A method for preparing MgB2 superconducting wire using a thousand-core pre-position method

Abstract

The present invention belongs to the technical field of superconducting material processing engineering, and specifically relates to a method for preparing a thousand-core pre-positioned MgB2 superconducting wire. The present invention discloses a method for preparing a multi-core MgB2 superconducting wire using a drilling process. The method uses pure iron ingots to directly prepare multi-core subcomponents by drilling. Pure iron serves as both a barrier layer and a stabilizer, avoiding the problem of core wire rupture and the introduction of impurities during the cold working process of the multi-core wire using the secondary assembly method. In addition, the method induces recrystallization of the original MgB2 powder particles by prefabricating (MgB2‑Mg+B) precursor powder, repairing and compensating for the defects of MgB2 grain microcracks and poor intercrystalline connectivity caused by continuous cold working. The MgB2 superconducting wire prepared by this method has been tested and its critical current density and long-line uniformity have been greatly improved, and it has broad market application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting material processing engineering, and in particular relates to a method for preparing a MgB2 superconducting wire by a thousand-core pre-position method. Background Art

[0002] In the field of superconducting materials, MgB2 superconducting wire and tape, thanks to its relatively low cost, moderate critical temperature, and simple preparation process, demonstrates enormous potential for application in a wide range of fields, including power transmission, magnetic levitation technology, and magnetic resonance imaging (MRI). The powder-in-tube (PIT) method for preparing MgB2 superconducting wire and tape has become the mainstream method for practical MgB2 superconducting wire and tape production due to its relatively mature process and ease of large-scale production.

[0003] At present, in the practical production process of MgB2 superconducting wire strip using the ex-situ PIT method, commercial MgB2 powder is usually filled into a pure nickel tube, followed by a series of plastic processing steps such as swaging and rolling to give the wire strip a preliminary shape. Finally, a phase-forming heat treatment is performed to promote the formation of the MgB2 superconducting phase, thereby obtaining the MgB2 superconducting wire strip.

[0004] However, MgB2 material itself exhibits ceramic-like hardness and brittleness, belonging to the ionic compound category. Commercial MgB2 powders often exhibit numerous factors that hinder the improvement of superconducting performance. For one thing, the powder often contains MgO impurities, which are difficult to completely remove during subsequent processing and heat treatment and remain as a non-superconducting phase in the superconducting wire tape. Furthermore, the powder also contains large MgB2 crystals. After undergoing multiple continuous plastic processing passes, the MgB2 grains in the core wire are prone to numerous microcracks due to the hardness and brittleness of MgB2, as well as the presence of impurities and large grains. These impurities, large grains, and localized microcracks severely impair the good connectivity between the MgB2 superconducting phase grains. These coarse grains, reduced number of grain boundaries, and weak grain connectivity significantly reduce the current-carrying capacity of the superconducting wire tape, thereby impacting its performance in various applications.

[0005] Furthermore, a key issue commonly encountered with the pre-powder tube method is that the tube serving as the barrier layer faces significant challenges during processing. As the cumulative processing volume increases, the barrier layer tube will experience significant work hardening, gradually degrading its mechanical properties and ultimately leading to rupture. This barrier layer rupture can trigger a series of serious consequences. The superconducting core reacts with the external matrix material, generating compound impurities and forming an intermediate reaction layer between the superconducting core and the matrix. The presence of this reaction layer has two negative effects: first, it reduces the effective cross-sectional area of ​​the superconducting wire, reducing the cross-sectional area capable of carrying current and directly limiting the current-carrying capacity of the superconducting wire strip; second, it exacerbates the thermal stability issues of the MgB2 superconducting wire. Thermal stability is crucial in the operation of superconducting materials. The presence of a reaction layer interferes with the transfer and distribution of heat, leading to localized temperature anomalies, which in turn affects the stability of the superconducting performance and ultimately reduces the critical current density of the superconducting wire strip.

[0006] Because MgB2 has a hardness of up to 2000 MPa, if the barrier layer deforms unevenly during processing, it is easily punctured by powder particles in weak areas. This is particularly true in multi-core wires, where the structure is more complex and the stress distribution on the barrier layer is uneven, making localized weak areas more likely to occur. This barrier layer vulnerability has become a bottleneck limiting the ability to achieve multi-core production and ensure long-line uniformity using the pre-powder tube method. Multi-core production is an important path to achieving high current carrying capacity, while long-line uniformity is key to ensuring the stable performance of superconducting wires in practical applications. These issues not only hinder further improvements in the performance of MgB2 superconducting wires, but also severely impact their promotion and application in AC applications and those with stringent loss requirements. Therefore, resolving these issues and improving the performance and quality of MgB2 superconducting wire tapes has become a key technical challenge that urgently needs to be addressed in this field. Summary of the Invention

[0007] The present invention aims to solve the problems of poor grain connectivity, difficult processing of multi-core wires and poor uniformity of long wires in MgB2 superconducting wires produced by the pre-powder tube method, and establishes a method for preparing MgB2 superconducting wires produced by the pre-powder tube method.

