Preparation method of silicon carbide coating by CVD (Chemical Vapor Deposition) method

Abstract

The invention relates to a preparation method of a CVD method silicon carbide coating, and relates to the field of coating preparation, and the preparation method comprises the following steps: carrying out ultrasonic cleaning and drying on a substrate to obtain a cleaned substrate; performing pyrolytic carbon deposition on the cleaned substrate to obtain a substrate with a pyrolytic carbon layer; activating the matrix with the pyrolytic carbon layer to obtain an activated matrix; introducing mixed reaction gas to perform deposition treatment on the activated substrate to obtain a substrate with a silicon carbide coating; and carrying out heat treatment and passivation treatment on the substrate with the silicon carbide coating to complete the preparation of the silicon carbide coating by the CVD method. The compactness, the bonding strength and the stability of the coating are improved, and the silicon carbide coating is compact, uniform and free of cracks and has good coverage on a matrix in a complex shape.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coating preparation, in particular to a preparation method of a CVD silicon carbide coating. BACKGROUND

[0002] In the field of chemical coating preparation, silicon carbide coatings have many excellent properties and play an important role in many industries. With the continuous development of industrial technology, the requirements for material performance are increasing, and the application range of silicon carbide coatings is also continuously expanding. For example, in the fields of aerospace and mechanical manufacturing, its good high-temperature resistance and corrosion resistance can help improve the performance and service life of related components, and promote the technological progress and product upgrading of these industries.

[0003] In order to prepare a silicon carbide coating, a conventional chemical vapor deposition (CVD) process is often used. In this process, the substrate is generally placed directly in the reaction environment, and the gas is introduced and reacted according to the conventional process. This process can achieve the deposition of the coating to some extent when applied to substrates with simple shapes and structures. However, when facing complex shapes or porous substrates (such as graphite and carbon-carbon composites), the process usually relies on experience to adjust the reaction parameters in an attempt to improve the deposition effect of the coating.

[0004] The traditional CVD process has obvious defects. When depositing on complex shapes or porous substrates (such as graphite and carbon-carbon composites), it is difficult to achieve uniform distribution of coating thickness and composition, and defects such as pores and cracks are easily produced, which seriously affects the density and integrity of the coating, and therefore needs to be improved. SUMMARY

[0005] In order to improve the performance of the silicon carbide coating, the present application provides a preparation method of a CVD silicon carbide coating.

[0006] The preparation method of a CVD silicon carbide coating provided by the present application adopts the following technical scheme: A preparation method of a CVD silicon carbide coating, comprising the following steps: S1, ultrasonic cleaning and drying the substrate to obtain a cleaned substrate; pyrolytic carbon deposition is performed on the cleaned substrate to obtain a substrate with a pyrolytic carbon layer; S2, activating the substrate with the pyrolytic carbon layer to obtain an activated substrate; S3, depositing the activated substrate by introducing a mixed reaction gas to obtain a substrate with a silicon carbide coating; S4, heat treating and passivating the substrate with the silicon carbide coating to complete the preparation of the CVD silicon carbide coating.

[0007] By constructing a pyrolytic carbon interface layer, the thermal stress caused by the difference in thermal expansion coefficients between the silicon carbide coating and the substrate is effectively buffered, thereby enhancing the bonding strength of the coating. Activation treatment cleans and moderately roughens the interface, increasing the nucleation sites for the coating and providing a more uniform and dense initial growth surface for subsequent deposition. Deposition treatment using mixed reactive gases optimizes the crystal structure of the coating, improving its intrinsic density and long-term stability at high temperatures. Finally, heat treatment and passivation further eliminate the internal stress of the coating, and in-situ passivation forms a protective film that seals microscopic defects, thus comprehensively improving the density, bonding strength, and stability of the coating. The silicon carbide coating is dense, uniform, and crack-free, exhibiting excellent coverage on complex-shaped substrates.

[0008] Preferably, the pyrolysis carbon deposition conditions in step S1 are: deposition pressure of 1-3 kPa, temperature of 900-1100℃, propane introduced for pyrolysis carbon deposition, propane flow rate of 30-70 sccm, and deposition time of 20-40 min.

[0009] By optimizing the pressure, temperature, and reaction gas flow rate in the pyrolytic carbon deposition step, a pyrolytic carbon transition layer with suitable structure and thickness was formed on the substrate surface. This transition layer has good flexibility and chemical compatibility, which can effectively alleviate the internal stress caused by the thermal expansion mismatch between the silicon carbide coating and the substrate, thereby enhancing the bonding strength of the coating. At the same time, the deposition conditions are conducive to the formation of a uniform and dense interface structure, providing a good nucleation basis for the subsequent deposition of silicon carbide coatings, thereby promoting the improvement of the overall coating density and stability.

