Nanoporous carbon-coated SiC whisker-modified AgCuTi solder, its preparation method and application

Abstract

This invention discloses a nanoporous carbon-coated SiC whisker-modified AgCuTi solder, its preparation method, and its application, belonging to the field of brazing technology. The method disclosed in this invention first involves nanoporous carbon coating of SiC whiskers, then combining them with AgCuTi to form a composite solder. The spatial distribution around the SiC whiskers is optimized by the porous carbon coating. The dispersed polymorphic nucleation sites of the porous carbon make multi-point contact with the solder during the brazing reaction, resulting in a discontinuous distribution of the brittle Ti-Cu phase around the whiskers and inhibiting its growth, ultimately refining the brittle phase in the solder layer. Simultaneously, the porous carbon coating prevents excessive reaction between the solder and SiC whiskers at the brazing temperature, reducing the loss of the SiC nanophase by the solder and maximizing the mechanical properties of the nano-reinforcing phase, thus increasing the shear strength of the joint.

Description

Technical Field

[0001] This invention belongs to the field of brazing technology, specifically relating to a nanoporous carbon-coated SiC whisker-modified AgCuTi brazing filler metal, its preparation method, and its application. Background Technology

[0002] AgCuTi brazing filler metal is currently one of the most widely used active brazing filler metals. Because the active element Ti can react with most ceramics and C / C composites, achieving a wetting effect on the base material surface, AgCuTi active brazing filler metal is widely used for brazing connections between dissimilar materials such as metals, ceramics, and C / C composites. However, the significant difference in the coefficient of thermal expansion (CTE) between AgCuTi brazing filler metal and C / C and ceramics leads to high residual thermal stress at the joint. To further eliminate the influence of thermal stress, many related studies in recent years have shown that adding a ductile metal interlayer or incorporating a low-CTE reinforcing phase into the brazing filler metal can mitigate the negative impact of thermal stress on the joint and improve its performance.

[0003] Reference 1, “In-Situ synthesized TiC nano-flakes reinforced C / C composite-Nbbrazed joint[J]. Journal of the European Ceramic Society, 2018, 38(4): 1059-1068,” utilizes a polymer carbonization process to obtain a carbon-coated Cu foam composite interlayer, which is then assembled with AgCuTi foil to achieve brazing of the C / C composite and Nb. The carbon layer coated on the Cu foam reacts with Ti, forming uniformly distributed in-situ TiC nanosheets in the joint seam. However, current research on carbon-based reinforced metal foam materials (Reference 2, A novel in-situforming 3D core-sheath interlayer designed to strengthen C…) fThe study of C / C composite-Nbjoints during brazing [J]. Materials Characterization, 2024, 208: 113661) indicates that the large difference in CTE between the carbon and metal foam matrix leads to unstable mechanical properties of the network structure, reducing the strain regulation capability of the complete mesh structure. Another commonly used method is to add micro- and nano-scale reinforcing phases to the brazing alloy. For example, micron-scale SiC particles are added to AgCuTi brazing alloy, and the effect of the volume percentage of reinforcing particles on the microstructure of the brazed joint is studied (Reference 3 “Joining of C / C composite to TC4 using SiC particle-reinforced brazing alloy [J] Materials Characterization, 2010, 61(6): 635-639”). The results show that adding SiC particles can reduce the coefficient of thermal expansion of the brazing alloy, thereby reducing the residual stress of the C / C-metal joint. However, a large number of SiC particles (vol.% ~35 vol.%) excessively consume Ti elements in the brazing alloy, agglomerate, and form defects such as pores. By adding graphene nanoplatelets (GNPs) to AgCuTi solder to braze SiC ceramics (Reference 4 "Graphene nanoplatelets reinforced AgCuTi composite filler for brazing SiCceramic[J] Journal of the European Ceramic Society, 2019, 39: 696–704."), TiC particles synthesized by in-situ reaction of Ti and GNPs promote heterogeneous nucleation of TiCu and Cu(s,s). However, the reinforcing phase GNPs reacts extensively with Ti, weakening its reinforcing effect and resulting in a joint shear strength of only 38 MPa.

