CN111106453A - Connecting method of second-generation high-temperature superconducting tapes and superconducting wire - Google Patents
Connecting method of second-generation high-temperature superconducting tapes and superconducting wire Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
- H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
- H01R4/02—Soldered or welded connections
- H01R4/029—Welded connections
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- H—ELECTRICITY
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
Abstract
The invention relates to a connecting method of a second generation high temperature superconducting strip and a superconducting wire, wherein the connecting method comprises the following steps: removing the protective layer: removing part of the silver layer in the region to be connected of the second-generation high-temperature superconducting tape, and enabling the residual silver layer and the exposed superconducting layer to be distributed at intervals; and silver layer diffusion welding: overlapping the areas to be connected of at least two second-generation high-temperature superconducting tapes which are treated by the step of removing the protective layer pairwise to form lap joint areas, enabling the residual silver layers to be overlapped and contacted, then clamping the lap joint areas, and performing diffusion welding on the silver layers; fusion diffusion welding of the superconducting layer; and superconducting properties are restored. The method of the invention can not damage the superconducting layer structure, and simultaneously can provide an oxygen diffusion channel, the prepared superconducting joint has high mechanical strength while having superconducting characteristic in a liquid nitrogen temperature region, and simultaneously the residual silver layer can also pass current, so that the superconducting joint also has certain quench protection capability.
Description
Technical Field
The invention relates to the field of superconducting electricians, in particular to a connection method of second-generation high-temperature superconducting tapes and a superconducting wire.
Background
The second generation high temperature superconducting material has excellent comprehensive performance (the irreversible field reaches 7T under 77K, and the critical current density reaches 10 under the self-field)6A/cm2) The method can comprehensively meet the application in the field of strong current of liquid nitrogen temperature regions and strong magnetic fields, and greatly promote the practical process of superconducting power technology. Many superconducting devices based on second-generation high-temperature superconducting tapes are also being continuously developed. In these superconducting devices, very long superconducting wires are often required, and particularly in the development of large and medium-sized magnets, the superconducting wires may weigh several tons. However, because the whole superconducting wire cannot be prepared due to the limited process, relatively short tapes need to be connected by preparing joints, so that the requirement of using length is met. Compared with the superconducting tape, the conductivity and the mechanical property of the superconducting tape joint are greatly reduced, the superconducting tape does not have complete superconducting property in practical application due to the existence of the joint resistance, and Joule heat generated in operation directly influences the design parameters and stable operation of the whole superconducting device, so that the performance of the superconducting tape joint is one of key factors influencing the practicability of a second-generation high-temperature superconducting coated conductor. Good joint preparation techniques are required to ensure that the superconducting tapes always remain after joiningThe performance of the body does not degenerate to influence the operation of a superconducting device, which is also a key problem for researching the superconducting joint technology.
