A method for improving critical current density of multi-core iron-based superconducting tape and multi-core iron-based superconducting tape
By adjusting the heat treatment process and increasing the sintering temperature and time, the grain growth of the superconducting core in the multi-core iron-based superconducting tape was promoted, which solved the problem of reduced critical current density after multi-core construction and improved the current carrying capacity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF ELECTRICAL ENG CHINESE ACAD OF SCI
- Filing Date
- 2026-04-17
- Publication Date
- 2026-06-12
AI Technical Summary
After multi-core processing, the critical current density of 122 series iron-based superconducting tapes is significantly reduced. Existing technologies cannot restore the grain size to an appropriate range through heat treatment processes, resulting in insufficient current carrying capacity.
By adjusting the heat treatment process, increasing the sintering temperature to 895℃, and adjusting the sintering time according to the number of superconducting core layers, the grain growth of the superconducting core of the multi-core iron-based superconducting tape is promoted to 5μm~15μm, ensuring that more than 80% of the grain size is within the appropriate range.
It significantly improves the critical current density of multi-core iron-based superconducting tapes, bringing it close to or reaching the level of 7-core tapes, thus solving the problem of reduced current carrying capacity after multi-core construction.
Smart Images
Figure CN122201923A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of superconducting materials technology, and in particular to a method for increasing the critical current density of multi-core iron-based superconducting tapes and the multi-core iron-based superconducting tapes themselves. Background Technology
[0002] In February 2008, a research group discovered LaFeAsO₂ 1-x F x It has a critical transition temperature of 26 K (T c This sparked a research boom in iron-based superconductors (IBS). Subsequently, a series of iron-based superconducting materials with different structures were discovered, including T… c It was also rapidly increased to 55 K. Furthermore, IBS exhibits a high upper critical field (H). c2 Its advantages, such as low anisotropy (γ), make it a promising candidate for high-field applications in nuclear magnetic resonance imaging (MRI), nuclear magnetic resonance spectrometers (NMR), superconducting energy storage systems (SMES), and high-energy physics accelerators. The journal *Science* has named it one of the most promising new high-temperature superconductors currently available.
[0003] There are four main systems of iron-based superconductors: 1111-type REFeAsO, 111-type LiFeAs, 122-type AEFe2As2, and 11-type FeSe. Among them, the 122-type iron-based superconductors have the greatest potential for practical application. (The text then abruptly shifts to a seemingly unrelated topic: 122-type iron-based superconductor T...) c 38 K, H c2 It can exceed 100 T, and more importantly, it has low anisotropy (1-2) and the weak grain boundary bonding effect is not obvious. Therefore, it can be prepared using the low-cost powder-in-tube method (PIT) to produce high J-values. c The PIT method has been used to prepare 122 iron-based superconducting tapes. Currently, through continuous optimization by researchers, the JT of these tapes prepared by the PIT method has been successfully tested at 4.2 K and 10 T. c It has exceeded 10 5 A / cm 2 It has reached the threshold for practical application.
[0004] From a practical application perspective, to prevent magnetic flux fluctuations and reduce AC losses, superconducting wires and tapes (such as NbTi, Nb3Sn, Bi-2212, and Bi-2223) typically employ multi-core filament composite structures. The multi-core development of iron-based superconducting tapes is also an essential step towards their engineering applications. Currently, the commonly fabricated 122-series iron-based superconducting tapes have a relatively small core count of 7 cores. This is mainly because further multi-core development (such as 19, 37, and 114 cores) significantly reduces the tape's current-carrying capacity (reflected in the critical current density). Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a method for increasing the critical current density of multi-core iron-based superconducting tapes and the multi-core iron-based superconducting tape itself.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] A method for increasing the critical current density of multi-core iron-based superconducting tapes includes the following steps:
[0008] S1: Several cut single-core wires are loaded into a metal tube to form a multi-core composite tube. The multi-core composite tube is then drawn and rolled to obtain a multi-core strip.
[0009] S2: The multi-core tape is heat-treated and cooled to obtain a multi-core iron-based superconducting tape; wherein the proportion of grains with a size of 5μm~15μm in the superconducting core of the multi-core iron-based superconducting tape controlled by heat treatment exceeds 80%.
[0010] In step S2, the sintering temperature of the heat treatment is higher than 890℃.
[0011] In step S2, the sintering temperature for heat treatment is 895℃±2℃.
[0012] The sintering time in step S2 is calculated according to the following formula:
[0013] ;
[0014] Where T is the sintering time in hours, and n is the number of superconducting core layers, n≥3.