[0008] In order to fully and unambiguously understand the technical solution of the present invention, it is necessary to supplement that, in the present invention, the (Mg+B) spherical powder refers to: Mg powder, B powder and a carbon-based binder are mixed and pelletized to obtain the (Mg+B) spherical mixed powder; the (MgB2-Mg+B) precursor powder refers to: (Mg+B) spherical powder is added to MgB2 powder and mixed evenly again to obtain the (MgB2-Mg+B) mixed powder.

[0009] In one aspect, the present invention provides a method for preparing a MgB2 superconducting wire by a thousand-core pre-position method, comprising the following steps:

[0010] Step 1: Mix Mg powder, B powder and carbon-based binder and form balls to obtain (Mg+B) spherical powder; then add the (Mg+B) spherical powder into MgB2 powder and mix them evenly to obtain (MgB2-Mg+B) precursor powder;

[0011] Step 2: drilling powder filling holes of the same specifications on the electromagnetic pure iron ingot to obtain a porous electromagnetic pure iron ingot, wherein one end of the powder filling hole is closed, and the inner wall of the powder filling hole is smooth and free of inclusions, and then degreasing, cleaning, and drying the porous electromagnetic pure iron ingot to obtain a treated porous electromagnetic pure iron ingot;

[0012] Step 3: Weigh the (MgB2-Mg+B) precursor powder obtained in step 1, and fill it into each powder filling hole on the treated porous electromagnetic pure iron ingot obtained in step 2. After filling, close the ports of each powder filling hole, install a sealing cover, and vacuum weld to obtain a multi-core MgB2 primary composite ingot;

[0013] Step 4: Processing the multi-core MgB2 primary composite ingot obtained in step 3 to the required specifications by extrusion and cold drawing, and then cutting and straightening to obtain a multi-core MgB2 subcomponent;

[0014] Step 5: After cleaning and drying the multi-core MgB2 subcomponents obtained in step 4, they are densely packed into an oxygen-free copper sheath by a tube-through method to obtain a multi-core MgB2 secondary composite ingot, and the multi-core MgB2 secondary composite ingot is processed to the final specification by a cold drawing method to obtain a thousand-core grade MgB2 composite wire;

[0015] Step 6: subjecting the MgB2 composite wire obtained in step 5 to high-temperature phase-forming heat treatment to obtain a thousand-core-level MgB2 superconducting wire.

[0016] Furthermore, in the preparation method, the B powder in step 1 is an amorphous boron powder with an average particle size of 50 nm and a purity of 99.9%; and the Mg powder is a spherical magnesium powder with an average particle size of 400 nm and a purity of 99.9%.

[0017] Furthermore, in the preparation method, the Mg powder and the B powder are mixed at a mass ratio of 1.1-1.4:2.

[0018] Furthermore, in the preparation method, the amount of the carbon-based binder in step one is 3%-5% of the total mass of the Mg powder and the B powder; the average particle size of the (Mg+B) spherical powder is 500 nm; the average particle size of the MgB2 powder is 500 nm and the purity is 99.9%, and the doping amount of the (Mg+B) spherical powder is 5%-15% of the mass of the MgB2 powder.

[0019] Furthermore, in the preparation method, the outer diameter of the electromagnetic pure iron ingot described in step 2 is 100 mm~200 mm, and the length is 800 mm-1000 mm; the number of the powder filling holes is ≥60 and is evenly distributed, and the non-opening end is 10 mm-15 mm away from the ingot tail; the degreasing uses a metal degreasing agent, and the cleaning uses dilute hydrochloric acid with a volume ratio of 10%-15%.

[0020] Furthermore, in the preparation method, the mass of the (MgB2-Mg+B) precursor powder filled in the powder filling hole in step 3 is the same, and the filling density is 1.0 g / cm 3 -1.5g / cm 3 The powder filling hole ports are sealed with cone-shaped plugs.

[0021] Furthermore, in the preparation method, the final extrusion size of the multi-core MgB2 composite ingot described in step four is less than Ф60mm, the extrusion temperature is 480℃-550℃, and the time is 3h-5h; the pass processing amount in the cold drawing process is 15%-20%, and the specification of the multi-core MgB2 subcomponent is Ф5.0mm-Ф8.0mm.

[0022] Furthermore, in the preparation method, the final specification in step five is Ф0.5mm-Ф1.0mm.

