A method for preparing a surface high-entropy metalized layer assisted brazing large-size ceramic matrix composite and niobium joint based on joule heat shock

Abstract

The application discloses a method for preparing a joint of a large-size ceramic matrix composite and niobium by brazing with the aid of a high-entropy metallized layer based on Joule heat impact, and belongs to the brazing field.The application aims at solving the problem of excessive residual stress in the brazing connection of an existing C / SiC composite and niobium.Methods: 1, coating of an alloy mixed solution;2, high-entropy alloying of the surface of the C / SiC composite;3, assembly of the welding part;4, vacuum brazing.The application is used for preparing a joint of a large-size ceramic matrix composite and niobium by brazing with the aid of a high-entropy metallized layer based on Joule heat impact.

Description

Technical Field

[0001] The invention belongs to the field of brazing. Background Art

[0002] In modern aerospace propulsion systems, rocket engine nozzles are one of the key components, and their material selection and connection technology are crucial to the overall performance of the engine. C / SiC composites have become one of the ideal materials for the nozzles of the new generation of rocket engines due to their excellent mechanical properties, low density and good chemical stability. Due to the poor processing performance of C / SiC composites, in applications, C / SiC composites are usually connected to metal materials such as niobium (Nb) through brazing technology. During this process, the significant CTE difference between C / SiC and niobium leads to large residual stresses during brazing, especially for large-sized joints, where the stress increases exponentially. Long-term residual stress not only reduces the fatigue life of the joint, but may also cause crack initiation and propagation, thereby affecting the safety and reliability of the nozzle and even the entire engine.

[0003] In recent years, surface metallization has been proposed as an effective solution, aiming to improve the interfacial compatibility between ceramic materials and the metal substrate by depositing a metal coating on the surface, thereby reducing residual stress. High-entropy alloys (HEAs) are considered ideal metallization materials due to their excellent overall mechanical properties, corrosion resistance, and high-temperature stability. However, the high melting point of HEAs limits the application of traditional metallization processes, particularly when processing large components. Summary of the Invention

[0004] The present invention aims to solve the problem of excessive residual stress in the existing brazing connection between C / SiC composite materials and niobium, and further provides a method for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-sized ceramic-based composite material and niobium joints.

[0005] A method for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing a large-sized ceramic matrix composite and niobium joint is provided, which is carried out in the following steps:

[0006] 1. Coating alloy mixture:

[0007] The FeCoCrNiMo alloy powder and the N-methylpyrrolidone solution of polyvinylidene fluoride are stirred and mixed until they become viscous to obtain an alloy mixture, and the alloy mixture is applied to a surface of the C / SiC composite material perpendicular to the growth direction of the carbon fibers to obtain a C / SiC composite material coated with the mixture;

[0008] 2. High entropy alloying on the surface of C / SiC composite materials:

[0009] Under the conditions of a metallization voltage of 25V to 35V and a metallization current of 40A to 60A, the C / SiC composite material coated with the mixed solution is heated for 10s to 20s to form a high entropy alloy layer, and then the high entropy alloy layer is polished and cleaned to obtain a C / SiC composite material having a high entropy alloy layer;

[0010] 3. Assembly of parts to be welded:

[0011] Assembling the components in the order of metal niobium, AgCuTi solder sheet, and C / SiC composite material with a high entropy alloy layer from bottom to top, and laminating the high entropy alloy layer of the C / SiC composite material with a high entropy alloy layer to the AgCuTi solder sheet to obtain a component to be welded;

[0012] 4. Vacuum brazing:

[0013] The parts to be welded are placed in a vacuum brazing furnace and evacuated. The parts are first kept warm at 100°C to 200°C for 5 to 20 minutes, then kept warm at 800°C to 950°C for 5 to 20 minutes, and finally cooled to room temperature. This completes the method for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-size ceramic-based composite materials and niobium joints.

[0014] The beneficial effects of the present invention are:

[0015] 1. The method of the present invention can effectively alleviate the problem of a large difference in thermal expansion coefficients between ceramics and metallic niobium. Such a large difference in thermal expansion coefficients will lead to excessive residual stress in the joint, which will eventually cause cracks in the joint. By adding a high-entropy alloy surface metallization layer to the surface of the C / SiC composite material, Joule thermal shock energy can significantly increase the lattice distortion of the high-entropy alloy, improve the plastic deformation ability, and form a stress buffer zone, which can alleviate the residual stress in the joint and prevent the occurrence of cracks.

