Silicon carbide ceramic with composite coating and preparation method thereof

Abstract

The invention discloses silicon carbide ceramic with a composite coating and a preparation method of the silicon carbide ceramic. The silicon carbide ceramic with the composite coating comprises a silicon carbide ceramic matrix and the composite coating, the composite coating is located on the surface of the silicon carbide ceramic matrix, and the composite coating comprises a boron carbide transition layer, a beta-SiC coating and a silicon carbide-silicon oxide composite surface layer which are sequentially arranged in the direction away from the silicon carbide ceramic matrix, the bonding strength of the composite coating and the silicon carbide ceramic matrix is larger than or equal to 60 N. Therefore, the bonding strength between the composite coating and the silicon carbide ceramic matrix is relatively high, and the composite coating is not easy to peel off from the matrix; the composite coating with the multi-layer structure can improve the oxidation resistance and corrosion resistance of the silicon carbide ceramic material, and can at least prevent impurities in the silicon carbide ceramic from overflowing under a high-temperature condition to a certain extent, so that the stability and reliability of the silicon carbide ceramic material are improved.

Description

Technical Field

[0001] This application relates to the field of coated silicon carbide ceramics, and more specifically, to silicon carbide ceramics with composite coatings and methods for preparing the same. Background Technology

[0002] Silicon carbide (SiC) is a compound with strong covalent bonds; the ionic Si-C bond accounts for only about 12%. It possesses excellent properties such as high strength, high hardness, high temperature resistance, wear resistance, and thermal shock resistance. Silicon carbide materials have been widely used in high-temperature bearings, combustion nozzles, bulletproof armor materials, clamping materials used in semiconductor wafer fabrication, and nuclear fuel cladding materials. However, silicon carbide ceramics suffer from high porosity and insufficient density, as well as numerous impurities during preparation. In oxidizing environments, the pores provide pathways for oxygen to enter the material and undergo oxidation, leading to rapid material failure. In corrosive environments, the presence of pores and impurities allows corrosive substances to penetrate the material, severely corroding its structure, reducing strength, and affecting its lifespan. In high-purity environments, impurities can overflow along pores or grain boundaries, contaminating the environment and affecting product quality.

[0003] To address these issues, researchers have attempted to fabricate dense, high-purity silicon carbide ceramic films on silicon carbide ceramic surfaces. Commonly used methods include magnetron sputtering or atomic layer deposition. However, these methods still have some limitations in practical applications, and the performance of the resulting coatings needs further improvement.

[0004] Furthermore, in certain specialized applications, such as the manufacture of fault-tolerant fuel cladding for nuclear power plants, it is necessary to further improve the corrosion resistance and abrasion resistance of the materials. In these areas, the bonding strength between the coating and the substrate is also a critical issue. Therefore, developing a multilayer composite coating technology that can improve the purity, density, and bonding strength of silicon carbide ceramic coatings while also possessing good oxidation resistance is of great significance for enhancing the application performance of silicon carbide ceramic materials in high-performance environments. Summary of the Invention

[0005] This application is based on the inventor's discoveries and understanding of the following facts and problems: Several improved technical solutions have been developed to address the challenges of improving the wear resistance, thermal conductivity, electrical conductivity, and preventing oxidation and corrosion of silicon carbide ceramics. For example, a method for preparing a hafnium-based ultra-high temperature ceramic coating with high bonding strength has been disclosed. This method involves preparing a hafnium-tantalum carbon-silicon carbide ceramic coating via plasma spraying, followed by rapid high-temperature sintering, which significantly improves the bonding strength between the coating and the substrate. However, this method still suffers from insufficient coating deposition efficiency and quality uniformity in the plasma spraying process.

[0006] Current silicon carbide ceramic coatings still have the following drawbacks: 1. Silicon carbide ceramic materials are prone to oxidation at high temperatures, forming loose SiO2, which affects their performance. Furthermore, pure SiO2 coatings are brittle and have weak adhesion to the substrate. 2. Existing coating preparation methods, such as magnetron sputtering or atomic layer deposition, have problems in practical applications, such as low coating purity, insufficient density, and uneven microstructure. 3. In terms of the process of preparing coatings by plasma spraying, the deposition efficiency and quality uniformity of the coatings still need to be improved; 4. The bonding strength between the coating and the substrate is insufficient, making it difficult to meet the requirements of special application scenarios (such as the manufacturing of fault-tolerant fuel cladding for nuclear power plant accidents).

[0007] This application aims to at least partially alleviate or resolve at least one of the aforementioned problems.

[0008] In one aspect of this application, a silicon carbide ceramic with a composite coating is proposed. In some embodiments of this application, the silicon carbide ceramic with a composite coating includes a silicon carbide ceramic substrate and a composite coating. The composite coating is located on the surface of the silicon carbide ceramic substrate. Along a direction away from the silicon carbide ceramic substrate, the composite coating includes a boron carbide transition layer, a β-SiC coating, and a silicon carbide-silicon oxide composite surface layer sequentially disposed therefrom. The bonding strength between the composite coating and the silicon carbide ceramic substrate is ≥60N. Therefore, the bonding strength between the composite coating and the silicon carbide ceramic substrate is high, and the composite coating is not easily peeled off from the substrate. The multi-layered composite coating can improve the oxidation resistance and corrosion resistance of the silicon carbide ceramic material, and can at least to a certain extent prevent impurities in the silicon carbide ceramic from escaping under high-temperature conditions, thereby improving the stability and reliability of the silicon carbide ceramic material.

[0009] In some embodiments of this application, the silicon carbide ceramic with the composite coating satisfies at least one of the following conditions: the silicon carbide ceramic substrate is selected from one or more of pressureless sintered silicon carbide ceramic, reaction sintered silicon carbide ceramic, hot-pressed sintered silicon carbide ceramic, hot isostatic pressing sintered silicon carbide ceramic, and recrystallized silicon carbide ceramic; the thickness of the boron carbide transition layer is 1 μm-10 μm; the thickness of the β-SiC coating is 30 μm-140 μm; and the thickness of the silicon carbide-silicon oxide composite surface layer is 10 μm-20 μm.

