Preparation method of lightweight high-stability MgB2 multi-core superconducting wire

Abstract

The invention discloses a preparation method of a lightweight high-stability MgB2 multi-core superconducting wire. The method comprises the following steps: 1, loading an Al2O3-Al rod into a Cu tube, and processing to obtain a reinforced core; 2, putting the Mg powder / rod and the B powder precursor into an Nb tube, putting the Nb tube into a Cu tube, and processing to obtain a single core wire; 3, inserting the reinforced core and the single-core wire into the composite sheath which is filled into the Al2O3-Al tube from the Monel tube to obtain a secondary composite tube body; 4, processing the secondary composite tube body into a wire rod; and 5, performing phase heat treatment on the wire. According to the invention, the low-density nano Al2O3 reinforced aluminum-based composite material is adopted to partially replace a high-density metal sheath and optimize the Al2O3-Al area proportion, so that the weight of the wire is reduced, and the electrical-thermal-mechanical comprehensive stability of the MgB2 superconducting wire is synergistically improved by utilizing the excellent mechanical, electrical and thermal conductivity of the composite material; and the requirements of light weight and high stability of the aviation-level superconducting motor are met.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire preparation technology, specifically relating to a method for preparing lightweight and highly stable MgB2 multi-core superconducting wire. Background Technology

[0002] Driven by the strategic demand for the electrification and high energy efficiency of global aviation equipment, superconducting motors, with their breakthrough potential in power density and energy efficiency, have become a key research direction for next-generation aviation propulsion systems. Superconducting motors rely on the ability of superconducting materials to achieve high energy density and energy efficiency at critical temperatures (CHT). T c The zero-resistance characteristics exhibited below allow it to carry continuous current without Joule heat loss, thus achieving an efficiency improvement of over 30% compared to traditional silicon steel motors, breaking through the efficiency limits imposed by iron and copper losses. However, the engineering application of superconducting motors still faces a series of technical challenges. First, the aerospace field is extremely sensitive to the weight of the power system, requiring superconducting materials to possess low-density characteristics to achieve higher power output per unit weight. Second, superconducting materials are subjected to strong rotor magnetic fields (typically not less than 2T) and significant centrifugal stress from high-speed rotation during operation; therefore, they must possess excellent mechanical, electrical, and thermal conductivity properties to ensure their overall stability in complex multi-physics coupling environments.