[0016] 2. The method of the present invention can form a buffer metal layer in the internal area of ​​the ceramic joint to alleviate the difference in thermal expansion coefficient by adding a high-entropy alloy surface metallization layer, thereby regulating the distribution of residual stress in the overall weld joint. On the other hand, the high-entropy alloy surface metallization layer reduces the growth of brittle compounds on the ceramic joint side, optimizes the weld structure of the silver-copper-titanium (AgCuTi) solder, and improves the plasticity and toughness of the weld; a good solid solution structure is formed in the joint, thereby improving the toughness and strength of the joint.

[0017] 3. The present invention utilizes a high entropy metallization layer to effectively improve the wettability and bonding strength between the solder and the ceramic composite material, thereby ensuring a good connection between the large-sized ceramic composite material and the niobium-based solder.

[0018] 4. High-entropy metallization of the surface of C / SiC composite materials usually requires a high metallization temperature. The Joule thermal shock method of the present invention can reach extremely high temperatures in a short time and quickly cool down, reducing the damage to the parent material caused by long-term heating of traditional metallization. In addition, Joule thermal shock can effectively improve the problem of excessively thick brittle compound reaction layer generated between the metallization layer and the C / SiC composite material. The thickness of the interface reaction layer is relatively thin, which greatly improves the mechanical properties of the joint.

[0019] 5. The present invention uses high entropy alloy as the ceramic surface metallization layer to assist the AgCuTi solder joint, and the corresponding room temperature shear strength is 177 MPa, which is 2.3 times that of the non-metallized surface ceramic joint (77 MPa). At the same time, the joint has good high-temperature performance, and the shear strength at 500°C is 102 MPa, which is suitable for service environments under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Transmission electron microscopy images and geometric phase analysis diagrams of the high-entropy metallization layer in the C / SiC composite material with a high-entropy alloy layer prepared in step 2 of Example 1, (a) TEM of a typical high-entropy alloy solid solution structure, (b) electron diffraction spots of the solid solution structure, and (c) TEM geometric phase analysis;

[0021] Figure 2 This is a scanning electron microscope photograph of the joint of the C / SiC composite material-niobium weldment prepared in Example 1;

[0022] Figure 3 Figures 1 and 2 are joint test data graphs of the C / SiC composite material-niobium weldments prepared in Examples 1 to 3 and the comparative experiment, (a) room temperature joint strength corresponding to different high entropy layer thicknesses, (b) joint strength of the C / SiC composite material-niobium weldment prepared in Example 1 at room temperature and 500°C, (c) joint shear stress-strain curve, 1 is the stress-strain curve of the room temperature joint strength of the C / SiC composite material-niobium weldment prepared in the comparative experiment, 2 is the stress-strain curve of the room temperature joint strength of the C / SiC composite material-niobium weldment prepared in Example 1, and 3 is the stress-strain curve of the joint strength of the C / SiC composite material-niobium weldment prepared in Example 1 at 500°C. DETAILED DESCRIPTION

[0023] Specific embodiment 1: This embodiment is a method for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing a large-sized ceramic matrix composite material and niobium joint, which is carried out in the following steps:

[0024] 1. Coating alloy mixture:

[0025] The FeCoCrNiMo alloy powder and the N-methylpyrrolidone solution of polyvinylidene fluoride are stirred and mixed until they become viscous to obtain an alloy mixture, and the alloy mixture is applied to a surface of the C / SiC composite material perpendicular to the growth direction of the carbon fibers to obtain a C / SiC composite material coated with the mixture;

[0026] 2. High entropy alloying on the surface of C / SiC composite materials:

[0027] Under the conditions of a metallization voltage of 25V to 35V and a metallization current of 40A to 60A, the C / SiC composite material coated with the mixed solution is heated for 10s to 20s to form a high entropy alloy layer, and then the high entropy alloy layer is polished and cleaned to obtain a C / SiC composite material having a high entropy alloy layer;

[0028] 3. Assembly of parts to be welded:

[0029] Assembling the components in the order of metal niobium, AgCuTi solder sheet, and C / SiC composite material with a high entropy alloy layer from bottom to top, and laminating the high entropy alloy layer of the C / SiC composite material with a high entropy alloy layer to the AgCuTi solder sheet to obtain a component to be welded;

[0030] 4. Vacuum brazing:

[0031] The parts to be welded are placed in a vacuum brazing furnace and evacuated. The parts are first kept warm at 100°C to 200°C for 5 to 20 minutes, then kept warm at 800°C to 950°C for 5 to 20 minutes, and finally cooled to room temperature. This completes the method for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-size ceramic-based composite materials and niobium joints.

