Preparation method of thousand-core in-situ method MgB2 superconducting wire

Abstract

The invention belongs to the technical field of superconducting material processing engineering, and particularly relates to a preparation method of a thousand-core in-situ method MgB2 superconducting wire. The invention discloses a method for preparing a multi-core MgB2 superconducting wire by adopting a drilling process, which is characterized in that a multi-core subcomponent is directly prepared by drilling a pure iron ingot, the pure iron is a barrier layer and a stabilizer, and the problem of impure phase introduction caused by core wire fracture in the cold working process of a multi-core wire in a secondary assembly method is avoided. In addition, according to the method, recrystallization of original MgB2 powder particles is induced by prefabricating (MgB2-Mg + B) precursor powder, and the defects of MgB2 grain microcracks and poor intercrystalline connectivity caused by continuous cold machining are repaired and overcome. Tests show that the critical current density and the long-line uniformity of the MgB2 superconducting wire prepared by the method are greatly improved, and the market application prospect is wide.

Description

Technical Field

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

[0002] In the field of superconducting materials, MgB2 superconducting wire and tape exhibit great application potential in many fields such as power transmission, magnetic levitation technology, nuclear magnetic resonance imaging (MRI), etc. due to its relatively low cost, moderate critical temperature, and relatively simple preparation process. Among them, the preparation of MgB2 superconducting wire and tape by the Powder-In-Tube (PIT) method has become the mainstream method for the production of practical MgB2 superconducting wire and tape due to its relatively mature process and easy realization of large-scale production.

[0003] Currently, in the production process of practical ex-situ PIT method MgB2 superconducting wire and tape, commercial MgB2 powder is usually filled into a pure nickel tube, and then through a series of plastic processing procedures such as rotary forging and rolling, the wire and tape are initially formed, and finally, through phase-forming heat treatment, the MgB2 superconducting phase is promoted to form, thereby obtaining MgB2 superconducting wire and tape.

[0004] However, the MgB2 material itself has hard and brittle characteristics similar to ceramics and belongs to an ionic compound. And commercial MgB2 powder often has many factors that are not conducive to improving superconducting properties. On the one hand, the powder usually contains MgO impurities, which are difficult to completely remove during subsequent processing and heat treatment and will exist as non-superconducting phases in the superconducting wire and tape. On the other hand, there are also large-grain MgB2 crystals in the powder. After undergoing multiple consecutive plastic processing steps, due to the hard brittleness of MgB2 and the presence of impurities and large-grain crystals, a large number of microcracks are extremely likely to appear in the MgB2 grains in the core wire. The existence of these impurities, large-grain crystals, and local microcracks seriously damages the good connectivity between the MgB2 superconducting phase grains. Problems such as large grain size, reduced grain boundary quantity, and weak grain connectivity will significantly reduce the current-carrying performance of the superconducting wire and tape, thereby affecting its performance in various application scenarios.

[0005] In addition, there is a key problem in the pre-powder tube method, that is, the tube as the barrier layer will face severe challenges during the processing. With the continuous increase in the cumulative processing volume, the barrier layer tube will show obvious work hardening phenomenon, and its mechanical properties will gradually decrease, eventually leading to rupture. The rupture of the barrier layer will lead to a series of serious consequences. The superconducting core will react with the external matrix material to generate compound impurities, forming an intermediate reaction layer between the superconducting core wire and the matrix material. The existence of this reaction layer has a dual negative impact: first, it reduces the effective cross-sectional area of ​​the superconducting wire, so that the cross-sectional area that can carry current is reduced, which directly limits the current carrying capacity of the superconducting wire strip; second, it makes the thermal stability problem of MgB2 superconducting wire more prominent. In the working process of superconducting materials, thermal stability is very important. The appearance of the reaction layer will interfere with the transfer and distribution of heat, resulting in local temperature anomalies, which in turn affects the stability of superconducting performance and ultimately reduces the critical current density of the superconducting wire strip.

