Brazing method for modified porous SiC ceramic and 2507 duplex stainless steel

Abstract

The invention provides a brazing method for modified porous SiC ceramic and 2507 duplex stainless steel, and belongs to the technical field of welding. The brazing method comprises the following steps that silicon carbide suspension slurry is prepared; adhering the silicon carbide suspension slurry to the surface of the porous SiC ceramic, drying, discharging glue, and sintering to obtain the modified porous SiC ceramic; and after the surface of the pretreated porous SiC ceramic is polished, 2507 duplex stainless steel, the high-entropy alloy brazing filler metal and the modified porous SiC ceramic are stacked from top to bottom, vacuum brazing is carried out, and natural cooling is carried out at the room temperature after the reaction is finished. According to the method, the porous SiC ceramic surface with poor welding performance is subjected to densification modification treatment, the high-entropy alloy brazing filler metal is good in fluidity and can be well combined with the densified surface layer, the residual stress of the porous ceramic and a metal reaction layer is reduced, and the porous ceramic and metal can form the compact reaction layer with a stable structure under the action of the brazing filler metal.

Description

Technical Field

[0001] This invention relates to the field of welding technology, specifically to a brazing method for modified porous SiC ceramics and 2507 duplex stainless steel. Background Technology

[0002] As the preparation process of porous silicon carbide (SiC) materials in membrane separation technology becomes increasingly mature, its application potential under harsh conditions is gradually becoming apparent, especially in two core scenarios: water treatment (such as high-salinity wastewater and industrial wastewater containing heavy metals) and wet phosphoric acid purification. In these cases, the process systems often exhibit extremely complex operating characteristics: on the one hand, the wet phosphoric acid system contains P2O5, accompanied by high concentrations of Cl... - F - Corrosive ions may be present in water treatment scenarios, along with acidic / alkaline wastewater and suspended particles. On the other hand, some processes require operation at high operating temperatures of 150~200℃, and the high solid content in the system (such as sulfur gypsum crystals in phosphoric acid and colloidal impurities in wastewater) can easily lead to interfacial scaling.

[0003] In such extreme environments, traditional membrane separation materials (such as organic polymer membranes and ordinary alumina ceramic membranes) and their metal structural components (such as 316L stainless steel) face significant performance bottlenecks: organic membranes are prone to swelling or degradation due to high temperatures and strong corrosion, ordinary ceramic membranes lack sufficient impact resistance, and metal structural components are easily corroded by ions, leading to surface corrosion. These problems not only cause membrane pore blockage but also accelerate the failure of membrane materials and components, shortening the service life of equipment and restricting the large-scale application of membrane separation technology in high-end chemical fields. Therefore, membrane separation equipment designed for harsh environments must simultaneously meet core requirements such as higher structural strength (resistance to high pressure and impact), better corrosion resistance (resistance to acid, alkali, and ion erosion), and more stable separation performance (avoiding pore blockage or structural damage).

[0004] In current material systems, porous SiC ceramics and 2507 duplex stainless steel are two outstanding candidate materials, but both have significant limitations when used alone or in combination. Porous SiC ceramics, due to their covalent crystal structure, possess excellent resistance to acid and alkali corrosion (withstanding concentrated phosphoric acid corrosion below 90℃) and impact resistance, and their high-temperature stability is significantly better than organic films and ordinary ceramic films. 2507 duplex stainless steel, as a high-performance alloy containing 25% Cr, 7% Ni, and 4% Mo, combines the good toughness of austenitic stainless steel with the high strength of ferritic stainless steel, achieving a room temperature tensile strength of over 800 MPa, and exhibiting good resistance to Cl. - F -It exhibits excellent resistance to corrosive ions. In industries such as heavy metal industrial wastewater treatment and wet phosphoric acid purification, 2507 duplex stainless steel has become the preferred material for core equipment such as storage tanks, pipelines, and reactors, and can achieve stable service for 3 to 5 years.

[0005] However, the synergistic application of porous SiC ceramics and 2507 duplex stainless steel has long been limited by the difficulty in achieving a reliable connection between the two: on the one hand, porous SiC ceramics are typical inorganic non-metallic materials with low surface energy, strong chemical inertness, and extremely poor wettability with metals; on the other hand, the two have significantly different coefficients of thermal expansion (SiC is approximately 4.5 × 10⁻⁶). -6 / ℃, 2507 duplex stainless steel is approximately 13×10 -6 (℃), traditional welding or bonding processes are prone to generating huge internal stress at the joint, leading to cracking or sealing failure, and failing to form a composite structure that combines strength and corrosion resistance. Ultimately, this limits the synergistic effect of SiC's corrosion-resistant separation performance and duplex stainless steel's high-strength support performance. Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides a brazing method for modified porous SiC ceramics and 2507 duplex stainless steel, aiming to solve the technical problem that it is difficult to achieve a reliable connection between porous SiC ceramics and 2507 duplex stainless steel.

