Nb3Sn superconducting tape based on cold deformation processing and its preparation method

Abstract

The application relates to a Nb3Sn superconducting strip based on cold deformation processing and a preparation method thereof, and belongs to the technical field of superconducting material processing. The preparation method of the Nb3Sn superconducting strip based on cold deformation processing comprises the following steps: stacking pretreated copper plates, tin plates and niobium plates from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, then performing single-pass cold rolling to obtain a Cu / Sn / Nb / Sn / Cu composite precursor, performing gradient phase formation heat treatment on the Cu / Sn / Nb / Sn / Cu composite precursor, performing gradient cooling on the Cu / Sn / Nb / Sn / Cu composite precursor after the gradient phase formation heat treatment, and then performing post-processing to obtain the Nb3Sn superconducting strip. The application can avoid complicated process and poor component coordination deformation, can further provide a phase change driving force, can inhibit interface holes, and can realize the Nb3Sn superconducting strip with complete interface and uniform structure in a shorter time.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material processing technology, specifically relating to a Nb3Sn superconducting tape based on cold deformation processing and its preparation method. Background Technology

[0002] Nb3Sn is a typical low-temperature superconducting material with an A15 structure. Due to its high critical temperature, excellent upper critical magnetic field, and slow performance decay characteristics under strong magnetic field environment, it has become the preferred key material in fields such as high-field superconducting magnets, particle accelerators, nuclear fusion devices, and nuclear magnetic resonance spectrometers.

[0003] Currently, the mainstream fabrication path for Nb3Sn superconducting magnets relies on large plastic deformation of Cu / Sn / Nb composite precursors and frequent mold changes to obtain the required size and shape. This is followed by long-term heat treatment at 700–825℃ for 149–225 hours to achieve sufficient diffusion of Nb and Sn within the composite structure, generating a continuous A15 superconducting phase layer. However, this process suffers from the following problems: First, the multi-stage deformation process is cumbersome and inefficient, and it is difficult to simultaneously overcome the poor coordinated deformation ability and insufficient phase driving force caused by the significant differences in the physical properties of Cu, Sn, and Nb components. It is also impossible to achieve good interfacial bonding between the components in a single-stage large deformation process. Second, during the long-term high-temperature heat treatment, the thermal expansion coefficients and mechanical properties of the components are mismatched, easily leading to pores at the phase interfaces and within the structure, severely damaging the continuity of the superconducting phase and the overall performance of the magnet.

[0004] Therefore, existing technologies suffer from problems such as cumbersome multi-stage large plastic deformation processes, poor component coordination deformation capabilities, insufficient phase driving force, and the tendency to generate interface voids during long-term high-temperature heat treatment, which urgently need to be solved. Summary of the Invention

[0005] To address the above issues, this invention provides a cold-deformation-based Nb3Sn superconducting tape and its preparation method. The single-pass cold rolling process avoids the cumbersome process and poor component coordination caused by multi-pass large plastic deformation. Gradient phase-forming heat treatment provides the driving force for phase transformation, and gradient cooling suppresses the formation of interface voids, enabling the production of Nb3Sn superconducting tapes with intact interfaces and uniform microstructure in a shorter time. This method is suitable for efficient industrial-scale preparation.

[0006] The technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a method for preparing Nb3Sn superconducting tape based on cold deformation processing, comprising the following steps: S1. Raw material preparation and pretreatment: Prepare copper plates, tin plates and niobium plates as raw materials, and perform pretreatment to obtain pretreated copper plates, tin plates and niobium plates. S2. Cold deformation processing: The pretreated copper plate, tin plate and niobium plate are stacked from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, and then cold rolled in a single pass to obtain Cu / Sn / Nb / Sn / Cu composite precursor. S3. Gradient phase formation heat treatment: The Cu / Sn / Nb / Sn / Cu composite precursor is subjected to gradient phase formation heat treatment; wherein, the gradient phase formation heat treatment includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with the temperature increasing sequentially. S4. Gradient cooling: The Cu / Sn / Nb / Sn / Cu composite precursor after gradient phase formation heat treatment is subjected to gradient cooling to achieve interfacial diffusion bonding of Cu / Sn / Nb / Sn / Cu composite material and the generation of Nb3Sn superconducting phase, resulting in a rough-processed Nb3Sn superconducting tape; wherein, the gradient cooling includes a first cooling stage, a second cooling stage and a third cooling stage. S5. Post-processing: Post-processing is performed on the rough-machined Nb3Sn superconducting tape to obtain Nb3Sn superconducting tape.

[0007] In some embodiments, the volume ratio of the copper plate, tin plate and niobium plate in step S1 is 1:1:1.

[0008] Preferably, the size of the raw material in step S1 is 30mm × 120mm × (1-3)mm.

[0009] In some embodiments, the pretreatment in step S1 includes: grinding and polishing the raw material with sandpaper of 80#, 400#, 600#, 800#, 1000#, 1500#, and 2000# in sequence, followed by ultrasonic cleaning in anhydrous ethanol to remove impurities from the surface of the board, and then drying for later use.

[0010] In some embodiments, the temperature of ultrasonic cleaning in the pretreatment is 20-30°C, the time of ultrasonic cleaning is 20-30 min, and the power of ultrasonic cleaning is 40%-50%.

[0011] In some embodiments, the drying temperature in the pretreatment is 40-50°C, and the drying time is 24 hours.

[0012] In some embodiments, the reduction in single-pass cold rolling in step S2 is 40%-60%.

