A method for hot processing of IMD-MgB2 high-temperature superconducting multi-core wire based on intermediate-temperature hot extrusion

Abstract

This invention discloses a method for hot-processing IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion. The method comprises: 1. After assembly, cold rotary forging deformation, followed by preheating, spinning, heating, and hot drawing deformation to obtain a single-core composite round wire; 2. After surface treatment, cutting, bundling, and welding, followed by homogenization heat treatment and medium-temperature hot extrusion deformation to obtain a multi-core composite round bar; 3. After cold rotary forging deformation, preheating, spinning, heating, and hot drawing deformation to obtain a multi-core composite round wire; 4. High-temperature vacuum sintering to obtain a high-temperature superconducting multi-core wire. This invention achieves a triaxial compressive stress state within the material through medium-temperature hot extrusion deformation, improving the flow deformation of the intermediate B powder layer, enhancing the uniformity of synergistic deformation among subcomponents during multi-core deformation, improving the superconducting phase density, and reducing central voids, thereby improving the current-carrying capacity of the high-temperature superconducting multi-core wire. This method is applicable to fields such as MRI, superconducting cables, and superconducting wind turbines.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature superconducting multi-core wire thermal processing technology, specifically relating to a method for preparing IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion. Background Technology

[0002] Magnesium diboride (MgB2) high-temperature superconducting wires have broad application prospects in fields such as magnetic resonance imaging and nuclear fusion devices due to their advantages such as high superconducting transition temperature, low cost, and absence of intrinsic grain boundary weak bonding. However, how to transform its intrinsic superconducting potential into high-performance engineering wires is the core bottleneck for its industrialization. Although MgB2 wires based on central magnesium diffusion (IMD) technology can improve critical current density and microscopic uniformity and avoid the problem of numerous pores in in-situ methods, they suffer from macroscopic defects such as core breakage and Nb layer rupture in the fabrication of multi-core long wires, as well as microscopic problems such as insufficient magnetic flux pinning and low superconducting phase density, which restrict their large-scale application.

[0003] In the hot processing of IMD-Mg B2 multi-core wire, the synergistic rheology of the central Mg rod, metal sheath, and B powder determines the wire's properties. However, existing processes rely on cold processing, which makes it difficult to achieve large-scale deformation rates and introduce extrusion stress and triaxial compressive stress. This results in poor flow deformation of the B powder layer and poor uniformity of subcomponent synergistic deformation. In addition, the deformation performance of pure Mg rods is insufficient, which further leads to problems such as wire breakage and high porosity of the superconducting core. Ultimately, this results in prominent defects after sintering, such as excessively large central pores, weak intergranular connections, and high interfacial stress.

