Preparation method of 122-type iron-based composite metal-sheathed superconducting tape

Abstract

The present invention provides a method for preparing a 122 type iron-based composite metal sheathed superconducting tape, and belongs to the technical field of superconducting tape preparation. The present invention connects two metal sheaths tightly to form a whole by rotary forging and heat treatment before the precursor powder is loaded into a tube, and can discharge the gas between the two metal sheaths, thereby greatly reducing or even eliminating the bulging caused by gas expansion in the heat treatment link of the composite sheathed tape, improving the critical current density of the tape, improving the practicality of the composite sheathed tape, and significantly improving the yield of the composite sheathed superconducting tape. The present invention first forms a composite metal tube by rotary forging of two metal tubes, and only needs to be rotated 1 to 2 times to form a composite metal tube, and performs a round of rotary forging and drawing process on the precursor powder, eliminating the second tube loading link, greatly shortening the time for preparing the composite tape, and saving manpower and time costs.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting tape preparation, and particularly to a method for preparing a 122-type iron-based composite metal-sheathed superconducting tape. Background Art

[0002] Currently, the method for preparing a Cu / Ag composite-sheathed iron-based superconducting tape is usually a two-step composite method. As Figure 1 shown, first, a precursor powder is prepared under the protection of an inert gas. Then, the precursor powder is filled into an Ag tube. The Ag tube filled with the precursor powder is processed into an Ag-sheathed superconducting wire through rotary swaging and drawing processes. After the wire is cut, it is loaded into a Cu tube. The formed Cu / Ag composite tube is prepared into an iron-based superconducting tape through processes such as rotary swaging, drawing, and rolling, and is prepared into a Cu / Ag composite superconducting tape after heat treatment. This method requires two rounds of rotary swaging and drawing processes (rotary swaging - drawing - composite - rotary swaging - drawing), and the number of rotary swaging and drawing times in each round is more than 10 passes, consuming time and energy and having a high cost. Moreover, the connectivity between the Cu sheath and the Ag sheath of the prepared Cu / Ag composite-sheathed tape is poor, resulting in a low critical current density of the tape and being very prone to bulging during heat treatment, seriously affecting the yield of the Cu / Ag composite-sheathed tape and the practical effect of the wire. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a 122-type iron-based composite metal-sheathed superconducting tape, which can avoid bulging, improve the critical current density and yield of the tape, and has a short processing time.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing a 122-type iron-based composite metal-sheathed superconducting tape, including the following steps:

[0006] Install a first metal tube inside a second metal tube, and seal the gaps formed at both ends of the first metal tube and the second metal tube;

[0007] After spraying a release agent on the inner wall of the first metal tube, install a cemented carbide rod in the first metal tube. After rotary swaging, remove the cemented carbide rod and perform a first heat treatment to obtain a composite metal tube;

[0008] Install an iron-based precursor powder in the composite metal tube, seal it, and then perform rotary swaging, drawing, and rolling in sequence. The obtained composite tape is subjected to a second heat treatment to obtain a 122-type iron-based composite metal-sheathed superconducting tape.

[0009] Preferably, the first metal tube includes an Ag tube or an Nb tube; the second metal tube includes a Cu tube or a stainless steel tube.

[0010] Preferably, the inner diameter of the second metal tube is 0.1 - 0.2 mm larger than the outer diameter of the first metal tube.

[0011] Preferably, the diameter of the cemented carbide rod is 0.2 - 0.5 mm smaller than the inner diameter of the first metal tube.

[0012] Preferably, the length of the cemented carbide rod is 30 - 50 mm longer than the length of the first metal tube.

[0013] Preferably, the release agent is a polyurethane release agent.

[0014] Preferably, the temperature of the first heat treatment is 300°C - 400°C, the vacuum degree is 10 -3 Pa, and the time is 5 h.

[0015] Preferably, the iron-based precursor powder includes Ba-122 precursor powder or Sr-122 precursor powder.