[0003] Magnesium diboride (MgB2) is currently considered to have the lowest theoretical density (2.6 g / cm³). 3 Practical superconducting materials have shown significant potential in achieving lightweight superconducting motors. T c Reaching a temperature of up to 39K, higher than traditional low-temperature superconductors (Niobium-Ti and Niobium-Tin Nb3Sn), it can operate in the temperature range of direct cooling by a cryostat (approximately 20K), avoiding dependence on expensive liquid helium (4.2K) and significantly reducing the complexity of the cooling system and the overall weight. To suppress AC losses and improve electromagnetic stability, the powder-in-tube (PIT) method is commonly used to prepare MgB2 multi-core superconducting wires. The specific preparation process is as follows: Mg powder and B powder are mixed and filled into a niobium (Nb) tube, which is then placed into a copper (Cu) tube and processed into single-core rods through drawing and other methods. Subsequently, multiple single-core rods are reassembled with a copper-nickel alloy (Monel) tube and processed into multi-core wires of the final size (0.8mm~1.4mm diameter). Finally, heat treatment completes the formation of the MgB2 superconducting phase. However, the metal cladding used in existing PIT processes, such as Monel, Nb, and Cu, has a density as high as approximately 8.8 g / cm³. 3This severely weakens the lightweight advantage of MgB2 itself. Furthermore, the limitations of these materials in terms of thermal, electrical, and mechanical properties also restrict further improvements in wire stability. For example, Monel, as the main mechanical support (accounting for approximately 40% of the volume), while possessing a high yield strength of 280 MPa to 320 MPa and effectively protecting the brittle MgB2 superconducting core wire, has a low thermal conductivity at 50 K (approximately 12 W·K). -1 ·m -1 The conductivity is also unsatisfactory (approximately 0.55 μΩ·m), making it difficult to dissipate heat disturbances or provide an effective current shunting path in a timely manner, thus affecting the thermal stability and quench protection capability of the wire; Cu (approximately 25% by volume) possesses excellent electrical and thermal conductivity (thermal conductivity of approximately 1000 W·K at 50 K). -1 ·m -1 The resistivity is approximately 3.0 × 10⁻⁶. -10 While its yield strength is relatively low (70MPa~120MPa), it is not conducive to maintaining the mechanical integrity of the wire under high stress conditions. Therefore, developing a new type of cladding material with low density and optimized thermo-electrical-mechanical properties to replace the existing high-density metal components, thereby reducing the weight of MgB2 multi-core superconducting wires while improving their overall stability, has become a key technical issue that urgently needs to be addressed to promote the development of superconducting motors. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the shortcomings of the existing technology by providing a method for preparing lightweight and highly stable MgB2 multi-core superconducting wires. This method utilizes a low-density nano-Al2O3-reinforced aluminum-based (Al2O3-Al) composite material, combined with a multi-core superconducting wire structure design, to partially replace the high-density metal sheath. This significantly reduces the overall weight of the wire while leveraging the excellent mechanical properties, high thermal conductivity, and good electrical conductivity of the Al2O3-Al composite material to synergistically improve the electro-thermal-mechanical stability of the MgB2 superconducting wire. This solves the problems of high weight and difficulty in synergistically optimizing thermo-electrical-mechanical properties caused by the use of high-density metal sheath materials in existing MgB2 superconducting wires.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing lightweight and highly stable MgB2 multi-core superconducting wire, characterized in that the method includes the following steps: Step 1: Insert the Al2O3-Al rod into the Cu tube to form a Cu / Al2O3-Al composite rod, and then process it to the target size to obtain the reinforcing core; Step 2: Load the Mg powder / rod and B powder precursor with a stoichiometric ratio of 1:2 into the Nb tube, and then load the whole into the Cu tube to form a Cu / Nb / powder composite rod. Then process it to the target size to obtain a single-core wire. Step 3: Insert the Monel tube into the Al2O3-Al tube to form a composite sheath. Then, insert the reinforcing core obtained in Step 1 and the single-core wire obtained in Step 2 into the composite sheath for secondary assembly. The reinforcing core is placed in the center of the composite sheath, and the single-core wires are arranged regularly around the single-core wires to obtain a secondary composite tube body. Step 4: Process the secondary composite tube obtained in Step 3 into wire; Step 5: Heat the wire processed in Step 4 to the target temperature in an inert or vacuum environment and hold for phase formation heat treatment to obtain lightweight and highly stable MgB2 multi-core superconducting wire.

[0006] The above-mentioned method for preparing lightweight, highly stable MgB2 multi-core superconducting wire is characterized in that the Al2O3-Al rod in step one and the Al2O3-Al tube in step three are both metal matrix composites with Al as the matrix and 20nm~100nm nano-Al2O3 as the reinforcing phase, wherein the content of nano-Al2O3 is 1vol%~10vol%. By using nano-Al2O3 as the reinforcing phase in the metal matrix composite, the mechanical properties of the material are significantly improved by utilizing the dispersion strengthening effect of the reinforcing phase, resulting in excellent mechanical properties (yield strength of 280MPa~320MPa) and high thermal conductivity (approximately 1000W·K at 50K). -1 ·m -1 It also has good electrical conductivity (approximately 1.5 × 10⁻⁶ at 50 K) and good electrical conductivity. -9 Al2O3-Al composite material with μΩ·m.

[0007] The above-mentioned method for preparing lightweight and highly stable MgB2 multi-core superconducting wire is characterized in that the number of single cores in the secondary composite tube in step three is 6, 18, or 30, and the corresponding reinforcing core has no less than 1, 1, or 7 core wires.

[0008] The above-mentioned method for preparing a lightweight and highly stable MgB2 multi-core superconducting wire is characterized in that the area ratio of Al2O3-Al in the cross-section of the lightweight and highly stable MgB2 multi-core superconducting wire in step five is not less than 30%.

