Method for preparing a silicon carbide coating on the surface of a graphite block and composite material

Abstract

The application discloses a method for preparing a silicon carbide coating on the surface of a graphite block and a composite material. The method solves the technical problem of defects, easy peeling or cracking at the interface of a traditional double-layer silicon carbide coating by using a progressive interface optimization system combining interface activation pretreatment and gradient transition layer design. The method comprises the following steps: using silicon particles and a graphite block to perform a silicon vapor reaction 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 by using a gradient transition layer design in three dimensions of stoichiometric ratio gradient, doping element gradient and structure gradient. The silicon carbide coating prepared by the method has excellent thermal stability and interface bonding strength under high-temperature cycle conditions, and is particularly suitable for high-end application scenarios that need to work in extreme temperature and thermal shock environments for a long time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material preparation, in particular to a method for preparing a silicon carbide coating on the surface of a graphite block and a composite material. BACKGROUND

[0002] Silicon carbide coated graphite composites are widely used in high-end technical fields such as semiconductor manufacturing, aerospace and nuclear energy due to their high thermal conductivity, low expansion coefficient, high temperature oxidation resistance and wear resistance of graphite and silicon carbide. This type of composite material is usually prepared by chemical vapor deposition (CVD), liquid silicon infiltration or direct gas siliconization, among which the CVD method produces the best purity and density of the silicon carbide coating.

[0003] Currently, the preparation method of silicon carbide coating on the surface of graphite substrate mainly includes two key steps: silicon vapor reaction to form an initial silicon carbide layer, and CVD method to deposit an outer layer of silicon carbide. In the silicon vapor reaction process, silicon vapor formed by the reaction of metallic silicon at high temperature directly reacts with carbon atoms on the surface of the graphite substrate to form an initial silicon carbide layer; then an outer layer of silicon carbide is deposited on the surface of the initial layer by CVD method using trichloromethylsilane gas precursor to form a double-layer structure of silicon carbide coating.

[0004] However, the traditional double-layer silicon carbide coating preparation method has a significant defect: the interfacial bonding strength between the two layers of silicon carbide is insufficient, and peeling or cracking easily occurs under high temperature cycling or thermal shock conditions. This is mainly due to the lack of activity on the surface of the initial silicon carbide layer, and the existence of a significant composition and structure mutation between the two layers, resulting in stress concentration at the interface. This defect seriously restricts the application of silicon carbide coated graphite composites in more extreme conditions, and new interface optimization techniques are urgently needed to solve this problem. SUMMARY

[0005] In view of this, the present application provides a method for preparing a silicon carbide coating on the surface of a graphite block, which solves the problem of defects at the interface of the double-layer silicon carbide coating and easy peeling or cracking in the prior art.

[0006] The embodiment of the present application provides a method for preparing a silicon carbide coating on a graphite block surface, comprising: using metal silicon particles and a graphite block to perform a silicon vapor reaction in a vacuum environment to obtain a graphite block with an initial silicon carbide layer; placing the graphite block with the initial silicon carbide layer in a plasma processing chamber, performing surface etching via argon plasma, and performing surface activation treatment by using a mixed gas of hydrogen and nitrogen to obtain an activated graphite block; using the activated graphite block to perform CVD deposition by using trichloromethylsilane and methane gas in a preset ratio to obtain a CVD-deposited graphite block; performing CVD deposition of boron trichloride concentration gradient on the CVD-deposited graphite block to obtain a doped graphite block; and performing structure 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 for using metal silicon particles and a graphite block to perform a silicon vapor reaction in a vacuum environment to obtain a graphite block with an initial silicon carbide layer comprises: placing metal silicon particles with a particle size of 5-10 mm at the bottom of a reaction device and placing the graphite block in the reaction device; heating the reaction device to 1700-1800 DEG C at a temperature increasing rate of 10 DEG C / min under a vacuum degree of 500 Pa, and reacting for 2-4 hours to obtain the graphite block with the initial silicon carbide layer.

[0008] Preferably, the method for placing the graphite block with the initial silicon carbide layer in a plasma processing chamber, performing surface etching via argon plasma, and performing surface activation treatment by using a mixed gas of hydrogen and nitrogen to obtain an activated graphite block comprises: introducing argon under a pressure of 5-50 Pa, performing ion etching for 5-15 min by applying a power of 50-200 W 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 to the graphite block with the nanoscale micro-rough surface, performing surface activation treatment for 5-8 min by applying a power of 150-250 W to obtain the activated graphite block.

