A method for preparing high-performance MgB2 superconducting wires by rapid hot rolling and quenching

Abstract

This invention relates to a method for preparing high-performance MgB2 superconducting wire using rapid hot rolling and quenching. The method involves: 1) Passing the precursor wire between two opposing brushes until it contacts and locks into place between the twin rollers of the right-hand rolling mill; 2) Adjusting the roller movement valve to ensure the distance between the upper and lower rollers matches the target rolling thickness; 3) Checking and ensuring all circuit components are properly connected and adding coolant to the cryogenic Dewar; 4) Closing the device door and introducing protective gas; 5) Turning on the external power supply and inputting DC current into the device; 6) After the wire reaches the target temperature, immediately rolling it, and then quenching the rolled wire in the cryogenic Dewar; 7) After quenching, immediately turning off the power and gas, and removing the wire. This invention, through rapid hot rolling and quenching of MgB2 wire, can significantly improve the engineering current-carrying capacity of the wire and enhance its performance under high-field conditions, which is of great significance for promoting the practical development of MgB2 wire.

Description

Technical Field

[0001] This invention relates to the field of superconducting material preparation technology, specifically to a method for preparing high-performance MgB2 superconducting wires by rapid hot rolling and quenching. Background Technology

[0002] Since the discovery of superconductivity in MgB2 in 2001, its superconducting properties have been greatly improved over the past 20 years, and its current-carrying capacity under external fields has also been significantly enhanced. As a major application of MgB2 superconductors, MgB2 superconducting wires have received considerable attention in recent years. Due to its large coherence length and low anisotropy, it can be more easily fabricated into practical wires. Its relatively high critical transition temperature (…) T C =39K), which can greatly reduce application costs. In terms of practical applications, Columbus Superconductor in Italy has achieved mass production of kilometer-level MgB2 wire, and Hyper Tech in the United States has also produced 18-core high-performance, practical MgB2 wire. The Institute of Electrical Engineering of the Chinese Academy of Sciences and the Northwest Institute of Nonferrous Metals of China have also produced MgB2 wire with high performance.

[0003] It can be seen that through continuous research in recent years, the performance of MgB2 wire has been fundamentally improved, and it possesses great potential for practical application. However, due to defects in the current preparation process, there are still many problems in the preparation technology of MgB2 wire that urgently need to be solved. For example, the density of wire prepared by the in-situ method is poor, while the weak grain bonding phenomenon is serious in the wire prepared by the pre-situ method. At the same time, the lack of effective pinning centers leads to a rapid decrease in the performance of the wire under high fields. At present, the preparation of wire still mainly relies on heat treatment equipment such as tube furnaces and muffle furnaces. Although these equipment can meet the normal preparation requirements, they cannot overcome the problems caused by the in-situ and pre-situ methods mentioned above. These preparation problems will seriously affect the superconducting performance of MgB2 wire and hinder its further application development. Summary of the Invention

[0004] To effectively address the problems existing in the current MgB2 wire preparation technology, this invention proposes a method for preparing high-performance MgB2 superconducting wires by rapid hot rolling and quenching. This method enables the wire to be rolled simultaneously with rapid phase formation under the action of direct current and dual rollers. The rolled wire, which has not yet cooled, is immediately quenched in a low-temperature Dewar. The wire prepared by this method has strong current carrying capacity, good grain boundary connectivity, and high density, which greatly improves the superconducting performance and practical value of MgB2 wires.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing high-performance MgB2 superconducting wires by rapid hot rolling and quenching, comprising the following steps:

[0007] Step 1: Pass the MgB2 precursor wire through the middle of the two opposite positive electrode brushes until it just contacts and locks into place between the upper and lower rollers of the right rolling mill.

[0008] Step 2: Adjust the roller movement valve and rotate it at an appropriate angle until the distance between the upper and lower rollers is consistent with the target rolling thickness;

[0009] Step 3: Check and ensure that all circuit components are connected properly. Slowly add coolant from the upper edge of the cryogenic Dewar until the coolant submerges the lower part of the internal rollers of the cryogenic Dewar without overflowing from the cryogenic Dewar.