[0006] Since the hardness of MgB2 is as high as 2000MPa, once the barrier layer is deformed unevenly during processing, it is very easy to be punctured by powder particles in weak areas. This situation is particularly significant in multi-core wires, because the structure of multi-core wires is more complex, the stress distribution on the barrier layer is uneven, and local weak areas are more likely to appear. The problem of the barrier layer being easily punctured has become a bottleneck problem that restricts the realization of multi-core wires and the guarantee of long-line uniformity by the first-position powder tube method. Multi-core is an important way to achieve high current carrying capacity, and long-line uniformity is the key to ensuring the stable performance of superconducting wires in practical applications. These problems not only hinder the further improvement of the performance of MgB2 superconducting wires, but also seriously affect its promotion and application in the AC field and application scenarios with strict loss requirements. Therefore, how to solve the above problems and improve the performance and quality of MgB2 superconducting wire strips has become a key technical problem that needs to be solved urgently in this field. Summary of the invention

[0007] Aiming at 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 loading tube method, the present invention establishes a method for preparing MgB2 superconducting wires produced by the pre-powder loading tube method according to the thousand-core pre-powder loading tube method.

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

[0009] On the one hand, the present invention provides a method for preparing a MgB2 superconducting wire by a thousand-core first-place method, comprising the following steps: Step 1: Mix Mg powder, B powder and a carbon-based binder and pelletize them to obtain (Mg+B) spherical powder; then incorporate the (Mg+B) spherical powder into MgB2 powder and mix evenly to obtain (MgB2-Mg+B) precursor powder; Step 2: Drill powder filling holes with the same specifications on an electromagnetic pure iron ingot to obtain a porous electromagnetic pure iron ingot. One end of the powder filling hole is closed, and the inner wall of the powder filling hole is smooth and free of inclusions. Then degrease, clean and dry the porous electromagnetic pure iron ingot to obtain a processed 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 processed porous electromagnetic pure iron ingot obtained in Step 2. After filling, seal the ports of each powder filling hole, install a sealing cover, and perform vacuum welding to obtain a multi-core MgB2 primary composite ingot; Step 4: Process the multi-core MgB2 primary composite ingot obtained in Step 3 to the required specifications by extrusion and cold drawing methods, cut and straighten it to obtain multi-core MgB2 sub-elements; Step 5: After cleaning and drying the multi-core MgB2 sub-elements obtained in Step 4, closely arrange and load them into an oxygen-free copper sheath by the tube threading method to obtain a multi-core MgB2 secondary composite ingot. Process the multi-core MgB2 secondary composite ingot to the final specifications by cold drawing method to obtain a thousand-core MgB2 composite wire; Step 6: Perform high-temperature phase-forming heat treatment on the MgB2 composite wire obtained in Step 5 to obtain a thousand-core MgB2 superconducting wire.

[0010] Further, in the preparation method, the B powder in Step 1 is amorphous boron powder with an average particle size of 50 nm and a purity of 99.9%; the Mg powder is spherical magnesium powder with an average particle size of 400 nm and a purity of 99.9%.

[0011] Further, in the preparation method, the Mg powder and B powder are mixed in a mass ratio of 1.1-1.4:2.

[0012] Further, in the preparation method, the dosage of the carbon-based binder in Step 1 is 3%-5% of the total mass of the Mg powder and 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.

[0013] Further, in the preparation method, the outer diameter of the electromagnetic pure iron ingot in the second step is 100 mm to 200 mm, and the length is 800 mm - 1000 mm; the number of powder filling holes is ≥60 and they are 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%.

[0014] Further, in the preparation method, the (MgB2 - Mg + B) precursor powder filled in the powder filling holes in the third step has the same mass, and the filling density is 1.0 g / cm 3 -1.5 g / cm 3 ; the ports of each powder filling hole are closed with frustum-shaped plugs.

[0015] Further, in the preparation method, the size of the multi-core MgB2 primary composite ingot after extrusion in the fourth step is less than Ф60 mm, the extrusion temperature is 480°C - 550°C, and the time is 3 h - 5 h; the pass processing amount in the cold drawing process is 15% - 20%, and the multi-core MgB2 sub-element specification is Ф5.0 mm - Ф8.0 mm.

[0016] Further, in the preparation method, the final specification in the fifth step is Ф0.5 mm - Ф1.0 mm.

[0017] Further, in the preparation method, the temperature of the high-temperature phase-forming heat treatment in the sixth step is 800°C - 950°C, and the treatment time is 6 h - 10 h.

