Mgb 2 superconducting wire and preparation method therefor

Abstract

The present invention relates to the technical field of superconducting materials. Disclosed are a MgB2 superconducting wire and a preparation method therefor. The preparation method comprises: melting Mg, Cu and Ti to obtain a Mg alloy ingot, processing the Mg alloy ingot to obtain a Mg alloy rod, loading the Mg alloy rod and B powder into a 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, then loading into a monel tube in a densely-packed manner, and performing cold-forming treatment to obtain a multi-core composite wire; and performing high-temperature phase-forming heat treatment on the multi-core composite wire to prepare the MgB2 superconducting wire. In the present application, the Mg alloy rod containing Cu and Ti metal elements is used as a Mg source for preparing a MgB2 multi-core wire, so as to improve the plastic deformation ability of the Mg alloy rod in the wire treatment processes, and improve the grain boundary coupling, thereby improving the current carrying performance of the MgB2 superconducting wire.

Description

MgB2 superconducting wire and preparation method thereof TECHNICAL FIELD

[0001] The application belongs to the technical field of superconducting materials, and discloses a MgB2 superconducting wire and a preparation method thereof. BACKGROUND

[0002] MgB2 (magnesium diboride) superconducting material has a critical transition temperature of 39K, and can work in a liquid hydrogen or a refrigerator cooling temperature range (15-25K) without expensive liquid helium. The reserves of Mg and B in nature are abundant, and the industrial preparation cost is low. The engineering application of practical MgB2 superconducting material has a great competitive advantage. At present, the preparation of practical MgB2 superconducting wire / tape adopts a powder tube filling technology, mainly including an in-situ method, an ex-situ method and an internal Mg diffusion-IMD method. Researches show that the grain connectivity and filling density of the MgB2 phase are key factors affecting the superconducting transmission performance of the wire. The density of the MgB2 phase prepared by the IMD method is obviously higher than that prepared by the In-situ method or the Ex-situ method. In addition, the IMD method can make the MgB2 phase obtain a strong coupling of grain boundaries, so that the critical current density (Jc) of the MgB2 wire prepared by the IMD method is obviously higher than that prepared by the In-situ method or the Ex-situ method.

[0003] The IMD method usually places a Mg rod in a Nb or Ta tube, fills B powder in the gap between the Mg rod and the inner wall of the tube, processes a single core rod, further inserts the single core rod into a Cu-Ni alloy tube after assembly, and finally obtains a multi-core MgB2 wire through cold processing. However, since the Mg metal has a close-packed hexagonal lattice structure, the slip coefficient is low, and the plastic deformation ability is poor, so when the multi-core MgB2 wire is prepared by the IMD method, the Mg rod inside is prone to breakage, which finally reduces the stability of the long wire processing of the wire and also causes the current-carrying performance of the wire to decay. SUMMARY

[0004] In order to overcome the problems in the prior art, the application provides a MgB2 superconducting wire and a preparation method thereof. Compared with the prior art, the application has the advantages that a Mg alloy rod doped with Cu and Ti elements by smelting is used as a central Mg diffusion source, and the Mg alloy rod is further coated with an oxygen-free Cu tube. This method not only helps to improve the plastic deformation ability of the Mg alloy rod in the cold processing process of the MgB2 wire, but also makes the wire obtain good thermal stability and high current-carrying performance under an external field.

[0005] In one aspect, the application relates to a preparation method of MgB2 superconducting wire, which comprises the following steps: obtaining Mg alloy ingot by smelting method through Mg, Cu and Ti; processing the Mg alloy ingot to obtain Mg alloy rod; loading the Mg alloy rod and B powder into Nb tube to obtain composite rod;

[0006] processing the composite rod to obtain single core wire; loading the single core wire into oxygen-free copper tube; densely loading the single core wire into Monel alloy tube; and obtaining multi-core composite wire after cold plastic processing.

[0007] processing the multi-core composite wire to obtain the MgB2 superconducting wire.

