High corrosion resistant NbTi superconducting wire and method of making

Abstract

The application belongs to the technical field of superconducting material processing, and discloses a NbTi superconducting wire with high corrosion resistance and a preparation method thereof. The inner core structure of the NbTi superconducting wire is composed of a NbTi core, a Nb cylinder and a CuNiCr alloy tube, and is matched with a multi-stage composite structure of an acetal paint layer, an aluminum-magnesium alloy layer, a tinned metal braided layer and a PTFE outer layer. The wire can be used in a Cl ‑ The NbTi superconducting wire can be used in a Cl The inner core structure of the NbTi superconducting wire has diffusion barrier and long-term self-passivation performance, and the outer layer is coated with multiple physical-chemical composite barriers, so that cracks are inhibited, penetration is delayed, and interface corrosion is avoided, and long-term stability of the overall structure can be realized.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material processing technology, and relates to a highly corrosion-resistant NbTi superconducting wire and its preparation method. Background Technology

[0002] NbTi superconducting wire is a commercially mature and widely used low-temperature superconducting material. Belonging to the niobium-titanium binary alloy family, it boasts excellent superconducting properties, good processing plasticity, low cost, and strong stability, making it widely used in superconducting magnets in the liquid helium temperature range (4.2K). With the expansion of NbTi superconducting wire applications, the operating environments are becoming increasingly demanding. Performance requirements are no longer limited to basic properties such as high critical current and high thermal stability; environmental corrosion resistance has also become a key indicator. In recent years, with the expansion of superconducting technology in marine engineering, some shipboard devices such as superconducting motors, superconducting electromagnetic catapults, and superconducting magnetohydrodynamic propulsion also require the use of NbTi superconducting wire. Unlike laboratory environments, traditional NbTi superconducting wires in these applications are susceptible to surface corrosion and damage due to the marine atmosphere and seawater splashes, leading to magnet quenching failure or device malfunction and posing safety hazards. Therefore, developing a highly corrosion-resistant NbTi superconducting wire is of great significance for its use in corrosive environments.

[0003] Existing methods for improving the corrosion resistance of NbTi superconducting wires include surface coating and chemical / electrochemical passivation treatment. While metallic coatings, non-metallic coatings, and organic polymer coatings can provide some protection, the significant difference in thermal expansion coefficients between the coating and the NbTi substrate makes them prone to cracking, delamination, and blistering during low-temperature-to-room-temperature cycling, and they easily lose their protective capability in corrosive environments. Chemical / electrochemical passivation films are thin (nanoscale) and susceptible to scratches and dissolution, making long-term protection difficult in highly corrosive environments. Therefore, developing NbTi superconducting wires that combine high corrosion resistance and long-term stability is of great significance for expanding their application in highly corrosive environments. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a highly corrosion-resistant NbTi superconducting wire and its preparation method. The NbTi superconducting wire of this invention has an inner core structure composed of an NbTi core, an Nb cylinder, and a CuNiCr alloy tube, combined with a multi-level composite structure consisting of an acetal varnish layer, an aluminum-magnesium alloy layer, a tin-plated metal braided layer, and a PTFE outer layer. This wire maintains the superconducting performance of the NbTi core while significantly improving corrosion resistance, allowing it to withstand corrosion in Cl-containing environments. -Suitable for long-term service in seawater, high humidity, acid and alkali, and low temperature coupling environments, NbTi superconducting wires are applicable to harsh marine conditions such as superconducting motors and electromagnetic catapults. The core structure of NbTi superconducting wires has diffusion blocking and long-term self-passivation properties, while the outer layer is covered with multiple physical-chemical composite barriers. The layers support each other to inhibit crack initiation, delay penetration, and avoid interface corrosion, thus achieving long-term stability of the overall structure.

[0005] On the one hand, the present invention provides a highly corrosion-resistant NbTi superconducting wire, wherein the highly corrosion-resistant NbTi superconducting wire consists of, from the outermost layer to the innermost layer, a polytetrafluoroethylene layer, a metal shielding layer, an aluminum-magnesium alloy layer, an acetal varnish layer, and a composite wire.

[0006] The outer layer of the composite line is a drilled CuNiCr alloy rod, with 20 to 100 drilled holes, and a single core rod is inserted into each hole. The single core rod consists of a CuNiCr alloy tube, an Nb cylinder, and an NbTi rod, arranged sequentially from the outermost layer to the innermost layer.

[0007] Furthermore, by mass percentage, the raw materials for the CuNiCr alloy tube and the drilled CuNiCr alloy rod are both composed of 30%~50% Ni powder, 0.5%~3% Cr powder, and Cu powder as the balance.

[0008] On the other hand, the present invention seeks protection for a method for preparing the above-mentioned highly corrosion-resistant NbTi superconducting wire, which specifically includes the following steps: S1: Accurately weigh the powder raw materials according to the mass percentage: Ni 30%~50%, Cr 0.5%~3%, Cu to make up the balance. After mixing the powder raw materials, obtain CuNiCr alloy tubes and drilled CuNiCr alloy rods through powder metallurgy.