[0004] Existing technologies only optimize components or single process parameters, failing to achieve deep synergy between hot extrusion, hot drawing, and cold forging. This fails to solve the aforementioned core problems and results in low processing efficiency and high costs. Since existing methods have limited effectiveness in improving porosity and reducing central voids, there is an urgent need to develop novel preparation methods based on medium-temperature hot extrusion. These methods should introduce triaxial compressive stress through process synergy, increase the deformation rate per pass, address core defects, improve the current-carrying capacity and processing stability of the wire, and support its large-scale production. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for hot processing IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion. This method introduces extrusion pressure through medium-temperature hot extrusion, resulting in a triaxial compressive stress state within the material. This improves the uniformity of synergistic deformation among sub-components during multi-core deformation, significantly enhancing the hot deformation plasticity of the Mg rod. Combined with cold forging and hot drawing processes, it improves the superconducting phase density after sintering and reduces the central void after melting of the central Mg rod. This significantly improves the current-carrying capacity and processing stability of the IMD-MgB2 high-temperature superconducting multi-core wire, solving problems such as excessively large central voids after sintering, low superconducting phase density, weak intergranular bonding, and high interfacial stress and weak bonding between components and sub-components.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for hot processing preparation of IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion, characterized in that the method includes the following steps: Step 1: Fill the Nb tube with C-coated B powder into the Nb tube with the Mg rod inserted in the center, and then assemble it into the Cu tube to obtain a Cu / Nb / (B,Mg) single-core composite. Then, perform cold spinning forging on the Cu / Nb / (B,Mg) single-core composite to obtain a compact Cu / Nb / (B,Mg) single-core composite rod. Next, wrap the Cu / Nb / (B,Mg) single-core composite rod with an outer layer of graphite mud, preheat it, spin it, and then heat it to perform hot drawing deformation to obtain Cu / Nb / (B,Mg) single-core composite round wire. Step 2: The Cu / Nb / (B,Mg) single-core composite round wire from Step 1 is surface-polished to remove graphite, and then cleaned with a metal cleaner to remove oil stains and HNO3 aqueous solution to remove the oxide layer. After cutting, it is bundled and assembled into an oxygen-free Cu sheath. The Cu / Nb / (B,Mg) multi-core composite sheath is obtained by vacuum electron beam sealing. Then, the Cu / Nb / (B,Mg) multi-core composite sheath is subjected to homogenization heat treatment and then subjected to medium-temperature hot extrusion deformation to obtain Cu / Nb / (B,Mg) multi-core composite round bar. Step 3: The Cu / Nb / (B,Mg) multi-core composite round bar from Step 2 is subjected to cold spinning forging deformation to balance the internal residual stress. Then, it is coated with an outer layer of graphite, preheated, spun, and then heated for hot drawing deformation to obtain Cu / Nb / (B,Mg) multi-core composite round wire. Step 4: Perform high-temperature vacuum sintering on the Cu / Nb / (B,Mg) multi-core composite round wire from Step 3 to obtain IMD-MgB2 high-temperature superconducting multi-core wire.

[0007] This invention achieves precise fabrication of IMD-MgB2 high-temperature superconducting multi-core wires through a comprehensive process encompassing cold rotary forging of Cu / Nb / (B,Mg) single-core composites, graphite coating, preheating, rotary forging, hot drawing, surface treatment, multi-core bundle assembly, vacuum electron beam sealing, medium-temperature hot extrusion, cold rotary forging stress balancing, hot drawing deformation, and high-temperature vacuum sintering. In this process, the invention achieves a high pass deformation rate through medium-temperature hot extrusion deformation and introduces extrusion stress, resulting in a triaxial compressive stress state within the material. This improves the radial densification and axial shear flow deformation of the intermediate B powder layer, enhances the uniformity of synergistic deformation among subcomponents during multi-core deformation, and simultaneously inhibits excessive MgB2 grain growth, promoting the formation of uniformly sized, clean, and highly continuous superconducting phase grains, thereby increasing grain boundary density and enhancing flux pinning capability. Simultaneously, the triaxial compressive stress state increases the thickness of the B powder layer in the cross-section, enhances the deformation degree of the Mg rod, significantly improves the hot deformation plasticity of the Mg rod, avoids defects such as Nb barrier layer rupture and wire breakage caused by local stress concentration, optimizes the synergistic deformation effect between powder and metal, and between subcomponents, enabling the B powder to achieve higher density and regular layer thickness, thereby ensuring the density and shape regularity of the MgB2 superconducting phase after sintering. Furthermore, by precisely controlling the process parameters of cold forging, hot drawing, medium-temperature hot extrusion, and high-temperature vacuum sintering, the density of the superconducting phase after sintering is greatly improved and the central pore after melting of the central Mg rod is reduced. This fundamentally solves the problems of excessively large central pores, low superconducting phase density, weak intergranular connections, and large interfacial stress and weak bonding between components and subcomponents in multi-core wires after sintering, further improving the current carrying capacity and wire processing stability of IMD-MgB2 high-temperature superconducting multi-core wires.

[0008] Furthermore, this invention, through the synergistic effect of medium-temperature hot extrusion and multi-pass hot drawing, increases the per-pass deformation rate of hot drawing to 16%~24%, a significant improvement compared to traditional cold drawing processes. This effectively reduces the amount of processing dies used, shortens processing time, simplifies the preparation process, and lowers industrial-scale production costs. Simultaneously, this invention balances the residual internal stress within the Cu / Nb / (B,Mg) multi-core composite round bar through cold rotary forging deformation, further improving the dimensional accuracy and performance stability of the wire. Ultimately, this achieves a significant improvement in the current-carrying capacity and processing stability of the IMD-MgB2 high-temperature superconducting multi-core wire, laying a solid foundation for its engineering applications.