[0007] In a first aspect, embodiments of this application provide a brazing method for modified porous SiC ceramics and 2507 duplex stainless steel, comprising the following steps: S1. Preparation of silicon carbide suspension slurry; S2. Silicon carbide suspension slurry is attached to the surface of porous SiC ceramic, dried and debinded, and then sintered to obtain modified porous SiC ceramic. S3. After grinding the surface of the pretreated porous SiC ceramic, stack 2507 duplex stainless steel, high-entropy alloy brazing filler metal and modified porous SiC ceramic from top to bottom, and perform vacuum brazing. After the reaction is completed, allow it to cool naturally at room temperature.

[0008] The advantages of this application, which differ from existing technical solutions, include: 1. A significant advantage of this invention is that it densifies the surface of porous SiC ceramics with poor welding performance. The high-entropy alloy brazing filler metal has good fluidity and can form a good bond with the densified surface layer, reducing the residual stress in the reaction layer between the porous ceramic and the metal. This allows the porous ceramic and the metal to form a stable and dense reaction layer under the action of the brazing filler metal. Simultaneously, a 90-day corrosion resistance test was conducted on the welded parts. In a static phosphoric acid medium with a concentration of 29% and a temperature of 45°C, the corrosion rate of the high-entropy alloy was 0.073 mm / a, with no localized corrosion, demonstrating excellent resistance to phosphoric acid corrosion. The joint showed good gloss and no obvious corrosion products, meeting the requirements of chemical equipment operating conditions.

[0009] 2. Characterization tests were performed on the welded joint. SEM showed that the vacuum brazed joint was intact, and the brazing filler metal and the substrate were completely separated. The high-entropy brazing filler metal penetrated into the porous ceramic matrix through ultrasonic cavitation and capillary filling and reacted with stainless steel. The penetration layer was uniform in width. XRD results showed that there was a ZrC / TiC reaction layer on the ceramic side, with Zr and Ti elements distributed on both sides of the penetration layer. The product formed was the reaction product of SiC with the active elements Zr and Ti.

[0010] 3. This invention replaces the mechanical connection of core components in traditional skid-mounted equipment by brazing porous SiC ceramics to 2507 stainless steel. It fully leverages the corrosion resistance of SiC ceramics and the high strength and good processing performance of metals. The porous SiC surface is densified to improve its welding strength. Simultaneously, the high strength, good corrosion resistance, and excellent flowability of the high-entropy alloy brazing filler metal ensure the mechanical integrity and functionality of the SiC porous structure during vacuum brazing. This results in membrane separation equipment capable of stable operation in harsh chemical environments, improving the reliability and efficiency of the separation process, meeting industry requirements for the structural strength of membrane separation equipment, and ensuring long-term stable operation under complex conditions.

[0011] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0013] Figure 1 This is a schematic diagram of the brazing structure of the present invention.

[0014] Figure 2 This is a SEM scan image of the brazed joint in Embodiment 1 of the present invention.

[0015] Figure 3 This is a diagram showing the shear strength test results in Embodiment 1 of the present invention.

[0016] Figure 4 This is a layered diagram of the brazed joint in Embodiment 1 of the present invention.

[0017] Figure 5 This is the energy spectrum of the brazed joint in Embodiment 1 of the present invention.

[0018] Figure 6 This is an XRD scan of the brazed joint in Comparative Example 3 of the present invention. Detailed Implementation

[0019] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0021] The synergistic application of porous SiC ceramics and 2507 duplex stainless steel has long been limited by the difficulty in achieving a reliable connection between the two: on the one hand, porous SiC ceramics are typical inorganic non-metallic materials with low surface energy, strong chemical inertness, and extremely poor wettability with metals; on the other hand, the two have significantly different coefficients of thermal expansion (SiC is approximately 4.5 × 10⁻⁶). -6 / ℃, 2507 duplex stainless steel is approximately 13×10 -6 (℃), traditional welding or bonding processes are prone to generating huge internal stress at the joint, leading to cracking or sealing failure, and failing to form a composite structure that combines strength and corrosion resistance. Ultimately, this limits the synergistic effect of SiC's corrosion-resistant separation performance and duplex stainless steel's high-strength support performance.