[0010] Preferably, the activation treatment conditions in step S2 are as follows: an activation gas is introduced at a flow rate of 2-10 sccm, the gas is introduced for 1-2 minutes, then paused for 4-6 minutes, and the cycle is repeated 4-6 times.

[0011] By using a pulsed fluorine-containing activating gas treatment method, under suitable gas flow rate and circulation interval, the surface of the pyrolytic carbon layer is moderately cleaned and controllably roughened. This treatment method can effectively remove surface impurities and increase the density of surface active sites, providing a more uniform nucleation basis for subsequent silicon carbide deposition, thereby promoting the dense growth of the coating.

[0012] Preferably, the activating gas includes sulfur hexafluoride.

[0013] By selecting sulfur hexafluoride as the activating gas, the fluoride ions released at high temperatures are used to gently and uniformly etch the surface of carbon materials. This etching effectively cleans the surface and forms a suitable micro-roughness, increasing the mechanical interlocking and chemical bonding force between the silicon carbide coating and the pyrolytic carbon interface layer. At the same time, this process helps to form active sites at the interface, promoting the uniform nucleation and dense growth of silicon carbide, thereby synergistically optimizing the coating's bonding strength, structural density, and stability.

[0014] Preferably, the deposition conditions in step S3 are a deposition pressure of 1-3 kPa, a deposition temperature of 1050-1150℃, and a deposition time of 4-6 h.

[0015] By selecting appropriate deposition temperature and pressure, the reaction gas is fully decomposed and the deposited atoms have sufficient surface migration ability to form a dense coating, while avoiding grain coarsening and increased internal stress that may be caused by excessively high temperature. With sufficient deposition time, the complete construction of the coating and the optimization of its microstructure are achieved, thereby synergistically improving the overall density of the coating, the bonding strength with the substrate, and its long-term stability during thermal cycling.

[0016] Preferably, the mixed reaction gas in step S3 includes trichloromethylsilane carrier gas, silane carrier gas and trimethylaluminum carrier gas, and step S3 also includes a dilution gas, which includes hydrogen.

[0017] By employing trichloromethylsilane as the primary silicon-carbon source and supplementing it with silane as a secondary silicon source, the gas-phase reaction process can be optimized and the stoichiometry of the deposited coating can be improved, thereby promoting the formation of a more complete and dense crystal structure. At the same time, the introduction of trimethylaluminum as a dopant, utilizing its solid solution effect in the silicon carbide lattice, can regulate the intrinsic properties of the coating and help improve its structural stability under high-temperature conditions. Using hydrogen as a dilution gas and carrier gas can not only adjust the partial pressure and concentration of the precursor in the reaction zone and promote the uniformity of the deposition process, but also help maintain the reducing atmosphere of the reaction system and reduce the introduction of impurities, thereby synergistically improving the density, bonding strength and stability of the coating.

[0018] Preferably, the volumetric flow rate ratio of the dilution gas, trichloromethylsilane carrier gas, silane, and trimethylaluminum carrier gas is 15:1:0.1:(0.02-0.1).

[0019] By limiting the ratio range of the reactant gases, trichloromethylsilane achieves a moderate decomposition rate under sufficient hydrogen dilution, which is beneficial for forming structurally complete silicon carbide crystals and reducing the generation of free carbon. The introduction of supplementary silane further optimizes the silicon-carbon ratio in the gas phase, promoting precise control of the coating's stoichiometry. Regulating the doping of trimethylaluminum within a suitable concentration range not only improves the intrinsic structural stability of the coating through solid solution strengthening but also avoids lattice distortion that may be caused by excessive doping. This coordinated gas phase composition keeps the deposition process in balance, jointly promoting the formation of a dense coating structure, enhancing interfacial bonding, and improving high-temperature stability.

[0020] Preferably, during the deposition process in step S3, the deposition temperature fluctuates periodically between ±20 and ±30°C.

[0021] By introducing periodic temperature fluctuations during the deposition process, silicon carbide grains undergo repeated nucleation and structural adjustments during growth, effectively interrupting the continuous longitudinal growth trend of columnar crystals and forming a more uniform equiaxed fine-grained structure. This optimization of the microstructure reduces longitudinal crack channels within the coating, thereby improving its overall density. At the same time, the refined grain structure and improved crystal orientation help to make the interfacial stress distribution more uniform, enhance the bonding strength between the coating and the substrate, and improve the structural stability and damage resistance of the coating under thermal cycling conditions.

[0022] Preferably, the heat treatment conditions in step S4 are to raise the temperature to 1200-1300℃ at a rate of 4-10℃ / min and hold for 1-2 hours.