[0013] In some embodiments, step S3, the first stage of heat treatment, involves a vacuum degree of 10. -3 Pa, temperature 180-210℃, heat preservation time 50-70h.

[0014] In some embodiments, step S3, the second stage of heat treatment, involves a vacuum degree of 10. -3Pa, temperature 300-350℃, heat preservation time 25-50h.

[0015] In some embodiments, the third stage of heat treatment in step S3 has a vacuum degree of 10. -3 Pa, temperature 430-450℃, heat preservation time 25-50h.

[0016] In some embodiments, the fourth stage of heat treatment in step S3 has a vacuum degree of 10. -3 Pa, temperature 650-690℃, heat preservation time 50-70h.

[0017] In some embodiments, step S4, the first cooling stage, involves a vacuum degree of 10. -3 Pa, cool to 500-600℃ at a rate of 4-8℃ / min, and then hold for 25-40 minutes.

[0018] In some embodiments, step S4, the second cooling stage, involves a vacuum degree of 10. -3 Pa, cool down to 300-400℃ at a rate of 4-8℃ / min, and then hold for 10-20 minutes.

[0019] In some embodiments, the third cooling stage in step S4 has a vacuum degree of 10. -3 Pa, cool down to room temperature.

[0020] In some embodiments, the post-processing in step S5 includes: ultrasonically cleaning the rough-processed Nb3Sn superconducting tape in anhydrous ethanol to remove surface impurities, followed by drying to obtain the Nb3Sn superconducting tape.

[0021] In some embodiments, the temperature of ultrasonic cleaning in the post-processing is 20-30°C, the time of ultrasonic cleaning is 20-30 min, and the power of ultrasonic cleaning is 40%-50%.

[0022] In some embodiments, the drying temperature in the post-processing is 40-50°C, and the drying time is 24 hours.

[0023] Secondly, the present invention provides a Nb3Sn superconducting tape based on cold deformation processing, which is obtained by the aforementioned method for preparing Nb3Sn superconducting tape based on cold deformation processing.

[0024] Compared with the prior art, the beneficial effects of the present invention are: In a first aspect, the present invention provides a method for preparing Nb3Sn superconducting tape based on cold deformation processing. First, a Cu / Sn / Nb / Sn / Cu composite precursor is obtained by single-pass cold rolling, which can introduce lattice distortion and dislocation defects, resulting in mechanical bonding at the interface, providing additional nucleation driving force for the formation of the Nb3Sn superconducting phase, and shortening the process flow. Second, by combining gradient phase formation heat treatment, Cu-Sn bronze formation and Sn diffusion into the Nb matrix are promoted sequentially, effectively reducing the phase formation temperature and time of the Nb3Sn superconducting phase. In addition, gradient cooling can effectively avoid the formation of pores in the Nb3Sn superconducting tape during the cooling process.

[0025] In some embodiments, by combining stepwise grinding and polishing with ultrasonic cleaning and drying, the oxide layer and impurities on the surface of copper plates, tin plates, and niobium plates can be effectively removed, ensuring that the interface of Cu-Sn-Nb-Sn-Cu after stacking is clean and in close contact. This provides a reliable surface state for obtaining high-quality Cu / Sn / Nb / Sn / Cu composite precursors in a single-pass cold rolling process, which is beneficial for the uniform diffusion of elements and the stable formation of the Nb3Sn superconducting phase in subsequent gradient phase formation heat treatment.

[0026] In some embodiments, by controlling the temperature, time, and power of ultrasonic cleaning, grinding particles and grease adhering to the surface of copper, tin, and niobium plates can be efficiently removed under mild conditions, avoiding excessive cavitation damage to the plate surface, ensuring the interface cleanliness and bonding quality of Cu-Sn-Nb-Sn-Cu stacks, and providing a reliable guarantee for obtaining Cu / Sn / Nb / Sn / Cu composite precursors with good interface bonding and no defects in a single-pass cold rolling process.

[0027] In some embodiments, by controlling the drying temperature and time, residual cleaning liquid and moisture on the surfaces of copper, tin, and niobium plates can be fully removed at lower temperatures, thereby avoiding high-temperature oxidation or plate deformation. This ensures that the surfaces of each plate are dry and clean before Cu-Sn-Nb-Sn-Cu stacking, thus guaranteeing tight interface bonding during single-pass cold rolling. This provides good interface conditions for the uniform diffusion of Sn into the Nb matrix and high-quality formation of the Nb3Sn superconducting phase in subsequent gradient phase formation heat treatment.

[0028] In some embodiments, by controlling the reduction amount of a single-pass cold rolling to 40%-60%, sufficient lattice distortion and dislocation defects are introduced into the Cu / Sn / Nb / Sn / Cu composite precursor, generating huge distortion energy, which provides additional driving force for the nucleation of the Nb3Sn superconducting phase in the subsequent gradient phase formation heat treatment, while avoiding interface cracking caused by excessive deformation.

[0029] In some embodiments, a gradient phase-forming heat treatment with four stages of successively increasing temperature is used. First, the Cu-Sn interface pre-reaction is promoted at 180-210℃, then the Cu-Sn bronze phase is formed at 300-350℃ and 430-450℃, and finally, Sn is driven to fully diffuse into the Nb matrix at 650-690℃. This provides thermodynamic conditions for the uniform nucleation and continuous growth of the Nb3Sn superconducting phase, while avoiding component segregation and interface defects caused by direct high-temperature heating.