[0022] To address the technical problem of achieving a reliable connection between porous SiC ceramics and 2507 duplex stainless steel, this application provides a brazing method for modified porous SiC ceramics and 2507 duplex stainless steel. This invention densifies the surface of porous SiC ceramics with poor welding performance. The high-entropy alloy brazing filler metal has good fluidity and can form a good bond with the densified surface layer, reducing the residual stress in the reaction layer between the porous ceramics and the metal. This allows the porous ceramics and the metal to form a stable and dense reaction layer under the action of the brazing filler metal.

[0023] like Figure 1 As shown, in a first aspect, embodiments of this application provide a brazing method for modifying porous SiC ceramics to 2507 duplex stainless steel, comprising the following steps: S1. Preparation of silicon carbide suspension slurry; S2. Silicon carbide suspension slurry is attached to the surface of porous SiC ceramic, dried and debinded, and then sintered to obtain modified porous SiC ceramic. S3. After grinding the surface of the pretreated porous SiC ceramic, stack 2507 duplex stainless steel, high-entropy alloy brazing filler metal and modified porous SiC ceramic from top to bottom, and perform vacuum brazing. After the reaction is completed, allow it to cool naturally at room temperature.

[0024] In the technical solution of this application embodiment, silicon carbide suspension slurry is used to modify the surface of porous SiC ceramic to form a dense surface layer. High entropy alloy solder can better wet the modified porous SiC ceramic surface, with a measured wetting angle of less than 15°, so that the high entropy alloy solder can form a good bond with the dense surface layer of the porous SiC ceramic.

[0025] Furthermore, in some embodiments, the method for preparing the silicon carbide suspension slurry in step S1 includes the following steps: S11. Disperse polycarbosilane powder in the first solvent to obtain a polycarbosilane solution; S12. Add silicon carbide powder to the polycarbosilane solution, heat and stir until the hexane is completely volatilized, dry and grind into powder to obtain a mixed powder. S13. Disperse the mixed powder, binder and dispersant in the second solvent to obtain silicon carbide suspension slurry.

[0026] In the technical solution of this application embodiment, silicon carbide powder is used as the basic C / Si source. The finer silicon carbide powder can be better embedded in the porous SiC ceramic surface to achieve dense sintering. Polycarbosilane powder, as a supplementary silicon source, can fully react with the incompletely reacted carbon source, ensuring the structural integrity of silicon carbide, repairing compositional defects, and reducing the sintering temperature. Furthermore, the SiC phase grains generated by the pyrolysis of polycarbosilane are finer, which can improve the hardness, fracture toughness, and flexural strength of the material.

[0027] Furthermore, in some embodiments, the mass fraction of polycarbosilane powder in the polycarbosilane solution is 30% to 35%.

[0028] Furthermore, in some embodiments, the mass ratio of silicon carbide powder to polycarbosilane powder is 1:1.

[0029] Furthermore, in some embodiments, the mass ratio of the mixed powder, binder, dispersant, and second solvent is 100:(5~10):(2~5):150.

[0030] Furthermore, in some embodiments, the particle size of the silicon carbide powder is 1~3μm.

[0031] Furthermore, in some embodiments, the first solvent is n-hexane.

[0032] Furthermore, in some embodiments, the adhesive is polyethylene glycol.

[0033] Furthermore, in some embodiments, the dispersant is carboxymethyl cellulose.

[0034] Furthermore, in some embodiments, the second solvent is anhydrous ethanol.

[0035] Furthermore, in some embodiments, the dispersion conditions in step S13 are: planetary ball mill speed of 150~200 r / min, and mixing time of 4 h.

[0036] Furthermore, in some embodiments, the viscosity of the silicon carbide suspension slurry is 3000–3500 mPa·s.

[0037] Furthermore, in some embodiments, step S2, which involves attaching the silicon carbide suspension slurry to the porous SiC ceramic surface, specifically includes the following steps: After immersing the porous SiC ceramic in a silicon carbide suspension for 30-60 minutes, remove it and coat the porous SiC ceramic surface with the silicon carbide suspension under negative pressure conditions. The negative pressure is 0.01-0.1 MPa and the negative pressure time is 10-15 minutes. Repeat the coating 3-5 times.