[0023] By setting an appropriate heating rate and high-temperature holding treatment, the deposited silicon carbide coating undergoes a controllable atomic rearrangement and structural relaxation process. This heat treatment helps eliminate micro-stress within the coating, promotes grain boundary migration and defect healing, thereby improving the structural density of the coating. At the same time, this process can optimize the crystal integrity of the coating, making its interfacial bonding with the substrate stronger, and improving the phase stability and creep resistance of the coating under high-temperature service conditions, thus enhancing the overall performance of the coating.

[0024] Preferably, the passivation treatment conditions in step S4 are as follows: cooling to 850-950°C at a rate of 3-5°C / min, introducing 50-100ppm of oxygen, and passivating for 10-30min.

[0025] By controlling the cooling process and introducing a low concentration of oxygen in the intermediate temperature range for passivation treatment, a controllable slight oxidation occurs on the surface of the silicon carbide coating, generating a dense protective film in situ. This film can effectively fill the microscopic defects formed during the deposition process, thereby improving the overall density of the coating. At the same time, the passivation film acts as a diffusion barrier, enhancing the coating's oxidation resistance in high-temperature environments. Furthermore, its good chemical compatibility with the substrate coating and its matching thermal expansion characteristics also help maintain the integrity of the interface structure, thus synergistically optimizing the long-term stability and bonding strength of the coating.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. By constructing a pyrolytic carbon interface layer, the thermal stress caused by the difference in thermal expansion coefficients between the silicon carbide coating and the substrate is effectively buffered, thereby enhancing the bonding strength of the coating. Activation treatment cleans and moderately roughens the interface, increasing the nucleation sites of the coating and providing a more uniform and dense initial growth surface for subsequent deposition. Deposition treatment using mixed reactive gases optimizes the crystal structure of the coating, improving its intrinsic density and long-term stability at high temperatures. Finally, heat treatment and passivation further eliminate the internal stress of the coating, and in-situ passivation forms a protective film that seals microscopic defects, thereby comprehensively improving the density, bonding strength, and stability of the coating. The silicon carbide coating is dense, uniform, and crack-free, exhibiting good coverage on complex-shaped substrates.

[0027] 2. By optimizing the pressure, temperature, and reaction gas flow rate in the pyrolytic carbon deposition step, a pyrolytic carbon transition layer with suitable structure and thickness was formed on the substrate surface. This transition layer has good flexibility and chemical compatibility, which can effectively alleviate the internal stress caused by the thermal expansion mismatch between the silicon carbide coating and the substrate, thereby enhancing the bonding strength of the coating. At the same time, the deposition conditions are conducive to the formation of a uniform and dense interface structure, providing a good nucleation basis for the subsequent deposition of silicon carbide coating, thereby promoting the improvement of the overall coating density and stability.

[0028] 3. By introducing periodic temperature fluctuations during the deposition process, silicon carbide grains undergo repeated nucleation and structural adjustments during growth, effectively interrupting the continuous longitudinal growth trend of columnar crystals and forming a more uniform equiaxed fine-grained structure. This optimization of the microstructure reduces longitudinal crack channels within the coating, thereby improving its overall density. At the same time, the refined grain structure and improved crystal orientation help to make the interfacial stress distribution more uniform, enhance the bonding strength between the coating and the substrate, and improve the structural stability and damage resistance of the coating under thermal cycling conditions. Detailed Implementation

[0029] This application discloses a method for preparing silicon carbide coatings using CVD. Unless otherwise specified, all raw materials used in this application are commercially available. The following detailed description, in conjunction with embodiments, further illustrates this application: Raw material description: The matrix is ​​a carbon-carbon composite material, propane (CAS No.: 74-98-6), sulfur hexafluoride (CAS No.: 2551-62-4), trichloromethylsilane (CAS No.: 75-79-6), silane (CAS No.: 7803-62-5), and trimethylaluminum (CAS No.: 75-24-1).