[0030] In some embodiments, a three-stage gradient cooling process is used, with temperature holding at 500-600℃ and 300-400℃ respectively, to allow the generated Nb3Sn superconducting phase to grow fully and stabilize during the cooling process. At the same time, the cooling rate is controlled at 4-8℃ / min to avoid interface cracking or phase layer peeling caused by uneven volume shrinkage, thereby obtaining a rough-processed Nb3Sn superconducting tape with complete structure and good interface bonding.

[0031] In some embodiments, the rough-processed Nb3Sn superconducting tape is ultrasonically cleaned in anhydrous ethanol through post-processing, which can effectively remove residual impurities and contaminants on the surface. After drying, a clean Nb3Sn superconducting tape is obtained.

[0032] In some embodiments, by controlling the temperature, time and power of ultrasonic cleaning in the post-processing, surface impurities of the rough-processed Nb3Sn superconducting tape can be removed under mild conditions, avoiding cavitation damage to the Nb3Sn superconducting phase layer; then, after drying at a low temperature of 40-50℃ for 24 hours, residual cleaning liquid can be fully removed, preventing surface oxidation or deformation, and obtaining a clean and complete Nb3Sn superconducting tape.

[0033] Secondly, this invention provides a Nb3Sn superconducting tape based on cold deformation processing. The resulting Nb3Sn superconducting tape has the characteristics of fine Nb3Sn superconducting phase grains, large phase layer thickness, good interface bonding, and continuous and uniform structure, which can effectively improve the overall superconducting performance. At the same time, internal defects such as pores and microcracks in the resulting Nb3Sn superconducting tape are suppressed, and the structural integrity and service stability are improved, making it suitable for engineering applications such as high-field superconducting magnets. Attached Figure Description

[0034] Figure 1 This is a schematic flowchart of the method for preparing Nb3Sn superconducting tape based on cold deformation processing according to the present invention. Figure 2 This is a schematic diagram of the structure of the Cu / Sn / Nb / Sn / Cu composite precursor in Embodiment 2 of the present invention; Figure 3 This is a microstructure diagram of the Cu-Sn / Nb composite interface of the Cu / Sn / Nb / Sn / Cu composite precursor in Example 2 of the present invention. Figure 4 This is the energy spectrum distribution of Cu element in the gradient phase formation heat treatment of Embodiment 2 of the present invention; Figure 5 This is the energy spectrum distribution of Sn element in the gradient phase formation heat treatment of Embodiment 2 of the present invention; Figure 6 This is the energy spectrum distribution of Nb element in the gradient phase formation heat treatment of Embodiment 2 of the present invention; Figure 7 This is a schematic diagram illustrating the changes in gradient phase formation heat treatment and gradient cooling in Embodiments 1-5 of the present invention; Figure 8 This is a hysteresis loop diagram of the Cu / Sn / Nb / Sn / Cu composite precursor of Embodiment 1 of the present invention after the fourth stage of heat treatment; Figure 9 This is a hysteresis loop diagram of the Cu / Sn / Nb / Sn / Cu composite precursor of Example 3 of the present invention after the fourth stage of heat treatment; Figure 10 This is a hysteresis loop diagram of the Cu / Sn / Nb / Sn / Cu composite precursor of Embodiment 2 of the present invention after the fourth stage of heat treatment; Figure 11 The image shows the macroscopic cracking morphology of the Cu / Sn / Nb / Sn / Cu composite precursor in Comparative Example 1 during a multi-pass rolling process. Figure 12 This is a diagram showing the interface pore defect morphology of the rough-machined Nb3Sn superconducting tape in Comparative Example 2. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the embodiments of this application will be described in detail below with reference to specific examples. Unless otherwise defined, the technical and scientific terms used in this invention have the meanings commonly understood by those skilled in the art. Without departing from the concept of this invention, those skilled in the art can make various improvements and changes to the specific embodiments described in this specification, and all such improvements and changes fall within the scope of protection of this invention.

[0036] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0037] Currently, the mainstream fabrication process for Nb3Sn superconducting magnets is mainly based on multi-pass large plastic deformation and long-term high-temperature heat treatment of Cu / Sn / Nb composite precursors. Specifically, Cu, Sn, and Nb are first assembled into a composite precursor according to a specific structure. Then, through multi-pass large plastic deformation processes such as drawing and rolling, the cross-sectional size is gradually reduced and the shape is controlled. In the above process, due to the significant differences in the mechanical properties (such as yield strength and work hardening rate) and thermal properties (such as melting point and thermal conductivity) of Cu, Sn, and Nb, the ability to coordinate deformation is poor, and the quality of interfacial bonding is difficult to control. To alleviate this problem, a multi-pass, small-deformation processing strategy must be adopted, and molds must be frequently changed to adapt to the shape and size requirements at different stages. This process is cumbersome, inefficient, and makes it difficult to achieve high-quality interfacial bonding under single-pass large deformation.

[0038] After plastic forming, the composite precursor needs to undergo a long-term heat treatment at 700–825℃ for 149–225 hours to promote the full diffusion of Sn to the Nb interface and react to form a continuous A15-type Nb3Sn superconducting phase layer. However, during the long-term high-temperature heating process, the mismatch between the thermal expansion coefficients and high-temperature mechanical properties of the components will generate thermal stress and differences in microstructure at the phase interface and inside, which can easily induce porosity. Porosity will not only destroy the continuity of the Nb3Sn superconducting phase, but also weaken the current carrying capacity and mechanical strength of the magnet, seriously restricting the overall performance and reliability of the superconducting magnet.

