A MgB2 superconducting wire and its preparation method

Abstract

The present invention belongs to the technical field of superconducting materials and discloses a MgB2 superconducting wire and a preparation method thereof. The preparation method comprises: obtaining an Mg alloy ingot from Mg, Cu, and Ti through a smelting process; processing the Mg alloy ingot to obtain an Mg alloy rod; loading the Mg alloy rod and B powder into an Nb tube to obtain a composite rod; processing the composite rod to obtain a single-core wire; loading the single-core wire into an oxygen-free copper tube, which is then densely packed into a monel alloy tube; and cold-forming the composite rod to obtain a multi-core composite wire; and subjecting the multi-core composite wire to a high-temperature phase-forming heat treatment to obtain the MgB2 superconducting wire. This application utilizes an Mg alloy rod containing Cu and Ti metal elements as the Mg source for preparing the MgB2 multi-core wire, thereby improving the plastic deformation ability of the Mg alloy rod during wire processing and increasing the grain boundary coupling, thereby enhancing the current-carrying performance of the MgB2 superconducting wire.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting materials and discloses a MgB2 superconducting wire and a preparation method thereof. Background Art

[0002] MgB2 (magnesium diboride) superconducting material has a critical transition temperature of 39K, allowing it to operate in liquid hydrogen or cryostat-cooled temperatures (15-25K) without expensive liquid helium. The abundant reserves of Mg and B in nature and the low cost of industrial production give MgB2 superconducting materials a significant competitive advantage in engineering applications. Currently, practical MgB2 superconducting wires and tapes are produced using powder-filled tube techniques, primarily in-situ, ex-situ, and internal magnesium diffusion (IMD). Research has shown that grain connectivity and packing density of the MgB2 phase are key factors influencing the superconducting transmission properties of wires. Wires produced using the IMD method have significantly higher MgB2 phase density than those produced using in-situ or ex-situ methods. Furthermore, the IMD method allows for strong grain boundary coupling in the MgB2 phase, resulting in significantly higher critical current densities (Jc) for MgB2 wires produced using the IMD method than those produced using either the in-situ or ex-situ methods.

[0003] The IMD method typically involves placing a Mg rod in a Nb or Ta tube, filling the gap between the Mg rod and the inner wall of the tube with B powder, and processing it into a single-core rod. The single-core rods are then assembled and inserted into a Cu-Ni alloy tube, and finally formed into a multi-core MgB2 wire through cold working. However, due to the close-packed hexagonal lattice structure of Mg metal, its low slip coefficient and poor plastic deformation capacity, the internal Mg rods are prone to breakage when using the IMD method to prepare multi-core MgB2 wire, ultimately reducing the stability of the wire's long-length processing and attenuating the wire's current-carrying performance. Summary of the Invention

[0004] To overcome the problems of the prior art, the present invention provides a MgB2 superconducting wire and a method for preparing the same. Compared to existing technologies, the present invention utilizes a Mg alloy rod doped with Cu and Ti elements through melting as a central Mg diffusion source, and further utilizes an oxygen-free Cu tube to clad the Mg alloy rod. This method not only improves the plastic deformation capacity of the Mg alloy rod during cold working of the MgB2 wire, but also ensures excellent thermal stability and high current-carrying performance under external fields.

[0005] In one aspect, the present invention relates to a method for preparing a MgB2 superconducting wire, comprising: smelting Mg (magnesium), Cu (copper), and Ti (titanium) to obtain an Mg alloy ingot, processing the Mg alloy ingot to obtain an Mg alloy rod, and loading the Mg alloy rod and B powder into an Nb tube to obtain a composite rod;

[0006] Processing the composite rod to obtain a single-core wire, loading the single-core wire into an oxygen-free copper tube, closely packed into a monel alloy tube, and obtaining a multi-core composite wire after cold shaping;

[0007] The multi-core composite wire is subjected to high-temperature phase-forming heat treatment to obtain the MgB2 superconducting wire.