[0030] Example 1 S1. The substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 30 min each, and then vacuum dried at 120℃ for 2 h to obtain the cleaned substrate. The cleaned substrate was then placed into a chemical vapor deposition reaction chamber and evacuated to a vacuum of 5 × 10⁻⁶. -3 Under an argon protective atmosphere, the deposition pressure is 1 kPa, and the temperature is increased to 900°C at a rate of 5°C / min. High-purity propane gas is introduced to carry out pyrolytic carbon deposition at a propane flow rate of 30 sccm and a deposition time of 40 min. The propane is then stopped, and the current temperature is maintained under argon protection to obtain a matrix with a pyrolytic carbon layer. S2. The matrix with the pyrolytic carbon layer is activated by introducing an activation gas (sulfur hexafluoride) at a flow rate of 2 sccm. After 2 minutes of introduction, the flow is paused for 4 minutes. After 6 cycles, the activated matrix is ​​obtained. S3. Adjust the deposition pressure to 1 kPa, heat to 1050℃ at a rate of 5℃ / min, stabilize for 30 min, and then introduce a mixed reaction gas. The mixed reaction gas includes trichloromethylsilane carrier gas (carrier gas is argon, bubbler temperature 30℃, 50 sccm), silane and trimethylaluminum carrier gas (carrier gas is hydrogen, bubbler temperature 35℃), and dilution gas is hydrogen. The volume flow rate ratio of dilution gas, trichloromethylsilane carrier gas, silane and trimethylaluminum carrier gas is 15:1:0.1:0.02. Deposition for 6 h yields a substrate with a silicon carbide coating. S4. Under an argon protective atmosphere, the substrate with the silicon carbide coating is subjected to heat treatment and passivation treatment. The temperature is raised to 1200℃ at a rate of 4℃ / min and held for 2 hours. Then, it is cooled to 850℃ at a rate of 3℃ / min. 50ppm of oxygen is introduced and passivation is performed for 30 minutes. Under a pure argon protective atmosphere, it is cooled to below 30℃ at a rate of 3℃ / min to complete the preparation of the CVD silicon carbide coating.

[0031] Example 2 S1. The substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 30 min each, and then vacuum dried at 120℃ for 2 h to obtain the cleaned substrate. The cleaned substrate was then placed into a chemical vapor deposition reaction chamber and evacuated to a vacuum of 5 × 10⁻⁶.-3 Under an argon protective atmosphere, the deposition pressure was 3 kPa, and the temperature was increased to 1100 °C at a rate of 5 °C / min. High-purity propane gas was introduced to carry out pyrolytic carbon deposition at a propane flow rate of 70 sccm and a deposition time of 20 min. The propane was then stopped, and the current temperature was maintained under argon protection to obtain a matrix with a pyrolytic carbon layer. S2. The matrix with the pyrolytic carbon layer is activated by introducing an activation gas (sulfur hexafluoride) at a flow rate of 10 sccm. The gas is introduced for 1 minute and then paused for 6 minutes. After 4 cycles, the activated matrix is ​​obtained. S3. Adjust the deposition pressure to 3 kPa, heat to 1150℃ at a rate of 5℃ / min, stabilize for 30 min, and then introduce a mixed reaction gas. The mixed reaction gas includes trichloromethylsilane carrier gas (carrier gas is argon, bubbler temperature 30℃, 50 sccm), silane and trimethylaluminum carrier gas (carrier gas is hydrogen, bubbler temperature 35℃), and dilution gas is hydrogen. The volume flow rate ratio of dilution gas, trichloromethylsilane carrier gas, silane and trimethylaluminum carrier gas is 15:1:0.1:0.1. Deposition for 4 h yields a substrate with a silicon carbide coating. S4. Under an argon protective atmosphere, the substrate with the silicon carbide coating is subjected to heat treatment and passivation treatment. The temperature is raised to 1300℃ at a rate of 10℃ / min and held for 1 hour. Then, it is cooled to 950℃ at a rate of 5℃ / min. 100ppm of oxygen is introduced and passivation is performed for 10 minutes. Under a pure argon protective atmosphere, it is cooled to below 30℃ at a rate of 3℃ / min to complete the preparation of the CVD silicon carbide coating.

[0032] Example 3 S1. The substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 30 min each, and then vacuum dried at 120℃ for 2 h to obtain the cleaned substrate. The cleaned substrate was then placed into a chemical vapor deposition reaction chamber and evacuated to a vacuum of 5 × 10⁻⁶. -3 Under an argon protective atmosphere, the deposition pressure is 2 kPa, and the temperature is increased to 1000℃ at a rate of 5℃ / min. High-purity propane gas is introduced to carry out pyrolytic carbon deposition at a propane flow rate of 50 sccm and a deposition time of 30 min. The propane is then stopped, and the current temperature is maintained under argon protection to obtain a matrix with a pyrolytic carbon layer. S2. The matrix with the pyrolytic carbon layer is activated by introducing an activation gas (sulfur hexafluoride) at a flow rate of 6 sccm. After introducing the gas for 1.5 min, the flow is paused for 5 min. After 5 cycles, the activated matrix is ​​obtained. S3. Adjust the deposition pressure to 2 kPa, heat to 1100℃ at a rate of 5℃ / min, stabilize for 30 min, and then introduce a mixed reaction gas. The mixed reaction gas includes trichloromethylsilane carrier gas (carrier gas is argon, bubbler temperature 30℃, 50 sccm), silane and trimethylaluminum carrier gas (carrier gas is hydrogen, bubbler temperature 35℃), and dilution gas is hydrogen. The volume flow ratio of dilution gas, trichloromethylsilane carrier gas, silane and trimethylaluminum carrier gas is 15:1:0.1:0.06. Deposition for 5 h yields a substrate with a silicon carbide coating. S4. Under an argon protective atmosphere, the substrate with the silicon carbide coating is subjected to heat treatment and passivation treatment. The temperature is raised to 1250℃ at a rate of 7℃ / min and held for 1.5h. Then, it is cooled to 900℃ at a rate of 4℃ / min. 75ppm of oxygen is introduced and passivation is performed for 20min. Under a pure argon protective atmosphere, it is cooled to below 30℃ at a rate of 3℃ / min to complete the preparation of the CVD silicon carbide coating.

