A method for preparing a large-size rare earth barium copper oxide superconducting target

Abstract

The application discloses a method for preparing large-size rare earth barium copper oxygen superconducting target material and relates to the technical field of superconducting target material preparation. The method realizes the compatibility of a single set of molds with various specifications of target materials by optimizing the design of cold isostatic pressing molds, adopting a composite mold structure comprising upper and lower cover plates, a cylinder, isolation pads, a replaceable elastic lining and a clamp, and can press multiple target materials at a time by setting multiple isolation pads, and is suitable for the preparation of target materials with a diameter of 8-12 inches and a thickness of 10-20 mm. The preparation process comprises the following steps of mold assembly, superconducting powder filling and vibration treatment, segmented pressure cold isostatic pressing treatment, blank shaping, oxygen atmosphere sintering and grinding machine processing. The mold generality design and batch pressing technology of the application significantly improve the production efficiency, reduce the mold cost and powder loss, and at the same time, ensure the density (relative density 80%-85%) and surface flatness (less than or equal to 0.5 mm) of the target material, and meet the strict requirements of large-size target materials for high-end superconducting thin film preparation such as pulsed laser deposition.

Description

Technical Field

[0001] This invention relates to the field of superconducting target preparation technology, specifically to a method for preparing large-size rare-earth barium copper oxide superconducting targets using cold isostatic pressing technology, which is particularly suitable for the mass production of 8-inch and larger targets for second-generation high-temperature superconducting tapes using pulsed laser deposition (PLD) technology. Background Technology

[0002] Rare earth barium copper oxide superconducting targets are the core raw materials for preparing superconducting thin films by physical vapor deposition (PVD) and are widely used in fields such as magnetron sputtering (MS) and pulsed laser deposition (PLD). With the large-scale development of the second-generation high-temperature superconducting tape industry, the market demand for large-size targets of 8 inches and above has increased dramatically. However, existing preparation technologies face the following bottlenecks: conventional uniaxial molding processes are only suitable for small-size targets (<2 inches), while large-size targets are prone to problems such as uneven density and cracking, and have low density; hot pressing sintering technology can prepare large-size targets, but it needs to be carried out under high temperature (>900℃) and high pressure (>50 tons) conditions, resulting in high energy consumption, low efficiency, and graphite molds that easily lead to carbon contamination on the target surface, resulting in large subsequent processing volume and serious powder loss; existing isostatic pressing technology is limited by unreasonable mold design. Existing isostatic pressing molds (such as publication number CN101745974A) can only produce one type of target material per mold set, and can only press one target material per powder filling; moreover, the mold is a flat plate design, resulting in poor uniformity of pressure on the target blank, easy deformation and cracking, making it difficult to meet the density uniformity and dimensional accuracy requirements of large-size targets, and the mold has poor versatility and high manufacturing cost.

[0003] Therefore, developing a method for the efficient, low-cost, and mass-producible high-quality, large-size rare-earth barium copper oxide superconducting target has become an urgent industry need. This invention addresses these shortcomings through a replaceable liner and multiple insulating pads design. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing technologies and provide a method for preparing large-size rare-earth barium copper oxide superconducting targets. By optimizing the mold design, a single mold can be used to prepare multiple specifications of targets and increase the number of targets pressed in a single batch, thereby improving production efficiency, reducing costs, and ensuring the density and dimensional accuracy of the target material to meet the requirements of high-end applications.

