainly includes a wire unwinding device 1, a tension control system 2, an electromagnetic induction heating zone 3, a water-cooled rapid cooling zone 4, and a wire winding device 5. The schematic diagram of the system is shown in Figure 1 The electromagnetic induction heating zone 3 includes a preheating zone 3a, a reaction initiation zone 3b, a main reaction zone 3c and a holding zone 3d.

[0025] The four independent temperature control zones of the partition electromagnetic induction heating system are arranged along the wire transmission direction, and the functions of each zone are as follows: Preheating zone: used for removing adsorbed substances on the surface of the wire and activating atomic lattice diffusion energy.

[0026] Reaction initiation zone: Sn starts to diffuse to the Nb interface to form an initial Nb-Sn reaction layer.

[0027] Main reaction zone: Nb and Sn fully react to form Nb3Sn superconducting phase at this temperature, and the dieless drawing process is started simultaneously. By controlling the speed difference between the wire releasing device and the wire collecting device, effective plastic flow control of the rough wire is realized.

[0028] Temperature maintenance zone: maintain high temperature to ensure full phase transformation and homogenization of Nb3Sn.

[0029] Example 2 This embodiment is an integrated continuous production method of Nb3Sn superconducting wire. By combining dieless drawing with partition induction heating technology, deformation regulation is carried out while Nb3Sn phase is generated to produce high-performance finished superconducting wire. The specific preparation steps are as follows: Step one, basic wire assembly and processing The ITER type Nb3Sn superconducting wire with the classic structure is assembled, and from the inside out, it is Nb3Sn superconducting core (used to carry superconducting current), Ta barrier layer (wrapped around the outer periphery of the Nb3Sn superconducting core, used to prevent Sn element from diffusing to the copper stabilizing layer), copper stabilizing layer (wrapped around the outer periphery of the Ta barrier layer, used to provide a current shunt path when the superconducting state loses superconductivity) are assembled by pipe; the assembled ITER type Nb3Sn superconducting wire is cold drawn to the target diameter of φ1.0mm, and the ITER type Nb3Sn superconducting basic wire is obtained; Step two, intermediate annealing The ITER type Nb3Sn superconducting basic wire obtained in step one is subjected to intermediate annealing treatment to eliminate the stress accumulated during cold processing. The annealing process parameters are: in Ar gas protection atmosphere, at 400℃ for 5h. After treatment, the plasticity of the wire is restored, which is beneficial to the subsequent contact processing; Step three, process setting of integrated continuous production system The process parameters of the integrated continuous production system constructed in Example 1 are set.

[0030] The four independent temperature control zones of the partition electromagnetic induction heating system are arranged along the wire transmission direction, and the functions of each zone are as follows: Preheating zone (250±5℃): used for removing adsorbed substances on the surface of the wire and activating atomic lattice diffusion energy.

[0031] Reaction initiation zone (450±5℃): Sn starts to diffuse to the Nb interface, forming the initial Nb-Sn reaction layer.

[0032] Main reaction zone (660±5℃): Nb and Sn fully react to form the Nb3Sn superconducting phase at this temperature. The zone simultaneously initiates the dieless drawing process. By controlling the speed difference between the wire drawing device and the take-up device, the wire is subjected to axial dieless drawing at high temperature with a true strain ε=0.1, corresponding to an applied axial tensile stress of 150 MPa.

[0033] Soaking zone (660±5℃): Maintains high temperature to ensure the Nb3Sn phase transformation is complete and homogenized. The take-up tension throughout the process is 20 MPa, and the take-up device wire wheel diameter is φ0.5 m; Step four, continuous heat treatment and deformation The ITER-type Nb3Sn superconducting base wire obtained in step two after intermediate annealing is continuously passed through the integrated continuous production system with the process parameters set in step three at a constant speed of 0.1 m / min. The superconducting base wire undergoes preheating, reaction initiation, main reaction (with drawing), and soaking stages in turn, completing the Nb3Sn phase generation and grain structure regulation; Step five, repeated processing and post-processing The wire after take-up is subjected to the integrated processing process of step four once again to obtain the ITER-type Nb3Sn finished superconducting wire with a diameter of φ0.818 mm. Subsequently, the finished wire is subjected to surface cleaning and insulation coating treatment.