[0032] The beneficial effects of this embodiment are:

[0033] 1. The method of this embodiment can effectively alleviate the problem of a large difference in thermal expansion coefficient between ceramics and metallic niobium. Excessive difference in thermal expansion coefficient will lead to excessive residual stress in the joint, which will eventually cause cracks in the joint. By adding a high-entropy alloy surface metallization layer to the surface of the C / SiC composite material, Joule thermal shock energy can significantly increase the lattice distortion of the high-entropy alloy, improve the plastic deformation ability, and form a stress buffer zone, which can alleviate the residual stress of the joint and prevent the occurrence of cracks.

[0034] 2. This embodiment method can form a buffer metal layer in the internal area of ​​the ceramic joint to alleviate the difference in thermal expansion coefficient by adding a high entropy alloy surface metallization layer, thereby regulating the distribution of residual stress in the overall weld joint. On the other hand, the high entropy alloy surface metallization layer reduces the growth of brittle compounds on the ceramic joint side, optimizes the weld structure of the silver-copper-titanium (AgCuTi) solder, and improves the plasticity and toughness of the weld; a good solid solution structure is formed in the joint, thereby improving the toughness and strength of the joint.

[0035] 3. This embodiment utilizes a high entropy metallization layer to effectively improve the wettability and bonding strength between the brazing material and the ceramic composite material, thereby ensuring a good connection between the large-sized ceramic composite material and the niobium-based brazing material.

[0036] 4. Realizing high-entropy metallization of the surface of C / SiC composite materials usually requires a relatively high metallization temperature. The Joule thermal shock of this embodiment can reach an extremely high temperature in a short time and cool down quickly, reducing the damage to the parent material properties caused by long-term heating of traditional metallization. Moreover, Joule thermal shock can effectively improve the problem of an excessively thick brittle compound reaction layer generated between the metallization layer and the C / SiC composite material. The thickness of the interface reaction layer is relatively thin, which greatly improves the mechanical properties of the joint. 5. This embodiment uses a high-entropy alloy as a ceramic surface metallization layer to assist the AgCuTi solder joint. The corresponding room temperature shear strength is 177MPa, which is 2.3 times that of the surface unmetallized ceramic joint (77MPa). At the same time, the joint has good high-temperature performance, and the shear strength at 500°C is 102MPa, which is suitable for service environments under high temperature conditions.

[0037] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the concentration of the polyvinylidene fluoride N-methylpyrrolidone solution in step 1 is 0.05 g / L to 0.2 g / L. Other aspects are the same as those of specific embodiment 1.

[0038] Specific embodiment 3: This embodiment differs from either specific embodiment 1 or 2 in that the mass ratio of FeCoCrNiMo alloy powder to polyvinylidene fluoride in the alloy mixture in step 1 is (1-10):1. Other aspects are the same as specific embodiment 1 or 2.

[0039] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the stirring and mixing in step 1 until the mixture becomes viscous is carried out at a rotation speed of 300 rpm to 1000 rpm for 5 to 20 minutes. Other steps are the same as those in specific embodiment 3.

[0040] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the thickness of the high entropy alloy layer in the C / SiC composite material with the high entropy alloy layer described in step 2 is 50 μm to 300 μm. Other aspects are the same as specific embodiments 1 to 4.

[0041] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the C / SiC composite material described in step 1 is a pretreated C / SiC composite material, and the pretreatment is specifically performed by ultrasonically cleaning the high-entropy alloy layer with ethanol at a power of 50W to 200W for 5 minutes to 15 minutes; the polishing and cleaning of the high-entropy alloy layer described in step 2 is specifically performed by polishing the high-entropy alloy layer surface with 3000# sandpaper to a thickness of 50μm to 300μm, and then ultrasonically cleaning the high-entropy alloy layer with ethanol at a power of 50W to 200W for 5 minutes to 15 minutes. Other embodiments are the same as specific embodiments 1 to 5.

[0042] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the thickness of the AgCuTi solder sheet in step 3 is 100 μm to 500 μm. Other aspects are the same as specific embodiments 1 to 6.

