High-purity medium-grain niobium material for radio frequency superconducting cavity and preparation method of high-purity medium-grain niobium material

Abstract

The invention provides a high-purity medium-grain niobium material for a radio frequency superconducting cavity and a preparation method of the high-purity medium-grain niobium material for the radio frequency superconducting cavity. According to the method, niobium battens produced through an aluminothermic reduction method serve as raw materials, smelting is carried out for multiple times through a vacuum electron beam smelting technology to remove impurities, the purity of niobium ingots is further improved through a refining technology, and high-purity medium-grain niobium ingots are obtained; a radial forging mode is adopted, after a # imgabs0 # cast ingot is forged into a # imgabs1 # cast ingot, crystal grains are further crushed, and after annealing treatment is conducted, a multi-wire cutting machine is used for cutting a bar blank into the niobium plate. The prepared high-purity medium-grain niobium material has the excellent performance that the grains are fine, the structure is uniform, the residual resistivity ratio is larger than 400, and the impurity content is lower than 100 ppm, and the quality requirement of the niobium material for the radio frequency superconducting cavity is met. The niobium material prepared by the method can be used for manufacturing a radio frequency superconducting cavity and an acceleration resonator which are large in acceleration gradient, high in quality factor, small in energy loss and long in service life, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal smelting, and relates to a high-purity medium-grain niobium material for a radio frequency superconducting cavity and a preparation method thereof. Background Art

[0002] Niobium is an important rare high-melting-point metal with a series of excellent physical and chemical properties, such as high melting point, good plasticity, low vapor pressure, high chemical stability, strong resistance to liquid metal and acid-base corrosion, large dielectric constant of surface oxide film, small thermal neutron capture cross section, high superconducting transition temperature, good low-temperature ductility and thermal conductivity, etc. These characteristics make niobium widely used in many fields such as metallurgy, chemical industry, aerospace, atomic energy, electronics, and superconductivity. In particular, metallic niobium has excellent superconductivity and thermal conductivity. The higher its purity, the better the thermal conductivity of the material. Microwave superconducting cavities and accelerating resonators made of high-purity niobium materials can not only achieve higher acceleration field strengths and reduce energy losses, but also significantly extend their service life.

[0003] At present, high-purity niobium materials are widely used in the manufacture of superconducting accelerating cavities and are the best choice of materials for making superconducting accelerating resonant cavities. Radio frequency superconducting accelerators are important tools for high-energy physics research, and niobium superconducting cavities are the most critical core components of radio frequency superconducting accelerators. The development of high-purity medium-grain niobium materials and their preparation methods will provide a solid material foundation for research and applications in the field of nuclear science, especially the construction of high-current proton linear accelerators. This technology can also be widely used in accelerator-driven clean nuclear energy development, nuclear waste treatment, spallation neutron sources, proton and neutron imaging, accelerator tritium production, etc.

[0004] At present, high-purity niobium ingots produced by electron beam melting generally have the problem of coarse grains during processing. Normally, when using this large-grained niobium ingot as raw material to produce the niobium material required for the superconducting cavity, it is necessary to undergo multiple forgings to fully break up the large grain structure, and then annealing, rolling and other processes to make the required small-grained niobium plate. However, in this traditional processing technology, the material is easily contaminated during multiple mechanical processing and heat treatment processes, resulting in a loss of about 15% of the residual resistivity ratio (RRR value) of the material, which in turn affects the performance of the final superconducting cavity. Therefore, the development of a method for preparing high-purity medium-grained niobium materials that can effectively avoid the above-mentioned pollution problems and at the same time achieve high-purity medium-grained niobium materials is of great practical significance for improving the performance of superconducting cavity materials and production efficiency. Summary of the invention

[0005] In order to overcome the above problems, the present invention provides a high-purity medium-grain niobium material for radio frequency superconducting cavity and a preparation method thereof, which solves the problem of coarse cast grains in the existing smelting technology and the RRR value loss caused by material contamination in the subsequent niobium plate processing project required for the superconducting cavity.

