CN105702388B - A kind of heat treatment method of 2212 superconducting wires/strips of Bi - Google Patents

Abstract

The invention provides a heat treatment method for Bi-2212 superconducting wire/strip, comprising the following steps: 1. Place Bi-2212 multi-core wire/strip in a heat treatment furnace, and then feed oxygen and nitrogen mixture into the heat treatment furnace Gas or oxygen-argon mixed gas to remove the air in the furnace; 2. Continue to feed oxygen-nitrogen mixed gas or oxygen-argon mixed gas. Carry out partial melting heat treatment; 3. Stop feeding the mixed gas of oxygen and nitrogen or the mixed gas of oxygen and argon, and obtain Bi-2212 superconducting wire/strip after degassing. The invention can effectively suppress the expansion of the gas inside the Bi-2212 multi-core wire/strip, prevent bubbles or defects caused by the bubbles, increase the density of the core filaments, and obtain high-performance and uniform Bi-2212 superconducting wires/ Strip.

Description

A kind of heat treatment method of Bi-2212 superconducting wire/ribbon

technical field

The invention belongs to the technical field of high-temperature superconducting material preparation, and in particular relates to a heat treatment method for Bi-2212 superconducting wire/strip.

Background technique

Since the Bi ₂ Sr ₂ CaCu ₂ O _x (Bi-2212) wire high-temperature superconductor has excellent low-temperature high-magnetic field current-carrying properties, and is currently the only practical high-temperature superconducting material that can be prepared into isotropic round wires, the above characteristics make Bi -2212 high temperature superconductor material has become the material of choice for the preparation of intercalated coils of low temperature high field magnets.

At present, the preparation technology combining powder in tube method (PIT) and melting method is the mainstream technology for preparing high-performance Bi-2212 wire. The technology is to put the superconducting precursor powder into the silver tube, prepare a multi-core composite by drawing and assembling, and then process it to the designed wire size, and then perform partial melting and heat treatment to obtain a high-performance Bi-2212 superconductor. wire.

The powder tube method is to put the powder into a metal tube to make a composite, and then process the composite. However, during the process of loading the powder into the silver tube, the gas adsorbed on the powder surface and the interstitial gas between the powder are loaded into the silver tube together. After drawing, most of the gas is sealed in the final wire. At the initial stage of heating, the gas sealed in the wire expands according to Gay-Lussac's law, and the volume of the gas remains constant under the constraints of the sheath. When the temperature rises to the melting temperature of the core wire, the high-pressure gas sealed inside the Bi-2212 wire occupies a certain volume. The existence of the high-pressure gas makes part of the Bi-2212 melt to be discharged, and because the diameter of the core wire of the Bi-2212 wire is only 20 μm, The Bi-2212 melt in certain positions where more gas is accumulated in the core wire is completely discharged, resulting in the complete quenching of the core wire; the Bi-2212 core wire with less gas accumulation forms a sponge-like pore structure, resulting in Most of the superconducting grains form a large mismatch angle, which seriously affects the flow of superconducting current between the grains and greatly reduces the critical current of the Bi-2212 wire. On the other hand, during the heating process, the pressure of the external ambient gas of the wire remains unchanged. With the increase of temperature, the pressure difference between the inside and outside of the wire gradually increases. When the temperature reaches a certain level, the pressure difference between the internal pressure of the core wire and the external gas pressure that accumulates a large amount of gas exceeds the package. At the limit of the deformation of the sheath material, the sheath will expand, resulting in an increase in the inner space of the sheath. If the temperature continues to rise to the melting temperature of the core wire, the core wire will be completely discharged or a sponge with a lower density of Bi-2212 will appear. The bulk structure leads to lower current-carrying performance of the wire, and the excessive expansion of the wire core wire caused by excessive gas accumulation exceeds the creep limit of the sheath material, causing pores or even cracks in the wire core wire, resulting in serious leakage of the wire rod Leakage greatly affects the use of wire.

