Method for manufacturing a low temperature joint for a corc superconducting cable based on gradient diffusion welding

Abstract

This invention provides a method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding, comprising: forming a composite layer on at least a portion of the surface of a first superconducting tape and at least a portion of the surface of a second superconducting tape; the composite layer comprising a first silver layer, a copper layer, and a second silver layer stacked sequentially, the thickness of the composite layer being 400nm-500nm, wherein the thickness of the copper layer is 10%-12% of the thickness of the composite layer; stacking at least portions of the first and second superconducting tapes together and performing cryogenic gradient diffusion welding, so that the first and second composite layers at the stacked portions are connected to form a connecting layer; after welding, an insulating layer is formed on the outer peripheral surface to obtain a superconducting joint, thus obtaining a superconducting cable joint. This invention uses an Ag / Cu / Ag nanolayered composite layer combined with a cryogenic gradient diffusion welding process to ensure that the prepared superconducting cable joint has both low contact resistance and long service life.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature superconductivity, and particularly relates to a CORC superconducting cable low-temperature joint manufacturing method based on gradient diffusion welding. BACKGROUND

[0002] Second-generation high-temperature superconducting rare earth barium copper oxide (REBCO, Rare Earth Barium Copper Oxide) tapes have excellent critical current density, high upper critical field, high critical transition temperature and other advantages. The existing REBCO tape-based cabling methods mainly include stacking, braiding or spiral winding. The superconducting cable in the spiral winding method is commonly referred to as a CORC (Conductor on Round Core) cable, which is made by spirally winding a high-temperature superconducting layer conductor on a metal core and wrapping it with insulating material on the outside. The CORC cable has good flexibility, compact structure, high current-carrying capacity and other advantages.

[0003] At present, the CORC superconducting cable joints based on REBCO tapes are mainly prepared by high-temperature brazing, mechanical pressure bonding and superconducting solder connection. However, the high-temperature brazing process mainly uses Cu-containing solder (such as Sn-Ag-Cu solder), which can easily cause lattice oxygen to escape from the REBCO tape and Cu elements to diffuse during high-temperature welding, resulting in a critical current density (Jc) decay rate as high as 30%-50%, thereby affecting the contact resistance characteristics of the joint. Although the mechanical pressure bonding process can achieve low-temperature processing and avoid thermal damage, it is limited by the micro-roughness of the contact surface (Ra>1μm) and the stress relaxation effect. The contact resistance increases nonlinearly with pressure, and the contact resistance is still 8-12nΩ·m² under a typical pressure of 80MPa. Moreover, the resistance fluctuation exceeds ±20% after thermal cycling (100 times). The use of superconducting solder can be combined with low-temperature welding process, which can reduce the heat-affected zone and reduce the contact resistance. However, the lattice mismatch between the solder and the REBCO is large (>5%), which can cause micro-cracks at the interface and brittle fracture at 77K low temperature, thereby affecting the service life of the superconducting joint.

[0004] To solve the above problems, the existing technology also uses a multi-layer metal transition layer or a flexible conductive adhesive to assist the connection, and a low-temperature process (<200℃) is used in the connection process to avoid thermal damage. However, it still cannot meet the requirements of low contact resistance (<3nΩ·m²) and high service life (>100 thermal cycles). SUMMARY

[0005] The purpose of the present application is to solve the problem that the superconducting joint based on REBCO tapes prepared by the existing preparation process cannot simultaneously meet the requirements of low contact resistance and high service life.

[0006] To solve the above technical problems, the embodiment of the present application discloses a CORC superconducting cable low-temperature joint manufacturing method based on gradient diffusion welding, comprising: S1: separating a first superconducting tape from one end of a first superconducting cable and a second superconducting tape from one end of a second superconducting cable; S2: forming a first composite layer on at least part of the surface of the first superconducting tape and a second composite layer on at least part of the surface of the second superconducting tape; each of the first composite layer and the second composite layer comprises a first silver layer, a copper layer and a second silver layer arranged in sequence, and the thickness of the composite layer is 400-500 nm, wherein the thickness of the copper layer is 10-12% of the thickness of the composite layer; S3: superimposing at least part of the first superconducting tape and the second superconducting tape on each other to obtain a superconducting joint precursor, wherein the superimposed part has the first composite layer and the second composite layer; S4: gradient diffusion welding of the superconducting joint precursor in a vacuum environment, connecting the first composite layer and the second composite layer of the superimposed part and forming a connecting layer, wherein the welding temperature is 150-180℃, the pressure is 15-100 MPa, and the holding time is 2-4 h; a first pressure is applied for a first time, a second pressure is applied for a second time, and a third pressure is applied for a third time; wherein the first pressure is less than the second pressure, the second pressure is less than the third pressure, and the pressure loading rate during the pressure increasing process is 0.3-0.5 MPa / min; S5: forming an insulating layer on the outer peripheral surface of the superconducting joint precursor after welding to obtain a superconducting joint, so as to obtain a superconducting cable joint.

[0007] By adopting the above scheme, the Ag / Cu / Ag nano-laminated structure composite layer is arranged on the outer surface of the superconducting tapes to be connected, and the low-temperature gradient diffusion welding process is used to connect the first superconducting tape and the second superconducting tape together through the connecting layer, so as to avoid the increase of the contact resistance of the superconducting joint caused by high temperature, to ensure the maintenance of low contact resistance, to promote the formation of continuous solid solution of silver-copper interface through gradient pressure, to realize atomic-level metallurgical bonding; and to promote rapid and uniform diffusion and densification at low temperature by using a large interface area, to realize high-quality low-temperature connection, to improve the mechanical strength of the connection part, to ensure that the superconducting joint has good mechanical properties, and to improve the service life.