[0023] Furthermore, in the preparation method, the temperature of the high-temperature phase-forming heat treatment in step 6 is 800° C. to 950° C., and the treatment time is 6 h to 10 h.

[0024] On the other hand, a MgB2 superconducting wire prepared by the preparation method of the present invention is also provided.

[0025] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0026] (1) The present invention uniformly coats extremely small particles of B powder on the surface of spherical Mg powder through ball forming, and then mixes it into MgB2 powder with a particle size equivalent to that of the spherical Mg powder. The (Mg+B) spherical powder acts as a dopant and will first generate new MgB2 grains due to its high reaction activity during the high-temperature phase-forming heat treatment process to induce the recrystallization process of the original MgB2 powder particles. At the same time, it makes up for the defects of microcracks and poor intercrystalline connectivity of MgB2 grains caused by continuous cold working, thereby improving the technical problem of poor grain connectivity in the process of preparing MgB2 superconducting wires by the prior art method, and improving the critical current density of MgB2 superconducting wires. The critical current density of MgB2 superconducting wires prepared by the method provided by the present invention is much higher than that of the prior art.

[0027] (2) The present invention uses low-cost pure iron ingots to drill holes to directly prepare multi-core subcomponents. Pure iron acts as both a barrier layer and a stabilizer. Extrusion at large specifications is beneficial to the densification of the powder and the uniform plastic deformation of the metal matrix, avoiding the problem of core wire rupture during cold working of the multi-core wire produced by the secondary assembly method, which leads to the introduction of magnesium-copper compound impurities. This is beneficial to the preparation of phase-pure multi-core wires and solves the core wire breakage problem that is common in conventional PIT multi-core wires.

[0028] Through the above-mentioned synergistic effect, the critical current density and long-line uniformity of the MgB2 superconducting wire prepared by the preparation method provided by the present invention are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic cross-sectional view of a porous electromagnetic pure iron ingot for MgB2 powder filling obtained by drilling in Example 1. 1 is a 61-core MgB2 primary composite ingot; 2 is a powder filling hole; and 3 is a porous electromagnetic pure iron ingot.

[0030] Figure 2 This is a schematic cross-sectional view of a 1098-core MgB2 secondary composite ingot assembled using the tube-through assembly method in Example 1. Reference numeral 4 represents a 1098-core MgB2 secondary composite ingot; reference numeral 5 represents a 61-core MgB2 subcomponent; reference numeral 6 represents an oxygen-free copper core rod; and reference numeral 7 represents an oxygen-free copper tube. DETAILED DESCRIPTION

[0031] The technical solutions of the present invention are described below with reference to the following embodiments; however, the present invention is not limited to the following embodiments.

[0032] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0033] The experimental methods and detection methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0034] The electromagnetic pure iron grade is DT4, and its composition and electromagnetic properties meet the national standard GB / T6983-2022.

[0035] Example 1

[0036] This embodiment adopts the method for preparing MgB2 superconducting wire by the thousand-core first-place method provided by the present invention to prepare 1098-core MgB2 superconducting wire.

[0037] The preparation method of this embodiment comprises the following steps:

[0038] Step 1. First, spherical Mg powder with an average particle size of 400 nm and a purity of 99.9%, amorphous boron powder B powder with an average particle size of 50 nm and a purity of 99.9%, and carbon-based binder ethylene glycol accounting for 3% of the total mass of the Mg powder and B powder are uniformly mixed and granulated in a molar ratio of 1.4:2 to obtain (Mg+B) spherical powder; then, the obtained (Mg+B) spherical powder is added to MgB2 powder with an average particle size of 500 nm and a purity of 99.9% in an amount of 15% of the mass of the MgB2 powder, and the mixture is uniformly mixed to obtain (MgB2-Mg+B) precursor powder;

[0039] Step 2: Drill 61 powder filling holes of the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of 100mm, a length of 800mm, and a purity of 99.99%. The holes are arranged in layers, with the outermost hole 7mm away from the edge of the pure iron ingot, a hole diameter of 7.0mm, a depth of 785mm, and a closed end of the hole 15mm away from the ingot tail. The inner wall of the hole is smooth and free of inclusions. The obtained porous electromagnetic pure iron ingot is then ultrasonically degreased with a metal cleaning agent, cleaned with dilute hydrochloric acid at a volume ratio of 10%-15%, and dried before being used to fill the precursor powder.

[0040] Step 3. Weigh the (MgB2-Mg+B) precursor powder obtained in step 1 and fill it into each filling hole on the electromagnetic pure iron ingot obtained in step 2. After filling, use a 15 mm long frustum-shaped pure iron plug to seal the port of each hole. Then, install a pure iron sealing cover and perform vacuum electron beam sealing welding between the sealing cover and the iron ingot to obtain a 61-core MgB2 primary composite ingot.