[0009] The above-mentioned method for hot processing of IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion is characterized in that, in step one, the filling of C-coated B powder is carried out at a B / Mg mass ratio of 1:1 to 1:1.12; the outer diameter of the Cu / Nb / (B,Mg) single-core composite is Φ13mm to 20mm; the total deformation rate of the cold forging deformation is 30% to 40%, and the per-pass deformation rate is 15% to 30%; the preheating temperature is 400℃ to 450℃, and the time is 1min to 2min; the heating temperature is 350℃ to 400℃, and the time is 2min to 3min; the hot drawing deformation temperature is 350℃ to 400℃, the per-pass deformation rate is 16% to 24%, and the drawing speed is 2m / min to 4m / min; the diameter of the Cu / Nb / (B,Mg) single-core composite round wire is Φ1mm to 3.9mm. This invention ensures a compact and uniform single-core structure by precisely controlling the assembly ratio, cold forging, and hot drawing deformation process parameters of the single-core composite, laying the foundation for subsequent multi-core assembly and overall performance improvement. At the same time, graphite coating effectively reduces frictional loss during the drawing process, protecting the integrity of the single-core structure and laying the foundation for subsequent multi-core assembly and overall performance improvement. The above-mentioned method for hot-processing IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion is characterized in that the number of cores in the bundle assembly in step two is 37~189, and the welding vacuum degree of the vacuum electron beam sealing is 1.0×10⁻⁶. -3Pa, focusing current is 654mA, accelerating voltage is 85kV, welding speed is 500mm / min; the temperature of the homogenization heat treatment is 450℃~500℃, and the time is 2h~3h; the deformation temperature of the medium-temperature hot extrusion deformation is 450℃~500℃, the extrusion ratio is 8~11, and the extrusion speed is 10mm / s~40mm / s; the diameter of the Cu / Nb / (B,Mg) multi-core composite round bar is Φ10mm~20mm. This invention ensures the cleanliness of the single-core surface through step-by-step grinding and chemical cleaning, thereby improving the interfacial bonding strength after multi-core assembly. It guarantees the sealing of the cladding by controlling vacuum electron beam sealing, preventing impurities from entering during processing and sintering. By precisely controlling the homogenization and hot extrusion parameters, it regulates the deformation rate, drawing temperature, and drawing speed of single-core and multi-core hot drawing passes, achieving the degree and speed of dynamic recrystallization of Cu and Mg, as well as the degree and speed of dynamic recovery of Nb. This results in uniform and coordinated operation between the central Mg rod, the intermediate Nb barrier layer, the outer Cu cladding, and the sub-components of the multi-core wire. The uniform deformation of the multi-core composite is achieved through plastic deformation and uniform flow of B powder. Simultaneously, lateral compressive stress is introduced into the B powder layer through multiple hot extrusion and hot drawing deformations, changing its stress state from biaxial compressive stress to triaxial compressive stress. This increases the thickness of the B powder layer in the cross-section and the degree of deformation of the Mg rod, resulting in a significant reduction in the pores in the middle of the MgB2 superconducting phase after sintering. Thus, MgB2 multi-core wires with more than 37 cores can be prepared through medium-temperature extrusion deformation, solving the problem that drawing deformation cannot produce MgB2 multi-core wires with more cores.

[0010] Typically, vacuum electron beam sealing involves two preheating passes followed by three sealing passes, with electron beam currents of 10mA, 20mA, 30mA, 40mA, and 45mA respectively.