[0009] Preferably, the activated graphite block is used for CVD deposition of trichloromethylsilane and methane gas in a preset ratio to obtain a CVD-deposited graphite block, comprising: placing the activated graphite block in a CVD reaction chamber, introducing trichloromethylsilane and methane gas in a ratio of 1:1.5, and depositing for 0.5-1 hour to obtain a first silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane and methane gas to 1:1, and depositing on the first 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 on the second silicon carbide transition layer for 1.5-2 hours to obtain the CVD-deposited graphite block.

[0010] Preferably, the CVD-deposited graphite block is subjected to CVD deposition of boron trichloride concentration gradient to obtain a doped graphite block, comprising: introducing boron trichloride gas with a concentration of 0.5-1% and reaction gas mixture to deposit on the CVD-deposited graphite block to obtain a first doped layer; introducing boron trichloride gas with a concentration of 0.2-0.3% to deposit on the first doped layer to obtain a second doped layer; introducing boron trichloride gas with a concentration of 0.05-0.1% to deposit on the second doped layer to obtain the doped graphite block.

[0011] Preferably, the CVD-deposited graphite block is subjected to CVD deposition of boron trichloride concentration gradient to obtain a doped graphite block, comprising: introducing boron trichloride gas with a concentration of 0.5-1% and reaction gas mixture to deposit on the CVD-deposited graphite block to obtain a first doped layer; introducing boron trichloride gas with a concentration of 0.2-0.3% to deposit on the first doped layer to obtain a second doped layer; introducing boron trichloride gas with a concentration of 0.05-0.1% to deposit on the second doped layer to obtain the doped graphite block.

[0012] Preferably, the doped graphite block is subjected to structure gradient CVD deposition at a preset temperature and gas flow rate to obtain a silicon carbide coating, comprising: heating the doped graphite block 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; 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.

[0013] Preferably, the method further comprises: heating the doped graphite block 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 at a flow rate of 150-250mL / min to deposit a nanocrystalline structure layer.

[0014] Preferably, the method further comprises: placing the silicon carbide coating in a temperature environment of 1500-1600℃ for annealing for 2-4 hours to obtain an annealed silicon carbide coating.

[0015] The embodiment of the present application also provides a composite material, comprising a graphite block and a silicon carbide coating on the surface of the graphite block, wherein the silicon carbide coating is prepared by any one of the above methods.

[0016] The embodiment of the present application has the following technical effects:

[0017] The silicon vapor reaction of the metal silicon particles and the graphite block in a vacuum environment forms an initial silicon carbide layer which is firmly combined with the substrate, thereby providing a stable basis for subsequent processing; and the argon plasma etching and the hydrogen / nitrogen mixed gas activation treatment significantly improve the activity and roughness of the surface of the initial silicon carbide layer, thereby enhancing the bonding strength with the subsequent CVD layer, and the interface shear strength is increased by 40-60% compared with the traditional process. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings needed to be used in the embodiments. The drawings are incorporated into the specification and form a part of the specification, which show the embodiments consistent with the present disclosure, and are used to explain the technical solutions of the present disclosure together with the specification. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor.

[0019] Figure 1 is a flowchart of the method for preparing a silicon carbide coating on the surface of a graphite block provided by the embodiment of the present application;

[0020] Figure 2 is a schematic diagram of the initial silicon carbide layer formed by the silicon vapor reaction in the embodiment of the present application;

[0021] Figure 3 is a schematic diagram of the interface activation pretreatment in the embodiment of the present application. DETAILED DESCRIPTION

[0022] To make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the following will be combined with the accompanying drawings for the embodiments of the present disclosure to make a clear and complete description of the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure and not all the embodiments. The components of the embodiments of the present 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 the present disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed present disclosure, but only represents selected embodiments of the present disclosure. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present disclosure.

[0023] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0024] The term “and / or” in the present disclosure is only used to describe an association relationship, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the term “at least one” in the present disclosure means any one of multiple or any combination of at least two of multiple, 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.

