Silicon carbide surface coating on graphite block and composite material thereof

Abstract

This application discloses a method for preparing a silicon carbide coating on the surface of graphite bulk material and a composite material. Through a progressive interface optimization system combining interface activation pretreatment and gradient transition layer design, it solves the technical problems of defects, easy peeling, or cracking at the interface of traditional double-layer silicon carbide coatings. The method includes: using silicon particles and graphite bulk material to react with silicon vapor in a vacuum environment to form an initial silicon carbide layer; performing plasma etching and activation treatment on the initial silicon carbide layer; and performing CVD deposition using a gradient transition layer design with three dimensions: stoichiometric gradient, doping element gradient, and structural gradient. The silicon carbide coating prepared by this method exhibits excellent thermal stability and interfacial bonding strength under high-temperature cycling conditions, making it particularly suitable for high-end applications requiring long-term operation under extreme temperature and thermal shock environments.

Description

Technical Field

[0001] This application relates to the field of materials preparation technology, specifically to a method for preparing a silicon carbide coating on the surface of graphite bulk material and a composite material. Prior Technology

[0002] Silicon carbide-coated graphite composites combine the advantages of graphite (high thermal conductivity and low coefficient of thermal expansion) with silicon carbide (high-temperature oxidation resistance and wear resistance), making them widely used in high-end technology fields such as semiconductor manufacturing, aerospace, and nuclear energy. These composites are typically prepared using methods such as chemical vapor deposition (CVD), liquid-phase siliconizing, or direct vapor-phase silicification. Among these methods, silicon carbide coatings prepared by CVD exhibit the best purity and density.

[0003] Currently, the preparation methods for silicon carbide coatings on graphite substrates mainly involve two key steps: silicon vapor reaction to form an initial silicon carbide layer, and CVD deposition of an outer silicon carbide layer. During the silicon vapor reaction, silicon vapor reacts directly with carbon atoms on the graphite substrate surface at high temperatures to form the initial silicon carbide layer. Subsequently, using a gaseous precursor such as trichloromethylsilane, an outer silicon carbide layer is deposited on the surface of the initial layer via CVD, forming a bilayer silicon carbide coating.

[0004] However, traditional methods for preparing double-layer silicon carbide coatings have a significant drawback: insufficient interfacial bonding strength between the two silicon carbide layers, making them prone to peeling or cracking under high-temperature cycling or thermal shock conditions. This is mainly due to the inactive surface of the initial silicon carbide layer and the significant abrupt changes in composition and structure between the two layers, leading to stress concentration at the interface. This defect severely restricts the application of silicon carbide-coated graphite composites under more extreme conditions, necessitating the development of novel interface optimization techniques to address this issue. Summary of the Invention

[0005] In view of this, this application provides a method for coating the surface of graphite bulk silicon carbide, which solves the problems of defects, easy peeling or cracking at the interface of double-layer silicon carbide coatings in the prior art.

[0006] This application provides a method for preparing a silicon carbide coating on the surface of a graphite block, comprising: reacting silicon particles with the graphite block in a vacuum environment using silicon vapor to obtain a graphite block with an initial silicon carbide layer; placing the graphite block with the initial silicon carbide layer in a plasma treatment device, performing surface etching via argon plasma, and performing surface activation treatment using a mixed gas of hydrogen and nitrogen to obtain an activated graphite block; using the activated graphite block, performing CVD deposition via trichloromethylsilane and methane gas in a preset ratio to obtain a CVD-deposited graphite block; performing boron trichloride concentration gradient doping CVD deposition on the CVD-deposited graphite block to obtain a doped graphite block; and performing structural gradient CVD deposition on the doped graphite block at a preset temperature and gas flow rate to obtain a silicon carbide coating.

[0007] Preferably, the method of using silicon particles and graphite blocks to carry out a silicon vapor reaction in a vacuum environment to obtain graphite blocks with an initial silicon carbonization layer includes: placing silicon particles with a particle size of 5-10 mm at the bottom of the reaction device, and placing the graphite blocks inside the reaction device; heating the reaction device to 1700-1800°C at a heating rate of 10°C / min under a vacuum of 500 Pa, and reacting for 2-4 hours to obtain the graphite blocks with the initial silicon carbonization layer.

[0008] Preferably, the step of placing the graphite block with the initial silicon carbide layer in a plasma treatment device, performing surface etching via argon plasma, and performing surface activation treatment using a mixed gas of hydrogen and nitrogen to obtain the activated graphite block includes: introducing argon gas at a pressure of 5-50 Pa, applying 50-200 W power for 5-15 minutes of plasma etching to obtain a graphite block with a nanoscale micro-rough surface; introducing a mixed gas of hydrogen and nitrogen with a volume ratio of 4:1 into the graphite block with the nanoscale micro-rough surface, applying 150-250 W power for 5-8 minutes of surface activation treatment to obtain the activated graphite block.

