A method of superconducting tape fabrication and in situ stress release

Abstract

The application discloses a superconducting tape film preparation method, which comprises the following steps: when a superconducting tape is prepared by a pulse laser deposition (PLD) or a metal organic chemical vapor deposition (MOCVD) process, a plurality of "heat crystallization-quenching" process steps are performed, namely, the superconducting tape sequentially passes through a heat crystallization zone and a quenching zone multiple times, and each time, the superconducting tape is heated in the heat crystallization zone to complete directional crystallization, and then enters the quenching zone to be rapidly cooled. The plurality of "heat crystallization-quenching" process steps are realized by a plurality of "heat crystallization-quenching" functional units, and in the plurality of "heat crystallization-quenching" functional units, a plurality of heat crystallization zones and quenching zones are sequentially and crossly arranged to form a plurality of temperature control levels. The method solves the problem of thick film warping of the superconducting tape by stress release.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material preparation technology, and specifically relates to a method for preparing superconducting tapes and a method for in-situ stress release. Background Technology

[0002] In the industrial production of second-generation high-temperature superconducting tapes, pulsed laser deposition (PLD) technology is widely used to deposit REBCO (rare-earth barium copper oxide) superconducting layers on metal substrates. High-temperature crystallization is a crucial step in the preparation of superconducting thin films using PLD technology to promote the formation of a high-quality superconducting phase, ensuring the film possesses excellent superconducting properties, such as a high critical temperature (Tc) and a high critical current density (Jc). However, high-temperature processing brings two major challenges: excessive grain growth and internal stress accumulation. These problems restrict the performance and stability of superconducting thin films, thus affecting the practical applications of superconducting tapes. Stress accumulation can lead to tape warping, especially when preparing thick films on thin substrates, where this problem is more severe.

[0003] Under high-temperature conditions, superconducting layer grains are prone to overgrowth, resulting in coarse grain structures. Grain coarsening not only reduces the mechanical strength of the film but also leads to significant internal stress and lattice distortion. These stresses originate from several sources: First, the mismatch in thermal expansion coefficients between the film and the substrate generates significant thermal stress during high-temperature crystallization and subsequent cooling. Second, rapid grain growth along specific directions at high temperatures leads to uneven grain size distribution, further exacerbating internal stress accumulation. Furthermore, the coarse grain structure reduces the number of grain boundaries, making stress concentration at these boundaries more pronounced. These stresses accumulate further during film cooling, especially with thicker films, making crossbow warping more likely. Crossbow warping is particularly prominent in high-field applications of superconducting tapes; strong Lorentz forces can cause the tape to bend or even break, resulting in irreversible damage and severely limiting the practical application and promotion of superconducting tapes. Summary of the Invention

[0004] One embodiment of this disclosure provides a method for in-situ stress suppression of superconducting tapes under dynamic gradient quenching control, the method comprising:

[0005] The superconducting tape undergoes multiple "thermal crystallization-rapid cooling" processes during its fabrication using pulsed laser deposition, namely:

[0006] The superconducting tape passes through the thermal crystallization zone and the quenching zone in sequence multiple times. Each time, the superconducting tape completes directional crystallization by heating in the thermal crystallization zone, and then enters the quenching zone for rapid cooling.

[0007] One embodiment of this disclosure discloses a method for preparing superconducting tapes, employing a pulsed laser deposition system and a "thermal crystallization-rapid cooling" functional unit disposed within the pulsed laser deposition system.

[0008] After the superconducting tape is introduced into the pulsed laser deposition system, it undergoes multiple "thermal crystallization-quenching" process steps by the "thermal crystallization-quenching" functional unit, namely:

[0009] The superconducting tape passes through the thermal crystallization zone and the quenching zone in sequence multiple times. Each time, the superconducting tape completes directional crystallization by heating in the thermal crystallization zone, and then enters the quenching zone for rapid cooling.

[0010] This disclosure discloses a method and apparatus for in-situ stress suppression of superconducting tapes with dynamic gradient quenching control. It is applicable to grain refinement and mechanical property optimization in the high-temperature superconducting tape coating process in pulsed laser deposition (PLD) systems. By precisely controlling the timing of crystallization and quenching during the high-temperature crystallization process in the PLD system, a "heating-cooling-warming-cooling" cycle is formed to ensure that the superconducting film is cooled and quenched immediately after crystallization, inhibiting further grain growth, thereby obtaining a fine and uniform grain structure, releasing stress, solving the warping problem of superconducting tapes, and reducing film defects.

