High yield strength NbTi superconducting wire and method of making

Abstract

The application belongs to the technical field of superconducting wires, and discloses a high-yield-strength NbTi superconducting wire and a preparation method thereof. The method coats CuNi alloy powder on the outer wall of a thick-walled oxygen-free copper sheath and a drilled oxygen-free copper ingot by thermal spraying, simultaneously, an NbTi ingot is sleeved and processed to obtain an NbTi / Cu single-core rod, a CuNi alloy layer is sprayed on the surface of the NbTi / Cu single-core rod, the NbTi / Cu single-core rod is sequentially sleeved into the drilled oxygen-free copper ingot, the thick-walled oxygen-free copper sheath and a stainless steel sheath, and the finished product is obtained through processes such as extrusion, stretching and post-processing. The prepared wire forms a composite structure with high strength and high plasticity layers, the copper ratio is controlled at 10-15, the yield strength is excellent, the problem that high copper ratio and high yield strength are difficult to be considered together is solved, the coordination deformation ability of copper and NbTi and the core wire deformation uniformity are improved, and the prepared wire is suitable for scenes such as superconducting magnetic resonance imaging instruments.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire technology, and relates to a high yield strength NbTi superconducting wire and its preparation method. Background Technology

[0002] The development of superconducting materials technology has driven the upgrading and iteration of high-end medical equipment such as superconducting magnetic resonance imaging (MRI). NbTi superconducting wires, as a core component of superconducting magnets, directly determine the operational stability and applicable scenarios of the equipment. Currently, to meet the thermal stability requirements of MRI equipment, the industry generally optimizes performance by increasing the copper-to-superconducting ratio (CTR) of the wire. Traditional processes often employ a method of embedding and welding NbTi / Cu superconducting round wires to copper channel wires, i.e., Wire inchannel (WIC) type NbTi superconducting wires, which can increase the CTR to 10-15 or higher.

[0003] However, existing technologies still have significant limitations: on the one hand, wires produced by traditional high copper ratio fabrication processes have weak anti-interference capabilities and can only be adapted to low magnetic field environments of 0.5T, making it difficult to meet the adaptation requirements of liquid helium-free superconducting MRI and high-field MRI for complex working conditions; on the other hand, the significant differences in strength and hardness between copper and NbTi prevent existing processes from achieving efficient synergistic deformation between the two, resulting in a trade-off between the performance targets of high copper ratio and high yield strength. In addition, superconducting wires need to withstand large electromagnetic forces during superconducting magnet charging, and high yield strength is crucial to prevent wire breakage. However, in traditional embedded fabrication methods, the RRR value (the ratio of room temperature resistance to low temperature resistance of copper) and yield strength are mutually constrained, making it difficult to simultaneously meet the standards for use in high-end equipment.

[0004] With the advancement of medical imaging technology towards higher field and greater precision, the market demand for NbTi superconducting wires that combine high copper-to-superconducting ratio, high yield strength, and strong anti-interference capabilities is becoming increasingly urgent. The performance bottlenecks of existing technologies have severely limited technological breakthroughs and application expansion in equipment such as superconducting MRI. Therefore, developing a method for preparing NbTi superconducting wires that can balance high copper-to-superconducting ratio and high yield strength has significant technological value and practical application implications. Summary of the Invention

[0005] This invention aims to address key bottlenecks in existing NbTi superconducting wire fabrication technologies, specifically including: First, existing processes struggle to balance high copper-to-superconducting ratio with high yield strength. The significant differences in strength and hardness between copper and NbTi result in poor synergistic deformation, failing to meet the performance requirements of high-field superconducting MRI and helium-free superconducting MRI. Second, wires produced by traditional high-copper-to-superconducting processes (such as NbTi / Cu superconducting round wire inlay welding to copper channel wires) exhibit weak anti-interference capabilities, only suitable for low-magnetic-field environments (0.5T), making them unsuitable for high-field conditions. Third, using thick-walled oxygen-free copper sheaths to increase the copper ratio can lead to excessively high copper flow rates during extrusion, resulting in small and uneven deformation in the NbTi region. Fourth, stainless steel sheaths are prone to work hardening during cold drawing, reducing wire tensile properties and increasing the risk of wire or core breakage.

[0006] To achieve the above objectives, this invention provides a high yield strength NbTi superconducting wire and its preparation method, the specific technical solution of which is as follows:

[0007] In a first aspect, the present invention provides a method for preparing high-yield-strength NbTi superconducting wire, comprising the following steps:

[0008] S1, Raw material preparation: including: CuNi alloy powder, NbTi ingot, thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingot, thick-walled oxygen-free copper cladding, stainless steel cladding.

[0009] S2, Thermal spraying treatment: CuNi alloy powder is uniformly sprayed onto the outer wall of the thick-walled oxygen-free copper cladding (forming the first CuNi alloy layer) and the drilled oxygen-free copper ingot (forming the second CuNi alloy layer) through a thermal spraying process.