[0043] Specific Embodiment 8: This embodiment differs from Specific Embodiments 1 to 7 in that the niobium metal described in step 3 is pretreated niobium. The pretreatment specifically involves removing the oxide film on the niobium surface using 180#, 400#, and 800# sandpaper, followed by ultrasonic cleaning with ethanol at a power of 50W to 200W for 5 to 15 minutes. The AgCuTi solder sheet described in step 3 is pretreated AgCuTi solder sheet. The pretreatment specifically involves polishing the AgCuTi solder sheet with 500# sandpaper to remove surface oxides, followed by ultrasonic cleaning with ethanol at a power of 50W to 200W for 5 to 15 minutes. Other aspects are the same as Specific Embodiments 1 to 7.

[0044] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: in step 4, vacuum is drawn to 1×10 -4 Pa~1×10 -5 Pa. The rest is the same as the specific embodiments 1 to 8.

[0045] Specific implementation ten: the difference between this implementation and one of the specific implementations one to nine is that: in step four, the temperature is raised to 100-200°C at a rate of 5-10°C / min, and the temperature is kept at 100-200°C for 5-20 min, then the temperature is raised to 800-950°C at a rate of 5-10°C / min, and the temperature is kept at 800-950°C for 5-20 min, and finally cooled to room temperature at a rate of 5-10°C / min. The others are the same as specific implementations one to nine.

[0046] The beneficial effects of the application are verified by the following examples:

[0047] Example one:

[0048] A method for preparing a surface high-entropy metalized layer assisted brazing of large-size ceramic matrix composite and niobium joint based on joule heat shock, which is carried out according to the following steps:

[0049] I. Coating alloy mixed solution:

[0050] Under the condition of 300 rpm, the FeCoCrNiMo alloy powder and the N-methyl pyrrolidone solution of polyvinylidene fluoride were stirred and mixed for 10 min to a viscous state, to obtain an alloy mixed solution, and the alloy mixed solution was coated on the surface of the C / SiC composite material perpendicular to the growth direction of the carbon fiber to obtain a C / SiC composite material coated with the mixed solution;

[0051] The size of the C / SiC composite material is 50mmx50mmx50mm; the ratio of each element in the FeCoCrNiMo alloy powder (purchased) is 1:1:1:1:1; the concentration of the N-methyl pyrrolidone solution of polyvinylidene fluoride is 0.1g / L; the mass ratio of FeCoCrNiMo alloy powder to polyvinylidene fluoride in the alloy mixed solution is 4:1;

[0052] II. High-entropy alloying of C / SiC composite material surface:

[0053] The C / SiC composite material coated with the mixed solution was placed in a heat shock device, and the C / SiC composite material coated with the mixed solution was heated and treated at a metallization voltage of 31V and a metallization current of 50A for 15s to form a high-entropy alloy layer, then the high-entropy alloy layer was polished and cleaned to obtain a C / SiC composite material with a high-entropy alloy layer;

[0054] The thickness of the high-entropy alloy layer in the C / SiC composite material with the high-entropy alloy layer is 150μm;

[0055] III. Assembly of the parts to be welded:

[0056] Assembling the components in the order of metal niobium, AgCuTi solder sheet, and C / SiC composite material with a high entropy alloy layer from bottom to top, and laminating the high entropy alloy layer of the C / SiC composite material with a high entropy alloy layer to the AgCuTi solder sheet to obtain a component to be welded;

[0057] The size of the metal niobium is 100 mm × 100 mm × 50 mm; the thickness of the AgCuTi solder sheet is 400 μm; the mass percentage of Ag in the AgCuTi solder sheet is 68.8%, the mass percentage of Cu is 26.7%, and the mass percentage of Ti is 4.5%;

[0058] 4. Vacuum brazing:

[0059] Place the workpiece to be welded in a vacuum brazing furnace and evacuate to 1×10 -4 Pa, firstly, the temperature was increased to 150°C at a heating rate of 10°C / min, and kept at 150°C for 10 minutes, then the temperature was increased to 880°C at a heating rate of 10°C / min, and kept at 880°C for 10 minutes, and finally cooled to room temperature at a cooling rate of 5°C / min to obtain a C / SiC composite material-niobium weldment.