[0011] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example and not limitation, wherein:

[0012] Figure 1 A schematic diagram of the temperature change curve during the preparation of superconducting tape using a dynamic gradient quenching controlled in-situ stress suppression method according to one embodiment of the present invention.

[0013] Figure 2 A schematic diagram of X-ray diffraction (XRD) pattern and crystal orientation analysis of a superconducting tape according to one embodiment of the present invention.

[0014] Figure 3 A comparative schematic diagram of the warping of a physical superconducting tape according to one embodiment of the present invention.

[0015] Figure 4 A schematic diagram of current uniformity test performed using MCoder after a comparative long-band superconducting coating is completed according to one embodiment of the present invention.

[0016] Figure 5 A schematic diagram of the temperature change curve during the preparation of superconducting tape using a dynamic gradient quenching controlled in-situ stress suppression method according to one embodiment of the present invention.

[0017] Figure 6A schematic diagram of the temperature change curve during the preparation of superconducting tape using a dynamic gradient quenching controlled in-situ stress suppression method according to one embodiment of the present invention. Detailed Implementation

[0018] Pulsed laser deposition (PLD) is a physical vapor deposition (PVD) technique. It uses a high-energy pulsed laser beam to irradiate a target material, causing the material on the target surface to evaporate instantaneously, forming a plasma. Atoms, molecules, and ions in the plasma diffuse in a vacuum environment and deposit on the substrate surface to form a thin film. A pulsed laser deposition (PLD) system is used to prepare thin films and mainly consists of the following components:

[0019] Pulsed laser – this is the core component of the PLD system, used to generate high-energy laser beams;

[0020] The optical path system—including the aperture scanner, converging lens, laser window, etc.—is used to guide and focus the laser beam onto the target material;

[0021] The deposition system consists of a vacuum chamber, a vacuum pump, a gas filling system, a target material, a substrate heater, etc., and is used for thin film deposition in a vacuum environment.

[0022] Auxiliary equipment—including measurement and control devices, monitoring devices, motor cooling systems, etc.—is used to control and monitor the entire deposition process.

[0023] Similarly, MOCVD utilizes organometallic compounds (such as alkyl compounds of metals) and reactive gases (such as oxygen, hydrogen, etc.) to undergo a chemical reaction at high temperatures, generating metal oxides or other compounds that are deposited on the substrate surface.

[0024] To mitigate grain coarsening and internal stress issues during superconducting phase crystallization, existing methods typically employ post-processing techniques, such as annealing. Annealing, by heating the film to a certain temperature and holding it for a period, can partially release internal stress and refine the grains. However, post-processing of superconducting tapes has several limitations. Secondary heating after the superconducting tape deposition process leads to thickening of the interfacial oxide layer and interdiffusion of elements. Static stress compensation struggles to match the transient temperature field of PLD dynamic deposition, resulting in delayed stress release. Furthermore, the film surface is susceptible to oxidation or contamination during annealing, which can cause localized inhomogeneities in film performance, affecting overall performance.