At present, for the connection method of the second generation high temperature superconducting tape, the main reports at home and abroad are as follows: brazing, ultrasonic welding, diffusion welding, fusion diffusion welding and the like, the resistance of which is gradually reduced, but the manufacturing difficulty is gradually increased. The brazing is to form the connection of a sandwich structure of 'strip-solder-strip' by filling low-temperature solder in the lap joint area of two strips, and the ultrasonic welding and the diffusion welding are direct connection of copper layers and silver layers of the strips respectively. Between the two superconducting layers in the joint area there is a solder layer and the metal layer of the strip itself, so that the joint will also present a certain resistance and mechanical strength. In the application fields of nuclear Magnetic Resonance Imaging (MRI), nuclear magnetic resonance spectrometer (NMR) and the like, the magnet is required to reach the index of high magnetic field uniformity, and the superconducting magnet is required to be separated from an external power supply to realize lossless closed-loop operation. In this state, the superconducting tapes are connected by a resistance-free superconducting joint. To realize a resistance-free superconducting joint, it is necessary to directly connect superconducting layers of tapes, and since the superconducting layers of the second generation high temperature superconducting tapes are ceramic materials and extremely sensitive to oxygen and high temperature, typical metallurgical connection methods widely used in low temperature superconducting wires are not suitable for this. The fusion diffusion welding is a method for making a superconducting joint by fusing partial areas of the interface of two superconducting layers and mutually diffusing and tightly connecting the two superconducting layers into a whole. The method has quite complex process, mainly removes the metal layer of the strip material on the premise of not influencing the performance of the superconducting layer, then rapidly heats up and leads the interface part of the superconducting layer to be fused and connected into a whole in a very short time at high temperature, and finally recovers the superconducting property through oxidation annealing. The oxygen diffusion coefficient in the superconducting layer of the second-generation high-temperature superconducting tape is extremely low, so that the duration of the oxidation annealing process is long, the preparation efficiency of the superconducting joint is greatly influenced, and the practical application is difficult to carry out. The existing solution is to provide an oxygen diffusion channel by drilling a hole in the joint region by laser, but laser drilling requires expensive and precise laser equipment, and causes certain damage to the superconducting layer structure, which may cause the current carrying capacity of the superconducting layer to be reduced. In addition, in practical application, the superconducting joint needs to bear certain tensile stress and bending deformation, but the superconducting joint prepared by the prior art is very weak due to connection between superconducting layers taking ceramic materials as essence, so that the mechanical property of the superconducting joint is poor compared with that of the joint prepared by a traditional welding mode with a metal protective layer, and further improvement is needed.
Disclosure of Invention
Therefore, the present invention is directed to overcome the defects of the prior art that the superconducting layer structure needs to be destroyed to provide an oxygen diffusion channel and a superconducting joint prepared by purely connecting superconducting layers has poor mechanical properties, thereby providing a second generation high temperature superconducting tape connecting method.
The invention also provides a superconducting wire.
Therefore, the invention provides a method for connecting second-generation high-temperature superconducting tapes, which comprises the following steps:
removing the protective layer: removing part of the silver layer in the region to be connected of the second-generation high-temperature superconducting tape, and enabling the residual silver layer and the exposed superconducting layer to be distributed at intervals;
and silver layer diffusion welding: overlapping the areas to be connected of at least two second-generation high-temperature superconducting tapes which are treated by the step of removing the protective layer pairwise to form lap joint areas, enabling the residual silver layers to be overlapped and contacted, then clamping the lap joint areas, and performing diffusion welding on the silver layers;
fusion diffusion welding of the superconducting layer; and
the superconductivity is recovered.
In the step of removing the protective layer, the silver layer in the designated area may be removed by photolithography and wet etching, specifically, acetone may be used to clean oil stain on the surface of the area to be connected of the second-generation high-temperature superconducting tape, and then a photoresist is coated, and after pre-baking, exposure, development, cleaning and post-baking, the second-generation high-temperature superconducting tape is immersed in a silver etchant to remove the silver layer in the designated area, and then the residual photoresist is removed and dried, so that the residual silver layer in the area to be connected is uniformly distributed and patterns such as stripes, fishbone shapes and the like are obtained, but not limited thereto, as long as the silver layer and the superconducting layer are distributed at intervals. The photoresist used may be a conventional photoresist, preferably AZ P4620 photoresist manufactured by anzhi corporation, usa, and the Silver Etchant used may be a conventional Silver Etchant, preferably Silver Etchant TFS Etchant manufactured by chauss corporation, usa.
Further, the conditions of silver layer diffusion welding are as follows: under the oxygen atmosphere, applying a pressure of 20-50MPa to the lap joint area, raising the temperature of the lap joint area to 400-600 ℃, and preserving the heat for 1-8 h.
Further, the conditions of the superconducting layer fusion diffusion welding are as follows: under the inert gas atmosphere, applying the pressure of 20-50MPa to the lap joint area, raising the temperature of the lap joint area to 800-900 ℃ and preserving the temperature for 0.5-5 min.
