Multi-core composite wire for preparing superconductor wire containing magnesium diboride and preparation method of multi-core composite wire

Abstract

The invention belongs to the technical field of superconducting wires, and relates to a multi-core composite wire for preparing a magnesium diboride-containing superconductor wire and a preparation method of the multi-core composite wire. The multi-core composite wire provided by the invention comprises a plurality of single-core wire bundles which are densely arranged in a wrapping sleeve; the single core wire includes: a powder core including Mg powder and B powder; a barrier layer tube made of metal, the powder core being disposed inside the barrier layer tube; in the multi-core composite wire, the powder filling density of the powder core in the single-core wire increases from the center to the edge. According to the multi-core composite wire provided by the invention, when the multi-core composite wire is used for preparing a wire containing a magnesium diboride superconductor based on a powder tubing method, the core wire can obtain uniform and consistent plastic deformation under the action of machining stress by setting the powder density gradient change along the radial direction; and the stable processing of preparation of the kilometer-level ultra-fine core wire magnesium diboride superconducting wire is favorably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting wires, and relates to a multi-core composite wire for preparing a superconductor wire containing magnesium diboride and a preparation method thereof. Background Art

[0002] The advantages of magnesium diboride (MgB2) superconductor such as simple production process, short production cycle, high critical current density, low cost, and ability to work in a refrigerator environment make it a promising superconducting material for use in nuclear magnetic resonance superconducting magnets. However, like other superconducting materials, magnesium diboride superconductors will produce certain energy losses when transmitting alternating current or being in an alternating magnetic field, namely, AC losses. In the prior art, reducing the size of the core wire is widely considered to be an effective method to reduce hysteresis losses. By thinning the core wire, the magnetic flux pinning effect can be reduced, thereby reducing the energy loss of the superconductor when transmitting alternating current or being in an alternating magnetic field. However, when preparing longer-sized magnesium diboride superconducting wires, simply reducing the size of the core wire will bring a series of problems. Specifically, due to the reduction in the size of the core wire, its mechanical strength is correspondingly reduced, making the wire prone to breakage during cold processing, stretching and other preparation processes. In particular, in the center and edge local areas of the wire, due to factors such as stress concentration and uneven processing, the core wire is more likely to suffer severe rupture. This not only leads to frequent wire breakage during processing, but also seriously affects the stable processing and yield rate of kilometer-level wires. In addition, core wire breakage will also destroy the overall structure of the superconducting wire, affect the uniformity of current distribution, and further aggravate AC loss and reduce the overall performance of the superconductor. Therefore, how to reduce the core wire size to reduce hysteresis loss while ensuring the mechanical strength and processing stability of the superconducting wire has become a technical problem that needs to be solved urgently in the current field of superconducting wire technology. Summary of the invention

[0003] The purpose of the present invention is to provide a multi-core composite wire for preparing magnesium diboride superconductor wires based on powder tube filling. By setting a powder density gradient change along the radial direction, the core wire can obtain uniform and consistent plastic deformation under the action of mechanical processing stress, which is beneficial to improving the stable processing of the preparation of kilometer-level ultra-fine core wire magnesium diboride superconducting wires.

[0004] On the one hand, the present invention relates to a multi-core composite wire for preparing a superconductor wire containing magnesium diboride, wherein the multi-core composite wire comprises a plurality of single core wires which are processed into a desired size by cold plastic processing and are bundled and closely arranged inside a sheathing tube; the single core wire comprises: a powder core which contains Mg powder and B powder; a barrier layer tube made of metal, wherein the powder core is arranged inside the barrier layer tube; in the multi-core composite wire, the powder filling density of the powder core in the single core wire increases from the center to the edge. The multi-core composite wire according to the present invention is configured such that, when cold plastic processing is performed, the powder density of the single core wire in the central area of ​​the wire is less than that in the edge area, so that the wire can obtain an extremely fine core wire while the core wire along the radial direction of the wire can still obtain good plastic deformation uniformity and structural integrity.

[0005] Furthermore, in the multi-core composite wire for preparing a magnesium diboride superconductor wire provided by the present invention, the diameters of the plurality of single-core wires are the same, and the powder filling density increases in the range of 0.7 g / cm from the center to the edge. 3 ~2.1g / cm 3 .