[0010] Step 4: Close the equipment hatch and introduce a flow of protective gas into the equipment;

[0011] Step 5: Turn on the external power supply, set an appropriate current value, and then turn on the current input switch to input DC current into the device to heat the MgB2 precursor wire.

[0012] Step 6: Observe the temperature of the wire and calculate the temperature rise rate using a high-precision thermocouple probe. After the wire has been heated to a certain temperature for a specified time, roll it immediately. The rolled wire is then passed through a pre-reserved opening into a low-temperature Dewar for low-temperature quenching treatment.

[0013] Step 7: After all the wire rods have been hot-rolled and quenched, immediately turn off the power and protective gas, and remove the quenched wire rods.

[0014] Furthermore, the MgB2 precursor wire used is a single-core or multi-core wire with Cu / Monel material as the outer sheath, with a diameter of 0.3~5mm, and the deformation range after rolling is 5%~75% of the original wire thickness or diameter.

[0015] Furthermore, the coolant is liquid nitrogen, liquid gallium, or a gallium-indium alloy.

[0016] Furthermore, the protective gas is argon, helium, nitrogen, or other high-purity inert gas.

[0017] Furthermore, the input DC current value ranges from 10 to 500A.

[0018] Furthermore, the wire speed during rolling is 5~150mm / s.

[0019] Furthermore, the wire rolling temperature is 100~1000°C, and the quenching temperature is 25~-196°C.

[0020] By adopting the above technical solution, the beneficial effects of the present invention are as follows:

[0021] (1) This invention prepares MgB2 superconducting wires by a rapid hot rolling and quenching method, which enables the wires to form phases in a very short time. After quenching, the further growth of grains is greatly prevented, and the total area of ​​grain boundaries is effectively increased, thereby enhancing the magnetic flux pinning force of the wires. At the same time, the grains are rolled during the phase formation process, which effectively reduces the development space, destroys the pore structure, and effectively improves the density of the wires.

[0022] (2) This invention prepares MgB2 superconducting wires by a rapid hot rolling and quenching method. Since the wires are immediately biaxially rolled at high temperatures, the phenomenon of core wire breakage caused by stress concentration is greatly avoided, increasing the wire yield. At the same time, the grains are still growing during the rolling process, which can ensure the integrity of most grains. The small amount of lattice distortion and dislocation defects caused by rolling can form additional pinning centers, further improving the current carrying capacity of MgB2 superconducting wires. Since different quenching coolants can control the cooling rate, the grain size can be further controlled.

[0023] (3) The present invention prepares MgB2 superconducting wires by rapid hot rolling and quenching, which requires almost no chemical reagents to process the wires and is environmentally friendly. This method can precisely control the rolling thickness, rolling temperature and wire temperature rise rate, thereby producing MgB2 superconducting wires with high precision, stable performance and meeting the conditions for practical application. Attached Figure Description

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0025] Figure 1 This is a 5000x scanning electron microscope image of Embodiment 1 of the present invention;

[0026] Figure 2 This is a 20,000x scanning electron microscope image of Embodiment 1 of the present invention;

[0027] Figure 3 This is a 5000x scanning electron microscope image of Embodiment 2 of the present invention;

[0028] Figure 4 This is a 20,000x scanning electron microscope image of Embodiment 2 of the present invention;

[0029] Figure 5 This is a 5000x scanning electron microscope image of Embodiment 3 of the present invention;

[0030] Figure 6 This is a 20,000x scanning electron microscope image of Embodiment 3 of the present invention;

[0031] Figure 7 These are graphs showing the relationship between critical current density and magnetic field strength at 10K and 20K for Embodiments 1, 2, and 3 of the present invention.