[0004] Micro- and nano-scale reinforcing phases (micro- and nano-ceramic particles, nano-carbon, etc.) are widely used in the modification of AgCuTi solders. However, most reinforcing phases react with the active Ti element in the solder at the soldering temperature, making it difficult to fully exert their reinforcing effect. Excessive consumption of Ti element reduces the thickness of the reaction layer with the base material. Precursor carbonization or carbon coating can reduce the reactivity of the reinforcing phase with the solder, but the resulting cyclic carbon layer structure easily forms aggregated brittle products after soldering. Furthermore, the influence range of the reinforcing phase and carbon layer is limited, making it difficult to suppress the formation of large-sized brittle phases in the solder layer over a larger space. Therefore, how to reduce the distribution of large-sized brittle phases inside the weld while effectively avoiding excessive reaction between the nano-reinforcing phase and the active solder at the soldering temperature is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a nanoporous carbon-coated SiC whisker-modified AgCuTi solder, its preparation method, and its application, in order to solve the technical problem that the nano-reinforcing phase used in existing nanocomposite AgCuTi solder modification methods is prone to excessive reaction with the active solder.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention discloses a method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder, comprising the following steps:

[0008] SiC whiskers were subjected to chemical vapor deposition to obtain nanoporous carbon-coated SiC whiskers.

[0009] After mixing nanoporous carbon-coated SiC whiskers and AgCuTi powder, the mixture was added to a solvent and stirred. The powder was collected and ground to obtain nanoporous carbon-coated SiC whisker-modified AgCuTi solder.

[0010] Furthermore, the chemical vapor deposition process uses methanol as a precursor and deposits at 1140~1170℃ for 2-4 hours.

[0011] Furthermore, the ratio of the amount of the nanoporous carbon-coated SiC whiskers, AgCuTi powder and solvent is (0.0125g-0.05)g:(4.9875-4.975)g:30mL.

[0012] Furthermore, the solvent is ethanol;

[0013] The stirring is magnetic stirring; the temperature of the magnetic stirring is 75~85℃.

[0014] Furthermore, the grinding time is 30-60 minutes.

[0015] The present invention also discloses the nanoporous carbon-coated SiC whisker modified AgCuTi solder prepared by the above preparation method.

[0016] The present invention also discloses the application of the above-mentioned nanoporous carbon-coated SiC whisker modified AgCuTi solder, specifically its application in brazing C / C-Cu joints.

[0017] Furthermore, when the nanoporous carbon-coated SiC whisker-modified AgCuTi solder is used in brazing C / C-Cu joints, the following steps are included:

[0018] A mixed slurry was obtained by mixing nanoporous carbon-coated SiC whisker-modified AgCuTi solder with a binder.

[0019] C / C and Cu are pretreated, then a mixed slurry is applied to the surfaces of C / C and Cu to be joined, and then they are bonded together to form a sandwich-type prefabricated structure.

[0020] The obtained sandwich-type prefabricated structure is sintered to finally obtain a C / C-Cu joint.

[0021] Furthermore, the ratio of SiC whiskers, AgCuTi powder, and binder is (4~6g)g~(0.4~0.6)g:0.50g;

[0022] The adhesive is prepared by mixing petrolatum and liquid paraffin in a mass ratio of 1:1, heating in an oil bath at 75-85°C for 30-40 minutes, and then air-cooling to room temperature.

[0023] The pretreatment process includes polishing, cleaning, and drying in sequence.

[0024] Furthermore, the process parameters for the sintering treatment are as follows: brazing temperature is 860℃, brazing time is 10 min, and furnace vacuum degree is 6.0 × 10⁻⁶. -3 Pa-8.0×10 -3 Pa, heating rate is 6-8℃ / min, cooling rate is 4-6℃ / min.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention discloses a method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder. First, SiC whiskers are treated with nanoporous carbon coating, and then combined with AgCuTi to form a composite solder. The spatial distribution around the SiC whiskers is optimized by the porous carbon coating. The dispersed polynucleation sites of the porous carbon make multi-point contact with the solder during the brazing reaction, resulting in a discontinuous distribution of the brittle Ti-Cu phase around the whiskers and inhibiting its growth, ultimately refining the brittle phase. Simultaneously, the porous carbon coating on the whisker surface avoids direct contact between the SiC whiskers and the active solder, mitigating excessive reactions between them, reducing the solder's damage to the SiC nanophase, maximizing the mechanical properties of the reinforcing phase, and increasing the shear strength of the joint.