Further, the conditions for restoration of superconductivity are: the temperature of the lap joint area is adjusted to 400-600 ℃, and then oxygen with 0.1-15MPa is filled and the temperature is kept for 50-300 h.
Furthermore, in the step of the fusion diffusion welding of the superconducting layer, the temperature rise rate is 3-100 ℃/s.
Further, in the step of silver layer diffusion welding, the step of clamping the lap joint area is to sequentially overlap a silver foil, an aluminum nitride ceramic plate, a nickel-chromium alloy heating plate and a heat insulation mica plate from inside to outside on two sides of the lap joint area respectively.
Further, the thickness of the nichrome heating plate is 0.05-0.5 mm.
The silver foil has the characteristics of high temperature resistance, high heat conductivity coefficient, soft texture and oxidation resistance, can improve the uniformity of pressure distribution loaded in a joint area, and can also replace the silver foil with a pure nickel sheet; the aluminum nitride ceramic plate has the characteristics of high temperature resistance, high heat conductivity coefficient, electric insulation, smooth surface and high strength, and can improve the temperature field uniformity of a joint area and isolate the heating plate from the superconducting joint; the nickel-chromium alloy has the characteristics of high temperature resistance, high heat conductivity coefficient and oxidation resistance, can be used as a material for electric heating, other heat-resistant nickel-base alloys can also be used as an electric heating sheet, and the thinner nickel-chromium alloy heating sheet has the characteristics of high resistance and low heat capacity, and is beneficial to realizing the rapid temperature rise and drop process.
Furthermore, in the silver layer diffusion welding step, before the silver layer is subjected to diffusion welding, a temperature measuring device is arranged in the lap joint area.
Further, the rare earth element in the second generation high temperature superconducting strip is one or more of yttrium, gadolinium, samarium, dysprosium, holmium, erbium, neodymium and europium.
The invention also provides a superconducting wire prepared by the method for connecting the second-generation high-temperature superconducting tapes.
The technical scheme of the invention has the following advantages:
1. the second generation high temperature superconducting tape connecting method provided by the invention can not damage the superconducting layer structure, and simultaneously can provide an oxygen diffusion channel, the prepared superconducting joint has high mechanical strength while having superconducting characteristics in a liquid nitrogen temperature region, and simultaneously the residual silver layer can also pass current, so that the superconducting joint also has certain quench protection capability. Specifically, the silver layers in partial areas are removed, the residual silver layers and the superconducting layers are distributed at intervals, and then diffusion welding is carried out on the silver layers, so that the residual silver layers in the lap joint areas can be mutually diffused and connected into a whole, a low-resistance diffusion welding joint with certain mechanical strength is obtained, certain current carrying capacity can be kept when the superconducting strip loses time, and a certain quench protection effect is achieved; meanwhile, the high oxygen diffusion coefficient and the electromechanical property of silver are utilized, and a large number of rapid oxygen diffusion channels are provided by the silver layers distributed at intervals with the superconducting layer on the premise of not damaging the structural integrity of the superconducting layer, so that the superconducting property recovery time is shortened; the superconducting layers are fused and diffused, so that partial areas of the two overlapped superconducting layer interfaces can be fused and mutually diffused and tightly connected into a whole, the connection between the superconducting layers is realized, the joint has superconducting characteristics, and a zero-resistance superconducting joint is formed.