[0005] This invention is achieved through the following technical solution:

[0006] S1, Mold Structure Design. The cold isostatic pressing mold includes upper and lower cover plates, a cylinder, a spacer plate, an elastic liner, and clamps (see Figure 1 for details): - Upper and lower cover plates and cylinder: made of polyurethane, traditional rubber or silicone rubber with a Shore hardness of 60-80A, with a certain thickness to resist radial expansion under high pressure of 100-300 MPa; - Isolation pads: These serve both filling and shaping functions. The filling pads are made of the same material as the cover plates, while the shaping pads are made of low-carbon steel with a Brinell hardness of 100-200. Select the appropriate size and quantity of isolation pads according to the pressing requirements. - Elastic liner: Shore hardness 40-50A, material is high elastic silicone rubber, traditional rubber or polyurethane. The target material specifications can be adjusted by changing the liner with different wall thickness and height; select the appropriate size elastic liner according to the pressing requirements. - Clamps: Standard parts matching the mold size are used, with one clamp on each of the upper and lower covers to ensure a sealing effect.

[0007] S2, Powder Filling and Vibration Treatment. Commercial superconducting powder is directly loaded into the mold and placed on a vibration table, vibrating at a frequency of 50-100 Hz for 5-10 minutes with a vibration amplitude of 0.5-1 mm. This high-frequency vertical vibration increases the loose packing density of the powder by 10-15%, preventing voids from forming during subsequent pressing. The mold is then sealed; if necessary, a vacuum can be applied first to prevent gas interference during pressing, which could lead to the formation of pores or a loose structure inside the preform.

[0008] S3. Cold isostatic pressing. A segmented pressurization process is adopted: first, pressurize to 100 MPa at a rate of 5-10 MPa / min, hold for 10 min to eliminate powder porosity; then, pressurize to 150-250 MPa at a rate of 10-15 MPa / min, hold for 30-60 min to densify the green body. Depressurize after completion.

[0009] S4. Blank shaping. Use a specialized shaping machine to correct the edges and corners of the blank, control the dimensional error within ±1 mm, and collect the cutting powder for reuse.

[0010] S5. Sintering treatment. In the sintering furnace, the temperature is raised to 800-900℃ at a rate of 5-10℃ / min and held for 2-4 h to remove impurities and gases; then, in an oxygen atmosphere, the temperature is raised to 940-970℃ at a rate of 3-5℃ / min and held for 4-6 h, and then cooled to room temperature with the furnace.

[0011] S6. Grinding. High-precision surface grinding is used, with the grinding wheel speed set at 2000 r / min and the feed rate at 0.5 mm / min, to achieve a surface flatness of 0.5 mm for the target material.

[0012] Compared with the prior art, the present invention has the following advantages: Significant cost reduction and efficiency improvement. Multiple targets can be pressed at once by using an isolation pad, and combined with a pre-pressing process, production efficiency is increased several times. A single set of molds can be compatible with various specifications of targets by changing the elastic inner liner, saving more than 50% in mold costs. There is no carbon pollution during the target pressing process, and the powder is recycled and reused in the blank shaping process, reducing powder loss by more than 15%.

[0013] The target material is of excellent quality. Cold isostatic pressing, segmented pressurization, optimized mold design, and sintering process ensure that the relative density of the target material reaches 80%-85%; the surface flatness is controlled within 0.5 mm, meeting the high precision requirements of PLD strip production for the target material.

[0014] It has strong process compatibility. It is suitable for the preparation of large-size targets with diameters of 8-12 inches and thicknesses of 10-20 mm, and does not require high temperature and high pressure conditions, reducing energy consumption by more than 40% and eliminating the risk of carbon pollution. Attached Figure Description

[0015] Figure 1 shows the mold assembly diagram of the present invention, including upper and lower cover plates, cylinder, isolation pad, elastic liner and clamp.

[0016] Figure 2 shows the assembly relationship between the isolation pad, elastic liner and powder of the present invention.

[0017] Figure 3 shows the assembly relationship between the isolation pad, the elastic liner, and the powder when using an integral elastic liner.