[0008] Furthermore, in the method for preparing the MgB2 superconducting wire provided by the present invention, the mass percentages of Mg, Cu and Ti in the Mg alloy ingot are 0.8-0.9:0.05:0.05-0.15.

[0009] Furthermore, in the method for preparing the MgB2 superconducting wire provided by the present invention, the smelting method is electron beam melting.

[0010] Furthermore, in the preparation method of the MgB2 superconducting wire provided by the present invention, in the preparation process of the single-core wire, the purity of the Nb tube used is ≥99.99%, and the proportion of Nb in the MgB2 superconducting wire is 10% to 12%; the diameter of the single-core wire is Φ3.8mm to Φ7.8mm.

[0011] Furthermore, in the preparation method of the MgB2 superconducting wire provided by the present invention, the outer diameter of the oxygen-free copper tube is 12 mm, the wall thickness is 2 mm to 4 mm, and the purity is ≥99.9%; the number of cores of the multi-core composite wire is 37 to 136.

[0012] Furthermore, in the method for preparing the MgB2 superconducting wire provided by the present invention, the temperature of the high-temperature phase-forming heat treatment is 500°C to 900°C, and the holding time is 5h to 15h.

[0013] On the other hand, the present invention relates to a MgB2 superconducting wire, which is prepared by the above-mentioned method for preparing the MgB2 superconducting wire.

[0014] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects or advantages:

[0015] (1) The present invention uses a Mg alloy rod containing Cu and Ti metal elements as the Mg source for preparing MgB2 multi-core wire. On the one hand, the doping of Cu and Ti elements will improve the plastic deformation ability of the Mg alloy rod during the wire processing process. On the other hand, the Cu element provides a channel for the diffusion reaction of the Mg element to the B element, increasing the activity of the MgB2 phase formation reaction, and the Ti element further refines the MgB2 grains and improves the grain boundary coupling.

[0016] (2) In the present invention, the single-core wire (with Nb as the matrix) after primary processing and forming is loaded into an oxygen-free Cu tube, and then secondary assembly and processing are performed. This method provides a Cu matrix for the MgB2 wire to improve the thermal stability of the wire.

[0017] (3) The MgB2 grain size in the wire prepared by the preparation method of the MgB2 superconducting wire proposed in the present invention is 50 to 80 nm, and the grains have good connectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is the microscopic morphology of the MgB2 superconducting wire prepared in Example 1 of the present invention.

[0020] Figure 2 This is the microscopic morphology of the MgB2 superconducting wire prepared in Example 2 of the present invention.

[0021] Figure 3 This is the microscopic morphology of the MgB2 superconducting wire prepared in Example 3 of the present invention.

[0022] Figure 4 This is the microscopic morphology of the MgB2 superconducting wire prepared in Comparative Example 1 of the present invention.

[0023] Figure 5 J of the MgB2 superconducting wire prepared in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention c -B curve. DETAILED DESCRIPTION

[0024] 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.

[0025] 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.

[0026] The present invention provides a method for preparing a high critical current density MgB2 superconducting wire, which is specifically implemented according to the following steps:

[0027] Example 1

[0028] This embodiment provides a method for preparing a MgB2 superconducting wire.

[0029] Step 1: Mg, Cu, and Ti are subjected to electron beam melting to obtain a Mg alloy ingot, wherein the mass percentages of Mg, Cu, and Ti are 0.9:0.05:0.05.

[0030] Step 2: The Mg alloy ingot is processed into a Mg alloy rod by extrusion and rolling, and the straightness of the Mg alloy rod is 4 mm / 1000 mm. The surface of the Mg alloy rod is further cleaned and polished before use.

[0031] Step 3: In a glove box filled with 99.999% pure argon, the Mg alloy rod was placed into a 99.9% pure Nb tube with a straightness of 4 mm / 1000 mm. The gap between the Mg alloy rod and the inner wall of the Nb tube was filled with nano-B powder (99.9% pure, 2 μm particle size) to produce a composite rod. Finally, the composite rod was processed into a single core wire with a diameter of 7.8 mm, which was further straightened and cut.