[0018] On the other hand, MgB2 superconducting wire prepared by the preparation method of the present invention is also provided.

[0019] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: (1) In the present invention, the extremely fine B powder is uniformly coated on the surface of the spherical Mg powder by pelletizing and incorporated into the MgB2 powder with a particle size comparable to it. The (Mg + B) spherical powder, as a doping agent, will preferentially generate new MgB2 grains during the high-temperature phase-forming heat treatment due to its high reaction activity to induce the recrystallization process of the original MgB2 powder particles. At the same time, it makes up for the defects of poor MgB2 grain microcracks and intergranular connectivity caused by continuous cold working, improves the technical problem of poor grain connectivity in the process of preparing MgB2 superconducting wire by the prior in-situ method in the prior art, and improves the critical current density of the MgB2 superconducting wire. The critical current density of the MgB2 superconducting wire prepared by the method provided by the present invention is much higher than that of the prior art.

[0020] (2) The present invention directly prepares multi-core sub-elements by drilling low-cost pure iron ingots. The pure iron serves as both a barrier layer and a stabilizer. Extrusion at a large size is beneficial for powder densification and uniform plastic deformation of the metal matrix, avoiding the problem of introducing magnesium copper compound heterophases caused by the rupture of core wires during the cold working process of multi-core wire rods prepared by the secondary assembly method. It is conducive to preparing multi-core wire rods with pure phases and solves the problem of core wire breakage commonly existing in conventional PIT method multi-core wire rods.

[0021] Through the above synergistic effects, the critical current density and long-line uniformity of the MgB2 superconducting wire rods prepared by the preparation method provided by the present invention are significantly improved. Description of the Drawings

[0022] Figure 1 It is a cross-sectional schematic diagram of a porous electromagnetic pure iron ingot obtained by drilling for MgB2 powder-in-tube in Example 1. Among them, 1 is a 61-core MgB2 primary composite ingot; 2 is a powder filling hole; 3 is a porous electromagnetic pure iron ingot.

[0023] Figure 2 It is a cross-sectional schematic diagram of a 1098-core MgB2 secondary composite ingot prepared by the tube-passing assembly method in Example 1. Among them, 4 is a 1098-core MgB2 secondary composite ingot; 5 is a 61-core MgB2 sub-element; 6 is an oxygen-free copper core rod; 7 is an oxygen-free copper tube. Detailed Embodiments

[0024] Next, the technical solutions of the present invention will be described in conjunction with the embodiments. However, the present invention is not limited to the following embodiments.

[0025] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings, but the embodiments cited are not intended to limit the present invention.

[0026] In the following embodiments, the experimental methods and detection methods are conventional methods unless otherwise specified; the reagents and materials can be obtained in the market unless otherwise specified.

[0027] The electromagnetic pure iron grade is DT4, and its composition and electromagnetic properties meet the national standard GB / T6983-2022.

[0028] Example 1 This example is to prepare 1098-core MgB2 superconducting wire rods by using the preparation method of the thousand-core pre-position method MgB2 superconducting wire rods provided by the present invention.

[0029] The preparation method of this example includes the following steps: 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 Mg powder and B powder are evenly mixed and granulated to obtain (Mg + B) spherical powder; then, the obtained (Mg + B) spherical powder is incorporated into MgB2 powder with an average particle size of 500 nm and a purity of 99.9% according to an incorporation amount of 15% of the mass of the MgB2 powder and mixed evenly to obtain (MgB2 - Mg + B) precursor powder; Step 2: Drill 61 powder filling holes with the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of Ф100 mm, a length of 800 mm, and a purity of 99.99%. The positions of the holes are arranged in layers. The outermost holes are 7 mm away from the edge of the pure iron ingot. The hole diameter is Ф7.0 mm and the depth is 785 mm. The closed end of the hole is 15 mm away from the tail of the ingot. 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 cleaning agent, cleaned with dilute hydrochloric acid with a volume ratio of 10% - 15%, dried, and used for filling the precursor powder; Step 3: Weigh the (MgB2 - Mg + B) precursor powder obtained in Step 1, fill it into each filling hole on the electromagnetic pure iron ingot obtained in Step 2. After filling, use a 15 mm long conical pure iron plug to seal the port of each hole, then install a pure iron sealing cover and perform vacuum electron beam welding to seal the cover and the ingot to obtain a 61-core MgB2 primary composite ingot; Step 4: Extrude the 61-core MgB2 primary composite ingot obtained in Step 3 in a vacuum heat treatment furnace at an extrusion temperature of 550 °C for 4 h. After extruding to a size of Ф60 mm, use a multi-pass cold drawing method with a 15% processing amount to process it to Ф5.00 mm, then remove the head and tail cavity areas and uneven areas, cut and straighten to obtain 61-core MgB2 sub-elements.