[0010] In another aspect of this application, a method for preparing silicon carbide ceramics with a composite coating is proposed. In some embodiments of this application, the method for preparing silicon carbide ceramics with a composite coating includes: forming a boron carbide transition layer on the surface of a silicon carbide ceramic substrate using chemical vapor deposition (CVD), wherein the surface roughness Ra of the silicon carbide ceramic substrate on which the boron carbide transition layer is formed is 0.1 nm-0.5 nm; forming a β-SiC coating on the side of the boron carbide transition layer away from the silicon carbide ceramic substrate using CVD; and introducing an oxidizing gas and an inert gas into a deposition chamber, causing a portion of the β-SiC coating to transform into a silicon carbide-silicon oxide composite surface layer, wherein the volume of the oxidizing gas accounts for 5%-10% of the sum of the volumes of the oxidizing gas and the inert gas. Therefore, the composite coating exhibits high bonding strength with the silicon carbide ceramic substrate, making it less prone to peeling; the composite coating also exhibits high density and purity, which can at least partially prevent impurities in the silicon carbide ceramic substrate from escaping at high temperatures, thereby improving the stability and reliability of the material during use. The above methods are controllable and easy to implement, which helps to improve product yield.

[0011] In some embodiments of this application, before forming the boron carbide transition layer, the silicon carbide ceramic substrate is surface-treated using a mixed plasma. The surface treatment satisfies at least one of the following conditions: the mixed plasma is formed from oxygen and a first gas, the first gas including one or more of argon, helium, and nitrogen, with a volume ratio of oxygen to the first gas of 1:9 to 9:1; the power of the surface treatment is 100W-300W; the surface treatment time is 10min-30min; and after the surface treatment, the silicon carbide ceramic substrate is surface-cleaned. Thus, plasma treatment can activate the surface of the boron carbide ceramic substrate, forming a micro-roughened surface, thereby improving the bonding strength between the subsequently prepared coating and the substrate.

[0012] In some embodiments of this application, forming the boron carbide transition layer includes: raising the temperature of the deposition chamber to 800°C-1200°C, controlling the pressure to 1kPa-10kPa, introducing a boron source and a first carbon source, and depositing the boron carbide transition layer on the surface of the silicon carbide ceramic substrate.

[0013] In some embodiments of this application, the deposition time of the boron carbide transition layer is 1 min to 60 min.

[0014] In some embodiments of this application, the boron source includes one or more of trimethylboron, triethylboron, tripropylboron, and triphenylboron.

[0015] In some embodiments of this application, the flow rate of the boron source is 0.1 slm-20 slm.

[0016] In some embodiments of this application, the first carbon source includes one or more of methane, ethane, ethylene, propylene, propane, and acetylene.

[0017] In some embodiments of this application, the flow rate of the first carbon source is 0.1 slm-20 slm.

[0018] In some embodiments of this application, forming the β-SiC coating includes: raising the temperature of the deposition chamber to 1300℃-1500℃, introducing a second gas, hydrogen, and a precursor, controlling the pressure to 10kPa-20kPa, and depositing the β-SiC coating on the side of the boron carbide transition layer away from the silicon carbide ceramic substrate; wherein the second gas includes one or more of argon, helium, and nitrogen; the precursor includes a first silicon source and a second carbon source, the first silicon source including one or more of silane, monochlorosilane, dichlorosilane, trichlorosilane, and silicon tetrachloride, and the second carbon source including one or more of methane, ethane, ethylene, propylene, propane, and acetylene; or, the precursor includes a second silicon source, the second silicon source including one or more of trichloromethylsilane, hexamethyldisilane, dichlorodimethylsilane, and trimethylchlorosilane.

[0019] In some embodiments of this application, the flow rate of the first silicon source is 1 slm-30 slm.

[0020] In some embodiments of this application, the flow rate of the second carbon source is 1 slm-30 slm.

[0021] In some embodiments of this application, the flow rate of the second silicon source is 1 slm-30 slm.

[0022] In some embodiments of this application, the flow rate of the second gas is 1 slm-10 slm.

[0023] In some embodiments of this application, the hydrogen flow rate is 1 slm-50 slm.

[0024] In some embodiments of this application, the deposition time of the β-SiC coating is 60 min to 180 min.

[0025] In some embodiments of this application, the temperature of the deposition chamber is controlled at 1100℃-1300℃, the pressure is controlled at 10kPa-20kPa, and an oxidizing gas and an inert gas are introduced to convert a portion of the β-SiC coating into a silicon carbide-silicon oxide composite surface layer; the oxidizing gas includes one or more of oxygen, carbon dioxide, and carbon monoxide; the inert gas includes one or more of argon, helium, and nitrogen.

[0026] In some embodiments of this application, the silicon carbide-silicon oxide composite surface layer is formed under at least one of the following conditions: the flow rate of the oxidizing gas is 1 slm-5 slm; and the holding time is 60 min-120 min.

[0027] In some embodiments of this application, after forming the silicon carbide-silicon oxide composite surface layer, the method for preparing silicon carbide ceramics with the composite coating further includes: cooling to 600℃-1000℃ and holding for 4h-6h; and continuing to cool to 300℃-500℃ and holding for 1h-2h. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This shows a schematic diagram of the structure of a silicon carbide ceramic with a composite coating according to one embodiment of the present application; Figure 2 A flowchart illustrating the preparation of silicon carbide ceramics with a composite coating according to one embodiment of this application is shown.