[0010] S3, Composite Ingot Preparation: NbTi ingots are inserted into thin-walled oxygen-free copper sheaths, and then subjected to welding, extrusion, stretching, sawing, and straightening processes to obtain NbTi / Cu single-core rods. A CuNi alloy layer is then sprayed onto the surface of the rods using a thermal spraying process. Subsequently, the NbTi / Cu single-core rods are sequentially assembled into drilled oxygen-free copper ingots, thick-walled oxygen-free copper sheaths, and stainless steel sheaths to obtain stainless steel-coated NbTi / Cu composite ingots.

[0011] S4, Extrusion and stretching: The stainless steel-coated NbTi / Cu composite ingot is welded with upper and lower covers for sealing, and then extruded and stretched. During the stretching process, the surface stainless steel layer is removed by a precision peeling process to obtain an NbTi / Cu composite rod. After stretching, heat treatment, twisting, and final stretching, a high copper ratio NbTi / Cu composite wire is obtained.

[0012] S5, Post-processing: After annealing and painting the NbTi / Cu composite wire with a high copper ratio, a small deformation process is performed to obtain a high yield strength NbTi superconducting wire.

[0013] Furthermore, in step S1 of the above preparation method: the CuNi alloy powder particle diameter is 70~100μm, and the Ni content is 10~30%. Higher Ni content results in higher CuNi alloy strength but reduced processing performance. Therefore, the Ni content selection depends on the copper cladding thickness; greater thickness requires higher Ni content. The oxygen-free copper used in the CuNi alloy powder is high-purity oxygen-free copper with a copper content ≥99.99% and an oxygen content ≤0.0005%. CuNi alloy powder is used because CuNi alloy and Cu can bond relatively stably. If NiTi alloy powder is used, CuTi intermetallic compounds will form, causing wire breakage or performance degradation. The NbTi ingot diameter is 100~200mm. The thin-walled oxygen-free copper cladding has a wall thickness of 15~30mm, and its inner diameter is 3~5mm larger than the NbTi ingot diameter for ease of assembly. The drilled oxygen-free copper ingot diameter is 100~200mm, with 20~50 holes evenly drilled around the center. The inner diameter of the thick-walled oxygen-free copper cladding is 4-6 mm larger than the diameter of the drilled oxygen-free copper ingot, and the wall thickness is 50-100 mm. The stainless steel cladding is made of 316L, with an inner diameter 4-6 mm larger than the outer diameter of the thick-walled oxygen-free copper cladding, a wall thickness of 10-15 mm, and a yield strength >250 MPa, which can constrain the copper layer during extrusion. Preferably, all the above raw materials are cleaned and dried before use.

[0014] Furthermore, in step S2 of the above preparation method, the thermal spraying process is arc spraying, and the thickness of the CuNi alloy layer formed on the substrate surface after spraying is 1.0~2.0 mm. Preferably, the spraying temperature is 4000~4500℃, the spraying distance is 100~150 mm, the spraying speed is 0.5~1.5 m / s, the powder feed rate is 50~80 g / min, and the substrate is in a clean environment at room temperature. Forming a CuNi alloy layer through thermal spraying can improve the surface strength of thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingots, and thick-walled oxygen-free copper cladding, while maintaining the plastic deformation capacity of copper.

[0015] Furthermore, in step S3 of the above preparation method, the copper ratio of the NbTi / Cu single-core rod is 0.2~0.4, the specifications are Φ15.0~30.0mm, and the thickness of the CuNi alloy layer sprayed on the surface is 0.5~1.0mm, with the spraying process being the same as in step S2. Spraying a CuNi alloy layer onto the surface of the NbTi / Cu single-core rod is to increase the strength of the copper layer, thus better constraining the deformation of NbTi. Using a thick-walled oxygen-free copper cladding is to increase the copper content in the NbTi / Cu composite ingot. However, because the thick-walled oxygen-free copper cladding causes excessively high copper layer flow rate during subsequent extrusion, resulting in small deformation and uneven deformation in the NbTi region, a stainless steel cladding is added around the thick-walled oxygen-free copper cladding to constrain copper layer deformation during extrusion and improve overall deformation uniformity. The obtained stainless steel-coated NbTi / Cu composite ingot consists of the following layers from the outside to the inside: stainless steel layer / CuNi layer / copper layer / CuNi layer / copper layer / CuNi layer / copper layer / NbTi layer, forming a composite structure in which a high-strength layer and a high-plasticity layer work together. This structure can improve the coordinated deformation ability of copper and NbTi ingots during extrusion and stretching, improve the deformation uniformity of NbTi core wire, and avoid the situation where the internal NbTi core wire cannot be deformed due to excessive copper layer thickness.

[0016] It should be noted that the reason for using a spraying method to form the CuNi alloy layer in this invention, rather than directly using CuNi alloy tubes, is as follows: Firstly, CuNi alloy has poor processing performance. If thin-walled CuNi alloy tubes are used for assembly and coating, the CuNi layer and the Cu layer are in an independent mechanical bonding state. The thin-walled CuNi tube is prone to stress concentration due to work hardening effect, leading to cracking. However, through spraying, CuNi powder forms a composite interface with high-strength mechanical interlocking and local micro-metallurgical bonding with the copper layer during the spraying process. The bonding is dense and there is no risk of relative slippage, significantly improving the interface bonding strength. This integrated structure can effectively transfer deformation stress and exhibits superior processing performance in subsequent plastic processing. Secondly, since the structure of this invention designs CuNi layers of multiple sizes and thicknesses, using CuNi tubes would require the preparation of various specifications of CuNi tubes, and the assembly process would be complex, which is not in line with production practice.