[0011] The above-mentioned method for hot processing of IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion is characterized in that, in step three, the total deformation rate of cold rotary forging is 30%~40%, and the deformation rate per pass is 15%~20%; the preheating temperature is 400℃~450℃, and the time is 1min~2min; the heating temperature is 350℃~400℃, and the time is 2min~3min; the hot drawing deformation temperature is 350℃~400℃, the deformation rate per pass is 16%~24%, and the drawing speed is 2m / min~4m / min; the diameter of the Cu / Nb / (B,Mg) multi-core composite round wire is Φ1mm~2mm. This invention balances residual internal stress through cold rotary forging, avoiding problems such as cracking and uneven deformation during subsequent processing. Simultaneously, leveraging the triaxial compressive stress processing characteristics of cold rotary forging, it further refines the grains and increases the material density, ensuring the formation of a high-quality superconducting phase during subsequent sintering. Furthermore, hot drawing further refines the multi-core structure, improves the uniformity of synergistic deformation among subcomponents, and further increases the density of boron powder, ensuring the formation of a high-quality superconducting phase during subsequent sintering. Ultimately, this invention significantly improves the current-carrying capacity and processing stability of IMD-MgB2 superconducting multi-core wires, laying a solid foundation for their engineering applications.

[0012] The above-mentioned method for preparing IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion is characterized in that the high-temperature vacuum sintering temperature in step four is 630℃~670℃, and the time is 2h. This invention promotes the full reaction of Mg and B to form the MgB2 superconducting phase by precisely controlling the vacuum sintering temperature and time. Simultaneously, by utilizing the stress field and densification effect introduced in the previous process, it reduces internal pores and weak intergranular connections in the superconducting phase, improves the density and grain uniformity of the superconducting phase, and thus significantly enhances the current-carrying capacity and processing stability of the wire.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention achieves precise control over the stress state, density, and current-carrying performance of MgB2 superconducting phase through the synergistic effect of medium-temperature hot extrusion and hot drawing. By combining hot drawing and medium-temperature hot extrusion processes, triaxial compressive stress is introduced into the material, effectively improving the radial densification flow and axial shear flow deformation of the B powder layer, enhancing the uniformity of synergistic deformation between subcomponents. At the same time, combined with the cold spinning forging stress balancing process, the porosity in the middle of the sintered MgB2 superconducting phase is significantly reduced, the density of the superconducting phase is significantly improved, the problem of weak intergranular bonding is solved, and thus the flux pinning ability and current-carrying performance of IMD-MgB2 high-temperature superconducting multi-core wire are enhanced.

[0014] 2. This invention significantly improves the synergistic deformation capability of multiphase materials through multi-process collaboration, greatly enhancing the processing stability and yield of the wire. By combining preheating, heating, cold rotary forging, and medium-temperature hot extrusion processes, the central Mg rod, Nb barrier layer, Cu sheath, and multi-core sub-components achieve coordinated matching of dynamic recrystallization and dynamic recovery during deformation, effectively overcoming the problems of poor cold deformation capability, easy cracking, and multiphase flow instability of pure Mg rods. Simultaneously, through step-by-step grinding, chemical cleaning, and vacuum electron beam sealing, the interfacial bonding is enhanced, avoiding defects common in traditional processes such as Nb layer cracking, core breakage, and superconducting core porosity, ensuring the long-range uniformity and yield of the IMD-MgB2 high-temperature superconducting multi-core wire.

[0015] 3. This invention significantly improves the single-pass deformation rate, shortens the processing flow, and reduces the cost of industrial-scale production. Through hot extrusion and process control, this invention enables the processing of MgB2 high-temperature superconducting multi-core wires with a higher core count (37 cores or more). Simultaneously, the hot drawing process increases the single-pass deformation rate from 8% in traditional cold drawing to 16%~24%, reducing the number of drawing passes required to reach the target size to approximately 1 / 5~1 / 6 of the traditional process. Furthermore, the combination of graphite mud lubrication and segmented heating strategies significantly reduces the number of dies used and processing time, simplifying the production process. In addition, the deep synergy between medium-temperature hot extrusion, hot drawing, and cold forging reduces redundant processing steps, providing a feasible approach for the large-scale, low-cost production of high-performance IMD-MgB2 high-temperature superconducting multi-core wires.

[0016] 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

[0017] Figure 1 This is a flowchart of the hot processing method for preparing IMD-MgB2 high-temperature superconducting multi-core wire based on medium-temperature hot extrusion according to the present invention.

