A method for thermal processing of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire

Abstract

This invention discloses a method for hot-processing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire. The method includes: 1. Powder mixing; 2. Cold spinning and forging deformation after powder loading and tubing; 3. Surface graphite mud coating, preheating, spinning, and hot drawing deformation after heating; 4. Surface grinding, alkaline washing, acid washing, cutting, and bundle assembly for cold spinning and forging; 5. Surface graphite mud coating, preheating, spinning, and hot drawing deformation after heating; 6. High-temperature vacuum sintering. This invention, through SiC doping and hot drawing deformation, regulates the nucleation and growth kinetics of MgB2 superconducting phase grains, obtaining uniformly sized, clean, and continuous nanoscale grains, forming more flux pinning centers, and improving the uniformity of synergistic deformation, ensuring the density and shape regularity of the superconducting phase, and enhancing the flux pinning capability and high-field current transfer performance of the high-temperature superconducting multi-core wire. It is applicable to MRI, superconducting cables, and superconducting wind turbines.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature superconducting multi-core wire preparation, processing and microstructure control technology, specifically involving a thermal processing method for preparing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire. Background Technology

[0002] Magnesium diboride (MgB2), a high-temperature superconducting wire, possesses unique advantages such as a superconducting transition temperature as high as 39K, low raw material costs, and the absence of intrinsic grain boundary weak connections. These advantages make it suitable for large-scale magnets operating above liquid helium temperatures (~20K), making it a highly competitive candidate material in fields such as magnetic resonance imaging (MRI), compact nuclear fusion devices, and next-generation particle accelerators. However, the stable and reliable conversion of its outstanding intrinsic superconducting potential into a high critical current density (…) remains a challenge. J c) The excellent mechanical properties and long-range uniformity of engineered wires (strips) have always been the core bottleneck restricting their transition from laboratory to industrial application. New-generation high-temperature superconducting MgB2 wires based on central magnesium diffusion (IMD) technology form a superconducting phase through the reaction and diffusion of magnesium and boron, effectively improving the critical current density and microstructure uniformity of the wire. This provides a feasible path to meet the requirements of high mechanical strength and high current-carrying capacity for strong magnetic field applications. However, in the actual fabrication process of IMD-MgB2 wires, especially kilometer-long wires, there are still widespread macroscopic problems such as core breakage, wire breakage, and internal barrier layer (such as Nb layer) rupture, as well as microscopic problems such as insufficient magnetic flux pinning, insufficient control of grain size uniformity, and residual impurities at the grain interface. These problems severely restrict the yield and performance stability of the wires, thus hindering their large-scale fabrication and engineering application.

[0003] In the hot forming process of high-temperature superconducting wire MgB2, the multiphase synergistic rheological behavior of the central Mg rod, the metal cladding (Cu / Nb), and the filler B powder is crucial in determining the final performance and fabrication stability of the wire. In existing processes, pure Mg rods suffer from poor deformability, uneven deformation, and significant anisotropy, easily leading to localized stress concentration and powder flow instability during drawing, which in turn causes a series of defects such as Nb barrier layer rupture, wire breakage, and high porosity of the superconducting core after heat treatment. To address these issues, existing technologies mainly focus on component optimization or adjustment of single process parameters, but these are insufficient to effectively solve core challenges such as uneven Mg / B interface reaction, superconducting phase grain coarsening, and high-field current degradation. In particular, how to improve powder density and microstructure uniformity while introducing effective flux pinning centers to achieve synergistic control of grain refinement, porosity reduction, and grain boundary cleanliness remains a significant technical challenge in the current field of IMD-MgB2 wire fabrication. Therefore, there is an urgent need to develop a novel preparation method that deeply synergizes specific doping and thermal processing techniques to address the shortcomings of existing technologies in terms of multiphase coordinated deformation, microstructure control, and current-carrying capacity improvement, and to provide effective technical support for the stable preparation of high-performance MgB2 multicore long wires. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a hot-processing method for preparing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wires. This method introduces localized lattice distortion and stress fields through SiC doping and hot drawing deformation, forming nanoscale pinning centers, increasing grain boundary density, and thus forming more flux pinning centers. Simultaneously, it improves the uniformity of synergistic deformation, ensuring the density and shape regularity of the MgB2 superconducting phase. This results in a nanoscale superconducting phase structure with uniform grain size, clean grain boundaries, and strong continuity, significantly improving the flux pinning capability and high-field current transfer performance of the SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire. This solves the problems of superconducting phase grain coarsening and high-field current transfer performance degradation in existing MgB2 high-temperature superconducting multi-core wires.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire by thermal processing, characterized in that the method includes the following steps: Step 1: Mix SiC powder with C-coated B powder to obtain a mixed powder; Step 2: Insert the Mg rod into the Nb tube and place it in the center of the Nb tube. Fix the Mg rod with a copper plug and seal the Nb tube. Then, fill the Nb tube with the mixed powder from Step 1 with the Mg rod inserted in the center and seal it with a copper plug. Then, put the Cu tube over the Nb tube to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite. Then, perform cold spinning forging on the Cu / Nb / (SiC+C+B,Mg) single-core composite to make the Cu tube and Nb tube fit together and the mixed powder inside compact, to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite rod. Step 3: Coat the surface of the Cu / Nb / (SiC+C+B,Mg) single-core composite rod from Step 2 with graphite mud. Then, place the graphite mud-coated Cu / Nb / (SiC+C+B,Mg) single-core composite rod into a heating furnace for preheating. Then, spin the rod and place it back into the heating furnace for heating. Finally, perform hot drawing deformation to obtain Cu / Nb / (SiC+C+B,Mg) single-core composite round wire. Step 4: The Cu / Nb / (SiC+C+B,Mg) single-core composite round wire from Step 3 is surface-polished to remove surface graphite, then alkaline-washed with a metal cleaning agent and acid-washed with HNO3 aqueous solution. After cutting, it is bundled and assembled with copper wire into a Monel alloy sheath to obtain a multi-core Cu / Nb / (SiC+C+B,Mg) composite. Then, it is cold-forged to make the interface between the Monel alloy sheath and the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire contact, and the interfaces between the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wires contact, to obtain a Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod. Step 5: Coat the surface of the Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod from Step 4 with graphite mud. Then, place the graphite mud-coated Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod into a heating furnace for preheating. Then, spin the rod and place it back into the heating furnace for heating. Finally, perform hot drawing deformation to obtain Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire. Step 6: Perform high-temperature vacuum sintering on the Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire obtained in Step 5 to obtain SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