[0027] This invention also discloses the application of nanoporous carbon-coated SiC whisker modified AgCuTi brazing filler metal prepared by the above preparation method in brazing C / C-Cu joints. The pre-coated porous carbon grows upright around the SiC whiskers, forming a porous thin-layer spatial structure. The porous carbon-coated SiC whiskers and AgCuTi are mixed in a certain proportion to prepare a composite brazing filler metal. According to relevant experimental results, the strength of the prepared C / C-Cu joint increases from 31.5 MPa to 37.1-53.0 MPa compared with the untreated AgCuTi composite brazing filler metal. Attached Figure Description

[0028] Figure 1 The images show the microstructure of the nanoporous carbon-coated SiC whiskers prepared in Comparative Examples 2, 3 and 2 of this invention, as well as the microstructure of the composite solder in Comparative Example 2.

[0029] Wherein: a1-a3 are the microscopic morphology images of SiC whiskers, pyrolytic carbon-coated SiC whiskers, and nanoporous carbon-coated SiC whiskers used in the composite solders prepared in Comparative Examples 2, 3, and 2, respectively; b-a high-magnification TEM image of the porous carbon-coated nanowhiskers prepared in Example 2 of this invention; c-a microscopic morphology image of the composite solder in Comparative Example 2.

[0030] Figure 2 Backscattered electron microstructure images and magnified images of C / C-Cu junctions prepared in Examples 2 and 4 of this invention;

[0031] Wherein: a is the overall morphology of the C / C-Cu joint brazed seam prepared in Example 2 of the present invention; b is a locally magnified morphology of the intermediate layer of the C / C-Cu joint brazed seam prepared in Example 2 of the present invention; c is the overall morphology of the C / C-Cu joint brazed seam prepared in Example 4 of the present invention; d is a locally magnified morphology of the intermediate layer of the C / C-Cu joint brazed seam prepared in Example 4 of the present invention;

[0032] Figure 3 The bar chart shows the room temperature average shear strength of C / C-Cu joints prepared in Examples 1, 2, 3, and 4 of this invention.

[0033] Figure 4 The thermal expansion coefficient of the composite brazing filler metals prepared in Example 2 and Comparative Examples 1, 2 and 3 varies with temperature.

[0034] Figure 5 These are microscopic images of the brazed seams of C / C-Cu joints prepared in Comparative Examples 1, 2, and 3 of this invention, and a partially enlarged image of Comparative Example 3.

[0035] Figure 6 The bar chart shows the room temperature average shear strength of C / C-Cu joints prepared in Comparative Examples 1, 2, 3 and 2 of this invention. Detailed Implementation

[0036] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0037] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0038] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0039] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0040] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0041] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0042] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0043] Example 1

[0044] A method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder includes the following steps:

[0045] Step 1: Place SiC whisker powder in a chemical vapor deposition furnace, use methanol as a precursor, and perform chemical vapor deposition at 1170℃ for 4 h to obtain nanoporous carbon-coated SiC whiskers.

[0046] Step 2: Using an analytical balance, 0.0125g of nanoporous carbon-coated SiC whiskers and 4.9875g of AgCuTi powder were mixed. Then, the mixture was placed in a 50mL beaker with 30mL of anhydrous ethanol and stirred evenly on a magnetic stirrer at 75℃ until the anhydrous ethanol evaporated. The powder was collected and ground in a mortar for 30min until the powder color was uniform and there was no obvious layering. Finally, a nanoporous carbon-coated SiC whisker-modified AgCuTi solder with a SiC mass fraction of 0.25wt.% was obtained.

[0047] The obtained nanoporous carbon-coated SiC whisker-modified AgCuTi solder was applied to brazing C / C-Cu joints:

[0048] Step 3: Add 0.5g of liquid paraffin and petrolatum in a 1:1 mass ratio to 5g of nanoporous carbon-coated SiC whisker-modified AgCuTi solder, and mix thoroughly to obtain a mixed slurry;

[0049] Step 4: Cut C / C and Cu into small pieces of 15mm×10mm×4mm, polish the joint surface with 600# sandpaper, and then place them in anhydrous ethanol for ultrasonic cleaning for 15 minutes. Then place the samples in a drying oven at 65℃ for 1 hour.