[0016] Preferably, the temperature of the second heat treatment is 740°C - 750°C, and the time is 3 h.

[0017] The present invention provides a method for preparing a 122-type iron-based composite metal-sheathed superconducting tape. Before loading the precursor powder into the tube, the present invention tightly connects the two metal sheaths into a whole through swaging and heat treatment, which can discharge the gas between the two metal sheaths, thereby greatly reducing or even eliminating the generation of bulges caused by gas expansion in the heat treatment process of the composite-sheathed tape, improving the critical current density of the tape, and at the same time significantly improving the yield of the composite-sheathed superconducting tape and the practicability of the composite-sheathed tape.

[0018] The present invention uses a pre-composite method to prepare a composite-sheathed tape. The two metal tubes are first swaged to form a composite metal tube, and only 1 - 2 passes are required to form the composite metal tube. Then, the precursor powder is added, and a round of swaging and drawing processes is carried out on the precursor powder, omitting the second tube-loading link, greatly shortening the time for preparing the composite tape and saving labor and time costs.

[0019] The present invention only needs to perform a round of swaging and drawing processes on the precursor powder, avoiding the fragmentation of Ba-122 polycrystals caused by multiple swaging and drawing, and improving the density of the superconducting core of the tape.

[0020] The pre-composite method of the present invention can increase the initial thickness by preparing a composite metal tube, avoiding the problem of fracture during the first-round drawing of the metal tube with a relatively thin wall thickness in the existing two-step composite method, and using a metal tube with a relatively thin wall thickness can greatly reduce the cost. Brief Description of the Drawings

[0021] Figure 1It is a process flow chart of the method for preparing Cu / Ag composite sheathed superconducting tapes by a two-step composite method in the background art;

[0022] Figure 2 It is a schematic diagram of the method for preparing Cu / Ag composite tubes by the rotary swaging method in the present invention;

[0023] Figure 3 It is a process flow chart of the method for preparing Cu / Ag composite sheathed superconducting tapes by a one-step composite method in the present invention;

[0024] Figure 4 It is a photo of the Cu / Ag composite superconducting tape prepared in Example 1;

[0025] Figure 5 It is a photo of the Cu / Ag composite superconducting tape prepared in Comparative Example 1. Detailed implementation manners

[0026] The present invention provides a method for preparing a 122-type iron-based composite metal sheathed superconducting tape, which includes the following steps:

[0027] Install the first metal tube inside the second metal tube, and seal the gaps formed at both ends of the first metal tube and the second metal tube;

[0028] After spraying a release agent on the inner wall of the first metal tube, install a cemented carbide rod in the first metal tube, perform rotary swaging, remove the cemented carbide rod, and perform a first heat treatment to obtain a composite metal tube;

[0029] Install the iron-based precursor powder in the composite metal tube, seal it, and then perform rotary swaging, drawing and rolling in sequence. The obtained composite tape is subjected to a second heat treatment to obtain a 122-type iron-based composite metal sheathed superconducting tape.

[0030] In the present invention, unless otherwise specified, the raw materials required for preparation are all commercially available products well-known to those skilled in the art.

[0031] The present invention installs the first metal tube inside the second metal tube, and seals the gaps formed at both ends of the first metal tube and the second metal tube.

[0032] In the present invention, the first metal tube, the second metal tube and the cemented carbide rod used are preferably cleaned and dried before use. The cleaning and drying process is preferably to clean the first metal tube, the second metal tube and the cemented carbide rod with absolute ethanol respectively, then ultrasonic them in an ultrasonic instrument in an immersion environment of absolute ethanol solution for 10 minutes, take them out, rinse them with clean absolute ethanol, and then dry them in a constant temperature drying oven at 50°C for 1 hour.