[0006] This invention employs a process of mixed doping of SiC powder and C-coated B powder, followed by cold spinning forging after powder sleeve loading, hot drawing deformation, bundled structure followed by cold spinning forging, hot drawing deformation, and high-temperature vacuum sintering. By controlling the SiC doping amount and the process parameters of hot drawing deformation, the stress distribution inside the B powder after deformation and before sintering is controlled. This introduces local lattice distortion and stress field, forming nanoscale pinning centers, inhibiting the excessive growth of MgB2 grains, promoting the formation of finer superconducting phase grains, and regulating the nucleation and growth kinetics of MgB2 superconducting phase grains. This results in uniform, nanoscale grains with clean and continuous grain boundaries, increasing grain boundary density and thus forming more flux pinning centers. Simultaneously, based on the thermo-mechanical coupling effect, hot drawing deformation improves the hot deformation plasticity of the Mg rod and the synergistic deformation uniformity between the powder and metal and between subcomponents, giving the B powder high density and regular layer thickness, thereby ensuring the density and shape regularity of the MgB2 superconducting phase after sintering. Furthermore, the hot drawing deformation of the large number of passes introduces lateral compressive stress into the B powder layer, changing the 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. At the same time, hot drawing deformation increases the single-pass deformation rate from 8% in cold drawing deformation to 16%~24%, and the dies used in the drawing process are reduced to 1 / 3 of those used in cold drawing deformation, significantly reducing processing time and preparation process.

[0007] The above-mentioned method for preparing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wires by thermal processing is characterized in that, in step one, the SiC powder has a purity of 99.9% or higher and a particle size of no more than 150 nm; the C-coated B powder has a particle size of less than 300 nm and a B content of 95%; the mixing method is grinding in an argon glove box for 30 min; the mixed powder is uniformly dispersed, non-agglomerated, and spherical, and the mass percentage of SiC powder in the mixed powder is 5%~15%. This invention obtains uniformly dispersed, non-agglomerated, and spherical SiC and C-coated B mixed powders through grinding and mixing, which is more conducive to the doping elements entering the MgB2 lattice to replace B atoms in the lattice, introducing lattice distortion and providing driving energy for grain nucleation; simultaneously, the doped elements can form nanoparticle phases with Mg, or act as nanoparticle phases themselves, hindering continuous grain growth, refining grains, and controlling the grain boundaries of the superconducting phase in high-temperature superconducting multi-core wires, thereby improving their current-carrying capacity.