2. According to the connection method of the second-generation high-temperature superconducting strip, in the diffusion welding process of the silver layer, the welding pressure is 20-50MPa, so that the interface of the silver layer can be effectively connected on the premise of not damaging the superconducting layer structure, the silver layer can be kept for a long time in the oxygen atmosphere at the temperature of 400 ℃ and 600 ℃, the performances of the superconducting strip can be kept, the silver layer can be continuously subjected to mutual diffusion connection, water and air adsorbed on the exposed superconducting layer can be removed, and the influence of the water and the air on the subsequent melting diffusion welding of the interface of the superconducting layer can be avoided. In the process of the fusion diffusion welding of the superconducting layer, the heating rate is 3-100 ℃/s, so that the oxygen in the superconducting layer can be reduced to be diffused out at a high temperature as much as possible; in addition, the silver layer can effectively protect the superconducting layer, and the oxygen partial pressure can be reduced under the inert gas atmosphere, so that the melting possibly caused by the reduction of the melting point of the silver layer is avoided. The oxygen of 0.1-15MPa is charged in the superconducting recovery process because the improvement of the oxygen partial pressure is beneficial to improving the diffusion efficiency of oxygen; however, since the diffusion coefficient of oxygen in the superconducting layer is low, a long oxygen permeation time is also required.
3. According to the connection method of the second-generation high-temperature superconducting tape, the thickness of the nickel-chromium alloy heating sheet is 0.05-0.5mm, the heating sheet is low in thickness, large in resistance and small in heat capacity, the rapid temperature rise and fall process can be achieved, and the superconducting layer is prevented from being damaged to a large extent due to the fact that the stay time of a joint area is too long near the highest temperature.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic view showing a reaction process for removing a silver layer from a partial region of a region to be joined of a superconducting tape according to example 1 of the present invention;
fig. 2 is a schematic diagram of a stripe pattern formed by spacing the remaining silver layer and the exposed superconducting layer in the etched region to be connected according to embodiment 1 of the present invention;
FIG. 3 is a schematic view showing clamping of the superconducting tapes at the region to be joined according to example 1 of the present invention;
FIG. 4 is a V-I plot of a superconducting joint prepared in example 1 of the present invention;
FIGS. 5(a) to 5(b) are SEM electron micrographs of a superconducting joint produced in example 1 of the present invention after the superconducting layers are peeled from each other at the same position;
FIG. 5(c) is an enlarged view of portion A in FIG. 5 (a);
fig. 5(d) is an enlarged view of a portion B in fig. 5 (B);
fig. 6(a) -6 (b) are metallographic structure views of cross sections of superconducting joints prepared in example 2 of the present invention.
FIG. 7 is a mechanical tensile stress-strain curve of the superconducting joint prepared in example 2 of the present invention;
FIG. 8 is a V-I plot of a superconducting joint prepared in example 2 of the present invention;
FIG. 9 is a V-I graph of a superconducting joint prepared in example 3 of the present invention.
Detailed Description
The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.
The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents or instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.
Example 1
a. Removing the silver layer in a partial area: cleaning oil stains on the surfaces of to-be-connected areas of two Yttrium Barium Copper Oxide (YBCO) superconducting strips by using acetone, coating photoresist, immersing the strips in a silver etching agent to remove silver layers in a specified area after prebaking, exposing, developing, cleaning and postbaking, then removing residual photoresist and drying to ensure that the residual silver layers in the to-be-connected areas are uniformly distributed and obtain stripe-shaped patterns with the silver layers and the superconducting layers distributed at intervals.
b. Diffusion welding of the silver layer in the remaining area: after overlapping the residual silver layers of the to-be-connected areas of the two Yttrium Barium Copper Oxide (YBCO) superconducting strips processed in the step a, respectively and sequentially clamping silver foils, aluminum nitride ceramic plates and nickel-chromium alloy heating plates from inside to outside at the two sides of the overlapped part, wherein the thickness of each nickel-chromium alloy heating plate is 0.05 mm; welding a thermocouple at the edge of a silver foil in a spot welding mode, clamping the outer sides of the nickel-chromium alloy heating sheets at two sides by using a heat insulation mica plate, putting the nickel-chromium alloy heating sheets into a sealed pressure tool, introducing oxygen, and applying pressure of 20MPa to a region to be connected through a pressing block; and then electrifying the nichrome heating plate, heating to 500 ℃, and preserving heat for 1h to discharge water and air adsorbed on the lapping interface of the two strip superconducting layers and ensure that silver layers are mutually diffused and connected into a whole, thereby obtaining the low-resistance diffusion welding joint with certain mechanical strength.