Contents of the invention

The technical problem to be solved by the present invention is to provide a heat treatment method for Bi-2212 superconducting wire/strip in view of the above-mentioned deficiencies in the prior art. The method can effectively suppress the expansion of gas inside the wire rod, effectively prevent bubbles or defects caused by bubbles, increase the density of core filaments, and obtain high-performance and uniform Bi-2212 superconducting wires/tapes.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of heat treatment method of Bi-2212 superconducting wire/strip, it is characterized in that, this method comprises the following steps:

Step 1. Place the Bi-2212 multi-core wire/strip in a heat treatment furnace, and then pass an oxygen-nitrogen mixed gas or an oxygen-argon mixed gas into the heat treatment furnace to remove the air in the furnace;

Step 2. Continue to feed oxygen-nitrogen mixed gas or oxygen-argon mixed gas into the heat treatment furnace that has removed air in step 1. Under the condition that the pressure in the furnace is constant at 20atm～200atm and the oxygen partial pressure is constant at 0.5atm～1atm, Raise the temperature of the Bi-2212 multi-core wire/strip to 880°C-900°C first, then keep it warm for 20min-30min, then lower the temperature to 810°C-850°C, keep it warm for 24h-48h, and then cool it to 25°C room temperature with the furnace;

Step 3. Stop feeding oxygen-nitrogen mixed gas or oxygen-argon mixed gas into the heat treatment furnace cooled in step 2, and then discharge the oxygen-nitrogen mixed gas or oxygen-argon mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure , to obtain Bi-2212 superconducting wire/tape.

The heat treatment method of the above-mentioned Bi-2212 superconducting wire/strip is characterized in that the number of cores of the Bi-2212 multi-core wire/strip described in step 1 is 49-7725 cores.

The above-mentioned heat treatment method of Bi-2212 superconducting wire/strip is characterized in that the rate of temperature increase in step 2 is 50°C/h-100°C/h.

The above-mentioned heat treatment method of Bi-2212 superconducting wire/strip is characterized in that the cooling rate in step 2 is 1° C./h to 10° C./h.

The heat treatment method of above-mentioned a kind of Bi-2212 superconducting wire/strip, it is characterized in that, the exhaust rate of the oxygen-nitrogen mixed gas or the oxygen-argon mixed gas in the heat treatment furnace described in step 3 is to make the pressure in the heat treatment furnace be 2MPa /h～5MPa/h rate decreases.

Compared with the prior art, the present invention has the following advantages:

1. The preparation process of the present invention is simple, the design is reasonable, the manufacturing cost is low, and the popularization area is large, which is beneficial to be applied to the production of Bi-2212 long lines.

2. The heat treatment method of the Bi-2212 superconducting wire/strip of the present invention can effectively prevent holes or bubbling in the core wire of the Bi-2212 wire/strip.

3. During the heat treatment process of the Bi-2212 multi-core wire/strip of the present invention, the pressure of the external environment is relatively high, which effectively inhibits the expansion of the internal gas, effectively prevents the defects caused by bubbling or bubbling, and can improve the quality of the core wire at the same time. Density, and finally obtain high-performance and uniform Bi-2212 superconducting wire/tape.

4. The core filament density of the Bi-2212 superconducting wire/strip prepared after the heat treatment of the present invention almost reaches the theoretical density (the core filament density of the conventional wire/strip is only about 65%), and its engineering critical current density reaches 400 ～500A/mm ² (4.2K, 20T), about 1.3 to 1.5 times the current-carrying performance of conventional wires/strips, there are no defects such as bubbling and seepage in the wires/strips, and the current-carrying performance of the wires/strips is uniform Sex is within ±5%.