[0041] Step 4: The 61-core MgB2 primary composite ingot obtained in step 3 is extruded in a vacuum heat treatment furnace at an extrusion temperature of 550°C and a time of 4 hours. After being extruded to a size of Ф60mm, it is processed by a multi-pass cold drawing method with a processing amount of 15% to Ф5.00mm. Then, the head and tail cavity areas and uneven areas are removed, and the 61-core MgB2 subcomponent is obtained after cutting and straightening.

[0042] Step 5: Ultrasonic degreasing the 61-core MgB2 subcomponent described in Step 4 with a metal cleaner, followed by cleaning and drying with 15% by volume dilute hydrochloric acid. Then, using the tube-through method, a 5.00 mm diameter oxygen-free copper core rod and 18 5.00 mm diameter 61-core MgB2 subcomponents are densely packed into an oxygen-free copper sheath, with the oxygen-free copper rod positioned at the center, to produce a secondary MgB2 composite ingot. This secondary composite ingot is then cold-drawn in multiple passes with a 15% processing allowance to a final specification of 1.00 mm diameter, yielding a 1098-core MgB2 composite wire.

[0043] Step 6: Place the MgB2 composite wire obtained in step 5 in a vacuum heat treatment furnace (vacuum degree <1.0×10 -2Pa started heating) and then subjected to high temperature phase forming heat treatment at 900℃ for 10h to obtain thousand-core grade MgB2 superconducting wire.

[0044] After the above-mentioned MgB2 superconducting wire was heat-treated and the inhomogeneous area was removed, a sample was taken to test the current carrying performance. The critical electric density fluidity Jc at 4.2K and 2T was 4.348×10 3 A / mm 2 Compared with the current practical ex-situ PIT MgB2 superconducting wire tape, the Jc is 2.1×10 3 A / mm 2 In addition, to characterize the uniformity of long-line performance, samples were taken at different locations on the wire and their Jc values ​​at 4.2K and 2T were measured, as shown in Table 1.

[0045] Table 1 Test results of uniformity of MgB2 long wire prepared in Example 1

[0046]

[0047] As can be seen from Table 1, the long MgB2 wires prepared in this embodiment have good uniformity.

[0048] The cross section of the porous electromagnetic pure iron ingot for MgB2 powder tube filling obtained by drilling in this embodiment is as follows: Figure 1 As shown; the cross section of the 1098 core MgB2 secondary composite ingot assembled by the tube method is as follows Figure 2 shown.

[0049] Example 2

[0050] This embodiment adopts the method for preparing MgB2 superconducting wire by the thousand-core first-place method provided by the present invention to prepare 1098-core MgB2 superconducting wire.

[0051] The preparation method of this embodiment comprises the following steps:

[0052] Step 1. First, spherical Mg powder with an average particle size of 400nm and a purity of 99.9%, amorphous boron powder B powder with an average particle size of 50nm and a purity of 99.9%, and carbon-based binder ethylene glycol accounting for 5% of the total mass of Mg powder and B powder are uniformly mixed and granulated in a molar ratio of 1.2:2 to obtain (Mg+B) spherical powder; then, the obtained (Mg+B) spherical powder is added to MgB2 powder with an average particle size of 500nm and a purity of 99.9% at a doping amount of 15% of the mass of MgB2 powder, and the mixture is uniformly mixed to obtain (MgB2-Mg+B) precursor powder;

[0053] Step 2: Drill 61 powder filling holes of the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of 142mm, a length of 900mm, and a purity of 99.99%. The holes are arranged in layers, with the outermost hole 10mm away from the edge of the pure iron ingot, a hole diameter of 10mm, a depth of 785mm, and a closed end of the hole 12mm away from the ingot tail. The inner wall of the hole is smooth and free of inclusions. The obtained porous electromagnetic pure iron ingot is then ultrasonically degreased with a metal cleaner, cleaned with 10% by volume dilute hydrochloric acid, and dried before being used to fill the precursor powder.

[0054] Step 3. Weigh the (MgB2-Mg+B) precursor powder obtained in step 1 and fill it into each filling hole on the electromagnetic pure iron ingot obtained in step 2. After filling, use a 15 mm long frustum-shaped pure iron plug to seal the port of each hole. Then, install a pure iron sealing cover and perform vacuum electron beam sealing welding between the sealing cover and the iron ingot to obtain a 61-core MgB2 primary composite ingot.

[0055] Step 4: The 61-core MgB2 primary composite ingot obtained in step 3 is extruded in a vacuum heat treatment furnace at an extrusion temperature of 480°C and a time of 5 hours. After being extruded to a size of Ф60mm, it is processed by a multi-pass cold drawing method with an 18% processing amount to Ф7.00mm. Then, the head and tail cavity areas and uneven areas are removed, and the 61-core MgB2 subcomponent is obtained after cutting and straightening.