[0030] Step 5: Ultrasonically degrease the 61-core MgB2 sub-elements described in Step 4 with a metal cleaning agent, then clean with dilute hydrochloric acid with a volume ratio of 15%, dry, and use the tube threading method to closely pack 1 Ф5.00 mm oxygen-free copper core rod and 18 Ф5.00 mm 61-core MgB2 sub-elements into an oxygen-free copper sheath to obtain a MgB2 secondary composite ingot, where the oxygen-free copper rod is located at the center position. Process the secondary composite ingot to a final specification of Ф1.00 mm using a multi-pass cold drawing method with a 15% processing amount to obtain a 1098-core MgB2 composite wire; Step 6: Heat the MgB2 composite wire obtained in Step 5 in a vacuum heat treatment furnace (starting to heat at a vacuum degree <1.0×10 -2 Pa) at 900 °C for 10 h for high-temperature phase-forming heat treatment to obtain a thousand-core MgB2 superconducting wire.

[0031] After removing the non-uniform area from the above-mentioned MgB₂ superconducting wire after phase-forming heat treatment, samples were taken for current-carrying performance testing, and the critical current density Jc at 4.2 K and 2 T was measured to be 4.348×10 3 A / mm 2 , compared with the Jc of 2.1×10 3 A / mm 2 of the ex-situ PIT MgB₂ superconducting wire and strip at the current stage, there is a significant improvement. In addition, to characterize the uniformity of the long wire performance, samples were taken at different positions of the wire and the Jc at 4.2 K and 2 T was measured as shown in Table 1.

[0032] Table 1 Test results of the uniformity of the MgB₂ long wire prepared in Example 1

[0033] As can be seen from Table 1, the MgB₂ long wire prepared in this example has good uniformity.

[0034] In this example, the cross-section of the porous electromagnetic pure iron ingot obtained by drilling for MgB₂ powder tube filling is as Figure 1 shown; the cross-section of the 1098-core MgB₂ secondary composite ingot by the tube-passing assembly method 1098 is as Figure 2 shown.

[0035] Example 2 This example is to prepare a 1098-core MgB₂ superconducting wire by using the preparation method of the thousand-core in-situ MgB₂ superconducting wire provided by the present invention.

[0036] The preparation method of this example includes the following steps: 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 5% of the total mass of Mg powder and B powder were evenly mixed and granulated to obtain (Mg + B) spherical powder; then, the obtained (Mg + B) spherical powder was doped into MgB₂ powder with an average particle size of 500 nm and a purity of 99.9% according to a doping amount of 15% of the mass of the MgB₂ powder and mixed evenly to obtain (MgB₂ - Mg + B) precursor powder; Step 2: Drill 61 powder filling holes with the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of Ф142 mm, a length of 900 mm, and a purity of 99.99%. The positions of the holes are arranged in layers. The distance from the outermost hole to the edge of the pure iron ingot is 10 mm, the hole diameter is Ф10 mm, the depth is 785 mm, the closed end of the hole is 12 mm away from the ingot tail, and the inner wall of the hole is smooth without inclusions. Then, the obtained porous electromagnetic pure iron ingot was ultrasonically degreased with a metal cleaning agent, washed with 10% dilute hydrochloric acid by volume, and dried for loading the precursor powder; Step 3: Weigh the (MgB2-Mg+B) precursor powder obtained in Step 1, and fill each filling hole in the electromagnetic pure iron ingot obtained in Step 2 with it. After filling, use a 15-mm-long conical pure iron plug to seal the port of each hole, then install a pure iron sealing cover and perform vacuum electron beam welding to seal the cover and the iron ingot to obtain a 61-core MgB2 primary composite ingot; Step 4: Extrude the 61-core MgB2 primary composite ingot obtained in Step 3 in a vacuum heat treatment furnace at an extrusion temperature of 480 °C for 5 h. After extruding to a size of Ф60 mm, use a multi-pass cold drawing method with a processing amount of 18% to process it to Ф7.00 mm, and then remove the head and tail cavity areas and uneven areas. After cutting and straightening, obtain a 61-core MgB2 sub-component.