[0038] In the technical solution of this application embodiment, a negative pressure is set below the porous SiC ceramic, which can be used to make the surface of the porous SiC ceramic fully adsorb silicon carbide suspension.

[0039] Furthermore, in some embodiments, the sintering conditions in step S2 are as follows: sintering in an argon atmosphere, sintering temperature of 1800℃, and heating rate as follows: The temperature was increased from room temperature to 1600℃ at a rate of 15℃ / min, and held for 30min. The temperature was increased from 1600℃ to 1800℃ at a rate of 10℃ / min, and held for 2 hours. Modified porous SiC ceramics were obtained after natural cooling at room temperature.

[0040] Furthermore, in some embodiments, the high-entropy alloy solder comprises, by mass percentage, 52%–60% Ti, 11%–14% Zr, 21%–24% Cu, and 8%–10% Ni.

[0041] In the technical solution of this application embodiment, the high-entropy alloy brazing filler metal of the present invention can achieve CTE gradient transition (mainly generating FCC / BCC solid solution phases such as ZrC and TiC), which can alleviate thermal stress between dissimilar materials; at the same time, the disordered atomic arrangement of the amorphous state avoids stress concentration at the grain boundaries, and can form a dense structure without voids / cracks in the welded joint to a certain extent, thereby reducing the residual stress of the porous ceramic and metal reaction layer.

[0042] Furthermore, in some embodiments, the conditions for vacuum brazing are: 8. Vacuum degree not less than 2 × 10⁻⁶. -3 When Pa, heat to 800℃ at a rate of 8-10℃ / min, hold for 20min, then continue heating at a rate of 4-5℃ / min to brazing temperature of 1000-1050℃, hold for 10-20min, and finally cool to room temperature with the furnace.

[0043] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0044] I. Preparation Method Example 1 Step 1: Prepare a 35% (v / v) polycarbosilane powder solution using n-hexane solution. Heat in a water bath until the polycarbosilane dissolves. Add an equal proportion of silicon carbide powder (1 μm particle size) to the prepared polycarbosilane solution. Continue heating and stirring until completely dissolved, then dry until the solvent completely evaporates. After drying, grind into powder. Add an appropriate amount of anhydrous ethanol, binder PEG, and dispersant CMC. The mass ratio of silicon carbide powder, binder, dispersant, and solvent is 100:5:4:150. Mix in a planetary ball mill at 150 rpm for 4 hours to obtain a stable suspension slurry with a final viscosity range of 3250 mPa•s. Immerse a porous silicon carbide substrate in the suspension for 30 minutes, then repeatedly coat the porous silicon carbide substrate with the suspension under negative pressure at a pressure of 0.1 MPa.

[0045] Step 2: The prepared sample was sintered in an argon atmosphere at a temperature of 1800℃. The temperature was increased to 1600℃ at a rate of 15℃ / min and held for 30 min. The temperature was then increased to 1800℃ at a rate of 10℃ / min and held for 2 hours. The sample was then cooled with the furnace temperature to obtain surface-modified porous SiC ceramic. Step 3: Cut 10mm × 10mm high-entropy alloy brazing filler metal (composition: Ti 55.5%, Zr 12.5%, Cu 23%, Ni 9%). Place the prepared substrate and brazing filler metal in a crucible and put it into a vacuum brazing furnace with a vacuum degree of 2 × 10⁻⁶. -3 MPa, first heat up to 800℃ at 8℃ / min and hold for 20min, then heat up to 1000℃ at 4℃ / min and hold for 15min, then begin vacuum brazing and allow to cool naturally to room temperature to obtain the sample.

[0046] SEM scanning was performed on the brazed joint of Example 1 to obtain... Figure 2 ,from Figure 2 It can be seen that the brazed joint is well formed, the joint is completely welded, and the penetration layer width is uniform.

[0047] Shear strength tests were performed on the brazed joints of Example 1, and the results are shown below. Figure 3 ,from Figure 3 It can be seen that the shear strength at the brazed joint of Example 1 is 12.19 MPa, indicating that the welding performance of the method of the present invention is good.

[0048] EDS scanning was performed on the brazed joint of Example 1, such as... Figures 4-5 As shown, EDS results indicate that the solder layer exhibits a Ti-rich phase with overlapping Zr / Cu / Ni elements, forming (Zr,Ti)(Ni,Cu) compounds. The formation is primarily a product of the reaction between SiC and the active elements Zr and Ti. The active material in the solder layer is uniformly distributed and combines with the porous ceramic to form stable compounds. The interdiffusion and reaction of elements eliminate the interface boundary between the solder and stainless steel, achieving a metallurgical bond between them (e.g., Ti₂Si / Zr₂Si, NiSi₂, and small amounts of TiC and ZrC).