[0006] Furthermore, in the multi-core composite wire for preparing a magnesium diboride-containing superconductor wire provided by the present invention, the material of the barrier layer tube is at least one of Ta, Nb, Ag, Zr, Ti, Cu, Mo, Fe, and W.

[0007] In the construction of a single core wire, a barrier layer tube (also called a sleeve or a substrate) is usually included. The barrier layer tube can be made of various metals with a melting point above 900°C and good thermal conductivity, such as Ta, Nb, Ag, Zr, Ti, Cu, Mo, Fe, W or their alloys.

[0008] In the construction of the multi-core composite wire, a sheath tube is usually included, which can be made of various metals with a melting point higher than 900°C and certain toughness, strength and good thermal conductivity and electrical conductivity, such as at least one of Cu, Zr, Mo, Sn, Fe, Ni, Ti, Ag, Nb or their alloys.

[0009] Furthermore, in the multi-core composite wire for preparing a magnesium diboride-containing superconductor wire provided by the present invention, the material of the barrier layer tube is NbCu alloy.

[0010] Furthermore, in the multi-core composite wire for preparing a magnesium diboride superconductor wire provided by the present invention, in order to ensure that the plastic deformation of all core wires of the composite wires with different core numbers is well uniform during plastic processing, the volume ratio of Nb and Cu in the single core wire is designed to be a fixed value. In some embodiments, the volume ratio of Nb in the single core wire is 34% to 35%, and the volume ratio of Cu is 30% to 31%.

[0011] Furthermore, in the multi-core composite wire for preparing a magnesium diboride-containing superconductor wire provided by the present invention, the number of cores of the multi-core composite wire is 91-169.

[0012] On the other hand, the present invention relates to a method for preparing a superconducting wire, which comprises: subjecting the multi-core composite wire to cold plastic processing to a desired size, and then subjecting the multi-core composite wire to heat treatment to generate a superconducting wire containing a magnesium diboride superconducting phase.

[0013] Furthermore, in the preparation method provided by the present invention, the heat treatment comprises: maintaining the temperature at 500° C. to 900° C. for 5 h to 15 h to generate a magnesium diboride superconducting phase.

[0014] On the other hand, the present invention relates to a superconducting wire, which is prepared by the preparation method.

[0015] Furthermore, in the superconducting wire provided by the present invention, the diameter of the core wire in the superconducting wire is 15-25 μm.

[0016] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: In the multi-core composite wire and magnesium diboride superconductor wire preparation process proposed by the present invention, the wire is assembled and processed by the gradient method, and the powder density gradient of the wire core along the radial direction enables the core to obtain uniform plastic deformation under the action of mechanical processing stress, which provides a good guarantee for the stable processing of kilometer-level ultra-fine core magnesium diboride wire. The core diameter of the magnesium diboride wire prepared by the method proposed by the present invention can be as small as 15μm, so that the wire has lower AC loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0018] Figure 1 This is a cross-sectional structural diagram of a 91-core magnesium diboride superconducting wire prepared in Example 1 of the present invention.

[0019] Figure 2 This is a cross-sectional structural diagram of a 127-core magnesium diboride superconducting wire prepared in Example 2 of the present invention.

[0020] Figure 3 This is a cross-sectional structural diagram of a 169-core magnesium diboride superconducting wire prepared in Example 3 of the present invention.

[0021] Figure 4 It is a cross-sectional structural diagram of a 169-core magnesium diboride superconducting wire prepared in a comparative example of the present invention. DETAILED DESCRIPTION

[0022] The technical scheme of the present invention is described below in conjunction with the examples, but the present invention is not limited to the following examples. The experimental methods and detection methods described in each example are conventional methods unless otherwise specified; the reagents and materials are available on the market unless otherwise specified, and the % in the following examples are all mass percentages unless otherwise specified.

[0023] Example 1 This embodiment provides a method for preparing a magnesium diboride superconducting wire.

[0024] Step 1: In a glove box with argon gas purity of 99.999%, Mg powder with a purity of 99.9% and a particle size of 60 μm and amorphous B powder with a purity of 99% and a particle size of 2 μm are calculated, weighed and uniformly mixed according to an atomic ratio of Mg:B=1:2; Step 2: In a protective atmosphere, the precursor mixed powder is pressed into a number of powder rods by isostatic pressing. The powder rods have the same appearance size and different filling densities. The filling density of the powder rods varies within a range of 1.6 g / cm 3 ~2.1g / cm 3 .