[0033] Example 4 Example 4 is based on Example 3. The only difference between Example 4 and Example 3 is that in Example 4, the pyrolysis carbon deposition conditions in step S1 are: deposition pressure 0.5 kPa, temperature raised to 800°C, propane introduced for pyrolysis carbon deposition, propane flow rate 20 sccm, and deposition time 60 min.

[0034] Example 5 Example 5 is based on Example 3. The only difference between Example 5 and Example 3 is that in Example 5, the pyrolysis carbon deposition conditions in step S1 are: deposition pressure 4 kPa, temperature raised to 1200°C, propane introduced for pyrolysis carbon deposition, propane flow rate 90 sccm, and deposition time 10 min.

[0035] Example 6 Example 6 is based on Example 3. The only difference between Example 6 and Example 3 is that in Example 6, the activation treatment conditions in step S2 are: an activation gas is introduced, the activation gas flow rate is 1 sccm, the gas is introduced for 3 minutes and then paused for 2 minutes, and the cycle is repeated 7 times.

[0036] Example 7 Example 7 is based on Example 3. The only difference between Example 7 and Example 3 is that in Example 7, the activation treatment conditions in step S2 are: an activation gas is introduced, the activation gas flow rate is 15 sccm, the gas is introduced for 0.5 min and then paused for 7 min, and the cycle is repeated 3 times.

[0037] Example 8 Example 8 is based on Example 3. The only difference between Example 8 and Example 3 is that in Example 8, the deposition treatment conditions in step S3 are a deposition pressure of 0.5 kPa, a deposition temperature of 1000℃, and a deposition time of 7 h.

[0038] Example 9 Example 9 is based on Example 3. The only difference between Example 9 and Example 3 is that in Example 9, the deposition treatment conditions in step S3 are a deposition pressure of 4 kPa, a deposition temperature of 1200℃, and a deposition time of 3 h.

[0039] Example 10 Example 10 is based on Example 3. The only difference between Example 10 and Example 3 is that in Example 10, trimethylaluminum carrier gas is not added in step S3, and the volume flow ratio of dilution gas, trichloromethylsilane carrier gas and silane is 15:1:0.1.

[0040] Example 11 Example 11 is based on Example 3. The only difference between Example 11 and Example 3 is that in step S3 of Example 11, the volume flow ratio of dilution gas, trichloromethylsilane carrier gas, silane and trimethylaluminum carrier gas is 15:1:0.1:0.15.

[0041] Example 12 Example 12 is based on Example 3. The only difference between Example 12 and Example 3 is that in Example 12, during the deposition process in step S3, the deposition temperature fluctuates periodically by ±20°C.