[0008] According to another specific embodiment of the present application, the manufacturing method of the CORC superconducting cable low-temperature joint based on gradient diffusion welding disclosed by the embodiments of the present application, in step S2, the forming process of each of the first composite layer and the second composite layer comprises: sequentially depositing a first silver layer, a copper layer and a second silver layer on at least part of the surface of the corresponding superconducting tape by using magnetron sputtering; wherein the deposition process parameters of the first silver layer include: power 140W-180W, argon flow rate 35sccm-45sccm, substrate temperature 75℃-85℃, deposition rate 0.4Å / s-0.6Å / s, and thickness 180nm-220nm; the deposition process parameters of the copper layer include: power 80W-120W, argon flow rate 30sccm-40sccm, substrate temperature 40℃-60℃, deposition rate 0.1Å / s-0.3Å / s, and thickness 40nm-60nm; and the deposition process parameters of the second silver layer include: power 140W-180W, argon flow rate 35sccm-45sccm, substrate temperature 75℃-85℃, deposition rate 0.4Å / s-0.6Å / s, and thickness 180nm-220nm.

[0009] By using the above technical solution, the composite layer formed has strong bonding force with the superconducting tape, high purity of the composite layer, and the composite layer is dense and uniform.

[0010] According to another specific embodiment of the present application, the manufacturing method of the CORC superconducting cable low-temperature joint based on gradient diffusion welding disclosed by the embodiments of the present application, in step S2, the first composite layer is formed on both sides of the first superconducting tape along the thickness direction thereof, and the second composite layer is formed on both sides of the second superconducting tape along the thickness direction thereof; and in each of the first composite layer and the second composite layer, the thickness ratio of the first silver layer to the copper layer and the thickness ratio of the second silver layer to the copper layer are both within the range of 3.5:1-4:1.

[0011] According to another specific embodiment of the present application, the manufacturing method of the CORC superconducting cable low-temperature joint based on gradient diffusion welding disclosed by the embodiments of the present application, in step S3, the first superconducting tape and the second superconducting tape are spirally wound around the outer periphery of the metal core in a staggered manner, so that the first superconducting tape and the second superconducting tape are at least partially superimposed on each other; wherein the degree of the spiral angle is 30°-35°.

[0012] By using the above technical solution, the shear stress at the interface of the superconducting joint is reduced through the synergistic effect of the mechanical interlocking effect and the stress dispersion mechanism, and the risk of interface delamination caused by thermal cycling is eliminated.

[0013] According to another specific embodiment of the present application, the method for manufacturing a CORC superconducting cable cryogenic joint disclosed by the embodiments of the present application is based on gradient diffusion welding, and step S1 further comprises: separating a first metal core from one end of the first superconducting cable and separating a second metal core from one end of the second superconducting cable; and step S3 further comprises: arranging the first metal core and the second metal core side by side to form the metal core.

[0014] The above technical solution forms the metal core of the superconducting joint at the end of the metal core of the first superconducting cable and the metal core of the second superconducting cable, and further embeds the superconducting tape helical tooth of each superconducting cable in the metal core of the other superconducting cable to form a three-dimensional anchoring mechanical interlocking structure, thereby preventing the interface crack from propagating along the plane.

[0015] According to another specific embodiment of the present application, the method for manufacturing a CORC superconducting cable cryogenic joint disclosed by the embodiments of the present application is based on gradient diffusion welding, and the first metal core and the second metal core are both copper pipes. According to another specific embodiment of the present application, the method for manufacturing a CORC superconducting cable cryogenic joint disclosed by the embodiments of the present application is based on gradient diffusion welding, and the first time is 25 min-35 min, the first pressure is 15 MPa-25 MPa, the second time is 80 min-100 min, the second pressure is 40 MPa-60 MPa, the third time is 50 min-70 min, and the third pressure is 70 MPa-90 MPa.

[0016] The above technical solution increases the physical contact area at the first pressure, makes the copper layer yield at the second pressure, and makes the silver-copper interdiffuse at the third pressure to form a continuous gradient solid solution.

[0017] According to another specific embodiment of the present application, the method for manufacturing a CORC superconducting cable cryogenic joint disclosed by the embodiments of the present application is based on gradient diffusion welding, and step S4 further comprises: before the gradient diffusion welding, applying radio frequency to the superconducting joint precursor to form a plasma, wherein the temperature is 110℃-130℃, the power is 250 W-350 W, and the time is 25 min-35 min; and after the gradient diffusion welding, cooling to 70℃-90℃ and reducing the pressure to 8 MPa-12 MPa.

[0018] The above technical solution uses the plasma method to perform atomic-level cleaning on the connection interface to reduce the surface oxygen content to 5at%-10at%, and reduces the interface residual stress through cooling and pressure reduction after the gradient diffusion welding.

[0019] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding. Step S5 includes: mixing 60wt%-65wt% of a polyimide precursor, 20wt%-25wt% of hexagonal boron nitride, 5wt%-10wt% of γ-alumina, and 3wt%-5wt% of γ-aminopropyltriethoxysilane by mass percentage, and then mixing them in a ball mill at a speed of 180rpm-220rpm for 22h-26h to form an insulating slurry; covering the surface of the welded superconducting joint precursor with the insulating slurry and applying a pressure of 0.7MPa-0.9M... Hold the pressure at 15-30 min under 1 Pa of pressure; heat to 75℃-85℃ and pre-cur under 0.08MPa-0.15MPa of pressure for 50-70 min; reheat to 110℃-130℃ and cross-link under 0.2MPa-0.4MPa of pressure for 25-35 min; reheat to 140℃-160℃ and cure under 0.4MPa-0.6MPa of pressure for 1.5-2.5 h; forming an insulating layer with a wall thickness of 0.4mm-0.6mm; wherein the viscosity of the polyimide precursor is 3400cP-3600cP, the particle size of hexagonal boron nitride is 1μm-3μm, and the specific surface area of ​​γ-alumina is 160m² / g-200m² / g.

[0020] The above technical solution employs a polyimide / boron nitride nanocomposite insulation system that combines high thermal conductivity with high insulation properties, and its coefficient of thermal expansion matches that of the superconducting joint, thus avoiding cracking of the interface superconducting joint and improving the service life of the superconducting joint.

[0021] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding. Step S1 further includes: cleaning the separated first superconducting tape and second superconducting tape; and respectively treating the surfaces of the first superconducting tape and the second superconducting tape with ion beam etching, wherein the etching process parameters include an energy of 400eV-600eV and a beam current density of 0.4mA / cm²-0.6mA / cm².