[0025] Therefore, while existing processes can alleviate grain coarsening and internal stress problems to some extent, their effects are limited. They cannot achieve in-situ synergistic control of grain nucleation and stress evolution, and thus cannot fundamentally solve the problem, making it difficult to meet the requirements for the preparation of high-performance superconducting thin films. For example, in patent document JP2016076343A, the purpose of this document is to provide a method for manufacturing oxide superconducting wires that can maintain high superconductivity under a magnetic field environment. This method involves sequentially forming multiple intermediate layers on a metal substrate, including Gd2Zr2O7 layers, MgO layers, LaMnO3 layers, and CeO2 layers; coating the intermediate layers with a mixed solution containing RE (rare earth elements), Ba, and Cu, and adding at least one element such as Zr, Sn, Ce, Ti, Hf, and Nb to form flux pinning points. The method includes a heat treatment process: pre-sintering the coated substrate to form an amorphous superconducting precursor; before the final sintering, an intermediate heat treatment is performed, where the precursor is sintered at a temperature lower than the final sintering temperature, followed by rapid cooling to room temperature; after the intermediate heat treatment, the precursor is sintered to finally form a REBa2Cu3O7 superconducting layer. Rapid cooling after the intermediate heat treatment is a key feature of this method. Through intermediate heat treatment and rapid cooling, flux pinning points (such as BaZrO3) can be uniformly dispersed in the superconducting layer and maintain a fine size. This helps improve the stability of the superconducting wire in a magnetic field environment and prevents coarsening during subsequent sintering, thus ensuring the stability and high performance of the superconducting layer. However, the heat treatment scheme in this approach is a staged and displaced process for the system, and cannot solve the problems of thick film warpage and stress accumulation in superconducting tapes that need to be addressed in pulsed laser deposition (PLD) systems or metal-organic chemical vapor deposition (MOCVD) superconducting tape fabrication. This is because there are two reaction methods for preparing superconducting thin films: "in-situ" and "ex-situ." "In-situ" and "ex-situ" refer to the timing and environment of key steps in the thin film preparation process (especially annealing) relative to the coating step. In-situ processes are carried out continuously within the same vacuum chamber or interconnected vacuum systems, without disrupting the vacuum environment. Ex-situ processes are carried out stepwise in different equipment or environments. The PLD or MOCVD process systems described in this disclosure both belong to the in-situ reaction method.

[0026] Therefore, to address the aforementioned technical problems, this disclosure proposes a method for in-situ stress suppression of superconducting tapes through dynamic gradient quenching control. By establishing a closed-loop process chain of "laser deposition-transient crystallization-gradient quenching," a good match between crystallization phase transformation and in-situ stress release is achieved during the continuous movement of the tape. The core of this method lies in constructing a quenching field with a nonlinear temperature gradient. Immediately after the epitaxial crystallization of the tape deposition layer within the PLD cavity, sub-microsecond rapid quenching is performed, achieving synergistic control of superconducting grain size refinement and tape stress reduction. Compared to static post-processing, this method achieves stress-structure synergistic control during dynamic deposition, effectively solving grain coarsening and internal stress problems, significantly improving the mechanical properties and stability of superconducting tapes, and providing a reliable technical guarantee for their promotion in high-field applications.

[0027] According to one or more embodiments, a method for in-situ stress suppression of superconducting tapes with dynamic gradient quenching control includes the following steps:

[0028] S101: Pre-treatment of superconducting tape, including surface cleaning and buffer layer deposition, to obtain a clean substrate tape;

[0029] S102: Transfer the superconducting tape from step S101 into the pulsed laser deposition (PLD) system and set the deposition parameters;

[0030] S103: Set parameters for the multi-level "hot crystallization-rapid cooling" functional unit. The heating temperature range of each hot crystallization zone is 1000℃-1100℃, the target cooling temperature of the rapid cooling zone is ≤300℃, and the instantaneous temperature difference between the crystallization zone and the rapid cooling zone is >700℃. The combined term "hot crystallization-rapid cooling" here means connecting and combining the hot crystallization zone and the rapid cooling zone.

[0031] S104: After step S103 is completed, the strip transmission system is started. The strip passes through multiple "hot crystallization-rapid cooling" functional units in sequence. After each unit, the strip is first heated in the hot crystallization zone to complete directional crystallization, and then enters the rapid cooling zone for rapid cooling. The transmission speed is 10-30 mm / s, the length of each hot crystallization zone is 30-50 mm, and the length of each rapid cooling zone is 20-40 mm. The strip undergoes directional crystallization in the hot crystallization zone for 10 seconds, and then enters the rapid cooling zone for 8 seconds.

[0032] S105: After the multi-stage "hot crystallization-quenching" process in step S104 is completed, the strip is conveyed to the last stage quenching zone for cooling.

[0033] S106: After cooling, the tape is transferred to an inert gas protective environment to cool naturally to room temperature, completing a dynamic multi-stage "thermal crystallization-rapid cooling" stress control process to obtain a high-quality superconducting tape.

[0034] Here, the multi-level "thermal crystallization-rapid cooling" functional unit has a multi-level structure. By precisely controlling the heating and rapid cooling cycle, it forms a "heating-cooling-warming-cooling" cycle, ensuring that the superconducting thin film is immediately cooled and quenched after crystallization, thereby optimizing the material's microstructure and properties. Therefore, this functional unit includes at least the following subsystems:

[0035] Heating subsystem – responsible for heating the material to a specific crystallization temperature, including resistance heaters, induction heaters, or laser heaters;

[0036] Cooling subsystem – After the material reaches the crystallization temperature, it is rapidly cooled to a lower temperature, including gas cooling, liquid cooling or spray cooling, etc.