[0029] Explanation of reference numerals in the attached figures: 1: Silicon carbide ceramic substrate; 2: Boron carbide transition layer; 3: β-SiC coating; 4: Silicon carbide-silicon oxide composite surface layer. Detailed Implementation

[0030] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0031] In one aspect of this application, a silicon carbide ceramic with a composite coating is proposed. In some embodiments of this application, reference is made to... Figure 1The silicon carbide ceramic with composite coating includes a silicon carbide ceramic substrate 1 and a composite coating. The composite coating is located on the surface of the silicon carbide ceramic substrate 1. Along the direction away from the silicon carbide ceramic substrate 1, the composite coating includes a boron carbide (B4C) transition layer 2, a β-SiC (β-phase silicon carbide) coating 3, and a silicon carbide-silicon oxide composite surface layer 4 arranged sequentially. The bonding strength between the composite coating and the silicon carbide ceramic substrate 1 can be ≥60N. For example, the bonding strength between the composite coating and the silicon carbide ceramic substrate 1 can be 60N, 65N, 67N, 71N, 75N, etc. Therefore, the composite coating bonds well with the silicon carbide ceramic substrate, and the composite coating is not easily peeled off. The boron carbide transition layer can take advantage of the chemical compatibility between silicon carbide and boron carbide to form a Si-BC solid solution. Through interface regulation, stress mutation and lattice mismatch problems can be alleviated or even eliminated, effectively alleviating or even solving the bonding problem between the SiC ceramic substrate and the β-SiC coating. The composite coating composed of the above multiple coatings can improve the oxidation resistance and corrosion resistance of silicon carbide ceramics, and can at least to a certain extent prevent impurities in silicon carbide ceramics from escaping at high temperatures, thereby improving the stability and reliability of the material.

[0032] In some embodiments of this application, the silicon carbide ceramic substrate 1 may be selected from one or more of pressureless sintered silicon carbide ceramics, reaction-sintered silicon carbide ceramics, hot-pressed silicon carbide ceramics, hot isostatic pressing silicon carbide ceramics, and recrystallized silicon carbide ceramics. The composite coating consisting of multiple coatings proposed in this application is suitable for silicon carbide ceramic substrates prepared by various methods. The composite coating bonds well with various silicon carbide ceramic substrates and can improve the oxidation resistance, corrosion resistance, stability, and reliability of silicon carbide ceramic materials during use.

[0033] In some embodiments of this application, the thickness of the boron carbide transition layer 2 can be 1 μm-10 μm, for example, the thickness of the boron carbide transition layer 2 can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, etc. A thickness within the above range is beneficial for further improving the bonding strength between the composite coating and the ceramic substrate, thereby further improving the stability and reliability of the silicon carbide ceramic.

[0034] In some embodiments of this application, the thickness of the β-SiC coating 3 can be 30μm-140μm, for example, the thickness of the β-SiC coating 3 can be 30μm, 50μm, 70μm, 90μm, 120μm, 140μm, etc. Therefore, the above coating can better protect the ceramic substrate and effectively prevent the ceramic substrate from oxidizing or corroding at high temperatures.

[0035] In some embodiments of this application, the thickness of the silicon carbide-silicon oxide composite surface layer 4 can be 10 μm-20 μm, for example, the thickness of the silicon carbide-silicon oxide composite surface layer 4 can be 10 μm, 12 μm, 15 μm, 17 μm, 20 μm, etc. Thus, the silicon oxide (SiO2) in the composite surface layer can fill the grain boundaries, blocking the oxygen diffusion channels. The silicon carbide-silicon oxide composite surface layer can improve the hardness and oxidation resistance of the coating, effectively reducing the thermal stress of the silicon carbide ceramic.

[0036] In another aspect of this application, a method for preparing silicon carbide ceramics with a composite coating is proposed. (Reference) Figure 2 A method for preparing silicon carbide ceramics with composite coatings may include the following steps: S10: A boron carbide transition layer 2 is formed on the surface of a silicon carbide ceramic substrate 1 using chemical vapor deposition.

[0037] In some embodiments, the silicon carbide ceramic matrix 1 may be selected from one or more of pressureless sintered silicon carbide ceramics, reaction sintered silicon carbide ceramics, hot-pressed sintered silicon carbide ceramics, hot isostatic pressing sintered silicon carbide ceramics, and recrystallized silicon carbide ceramics.

[0038] In this application, the surface roughness Ra of the silicon carbide ceramic substrate 1 to which the boron carbide transition layer 2 is formed is 0.1 nm to 0.5 nm, for example, Ra = 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, etc. The low surface roughness of the boron carbide ceramic substrate allows for sufficient gas contact with the surface of the ceramic substrate during the subsequent chemical vapor deposition coating preparation process, thereby forming a uniform coating on the ceramic substrate surface and resulting in a high bonding strength between the coating and the ceramic substrate.

[0039] Silicon carbide ceramic substrates readily adsorb impurities such as carbon dioxide, water vapor, and dust from the air, and their surfaces may retain dust and other impurities, as well as residual oxygen-containing functional groups such as hydroxyl groups. In some embodiments of this application, before forming the boron carbide transition layer 2, the silicon carbide ceramic substrate 1 can be surface-treated using mixed plasma. Surface treatment can remove residual hydroxyl groups on the substrate surface and reduce the surface roughness, thereby improving the bonding strength between the subsequently prepared coating and the substrate. If the surface roughness of the substrate is too high, during the CVD coating preparation process, the gas has difficulty contacting the pits on the substrate surface, resulting in some areas of the substrate surface failing to contact the coating or having low bonding strength with the coating. The coating is prone to peeling off from the substrate, making it difficult to provide good protection during the use of silicon carbide ceramics.

[0040] In some embodiments of this application, the mixed plasma is formed by oxygen and a first gas, which may include one or more of argon, helium, and nitrogen. The volume ratio of oxygen to the first gas can be from 1:9 to 9:1. For example, the first gas can be argon, helium, or nitrogen, or it can be composed of two or three of argon, helium, and nitrogen. The volume ratio of oxygen to the first gas can be 1:9, 1:5, 1:1, 3:1, 6:1, or 9:1. Using the above-mentioned mixed plasma to treat the surface of the ceramic substrate can reduce its surface roughness, thereby improving the adhesion between the substrate and the coating.