[0022] By adopting the above technical solution, the oxide layer on the surface of the superconducting tape to be joined can be removed, which can improve the welding quality. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a superconducting cable joint manufactured using one embodiment of the CORC superconducting cable cryogenic joint manufacturing method based on gradient diffusion welding provided by the present invention.

[0024] Figure 2This is a schematic diagram of the structure of a superconducting cable joint manufactured using another embodiment of the CORC superconducting cable cryogenic joint manufacturing method based on gradient diffusion welding provided by the present invention.

[0025] Figure 3 This is a partial cross-sectional structural diagram of a superconducting cable joint manufactured using the CORC superconducting cable cryogenic joint manufacturing method based on gradient diffusion welding provided by the present invention.

[0026] Figure 4 This is a flowchart of the CORC superconducting cable cryogenic joint manufacturing method based on gradient diffusion welding provided by the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. First superconducting cable; 2. Second superconducting cable; 3. Superconducting connector; 31. First superconducting tape; 32. Second superconducting tape; 33. First composite layer; 34. Second composite layer; 35. First metal core; 36. Second metal core. Detailed Implementation

[0029] To better understand the superconducting cable connector and its preparation method provided in this application, a detailed description is provided below with reference to the accompanying drawings.

[0030] To more easily understand the CORC superconducting cable cryogenic joint manufacturing method based on gradient diffusion welding provided by this invention, please refer to the appendix first. Figures 1-3 The structure of the superconducting cable joint manufactured using the CORC superconducting cable cryogenic joint manufacturing method based on gradient diffusion welding provided by this invention will be described, such as... Figure 1 and Figure 2 As shown, the superconducting cable connector includes a first superconducting cable 1 and a second superconducting cable 2. One end of the first superconducting cable 1 is fixedly connected to one end of the second superconducting cable 2, forming a superconducting connector 3, thereby connecting the first superconducting cable 1 and the second superconducting cable 2 together to extend the superconducting cable. Specifically, the first superconducting cable 1 and the second superconducting cable 2 of the present invention have the same structure and are CORC superconducting cables formed by a helical winding method based on REBCO tape. Each superconducting cable includes a superconducting tape, an outer protective layer, a metal core, etc.

[0031] like Figures 1-3 As shown, the superconducting connector 3 includes a first superconducting tape 31, a second superconducting tape 32, and an insulating layer (not shown in the figure). The first superconducting tape 31 and the second superconducting tape 32 are at least partially superimposed on each other and fixedly connected by a connecting layer, and the superimposed first superconducting tape 31 and the second superconducting tape 32 are wrapped within the insulating layer. The insulating layer is a material layer used to isolate the superconducting connector 3 from the outside world to prevent external factors such as temperature, pressure, and humidity from affecting the superconductor; specifically, it can be a polyimide coating, etc.

[0032] like Figures 1-2 As shown, the first superconducting tape 31 is the superconducting tape of the first superconducting cable 1; the second superconducting tape 32 is the superconducting tape of the second superconducting cable 2. Specifically, the first superconducting tape 31 and the second superconducting tape 32 are obtained by processing the portions of the first superconducting cable 1 and the second superconducting cable 2 used to form the superconducting joint, respectively. Both the first superconducting tape 31 and the second superconducting tape 32 are REBCO tapes, specifically including a metal base tape, a buffer layer, a superconducting layer, and a stabilizing layer. The metal base tape accounts for about half of the total tape thickness and mainly plays a supporting role, generally being Ni or Ni alloy, etc.; the buffer layer is located between the metal base tape and the superconducting layer, preventing atomic interdiffusion between the atoms of the metal base tape and the superconducting layer, and contains oxides of different types and thicknesses; the superconducting layer is the core of the entire tape, with a thickness of about 1-2 micrometers, which exerts the characteristics of high-temperature superconducting materials; the protective layer independently includes a silver layer and / or a copper layer.

[0033] like Figure 3 As shown, at least a portion of the surface of the first superconducting tape 31 is covered with a first composite layer 33, and at least a portion of the surface of the second superconducting tape 32 is covered with a second composite layer 34. The first composite layer 33 on the surface of the first superconducting tape 31 and the second composite layer 34 on the surface of the second superconducting tape 32 are butted together and gradient diffusion welding is performed to form a connecting layer. The low-temperature welding process (temperature is 150℃-180℃) is further adopted. The first composite layer 33 and the second composite layer 34 have the same structure. Each composite layer includes a first silver layer, a copper layer, and a second silver layer stacked sequentially to form a silver (Ag) / copper (Cu) / silver (Ag) nanolayer structure, which is used to connect the first superconducting tape 31 and the second superconducting tape 32 together by a welding process. Further, the thickness of the composite layer is 400nm-500nm, preferably 450nm, wherein the thickness of the copper layer is 10%-12% of the thickness of the composite layer, preferably 11%. Even further, the thickness ratio of the first silver layer to the copper layer and the thickness ratio of the second silver layer to the copper layer are both in the range of 3.5:1-4:1.

[0034] In one specific embodiment of the present invention, such as Figure 1 and Figure 2 As shown, the first composite layer 33 is disposed on both sides of the first superconducting tape 31, and the second composite layer 34 is disposed on both sides of the second superconducting tape 32. The superconducting connector 3 also includes a metal core to provide support for the superconducting tape, such as... Figures 1-3 As shown, the first superconducting tape 31 and the second superconducting tape 32 are interlaced and spirally wound around the metal core. Figures 1-3 The outer periphery of the first metal core 35 and the second metal core 36 (shown in the image) forms a double-helix interlocking structure, such that the first superconducting tape 31 and the second superconducting tape 32 at least partially overlap each other; wherein the helix angle ( Figure 1The degree measure of θ in the equation is 30°-35°.