[0009] Furthermore, the purity of the powder raw materials is 99.99%, and the diameter of the Ni, Cr, and Cu powders is 70~100μm. The mixing method is as follows: the powder is loaded into a three-dimensional powder mixer, the rotation speed is set to 8~15r / min, and the mixing time is 3~5h. The powder metallurgy is as follows: the obtained uniformly mixed powder is loaded into a graphite mold, pressed into a compact, and sintered. The pressing pressure is 300~600Mpa, the pressing time is 100~150s, and the sintering process is carried out in a vacuum furnace with a vacuum degree <2×10⁻⁶. -4 The sintering temperature is 1400~1600℃, and the holding time is 2~4h; the inner diameter of the CuNiCr alloy tube is 120~200mm, and the wall thickness is 20~40mm. The outer diameter of the drilled CuNiCr alloy rod is 140~250mm, the number of drill holes is 20~100, and the diameter of the drill holes is 10~30mm.

[0010] Furthermore, the addition of Cr metal powder to the powdered raw material can promote the formation of a dense Cr2O3 passivation layer on the metal surface, effectively inhibiting Cl... - This further improves the corrosion resistance of the alloy.

[0011] S2: NbTi rods and Nb cylinders are inserted into CuNiCr alloy tubes to obtain NbTi / CuNiCr single-core ingots. These ingots are then sequentially welded, hot-extruded, hot-drawn, and peeled. Finally, they are cut to length to obtain single-core rods with a diameter of 10-30 mm. 20-100 single-core rods are inserted into drilled CuNiCr alloy rods to form composite ingots. After degassing, the above welding, hot extrusion, hot drawing, and peeling processes are repeated to obtain composite rods. The composite rods are then subjected to aging heat treatment, twisting, and stretching to obtain composite wires with a diameter of 0.80-1.60 mm.

[0012] Further, the diameter of the NbTi rod is 120~200mm, and the thickness of the Nb cylinder is 0.5~1.0mm; the welding is performed by welding the upper and lower covers of the NbTi / CuNiCr single-core ingot and composite ingot together in a vacuum electron beam welder for sealing, the welding is rotary welding, the welding power is 100~200kW, and the welding speed is 10~20° / min. The holding temperature during the hot extrusion process is 500~700℃, the holding time is 4~8h, the extrusion ratio is 10~15, and the extrusion speed is 15~30m / min. The processing rate of each pass in the hot drawing process is controlled at 20%~30%, and the processing rate of the peeling process is controlled at 10%~15% to remove the surface oxide layer and inclusions. The aging heat treatment temperature is 350~550℃, the holding time is 50~70h, the number of holding times is 5~7, the twisting speed is 1200~3000r / min, and the stretching processing rate is controlled at 10%~20%.

[0013] S3: Coat the surface of the composite wire with acetal varnish to obtain an enameled wire, wrap an aluminum-magnesium alloy foil around the surface of the enameled wire, and weave a metal shielding layer on the surface of the aluminum-magnesium alloy foil to obtain a metal shielded wire.

[0014] Furthermore, the coating of acetal paint includes annealing, cyclic coating and baking. The annealing temperature is 250~400℃, the annealing time is 30~60s, the number of cyclic coatings is 5~10 times, the thickness of the paint film is 0.04~0.08mm, the baking temperature is 60℃, and the baking time is 10~30s.

[0015] Furthermore, gel permeation chromatography was used to monitor the molecular weight distribution of acetal paint, controlling the mass percentage of acetal groups to be >90% and the mass percentage of free hydroxyl and carboxyl groups to be <5%, in order to avoid excessive low molecular weight components causing pores after painting, which would affect the density of the paint film and the surface corrosion resistance.

[0016] Furthermore, the aluminum-magnesium alloy foil contains 95% ± 2% aluminum by mass, has a thickness of 0.005 mm to 0.02 mm, a wrapping speed of 20 to 50 m / min, and an overlap rate of 15% to 20%. The aluminum-magnesium alloy foil provides high-frequency signal shielding above 1 MHz.

[0017] Furthermore, the metal shielding layer is obtained by braiding one of tin-plated titanium wire and tin-plated copper wire, wherein the diameter of the tin-plated titanium wire and tin-plated copper wire is 0.1mm~0.2mm. The braiding density is 89%~92%, the braiding angle is 45°, and the number of braids is 1 layer. The metal shielding layer provides shielding for low-frequency signals below 1MHz.

[0018] S4: After finishing, ultrasonically cleaning and drying the surface of the wire, wrap it with a polytetrafluoroethylene (PTFE) protective layer and bake it to obtain the high corrosion resistance NbTi superconducting wire.