[0018] Figure 2 This is a schematic diagram and a physical image of the core wire bundle structure of the Cu / Nb / (B,Mg) multi-core composite sheath prepared in Example 1 of the present invention.

[0019] Figure 3 This is a CT scan image of the Cu / Nb / (B,Mg) multi-core composite rod prepared in Example 1 of the present invention.

[0020] Figure 4 The current-carrying performance diagram of the IMD-MgB2 high-temperature superconducting multi-core wire prepared in Example 1 of this invention is shown.

[0021] Figure 5 This is a schematic diagram and a physical image of the core wire bundle structure of the Cu / Nb / (B,Mg) multi-core composite sheath prepared in Example 3 of the present invention.

[0022] Figure 6 This is a CT scan image of the Cu / Nb / (B,Mg) multi-core composite rod prepared in Example 3 of the present invention. Detailed Implementation

[0023] Example 1 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Fill the Nb tube with C-coated B powder according to the B / Mg mass ratio of 1:1.12 and insert the Mg rod in the center. Then assemble it in the Cu tube to obtain a Cu / Nb / (B,Mg) single-core composite with an outer diameter of Φ20mm. Then, perform cold spinning forging deformation on the Cu / Nb / (B,Mg) single-core composite with a total deformation rate of 40% and a pass deformation rate of 15% to obtain a compact Cu / Nb / (B,Mg) single-core composite rod. Next, wrap the Cu / Nb / (B,Mg) single-core composite rod with an outer layer of graphite mud. After preheating at 450℃ for 2 minutes, spin the rod and then heat it at 350℃ for 3 minutes. Then, perform hot drawing deformation at 350℃, a pass deformation rate of 24%, and a drawing speed of 4m / min to obtain a Cu / Nb / (B,Mg) single-core composite round wire with a diameter of Φ3.9mm. Step 2: The Cu / Nb / (B,Mg) single-core composite round wire from Step 1 is surface-polished using 400-grit, 600-grit, and 800-grit sandpaper to remove graphite. Oil stains are removed using an alkaline metal cleaner, and the oxide layer is removed by acid washing with HNO3 aqueous solution. After cutting, 37 wires are bundled and assembled into an oxygen-free Cu sheath. Vacuum electron beam sealing is then performed to obtain a 37-core Cu / Nb / (B,Mg) multi-core composite sheath. Figure 2 As shown, the welding vacuum degree of vacuum electron beam sealing is 1.0 × 10⁻⁶. -3 Pa, focusing current of 654mA, accelerating voltage of 85kV, welding speed of 500mm / min, followed by homogenization heat treatment at 500℃ for 3h on the Cu / Nb / (B,Mg) multi-core composite cladding, and then medium-temperature hot extrusion deformation at 450℃, extrusion ratio of 11, and extrusion speed of 40mm / s to obtain Cu / Nb / (B,Mg) multi-core composite round bar with a diameter of Φ10mm; Step 3: The Cu / Nb / (B,Mg) multi-core composite round bar from Step 2 is subjected to cold spinning forging deformation with a total deformation rate of 40% and a pass deformation rate of 20% to balance the internal residual stress. Then, the outer layer of graphite is coated, and after preheating at 400℃ for 1 min, the bar is spun. Then, it is heated at 350℃ for 2 min, followed by hot drawing deformation at 350℃, a pass deformation rate of 24%, and a drawing speed of 4 m / min to obtain a Cu / Nb / (B,Mg) multi-core composite round wire with a diameter of Φ1 mm. Step 4: The Cu / Nb / (B,Mg) multi-core composite round wire from Step 3 is subjected to high-temperature vacuum sintering at 670℃ for 2 hours to obtain an IMD-MgB2 high-temperature superconducting multi-core wire with a diameter of Φ1mm. Figure 4 As shown.

[0024] At 4.2K and 2T, the critical current density Jc of the IMD-MgB2 high-temperature superconducting multi-core wire prepared in this embodiment is ≥1.2×10⁻⁶. 4 A / cm 2 .