c. And (3) superconducting layer fusion diffusion welding: argon is filled into the sealing pressure tool, and a pressure of 30MPa is applied to the lap joint area through a pressing block; and then heating to 840 ℃ at the heating rate of 3 ℃/s and preserving heat for 1min, so that partial areas of the two overlapped superconducting layer interfaces are melted and mutually diffused to be tightly connected into a whole, and the connection between the superconducting layers is realized.
d. And (3) superconductive property recovery: reducing the temperature to 500 ℃, then filling 10MPa of oxygen, and preserving the temperature for 100h to ensure that the superconducting layer after connection recovers the superconductivity; and finally, reducing the temperature to room temperature to finish the preparation of the superconducting joint.
As shown in FIG. 1, a schematic diagram of the reaction process for removing the silver layer from the partial region of the region to be joined of the superconducting tapes according to this embodiment is shown.
As shown in fig. 2, a schematic diagram of stripe patterns formed at intervals between the remaining silver layer and the exposed superconducting layer in the etched region to be connected according to this embodiment is shown;
FIG. 3 is a schematic view showing the clamping of the superconducting tapes in the present embodiment in the region to be joined.
As shown in fig. 4, the voltage-current (V-I) curve measured by the four-lead method at a zero field of 77K was obtained for the superconducting joint prepared in this example. The critical current of the superconducting joint is 37A through a criterion of 1 muV/cm, which indicates that the joint prepared by the method is the superconducting joint.
As shown in fig. 5(a) -5 (B), in the scanning electron microscope images of the superconducting joint prepared in this example, in which the superconducting layers are peeled off from each other at the same position, fig. 5(c) is an enlarged view of a portion a in fig. 5(a), fig. 5(d) is an enlarged view of a portion B in fig. 5(B), it can be seen from fig. 5(a) and 5(B) that the patterns of the concavo-convex portions peeled off at the same position match each other, region 1 in fig. 5(c) and region 2 in fig. 5(d) are partially connected superconducting layers, region 3 in fig. 5(c) and region 4 in fig. 5(d) are two superconducting layers which are completely connected, region 4 is a 3 region of a bare buffer layer after peeling off, and it can be seen that the superconducting layers of most regions are completely connected together.
Example 2
a. Removing the silver layer in a partial area: cleaning oil stains on the surfaces of to-be-connected areas of two Yttrium Barium Copper Oxide (YBCO) superconducting strips by using acetone, coating photoresist, immersing the strips in a silver etching agent to remove silver layers in a specified area after prebaking, exposing, developing, cleaning and postbaking, then removing residual photoresist and drying to ensure that the residual silver layers in the to-be-connected areas are uniformly distributed and obtain stripe-shaped patterns with the silver layers and the superconducting layers distributed at intervals.
b. Diffusion welding of the silver layer in the remaining area: after overlapping the residual silver layers of the to-be-connected areas of the two Yttrium Barium Copper Oxide (YBCO) superconducting strips processed in the step a, respectively and sequentially clamping silver foils, aluminum nitride ceramic plates and nickel-chromium alloy heating plates from inside to outside at the two sides of the overlapped part, wherein the thickness of each nickel-chromium alloy heating plate is 0.1 mm; welding a thermocouple at the edge of a silver foil in a spot welding mode, clamping the outer sides of the nickel-chromium alloy heating plates at two sides by using a heat insulation mica plate, putting the nickel-chromium alloy heating plates into a sealed pressure tool, introducing oxygen, and applying pressure of 30MPa to a region to be connected through a pressing block; and then electrifying the nichrome heating plate, heating to 600 ℃, and preserving heat for 2 hours to discharge water and air adsorbed on the lapping interface of the two strip superconducting layers and ensure that silver layers are mutually diffused and connected into a whole, thereby obtaining the low-resistance diffusion welding joint with certain mechanical strength.