[0006] The preparation method of the present invention comprises the following steps:

[0007] A method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity, the method comprising the following steps:

[0008] (1) using aluminothermic reduction method to reduce niobium oxide to form niobium aluminum alloy, and then melting it in a horizontal electron beam furnace to form niobium plate;

[0009] (2) After the niobium plate is cut into niobium strips, the niobium strips are melted into The ingot is then melted 2 to 4 times for further purification. The process parameters of the vacuum electron beam melting are as follows:

[0010] The melting rate of the first melting is 60-80 kg / h, the melting power is 550-650 kW, and the vacuum degree is better than 5×10 -3 Pa, cooling water temperature is controlled at 25±5℃;

[0011] The rotation speed during the second to fourth smelting is 0.5-1r / min, the smelting rate is 40-60kg / h, the smelting power is 500-600kW, and the vacuum degree is better than 2×10 -3 Pa, cooling water temperature is controlled at 25±5℃;

[0012] (3) The ingot obtained in step (2) is refined once in a vacuum electron beam furnace, and the parameters of the refining process are as follows:

[0013] The melting rate is 80-100 kg / h, the melting power is 650-750 kW, and the vacuum degree is better than 1×10 -3 Pa, the cooling water temperature is controlled at 10-20°C, and a high-purity medium-grain niobium ingot is obtained;

[0014] (4) Forge the ingot into a diameter of The niobium ingot is then annealed and sliced ​​using a multi-wire saw.

[0015] During the vacuum electron beam melting process, the melting order of the head and tail of the ingot remains unchanged during each melting. After the vacuum electron beam melting is completed, the ingot is cooled and then the ingot and the bottom ingot head are separated using a sawing machine.

[0016] The separated ingot and bottom ingot head are placed in an ultrasonic cleaning machine for degreasing and cleaning, and the water in the cleaning machine is heated to 40°C. Clean 2 to 3 times, and replace the water in the ultrasonic cleaning machine after each cleaning.

[0017] The impurity mass content of the niobium strip is: tantalum ≤100ppm, silicon ≤80ppm, tungsten <5ppm, molybdenum <5ppm, titanium ≤5ppm, zirconium ≤5ppm, copper ≤5ppm, chromium + cobalt ≤10ppm, nickel ≤5ppm, iron ≤5ppm, oxygen ≤100ppm, nitrogen ≤100ppm, carbon ≤20ppm.

[0018] The first electron beam melting in the melting process adopts a horizontal feeding method, and the second and subsequent melting adopts a vertical feeding method, and the electrode rotation speed is controlled to be 0.5-1r / min during the melting process. In the last melting, the electrode rotation speed is controlled to be 1-2r / min, the melting rate is 60-80kg / h, the melting power is 650kw-750kw, and the vacuum degree is better than 1×10 -3 Pa, the crystallizer cooling water temperature is controlled at 15±5℃.

[0019] The ingot has a grain size of less than 20 mm, an RRR value greater than 400, and meets the following impurity content requirements: tantalum ≤100 ppm, silicon ≤10 ppm, tungsten ≤5 ppm, molybdenum ≤5 ppm, titanium ≤1 ppm, zirconium ≤1 ppm, copper ≤1 ppm, chromium + cobalt ≤6 ppm, nickel ≤1 ppm, iron ≤3 ppm, oxygen ≤10 ppm, nitrogen <10 ppm, carbon ≤10 ppm, and hydrogen ≤1 ppm.

[0020] When the ingot is used to manufacture a radio frequency superconducting accelerating cavity, it can maintain a high acceleration field strength, a small energy divergence, and significantly extend the service life.

[0021] The present invention provides a high-purity medium-grain niobium material for a radio frequency superconducting cavity and a preparation method thereof, which has the following beneficial effects:

[0022] 1. Improve material purity and reduce impurity content: Through multiple vacuum electron beam melting and refining processes, the metal and non-metal impurities in the niobium material are effectively removed, and the mass content of impurities such as tantalum, tungsten, silicon, oxygen, nitrogen, and carbon is significantly reduced, so that the final prepared niobium ingot has extremely high purity, meeting the strict requirements of radio frequency superconducting cavities for high-purity niobium materials.

[0023] 2. Optimize the grain structure and uniformity of niobium ingots: The present invention uses precisely controlled melting and cooling process parameters, such as melting power, vacuum degree and cooling water temperature, to effectively refine the grain size and reduce the grain growth effect during the melting process, so that the grain size of the final niobium ingot is less than 20mm and the internal structure of the material is uniform. Compared with the traditional process, the niobium ingot prepared by the present invention is easier to deform and less likely to crack during subsequent processing, which improves the mechanical properties and processing performance of the material.

[0024] 3. Improve the residual resistivity ratio (RRR value): Through multiple melting and refining steps, the RRR value of the high-purity medium-grained niobium material prepared by the present invention is greater than 400, which significantly improves the conductivity of the material. A higher RRR value can reduce the energy loss of the radio frequency superconducting cavity during operation, increase the acceleration field strength, and thus improve the working efficiency and stability of the superconducting cavity.

