Nb3sn superconducting wire with integrated piezoelectric sensing function and preparation method thereof

Abstract

This invention belongs to the field of superconducting materials technology and discloses an internal tin-based Nb3Sn superconducting wire with integrated piezoelectric sensing function and its preparation method. The method involves preparing a piezoelectric functional layer and a dielectric layer on the surface of a SnAl alloy rod, drilling a hole, inserting a CuAg alloy rod to form a composite rod, inserting it into an internal tin-based Nb3Sn / CuNb composite tube, drawing it into sub-components, and then bundling them into a Ta tube and an oxygen-free copper tube. The wire is then obtained through multiple stretching operations. The piezoelectric functional layer can convert minute strains into measurable electrical signals, enabling in-situ real-time monitoring of internal mechanical stresses within the wire. The CuAg alloy rod can stabilize the tensile strength of the wire and promote the formation of the Nb3Sn phase, improving the operational reliability and safety of high-field magnets under extreme conditions without affecting superconducting performance.

Description

Technical Field

[0001] This invention belongs to the field of superconducting materials technology, and relates to an internal tin method Nb3Sn superconducting wire with integrated piezoelectric sensing function and its preparation method. Background Technology

[0002] Due to its high critical current density, Nb3Sn superconducting wire is a core raw material for manufacturing high-field magnets and is widely used in fields with stringent magnet performance requirements, such as fusion devices and particle accelerators. Currently, the highest-performing and most widely used Nb3Sn superconducting wires internationally are prepared using the internal tin method. The typical process is as follows: a SnTi alloy rod is inserted into an internal tin Nb3Sn / CuNb composite rod to assemble internal tin Nb3Sn sub-components. Subsequently, the sub-components are bundled into Ta tubes and oxygen-free copper tubes, and after multiple drawing processes, Nb3Sn superconducting composite wires are obtained.

[0003] However, existing Nb3Sn superconducting wires prepared by the internal tin method have two key technical defects: First, the wires do not have piezoelectric sensing capabilities, making it impossible to monitor the mechanical stress, vibration, and impact generated internally during use in situ and in real time. This makes it difficult to predict the generation of microcracks and quenching phenomena caused by Lorentz force, thermal stress, or electromagnetic force, which seriously threatens the operational stability of high-field magnets under extreme conditions. Second, the wires are relatively brittle after heat treatment and have insufficient tensile strength. During transportation, installation, or subsequent operations after winding the magnets, they are easily damaged by impacts, which in turn affects the overall performance and service life of the magnets.

[0004] Given the core application status of Nb3Sn superconducting wires in high-tech fields, solving the problems of missing monitoring functions and weak mechanical properties is of great significance for improving the operational reliability, safety and service life of high-field magnets. Therefore, developing an internal tin method Nb3Sn superconducting wire with both piezoelectric sensing function and stable mechanical properties and the corresponding preparation method has become a technical need that urgently needs to be overcome in this field. Summary of the Invention

[0005] This invention aims to solve two technical problems existing in the current tin-based Nb3Sn superconducting wire: First, the existing wire uses SnTi alloy rods to assemble sub-components, which lacks piezoelectric sensing characteristics and cannot monitor the mechanical stress, vibration and impact generated internally during use in situ and in real time. This makes it difficult to prevent microcracks and quenching caused by Lorentz force, thermal stress or electromagnetic force, threatening the operational safety of high-field magnets. Second, the existing wire is relatively brittle after heat treatment and has insufficient tensile strength. After being wound into magnets, it is easily damaged by bumps during transportation and installation, affecting the reliability of subsequent applications.

[0006] The technical solution adopted in this invention is to provide an internal tin-based Nb3Sn superconducting wire with integrated piezoelectric sensing function and its preparation method by optimizing the core structure design and fabrication process of the wire, as detailed below:

[0007] In a first aspect, the present invention provides a method for preparing an internal tin-based Nb3Sn superconducting wire with integrated piezoelectric sensing function, comprising the following steps:

[0008] S1: A comb-shaped electrode pattern is prepared on the surface of a SnAl alloy rod and sintered to form a conductive electrode;

[0009] S2: PZT(Pb(Zr) 0.52 Ti 0.48 O3) nanofibers were dispersed in an epoxy-polyurethane precursor solution to prepare the precursor solution;

[0010] S3: The precursor solution obtained in S2 is coated on the surface of the SnAl alloy rod obtained in S1, and the PZT nanofibers are oriented under the action of an electric field to form a helical orientation structure. After curing, a SnAl alloy rod with a piezoelectric functional layer is obtained.

[0011] S4: An Al2O3 thin film is deposited on the surface of the SnAl alloy rod obtained in S3 to obtain a SnAl alloy rod with a dielectric layer.

[0012] S5: Wrap a biaxially stretched polyimide film around the surface of the SnAl alloy rod obtained in S4 and cure it to obtain a SnAl alloy rod with piezoelectric sensing function.

[0013] S6: Drill a hole in the center of the SnAl alloy rod obtained in S5 to obtain a SnAl alloy tube, and insert a CuAg alloy rod into it to obtain a SnAl / CuAg alloy rod.

[0014] S7: After cleaning the SnAl / CuAg alloy rod obtained in S6, insert it into the Nb3Sn / CuNb composite tube obtained by the inner tin method, and obtain the sub-component by multiple drawing processes;

[0015] S8: After cleaning the subcomponents obtained in S7, they are bundled and sequentially loaded into Ta tube and oxygen-free copper tube to obtain the final billet. The Nb3Sn superconducting wire is then produced by the internal tin method through multiple stretching passes.