The present invention is described in further detail below in conjunction with embodiment.

detailed description

Example 1

The heat treatment method of the present embodiment Bi-2212 superconducting wire comprises the following steps:

Step 1. Place the Bi-2212 multi-core wire rod with a diameter of 2 mm and a core number of 666 cores in a heat treatment furnace, and then pass an oxygen-argon mixed gas with an oxygen volume content of 1% into the heat treatment furnace to eliminate the air in the furnace;

Step 2. Continue to feed the oxygen-argon mixed gas with an oxygen volume content of 1% in the heat treatment furnace that has excluded air in step 1. Under the condition that the pressure in the furnace is constant at 100 atm and the oxygen partial pressure is constant at 1 atm, Bi- The 2212 multi-core wire is first heated up to 890°C at a heating rate of 80°C/h and then kept for 25 minutes, then cooled to 830°C at a cooling rate of 8°C/h and kept for 30 hours, and then cooled to room temperature of 25°C with the furnace;

Step 3, stop feeding the oxygen-argon mixed gas with an oxygen volume content of 1% in the heat treatment furnace cooled in step 2, then discharge the oxygen-argon mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure (atmospheric pressure) refers to one atmospheric pressure) to obtain a Bi-2212 superconducting wire; the exhaust rate of the oxygen-argon mixed gas in the heat treatment furnace is to reduce the pressure in the heat treatment furnace at a rate of 3MPa/h.

The core filament density of the Bi-2212 multi-core superconducting wire prepared after the heat treatment in this embodiment reaches more than 99% of the theoretical density (the core filament density of the conventional wire is only about 65%), and its engineering critical current density reaches 450A/mm ² (4.2K, 20T), which is about 1.5 times the current-carrying performance of conventional wire rods. There are no defects such as bubbles and seepage points in the wire rods, and the uniformity of the current-carrying performance of the wire rods is within ±5%.

Example 2

The heat treatment method of the present embodiment Bi-2212 superconducting tape comprises the following steps:

Step 1. Place the Bi-2212 multi-core strip with a thickness of 1.5mm and 595 cores in a heat treatment furnace, and then feed an oxygen-nitrogen mixed gas with an oxygen volume content of 1% into the heat treatment furnace to remove the heat from the furnace. Air;

Step 2, in the heat treatment furnace that has got rid of air in step 1, continue to pass into the oxygen-nitrogen mixed gas that oxygen volume content is 1%, in furnace pressure constant is 50atm, under the condition that oxygen partial pressure is constant 0.5atm, Bi -2212 multi-core strips are first heated to 880°C at a heating rate of 60°C/h and then held for 25 minutes, then cooled to 830°C at a cooling rate of 5°C/h and held for 40 hours, and then cooled to room temperature of 25°C with the furnace;

Step 3, stop feeding the oxygen-nitrogen mixed gas with an oxygen volume content of 1% in the heat treatment furnace cooled in step 2, and discharge the oxygen-nitrogen mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure (normal pressure is Refer to one atmospheric pressure) to obtain Bi-2212 superconducting strips; the discharge rate of the oxygen-nitrogen mixed gas in the heat treatment furnace is to reduce the pressure in the heat treatment furnace at a rate of 3MPa/h.

The core filament density of the Bi-2212 superconducting tape prepared after the heat treatment in this embodiment reaches more than 90% of the theoretical density (the core filament density of the conventional strip is only about 65%), and its engineering critical current density reaches 400A/mm ² (4.2K, 20T), which is about 1.33 times the current-carrying performance of conventional strips. The strip has no defects such as bubbles and seepage points, and the uniformity of the current-carrying performance is within ±5%.

Example 3

The heat treatment method of the present embodiment Bi-2212 superconducting wire comprises the following steps:

Step 1. Place a Bi-2212 multi-core wire rod with a diameter of 1mm and a core number of 1530 cores in a heat treatment furnace, and then pass an oxygen-nitrogen mixed gas with an oxygen volume content of 0.5% into the heat treatment furnace to remove the air in the furnace;

Step 2, continue to pass into the heat treatment furnace that has removed air in step 1 and be the oxygen-nitrogen mixed gas of 0.5% by volume, in the furnace pressure constant is 200atm, under the condition that oxygen partial pressure is constant 1atm, Bi- The 2212 multi-core wire is first heated to 880°C at a heating rate of 80°C/h and then kept for 30 minutes, then cooled to 830°C at a cooling rate of 10°C/h and kept for 40 hours, and then cooled to room temperature of 25°C with the furnace;

Step 3, stop feeding the oxygen-nitrogen mixed gas with an oxygen volume content of 0.5% in the heat treatment furnace cooled in step 2, and discharge the oxygen-nitrogen mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure (normal pressure is Refer to one atmospheric pressure) to obtain a Bi-2212 superconducting wire; the exhaust rate of the oxygen-nitrogen mixed gas in the heat treatment furnace is to reduce the pressure in the heat treatment furnace at a rate of 2MPa/h.