[0019] Furthermore, the thickness of the polytetrafluoroethylene layer is 0.06~0.1mm, the overlap rate is 15%~20%, the baking temperature is 150~300℃, the wrapping speed is 15~30m / min, and the baking time is 30min~45min.

[0020] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: The NbTi superconducting wire prepared by this invention exhibits superior corrosion resistance and can be used in Cl-containing environments. - This invention enables long-term stable operation in seawater, high humidity, acid-alkali, and low-temperature coupled environments, significantly reducing the risk of pitting corrosion, intergranular corrosion, and crevice corrosion. The protective layer of the NbTi superconducting wire does not damage the superconducting properties of the NbTi core, and the wire's superconductivity remains unchanged while its corrosion resistance is significantly improved. This invention uses Cu, Ni, and Cr powders as raw materials to prepare alloy tubes. The mass percentage of Cr in the powder is 0.5%~3%. At this addition amount, Cr oxidizes to form a continuous, dense, and strongly adherent Cr2O3 passivation layer, effectively blocking Cl... - Initiated by penetration, adsorption, and pitting corrosion, this process fundamentally inhibits electrochemical corrosion and halide ion erosion, providing a primary corrosion-resistant structure. Even minor surface damage allows for re-passivation and self-healing, achieving long-term corrosion resistance of the metal substrate. The Nb-coated barrier layer possesses excellent passivation capabilities while simultaneously blocking the interdiffusion between CuNiCr and NbTi, preventing the formation of brittle interfacial phases, galvanic corrosion, and grain boundary corrosion. This ensures long-term stability and non-deterioration of the internal interface. The Nb-coated shell and CuNiCr alloy layer work together to achieve a "highly corrosion-resistant outer shell + pure superconducting core." The inner acetal varnish and outer polytetrafluoroethylene (PTFE) layer form a dual chemical barrier, providing resistance to acids, alkalis, and chloride ions. -The NbTi superconducting wire of this invention possesses oil and hydrolysis resistance properties, preventing corrosive media from reaching the metal layer. This invention combines these two properties: the inner acetal varnish provides a robust base and a tough buffer, while the outer PTFE layer provides an inert chemical barrier, preventing both cracking and delamination, achieving a dual effect of "toughness + high corrosion resistance." The aluminum-magnesium alloy layer and the metal shielding layer serve both structural reinforcement and secondary barrier functions, physically blocking the intrusion of moisture, ions, and particles, and reducing the probability of cracking under bending, vibration, and thermal cycling, indirectly improving corrosion resistance lifespan. Furthermore, this invention's NbTi superconducting wire exhibits superior electromagnetic shielding performance, simultaneously achieving high-frequency + low-frequency dual-band shielding, making it suitable for complex operating conditions such as strong electromagnetic interference, precision superconducting magnets, and deep-sea / nuclear power plants. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a cross-sectional view of a high corrosion-resistant NbTi superconducting wire. The labels are as follows: 1. Polytetrafluoroethylene layer; 2. Metal shielding layer; 3. Aluminum-magnesium alloy layer; 4. Acetal varnish layer; 5. Composite wire.

[0023] Figure 2 This is a cross-sectional view of the composite line. The figures are labeled as follows: 6. Single-core rod; 7. Drilled CuNiCr alloy rod. Detailed Implementation

[0024] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially. Unless otherwise specified, the percentages in the following embodiments refer to mass percentages.

[0025] A method for preparing a highly corrosion-resistant NbTi superconducting wire, specifically including the following steps: S1: Accurately weigh the powder raw materials according to the mass percentage: Ni 30%~50%, Cr 0.5%~3%, Cu to make up the balance. After mixing the powder raw materials, obtain CuNiCr alloy tubes and drilled CuNiCr alloy rods through powder metallurgy.

[0026] Furthermore, the purity of the powder raw materials is 99.99%, and the diameter of the Ni, Cr, and Cu powders is 70~100μm. The mixing method is as follows: the powder is loaded into a three-dimensional powder mixer, the rotation speed is set to 8~15r / min, and the mixing time is 3~5h. The powder metallurgy is as follows: the obtained uniformly mixed powder is loaded into a graphite mold, pressed into a compact, and sintered. The pressing pressure is 300~600MPa, the pressing time is 100~150s, and the sintering process is carried out in a vacuum furnace with a vacuum degree of less than 2×10⁻⁶. -4 The sintering temperature is 1400~1600℃, and the holding time is 2~4h; the inner diameter of the CuNiCr alloy tube is 120~200mm, and the wall thickness is 20~40mm. The outer diameter of the drilled CuNiCr alloy rod is 140~250mm, the number of drill holes is 20~100, and the diameter of the drill holes is 10~30mm.

[0027] Furthermore, the addition of Cr metal powder to the powdered raw material can promote the formation of a dense Cr2O3 passivation layer on the metal surface, effectively inhibiting Cl... - This further improves the corrosion resistance of the alloy.