[0016] Furthermore, in step S1 of the above preparation method, the process for preparing the comb-shaped electrode pattern includes: micro-inkjet printing or laser direct writing.

[0017] Furthermore, in step S2 of the above preparation method, PZT nanofibers are prepared by electrospinning, and the PZT nanofibers have a diameter of 80~150nm and a length of 5~20μm.

[0018] Furthermore, in step S2 of the above preparation method, the volume fraction of PZT nanofibers in the precursor solution is 35-50%.

[0019] Furthermore, in step S3 of the above preparation method, the process of coating the precursor solution onto the surface of the SnAl alloy rod includes micro-extrusion or spin coating.

[0020] Furthermore, in step S3 of the above preparation method, a DC electric field is used with an electric field strength of 5~15kV / cm, the pitch of the spiral orientation structure is 5~20mm, and the thickness of the piezoelectric functional layer is 20~80μm.

[0021] Furthermore, in step S4 of the above preparation method, the method for depositing an Al2O3 thin film on the surface of the SnAl alloy rod includes: atomic layer deposition; the dielectric strength of the dielectric layer is ≥500V / μm.

[0022] Furthermore, in step S5 of the above preparation method, the biaxially oriented polyimide film has an overlay rate of 50-70% and a number of wrapping layers of 2-5; the curing process after wrapping is: 180-200℃ for 30-120 minutes, and the curing process is carried out in a vacuum.

[0023] Furthermore, before proceeding to S1, the surface of the SnAl alloy rod is cleaned.

[0024] Secondly, the present invention provides an internal tin-based Nb3Sn superconducting wire with integrated piezoelectric sensing function, which is prepared by the above method and includes: a sub-component, a Ta tube and an oxygen-free copper tube; the sub-component includes, in radial order: a CuAg alloy rod, a SnAl alloy tube, a piezoelectric functional layer, a dielectric layer and an internal tin-based Nb3Sn / CuNb composite tube.

[0025] Compared with existing Nb3Sn superconducting wires produced by the internal tin method, the present invention has the following advantages:

[0026] This invention constructs a piezoelectric functional layer composed of PZT nanofibers and an epoxy-polyurethane matrix on the surface of a SnAl alloy rod. The addition of the epoxy-polyurethane matrix (which possesses excellent flexibility and film-forming properties) overcomes the brittleness and processing difficulties of inorganic piezoelectric ceramics. The use of PZT nanofibers overcomes the problem of poor compatibility between organic and inorganic interfaces, allowing for the fabrication of ≥10... -6 The minute strain is converted into a measurable electrical signal of ≥1mV / με. Combined with the built-in microelectrode, it can monitor the mechanical stress, vibration and impact inside the wire in situ and in real time, effectively preventing microcracks and quenching caused by Lorentz force, thermal stress or electromagnetic force, and significantly improving the operational reliability of high field magnets under extreme conditions such as fusion devices and particle accelerators.

[0027] This invention embeds a CuAg alloy rod within a SnAl alloy rod with piezoelectric properties. On one hand, this stabilizes the tensile strength of the wire after heat treatment, preventing damage caused by bumps during transportation and installation after the wire is wound into a magnet. On the other hand, the Ag element in the CuAg alloy promotes the diffusion of Sn element during heat treatment, helping to form the Nb3Sn phase and ensuring the superconducting performance of the wire.

[0028] The preparation process of this invention is based on the traditional internal tin method and is optimized without introducing complex equipment that conflicts with existing production lines. Furthermore, the design of the piezoelectric functional layer, dielectric layer and insulating layer does not affect the core superconducting properties of the Nb3Sn wire itself, such as the critical current density, thus achieving the synergistic integration of superconducting and sensing functions. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the cross-sectional structure of the Nb3Sn subcomponent assembly. In the figure: 1-Inner tin method Nb3Sn / CuNb composite tube, 2-Dielectric layer, 3-Piezoelectric functional layer, 4-SnAl alloy tube, 5-CuAg alloy rod. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] This invention provides a method for preparing the Nb3Sn superconducting wire with integrated piezoelectric sensing function using the internal tin method, comprising the following steps:

[0032] S1: A comb-shaped electrode pattern is prepared on the surface of a SnAl alloy rod and sintered to form a conductive electrode;

[0033] S2: PZT(Pb(Zr) 0.52 Ti 0.48 O3) nanofibers were dispersed in an epoxy-polyurethane precursor solution to prepare the precursor solution;

[0034] S3: The precursor solution obtained in S2 is coated on the surface of the SnAl alloy rod obtained in S1, and the PZT nanofibers are oriented under the action of an electric field to form a helical orientation structure. After curing, a SnAl alloy rod with a piezoelectric functional layer is obtained.

[0035] S4: An Al2O3 thin film is deposited on the surface of the SnAl alloy rod obtained in S3 to obtain a SnAl alloy rod with a dielectric layer.

[0036] S5: Wrap a biaxially stretched polyimide film around the surface of the SnAl alloy rod obtained in S4 and cure it to obtain a SnAl alloy rod with piezoelectric sensing function.

[0037] S6: Drill a hole in the center of the SnAl alloy rod obtained in S5 to obtain a SnAl alloy tube, and insert a CuAg alloy rod into it to obtain a SnAl / CuAg alloy rod.

[0038] S7: After cleaning the SnAl / CuAg alloy rod obtained in S6, insert it into the Nb3Sn / CuNb composite tube obtained by the inner tin method, and obtain the sub-component by multiple drawing processes;

[0039] S8: After cleaning the subcomponents obtained in S7, they are bundled and sequentially loaded into Ta tube and oxygen-free copper tube to obtain the final billet. The Nb3Sn superconducting wire is then produced by the internal tin method through multiple stretching passes.

