Method for manufacturing magnesium boride superconductive belt material

Abstract

The invention provides a method for manufacturing a magnesium boride superconductive belt material. The method comprises the following steps: A, uniformly distributing amorphous boron on a conductive substrate by adopting a coating method to form an amorphous boron layer with thickness of between 0.1 and 2.0mm; B, covering a magnesium or magnesium alloy flake with thickness of between 0.1 and 2.0mm on the boron layer, and rolling to form a magnesium-boron-substrate combination; C, putting the combination in the step B in a thermal treatment furnace, under the protection of argon atmosphere, heating to the temperature of between 550 and 800 DEG C, preserving the temperature for 0.1 to 3 hours, and cooling; D, coating metal, metallic oxide, silicon carbide or diamond like carbon film on thecombination which is treated in the step C to serve as a protective layer to form a composite body; and E, cutting the composite body in the step D into long belts. The MgB2 superconductive belt prepared by the method has the advantages of good compactness and grain connection, high critical current density, uniform current density distribution and high fatigue life, and is suitable for commercial application. The method is simple, and is suitable for industrial production.

Description

technical field [0001] The invention relates to a method for manufacturing a superconducting strip, in particular to a method for manufacturing a magnesium diboride superconducting strip. Background technique [0002] High-performance superconducting materials are the basis for the development of large-scale superconducting power transmission, superconducting transformers, superconducting current limiters, superconducting magnets, superconducting energy storage and other applications. Magnesium diboride (MgB 2 ) superconducting tape is expected to replace traditional low-temperature superconducting materials and achieve large-scale commercial applications due to its high superconducting transition temperature, very high current carrying capacity, low raw material cost, and easy fabrication; especially in 15 Magnets with a temperature of ~26K and a magnetic field of less than 5T have huge market potential and are ideal for future medical nuclear magnetic resonance supercondu...

AI Technical Summary

Problems solved by technology

[0005] 1) The critical current density is low and the superconductivity is poor; this method first mixes Mg powder and B powder, and then performs high temperature heat treatment

During the heat treatment, Mg diffuses to B, leaving holes in the Mg site, so that the generated MgB 2 The superconducting core is obviously porous and has a low density (usually only MgB 2 50% of theoretical density), resulting in MgB 2 The critical current density of the superconducting strip (J c ) is low and cannot meet the requirements of commercial applications

For example: usually at 20K, 3T, this strip J c Can only reach 500~600A / mm 2 ; Unable to satisfy MgB 2 Under the conditions of working temperature 20-26K and magnetic field 1.5-5T, the critical current density of superconducting strip is 1000A / mm 2 business application requirements

[0006] 2) When the current is transmitted, the current density distribution is uneven, which increases the risk of "quenching" of the material and makes the fatigue life lower; the existing preparation method is to make the cylindrical MgB 2 The wire is rolled to form a ribbon, resulting in MgB 2 The cross-section of the superconducting core of the tape is thick in the middle and thin at the edges; therefore, when current is transferred, the thicker middle portion carries more current, while the thinner edge portions carry less current

Due to the "AC loss" of the superconducting material itself, a certain amount of heat will be generated; while MgB 2 The thermal conductivity of the superconducting material itself is not good, so it is easy to cause thermal stress concentration in the middle part, making local heat dissipation difficult; resulting in a sudden increase in local temperature, when the temperature rises to more than MgB 2 When the superconducting transition temperature is lower than the superconducting transition temperature, the superconducting tape will be in danger of losing superconductivity

Once quenched, it will lead to strip damage

[0007] 3) Poor toughness, not easy to bend, and inconvenient to use: In order to improve the MgB in the superconducting core 2 The denseness of the coating layer used in the existing method is usually a high-strength metal or alloy in order to obtain a finer diameter wire, which is then rolled into a strip

The existence of the high-strength metal sheath cavity makes the overall toughness of the strip not enough, which brings difficulties in use and transportation

For example: for a superconducting strip with a thickness of 0.5mm and a width of 4mm produced by the existing method, the radius of curvature that does not damage the performance of the superconducting core is usually about 1 meter, and MgB is used to make magnets. 2 When making a superconducting tape, it usually needs to be wound on a cylindrical magnet with a radius not greater than 15cm. Therefore, it is difficult for the superconducting tape produced by the existing method to be used in commercial magnet applications.