[0009] Preferably, the step of using the activated graphite block and performing CVD deposition with trichloromethylsilane and methane gas in a preset ratio to obtain CVD-deposited graphite block includes: placing the activated graphite block in a CVD reactor, introducing trichloromethylsilane and methane gas, and depositing at a ratio of 1:1.5 for 0.5-1 hours to obtain a first silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane to methane gas to 1:1, and depositing the carbon-rich silicon carbide transition layer for 1-2 hours to obtain a second silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane to methane gas to 1.2:1, and depositing the second silicon carbide transition layer for 1.5-2 hours to obtain the CVD-deposited graphite block.

[0010] Preferably, the step of performing boron trichloride concentration gradient doping CVD deposition on the CVD-deposited graphite bulk material to obtain doped graphite bulk material includes: introducing 0.5-1% boron trichloride gas and mixing it with the reaction gas to deposit a first doped layer on the CVD-deposited graphite bulk material; introducing 0.2-0.3% boron trichloride gas into the first doped layer and depositing it to obtain a second doped layer; introducing 0.05-0.1% boron trichloride gas into the second doped layer and depositing it to obtain the doped graphite bulk material.

[0011] Preferably, the introduction of boron trichloride gas at a concentration of 0.5-1% is mixed with the reaction gas to deposit a first doped layer on the CVD-deposited graphite block, comprising: evacuating the CVD furnace to a vacuum of 100-500 Pa to obtain a pretreated graphite block; introducing a mixed gas of boron trichloride, trichloromethylsilane, and methane into the pretreated graphite block, controlling the concentration of boron trichloride to be 0.5-1% and the total gas flow rate to be 200-300 mL / min, and depositing for 2 hours to obtain the first doped layer.

[0012] Preferably, the step of performing structural gradient CVD deposition on the doped graphite bulk material at a preset temperature and gas flow rate to obtain a silicon carbide coating includes: heating the doped graphite bulk material to 1100-1150℃, adjusting the reaction gas flow rate to 150-250mL / min, and depositing for 2-3 hours to obtain a nanocrystalline structure layer; raising the temperature of the nanocrystalline structure layer to 1200-1300℃, adjusting the gas flow rate to 250-350mL / min, and depositing for 2-3 hours to obtain a microcrystalline structure layer; raising the temperature of the microcrystalline structure layer to 1350-1400℃, adjusting the gas flow rate to 350-450mL / min, and depositing for 2-3 hours to obtain the silicon carbide coating.

[0013] Preferably, the step of heating the doped graphite bulk material to 1100-1150℃, adjusting the reaction gas flow rate to 150-250mL / min, and depositing for 2-3 hours to obtain a nanocrystalline structure layer includes: heating the doped graphite bulk material to 1100-1150℃ at a heating rate of 5-10℃ / min to obtain a substrate at a predetermined temperature; introducing a mixed gas of trichloromethylsilane and methane into the substrate at the predetermined temperature, adjusting the flow rate to 150-250mL / min, and depositing for 2-3 hours to obtain the nanocrystalline structure layer.

[0014] Preferably, after obtaining the silicon carbide coating, the process further includes: placing the silicon carbide coating in a temperature environment of 1500-1600℃ and annealing it for 2-4 hours to obtain the annealed silicon carbide coating.

[0015] This application also provides a composite material, including a graphite block and a silicon carbide coating on the surface of the graphite block, wherein the silicon carbide coating is prepared by any of the methods described above for preparing a silicon carbide coating on the surface of the graphite block.

[0016] This application has the following technical effects:

[0017] By using silicon particles and graphite blocks, a silicon vapor reaction is carried out in a vacuum environment to form an initial silicon carbide layer that is firmly bonded to the substrate, providing a stable foundation for subsequent processing. Argon plasma etching and hydrogen / nitrogen mixed gas activation treatment are used to significantly improve the activity and roughness of the surface of the initial silicon carbide layer, enhance the bonding strength with the subsequent CVD layer, and improve the interfacial shear strength by 40-60% compared with traditional technology. Simple Explanation of the Diagram

[0018] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. These drawings are incorporated in and constitute a part of this specification. They illustrate embodiments conforming to this disclosure and, together with the specification, serve to explain the technical solutions of this disclosure. It should be understood that the following drawings only show some embodiments of this disclosure and should not be considered as limiting the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort. Figure 1 is a schematic flowchart of the method for preparing a silicon carbide coating on the surface of a graphite block provided in the embodiments of this application. Figure 2 is a schematic diagram of the formation of the initial carbonized silicon layer by silicon vapor reaction in an embodiment of this application. Figure 3 is a schematic diagram of the interface activation pretreatment in an embodiment of this application. Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. The elements of the embodiments of this disclosure described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed disclosure, but merely represents selected embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In this document, the term "and / or" merely describes a relationship, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0022] As shown in Figure 1, this application provides a method for preparing a silicon carbide coating on the surface of a graphite block, comprising:

[0023] Step 1: Using silicon particles and graphite blocks, a silicon vapor reaction is carried out in a vacuum environment to obtain graphite blocks with an initial carbonized silicon layer;

[0024] For example, firstly, high-purity silicon particles with a diameter of 5-10 mm are placed in a graphite crucible at the bottom of the reaction apparatus, and the graphite block to be treated is placed on a support approximately 30 mm away from the silicon material inside the crucible. Then, the entire apparatus is placed in a high-temperature furnace, and under a vacuum of 500 Pa, the temperature is increased to 1700-1800 °C at a rate of 10 °C / min, and the reaction is maintained at this temperature for 2-4 hours. During this process, silicon evaporates at high temperature to form silicon vapor, which reacts directly with carbon atoms on the surface of the graphite matrix to generate a chemically bonded initial silicon carbide layer. This initial layer is typically 10-20 μm thick and tightly bonded to the graphite matrix, providing a good foundation for subsequent processing. After the reaction is complete, the sample is naturally cooled to room temperature and removed, yielding a graphite block with the initial silicon carbide layer.

[0025] Step 2: Place the graphite block with the initial silicon carbide layer in a plasma treatment device, perform surface etching using argon plasma, and perform surface activation treatment using a mixed gas of hydrogen and nitrogen to obtain the activated graphite block;

[0026] This step is one of the key innovations of this method, optimizing interface properties through a dual plasma modification process. For example, the graphite block with the initial silicon carbide layer is first transferred to a plasma treatment device and evacuated to a low-pressure state. High-purity argon gas is introduced at a pressure of 5-50 Pa, and a stable argon plasma is generated at a power of 50-200 W to perform plasma etching on the sample surface for 5-15 minutes. This etching process forms a nanoscale micro-rough structure on the silicon carbide surface, significantly increasing the surface area and mechanical interlocking effect. Subsequently, while maintaining the device pressure, a hydrogen and nitrogen mixture with a volume ratio of 4:1 is switched, and the power is adjusted to the range of 150-250 W for a surface activation treatment of 5-8 minutes. The hydrogen-nitrogen plasma treatment forms a large number of active sites and dangling bonds on the roughened surface after etching, significantly improving surface chemical activity. Finally, high-purity helium gas is introduced for 3-5 minutes of purging to remove any possible residual substances, resulting in an activated graphite block with ideal interface properties.

[0027] Step 3: Using the activated graphite block, CVD deposition is performed using trichloromethylsilane and methane gas in a preset ratio to obtain the CVD-deposited graphite block;

[0028] This step achieves a stoichiometric gradient transition of carbon and silicon content in silicon carbide, representing the first stage of multidimensional gradient design. For example, activated graphite blocks are transferred to a CVD reactor. First, trichloromethylsilane and methane gas are introduced and deposited at a 1:1.5 ratio for 0.5-1 hour, forming a carbon-rich silicon carbide transition layer. This carbon-rich layer exhibits better chemical compatibility with the initial activated silicon carbide layer. Subsequently, the gas ratio is gradually adjusted to 1:1, and deposition continues for 1-2 hours, forming a stoichiometric silicon carbide transition layer on top of the carbon-rich layer. Finally, the gas ratio is adjusted to 1.2:1, and deposition continues for 1.5-2 hours, forming a slightly silicon-rich silicon carbide layer. The entire process typically lasts 3-5 hours. This gradual transition of composition effectively reduces interfacial stress caused by differences in chemical composition between layers, laying a good foundation for subsequent processing.

[0029] Step 4: Perform boron trichloride concentration gradient doping CVD deposition on the CVD-deposited graphite bulk material to obtain doped graphite bulk material;

[0030] This step achieves a gradient transition of doping elements, constituting the second stage of multidimensional gradient design. For example, the CVD-deposited graphite bulk material is first placed back into the CVD reactor, and a vacuum of 100-500 Pa is applied. Then, a mixture of boron trichloride gas (0.5-1%) with trichloromethylsilane and methane is introduced, with the total gas flow rate controlled at 200-300 mL / min, and deposition continues for approximately 2 hours to form a high-concentration boron-doped first layer. Boron doping significantly improves the conductivity and thermal stability of the silicon carbide layer. Subsequently, the boron trichloride concentration is reduced to the range of 0.2-0.3%, and deposition continues to form a medium-concentration second doped layer. Finally, the boron trichloride concentration is further reduced to 0.05-0.1%, completing the deposition of the outermost low-concentration doped layer. The entire doping process typically lasts 5-8 hours. Through the gradient change in doping concentration, the performance gradient transition of the coating system is further optimized, reducing thermal stress concentration caused by abrupt changes in material properties.

[0031] Step 5: The doped graphite block is subjected to structural gradient CVD deposition at a preset temperature and gas flow rate to obtain a silicon carbide coating.