[0008] The above-mentioned method for hot-processing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire is characterized in that, in step two, the diameter of the Mg rod is 4mm~8mm and the mass purity is 99.99%; the inner diameter of the Nb tube is 8mm~15mm and the wall thickness is 1mm~2mm; the inner diameter of the Cu tube is 11mm~20mm and the wall thickness is 1mm~2mm; the mixed powder is filled at a B to Mg mass ratio of 1:1.12; the total deformation rate of the cold forging deformation is 30%~40%, and the pass rate is 15%~30%.

[0009] The above-mentioned method for hot-processing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire is characterized in that, in step three, the preheating temperature is 350℃~400℃ and the time is 1min~3min; the heating temperature after the spin-head process is 300℃ and the time is 2min~3min; the hot drawing deformation temperature is 300℃, the deformation rate per pass is 16%~24%, and the drawing speed is 2m / min~4m / min; the diameter of the Cu / Nb / (SiC+C+B,Mg) single-core composite round wire is 3.9mm, and when the diameter of the product single-core composite round wire is more than 5mm after hot drawing deformation, the preheating, spin-head, and heating processes need to be repeated before continuing the hot drawing deformation; when the diameter of the product single-core composite round wire is less than 5mm, the length is greater than 10m, and it passes through the entire heating furnace, only the spin-head and heating processes need to be repeated before continuing the hot drawing deformation.

[0010] This invention controls the preheating temperature and time, heating temperature and time, and, in combination with controlling the deformation rate, drawing temperature, and drawing speed of the single-core hot drawing deformation, regulates the degree and speed of dynamic recrystallization of Cu and Mg, as well as the degree and speed of dynamic recovery of Nb, to achieve coordinated and uniform plastic deformation of the central Mg rod, the intermediate Nb barrier layer, and the outer Cu cladding, and uniform flow of B powder. At the same time, the hot drawing deformation of the multiple passes introduces lateral compressive stress into the B powder layer, changing the stress state from biaxial compressive stress to triaxial compressive stress, which 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.

[0011] The above-mentioned method for hot-processing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire is characterized in that, in step four, the bundling assembly is carried out by cutting 30 cores (Cu / Nb / (SiC+C+B,Mg) single-core composite round wire) + 7 cores (copper wire), the outer diameter of the Monel alloy sheath is Φ32mm and the wall thickness is 2mm; the total deformation rate of the cold forging is 20%~30%, and the per-pass deformation rate is 10%~12%, to obtain a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod.

[0012] The above-mentioned method for hot-processing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire is characterized in that, in step five, the preheating temperature is 400℃~450℃ and the time is 3min~5min; the heating temperature after the spin-head process is 300℃~350℃ and the time is 2min~3min; the hot drawing deformation temperature is 300℃, the deformation rate per pass is 16%~18%, and the drawing speed is 2m / min~4m / min; the diameter of the Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire is 1mm~2mm, and when the diameter of the product multi-core composite round wire is more than 5mm, the preheating, spin-head process and heating process need to be repeated before continuing the hot drawing deformation; when the diameter of the product multi-core composite round wire is less than 5mm, the length is greater than 10m and it passes through the entire heating furnace, the spin-head process and heating process only need to be repeated before continuing the hot drawing deformation. This invention controls the preheating temperature and time, heating temperature and time, and, in conjunction with controlling the pass deformation rate, drawing temperature, and drawing speed of multi-core hot drawing deformation, to regulate the degree and speed of dynamic recrystallization of the Monel cladding, Cu, and Mg, and the degree and speed of dynamic recovery of Nb. This ensures that the central Mg retains excellent thermoplasticity while maintaining the low-temperature plastic deformation capability of Nb. Furthermore, this control enhances the synergistic and uniform deformation among subcomponents, resulting in a uniform distribution and shape of the deformed Cu / Nb / (SiC+C+B,Mg) single core. Simultaneously, the multi-pass hot drawing deformation further introduces lateral extrusion stress into the B powder layer, increasing the density of the B powder and introducing greater extrusion stress. This provides more sites for the nucleation and growth of MgB2 superconducting phase grains, thereby ensuring nanoscale grain size.

[0013] The above-mentioned method for thermally processing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire is characterized in that, in step six, the heating rate of the high-temperature vacuum sintering is 10℃ / min~15℃ / min, the temperature is 630℃~670℃, and the time is 2h, resulting in a 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire. This invention achieves control over the grain size of the MgB2 superconducting phase through short-time, low-temperature sintering, thus avoiding grain growth. Compared with the prior art, the present invention has the following advantages: 1. Achieved precise control over the grain size, grain boundary state, and magnetic flux pinning capability of MgB2 superconducting phase: This invention introduces triaxial compressive stress and local lattice distortion into the B powder layer through the synergistic effect of SiC doping and thermal drawing deformation. The doped SiC particles serve as nucleation sites to refine the grains on the one hand, and react with Mg to generate a nanoscale second phase or act as pinning centers on the other hand, effectively suppressing the excessive growth of MgB2 grains. Ultimately, a nanoscale superconducting phase structure with uniform grain size, clean grain boundaries, and strong continuity is obtained, which significantly improves the magnetic flux pinning capability and high-field current transfer performance of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