[0009] Compared with the prior art, the present invention has the following advantages: 1. This invention uses Al2O3-Al material (density approximately 2.7 g / cm³). 3 It can replace some traditional high-density metals (density approximately 8.8 g / cm³). 3 By optimizing its area ratio in the wire, MgB2 multi-core superconducting wires can be significantly reduced in weight while maintaining a high critical current density. This achieves lightweighting of MgB2 multi-core superconducting wires and breaks through the technical bottleneck of lightweight design of superconducting materials.

[0010] 2. This invention utilizes the excellent mechanical properties (yield strength of 280MPa~320MPa) and high thermal conductivity (approximately 1000W·K at 50K) of Al2O3-Al materials. -1 ·m -1 It also has good electrical conductivity (approximately 1.5 × 10⁻⁶ at 50 K) and good electrical conductivity. -9 (μΩ·m), synergistically enhance the electro-thermal-mechanical comprehensive stability of MgB2 superconducting wires, meeting the dual requirements of lightweight and high stability for aerospace-grade superconducting motors.

[0011] 3. The lightweight and highly stable MgB2 multi-core superconducting wire prepared by this invention maintains a high critical current density ( J c ≥10 5 A / mm 2 Under the premise of (4.2K, 4T), the mass per unit length is reduced by up to 24%, providing a feasible solution for the lightweighting of superconducting motors, which is suitable for the aerospace field.

[0012] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the Cu / Al2O3-Al reinforcing core and MgB2 single-core wire prepared in Example 1 of the present invention.

[0014] Figure 2 This is a schematic diagram of the structure of the secondary composite tube prepared in Embodiment 1 of the present invention.

[0015] Figure 3 This is a schematic diagram of the structure of the secondary composite tube prepared in Example 2 of the present invention.

[0016] Figure 4 This is a schematic diagram of the structure of the secondary composite tube prepared in Example 3 of the present invention. Detailed Implementation

[0017] Example 1 This embodiment includes the following steps: Step 1: Insert an Al₂O₃-Al rod with a diameter × length of Φ11mm × 500mm into a Cu tube with a diameter × wall thickness × length of Φ13mm × 1mm × 500mm to form a Cu / Al₂O₃-Al composite rod. Then, process it to a diameter of Φ8mm to obtain a Cu / Al₂O₃-Al reinforcing core, as shown below. Figure 1 The above; The Al2O3-Al rod is a metal matrix composite material with Al as the matrix and 20nm~100nm nano-Al2O3 as the reinforcing phase, wherein the content of nano-Al2O3 is 1.6 vol%. Step 2: Weigh 24.5g of Mg powder and 21.8g of B powder precursor according to a stoichiometric ratio of 1:2, grind for 30 minutes, and then pack into an Nb tube with a diameter × wall thickness × length of Φ11mm × 1mm × 500mm. Then, pack the entire tube into a Cu tube with a diameter × wall thickness × length of Φ13mm × 1mm × 500mm to form a Cu / Nb / powder composite rod. Finally, process the rod to a diameter of Φ8mm to obtain a MgB2 single-core wire. Figure 1 The above; Step 3: Insert a Monel tube with a diameter × wall thickness × length of Φ28mm × 2mm × 500mm into an Al2O3-Al tube with a diameter × wall thickness × length of Φ32mm × 2mm × 500mm to form a composite sheath. Then, take one Cu / Al2O3-Al reinforcing core prepared in Step 1 and six MgB2 single-core wires prepared in Step 2 and insert them into the composite sheath for secondary assembly. The Cu / Al2O3-Al reinforcing core is located in the center, and the six MgB2 single-core wires are arranged circumferentially around the reinforcing core to form a ring, resulting in a secondary composite tube body. Figure 2 As shown; Step 4: Process the secondary composite tube obtained in Step 3 into a wire with a diameter of Φ0.8mm; Step 5: Heat the wire processed in Step 4 to 600℃ in a vacuum environment and hold for 1 hour to perform phase formation heat treatment to obtain a lightweight and highly stable 6-core MgB2 superconducting wire, in which the area ratio of Al2O3-Al is about 31%.