[0041] In some embodiments of this application, the surface treatment power can be 100W-300W, for example, 100W, 140W, 170W, 200W, 230W, 260W, 300W, etc. Therefore, surface treatment of the silicon carbide ceramic substrate at the above power levels can effectively reduce its surface roughness.

[0042] In some embodiments of this application, the surface treatment time can be 10 min to 30 min, for example, 10 min, 15 min, 20 min, 25 min, 30 min, etc. This effectively reduces the surface roughness of the ceramic substrate without significantly increasing the coating preparation cost.

[0043] In some embodiments of this application, the silicon carbide ceramic substrate is cleaned after surface treatment. This makes the surface of the ceramic substrate cleaner, which is beneficial for the subsequent preparation of the coating. The specific methods for surface cleaning are not particularly limited in this application; those skilled in the art can choose conventional cleaning methods as needed.

[0044] In some embodiments of this application, forming the boron carbide transition layer 2 includes: raising the temperature of the deposition chamber to 800℃-1200℃, controlling the pressure to 1kPa-10kPa, introducing a boron source and a first carbon source, and depositing the boron carbide transition layer 2 on the surface of the silicon carbide ceramic substrate 1. It should be noted that before heating, the entire deposition system needs to be evacuated until the vacuum level of the deposition chamber is <5Pa, and then an inert gas (such as argon, helium, etc.) is introduced for gas purging. The number of gas purging cycles is not specifically limited in this application; those skilled in the art can set and adjust them according to actual conditions. For example, one, two, or more gas purging cycles can be performed.

[0045] In some embodiments, the temperature of the deposition chamber can be raised to 800°C, 900°C, 1000°C, 1100°C, or 1200°C, and the pressure can be controlled to 1 kPa, 3 kPa, 5 kPa, 8 kPa, or 10 kPa. Under these conditions, the boron source and the first carbon source can react and deposit a boron carbide transition layer on the surface of the ceramic substrate. Depositing the B4C transition layer, utilizing the chemical compatibility of SiC and B4C, can form a Si-BC solid solution. Through interface regulation, stress abrupt changes and lattice mismatch problems can be alleviated or even eliminated, effectively alleviating or even solving the problem of low bonding strength between the SiC ceramic substrate and the β-SiC coating.

[0046] In some embodiments, the deposition time of the boron carbide transition layer 2 can be 1 min to 60 min, for example, the deposition time of the boron carbide transition layer 2 can be 1 min, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, etc. Thus, the formed boron carbide transition layer has a suitable thickness, for example, the thickness of the boron carbide transition layer can be 1 μm to 10 μm, which can effectively improve the bonding strength between the coating and the ceramic substrate.

[0047] In some embodiments, the boron source may include one or more of trimethylboron, triethylboron, tripropylboron, and triphenylboron. The above materials can provide boron and can react with a carbon source under certain conditions to form boron carbide.

[0048] In some embodiments, the flow rate of the boron source can be 0.1 slm to 20 slm, for example, the flow rate of the boron source can be 0.1 slm, 0.5 slm, 1 slm, 5 slm, 10 slm, 15 slm, 20 slm, etc. Within the above-mentioned flow rate range, boron carbide can be deposited at a suitable rate, which is more conducive to mitigating or even eliminating stress abrupt changes and lattice mismatch problems through interface control, thereby further improving the bonding strength between the coating and the substrate.

[0049] In some embodiments, the first carbon source may include one or more of methane, ethane, ethylene, propylene, propane, and acetylene. The carbon source can provide carbon and can react with a boron source under certain conditions to form boron carbide.

[0050] In some embodiments, the flow rate of the first carbon source can be 0.1 slm to 20 slm, for example, the flow rate of the first carbon source can be 0.1 slm, 0.5 slm, 1 slm, 5 slm, 10 slm, 15 slm, 20 slm, etc. This allows boron carbide to be deposited at a suitable rate, improving the quality of the coating; and further enhancing the bonding strength between the coating and the substrate.

[0051] S20: A β-SiC coating 3 is formed on the side of the boron carbide transition layer 2 away from the silicon carbide ceramic substrate 1 using chemical vapor deposition.

[0052] In some embodiments, forming a β-SiC coating includes: raising the temperature of the deposition chamber to 1300°C-1500°C, introducing a second gas, hydrogen, and a precursor, controlling the pressure to 10 kPa-20 kPa, and depositing a β-SiC coating on the side of the boron carbide transition layer away from the silicon carbide ceramic substrate. The β-SiC coating prepared by CVD has high purity and high density, effectively solving the problems of low coating purity and insufficient density in related technologies.

[0053] In some embodiments, the deposition temperature of the β-SiC coating can be 1300°C, 1350°C, 1400°C, 1450°C, or 1500°C, and the pressure in the deposition chamber can be controlled at 10 kPa, 13 kPa, 15 kPa, 17 kPa, or 20 kPa. Under these conditions, a coating with high density can be obtained, which can effectively protect the ceramic substrate.

[0054] In some embodiments, the second gas may include one or more of argon, helium, and nitrogen, which can regulate the pressure in the deposition chamber and improve the uniformity of the coating.

[0055] In some embodiments, the flow rate of the second gas can be 1 slm-10 slm, for example, the flow rate of the second gas can be 1 slm, 3 slm, 5 slm, 8 slm, 10 slm, etc. The flow rate of the second gas within the above range can adjust the partial pressure of the reactant gas, which is beneficial to improving the film formation quality of the coating.

[0056] In some embodiments, the hydrogen flow rate can be 1 slm-50 slm, for example, the hydrogen flow rate can be 1 slm, 5 slm, 10 slm, 20 slm, 30 slm, 40 slm, 50 slm, etc. On the one hand, hydrogen can serve as a carrier gas to promote the uniform distribution of the precursor in the deposition chamber; on the other hand, hydrogen can participate in the reaction to promote the deposition of the coating.