[0037] Step 5: Ultrasonically degrease the 61-core MgB2 sub-component described in Step 4 with a metal cleaning agent, then clean it with 10% dilute hydrochloric acid by volume ratio, dry it, and use the tube threading method to tightly pack 1 Ф7.00-mm oxygen-free copper core rod and 18 Ф7.00-mm 61-core MgB2 sub-components into an oxygen-free copper sheath to obtain a MgB2 secondary composite ingot, where the oxygen-free copper rod is located in the center position. The secondary composite ingot is processed to a Ф0.50-mm specification by a multi-pass cold drawing method with a processing amount of 15%. During the process, when the Vickers hardness of the Fe matrix ≥ 350 HV, low-temperature annealing is introduced at an annealing temperature of 500 °C, and finally a 1098-core MgB2 composite wire is obtained; Step 6: Heat the MgB2 composite wire obtained in Step 5 in a vacuum heat treatment furnace (starting to heat when the vacuum degree < 1.0×10 -2 Pa) at 950 °C for 6 h for high-temperature phase-forming heat treatment to obtain a thousand-core-level MgB2 superconducting wire.

[0038] After removing the uneven area from the above MgB2 superconducting wire after phase-forming heat treatment, samples are taken for current-carrying performance testing. The critical current density Jc at 4.2 K and 2 T is measured to be 3.863×10 3 A / mm 2 , which is significantly higher than the Jc = 2.1×10 3 A / mm 2 of the current-stage practical ex-situ PIT MgB2 superconducting wire strip. In addition, to characterize the uniformity of the long wire performance, samples are taken at different positions of the wire and the Jc at 4.2 K and 2 T is shown in Table 2.

[0039] Table 2 Uniformity test results of the MgB2 long wire prepared in Example 2

[0040] As can be seen from Table 2, the MgB2 long wire prepared in this example has good uniformity.

[0041] Example 3 In this example, 1098-core MgB2 superconducting wire was prepared by using the preparation method of the thousand-core first-position method MgB2 superconducting wire provided by the present invention.

[0042] The preparation method of this example includes the following steps: 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 ethylene glycol, a carbon-based binder accounting for 4% of the total mass of Mg powder and B powder, were uniformly mixed and granulated to obtain (Mg + B) spherical powder; then, the obtained (Mg + B) spherical powder was incorporated into MgB2 powder with an average particle size of 500 nm and a purity of 99.9% according to a doping amount of 5% of the mass of the MgB2 powder and mixed evenly to obtain (MgB2 - Mg + B) precursor powder; Step 2: Drill 61 powder filling holes with the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of Ф200 mm, a length of 850 mm, and a purity of 99.99%. The positions of the holes are arranged in layers. The distance from the outermost hole to the edge of the pure iron ingot is 14 mm, the hole diameter is Ф14 mm, the depth is 785 mm, the closed end of the hole is 10 mm 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 was ultrasonically degreased with a metal cleaning agent, washed with 13% dilute hydrochloric acid by volume, dried, and used for filling the precursor powder; Step 3: Weigh the (MgB2 - Mg + B) precursor powder obtained in Step 1, 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 welding to seal the cover and the iron ingot to obtain a 61-core MgB2 primary composite ingot; Step 4: Extrude the 61-core MgB2 primary composite ingot obtained in Step 3 in a vacuum heat treatment furnace at an extrusion temperature of 550 °C for 3 h. After extruding to a size of Ф60 mm, it was processed to Ф5.00 mm by multi-pass cold drawing with a processing amount of 15%. Then, the head and tail cavity areas and uneven areas were removed, and after cutting and straightening, 61-core MgB2 sub-elements were obtained.