[0039] This invention provides a method for preparing Nb3Sn superconducting tapes based on cold deformation processing, see [link to relevant documentation]. Figure 1 This includes the following steps: Raw material preparation and pretreatment: Prepare copper plates, tin plates and niobium plates as raw materials, and perform pretreatment to obtain pretreated copper plates, tin plates and niobium plates; Cold deformation processing: The pretreated copper plate, tin plate and niobium plate are stacked from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, and then subjected to single-pass cold rolling to obtain Cu / Sn / Nb / Sn / Cu composite precursor; Gradient phase formation heat treatment: The Cu / Sn / Nb / Sn / Cu composite precursor is subjected to gradient phase formation heat treatment; wherein, the gradient phase formation heat treatment includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with the temperature increasing sequentially. Gradient cooling: The Cu / Sn / Nb / Sn / Cu composite precursor after gradient phase formation heat treatment is subjected to gradient cooling to obtain rough-processed Nb3Sn superconducting tape; wherein, the gradient cooling includes a first cooling stage, a second cooling stage and a third cooling stage. Post-processing: The rough-machined Nb3Sn superconducting tape is post-processed to obtain Nb3Sn superconducting tape.

[0040] This invention utilizes single-pass cold rolling to obtain a Cu / Sn / Nb / Sn / Cu composite precursor with large plastic deformation. This provides a driving force for the formation of the Nb3Sn superconducting phase, introducing lattice distortion and dislocation defects to achieve internal grain fragmentation and mechanical bonding at the interface. The enormous distortion energy generated by the large plastic deformation provides additional nucleation work, phase transformation driving force, and element diffusion channels for gradient phase formation, promoting grain refinement and increasing the thickness of the Nb3Sn superconducting phase layer, thereby increasing the critical current density of the Nb3Sn superconducting tape. Simultaneously, single-pass cold rolling offers high forming speed and fewer steps, making it suitable for mass production and reducing the process costs associated with multiple heat treatments or repeated processing. Furthermore, through… Gradient phase-forming heat treatment is applied to the Cu / Sn / Nb / Sn / Cu composite precursor. First, the first heat treatment promotes the pre-reaction of the Cu-Sn interface. Then, the second and third heat treatments form the Cu-Sn bronze phase, resulting in an intermetallic compound. A fourth heat treatment increases the diffusion rate of Sn into the Nb matrix, which is more conducive to the formation of the Nb3Sn superconducting phase. Gradient cooling is then applied to the Cu / Sn / Nb / Sn / Cu composite precursor after gradient phase-forming heat treatment to avoid uneven volume shrinkage and porosity caused by excessively rapid cooling. This results in a fine-grained and uniform Nb3Sn superconducting phase. Finally, post-processing yields a high-performance Nb3Sn superconducting tape.

[0041] It should be noted that, for the sake of brevity, the room temperature in this invention is 25°C, and the specific room temperature will not be described separately in the following.

[0042] Example 1: This embodiment provides a method for preparing Nb3Sn superconducting tape based on cold deformation processing, including the following steps: S1. Raw material preparation and pretreatment: Copper, tin, and niobium plates with dimensions of 30mm×120mm×1mm and a volume ratio of 1:1:1 were prepared as raw materials and pretreated. The copper, tin, and niobium plates were polished sequentially using sandpaper of 80#, 400#, 600#, 800#, 1000#, 1500#, and 2000# respectively. Then, they were ultrasonically cleaned for 20 minutes at 40% full power in anhydrous ethanol at 20℃ to remove impurities from the surface of the plates. Finally, they were dried at 40℃ for 24 hours to obtain the pretreated copper, tin, and niobium plates.

[0043] S2, Cold deformation processing: Pretreated copper, tin, and niobium plates are stacked from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, and then subjected to single-pass cold rolling on a cold rolling mill to obtain the Cu / Sn / Nb / Sn / Cu composite precursor. The single-pass cold rolling reduction is 50%, and the cold rolling mill speed is 10 rad / min.

[0044] S3, Gradient phase formation heat treatment: A tube furnace was used to perform gradient phase-forming heat treatment on the Cu / Sn / Nb / Sn / Cu composite precursor to achieve interfacial diffusion and the formation of the Nb3Sn superconducting phase in the Cu / Sn / Nb / Sn / Cu composite material. The gradient phase-forming heat treatment included a first stage heat treatment, a second stage heat treatment, a third stage heat treatment, and a fourth stage heat treatment with sequentially increasing temperatures. The first stage heat treatment involved a vacuum degree of 10... -3 Pa, temperature 210℃, holding time 50h; second stage heat treatment: vacuum degree 10 -3 Pa, temperature 340℃, holding time 25h; third stage heat treatment: vacuum degree 10 -3 Pa, temperature 450℃, holding time 25h; fourth stage heat treatment: vacuum degree 10 -3 Pa, temperature 650℃, heat preservation time 50h.

[0045] S4, Gradient cooling: A gradient cooling process is applied to the Cu / Sn / Nb / Sn / Cu composite precursor after gradient phase-forming heat treatment to avoid porosity caused by uneven volume shrinkage, resulting in a rough-finished Nb3Sn superconducting tape. The gradient cooling process includes a first cooling stage, a second cooling stage, and a third cooling stage. The first cooling stage has a vacuum degree of 10... -3 Pa, cooled to 500℃ at a rate of 5℃ / min, and held at that temperature for 30min; Second cooling stage: vacuum degree 10 -3 Pa, cooled to 300℃ at a rate of 5℃ / min, and held at that temperature for 15min; third cooling stage: vacuum degree 10 -3 Pa is cooled to room temperature at a rate of 5℃ / min.