[0025] Figure 3 Figure 1 shows the CT scan images of the Cu / Nb / (B,Mg) multi-core composite rod prepared in Example 1 of this invention. Figure (a) is a CT scan cross-sectional view of the 37-core Cu / Nb / (B,Mg) multi-core composite rod prepared by medium-temperature hot extrusion. Figure (a0) is a CT scan cross-sectional view of the multi-core composite rod along the xz direction and position in Figure (a). Figure (a1) is a CT scan cross-sectional view of the multi-core composite rod along the yz direction and position in Figure (a). Figure (a2) is a three-dimensional morphology of the Nb barrier layer along the Z direction in Figure (a) after CT scanning of the 37-core Cu / Nb / (B,Mg) multi-core composite rod. Figure (a3) ​​is a three-dimensional morphology of the Nb barrier layer along the -Z direction in Figure (a) after CT scanning of the 37-core Cu / Nb / (B,Mg) multi-core composite rod. In summary, the 37-core Cu / Nb / (B,Mg) multi-core composite round bar prepared by medium-temperature hot extrusion has the most uniform internal core wire size, the Nb barrier layer basically does not break, and most of the Nb barrier layer maintains a uniform thickness, with local thinning.

[0026] Example 2 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Fill the Nb tube with C-coated B powder according to the B / Mg mass ratio of 1:1 and insert the Mg rod in the center. Then assemble it in the Cu tube to obtain a Cu / Nb / (B,Mg) single-core composite with an outer diameter of Φ16mm. Then, perform cold spinning forging deformation on the Cu / Nb / (B,Mg) single-core composite with a total deformation rate of 35% and a pass deformation rate of 20% to obtain a compact Cu / Nb / (B,Mg) single-core composite rod. Next, wrap the Cu / Nb / (B,Mg) single-core composite rod with an outer layer of graphite mud. After preheating at 425℃ for 1.5min, spin the rod and then heat it at 375℃ for 2.5min. Then, perform hot drawing deformation at 375℃, a pass deformation rate of 20%, and a drawing speed of 3m / min to obtain a Cu / Nb / (B,Mg) single-core composite round wire with a diameter of Φ2mm. Step 2: The Cu / Nb / (B,Mg) single-core composite round wire from Step 1 is polished with 400-grit, 600-grit, and 800-grit sandpaper to remove graphite. Oil is removed by alkaline cleaning with a metal cleaner, and the oxide layer is removed by acid washing with HNO3 aqueous solution. After cutting, 91 wires are bundled and assembled into an oxygen-free Cu sheath. Vacuum electron beam welding is then used to obtain a 91-core Cu / Nb / (B,Mg) multi-core composite sheath. The Cu / Nb / (B,Mg) multi-core composite sheath is then subjected to homogenization heat treatment at 475℃ for 2.5 hours, followed by medium-temperature hot extrusion deformation at a deformation temperature of 475℃, an extrusion ratio of 9.5, and an extrusion speed of 20 mm / s to obtain a Cu / Nb / (B,Mg) multi-core composite round bar with a diameter of Φ15 mm. Step 3: The Cu / Nb / (B,Mg) multi-core composite round bar from Step 2 is subjected to cold spinning forging deformation with a total deformation rate of 35% and a pass deformation rate of 18% to balance the internal residual stress. Then, the outer layer of graphite is coated, and after preheating at 425℃ for 1.5 min, the bar is spun, heated at 375℃ for 2.5 min, and then hot drawn at 375℃ with a pass deformation rate of 20% and a drawing speed of 3 m / min to obtain a Cu / Nb / (B,Mg) multi-core composite round wire with a diameter of Φ1.5 mm. Step 4: The Cu / Nb / (B,Mg) multi-core composite round wire from Step 3 is subjected to high-temperature vacuum sintering at 650℃ for 2 hours to obtain IMD-MgB2 high-temperature superconducting multi-core wire with a diameter of Φ1.5mm.

[0027] At 4.2K and 2T, the critical current density Jc of the IMD-MgB2 high-temperature superconducting multi-core wire prepared in this embodiment is ≥1.2×10⁻⁶. 4 A / cm 2 .