[0042] S1. The substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 30 min each, and then vacuum dried at 120℃ for 2 h to obtain the cleaned substrate. The cleaned substrate was then placed into a chemical vapor deposition reaction chamber and evacuated to a vacuum of 5 × 10⁻⁶. -3 Under an argon protective atmosphere, the deposition pressure is 2 kPa, and the temperature is increased to 1000℃ at a rate of 5℃ / min. High-purity propane gas is introduced to carry out pyrolytic carbon deposition at a propane flow rate of 50 sccm and a deposition time of 30 min. The propane is then stopped, and the current temperature is maintained under argon protection to obtain a matrix with a pyrolytic carbon layer. S2. The matrix with the pyrolytic carbon layer is activated by introducing an activation gas (sulfur hexafluoride) at a flow rate of 6 sccm. After introducing the gas for 1.5 min, the flow is paused for 5 min. After 5 cycles, the activated matrix is ​​obtained. S3. Adjust the deposition pressure to 2 kPa, heat to 1100℃ at a rate of 5℃ / min, stabilize for 30 min, and then introduce a mixed reaction gas. The mixed reaction gas includes trichloromethylsilane carrier gas (argon, bubbler temperature 30℃, 50 sccm), silane and trimethylaluminum carrier gas (hydrogen, bubbler temperature 35℃), and hydrogen as dilution gas. The volumetric flow rate ratio of dilution gas, trichloromethylsilane carrier gas, and silane and trimethylaluminum carrier gas is 15: The ratio of silicon carbide to silicon carbide coating was 1:0.1:0.06. The deposition time was 5 hours. The deposition temperature was started at 1100℃, increased to 1120℃ at a rate of 5℃ / min, held for 20 minutes, decreased to 1100℃ at a rate of 5℃ / min, held for 20 minutes, decreased to 1080℃ at a rate of 5℃ / min, held for 20 minutes, and increased to 1100℃ at a rate of 5℃ / min to start the next cycle. This periodic fluctuation was repeated to obtain a substrate with silicon carbide coating. S4. Under an argon protective atmosphere, the substrate with the silicon carbide coating is subjected to heat treatment and passivation treatment. The temperature is raised to 1250℃ at a rate of 7℃ / min and held for 1.5h. Then, it is cooled to 900℃ at a rate of 4℃ / min. 75ppm of oxygen is introduced and passivation is performed for 20min. Under a pure argon protective atmosphere, it is cooled to below 30℃ at a rate of 3℃ / min to complete the preparation of the CVD silicon carbide coating.

[0043] Example 13 Example 13 is based on Example 12. The only difference between Example 13 and Example 12 is that in Example 13, during the deposition process in step S3, the deposition temperature fluctuates periodically by ±30°C.

[0044] Example 14 Example 14 is based on Example 12. The only difference between Example 14 and Example 12 is that in Example 14, during the deposition process in step S3, the deposition temperature fluctuates periodically by ±25°C.

[0045] Example 15 Example 15 is based on Example 3. The only difference between Example 15 and Example 3 is that in Example 15, the heat treatment conditions in step S4 are to raise the temperature to 1150°C at a rate of 2°C / min and hold for 2.5 hours.

[0046] Example 16 Example 16 is based on Example 3. The only difference between Example 16 and Example 3 is that in Example 16, the heat treatment conditions in step S4 are to raise the temperature to 1350°C at a rate of 15°C / min and hold for 0.5h.

[0047] Example 17 Example 17 is based on Example 3. The only difference between Example 17 and Example 3 is that in Example 17, the passivation treatment conditions in step S4 are: cooling to 800°C at a rate of 2°C / min, introducing 25ppm of oxygen, and passivating for 40min.

[0048] Example 18 Example 18 is based on Example 3. The only difference between Example 18 and Example 3 is that in Example 18, the passivation treatment conditions in step S4 are: cooling to 1000°C at a rate of 6°C / min, introducing 125ppm of oxygen, and passivating for 10min.

[0049] Comparative Example 1 In Comparative Example 1, no pyrolytic carbon deposition treatment was performed.

[0050] S1. The substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 30 min and then vacuum dried at 120℃ for 2 h to obtain the cleaned substrate. S2. The cleaned substrate is activated by introducing an activation gas (sulfur hexafluoride) at a flow rate of 6 sccm. The gas is introduced for 1.5 min and then paused for 5 min. After 5 cycles, the activated substrate is obtained. S3. Adjust the deposition pressure to 2 kPa, heat to 1100℃ at a rate of 5℃ / min, stabilize for 30 min, and then introduce a mixed reaction gas. The mixed reaction gas includes trichloromethylsilane carrier gas (carrier gas is argon, bubbler temperature 30℃, 50 sccm), silane and trimethylaluminum carrier gas (carrier gas is hydrogen, bubbler temperature 35℃), and dilution gas is hydrogen. The volume flow ratio of dilution gas, trichloromethylsilane carrier gas, silane and trimethylaluminum carrier gas is 15:1:0.1:0.06. Deposition for 5 h yields a substrate with a silicon carbide coating. S4. Under an argon protective atmosphere, the substrate with the silicon carbide coating is subjected to heat treatment and passivation treatment. The temperature is raised to 1250℃ at a rate of 7℃ / min and held for 1.5h. Then, it is cooled to 900℃ at a rate of 4℃ / min. 75ppm of oxygen is introduced and passivation is performed for 20min. Under a pure argon protective atmosphere, it is cooled to below 30℃ at a rate of 3℃ / min to complete the preparation of the CVD silicon carbide coating.

[0051] Comparative Example 2 No activation treatment was performed in Comparative Example 2.