[0057] In some embodiments, the precursor may include a first silicon source and a second carbon source. The first silicon source may include one or more of silane, monochlorosilane, dichlorosilane, trichlorosilane, and silicon tetrachloride, and the second carbon source may include one or more of methane, ethane, ethylene, propylene, propane, and acetylene. The first silicon source, the second carbon source, and hydrogen can react under certain conditions to deposit a β-SiC coating on a ceramic substrate.

[0058] In some embodiments, the flow rate of the first silicon source can be 1 slm-30 slm, for example, the flow rate of the first silicon source can be 1 slm, 5 slm, 10 slm, 15 slm, 20 slm, 25 slm, 30 slm, etc. In some embodiments, the flow rate of the second carbon source can be 1 slm-30 slm, for example, the flow rate of the second carbon source can be 1 slm, 5 slm, 10 slm, 15 slm, 20 slm, 25 slm, 30 slm, etc. When the flow rates of the first silicon source and the second carbon source are within the above ranges, a β-SiC coating can be deposited at a suitable rate, which is beneficial for further improving the quality of the coating.

[0059] In other embodiments, the precursor may include a second silicon source, which may include one or more of trichloromethylsilane, hexamethyldisilane, dichlorodimethylsilane, and trimethylchlorosilane. The precursor may simultaneously provide both a silicon source and a carbon source, and under certain conditions, deposit to form a β-SiC coating.

[0060] In some embodiments, the flow rate of the second silicon source can be 1 slm-30 slm, for example, the flow rate of the second silicon source can be 1 slm, 5 slm, 10 slm, 15 slm, 20 slm, 25 slm, 30 slm, etc. This is beneficial to improving the quality of the coating, and the formed coating can better protect the silicon carbide ceramic substrate.

[0061] In some embodiments, the deposition time of the β-SiC coating can be 60 min to 180 min, for example, the deposition time of the β-SiC coating can be 60 min, 80 min, 100 min, 130 min, 150 min, 180 min, etc. Thus, a β-SiC coating of suitable thickness can be obtained.

[0062] S30: Oxidizing and inert gases are introduced into the deposition chamber to convert a portion of the β-SiC coating into a silicon carbide-silicon oxide composite surface layer.

[0063] In this step, the volume of the oxidizing gas accounts for 5%-10% of the sum of the volumes of the oxidizing gas and the inert gas. For example, the volume of the oxidizing gas accounts for 5%, 6%, 7%, 8%, 9%, or 10% of the sum of the volumes of the oxidizing gas and the inert gas. As a result, the β-SiC coating can be partially oxidized, transforming a portion of it away from the ceramic substrate into a silicon carbide-silicon oxide composite surface layer.

[0064] The first direction is defined as the direction from the silicon carbide ceramic substrate to the composite coating. On the cross section of the silicon carbide-silicon oxide composite surface perpendicular to the first direction, silicon carbide and silicon oxide can coexist.

[0065] In some embodiments of this application, after the β-SiC coating is formed, the introduction of hydrogen and precursor is stopped, the temperature of the deposition chamber is controlled at 1100℃-1300℃, the pressure is controlled at 10kPa-20kPa, and oxidizing gas and inert gas are introduced to convert a portion of the β-SiC coating into a silicon carbide-silicon oxide composite surface layer.

[0066] In some embodiments, the temperature of the deposition chamber can be controlled at 1100°C, 1150°C, 1200°C, 1250°C, or 1300°C, and the pressure can be controlled at 10 kPa, 12 kPa, 15 kPa, 17 kPa, or 20 kPa. This facilitates the conversion of a portion of the β-SiC coating into a silicon carbide-silicon oxide composite surface, thereby improving the hardness and oxidation resistance of the composite coating.

[0067] In some embodiments, the oxidizing gas may include one or more of oxygen, carbon dioxide, and carbon monoxide. For example, the oxidizing gas may be oxygen or carbon dioxide, or it may be composed of two or three of oxygen, carbon dioxide, and carbon monoxide. The aforementioned gases have oxidizing properties, can oxidize part of the β-SiC coating, and do not introduce other impurities.

[0068] In some embodiments, the inert gas may include one or more of argon, helium, and nitrogen. Mixing these gases with an oxidizing gas can reduce the content of the oxidizing gas, which helps to avoid excessive oxidation.

[0069] In some embodiments, the flow rate of the oxidizing gas can be 1 slm-5 slm, for example, the flow rate of the oxidizing gas can be 1 slm, 2 slm, 3 slm, 4 slm, 5 slm, etc. When the flow rate of the oxidizing gas is within the above range, the β-SiC coating can be oxidized at a suitable rate, which is beneficial for forming a silicon carbide-silicon oxide composite surface layer.

[0070] In some embodiments, the holding time in step S30 can be 60 min to 120 min, for example, 60 min, 80 min, 100 min, 120 min, etc. This facilitates the formation of a silicon carbide-silicon oxide composite surface layer of suitable thickness, thereby further improving the oxidation resistance of the composite coating.

[0071] S40: After forming the silicon carbide-silicon oxide composite surface layer, the method for preparing silicon carbide ceramics with composite coating further includes: cooling to 600℃-1000℃ and holding for 4h-6h; continuing to cool to 300℃-500℃ and holding for 1h-2h.

[0072] In some embodiments, after forming the silicon carbide-silicon oxide composite surface layer, the temperature of the deposition chamber can be first reduced to 600°C, 700°C, 800°C, 900°C, or 1000°C at a rate of 3°C / min to 5°C / min, and held for 4h, 4.5h, 5h, 5.5h, or 6h to fully release the thermal stress inside the silicon carbide crystals and avoid problems such as cracking of the composite coating caused by thermal stress. Then, the temperature is reduced to 300°C, 350°C, 400°C, 450°C, or 500°C at a rate of 5°C / min, and held for 1h, 1.2h, 1.5h, 1.8h, or 2h to eliminate the internal stress generated during oxidation and improve the density of the coating. Finally, the temperature can be reduced to room temperature at a rate of 5°C / min to 10°C / min, and the sample is removed. In this article, room temperature can be 20°C-35°C. The cooling rate in the above steps can be adjusted as needed.