[0037] The drive subsystem moves the strip between the heating and cooling zones, ensuring that the material is heated and cooled evenly.

[0038] The multi-level "hot crystallization-rapid cooling" functional unit includes multiple heating and cooling subsystems. The heating and cooling subsystems are arranged in an alternating sequence. Through the transmission subsystem, the strip to be processed passes through a region with temperature gradient control due to the alternating hot and cold temperatures of the processing temperature, thus achieving the effect of multiple "hot crystallization-rapid cooling" processes.

[0039] In step S102, the pulsed laser deposition system cavity energy is 1J, the frequency is 300Hz, the oxygen flow rate is 20sccm-50sccm, and a spiral plume dotting method is used.

[0040] In step S103, the specific temperature can be freely adjusted according to the strip thickness and crystallization requirements; the heating time for each stage depends on the transmission speed and the transmission range of each heating zone. Under normal circumstances, the transmission speed remains constant.

[0041] In step S103, the cooling medium in the quench zone is a mixture of high-purity argon and liquid nitrogen (volume ratio of 8:2), and the cooling rate is controlled at 100℃ / s-200℃ / s to achieve rapid phase transformation and grain refinement.

[0042] In step S103, the cooling medium in the quench zone is uniformly sprayed onto the strip surface through a multi-hole nozzle to ensure cooling uniformity. The multi-hole nozzle adopts a flat fan-shaped design, with a width matching the strip width, a micro-hole diameter of 0.1-0.5 mm, and a hole spacing of 1-2 mm.

[0043] Furthermore, the flow rate of the cooling gas is adjusted in real time by a high-precision flow meter and a proportional valve, with a flow rate range of 10 to 50 L / min to adapt to different strip thicknesses and cooling rate requirements.

[0044] Furthermore, the spray angle of the cooling gas is adjustable, ranging from 30° to 60°, to ensure uniform coverage of the strip surface. The temperature of the cooling gas is adjusted in real time via a liquid nitrogen cooling system, with the cooling rate controlled between 100°C / s and 200°C / s.

[0045] In step S104, the length of the hot crystallization zone is 50-120 mm, and the length of the quenching zone is 10-30 mm. The ratio of the lengths of the hot crystallization zone to the quenching zone is controlled to be >2, and the physical dimensions of each unit are dynamically matched based on the dynamic gradient quenching level.

[0046] In step S106, the strip is conveyed to an inert gas protective environment and allowed to cool naturally to room temperature. After cooling, the strip is conveyed to an inert gas protective environment and allowed to cool naturally to room temperature. During the natural cooling process, the strip is protected by high-purity argon gas to prevent oxidation of the strip surface. The gas flow rate is 10-20 L / min and the gas pressure is 0.5-1.0 bar.

[0047] The beneficial effects of this disclosed embodiment compared to existing processes include:

[0048] This disclosure constructs a closed-loop process system of "laser deposition-transient crystallization-gradient quenching," achieving spatiotemporal matching of grain nucleation and growth with stress relaxation by precisely controlling the thermodynamic path during the continuous movement of the strip. The method employs in-situ synchronous quenching, cyclically heating and quenching within the critical crystallization temperature window of the superconducting phase to stabilize the grain size at the submicron level. Simultaneously, it utilizes a multi-stage quenching process to continuously release the stress gradient. The combined term "laser deposition-transient crystallization-gradient quenching" refers to the multi-stage "thermal crystallization-quenching" process on the strip within the pulsed laser deposition (PLD) system. This multi-stage gradient thermal crystallization, transient crystallization, and quenching process suppresses in-situ stress in the superconducting strip, achieving in-situ stress release.

[0049] Compared to the traditional high-temperature crystallization and static annealing process of PLD superconducting tapes, this invention integrates in-situ stress relaxation, completing the entire process control of grain nucleation-growth-stabilization during PLD deposition, effectively suppressing film warping caused by the crossbow effect, and significantly improving the mechanical stability and current carrying uniformity of superconducting tapes under high field strength Lorentz force environment.

[0050] To further illustrate the technical solution and beneficial effects of this disclosure, Embodiment 1 and Comparative Example 1 of this disclosure are given below.