The core filament density of the Bi-2212 superconducting wire prepared after the heat treatment in this example almost reaches the theoretical density (the core filament density of the conventional wire is only about 65%), and its engineering critical current density reaches 500A/mm ² (4.2K , 20T), which is about 1.67 times the current-carrying performance of conventional wire rods. There are no defects such as bubbles and seepage points in the wire rods, and the uniformity of the current-carrying performance of the wire rods is within ±5%.

Example 4

The heat treatment method of the present embodiment Bi-2212 superconducting tape comprises the following steps:

Step 1. Place the Bi-2212 multi-core strip with a thickness of 2.5mm and 7725 cores in a heat treatment furnace, and then feed an oxygen-argon mixed gas with an oxygen volume content of 0.3% into the heat treatment furnace to remove Air;

Step 2, continue to pass into the heat treatment furnace that has removed air in step 1 and be the oxygen-argon mixed gas of 0.3% by volume of oxygen, in furnace pressure is constant 200atm, under the condition that oxygen partial pressure is constant 0.6atm, Bi -2212 multi-core strips are heated up to 900°C at a heating rate of 70°C/h and then held for 20 minutes, then cooled to 810°C at a cooling rate of 1°C/h and held for 24 hours, and then cooled to room temperature of 25°C with the furnace;

Step 3, stop feeding the oxygen-argon mixed gas with an oxygen volume content of 0.3% in the heat treatment furnace cooled in step 2, and discharge the oxygen-argon mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure (normal pressure is Refer to one atmospheric pressure) to obtain Bi-2212 superconducting strips; the exhaust rate of the oxygen-argon mixed gas in the heat treatment furnace is to reduce the pressure in the heat treatment furnace at a rate of 3MPa/h.

The core filament density of the Bi-2212 superconducting tape prepared after the heat treatment in this example almost reaches the theoretical density (the core filament density of the conventional tape is only about 65%), and its engineering critical current density reaches 440A/mm ² ( 4.2K, 20T), which is about 1.46 times the current-carrying performance of the conventional strip, and the strip has no defects such as bubbles and seepage points, and the uniformity of the current-carrying performance is within ±5%.

Example 5

The heat treatment method of the present embodiment Bi-2212 superconducting wire comprises the following steps:

Step 1. Place the Bi-2212 multi-core wire rod with a diameter of 1.5mm and 49 cores in a heat treatment furnace, and then pass an oxygen-argon mixed gas with an oxygen volume content of 2.5% into the heat treatment furnace to remove the air in the furnace ;

Step 2, continue to pass into the heat treatment furnace that has excluded air in step 1 and be the oxygen-argon mixed gas of 2.5% by volume of oxygen, in the furnace pressure constant is 20atm, under the condition that oxygen partial pressure is constant 0.5atm, Bi -2212 multi-core wire is first heated to 880°C at a heating rate of 50°C/h and then kept for 30 minutes, then cooled to 850°C at a cooling rate of 10°C/h and kept for 48 hours, and then cooled to room temperature of 25°C with the furnace;

Step 3, stop feeding the oxygen-argon mixed gas with an oxygen volume content of 2.5% in the heat treatment furnace cooled in step 2, and discharge the oxygen-argon mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure (normal pressure is Refer to one atmospheric pressure), obtain Bi-2212 single-core superconducting wire/strip material or Bi-2212 superconducting wire rod; The discharge rate of the oxygen-argon mixed gas in the described heat treatment furnace is to make the pressure in the heat treatment furnace at the rate of 2MPa/h reduce.