[0033] In the present invention, the first metal tube preferably comprises an Ag tube or an Nb tube; the second metal tube preferably comprises a Cu tube or a stainless steel tube; the way of compounding the first metal tube and the second metal tube is preferably Cu / Ag, Cu / Nb or stainless steel / Ag. In the present invention, the inner diameter of the second metal tube is preferably 0.1 - 0.2 mm larger than the outer diameter of the first metal tube; the present invention has no special limitation on the lengths of the first metal tube and the second metal tube, and it is only required that the length of the second metal tube is shorter than that of the first metal tube. In the embodiments of the present invention, the inner and outer diameter dimensions of the used Cu tube are Φ5×8 mm and the length is 9.5 cm; the inner and outer diameter dimensions of the Ag tube are Φ4×4.8 mm and the length is 10 cm.

[0034] In the present invention, the materials used for plugging preferably include dust-free paper and tape; the present invention has no special limitation on the plugging process, and it can be completely plugged according to the processes well-known in the art.

[0035] After plugging the gaps formed at both ends of the first metal tube and the second metal tube, in the present invention, after spraying a release agent on the inner wall of the first metal tube, a cemented carbide rod is installed in the first metal tube, and after rotary forging, the cemented carbide rod is removed, and a first heat treatment is carried out to obtain a composite metal tube.

[0036] In the present invention, the release agent is preferably a polyurethane release agent; the present invention has no special limitation on the polyurethane release agent, and commercially available products well-known in the art can be used.

[0037] The present invention has no special limitation on the spraying process. After shaking the release agent evenly, it can be introduced into the first metal tube. After inserting the cemented carbide rod, since the difference between the inner diameter of the cemented carbide rod and the first metal tube is not large, the release agent is evenly distributed between the cemented carbide rod and the first metal tube.

[0038] In the present invention, the diameter of the cemented carbide rod is preferably 0.2 - 0.5 mm smaller than the inner diameter of the first metal tube; in order to ensure the increase in the length of the composite tube during rotary forging and facilitate demolding, the length of the cemented carbide rod is 30 - 50 mm longer than the length of the first metal tube. In the embodiments of the present invention, the diameter of the cemented carbide rod is 3.5 mm and the length is 15 cm.

[0039] The present invention has no special limitation on the cemented carbide rod, and commercially available cemented carbide rods well-known in the art can all be used. The present invention uses the cemented carbide rod as a mold.

[0040] In the present invention, the rotary swaging is preferably carried out on a rotary swaging machine; the number of rotary swaging passes is preferably 1 to 2 passes; the present invention does not have special limitations on the rotary swaging machine, and a rotary swaging machine well-known in the art can be used. Under the action of the internal die cemented carbide rod and the external rotary swaging die, the first metal tube sheath and the second metal tube sheath are tightly connected together. After the precursor powder is loaded into the formed composite metal tube, the preparation of the composite strip can be achieved only through one round of rotary swaging + drawing and rolling steps.

[0041] Figure 2 FIG. 4 is a schematic diagram of the preparation of a Cu / Ag composite tube by the rotary swaging method. Taking a Cu tube and an Ag tube as examples, in the present invention, a Cu / Ag composite tube is formed by rotary swaging with a cemented carbide rod as the die.

[0042] The present invention does not have special limitations on the process of loading the cemented carbide rod into the first metal tube and removing the cemented carbide rod, and it can be carried out according to the process well-known in the art.

[0043] In the present invention, the temperature of the first heat treatment is preferably 300 to 400 °C, the vacuum degree is preferably 10 -3 Pa, and the time is preferably 5 h.

[0044] In the present invention, through the first heat treatment, the interface where the two metal tubes are connected undergoes metallurgical bonding under the action of the heat treatment, making the combination of the two sheaths closer and forming an integral composite metal tube.

[0045] After obtaining the composite metal tube, the present invention loads the iron-based precursor powder into the composite metal tube, seals it, and then sequentially performs rotary swaging, drawing and rolling. The obtained composite strip is subjected to a second heat treatment to obtain a 122-type iron-based composite metal sheath superconducting strip.