[0051] Example 1

[0052] A method for in-situ stress suppression of superconducting tapes with dynamic gradient quenching control, specifically including the following steps:

[0053] S201: Pre-treat the superconducting tape, including surface cleaning and buffer layer deposition, to obtain a superconducting tape with a clean surface and a buffer layer;

[0054] S202: The superconducting tape obtained in step 1) is introduced into the pulsed laser deposition (PLD) system. The deposition parameters are set as follows: the cavity energy of the pulsed laser deposition system is 1J, the frequency is 300Hz, the oxygen flow rate is 20sccm-50sccm, and the spiral plume dotting method is adopted.

[0055] S203: Set the temperature and parameters of the multi-stage "hot crystallization-quenching" functional unit. The heating temperature of each stage of the hot crystallization zone is 1060℃, 1070℃ and 1080℃ respectively. The cooling rate of the quenching zone is controlled at 150℃ / s. The transmission speed is 20mm / s. The length of each stage of the hot crystallization zone is 80mm. The length of the quenching zone is 20mm. The strip crystallizes in the hot crystallization zone in a cycle of 4 seconds. Then it enters the quenching zone in a cycle of 1 second.

[0056] S204: Start the strip drive system so that the strip passes through multiple "hot crystallization-rapid cooling" functional units in sequence. After each unit, the strip is first heated in the hot crystallization zone to complete crystallization, and then enters the rapid cooling zone for rapid cooling. Each functional unit takes 5 seconds.

[0057] S205: After the multi-stage “hot crystallization-quenching” process in step S204 is completed, the strip is conveyed to the last-stage quenching zone for cooling, with a transit time of 5 seconds;

[0058] S206: After cooling, the tape is transferred to an inert gas protective environment to cool naturally to room temperature, completing a dynamic multi-stage "thermal crystallization-rapid cooling" stress control process to obtain high-quality superconducting tape.

[0059] Preferably, in step S202, the heating temperature of each thermal crystallization zone is independently controlled, and the heating temperature range of each zone is maintained between 1060℃ and 1080℃.

[0060] Preferably, in step S203, the cooling rate of each quench zone is controlled at 150°C / s.

[0061] Preferably, in step S204, the number of multi-level "thermal crystallization-rapid cooling" functional units is 3.

[0062] like Figure 1 , Figure 5 , Figure 6The figure shows the temperature variation curves during the multi-stage quenching cycle of superconducting tape prepared using a dynamic gradient quenching controlled in-situ stress suppression method. The red curve in the figure represents the temperature change of the superconducting tape at different time points. It can be seen that the superconducting tape experienced multiple rapid temperature rises and falls, corresponding to a "thermal crystallization-quenching" cycle. Each rapid temperature rise (the rising portion of the red curve) represents the thermal crystallization stage, where the superconducting tape is heated to a specific temperature to promote the formation and crystallization of the superconducting phase. The subsequent rapid temperature fall (the falling portion of the red curve) represents the quenching stage, where the superconducting tape is rapidly cooled to refine the grains and release stress. The different temperatures marked ΔT in the figure represent the maximum temperature difference experienced by the superconducting tape in different cycles. These temperature differences reflect the maximum thermal stress borne by the superconducting tape during thermal crystallization and quenching. The figure shows three distinct temperature rises and falls, indicating that the superconducting tape underwent three "thermal crystallization-quenching" cycles. Each cycle aims to further refine the grains, release stress, and optimize superconducting properties. After the final quench, the temperature curve shows a slow decrease, corresponding to the process described in step S206 of transferring the tape to an inert gas-protected environment for natural cooling to room temperature. The temperature change curves in the figure visually demonstrate the temperature changes of the superconducting tape during multiple quenching cycles in the in-situ stress suppression method for superconducting tapes controlled by dynamic gradient quenching. By precisely controlling the temperature, rate, and time of thermal crystallization and quenching, this method can effectively refine superconducting grains, release internal stress, and ultimately obtain high-quality superconducting tapes. This multi-stage quenching cycle process is of great significance for optimizing the microstructure and macroscopic properties of superconducting tapes.