[0017] Furthermore, in step S4 of the above preparation method, the precision peeling process consists of 2 to 3 passes, with a processing rate of less than 10% per pass. The purpose of removing the surface stainless steel layer is twofold: firstly, to remove surface oxides and inclusions, thereby improving surface smoothness; and secondly, to prevent the stainless steel layer from undergoing significant work hardening during cold drawing, which could reduce the wire's tensile properties and cause wire breakage or core breakage.

[0018] Furthermore, in step S4 of the above preparation method, the processing rate per pass of the stretching process is less than 20%.

[0019] Furthermore, in step S5 of the above preparation method, the annealing temperature is 180~250℃. The higher the copper ratio of the wire, the lower the annealing temperature. The processing rate of small deformation processing is 3~5%. This is because the CuNi layer in the wire structure provides greater strength. Even with a small processing rate, the NbTi core wire can be uniformly deformed, thus further improving the yield strength of the wire and finally obtaining NbTi / Cu superconducting wire with high yield strength and large copper ratio.

[0020] Secondly, the present invention claims protection for a high yield strength NbTi superconducting wire, which is prepared by the preparation method described above.

[0021] Furthermore, the copper ratio of the high yield strength NbTi superconducting wire is 10~15, and the specification is Φ0.7~1.5mm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Achieving a synergistic balance between high copper-to-superconducting ratio and high yield strength, a high-strength-high-plasticity composite structure composed of CuNi alloy layers, copper layers, and stainless steel layers enhances the coordinated deformation capability of copper and NbTi. Ultimately, the copper-to-superconducting ratio of the wire reaches 10~15, and the yield strength is significantly improved, making it suitable for the use of high-field superconducting MRI and liquid helium-free superconducting MRI, and solving the problem of mutual constraints between the two in the existing technology.

[0024] To improve deformation uniformity, the stainless steel sheath constrains the extrusion deformation of the thick-walled oxygen-free copper sheath, avoiding uneven deformation in the NbTi region caused by excessive copper layer flow rate. At the same time, the CuNi alloy layer constrains the NbTi deformation, preventing the internal NbTi core wire from being unable to deform due to excessive copper layer thickness.

[0025] To improve the reliability of wires, the stainless steel layer is removed through a 2-3 round precision stripping process. This process not only eliminates surface oxides and inclusions and improves surface smoothness, but also avoids the impact of work hardening of the stainless steel layer on tensile properties, significantly reducing the risk of wire breakage or core breakage.

[0026] The process is highly stable, with clear and controllable core process parameters. The uniform deformation of the NbTi core wire is further optimized through small deformation processing. While ensuring high copper-to-weight ratio and high yield strength, the plastic deformation capacity of copper is maintained, resulting in good product consistency and suitability for mass production.

[0027] Expanding application scenarios, compared with traditional low magnetic field compatible wires, the wires produced by this invention have significantly improved anti-interference capabilities, which can meet the technical requirements of high-end medical equipment such as 3T and above high field superconducting MRI and liquid helium-free superconducting MRI, and have broad practical application value. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation method of the high yield strength NbTi superconducting wire.

[0029] Figure 2 This is a schematic diagram of the cross-sectional structure of the NbTi / Cu single core rod. Reference numerals: 8 represents the NbTi ingot, 7 represents the thin-walled oxygen-free copper cladding, and 6 represents the third CuNi alloy layer.

[0030] Figure 3 This is a schematic cross-sectional view of the stainless steel-coated NbTi / Cu composite ingot. Reference numerals: 1 represents the stainless steel sheath, 2 represents the first CuNi alloy layer, 3 represents the thick-walled oxygen-free copper sheath, 4 represents the second CuNi alloy layer, and 5 represents the drilled oxygen-free copper ingot. Detailed Implementation

[0031] 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.

[0032] The experimental materials and equipment involved in the examples are as follows:

[0033] 1. Experimental Materials

[0034] CuNi alloy powder; NbTi ingots; thin-walled oxygen-free copper cladding; drilled oxygen-free copper ingots; thick-walled oxygen-free copper cladding; stainless steel cladding; cleaning reagent, nitric acid solution with a concentration of 1.0~3.0%.

[0035] 2. Experimental equipment

[0036] Arc spraying equipment for spraying CuNi alloy layers; vacuum electron beam welding machine for thin-walled oxygen-free copper cladding and sealing of composite ingots; extrusion press for single-core rod extrusion and composite ingot extrusion; stretching machine for single-core rod stretching, composite rod stretching, and final stretching; sawing and straightening equipment for sawing and straightening NbTi / Cu single-core rods; precision peeling equipment for removing surface stainless steel layers; heat treatment furnace for wire heat treatment; twisting machine for twisting composite wires; annealing furnace for annealing composite wires; painting equipment for painting composite wires; small deformation processing equipment for processing small deformations in painted wires; cleaning equipment for cleaning raw materials; and drying equipment for drying raw materials.

[0037] This invention provides a method for preparing the high yield strength NbTi superconducting wire, the flowchart of which is shown below. Figure 1 As shown, the specific steps include:

[0038] S1, Raw material preparation: including: CuNi alloy powder, NbTi ingot, thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingot, thick-walled oxygen-free copper cladding, stainless steel cladding.