[0035] In one specific implementation, such as Figures 1-3 As shown, the metal core includes a first metal core 35 and a second metal core 36 arranged side by side; wherein, the first metal core 35 is the metal core of the first superconducting cable 1, and the second metal core 36 is the metal core of the second superconducting cable 2; thus, the end portions of the metal cores of the first superconducting cable 1 and the second superconducting cable 2 are used to form a superconducting connector 3, more specifically, it can be as follows: Figure 1 As shown, the first superconducting cable 1 and the second superconducting cable 2 are connected in the same direction at their ends, so that the first metal core 35 and the second metal core 36 extend in parallel in the same direction; it can also be as follows: Figure 2 The first superconducting cable 1 and the second superconducting cable 2 are connected at opposite ends, such that the first metal core 35 and the second metal core 36 extend parallel to each other.

[0036] The present invention provides a method for manufacturing cryogenic joints for CORC superconducting cables based on gradient diffusion welding, such as... Figure 4 As shown, it includes the following steps S1-S5.

[0037] S1: Separate the first superconducting tape from one end of the first superconducting cable and the second superconducting tape from one end of the second superconducting cable; the lengths of the separated first and second superconducting tapes are determined according to the cable forming method, etc. For example, the lengths of the first and second superconducting tapes for spiral winding are generally greater than or equal to 200mm.

[0038] Specifically, the outer protective layers of the first and second superconducting cables in the joint area are removed, exposing the first and second superconducting tapes. After separation, the metal cores corresponding to the first and second superconducting tapes are obtained respectively, that is, the first metal core is separated from one end of the first superconducting cable and the second metal core is separated from one end of the second superconducting cable.

[0039] Furthermore, the separated first and second superconducting tapes are pretreated. Organic solvents can be used to clean the joint area of ​​the first and second superconducting tapes to remove organic contaminants from the joint area; more specifically, an acetone / ethanol mixture (3:1) can be used to clean the joint area of ​​the superconducting tapes for 10 minutes with ultrasonic assistance.

[0040] In one specific embodiment, the separated first superconducting tape and the superconducting tape are cleaned; the surfaces of the first and second superconducting tapes are respectively treated by ion beam etching, and the etching process parameters include an energy of 400eV-600eV and a beam current density of 0.4mA / cm²-0.6mA / cm².

[0041] Specifically, the surface of the superconducting tape joint area can be treated with Ar ion beam etching. The specific process parameters are: energy 500 eV, beam current density 0.5 mA / cm², and time 90 seconds. Ion beam etching can remove the oxide layer to improve welding quality; after treatment, the material should be immediately transferred to a vacuum environment (≤...). Pa) to prevent re-oxidation.

[0042] S2: A first composite layer is formed on at least a portion of the surface of the first superconducting tape, and a second composite layer is formed on at least a portion of the surface of the second superconducting tape. Each of the first and second composite layers includes a first silver layer, a copper layer, and a second silver layer stacked sequentially. The thickness of the composite layer is 400 nm-500 nm, wherein the thickness of the copper layer is 10%-12% of the thickness of the composite layer.

[0043] Specifically, the positions of the first and second composite layers are determined based on the stacking method of the first and second superconducting tapes in the superconducting connector, ensuring that at least the overlapping portions have both the first and second composite layers. The first composite layer can be formed on both surfaces of the first superconducting tape along its thickness direction, and the second composite layer can be formed on both surfaces of the second superconducting tape along its thickness direction.

[0044] Furthermore, the methods for forming the first and second composite layers can include spraying, electroplating, chemical solution methods, or physical vapor deposition. In one specific embodiment, magnetron sputtering, a method within physical vapor deposition, is used. Specifically, a dual-target magnetron sputtering system is used to sequentially deposit a first silver layer, a copper layer, and a second silver layer on at least a portion of the surface of the corresponding superconducting tape (first or second superconducting tape). The Ag target in the dual-target magnetron sputtering system has a purity of 99.99%, and the Cu target has a purity of 99.995%. During the preparation process, the deposition parameters for the first silver layer include: power 140W-180W, preferably 150W; argon flow rate 35sccm-45sccm, preferably 40sccm; substrate temperature 75℃-85℃, preferably 80℃; deposition rate 0.4Å / s-0.6Å / s, preferably 0.5Å / s; and thickness 180nm-220nm, preferably 190nm-210nm. The deposition process parameters for the copper layer include: power 80W-120W, preferably 100W; argon flow rate 30sccm-40sccm, preferably 35sccm; substrate temperature 40℃-60℃, preferably 50℃; deposition rate 0.1Å / s-0.3Å / s, preferably 0.2Å / s; and thickness 40nm-60nm, preferably 45nm-55nm. The deposition process parameters for the second silver layer include: power 140W-180W, preferably 150W; argon flow rate 35sccm-45sccm, preferably 40sccm; substrate temperature 75℃-85℃, preferably 80℃; deposition rate 0.4Å / s-0.6Å / s, preferably 0.5Å / s; and thickness 180nm-220nm, preferably 190nm-210nm. During the fabrication process, a quartz crystal film thickness gauge was used to monitor the thickness of the formed copper or silver layer in real time to ensure that the thickness was within a predetermined range; and the vacuum residence time between layers was controlled to be ≤5 seconds to avoid interface contamination. The composite layer formed by magnetron sputtering has strong adhesion to the superconducting tape, high purity of components, and is dense and uniform.

[0045] Furthermore, in one specific embodiment, a first composite layer is formed on both sides of the first superconducting tape along its thickness direction, and a second composite layer is formed on both sides of the second superconducting tape along its thickness direction; and in each of the first and second composite layers, the thickness ratio of the first silver layer to the copper layer and the thickness ratio of the second silver layer to the copper layer are both in the range of 3.5:1 to 4:1.

[0046] S3: At least a portion of the first superconducting tape and the second superconducting tape are superimposed on each other to obtain a superconducting junction precursor, wherein the superimposed portions have a first composite layer and a second composite layer. Specifically, the first superconducting tape and the second superconducting tape are superimposed on each other by a helical winding method.

[0047] In one specific embodiment, a first superconducting tape and a second superconducting tape are spirally wound around the outer periphery of a metal core in an alternating manner, such that the first superconducting tape and the second superconducting tape are at least partially superimposed on each other, and the spiral angle is controlled to be 30°-35°, preferably 32°±0.5°. Further, multiple layers can be wound, for example, 1-20 layers can be wound. After winding, the superconducting tape is fixed.