[0034] Performance measurement and characterization results: After testing, the critical current Ic of the Nb3Sn superconducting wire prepared in this embodiment is 310 A (12T@4.2K), and after wire morphology characterization, the Nb3Sn grain size of the wire is 130 nm, which is comparable to the Nb3Sn grain size of 150 nm of the wire prepared by conventional process; the residual resistance ratio (RRR) value of the wire under the condition of 273K / 20K is 150-170, which meets the delivery standard of superconducting wire, indicating that the purity and electrical conductivity of the copper stabilizing layer are good; the mechanical properties are tested by GB / T 38841-2020 "Reaction Nb3Sn composite superconducting wire room temperature tensile test method", and the results are as follows: tensile strength (UTS) is 865 MPa, yield strength (Rp 0.2 ) is 610 MPa, elastic modulus (E) is 132 Gpa, and elongation (A 50 ) is 0.48%. The results show that although the Nb3Sn phase has been completely generated and the material as a whole shows brittle characteristics, the stress field is uniformly distributed during the dieless drawing process, effectively inhibiting the propagation of microcracks, thereby ensuring the stability of the mechanical properties. The mechanical property indicators meet the strict requirements of the mechanical load capacity of superconducting wire for winding high-field magnets.

[0035] Example 3 This embodiment is an integrated continuous production method of Nb3Sn superconducting wire, which combines dieless drawing and zoned induction heating technology to regulate deformation while generating Nb3Sn phase, to produce high-performance finished superconducting wire. The specific preparation steps are as follows: Step one, basic wire assembly and processing The ITER type Nb3Sn superconducting wire was assembled using the classical structure, from the inside out, the Nb3Sn superconducting core (used to carry superconducting current), Ta barrier layer (coated on the outer periphery of the Nb3Sn superconducting core, used to prevent Sn element from diffusing to the copper stabilizing layer), copper stabilizing layer (coated on the outer periphery of the Ta barrier layer, used to provide a current shunt path when the superconducting state loses superconductivity) were assembled by pipe drawing; the assembled ITER type Nb3Sn superconducting wire was cold drawn to the target diameter φ35.0mm, and the ITER type Nb3Sn superconducting basic wire was obtained; Step two, intermediate annealing The ITER type Nb3Sn superconducting basic wire obtained in step one was subjected to intermediate annealing treatment to eliminate the stress accumulated during cold processing. The annealing process parameters are: in Ar gas protection atmosphere, at 600℃ for 1h. After treatment, the plasticity of the wire is restored, which is beneficial to the subsequent contact processing; Step three, process setting of integrated continuous production system The process parameters of the integrated continuous production system constructed in Example 1 were set.

[0036] Among them, the four independent temperature control zones of the zoned electromagnetic induction heating system are set along the transmission direction of the wire, and the functions and temperature settings of each zone are as follows: Preheating zone (300±5℃): used to remove adsorbed substances on the surface of the wire and activate atomic lattice diffusion energy.

[0037] Reaction initiation zone (500±5℃): Sn begins to diffuse to the Nb interface, forming an initial Nb-Sn reaction layer.

[0038] Main reaction zone (670±5℃): Nb and Sn fully react to form Nb3Sn superconducting phase at this temperature. At the same time, the dieless drawing process is started, and by controlling the speed difference between the unwinding device and the winding device, the wire is subjected to axial dieless drawing with true strain ε=0.5 at high temperature, corresponding to an applied axial tensile stress of 250MPa.

[0039] Soaking zone (670±5℃): maintain high temperature to ensure full phase transformation and homogenization of Nb3Sn. The winding tension is 50MPa, and the winding device wheel diameter is φ2.0m; Step four, continuous heat treatment and deformation The ITER type Nb3Sn superconducting base wire obtained by intermediate annealing treatment in step two is continuously passed through the integrated continuous production system set in step three with constant speed of 2.0 m / min, and the superconducting base wire sequentially experiences preheating, reaction initiation, main reaction (with stretching) and holding stages, and the Nb3Sn phase generation and crystalline grain structure regulation are completed; Step five, repeated processing and post-processing The wire after take-up is repeated once the integrated processing process of step four to obtain the ITER type Nb3Sn finished superconducting wire with φ0.818 mm. Subsequently, the finished wire is subjected to surface cleaning and insulation coating treatment.

[0040] Performance measurement and characterization results: The Nb3Sn superconducting wire prepared in this embodiment has a critical current Ic of 305 A (12T@4.2K) after testing. The Nb3Sn grain size of the wire is 140 nm, which is comparable to the Nb3Sn grain size of 150 nm of the wire prepared by conventional process. The residual resistance ratio (RRR) value of the wire under the condition of 273K / 20K is 160-170, which meets the delivery standard of superconducting wire, indicating that the purity and electrical conductivity of the copper stabilizing layer are good. The mechanical properties are tested by GB / T 38841-2020 "Reaction Nb3Sn composite superconducting wire room temperature tensile test method", and the test results are as follows: tensile strength (UTS) is 840 Mpa, yield strength (Rp 0.2 ) is 600 Mpa, elastic modulus (E) is 130 Gpa, and elongation (A 50 ) is 0.47%. The results show that although the Nb3Sn phase has been completely generated and the material as a whole shows brittle characteristics, the uniform distribution of stress field in the free-form stretching process effectively inhibits the propagation of micro-cracks, thereby ensuring the stability of the mechanical properties. The mechanical properties meet the strict requirements of the mechanical load capacity of superconducting wire for winding high-field magnets.