[0050] Step 5: Apply the mixed slurry evenly to the surfaces of C / C and Cu to be joined, and then bond them together to form a sandwich-type prefabricated structure;

[0051] Step Six: Place the sandwich-type prefabricated structure in a vacuum brazing furnace for sintering. The brazing temperature is 860℃, the brazing time is 10 minutes, and the vacuum degree of the furnace is 6.6×10⁻⁶. -3 Pa, heating rate of 6℃ / min, cooling rate of 4℃ / min, finally obtained C / C-Cu joint with an average shear strength of 37.1MPa.

[0052] Example 2

[0053] A method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder includes the following steps:

[0054] Step 1: Place SiC whisker powder in a chemical vapor deposition furnace, use methanol as a precursor, and perform chemical vapor deposition at 1170℃ for 4 h to obtain nanoporous carbon-coated SiC whiskers.

[0055] Step 2: Using an analytical balance, 0.025g of nanoporous carbon-coated SiC whiskers and 4.975g of AgCuTi powder were mixed. Then, the mixture was placed in a 50mL beaker with 30mL of anhydrous ethanol and stirred evenly on a magnetic stirrer at 75℃ until the anhydrous ethanol evaporated. The powder was collected and ground in a mortar for 30min until the powder color was uniform and there was no obvious layering. Finally, a nanoporous carbon-coated SiC whisker modified AgCuTi solder with a SiC mass fraction of 0.50wt.% was obtained.

[0056] The obtained nanoporous carbon-coated SiC whisker-modified AgCuTi solder was applied to brazing C / C-Cu joints:

[0057] Step 3: Add 0.5g of liquid paraffin and petrolatum in a 1:1 mass ratio to 5g of nanoporous carbon-coated SiC whisker-modified AgCuTi solder, and mix thoroughly to obtain a mixed slurry;

[0058] Step 4: Cut C / C and Cu into small pieces of 15mm×10mm×4mm, polish the joint surface with 600# sandpaper, and then place them in anhydrous ethanol for ultrasonic cleaning for 15 minutes. Then place the samples in a drying oven at 65℃ for 1 hour.

[0059] Step 5: Apply the mixed slurry evenly to the surfaces of C / C and Cu to be joined, and then bond them together to form a sandwich-type prefabricated structure;

[0060] Step Six: Place the sandwich-type prefabricated structure in a vacuum brazing furnace for sintering. The brazing temperature is 860℃, the brazing time is 10 minutes, and the vacuum degree of the furnace is 6.6×10⁻⁶. -3 Pa, heating rate of 6℃ / min, cooling rate of 4℃ / min, finally obtained C / C-Cu joint with an average shear strength of 53.0MPa.

[0061] Example 3

[0062] A method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder includes the following steps:

[0063] Step 1: Place SiC whisker powder in a chemical vapor deposition furnace, use methanol as a precursor, and perform chemical vapor deposition at 1170℃ for 4 h to obtain nanoporous carbon-coated SiC whiskers.

[0064] Step 2: Using an analytical balance, 0.0375g of nanoporous carbon-coated SiC whiskers and 4.9625g of AgCuTi powder were mixed. Then, the mixture was placed in a 50mL beaker with 30mL of anhydrous ethanol and stirred evenly on a magnetic stirrer at 75℃ until the anhydrous ethanol evaporated. The powder was collected and ground in a mortar for 30min until the powder color was uniform and there was no obvious layering. Finally, a nanoporous carbon-coated SiC whisker-modified AgCuTi solder with a SiC mass fraction of 0.75wt.% was obtained.

[0065] The obtained nanoporous carbon-coated SiC whisker-modified AgCuTi solder was applied to brazing C / C-Cu joints:

[0066] Step 3: Add 0.5g of liquid paraffin and petrolatum in a 1:1 mass ratio to 5g of nanoporous carbon-coated SiC whisker-modified AgCuTi solder, and mix thoroughly to obtain a mixed slurry;

[0067] Step 4: Cut C / C and Cu into small pieces of 15mm×10mm×4mm, polish the joint surface with 600# sandpaper, and then place them in anhydrous ethanol for ultrasonic cleaning for 15 minutes. Then place the samples in a drying oven at 65℃ for 1 hour.

[0068] Step 5: Apply the mixed slurry evenly to the surfaces of C / C and Cu to be joined, and then bond them together to form a sandwich-type prefabricated structure;

[0069] Step Six: Place the sandwich-type prefabricated structure in a vacuum brazing furnace for sintering. The brazing temperature is 860℃, the brazing time is 10 minutes, and the vacuum degree of the furnace is 6.6×10⁻⁶. -3Pa, heating rate of 6℃ / min, cooling rate of 4℃ / min, finally obtained C / C-Cu joint with an average shear strength of 47.5MPa.