[0025] As Figure 1 shown, the embodiment of the present application provides a method for preparing a silicon carbide coating on the surface of a graphite block, comprising:

[0026] Step 1, using metal silicon particles and graphite block, carrying out silicon vapor reaction in a vacuum environment to obtain a graphite block with an initial silicon carbide layer;

[0027] Exemplarily, first, high-purity metal silicon particles with a particle size of 5-10 mm are placed in a graphite crucible at the bottom of a reaction device, and the graphite block to be treated is placed on a support about 30 mm away from the silicon material in the crucible. Then the whole device is placed in a high-temperature furnace, and heated to a temperature in the range of 1700-1800 °C at a rate of 10 °C / min under a vacuum degree of 500 Pa, and kept for 2-4 hours. In this process, the metal silicon evaporates to form silicon vapor at high temperature, and the silicon vapor directly reacts with the carbon atoms on the surface of the graphite matrix to form an initial silicon carbide layer with strong chemical bonding. The thickness of the initial layer is usually 10-20 μm, which is tightly combined with the graphite matrix and provides a good basis for subsequent processing. After the reaction is completed, the sample is naturally cooled to room temperature and taken out, obtaining a graphite block with an initial silicon carbide layer.

[0028] Step 2, the graphite block with the initial silicon carbide layer is placed in a plasma treatment chamber, surface etching is carried out via argon plasma, and surface activation treatment is carried out using a mixed gas of hydrogen and nitrogen, obtaining an activated graphite block;

[0029] This step is one of the key innovations of the method, which optimizes the interface properties through plasma double modification treatment. Exemplarily, first, the graphite block with the initial silicon carbide layer is transferred to the plasma treatment chamber and vacuumed 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 by applying a power of 50-200 W, and the sample surface is subjected to ion etching treatment for 5-15 minutes. This etching process can form a nanoscale micro-rough structure on the surface of the silicon carbide, significantly increasing the surface area and mechanical interlocking effect. Subsequently, while maintaining the chamber pressure unchanged, the mixed gas of hydrogen and nitrogen with a volume ratio of 4:1 is switched, and the power is adjusted to the range of 150-250 W, and the surface activation treatment is carried out for 5-8 minutes. Hydrogen-nitrogen plasma treatment can form a large number of active sites and dangling bonds on the etched rough surface, significantly improving the surface chemical activity. Finally, high-purity helium gas is introduced for 3-5 minutes of purging and cleaning to remove possible residual substances, obtaining an activated graphite block with ideal interface properties.

[0030] Step 3, using the activated graphite block, CVD deposition is carried out via trichloromethylsilane and methane gas according to a predetermined ratio, obtaining a CVD-deposited graphite block;

[0031] This step realizes the stoichiometric ratio gradient transition of carbon and silicon content in silicon carbide, which is the first phase of multi-dimensional gradient design. Illustratively, the activated graphite block is transferred to the CVD reaction chamber, and trichloromethylsilane and methane gas are first introduced in a ratio of 1:1.5 for deposition, lasting for 0.5-1 hour, to form a carbon-rich silicon carbide transition layer. This carbon-rich layer has better chemical compatibility with the activated initial silicon carbide layer. Then the ratio of the reaction gas is gradually adjusted to 1:1, and deposition is continued for 1-2 hours to form a stoichiometric silicon carbide transition layer on the carbon-rich layer. Finally, the gas ratio is adjusted to 1.2:1, and deposition is performed for 1.5-2 hours to form a slightly silicon-rich silicon carbide layer. The entire process usually lasts for 3-5 hours, and through the gradual transition of composition, the interface stress caused by the difference in chemical composition between different layers is effectively reduced, laying a good foundation for subsequent processing.

[0032] Step 4, CVD deposition of the graphite block after CVD deposition is performed with a boron trichloride concentration gradient doping CVD deposition to obtain a doped graphite block;

[0033] This step realizes the gradient transition of doping elements, constituting the second phase of multi-dimensional gradient design. Illustratively, the CVD-deposited graphite block is first placed back into the CVD reaction chamber, and vacuum is extracted to 100-500 Pa. Then, boron trichloride gas with a concentration of 0.5-1% is introduced together with the mixed reaction gas of trichloromethylsilane and methane, and the total gas flow is controlled at 200-300 mL / min, and deposition is performed for about 2 hours to form a first doping layer with high boron doping concentration. Boron doping can significantly improve the electrical conductivity and thermal stability of the silicon carbide layer. Then, the concentration of boron trichloride is reduced to the range of 0.2-0.3% to continue deposition to form a second doping layer with medium concentration. Finally, the concentration of boron trichloride is further reduced to 0.05-0.1% to complete the deposition of the outermost layer of low-concentration doping layer. The entire doping process usually lasts for 5-8 hours, and through the gradient change of doping concentration, the performance gradient transition of the coating system is further optimized, and the thermal stress concentration caused by sudden change of material performance is reduced.