[0008] Further, in the preparation method of MgB2 superconducting wire, the mass percentage of Mg, Cu and Ti in the Mg alloy ingot is 0.8-0.9:0.05:0.05-0.15.

[0009] Further, in the preparation method of MgB2 superconducting wire, the smelting method is electron beam smelting.

[0010] Further, in the preparation method of MgB2 superconducting wire, the purity of the Nb tube used in the preparation process of the single core wire is greater than or equal to 99.99%, and the proportion of Nb in the MgB2 superconducting wire is 10%-12%; the diameter of the single core wire is F3.8mm-F7.8mm.

[0011] Further, in the preparation method of MgB2 superconducting wire, the outer diameter of the oxygen-free Cu tube is 12mm, the wall thickness is 2mm-4mm, and the purity is greater than or equal to 99.9%; the core number of the composite wire is 37-136.

[0012] Further, in the preparation method of MgB2 superconducting wire, the temperature of the high-temperature phase formation heat treatment is 500℃-900℃, and the holding time is 5h-15h.

[0013] On the other hand, the application relates to a MgB2 superconducting wire prepared by the above preparation method.

[0014] Compared with the prior art, the technical scheme provided by the application has the following beneficial effects or advantages:

[0015] (1) The Mg alloy rod containing Cu and Ti metal elements is used as the Mg source for preparing the MgB2 multi-core wire. On the one hand, the doping of Cu and Ti elements improves the plastic deformation capacity of the Mg alloy rod in the wire processing process. On the other hand, the Cu element provides a channel for the diffusion reaction of Mg element to B element, increases the activity of MgB2 phase reaction, and the Ti element further refines the MgB2 grains and improves the grain boundary coupling degree.

[0016] (2) In the present application, the single-core wire (the substrate is Nb) processed by one-time molding is loaded into an oxygen-free Cu tube, and then secondary assembly and processing are carried out, so as to provide a Cu substrate for the MgB2 wire to improve the thermal stability of the wire.

[0017] (3) The MgB2 superconducting wire prepared by the preparation method of the present application has a MgB2 grain size of 50-80 nm, and the grains have good connectivity. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Fig. 1 is the micro-morphology of the MgB2 superconducting wire prepared in Example 1 of the present application.

[0020] Fig. 2 is the micro-morphology of the MgB2 superconducting wire prepared in Example 2 of the present application.

[0021] Fig. 3 is the micro-morphology of the MgB2 superconducting wire prepared in Example 3 of the present application.

[0022] Fig. 4 is the micro-morphology of the MgB2 superconducting wire prepared in Comparative Example 1 of the present application.

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

[0024] In the following, the technical solutions of the present application will be described in conjunction with the embodiments, but the present application is not limited to the following embodiments.

[0025] The experimental methods and detection methods described in the following embodiments are all conventional methods unless otherwise specified; and the reagents and materials described are all commercially available unless otherwise specified.

[0026] The application provides a preparation method of high critical current density MgB2 superconducting wire, and is specifically implemented according to the following steps. Example 1

[0027] The embodiment provides preparation of MgB2 superconducting wire.

[0028] Step one, Mg, Cu and Ti are obtained by electron beam melting to obtain Mg alloy ingot, wherein the mass percentage of Mg, Cu and Ti is 0.9:0.05:0.05.

[0029] Step two, the Mg alloy ingot is processed into a Mg alloy rod by extrusion and rolling, and the flatness of the Mg alloy rod is 4mm / 1000mm. The Mg alloy rod is further subjected to surface cleaning and polishing treatment and is ready for use.

[0030] Step three, in a glove box with a purity of 99.999% of flowing argon, the Mg alloy rod is loaded into a Nb tube with a purity of 99.9% and a flatness of 4mm / 1000mm, and the gap area between the Mg alloy rod and the inner wall of the Nb tube is filled with nano B powder (purity 99.9%, particle size 2mm) to obtain a composite rod. Finally, the composite rod is processed into a single-core wire with a diameter of F7.8mm, and the single-core wire is further subjected to straightening treatment and cut off.