[0043] Step 5: Ultrasonically degrease the 61-core MgB2 sub-element described in Step 4 with a metal cleaning agent, then clean it with 15% dilute hydrochloric acid by volume, dry it, and use the tube threading method to closely pack 1 Ф5.00 mm oxygen-free copper core rod and 18 Ф5.00 mm 61-core MgB2 sub-elements into an oxygen-free copper sheath to obtain a MgB2 secondary composite ingot, where the oxygen-free copper rod is located at the central position. Process the secondary composite ingot by multi-pass cold drawing with a 15% processing amount to a Ф0.80 mm specification. When the Vickers hardness of the Fe matrix ≥ 350 HV during the process, introduce low-temperature annealing at an annealing temperature of 500 °C to finally obtain a 1098-core MgB2 composite wire; Step 6: Heat the MgB2 composite wire obtained in Step 5 in a vacuum heat treatment furnace (starting to heat when the vacuum degree < 1.0×10 -2 Pa) at 800 °C for 10 h of high-temperature phase-forming heat treatment to obtain a thousand-core MgB2 superconducting wire.

[0044] After removing the non-uniform area from the MgB2 superconducting wire after the above phase-forming heat treatment, sample it for current-carrying performance testing. The measured critical current density Jc at 4.2 K and 2 T is 3.278×10 3 A / mm 2 , which is significantly higher than the Jc = 2.1×10 3 A / mm 2 of the current state-of-the-art ex-situ PIT MgB2 superconducting wire and strip. In addition, to characterize the uniformity of the long wire performance, samples are taken at different positions of the wire and the Jc at 4.2 K and 2 T is shown in Table 3.

[0045] Table 3 Test results of the uniformity of the MgB2 long wire prepared in Example 3

[0046] As can be seen from Table 3, the MgB2 long wire prepared in this example has good uniformity.

[0047] Example 4 This example is to prepare a 1098-core MgB2 superconducting wire using the preparation method of the thousand-core in-situ MgB2 superconducting wire provided by the present invention.

[0048] The preparation method of this example includes the following steps: 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 ethylene glycol, a carbon-based binder accounting for 3% of the total mass of Mg powder and B powder, are uniformly mixed and granulated to obtain (Mg + B) spherical powder; then, the obtained (Mg + B) spherical powder is incorporated into MgB2 powder with an average particle size of 500 nm and a purity of 99.9% according to a doping amount of 10% of the mass of MgB2 powder and mixed evenly to obtain (MgB2 - Mg + B) precursor powder; Step 2: Drill 61 powder filling holes with the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of Ф142 mm, a length of 800 mm, and a purity of 99.99%. The positions of the holes are arranged in layers. The distance from the outermost holes to the edge of the pure iron ingot is 10 mm. The hole diameter is Ф10 mm and the depth is 785 mm. The closed end of the hole is 13 mm away from the end of the ingot. 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 cleaning agent, washed with 15% dilute hydrochloric acid by volume, dried, and used for filling the precursor powder; Step 3: Weigh the (MgB2 - Mg + B) precursor powder obtained in Step 1, 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 welding to seal the cover and the iron ingot to obtain a 61-core MgB2 primary composite ingot; Step 4: Extrude the 61-core MgB2 primary composite ingot obtained in Step 3 in a vacuum heat treatment furnace at an extrusion temperature of 520 °C for 4 h. After extruding to a size of Ф60 mm, use a multi-pass cold drawing method with a 20% processing amount to process it to Ф8.00 mm. Then, remove the head and tail cavity areas and uneven areas, cut and straighten to obtain 61-core MgB2 sub-elements.