[0040] The schematic diagram of the cross-sectional structure of the Nb3Sn superconducting wire prepared by the internal tin method after the above steps is shown below. Figure 1 As shown in the figure: 1-Inner tin method Nb3Sn / CuNb composite tube, 2-Dielectric layer, 3-Piezoelectric functional layer, 4-SnAl alloy tube, 5-CuAg alloy rod.

[0041] For example, in S1 of the above preparation method, the process for preparing the comb-shaped electrode pattern includes: micro-inkjet printing or laser direct writing. Preferably, in the micro-inkjet printing process, nano-silver or copper ink is used, with a particle size of 20-50 nm, viscosity of 8-12 mPa·s, solid content of 20-40 wt%, nozzle diameter of 20-30 μm, nozzle-to-wire distance of 0.5-2 mm, positioning error of <5 μm, single drop size of 20-50 pL, temperature of 60-80 °C, and humidity of 40-60%; the solvent is removed by infrared or hot air (60-80 °C, 5-10 min); the sintering process is 150-200 °C, 30-60 min (nano-silver ink), or 250-300 °C, 15-30 min (nano-copper ink). Preferably, in the laser direct writing process, copper salt or copper oxide nano-ink is used, with a coating thickness of 1~5μm; scanning is performed using a 255nm ultraviolet or near-infrared laser with a laser power of 10~50mw, a scanning speed of 100~500mm / s, and a linewidth of 50~100μm; the solvent is thermally decomposed by laser to instantly reduce copper ions to metallic copper, and simultaneously sintering into a continuous conductive electrode under Ar inert gas protection, with sintering conditions of 200~240℃ for 10~30min. Preferably, the SnAl alloy rod has dimensions of φ (15~30mm) × (1000~2500mm).

[0042] For example, in step S2 of the above preparation method, PZT nanofibers are prepared by electrospinning, with a diameter of 80-150 nm and a length of 5-20 μm. Preferably, the spinning solution is a PZT sol-gel precursor solution, the spinning voltage is 15-25 kV, the receiving distance is 15-20 cm, the nanofibers are collected on the surface of a rotating copper rod, and crystallized after annealing at 600-700 °C for 2-4 h.

[0043] For example, in step S2 of the above preparation method, the volume fraction of PZT nanofibers in the precursor solution is 35-50%. Preferably, in order to adjust the coefficient of thermal expansion to match the wire and prevent cracking during thermal cycling, 5-10 wt% of nano-SiO2 particles may be added to the epoxy-polyurethane.

[0044] For example, in S3 of the above preparation method, the process of coating the precursor solution onto the surface of the SnAl alloy rod includes: micro-extrusion or spin coating.

[0045] For example, in step S3 of the above preparation method, a DC electric field is used with an electric field strength of 5~15kV / cm, the pitch of the spiral orientation structure is 5~20mm, and the thickness of the piezoelectric functional layer is 20~80μm. Preferably, the electric field direction forms an angle of 30~60° with the wire axis; the outer surface of the piezoelectric functional layer is formed with a periodic groove or raised array texture with a depth of 5~20μm through the aforementioned process, which helps to enhance the mechanical interlocking with the dielectric layer and improve the interfacial bonding strength; the curing conditions are preferably 80~120℃ for 4~6h.

[0046] For example, in step S4 of the above preparation method, the method of depositing an Al2O3 thin film on the surface of the SnAl alloy rod includes: atomic layer deposition; the dielectric strength of the dielectric layer is ≥500V / μm. Preferably, the deposition temperature is 150~200°C, the deposition cycle is 500~1000 times, and the thickness of the resulting dielectric layer is 50~100μm, wherein the dielectric layer is used for electrical insulation and environmental protection.

[0047] For example, in S5 of the above preparation method, the biaxially oriented polyimide film has an overlay rate of 50-70% and a number of wrapping layers of 2-5; the curing process after wrapping is: 180-200℃ for 30-120 minutes, and the curing process is carried out under vacuum (vacuum degree ≤10). -3 The process is carried out in Pa). Preferably, in order to improve its thermal conductivity and mechanical strength, and to achieve rapid heat dissipation and impact protection, the biaxially oriented polyimide film may be doped with 0.5~2wt% SiC nanowires.

[0048] Preferably, in step S6 of the above preparation method, the drilling diameter is φ (5~20mm), the CuAg alloy rod size is φ (4.5~19.5mm)×(1000~2500mm), and the mass fraction of Ag content in the CuAg alloy rod is 0.08~0.2%.

[0049] Preferably, in step S7 of the above preparation method, the size of the Nb3Sn / CuNb composite tube prepared by the internal tin method is φ (40~55mm) / φ (16.5~31.5mm)×(800~2200mm); the specifications of the subcomponents are H (2~15mm) / semicircle (2~15mm) / fan (2~15mm)×(600~4000mm).

[0050] Preferably, in step S8 of the above preparation method, the Ta tube has a specification of φ (14.5~59.5mm) × (600~4000mm); the oxygen-free copper tube has a specification of (φ20~75mm) / (15~60mm) × (600~4000mm); the stretching pass processing rate is 2~30% and the stretching speed is 1~100m / min.

[0051] For example, before performing S1, the process further includes cleaning the surface of the SnAl alloy rod. Preferably, the cleaning process is as follows: first, ultrasonic cleaning with an organic solvent such as acetone or ethanol is used to remove oil stains, then rinsing with deionized water, and then treating with plasma or ozone; the treatment power is 100~300W, and the time is 10~30min.