[0028] S2: NbTi rods and Nb cylinders are inserted into CuNiCr alloy tubes to obtain NbTi / CuNiCr single-core ingots. These ingots are then sequentially welded, hot-extruded, hot-drawn, and peeled. The ingots are then cut to length to obtain single-core rods with a diameter of 10.00~30.00mm. 20~100 single-core rods are inserted into drilled CuNiCr alloy rods to form composite ingots. After degassing, the above welding, hot extrusion, hot drawing, and peeling processes are repeated to obtain composite rods. The composite rods are then subjected to aging heat treatment, twisting, and stretching to obtain composite wires with a diameter of 0.80~1.60mm.

[0029] Further, the diameter of the NbTi rod is 120~200mm, and the thickness of the Nb cylinder is 0.5~1.0mm; the welding is performed by welding the upper and lower covers of the NbTi / CuNiCr single-core ingot and composite ingot together in a vacuum electron beam welder for sealing, the welding is rotary welding, the welding power is 100~200kW, and the welding speed is 10~20° / min. The hot extrusion process has a holding temperature of 500~700℃, a holding time of 4~8h, an extrusion ratio of 10~15, and an extrusion speed of 15~30m / min. The processing rate of each pass in the hot drawing process is controlled at 20%~30%, and the processing rate of the peeling process is controlled at 10%~15% to remove the surface oxide layer and inclusions. The aging heat treatment temperature is 350~550℃, the holding time is 50~70h, the number of holding times is 5~7, the twisting speed is 1200~3000r / min, and the final stretching rate is controlled at 10%~20%.

[0030] S3: Coat the surface of the composite wire with acetal varnish to obtain an enameled wire, wrap an aluminum-magnesium alloy foil around the surface of the enameled wire, and weave a metal shielding layer on the surface of the aluminum-magnesium alloy foil to obtain a metal shielded wire.

[0031] Furthermore, the coating of acetal paint includes annealing, cyclic coating and baking. The annealing temperature is 250~400℃, the annealing time is 30~60s, the number of cyclic coatings is 5~10 times, the thickness of the paint film is 0.04~0.08mm, the baking temperature is 60℃, and the baking time is 10~30s.

[0032] Furthermore, gel permeation chromatography was used to monitor the molecular weight distribution of acetal paint, controlling the mass percentage of acetal groups to be >90% and the mass percentage of free hydroxyl and carboxyl groups to be <5%, in order to avoid excessive low molecular weight components causing pores after painting, which would affect the density of the paint film and the surface corrosion resistance.

[0033] Furthermore, the aluminum-magnesium alloy foil contains 95% ± 2% aluminum by mass, has a thickness of 0.005 mm to 0.02 mm, a wrapping speed of 20 to 50 m / min, an overlap rate of 15% to 20%, and is wrapped in one layer. The aluminum-magnesium alloy foil provides shielding for high-frequency signals above 1 MHz.

[0034] Furthermore, the metal shielding layer is obtained by braiding one of tin-plated titanium wire and tin-plated copper wire, wherein the diameter of the tin-plated titanium wire and tin-plated copper wire is 0.1mm~0.2mm. The braiding density is 89%~92%, the braiding angle is 45°, and the number of braids is 1 layer. The metal shielding layer provides shielding for low-frequency signals below 1MHz.

[0035] S4: After finishing, ultrasonically cleaning and drying the surface of the wire, wrap it with a polytetrafluoroethylene (PTFE) protective layer and bake it to obtain the high corrosion resistance NbTi superconducting wire.

[0036] Furthermore, the thickness of the polytetrafluoroethylene layer is 0.06~0.1mm, the overlap rate is 15%~20%, the baking temperature is 150~300℃, the baking time is 30min~45min, the wrapping speed is 15~30m / min, and the number of wrapping layers is 1.

[0037] Example 1 This embodiment provides a method for preparing highly corrosion-resistant NbTi superconducting wire, which specifically includes the following steps: S1: Accurately weigh the powder raw materials according to the following mass percentages: Ni 40%, Cr 1.5%, Cu 58.5%. The purity of all powder raw materials is 99.99%, and the diameter is 80 μm. Mix the powder raw materials in a three-dimensional powder mixer at a speed of 10 r / min for 4 hours. Subsequently, CuNiCr alloy tubes and drilled CuNiCr alloy rods are obtained through powder metallurgy. The pressing pressure is 450 MPa, and the pressing time is 120 s. The sintering process is carried out in a vacuum furnace with a vacuum degree less than 2 × 10⁻⁶. -4 The sintering temperature is 1450℃, and the holding time is 3h. The inner diameter of the CuNiCr alloy tube is 140mm, the wall thickness is 30mm, the outer diameter of the drilled CuNiCr alloy rod is 210mm, the number of drilled holes is 28, and the diameter of the drilled holes is 16.8mm.