[0028] Example 3 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Fill the Nb tube with C-coated B powder according to the B / Mg mass ratio of 1:1 and insert the Mg rod in the center. Then assemble it in the Cu tube to obtain a Cu / Nb / (B,Mg) single-core composite with an outer diameter of Φ13mm. Then, perform cold spinning forging deformation on the Cu / Nb / (B,Mg) single-core composite with a total deformation rate of 30% and a pass deformation rate of 30% to obtain a compact Cu / Nb / (B,Mg) single-core composite rod. Next, wrap the Cu / Nb / (B,Mg) single-core composite rod with an outer layer of graphite mud. After preheating at 400℃ for 1min, spin the rod and then heat it at 400℃ for 3min. Then, perform hot drawing deformation at 400℃, a pass deformation rate of 16%, and a drawing speed of 2m / min to obtain a Cu / Nb / (B,Mg) single-core composite round wire with a diameter of Φ1mm. Step 2: The Cu / Nb / (B,Mg) single-core composite round wire from Step 1 is surface-polished using 400-grit, 600-grit, and 800-grit sandpaper to remove graphite. Oil stains are removed using an alkaline metal cleaner, and the oxide layer is removed by acid washing with HNO3 aqueous solution. After cutting, 189 wires are bundled and assembled into an oxygen-free Cu sheath. Vacuum electron beam sealing is then performed to obtain a 189-core Cu / Nb / (B,Mg) multi-core composite sheath. Figure 5 As shown, the Cu / Nb / (B,Mg) multi-core composite cladding is then subjected to a homogenization heat treatment at 450℃ for 2 hours, followed by a medium-temperature hot extrusion deformation at a deformation temperature of 450℃, an extrusion ratio of 8, and an extrusion speed of 10 mm / s to obtain a Cu / Nb / (B,Mg) multi-core composite round bar with a diameter of Φ20 mm. Step 3: The Cu / Nb / (B,Mg) multi-core composite round bar from Step 2 is subjected to cold spinning forging deformation with a total deformation rate of 30% and a pass deformation rate of 15% to balance the internal residual stress. Then, the outer layer of graphite is coated, and after preheating at 450℃ for 2 minutes, the bar is spun. Then, it is heated at 400℃ for 3 minutes, followed by hot drawing deformation at 400℃, a pass deformation rate of 16%, and a drawing speed of 2 m / min to obtain a Cu / Nb / (B,Mg) multi-core composite round wire with a diameter of Φ1 mm. Step 4: The Cu / Nb / (B,Mg) multi-core composite round wire from Step 3 is subjected to high-temperature vacuum sintering at 670℃ for 2 hours to obtain IMD-MgB2 high-temperature superconducting multi-core wire with a diameter of Φ1mm.

[0029] At 4.2K and 2T, the critical current density Jc of the IMD-MgB2 high-temperature superconducting multi-core wire prepared in this embodiment is ≥1.2×10⁻⁶.4 A / cm 2 .

[0030] Figure 6 Figure 1 shows the CT scan images of the Cu / Nb / (B,Mg) multi-core composite round rod prepared in this embodiment. Figure 2(a) is a CT scan cross-sectional view of the 189-core Cu / Nb / (B,Mg) multi-core composite round rod prepared by medium-temperature hot extrusion. Figure 3(a0) is a CT scan image of the internal cross-section of the rod along the direction and position indicated by the arrow in Figure 3(a1). Figure 4(a1) is a three-dimensional morphology of the Nb barrier layer inside the rod along the extrusion direction. Figure 5(a2) is a morphology of the Nb barrier layer inside the rod perpendicular to the extrusion direction. In summary, after medium-temperature hot extrusion deformation, the core wires of the multi-core composite round rod exhibit an approximately elliptical shape according to their distance from the center point. A small number of cracks exist in the Nb barrier layer. The Nb barrier layer inside the multi-core composite round rod is more parallel to the extrusion direction, and there is basically no twisting of the Nb barrier layer (or core wires).