[0056] Step 5: Ultrasonic degreasing of the 61-core MgB2 subcomponent described in Step 4 is performed using a metal cleaning agent. The subcomponent is then cleaned and dried with 10% by volume dilute hydrochloric acid. A 7.00mm diameter oxygen-free copper core rod and 18 7.00mm diameter 61-core MgB2 subcomponents are then densely packed into an oxygen-free copper sheath using a tube-through method, with the oxygen-free copper rod positioned at the center. The secondary composite ingot is then processed to a 0.50mm diameter diameter using a multi-pass cold drawing process with a 15% processing allowance. During this process, low-temperature annealing is performed when the Vickers hardness of the Fe matrix is ​​≥350HV. The annealing temperature is 500°C, ultimately yielding a 1098-core MgB2 composite wire.

[0057] Step 6: Place the MgB2 composite wire obtained in step 5 in a vacuum heat treatment furnace (vacuum degree <1.0×10 -2 Pa (start heating) high temperature phase forming heat treatment at 950℃ for 6h to obtain thousand-core grade MgB2 superconducting wire.

[0058] After the above-mentioned MgB2 superconducting wire was heat-treated and the inhomogeneous area was removed, a sample was taken to test the current carrying performance. The critical electric density fluidity Jc at 4.2K and 2T was 3.863×10 3 A / mm 2 Compared with the current practical ex-situ PIT MgB2 superconducting wire tape, the Jc is 2.1×103 A / mm 2 In addition, to characterize the uniformity of long-line performance, samples were taken at different locations on the wire and their Jc values ​​at 4.2K and 2T were measured, as shown in Table 2.

[0059] Table 2 Uniformity test results of MgB2 long wire prepared in Example 2

[0060]

[0061] As can be seen from Table 2, the long MgB2 wires prepared in this embodiment have good uniformity.

[0062] Example 3

[0063] This embodiment adopts the method for preparing MgB2 superconducting wire by the thousand-core first-place method provided by the present invention to prepare 1098-core MgB2 superconducting wire.

[0064] The preparation method of this embodiment comprises the following steps:

[0065] Step 1. First, spherical Mg powder with an average particle size of 400nm and a purity of 99.9%, amorphous boron powder B powder with an average particle size of 50nm and a purity of 99.9%, and carbon-based binder ethylene glycol accounting for 4% of the total mass of the Mg powder and B powder are uniformly mixed and granulated in a molar ratio of 1.1:2 to obtain (Mg+B) spherical powder; then, the obtained (Mg+B) spherical powder is added to MgB2 powder with an average particle size of 500nm and a purity of 99.9% at a doping amount of 5% of the mass of the MgB2 powder, and the mixture is uniformly mixed to obtain (MgB2-Mg+B) precursor powder;

[0066] Step 2: Drill 61 powder filling holes of the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of 200mm, a length of 850mm, and a purity of 99.99%. The holes are arranged in layers, with the outermost hole 14mm away from the edge of the pure iron ingot, a hole diameter of 14mm, a depth of 785mm, and a closed end of the hole 10mm away from the ingot tail. The inner wall of the hole is smooth and free of inclusions. The obtained porous electromagnetic pure iron ingot is then ultrasonically degreased with a metal cleaner, cleaned with 13% by volume dilute hydrochloric acid, and dried before being used to fill the precursor powder.

[0067] Step 3. Weigh the (MgB2-Mg+B) precursor powder obtained in step 1 and fill it into each filling hole on the electromagnetic pure iron ingot obtained in step 2. After filling, use a 15 mm long frustum-shaped pure iron plug to seal the port of each hole. Then, install a pure iron sealing cover and perform vacuum electron beam sealing welding between the sealing cover and the iron ingot to obtain a 61-core MgB2 primary composite ingot.

[0068] Step 4: The 61-core MgB2 primary composite ingot obtained in step 3 is extruded in a vacuum heat treatment furnace at an extrusion temperature of 550°C and a time of 3 hours. After being extruded to a size of Ф60mm, it is subjected to multi-pass cold drawing with a processing amount of 15% to a size of Ф5.00mm. The head and tail cavity areas and uneven areas are then removed, and the 61-core MgB2 subcomponent is obtained after cutting and straightening.

[0069] Step 5: Ultrasonic degreasing of the 61-core MgB2 subcomponent described in Step 4 is performed using a metal cleaning agent. The subcomponent is then cleaned and dried using 15% by volume dilute hydrochloric acid. A 5.00mm diameter oxygen-free copper core rod and 18 5.00mm diameter 61-core MgB2 subcomponents are then densely packed into an oxygen-free copper sheath using a pipe-through method, with the oxygen-free copper rod positioned at the center. The secondary composite ingot is then processed to a 0.80mm diameter by multiple cold drawing passes using a 15% processing allowance. During this process, low-temperature annealing is performed when the Vickers hardness of the Fe matrix is ​​≥350HV. The annealing temperature is 500°C, ultimately yielding a 1098-core MgB2 composite wire.