[0034] Step 5, structure gradient CVD deposition of the doped graphite block according to the preset temperature and gas flow rate to obtain a silicon carbide coating.

[0035] The step realizes the microstructure gradient transition, which is the third stage of the multi-dimensional gradient design. Illustratively, first, the doped graphite block is heated to 1100-1150°C at a heating rate of 5-10°C / min, the flow rate of the mixed gas of trichloromethylsilane and methane is controlled in the range of 150-250 mL / min, and low-temperature deposition is performed for 2-3 hours to form a nanocrystalline structure layer. The nanocrystalline structure has high toughness and interface bonding capacity. Subsequently, the temperature is gradually increased to 1200-1300°C, and the gas flow rate is increased to 250-350 mL / min, and deposition is continued for 2-3 hours to form a microcrystalline structure transition layer. Finally, the temperature is further increased to 1350-1400°C, the gas flow rate is increased to 350-450 mL / min, and deposition is performed for 2-3 hours to form an outer layer of well-oriented polycrystalline structure. The polycrystalline structure has excellent high-temperature stability and oxidation resistance performance. The entire structure gradient process usually lasts for 5-10 hours, and through the gradual transition of grain size and orientation, the mechanical and thermal properties of the coating are smoothly transitioned from the inside to the outside, further reducing thermal stress concentration and improving the stability and service life of the coating system under high-temperature cyclic working conditions.

[0036] Through the above five continuous process steps, the method successfully realizes the multi-dimensional gradient transition from the graphite substrate to the silicon carbide coating, and forms a silicon carbide composite coating with excellent interface bonding strength and high-temperature stability. Compared with the traditional process, the coating prepared by the method shows significantly improved stability in the 1600°C thermal cycle test, the interface peeling rate is reduced by more than 85%, and the shear strength is increased by 40-90%, which provides reliable technical support for high-temperature extreme environment applications.

[0037] In an embodiment of the present application, as shown in Figure 2 The method for preparing the silicon carbide coating on the graphite substrate in the present application comprises the following steps:

[0038] The metal silicon particles with a particle size of 5-10 mm are placed at the bottom of the reaction device, and the graphite block is placed in the reaction device;

[0039] The reaction device is heated to 1700-1800°C at a heating rate of 10°C / min under a vacuum degree of 500 Pa, and reacted for 2-4 hours to obtain the graphite block with an initial silicon carbide layer.

[0040] In the present embodiment, the silicon vapor generated by the metal silicon particles at high temperature reacts with the carbon atoms on the surface of the graphite substrate to form an initial silicon carbide layer. The layer has good bonding strength with the graphite substrate, laying a foundation for subsequent processing. In specific operation, the graphite block can be placed at a position about 30 mm away from the silicon particles to ensure uniform reaction.

[0041] In one embodiment of the present application, as shown in Figure 3 In one embodiment of the present application, as shown in

[0042] In this embodiment, plasma treatment is one of the key innovations of the method. Argon plasma etching forms a nanoscale rough structure on the surface of silicon carbide through physical collision, increasing the mechanical interlocking effect; and hydrogen / nitrogen mixed gas plasma treatment forms a large number of active sites and dangling bonds on the surface, significantly improving the chemical adsorption capacity of the subsequent CVD deposition layer. After etching treatment, high-purity helium can be introduced for 3-5 minutes of blowing cleaning to remove residual substances.

[0043] In one embodiment of the present application, the use of the activated graphite block for CVD deposition of trichloromethylsilane and methane gas in a predetermined ratio to obtain a CVD-deposited graphite block, including: placing the activated graphite block in a CVD reaction chamber, introducing trichloromethylsilane and methane gas in 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 and methane gas to 1:1, and depositing on the first 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 on the second silicon carbide transition layer for 1.5-2 hours to obtain the CVD-deposited graphite block.

[0044] In this embodiment, by adjusting the ratio of trichloromethylsilane and methane gas, a stoichiometric ratio gradient transition is achieved, from carbon-rich to stoichiometric ratio to slightly silicon-rich silicon carbide layer, forming a first-dimensional gradient structure. This gradient design effectively alleviates the thermal stress caused by composition differences between different layers, improving the overall stability of the coating system.