[0039] S2, Thermal spraying treatment: CuNi alloy powder is uniformly sprayed onto the outer wall of the thick-walled oxygen-free copper cladding (forming the first CuNi alloy layer) and the drilled oxygen-free copper ingot (forming the second CuNi alloy layer) through a thermal spraying process.

[0040] S3, Composite Ingot Preparation: NbTi ingots are inserted into thin-walled oxygen-free copper sheaths, and then subjected to welding, extrusion, stretching, sawing, and straightening processes to obtain NbTi / Cu single-core rods. CuNi alloy powder is then sprayed onto the surface using a thermal spraying process to form a third CuNi alloy layer. A schematic diagram of the cross-sectional structure of the sprayed NbTi / Cu single-core rod is shown below. Figure 2 As shown, 8 represents an NbTi ingot, 7 represents a thin-walled oxygen-free copper cladding, and 6 represents the third CuNi alloy layer. Subsequently, NbTi / Cu single-core rods are sequentially assembled into a drilled oxygen-free copper ingot, a thick-walled oxygen-free copper cladding, and a stainless steel cladding to obtain a stainless steel-coated NbTi / Cu composite ingot. A schematic cross-sectional view of the stainless steel-coated NbTi / Cu composite ingot is shown below. Figure 3 As shown, 1 is a stainless steel sheath, 2 is the first CuNi alloy layer, 3 is a thick-walled oxygen-free copper sheath, 4 is the second CuNi alloy layer, and 5 is a drilled oxygen-free copper ingot.

[0041] S4, Extrusion and stretching: The stainless steel-coated NbTi / Cu composite ingot is welded with upper and lower covers for sealing, and then extruded and stretched. During the stretching process, the surface stainless steel layer is removed by a precision peeling process to obtain an NbTi / Cu composite rod. After stretching, heat treatment, twisting, and final stretching, a high copper ratio NbTi / Cu composite wire is obtained.

[0042] S5, Post-processing: After annealing and painting the NbTi / Cu composite wire with a high copper ratio, a small deformation process is performed to obtain a high yield strength NbTi superconducting wire.

[0043] Secondly, embodiments of the present invention provide high yield strength NbTi superconducting wires prepared by the above method.

[0044] Example 1

[0045] This embodiment provides a method for preparing high-yield-strength NbTi superconducting wire, the specific steps of which are as follows:

[0046] S1. Raw material preparation: Obtain CuNi alloy powder, NbTi ingots, thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingots, thick-walled oxygen-free copper cladding, stainless steel cladding, and other raw materials. The CuNi alloy powder has a particle diameter of 70μm and a Ni content of 10%. The oxygen-free copper used in the powder is high-purity oxygen-free copper with a copper content ≥99.99% and an oxygen content ≤0.0005%. The NbTi ingot has a diameter of Φ140mm. The thin-walled oxygen-free copper cladding has a wall thickness of 20mm and an inner diameter of Φ145mm. The drilled oxygen-free copper ingot has a diameter of Φ150mm, with 20 evenly drilled holes around the center, each hole having a diameter of Φ18.8mm. The thick-walled oxygen-free copper cladding has an inner diameter of Φ155mm and a wall thickness of 100mm. The stainless steel cladding uses 316L stainless steel with an inner diameter of Φ260mm, a wall thickness of 10mm, and a yield strength >250MPa. All raw materials were cleaned and dried. The cleaning agent was a 2.0% nitric acid solution. After soaking and cleaning, the cleaning agent was removed by three spray cleaning cycles. The drying conditions were 60℃.

[0047] S2, Thermal Spraying Treatment: Using arc spraying equipment, CuNi alloy powder is uniformly sprayed onto the outer wall of the thick-walled oxygen-free copper cladding (forming the first CuNi alloy layer) and the drilled oxygen-free copper ingot (forming the second CuNi alloy layer). The spraying temperature is controlled at 4000℃, the spraying distance is 120mm, the spraying speed is 1.0m / s, the powder feed rate is 60g / min, and the substrate is in a clean environment at room temperature. After spraying, a CuNi alloy layer with a thickness of 1.5±0.2mm is formed on the substrate surface.

[0048] S3, Composite Ingot Preparation: NbTi ingots are placed in thin-walled oxygen-free copper sheaths and sequentially subjected to vacuum electron beam welding (welding current 100mA, shielding gas nitrogen, welding speed 80° / min), extrusion, stretching, sawing and straightening processes to obtain NbTi / Cu single-core rods with a diameter of Φ17.6mm and a copper ratio of 0.2±0.02. Using the same arc spraying process, CuNi alloy powder is uniformly sprayed onto the surface of the NbTi / Cu single-core rod to form a third CuNi alloy layer with a thickness of 0.5mm. Subsequently, the single-core rod is assembled into a drilled oxygen-free copper ingot, and further placed into a thick-walled oxygen-free copper sheath to obtain a thick-walled NbTi / Cu composite ingot. Finally, the thick-walled NbTi / Cu composite ingot is assembled into a stainless steel sheath to obtain a stainless steel-coated NbTi / Cu composite ingot.