[0014] 2. Significantly improves the synergistic deformation capability of multiphase materials, greatly enhancing the structural uniformity and density of the wire: This invention, through a hot drawing deformation process, enables the central Mg rod, Nb barrier layer, Cu cladding, and multi-core sub-components in the Cu / Nb / (SiC+C+B,Mg) single-core composite rod to 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 the Mg rod; at the same time, the second hot drawing introduces triaxial compressive stress into the B powder layer, increasing the density of the B powder and making the layer thickness distribution regular, thereby significantly reducing the internal pores of the MgB2 superconducting phase after high-temperature vacuum sintering, avoiding defects such as Nb layer cracking, core breakage, and loose superconducting core common in traditional processes, and ensuring the long-range uniformity and yield of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

[0015] 3. Significantly improved single-pass deformation rate, significantly shortened processing flow, and improved preparation efficiency: This invention increases the single-pass deformation rate from 8% in traditional cold drawing to 16%~24% through hot drawing, reducing the number of drawing passes required to reach the target size to about 1 / 3 of that in cold drawing. At the same time, with the combination of graphite mud lubrication and segmented heating strategy, the number of hot drawing dies used and processing time are significantly reduced, simplifying the preparation process and providing a feasible way for the large-scale and low-cost preparation of high-performance SiC-doped 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 SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire according to the present invention.

[0018] Figure 2 The image shows the grain morphology of the Cu / Nb / (SiC+C+B,Mg) single-core composite circular wire prepared in Example 1 of this invention.

[0019] Figure 3 This is a CT scan image of the 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite circular wire prepared in Example 1 of this invention.

[0020] Figure 4 This is a microstructure diagram of the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire prepared in Example 1 of this invention.

[0021] Figure 5 This is a comparison chart of the current-carrying performance of the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire prepared in Example 1 of this invention. Detailed Implementation

[0022] Example 1 like Figure 1 As shown, this embodiment includes the following steps: Step 1: SiC powder with a purity of 99.9% or higher and a particle size not exceeding 150 nm is mixed with C-coated B powder with a particle size less than 300 nm by grinding in an argon-filled glove box for 30 minutes to obtain a uniformly dispersed, non-agglomerated, and spherical mixed powder; the C-coated B powder has a B content of 95% by mass; the mass percentage of SiC powder in the mixed powder is 15%. Step 2: Insert a Mg rod with a diameter of 4 mm and a purity of 99.99% into an Nb tube with an inner diameter of 8 mm and a wall thickness of 1 mm, and place it in the center of the Nb tube. Fix the Mg rod with a copper plug and seal the Nb tube. Then, fill the Nb tube with the Mg rod inserted in the center with the mixed powder from Step 1 at a B to Mg mass ratio of 1:1.12, and seal both ends with a copper plug. Then, put a Cu tube with an inner diameter of 11 mm and a wall thickness of 1 mm over the Nb tube to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite. Then, perform cold spinning forging deformation on the Cu / Nb / (SiC+C+B,Mg) single-core composite with a total deformation rate of 40% and a pass rate of 30% to make the Cu tube and Nb tube fit together and the internal mixed powder compacted, to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite rod. Step 3: The Cu / Nb / (SiC+C+B,Mg) single-core composite rod from Step 2 is coated with graphite mud. Then, the graphite-coated Cu / Nb / (SiC+C+B,Mg) single-core composite rod is placed in a heating furnace for preheating at 350℃ for 1 minute. Afterward, it is spun and placed back into the heating furnace for heating at 300℃ for 2 minutes. Finally, it is drawn at 300℃ with a pass deformation rate of 24% at a certain speed. The hot drawing deformation rate is 4 m / min. When the diameter of the hot drawing deformation product single-core composite round wire is more than 5 mm, the preheating, spinning and heating processes need to be repeated before the hot drawing deformation can continue. When the diameter of the hot drawing deformation product single-core composite round wire is less than 5 mm, the length is more than 10 m and it passes through the entire heating furnace, only the spinning and heating processes need to be repeated before the hot drawing deformation can continue to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite round wire with a diameter of 3.9 mm. Step 4: The Cu / Nb / (SiC+C+B,Mg) single-core composite round wire from Step 3 is surface-polished to remove surface graphite, and then subjected to alkaline washing with a metal cleaning agent and acid washing with HNO3 aqueous solution. After cutting, it is bundled with copper wire in a bundle of 30 cores (Cu / Nb / (SiC+C+B,Mg) single-core composite round wire) + 7 cores (copper wire) into a Monel alloy sheath with an outer diameter of Φ32mm and a wall thickness of 2mm, resulting in a 37-core Cu / Nb / (SiC+C+B,Mg) composite. Then, it is cold-forged with a total deformation rate of 30% and a per-pass deformation rate of 12%, so that the Monel alloy sheath is in contact with the interface of the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire, and the interfaces of the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire are in contact with each other, resulting in a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod. Step 5: The 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod from Step 4 is coated with graphite mud. Then, the graphite-coated Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod is placed in a heating furnace for preheating at 400℃ for 3 minutes. Afterward, it is spun and placed back into the heating furnace for heating at 300℃ for 2 minutes. Finally, a drawing process is performed with a pass deformation rate of 18% and a drawing speed of... The hot drawing deformation speed is 2m / min. When the diameter of the hot drawing deformation product multi-core composite round wire is more than 5mm, the preheating, spinning and heating processes need to be repeated before the hot drawing deformation can continue. When the diameter of the hot drawing deformation product multi-core composite round wire is less than 5mm, the length is more than 10m and it passes through the entire heating furnace, only the spinning and heating processes need to be repeated before the hot drawing deformation can continue to obtain a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire with a diameter of 1mm. Step 6: The 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire obtained in Step 5 is subjected to high-temperature vacuum sintering at a heating rate of 13℃ / min, a temperature of 650℃, and a time of 2h to obtain a 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