[0031] Step four, the single-core wire is cleaned and loaded into an oxygen-free Cu tube with an outer diameter of F12mm and a wall thickness of 2mm, then densely packed into a Monel alloy tube, and finally cold plastic processed into a 37-core structure multi-core composite wire with a diameter of 2mm.

[0032] Step five, the multi-core composite wire is obtained in a vacuum environment after being kept at 500℃ for 15h to obtain MgB2 superconducting wire with superconducting performance.

[0033] Fig. 1 is the microstructure of the MgB2 superconducting wire prepared in the embodiment, and it can be seen from the figure that the MgB2 grain size of the MgB2 superconducting wire prepared in the embodiment is about 80nm, there is no hole between the grains and the connection is dense. Fig. 5 is the critical current density value (J c -B curve) of the prepared MgB2 superconducting wire under different test conditions, and the critical current density of the MgB2 superconducting wire prepared in the embodiment reaches 7200A / mm 2 . Example 2

[0034] The embodiment provides preparation of MgB2 superconducting wire.

[0035] Step one, Mg, Cu and Ti are obtained by electron beam melting to obtain Mg alloy ingot, wherein the mass percentage of Mg, Cu and Ti is 0.85:0.05:0.1.

[0036] Step two, the Mg alloy ingot is processed into a Mg alloy rod by extrusion and rolling, and the flatness of the Mg alloy rod is 4mm / 1000mm. The Mg alloy rod is further subjected to surface cleaning and polishing treatment before use.

[0037] Step three, in a glove box with a purity of 99.999% flowing argon, the Mg alloy rod is loaded into a Nb tube with a purity of 99.9% and a flatness of 4mm / 1000mm, and the gap between the Mg alloy rod and the inner wall of the Nb tube is filled with nano-B powder (purity 99.9%, particle size 2mm) to obtain a composite rod. Finally, the composite rod is processed into a single-core wire with a diameter of F5.8mm, and the single-core wire is further subjected to straightening treatment and cutting.

[0038] Step four, the single-core wire is cleaned and loaded into an oxygen-free Cu tube with an outer diameter of F12mm and a wall thickness of 3mm, then densely packed into a Monel alloy tube, and finally cold plastic processed into a 88-core structure multi-core composite wire with a diameter of 2mm.

[0039] Step five, the multi-core composite wire is obtained in a vacuum environment after heat preservation at 700℃ for 10h, and the MgB2 superconducting wire has superconducting performance.

[0040] Figure 2 is the micro-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 is the critical current density value (J c -B curve) of the prepared MgB2 superconducting wire under different test conditions. At 4.2K, 3T, the critical current density of the MgB2 wire prepared in this embodiment reaches 7600A / mm 2 . Example 3

[0041] The embodiment provides a preparation of MgB2 superconducting wire.

[0042] Step one, Mg, Cu and Ti are obtained by electron beam melting to obtain Mg alloy ingot, wherein the mass percentage of Mg, Cu and Ti is 0.80:0.05:0.15.

[0043] Step two, the Mg alloy ingot is processed into a Mg alloy rod by extrusion and rolling, and the flatness of the Mg alloy rod is 4mm / 1000mm. The Mg alloy rod is further subjected to surface cleaning and polishing treatment before use.

[0044] Step three, in a flowing argon glove box with purity of 99.999%, Mg alloy rod was loaded into Nb tube with purity of 99.9% and flatness of 4mm / 1000mm, and nano B powder (purity of 99.9%, particle size of 2mm) was filled in the gap between Mg alloy rod and Nb tube inner wall to prepare a composite rod. Finally, the composite rod was processed into a single core wire with a diameter of F3.8mm, and the single core wire was further subjected to straightening treatment and cutting.

[0045] Step four, after the surface of the single core wire was cleaned, it was loaded into an oxygen-free Cu tube with an outer diameter of F12mm and a wall thickness of 4mm, and then densely packed into a Monel alloy tube. Finally, the multi-core composite wire with a 136-core structure and a diameter of 2mm was obtained through cold plastic processing.