[0018] Testing showed that the lightweight, highly stable 6-core MgB2 superconducting wire prepared in this embodiment performed well at 4.2K and 4T. J c 2.5×10 5 A / cm 2 Compared to 6-core MgB2 superconducting wires made of traditional metallic materials, J c (2.2×10 at 4.2K, 4T) 5 A / cm 2 The mass increased by about 10%, while the mass decreased by about 20% for the same length.

[0019] Example 2 This embodiment includes the following steps: Step 1: Insert an Al2O3-Al rod with a diameter × length of Φ11mm × 500mm into a Cu tube with a diameter × wall thickness × length of Φ13mm × 1mm × 500mm to form a Cu / Al2O3-Al composite rod, and then process it to a diameter of Φ4.8mm to obtain a Cu / Al2O3-Al reinforcing core. The Al2O3-Al rod is a metal matrix composite material with Al as the matrix and 20nm~100nm nano-Al2O3 as the reinforcing phase, wherein the content of nano-Al2O3 is 3.5 vol%. Step 2: Weigh 43.7g of B powder precursor and one Mg rod with a diameter × length of Φ5mm × 100mm according to a stoichiometric ratio of 1:2. Place them into an Nb tube with a diameter × wall thickness × length of Φ15mm × 2mm × 1000mm, and then place the whole thing into a Cu tube with a diameter × wall thickness × length of Φ18mm × 1.5mm × 1000mm to form a Cu / Nb / powder composite rod. Then process it to a diameter of Φ4.8mm to obtain MgB2 single-core wire. Step 3: A Monel tube with a diameter × wall thickness × length of Φ28mm × 2mm × 500mm is inserted into an Al2O3-Al tube with a diameter × wall thickness × length of Φ32mm × 2mm × 500mm to form a composite sheath. One Cu / Al2O3-Al reinforcing core prepared in Step 1 and 18 MgB2 single-core wires prepared in Step 2 are then inserted into the composite sheath for secondary assembly. The Cu / Al2O3-Al reinforcing core is located in the center, and six MgB2 single-core wires are arranged circumferentially around the reinforcing core to form the first ring. The remaining 12 MgB2 single-core wires are arranged circumferentially around the first ring of single-core wires to form the second ring, resulting in a secondary composite tube body. Figure 3 As shown; Step 4: Process the secondary composite tube obtained in Step 3 into a wire with a diameter of Φ1.0mm; Step 5: Heat the wire processed in Step 4 to 680℃ and hold for 1 hour under an argon atmosphere for phase formation heat treatment to obtain a lightweight and highly stable 18-core MgB2 superconducting wire, in which the area ratio of Al2O3-Al is about 30%.

[0020] Testing showed that the lightweight, highly stable 18-core MgB2 superconducting wire prepared in this embodiment performed well at 4.2K and 4T. J c 1.4×10 5 A / cm 2 Compared with 18-core MgB2 superconducting wires made of traditional metallic materials J c The mass is comparable, but for the same length, the mass is reduced by about 21%.