[0060] The C / SiC composite material described in step 1 is a pretreated C / SiC composite material, wherein the pretreatment is specifically performed by ultrasonically assisted cleaning with ethanol for 10 minutes at a power of 100 W;

[0061] The polishing and cleaning of the high entropy alloy layer in step 2 is specifically to use 3000# sandpaper to polish the surface of the high entropy alloy layer to a thickness of 150 μm, and then use ethanol ultrasonic assisted cleaning for 10 minutes under the condition of power of 100 W;

[0062] The niobium metal described in step 3 is pretreated niobium metal, and the pretreatment is specifically to remove the oxide film on the surface of the niobium metal with 180#, 400# and 800# sandpaper in sequence, and then use ethanol ultrasonic assisted cleaning for 10 minutes at a power of 100W; the AgCuTi solder sheet described in step 3 is pretreated AgCuTi solder sheet, and the pretreatment is specifically carried out according to the following steps: use 500# sandpaper to polish the AgCuTi solder sheet to remove surface oxide, and then use ethanol ultrasonic assisted cleaning for 10 minutes at a power of 100W.

[0063] Example 2: This example differs from Example 1 in that the thickness of the high entropy alloy layer in the C / SiC composite material with the high entropy alloy layer described in step 2 is 50 μm. Other aspects are the same as Example 1.

[0064] Example 3: This example differs from Example 1 in that the thickness of the high entropy alloy layer in the C / SiC composite material with the high entropy alloy layer described in step 2 is 300 μm. Other aspects are the same as Example 1.

[0065] Comparative Experiment: This comparative experiment differs from Example 1 in that steps 1 and 2 are omitted, and in step 3, niobium metal, AgCuTi brazing filler metal sheet, and C / SiC composite material are assembled in this order from bottom to top to obtain the welded component. Other steps are the same as Example 1.

[0066] Figure 1 Transmission electron microscope images and geometric phase analysis diagrams of the high-entropy metallization layer in the C / SiC composite material with a high-entropy alloy layer prepared in step 2 of Example 1, (a) TEM of a typical solid solution structure of a high-entropy alloy, (b) electron diffraction spots of the solid solution structure, and (c) TEM geometric phase analysis; it can be seen from the figure that the electron diffraction spots have linear strip-shaped spots. In the geometric phase analysis diagram, red represents tensile strain and blue represents compressive strain. Both figures indicate that there is a large lattice distortion in the high-entropy metallization layer.

[0067] Figure 2 This is a scanning electron microscope image of the joint of the C / SiC composite material-niobium weld prepared in Example 1. As can be seen from the image, the joint obtained by the method in Example 1 has a good interface, with no cracks at the interface. A uniform solid solution structure is formed in the joint, with no obvious continuous brittle compound phase, resulting in a reliable connection.

[0068] According to the GB / T 22617-2008 test standard, the C / SiC composite material-niobium welded parts prepared in Examples 1 to 3 and the comparative experiment were tested; Figure 3Figures 1 and 2 are joint test data of C / SiC composite material-niobium weldments prepared in Examples 1 to 3 and comparative experiments, (a) room temperature joint strength corresponding to different high entropy layer thicknesses, (b) joint strength of C / SiC composite material-niobium weldment prepared in Example 1 at room temperature and 500°C, (c) joint shear stress-strain curve, 1 is the stress-strain curve of the room temperature joint strength of C / SiC composite material-niobium weldment prepared in the comparative experiment, 2 is the stress-strain curve of the room temperature joint strength of C / SiC composite material-niobium weldment prepared in Example 1, and 3 is the stress-strain curve of the joint strength of C / SiC composite material-niobium weldment prepared in Example 1 at 500°C; it can be seen from the figure that the room temperature shear strength corresponding to the brazing joint in Example 1 is 177 MPa, which is 2.3 times that of the non-metallized ceramic joint (77 MPa) on the surface of the comparative experiment. At the same time, the joint has good high temperature performance, and the shear strength tested at 500°C is 102 MPa, which is suitable for service environment under high temperature conditions. The stress-strain curves of the joint show that without the high-entropy layer, the fracture mode of the joint at room temperature is brittle fracture, with rapid failure and a fracture travel of only 10%. After adding the high-entropy layer, the fracture mode of the joint at room temperature changes to ductile fracture with a fracture travel of 27%. Instead of rapid failure, the joint's mechanical properties slowly degrade, and it exhibits ductile fracture characteristics even at 500°C, indicating that the joint has good serviceability at high temperatures.