[0070] Step 6: Place the MgB2 composite wire obtained in step 5 in a vacuum heat treatment furnace (vacuum degree <1.0×10 -2 Pa started heating) and then subjected to high temperature phase forming heat treatment at 800℃ for 10h to obtain thousand-core grade MgB2 superconducting wire.

[0071] After the above-mentioned MgB2 superconducting wire was heat-treated and the inhomogeneous area was removed, a sample was taken to test the current carrying performance. The critical electric density fluidity Jc at 4.2K and 2T was 3.278×10 3 A / mm 2 Compared with the current practical ex-situ PIT MgB2 superconducting wire tape, the Jc is 2.1×10 3 A / mm 2 In addition, to characterize the uniformity of long-line performance, samples were taken at different locations on the wire and their Jc values ​​at 4.2K and 2T were measured, as shown in Table 3.

[0072] Table 3 Uniformity test results of MgB2 long wire prepared in Example 3

[0073]

[0074] As can be seen from Table 3, the long MgB2 wires prepared in this embodiment have good uniformity.

[0075] Example 4

[0076] This embodiment adopts the method for preparing MgB2 superconducting wire by the thousand-core first-place method provided by the present invention to prepare 1098-core MgB2 superconducting wire.

[0077] The preparation method of this embodiment comprises the following steps:

[0078] Step 1. First, spherical Mg powder with an average particle size of 400nm and a purity of 99.9%, amorphous boron powder B powder with an average particle size of 50nm and a purity of 99.9%, and carbon-based binder ethylene glycol accounting for 3% of the total mass of the Mg powder and B powder are uniformly mixed and granulated in a molar ratio of 1.3:2 to obtain (Mg+B) spherical powder; then, the obtained (Mg+B) spherical powder is added to MgB2 powder with an average particle size of 500nm and a purity of 99.9% at a doping amount of 10% of the mass of the MgB2 powder, and the mixture is uniformly mixed to obtain (MgB2-Mg+B) precursor powder;

[0079] Step 2: Drill 61 powder filling holes of the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of 142mm, a length of 800mm, and a purity of 99.99%. The holes are arranged in layers, with the outermost hole 10mm away from the edge of the pure iron ingot, a hole diameter of 10mm, a depth of 785mm, and a closed end of the hole 13mm away from the ingot tail. The inner wall of the hole is smooth and free of inclusions. The obtained porous electromagnetic pure iron ingot is then ultrasonically degreased with a metal cleaner, cleaned with 15% by volume dilute hydrochloric acid, and dried before being used to fill the precursor powder.

[0080] Step 3. Weigh the (MgB2-Mg+B) precursor powder obtained in step 1 and fill it into each filling hole on the electromagnetic pure iron ingot obtained in step 2. After filling, use a 15 mm long frustum-shaped pure iron plug to seal the port of each hole. Then, install a pure iron sealing cover and perform vacuum electron beam sealing welding between the sealing cover and the iron ingot to obtain a 61-core MgB2 primary composite ingot.

[0081] Step 4: The 61-core MgB2 primary composite ingot obtained in step 3 is extruded in a vacuum heat treatment furnace at an extrusion temperature of 520°C and a time of 4 hours. After being extruded to a size of Ф60mm, it is processed by a multi-pass cold drawing method with a processing amount of 20% to Ф8.00mm. Then, the head and tail cavity areas and uneven areas are removed, and the 61-core MgB2 subcomponent is obtained after cutting and straightening.

[0082] Step 5: Ultrasonic degreasing of the 61-core MgB2 subcomponent described in Step 4 is performed using a metal cleaning agent. The subcomponent is then cleaned and dried using 12% by volume dilute hydrochloric acid. Then, a Ø8.00mm oxygen-free copper core rod and 18 Ø8.00mm 61-core MgB2 subcomponents are densely packed into an oxygen-free copper sheath using a tube-through method, with the oxygen-free copper rod located in the center. The secondary composite ingot is then processed to a Ø1.00mm specification using a multi-pass cold drawing process with a 15% processing allowance. During this process, low-temperature annealing is performed when the Vickers hardness of the Fe matrix is ​​≥350HV. The annealing temperature is 500°C, ultimately yielding a 1098-core MgB2 composite wire.