[0025] Step 3: Use mechanical extrusion to compound Nb tube (purity 99.99%) and oxygen-free Cu tube (purity 99.9%) into Nb / Cu alloy tube. Put rods with different powder densities into the composite Nb / Cu alloy tube, and further process them into single core wires of specific forming size, and then straighten and cut them into single core rods of specific length; for the above single core rods, the volume ratios of Nb, Cu and powder are 35%, 30% and 35% respectively.

[0026] Step 4: Clean the surface of the single core rods obtained in "Step 3", and then pack 91 single core rods into the monel alloy tube. There are 6 layers of single core rods in the dense packing. The powder filling density of the single core rods from the inside to the outside is 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 Finally, the assembled composite rods were processed by cold plastic processing into a 91-core composite wire with a length of 2000m and a diameter of 0.84mm; Step 5: Place the multi-core composite wire under vacuum and heat it at 500°C for 15 hours to obtain a MgB2 superconducting wire with superconducting properties. Figure 1 The cross section of the 91-core MgB2 wire structure prepared in this embodiment is shown. The wire core wire diameter shown in the figure is about 25 μm, and the core wire structure is complete and has good uniformity.

[0027] Example 2 This embodiment provides a method for preparing a magnesium diboride superconducting wire.

[0028] Step 1: In a glove box with argon gas purity of 99.999%, Mg powder with a purity of 99.9% and a particle size of 60 μm and amorphous B powder with a purity of 99% and a particle size of 2 μm are calculated, weighed and uniformly mixed at an atomic ratio of Mg:B=1:2; Step 2: In a protective atmosphere, the precursor mixed powder is pressed into a number of powder rods by isostatic pressing. The powder rods have the same appearance size and different filling densities. The filling density of the powder rods varies within a range of 1.2 g / cm 3 ~2.1 g / cm 3 .

[0029] Step 3: Use mechanical extrusion to compound Nb tube (purity 99.99%) and oxygen-free Cu tube (purity 99.9%) into Nb / Cu alloy tube. Put rods with different powder densities into the composite Nb / Cu alloy tube, and further process them into single core wires of specific forming size, and then straighten and cut them into single core rods of specific length; for the above single core rods, the volume ratios of Nb, Cu and powder are 35%, 30% and 35% respectively.

[0030] Step 4: Clean the surface of the single core rods obtained in "Step 3", and then pack 127 single core rods into the monel alloy tube. There are 7 layers of single core rods in the dense packing. The powder filling density of the single core rods from the inside to the outside is 1.2g / cm 3 , 1.4g / cm 3 , 1.6g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 Finally, the assembled composite rods were processed by cold plastic processing into a 127-core composite wire with a length of 2000m and a diameter of 0.84mm; Step 5: Place the multi-core composite wire under vacuum and heat it at 700 °C for 10 h to obtain a MgB2 superconducting wire with superconducting properties. Figure 2The cross section of the 127-core MgB2 wire structure prepared in this embodiment is shown. The wire core wire diameter shown in the figure is about 21 μm, and the core wire structure is complete and has good uniformity.

[0031] Example 3 This embodiment provides a method for preparing a magnesium diboride superconducting wire.

[0032] Step 1: In a glove box with argon gas purity of 99.999%, Mg powder with a purity of 99.9% and a particle size of 60 μm and amorphous B powder with a purity of 99% and a particle size of 2 μm are calculated, weighed and uniformly mixed at an atomic ratio of Mg:B=1:2; Step 2: In a protective atmosphere, the precursor mixed powder is pressed into a number of powder rods by isostatic pressing. The powder rods have the same appearance size and different filling densities. The filling density of the powder rods varies within a range of 0.7 g / cm 3 ~2.1 g / cm 3 .

[0033] Step 3: Use mechanical extrusion to compound Nb tube (purity 99.99%) and oxygen-free Cu tube (purity 99.9%) into Nb / Cu alloy tube. Put rods with different powder densities into the composite Nb / Cu alloy tube, and further process them into single core wires of specific forming size, and then straighten and cut them into single core rods of specific length; for the above single core rods, the volume ratios of Nb, Cu and powder are 35%, 30% and 35% respectively.