[0063] The superconducting tape prepared in this embodiment was subjected to SEM analysis. The SEM images show that after multiple stages of "thermal crystallization-rapid quenching" treatment, the superconducting tape exhibits small and uniform grain size distribution, ranging from 2.8 ± 0.5 nm (Gaussian distribution, R0). 2 =0.98), and there were no obvious pores or cracks, indicating that the multi-stage "thermal crystallization-rapid cooling" process effectively refined the grains and improved the density of the film.

[0064] Scanning electron microscope (SEM) images of superconducting tapes after multi-stage "thermal crystallization-quenching" treatment. The images show numerous fine grains distributed uniformly on the surface of the superconducting tape. This indicates that the microstructure of the superconducting material was optimized after specific heat treatment. The grain size distribution ranges from 2.8 ± 0.5 nm, indicating good grain uniformity, which is extremely beneficial for the performance of superconducting materials, as uniform grain size helps to improve the critical current density and mechanical strength of the material. Gaussian distribution and R... 2=0.98 indicates that the grain size distribution is highly concentrated, close to the ideal state, which is one of the goals pursued in the preparation of superconducting materials. SEM images of the superconducting tape show the improvement in the microstructure of the superconducting tape after multi-stage "thermal crystallization-rapid cooling" treatment, including grain refinement, uniform distribution, and enhanced compactness. This demonstrates the good microstructure of the superconducting tape surface after this process, strongly supporting the conclusion of this disclosure that the multi-stage "thermal crystallization-rapid cooling" process effectively refines the grains and improves the compactness of the film.

[0065] In this embodiment, the bending radius of the superconducting tape treated by the dynamic multi-stage "thermal crystallization-quenching" process was tested. The results are shown in Table 1 below, which shows the warpage test results of different tapes prepared by dynamic quenching and conventional heating plate processes. Example 1 in Table 1 is this embodiment, and Comparative Example 1 is described below.

[0066] Table 1

[0067]

[0068] Bending loads with different radii of curvature were applied to the tape under a liquid nitrogen environment at 77°C, and its mechanical stability was evaluated by the critical current decay rate. The results show that the superconducting tape prepared in this embodiment maintains a low decay rate even at a smaller bending radius (R = 6 mm) (corresponding to strain ε ≈ 0.3%), with a critical current decay rate ≤ 10%. The bending radius test indicates that the fine grain structure of the superconducting tape prepared in this embodiment increases grain boundary density, suppresses crack propagation paths, reduces the risk of interface delamination caused by stress concentration during bending, and significantly improves bending resistance.

[0069] Figure 2 This is a schematic diagram comparing the X-ray diffraction (XRD) analysis of the superconducting tapes disclosed in this paper. The English and English terms in the diagram include:

[0070] EuBCO – Eubarium copper oxide, substrate – substrate, CeO2 – cerium dioxide, BaHfO3 – barium hafnium oxide, (hkl) – crystal plane index, logarithmic intensity – logarithmic intensity, θ-2θ – diffraction angle.

[0071] Figure 2X-ray diffraction (XRD) θ-2θ scan curves of two superconducting ribbon samples (S1 and S2) are shown. The peaks in the figure correspond to specific crystal plane reflections of different phases in the samples. Black dots mark characteristic peaks of EuBCO, asterisks mark characteristic peaks of the substrate, squares mark characteristic peaks of cerium dioxide (CeO2), and squares mark characteristic peaks of barium hafnium oxide (BaHfO3). Both samples show sharp and narrow EuBCO(00l) series peaks, indicating that the EuBCO grains are mainly c-axis oriented. Compared with S1, the peak intensity of S2 is significantly enhanced, which is consistent with the data in Table 2, indicating that the XRD peak intensity increases with the increase of superconducting layer thickness. Combining the data in Table 2, the c-axis lattice constants of the two EuBCO samples remain comparable, approximately [value missing]. Although S2 has a smaller FWHM (full width at half height), its microstrain value is 20% higher than that of S1, indicating that S2 has a larger grain size. This is because the grains tend to coarsen with increasing thickness. The superconducting tape sample S1 was processed using the process disclosed in this disclosure, demonstrating that the strain of the superconducting tape decreases after processing. The table data is as follows.

[0072] Table 2

[0073]

[0074] We investigated the phase composition and crystal structure of two superconducting layer samples with different thicknesses using XRD analysis. The XRD θ-2θ scan curves of both samples showed sharp and narrow EuBCO(00l) series peaks, as well as weaker peaks from the substrate, CeO2, and BaHfO3 phases, indicating that the EuBCO grains are mainly oriented along the c-axis. Compared to sample S1, the peak intensity of sample S2 was significantly enhanced, which can be attributed to the increased superconducting layer thickness.