[0052] Example 1

[0053] This embodiment provides a method for preparing Nb3Sn superconducting wire with integrated piezoelectric sensing function using the internal tin method. The specific steps are as follows:

[0054] 1. Preprocessing

[0055] Take a SnAl alloy rod with a specification of φ15mm×1000mm, first use ethanol for ultrasonic cleaning to remove surface oil, and then rinse it clean with deionized water; use plasma to bombard the surface of SnAl alloy rod with a treatment power of 100W and a treatment time of 30min to increase surface energy and improve the wettability and adhesion of subsequent coatings.

[0056] 2. Electrode preparation

[0057] Comb-shaped silver electrode patterns were prepared on the surface of a SnAl alloy rod using a micro-inkjet printing process. The nano-silver ink used had a particle size of 20 nm, a viscosity of 8 mPa·s, and a solid content of 20 wt%. The printing nozzle diameter was 20 μm, the distance from the nozzle to the surface of the SnAl alloy rod was 0.5 mm, the positioning error was <5 μm, the volume of a single ink drop was 20 pL, and the printing environment temperature was 60℃ and the humidity was 40%. After printing, the rod was treated with hot air at 60℃ for 10 min to remove the solvent, and then sintered at 150℃ for 60 min to form a conductive path, thus obtaining a micron-sized conductive electrode.

[0058] 3. Preparation of precursor solution

[0059] Preparation of PZT (Pb(Zr)) 0.52 Ti 0.48 PZT nanofibers were prepared by electrospinning using a PZT sol-gel precursor solution. The spinning voltage was 15 kV, and the receiving distance was 15 cm. The spun fibers were collected on the surface of a rotating copper rod and then annealed at 600 °C for 4 h to crystallize. The resulting PZT nanofibers had a diameter of 80 nm and a length of 5 μm. The prepared PZT nanofibers were dispersed in a low-viscosity epoxy-polyurethane precursor solution, with a PZT nanofiber volume fraction of 35%. The precursor solution also contained 5 wt% nano-SiO2 particles (used to adjust the coefficient of thermal expansion, match the wire material, and prevent cracking during thermal cycling).

[0060] 4. Fabrication of piezoelectric functional layer

[0061] The precursor solution was uniformly coated onto the surface of a SnAl alloy rod with a pre-prepared conductive electrode using a micro-extrusion process. During the coating process, a DC electric field of 5 kV / cm was applied, with the direction of the electric field forming a 30° angle with the axial direction of the SnAl alloy rod. This caused the PZT nanofibers to form a helical orientation structure with a pitch of 5 mm, which is the piezoelectric functional layer (used to simultaneously sense axial and torsional stress). The thickness of the piezoelectric functional layer is 20 μm, and its outer surface forms a periodic groove array texture with a depth of 5 μm. Finally, the rod was cured at 80 °C for 4 h to obtain the SnAl alloy rod with the piezoelectric functional layer.

[0062] 5. Dielectric layer fabrication

[0063] An Al2O3 thin film was deposited on the surface of the SnAl alloy rod with a piezoelectric functional layer using atomic layer deposition (ALD) technology. The deposition temperature was 150℃, and the deposition cycle was 500 times. The resulting dielectric layer had a thickness of 50μm and a dielectric strength of 536V / μm, thus obtaining a SnAl alloy rod with a dense dielectric layer.

[0064] 6. Insulation layer wrapping

[0065] On the surface of a SnAl alloy rod with a dense dielectric layer, a biaxially stretched polyimide film is wrapped with two layers at a 50% overlap. The polyimide film is doped with 0.5 wt% silicon carbide (SiC) nanowires (to improve thermal conductivity and mechanical strength, enabling rapid heat dissipation and impact protection). The film is then cured at 180°C for 120 min under vacuum (vacuum degree ≤ 10). -3 The process is carried out in Pa) to obtain a SnAl alloy rod with piezoelectric function.

[0066] 7. Preparation of composite rods

[0067] A hole with a diameter of φ5mm is drilled in the center of the SnAl alloy rod with piezoelectric function; a CuAg alloy rod with a specification of φ4.5mm×1000mm and a mass fraction of Ag content of 0.08% is taken and inserted into the cleaned hole to obtain a SnAl / CuAg alloy rod with piezoelectric function.

[0068] 8. Subcomponent preparation

[0069] The SnAl / CuAg alloy rod with piezoelectric function was cleaned and then inserted into an internally tin-grown Nb3Sn / CuNb composite tube, which was also cleaned. The internally tin-grown Nb3Sn / CuNb composite tube had a specification of φ40mm / φ16.5mm×800mm. After multiple drawing processes, an internally tin-grown Nb3Sn sub-component with a specification of H2mm / semicircle 2mm / fan 2mm×600mm was obtained.

[0070] 9. Final wire preparation

[0071] Ta tubes with specifications of φ14.5mm×600mm and oxygen-free copper tubes with specifications of φ20mm / φ15mm×600mm were cleaned. The cleaned and bundled Nb3Sn subcomponents were then sequentially loaded into the Ta tubes and oxygen-free copper tubes to obtain the final Nb3Sn billet. The final billet was subjected to multiple stretching passes: a processing rate of 2~15% and a stretching speed of 1~20m / min were used for diameters above φ10.00mm, and a processing rate of 15~30% and a stretching speed of 30~100m / min were used for diameters below φ10.00mm, until the wire diameter was φ0.7mm, thus obtaining the Nb3Sn superconducting wire with integrated piezoelectric sensing function.