[0015] The multi-core iron-based superconducting tape is a 122-series iron-based superconducting tape.
[0016] In step S1, the metal tube is made of AgSn alloy (silver-tin alloy).
[0017] The method also includes the following steps:
[0018] S0: The precursor powder is filled into a metal tube, and then the tube is sealed to obtain a tube-mounted composite. The tube-mounted composite is drawn to obtain a single-core wire. The single-core wire is then cut to length, cleaned, and cut to obtain the cut single-core wire.
[0019] The lengths of the cut single-core wires are equal.
[0020] The number of cores in the multi-core iron-based superconducting tape is greater than 7.
[0021] A multi-core iron-based superconducting tape is prepared by the above-mentioned method for increasing the critical current density of multi-core iron-based superconducting tape.
[0022] The beneficial effects of this invention are as follows:
[0023] This invention modifies only the heat treatment process based on existing 122-series iron-based multi-core superconducting tape fabrication technology. After the multi-core tape is cold-processed, it undergoes heat treatment at a higher temperature. The heat treatment time formula of this invention is used to adjust the heat treatment time according to the number of superconducting core layers, thereby promoting grain growth and restoring the grain size in the superconducting core of the multi-core tape to the same size as that of the 7-core tape. This, in turn, increases the critical current density of the multi-core tape to the same level as that of the 7-core tape. Attached Figure Description
[0024] Figure 1 The images show the grain morphology and size distribution of 7-core and 30-core superconducting tapes obtained using the current process (before heat treatment). Figure 1 (a) shows the grain morphology and size distribution of the 7-core superconducting tape obtained by the current process; Figure 1 (b) shows the grain morphology and size distribution of the 30-core superconducting tape obtained by the current process; Figure 1 (c) in the figure shows the percentage distribution of grain size in the 7-core superconducting tape obtained by the current process; Figure 1 (d) in the figure is the percentage distribution of grain size of the 30-core superconducting tape obtained by the current process.
[0025] Figure 2 The images show the grain morphology of the multi-core superconducting tapes prepared in Comparative Examples 1, 2, and 1 of this invention. Figure 2 Image (a) in the figure shows the grain morphology of the multi-core superconducting tape prepared in Comparative Example 1. Figure 2 (b) in the figure is a grain morphology diagram of the multi-core superconducting tape prepared in Comparative Example 2; Figure 2 (c) is a grain morphology diagram of the multi-core superconducting tape prepared in Example 1.
[0026] Figure 3 The images show the grain morphology and size distribution of the multi-core superconducting tapes prepared in Comparative Example 1 and Example 1. Figure 3 Images (a) and (c) in the diagram show the grain morphology and size distribution of the multi-core superconducting tape prepared in Comparative Example 1. Figure 3 (b) and (d) in the figure are the grain morphology and size distribution diagrams of the multi-core superconducting tape prepared in Example 1. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0028] One reason for the lower critical current density of multi-core superconducting tapes is that it is difficult to ensure the deformation uniformity of the superconducting cores after multi-core addition, resulting in non-uniform density and texture of the superconducting cores in the tape. However, although optimizing the deformation uniformity can significantly improve the current carrying capacity of tapes with more cores, it cannot reach the same level as tapes with fewer cores.
[0029] Through analysis of the cold working process and summarization of experimental data, the inventors discovered that a significant change after multi-core processing is that the amount of cold working on a single superconducting core increases, leading to more severe fragmentation of the precursor powder. This results in a significant reduction in the particle size of the precursor powder in the superconducting core after cold working. At this point, continuing with conventional sintering processes prevents the grains in the superconducting core from growing to an appropriate size.
[0030] Specifically, the commonly produced 122-series iron-based superconducting tapes currently have 7 cores. The process involves drawing a single core to a certain size, cutting it into 7 strips of equal length, bonding them into a secondary tube, and then drawing again to obtain a 7-core round wire (2-layer superconducting core). This is followed by rolling and finally heat treatment and sintering. Typically, for the sake of operability in the bonding process, the size of the secondary tube remains unchanged. Therefore, when the number of cores needs to be increased, the single core needs to be drawn to a smaller diameter and then cut into 19 strips (3-layer superconducting core), 37 strips, or 30 strips (4-layer superconducting core), etc., of equal length. Thus, as the number of cores increases, the processing volume of a single superconducting core increases significantly. When the number of cores increases even further, the secondary tube needs to be drawn to a specific size, cut into several strips, and then undergo three or even more bonding operations. In this case, the processing volume of a single superconducting core will increase even further. The above analysis shows that a significant problem with multi-core strips is that the processing amount of a single superconducting core increases, the precursor powder in the metal tube is subjected to more severe crushing, resulting in a reduction in the particle size of the precursor powder in the superconducting core after cold processing.