[0038] S2: A 138mm diameter NbTi rod and a 1mm thick Nb cylinder are inserted into a CuNiCr alloy tube. The tube is then sequentially welded, hot-extruded, hot-drawn, and peeled. The resulting single-core rod is cut to length to obtain a 16.8mm diameter rod. The welding power is 140kW, and the welding speed is 15°C / min. The hot extrusion process is held at 680℃ for 6 hours, with an extrusion ratio of 12 and an extrusion speed of 20m / min. The processing rate is controlled at 20% per pass during hot drawing and 10% during peeling. 28 single-core rods are then inserted into drilled CuNiCr alloy rods to form a composite ingot. Figure 2 After degassing, the above welding, hot extrusion, hot drawing, and peeling processes are repeated to obtain a composite rod. The composite rod is then subjected to aging heat treatment, twisting, and stretching to obtain a composite wire with a diameter of 0.85 mm. The aging heat treatment temperature is 480℃, the holding time is 65 h, and the holding times are 6. The twisting speed is 1300 r / min. The final stretching rate is controlled at 10%.

[0039] S3: Anneal the composite wire at 300℃ for 50s. Then coat the surface of the composite wire with acetal varnish, repeating the coating process 8 times. After each coating, bake the wire at 60℃ for 20s, resulting in a varnish film thickness of 0.08mm. This yields an enameled wire. Wrap a layer of aluminum-magnesium alloy foil with a thickness of 0.01mm around the surface of the enameled wire at a speed of 40m / min and an overlap rate of 15%. Then, braid a metal shielding layer on the surface of the aluminum-magnesium alloy foil using tin-plated titanium wire with a diameter of 0.1mm. The shielding layer has a braiding density of 90% and a braiding angle of 45°, resulting in a metal shielded wire.

[0040] S4: After finishing, ultrasonically cleaning, and drying the surface of the metal shielded wire, a layer of polytetrafluoroethylene (PTFE) film with a thickness of 0.08 mm is wrapped around it at a speed of 15 m / min and an overlap rate of 15%. After wrapping, it is baked and cured at 180°C for 30 min to obtain the high corrosion-resistant NbTi superconducting wire. Figure 1 ).

[0041] Verification showed that the high corrosion-resistant NbTi superconducting wire of this embodiment, compared with the traditional enameled NbTi superconducting wire of the same specification (i.e., the product in step S3 only performs the surface coating process of acetal varnish, with the superconducting composite wire surface coated with 0.08mm of acetal varnish, without subsequent processes), has the same critical current density at 4.2K. Referring to GB / T 4074.5-2024 "Test Methods for Winding Wires Part 5: Electrical Properties", a salt water pinhole test was conducted. To simulate a marine environment, the salt water pinhole solution was replaced with a 30g / L NaCl solution. After testing, it was found that the wire of this embodiment had 0 pinholes per 30 meters, while the traditional enameled NbTi superconducting wire had 6 pinholes per 30 meters, indicating that the wire of this embodiment has high corrosion resistance.

[0042] Example 2 This embodiment provides a method for preparing highly corrosion-resistant NbTi superconducting wire, which specifically includes the following steps: S1: Accurately weigh the powder raw materials according to the following mass percentages: Ni 30%, Cr 3.0%, Cu 67.0%. The purity of all powder raw materials is 99.99%, and the diameter is 70 μm. Mix the powder raw materials in a three-dimensional powder mixer at a speed of 15 r / min for 3 hours. Subsequently, CuNiCr alloy tubes and drilled CuNiCr alloy rods are obtained through powder metallurgy. The pressing process is carried out at a pressure of 600 MPa for 100 s. The sintering process is conducted in a vacuum furnace with a vacuum degree of less than 2 × 10⁻⁶. -4 The sintering temperature is 1600℃, and the holding time is 4h. The inner diameter of the CuNiCr alloy tube is 200mm, the wall thickness is 40mm, the outer diameter of the drilled CuNiCr alloy rod is 250mm, the number of drilled holes is 36, and the diameter of the drilled holes is 29.8mm.

[0043] S2: A 198mm diameter NbTi rod and a 1mm thick Nb cylinder are inserted into a CuNiCr alloy tube, and then welded, hot extruded, hot drawn, and peeled in sequence. The tube is then cut to length to obtain a single-core rod with a diameter of 29.8mm. The welding process uses a power of 200kW and a welding speed of 20° / min. The hot extrusion process uses a holding temperature of 600℃ and a holding time of 8h. The extrusion ratio is 15 and the extrusion speed is 15m / min. The processing rate of each pass in the hot drawing process is controlled at 30%, and the processing rate of the peeling process is controlled at 15%. Thirty-six single-core rods were inserted into drilled CuNiCr alloy rods to form a composite ingot. After degassing, the above-mentioned welding, hot extrusion, hot drawing, and peeling processes were repeated to obtain a composite rod. The composite rod was then subjected to aging heat treatment, twisting, and stretching to obtain a composite wire with a diameter of 1.55 mm. The aging heat treatment temperature was 550℃, the holding time was 70 h, and the holding times were 7. The twisting speed was 2300 r / min, and the stretching rate was controlled at 10%.