[0032] This step achieves a gradient transition in microstructure and is the third stage of multidimensional gradient design. For example, the doped graphite bulk material is first heated to 1100-1150℃ at a heating rate of 5-10℃ / min, while the flow rate of the trichloromethylsilane and methane mixed gas is controlled within the range of 150-250 mL / min for 2-3 hours of low-temperature deposition, forming a nanocrystalline structure layer. The nanocrystalline structure exhibits high toughness and interfacial bonding ability. Subsequently, the temperature is gradually increased to 1200-1300℃, while the gas flow rate is increased to 250-350 mL / min, and deposition continues for 2-3 hours to form a microcrystalline transition layer. Finally, the temperature is further increased to 1350-1400℃, and the gas flow rate is increased to 350-450 mL / min, with deposition continuing for 2-3 hours to form a well-oriented polycrystalline outer layer. The polycrystalline structure exhibits excellent high-temperature stability and oxidation resistance. The entire structural gradient process typically lasts 5-10 hours. Through the gradual transition of grain size and orientation, a smooth transition of the coating's mechanical and thermal properties from the inside to the outside is achieved, further reducing thermal stress concentration and improving the stability and service life of the coating system under high-temperature cycling conditions.

[0033] Through the five consecutive technical steps described above, this method successfully achieved a multi-dimensional gradient transition from a graphite substrate to a silicon carbide coating, forming a silicon carbide composite coating with excellent interfacial bonding strength and high-temperature stability. Compared with traditional techniques, the coating prepared by this method exhibits significantly improved stability in a 1600℃ thermal cycling test, with an interfacial peeling rate reduced by more than 85% and a shear strength increased by 40-90%, providing reliable technical support for applications in high-temperature extreme environments.

[0034] In one embodiment of this application, as shown in FIG2, the method of using silicon particles and graphite blocks to perform a silicon vapor reaction in a vacuum environment to obtain graphite blocks with an initial carbonized silicon layer includes: plasma treatment equipment 10, air inlet 11, vacuum pump interface 12, plasma source 13, graphite blocks 14, and sample placement area 15;

[0035] Silicon particles with a particle size of 5-10 mm are placed at the bottom of the reaction device, and the graphite block 14 is placed inside the reaction device;

[0036] The reaction apparatus was heated to 1700-1800°C under a vacuum of 500 Pa at a heating rate of 10°C / min for 2-4 hours to obtain the graphite block material with the initial silicon carbide layer.

[0037] In this embodiment, an initial silicon carbide layer is formed by the reaction of silicon vapor generated from silicon particles at high temperature with carbon atoms on the surface of the graphite matrix. This layer has good bonding strength with the graphite matrix, laying the foundation for subsequent processing. In practice, the graphite block can be placed approximately 30 mm away from the silicon particles to ensure uniform reaction.

[0038] In one embodiment of this application, as shown in Figure 3, the system includes a plasma treatment device 10, an air inlet 11, a vacuum pump interface 12, a plasma source 13, a graphite block 14, and a sample placement area 15. The process involves placing the graphite block with an initial silicon carbide layer in the plasma treatment device 10, performing surface etching via argon plasma, and then performing surface activation treatment using a mixed gas of hydrogen and nitrogen to obtain an activated graphite block. This includes: introducing argon gas at a pressure of 5-50 Pa, applying 50-200 W of power for 5-15 minutes of plasma etching to obtain a graphite block with a nanoscale micro-rough surface; and introducing a hydrogen and nitrogen mixed gas with a volume ratio of 4:1 onto the graphite block with the nanoscale micro-rough surface, applying 150-250 W of power for 5-8 minutes of surface activation treatment to obtain the activated graphite block.

[0039] In this embodiment, plasma treatment is one of the key innovations of this method. Argon plasma etching forms a nanoscale rough structure on the silicon carbide surface through physical collision, increasing the mechanical interlocking effect; while hydrogen / nitrogen mixed gas plasma treatment forms a large number of active sites and dangling bonds on the surface, significantly improving the chemisorption capacity of the subsequent CVD deposited layer. After etching, high-purity helium gas can be introduced for 3-5 minutes for purging and cleaning to remove residual substances.

[0040] In one embodiment of this application, as shown in FIG4, the step of using the activated graphite block to perform CVD deposition via trichloromethylsilane and methane gas in a preset ratio to obtain CVD-deposited graphite block includes: placing the activated graphite block in a CVD reactor, introducing trichloromethylsilane and methane gas in a 1:1.5 ratio, and depositing for 0.5-1 hours to obtain a first silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane and methane gas to 1:1, and depositing the carbon-rich silicon carbide transition layer for 1-2 hours to obtain a second silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane and methane gas to 1.2:1, and depositing the second silicon carbide transition layer for 1.5-2 hours to obtain the CVD-deposited graphite block.

[0041] In this embodiment, by adjusting the ratio of trichloromethylsilane to methane gas, a stoichiometric gradient transition is achieved, forming a first-dimensional gradient structure from carbon-rich to stoichiometric to slightly silicon-rich silicon carbide layers. This gradient design effectively alleviates the thermal stress caused by compositional differences between different layers, improving the overall stability of the coating system.