[0072] Samples were taken every 100m of the superconducting wire prepared in this embodiment, and the heat treatment regime was as follows: heating to 650℃ at a rate of 5℃ / h and holding at that temperature for 100h, followed by furnace cooling. The entire heat treatment process was carried out at temperatures less than 10℃. -2The process was conducted under a vacuum of 10 Pa. After this heat treatment, the critical current was tested under a magnetic field of 12 T. The test results showed that the critical current density remained at 800 A / mm². 2 After the wire is wound into a magnet, it can achieve a magnetic field depth of ≥10 mm inside the wire. -6 The minute strain is converted into a measurable electrical signal of 1.5mV / με. The dynamic strain caused by the internal Lorentz force can be collected in situ and in real time through a distributed piezoelectric sensing network. This can be used to evaluate the fatigue life of the magnet structure and effectively prevent magnet quenching caused by cracks on the wire surface due to Lorentz force inside the magnet.

[0073] Example 2

[0074] This embodiment provides a method for preparing Nb3Sn superconducting wire with integrated piezoelectric sensing function using the internal tin method. The specific steps are as follows:

[0075] 1. Preprocessing

[0076] Take a SnAl alloy rod with a specification of φ30mm×2500mm, first use acetone for ultrasonic cleaning to remove surface oil, and then rinse it clean with deionized water; use ozone to bombard the surface of the SnAl alloy rod with a treatment power of 300W, an ozone concentration of 17mg / L, and a treatment time of 30min. The whole process is maintained at atmospheric pressure (0.1MPa) to increase surface energy and improve the wettability and adhesion of subsequent coatings.

[0077] 2. Electrode preparation

[0078] Comb-shaped copper electrode patterns were prepared on the surface of SnAl alloy rods using a laser direct writing process. The ink used was copper salt nano-ink with a coating thickness of 5 μm. A 255 nm ultraviolet laser was used for scanning with a laser power of 10 mw, a scanning speed of 500 mm / s, and a linewidth of 100 μm. The solvent was thermally decomposed by laser, instantly reducing copper ions to metallic copper and forming a continuous conductive path. Subsequently, the electrode was sintered at 240 °C for 30 min under Ar inert gas protection to obtain micron-sized conductive electrodes.

[0079] 3. Preparation of precursor solution

[0080] Preparation of PZT (Pb(Zr)) 0.52 Ti 0.48PZT nanofibers were prepared by electrospinning using a PZT sol-gel precursor solution. The spinning voltage was 25 kV, and the receiving distance was 20 cm. The spun fibers were collected on the surface of a rotating copper rod and then annealed at 700 °C for 2 h to crystallize. The resulting PZT nanofibers had a diameter of 150 nm and a length of 20 μm. The prepared PZT nanofibers were dispersed in a low-viscosity epoxy-polyurethane precursor solution, with a PZT nanofiber volume fraction of 50%. The precursor solution also contained 10 wt% nano-SiO2 particles (used to adjust the coefficient of thermal expansion, match the wire material, and prevent cracking during thermal cycling).

[0081] 4. Fabrication of piezoelectric functional layer

[0082] The precursor solution was uniformly coated onto the surface of a SnAl alloy rod with a pre-prepared conductive electrode using a spin coating process. During the coating process, a DC electric field of 15 kV / cm was applied, with the direction of the electric field forming a 60° angle with the axis of the SnAl alloy rod. This caused the PZT nanofibers to form a helical orientation structure with a pitch of 20 mm, which is the piezoelectric functional layer (used to simultaneously sense axial and torsional stress). The thickness of the piezoelectric functional layer is 80 μm, and its outer surface forms a periodic groove array texture with a depth of 20 μm. Finally, the rod was cured at 120 °C for 6 h to obtain the SnAl alloy rod with the piezoelectric functional layer.

[0083] 5. Dielectric layer fabrication

[0084] An Al2O3 thin film was deposited on the surface of the SnAl alloy rod with a piezoelectric functional layer using atomic layer deposition (ALD) technology. The deposition temperature was 200℃, the deposition cycle was 1000 times, and the resulting dielectric layer thickness was 100μm with a dielectric strength of 581V / μm, thus obtaining a SnAl alloy rod with a dense dielectric layer.

[0085] 6. Insulation layer wrapping

[0086] On the surface of a SnAl alloy rod with a dense dielectric layer, a biaxially stretched polyimide film is wrapped with five layers at a 70% overlap. The polyimide film is doped with 2.0 wt% silicon carbide (SiC) nanowires (to improve thermal conductivity and mechanical strength, enabling rapid heat dissipation and impact protection). The film is then cured at 200°C for 30 minutes under vacuum (vacuum degree ≤ 10). -3 The process is carried out in Pa) to obtain a SnAl alloy rod with piezoelectric function.

[0087] 7. Preparation of composite rods

[0088] A hole with a diameter of φ20mm was drilled in the center of the SnAl alloy rod with piezoelectric function; a CuAg alloy rod with a specification of φ19.5mm×2500mm and a mass fraction of Ag content of 0.2% was taken and inserted into the cleaned hole to obtain a SnAl / CuAg alloy rod with piezoelectric function.

[0089] 8. Subcomponent preparation

[0090] The SnAl / CuAg alloy rod with piezoelectric function was cleaned and then inserted into an internally tin-grown Nb3Sn / CuNb composite tube, which was also cleaned. The internally tin-grown Nb3Sn / CuNb composite tube had a specification of φ55mm / φ31.5mm×2200mm. After multiple drawing processes, an internally tin-grown Nb3Sn subunit with a specification of H15mm / 15mm semicircle / 15mm fan-shaped×4000mm was obtained.

