Heat treatment method of Nb / Monel-based MgB2 multi-core wire
By employing a two-stage gradient heat treatment process, a high-density dislocation network and pinning centers are formed, which solves the performance degradation problem of MgB2 superconducting wires under medium and high fields, achieves efficient grain refinement and densification, and improves the critical current density.
Patent Information
- Application Number
- CN202511748534.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-02-10
AI Technical Summary
MgB2 superconducting wires exhibit a rapid decrease in critical current density under medium-to-high field conditions, and the lack of pinning centers leads to performance degradation. Existing sintering methods struggle to address grain growth and densification issues.
A two-stage gradient heat treatment process is adopted, which forms a high-density dislocation network through rotary forging, drawing and resistance heating, increases pinning centers, and achieves grain refinement and densification.
It significantly suppressed the rapid current decay of MgB2 superconducting wires under high fields, increased the critical current value under medium and high fields, simplified the preparation process, and improved efficiency.
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Figure CN121506618A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of superconducting material preparation technology, specifically relating to a heat treatment method for Nb / Monel-based MgB2 multi-core wire. Background Technology
[0002] MgB2, as a practical high-temperature superconducting material, is being considered by researchers for use in the fabrication of superconducting motor components for future all-electric aircraft due to its lightweight, high elemental abundance, low cost, and good grain boundary connectivity, thus meeting the requirements for lightweight aircraft design. MgB2's superconducting critical transition temperature is 39 K, which falls within the liquid hydrogen temperature range, allowing it to operate stably in liquid hydrogen environments. This aligns perfectly with the development and utilization needs of hydrogen energy, making MgB2 a potential candidate for one of the most widely used and extensively applied superconducting materials in the future. The multinational collaborative SUPRAPOWER project has successfully developed a 10MW wind turbine prototype using MgB2, demonstrating its feasibility for practical application in superconducting motors. Superconducting wires and tapes are currently the best carriers for MgB2 applications, and the technology is relatively mature. Although MgB2 wires and tapes have demonstrated critical current densities exceeding commercialization thresholds, the rapid decrease in critical current density under medium-to-high field conditions still limits their application scope and cost-effectiveness. MgB2 exhibits strong crystallinity but lacks pinning centers, which is the fundamental reason for its rapid degradation in high-field current-carrying performance. Conventional sintering methods can induce the superconducting phase formation of MgB2 in superconducting wires and strips at specific temperatures in a vacuum or protective atmosphere for 1-3 hours. However, the limited heating and cooling rates hinder grain growth and densification, and the lack of pinning centers makes it difficult to solve the performance degradation problem of MgB2 wires and strips under high fields. Summary of the Invention
[0003] The technical problem to be solved by this invention is to provide a heat treatment method for Nb / Monel-based MgB2 multi-core wires, addressing the shortcomings of the prior art. This method, through a two-stage gradient heat treatment process, facilitates the formation of a high-density dislocation network during the MgB2 phase formation process in the MgB2 superconducting wire, increasing additional pinning centers. This significantly suppresses the rapid current decay under high fields in the MgB2 superconducting wire, thus solving the performance degradation problem under high fields in MgB2 superconducting wires.
[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a heat treatment method for Nb / Monel-based MgB2 multi-core wire, characterized in that the method includes the following steps: Step 1: Mix Mg powder and B powder and grind them thoroughly in an agate mortar until they are evenly mixed to obtain Mg and B blended powder; Step 2: Load the Mg and B blended powder from Step 1 into an acid-washed niobium tube and compact it. Seal the tube opening to prevent oxygen from seeping in, and obtain the powder. Step 3: Perform continuous multi-pass rotary forging on the powder from Step 2 to obtain a single-core wire; Step 4: Cut the single-core wire from Step 3 to length, add end caps to both ends, pickle it, and then bundle it with copper rods of the same diameter and length into a pickled Monel tube to obtain a tube body. Then, alternately spin-forge and draw the tube body to obtain a multi-core wire. Step 5: Wind the multi-core wire from Step 4 into a solenoid and wrap it in carbon foil. Then place it in a resistance heat treatment device. In an argon atmosphere, adjust the heating rate by controlling the current to heat the multi-core wire in the carbon foil to the first platform temperature and hold it there. Step 6: Heat the multi-core wire in the carbon foil after it has been kept at the first platform temperature in Step 5 to the second platform temperature for heat preservation, and then cool it down to room temperature. After taking it out, a MgB2 superconducting wire with densification, fine grains and a significant increase in pinned centers is obtained.