[0048] Specifically, the metal core can be a metal core specifically designed for the superconducting connector. It can be a single metal core or composed of two metal cores arranged side-by-side. For a single metal core, its end is fixedly connected to the ends of the metal cores of the first and second superconducting cables by welding. For a metal core composed of two separate metal cores, each separate core is fixedly connected to one of the metal cores of the first and second superconducting cables at its end by welding. In one specific embodiment, a first metal core separated from one end of the first superconducting cable and a second metal core separated from one end of the second superconducting cable are arranged side-by-side to form the metal core. The first and second metal cores can extend parallel to each other in the same direction or parallel to each other in opposite directions. Further, in one specific embodiment, both the first and second metal cores are copper tubes, specifically oxygen-free copper tubes with an RRR value greater than 50.

[0049] To eliminate the risk of interfacial delamination caused by thermal cycling and improve the service life of superconducting joints, this invention designs the aforementioned double-helix interlocking structure. Through the synergistic effect of mechanical interlocking and stress dispersion mechanisms, the shear stress at the superconducting joint interface is reduced. Furthermore, the helix angle during the helical winding process is determined based on finite element optimization. Figure 1 A helix angle (θ) of 30°-35° is effective, with a preferred helix angle of 32°±0.5°. Particularly effective is the arrangement where the first metal core is the core of the first superconducting cable and the second metal core is the core of the second superconducting cable. The first and second superconducting tapes are staggered and spirally wound around the parallel-arranged first and second metal cores, allowing the helical teeth of each superconducting cable's tape to embed into the metal core of the other superconducting cable, forming a three-dimensional anchoring mechanical interlocking structure. This prevents interface cracks from propagating along the plane. Furthermore, it decomposes shear stress into normal pressure and tangential force, significantly reducing peak stress. Additionally, it increases the contact area between the first and second superconducting tapes, and the spiral wound ring spring provides a ±0.15mm displacement margin, absorbing thermal mismatch strain. The spiral structure induces localization of plastic strain, reducing the stress concentration factor of the REBCO brittle layer.

[0050] S4: Under vacuum conditions, gradient diffusion welding is performed on the superconducting connector precursor using a low-temperature welding process, namely gradient hot pressing, to connect the first and second composite layers at overlapping locations and form a bonding layer. The welding temperature is 150℃-180℃, the pressure is 15MPa-100MPa, and the holding time is 2h-4h. The pressure is increased to a first pressure and applied for a first time period, then increased to a second pressure and applied for a second time period, and finally increased to a third pressure and applied for a third time period. Furthermore, the first pressure is lower than the second pressure, the second pressure is lower than the third pressure, and the pressure loading rate during the pressurization process is 0.3MPa / min-0.5MPa / min. Gradient pressurization promotes the formation of a continuous solid solution at the silver-copper interface, achieving atomic-level metallurgical bonding.

[0051] Furthermore, in one specific embodiment, the first time is 25min-35min, the first pressure is 15MPa-25MPa, the second time is 80min-100min, the second pressure is 40MPa-60MPa, the third time is 50min-70min, and the third pressure is 70MPa-90MPa.

[0052] This invention features an Ag / Cu / Ag nano-layer composite layer on the surface of the superconducting tapes to be joined, which, combined with a low-temperature welding process, connects the first and second superconducting tapes together through the connecting layer. This avoids the increase in contact resistance of the superconducting joint caused by high temperatures, thus ensuring low contact resistance and good mechanical properties of the superconducting joint, thereby improving its service life.

[0053] Furthermore, in one specific embodiment, in step S3 above, the first superconducting tape and the second superconducting tape are spirally wrapped around the outer periphery of the metal core in an alternating manner to obtain the superconducting connector precursor; step S4 specifically includes the following steps S41-S43.

[0054] S41: Surface activation process, applying radio frequency to the superconducting connector precursor to form plasma, wherein the temperature is 110℃-130℃, the power is 250W-350W, and the time is 25min-35min; to reduce the oxygen content on the surface of the superconducting connector precursor to 5at%-10at%. Specifically, the obtained superconducting connector precursor can be placed in a vacuum chamber ( Pa), into =4:1 mixed gas (total pressure 0.5Pa), radio frequency is applied; preferably, the parameters for applying radio frequency are: temperature 120℃, power 300W, time 30min. As verified by X-ray photoelectron spectroscopy (XPS), the oxygen content on the surface of the superconducting connector precursor is reduced to <8.3at under these parameters.

[0055] S42: Gradient diffusion welding process, heating to 150℃-180℃; pressurizing to a first pressure of 15MPa-25MPa and maintaining this pressure for a first time of 25min-35min, causing the first and second silver layers to plastically flow, fill surface micropores, and increase the physical contact area to >95%; continuing to pressurize to a second pressure of 40MPa-60MPa and maintaining this pressure for a second time of 80min-100min, causing the copper layer to yield, and silver and copper to diffuse into each other, forming a 5-8nm thick silver-copper solid solution transition layer; continuing to pressurize to a third pressure of 70MPa-90MPa and maintaining this pressure for a third time of 50min-70min, causing the solid solution transition layer to expand to a thickness of 15nm-20nm, forming a continuous gradient solid solution, wherein the copper content increases in a gradient from 10at% to 35at%. Preferably, the welding temperature is 160℃, the first time is 30min, the first pressure is 20MPa, the second time is 90min, the second pressure is 50MPa, the third time is 60min, and the third pressure is 80MPa.

[0056] S43: Stress relaxation process, cooling to 70℃-90℃, pressure reduction to 8MPa-12MPa, time 1h-1.5h; preferably, cooling to 80℃, pressure reduction to 10MPa, time 1h; so that the residual stress at the interface is reduced to below 35MPa.

[0057] S5: An insulating layer is formed on the outer peripheral surface of the superconducting connector precursor after welding to obtain a superconducting connector, thereby producing a superconducting cable connector.