[0021] Example 3 This embodiment includes the following steps: Step 1: Insert an Al2O3-Al rod with a diameter × length of Φ11mm × 500mm into a Cu tube with a diameter × wall thickness × length of Φ13mm × 1mm × 500mm to form a Cu / Al2O3-Al composite rod, and then process it to a diameter of Φ3.4mm to obtain a Cu / Al2O3-Al reinforcing core; The Al2O3-Al rod is a metal matrix composite material with Al as the matrix and nano-Al2O3 with a particle size of 20nm~100nm as the reinforcing phase, wherein the content of nano-Al2O3 is 2.1 vol%. Step 2: Weigh 49g of Mg powder and 43.7g of B powder precursor according to a stoichiometric ratio of 1:2, grind them for 30 minutes, and then pack them into an Nb tube with a diameter × wall thickness × length of Φ15mm × 2mm × 500mm. Then pack the whole thing into a Cu tube with a diameter × wall thickness × length of Φ18mm × 1.5mm × 500mm to form a Cu / Nb / powder composite rod. Then process it to a diameter of Φ3.4mm to obtain MgB2 single core wire. Step 3: Insert a Monel tube with a diameter × wall thickness × length of Φ28mm × 2mm × 500mm into an Al2O3-Al tube with a diameter × wall thickness × length of Φ32mm × 2mm × 500mm to form a composite sheath. Take 7 Cu / Al2O3-Al reinforcing cores prepared in Step 1 and 30 MgB2 single-core wires prepared in Step 2 and insert them into the Monel tube with a diameter × wall thickness × length of Φ28mm × 2mm × 500mm. Among them, 1 Cu / Al2O3-Al reinforcing core is located in the center, 6 Cu / Al2O3-Al reinforcing cores are arranged circumferentially around the central reinforcing core to form the first ring, 12 MgB2 single-core wires are arranged circumferentially around the first ring of reinforcing cores to form the second ring, and the remaining 18 MgB2 single-core wires are arranged circumferentially around the second ring of single-core wires to form the third ring, thus obtaining a secondary composite sheath. Figure 4 As shown; Step 4: Process the secondary composite tube obtained in Step 3 into a wire with a diameter of Φ1.4mm; Step 5: Heat the wire processed in Step 4 to 580℃ in a vacuum environment and hold for 1 hour to perform phase formation heat treatment to obtain a lightweight and highly stable 30-core MgB2 superconducting wire, in which the area ratio of Al2O3-Al is about 32%.

[0022] Testing showed that the lightweight, highly stable 30-core MgB2 superconducting wire prepared in this embodiment performed well at 4.2K and 4T. J c 2.0×10 5 A / cm 2Compared to 30-core MgB2 superconducting wires made from traditional metallic materials, J c (1.9×10 at 4.2K, 4T) 5 A / cm 2 The mass increased by about 5%, while the mass decreased by about 24% for the same length.

[0023] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing lightweight, highly stable MgB2 multi-core superconducting wire, characterized in that, The method includes the following steps: Step 1: Insert the Al2O3-Al rod into the Cu tube to form a Cu / Al2O3-Al composite rod, and then process it to the target size to obtain the reinforcing core; Step 2: Load the Mg powder / rod and B powder precursor with a stoichiometric ratio of 1:2 into the Nb tube, and then load the whole into the Cu tube to form a Cu / Nb / powder composite rod. Then process it to the target size to obtain a single-core wire. Step 3: Insert the Monel tube into the Al2O3-Al tube to form a composite sheath. Then, insert the reinforcing core obtained in Step 1 and the single-core wire obtained in Step 2 into the composite sheath for secondary assembly. The reinforcing core is placed in the center of the composite sheath, and the single-core wires are arranged regularly around the single-core wires to obtain a secondary composite tube body. Step 4: Process the secondary composite tube obtained in Step 3 into wire; Step 5: Heat the wire processed in Step 4 to the target temperature in an inert or vacuum environment and hold for phase formation heat treatment to obtain lightweight and highly stable MgB2 multi-core superconducting wire.

2. The method for preparing a lightweight, highly stable MgB2 multi-core superconducting wire according to claim 1, characterized in that, The Al2O3-Al rod mentioned in step one and the Al2O3-Al tube mentioned in step three are both metal matrix composites with Al as the matrix and nano Al2O3 with a particle size of 20nm~100nm as the reinforcing phase, wherein the content of nano Al2O3 is 1vol%~10vol.

3. The method for preparing a lightweight, highly stable MgB2 multi-core superconducting wire according to claim 1, characterized in that, In step three, the number of single-core wires in the secondary composite tube body is 6, 18, or 30, and the corresponding reinforcing core has no less than 1, 1, or 7 core wires.

4. The method for preparing a lightweight, highly stable MgB2 multi-core superconducting wire according to claim 1, characterized in that, In step five, the area ratio of Al2O3-Al in the cross-section of the lightweight, highly stable MgB2 multi-core superconducting wire is not less than 30%.

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