[0032] Step 4: After cleaning the surface of the single-core wire, place it into an oxygen-free Cu tube with an outer diameter of Φ12mm and a wall thickness of 2mm, then densely pack it into a monel alloy tube, and finally cold-plastic process it into a multi-core composite wire with a 37-core structure and a diameter of 2mm.

[0033] Step 5: Heat the multi-core composite wire at 500° C. for 15 hours in a vacuum environment to obtain a MgB2 superconducting wire with superconducting properties.

[0034] Figure 1 This is the microscopic morphology of the MgB2 superconducting wire prepared in this embodiment. As can be seen from the figure, the MgB2 grain size of the MgB2 superconducting wire prepared in this embodiment is about 80nm, there are no holes between the grains and the connections are dense. Figure 5 The critical current density (J) of the prepared MgB2 superconducting wire under different test conditions c -B curve), at 4.2K and 3T, the critical current density of the MgB2 superconducting wire prepared in this embodiment reaches 7200A / mm 2 .

[0035] Example 2

[0036] This embodiment provides a method for preparing a MgB2 superconducting wire.

[0037] Step 1: Mg, Cu, and Ti are subjected to electron beam melting to obtain a Mg alloy ingot, wherein the mass percentage of Mg, Cu, and Ti is 0.85:0.05:0.1.

[0038] Step 2: The Mg alloy ingot is processed into a Mg alloy rod by extrusion and rolling, and the straightness of the Mg alloy rod is 4 mm / 1000 mm. The surface of the Mg alloy rod is further cleaned and polished before use.

[0039] Step 3: In a glove box filled with 99.999% pure argon, the Mg alloy rod was placed into a 99.9% pure Nb tube with a straightness of 4 mm / 1000 mm. The gap between the Mg alloy rod and the inner wall of the Nb tube was filled with nano-B powder (99.9% pure, 2 μm particle size) to produce a composite rod. Finally, the composite rod was processed into a single core wire with a diameter of 5.8 mm, which was further straightened and cut.

[0040] Step 4: After cleaning the surface of the single-core wire, place it into an oxygen-free Cu tube with an outer diameter of Φ12mm and a wall thickness of 3mm, then densely pack it into a monel alloy tube, and finally cold-plastic process it into a multi-core composite wire with an 88-core structure and a diameter of 2mm.

[0041] Step 5: Heat the multi-core composite wire at 700° C. for 10 hours in a vacuum environment to obtain a MgB2 superconducting wire with superconducting properties.

[0042] Figure 2 This is the microscopic morphology of the MgB2 superconducting wire prepared in this embodiment. As can be seen from the figure, the MgB2 grain size of the MgB2 superconducting wire prepared in this embodiment is about 65nm. Compared with Example 1, as the grain size decreases, the density between MgB2 grains is also enhanced. Figure 5 The critical current density (J) of the prepared MgB2 superconducting wire under different test conditions c -B curve), at 4.2K and 3T, the critical current density of the MgB2 wire prepared in this embodiment reaches 7600A / mm 2 .

[0043] Example 3

[0044] This embodiment provides a method for preparing a MgB2 superconducting wire.

[0045] Step 1: Mg, Cu, and Ti are subjected to electron beam melting to obtain a Mg alloy ingot, wherein the mass percentages of Mg, Cu, and Ti are 0.80:0.05:0.15.

[0046] Step 2: The Mg alloy ingot is processed into a Mg alloy rod by extrusion and rolling, and the straightness of the Mg alloy rod is 4 mm / 1000 mm. The surface of the Mg alloy rod is further cleaned and polished before use.

[0047] Step 3: In a glove box filled with 99.999% pure argon, the Mg alloy rod was placed into a 99.9% pure Nb tube with a straightness of 4 mm / 1000 mm. The gap between the Mg alloy rod and the inner wall of the Nb tube was filled with nano-B powder (99.9% pure, 2 μm particle size) to produce a composite rod. Finally, the composite rod was processed into a single core wire with a diameter of 3.8 mm, which was further straightened and cut.