[0075] Further comparison of the structural parameters obtained from the θ-2θ curves in Table 2 shows that the c-axis lattice constants of the two EuBCO samples are basically the same, approximately [value missing]. When using the Williamson-Hall method to calculate microstrain, although the FWHM (full width at half height) value of sample S2 is smaller, its microstrain value is 20% higher than that of sample S1.

[0076] Furthermore, this disclosure compares the superconducting tapes fabricated using the conventional method of Tc (superconducting transition temperature) and Ic (superconducting critical current) with those fabricated using the process of this disclosure. It can be found that this disclosure does not reduce the superconducting critical current or superconducting transition temperature when preparing superconducting films of the same thickness. See Table 3 below.

[0077] Table 3

[0078] process Ic / A Tc / ℃ △Tc / ℃ Thickness / μm This invention 722 92.5 2.2 2.2 Traditional crafts 720 92.4 2.3 2.2

[0079] Here, the superconducting transition temperature (Tc) is the temperature at which a material transitions from a normally conductive state to a superconducting state. The superconducting critical current (Ic) is the maximum current that a material can withstand in the superconducting state; exceeding this current will cause the material to lose its superconductivity.

[0080] Figure 3 This is a comparative diagram showing the warping of actual superconducting tapes. Figure 3 (a) shows the warping of the tape after the superconducting film is deposited. The left side is the superconducting tape processed by the process disclosed in this invention, and the right side is the superconducting tape processed by the existing process. It can be seen that the warping problem of the tape in this invention is significantly improved. Figure 3 (b) shows the warping of the strip after subsequent silver plating and post-treatment. The left side shows the superconducting strip processed by the process disclosed in this disclosure, and the right side shows the superconducting strip processed by the existing process. Specific evaluation data are shown in Table 4 below.

[0081] Table 4

[0082] Evaluation indicators Traditional methods New invention patent Improvement range <![CDATA[Mean curvature (mm -1 )]]> 1.8±0.2 0.5±0.1 72％↓ <![CDATA[Critical curvature (mm -1 )]]> 1 1 — Curvature / critical curvature ratio 1.8 0.5 72％↓ <![CDATA[Critical current I c Retention rate]]> 90％±5％ 98％±2％ 8％↑ Substrate thickness (μm) 50 50 — Superconducting film thickness (μm) 2.2 2.2 —

[0083] Comparative Example 1

[0084] Comparative Example 1 uses the traditional PLD heating plate method for superconducting coating process, including:

[0085] (1) The superconducting tape is pretreated, including surface cleaning and buffer layer deposition, to obtain a superconducting tape with a clean surface and a buffer layer.

[0086] (2) Pulsed laser deposition system parameter setting: The superconducting tape obtained in step 1) is introduced into the conventional pulsed laser deposition (PLD) system. The heating temperature is set to 1080℃, the heating time is 24 seconds, the cooling process is natural cooling, and the cooling rate is 10℃ / s.

[0087] (3) Heating and crystallization process: Start the strip transmission system, and the strip completes directional crystallization through a single heating zone of the heating plate. Then it is naturally cooled to room temperature and then post-processed.

[0088] (4) SEM analysis was performed on the superconducting tape prepared by the PLD traditional heating plate method. The SEM images show that the superconducting tape prepared by the traditional heating plate process has a large grain size and uneven distribution. The grain size is above 5nm and there are a small number of pores and cracks, indicating that the traditional process has a poor grain refinement effect and insufficient film density.

[0089] Mcorder was used to test the long-band current uniformity of the superconducting tape prepared by the conventional heating plate single heating mode in Comparative Example 1. The results are as follows: Figure 4As shown, the superconducting tape of Comparative Example 1 exhibited different results from that of Example 1 in the Mcorder test. The superconducting tape of Comparative Example 1 showed fluctuations in current distribution and distinct low points in the long-band current test. This inhomogeneity and low points indicate that the critical current density (Ic) in certain regions is significantly lower than the overall level, which is due to defects and stress concentration within the superconducting layer.