[0046] In the present invention, the iron-based precursor powder preferably includes a Ba-122 precursor powder or an Sr-122 precursor powder. In the present invention, the preparation method of the Ba-122 precursor powder preferably includes: respectively chopping K pieces (99.9% pure), Ba rods (99.9% pure), Fe powder (99.9% pure) and As pieces (99.99% pure), mixing them evenly, loading the obtained mixed material into a ball milling tank and sealing it, and performing ball milling in a planetary ball mill (to make up for the loss of K element during the sintering process of the precursor powder, 15 wt% excess K pieces are added to the raw materials); after ball milling sufficiently for 10 h multiple times, the mixed powder is loaded into a niobium tube and sealed under an argon atmosphere, the niobium tube is loaded into an iron tube and welded, and sintered at 900 °C for 35 h to obtain a rod-shaped Ba-122 superconducting phase. After grinding, the Ba-122 precursor powder is obtained.

[0047] The present invention does not have special limitations on the filling amount of the iron-based precursor powder. It can be filled to the full under the condition of being able to be sealed to prevent waste of the sheath material.

[0048] In the present invention, the temperature of the second heat treatment is preferably 740-750° C., and the time is preferably 3 hours.

[0049] The present invention uses the second heat treatment to make the powdered precursor powder form a superconducting phase again at a high temperature, thereby achieving high performance of the superconducting tape.

[0050] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Example 1

[0052] K block (99.9% pure), Ba rod (99.9% pure), Fe powder (99.9% pure) and As block (99.99% pure) were chopped up respectively and mixed evenly, the obtained mixture was put into a ball mill jar and sealed, and ball milled in a planetary ball mill (adding an excess of 15wt% K block to the raw materials); after multiple ball millings for 10 hours, the mixed powder was put into a niobium tube under an argon atmosphere and sealed, the niobium tube was put into an iron tube and welded, and sintered at 900°C for 35 hours to obtain a rod-shaped Ba-122 superconducting phase, and after grinding, a Ba-122 precursor powder was obtained;

[0053] Materials used: Cu tube: inner and outer diameter dimensions: Φ5×8mm, 9.5cm long; Ag tube: inner and outer diameter dimensions: Φ4×4.8mm, 10cm long; Carbide rod: diameter Φ3.5mm, 15cm long; Polyurethane release agent: appropriate amount;

[0054] Use anhydrous ethanol to clean the oil and impurities of the Cu tube, Ag tube and cemented carbide rod, soak them in anhydrous ethanol solution and ultrasonicate them in an ultrasonic instrument for 10 minutes, take them out, rinse them with clean anhydrous ethanol, and then put them in a 50°C constant temperature drying oven for drying for 1 hour;

[0055] like Figure 3 As shown, the treated Ag tube is placed into the Cu tube, and the gaps at both ends of the copper-silver tube are sealed with dust-free paper and tape;

[0056] Spray polyurethane release agent inside the Ag tube, put the carbide rod into the Ag tube as a mold, and evenly distribute the release agent between the carbide rod and the Ag tube;

[0057] The composite is made by rotary forging on a rotary forging machine, the number of rotary forging is 2, and the cemented carbide rod is pulled out to form a Cu / Ag composite tube;

[0058] The Cu / Ag composite tube is heat-treated at 300 °C under a vacuum of 10 -3 Pa for 5 h to form an integral Cu / Ag composite tube;

[0059] 3.5 g of Ba-122 precursor powder is loaded into the copper-silver composite tube and sealed, and then subjected to rotary swaging, drawing, and rolling processes to form a Cu / Ag composite superconducting tape. The tape is heat-treated at 740 °C for 3 h to obtain a 122-type iron-based composite metal-sheathed superconducting tape.