[0046] S5. Post-processing: The rough-processed Nb3Sn superconducting tape is post-processed to obtain the Nb3Sn superconducting tape; wherein, the post-processing includes ultrasonically cleaning the rough-processed Nb3Sn superconducting tape in anhydrous ethanol at 20°C with full power of 40% for 20 min to remove surface impurities, and then drying it at 40°C for 24 h to obtain the Nb3Sn superconducting tape.

[0047] Example 2: This embodiment provides a method for preparing Nb3Sn superconducting tape based on cold deformation processing, including the following steps: S1. Raw material preparation and pretreatment: Copper, tin, and niobium plates with dimensions of 30mm×120mm×1mm and a volume ratio of 1:1:1 were prepared as raw materials and pretreated. The copper, tin, and niobium plates were polished sequentially using sandpaper of 80#, 400#, 600#, 800#, 1000#, 1500#, and 2000# respectively. Then, they were ultrasonically cleaned for 30 minutes at 50% full power in anhydrous ethanol at 30℃ to remove impurities from the surface of the plates. Finally, they were dried at 50℃ for 24 hours to obtain the pretreated copper, tin, and niobium plates.

[0048] S2, Cold deformation processing: Pretreated copper, tin, and niobium plates are stacked from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, and then subjected to single-pass cold rolling on a cold rolling mill to obtain the Cu / Sn / Nb / Sn / Cu composite precursor. The single-pass cold rolling reduction is 50%, and the cold rolling mill speed is 5 rad / min.

[0049] See Figure 2 The Cu / Sn / Nb / Sn / Cu composite precursor is a continuous strip with a relatively flat surface. No obvious delamination, warping or macroscopic cracking was observed. This indicates that the pretreated copper, tin and niobium plates can achieve good mechanical bonding under single-pass cold rolling, providing a good composite interface foundation for Sn diffusion and Nb3Sn superconducting phase formation during the subsequent gradient phase formation heat treatment process.

[0050] S3, Gradient phase formation heat treatment: A tube furnace was used to perform gradient phase-forming heat treatment on the Cu / Sn / Nb / Sn / Cu composite precursor to achieve interfacial diffusion and the formation of the Nb3Sn superconducting phase in the Cu / Sn / Nb / Sn / Cu composite material. The gradient phase-forming heat treatment included a first stage heat treatment, a second stage heat treatment, a third stage heat treatment, and a fourth stage heat treatment with sequentially increasing temperatures. The first stage heat treatment involved a vacuum degree of 10... -3 Pa, temperature 210℃, holding time 50h; second stage heat treatment: vacuum degree 10 -3 Pa, temperature 340℃, holding time 25h; third stage heat treatment: vacuum degree 10 -3 Pa, temperature 450℃, holding time 25h; fourth stage heat treatment: vacuum degree 10 -3 Pa, temperature 690℃, heat preservation time 50h.

[0051] See Figure 3During the gradient phase formation heat treatment of the Cu / Sn / Nb / Sn / Cu composite precursor, a continuous diffusion reaction layer was formed between the Cu-Sn / Nb composite interface of the Cu / Sn / Nb / Sn / Cu composite precursor. The diffusion reaction layer is mainly composed of Nb3Sn superconducting phase with a thickness of about 37μm. This indicates that in Example 2 of the present invention, cold deformation processing and gradient phase formation heat treatment can promote the diffusion of Sn to the Nb side and generate Nb3Sn superconducting phase.

[0052] See Figure 4 Cu elements are mainly distributed in the upper region, and there is a certain degree of element diffusion near the interface, indicating that a diffusion reaction occurred between the Cu layer and the adjacent Sn layer during the gradient phase formation heat treatment process.

[0053] See Figure 5 Sn is mainly distributed in the middle and upper regions and diffuses towards Cu along the interface, indicating that Sn participates in Cu-Sn diffusion reaction during gradient phase formation heat treatment, providing Sn source for the subsequent formation of bronze phase and Nb3Sn superconducting phase.

[0054] See Figure 6 The Nb element is mainly concentrated in the lower region, with good overall continuity. There are local undulations at the interface, indicating that the Nb layer still maintains its main structure after cold deformation processing and gradient phase formation heat treatment, providing a reaction matrix for the subsequent formation of the Nb3Sn superconducting phase.

[0055] S4, Gradient cooling: A gradient cooling process is applied to the Cu / Sn / Nb / Sn / Cu composite precursor after gradient phase-forming heat treatment to avoid porosity caused by uneven volume shrinkage, resulting in a rough-finished Nb3Sn superconducting tape. The gradient cooling process includes a first cooling stage, a second cooling stage, and a third cooling stage. The first cooling stage has a vacuum degree of 10... -3 Pa, cooled to 500℃ at a rate of 5℃ / min, and held at that temperature for 30min; Second cooling stage: vacuum degree 10 -3 Pa, cooled to 300℃ at a rate of 5℃ / min, and held at that temperature for 15min; third cooling stage: vacuum degree 10 -3 Pa is cooled to room temperature at a rate of 5℃ / min.

[0056] S5. Post-processing: The rough-processed Nb3Sn superconducting tape is post-processed to obtain the Nb3Sn superconducting tape; wherein, the post-processing includes ultrasonically cleaning the rough-processed Nb3Sn superconducting tape in anhydrous ethanol at 30°C with 50% full power for 30 min to remove surface impurities, and drying it at 50°C for 24 h to obtain the Nb3Sn superconducting tape.