[0045] In one embodiment of the present application, the CVD-deposited graphite block is subjected to a boron trichloride concentration gradient doping CVD deposition to obtain a doped graphite block, including: introducing a boron trichloride gas with a concentration of 0.5-1% into the reaction gas mixture to deposit on the CVD-deposited graphite block to obtain a first doping layer; introducing a boron trichloride gas with a concentration of 0.2-0.3% into the first doping layer to deposit to obtain a second doping layer; introducing a boron trichloride gas with a concentration of 0.05-0.1% into the second doping layer to deposit to obtain the doped graphite block.

[0046] wherein the concentration refers to the volume percentage concentration of boron trichloride (BCl3) in the entire reaction gas mixture. That is, the volume ratio of boron trichloride gas in the total gas flow is 0.5-1%. This is a relatively low but effective doping concentration range, which is sufficient to achieve boron doping modification of the silicon carbide coating, while avoiding the structural defects of the coating that may be caused by excessively high concentration.

[0047] The reaction gas mainly includes:

[0048] Trichloromethylsilane (CH3SiCl3): as a silicon source;

[0049] Methane (CH4): as a carbon source;

[0050] Hydrogen (H2): as a carrier gas and reducing atmosphere;

[0051] In this step, boron trichloride is used as a doping gas mixed with the above-mentioned main reaction gas. Trichloromethylsilane and methane are still the main reaction gases for forming the silicon carbide matrix, and their ratio is usually kept in the range of close to 1:1 (may be slightly adjusted to adapt to the doping process). Hydrogen as a carrier gas helps the reaction gas to be uniformly distributed and creates a reducing atmosphere conducive to deposition. The addition amount of boron trichloride in this mixed gas is controlled in the range of 0.5-1%, so that during the CVD process, boron atoms can partially replace carbon or silicon atoms in the silicon carbide lattice, thereby achieving the doping effect.

[0052] The entire reaction gas system is usually supplemented with an inert gas (such as argon or helium) for adjusting the total flow and partial pressure of the reaction gas, which is adjusted according to specific process requirements. The total gas flow is generally controlled in the range of 200-300 mL / min to ensure a uniform and stable deposition process.

[0053] In this embodiment, the doping element gradient forms a gradient structure in the second dimension. Boron doping not only improves the electrical conductivity and thermal stability of the silicon carbide layer, but also further reduces the interlayer stress through the concentration gradient change, optimizing the overall performance of the coating.

[0054] In an embodiment of the present application, the introduced concentration of boron trichloride gas is 0.5-1%, mixed with the reaction gas, and the graphite block after CVD deposition is deposited to obtain a first doped layer, comprising: extracting vacuum in the CVD furnace to 100-500 Pa to obtain a pretreated graphite block; introducing a mixed gas of boron trichloride, trichloromethylsilane and methane to the pretreated graphite block, controlling the concentration of boron trichloride to be 0.5-1%, and the total gas flow to be 200-300 mL / min, and depositing for 2 hours to obtain the first doped layer.

[0055] In the present embodiment, before the doping treatment, the CVD furnace needs to be vacuumed to a suitable pressure range to ensure the stability of the deposition process and the consistency of the doping effect. The control of the total gas flow is crucial to the formation of a uniform doped layer.

[0056] In an embodiment of the present application, the doped graphite block is heated to 1100-1150℃ and the reaction gas flow rate is adjusted to 150-250 mL / min to obtain a nanocrystalline structure layer, comprising: heating the doped graphite block 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 to 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.

[0057] In the present embodiment, by controlling the temperature and gas flow rate, a gradient change from nanocrystalline to microcrystalline to polycrystalline structure is achieved, forming a third-dimensional gradient structure. The silicon carbide layer with different grain sizes has different mechanical and thermal properties, and this microstructure gradient further improves the thermal stability and mechanical properties of the coating system.

[0058] In an embodiment of the present application, the doped graphite block is heated to 1100-1150℃ and the reaction gas flow rate is adjusted to 150-250 mL / min to obtain a nanocrystalline structure layer, comprising: heating the doped graphite block 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 to 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.

[0059] In this embodiment, controlling the heating rate is crucial to avoiding thermal stress on the graphite substrate and the deposited coating due to excessively rapid temperature changes. A suitable heating rate ensures that the coating system maintains structural integrity during the heating process.

[0060] In one embodiment of this application, after obtaining the silicon carbide coating, the process further includes: placing the silicon carbide coating in a temperature environment of 1500-1600°C and annealing it for 2-4 hours to obtain an annealed silicon carbide coating.

[0061] 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.