[0005] The above-mentioned heat treatment method for Nb / Monel-based MgB2 multi-core wire is characterized in that the mass ratio of Mg powder to B powder in step one is 0.9~1.5:1.
[0006] The above-mentioned heat treatment method for Nb / Monel-based MgB2 multi-core wire is characterized in that the time for thorough grinding in step one is 5 min to 30 min.
[0007] The above-mentioned heat treatment method for Nb / Monel-based MgB2 multi-core wire is characterized in that the processing rate of each pass of the rotary forging process in step three is 8%~20%.
[0008] The above-mentioned heat treatment method for Nb / Monel-based MgB2 multi-core wire is characterized in that the processing rate of each pass of the rotary forging and drawing in step four is 8%~20%.
[0009] The above-mentioned heat treatment method for Nb / Monel-based MgB2 multi-core wire is characterized in that the heating rate in step five is 200℃ / s~300℃ / s, the first platform temperature is 500℃~700℃, and the holding time is 5min~15min.
[0010] The above-mentioned heat treatment method for Nb / Monel-based MgB2 multi-core wire is characterized in that the heating rate in step six is 50℃ / s~150℃ / s, the second platform temperature is 700℃~900℃, and the holding time is 3min~10min.
[0011] The above-mentioned heat treatment method for Nb / Monel-based MgB2 multi-core wire is characterized in that the cooling rate in step six is 100℃ / min to 300℃ / min.
[0012] Compared with the prior art, the present invention has the following advantages: 1. The present invention employs a two-stage gradient heat treatment process, which is beneficial for the formation of a high-density dislocation network in the MgB2 superconducting wire during the MgB2 phase formation process, increases additional pinning centers, and significantly suppresses the rapid decay of high-field current in the MgB2 superconducting wire.
[0013] 2. The rapid heating and cooling process in the heat treatment process of the present invention helps to achieve grain refinement and densification, increase the number of grain boundaries and surface pinning force, and further suppress the rapid decay of the critical current density of MgB2 superconducting wire under medium and high field.
[0014] 3. The heat treatment process of the present invention is simple and easy to implement, which greatly reduces the overall preparation time of MgB2 superconducting wire and improves the preparation efficiency.
[0015] 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
[0016] Figure 1 This is a schematic diagram of the heat treatment process of the present invention.
[0017] Figure 2 This is a comparison chart of the critical currents of the MgB2 superconducting wires prepared in Example 1 and Comparative Example 1 under different magnetic field conditions. Detailed Implementation
[0018] Example 1 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Mix Mg powder and B powder in a mass ratio of 1.1:1 and grind them thoroughly in an agate mortar for 10 minutes until they are evenly mixed to obtain Mg and B blended powder. Step 2: Load the Mg and B blended powder from Step 1 into an acid-washed niobium tube and compact it. Seal the tube opening to prevent oxygen from seeping in, and obtain the powder. Step 3: Perform continuous multi-pass rotary forging on the powder from Step 2, with a processing rate of 8%~12% per pass, to obtain a single-core wire; Step 4: Cut the single-core wire from Step 3 to length, add end caps, pickle, and then bundle it with copper rods of the same diameter and length into a pickled Monel tube to obtain a tube body. Then, alternately spin forging and drawing the tube body, with a processing rate of 10% to 15% per pass, to obtain multi-core wire. Step 5: Wind the multi-core wire from Step 4 into a solenoid and wrap it in carbon foil. Then place it in a resistance heat treatment device. In an argon atmosphere, adjust the heating rate by controlling the current to raise the multi-core wire in the carbon foil to 600℃ at a rate of 250℃ / s and hold it at that temperature for 10 minutes. Step 6: Heat the multi-core wire in the carbon foil after holding at 600℃ in Step 5 to 800℃ at a rate of 100℃ / s and hold for 5 minutes. Then cool it down to room temperature at a rate of 100℃ / min. After taking it out, a MgB2 superconducting wire with densified grains and significantly increased pinning centers is obtained.
[0019] Comparative Example 1 The difference between this comparative example and Example 1 is that a conventional heat treatment process is used, namely, the multi-core wire in step four is wound into a solenoid and wrapped in carbon foil, and then directly heated to 650°C and held for 120 minutes.
[0020] Figure 2 This is a comparison chart of the critical currents of the MgB2 superconducting wires prepared in Example 1 and Comparative Example 1 under different magnetic field conditions. Figure 2 As can be seen, compared with conventional heat treatment, the MgB2 superconducting wire obtained by heat treatment through a two-stage gradient heat preservation process in Example 1 of the present invention exhibits higher values in the magnetic field range of 4T~10T, and has higher critical current values in medium and high fields, indicating that the densification and pinning force of the MgB2 superconducting wire have been significantly improved.