[0070] Example 4

[0071] A method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder includes the following steps:

[0072] Step 1: Place SiC whisker powder in a chemical vapor deposition furnace, use methanol as a precursor, and perform chemical vapor deposition at 1170℃ for 4 h to obtain nanoporous carbon-coated SiC whiskers.

[0073] Step 2: Using an analytical balance, 0.05g of nanoporous carbon-coated SiC whiskers and 4.95g of AgCuTi powder were mixed. Then, the mixture was placed in a 50mL beaker with 30mL of anhydrous ethanol and stirred evenly on a magnetic stirrer at 75℃ until the anhydrous ethanol evaporated. The powder was collected and ground in a mortar for 30min until the powder color was uniform and there was no obvious layering. Finally, a nanoporous carbon-coated SiC whisker modified AgCuTi solder with a SiC mass fraction of 1.0wt.% was obtained.

[0074] The obtained nanoporous carbon-coated SiC whisker-modified AgCuTi solder was applied to brazing C / C-Cu joints:

[0075] Step 3: Add 0.5g of liquid paraffin and petrolatum in a 1:1 mass ratio to 5g of nanoporous carbon-coated SiC whisker-modified AgCuTi solder, and mix thoroughly to obtain a mixed slurry;

[0076] Step 4: Cut C / C and Cu into small pieces of 15mm×10mm×4mm, polish the joint surface with 600# sandpaper, and then place them in anhydrous ethanol for ultrasonic cleaning for 15 minutes. Then place the samples in a drying oven at 65℃ for 1 hour.

[0077] Step 5: Apply the mixed slurry evenly to the surfaces of C / C and Cu to be joined, and then bond them together to form a sandwich-type prefabricated structure;

[0078] Step Six: Place the sandwich-type prefabricated structure in a vacuum brazing furnace for sintering. The brazing temperature is 860℃, the brazing time is 10 minutes, and the vacuum degree of the furnace is 6.6×10⁻⁶. -3 Pa, heating rate of 6℃ / min, cooling rate of 4℃ / min, finally obtained C / C-Cu joint with an average shear strength of 39.4MPa.

[0079] Example 5

[0080] A method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder includes the following steps:

[0081] Step 1: Place SiC whisker powder in a chemical vapor deposition furnace, use methanol as a precursor, and perform chemical vapor deposition at 1140℃ for 2 hours to obtain nanoporous carbon-coated SiC whiskers.

[0082] Step 2: Using an analytical balance, 0.05g of nanoporous carbon-coated SiC whiskers and 4.95g of AgCuTi powder were mixed. Then, the mixture was placed in a 30mL beaker with 50mL of acetone and stirred evenly on a magnetic stirrer at 85℃ until the anhydrous ethanol evaporated. The powder was collected and ground in a mortar for 60min until the powder color was uniform and there was no obvious layering. Finally, nanoporous carbon-coated SiC whisker modified AgCuTi solder was obtained.

[0083] Comparative Example 1:

[0084] Step 1: Label the untreated pure AgCuTi powder as Powder A;

[0085] Step 2: Add 0.5g of binder to powder A, mix well to obtain slurry B;

[0086] Step 3: Cut C / C and Cu into small pieces of 15mm×10mm×4mm, polish the joint surface with 600# sandpaper, and then place them in anhydrous ethanol for ultrasonic cleaning for 15min. Then place the samples in a drying oven at 65℃ for 2h to obtain sample C.

[0087] Step 4: Apply slurry B evenly to the surfaces of samples C and D, and assemble sample C into a sandwich-type prefabricated structure to obtain sample E;

[0088] Step 5: Place E in a vacuum brazing furnace for sintering. The brazing temperature is 860℃, the brazing time is 10 minutes, and the vacuum degree of the furnace is 6.6×10⁻⁶. -3 Pa, heating rate of 6℃ / min, cooling rate of 4℃ / min, finally obtained C / C-Cu joint with an average shear strength of 31.5 MPa.