[0049] Example 2 Step 1: Prepare a 35% (v / v) polycarbosilane powder solution using n-hexane solution. Heat in a water bath until the polycarbosilane dissolves. Add an equal proportion of silicon carbide powder (1 μm particle size) to the prepared polycarbosilane solution. Continue heating and stirring until completely dissolved, then dry until the solvent completely evaporates. After drying, grind into powder. Add an appropriate amount of anhydrous ethanol, along with PEG binder and CMC dispersant. The mass ratio of silicon carbide powder, binder, dispersant, and solvent is 100:10:5:150. Mix in a planetary ball mill at 200 rpm for 4 hours to obtain a stable suspension slurry with a final viscosity range of 3250 mPa•s. Immerse a porous silicon carbide substrate in the suspension for 60 minutes, then repeatedly coat the porous silicon carbide substrate with the suspension under negative pressure at 0.01 MPa.

[0050] Step 2: The prepared sample was sintered in an argon atmosphere at a temperature of 1800℃. The temperature was increased to 1600℃ at a rate of 15℃ / min and held for 30 min. The temperature was then increased to 1800℃ at a rate of 10℃ / min and held for 2 hours. The sample was then cooled with the furnace temperature to obtain surface-modified porous SiC ceramic. Step 3: Cut 10mm × 10mm high-entropy alloy brazing filler metal (composition: Ti 52%, Zr 14%, Cu 24%, Ni 10%). Place the prepared substrate and brazing filler metal in a crucible and put it into a vacuum brazing furnace with a vacuum degree of 5 × 10⁻⁶. -3 MPa, first heat up to 800℃ at 8℃ / min and hold for 20min, then heat up to 1000℃ at 4℃ / min and hold for 20min, then begin vacuum brazing and allow to cool naturally to room temperature to obtain the sample.

[0051] Example 2 shows that the brazed joint is well formed, the joint is completely welded, and the penetration layer width is uniform.

[0052] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that polycarbosilane is replaced with ordinary silicon powder, and the amount added is less than 2%. The silicon carbide suspension is prepared according to the above ratio, while other processes remain unchanged.

[0053] The final measured shear strength of Comparative Example 1 was 7.04 MPa, which was significantly lower than that of Example 1. This indicates that the SiC phase grains generated by the pyrolysis of polycarbosilane are finer, which can improve the hardness, fracture toughness and bending strength of the material.

[0054] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the Ti content in the high-entropy alloy solder is increased, the Ti content in the active solder is decreased, and the Zr content is increased (component content: Ti 37.68%, Zr 36.79%, Cu 14.78%, Ni 10.75%), while other conditions remain unchanged.

[0055] In Comparative Example 2, the brazed joint showed complete surface bonding. XRD test results indicated that excess Zr might generate Zr. x C y The phase is brittle and requires control and optimization of brazing temperature and holding time. The measured shear strength is 10.86 MPa.

[0056] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the first step was omitted, and the porous SiC ceramic surface was not modified. The specific steps are as follows: Step 1: The prepared sample was sintered in an argon atmosphere at a temperature of 1800℃. The temperature was increased to 1600℃ at a rate of 15℃ / min and held for 30 min. The temperature was then increased to 1800℃ at a rate of 10℃ / min and held for 2 hours. The sample was then cooled with the furnace temperature to obtain surface-modified porous SiC ceramic. Step 2: Cut 10mm × 10mm high-entropy alloy brazing filler metal (composition: Ti 55.5%, Zr 12.5%, Cu 23%, Ni 9%). Place the prepared substrate and brazing filler metal in a crucible and put it into a vacuum brazing furnace with a vacuum degree of 2 × 10⁻⁶. -3 MPa, first heat up to 800℃ at 8℃ / min and hold for 20min, then heat up to 1000℃ at 4℃ / min and hold for 15min, then begin vacuum brazing and allow to cool naturally to room temperature to obtain the sample.