[0023] Figure 2 Figure 1 shows the grain morphology of the Cu / Nb / (SiC+C+B,Mg) single-core composite circular wire prepared in this embodiment. Figure 2(a) is a SEM image of the MgB2 superconducting phase in the Cu / Nb / (SiC+C+B,Mg) single-core composite circular wire. Figure 3(a1) is an enlarged view of a selected area in Figure 3(a), showing the grain morphology of the MgB2 superconducting phase. Figures 3(a2) and 3(a3) are enlarged views of region 1 and region 2 in Figure 3(a1), respectively. It can be clearly seen that with 15% SiC doping, the MgB2 superconducting phase has a small grain size and a large number of grain boundaries.

[0024] Figure 3Figure 1 shows the CT scan images of the 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite circular wire prepared in this embodiment. Figure 2 shows the cross-sectional metallographic image of the 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite circular wire, Figure 3 shows the cross-sectional image of the 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite circular wire after CT scanning, Figure 4 shows the cross-sectional view of the multi-core structure along the xz direction and position of Figure 4 (a0), Figure 5 shows the cross-sectional view of the multi-core structure along the yz direction and position of Figure 4 (a0), and Figure 6 shows the three-dimensional morphology of the internal Nb barrier layer of the 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite circular wire after CT scanning. In summary, during the hot drawing process, the Mg inside the core wire deforms uniformly and maintains the same overall morphology as the core wire, without any breakage or distortion. The Nb barrier layer deforms uniformly. The core wires inside the 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire are evenly distributed, and their shapes are more consistent after deformation. Furthermore, no cracking was observed in the Nb barrier layer.

[0025] Figure 4 Figure 1 shows the microstructure of the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire prepared in this embodiment. Figure (a) shows the microstructure of the MgB2 superconducting phase within a single filament in the cross-section of the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire. Figure (a1) is a selected magnified view of Figure (a1), Figure (a2) is a selected magnified view of Figure (a1), Figure (a3) ​​shows the microstructure of the MgB2 superconducting phase in the longitudinal section of the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire, and Figure (a4) is a selected magnified view of Figure (a3). In summary, the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire exhibits fewer pores and smaller pore sizes within the superconducting phase, resulting in a more dense superconducting phase. Figure 5 This is a comparison chart of the current-carrying performance of the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire prepared in this embodiment. Figure 5 It can be seen that at 4.2K and 1T, the current-carrying capacity of the 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire is... Jc Exceeding 1.5×10 6 A / cm 2 The critical current density of a 15% SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire at 4.2K and 4T. J c reaches 8×10 5 A / cm 2This indicates that the smaller grain size of the superconducting phase leads to a significant increase in the number of grain boundaries, which in turn enables the formation of more pinning centers and effectively pins the magnetic flux lines, resulting in an increase in the hysteresis loop width ΔM and the critical current density Jc.