[0049] Step 5: Ultrasonically degrease the 61-core MgB2 sub-elements described in Step 4 with a metal cleaning agent, then wash with 12% dilute hydrochloric acid by volume, dry, and use the tube-passing method to closely pack 1 Ф8.00-mm oxygen-free copper core rod and 18 Ф8.00-mm 61-core MgB2 sub-elements into an oxygen-free copper sheath to obtain a MgB2 secondary composite ingot, where the oxygen-free copper rod is located in the center position. The secondary composite ingot is processed to a Ф1.00-mm specification by a multi-pass cold drawing method with a 15% processing amount. During the process, when the Vickers hardness of the Fe matrix ≥ 350 HV, low-temperature annealing is introduced at an annealing temperature of 500 °C to finally obtain a 1098-core MgB2 composite wire; Step 6: Heat the MgB2 composite wire obtained in Step 5 in a vacuum heat treatment furnace (starting to heat when the vacuum degree < 1.0×10 -2 Pa) at 800 °C for 6 h for high-temperature phase-forming heat treatment to obtain a thousand-core-level MgB2 superconducting wire.

[0050] After removing the non-uniform area from the above-mentioned MgB2 superconducting wire after phase-forming heat treatment, samples were taken for current-carrying performance testing, and the critical current density Jc at 4.2 K and 2 T was measured to be 3.449×10 3 A / mm 2 , compared with the Jc of 2.1×10 3 A / mm 2 of the current state-of-the-art ex-situ PIT MgB2 superconducting wire and tape, there is a significant improvement. In addition, to characterize the uniformity of the long wire performance, samples were taken at different positions of the wire and the Jc at 4.2 K and 2 T was measured as shown in Table 4.

[0051] Table 4 Test results of the uniformity of the MgB2 long wire prepared in Example 4

[0052] As can be seen from Table 4, the MgB2 long wire prepared in this example has good uniformity.

[0053] Example 5 In this example, a 1080-core MgB2 superconducting wire was prepared by using the method for preparing a multi-core in-situ MgB2 superconducting wire provided by the present invention.

[0054] The preparation method of this example includes the following steps: 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 3% of the carbon-based binder ethylene glycol based on the total mass of Mg powder and B powder were uniformly mixed and granulated to obtain (Mg + B) spherical powder; then, the obtained (Mg + B) spherical powder was incorporated into MgB2 powder with an average particle size of 500 nm and a purity of 99.9% according to a doping amount of 15% of the MgB2 powder mass and mixed evenly to obtain (MgB2 - Mg + B) precursor powder; Step 2: Drill 60 powder filling holes with the same specifications on a DT4C electromagnetic pure iron ingot with an outer diameter of Ф170 mm, a length of 800 mm, and a purity of 99.99%. The positions of the holes are arranged in layers, and no hole is drilled at the most central position. The distance from the outermost hole to the edge of the pure iron ingot is 12 mm, the hole diameter is Ф12 mm, the depth is 785 mm, the closed end of the hole is 15 mm 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 was ultrasonically degreased with a metal cleaning agent, cleaned with 15% dilute hydrochloric acid by volume, and dried for loading the precursor powder; Step 3: Weigh the (MgB2-Mg+B) precursor powder obtained in Step 1 and fill each filling hole in the electromagnetic pure iron ingot obtained in Step 2. After filling, use a 15-mm-long conical pure iron plug to seal the port of each hole, and then install a pure iron sealing cover and perform vacuum electron beam welding to seal the cover and the iron ingot to obtain a 60-core MgB2 primary composite ingot. Step 4: Extrude the 60-core MgB2 primary composite ingot obtained in Step 3 in a vacuum heat treatment furnace at an extrusion temperature of 550°C for 4 hours. After extruding to a size of Ф60 mm, use a multi-pass cold drawing method with a 15% processing amount to process it to Ф5.00 mm. Then remove the head and tail cavity areas and the uneven areas, and cut and straighten to obtain a 60-core MgB2 sub-element.

[0055] Step 5: Ultrasonically degrease the 60-core MgB2 sub-element described in Step 4 with a metal cleaning agent, then clean it with 15% dilute hydrochloric acid by volume ratio, dry it, and use the tube-passing method to closely pack 1 Ф5.00-mm oxygen-free copper core rod and 18 Ф5.00-mm 60-core MgB2 sub-elements into an oxygen-free copper sheath to obtain a MgB2 secondary composite ingot, where the oxygen-free copper rod is located in the center position. Process the secondary composite ingot to a Ф1.00-mm specification using a multi-pass cold drawing method with a 15% processing amount. During the process, when the Vickers hardness of the Fe matrix ≥ 350 HV, introduce low-temperature annealing at an annealing temperature of 500°C to finally obtain a 1080-core MgB2 composite wire. Step 6: Heat the MgB2 composite wire obtained in Step 5 in a vacuum heat treatment furnace (starting to heat when the vacuum degree < 1.0×10 -2 Pa) at 900°C for 10 hours for high-temperature phase-forming heat treatment to obtain a thousand-core-level MgB2 superconducting wire.