c. And (3) superconducting layer fusion diffusion welding: argon is filled into the sealing pressure tool, and 20MPa pressure is applied to the lap joint area through a pressing block; and then heating to 830 ℃ at the heating rate of 20 ℃/s and preserving heat for 2min, so that partial areas of the two overlapped superconducting layer interfaces are fused and mutually diffused to be tightly connected into a whole, and the connection between the superconducting layers is realized.
d. And (3) superconductive property recovery: reducing the temperature to 550 ℃, then filling oxygen with the pressure of 5MPa, and preserving the temperature for 150h to ensure that the superconducting layer after connection recovers the superconducting property; and finally, reducing the temperature to room temperature to finish the preparation of the superconducting joint.
The cross-sectional morphology of the prepared superconducting joint is observed by an optical microscope, and the interface of the residual silver layers and the exposed superconducting layers of the two tapes is well connected, as shown in fig. 6(a) and 6 (b). FIG. 6(a) shows a diffusion solder joint of the remaining partial silver layer, wherein region 1 is a hastelloy base tape, region 2 is a YBCO superconducting layer, and region 3 is a partial silver layer; fig. 6(b) shows the exposed superconducting layer after etching, wherein 1 region is the hastelloy base band, and 4 regions are the exposed YBCO superconducting layer after etching.
The mechanical properties of the prepared superconducting joint were measured, and the stress-strain curve thereof is shown in fig. 7. Referring to the original strip and comparing the joints joined entirely by the superconducting layer, it can be seen that the joints with partial area silver layer welds have a higher mechanical strength than the joints with the superconducting layer welded directly.
As shown in fig. 8, the voltage-current (V-I) curve measured by the four-lead method at zero field of 77K was obtained for the superconducting joint prepared in this example. The critical current of the superconducting joint is 31A through a criterion of 1 muV/cm, which indicates that the joint prepared by the method is the superconducting joint.
Example 3
a. Removing the silver layer in a partial area: cleaning oil stains on the surfaces of to-be-connected areas of two yttrium gadolinium barium copper oxide (YGdBCO) superconducting strips by using acetone, coating photoresist, immersing the strips in a silver etching agent to remove silver layers in a specified area after pre-baking, exposure, development, cleaning and post-baking, and then removing residual photoresist and drying to uniformly distribute the residual silver layers in the to-be-connected areas and obtain stripe patterns with the silver layers and the superconducting layers distributed at intervals.
b. Diffusion welding of the silver layer in the remaining area: after overlapping the residual silver layers of the to-be-connected areas of the two yttrium-gadolinium-barium-copper-oxygen (YGdBCO) superconducting strips processed in the step a, respectively and sequentially clamping silver foils, aluminum nitride ceramic plates and a nickel-chromium alloy heating sheet from inside to outside at two sides of the overlapped part, wherein the thickness of the nickel-chromium alloy heating sheet is 0.2 mm; welding a thermocouple at the edge of a silver foil in a spot welding mode, clamping the outer sides of the nickel-chromium alloy heating sheets at two sides by using a heat insulation mica plate, putting the nickel-chromium alloy heating sheets into a sealed pressure tool, introducing oxygen, and applying pressure of 40MPa to a region to be connected through a pressing block; and then electrifying the nichrome heating plate, heating to 400 ℃, and preserving heat for 8 hours to discharge water and air adsorbed on the lapping interface of the two strip superconducting layers and ensure that silver layers are mutually diffused and connected into a whole, thereby obtaining the low-resistance diffusion welding joint with certain mechanical strength.
c. And (3) superconducting layer fusion diffusion welding: argon is filled into the sealing pressure tool, and 50MPa pressure is applied to the lap joint area through a pressing block; and then heating to 800 ℃ at the heating rate of 50 ℃/s and preserving heat for 5min, so that partial areas of the two overlapped superconducting layer interfaces are fused and mutually diffused to be tightly connected into a whole, and the connection between the superconducting layers is realized.
d. And (3) superconductive property recovery: reducing the temperature to 600 ℃, then filling 3MPa of oxygen, and preserving the temperature for 200h to ensure that the superconductivity of the connected superconductivity layer is recovered; and finally, reducing the temperature to room temperature to finish the preparation of the superconducting joint.