[0062] Example 1: Preparation of silicon carbide coating for graphite components of aero-engines

[0063] Raw materials and equipment: 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%); Metallic silicon particles, particle size 5-10 mm; Plasma treatment equipment: Radio frequency plasma treatment system, maximum power 500 W; CVD equipment: Vertical hot-wall CVD furnace, maximum temperature 1800℃;

[0064] Process flow:

[0065] Step 1: Silicon vapor reaction

[0066] Place 10g of solid silicon particles at the bottom of the graphite crucible and place the graphite substrate on the graphite support 30mm away from the silicon material inside the crucible.

[0067] Inside the graphitization furnace, the temperature is increased to 1750℃ at a rate of 10℃ / min;

[0068] The sample was kept under a vacuum of 500 Pa for 3 hours, then allowed to cool naturally to room temperature before being removed.

[0069] Step 2: Interface activation pretreatment involves transferring the sample to the plasma processing chamber;

[0070] Evacuate to 1 Pa, introduce high-purity argon gas, and adjust the pressure to 25 Pa;

[0071] Turn on the RF power supply, set the power to 120W, and perform ion etching for 10 minutes;

[0072] Maintain 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.

[0073] Third step: Gradient transition layer deposition

[0074] Phase one (stoichiometric ratio gradient, total time 4 hours);

[0075] Initial stage (1 hour): Trichloromethylsilane to methane gas ratio 1:1.5;

[0076] Intermediate stage (1.5 hours): Gas ratio gradually adjusted to 1:1;

[0077] Later stage (1.5 hours): Gas ratio adjusted to 1.2:1;

[0078] Phase two (doping element gradient, total time 6 hours) Initial sub-stage (2 hours): Introduce 0.8% boron trichloride Intermediate sub-stage (2 hours): Linearly reduce boron trichloride concentration to 0.3% Later sub-stage (2 hours): Reduce boron trichloride concentration to 0.08%

[0079] Phase three (structure gradient, total time 8 hours) Initial temperature 1120°C, gas flow rate 200 mL / min (2 hours) Mid-term temperature gradually increased to 1250°C, flow rate 300 mL / min (3 hours) Later temperature increased to 1380°C, flow rate 400 mL / min (3 hours)

[0080] Test results: Total coating thickness: 65±3 μm (about 15 μm for initial reaction layer, about 50 μm for gradient CVD layer) Interface peeling area less than 2% after 1600°C thermal cycle test for 50 times Shear strength: 35.6 MPa, increased by 92.4% compared to traditional process Oxidation test: Weight increase rate less than 0.5% after 1500°C air environment exposure for 100 hours.

[0081] Example 2: Preparation of silicon carbide coating for high-temperature graphite products for nuclear energy

[0082] Raw materials and equipment:

[0083] Graphite substrate: Nuclear-grade graphite tube with density 1.85 g / cm³, outer diameter 80 mm, inner diameter 60 mm, length 120 mm; Plasma equipment: Microwave plasma treatment system, 2.45 GHz frequency; CVD equipment: Horizontal hot-wall CVD furnace, equipped with rotating sample table;

[0084] Process: Similar to Example 1, but the main differences: In the first step of silicon vapor reaction, the graphite tube rotates at a speed of 5 rpm during the reaction to ensure uniform reaction interface. The interface activation pretreatment uses microwave plasma, with a power controlled at 350 W. Aluminum nitride doping is added in the gradient transition layer deposition, gradually decreasing from 0.3% to 0.05%. The graphite tube remains rotating throughout the entire process to ensure uniformity of the coating.

[0085] Test results:

[0086] Coating thickness uniformity: The thickness deviation between the inner and outer surfaces is less than 5%

[0087] Thermal neutron absorption cross-section: Less than 5.2 x 10-24 cm² After 100 times of 1600°C thermal cycle test, the interface peeling area is less than 1% Oxidation resistance: The weight gain rate is less than 0.3% after 200 hours of exposure in air at 1450°C.

[0088] Comparative Example 1:

[0089] Traditional double-layer silicon carbide coating process According to the traditional process, the graphite block is sequentially subjected to silicon vapor reaction and CVD deposition to prepare a double-layer silicon carbide coating. After the first step of reaction at 1700°C and 500 Pa for 3 hours, it directly enters the second step of conventional CVD deposition at 1300°C for 25 hours. The obtained coating is subjected to 1600°C thermal cycle test for 10 times, and it is found that obvious peeling occurs at the interface, with a peeling area accounting for about 28% of the total area. In the shear strength test, the interface strength is 18.5 MPa.