[0091] 9. Final wire preparation

[0092] Ta tubes with specifications of φ59.5mm×4000mm and oxygen-free copper tubes with specifications of φ75mm / φ60mm×4000mm were cleaned. The cleaned and bundled Nb3Sn subcomponents were then sequentially loaded into the Ta tubes and oxygen-free copper tubes to obtain the final Nb3Sn billet. The final billet was subjected to multiple stretching passes: a processing rate of 2~15% and a stretching speed of 1~20m / min were used for diameters above φ10.00mm, and a processing rate of 15~30% and a stretching speed of 30~100m / min were used for diameters below φ10.00mm, until the wire diameter was φ0.818mm, thus obtaining an Nb3Sn superconducting wire with integrated piezoelectric sensing function.

[0093] Samples were taken every 100m of the superconducting wire prepared in this embodiment, and the heat treatment regime was as follows: heating to 650℃ at a rate of 5℃ / h and holding at that temperature for 100h, followed by furnace cooling. The entire heat treatment process was carried out at temperatures less than 10℃. -2 The process was conducted under a vacuum of 10 Pa. After this heat treatment, the critical current was tested under a magnetic field of 12 T. The test results showed that the critical current density remained at 1200 A / mm². 2 After the wire is wound into a magnet, it can achieve a magnetic field depth of ≥10 mm inside the wire. -6 The minute strain is converted into a measurable electrical signal of 4mV / με. It can realize early warning of magnet quench by in-situ and real-time acquisition of micro-strain changes caused by local thermal expansion before magnet quench. The response time is ≤10ms, which can effectively prevent magnet quench caused by cracks on the wire surface due to Lorentz force inside the magnet.

[0094] Example 3

[0095] This embodiment provides a method for preparing Nb3Sn superconducting wire with integrated piezoelectric sensing function using the internal tin method. The specific steps are as follows:

[0096] 1. Preprocessing

[0097] Take a SnAl alloy rod with a specification of φ20mm×1500mm, first use acetone for ultrasonic cleaning to remove surface oil, and then rinse it clean with deionized water; use ozone to bombard the surface of SnAl alloy rod with a treatment power of 200W, an ozone concentration of 21mg / L, and a treatment time of 20min. The whole process is carried out under normal pressure (0.1MPa) to increase surface energy and improve the wettability and adhesion of subsequent coatings.

[0098] 2. Electrode preparation

[0099] Comb-shaped copper electrode patterns were prepared on the surface of SnAl alloy rods using a micro-inkjet printing process. The nano-copper ink used had a particle size of 30 nm, a viscosity of 10 mPa·s, and a solid content of 30 wt%. The printing nozzle diameter was 25 μm, the distance from the nozzle to the surface of the SnAl alloy rod was 1 mm, the positioning error was <5 μm, the volume of a single ink drop was 25 pL, and the printing environment temperature was 70℃ and the humidity was 50%. After printing, the rods were treated with hot air at 70℃ for 8 min to remove the solvent, and then sintered at 270℃ for 20 min to form conductive pathways and obtain micron-sized conductive electrodes.

[0100] 3. Preparation of precursor solution

[0101] Preparation of PZT (Pb(Zr)) 0.52 Ti 0.48 PZT nanofibers were prepared by electrospinning using a PZT sol-gel precursor solution. The spinning voltage was 20 kV, and the receiving distance was 17 cm. The spun fibers were collected on the surface of a rotating copper rod and then annealed at 650 °C for 3 h to crystallize. The resulting PZT nanofibers had a diameter of 100 nm and a length of 15 μm. The prepared PZT nanofibers were dispersed in a low-viscosity epoxy-polyurethane precursor solution, with a PZT nanofiber volume fraction of 45%. The precursor solution also contained 7 wt% nano-SiO2 particles (used to adjust the coefficient of thermal expansion, match the wire material, and prevent cracking during thermal cycling).

[0102] 4. Fabrication of piezoelectric functional layer

[0103] The precursor solution was uniformly coated onto the surface of a SnAl alloy rod with a pre-prepared conductive electrode using a spin coating process. During the coating process, a DC electric field of 10 kV / cm was applied, with the direction of the electric field forming a 45° angle with the axial direction of the SnAl alloy rod. This caused the PZT nanofibers to form a helical orientation structure with a pitch of 13 mm, which is the piezoelectric functional layer (used to simultaneously sense axial and torsional stress). The thickness of the piezoelectric functional layer is 50 μm, and its outer surface forms a periodic array texture of alternating grooves and protrusions with a depth of 10 μm. Finally, the rod was cured at 100 °C for 5 h to obtain the SnAl alloy rod with the piezoelectric functional layer.

[0104] 5. Dielectric layer fabrication

[0105] An Al2O3 thin film was deposited on the surface of the SnAl alloy rod with a piezoelectric functional layer using atomic layer deposition (ALD) technology. The deposition temperature was 180℃, the deposition cycle was 800 times, the resulting dielectric layer thickness was 80μm, and the dielectric strength was 556V / μm, thus obtaining a SnAl alloy rod with a dense dielectric layer.

[0106] 6. Insulation layer wrapping

[0107] On the surface of a SnAl alloy rod with a dense dielectric layer, a biaxially stretched polyimide film is wrapped with three layers at a 60% overlap. The polyimide film is doped with 1.0 wt% silicon carbide (SiC) nanowires (to improve thermal conductivity and mechanical strength, enabling rapid heat dissipation and impact protection). The film is then cured at 190°C for 60 minutes under vacuum (vacuum degree ≤ 10). -3 The process is carried out in Pa) to obtain a SnAl alloy rod with piezoelectric function.