[0042] In one embodiment of this application, the step of performing boron trichloride concentration gradient doping CVD deposition on the CVD-deposited graphite bulk material to obtain doped graphite bulk material includes: introducing boron trichloride gas with a concentration of 0.5-1% and mixing it with a reaction gas to deposit a first doped layer on the CVD-deposited graphite bulk material; introducing boron trichloride gas with a concentration of 0.2-0.3% and depositing it on the first doped layer to obtain a second doped layer; and introducing boron trichloride gas with a concentration of 0.05-0.1% and depositing it on the second doped layer to obtain the doped graphite bulk material.

[0043] Here, concentration refers to the volume percentage concentration of boron trichloride (BCl₃) in the entire reactive gas mixture. That is, boron trichloride gas accounts for 0.5-1% of the total gas flow rate. This is a relatively low but effective doping concentration range, sufficient to achieve boron doping modification of silicon carbide coatings while avoiding coating structural defects that may be caused by excessively high concentrations.

[0044] The reactant gases mainly include:

[0045] Trichloromethylsilane (CH₃SiCl₃): as a silicon source;

[0046] Methane (CH₄): as a carbon source;

[0047] Hydrogen (H₂): used as a carrier gas and reducing atmosphere;

[0048] In this step, boron trichloride is used as a dopant gas mixed with the main reactant gases. Trichloromethylsilane and methane remain the main reactant gases for forming the silicon carbide matrix, and their ratio is typically maintained close to 1:1 (may be slightly adjusted to suit the doping process). Hydrogen acts as a carrier gas to help distribute the reactant gases evenly and create a reducing atmosphere conducive to deposition. The amount of boron trichloride added to this gas mixture is controlled within the range of 0.5-1%, allowing boron atoms to partially replace carbon or silicon atoms in the silicon carbide lattice during the CVD process, thereby achieving the doping effect.

[0049] The entire reaction gas system is usually supplemented with an inert gas (such as argon or helium) to regulate the total flow rate and partial pressure of the reaction gases, which is adjusted according to specific technical requirements. The total gas flow rate is generally controlled in the range of 200-300 mL / min to ensure a uniform and stable deposition process.

[0050] In this embodiment, the dopant element gradient forms a second-dimensional gradient structure. Boron doping not only improves the electrical conductivity and thermal stability of the silicon carbide layer, but also further reduces interlayer stress through concentration gradient changes, thus optimizing the overall performance of the coating.

[0051] In one embodiment of this application, the introduction of boron trichloride gas at a concentration of 0.5-1% is mixed with the reaction gas to deposit a first doped layer on a CVD-deposited graphite block, comprising: evacuating the CVD furnace to a vacuum of 100-500 Pa to obtain a pretreated graphite block; introducing a mixed gas of boron trichloride, trichloromethylsilane, and methane into the pretreated graphite block, controlling the concentration of boron trichloride to be 0.5-1% and the total gas flow rate to be 200-300 mL / min, and depositing for 2 hours to obtain the first doped layer.

[0052] In this embodiment, before the doping process, the CVD furnace needs to be evacuated to a suitable pressure range to ensure the stability of the deposition process and the consistency of the doping effect. Controlling the total gas flow rate is crucial for forming a uniform doped layer.

[0053] In one embodiment of this application, the step of performing structural gradient CVD deposition on the doped graphite bulk material at a preset temperature and gas flow rate to obtain a silicon carbide coating includes: heating the doped graphite bulk material to 1100-1150℃, adjusting the reaction gas flow rate to 150-250mL / min, and depositing for 2-3 hours to obtain a nanocrystalline structure layer; raising the temperature of the nanocrystalline structure layer to 1200-1300℃, adjusting the gas flow rate to 250-350mL / min, and depositing for 2-3 hours to obtain a microcrystalline structure layer; raising the temperature of the microcrystalline structure layer to 1350-1400℃, adjusting the gas flow rate to 350-450mL / min, and depositing for 2-3 hours to obtain the silicon carbide coating.

[0054] In this embodiment, by controlling the temperature and gas flow rate, a gradient change from nanocrystals to microcrystals and then to polycrystalline structures was achieved, forming a third-dimensional gradient structure. Silicon carbide layers with different grain sizes have different mechanical and thermal properties, and this microstructure gradient further improves the thermal stability and mechanical properties of the coating system.

[0055] In one embodiment of this application, the step of heating the doped graphite bulk material to 1100-1150°C, adjusting the flow rate of the reaction gas to 150-250 mL / min, and depositing for 2-3 hours to obtain a nanocrystalline structure layer includes: heating the doped graphite bulk material to 1100-1150°C at a heating rate of 5-10°C / min to obtain a substrate at a predetermined temperature; introducing a mixed gas of trichloromethylsilane and methane into the substrate at the predetermined temperature, adjusting the flow rate to 150-250 mL / min, and depositing for 2-3 hours to obtain the nanocrystalline structure layer.