[0044] S3: Anneal the composite wire at a temperature of 400℃ for 40 seconds. Then, coat the surface of the composite wire with acetal varnish, repeating the coating process 10 times. After each coating, bake the wire at a temperature of 60℃ for 10 seconds, resulting in a varnish film thickness of 0.08 mm. This yields an enameled wire. Wrap a layer of aluminum-magnesium alloy foil around the surface of the enameled wire. The aluminum-magnesium alloy foil has a thickness of 0.02 mm and a wrapping speed of 20 m / min. The overlap rate of the aluminum-magnesium alloy foil is 20%. Then, braid a metal shielding layer onto the surface of the aluminum-magnesium alloy foil using tin-plated titanium wire with a diameter of 0.2 mm. The shielding layer has a braiding density of 92% and a braiding angle of 45°, resulting in a metal shielded wire.

[0045] S4: After finishing, ultrasonically cleaning and drying the surface of the metal shielded wire, a layer of polytetrafluoroethylene film with a thickness of 0.10 mm is wrapped around it. The wrapping speed is 15 m / min and the overlap rate is 15%. After wrapping, it is baked and cured at 290°C for 45 min to obtain the high corrosion resistance NbTi superconducting wire.

[0046] Verification showed that the high corrosion-resistant NbTi superconducting wire of this embodiment had the same critical current density at 4.2K as the traditional enameled NbTi superconducting wire of the same specification (i.e., the product in step S3 only undergoes surface coating with acetal varnish, with the superconducting composite wire surface coated with 0.08mm of acetal varnish, without subsequent processes). Referring to GB / T 4074.5-2024 "Test Methods for Winding Wires Part 5: Electrical Properties", a salt water pinhole test was conducted. To simulate a marine environment, the salt water pinhole solution was replaced with a 30g / L NaCl solution. After testing, it was found that the wire of this embodiment had 0 pinholes per 30 meters, while the traditional enameled NbTi superconducting wire had 9 pinholes per 30 meters.

[0047] Example 3 This embodiment provides a method for preparing highly corrosion-resistant NbTi superconducting wire, which specifically includes the following steps: S1: Accurately weigh the powder raw materials according to the following mass percentages: Ni 50%, Cr 0.5%, Cu 49.5%. The purity of all powder raw materials is 99.99%, and the diameter is 100 μm. Mix the powder raw materials in a three-dimensional powder mixer at a speed of 8 r / min for 5 hours. Subsequently, obtain CuNiCr alloy tubes and drilled CuNiCr alloy rods through powder metallurgy. The pressing process is carried out at a pressure of 300 MPa for 150 s. The sintering process is conducted in a vacuum furnace with a vacuum degree of less than 2 × 10⁻⁶. -4 The sintering temperature is 1400℃, and the holding time is 2h. The inner diameter of the CuNiCr alloy tube is 125mm, the wall thickness is 20mm, the outer diameter of the drilled CuNiCr alloy rod is 140mm, the number of drilled holes is 98, and the diameter of the drilled holes is 10.4mm.

[0048] S2: A 123mm diameter NbTi rod and a 0.5mm thick Nb cylinder are inserted into a CuNiCr alloy tube, and then sequentially welded, hot-extruded, hot-drawn, and peeled. The tube is then cut to length to obtain a 10.4mm diameter single-core rod. The welding process uses a power of 110kW and a welding speed of 10° / min. The hot extrusion process uses a holding temperature of 510℃ for 4 hours, an extrusion ratio of 10, and an extrusion speed of 30m / min. The processing rate of each pass in the hot drawing process is controlled at 15%. The processing rate of the peeling process is controlled at 10%. Ninety-eight single-core rods were inserted into drilled CuNiCr alloy rods to form a composite ingot. After degassing, the above-mentioned welding, hot extrusion, hot drawing, and peeling processes were repeated to obtain a composite rod. The composite rod was then subjected to aging heat treatment, twisting, and stretching to obtain a composite wire with a diameter of 0.82 mm. The aging heat treatment temperature was 350℃, the holding time was 50 h, and the holding times were 5. The twisting speed was 3000 r / min, and the stretching rate was controlled at 10%.

[0049] S3: Anneal the composite wire at 250°C for 60 seconds. Then, coat the surface of the composite wire with acetal varnish, repeating the coating process 5 times. After each coating, bake the wire at 60°C for 15 seconds, resulting in a varnish film thickness of 0.04 mm. This yields an enameled wire. Wrap a layer of aluminum-magnesium alloy foil around the surface of the enameled wire. The aluminum-magnesium alloy foil has a thickness of 0.005 mm and a wrapping speed of 25 m / min. The overlap rate of the aluminum-magnesium alloy foil is 15%. Then, braid a metal shielding layer on the surface of the aluminum-magnesium alloy foil using tin-plated titanium wire with a diameter of 0.15 mm. The shielding layer has a braiding density of 89% and a braiding angle of 45°, resulting in a metal shielded wire.