[0026] Example 2 like Figure 1 As shown, this embodiment includes the following steps: Step 1: SiC powder with a purity of 99.9% or higher and a particle size not exceeding 150 nm is mixed with C-coated B powder with a particle size less than 300 nm by grinding in an argon-filled glove box for 30 minutes to obtain a uniformly dispersed, non-agglomerated, and spherical mixed powder; the C-coated B powder has a B content of 95% by mass; the mass percentage of SiC powder in the mixed powder is 10%. Step 2: Insert a Mg rod with a diameter of 6 mm and a purity of 99.99% into an Nb tube with an inner diameter of 11 mm and a wall thickness of 1.5 mm, and place it in the center of the Nb tube. Fix the Mg rod with a copper plug and seal the Nb tube. Then, fill the Nb tube with the Mg rod inserted in the center with the mixed powder from Step 1 at a B to Mg mass ratio of 1:1.12, and seal both ends with a copper plug. Then, put a Cu tube with an inner diameter of 15 mm and a wall thickness of 1.5 mm over the Nb tube to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite. Then, perform cold spinning forging deformation on the Cu / Nb / (SiC+C+B,Mg) single-core composite with a total deformation rate of 35% and a pass rate of 25% to make the Cu tube and Nb tube fit together and the internal mixed powder compacted, to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite rod. Step 3: The Cu / Nb / (SiC+C+B,Mg) single-core composite rod from Step 2 is coated with graphite mud. Then, the graphite-coated Cu / Nb / (SiC+C+B,Mg) single-core composite rod is placed in a heating furnace for preheating at 375℃ for 2 minutes. Afterward, it is spun and placed back into the heating furnace for heating at 300℃ for 2.5 minutes. Finally, it is drawn at 300℃ with a pass deformation rate of 20% and a drawing speed of... The hot drawing deformation speed is 3m / min. When the diameter of the hot drawing deformation product single-core composite round wire is more than 5mm, the preheating, spinning and heating processes need to be repeated before the hot drawing deformation can continue. When the diameter of the hot drawing deformation product single-core composite round wire is less than 5mm, the length is more than 10m and it passes through the entire heating furnace, only the spinning and heating processes need to be repeated before the hot drawing deformation can continue to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite round wire with a diameter of 3.9mm. Step 4: The Cu / Nb / (SiC+C+B,Mg) single-core composite round wire from Step 3 is surface-polished to remove surface graphite, and then subjected to alkaline washing with a metal cleaning agent and acid washing with HNO3 aqueous solution. After cutting, it is bundled with copper wire in a bundle of 30 cores (Cu / Nb / (SiC+C+B,Mg) single-core composite round wire) + 7 cores (copper wire) into a Monel alloy sheath with an outer diameter of Φ32mm and a wall thickness of 2mm, resulting in a 37-core Cu / Nb / (SiC+C+B,Mg) composite. Then, it is cold-forged with a total deformation rate of 25% and a pass deformation rate of 11%, so that the Monel alloy sheath is in contact with the interface of the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire, and the interfaces of the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire are in contact with each other, resulting in a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod. Step 5: The 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod from Step 4 is coated with graphite mud. Then, the graphite-coated Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod is placed in a heating furnace for preheating at 475℃ for 4 minutes. Afterward, it is spun and placed back into the heating furnace for heating at 325℃ for 2.5 minutes. Finally, a drawing process is performed with a pass deformation rate of 17% and a drawing speed of... The hot drawing deformation speed is 3m / min. When the diameter of the multi-core composite round wire of the product is more than 5mm, the preheating, spinning and heating processes need to be repeated before the hot drawing deformation can continue. When the diameter of the multi-core composite round wire of the product is less than 5mm, the length is more than 10m and it passes through the entire heating furnace, the spinning and heating processes only need to be repeated before the hot drawing deformation can continue to obtain a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire with a diameter of 1.5mm. Step 6: The 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire obtained in Step 5 is subjected to high-temperature vacuum sintering at a heating rate of 15℃ / min, a temperature of 630℃, and a time of 2h to obtain a 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

[0027] The critical current density of a 10% SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire at 4.2K and 4T. J c is 1.4 × 10 5 A / cm 2 .