[0021] Example 2 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Mix Mg powder and B powder at a mass ratio of 0.9:1 and grind them thoroughly in an agate mortar for 5 minutes until they are evenly mixed to obtain Mg and B blended powder. Step 2: Load the Mg and B blended powder from Step 1 into an acid-washed niobium tube and compact it. Seal the tube opening to prevent oxygen from seeping in, and obtain the powder. Step 3: Perform continuous multi-pass rotary forging on the powder from Step 2, with a processing rate of 15%~20% per pass, to obtain a single-core wire; Step 4: Cut the single-core wire from Step 3 to length, add end caps, pickle, and then bundle it with copper rods of the same diameter and length into a pickled Monel tube to obtain a tube body. Then, alternately spin forging and drawing the tube body, with a processing rate of 15% to 20% per pass, to obtain multi-core wire. Step 5: Wind the multi-core wire from Step 4 into a solenoid and wrap it in carbon foil. Then place it in a resistance heat treatment device. In an argon atmosphere, adjust the heating rate by controlling the current to heat the multi-core wire in the carbon foil to 700℃ at a rate of 300℃ / s and hold it at that temperature for 5 minutes. Step 6: Heat the multi-core wire in the carbon foil after holding at 600℃ in Step 5 to 900℃ at a rate of 150℃ / s and hold for 3 minutes. Then cool it down to room temperature at a rate of 300℃ / min. After taking it out, a MgB2 superconducting wire with densification, grain refinement and significantly increased pinning centers is obtained.
[0022] Example 3 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Mix Mg powder and B powder at a mass ratio of 1.0:1 and grind them thoroughly in an agate mortar for 25 minutes until they are evenly mixed to obtain Mg and B blended powder. Step 2: Load the Mg and B blended powder from Step 1 into an acid-washed niobium tube and compact it. Seal the tube opening to prevent oxygen from seeping in, and obtain the powder. Step 3: Perform continuous multi-pass rotary forging on the powder from Step 2, with a processing rate of 12%~18% per pass, to obtain a single-core wire; Step 4: Cut the single-core wire from Step 3 to length, add end caps, pickle, and then bundle it with copper rods of the same diameter and length into a pickled Monel tube to obtain a tube body. Then, alternately spin forging and drawing the tube body, with a processing rate of 12% to 18% per pass, to obtain multi-core wire. Step 5: Wind the multi-core wire from Step 4 into a solenoid and wrap it in carbon foil. Then place it in a resistance heat treatment device. In an argon atmosphere, adjust the heating rate by controlling the current to heat the multi-core wire in the carbon foil to 500℃ at a rate of 200℃ / s and hold it at that temperature for 15 minutes. Step 6: Heat the multi-core wire in the carbon foil after holding at 500℃ in Step 5 to 700℃ at a rate of 100℃ / s and hold for 10 min. Then cool it down to room temperature at a rate of 250℃ / min. After taking it out, a MgB2 superconducting wire with densification, fine grains and a significant increase in pinned centers is obtained.
[0023] Example 4 like Figure 1As shown, this embodiment includes the following steps: Step 1: Mix Mg powder and B powder at a mass ratio of 1.5:1 and grind them thoroughly in an agate mortar for 30 minutes until they are evenly mixed to obtain Mg and B blended powder. Step 2: Load the Mg and B blended powder from Step 1 into an acid-washed niobium tube and compact it. Seal the tube opening to prevent oxygen from seeping in, and obtain the powder. Step 3: Perform continuous multi-pass rotary forging on the powder from Step 2, with a processing rate of 10%~15% per pass, to obtain a single-core wire; Step 4: Cut the single-core wire from Step 3 to length, add end caps, pickle, and then bundle it with copper rods of the same diameter and length into a pickled Monel tube to obtain a tube body. Then, alternately spin forging and drawing the tube body, with a processing rate of 12% to 18% per pass, to obtain multi-core wire. Step 5: Wind the multi-core wire from Step 4 into a solenoid and wrap it in carbon foil. Then place it in a resistance heat treatment device. In an argon atmosphere, adjust the heating rate by controlling the current to heat the multi-core wire in the carbon foil to 600℃ at a rate of 200℃ / s and hold it at that temperature for 15 minutes. Step 6: Heat the multi-core wire in the carbon foil after holding at 600℃ in Step 5 to 700℃ at a rate of 50℃ / s and hold for 10 minutes. Then cool it down to room temperature at a rate of 250℃ / min. After taking it out, a MgB2 superconducting wire with densification, grain refinement and significantly increased pinning centers is obtained.