[0056] In this embodiment, controlling the heating rate is crucial to avoid thermal stress on the graphite substrate and the deposited coating caused by excessively rapid temperature changes. A suitable heating rate ensures that the coating system maintains structural integrity during the heating process.

[0057] In one embodiment of this application, after obtaining the silicon carbide coating, the method further includes: placing the silicon carbide coating in a temperature environment of 1500-1600℃ and annealing it for 2-4 hours to obtain an annealed silicon carbide coating.

[0058] In this embodiment, high-temperature annealing can further improve the crystallinity and internal structural integrity of the silicon carbide coating, release residual stress generated during the deposition process, and optimize the overall performance and thermal stability of the coating.

[0059] Example 1: Preparation of silicon carbide coating for graphite components of aero-engines

[0060] Raw materials and equipment:

[0061] Graphite matrix: High-purity graphite blocks with a density of 1.75 g / cm³, dimensions 50 mm × 50 mm × 10 mm; Solid silicon material: 4N purity (99.99%); Silicon particles, particle size 5-10 mm; Plasma treatment equipment 10: Radio frequency plasma treatment system, maximum power 500 W; CVD equipment: Vertical hot-wall CVD furnace, maximum temperature 1800℃;

[0062] Technical process:

[0063] Step 1: Silicon vapor reaction

[0064] Place 10g of solid silicon particles at the bottom of a graphite crucible, and place the graphite matrix on a graphite support 30mm away from the silicon material inside the crucible;

[0065] Inside the graphitization furnace, the temperature was increased to 1750℃ at a rate of 10℃ / min;

[0066] The sample was kept under a vacuum of 500 Pa for 3 hours, then allowed to cool naturally to room temperature before being removed.

[0067] Step 2: Interface activation pretreatment, transferring the sample to plasma processing equipment 10;

[0068] Evacuate to 1 Pa, introduce high-purity argon gas, and adjust the pressure to 25 Pa;

[0069] Turn on the RF power supply, set the power to 120W, and perform plasma etching for 10 minutes;

[0070] Maintaining the same pressure, switch the gas to a hydrogen / nitrogen mixture (volume ratio 4:1), adjust the power to 180W, perform surface activation treatment for 7 minutes, and then purge with high-purity helium for 4 minutes;

[0071] Step 3: Gradient transition layer deposition

[0072] Phase 1 (Stoichiometric gradient, total time 4 hours):

[0073] Initial stage (1 hour): The ratio of trichloromethylsilane to methane gas is 1:1.5;

[0074] Intermediate stage (1.5 hours): Gradually adjust the gas ratio to 1:1;

[0075] Later stage (1.5 hours): Adjust the gas ratio to 1.2:1;

[0076] Phase Two (Doping Element Gradient, Total Time 6 Hours) Initial Sub-phase (2 hours): Introducing 0.8% boron trichloride; Intermediate Sub-phase (2 hours): The boron trichloride concentration linearly decreases to 0.3%; Late Sub-phase (2 hours): The boron trichloride concentration decreases to 0.08%.

[0077] Phase 3 (Structural Gradient, Total Time 8 Hours): Initial temperature 1120℃, gas flow rate 200 mL / min (2 hours); intermediate temperature gradually increased to 1250℃, flow rate 300 mL / min (3 hours); final temperature increased to 1380℃, flow rate 400 mL / min (3 hours).

[0078] Test Results: Total coating thickness: 65±3μm (initial reaction layer approximately 15μm, gradient CVD layer approximately 50μm); After 50 cycles of thermal cycling at 1600℃, the interfacial peeling area is less than 2%; Shear strength: 35.6MPa, 92.4% higher than traditional technology; Oxidation test: After 100 hours of exposure to air at 1500℃, the weight gain rate is less than 0.5%.

[0079] Example 2: Preparation of silicon carbide coating on high-temperature graphite products for nuclear energy

[0080] Raw materials and equipment:

[0081] Graphite matrix: Nuclear-grade graphite tubes with a density of 1.85 g / cm³, outer diameter 80 mm, inner diameter 60 mm, and length 120 mm; Plasma equipment: Microwave plasma processing system, 2.45 GHz frequency; CVD equipment: Horizontal hot-wall CVD furnace equipped with a rotating sample stage;

[0082] Technical process: Similar to Example 1, but the main differences are: In the first step of silicon vapor reaction, the graphite tube rotates at 5 rpm during the reaction to ensure uniform reaction interface activation pretreatment. Microwave plasma is used with power controlled at 350W. In gradient transition layer deposition, aluminum nitride doping is added, gradually decreasing from 0.3% to 0.05%. The graphite tube is kept rotating throughout the process to ensure coating uniformity.

[0083] Test results:

[0084] Coating thickness uniformity: thickness deviation between inner and outer surfaces less than 5%.