[0050] S4: After finishing, ultrasonically cleaning and drying the surface of the metal shielded wire, a layer of polytetrafluoroethylene film with a thickness of 0.06 mm is wrapped around it at a speed of 15 m / min and an overlap rate of 20%. After wrapping, the wire is baked and cured at 160°C for 30 min to obtain the high corrosion resistance NbTi superconducting wire.

[0051] Verification showed that the high corrosion-resistant NbTi superconducting wire of this embodiment had the same critical current density at 4.2K as the traditional enameled NbTi superconducting wire of the same specification (i.e., the product in step S3 only undergoes the surface coating process of acetal varnish, with the superconducting composite wire surface coated with 0.04mm of acetal varnish, without subsequent processes). Referring to GB / T 4074.5-2024 "Test Methods for Winding Wires Part 5: Electrical Properties", a salt water pinhole test was conducted. To simulate a marine environment, the salt water pinhole solution was replaced with a 30g / L NaCl solution. After testing, it was found that the wire of this embodiment had 0 pinholes per 30 meters, while the traditional enameled NbTi superconducting wire had 12 pinholes per 30 meters.

[0052] Example 4 This embodiment provides performance testing of highly corrosion-resistant NbTi superconducting wires.

[0053] The performance of the high corrosion-resistant NbTi superconducting wires prepared in Examples 1-3 and the traditional enameled NbTi superconducting wires was compared, and the results are shown in Table 1.

[0054] Table 1: Performance Comparison of Examples 1-3 with Traditional Enameled NbTi Superwires

[0055] As shown in Table 1, in the salt water pinhole test, the number of pinholes in the high corrosion-resistant NbTi superconducting wire was 0, while pinholes were present in all conventional wires. This indicates that the wire of the present invention has high corrosion resistance. Furthermore, after the salt water pinhole test, high-voltage pinhole tests were performed on all wires. The performance of the high corrosion-resistant NbTi superconducting wire of the present invention showed no significant difference compared to before the test, while the high-voltage pinhole value of the conventional wire decreased, indicating that the wire of the present invention has more stable performance in corrosive environments.

[0056] Comparative Example 1 The preparation method of this comparative NbTi superconducting wire is the same as in Example 1, except that 5 wt% Cr is used in S1, and any excess is subtracted by Cu powder. The performance of this comparative NbTi superconducting wire was tested using a salt water pinhole test, and the number of pinholes was found to be 3 per 30 meters. It is evident that although adding Cr improves corrosion resistance compared to traditional wires, excessive Cr addition leads to the formation of a Cr-rich brittle phase. Simultaneously, the increased strength and hardness of the wire reduce its processing performance, causing breakage during extrusion and drawing, resulting in a decline in long-term service performance.

[0057] Comparative Example 2 The preparation method of this comparative NbTi superconducting wire is the same as in Example 1, except that the acetal coating process in S3 is omitted. In the NbTi superconducting wire, the aluminum-magnesium alloy layer within the metal shielding layer directly contacts the CuNiCr alloy tube. On one hand, galvanic corrosion occurs due to the difference in electrode potential, damaging the Cr2O3 passivation film on the CuNiCr surface. On the other hand, numerous micro-gaps form at the interface, leading to crevice corrosion, causing insulation failure, partial discharge, and interlayer slippage. This results in the overall failure of the multi-level anti-corrosion system, significantly degrading the wire's corrosion resistance and long-term service performance. Testing revealed 12 pinholes in the salt water pinhole test.

[0058] Comparative Example 3 The preparation method of this comparative NbTi superconducting wire is the same as in Example 1, except that the structures of the acetal varnish layer in S3 and the polytetrafluoroethylene layer in S4 are interchanged. The outermost layer of the prepared NbTi superconducting wire is an acetal varnish layer, which has significantly worse chemical corrosion resistance, wear resistance, and aging resistance than polytetrafluoroethylene, resulting in poorer corrosion resistance. Testing showed that it exhibited 15 pinholes in the salt water pinhole test.

[0059] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A highly corrosion-resistant NbTi superconducting wire, characterized in that, The highly corrosion-resistant NbTi superconducting wire consists of, from the outermost layer to the innermost layer, a polytetrafluoroethylene layer, a metal shielding layer, an aluminum-magnesium alloy layer, an acetal varnish layer, and a composite wire. The outer layer of the composite line is a drilled CuNiCr alloy rod with 20 to 100 holes, and a single core rod is inserted into each hole. The single core rod consists of a CuNiCr alloy tube, an Nb cylinder, and an NbTi rod, arranged sequentially from the outermost layer to the innermost layer.