[0025] 4. Reduce processing pollution and reduce performance loss: In the processing of traditional niobium materials, grain refinement often requires multiple forging and annealing treatments, which easily introduces impurity pollution and causes material performance degradation. The present invention reduces multiple mechanical processing steps by optimizing the vacuum electron beam melting process, thereby effectively avoiding the introduction of pollution and the increase of impurity content, and avoiding the loss of residual resistivity ratio (RRR value).

[0026] 5. Improve the application effect of the material in the radio frequency superconducting cavity: The high-purity medium-grained niobium material prepared by the present invention has a higher acceleration field strength, smaller energy loss and longer service life in the radio frequency superconducting cavity, which can significantly improve the working efficiency of the radio frequency superconducting cavity, reduce maintenance costs, and has excellent corrosion resistance and thermal stability.

[0027] 6. Has broad application prospects: The prepared high-purity medium-grain niobium material is not only suitable for the manufacture of radio frequency superconducting cavities and accelerating resonators, but can also be used in accelerator-driven clean nuclear energy, nuclear waste treatment, spallation neutron sources, proton and neutron imaging, accelerator tritium production and other fields, which is of great significance to the development of nuclear science and technology.

[0028] In summary, the present invention improves the purity, grain structure, electrical conductivity and processing performance of niobium materials by optimizing the preparation process of niobium materials, significantly improves the overall performance of radio frequency superconducting cavities, and provides reliable material guarantees for technological progress in high-energy physics research and nuclear science. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail below in conjunction with the preferred embodiments of the present invention.

[0030] Example:

[0031] 1. Raw material selection and preparation

[0032] Niobium strips produced by aluminothermic reduction method are selected as raw materials, and the mass content of each impurity in the niobium strips is: tantalum ≤100ppm, silicon ≤80ppm, tungsten <5ppm, molybdenum <5ppm, titanium ≤5ppm, zirconium ≤5ppm, copper ≤5ppm, chromium + cobalt ≤10ppm, nickel ≤5ppm, iron ≤5ppm, oxygen ≤100ppm, nitrogen ≤100ppm, carbon ≤20ppm.

[0033] 2. Vacuum electron beam melting

[0034] The niobium strips are placed in a vacuum electron beam melting furnace for 5 smeltings to remove possible impurities in the raw materials and improve the purity of the materials. The process parameters for each smelting are as follows:

[0035] First smelting

[0036] Melting rate: 60~80kg / h;

[0037] Melting power: 550~650kW;

[0038] Vacuum degree: better than 5×10 -3 Pa;

[0039] Crystallizer cooling water temperature: 25±5℃.

[0040] 2nd to 4th smelting

[0041] Rotation speed: 0.5~1r / min;

[0042] Melting rate: 40~60kg / h;

[0043] Melting power: 500~600kW;

[0044] Vacuum degree: better than 2×10 -3 Pa;

[0045] Crystallizer cooling water temperature: 25±5℃.

[0046] The 5th smelting

[0047] Rotation speed: 1~2r / min;

[0048] Melting rate: 60~80kg / h;

[0049] Melting power: 650~750kW;

[0050] Vacuum degree: better than 1×10 -3 Pa;

[0051] Crystallizer cooling water temperature: 15±5℃.

[0052] 3. Ingot processing

[0053] After each vacuum electron beam melting, the ingot is cooled and the ingot and the bottom ingot head are separated. Then the ingot and the bottom ingot head are placed in an ultrasonic cleaning machine, degreasing agent is added, and the water in the cleaning machine is heated to 40°C. The cleaning process is carried out 2 to 3 times, and the water in the ultrasonic cleaning machine is replaced after each cleaning.

[0054] 4. Material composition testing

[0055] The prepared high-purity medium-grain niobium ingot was tested and its RRR value was 440. The impurity mass content was as follows:

[0056] Tantalum: 100ppm;

[0057] Tungsten: 5ppm;

[0058] Molybdenum: 5ppm;

[0059] Silicon: 10ppm;

[0060] Titanium: 1ppm;

[0061] Zirconium: 1ppm;

[0062] Chromium + cobalt: ≤6ppm;

[0063] Nickel: 1ppm;

[0064] Iron: 3ppm;

[0065] Oxygen: 5ppm;

[0066] Nitrogen: 5ppm;

[0067] Carbon: 5ppm;

[0068] Hydrogen: 1ppm.

[0069] The test results show that the impurity content and RRR value of the high-purity medium-grain niobium ingot prepared in this embodiment meet the requirements of high-purity niobium ingots for radio frequency superconducting cavities.