[0049] S4, Extrusion and Drawing Process: The stainless steel-clad NbTi / Cu composite ingot is vacuum electron beam welded (method same as S3), sealed with top and bottom covers, and then extruded. During the subsequent drawing process, for wire diameters of Φ56.00mm, Φ51.00mm, and Φ45.00mm, a precision stripping device is used for three passes of stripping, with a processing rate of 8% per pass, removing the surface stainless steel layer to obtain an NbTi / Cu composite rod. This composite rod is then subjected to drawing, aging heat treatment (360℃, 5 times), twisting, and final drawing processes. The processing rate for each drawing pass is less than 20%, ultimately yielding a high copper ratio NbTi / Cu composite wire with a copper ratio of 10 and a diameter of Φ1.200mm.

[0050] S5, Post-processing: The above-mentioned high copper ratio NbTi / Cu composite wire is placed in an annealing furnace and annealed at 250°C. After annealing, it is coated with acetal varnish (PVF). Then, the coated wire is processed in one pass using a small deformation stretching device. The stretching die is a polycrystalline die, the processing rate is 3%, the stretching speed is controlled at 30m / min, and the wire is lubricated by soaking in saponified liquid. Finally, high yield strength NbTi superconducting wire is obtained.

[0051] Example 2

[0052] This embodiment provides a method for preparing high-yield-strength NbTi superconducting wire, the specific steps of which are as follows:

[0053] S1. Raw material preparation: Obtain CuNi alloy powder, NbTi ingots, thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingots, thick-walled oxygen-free copper cladding, stainless steel cladding, and other raw materials. The CuNi alloy powder has a particle diameter of 70μm and a Ni content of 20%. The oxygen-free copper used in the powder is high-purity oxygen-free copper with a copper content ≥99.99% and an oxygen content ≤0.0005%. The NbTi ingot has a diameter of Φ150mm. The thin-walled oxygen-free copper cladding has a wall thickness of 30mm and an inner diameter of Φ155mm. The drilled oxygen-free copper ingot has a diameter of Φ200mm, with 30 evenly drilled holes around the center, each hole having a diameter of Φ16.6mm. The thick-walled oxygen-free copper cladding has an inner diameter of Φ205mm and a wall thickness of 100mm. The stainless steel cladding uses 316L stainless steel with an inner diameter of Φ310mm, a wall thickness of 10mm, and a yield strength >250MPa. All raw materials were cleaned and dried. The cleaning agent was a 2.0% nitric acid solution. After soaking and cleaning, the cleaning agent was removed by three spray cleaning cycles. The drying conditions were 70℃.

[0054] S2, Thermal Spraying Treatment: Using arc spraying equipment, CuNi alloy powder is uniformly sprayed onto the outer wall of the thick-walled oxygen-free copper cladding (forming the first CuNi alloy layer) and the drilled oxygen-free copper ingot (forming the second CuNi alloy layer). The spraying temperature is controlled at 4300℃, the spraying distance is 140mm, the spraying speed is 1.5m / s, the powder feed rate is 80g / min, and the substrate is in a clean environment at room temperature. After spraying, a CuNi alloy layer with a thickness of 1.5±0.2mm is formed on the substrate surface.

[0055] S3, Composite Ingot Preparation: NbTi ingots are placed in thin-walled oxygen-free copper sheaths and sequentially subjected to vacuum electron beam welding (welding current 150mA, shielding gas nitrogen, welding speed 100° / min), extrusion, stretching, sawing and straightening processes to obtain NbTi / Cu single-core rods with a diameter of Φ15.4mm and a copper ratio of 0.3±0.03. Using the same arc spraying process, CuNi alloy powder is uniformly sprayed onto the surface of the NbTi / Cu single-core rod to form a third CuNi alloy layer with a thickness of 0.5mm. Subsequently, the single-core rod is assembled into a drilled oxygen-free copper ingot, and further placed into a thick-walled oxygen-free copper sheath to obtain a thick-walled NbTi / Cu composite ingot. Finally, the thick-walled NbTi / Cu composite ingot is assembled into a stainless steel sheath to obtain a stainless steel-coated NbTi / Cu composite ingot.

[0056] S4, Extrusion and Stretching: The stainless steel-clad NbTi / Cu composite ingot is vacuum electron beam welded (method same as S3), sealed with top and bottom covers, and then extruded. During the subsequent stretching process, for wire diameters of Φ64.00mm, Φ61.00mm, and Φ57.00mm, a precision peeling device is used for three passes of peeling, with a processing rate of 6% per pass, removing the surface stainless steel layer to obtain an NbTi / Cu composite rod. This composite rod is then subjected to stretching, aging heat treatment (340℃, 4 times), twisting, and final stretching. The processing rate for each stretching pass is less than 20%, ultimately yielding a high copper ratio NbTi / Cu composite wire with a copper ratio of 15 and a diameter of Φ0.850mm.

[0057] S5, Post-processing: The above-mentioned high copper ratio NbTi / Cu composite wire is placed in an annealing furnace and annealed at 180°C. After annealing, it is coated with acetal varnish (PVF). Then, the coated wire is processed in one pass using a small deformation stretching device. The stretching die is a polycrystalline die, the processing rate is 3%, the stretching speed is controlled at 50m / min, and the wire is lubricated by soaking in saponified liquid. Finally, high yield strength NbTi superconducting wire is obtained.