[0073] In summary, the method proposed in this application for preparing silicon carbide ceramics with composite coatings (multilayer composite SiC-based coatings) has the following advantages: 1. The surface roughness of silicon carbide ceramic substrate is low. For example, by activating the surface through plasma treatment to form a micro-rough surface, the bonding strength between the coating and the silicon carbide ceramic substrate can be significantly improved, alleviating or even solving the problem of weak bonding between the coating and the substrate in related technologies. 2. The multi-layer composite SiC-based coating structure is designed, which includes a silicon carbide transition layer, a β-SiC coating and a silicon carbide-silicon oxide composite surface layer. This can effectively prevent the silicon carbide ceramic material from oxidizing and corroding at high temperatures, thus improving the material's corrosion resistance. 3. By setting a boron carbide transition layer, the chemical compatibility of SiC and B4C can be utilized to form a Si-BC solid solution. Through interface regulation, stress mutation and lattice mismatch problems can be alleviated or even eliminated, effectively alleviating or even solving the bonding problem between the SiC ceramic matrix and the β-SiC coating. 4. β-SiC coatings prepared by CVD can obtain high-purity and high-density coatings, effectively alleviating or even solving the problems of low coating purity and insufficient density in related technologies; 5. The structural design of using SiC as a skeleton support and combining it with SiO2 to fill grain boundaries and block diffusion channels gives the coating high hardness and good oxidation resistance, effectively reducing the thermal stress of silicon carbide ceramics. 6. The multilayer composite SiC-based coating of this application can effectively prevent impurities in silicon carbide ceramics from overflowing at high temperatures, thereby improving the stability and reliability of the material under extreme environments.

[0074] The present application will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the present application in any way. Furthermore, in the following embodiments, unless otherwise specified, the materials and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0075] Example 1 Example 1 provides a method for preparing silicon carbide ceramics with a composite coating (multilayer composite SiC-based coating), the specific steps of which are as follows: (1) Surface treatment: Pressureless sintered silicon carbide ceramic substrate was selected and placed in a mixed plasma of Ar / O2=9:1 for 20 min (power of 200W) to obtain a micro-rough surface with Ra=0.3nm; after surface cleaning and testing, the cleanliness and roughness met the requirements.

[0076] (2) Preparation of B4C transition layer: The substrate was placed in the deposition reaction chamber and evacuated to 3 Pa. It was then purged twice with argon gas. The temperature was raised to 900 °C and the pressure was controlled at 5 kPa. Trimethylboron and methane with a flow rate of 5 slm were introduced. The deposition was carried out for 30 min to form a B4C transition layer with a thickness of 5 μm.

[0077] (3) Preparation of β-SiC coating: Continue heating to 1400℃, adjust the pressure to 15kPa, introduce argon gas with a flow rate of 5slm, hydrogen gas with a flow rate of 20slm, silicon tetrachloride with a flow rate of 15slm and methane with a flow rate of 5slm, deposit for 90min to form a β-SiC coating with a thickness of 70μm.

[0078] (4) Preparation of silicon carbide-silicon oxide composite surface: The hydrogen, silicon tetrachloride and methane feed were turned off, the temperature of the deposition reactor was controlled at 1200℃, the pressure of the reaction chamber was 15kPa, oxygen with a flow rate of 1slm and argon with a flow rate of 19slm were introduced, and the temperature was kept constant for 90min to form a composite surface with a thickness of 15μm.

[0079] (5) Post-treatment densification: Cool to 800℃ at a rate of 4°C / min and hold for 5h; then cool to 400℃ at a rate of 5°C / min and hold for 1.5h; finally cool to room temperature at a rate of 8°C / min.

[0080] Example 2 Example 2 provides a method for preparing silicon carbide ceramics with a composite coating (multilayer composite SiC-based coating), the specific steps of which are as follows: (1) Surface treatment: Hot-pressed sintered silicon carbide ceramic substrate was selected and placed in a mixed plasma of Ar / O2=9:1 for 10 min (power of 100W) to obtain a micro-rough surface with Ra=0.1nm; after surface cleaning and testing, the cleanliness and roughness met the requirements.

[0081] (2) Preparation of B4C transition layer: The substrate was placed in the deposition reaction chamber and evacuated to 2 Pa. It was then purged twice with N2 gas. The temperature was raised to 800 °C and the pressure was controlled at 1 kPa. Triethylboron and ethane with a flow rate of 1 slm were introduced. The deposition was carried out for 10 min to form a B4C transition layer with a thickness of 3 μm.

[0082] (3) Preparation of β-SiC coating: Continue heating to 1300℃, adjust the pressure to 10kPa, introduce nitrogen gas with a flow rate of 5slm, hydrogen gas with a flow rate of 20slm, and trichloromethylsilane with a flow rate of 5slm, deposit for 120min to form a β-SiC dense layer with a thickness of 100μm.

[0083] (4) Preparation of silicon carbide-silicon oxide composite surface: The hydrogen and trichloromethylsilane feeds were turned off, the temperature of the deposition reactor was controlled at 1100℃, the pressure of the reaction chamber was 10kPa, carbon dioxide with a flow rate of 1slm and nitrogen with a flow rate of 19slm were introduced, and the temperature was kept constant for 60min to form a composite surface with a thickness of 10μm.

[0084] (5) Post-treatment densification: Cool to 800℃ at a rate of 3°C / min and hold for 4 hours; then cool to 300℃ at a rate of 5°C / min and hold for 1 hour; finally cool to room temperature at a rate of 5°C / min.