[0108] 7. Preparation of composite rods

[0109] A hole with a diameter of φ10mm was drilled in the center of the SnAl alloy rod with piezoelectric function; a CuAg alloy rod with a specification of φ9.5mm×1500mm and a mass fraction of Ag content of 0.14% was taken and inserted into the cleaned hole to obtain a SnAl / CuAg alloy rod with piezoelectric function.

[0110] 8. Subcomponent preparation

[0111] The SnAl / CuAg alloy rod with piezoelectric function was cleaned and then inserted into an internally tin-grown Nb3Sn / CuNb composite tube, which was also cleaned. The internally tin-grown Nb3Sn / CuNb composite tube had a specification of φ45mm / φ20.5mm×1300mm. After multiple drawing processes, an internally tin-grown Nb3Sn subunit with a specification of H8mm / 8mm semicircle / 8mm fan-shaped×2000mm was obtained.

[0112] 9. Final wire preparation

[0113] Ta tubes with specifications of φ30mm×2000mm and oxygen-free copper tubes with specifications of φ40mm / φ30.5mm×2000mm were cleaned. The cleaned and bundled Nb3Sn subcomponents were then sequentially loaded into the Ta tubes and oxygen-free copper tubes to obtain the final Nb3Sn billet. The final billet was subjected to multiple stretching passes: a processing rate of 2~15% and a stretching speed of 1~20m / min were used for diameters above φ10.00mm, and a processing rate of 15~30% and a stretching speed of 30~100m / min were used for diameters below φ10.00mm, until the wire diameter was φ0.988mm, thus obtaining an Nb3Sn superconducting wire with integrated piezoelectric sensing function.

[0114] Samples were taken every 100m of the superconducting wire prepared in this embodiment, and the heat treatment regime was as follows: heating to 650℃ at a rate of 5℃ / h and holding at that temperature for 100h, followed by furnace cooling. The entire heat treatment process was carried out at temperatures less than 10℃. -2 The process was conducted under a vacuum of 10 Pa. After this heat treatment, the critical current was tested under a magnetic field of 12 T. The test results showed that the critical current density remained at 1300 A / mm². 2 When this wire is used in a magnet, the internal temperature of the wire should be ≥10. -6 The minute strain is converted into a measurable electrical signal of 2.5mV / με. The piezoelectric signal can be fused with voltage taps and temperature sensor data to acquire dynamic strain caused by internal Lorentz force in situ and in real time, evaluate the fatigue life of the magnet structure, effectively prevent magnet quenching caused by wire surface cracks due to Lorentz force inside the magnet, and be used for magnet operation status diagnosis and active control.

[0115] Example 4

[0116] This embodiment provides a performance comparison between the Nb3Sn superconducting wires prepared by the internal tin method in Examples 1-3 and the Nb3Sn superconducting wires prepared by existing technologies.

[0117] To verify the performance and extreme condition adaptability of the tin-based Nb3Sn superconducting wire with integrated piezoelectric sensing function of this invention, the wires prepared in Examples 1-3 were compared with conventional tin-based Nb3Sn superconducting wires (control group, using SnTi alloy rods to assemble sub-components, without piezoelectric sensing function) in a performance comparison test. The test conditions and results are as follows:

[0118] 1. Test conditions

[0119] All test samples underwent a uniform heat treatment process: heating to 650℃ at a rate of 5℃ / h, holding at that temperature for 100h, followed by furnace cooling. The heat treatment process was carried out within ≤10℃. -2The test was conducted under a vacuum of Pa; the cryogenic performance test environment was 4.2K (liquid helium temperature).

[0120] 2. Performance test items and results

[0121] 1) Stability test of critical current density (Jc) and upper critical magnetic field (Hc2)

[0122] Table 1. Stability test results of critical current density (Jc) and upper critical magnetic field (Hc2)

[0123]

[0124] The wire of this invention is 10 4 After multiple cycles of strain loading, the Jc attenuation rate was <2% and the Hc2 attenuation rate was <2%, while the Jc attenuation rate of existing wires reached 9.33~13.64% and the Hc2 attenuation rate reached 5~6.67%, indicating that the mechanical stability and superconducting performance stability of the wire of this invention are significantly better than those of existing technologies.

[0125] 2) Stability test of piezoelectric sensing performance

[0126] Table 2. Test results of piezoelectric sensing performance stability

[0127]

[0128] The wire of this invention is 10 4 After multiple cycles of strain loading, it can still stably handle ≥10 -6 The minute strain is converted into a measurable electrical signal of ≥1.2mV / με, and the sensing function is not faulty. However, existing wire technology does not have piezoelectric sensing capability and cannot realize in-situ monitoring of internal stress and vibration.

[0129] 3) Extreme operating condition adaptability test (irradiation, strong magnetic field)

[0130] Table 3. Results of Extreme Operating Condition Adaptability Tests

[0131]

[0132] Table 3 presents the results of comparing the wires of the present invention (Examples 1-3) with the control group wires at 10... 6 Performance adaptability test results under extreme conditions of Gy strong irradiation + 25T alternating magnetic field: The results show that:

[0133] Critical current density (Jc): After extreme operating conditions, under a 12T magnetic field, the Jc of Examples 1-3 reached 791, 1179, and 1287 A / mm², respectively. 2 The control group had only 650~900 A / mm 2In Example 3, Jc was 1.43 times the upper limit of the control group, demonstrating better current-carrying stability.