[0058] In one specific embodiment, 60wt%-65wt% of a polyimide precursor, 20wt%-25wt% of hexagonal boron nitride, 5wt%-10wt% of γ-alumina, and 3wt%-5wt% of γ-aminopropyltriethoxysilane are mixed and then milled in a ball mill at 180rpm-220rpm for 22-26 hours. After vacuum degassing (-0.1MPa, 30min), an insulating slurry is formed. Vacuum pressure impregnation encapsulation is then performed: the welded superconducting connector precursor is preheated to 50℃-70℃, preferably 60℃, placed in a mold, and evacuated to... Pa, inject insulating slurry, apply pressure of 0.7MPa-0.9MPa and hold for 15min-30min; perform step curing: heat to 70℃-90℃, pre-curing at 0.08MPa-0.15MPa for 50min-70min, then heat to 110℃-130℃, cross-linking reaction at 0.2MPa-0.4MPa for 25min-35min, then heat to 140℃-160℃, curing at 0.4MPa-0.6MPa for 1.5h-2.5h, forming an insulating layer with a wall thickness of 0.4mm-0.6mm, preferably 0.5mm; wherein the viscosity of the polyimide precursor is 3400cP-3600cP, the particle size of hexagonal boron nitride is 1μm-3μm, and the specific surface area of ​​γ-alumina is 160m² / g-200m² / g.

[0059] Furthermore, it is preferred to use 60wt% polyimide precursor (viscosity 3500 cP), 25wt% hexagonal boron nitride (h-BN, particle size 1-3 μm), and 10wt% γ-alumina (γ- The insulation layer formed by the above method consists of nanoparticles (specific surface area 180 m² / g) and 5 wt% aminopropyltriethoxysilane (KH-550). This insulation system is a polyimide / boron nitride (PI / h-BN) nanocomposite insulation system, which possesses both high thermal conductivity and high insulation properties. Furthermore, its coefficient of thermal expansion matches that of the superconducting joint, thus preventing interface cracking and improving the service life of the superconducting joint.

[0060] The manufacturing method provided by this invention connects the first superconducting tape 31 and the second superconducting tape 32 to be joined via low-temperature diffusion welding based on an Ag / Cu / Ag intermediate composite layer. The Cu layer in the Ag / Cu / Ag composite layer acts as a diffusion barrier layer, effectively inhibiting the diffusion of harmful elements into the sensitive REBCO superconducting tape, protecting its superconducting performance. Furthermore, the Cu layer improves the mechanical strength of the joint and its stability and reliability at high temperatures. The addition of the Cu layer reduces the amount of Ag used, lowering costs and improving economic efficiency. Moreover, the thickness of the Cu layer in this invention is controlled within 60 nm, keeping it within a certain multiple of the REBCO lattice constant (0.38 nm), which inhibits the transition diffusion of Cu atoms into the REBCO layer, ensuring the low contact resistance characteristics of the superconducting joint 3. Further, the Cu layer thickness can be controlled within 50 nm, keeping it within approximately 130 times the REBCO lattice constant. Furthermore, the Ag / Cu / Ag intermediate composite layer structure, combined with low-temperature gradient diffusion welding technology, utilizes a large interface area to promote rapid and uniform diffusion and densification at low temperatures, achieving high-quality low-temperature connection, improving the mechanical strength of the connection part, and thus ensuring that the superconducting joint 3 has good mechanical properties and improving its service life.

[0061] After preparing the superconducting cable connector, this invention further conducts quality testing on the superconducting connector, including: using a four-probe method (liquid nitrogen temperature range 77K, self-field) to detect the contact resistance. The test results show that the contact resistance of the superconducting connector in the superconducting cable connector of this invention is <3nΩ·m², and can even reach 1.5nΩ·m², indicating that the superconducting connector in the superconducting cable connector of this invention has low contact resistance; thermal cycling tests are performed, cycling 100 times in the range of 77K to 300K, with no interface delamination, indicating that the superconducting connector in the superconducting cable connector of this invention has a long service life. In summary, the superconducting cable connector provided by this invention achieves both low contact resistance and a long service life.

[0062] Insulation performance was also tested with reference to the national standard GB / T1408.1-2016. The test results showed that the insulation performance of the superconducting connector in the superconducting cable connector of this invention meets the relevant requirements. Specifically, for the superconducting cable connector having an insulation layer based on a mass percentage content of 60wt%-65wt% polyimide precursor, 20wt%-25wt% hexagonal boron nitride, 5wt%-10wt% γ-alumina, and 3wt%-5wt% γ-aminopropyltriethoxysilane, the measured room temperature dielectric strength is ≥35kV / mm, and the 77K volume resistivity is ≥ The value of Ω·cm indicates that the polyimide / boron nitride (PI / h-BN) nanocomposite insulation system used in this invention has both high thermal conductivity and high insulation properties, and the superconducting connector in the superconducting cable joint has high insulation performance.

[0063] Furthermore, ANSYS simulations are used to detect the interfacial shear stress of the superconducting joint in the superconducting cable joint, as needed.

[0064] The CORC superconducting cable cryogenic joint manufacturing method based on gradient diffusion welding provided by this invention is particularly suitable for the modular assembly of superconducting power equipment, including but not limited to: rapid field joint fabrication of superconducting current limiters (15-35kV voltage level), interlayer interconnection of superconducting transformer windings (500kVA-10MVA), cryogenic segmented connection of magnet systems in nuclear fusion devices, toroidal magnet splicing of superconducting energy storage systems (SMES), and kilometer-scale extension joints of superconducting cables for ultra-high voltage direct current transmission. It can significantly improve the engineering applicability and economy of superconducting power equipment, especially suitable for harsh operating conditions such as strong magnetic fields (>3T), high mechanical loads (>100MPa), and frequent thermal shocks (77K-300K).

[0065] The following examples illustrate specific embodiments of the CORC superconducting cable joint manufacturing method based on gradient diffusion welding of the present invention for preparing superconducting cable joints, as well as comparative examples of superconducting cable joints prepared according to existing technologies, and provide a comparison.

[0066] Example 1

[0067] The fabrication method for a superconducting cable connector includes the following steps:

[0068] S1: Separate the first superconducting tape and the first metal core from one end of the first superconducting cable, and separate the second superconducting tape and the second metal core from one end of the second superconducting cable; use an acetone / ethanol mixture (3:1) to ultrasonically clean the superconducting tape joint area for 10 minutes, and use Ar ion beam etching to treat the surface of the superconducting tape joint area to remove the oxide layer.