[0057] Example 3: This embodiment provides a method for preparing Nb3Sn superconducting tape based on cold deformation processing, including the following steps: S1. Raw material preparation and pretreatment: Copper, tin, and niobium plates with dimensions of 30mm×120mm×3mm and a volume ratio of 1:1:1 were prepared as raw materials and pretreated. The copper, tin, and niobium plates were polished sequentially using sandpaper of 80#, 400#, 600#, 800#, 1000#, 1500#, and 2000# respectively. Then, they were ultrasonically cleaned for 20 minutes at 50% full power in anhydrous ethanol at 25℃ to remove impurities from the surface of the plates. Finally, they were dried at 50℃ for 24 hours to obtain the pretreated copper, tin, and niobium plates.

[0058] S2, Cold deformation processing: Pretreated copper, tin, and niobium plates are stacked from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, and then subjected to single-pass cold rolling on a cold rolling mill to obtain the Cu / Sn / Nb / Sn / Cu composite precursor. The single-pass cold rolling reduction is 60%, and the cold rolling mill speed is 5 rad / min.

[0059] S3, Gradient phase formation heat treatment: A tube furnace was used to perform gradient phase-forming heat treatment on the Cu / Sn / Nb / Sn / Cu composite precursor to achieve interfacial diffusion and the formation of the Nb3Sn superconducting phase in the Cu / Sn / Nb / Sn / Cu composite material. The gradient phase-forming heat treatment included a first stage heat treatment, a second stage heat treatment, a third stage heat treatment, and a fourth stage heat treatment with sequentially increasing temperatures. The first stage heat treatment involved a vacuum degree of 10... -3 Pa, temperature 210℃, holding time 50h; second stage heat treatment: vacuum degree 10 -3 Pa, temperature 340℃, holding time 25h; third stage heat treatment: vacuum degree 10 -3 Pa, temperature 450℃, holding time 25h; fourth stage heat treatment: vacuum degree 10 -3 Pa, temperature 680℃, heat preservation time 50h.

[0060] S4, Gradient cooling: A gradient cooling process is applied to the Cu / Sn / Nb / Sn / Cu composite precursor after gradient phase-forming heat treatment to avoid porosity caused by uneven volume shrinkage, resulting in a rough-processed Nb3Sn superconducting tape. The gradient cooling process includes a first cooling stage, a second cooling stage, and a third cooling stage. The first cooling stage maintains a vacuum level of 10... -3Pa, cooling to 600℃ at a rate of 5℃ / min, then holding at that temperature for 30min; Second cooling stage: maintaining a vacuum of 10 -3 Pa, cooling to 400℃ at a rate of 5℃ / min, then holding at that temperature for 15min; Third cooling stage: maintaining a vacuum of 10 -3 Pa is cooled to room temperature at a rate of 5℃ / min.

[0061] S5. Post-processing: The rough-processed Nb3Sn superconducting tape is post-processed to obtain the Nb3Sn superconducting tape; wherein, the post-processing includes ultrasonically cleaning the rough-processed Nb3Sn superconducting tape in anhydrous ethanol at 25°C with 50% full power for 30 min to remove surface impurities, and then drying it at 50°C for 24 h to obtain the Nb3Sn superconducting tape.

[0062] Example 4: This embodiment provides a method for preparing Nb3Sn superconducting tape based on cold deformation processing, which differs from Embodiment 1 in that: S2, Cold deformation processing: The reduction in single-pass cold rolling is 40%.

[0063] S3, Gradient phase formation heat treatment: First stage of heat treatment: vacuum level 10 -3 Pa, temperature 180℃, holding time 70h; second stage heat treatment: vacuum degree 10 -3 Pa, temperature 300℃, holding time 50h; third stage heat treatment: vacuum degree 10 -3 Pa, temperature 430℃, holding time 50h; fourth stage heat treatment: vacuum degree 10 -3 Pa, temperature 650℃, heat preservation time 70h.

[0064] S4, Gradient cooling: First cooling stage: Maintain a vacuum level of 10. -3 Pa, cooling to 600℃ at a rate of 8℃ / min, then holding at that temperature for 25min; Second cooling stage: maintaining a vacuum of 10 -3 Pa was cooled to 350°C at a rate of 8°C / min and then held at that temperature for 10 min.

[0065] Example 5: This embodiment provides a method for preparing Nb3Sn superconducting tape based on cold deformation processing, which differs from Embodiment 1 in that: S3, Gradient phase formation heat treatment: Second stage heat treatment: vacuum degree 10 -3Pa, temperature 350℃, heat preservation time 30h.

[0066] S4, Gradient cooling: First cooling stage: Maintain a vacuum level of 10. -3 Pa, cooling to 550℃ at a rate of 4℃ / min, then holding at that temperature for 40min; Second cooling stage: maintaining a vacuum of 10 -3 Pa was cooled to 300℃ at a rate of 4℃ / min and then held at that temperature for 20min.

[0067] See Figure 7 In Examples 1-5, during the first stage of heat treatment (180-210℃), Cu and Sn first undergo a solid-phase diffusion reaction to form Cu-Sn intermetallic compounds such as Cu6Sn5 and Cu3Sn, which is the bronze stage. This stage can effectively stabilize the Sn element, inhibit Sn melting and loss, and form a continuous Cu-Sn diffusion layer, providing a stable Sn source for subsequent Sn diffusion to Nb.