[0031] 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 the hot processing of an IMD-MgB2 high temperature superconductor multi-filament wire based on medium temperature hot extrusion, characterized in that, The method includes the following steps: Step 1: Fill the Nb tube with C-coated B powder into the Nb tube with the Mg rod inserted in the center, and then assemble it into the Cu tube to obtain a Cu / Nb / (B,Mg) single-core composite. Then, perform cold spinning forging on the Cu / Nb / (B,Mg) single-core composite to obtain a compact Cu / Nb / (B,Mg) single-core composite rod. Next, wrap the Cu / Nb / (B,Mg) single-core composite rod with an outer layer of graphite mud, preheat it, spin it, and then heat it to perform hot drawing deformation to obtain Cu / Nb / (B,Mg) single-core composite round wire. Step 2: The Cu / Nb / (B,Mg) single-core composite round wire from Step 1 is surface-polished to remove graphite, and then cleaned with a metal cleaner to remove oil stains and HNO3 aqueous solution to remove the oxide layer. After cutting, it is bundled and assembled into an oxygen-free Cu sheath. The Cu / Nb / (B,Mg) multi-core composite sheath is obtained by vacuum electron beam sealing. Then, the Cu / Nb / (B,Mg) multi-core composite sheath is subjected to homogenization heat treatment and then subjected to medium-temperature hot extrusion deformation to obtain Cu / Nb / (B,Mg) multi-core composite round bar. Step 3: The Cu / Nb / (B,Mg) multi-core composite round bar from Step 2 is subjected to cold spinning forging deformation to balance the internal residual stress. Then, it is coated with an outer layer of graphite, preheated, spun, and then heated for hot drawing deformation to obtain Cu / Nb / (B,Mg) multi-core composite round wire. Step 4: Perform high-temperature vacuum sintering on the Cu / Nb / (B,Mg) multi-core composite round wire from Step 3 to obtain IMD-MgB2 high-temperature superconducting multi-core wire.

2. The method according to claim 1, wherein the method is characterized by, In step one, the filling of C-coated B powder is carried out at a B / Mg mass ratio of 1:1 to 1:1.12; the outer diameter of the Cu / Nb / (B,Mg) single-core composite is Φ13mm to 20mm; the total deformation rate of the cold forging is 30% to 40%, and the per-pass deformation rate is 15% to 30%; the preheating temperature is 400℃ to 450℃ for 1min to 2min, the heating temperature is 350℃ to 400℃ for 2min to 3min, the hot drawing deformation temperature is 350℃ to 400℃, the per-pass deformation rate is 16% to 24%, and the drawing speed is 2m / min to 4m / min; the diameter of the Cu / Nb / (B,Mg) single-core composite round wire is Φ1mm to 3.9mm.

3. The method according to claim 1, wherein the method is characterized by, The number of cores in the cluster assembly in step two is 37 to 189, and the welding vacuum degree of the vacuum electron beam sealing is 1.0 × 10⁻⁶. -3 Pa, focusing current is 654mA, accelerating voltage is 85kV, welding speed is 500mm / min; the temperature of the homogenization heat treatment is 450℃~500℃, and the time is 2h~3h; the deformation temperature of the medium-temperature hot extrusion deformation is 450℃~500℃, the extrusion ratio is 8~11, and the extrusion speed is 10mm / s~40mm / s; the diameter of the Cu / Nb / (B,Mg) multi-core composite round bar is Φ10mm~20mm.

4. The method according to claim 1, wherein the method is characterized by, In step three, the total deformation rate of cold rotary forging is 30%~40%, and the deformation rate per pass is 15%~20%; the preheating temperature is 400℃~450℃, and the time is 1min~2min; the heating temperature is 350℃~400℃, and the time is 2min~3min; the hot drawing deformation temperature is 350℃~400℃, the deformation rate per pass is 16%~24%, and the drawing speed is 2m / min~4m / min; the diameter of the Cu / Nb / (B,Mg) multi-core composite round wire is Φ1mm~2mm.

5. The method according to claim 1, wherein the method is characterized by the following steps: The high-temperature vacuum sintering in step four is carried out at a temperature of 630℃~670℃ for 2 hours.

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