[0069] S2: A dual-target magnetron sputtering system was used to sequentially deposit a first silver layer, a copper layer, and a second silver layer on both sides of the first and second superconducting tapes, respectively. The deposition parameters for the first and second silver layers were: power 150W, argon flow rate 40 sccm, substrate temperature 80℃, deposition rate 0.5 Å / s, and thickness 190nm-210nm. The deposition parameters for the copper layer were: power 100W, argon flow rate 35 sccm, substrate temperature 50℃, deposition rate 0.2 Å / s, and thickness 45nm-55nm. During the fabrication process, a quartz crystal thickness gauge was used to monitor the thickness of the formed copper or silver layers in real time to ensure that the thickness remained within the predetermined range; and the interlayer vacuum dwell time was controlled to be ≤5 seconds to avoid interface contamination.

[0070] S3: The first and second superconducting tapes are spirally wound around the outer periphery of the first and second metal cores arranged side by side in an alternating manner, with the spiral angle controlled at 32°±0.5°. After winding, the superconducting tapes are fixed.

[0071] S4: Place the obtained superconducting connector precursor in a vacuum chamber and introduce air... A 4:1 gas mixture was applied with radio frequency (RF) parameters: temperature 120℃, power 300W, and time 30min.

[0072] The temperature was increased to 160℃, the pressure was increased to 20 MPa and held for 30 min, the pressure was increased to 50 MPa at a rate of 0.4 MPa / min and held for 90 min, and the pressure was increased to 80 MPa at a rate of 0.4 MPa / min and held for 60 min.

[0073] Cool down to 80℃ and reduce pressure to 10 MPa for 1 hour.

[0074] S5: 60 wt% polyimide precursor, 25 wt% hexagonal boron nitride, 10 wt% γ-alumina nanoparticles, and 5 wt% aminopropyltriethoxysilane (KH-550) are mixed and then milled in a ball mill at 200 rpm for 24 hours. After vacuum degassing, an insulating slurry is formed. The superconducting connector precursor obtained in step S4 is preheated to 60°C, placed in a mold, and evacuated to... Pa, inject insulating slurry, apply 0.8MPa pressure and hold for 20min; pre-cur at 0.1MPa pressure for 60min; reheat to 120℃, cross-link reaction at 0.3MPa pressure for 30min; reheat to 150℃, cure at 0.5MPa pressure for 2h to form an insulating layer with a wall thickness of about 0.5mm, thereby obtaining a superconducting cable joint.

[0075] The contact resistance and interfacial shear stress of the superconducting joint of the superconducting cable are tested.

[0076] Example 2

[0077] The superconducting cable connector is prepared according to the preparation method in Example 1. The difference from Example 1 is that in step S3, the first superconducting tape and the second superconducting tape are stacked together in a parallel manner and the superconducting tape is fixed by a metal wire.

[0078] The contact resistance and interfacial shear stress of the superconducting joint of the superconducting cable are tested.

[0079] Example 3

[0080] The superconducting cable connector was prepared according to the preparation method in Example 1. The difference from Example 1 is that in step S4, after applying radio frequency, the temperature was raised to 160°C and the voltage was raised to 80 MPa for 180 min.

[0081] The contact resistance and interfacial shear stress of the superconducting joint of the superconducting cable are tested.

[0082] Comparative Example 1

[0083] The fabrication method for a superconducting cable connector includes the following steps:

[0084] S1: Separate the first superconducting tape and the first metal core from one end of the first superconducting cable, and separate the second superconducting tape and the second metal core from one end of the second superconducting cable; use an acetone / ethanol mixture (3:1) to ultrasonically clean the superconducting tape joint area for 10 minutes, and use Ar ion beam etching to treat the surface of the superconducting tape joint area to remove the oxide layer.

[0085] S2: Sn-Ag-Cu solder (SAC305) is uniformly coated on both sides of the first and second superconducting tapes respectively.

[0086] S3: The first superconducting tape and the second superconducting tape are spirally wrapped around the outer periphery of the first and second metal cores arranged side by side in an alternating manner.

[0087] S4: Place the obtained superconducting connector precursor in a vacuum chamber and introduce air... =4:1 gas mixture; heat to 220℃, pressurize to 80MPa and maintain for 40min.

[0088] Cool down to 80℃ and reduce pressure to 10 MPa for 1 hour.

[0089] Step S5 is described in Example 1.

[0090] The contact resistance and interfacial shear stress of the superconducting joint of the superconducting cable are tested.

[0091] Test results

[0092] The detection results of Examples 1-3 and Comparative Example 1 are shown in Table 1 below.

[0093] Table 1

[0094] Example 1 Example 2 Example 3 Comparative Example 1 Contact Resistance 1.5 nQ-m2 2.0 nQ-m2 2.8 nQ-m2 10 nQ-m2 Interfacial Shear Stress 72 MPa 118 MPa 76 MPa 88 MPa

[0095] As shown in Table 1, the contact resistance of the superconducting cable joints obtained in Examples 1-3 is less than 3 nΩ·m², significantly lower than that of Comparative Example 1, with a contact resistance reduction rate exceeding 70%. This indicates that the present invention employs an Ag / Cu / Ag nanolayered composite layer with a synergistic low-temperature gradient diffusion welding technology, ensuring a long service life while significantly reducing contact resistance. Furthermore, the contact resistance of Examples 1 and 2 is less than or equal to 2.0 nΩ·m², and the critical current retention rate is >98%. Compared to Comparative Example 1, the contact resistance reduction rate reaches 80% or more, demonstrating a better optimization effect than that of Example 3. This indicates that the gradient pressure process used in gradient diffusion welding further reduces the contact resistance. The interfacial shear stress in Examples 1, 3, and Comparative Example 1 is significantly lower than that in Example 2, and also lower than the REBCO copper interfacial bonding strength (95 MPa). This indicates that the present invention significantly reduces the interfacial shear stress by using a double-helix interlocking structure in the superconducting joint. In particular, the interfacial shear stress reduction rate of Example 1 compared to Example 2 is close to 40%. Moreover, calculations show that the contact area of ​​the first and second superconducting tapes in Example 1 is 2.15 times larger than that in Example 2.