[0058] Example 3

[0059] This embodiment provides a method for preparing high-yield-strength NbTi superconducting wire, the specific steps of which are as follows:

[0060] S1. Raw material preparation: Obtain CuNi alloy powder, NbTi ingots, thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingots, thick-walled oxygen-free copper cladding, stainless steel cladding, and other raw materials. The CuNi alloy powder has a particle diameter of 80μm and a Ni content of 15%. The oxygen-free copper used in the powder is high-purity oxygen-free copper with a copper content ≥99.99% and an oxygen content ≤0.0005%. The NbTi ingot has a diameter of Φ145mm. The thin-walled oxygen-free copper cladding has a wall thickness of 30mm and an inner diameter of Φ150mm. The drilled oxygen-free copper ingot has a diameter of Φ200mm, with 38 holes evenly drilled around the center, each hole having a diameter of Φ14.6mm. The thick-walled oxygen-free copper cladding has an inner diameter of Φ205mm and a wall thickness of 90mm. The stainless steel cladding uses 316L stainless steel with an inner diameter of Φ300mm, a wall thickness of 10mm, and a yield strength >250MPa. All raw materials were cleaned and dried. The cleaning agent was a 2.0% nitric acid solution. After soaking and cleaning, the cleaning agent was removed by three spray cleaning cycles. The drying conditions were 80℃.

[0061] S2, Thermal Spraying Treatment: Using arc spraying equipment, CuNi alloy powder is uniformly sprayed onto the outer wall of the thick-walled oxygen-free copper cladding (forming the first CuNi alloy layer) and the drilled oxygen-free copper ingot (forming the second CuNi alloy layer). The spraying temperature is controlled at 4400℃, the spraying distance is 100mm, the spraying speed is 0.5m / s, the powder feed rate is 50g / min, and the substrate is in a clean environment at room temperature. After spraying, a CuNi alloy layer with a thickness of 1.5±0.2mm is formed on the substrate surface.

[0062] S3, Composite Ingot Preparation: NbTi ingots are placed in thin-walled oxygen-free copper sheaths and sequentially subjected to vacuum electron beam welding (welding current 180mA, shielding gas nitrogen, welding speed 110° / min), extrusion, stretching, sawing and straightening processes to obtain NbTi / Cu single-core rods with a diameter of Φ15.6mm and a copper ratio of 0.35±0.03. Using the same arc spraying process, CuNi alloy powder is uniformly sprayed onto the surface of the NbTi / Cu single-core rod to form a third CuNi alloy layer with a thickness of 0.5mm. Subsequently, the single-core rod is assembled into a drilled oxygen-free copper ingot, and further placed into a thick-walled oxygen-free copper sheath to obtain a thick-walled NbTi / Cu composite ingot. Finally, the thick-walled NbTi / Cu composite ingot is assembled into a stainless steel sheath to obtain a stainless steel-coated NbTi / Cu composite ingot.

[0063] S4, Extrusion and Drawing Process: The stainless steel-clad NbTi / Cu composite ingot is vacuum electron beam welded (method same as S3), sealed with top and bottom covers, and then extruded. During the subsequent drawing process, for wire diameters of Φ63.40mm, Φ60.20mm, and Φ58.20mm, a precision stripping device is used for three passes of stripping, with a processing rate of 6% per pass, removing the surface stainless steel layer to obtain an NbTi / Cu composite rod. This composite rod is then subjected to drawing, aging heat treatment (350℃, 3 times), twisting, and final drawing processes. The processing rate for each drawing pass is less than 20%, ultimately yielding a high copper ratio NbTi / Cu composite wire with a copper ratio of 13 and a diameter of Φ0.900mm.

[0064] S5, Post-processing: The above-mentioned high copper ratio NbTi / Cu composite wire is placed in an annealing furnace and annealed at 200℃. After annealing, it is coated with acetal varnish (PVF). Then, the coated wire is processed in one pass using a small deformation stretching device. The stretching die is a polycrystalline die, the processing rate is 3%, the stretching speed is controlled at 70m / min, and the wire is lubricated by soaking in saponified liquid. Finally, high yield strength NbTi superconducting wire is obtained.

[0065] Example 4

[0066] This embodiment provides a performance comparison between the NbTi superconducting wires prepared in Examples 1-3 and those prepared using existing techniques. The existing method for preparing NbTi superconducting wires is as follows:

[0067] Raw material preparation: Obtain NbTi ingots, single-core and composite oxygen-free copper cladding, drilled oxygen-free copper ingots, and other raw materials. The NbTi ingots have a diameter of Φ200mm, the single-core oxygen-free copper cladding has an inner diameter of Φ205mm and a cladding thickness of 50mm, and the composite oxygen-free copper cladding has an inner diameter of Φ250mm and a wall thickness of 35mm.

[0068] Composite ingot preparation: NbTi ingots were placed into single-core oxygen-free copper sheaths and subjected to welding, extrusion, stretching, sawing, and straightening processes to obtain NbTi / Cu single-core rods with a diameter of Φ28.00mm and a copper ratio of 0.6±0.03. Subsequently, 62 single-core rods were stacked and assembled into composite oxygen-free copper sheaths, with oxygen-free rods filling the gaps to obtain NbTi / Cu composite ingots.