[0056] After removing the uneven area from the above-mentioned MgB2 superconducting wire after phase-forming heat treatment, take samples for current-carrying performance testing. The critical current density Jc at 4.2 K and 2 T is measured to be 4.147×10 3 A / mm 2 , which is significantly higher than the Jc = 2.1×10 3 A / mm 2 of the current-stage practical ex-situ PIT MgB2 superconducting wire strip. In addition, to characterize the uniformity of the long wire performance, samples are taken at different positions of the wire and the Jc at 4.2 K and 2 T is shown in Table 5.

[0057] Table 5 Test results of the uniformity of the MgB2 long wire prepared in Example 5

[0058] As can be seen from Table 5, the MgB2 long wire prepared in this example has good uniformity.

[0059] As described above, the basic principles, main features, and advantages of the present invention have been preferably described. The above embodiments and the description are merely descriptions of the preferred embodiments of the present invention. The present invention is not limited by the above embodiments. Without departing from the spirit and scope of the present invention, various changes and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the present invention.

Claims

1. A preparation method of a thousand-core first-position method MgB2 superconducting wire, characterized in that, It includes the following steps: Step 1: Uniformly mix Mg powder, B powder and a carbon-based binder and form pellets to obtain (Mg + B) spherical powder; then incorporate the (Mg + B) spherical powder into MgB2 powder and mix evenly to obtain (MgB2 - Mg + B) precursor powder; Step 2: Drill powder filling holes with the same specifications on an electromagnetic pure iron ingot to obtain a porous electromagnetic pure iron ingot. One end of the powder filling hole is closed, and the inner wall of the powder filling hole is smooth and free of inclusions. Then degrease, clean and dry the porous electromagnetic pure iron ingot to obtain a processed porous electromagnetic pure iron ingot; Step 3: Weigh the (MgB2 - Mg + B) precursor powder obtained in Step 1, fill it into each powder filling hole on the processed porous electromagnetic pure iron ingot obtained in Step 2. After filling, seal 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: Process the multi-core MgB2 primary composite ingot obtained in Step 3 to the required specifications by extrusion and cold drawing methods, cut and straighten to obtain multi-core MgB2 sub-elements; Step 5: After cleaning and drying the multi-core MgB2 sub-elements obtained in Step 4, closely pack them into an oxygen-free copper sheath by the tube-passing method to obtain a multi-core MgB2 secondary composite ingot. Process the multi-core MgB2 secondary composite ingot to the final specifications by cold drawing to obtain a thousand-core MgB2 composite wire; Step 6: Perform high-temperature phase-forming heat treatment on the MgB2 composite wire obtained in Step 5 to obtain a thousand-core MgB2 superconducting wire.

2. The preparation method according to claim 1, characterized in that, The B powder described in Step 1 is amorphous boron powder with an average particle size of 50 nm and a purity of 99.9%; the Mg powder is 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 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 described in Step 1 is 3% - 5% of the total mass of the Mg powder and 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.

5. The preparation method according to claim 1, wherein 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 they are evenly distributed, and the non-opening end is 10 mm - 15 mm away from the ingot tail; the degreasing is carried out with a metal degreasing agent, and the cleaning is carried out with dilute hydrochloric acid with a volume ratio of 10% - 15%.

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

7. The preparation method according to claim 1, characterized in that, The size of the multi-core MgB2 primary composite ingot after extrusion in Step 4 is less than Ф60 mm, the extrusion temperature is 480℃ - 550℃, and the time is 3 h - 5 h; the pass processing amount during the cold drawing process is 15% - 20%, and the specifications of the multi-core MgB2 sub-elements are Ф5.0 mm - Ф8.0 mm.

8. The preparation method according to claim 1, characterized in that, The final specifications in Step 5 are Ф0.5 mm - Ф1.0 mm.

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

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

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