[0041] Example 4 This embodiment is an integrated continuous preparation method of Nb3Sn superconducting wire. By combining free-form stretching with zoned induction heating technology, the Nb3Sn phase is generated while the deformation is regulated, and high-performance finished superconducting wire is prepared. The specific preparation steps are as follows: Step one, base wire assembly and processing The ITER type Nb3Sn superconducting wire is assembled by using the classical structure, from inside to outside, respectively, Nb3Sn superconducting core (for carrying superconducting current), Ta barrier layer (wrapped around the outer periphery of the Nb3Sn superconducting core, for preventing Sn element from diffusing to the copper stabilizing layer), copper stabilizing layer (wrapped around the outer periphery of the Ta barrier layer, for providing a current shunt path when the superconducting state loses superconductivity); the assembled ITER type Nb3Sn superconducting wire is cold-drawn to a target diameter of φ3.0 mm, and an ITER type Nb3Sn superconducting base wire is obtained; Step two, intermediate annealing The ITER type Nb3Sn superconducting base wire obtained in step one is subjected to intermediate annealing treatment to eliminate the stress accumulated during cold processing. The annealing process parameters are: under Ar gas protection atmosphere, at 500℃ for 3h. After treatment, the plasticity of the wire is restored, which is beneficial to subsequent contact processing; Step three, process setting of integrated continuous production system The process parameters of the integrated continuous production system constructed in embodiment 1 are set.

[0042] Among them, the four independent temperature control zones of the partition electromagnetic induction heating system are arranged along the transmission direction of the wire, and the functions and temperature settings of each zone are as follows: Preheating zone (280±5℃): used for removing adsorbed substances on the surface of the wire and activating atomic lattice diffusion energy.

[0043] Reaction initiation zone (470±5℃): Sn starts to diffuse to the Nb interface to form an initial Nb-Sn reaction layer.

[0044] Main reaction zone (665±5℃): Nb and Sn fully react to form Nb3Sn superconducting phase at this temperature. The zone synchronously starts the dieless stretching process. By controlling the speed difference between the unwinding device and the winding device, the wire is subjected to axial dieless stretching with a true strain ε=0.3 at high temperature, and the corresponding axial tensile stress is 200MPa.

[0045] Soaking zone (665±5℃): maintain high temperature to ensure full phase transformation and homogenization of Nb3Sn. The winding tension is 30MPa, and the winding device wheel diameter is φ1.0m; Step four, continuous heat treatment and deformation The ITER type Nb3Sn superconducting base wire obtained in step two is continuously passed through the integrated continuous production system with the process parameters set in step three at a constant speed of 1.0m / min. The superconducting base wire sequentially experiences preheating, reaction initiation, main reaction (with stretching) and soaking stages, and the Nb3Sn phase generation and crystal grain structure regulation are completed; Step five, repeated processing and post-processing The wire after take-up is subjected to the integrated process of step four again to obtain ITER type Nb3Sn finished superconducting wire with a diameter of 0.818 mm. Then, the finished wire is subjected to surface cleaning and insulation coating treatment.

[0046] Performance measurement and characterization results: The Nb3Sn superconducting wire prepared in the embodiment has a critical current Ic of 315 A (12T@4.2K) after testing. The Nb3Sn grain size of the wire is 120 nm after wire morphology characterization, which is comparable to the Nb3Sn grain size of 150 nm of the wire prepared by a conventional process. The residual resistance ratio (RRR) value of the wire is 160-170 under the condition of 273K / 20K, which meets the delivery standard of superconducting wire, indicating that the purity and electrical conductivity of the copper stabilizing layer are good. The mechanical property test is performed by using GB / T 38841-2020 “Reaction Nb3Sn composite superconducting wire room temperature tensile test method”, and the results are as follows: tensile strength (UTS) is 828Mpa, yield strength (Rp0.2) is 615Mpa, elastic modulus (E) is 135Gpa, and elongation (A 50 ) is 0.49%. The results show that although the Nb3Sn phase has been completely generated and the material as a whole has a brittle characteristic, the uniform distribution of stress field in the process of free die drawing effectively inhibits the propagation of micro-cracks, thereby ensuring the stability of the mechanical properties. The mechanical property indicators meet the strict requirements of the mechanical load capacity of superconducting wire during winding of high-field magnets.

[0047] It is apparent for those skilled in the art that the present application is not limited to the details of the foregoing exemplary embodiments, and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the present application is defined by the appended claims rather than the foregoing description, and it is intended to encompass all changes falling within the meaning and range of equivalents of the claims. Any reference signs in the claims should not be considered as limiting the claims involved. Any person skilled in the art can make equivalent substitutions or changes to the technical solutions and inventive concepts of the present application within the technical scope disclosed by the present application, and such substitutions or changes should be covered within the protection scope of the present application.

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.

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