[0034] Step 4: Clean the surface of the single core rods obtained in "Step 3", and then pack 169 single core rods into the monel alloy tube. There are 8 layers of single core rods in total. The powder filling density of the single core rods from inside to outside is 0.7g / cm 3 , 0.9g / cm 3 , 1.1g / cm 3 , 1.3g / cm 3 , 1.5g / cm 3 , 1.7g / cm 3 , 1.9g / cm 3 , 2.1g / cm 3 Finally, the assembled composite rods were processed by cold plastic processing into a 169-core composite wire with a length of 2000m and a diameter of 0.84mm; Step 5: Place the multi-core composite wire under vacuum and heat it at 900°C for 5 hours to obtain a MgB2 superconducting wire with superconducting properties. Figure 3The cross section of the 169-core MgB2 wire structure prepared in this embodiment is shown. The wire core wire diameter shown in the figure is about 15 μm, and the core wire structure is complete and has good uniformity.

[0035] Comparative Example This embodiment provides a method for preparing a magnesium diboride superconducting wire.

[0036] The difference between this comparative example and Example 3 is that the powder filling density is 2.1 g / cm 3 The single core rod is assembled and processed to obtain a 169-core composite wire with a diameter of 0.84 mm. Figure 4 Shown is a cross-section of the 169-core MgB2 wire structure prepared in this comparative example. The core wires in the center and local edge areas of the wire are severely cracked, which results in frequent wire breakage during processing, seriously affecting the stable processing of kilometer-level wires.

[0037] As described above, the basic principle, main features and advantages of the present invention are well described. The above embodiments and descriptions are only descriptions of the preferred implementation modes of the present invention, and 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 ordinary technicians in this field to the technical solution of the present invention should fall within the protection scope determined by the present invention.

Claims

1. A multi-core composite wire for preparing a magnesium diboride superconductor wire, wherein the multi-core composite wire comprises a plurality of single core wires which are processed by cold plastic processing to a desired size and are bundled and densely arranged inside a sheath; The single core wire include: A powder core comprising Mg powder and B powder; a barrier layer tube made of metal, wherein the powder core is disposed inside the barrier layer tube; The invention is characterized in that, in the multi-core composite wire, the powder filling density of the powder core in the single core wire increases from the center to the edge.

2. The multi-core composite wire for preparing a magnesium diboride superconductor wire according to claim 1, It is characterized in that The diameters of the multiple single core wires are the same, and the powder filling density increases in the range of 0.7 g / cm from the center to the edge. 3 ~2.1g / cm 3 .

3. The multi-core composite wire for preparing a superconductor wire containing magnesium diboride according to claim 1, It is characterized in that The material of the barrier layer tube is at least one of Ta, Nb, Ag, Zr, Ti, Cu, Mo, Fe, and W.

4. The multi-core composite wire for preparing a magnesium diboride superconductor wire according to claim 3, It is characterized in that The material of the barrier layer tube is NbCu alloy.

5. The multi-core composite wire for preparing a superconductor wire containing magnesium diboride according to claim 4, It is characterized in that In the single core wire, the volume proportion of Nb is 34% to 35%, and the volume proportion of Cu is 30% to 31%.

6. The multi-core composite wire for preparing a magnesium diboride superconductor wire according to claim 1, It is characterized in that The number of cores of the multi-core composite wire is 91-169.

7. A method for preparing a superconducting wire, It is characterized in that include: The multi-core composite wire according to claim 1 is subjected to cold plastic working to a desired size and then subjected to heat treatment to produce a superconducting wire containing a magnesium diboride superconducting phase.

8. The preparation method according to claim 7, It is characterized in that The heat treatment comprises: maintaining the temperature at 500° C. to 900° C. for 5 h to 15 h to generate a magnesium diboride superconducting phase.

9. A superconducting wire, It is characterized in that The method is prepared by the preparation method according to any one of claims 7 to 8.

10. The superconducting wire according to claim 9, It is characterized in that The diameter of the core wire in the superconducting wire is 15-25 μm.

Images