[0134] Upper critical magnetic field (Hc2): The Hc2 of Examples 1 to 3 remained at 23.1 to 23.5 T, which was significantly higher than that of the control group at 20.5 to 22.5 T, indicating that the superconducting critical magnetic field attenuation of the wire of the present invention is weaker under the combined environment of strong irradiation and high magnetic field.

[0135] Piezoelectric conversion efficiency: Examples 1-3, after irradiation, showed ≥10 -6 The strain can still maintain a conversion efficiency of 1.1~3.1mV / με, and has a stable in-situ monitoring capability; while the control group has no piezoelectric sensing function and cannot realize strain monitoring.

[0136] Analysis shows that the wire of this invention is in 10 6 Under extreme conditions of strong Gy irradiation and a 25T alternating magnetic field, it maintains superior superconducting performance (Jc, Hc2) and also possesses piezoelectric sensing capabilities that are lacking in the control group, fully meeting the application requirements of extreme scenarios such as fusion devices and particle accelerators.

[0137] In summary, the Nb3Sn superconducting wire with integrated piezoelectric sensing function prepared by this invention exhibits the following advantages while maintaining original superconducting properties (Jc, Hc2) comparable to existing technologies: it possesses stable piezoelectric sensing capabilities, enabling in-situ, real-time monitoring of internal mechanical stress, vibration, and impact; its mechanical stability is significantly improved, with superconducting performance degradation rates under cyclic strain, irradiation, and strong magnetic fields being far lower than existing technologies; the superconducting and sensing functions are synergistically integrated without sacrificing the core superconducting performance of the wire, and the fabrication process is compatible with existing production lines. This invention effectively solves the shortcomings of existing technologies, such as lack of monitoring functionality and weak mechanical properties, meeting the reliability and safety requirements of high-field magnets under extreme conditions.

[0138] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for preparing an internal tin-based Nb3Sn superconducting wire with integrated piezoelectric sensing function, characterized in that, Includes the following steps: S1: A comb-shaped electrode pattern is prepared on the surface of a SnAl alloy rod and sintered to form a conductive electrode; S2: PZT nanofibers are dispersed in an epoxy-polyurethane mixture to prepare a precursor solution; S3: The precursor solution obtained in S2 is coated on the surface of the SnAl alloy rod obtained in S1, and the PZT nanofibers are oriented under the action of an electric field to form a helical orientation structure. After curing, a SnAl alloy rod with a piezoelectric functional layer is obtained. S4: An Al2O3 thin film is deposited on the surface of the SnAl alloy rod obtained in S3 to obtain a SnAl alloy rod with a dielectric layer. S5: Wrap a biaxially stretched polyimide film around the surface of the SnAl alloy rod obtained in S4 and cure it to obtain a SnAl alloy rod with piezoelectric sensing function. S6: Drill a hole in the center of the SnAl alloy rod obtained in S5 to obtain a SnAl alloy tube, and insert a CuAg alloy rod into it to obtain a SnAl / CuAg alloy rod. S7: After cleaning the SnAl / CuAg alloy rod obtained in S6, insert it into the Nb3Sn / CuNb composite tube obtained by the inner tin method, and obtain the sub-component by multiple drawing processes; S8: After cleaning the subcomponents obtained in S7, they are bundled and sequentially loaded into Ta tube and oxygen-free copper tube to obtain the final billet. The Nb3Sn superconducting composite wire obtained by the inner tin method is then produced by multiple stretching passes.

2. The preparation method according to claim 1, characterized in that, In S1, the process for preparing the comb-shaped electrode pattern includes: micro-inkjet printing or laser direct writing.

3. The preparation method according to claim 1, characterized in that, In S2, PZT nanofibers are prepared by electrospinning. The PZT nanofibers have a diameter of 80~150nm and a length of 5~20μm.

4. The preparation method according to claim 1, characterized in that, In S2, the volume fraction of PZT nanofibers in the precursor solution is 35-50%.

5. The preparation method according to claim 1, characterized in that, In S3, the process of coating the precursor solution onto the surface of the SnAl alloy rod includes micro-extrusion or spin coating.

6. The preparation method according to claim 1, characterized in that, In S3, a DC electric field is used with an electric field strength of 5~15kV / cm, the pitch of the spiral orientation structure is 5~20mm, and the thickness of the piezoelectric functional layer is 20~80μm.

7. The preparation method according to claim 1, characterized in that, In S4, the method for depositing an Al2O3 thin film on the surface of a SnAl alloy rod includes: atomic layer deposition; the dielectric strength of the dielectric layer is ≥500V / μm.

8. The preparation method according to claim 1, characterized in that, In S5, the biaxially oriented polyimide film has a stacking rate of 50-70% and a number of wrapping layers of 2-5. The curing process after wrapping is: 180-200℃ for 30-120 minutes, and the curing process is carried out in a vacuum.

9. The preparation method according to claim 1, characterized in that, Before proceeding with S1, the surface of the SnAl alloy rod is cleaned.

10. A tin-insulated Nb3Sn superconducting wire with integrated piezoelectric sensing function, characterized in that, Prepared by the method according to any one of claims 1 to 9, comprising: a sub-component, a Ta tube, and an oxygen-free copper tube; wherein the sub-component comprises, in radial order: a CuAg alloy rod, a SnAl alloy tube, a piezoelectric functional layer, a dielectric layer, and an inner tin-based Nb3Sn / CuNb composite tube.

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