[0085] Thermal neutron absorption cross section: less than 5.2×10-24 cm². After 100 cycles of thermal cycling at 1600℃, the interfacial peeling area is less than 1%. Antioxidant performance: after exposure to air at 1450℃ for 200 hours, the weight gain rate is less than 0.3%.

[0086] Comparative Example 1:

[0087] Traditional double-layer silicon carbide coating technology: Following conventional techniques, graphite blocks are subjected to two steps: silicon vapor reaction and CVD deposition, to prepare a double-layer silicon carbide coating. After reacting at 1700℃ and 500Pa for 3 hours in the first step, the second step proceeds directly to conventional CVD deposition at 1300℃ for 25 hours. After 10 thermal cycling tests at 1600℃, significant delamination was observed at the interface, with the delamination area accounting for approximately 28% of the total area. In the shear strength test, the interface strength was 18.5 MPa.

[0088] Comparative Example 2:

[0089] Interface activation pretreatment was used only: an interface activation pretreatment step was added between the two steps of the conventional technique, including 10 minutes of argon plasma etching (150 W power, 20 Pa pressure) and 6 minutes of hydrogen-nitrogen mixed gas plasma activation (200 W power). The second step of CVD deposition parameters were the same as those in Comparative Example 1. After 20 cycles of thermal cycling at 1600 °C, the resulting coating showed an interface peeling area of ​​approximately 12% of the total area. In the shear strength test, the interface strength increased to 27.3 MPa.

[0090] Comparative Example 3:

[0091] A gradient transition layer design was used: based on traditional techniques, the second-step CVD deposition was replaced with a three-stage gradient transition layer design, but without interface activation pretreatment. The three-stage deposition included a stoichiometric gradient (4 hours), a dopant element gradient (6 hours), and a structural gradient (8 hours). After 30 cycles of thermal cycling at 1600℃, the resulting coating showed an interface peeling area of ​​approximately 8% of the total area. In the shear strength test, the interface strength was 25.1 MPa.

[0092] As can be seen from the above embodiments and comparative examples, the progressive approach combining interface activation pretreatment with gradient transition layer design can significantly improve the interface bonding strength and high-temperature stability of the double-layer silicon carbide coating, especially in applications requiring long-term exposure to extreme conditions. In all test indicators, this technical solution outperforms the three comparative examples, with the most significant improvement in thermal cycling stability.

[0093] In summary, the method for preparing silicon carbide coatings on the surface of graphite blocks provided in this application fundamentally solves the technical problems of defects, easy peeling, or cracking at the interface of traditional double-layer silicon carbide coatings through a progressive interface optimization system combining interface activation pretreatment and gradient transition layer design. The silicon carbide coating prepared by this method exhibits excellent thermal stability and interfacial bonding strength under high-temperature cycling conditions, providing reliable technical support for high-end applications.

[0094] This application also provides a composite material comprising a graphite bulk material and a silicon carbide coating on the surface of the graphite bulk material. The composite material is prepared by any of the methods described above for preparing a silicon carbide coating on the surface of the graphite bulk material. This composite material combines the thermal conductivity and electrical conductivity of graphite with the high-temperature stability and oxidation resistance of silicon carbide, making it particularly suitable for various extreme environmental applications. In the semiconductor manufacturing field, this composite material can be used to manufacture high-temperature furnace components, wafer carriers, and diffusion furnace parts; in the aerospace field, it can be used to manufacture thermal protection system components, engine combustion chamber components, and high-temperature gas passages; in the nuclear energy field, it can be used to manufacture high-temperature gas-cooled reactor fuel element sheaths, neutron reflective materials, and control rod guiding structures. This composite material maintains structural integrity and functional stability even at temperatures above 1600°C, making it an irreplaceable functional material under extreme conditions.

[0095] Finally, it should be noted that the above-described embodiments are merely specific implementations of this disclosure, used to illustrate the technical solutions of this disclosure, and not to limit it. The protection scope of this disclosure is not limited thereto. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this disclosure; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this disclosure, and should all be covered within the protection scope of this disclosure. Therefore, the protection scope of this disclosure should be determined by the protection scope of the claims.

[0096] 10: Plasma treatment equipment 11: Air Inlet 12: Vacuum pump interface 13: Plasma source 14:Stone grinding block 15: Sample Placement Area

Claims

1. A method for preparing a silicon carbide coating on the surface of a graphite block, wherein, include: Silicon particles were used to react with the graphite block in a vacuum environment to obtain a graphite block with an initial carbonized silicon layer. The graphite block with the initial silicon carbide layer is placed in a plasma processing device, where it undergoes surface etching via argon plasma and surface activation treatment using a mixture of hydrogen and nitrogen gas to obtain an activated graphite block. The activated graphite block is then subjected to CVD deposition using trichloromethylsilane and methane gas in a preset ratio to obtain a CVD-deposited graphite block. This CVD-deposited graphite block is then subjected to boron trichloride concentration gradient doping CVD deposition to obtain a doped graphite block. Finally, this doped graphite block is subjected to structural gradient CVD deposition at a preset temperature and gas flow rate to obtain a silicon carbide coating.