[0089] Comparative Example 2:

[0090] Step 1: Label the untreated SiC whiskers as powder A;

[0091] Step 2: Add 0.5% by mass of powder A to pure AgCuTi powder to obtain powder B;

[0092] Step 3: Place powder B in anhydrous ethanol and stir evenly on a constant temperature magnetic stirrer until the anhydrous ethanol evaporates. Then grind the powder in a mortar for 40 minutes until the powder color is uniform and there is no obvious layering. Add 0.5g of binder and mix evenly to obtain slurry C.

[0093] Step 4: Cut C / C and Cu into small pieces of 15mm×10mm×4mm, polish the joint surface with 600# sandpaper, and then place them in anhydrous ethanol for ultrasonic cleaning for 15min. Then place the samples in a drying oven at 65℃ for 1h to obtain samples D and E.

[0094] Step 5: Apply slurry C evenly to the surfaces of samples D and E, and assemble C, D, and E into a sandwich-type prefabricated structure to obtain sample F;

[0095] Step Six: Place F in a vacuum brazing furnace for sintering. The brazing temperature is 860℃, the brazing time is 10 minutes, and the vacuum degree of the furnace is 6.6 × 10⁻⁶. -3 Pa, heating rate of 6℃ / min, cooling rate of 4℃ / min, finally obtained C / C-Cu joint with an average shear strength of 43.3 MPa.

[0096] Comparative Example 3:

[0097] Step 1: Place SiC whiskers in a chemical vapor deposition furnace, use methane as a precursor, and deposit at 1070°C for 10 min to obtain powder A with a pyrolytic carbon layer coating thickness similar to that of the nanoporous carbon coating thickness in Examples 1-4.

[0098] Step 2: Using an analytical balance, take 0.025g of powder A and 4.975g of AgCuTi powder and mix them to obtain 5g of composite solder with SiC content of 0.5wt%, which is denoted as powder B;

[0099] Step 3: Place powder B in anhydrous ethanol and stir evenly on a constant temperature magnetic stirrer until the anhydrous ethanol evaporates. Then grind the powder in a mortar for 40 minutes until the powder color is uniform and there is no obvious layering. Add 0.5g of binder and mix evenly to obtain slurry C.

[0100] Step 4: Cut C / C and Cu into small pieces of 15mm×10mm×4mm, polish the joint surface with 600# sandpaper, and then place them in anhydrous ethanol for ultrasonic cleaning for 15min. Then place the samples in a drying oven at 65℃ for 1h to obtain samples D and E.

[0101] Step 5: Apply slurry C evenly to the surfaces of samples D and E, and assemble C, D, and E into a sandwich-type prefabricated structure to obtain sample F;

[0102] Step Six: Place F in a vacuum brazing furnace for sintering. The brazing temperature is 860℃, the brazing time is 10 minutes, and the vacuum degree of the furnace is 6.6 × 10⁻⁶. -3 Pa, heating rate of 6℃ / min, cooling rate of 4℃ / min, finally obtained C / C-Cu joint with an average shear strength of 36.7 MPa.

[0103] Figure 1 The images show the microstructure of the nanoporous carbon-coated SiC whiskers prepared in Comparative Examples 2, 3 and 2 of this invention, as well as the microstructure of the composite solder in Comparative Example 2. As can be seen from the images, the nanocarbon layer successfully encapsulates the SiC whiskers, and the SiC whiskers and AgCuTi metallurgical powder in the composite solder are uniformly mixed, indicating that the whisker content is appropriate.

[0104] Figure 2 The images shown are backscattered electron microstructure images and magnified views of the C / C-Cu joints prepared in Examples 2 and 4 of this invention. It can be seen that when the mass fraction of porous carbon-coated SiC whiskers is 0.5 wt%, due to the introduction of appropriate amounts of whiskers and porous carbon, small-sized Ti-Cu grains are discontinuously distributed along the edges of the remaining whiskers. Simultaneously, Ag and Cu solid solutions are uniformly distributed throughout the entire brazing layer, resulting in a refined overall microstructure. When the mass fraction of porous carbon-coated SiC is 1.0 wt.%, excessive whiskers easily lead to agglomeration, causing damage to the Ag matrix and resulting in varying degrees of defects in both the intermediate and reaction layers. Furthermore, Ti-Cu phase aggregation occurs in areas with fewer whiskers.

[0105] Figure 3 The bar chart shows the average strength of the C / C-Cu joints prepared in Examples 1, 2, 3 and 4 of this invention. It can be seen from the figure that the composite brazed joint with the porous carbon-coated SiC content corresponding to Example 2 has the best mechanical properties, which is 53.0 MPa.