As shown in fig. 9, the voltage-current (V-I) curve measured by the four-lead method at a zero field of 77K was obtained for the superconducting joint prepared in this example. The critical current of the superconducting joint is 23A through a criterion of 1 muV/cm, which indicates that the joint prepared by the method is the superconducting joint.
Example 4
a. Removing the silver layer in a partial area: cleaning oil stains on the surfaces of to-be-connected areas of two Yttrium Barium Copper Oxide (YBCO) superconducting strips by using acetone, coating photoresist, immersing the strips in a silver etching agent to remove silver layers in a specified area after prebaking, exposing, developing, cleaning and postbaking, then removing residual photoresist and drying to ensure that the residual silver layers in the to-be-connected areas are uniformly distributed and obtain stripe-shaped patterns with the silver layers and the superconducting layers distributed at intervals.
b. Diffusion welding of the silver layer in the remaining area: after overlapping the residual silver layers of the to-be-connected areas of the two Yttrium Barium Copper Oxide (YBCO) superconducting strips processed in the step a, respectively and sequentially clamping silver foils, aluminum nitride ceramic plates and nickel-chromium alloy heating plates from inside to outside at the two sides of the overlapped part, wherein the thickness of each nickel-chromium alloy heating plate is 0.4 mm; welding a thermocouple at the edge of a silver foil in a spot welding mode, clamping the outer sides of the nickel-chromium alloy heating sheets at two sides by using a heat insulation mica plate, putting the nickel-chromium alloy heating sheets into a sealed pressure tool, introducing oxygen, and applying 50MPa pressure to a region to be connected through a pressing block; and then electrifying the nichrome heating plate, heating to 550 ℃, and preserving heat for 6 hours to discharge water and air adsorbed on the lapping interface of the two strip superconducting layers and ensure that silver layers are mutually diffused and connected into a whole, thereby obtaining the low-resistance diffusion welding joint with certain mechanical strength.
c. And (3) superconducting layer fusion diffusion welding: filling nitrogen into the sealing pressure tool, and applying 40MPa pressure to the lap joint area through a pressing block; and then heating to 900 ℃ at the heating rate of 80 ℃/s and preserving the heat for 0.5min, so that partial areas of the two overlapped superconducting layer interfaces are melted and mutually diffused to be tightly connected into a whole, and the connection between the superconducting layers is realized.
d. And (3) superconductive property recovery: reducing the temperature of the heating sheet to 400 ℃, then filling oxygen with the pressure of 15MPa, and preserving the temperature for 50h to ensure that the superconducting layer after connection recovers the superconductivity; and finally, reducing the temperature to room temperature to finish the preparation of the superconducting joint.
Example 5
a. Removing the silver layer in a partial area: cleaning oil stains on the surfaces of to-be-connected areas of two gadolinium barium copper oxide (GdBCO) superconducting strips by using acetone, coating photoresist, immersing the strips in a silver etching agent to remove silver layers in a specified area after prebaking, exposing, developing, cleaning and postbaking, and then removing residual photoresist and drying to uniformly distribute the residual silver layers in the to-be-connected areas and obtain stripe-shaped patterns with the silver layers and the superconducting layers distributed at intervals.
b. Diffusion welding of the silver layer in the remaining area: after overlapping the residual silver layers of the to-be-connected areas of the two processed YBCO superconductive tapes, respectively clamping the two sides of the overlapped part from inside to outside by a silver foil, an aluminum nitride ceramic plate and a nichrome heating plate, wherein the thickness of the nichrome heating plate is 0.5 mm; welding a thermocouple at the edge of a silver foil in a spot welding mode, clamping the outer sides of the nickel-chromium alloy heating sheets at two sides by using a heat insulation mica plate, putting the nickel-chromium alloy heating sheets into a sealed pressure tool, introducing oxygen, and applying pressure of 20MPa to a region to be connected through a pressing block; and then electrifying the nichrome heating plate, heating to 500 ℃, and preserving heat for 1h to discharge water and air adsorbed on the lapping interface of the two strip superconducting layers and ensure that silver layers are mutually diffused and connected into a whole, thereby obtaining the low-resistance diffusion welding joint with certain mechanical strength.