[0024] Example 5 like Figure 1 As shown, this embodiment includes the following steps: Step 1: Mix Mg powder and B powder in a mass ratio of 1.3:1 and grind them thoroughly in an agate mortar for 20 minutes until they are evenly mixed to obtain Mg and B blended powder. Step 2: Load the Mg and B blended powder from Step 1 into an acid-washed niobium tube and compact it. Seal the tube opening to prevent oxygen from seeping in, and obtain the powder. Step 3: Perform continuous multi-pass rotary forging on the powder from Step 2, with a processing rate of 8% to 15% per pass, to obtain a single-core wire; Step 4: Cut the single-core wire from Step 3 to length, add end caps, pickle, and then bundle it with copper rods of the same diameter and length into a pickled Monel tube to obtain a tube body. Then, alternately spin forging and drawing the tube body, with a processing rate of 8% to 15% per pass, to obtain multi-core wire. Step 5: Wind the multi-core wire from Step 4 into a solenoid and wrap it in carbon foil. Then place it in a resistance heat treatment device. In an argon atmosphere, adjust the heating rate by controlling the current to heat the multi-core wire in the carbon foil to 500℃ at a rate of 200℃ / s and hold it at that temperature for 15 minutes. Step 6: Heat the multi-core wire in the carbon foil after holding at 500℃ in Step 5 to 900℃ at a rate of 150℃ / s and hold for 5 minutes. Then cool it down to room temperature at a rate of 300℃ / min. After taking it out, a MgB2 superconducting wire with densified grains and significantly increased pinning centers is obtained.
[0025] 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 heat treatment method for Nb / Monel-based MgB2 multi-core wire, characterized in that, The method includes the following steps: Step 1: Mix Mg powder and B powder and grind them thoroughly in an agate mortar until they are evenly mixed to obtain Mg and B blended powder; Step 2: Load the Mg and B blended powder from Step 1 into an acid-washed niobium tube and compact it. Seal the tube opening to prevent oxygen from seeping in, and obtain the powder. Step 3: Perform continuous multi-pass rotary forging on the powder from Step 2 to obtain a single-core wire; Step 4: Cut the single-core wire from Step 3 to length, add end caps to both ends, pickle it, and then bundle it with copper rods of the same diameter and length into a pickled Monel tube to obtain a tube body. Then, alternately spin-forge and draw the tube body to obtain a multi-core wire. Step 5: Wind the multi-core wire from Step 4 into a solenoid and wrap it in carbon foil. Then place it in a resistance heat treatment device. In an argon atmosphere, adjust the heating rate by controlling the current to heat the multi-core wire in the carbon foil to the first platform temperature and hold it there. Step 6: Heat the multi-core wire in the carbon foil after it has been kept at the first platform temperature in Step 5 to the second platform temperature for heat preservation, and then cool it down to room temperature. After taking it out, a MgB2 superconducting wire with densification, fine grains and a significant increase in pinned centers is obtained.
2. The heat treatment method for Nb / Monel-based MgB2 multi-core wire according to claim 1, characterized in that, The mass ratio of Mg powder to B powder in step one is 0.9~1.5:
1.
3. The heat treatment method for Nb / Monel-based MgB2 multi-core wire according to claim 1, characterized in that, The grinding time mentioned in step one is 5 to 30 minutes.
4. The heat treatment method for Nb / Monel-based MgB2 multi-core wire according to claim 1, characterized in that, The machining rate for each pass of the rotary forging process described in step three is 8% to 20%.
5. The heat treatment method for Nb / Monel-based MgB2 multi-core wire according to claim 1, characterized in that, The processing rate for each pass of rotary forging and drawing in step four is 8% to 20%.
6. The heat treatment method for Nb / Monel-based MgB2 multi-core wire according to claim 1, characterized in that, In step five, the heating rate is 200℃ / s~300℃ / s, the first platform temperature is 500℃~700℃, and the holding time is 5min~15min.
7. The heat treatment method for Nb / Monel-based MgB2 multi-core wire according to claim 1, characterized in that, The heating rate in step six is 50℃ / s to 150℃ / s, the temperature of the second platform is 700℃ to 900℃, and the holding time is 3 min to 10 min.
8. The heat treatment method for Nb / Monel-based MgB2 multi-core wire according to claim 1, characterized in that, The cooling rate described in step six is 100℃ / min to 300℃ / min.