[0060] Comparative Example 1

[0061] Materials used: Cu tube: inner and outer diameter dimensions: Φ2×4 mm, 9.5 cm long; Ag tube: inner and outer diameter dimensions: Φ5×8 mm, 7 cm long;

[0062] The Cu tube and Ag tube are cleaned of oil stains and impurities using absolute ethanol, ultrasonically treated in an ultrasonic instrument for 10 min in an immersion environment of absolute ethanol solution, taken out, rinsed with clean absolute ethanol, and then placed in a constant-temperature drying oven at 50 °C for drying for 1 h;

[0063] 3.5 g of the Ba-122 precursor powder prepared in Example 1 is filled into the Ag tube and sealed. The Ag tube filled with the precursor powder is processed into an Ag-sheathed superconducting wire with a diameter of 1.95 mm through rotary swaging and drawing processes. The wire is cut into 8 cm and then loaded into the Cu tube. After blocking both ends of the Cu tube with dust-free paper, the formed Cu / Ag composite tube is successively subjected to rotary swaging, drawing, and rolling to form an iron-based superconducting tape. After heat treatment at 740 °C for 3 h, a Cu / Ag composite superconducting tape is obtained.

[0064] Characterization and performance testing

[0065] 1) Figure 4 is a photograph of the Cu / Ag composite superconducting tape prepared in Example 1; As can be Figure 4 seen, the tape prepared by the pre-composite method in Example 1 has no bulges on the surface, is bright on the surface, has no protrusions, and can improve the performance and increase the yield.

[0066] 2) Figure 5 is a photograph of the Cu / Ag composite superconducting tape prepared in Comparative Example 1; As can be Figure 5 seen, bulges appear on the tape prepared by the two-step composite method after heat treatment, affecting the performance and yield of the tape.

[0067] 3) The critical current density of the 122-type iron-based composite metal-sheathed superconducting tape prepared in Example 1 is measured by the standard four-probe method. The obtained critical current density (Jc) is 5.2×10 4 A / cm -2 , and the critical current density of the Cu / Ag composite superconducting tape prepared in Comparative Example 1 is 3.9×10 4Acm -2 , indicating that the method of the present invention can significantly improve the critical current density of the composite superconducting tape.

[0068] 4) Yield: The tape with no bulges on the surface and a critical current density exceeding 2×10 4 Acm -2 is determined as a finished product; the yield of the Cu / Ag composite tape prepared by the pre-composite method in Example 1 of the present invention is almost 100%, and the yield of the tape prepared in Comparative Example 1 is less than 30%.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a 122-type iron-based composite metal-sheathed superconducting tape, characterized in that, The steps include: Install the first metal tube inside the second metal tube, and seal the gap formed at both ends of the first metal tube and the second metal tube; After spraying a release agent on the inner wall of the first metal tube, install the cemented carbide rod in the first metal tube, perform rotary forging for 1 to 2 passes, remove the cemented carbide rod, and perform the first heat treatment to obtain a composite metal tube; Load the iron-based precursor powder into the composite metal tube, seal it, and then perform one round of rotary forging, drawing, and rolling in sequence. Subject the obtained composite strip to the second heat treatment to obtain a 122-type iron-based composite metal-sheathed superconducting strip; The temperature of the first heat treatment is 300°C to 400°C, the vacuum degree is 10 -3 Pa, and the time is 5 h; The temperature of the second heat treatment is 740°C to 750°C, and the time is 3 h; The inner diameter of the second metal tube is 0.1 to 0.2 mm larger than the outer diameter of the first metal tube; The diameter of the cemented carbide rod is 0.2 to 0.5 mm smaller than the inner diameter of the first metal tube; the length of the cemented carbide rod is 30 to 50 mm longer than the length of the first metal tube; The iron-based precursor powder includes Ba-122 precursor powder or Sr-122 precursor powder.

2. The preparation method according to claim 1, characterized in that, The first metal tube includes an Ag tube or an Nb tube; the second metal tube includes a Cu tube or a stainless steel tube.

3. The preparation method according to claim 1, characterized in that, The release agent is a polyurethane release agent.

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