[0052] S1. The substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 30 min each, and then vacuum dried at 120℃ for 2 h to obtain the cleaned substrate. The cleaned substrate was then placed into a chemical vapor deposition reaction chamber and evacuated to a vacuum of 5 × 10⁻⁶. -3Under an argon protective atmosphere, the deposition pressure was 2 kPa, and the temperature was increased to 1000°C at a rate of 5°C / min. High-purity propane gas was introduced to carry out pyrolytic carbon deposition at a propane flow rate of 50 sccm and a deposition time of 30 min. The propane was then stopped to obtain a matrix with a pyrolytic carbon layer. S2. Adjust the deposition pressure to 2 kPa, heat to 1100℃ at a rate of 5℃ / min, stabilize for 30 min, and then introduce a mixed reaction gas. The mixed reaction gas includes trichloromethylsilane carrier gas (carrier gas is argon, bubbler temperature 30℃, 50 sccm), silane and trimethylaluminum carrier gas (carrier gas is hydrogen, bubbler temperature 35℃), and dilution gas is hydrogen. The volume flow ratio of dilution gas, trichloromethylsilane carrier gas, silane and trimethylaluminum carrier gas is 15:1:0.1:0.06. Deposition for 5 h yields a substrate with a silicon carbide coating. S3. Under an argon protective atmosphere, the substrate with the silicon carbide coating is subjected to heat treatment and passivation treatment. The temperature is raised to 1250℃ at a rate of 7℃ / min and held for 1.5h. Then, it is cooled to 900℃ at a rate of 4℃ / min. 75ppm of oxygen is introduced and passivation is performed for 20min. Under a pure argon protective atmosphere, it is cooled to below 30℃ at a rate of 3℃ / min to complete the preparation of the CVD silicon carbide coating.

[0053] Performance testing (1) Density test: The cross section of the sample was tested using a scanning electron microscope. After the sample was cut, resin inlaid, finely polished and sputtered with gold, five different fields of view were randomly selected to collect images at a magnification of 5000x. The percentage of the area occupied by pores was calculated using image analysis software, and the average value was taken as the porosity of the coating. The results are recorded in Table 1.

[0054] (2) High-temperature antioxidant performance test: Thermogravimetric analysis was used for the test. A 5mm×5mm×2mm sample was weighed and placed in an alumina crucible. The temperature was increased to 1200℃ at 10℃ / min under static air atmosphere and maintained at a constant temperature for 50h. The mass after treatment was measured and the change in mass per unit area (mg / cm²) was calculated. 2 For each test sample, three samples were prepared, and the average value was taken after testing. The results are recorded in Table 1.

[0055] (3) Bond strength test: Fix the sample on the stage of the scratch tester, select a diamond indenter with a radius of 200μm, and increase the loading rate from 0N to 100N linearly at 100N / min. At the same time, make the indenter scratch a 10mm long track on the coating surface at a speed of 10mm / min. Observe the coating peeling situation and record the critical load when the coating fails for the first time. Each sample is tested 5 times, and the average value is taken after the test. The results are recorded in Table 1.

[0056] Table 1. Test results of density, high-temperature oxidation resistance and bonding strength Test results Porosity (%) Variation (mg / cm 2 )]]> Bonding strength (N) Example 1 0.55 0.75 55 Example 2 0.61 0.66 49 Example 3 0.56 0.70 53 Example 4 0.85 0.72 46 Example 5 0.95 0.68 42 Example 6 0.75 0.74 48 Example 7 0.82 0.76 45 Example 8 0.69 0.73 48 Example 9 0.92 0.67 47 Example 10 0.60 1.25 51 Example 11 0.78 0.55 48 Example 12 0.48 0.65 58 Example 13 0.45 0.63 60 Example 14 0.43 0.61 63 Example 15 0.62 0.78 48 Example 16 0.68 0.75 47 Example 17 0.63 0.85 48 Example 18 0.65 0.80 46 Comparative Example 1 1.25 0.78 32 Comparative Example 2 0.98 0.77 38 As shown in Table 1, the porosity of Examples 1-3 is less than 0.61%, and the variation is less than 0.75 mg / cm³. 2 The bonding strength is greater than 49N, which shows that the silicon carbide coating prepared in this application has good bonding strength, stability and density.

[0057] As shown in Table 1, the only difference between Examples 4 and 5 and Example 3 is that the conditions for pyrolytic carbon deposition were disrupted in Examples 4 and 5. Low temperature, low pressure and long time deposition resulted in a loose structure of pyrolytic carbon layer, a decrease in density and bonding strength, while high temperature and high pressure short time deposition increased the brittleness of pyrolytic carbon layer and reduced bonding strength.

[0058] As shown in Table 1, the only difference between Examples 6 and 7 and Example 3 is that the activation conditions were disrupted in Examples 6 and 7. Weak activation resulted in insufficient surface cleaning and insufficient nucleation sites, affecting density and bonding strength. Strong activation caused excessive etching of the surface, damaging the interface integrity.