[0048] Step 4: After cleaning the surface of the single-core wire, place it into an oxygen-free Cu tube with an outer diameter of Φ12mm and a wall thickness of 4mm, then densely pack it into a monel alloy tube, and finally cold-plastic process it into a multi-core composite wire with a 136-core structure and a diameter of 2mm.

[0049] Step 5: Heat the multi-core composite wire at 700° C. for 10 hours in a vacuum environment to obtain a MgB2 superconducting wire with superconducting properties.

[0050] Figure 3 This is the microscopic morphology of the MgB2 superconducting wire prepared in this embodiment. As can be seen from the figure, the MgB2 grain size of the MgB2 superconducting wire prepared in this embodiment is about 50 nm, and the density of the MgB2 grains is also significantly improved. Compared with Examples 1 and 2, the MgB2 grain size of the wire prepared in this embodiment is further reduced. Figure 5 The critical current density (J) of the prepared MgB2 superconducting wire under different test conditions c -B curve), at 4.2K and 3T, the critical current density of the MgB2 wire prepared in this embodiment reaches 8000A / mm 2 .

[0051] Comparative Example 1

[0052] This comparative example provides a preparation method for a MgB2 superconducting wire.

[0053] The difference between this comparative example and Example 1 is that Mg rods not doped with Cu and Ti elements are directly used as the diffusion Mg source during the wire preparation process, and finally a MgB2 superconducting wire with a 37-core structure is prepared.

[0054] Figure 4 This is the microscopic morphology of the MgB2 superconducting wire prepared in this comparative example. As can be seen from the figure, the MgB2 grain size of the MgB2 superconducting wire prepared in this embodiment is about 100nm, and there are a certain amount of microscopic holes in the crystal structure, which reduces the density and connectivity between the grains. Figure 5 The critical current density (J) of the prepared MgB2 superconducting wire under different test conditions c-B curve), at 4.2K and 3T, the critical current density of the MgB2 wire prepared in this embodiment reaches 6500A / mm 2 Compared to Examples 1, 2, and 3, the wire prepared in this comparative example has a larger MgB2 grain size, corresponding to a lower critical current density. This indicates that the present invention, by doping the Mg rod with trace amounts of Cu and Ti through the smelting method, increases the reactivity of the MgB2 phase formation process, refines the MgB2 grains, and improves grain boundary connectivity, thereby enabling the wire to achieve higher current-carrying performance.

[0055] 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, characterized in that: include: Mg, Cu, and Ti are smelted to obtain an Mg alloy ingot, the Mg alloy ingot is processed to obtain an Mg alloy rod, and the Mg alloy rod and B powder are loaded into an Nb tube to obtain a composite rod; Processing the composite rod to obtain a single-core wire, loading the single-core wire into an oxygen-free copper tube, closely packed into a monel alloy tube, and obtaining a multi-core composite wire after cold shaping; The multi-core composite wire is subjected to a high-temperature phase forming heat treatment to obtain the MgB2 superconducting wire; in the Mg alloy ingot, the mass percentages of Mg, Cu, and Ti are 0.8-0.9:0.05:0.05-0.15; The purity of the Nb tube is ≥99.99%, and the diameter of the single core wire is Φ3.8mm~Φ7.8mm; The outer diameter of the oxygen-free copper tube is 12 mm, the wall thickness is 2 mm to 4 mm, and the purity is ≥99.9%; the number of cores of the multi-core composite wire is 37 to 136.

2. The preparation method according to claim 1, characterized in that The melting method is electron beam melting.

3. The preparation method according to claim 1, characterized in that The temperature of the high-temperature phase forming heat treatment is 500° C. to 900° C., and the holding time is 5 hours to 15 hours.

4. A MgB2 superconducting wire, characterized in that: The superconducting wire is prepared by the method for preparing the MgB2 superconducting wire according to any one of claims 1 to 3.

5. The superconducting wire according to claim 4, wherein The MgB2 grain size in the superconducting wire is 50-80 nm.

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