[0046] Step five, the multi-core composite wire was obtained by heat treatment at 700℃ for 10h in a vacuum environment to obtain MgB2 superconducting wire material with superconducting properties.

[0047] Figure 3 is the microstructure of the MgB2 superconducting wire material prepared in this embodiment. As can be seen from the figure, the MgB2 grain size of the MgB2 superconducting wire material prepared in this embodiment is about 50nm, and the compactness of the MgB2 grain is also significantly improved. Compared with Example 1 and Example 2, the MgB2 grain size of the wire material prepared in this embodiment is further reduced. Figure 5 is the critical current density value (J c -B curve) of the prepared MgB2 superconducting wire material under different test conditions. At 4.2K, 3T, the critical current density of the MgB2 wire material prepared in this embodiment reaches 8000A / mm 2 .

[0048] Comparative Example 1

[0049] This comparative example provides a preparation method of MgB2 superconducting wire material.

[0050] This comparative example is different from Example 1 in that the Mg rod without doped Cu and Ti elements is directly used as a diffusion Mg source in the wire material preparation process, and finally a 37-core structure MgB2 superconducting wire material is prepared.

[0051] Figure 4 is the microstructure of the MgB2 superconducting wire material prepared in this comparative example. As can be seen from the figure, the MgB2 grain size of the MgB2 superconducting wire material prepared in this embodiment is about 100nm, and a certain amount of micro-holes exist in the crystal structure, which reduces the compactness and connectivity between the grains. Figure 5 is the critical current density value (J c -B curve) of the prepared MgB2 superconducting wire material under different test conditions. At 4.2K, 3T, the critical current density of the MgB2 wire material prepared in this embodiment reaches 6500A / mm 2Compared with example 1, example 2 and example 3, the MgB2 grain size of the wire prepared in the present comparative example is larger, and the critical current density of the wire is lower. Therefore, by doping trace amounts of Cu and Ti elements in the Mg rod through the melting method in the present application, the reaction activity in the MgB2 phase formation process is increased, the MgB2 grain is refined, and the grain boundary connectivity is improved, so that the wire has higher current carrying performance.

[0052] The above description describes the basic principles, main features and advantages of the present application. The above examples and descriptions are only used to describe the preferred embodiments of the present application, and the present application is not limited by the above examples. Without departing from the spirit and scope of the present application, various changes and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the scope of protection of the present application.

Claims

1. A method of producing a MgB2 superconducting wire, characterized by, The application relates to a MgB2 superconducting wire material and a preparation method thereof. Mg, Cu and Ti are used to obtain a Mg alloy ingot through a melting method, the Mg alloy ingot is processed to obtain a Mg alloy rod, the Mg alloy rod and B powder are loaded into a Nb tube to obtain a composite rod; The composite rod is processed to obtain a single core wire, the single core wire is loaded into an oxygen-free copper tube, and the oxygen-free copper tube is densely loaded into a monel alloy tube to obtain a multi-core composite wire after cold plastic forming processing; The multi-core composite wire is subjected to high-temperature phase formation heat treatment to obtain the MgB2 superconducting wire material.

2. The production method according to claim 1, characterized by, In the Mg alloy ingot, the mass percentage of Mg, Cu and Ti is 0.8-0.9:0.05:0.05-0.

15.

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

4. The method of claim 1, wherein, The purity of the Nb tube is greater than or equal to 99.99%, and the diameter of the single core wire is F3.8mm-F7.8mm.

5. The preparation method according to claim 1, characterized in that, The outer diameter of the oxygen-free Cu tube is 12mm, the wall thickness is 2mm-4mm, and the purity is greater than or equal to 99.9%; the core number of the composite wire is 37-136.

6. The method of claim 1, wherein, The high-temperature phase formation heat treatment is carried out at a temperature of 500-900 DEG C for 5-15h.

7. A MgB2 superconducting wire, characterized by, The application relates to a MgB2 superconducting wire material and a preparation method thereof.

8. The superconducting wire of claim 7, wherein, The MgB2 grain size in the superconducting wire material is 50-80nm.

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