[0032] Figure 8 This is a schematic diagram of the device involved in the present invention. Detailed Implementation

[0033] like Figure 8 As shown, this invention discloses a method for preparing high-performance MgB2 superconducting wires by rapid hot rolling and quenching. The steps of this method are as follows:

[0034] Step 1: Pass the MgB2 precursor wire 1 through the middle of the two opposite positive electrode brushes 2 until it just makes contact with and locks into place the upper and lower rollers 3 of the right rolling mill (which are in contact with the negative electrode brush 9);

[0035] Step 2: Adjust the roller movement valve 4 and rotate it at an appropriate angle until the distance between the upper and lower rollers 3 is consistent with the target rolling thickness;

[0036] Step 3: Check and ensure that all circuit components are connected properly. Slowly add coolant from the upper edge of the cryogenic Dewar 5 until the coolant submerges the lower part of the internal roller 6 of the cryogenic Dewar 5 and does not overflow from the cryogenic Dewar 5.

[0037] Step 4: Close the equipment hatch and introduce a flow of protective gas into the equipment;

[0038] Step 5: Turn on the external power supply 7, set an appropriate current value, and then turn on the current input switch to input DC current into the device to heat the MgB2 precursor wire 1.

[0039] Step 6: Observe the temperature of the wire and calculate the temperature rise rate using a high-precision thermocouple probe. After the wire has been heated to a certain temperature for a specified time, roll it immediately. The rolled wire is then passed through a pre-reserved opening into a low-temperature Dewar for low-temperature quenching treatment.

[0040] Step 7: After all the wire rods have been hot-rolled and quenched, immediately turn off the power and protective gas, and take out the quenched wire rods 8.

[0041] The MgB2 precursor wire used is a single-core or multi-core wire with Cu / Monel material as the outer sheath, with a diameter of 0.3~5mm, and the deformation range after rolling is 5%~75% of the original wire thickness or diameter.

[0042] The coolant can be liquid nitrogen, liquid gallium metal, or gallium-indium alloy, etc.

[0043] The protective gas can be argon, helium, nitrogen, or other high-purity inert gases.

[0044] The input DC current of the external power supply 7 ranges from 10 to 500A. The wire speed during rolling is 5 to 150 mm / s. The wire rolling temperature is 100 to 1000°C, and the quenching temperature is 25 to -196°C. Example 1

[0045] Step 1: Pass the 6+1 core MgB2 precursor wire with a diameter of 1.4mm through the middle of the two opposite positive electrode high carbon brushes until it just contacts and locks into place between the upper and lower rollers of the right rolling mill.

[0046] Step 2: Adjust the roller movement valve, rotate it at an appropriate angle of about 15°~20° until the distance between the upper and lower rollers is consistent with the target rolling thickness of 0.6mm.

[0047] Step 3: Check and ensure that all circuit components are connected properly. Slowly add liquid nitrogen from the upper edge of the cryogenic Dewar until the coolant submerges the lower part of the internal rollers of the cryogenic Dewar without overflowing from the cryogenic Dewar.

[0048] Step 4: Close the device door and introduce flowing argon gas into the device as a protective gas.

[0049] Step 5: Turn on the external power supply and set the current value to 90A. Then turn on the current input switch to input DC current into the device to heat the MgB2 wire for 60 seconds.

[0050] Step 6: Observe the temperature of the wire and calculate the temperature rise rate using a high-precision thermocouple probe. After the wire is rapidly heated for 60 seconds to reach approximately 170°C, it is immediately rolled. The wire speed during rolling is 10 mm / s. After rolling, the wire enters the low-temperature Dewar through a pre-reserved opening and is subjected to low-temperature quenching treatment with liquid nitrogen.

[0051] Step 7: After all the wire rods have been hot-rolled and quenched, immediately turn off the power and protective gas, and remove the quenched wire rods.