[0018] In the diagram, 1—upper and lower cover plates, 2—clamp, 3—isolation pad, 4—elastic liner, 5—powder, 6—cylinder. The clamp is made of stainless steel, 20-30 mm wide, and is fastened with bolts (pre-tightening force 50-100 N) to ensure a sealing pressure ≥100 MPa. The isolation pad has rounded edges (R2-R3 mm) to prevent stress concentration at the edges of the blank during pressing. Detailed Implementation

[0019] Example 1 Four superconducting targets with a diameter of 160 mm and a thickness of 12 mm were fabricated in one batch. 1. Mold parameters: The cylinder is made of high-strength polyurethane (Shore hardness 70-80A), with an outer diameter of 190 mm, an inner diameter of 170 mm, and a height of 300 mm; the upper and lower cover plates have a diameter of 170 mm and a height of 50 mm; there are 5 low-carbon steel isolation pads (diameter 170 mm, thickness 20 mm). 2. Filling and Vibration: Fill each layer with 1.5-1.6 kg of powder, vibrate at 50 Hz with an amplitude of 0.5 mm for 5 min, and then seal. 3. Cold isostatic pressing: Increase the pressure at 5 MPa / min to 100 MPa (hold for 10 min), then increase the pressure at 10 MPa / min to 150 MPa (hold for 30 min). 4. Sintering: Hold at 800℃ for 2 hours, then hold at 960℃ in an oxygen atmosphere for 4 hours; 5. Results: The relative density of the superconducting target was 82.5%, and the surface flatness was < 0.4 mm.

[0020] Example 2 A superconducting target with a diameter of 270 mm and a thickness of 15 mm was prepared by pressing one piece at a time. 1. Mold parameters: The cylinder is made of high-strength polyurethane (Shore hardness 70-80A), with an outer diameter of 310 mm, an inner diameter of 280 mm, and a height of 220 mm; the upper and lower cover plates have a diameter of 280 mm and a height of 70 mm; there are 2 low-carbon steel isolation pads (diameter 280 mm, thickness 30 mm). 2. Filling and Vibration: Fill with 4.5-5.0 kg of powder, vibrate at 50Hz with an amplitude of 1 mm for 5 minutes, then seal; 1000022023.03 4 Instruction Manual 3. Cold isostatic pressing: Increase the pressure to 100 MPa at 5 MPa / min (hold for 10 min), then increase the pressure to 250 MPa at 15 MPa / min (hold for 60 min). 4. Sintering: Hold at 800℃ for 2 hours, then hold at 940℃ in an oxygen atmosphere for 10 hours; 5. Results: The relative density of the target material was 80.2%, and the surface flatness was < 0.2 mm.

[0021] Example 3 A superconducting target with a diameter of 213 mm and a thickness of 15 mm was prepared using the mold of Example 2: 1. Mold parameters: A silicone liner (Shore hardness 40-50A, outer diameter 280mm, inner diameter 230mm, height 20mm) is installed inside the mold of Example 2; the elastic liner and the cylinder are interference fit, with an interference amount of 0.1-0.2mm. 2. Filling and Vibration: Fill the silicone liner with 2.5-3.0 kg of superconducting powder, vibrate at 50 Hz and 0.5 mm amplitude for 5 min, and then seal. 3. Cold isostatic pressing: Increase the pressure to 100 MPa at 5 MPa / min (hold for 10 min), then increase the pressure to 200 MPa at 12 MPa / min (hold for 45 min). 4. Sintering: Hold at 800℃ for 2 hours, then hold at 950℃ in an oxygen atmosphere for 6 hours; 5. Results: The relative density of the target material was 83.1%, and the surface flatness was < 0.7 mm.

[0022] Comparative experiment: Using the existing hot pressing process to prepare the same size target material, the density is 72-79%, the surface flatness is 0.3-0.5 mm, and the pressing production cycle is 24 h / piece; In this embodiment, the target material density is 80.2-82.5%, the flatness is 0.2-0.5 mm, and the cycle of producing 4 target material blanks with a single set of molds is shortened to 3 h.