[0059] As shown in Table 1, the only difference between Examples 8 and 9 and Example 3 is that the deposition conditions of the silicon carbide coating were disrupted in Examples 8 and 9. Low-temperature deposition resulted in insufficient atomic mobility and general density, while high-temperature rapid deposition led to coarse columnar crystals and increased porosity.

[0060] As shown in Table 1, the only difference between Examples 10 and 11 and Example 3 is that the specified ratio of aluminum dopant was disrupted in Examples 10 and 11, and there was no aluminum doping. The antioxidant performance was significantly reduced, while excessive aluminum doping would cause lattice distortion and decrease compactness.

[0061] As shown in Table 1, the only difference between Examples 12-14 and Example 3 is that in Examples 12-14, by controlling the periodic fluctuation of the deposition temperature, the fine-grained structure effectively improves the density, bonding strength and stability.

[0062] As shown in Table 1, the only difference between Examples 15 and 16 and Example 3 is that the heat treatment conditions were disrupted in Examples 15 and 16. Low-temperature annealing resulted in insufficient stress relief, and rapid high-temperature annealing caused abnormal grain growth, resulting in a decrease in performance.

[0063] As shown in Table 1, the only difference between Examples 17 and 18 and Example 3 is that the passivation conditions were disrupted in Examples 17 and 18. Weak passivation resulted in an incomplete protective film and decreased stability, while strong passivation led to an excessively thick oxide layer, which easily generated microcracks and reduced performance.

[0064] As shown in Table 1, the only difference between Comparative Example 1 and Example 3 is that no pyrolytic carbon layer was prepared in Comparative Example 1, resulting in a significant decrease in interfacial bonding strength and a marked deterioration in performance.

[0065] As shown in Table 1, the only difference between Comparative Example 2 and Example 3 is that Comparative Example 2 does not undergo activation treatment, resulting in insufficient coating adhesion and reduced bonding strength.

[0066] This specific embodiment is merely an explanation of this application and is not intended to limit it. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification but must be determined according to the scope of the claims.

Claims

1. A method of producing a CVD silicon carbide coating, characterized by: The method comprises the following steps: S1, ultrasonic cleaning and drying the substrate to obtain a cleaned substrate; and depositing pyrolytic carbon on the cleaned substrate to obtain a substrate with a pyrolytic carbon layer; S2, activating the substrate with the pyrolytic carbon layer to obtain an activated substrate; S3, depositing a silicon carbide coating on the activated substrate by introducing a mixed reaction gas to obtain a substrate with a silicon carbide coating; S4, performing heat treatment and passivation treatment on the substrate with the silicon carbide coating to complete the preparation of the silicon carbide coating by the CVD method.

2. The method of claim 1 wherein: In the step S1, the pyrolytic carbon deposition conditions are as follows: a deposition pressure of 1-3 kPa, heating to 900-1100℃, and introducing propane for pyrolytic carbon deposition, with a propane flow rate of 30-70 sccm and a deposition time of 20-40 min.

3. The method of claim 1 wherein: In the step S2, the activation treatment conditions are as follows: introducing an activation gas with a flow rate of 2-10 sccm, pausing for 4-6 min after 1-2 min of activation gas introduction, and repeating the cycle 4-6 times.

4. The method of claim 3 wherein: The activation gas comprises sulfur hexafluoride.

5. The method for preparing a silicon carbide coating by CVD according to claim 1, characterized in that: In the step S3, the deposition treatment conditions are as follows: a deposition pressure of 1-3 kPa, a deposition temperature of 1050-1150℃, and a deposition time of 4-6 h.

6. The method of claim 5 wherein: In the step S3, the mixed reaction gas comprises trichloromethylsilane carrier gas, silane carrier gas, and trimethylaluminum carrier gas, and further comprises a dilution gas, which comprises hydrogen.

7. The method of claim 6 wherein: The volume flow rate ratio of the dilution gas, trichloromethylsilane carrier gas, silane, and trimethylaluminum carrier gas is 15:1:0.1:(0.02-0.1).

8. The method for preparing a CVD silicon carbide coating according to claim 7, characterized in that: In the step S3, the deposition temperature is periodically fluctuated by ±20-±30℃ during the deposition treatment.

9. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that: In the step S4, the heat treatment conditions are as follows: heating to 1200-1300℃ at a rate of 4-10℃ / min and maintaining the temperature for 1-2 h.

10. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that: In the step S4, the passivation treatment conditions are as follows: cooling to 850-950℃ at a rate of 3-5℃ / min, introducing 50-100 ppm of oxygen, and passivating for 10-30 min.