[0031] like Figure 1As shown, when the number of cores increases from 7 to 30, the proportion of grains with a size between 100 nm and 200 nm in the strip after cold processing increases from 38.61% to 47.73%, while the proportion of grains with a size greater than 500 nm decreases from 17.99% to 8.43%, indicating that the grain size in the strip decreases significantly after increasing the number of cores. At this point, if the previous heat treatment process is used, the grains in the sintered strip cannot grow to the normal size. Therefore, even if the uniformity of the strip is the same as that of the 7-core strip after optimization, its critical current density is still lower than that of the 7-core strip.
[0032] Based on the above analysis, the inventors believe that for 122-series iron-based superconducting tapes, the tapes only possess good current-carrying capacity when the grain size is within an appropriate range. The principle of this invention is detailed below:
[0033] For 122-series iron-based superconducting tapes, the inventors discovered that the critical current density is highest when the grain size in the superconducting core is around 10 μm. Typically, the grain size of a 7-core superconducting tape is between 5 μm and 15 μm. However, if multi-core tapes are processed using conventional heat treatment methods (usually 880℃ for 1 hour), the grain size is generally less than 5 μm, leading to a decrease in critical current density. Therefore, if the grain size of the multi-core superconducting tape's core can be restored to around 10 μm, its critical current density can be increased to the level of tapes with fewer cores. During heat treatment, increasing the sintering temperature is the most effective way to promote grain growth. However, because the 122-series iron-based superconducting tape uses an AgSn alloy with a melting point of 900℃ as the outer sheath, the potential for increasing the sintering temperature is very limited. Therefore, it is necessary to appropriately extend the sintering time to promote grain growth. Considering that increasing the sintering temperature has a more significant effect on improving grain growth, the multi-core strip should be sintered at the highest possible temperature, such as 895℃. The sintering time varies depending on the degree of multi-core formation. Based on calculations and experimental verification, the following patterns are summarized:
[0034] ;
[0035] Where T is the sintering time in hours, and n is the number of superconducting core layers, n≥3. For example, a 19-core superconducting core has 3 superconducting core layers and a sintering time of 3.04±0.45 hours, while a 37-core or 30-core superconducting core has 4 superconducting core layers and a sintering time of 4.39±0.6 hours.
[0036] Example 1
[0037] This embodiment prepares a 30-core superconducting tape.
[0038] The sintering time calculated using the above formula is 4.39 hours.
[0039] Its preparation process includes the following steps: the preparation process of cutting single-core wire is the same as the existing process, the change lies in the heat treatment process.
[0040] (1) Under the atmosphere of protective gas Ar, the raw materials required for 122 iron-based superconductor are weighed and ball-milled. The ball-milled powder is loaded into Nb tube and the two ends of Nb tube are sealed with the first plug and then heat-treated to obtain the precursor powder for preparing superconducting wires and tapes.
[0041] (2) The precursor powder obtained in step (1) is filled into a metal tube, and then the two ends are sealed with a second plug to obtain a tube-filled composite. The tube-filled composite is drawn to obtain a single-core wire. The single-core wire is then cut to length, cleaned, and cut to obtain a cut single-core wire. The cut single-core wires are of equal length.
[0042] (3) Take 30 cut single-core wires of equal length from step (2) and put them into a metal tube to form a multi-core composite tube. Then draw the multi-core composite tube to obtain multi-core wires and repeatedly roll the multi-core wires to obtain multi-core strips.
[0043] (4) The multi-core tape obtained in step (3) is heat-treated in vacuum at a sintering temperature of 895°C and held for 4.39 hours. Finally, the muffle furnace is cooled to room temperature to obtain the iron-based superconducting tape.
[0044] Example 2
[0045] The steps in Example 2 are the same as those in Example 1, except that the sintering time is 4.9 hours.
[0046] Example 3
[0047] The steps in Example 3 are the same as those in Example 1, except that the sintering time is 3.8 hours.
[0048] Example 4
[0049] The steps in Example 4 are the same as in Example 1, except that the superconducting core is prepared as a 12-core (19-core optimized) superconducting tape with 3 layers, and the sintering time is 3.04 hours.
[0050] Comparative Example 1
[0051] Steps (1) to (3) are the same as in Example 1; in step (4), the sintering temperature is 880°C and the time is 1 hour.