[0096] It should be noted that, in addition to the specific embodiments described above, those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with the embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details are included in the above description, and the invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0097] It should be noted that similar reference numerals and letters in this specification are similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0098] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding, characterized in that, Manufacturing methods include: S1: Separate the first superconducting tape from one end of the first superconducting cable, and separate the second superconducting tape from one end of the second superconducting cable; S2: A first composite layer is formed on at least a portion of the surface of the first superconducting tape, and a second composite layer is formed on at least a portion of the surface of the second superconducting tape; Each of the first composite layer and the second composite layer includes a first silver layer, a copper layer, and a second silver layer stacked sequentially. The thickness of the composite layer is 400nm-500nm, and the thickness of the copper layer is 10%-12% of the thickness of the composite layer. S3: At least a portion of the first superconducting tape and the second superconducting tape are superimposed on each other to obtain a superconducting connector precursor, wherein the superimposed portions have the first composite layer and the second composite layer. S4: Under vacuum conditions, gradient diffusion welding is performed on the superconducting connector precursor to connect the first composite layer and the second composite layer at the overlapping parts and form a connecting layer. The welding temperature is 150℃-180℃, the pressure is 15MPa-100MPa, and the holding time is 2h-4h; the first pressure is applied in the first time period, the second pressure is applied in the second time period, and the third pressure is applied in the third time period. Furthermore, the first pressure is less than the second pressure, the second pressure is less than the third pressure, and the pressure loading rate during the pressurization process is 0.3 MPa / min - 0.5 MPa / min; S5: An insulating layer is formed on the outer peripheral surface of the superconducting connector precursor after welding to obtain a superconducting connector, thereby producing a superconducting cable connector.

2. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in claim 1, characterized in that, In step S2, the formation process of each composite layer in the first composite layer and the second composite layer includes: sequentially depositing a first silver layer, a copper layer, and a second silver layer on at least a portion of the surface of the corresponding superconducting tape using magnetron sputtering; The deposition process parameters of the first silver layer include: power 140W-180W, argon flow rate 35sccm-45sccm, substrate temperature 75℃-85℃, deposition rate 0.4Å / s-0.6Å / s, and thickness 180nm-220nm. The deposition process parameters for the copper layer include: power 80W-120W, argon flow rate 30sccm-40sccm, substrate temperature 40℃-60℃, deposition rate 0.1Å / s-0.3Å / s, and thickness 40nm-60nm. The deposition process parameters for the second silver layer include: power 140W-180W, argon flow rate 35sccm-45sccm, substrate temperature 75℃-85℃, deposition rate 0.4Å / s-0.6Å / s, and thickness 180nm-220nm.

3. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in claim 2, characterized in that, In step S2, the first composite layer is formed on both sides of the first superconducting tape along its thickness direction, and the second composite layer is formed on both sides of the second superconducting tape along its thickness direction; and in each of the first and second composite layers, the thickness ratio of the first silver layer to the copper layer and the thickness ratio of the second silver layer to the copper layer are both in the range of 3.5:1-4:

1.

4. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in claim 3, characterized in that, In step S3, the first superconducting tape and the second superconducting tape are spirally wrapped around the outer periphery of the metal core in an alternating manner, such that the first superconducting tape and the second superconducting tape are at least partially superimposed on each other; wherein the spiral angle is 30°-35°.

5. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in claim 4, characterized in that, Step S1 further includes: separating the first metal core from one end of the first superconducting cable and separating the second metal core from one end of the second superconducting cable; Step S3 further includes arranging the first metal core and the second metal core side by side to form the metal core.

6. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in claim 5, characterized in that, Both the first metal core and the second metal core are copper tubes.

7. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in claim 1, characterized in that, The first time is 25-35 minutes, the first pressure is 15 MPa-25 MPa, the second time is 80-100 minutes, the second pressure is 40 MPa-60 MPa, the third time is 50-70 minutes, and the third pressure is 70 MPa-90 MPa.

8. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in claim 7, characterized in that, Furthermore, step S4 also includes applying radio frequency to the superconducting connector precursor to form plasma before performing the gradient diffusion welding, wherein the temperature is 110℃-130℃, the power is 250W-350W, and the time is 25min-35min. After the gradient diffusion welding, the temperature is reduced to 70℃-90℃ and the pressure is reduced to 8MPa-12MPa.

9. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in any one of claims 1-8, characterized in that, Step S5 includes: A polyimide precursor with a mass percentage of 60wt%-65wt%, a hexagonal boron nitride with a mass percentage of 20wt%-25wt%, a γ-alumina with a mass percentage of 5wt%-10wt%, and a γ-aminopropyltriethoxysilane with a mass percentage of 3wt%-5wt% are mixed and then mixed in a ball mill at a speed of 180rpm-220rpm for 22h-26h to form an insulating slurry. The insulating slurry is applied to the surface of the superconducting connector precursor after welding, and a pressure of 0.7MPa-0.9MPa is applied and held for 15min-30min. Heat to 75℃-85℃ and pre-cur under a pressure of 0.08MPa-0.15MPa for 50-70 minutes; then heat to 110℃-130℃ and cross-link under a pressure of 0.2MPa-0.4MPa for 25-35 minutes; then heat to 140℃-160℃ and cure under a pressure of 0.4MPa-0.6MPa for 1.5-2.5 hours; forming an insulating layer with a wall thickness of 0.4mm-0.6mm. The polyimide precursor has a viscosity of 3400 cP-3600 cP, the hexagonal boron nitride has a particle size of 1 μm-3 μm, and the γ-alumina has a specific surface area of ​​160 m² / g-200 m² / g.

10. The method for manufacturing a CORC superconducting cable cryogenic joint based on gradient diffusion welding as described in any one of claims 1-8, characterized in that, Step S1 also includes: The first and second superconducting tapes were cleaned and separated. The surfaces of the first and second superconducting tapes were respectively treated with ion beam etching. The etching process parameters included an energy of 400 eV-600 eV and a beam current density of 0.4 mA / cm²-0.6 mA / cm².

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