2. The high corrosion resistance NbTi superconducting wire according to claim 1, characterized in that, By mass percentage, the raw materials for the CuNiCr alloy tube and the drilled CuNiCr alloy rod are both composed of 30%~50% Ni powder, 0.5%~3% Cr powder, and Cu powder as the balance.

3. The method for preparing the highly corrosion-resistant NbTi superconducting wire according to any one of claims 1 to 2, characterized in that, include: S1: Preparation of CuNiCr alloy tubes and drilling of CuNiCr alloy rods; S2: NbTi rods and Nb cylinders are inserted into the CuNiCr alloy tube, and after welding, hot extrusion, hot drawing, and peeling, a single core rod is obtained; 20 to 100 of the single core rods are inserted into a drilled CuNiCr alloy rod, and after degassing, the welding, hot extrusion, hot drawing, and peeling are repeated to obtain a composite rod; the composite rod is then subjected to aging heat treatment, twisting, and stretching to obtain a composite wire. S3: Coat the surface of the composite wire with acetal varnish to form an acetal varnish layer, and obtain an enameled wire; wrap aluminum-magnesium alloy foil around the surface of the enameled wire to form an aluminum-magnesium alloy layer; braid a metal shielding layer on the surface of the aluminum-magnesium alloy layer to obtain a metal shielded wire. S4: Wrap a polytetrafluoroethylene film around the surface of the metal shielded wire to form a polytetrafluoroethylene layer, and bake it to obtain the highly corrosion-resistant NbTi superconducting wire.

4. The preparation method according to claim 3, characterized in that, Ni powder, Cr powder and Cu powder are weighed and mixed, and then CuNiCr alloy tube and drilled CuNiCr alloy rod are obtained by powder metallurgy. By mass percentage, the raw material of the CuNiCr alloy tube consists of 30%~50% Ni powder, 0.5%~3% Cr powder, and Cu powder as the balance. The diameters of the Ni powder, Cr powder, and Cu powder are all 70~100μm; The mixing speed is 8~15 r / min, and the mixing time is 3~5 h; The powder metallurgy refers to the process of pressing the mixed powder into a shape and then sintering it.

5. The preparation method according to claim 4, characterized in that, The inner diameter of the CuNiCr alloy tube is 120~200mm, and the wall thickness is 20~40mm; The outer diameter of the drilled CuNiCr alloy rod is 140~250mm, and the diameter of the drill hole is 10~30mm. The pressing pressure is 300~600Mpa, and the pressing time is 100~150s; The sintering is performed under a vacuum degree <2×10 -4 The sintering process is carried out under MPa conditions, with a sintering temperature of 1400~1600℃ and a holding time of 2~4h.

6. The preparation method according to claim 3, characterized in that, The diameter of the NbTi rod is 120~200mm, and the thickness of the Nb cylinder is 0.5~1.0mm; The welding power is 100~200kW, and the welding speed is 10~20° / min; The hot extrusion temperature is 500~700℃, the holding time is 4~8h, the extrusion ratio is 10~15, and the extrusion speed is 15~30m / min; The processing rate per pass in the hot drawing process is controlled at 20%~30%; The processing rate of the peeling process is controlled at 10% to 15%.

7. The preparation method according to claim 3, characterized in that, The aging heat treatment temperature is 350~500℃, the holding time is 50~70h, and the number of holding times is 5~7. The twisting speed is 1200~3000 r / min; The stretching processing rate is controlled at 10%~20%; The diameter of the composite line is 0.80~1.60mm.

8. The preparation method according to claim 3, characterized in that, The coating of acetal paint includes: annealing, cyclic coating, and baking after each coating; The acetal varnish contains >90wt% acetal groups and <5wt% free hydroxyl and carboxyl groups. The annealing temperature is 250~400℃, and the annealing time is 30~60s; The number of times the paint is applied in a cycle is 5 to 10. The baking temperature is 60℃, and the baking time is 10~30s; The thickness of the acetal coating is 0.04~0.08 mm.

9. The preparation method according to claim 3, characterized in that, The aluminum-magnesium alloy foil contains 95% ± 2% aluminum by mass, and its thickness is 0.005 mm to 0.02 mm. The wrapping speed in S3 is 20~50m / min, and the overlap rate of the aluminum-magnesium alloy foil after wrapping is 15%~20%. The number of wrapping layers is 1.

10. The preparation method according to claim 3, characterized in that, The metal shielding layer is obtained by braiding tin-plated titanium wire or tin-plated copper wire; The diameter of the tin-plated titanium wire and tin-plated copper wire is 0.1mm~0.2mm; The weaving density is 89%~92%, the weaving angle is 45°, and the number of weaving layers is 1. The thickness of the polytetrafluoroethylene layer is 0.06~0.1mm; The wrapping speed in S4 is 15~30m / min, the overlap rate of the polytetrafluoroethylene film after wrapping is 15%~20%, and the number of wrapping layers is 1. The baking temperature is 150~300℃ and the time is 30~45min.

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