[0028] Example 3 like Figure 1 As shown, this embodiment includes the following steps: Step 1: SiC powder with a purity of 99.9% or higher and a particle size not exceeding 150 nm is mixed with C-coated B powder with a particle size less than 300 nm by grinding in an argon glove box for 30 minutes to obtain a uniformly dispersed, non-agglomerated, and spherical mixed powder; the C-coated B powder has a B content of 95% by mass; the mass percentage of SiC powder in the mixed powder is 5%. Step 2: Insert an 8mm diameter Mg rod with a purity of 99.99% into an Nb tube with an inner diameter of 15mm and a wall thickness of 2mm, and place it in the center of the Nb tube. Fix the Mg rod with a copper plug and seal the Nb tube. Then, fill the Nb tube with the Mg rod inserted in the center with the mixed powder from Step 1 at a B to Mg mass ratio of 1:1.12, and seal both ends with a copper plug. Then, fit a 20mm inner diameter Cu tube with a wall thickness of 2mm over the Nb tube to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite. Then, perform cold spinning forging deformation on the Cu / Nb / (SiC+C+B,Mg) single-core composite with a total deformation rate of 30% and a pass rate of 15%, so that the Cu tube and Nb tube fit together and the internal mixed powder is compacted, to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite rod. Step 3: Coat the surface of the Cu / Nb / (SiC+C+B,Mg) single-core composite rod from Step 2 with graphite mud. Then, place the graphite mud-coated Cu / Nb / (SiC+C+B,Mg) single-core composite rod into a heating furnace for preheating at 400℃ for 3 minutes. Then, spin the rod and place it back into the heating furnace for heating at 300℃ for 3 minutes. Then, perform hot drawing deformation at a pass deformation rate of 16% and a drawing speed of 2 m / min. When the diameter of the product single-core composite round wire is greater than 5 mm, the preheating, spinning, and heating processes need to be repeated before continuing the hot drawing deformation. When the diameter of the product single-core composite round wire is less than 5 mm, the length is greater than 10 m and passes through the entire heating furnace, only the spinning and heating processes need to be repeated before continuing the hot drawing deformation to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite round wire with a diameter of 3.9 mm. Step 4: The Cu / Nb / (SiC+C+B,Mg) single-core composite round wire from Step 3 is surface-polished to remove surface graphite, and then subjected to alkaline washing with a metal cleaning agent and acid washing with HNO3 aqueous solution. After cutting, it is bundled with copper wire in a bundle of 30 cores (Cu / Nb / (SiC+C+B,Mg) single-core composite round wire) + 7 cores (copper wire) into a Monel alloy sheath with an outer diameter of Φ32mm and a wall thickness of 2mm, resulting in a 37-core Cu / Nb / (SiC+C+B,Mg) composite. Then, it is cold-forged with a total deformation rate of 20% and a pass deformation rate of 10%, so that the Monel alloy sheath is in contact with the interface of the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire, and the interfaces of the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire are in contact with each other, resulting in a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod. Step 5: The 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod from Step 4 is coated with graphite mud. Then, the graphite-coated Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod is placed in a heating furnace for preheating at 450℃ for 5 minutes. Afterward, it is spun and placed back into the heating furnace for heating at 350℃ for 3 minutes. Finally, a drawing process is performed with a pass deformation rate of 16% and a drawing speed of... The hot drawing deformation speed is 4m / min. When the diameter of the hot drawing deformation product multi-core composite round wire is more than 5mm, the preheating, spinning and heating processes need to be repeated before the hot drawing deformation can continue. When the diameter of the hot drawing deformation product multi-core composite round wire is less than 5mm, the length is more than 10m and it passes through the entire heating furnace, only the spinning and heating processes need to be repeated before the hot drawing deformation can continue to obtain a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire with a diameter of 2mm. Step 6: The 37-core Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire obtained in Step 5 is subjected to high-temperature vacuum sintering at a heating rate of 10℃ / min, a temperature of 670℃, and a time of 2h to obtain a 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

[0029] The critical current density of a 10% SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire at 4.2K and 4T. J c is 2.6 × 10 5 A / cm 2 .

[0030] 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 thermally processing SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire, characterized in that, The method includes the following steps: Step 1: Mix SiC powder with C-coated B powder to obtain a mixed powder; Step 2: Insert the Mg rod into the Nb tube and place it in the center of the Nb tube. Fix the Mg rod with a copper plug and seal the Nb tube. Then, fill the Nb tube with the mixed powder from Step 1 with the Mg rod inserted in the center and seal it with a copper plug. Then, put the Cu tube over the Nb tube to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite. Then, perform cold spinning forging on the Cu / Nb / (SiC+C+B,Mg) single-core composite to make the Cu tube and Nb tube fit together and the mixed powder inside compact, to obtain a Cu / Nb / (SiC+C+B,Mg) single-core composite rod. Step 3: Coat the surface of the Cu / Nb / (SiC+C+B,Mg) single-core composite rod from Step 2 with graphite mud. Then, place the graphite mud-coated Cu / Nb / (SiC+C+B,Mg) single-core composite rod into a heating furnace for preheating. Then, spin the rod and place it back into the heating furnace for heating. Finally, perform hot drawing deformation to obtain Cu / Nb / (SiC+C+B,Mg) single-core composite round wire. Step 4: The Cu / Nb / (SiC+C+B,Mg) single-core composite round wire from Step 3 is surface-polished to remove surface graphite, then alkaline-washed with a metal cleaning agent and acid-washed with HNO3 aqueous solution. After cutting, it is bundled and assembled with copper wire into a Monel alloy sheath to obtain a multi-core Cu / Nb / (SiC+C+B,Mg) composite. Then, it is cold-forged to make the interface between the Monel alloy sheath and the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wire contact, and the interfaces between the internal Cu / Nb / (SiC+C+B,Mg) single-core composite round wires contact, to obtain a Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod. Step 5: Coat the surface of the Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod from Step 4 with graphite mud. Then, place the graphite mud-coated Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod into a heating furnace for preheating. Then, spin the rod and place it back into the heating furnace for heating. Finally, perform hot drawing deformation to obtain Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire. Step 6: Perform high-temperature vacuum sintering on the Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire obtained in Step 5 to obtain SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