c. And (3) superconducting layer fusion diffusion welding: argon is filled into the sealing pressure tool, and 20MPa pressure is applied to the lap joint area through a pressing block; and then heating to 850 ℃ at the heating rate of 100 ℃/s and preserving heat for 1min, so that partial areas of the two overlapped superconducting layer interfaces are fused and mutually diffused to be tightly connected into a whole, and the connection between the superconducting layers is realized.
d. And (3) superconductive property recovery: reducing the temperature to 450 ℃, then filling oxygen with 0.1MPa, and preserving the temperature for 300h to ensure that the superconductivity of the connected superconducting layer is recovered; and finally, reducing the temperature to room temperature to finish the preparation of the superconducting joint.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. A method for connecting second-generation high-temperature superconducting tapes is characterized by comprising the following steps:
removing the protective layer: removing part of the silver layer in the region to be connected of the second-generation high-temperature superconducting tape, and enabling the residual silver layer and the exposed superconducting layer to be distributed at intervals;
and silver layer diffusion welding: overlapping the areas to be connected of at least two second-generation high-temperature superconducting tapes which are treated by the step of removing the protective layer pairwise to form lap joint areas, enabling the residual silver layers to be overlapped and contacted, then clamping the lap joint areas, and performing diffusion welding on the silver layers;
fusion diffusion welding of the superconducting layer; and
the superconductivity is recovered.
2. The method for joining second-generation high-temperature superconducting tapes according to claim 1, wherein the conditions of silver layer diffusion welding are as follows: under the oxygen atmosphere, applying a pressure of 20-50MPa to the lap joint area, raising the temperature of the lap joint area to 400-600 ℃, and preserving the heat for 1-8 h.
3. The method for joining a second-generation high-temperature superconducting tape according to claim 1, wherein the conditions for the fusion diffusion welding of the superconducting layers are: under the inert gas atmosphere, applying the pressure of 20-50MPa to the lap joint area, raising the temperature of the lap joint area to 800-900 ℃ and preserving the temperature for 0.5-5 min.
4. A method for joining a second-generation high-temperature superconducting tape according to claim 1, wherein the conditions for restoring the superconductivity are: the temperature of the lap joint area is adjusted to 400-600 ℃, and then oxygen with 0.1-15MPa is filled and the temperature is kept for 50-300 h.
5. The method for joining a second-generation high-temperature superconducting tape according to claim 3, wherein the temperature increase rate in the step of fusion diffusion welding of the superconducting layers is 3 to 100 ℃/s.
6. The method according to claim 1, wherein in the step of silver layer diffusion welding, the silver foil, the aluminum nitride ceramic sheet, the nichrome heating sheet and the heat insulation mica plate are sequentially stacked on both sides of the lap-joint region from inside to outside.
7. The method for joining a second-generation high-temperature superconducting tape according to claim 6, wherein the thickness of the nichrome heating sheet is 0.05-0.5 mm.
8. The method for joining high-temperature superconducting tapes of the second generation as claimed in claim 1, wherein the step of diffusion welding the silver layer further comprises a step of providing a temperature measuring device in the lap joint region before the step of diffusion welding the silver layer.
9. The method according to claim 1, wherein the rare earth element in the second generation high temperature superconducting tape is one or more of yttrium, gadolinium, samarium, dysprosium, holmium, erbium, neodymium and europium.
10. The superconducting wire produced by the method for joining a second-generation high-temperature superconducting tape according to any one of claims 1 to 9.
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