[0068] During the second heat treatment (300-350℃), the diffusion reaction at the Cu-Sn interface is further enhanced, and the Cu-Sn intermetallic compounds Cu6Sn5 and Cu3Sn formed in the previous stage continue to grow, which further stabilizes the Sn element in the Cu-Sn diffusion layer and reduces the risk of local melting, segregation or loss of Sn during subsequent heating.

[0069] During the third stage of heat treatment (430-450℃), the Cu-Sn intermetallic compound is further homogenized, the Sn diffusion rate is significantly increased, and Sn gradually migrates towards the Nb interface. Since the large number of dislocations and grain boundaries introduced by single-pass cold rolling can serve as fast diffusion channels, Sn can diffuse into the Nb matrix more rapidly.

[0070] During the fourth-stage heat treatment (650-690℃), Sn and Nb react fully, gradually forming a continuous Nb3Sn superconducting phase layer at the Nb interface. Because the high distortion energy stored during the initial cold deformation lowers the nucleation barrier of the Nb3Sn superconducting phase, the resulting Nb3Sn superconducting phase exhibits fine grains, a relatively large layer thickness, and a uniform microstructure. Simultaneously, the gradient heating avoids severe Sn volatilization and interfacial thermal stress concentration, which is beneficial for obtaining a complete and continuous A15 structure Nb3Sn superconducting phase layer.

[0071] During the gradient cooling process, the thermal stress caused by the difference in thermal expansion coefficients between Cu, Sn and Nb can be effectively reduced by cooling slowly in stages, thus avoiding the generation of interface pores in the brittle Nb3Sn phase and improving the interface integrity and superconducting performance stability of the superconducting tape.

[0072] Comparative Example 1: This comparative example is used to verify the superiority of single-pass cold rolling and gradient phase formation heat treatment over traditional multi-pass rolling and isothermal long-term heat treatment. The difference between Comparative Example 1 and Example 1 is: S2, Multi-pass rolling process: Pretreated copper, tin, and niobium plates are stacked from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, and then rolled in multiple passes on a cold rolling mill to obtain the Cu / Sn / Nb / Sn / Cu composite precursor. The multi-pass rolling process includes 5-9 cycles, with a reduction of 30%-50% in each pass. After each pass, intermediate annealing is required before proceeding to the next pass.

[0073] S3, Heat Treatment: The Cu / Sn / Nb / Sn / Cu composite precursor was subjected to phase-forming heat treatment in a tube furnace to obtain the sample; the vacuum degree of the phase-forming heat treatment was 10. -3 Pa, temperature 650℃, heat preservation time 50h.

[0074] Comparative Example 2: This comparative example is used to verify the effect of gradient cooling. The difference between Comparative Example 2 and Example 1 is: S4, Cooling Phase: The Cu / Sn / Nb / Sn / Cu composite precursor, after gradient phase formation heat treatment, was kept under a vacuum of 10. -3 Pa was cooled to room temperature at a rate of 5℃ / min to obtain a rough-processed Nb3Sn superconducting tape.

[0075] Performance testing: To further verify the effect of the cold deformation processing method of the present invention on the superconducting properties and microstructure integrity of the Nb3Sn superconducting tape, superconducting properties were tested in Examples 1-3, and the macroscopic morphology and interface structure of the sample obtained in Comparative Example 1 and the rough-processed Nb3Sn superconducting tape obtained in Comparative Example 2 were observed.

[0076] The superconducting performance testing process: The Nb3Sn superconducting tapes obtained in Examples 1-3 were cut into test samples of uniform size. After cleaning and drying with anhydrous ethanol, magnetization-magnetic field curve tests, i.e., hysteresis loop tests, were performed using a vibrating sample magnetometer or a comprehensive physical property measurement system. During the test, the test sample was fixed on a sample rod and cooled to a set low temperature condition. After the temperature stabilized, an external magnetic field was applied, and a complete hysteresis loop was obtained by scanning the magnetic field in the forward direction, the reverse direction, and then scanning the magnetic field again. The flux pinning ability of the test sample was evaluated based on the difference in magnetic moment or magnetization intensity between the upper and lower branches of the hysteresis loop under the same external magnetic field. The larger the opening of the hysteresis loop, the stronger the flux pinning ability of the test sample, and the better the current carrying capacity and superconducting performance of the Nb3Sn superconducting phase.

[0077] The superconducting performance test results of Examples 1-3 show that all three Cu / Sn / Nb / Sn / Cu composite precursors exhibited obvious hysteresis loop characteristics at a low temperature of 4.2 K. (See also...) Figure 8 With the applied magnetic field as the x-axis and the magnetic moment as the y-axis, the hysteresis loop opening of the Cu / Sn / Nb / Sn / Cu composite precursor in Example 1 after undergoing the fourth stage heat treatment at 650°C is smaller compared to that in Examples 2 and 3. (See also...) Figure 9 With the applied magnetic field as the x-axis and the magnetic moment as the y-axis, the hysteresis loop opening of the Cu / Sn / Nb / Sn / Cu composite precursor in Example 3 after undergoing the fourth stage heat treatment at 680℃ is larger than that in Example 1, indicating that the diffusion reaction between Nb and Sn is more complete and the magnetic flux pinning ability is enhanced. See also Figure 10 With the applied magnetic field as the abscissa and the magnetic moment as the ordinate, the Cu / Sn / Nb / Sn / Cu composite precursor of Example 2 still maintains obvious hysteresis loop characteristics after undergoing the fourth stage heat treatment at 690℃. Furthermore, Sn diffuses more fully into the Nb matrix at 690℃, giving the Nb3Sn superconducting phase layer good current carrying capacity and magnetic field response capability.