[0085] Example 3 Example 3 provides a method for preparing silicon carbide ceramics with a composite coating (multilayer composite SiC-based coating), the specific steps of which are as follows: (1) Surface treatment: The reaction sintered silicon carbide ceramic substrate was selected and placed in a mixed plasma of Ar / O2=9:1 for 30 min (power of 300W) to obtain a micro-rough surface with Ra=0.5nm; after surface cleaning and testing, the cleanliness and roughness met the requirements.

[0086] (2) Preparation of B4C transition layer: The substrate was placed in the deposition reaction chamber and evacuated to 4 Pa. It was then purged twice with argon gas. The temperature was raised to 1200℃ and the pressure was controlled at 10 kPa. Triphenylboron and acetylene with a flow rate of 20 slm were introduced. The deposition was carried out for 60 min to form a B4C transition layer with a thickness of 10 μm.

[0087] (3) Preparation of β-SiC coating: Continue heating to 1500℃, adjust the pressure to 20kPa, introduce argon gas with a flow rate of 5slm, hydrogen gas with a flow rate of 30slm, silane with a flow rate of 15slm and methane with a flow rate of 10slm, deposit for 180min to form a β-SiC coating with a thickness of 150μm.

[0088] (4) Preparation of silicon carbide-silicon oxide composite surface: The hydrogen, silane and methane feeds were turned off, the temperature of the deposition reactor was controlled at 1300℃, the pressure of the reaction chamber was 20kPa, carbon dioxide with a flow rate of 2slm and argon with a flow rate of 38slm were introduced, and the temperature was kept constant for 90min to form a composite surface with a thickness of 20μm.

[0089] (5) Post-treatment densification: Cool to 800℃ at a rate of 5°C / min and hold for 6 hours; then cool to 500℃ at a rate of 5°C / min and hold for 2 hours; finally cool to room temperature at a rate of 10°C / min.

[0090] Example 4 Example 4 provides a method for preparing silicon carbide ceramics with a composite coating (multilayer composite SiC-based coating), the specific steps of which are as follows: (1) Surface treatment: Hot isostatic pressing sintered ceramic substrate was selected and placed in a mixed plasma of Ar / O2=9:1 for 20 min (power of 200W) to obtain a micro-rough surface with Ra=0.3nm; after surface cleaning and testing, the cleanliness and roughness met the requirements.

[0091] (2) Preparation of B4C transition layer: The substrate was placed in the deposition reaction chamber and evacuated to 1 Pa. It was then purged twice with argon gas. The temperature was raised to 1000℃ and the pressure was controlled at 10 kPa. Trimethylboron and methane with a flow rate of 10 slm were introduced. The deposition was carried out for 30 min to form a B4C transition layer with a thickness of 8 μm.

[0092] (3) Preparation of β-SiC coating: Continue heating to 1400℃, adjust the pressure to 15kPa, introduce argon gas with a flow rate of 5slm, hydrogen gas with a flow rate of 20slm, silicon tetrachloride with a flow rate of 15slm and methane with a flow rate of 5slm, deposit for 90min to form a β-SiC coating with a thickness of 70μm.

[0093] (4) Preparation of silicon carbide-silicon oxide composite surface: The hydrogen, silicon tetrachloride and methane feed were turned off, the temperature of the deposition reactor was controlled at 1200℃, the pressure of the reaction chamber was 15kPa, oxygen with a flow rate of 1slm and argon with a flow rate of 19slm were introduced, and the temperature was kept constant for 90min to form a composite surface with a thickness of 15μm.

[0094] (5) Post-treatment densification: Cool to 800℃ at a rate of 4°C / min and hold for 5h; then cool to 400℃ at a rate of 5°C / min and hold for 1.5h; finally cool to room temperature at a rate of 8°C / min.

[0095] Comparative Example 1 The difference between Comparative Example 1 and Example 1 lies in step (1). The difference is that step (1) is not performed, that is, the plasma activation treatment step is not performed. The surface roughness of the silicon carbide ceramic substrate in Comparative Example 1 is greater than 0.5 nm. Due to the lack of a micro-rough surface, the bonding strength between the coating and the substrate is weakened, and the coating is prone to separation from the substrate.

[0096] Comparative Example 2 The difference between Comparative Example 2 and Example 1 lies in step (2). The difference is that step (2) is not performed, that is, the B4C transition layer preparation step is not performed. Due to the lack of a transition layer, the bonding strength between the coating and the substrate in this comparative example is significantly reduced, and peeling is prone to occur.

[0097] Comparative Example 3 The difference between Comparative Example 3 and Example 1 lies in step (4), where the volume percentage of oxidizing gas is adjusted to 20%, while the remaining process parameters are the same as in Example 1. In this comparative example, due to excessive oxidizing gas, the composite surface layer was over-oxidized, resulting in cracking and pulverization, and a severe lack of density.

[0098] The coatings of each embodiment and comparative example were subjected to performance tests, including bond strength and coating density tests.

[0099] Bond strength: A scratch tester was used to scratch the coating surface at a loading rate of 10 N / min, and the critical load at which the coating peeled off was recorded. This critical load is the bond strength value between the coating and the substrate.

[0100] Coating density: The Archimedes drainage method was used to test the coating density. The apparent density of the coating was measured, and the ratio of the apparent density to the theoretical density was calculated to obtain the coating density. The theoretical density was calculated by weighted average of the material proportions of each layer.

[0101] The performance test results of the multilayer composite SiC-based coatings in each embodiment and comparative example are shown in Table 1 below.

[0102] Table 1

[0103] As shown in Table 1, the multilayer composite SiC-based coating prepared in Example 1 achieved a bonding strength of 69 N with the substrate, indicating high bonding strength. The coating also exhibited high density, reaching 98.2%. Examples 2-4 also yielded composite coatings with high density and strong bonding strength with the substrate.