2. The method for hot-processing preparation of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire according to claim 1, characterized in that, The SiC powder mentioned in step one has a purity of 99.9% or higher and a particle size of no more than 150 nm. The particle size of the C-coated B powder is less than 300 nm and the mass content of B is 95%. The mixing method is grinding in an argon glove box for 30 minutes. The mixed powder is uniformly dispersed, without agglomeration, and spherical. The mass percentage of SiC powder in the mixed powder is 5% to 15%.

3. The method for hot-processing preparation of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire according to claim 1, characterized in that, In step two, the Mg rod has a diameter of 4mm to 8mm and a purity of 99.99%; the Nb tube has an inner diameter of 8mm to 15mm and a wall thickness of 1mm to 2mm; and the Cu tube has an inner diameter of 11mm to 20mm and a wall thickness of 1mm to 2mm. The mixed powder is loaded at a B to Mg mass ratio of 1:1.

12. The total deformation rate of the cold forging is 30% to 40%, and the pass rate is 15% to 30%.

4. The method for hot-processing preparation of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire according to claim 1, characterized in that, In step three, the preheating temperature is 350℃~400℃ and the time is 1min~3min. The heating temperature after the spin-head process is 300℃ and the time is 2min~3min. The hot drawing deformation temperature is 300℃, the deformation rate per pass is 16%~24%, and the drawing speed is 2m / min~4m / min. The diameter of the Cu / Nb / (SiC+C+B,Mg) single-core composite round wire is 3.9mm. When the diameter of the product single-core composite round wire is more than 5mm after hot drawing deformation, the preheating, spin-head, and heating processes need to be repeated before continuing the hot drawing deformation. When the diameter of the product single-core composite round wire is less than 5mm, the length is greater than 10m, and it passes through the entire heating furnace, the spin-head and heating processes only need to be repeated before continuing the hot drawing deformation.

5. The method for hot-processing preparation of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire according to claim 1, characterized in that, The bundling assembly in step four is carried out by cutting 30 cores (Cu / Nb / (SiC+C+B,Mg) single-core composite round wire) + 7 cores (copper wire). The outer diameter of the Monel alloy sheath is Φ32mm and the wall thickness is 2mm. The total deformation rate of the cold forging is 20%~30%, and the deformation rate per pass is 10%~12%, resulting in a 37-core Cu / Nb / (SiC+C+B,Mg) multi-core bundled composite rod.

6. The method for hot-processing preparation of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire according to claim 1, characterized in that, The preheating temperature in step five is 400℃~450℃, and the time is 3min~5min. The heating temperature after the spin-head process is 300℃~350℃, and the time is 2min~3min. The hot drawing deformation temperature is 300℃, the deformation rate per pass is 16%~18%, and the drawing speed is 2m / min~4m / min. The diameter of the Cu / Nb / (SiC+C+B,Mg) multi-core composite round wire is 1mm~2mm. When the diameter of the product multi-core composite round wire is greater than 5mm, the preheating, spin-head process, and heating process need to be repeated before continuing the hot drawing deformation. When the diameter of the product multi-core composite round wire is less than 5mm, the length is greater than 10m, and it passes through the entire heating furnace, the spin-head process and heating process only need to be repeated before continuing the hot drawing deformation.

7. The method for hot-processing preparation of SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire according to claim 1, characterized in that, The heating rate of the high-temperature vacuum sintering in step six is ​​10℃ / min~15℃ / min, the temperature is 630℃~670℃, and the time is 2h, to obtain 37-core SiC-doped IMD-MgB2 high-temperature superconducting multi-core wire.

Images