[0083] Step 6: Place the MgB2 composite wire obtained in step 5 in a vacuum heat treatment furnace (vacuum degree <1.0×10 -2 Pa started heating) and then subjected to high temperature phase forming heat treatment at 800℃ for 6h to obtain thousand-core grade MgB2 superconducting wire.

[0084] After the above-mentioned MgB2 superconducting wire was heat-treated and the inhomogeneous area was removed, a sample was taken to test the current carrying performance. The critical electric density fluidity Jc at 4.2K and 2T was measured to be 3.449×10 3 A / mm 2 Compared with the current practical ex-situ PIT MgB2 superconducting wire tape, the Jc is 2.1×10 3 A / mm 2 In addition, to characterize the uniformity of long-line performance, samples were taken at different locations on the wire and their Jc values ​​at 4.2K and 2T were measured, as shown in Table 4.

[0085] Table 4 Uniformity test results of MgB2 long wire prepared in Example 4

[0086]

[0087] As can be seen from Table 4, the long MgB2 wire prepared in this embodiment has good uniformity.

[0088] Example 5

[0089] This embodiment uses the method for preparing MgB2 superconducting wire using the thousand-core first-place method provided by the present invention to prepare 1080-core MgB2 superconducting wire.

[0090] The preparation method of this embodiment comprises the following steps:

[0091] Step 1. First, spherical Mg powder with an average particle size of 400nm and a purity of 99.9%, amorphous boron powder B powder with an average particle size of 50nm and a purity of 99.9%, and carbon-based binder ethylene glycol accounting for 3% of the total mass of the Mg powder and B powder are uniformly mixed and granulated in a molar ratio of 1.4:2 to obtain (Mg+B) spherical powder; then, the obtained (Mg+B) spherical powder is added to MgB2 powder with an average particle size of 500nm and a purity of 99.9% at a doping amount of 15% of the mass of the MgB2 powder, and the mixture is uniformly mixed to obtain (MgB2-Mg+B) precursor powder;

[0092] Step 2: Drill 60 powder filling holes of the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of 170mm, a length of 800mm, and a purity of 99.99%. The holes are arranged in layers, the center position is not drilled, the outermost hole is 12mm away from the edge of the pure iron ingot, the hole diameter is 12mm, the depth is 785mm, the closed end of the hole is 15mm away from the ingot tail, and the inner wall of the hole is smooth and free of inclusions. Then, the obtained porous electromagnetic pure iron ingot is ultrasonically degreased with a metal cleaner, cleaned with 15% by volume dilute hydrochloric acid, and dried before being used to fill the precursor powder;

[0093] Step 3. Weigh the (MgB2-Mg+B) precursor powder obtained in step 1 and fill it into each filling hole on the electromagnetic pure iron ingot obtained in step 2. After filling, use a 15 mm long frustum-shaped pure iron plug to seal the port of each hole. Then, install a pure iron sealing cover and perform vacuum electron beam sealing welding between the sealing cover and the iron ingot to obtain a 60-core MgB2 primary composite ingot.

[0094] Step 4: The 60-core MgB2 primary composite ingot obtained in step 3 is extruded in a vacuum heat treatment furnace at an extrusion temperature of 550°C and a time of 4 hours. After being extruded to a size of Ф60mm, it is processed by a multi-pass cold drawing method with a processing amount of 15% to Ф5.00mm. Then, the head and tail cavity areas and uneven areas are removed, and the 60-core MgB2 subcomponent is obtained after cutting and straightening.

[0095] Step 5: Ultrasonic degreasing of the 60-core MgB2 subcomponent described in Step 4 is performed using a metal cleaning agent. The subcomponents are then cleaned and dried using 15% by volume dilute hydrochloric acid. A 5.00mm diameter oxygen-free copper core rod and 18 5.00mm diameter 60-core MgB2 subcomponents are then densely packed into an oxygen-free copper sheath using a tube-through method to obtain a secondary MgB2 composite ingot, with the oxygen-free copper rod located in the center. The secondary composite ingot is then processed to a 1.00mm diameter by a multi-pass cold drawing process using a 15% processing allowance. During this process, low-temperature annealing is performed when the Vickers hardness of the Fe matrix is ​​≥350HV. The annealing temperature is 500°C, ultimately yielding a 1080-core MgB2 composite wire.

[0096] Step 6: Place the MgB2 composite wire obtained in step 5 in a vacuum heat treatment furnace (vacuum degree <1.0×10 -2 Pa started heating) and then subjected to high temperature phase forming heat treatment at 900℃ for 10h to obtain thousand-core grade MgB2 superconducting wire.

[0097] After the above-mentioned MgB2 superconducting wire was heat-treated and the inhomogeneous area was removed, a sample was taken to test the current carrying performance. The critical electric density fluidity Jc at 4.2K and 2T was 4.147×10 3 A / mm 2Compared with the current practical ex-situ PIT MgB2 superconducting wire tape, the Jc is 2.1×10 3 A / mm 2 In addition, to characterize the uniformity of long-line performance, samples were taken at different locations on the wire and their Jc values ​​at 4.2K and 2T were measured, as shown in Table 5.