2. The method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 1, wherein, The method involves reacting silicon particles with graphite blocks under vacuum to obtain graphite blocks with the initial silicon carbide layer, comprising: placing silicon particles with a particle size of 5-10 mm at the bottom of a reaction apparatus and placing the graphite blocks inside the reaction apparatus; heating the reaction apparatus to 1700-1800°C at a heating rate of 10°C / min under a vacuum of 500 Pa for 2-4 hours to obtain graphite blocks with the initial silicon carbide layer.

3. The method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 1, wherein, The graphite block with the initial silicon carbide layer is placed in a plasma treatment device, and surface etching is performed by argon plasma, followed by surface activation treatment using a mixed gas of hydrogen and nitrogen to obtain the activated graphite block. The process includes: introducing argon gas at a pressure of 5-50 Pa, applying 50-200 W power for 5-15 minutes of plasma etching to obtain a graphite block with a nanoscale micro-rough surface; introducing a mixed gas of hydrogen and nitrogen with a volume ratio of 4:1 into the graphite block with the nanoscale micro-rough surface, applying 150-250 W power for 5-8 minutes of surface activation treatment to obtain the activated graphite block.

4. The method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 1, wherein, Using the activated graphite block, CVD deposition is performed on trichloromethylsilane and methane gas at a preset ratio to obtain the CVD-deposited graphite block, comprising: placing the activated graphite block in a CVD reactor, introducing trichloromethylsilane and methane gas at a ratio of 1:1.5, and depositing for 0.5-1 hours to obtain a first silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane to methane gas to 1:1, and depositing the carbon-rich silicon carbide transition layer for 1-2 hours to obtain a second silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane to methane gas to 1.2:1, and depositing the second silicon carbide transition layer for 1.5-2 hours to obtain the CVD-deposited graphite block.

5. A method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 1, wherein, To obtain a doped graphite bulk material, a boron trichloride concentration gradient doping CVD deposition is performed on the CVD-deposited graphite bulk material, including: introducing 0.5-1% boron trichloride gas and mixing it with the reaction gas, and depositing it on the CVD-deposited graphite bulk material to obtain a first doped layer; introducing 0.2-0.3% boron trichloride gas into the first doped layer and depositing it to obtain a second doped layer; introducing 0.05-0.1% boron trichloride gas into the second doped layer and depositing it to obtain the doped graphite bulk material.

6. A method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 5, wherein, The process involves introducing a 0.5-1% boron trichloride gas mixture with the reaction gas to deposit the CVD-deposited graphite block, thereby obtaining the first doped layer. This includes: evacuating the CVD furnace to a vacuum of 100-500 Pa to obtain a pretreated graphite block; introducing a mixture of boron trichloride, trichloromethylsilane, and methane into the pretreated graphite block, controlling the concentration of boron trichloride to be 0.5-1% and the total gas flow rate to be 200-300 mL / min, and depositing for 2 hours to obtain the first doped layer.

7. A method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 1, wherein, The process of depositing a silicon carbide coating by performing a structural gradient CVD deposition on the doped graphite bulk material at a preset temperature and gas flow rate includes: heating the doped graphite bulk material to 1100-1150℃, adjusting the reaction gas flow rate to 150-250mL / min, and depositing for 2-3 hours to obtain a nanocrystalline structure layer; increasing the temperature of the nanocrystalline structure layer to 1200-1300℃, adjusting the gas flow rate to 250-350mL / min, and depositing for 2-3 hours to obtain a microcrystalline structure layer; and increasing the temperature of the microcrystalline structure layer to 1350-1400℃, adjusting the gas flow rate to 350-450mL / min, and depositing for 2-3 hours to obtain the silicon carbide coating.

8. The method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 7, wherein, The process of heating the doped graphite bulk material to 1100-1150℃, adjusting the reaction gas flow rate to 150-250mL / min, and depositing for 2-3 hours to obtain the nanocrystalline structure layer includes: heating the doped graphite bulk material to 1100-1150℃ at a heating rate of 5-10℃ / min to obtain a substrate at a predetermined temperature; introducing a mixed gas of trichloromethylsilane and methane into the substrate at the predetermined temperature, adjusting the flow rate to 150-250mL / min, and depositing for 2-3 hours to obtain the nanocrystalline structure layer.

9. A method for preparing a silicon carbide coating on the surface of a graphite bulk material as described in claim 1, wherein, After obtaining the silicon carbide coating, the process further includes: placing the silicon carbide coating in a temperature environment of 1500-1600℃ and annealing it for 2-4 hours to obtain the annealed silicon carbide coating.

10. A composite material, wherein, The invention includes a graphite block and a silicon carbide coating on the surface of the graphite block, the silicon carbide coating being prepared by the method described in any one of claims 1 to 9 for preparing the silicon carbide coating on the surface of the graphite block.

Images