[0069] Extrusion and stretching: After sealing the NbTi / Cu composite ingot with welded top and bottom caps, it is extruded to obtain an NbTi / Cu composite rod. The composite rod is then subjected to stretching, heat treatment, twisting, and final stretching processes. The processing rate of each stretching pass is less than 20%, ultimately yielding an NbTi / Cu composite wire with a copper ratio of 1.5±0.3 and a specification of Φ0.700mm.

[0070] Embedded copper plating: The NbTi / Cu composite wire is embedded into the U-shaped copper channel wire by embedding and soldering. By controlling the specifications of the U-shaped copper channel wire, the copper ratio can be controlled within the range of 8 to 15. In this example, the specifications of the copper channel wire are 1.900×1.100, and a conventional Wire in Channel (WIC) superconducting wire with a copper ratio of 13±0.5 is finally obtained.

[0071] Performance testing: The WIC superconducting wires prepared above and the NbTi superconducting wires prepared in Examples 1-3 were subjected to performance testing. The yield strength test was conducted in accordance with GB / T 34505-2017, with a tensile rate of 0.3 mm / min. The critical current test was conducted in accordance with GB / T 30596-2014, with magnetic field strengths of 4T and 7T. The residual resistivity (RRR) test was conducted in accordance with GB / T 13811-2003, with test conditions of 300K / 10K.

[0072] The performance test results are from multiple batches of products, as shown in Table 1 below:

[0073] Table 1. Performance comparison of wires in various embodiments

[0074]

[0075] The test results show that the critical current densities of Examples 1-4 are basically the same at 4T, but the critical current densities of Examples 1-3 are higher than that of Example 4 at 7T, indicating that the wires prepared in Examples 1-3 have higher performance under high fields and can meet the requirements of high-field applications. Furthermore, the yield strength of the wires in Examples 1-3 is much higher than that in Example 4, while the RRR value does not decrease significantly, indicating that the present invention can significantly increase the yield strength of the wire and maintain its resistance to electromagnetic interference and thermal runaway under high magnetic field environments. Moreover, the experimental results from multiple batches show that after the final small deformation processing, the yield strength performance data of Examples 1-3 fluctuates little between batches, indicating that the production of the present invention is stable between batches.

[0076] Example 5

[0077] This embodiment provides a performance comparison between the NbTi superconducting wire prepared in Example 1 and the NbTi superconducting wire prepared using CuNi tubes instead of thermally sprayed CuNi alloy powder. The specific steps are as follows:

[0078] Raw material preparation: Obtain CuNi alloy tubes, NbTi ingots, thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingots, thick-walled oxygen-free copper cladding, and stainless steel cladding. The CuNi alloy tubes have wall thicknesses of 1.5mm and 0.5mm, with a Ni content of 10%; the NbTi ingots have a diameter of Φ140mm; the thin-walled oxygen-free copper cladding has a wall thickness of 20mm and an inner diameter of Φ145mm; the drilled oxygen-free copper ingots have a diameter of Φ150mm, with 20 evenly drilled holes around the center, each hole having a diameter of Φ18.8mm; the thick-walled oxygen-free copper cladding has an inner diameter of Φ155mm and a wall thickness of 100mm; the stainless steel cladding has an inner diameter of Φ260mm and a wall thickness of 10mm. All raw materials undergo cleaning and drying. The cleaning agent is a 2.0% nitric acid solution. After soaking and cleaning, the materials are rinsed three times with a spray to remove the cleaning agent. Drying is performed at 60℃.

[0079] Composite ingot preparation: NbTi ingots are placed into thin-walled oxygen-free copper sheaths, then into 1.5mm thick CuNi alloy tubes. The ingots undergo a series of processes including vacuum electron beam welding (welding current 100mA, shielding gas nitrogen, welding speed 80° / min), extrusion, stretching, and sawing and straightening to obtain NbTi / Cu single-core rods with a diameter of Φ17.6mm and a copper ratio of 0.2±0.02. The NbTi / Cu single-core rods are then placed into 0.5mm thick CuNi alloy tubes and assembled into drilled oxygen-free copper ingots. Subsequently, the drilled oxygen-free copper ingots are sequentially placed into CuNi alloy tubes, thick-walled oxygen-free copper sheaths, and CuNi alloy tubes to obtain thick-walled NbTi / Cu composite ingots. Finally, the thick-walled NbTi / Cu composite ingots are assembled into stainless steel sheaths to obtain stainless steel-coated NbTi / Cu composite ingots.

[0080] Extrusion and stretching: The stainless steel-clad NbTi / Cu composite ingot is vacuum electron beam welded (method as above), sealed with top and bottom covers, and then extruded. During the subsequent stretching process, for wire diameters of Φ56.00mm, Φ51.00mm, and Φ45.00mm, a precision peeling device is used for three passes of peeling, with a processing rate of 8% per pass, removing the surface stainless steel layer to obtain NbTi / Cu composite rods. These rods are then subjected to stretching, aging heat treatment (360℃, 5 times), twisting, and final stretching. The processing rate for each stretching pass is less than 15%, ultimately yielding a high copper ratio NbTi / Cu composite wire with a copper ratio of 10 and a diameter of Φ1.200mm.