[0052] Figure 1 , 2 These are scanning electron microscope (SEM) images of the MgB2 superconducting wire prepared in Example 1 at 5000x and 20000x magnification. The images show an improved density and a significant reduction in porosity. However, the grain development is not yet complete, mainly due to the low current and low heating temperature, resulting in lower grain development and poor grain uniformity. However, from... Figure 7 The critical current density and external magnetic field strength diagrams of the MgB2 superconducting wire prepared in Example 1 at 10K and 20K show that superconductivity has already appeared at this low current. Example 2

[0053] Step 1: Pass the 6+1 core MgB2 precursor wire with a diameter of 1.4mm through the middle of the two opposite positive electrode high carbon brushes until it just contacts and locks into place between the upper and lower rollers of the right rolling mill.

[0054] Step 2: Adjust the roller movement valve, rotate it at an appropriate angle of about 15°~20° until the distance between the upper and lower rollers is consistent with the target rolling thickness of 0.6mm.

[0055] Step 3: Check and ensure that all circuit components are connected properly. Slowly add liquid nitrogen from the upper edge of the cryogenic Dewar until the coolant submerges the lower part of the internal rollers of the cryogenic Dewar without overflowing from the cryogenic Dewar.

[0056] Step 4: Close the device door and introduce flowing argon gas into the device as a protective gas.

[0057] Step 5: Turn on the external power supply and set the current value to 100A. Then turn on the current input switch to input DC current into the device to heat the MgB2 wire for 60 seconds.

[0058] Step 6: Observe the temperature of the wire and calculate the temperature rise rate using a high-precision thermocouple probe. After the wire is rapidly heated for 60 seconds to reach about 200°C, it is immediately rolled. The wire speed during rolling is 10 mm / s. After rolling, the wire enters the liquid nitrogen in the low-temperature Dewar through the reserved opening for low-temperature quenching treatment.

[0059] Step 7: After all the wire rods have been hot-rolled and quenched, immediately turn off the power and protective gas, and remove the quenched wire rods.

[0060] Figure 3 , 4 The images shown are scanning electron microscope (SEM) images of the MgB2 superconducting wire prepared in Example 2 at 5000x and 20000x magnification. The wire exhibits good density; although some cracks are present, there are no obvious pores. The grain development is more complete compared to Example 1; however, due to the limitation of the current value, the temperature remains relatively low, and therefore the grains are not fully developed. Figure 7 The graphs show the critical current density and external magnetic field strength of the MgB2 superconducting wire prepared in Example 2 at 10K and 20K. The graphs show that its current-carrying capacity is further enhanced with increasing temperature. At 10K, its critical current density under the external field is... J C It reached 6.8×10 4 A / cm 2 Its irreversible field is 5.45T. At 20K, its critical current density under its own field is... J C It reached 2.86×10 4A / cm 2 Its irreversible field is 3.25T. This indicates that at a current of 100A, the superconducting performance of the wire has been significantly improved in just 60 seconds. Example 3

[0061] Step 1: Pass the 6+1 core MgB2 precursor wire with a diameter of 1.4mm through the middle of the two opposite positive electrode high carbon brushes until it just contacts and locks into place between the upper and lower rollers of the right rolling mill.

[0062] Step 2: Adjust the roller movement valve, rotate it at an appropriate angle of about 15°~20° until the distance between the upper and lower rollers is consistent with the target rolling thickness of 0.6mm.

[0063] Step 3: Check and ensure that all circuit components are connected properly. Slowly add liquid nitrogen from the upper edge of the cryogenic Dewar until the coolant submerges the lower part of the internal rollers of the cryogenic Dewar without overflowing from the cryogenic Dewar.

[0064] Step 4: Close the device door and introduce flowing argon gas into the device as a protective gas.

[0065] Step 5: Turn on the external power supply and set the current value to 100A. Then turn on the current input switch to input DC current into the device to heat the MgB2 wire for 90 seconds.