[0106] Figure 4 The diagram shows the change in the coefficient of thermal expansion of the composite solders prepared in Example 2 and Comparative Examples 1, 2, and 3 of this invention with temperature. It can be seen that the addition of SiC whiskers reduces the coefficient of thermal expansion of the AgCuTi solder, especially as the temperature increases. This reduces the difference in thermal expansion coefficient between the alloy and the base material, which helps alleviate residual thermal stress at the joint.

[0107] Figure 5The images show the microstructure of the C / C-Cu joints prepared in Comparative Examples 1, 2, and 3 of this invention, as well as a partially enlarged image of Comparative Example 3. As can be seen from the images, when brazing with a composite solder composed of uncoated SiC whiskers, the whisker phase agglomerates in the center of the brazing layer and cannot affect the entire brazing layer. When brazing with a composite solder composed of pyrolytic carbon-coated SiC whiskers, due to the lack of porous structure and fewer reactive sites, brittle TiC particles aggregate around the whisker phase, having a very limited impact on the spatial distribution of the Ti-Cu phase. The size of the brittle Ti-Cu phase increases significantly, resulting in limited improvement in the mechanical properties of the joint.

[0108] Figure 6 This is a bar chart showing the average strength of C / C-Cu joints prepared in Comparative Examples 1, 2, 3, and 2 of this invention. As can be seen from the chart, the shear resistance of all C / C-Cu joints brazed with composite solders containing SiC whiskers is improved compared to joints brazed with pure AgCuTi solder. Among these, the joint brazed with the composite solder prepared using spatially porous carbon-coated SiC whiskers exhibits the best mechanical properties.

[0109] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder, characterized in that, Includes the following steps: SiC whiskers were subjected to chemical vapor deposition to obtain nanoporous carbon-coated SiC whiskers. After mixing nanoporous carbon-coated SiC whiskers and AgCuTi powder, the mixture was added to a solvent and stirred. The powder was collected and ground to obtain nanoporous carbon-coated SiC whisker-modified AgCuTi solder.

2. The method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 1, characterized in that, The chemical vapor deposition process uses methanol as a precursor and deposits at 1140~1170℃ for 2-4 hours.

3. The method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 1, characterized in that, The ratio of the amount of nanoporous carbon-coated SiC whiskers, AgCuTi powder and solvent is (0.0125-0.05) g : (4.9875-4.975) g : 30 mL.

4. The method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 1, characterized in that, The solvent is ethanol; The stirring is magnetic stirring; the temperature of the magnetic stirring is 75~85℃.

5. The method for preparing nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 1, characterized in that, The grinding time is 30-60 minutes.

6. A nanoporous carbon-coated SiC whisker-modified AgCuTi solder, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. The application of the nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 6, characterized in that, Application of the nanoporous carbon-coated SiC whisker modified AgCuTi solder in brazing C / C-Cu joints.

8. The application of the nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 7, characterized in that, When the nanoporous carbon-coated SiC whisker-modified AgCuTi solder is used in brazing C / C-Cu joints, the following steps are included: A mixed slurry was obtained by mixing nanoporous carbon-coated SiC whisker-modified AgCuTi solder with a binder. C / C and Cu are pretreated, then a mixed slurry is applied to the surfaces of C / C and Cu to be joined, and then they are bonded together to form a sandwich-type prefabricated structure. The obtained sandwich-type prefabricated structure is sintered to finally obtain a C / C-Cu joint.

9. The application of the nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 8, characterized in that, The ratio of SiC whiskers, AgCuTi powder, and binder is (4~6)g:(0.4~0.6)g:0.50g; The adhesive is prepared by mixing petrolatum and liquid paraffin in a mass ratio of 1:1, heating in an oil bath at 75~85℃ for 30-40 minutes, and then air-cooling to room temperature. The pretreatment process includes polishing, cleaning, and drying in sequence.

10. The application of the nanoporous carbon-coated SiC whisker-modified AgCuTi solder according to claim 8, characterized in that, The sintering process parameters are as follows: brazing temperature 860℃, brazing time 10 min, and furnace vacuum degree 6.0 × 10⁻⁶. -3 Pa-8.0×10 -3 Pa, heating rate is 6-8℃ / min, cooling rate is 4-6℃ / min.

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