Claims

1. A method for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints, characterized in that It is carried out in the following steps:

1. Coating alloy mixture: The FeCoCrNiMo alloy powder and the N-methylpyrrolidone solution of polyvinylidene fluoride are stirred and mixed until they become viscous to obtain an alloy mixture, and the alloy mixture is applied to a surface of the C / SiC composite material perpendicular to the growth direction of the carbon fibers to obtain a C / SiC composite material coated with the mixture; 2. High entropy alloying on the surface of C / SiC composite materials: Under the conditions of a metallization voltage of 25V to 35V and a metallization current of 40A to 60A, the C / SiC composite material coated with the mixed solution is heated for 10s to 20s to form a high entropy alloy layer, and then the high entropy alloy layer is polished and cleaned to obtain a C / SiC composite material having a high entropy alloy layer; 3. Assembly of parts to be welded: Assembling the components in the order of metal niobium, AgCuTi solder sheet, and C / SiC composite material with a high entropy alloy layer from bottom to top, and laminating the high entropy alloy layer of the C / SiC composite material with a high entropy alloy layer to the AgCuTi solder sheet to obtain a component to be welded; 4. Vacuum brazing: The parts to be welded are placed in a vacuum brazing furnace and evacuated. The parts are first kept warm at 100°C to 200°C for 5 to 20 minutes, then kept warm at 800°C to 950°C for 5 to 20 minutes, and finally cooled to room temperature. This completes the method for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-size ceramic-based composite materials and niobium joints.

2. The method of preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints according to claim 1, characterized in that The concentration of the polyvinylidene fluoride N-methylpyrrolidone solution described in step 1 is 0.05 g / L to 0.2 g / L.

3. The method of preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints according to claim 1, characterized in that The mass ratio of FeCoCrNiMo alloy powder to polyvinylidene fluoride in the alloy mixture described in step 1 is (1-10):

1.

4. The method of claim 1 for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints, characterized in that The stirring and mixing in step 1 until the mixture becomes viscous is specifically performed at a rotation speed of 300 rpm to 1000 rpm for 5 min to 20 min.

5. The method of preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints according to claim 1, characterized in that The thickness of the high entropy alloy layer in the C / SiC composite material having the high entropy alloy layer described in step 2 is 50 μm to 300 μm.

6. The method of claim 1 for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints, characterized in that The C / SiC composite material described in step 1 is a pretreated C / SiC composite material, and the pretreatment is specifically performed under a power of 50W to 200W, using ethanol ultrasonic assisted cleaning for 5min to 15min; the polishing and cleaning of the high entropy alloy layer described in step 2 is specifically performed using 3000# sandpaper to polish the surface of the high entropy alloy layer to a thickness of 50μm to 300μm, and then under a power of 50W to 200W, using ethanol ultrasonic assisted cleaning for 5min to 15min.

7. The method of claim 1 for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints, characterized in that The thickness of the AgCuTi solder sheet described in step 3 is 100 μm to 500 μm.

8. The method of claim 1 for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints, characterized in that The niobium metal described in step 3 is pretreated niobium metal, and the pretreatment is specifically to remove the oxide film on the surface of the niobium metal with 180#, 400# and 800# sandpaper in sequence, and then use ethanol ultrasonic assisted cleaning for 5min to 15min at a power of 50W to 200W; the AgCuTi solder sheet described in step 3 is a pretreated AgCuTi solder sheet, and the pretreatment is specifically carried out according to the following steps: use 500# sandpaper to polish the AgCuTi solder sheet to remove surface oxide, and then use ethanol ultrasonic assisted cleaning for 5min to 15min at a power of 50W to 200W.

9. The method of claim 1 for preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints, characterized in that In step 4, vacuum the sample to 1×10 -4 Pa~1×10 -5 Pa.

10. The method of preparing a surface high entropy metallization layer based on Joule thermal shock to assist in brazing large-scale ceramic matrix composite and niobium joints according to claim 1, characterized in that In step 4, the temperature is increased to 100°C to 200°C at a heating rate of 5°C / min to 10°C / min, and kept at 100°C to 200°C for 5min to 20min, then the temperature is increased to 800°C to 950°C at a heating rate of 5°C / min to 10°C / min, and kept at 800°C to 950°C for 5min to 20min, and finally cooled to room temperature at a cooling rate of 5°C / min to 10°C / min.

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