[0066] Step 6: Observe the temperature of the wire and calculate the temperature rise rate using a high-precision thermocouple probe. After the wire is rapidly heated for 90 seconds to reach approximately 220°C, it is immediately rolled. The wire speed during rolling is 10 mm / s. After rolling, the wire enters the low-temperature Dewar through a pre-reserved opening for cryogenic quenching with liquid nitrogen.

[0067] Step 7: After all the wire rods have been hot-rolled and quenched, immediately turn off the power and protective gas, and remove the quenched wire rods.

[0068] Figure 5 , 6 These are scanning electron microscope images of the MgB2 superconducting wire prepared in Example 3 at 5000x and 20000x magnification. It can be seen that the density of the MgB2 superconducting wire in this example is further improved and the grains are larger, but the grains are still incomplete. At the same time, there are many undeveloped grains in the image. Figure 7 The graphs show the critical current density and external magnetic field strength of the MgB2 superconducting wire prepared in Example 3 at 10K and 20K. It can be seen that its low-field current carrying capacity is further improved; at 10K, its self-field critical current density... J C It reached 7.25×10 4 A / cm 2At 20K, its critical current density under self-field is... J C It reached 3.12×10 4 A / cm 2 .

[0069] The specific embodiments of the present invention have been described above. However, those skilled in the art should understand that this is merely an example. Those skilled in the art can make various changes or modifications to this embodiment without departing from the principles and essence of the present invention, but all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing high-performance MgB2 superconducting wires by rapid hot rolling and quenching, characterized in that: The steps of this method are as follows: Step 1: Pass the MgB2 precursor wire through the middle of the two opposite positive electrode brushes until it just contacts and locks into place between the upper and lower rollers of the right rolling mill. Step 2: Adjust the roller movement valve and rotate it at an appropriate angle until the distance between the upper and lower rollers is consistent with the target rolling thickness; Step 3: Check and ensure that all circuit components are connected properly. Slowly add coolant from the upper edge of the cryogenic Dewar until the coolant submerges the lower part of the internal rollers of the cryogenic Dewar without overflowing from the cryogenic Dewar. Step 4: Close the equipment hatch and introduce a flow of protective gas into the equipment; Step 5: Turn on the external power supply, set an appropriate current value, and then turn on the current input switch to input DC current into the device to heat the MgB2 precursor wire. Step 6: Observe the temperature of the wire and calculate the temperature rise rate through a high-precision thermocouple probe. After the wire has been heated to a certain temperature for a certain time, roll it immediately. The rolled wire enters the low-temperature Dewar through the reserved opening for low-temperature quenching treatment. Step 7: After all the wire rods have been hot-rolled and quenched, immediately turn off the power and protective gas, and remove the quenched wire rods.

2. The method for preparing high-performance MgB2 superconducting wire by rapid hot rolling and quenching according to claim 1, characterized in that: The MgB2 precursor wire used is a single-core or multi-core wire with Cu / Monel material as the outer sheath, with a diameter of 0.3~5mm, and the deformation range after rolling is 5%~75% of the original wire thickness or diameter.

3. The method for preparing high-performance MgB2 superconducting wire by rapid hot rolling and quenching according to claim 1, characterized in that: The coolant is liquid nitrogen, liquid gallium, or a gallium-indium alloy.

4. The method for preparing high-performance MgB2 superconducting wire by rapid hot rolling and quenching according to claim 1, characterized in that: The protective gas is argon, helium, nitrogen, or other high-purity inert gas.

5. The method for preparing high-performance MgB2 superconducting wire by rapid hot rolling and quenching according to claim 1, characterized in that: The input DC current range is 10~500A.

6. The method for preparing high-performance MgB2 superconducting wire by rapid hot rolling and quenching according to claim 1, characterized in that: The wire speed during rolling is 5~150mm / s.

7. The method for preparing high-performance MgB2 superconducting wire by rapid hot rolling and quenching according to claim 1, characterized in that: The rolling temperature of the wire rod is 100~1000°C, and the quenching temperature is 25~-196°C.

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