[0090] Comparative Example 2:

[0091] Only interface activation pretreatment In the traditional process, an interface activation pretreatment step is added between the two steps, including 10 minutes of argon ion etching (power 150 W, pressure 20 Pa) and 6 minutes of hydrogen-nitrogen mixed gas plasma activation (power 200 W). The second step CVD deposition process parameters are the same as those in Comparative Example 1. The obtained coating is subjected to 1600°C thermal cycle test for 20 times, and the interface peeling area accounts for about 12% of the total area. In the shear strength test, the interface strength is increased to 27.3 MPa.

[0092] Comparative Example 3:

[0093] Only gradient transition layer design Based on the traditional process, the second step of CVD deposition is changed to a three-stage gradient transition layer design, but no interface activation pretreatment is performed. The three-stage deposition includes stoichiometric ratio gradient (4 hours), doping element gradient (6 hours), and structure gradient (8 hours). The obtained coating is subjected to 1600°C thermal cycle test for 30 times, and the interface peeling area accounts for about 8% of the total area. In the shear strength test, the interface strength is 25.1 MPa.

[0094] It can be seen from the above examples and comparative examples that the progressive scheme combining interfacial activation pretreatment with gradient transition layer design can significantly improve the interfacial bonding strength and high-temperature stability of the double-layer silicon carbide coating, especially in application scenarios that need to withstand extreme working conditions for a long time. In all test indicators, the technical scheme is superior to the three comparative examples, especially in the aspect of thermal cycle stability, the improvement is the most significant.

[0095] In summary, the method for preparing a silicon carbide coating on the surface of a graphite block provided by the present application fundamentally solves the technical problems of defects, easy peeling or cracking at the interface of the traditional double-layer silicon carbide coating through a progressive interfacial optimization system combining interfacial activation pretreatment and gradient transition layer design. The silicon carbide coating prepared by the method exhibits excellent thermal stability and interfacial bonding strength under high-temperature cycle conditions, providing reliable technical support for high-end application fields.

[0096] The present application also provides a composite material comprising a graphite block and a silicon carbide coating on the surface of the graphite block. The composite material is prepared by any of the above-mentioned methods for preparing a silicon carbide coating on the surface of a graphite block. The composite material has both the thermal conductivity and electrical conductivity of graphite and the high-temperature stability and oxidation resistance of silicon carbide, and is particularly suitable for various extreme environment application scenarios. In the field of semiconductor manufacturing, the composite material can be used to make high-temperature furnace component, wafer carrier and diffusion furnace parts; in the field of aerospace, it can be used to make thermal protection system components, engine combustion chamber components and high-temperature gas passages; in the field of nuclear energy, it can be used to make high-temperature gas cooled reactor fuel element sheath, neutron reflecting material and control rod guide structure. The composite material still maintains structural integrity and functional stability in a high-temperature environment above 1600℃, making it an irreplaceable functional material in extreme working conditions.

[0097] Finally, it should be noted that the above examples are only specific embodiments of the present disclosure, which are used to illustrate the technical solutions of the present disclosure, but not to limit it. Although the present disclosure has been described in detail with reference to the foregoing examples, those skilled in the art should understand that any person skilled in the art within the technical scope disclosed by the present disclosure can modify or easily think of changes to the technical solutions recorded in the foregoing examples, or make equivalent substitutions for part of the technical features; and these modifications, changes or substitutions do not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure, and should be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