[0052] Comparative Example 2
[0053] Steps (1) to (3) are the same as in Example 1; in step (4), the sintering temperature is 895°C and the time is 1 hour.
[0054] Comparative Example 3
[0055] Comparative Example 3 is a 7-core superconducting tape prepared using existing processes; the sintering temperature in step (4) is 880℃ and the sintering time is 1h.
[0056] The grain morphology images of the multi-core superconducting tapes prepared in Comparative Example 1, Comparative Example 2, and Example 1 are shown below. Figure 2 As shown. Among them. Figure 2 Image (a) in the figure shows the grain morphology of the multi-core superconducting tape prepared in Comparative Example 1. Figure 2 (b) in the figure is a grain morphology diagram of the multi-core superconducting tape prepared in Comparative Example 2; Figure 2 Image (c) in the figure shows the grain morphology of the multi-core superconducting tape prepared in Example 1. Figure 2 It is evident that the grain size in Comparative Example 1 is relatively small, with few grains larger than 5 micrometers. In Comparative Example 2, the grain size begins to increase, but a large number of grains smaller than 5 micrometers still exist. The grains in Example 1 are significantly larger, generally larger than 5 micrometers.
[0057] The grain morphology and size distribution of the multi-core superconducting tapes prepared in Comparative Example 1 and Example 1 are shown in the figure. Figure 3 As shown. Among them. Figure 3 Images (a) and (c) in the diagram show the grain morphology and size distribution of the multi-core superconducting tape prepared in Comparative Example 1. Figure 3 Images (b) and (d) in the diagram are the grain morphology and size distribution of the multi-core superconducting tape prepared in Example 1. Figure 3 It can be clearly seen that, compared with Comparative Example 1, the grain size of the multi-core superconducting tape obtained in Example 1 is significantly increased, especially the proportion of grains with a size of 5 μm and above reaches 84%.
[0058] The critical current density of the multi-core superconducting tapes obtained in Example 1, Comparative Examples 1 to 3 was tested, and the results are shown in Table 1.
[0059] Table 1. Critical current density of strips with different sintering processes and its comparison with 7-core strips.
[0060]
[0061] As can be seen from Table 1, increasing the sintering temperature can increase the critical current density of multi-core superconducting tapes, and selecting a reasonable sintering time can further increase the critical current density of multi-core superconducting tapes.
[0062] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention. The above embodiments are provided only for the purpose of describing the present invention and are not intended to limit the present invention. Parts not described in detail in this specification are well-known in the art and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be covered within the scope of the present invention.
Claims
1. A method for increasing the critical current density of multi-core iron-based superconducting tapes, characterized in that, Includes the following steps: S1: Several cut single-core wires are loaded into a metal tube to form a multi-core composite tube. The multi-core composite tube is then drawn and rolled to obtain a multi-core strip. S2: The multi-core tape is heat-treated and cooled to obtain a multi-core iron-based superconducting tape; wherein the proportion of grains with a size of 5μm~15μm in the superconducting core of the multi-core iron-based superconducting tape controlled by heat treatment exceeds 80%.
2. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to claim 1, characterized in that, The sintering temperature of the heat treatment in step S2 is higher than 890℃.
3. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to claim 2, characterized in that, The sintering temperature for heat treatment in step S2 is 895℃±2℃.
4. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to claim 1, characterized in that, The sintering time in step S2 is calculated according to the following formula: ； Where T is the sintering time in hours, and n is the number of superconducting core layers, n≥3.
5. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to claim 1, characterized in that, The multi-core iron-based superconducting tape is a 122 series iron-based superconducting tape.
6. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to claim 1, characterized in that, The metal tube in step S1 is made of AgSn alloy.
7. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to any one of claims 1 to 6, characterized in that, The method also includes the following steps: S0: The precursor powder is filled into a metal tube, and then the tube is sealed to obtain a tube-mounted composite. The tube-mounted composite is drawn to obtain a single-core wire. The single-core wire is then cut to length, cleaned, and cut to obtain the cut single-core wire.
8. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to claim 7, characterized in that, The lengths of the cut single-core wires are equal.
9. The method for increasing the critical current density of multi-core iron-based superconducting tapes according to claim 1, characterized in that, The number of cores in the multi-core iron-based superconducting tape is greater than 7.
10. A multi-core iron-based superconducting tape, characterized in that, It is prepared by the method for increasing the critical current density of multi-core iron-based superconducting tape as described in any one of claims 1 to 9.