[0070] 5. Ingot forging and annealing

[0071] After cooling Ingot forging The niobium ingot is then annealed. The niobium ingot is then sliced ​​using a multi-wire cutting machine to obtain a high-purity niobium ingot with fine grains and uniform structure. The grain size of the obtained niobium ingot is less than 20mm, and the RRR value is greater than 400.

[0072] The high-purity niobium ingot prepared in this embodiment has excellent grain fineness and uniformity, and can meet the quality requirements of niobium materials for radio frequency superconducting cavities. The ingot material is suitable for manufacturing microwave superconducting cavities and accelerating resonators with high accelerating field strength, small energy dispersion and long service life, and has broad application prospects.

Claims

1. A method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity, characterized in that: The method comprises the following steps: (1) using aluminothermic reduction method to reduce niobium oxide to form niobium aluminum alloy, and then melting it in a horizontal electron beam furnace to form niobium plate; (2) After the niobium plate is cut into niobium strips, the niobium strips are melted into The ingot is then melted 2 to 4 times for further purification. The process parameters of the vacuum electron beam melting are as follows: The melting rate of the first melting is 60-80kg / h, the melting power is 550-650kW, the vacuum degree is better than 5×10-3Pa, and the cooling water temperature is controlled at 25±5℃; The rotation speed during the 2nd to 4th smelting is 0.5-1r / min, the smelting rate is 40-60kg / h, the smelting power is 500-600kW, the vacuum degree is better than 2×10-3Pa, and the cooling water temperature is controlled at 25±5℃; (3) The ingot obtained in step (2) is refined once in a vacuum electron beam furnace, and the parameters of the refining process are as follows: The melting rate is 80-100 kg / h, the melting power is 650-750 kW, the vacuum degree is better than 1×10-3 Pa, and the cooling water temperature is controlled at 10-20°C to obtain a high-purity medium-grain niobium ingot; (4) Forge the ingot into a diameter of The niobium ingot is then annealed and sliced ​​using a multi-wire saw.

2. The method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity according to claim 1, characterized in that: During the vacuum electron beam melting process, the melting order of the head and tail of the ingot remains unchanged during each melting. After the vacuum electron beam melting is completed, the ingot is cooled and then the ingot and the bottom ingot head are separated using a sawing machine.

3. The method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity according to claim 2, characterized in that: The separated ingot and bottom ingot head are placed in an ultrasonic cleaning machine for degreasing and cleaning, and the water in the cleaning machine is heated to 40°C. Clean 2 to 3 times, and replace the water in the ultrasonic cleaning machine after each cleaning.

4. The method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity according to claim 1, characterized in that: The impurity mass content of the niobium strip is: tantalum ≤100ppm, silicon ≤80ppm, tungsten <5ppm, molybdenum <5ppm, titanium ≤5ppm, zirconium ≤5ppm, copper ≤5ppm, chromium + cobalt ≤10ppm, nickel ≤5ppm, iron ≤5ppm, oxygen ≤100ppm, nitrogen ≤100ppm, carbon ≤20ppm.

5. The method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity according to claim 1, characterized in that: The residual resistivity ratio (RRR value) of the prepared high-purity medium-grain niobium ingot is greater than 400.

6. The method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity according to claim 1, characterized in that: The first electron beam melting in the melting process adopts a horizontal feeding method, and the second and subsequent melting adopts a vertical feeding method, and the electrode rotation speed is controlled to be 0.5-1r / min during the melting process.

7. The method for preparing a high-purity medium-grain niobium ingot for a radio frequency superconducting cavity according to claim 6, characterized in that: During the last smelting, the electrode rotation speed was controlled to be 1-2 r / min, the smelting rate was 60-80 kg / h, the smelting power was 650 kW-750 kW, the vacuum degree was better than 1×10-3 Pa, and the crystallizer cooling water temperature was controlled at 15±5°C.

8. A high-purity medium-grain niobium ingot for radio frequency superconducting cavity prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The ingot has a grain size of less than 20 mm, an RRR value greater than 400, and meets the following impurity content requirements: tantalum ≤ 100 ppm, silicon ≤ 10 ppm, tungsten ≤ 5ppm, molybdenum ≤5ppm, titanium ≤1ppm, zirconium ≤1ppm, copper ≤1ppm, chromium + cobalt ≤6ppm, nickel ≤1ppm, iron ≤3ppm, oxygen ≤10ppm, nitrogen <10ppm, carbon ≤10ppm, hydrogen ≤1ppm.

9. A high-purity medium-grain niobium material for radio frequency superconducting cavity, characterized in that: Prepared according to the method according to any one of claims 1 to 8.

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