[0081] Post-processing: The above-mentioned high copper ratio NbTi / Cu composite wire was placed in an annealing furnace and annealed at 250°C. After annealing, it was coated with acetal varnish (PVF). Then, the coated wire was processed in one pass using a small deformation stretching device. The stretching die was a polycrystalline die, the processing rate was 3%, the stretching speed was controlled at 15 m / min, and the wire was lubricated by soaking in saponified liquid. Finally, high yield strength NbTi superconducting wire was obtained.

[0082] The final wire length produced in this embodiment is the same as in Embodiment 1:

[0083] Table 2. Wire Production Length

[0084]

[0085] By comparing this embodiment with Embodiment 1, the final production line length of a single wire in Embodiment 1 exceeded 10,000 meters, while in this embodiment, wire breakage occurred during processing, resulting in shorter output lengths and significant waste due to the numerous breakages. This indicates that forming a CuNi alloy layer through spraying has superior processing performance compared to using CuNi alloy tubes. Furthermore, this embodiment involves a wide variety of CuNi alloy tube specifications, making the assembly process cumbersome and unsuitable for large-scale engineering production.

[0086] 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 a high-yield-strength NbTi superconducting wire, characterized in that, Includes the following steps: S1, Raw material preparation: including: CuNi alloy powder, NbTi ingot, thin-walled oxygen-free copper cladding, drilled oxygen-free copper ingot, thick-walled oxygen-free copper cladding, stainless steel cladding. S2, Thermal spraying treatment: CuNi alloy powder is uniformly sprayed onto the outer wall of the thick-walled oxygen-free copper cladding and the drilled oxygen-free copper ingot through a thermal spraying process. S3, Composite Ingot Preparation: NbTi ingots are inserted into thin-walled oxygen-free copper sheaths, and then subjected to welding, extrusion, stretching, sawing, and straightening processes to obtain NbTi / Cu single-core rods. A CuNi alloy layer is then sprayed onto the surface of the rods using a thermal spraying process. Subsequently, the NbTi / Cu single-core rods are sequentially assembled into drilled oxygen-free copper ingots, thick-walled oxygen-free copper sheaths, and stainless steel sheaths to obtain stainless steel-coated NbTi / Cu composite ingots. S4, Extrusion and stretching: The stainless steel-coated NbTi / Cu composite ingot is welded with upper and lower covers for sealing, and then extruded and stretched. During the stretching process, the surface stainless steel layer is removed by a precision peeling process to obtain an NbTi / Cu composite rod. After stretching, heat treatment, twisting, and final stretching, a high copper ratio NbTi / Cu composite wire is obtained. S5, Post-processing: After annealing and painting the NbTi / Cu composite wire with a high copper ratio, a small deformation process is performed to obtain a high yield strength NbTi superconducting wire.

2. The preparation method according to claim 1, characterized in that, In S1, the CuNi alloy powder has a particle diameter of 70~100μm and a Ni content of 10~30%. The oxygen-free copper used in the powder is high-purity oxygen-free copper with a copper content ≥99.99% and an oxygen content ≤0.0005%.

3. The preparation method according to claim 1, characterized in that, In S1, the diameter of the NbTi ingot is 100~200mm; the wall thickness of the thin-walled oxygen-free copper cladding is 15~30mm, and the inner diameter is 3~5mm larger than the diameter of the NbTi ingot; the diameter of the drilled oxygen-free copper ingot is 100~200mm, and the number of evenly drilled holes around the center is 20~50; the inner diameter of the thick-walled oxygen-free copper cladding is 4~6mm larger than the diameter of the drilled oxygen-free copper ingot, and the wall thickness is 50~100mm; the stainless steel cladding is made of 316L, the inner diameter is 4~6mm larger than the outer diameter of the thick-walled oxygen-free copper cladding, the wall thickness is 10~15mm, and the yield strength is >250MPa.

4. The preparation method according to claim 1, characterized in that, In S2, the thermal spraying process is arc spraying, and the thickness of the CuNi alloy layer formed on the substrate surface after spraying is 1.0~2.0mm.

5. The preparation method according to claim 1, characterized in that, In S3, the copper ratio of the NbTi / Cu single core rod is 0.2~0.4, the specifications are Φ15.0~30.0mm, the thickness of the CuNi alloy layer sprayed on the surface is 0.5~1.0mm, and the spraying process is the same as S2.

6. The preparation method according to claim 1, characterized in that, In S4, the precision peeling process consists of 2 to 3 passes, with a processing rate of less than 10% per pass.

7. The preparation method according to claim 1, characterized in that, In S4, the processing rate per pass of the stretching process is less than 20%.

8. The preparation method according to claim 1, characterized in that, In S5, the annealing temperature is 180~250℃, and the machining rate for small deformation machining is 3~5%.

9. A high yield strength NbTi superconducting wire, characterized in that, The high yield strength NbTi superconducting wire is prepared by the preparation method described in any one of claims 1 to 8.

10. The high yield strength NbTi superconducting wire according to claim 9, characterized in that, The copper ratio of the wire is 10~15, and the specification is Φ0.7~1.5mm.

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