[0057] XRD detection of Comparative Example 3 is shown in [reference]. Figure 6 ,from Figure 6 As can be seen, no stable compounds formed by Zr, Ti and Si were detected on the surface of the solder and the modified porous SiC ceramic. There were brittle phases formed by the solder and stainless steel metal (such as TiC / ZrC). The measured shear strength was less than 5 MPa, which was significantly lower than that of Example 1. This indicates that the bonding ability between the porous SiC ceramic without surface densification modification and the high-entropy alloy solder is weak.

[0058] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the holding time during the third step of vacuum brazing was 1000℃ for 5 minutes. The shear strength at the brazed joint in Comparative Example 4 was lower than that in Example 1. The reduced brazing holding time meant that the brazing filler metal did not react sufficiently with the Si in the porous ceramic, resulting in a decrease in strength.

[0059] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the holding time during the third step of vacuum brazing was 1000℃ for 30 minutes. The shear strength at the brazed joint in Comparative Example 5 was lower than that in Example 1. Extending the holding time caused excessive reaction between C and Si in the ceramic and the active elements, resulting in the formation of brittle substances (TiC / ZrC and Si-like compounds), which led to changes in strength.

[0060] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A brazing method for modified porous SiC ceramic and 2507 duplex stainless steel, characterized in that, Includes the following steps: S1. Preparation of silicon carbide suspension slurry; S2. The silicon carbide suspension slurry is attached to the surface of porous SiC ceramic, dried and debinded, and then sintered to obtain modified porous SiC ceramic. S3. After polishing the surface of the pretreated porous SiC ceramic, stack 2507 duplex stainless steel, high-entropy alloy brazing filler metal and modified porous SiC ceramic from top to bottom, perform vacuum brazing, and allow it to cool naturally at room temperature after the reaction is complete.

2. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 1, characterized in that, The preparation method of the silicon carbide suspension slurry in step S1 includes the following steps: S11. Disperse polycarbosilane powder in the first solvent to obtain a polycarbosilane solution; S12. Add silicon carbide powder to the polycarbosilane solution, heat and stir until the n-hexane is completely volatilized, dry and grind into powder to obtain mixed powder; S13. The mixed powder, binder and dispersant are dispersed in a second solvent to obtain a silicon carbide suspension slurry.

3. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 2, characterized in that, The mass fraction of polycarbosilane powder in the polycarbosilane solution is 30%~35%; The mass ratio of silicon carbide powder to polycarbosilane powder is 1:1; The mass ratio of the mixed powder, binder, dispersant and second solvent is 100:(5~10):(2~5):

150.

4. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 2, characterized in that, The particle size of the silicon carbide powder is 1~3μm.

5. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 2, characterized in that, The first solvent is n-hexane; The adhesive is polyethylene glycol; The dispersant is carboxymethyl cellulose; The second solvent is anhydrous ethanol.

6. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 2, characterized in that, The dispersion conditions in step S13 are: planetary ball mill speed of 150~200 r / min, mixing time of 4 h; The viscosity of the silicon carbide suspension slurry is 3000-3500 mPa·s.

7. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 1, characterized in that, Step S2 involves attaching the silicon carbide suspension slurry to the porous SiC ceramic surface, specifically including the following steps: After immersing the porous SiC ceramic in a silicon carbide suspension for 30-60 minutes, remove it and coat the porous SiC ceramic surface with the silicon carbide suspension under negative pressure conditions. The negative pressure is 0.01-0.1 MPa and the negative pressure time is 10-15 minutes. Repeat the coating 3-5 times.

8. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 1, characterized in that, The sintering conditions in step S2 are as follows: sintering in an argon atmosphere, sintering temperature of 1800℃, and heating rate as follows: The temperature was increased from room temperature to 1600℃ at a rate of 15℃ / min, and held for 30min. The temperature was increased from 1600℃ to 1800℃ at a rate of 10℃ / min, and held for 2 hours. Modified porous SiC ceramics were obtained after natural cooling at room temperature.

9. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 1, characterized in that, The high-entropy alloy brazing filler metal comprises, by mass percentage, 52%–60% Ti, 11%–14% Zr, 21%–24% Cu, and 8%–10% Ni.

10. The brazing method for modified porous SiC ceramic and 2507 duplex stainless steel according to claim 1, characterized in that, The conditions for vacuum brazing are: a vacuum degree of not less than 2 × 10⁻⁶. -3 When Pa, heat to 800℃ at a rate of 8-10℃ / min, hold for 20min, then continue heating at a rate of 4-5℃ / min to brazing temperature of 1000-1050℃, hold for 10-20min, and finally cool to room temperature with the furnace.

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