[0078] See Figure 11 Comparative Example 1 uses a multi-pass rolling process. Due to the significant differences in the plastic deformation capacity and work hardening behavior of the three components Cu, Sn, and Nb, the interfacial coordination deformation capacity is poor during the deformation process of multi-pass rolling, and the sample is prone to defects such as cracking. At the same time, the multi-pass rolling process is more complex and is not conducive to obtaining a continuous and complete Cu / Sn / Nb / Sn / Cu composite precursor.

[0079] See Figure 12Comparative Example 2 did not employ gradient cooling; instead, it was directly cooled to room temperature after gradient phase-forming heat treatment. Interfacial microstructure observation revealed significant porosity defects within the rough-processed Nb3Sn superconducting tape and near the reaction interface. This phenomenon is primarily due to the differences in thermal expansion coefficients and volume shrinkage behavior among the Cu, Sn, Nb, and Nb3Sn superconducting phases. Direct cooling makes it difficult to release thermal stress in a timely manner, leading to localized porosity formation. In contrast, Examples 1-3 employed gradient cooling, which gradually releases thermal stress during the cooling process, reducing the tendency for interfacial cracking and porosity formation, thereby obtaining Nb3Sn superconducting tapes with a more complete microstructure.

[0080] In summary, the Nb3Sn superconducting tape obtained in Example 2 exhibits the best overall performance. This demonstrates that, under the single-pass cold rolling, gradient phase formation heat treatment, and gradient cooling system of this invention, appropriately increasing the final phase formation temperature is beneficial for promoting the full diffusion of Sn into the Nb matrix, enhancing the continuity and integrity of the Nb3Sn superconducting phase, and thus improving the overall superconducting performance of the Nb3Sn superconducting tape. Meanwhile, Comparative Example 1 showed rolling cracking, and Comparative Example 2 showed post-phase formation pores, further proving that the single-pass cold rolling, gradient phase formation heat treatment, and gradient cooling of this invention have a synergistic effect, effectively improving the interface integrity of the Cu / Sn / Nb / Sn / Cu composite precursor, promoting the continuous formation of the Nb3Sn superconducting phase, and improving the superconducting performance of the Nb3Sn superconducting tape.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. 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 basic characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects.

[0082] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention fall within the scope of protection of this invention.

Claims

1. A method for preparing Nb3Sn superconducting tape based on cold deformation processing, characterized in that, Includes the following steps: The pretreated copper plate, tin plate and niobium plate are stacked from top to bottom in the order of Cu-Sn-Nb-Sn-Cu, and then subjected to single-pass cold rolling to obtain Cu / Sn / Nb / Sn / Cu composite precursor. A gradient phase-forming heat treatment is performed on the Cu / Sn / Nb / Sn / Cu composite precursor; wherein the gradient phase-forming heat treatment includes a first heat treatment, a second heat treatment, a third heat treatment, and a fourth heat treatment with the temperature increasing sequentially. A gradient cooling process is applied to the Cu / Sn / Nb / Sn / Cu composite precursor after gradient phase formation heat treatment to obtain a rough-processed Nb3Sn superconducting tape; wherein the gradient cooling process includes a first cooling stage, a second cooling stage, and a third cooling stage. Post-processing of the rough-machined Nb3Sn superconducting tape yields the Nb3Sn superconducting tape.

2. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 1, characterized in that, The pretreatment includes: grinding and polishing the copper plate, tin plate and niobium plate sequentially with sandpaper of 80#, 400#, 600#, 800#, 1000#, 1500# and 2000#, then ultrasonically cleaning them in anhydrous ethanol, and then drying them for later use.

3. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 2, characterized in that, In the pretreatment, the ultrasonic cleaning temperature is 20-30℃, the ultrasonic cleaning time is 20-30min, and the ultrasonic cleaning power is 40%-50%.

4. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 2, characterized in that, In the pretreatment, the drying temperature is 40-50℃ and the drying time is 24 hours.

5. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 1, characterized in that, The reduction in single-pass cold rolling is 40%-60%.

6. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 1, characterized in that, The first stage of heat treatment: the temperature is 180-210℃, and the holding time is 50-70h; The second stage of heat treatment: the temperature is 300-350℃, and the holding time is 25-50h; The third stage of heat treatment: the temperature is 430-450℃, and the holding time is 25-50h; The fourth stage of heat treatment involves a temperature of 650-690℃ and a holding time of 50-70 hours.

7. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 1, characterized in that, The first cooling stage: cool down to 500-600℃ at a rate of 4-8℃ / min, and then hold at that temperature for 25-40min; The second cooling stage: after cooling to 300-400℃ at a rate of 4-8℃ / min, hold the temperature for 10-20 minutes; The third cooling stage: cooling down to room temperature.

8. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 1, characterized in that, The post-processing includes: ultrasonically cleaning the rough-processed Nb3Sn superconducting tape in anhydrous ethanol to remove surface impurities, followed by drying to obtain the Nb3Sn superconducting tape.

9. The method for preparing Nb3Sn superconducting tape based on cold deformation processing according to claim 8, characterized in that, In the post-processing, the ultrasonic cleaning temperature is 20-30℃, the ultrasonic cleaning time is 20-30 minutes, and the ultrasonic cleaning power is 40%-50%. In the post-processing, the drying temperature is 40-50℃ and the drying time is 24 hours.

10. A Nb3Sn superconducting tape based on cold deformation processing, characterized in that, It is obtained by the method for preparing Nb3Sn superconducting tape based on cold deformation processing as described in any one of claims 1-9.

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