[0023] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing large-size rare-earth barium copper oxide superconducting targets, characterized in that, Includes the following steps: S1, Mold Assembly: A cold isostatic pressing mold is used, comprising upper and lower cover plates, a cylinder, a spacer plate, an elastic liner, and clamps. The upper and lower cover plates and the cylinder have a Shore hardness of 60-80A and are made of polyurethane (PU), conventional rubber, or silicone rubber. The spacer plate serves both filling and shaping functions; the filling spacer plate is made of the same material as the cover plate, while the shaping spacer plate is made of low-carbon steel with a Brinell hardness of 100-200. The elastic liner has a Shore hardness of 40-50A and is made of high-elasticity silicone rubber, conventional rubber, or polyurethane. S2, Powder loading and vibration treatment: The superconducting powder is loaded into the mold and placed on a vibration table to vibrate at a frequency of 50-100 Hz and an amplitude of 0.5-1 mm for 5-10 min, and then the mold is sealed. S3, Cold Isostatic Pressing: A segmented pressurization method is adopted. First, the pressure is increased to 100 MPa at a rate of 5-10 MPa / min and held for 10 min. Then, the pressure is increased to 150-250 MPa at a rate of 10-15 MPa / min and held for 30-60 min. S4, billet shaping: The shape of the billet after cold isostatic pressing is regularized so that the dimensional error is controlled within ±1 mm; S5, sintering treatment: first hold at 800-900℃ for 2-4 hours, then hold at 940-970℃ for 4-6 hours in an oxygen atmosphere, and then cool with the furnace; S6, Grinding: The surface grinding process is used to control the flatness of the target material within 0.5 mm.

2. The method for preparing large-size rare-earth barium copper oxide superconducting targets according to claim 1, wherein the superconducting powder is a commercially available rare-earth barium copper oxide superconducting phase powder with the general chemical formula REBa2Cu3O 7₋δ (RE stands for rare earth element), with an average particle size of 20-50 μm and a superconducting phase purity of ≥95%.

3. The method for preparing large-size rare-earth barium copper-oxygen superconducting targets according to claim 1, characterized in that, The mold is suitable for pressing targets with a diameter of 8-12 inches and a thickness of 10-20 mm. By changing the elastic liner with different wall thicknesses (5-30 mm) and heights (10-50 mm), various specifications of targets can be prepared. By setting 2-5 isolation plates, 1-4 targets can be prepared at a time.

4. The method for preparing large-size rare-earth barium copper-oxygen superconducting targets according to claim 1, characterized in that, When the isolation pad is used for shaping, its thickness is 1.5-2 times the thickness of the pressed blank. When used for filling, its thickness is generally ≤30 mm as needed. The wall thickness of the elastic liner is (inner diameter of cylinder - diameter of blank) / 2±1 mm, and its value is ≤30 mm, to ensure that the pressure is uniformly transmitted to the powder during cold isostatic pressing.

5. The method for preparing large-size rare-earth barium copper oxide superconducting target material according to claim 1, characterized in that, The spacing between the isolation pads is 1.2-1.5 times the thickness of the blank, and the parallelism error between adjacent pads is ≤1 mm; the elastic liner and the cylinder are interference fit, with an interference amount of 0.1-0.2 mm; the fit clearance between the upper and lower cover plates and the cylinder is ≤0.5 mm to ensure sealing.

6. The method for preparing large-size rare-earth barium copper oxide superconducting target material according to claim 1, characterized in that, The cutting superconducting powder collected during the blank forming process can be reused.

7. The method for preparing large-size rare-earth barium copper oxide superconducting target material according to claim 1, characterized in that, The heating rate for the sintering process is 5-10℃ / min, and the heating rate for the oxygen atmosphere stage is 3-5℃ / min.

8. The method for preparing large-size rare-earth barium copper oxide superconducting target material according to claim 1, characterized in that, The grinding wheel of the grinding machine rotates at 2000 r / min and the feed rate is 0.5 mm / min.

9. The method for preparing large-size rare-earth barium copper oxide superconducting target material according to claim 1, characterized in that, The relative density of the resulting target material is 80%-85%.

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