Claims

1. A method of preparing a silicon carbide coating on a surface of a graphite monolith, characterized by, The application relates to a method for preparing a silicon carbide coating on a graphite block, comprising the following steps: (1) using metal silicon particles and a graphite block to carry out silicon vapor reaction in a vacuum environment to obtain a graphite block with an initial silicon carbide layer; (2) placing the graphite block with the initial silicon carbide layer into a plasma processing chamber, carrying out surface etching through argon plasma, and carrying out surface activation treatment by using a mixed gas of hydrogen and nitrogen to obtain an activated graphite block; (3) using the activated graphite block to carry out CVD deposition by using trichloromethylsilane and methane gas according to a preset proportion to obtain a CVD-deposited graphite block; (4) carrying out CVD deposition of a boron trichloride concentration gradient on the CVD-deposited graphite block to obtain a doped graphite block, including: introducing boron trichloride gas with a concentration of 0.5-1% into a mixed reaction gas to deposit on the CVD-deposited graphite block to obtain a first doped layer; introducing boron trichloride gas with a concentration of 0.2-0.3% into the first doped layer to obtain a second doped layer; introducing boron trichloride gas with a concentration of 0.05-0.1% into the second doped layer to obtain the doped graphite block; (5) carrying out structure gradient CVD deposition on the doped graphite block according to a preset temperature and gas flow rate to obtain a silicon carbide coating, including: heating the doped graphite block to 1100-1150 DEG C, adjusting the reaction gas flow rate to 150-250 mL / min, and depositing for 2-3 hours to obtain a nanocrystalline structure layer; raising the temperature of the nanocrystalline structure layer to 1200-1300 DEG C, adjusting the gas flow rate to 250-350 mL / min, and depositing for 2-3 hours to obtain a microcrystalline structure layer; raising the temperature of the microcrystalline structure layer to 1350-1400 DEG C, adjusting the gas flow rate to 350-450 mL / min, and depositing for 2-3 hours to obtain the silicon carbide coating. The application further discloses a method for preparing a silicon carbide coating on a graphite block, comprising the following steps: (1) extracting vacuum in a CVD furnace to 100-500 Pa to obtain a pretreated graphite block; (2) introducing a mixed gas of boron trichloride, trichloromethylsilane and methane into the pretreated graphite block, controlling the concentration of the boron trichloride to be 0.5-1%, and controlling the total gas flow rate to be 200-300 mL / min, and depositing for 2 hours to obtain the first doped layer; (3) carrying out structure gradient CVD deposition on the doped graphite block according to a preset temperature and gas flow rate to obtain a silicon carbide coating, including: heating the doped graphite block to 1100-1150 DEG C, adjusting the reaction gas flow rate to 150-250 mL / min, and depositing for 2-3 hours to obtain a nanocrystalline structure layer; raising the temperature of the nanocrystalline structure layer to 1200-1300 DEG C, adjusting the gas flow rate to 250-350 mL / min, and depositing for 2-3 hours to obtain a microcrystalline structure layer; raising the temperature of the microcrystalline structure layer to 1350-1400 DEG C, adjusting the gas flow rate to 350-450 mL / min, and depositing for 2-3 hours to obtain the silicon carbide coating. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method of claim 1 wherein the graphite block surface is prepared by, The method for preparing the graphite block with initial silicon carbide layer by using metal silicon particles and graphite block in vacuum environment, comprising: placing the metal silicon particles with particle size of 5-10 mm at the bottom of the reaction device, and placing the graphite block in the reaction device; heating the reaction device to 1700-1800 DEG C at a heating rate of 10 DEG C / min under a vacuum degree of 500 Pa, and reacting for 2-4 hours to obtain the graphite block with initial silicon carbide layer.

3. The method of claim 1, wherein, The method for preparing the graphite block with initial silicon carbide layer by using metal silicon particles and graphite block in vacuum environment, comprising: introducing argon gas under a pressure of 5-50 Pa, and performing ion etching for 5-15 min by applying a power of 50-200 W to obtain the graphite block with nanoscale micro-rough surface; introducing the mixed gas of hydrogen and nitrogen with a volume ratio of 4:1 to the graphite block with nanoscale micro-rough surface, and performing surface activation treatment for 5-8 min by applying a power of 150-250 W to obtain the activated graphite block.

4. The method of claim 1 wherein the graphite block surface is prepared by, The method for preparing the graphite block with initial silicon carbide layer by using metal silicon particles and graphite block in vacuum environment, comprising: placing the activated graphite block in a CVD reaction chamber, introducing trichloromethylsilane and methane gas in a ratio of 1:1.5, and depositing for 0.5-1 h to obtain the first silicon carbide transition layer; adjusting the gas ratio of trichloromethylsilane and methane gas to 1:1, and depositing the first silicon carbide transition layer for 1-2 h to obtain the 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 h to obtain the CVD-deposited graphite block.

5. The method of claim 1 wherein the graphite block surface is prepared by, After obtaining the silicon carbide coating, the method further comprises: placing the silicon carbide coating in a temperature environment of 1500-1600 DEG C, and annealing for 2-4 h to obtain the annealed silicon carbide coating.

6. A composite material, characterized by, The graphite block with silicon carbide coating prepared by the method for preparing the graphite block with initial silicon carbide layer by using metal silicon particles and graphite block in vacuum environment, comprising: a graphite block, and a silicon carbide coating on the surface of the graphite block, wherein the silicon carbide coating is prepared by the method for preparing the graphite block with initial silicon carbide layer by using metal silicon particles and graphite block in vacuum environment according to any one of claims 1-5.

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