[0104] Comparative Example 1 did not undergo plasma activation treatment before coating preparation, resulting in a large surface roughness of the substrate, weakened adhesion between the coating and the substrate, and low bonding strength. Comparative Example 2 did not undergo the B4C transition layer preparation step, leading to low adhesion between the coating and the substrate and a significant decrease in bonding strength. In Comparative Example 3, the excessive oxidizing gas in step (4) caused excessive oxidation and cracking of the composite surface layer, damaging the integrity of the coating structure, and resulting in unsatisfactory bonding strength and density between the coating and the substrate.

[0105] In the description of this application, the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require this application to be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this application.

[0106] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0107] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A silicon carbide ceramic with a composite coating, characterized in that, include: Silicon carbide ceramic matrix; A composite coating is located on the surface of the silicon carbide ceramic substrate in a direction away from the silicon carbide ceramic substrate. The composite coating includes a boron carbide transition layer, a β-SiC coating, and a silicon carbide-silicon oxide composite surface layer arranged sequentially. The bonding strength between the composite coating and the silicon carbide ceramic substrate is ≥60N.

2. The silicon carbide ceramic with a composite coating according to claim 1, characterized in that, At least one of the following conditions must be met: The silicon carbide ceramic matrix is ​​selected from one or more of the following: pressureless sintered silicon carbide ceramics, reaction sintered silicon carbide ceramics, hot-pressed sintered silicon carbide ceramics, hot isostatic pressing sintered silicon carbide ceramics, and recrystallized silicon carbide ceramics. The thickness of the boron carbide transition layer is 1μm-10μm; The thickness of the β-SiC coating is 30μm-140μm; The thickness of the silicon carbide-silicon oxide composite surface layer is 10μm-20μm.

3. A method for preparing silicon carbide ceramics with a composite coating, characterized in that, include: A boron carbide transition layer is formed on the surface of a silicon carbide ceramic substrate using chemical vapor deposition. The surface roughness Ra of the silicon carbide ceramic substrate with the boron carbide transition layer is 0.1 nm-0.5 nm. A β-SiC coating is formed on the side of the boron carbide transition layer away from the silicon carbide ceramic substrate using chemical vapor deposition. An oxidizing gas and an inert gas are introduced into the deposition chamber to convert a portion of the β-SiC coating into a silicon carbide-silicon oxide composite surface layer, wherein the volume of the oxidizing gas accounts for 5%-10% of the sum of the volumes of the oxidizing gas and the inert gas.

4. The method according to claim 3, characterized in that, Prior to the formation of the boron carbide transition layer, the silicon carbide ceramic substrate is surface-treated using a mixed plasma, and the surface treatment satisfies at least one of the following conditions: The mixed plasma is formed by oxygen and a first gas, the first gas including one or more of argon, helium, and nitrogen, and the volume ratio of oxygen to the first gas is 1:9 to 9:

1. The power of the surface treatment is 100W-300W; The surface treatment time is 10-30 minutes; After the surface treatment, the silicon carbide ceramic substrate is cleaned.

5. The method according to claim 3, characterized in that, The formation of the boron carbide transition layer includes: raising the temperature of the deposition chamber to 800℃-1200℃, controlling the pressure to 1kPa-10kPa, introducing a boron source and a first carbon source, and depositing the boron carbide transition layer on the surface of the silicon carbide ceramic substrate. Optionally, the deposition time of the boron carbide transition layer is 1 min to 60 min; Optionally, the boron source includes one or more of trimethylboron, triethylboron, tripropylboron, and triphenylboron; Optionally, the flow rate of the boron source is 0.1 slm-20 slm; Optionally, the first carbon source includes one or more of methane, ethane, ethylene, propylene, propane, and acetylene; Optionally, the flow rate of the first carbon source is 0.1 slm to 20 slm.

6. The method according to claim 3, characterized in that, The formation of the β-SiC coating includes: raising the temperature of the deposition chamber to 1300℃-1500℃, introducing a second gas, hydrogen and a precursor, controlling the pressure to 10kPa-20kPa, and depositing the β-SiC coating on the side of the boron carbide transition layer away from the silicon carbide ceramic substrate. The second gas includes one or more of argon, helium, and nitrogen; The precursor includes a first silicon source and a second carbon source. The first silicon source includes one or more of silane, monochlorosilane, dichlorosilane, trichlorosilane, and silicon tetrachloride. The second carbon source includes one or more of methane, ethane, ethylene, propylene, propane, and acetylene. Alternatively, the precursor includes a second silicon source, which includes one or more of trichloromethylsilane, hexamethyldisilane, dichlorodimethylsilane, and trimethylchlorosilane. Optionally, the flow rate of the first silicon source is 1 slm-30 slm; Optionally, the flow rate of the second carbon source is 1 slm-30 slm; Optionally, the flow rate of the second silicon source is 1 slm-30 slm.

7. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The flow rate of the second gas is 1 slm-10 slm; The flow rate of hydrogen is 1 slm-50 slm; The deposition time of the β-SiC coating is 60 min to 180 min.

8. The method according to claim 3, characterized in that, The temperature of the deposition chamber is controlled at 1100℃-1300℃ and the pressure is controlled at 10kPa-20kPa. Oxidizing gas and inert gas are introduced to convert part of the β-SiC coating into a silicon carbide-silicon oxide composite surface layer. The oxidizing gas includes one or more of oxygen, carbon dioxide, and carbon monoxide; The inert gas includes one or more of argon, helium, and nitrogen.

9. The method according to claim 8, characterized in that, The formation of the silicon carbide-silicon oxide composite surface layer satisfies at least one of the following conditions: The flow rate of the oxidizing gas is 1 slm-5 slm; The heat preservation time is 60-120 minutes.

10. The method according to any one of claims 3-9, characterized in that, After forming the silicon carbide-silicon oxide composite surface layer, the method for preparing silicon carbide ceramics with the composite coating further includes: Cool down to 600℃-1000℃ and keep warm for 4-6 hours; Continue cooling to 300℃-500℃ and maintain the temperature for 1-2 hours.

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