The core filament density of the Bi-2212 superconducting wire prepared after the heat treatment in this example almost reaches the theoretical density (the core filament density of the conventional wire is only about 65%), and its engineering critical current density reaches 460A/mm ² (4.2K , 20T), which is about 1.53 times the current-carrying performance of conventional wire rods. There are no defects such as bubbles and seepage points in the wire rods, and the uniformity of the current-carrying performance of the wire rods is within ±5%.

Example 6

The heat treatment method of the present embodiment Bi-2212 superconducting tape comprises the following steps:

Step 1. Place the Bi-2212 multi-core strip with a thickness of 2.2mm and 1530 cores in a heat treatment furnace, and then feed an oxygen-nitrogen mixed gas with an oxygen volume content of 0.5% into the heat treatment furnace to remove Air;

Step 2, continue to pass into the heat treatment furnace that has removed air in step 1 and be the oxygen-nitrogen mixed gas of 0.5% by volume, in the furnace pressure constant is 200atm, under the condition that oxygen partial pressure is constant 1atm, Bi- The 2212 multi-core strip is first heated to 900°C at a heating rate of 100°C/h and then kept at a temperature of 30 minutes, then cooled to 850°C at a cooling rate of 10°C/h and kept at a temperature of 48 hours, and then cooled to a room temperature of 25°C with the furnace;

Step 3, stop feeding oxygen-nitrogen mixed gas or oxygen-argon mixed gas into the heat treatment furnace cooled in step 2, and discharge the oxygen-nitrogen mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure (normal pressure refers to a Atmospheric pressure) to obtain Bi-2212 superconducting strips; the discharge rate of the oxygen-nitrogen mixed gas in the heat treatment furnace is to reduce the pressure in the heat treatment furnace at a rate of 5MPa/h.

The core filament density of the Bi-2212 superconducting tape prepared after the heat treatment in this example almost reaches the theoretical density (the core filament density of the conventional tape is only about 65%), and its engineering critical current density reaches 440A/mm ² ( 4.2K, 20T), which is about 1.46 times the current-carrying performance of conventional strips. The strip has no defects such as bubbles and seepage points, and the uniformity of the strip’s current-carrying performance is within ±5%.

The above descriptions are only preferred embodiments of the present invention, and do not limit the present invention in any way. All any simple amendments, changes and equivalent changes made to the above embodiments according to the technical essence of the invention still belong to the protection scope of the technical solution of the present invention.

Claims (2)

1. a thermal treatment method of Bi-2212 superconducting wire/strip material, is characterized in that, the method may further comprise the steps: Step 1. Place the Bi-2212 multi-core wire/strip in a heat treatment furnace, and then pass an oxygen-nitrogen mixed gas or an oxygen-argon mixed gas into the heat treatment furnace to remove the air in the furnace; Step 2. Continue to feed oxygen-nitrogen mixed gas or oxygen-argon mixed gas into the heat treatment furnace that has removed air in step 1. Under the condition that the pressure in the furnace is constant at 20atm～200atm and the oxygen partial pressure is constant at 0.5atm～1atm, Raise the temperature of the Bi-2212 multi-core wire/strip to 880°C-900°C first, then keep it warm for 20min-30min, then cool it down to 810°C-850°C, keep it warm for 24h-48h, and then cool it to room temperature of 25°C with the furnace; The cooling rate is 50°C/h～100°C/h; the cooling rate is 1°C/h～10°C/h; Step 3. Stop feeding oxygen-nitrogen mixed gas or oxygen-argon mixed gas into the heat treatment furnace cooled in step 2, and then discharge the oxygen-nitrogen mixed gas or oxygen-argon mixed gas in the heat treatment furnace until the pressure in the furnace drops to normal pressure , to obtain Bi-2212 superconducting wire/strip; the exhaust rate of the oxygen-nitrogen mixed gas or oxygen-argon mixed gas in the heat treatment furnace is to reduce the pressure in the heat treatment furnace at a rate of 2MPa/h to 5MPa/h. 2. The heat treatment method of a kind of Bi-2212 superconducting wire/tape according to claim 1, characterized in that the number of cores of the Bi-2212 multi-core wire/tape described in step 1 is 49 cores to 7725 cores .