[0090] Comparing the results of Example 1 and Comparative Example 1, it can be seen that the dynamic multi-level "thermal crystallization-rapid cooling" stress control method provided in this disclosure is significantly superior to the traditional pulsed laser deposition process. Example 1 shows significant advantages in grain refinement, crystallization quality, internal stress release, and warpage control, providing a higher-quality technical means for the preparation of high-performance superconducting tapes.

[0091] In summary, this disclosure significantly improves the grain structure and stress distribution of superconducting tapes through a dynamic gradient quenching-controlled in-situ stress release method, particularly addressing the thick-film warpage problem. It enables the fabrication of high-performance superconducting tapes with REBCO film thicknesses exceeding 1 micrometer and substrate thicknesses below 100 micrometers. This disclosure achieves rapid cooling of the material during deposition by constructing a quenching field with a nonlinear temperature gradient. This rapid cooling occurs immediately after epitaxial crystallization, typically on the sub-microsecond scale, ensuring effective control of the grain structure and internal stress state. By establishing a closed-loop process chain of "laser deposition-transient crystallization-gradient quenching," a good match between crystallization phase transformation and in-situ stress release is ensured during the continuous movement of the tape. This effectively solves the problems of grain coarsening and internal stress. This method not only controls grain size but also reduces residual stress within the material, thereby improving the overall performance of the material.

[0092] This disclosure significantly improves the mechanical properties of superconducting tapes through in-situ stress relief. Reducing internal stress prevents cracking or fracture during use, thereby improving durability and reliability.

[0093] It is worth noting that although the spirit and principles of this invention have been described with reference to several specific embodiments, it should be understood that this invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that the features in these aspects cannot be combined; such division is merely for the convenience of description. This invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for preparing superconducting tape thin films, characterized in that, The method includes: When the superconducting tape is prepared into a thin film using pulsed laser deposition (PLD) or metal-organic chemical vapor deposition (MOCVD) processes, it undergoes multiple "thermal crystallization-rapid cooling" steps, namely: The superconducting tape passes through a thermal crystallization zone and a quenching zone multiple times in sequence. Each time, the superconducting tape undergoes directional crystallization by heating in the thermal crystallization zone, and then enters the quenching zone for rapid cooling. The multiple "hot crystallization-quenching" process steps are implemented by a multi-level "hot crystallization-quenching" functional unit. In this multi-level "hot crystallization-quenching" functional unit, multiple hot crystallization zones and quenching zones are arranged in a sequential and cross-arranged manner to form multiple levels of temperature control.

2. The method according to claim 1, characterized in that, The heating temperature range of each stage of the hot crystallization zone is 1000℃~1100℃, the target cooling temperature of each stage of the quenching zone is ≤300°C, and the instantaneous temperature difference between the crystallization zone and the quenching zone is >700°C.

3. The method according to claim 1, characterized in that, After completing the "thermal crystallization-rapid cooling" process, the superconducting tape is transferred to a low-oxygen environment and allowed to cool naturally to room temperature.

4. The method according to claim 3, characterized in that, After completing the "thermal crystallization-quenching" process steps, the superconducting tape is transferred to the final quenching zone for cooling, and then transferred to an inert gas protective environment to cool naturally to room temperature.

5. The method according to claim 1, characterized in that, The superconducting tape needs to be pretreated before it can be fabricated using pulsed laser deposition.

6. The method according to claim 5, characterized in that, The pretreatment includes cleaning the surface of the superconducting tape and depositing a buffer layer to obtain a clean substrate tape.

7. The method according to claim 6, characterized in that, This includes depositing a REBCO superconducting layer on the substrate strip.

8. A method for in-situ stress relief in laser deposition of superconducting tapes, characterized in that, In the pulsed laser deposition system, multiple "thermal crystallization-rapid cooling" functional units are set up. After the superconducting tape is introduced into the pulsed laser deposition system, it undergoes multiple "thermal crystallization-quenching" process steps by the multi-stage "thermal crystallization-quenching" functional unit, namely: The superconducting tape passes through a thermal crystallization zone and a quenching zone multiple times in sequence. Each time, the superconducting tape undergoes directional crystallization by heating in the thermal crystallization zone, and then enters the quenching zone for rapid cooling. The multi-level "thermal crystallization-rapid cooling" functional unit includes multiple thermal crystallization zones and rapid cooling zones arranged in a staggered manner to form multiple levels of temperature control zones.

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