[0098] Table 5 Uniformity test results of MgB2 long wire prepared in Example 5

[0099]

[0100] As can be seen from Table 5, the uniformity of the MgB2 long wire prepared in this embodiment is good.

[0101] As described above, the basic principles, main features and advantages of the present invention are well described. The above embodiments and descriptions are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the scope of protection determined by the present invention.

Claims

1. A method for preparing a MgB2 superconducting wire by a thousand-core pre-position method, characterized in that: The following steps are involved: Step 1: Mg powder, B powder and carbon-based binder are uniformly mixed and pelletized to obtain (Mg+B) spherical powder; then the (Mg+B) spherical powder is added to MgB2 powder and mixed uniformly to obtain (MgB2-Mg+B) precursor powder; Step 2: drilling powder filling holes of the same specifications on the electromagnetic pure iron ingot to obtain a porous electromagnetic pure iron ingot, wherein one end of the powder filling hole is closed, and the inner wall of the powder filling hole is smooth and free of inclusions, and then degreasing, cleaning, and drying the porous electromagnetic pure iron ingot to obtain a treated porous electromagnetic pure iron ingot; Step 3: Weigh the (MgB2-Mg+B) precursor powder obtained in step 1, and fill it into each powder filling hole on the treated porous electromagnetic pure iron ingot obtained in step 2. After filling, close the ports of each powder filling hole, install a sealing cover, and vacuum weld to obtain a multi-core MgB2 primary composite ingot; Step 4: Processing the multi-core MgB2 primary composite ingot obtained in step 3 to the required specifications by extrusion and cold drawing, and then cutting and straightening to obtain a multi-core MgB2 subcomponent; Step 5: After cleaning and drying the multi-core MgB2 subcomponents obtained in step 4, they are densely packed into an oxygen-free copper sheath by a tube-through method to obtain a multi-core MgB2 secondary composite ingot, and the multi-core MgB2 secondary composite ingot is processed to the final specification by a cold drawing method to obtain a thousand-core grade MgB2 composite wire; Step 6: subjecting the MgB2 composite wire obtained in step 5 to high-temperature phase-forming heat treatment to obtain a thousand-core-level MgB2 superconducting wire.

2. The preparation method according to claim 1, characterized in that The B powder described in step 1 is an amorphous boron powder with an average particle size of 50 nm and a purity of 99.9%; the Mg powder is a spherical magnesium powder with an average particle size of 400 nm and a purity of 99.9%.

3. The preparation method according to claim 2, characterized in that The Mg powder and the B powder are mixed in a mass ratio of 1.1-1.4:

2.

4. The preparation method according to claim 1, characterized in that The amount of the carbon-based binder used in step one is 3%-5% of the total mass of the Mg powder and the B powder; the average particle size of the (Mg+B) spherical powder is 500nm; the average particle size of the MgB2 powder is 500nm and the purity is 99.9%, and the doping amount of the (Mg+B) spherical powder is 5%-15% of the mass of the MgB2 powder.

5. The preparation method according to claim 1, characterized in that The outer diameter of the electromagnetic pure iron ingot described in step 2 is 100mm-200mm, and the length is 800mm-1000mm; the number of the powder filling holes is ≥60 and is evenly distributed, and the non-opening end is 10mm-15mm away from the ingot tail; the degreasing is performed using a metal degreasing agent, and the cleaning is performed using dilute hydrochloric acid with a volume ratio of 10%-15%.

6. The preparation method according to claim 1, characterized in that The mass of the (MgB2-Mg+B) precursor powder filled in each powder filling hole described in step 3 is the same, and the filling density is 1.0g / cm 3 -1.5g / cm 3 The powder filling hole ports are sealed with cone-shaped plugs.

7. The preparation method according to claim 1, characterized in that The final extrusion size of the multi-core MgB2 composite ingot described in step 4 is less than Ф60mm, the extrusion temperature is 480℃-550℃, and the time is 3h-5h; the pass processing amount during the cold drawing process is 15%-20%, and the specification of the multi-core MgB2 subcomponent is Ф5.0mm-Ф8.0mm.

8. The preparation method according to claim 1, characterized in that The final specification described in step five is Ф0.5mm-Ф1.0mm.

9. The preparation method according to claim 1, characterized in that The temperature of the high-temperature phase-forming heat treatment in step six is ​​800° C.-950° C., and the treatment time is 6 h-10 h.

10. The MgB2 superconducting wire prepared by the preparation method according to any one of claims 1 to 9.

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