Silicon carbide coating, preparation method of silicon carbide coating, carbon fiber with silicon carbide coating and ceramic-based composite material

Abstract

The invention provides a silicon carbide coating and a preparation method thereof, carbon fibers with the silicon carbide coating and a ceramic-based composite material, the carbon fibers with the silicon carbide coating take carbohydrate as a carbon source, a thermal cracking carbon layer is generated on the carbon fibers firstly, and then the thermal cracking carbon layer is converted into the silicon carbide coating through a silicon steam reaction, so that the silicon carbide coating is obtained. Therefore, the carbon fiber containing the silicon carbide coating is obtained under the conditions of no carbon fiber loss and short period. The silicon carbide coating is few in production steps in the forming process, simple in production process, short in technological process and suitable for large-scale industrial production. According to the method, specifically, through a silicon evaporation process, damage to the carbon fibers during preparation is reduced to a certain extent, and the performance of the prepared carbon fiber composite silicon carbide coating is guaranteed. The method is short in technological process, high in production efficiency, simple in material, low in equipment requirement in the whole technological process and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation technology, specifically to a silicon carbide coating and its preparation method, and carbon fiber and ceramic matrix composite materials with silicon carbide coating. Background Technology

[0002] Carbon fiber, as a reinforcing phase, is an effective measure to improve the performance of ultra-high temperature ceramics, strengthening the material through mechanisms such as debonding, pull-out, bridging, and increasing crack propagation paths. However, interface problems exist between carbon fibers and the ceramic matrix, which can reduce the performance of carbon fiber-reinforced ultra-high temperature ceramic matrix composites. In high-temperature, oxygen-rich environments, oxygen diffuses from the matrix surface into the internal carbon fibers and oxidizes them, leading to a decrease in the composite's performance. Therefore, a silicon carbide coating needs to be prepared on the carbon fiber surface. At high temperatures, silica is generated in the matrix. The contact mode between the matrix and oxygen changes from direct contact to gas diffusion of oxygen within the silica isolation layer. Due to the low diffusion rate of oxygen in the molten silica layer, the internal composite material is isolated from external oxygen, reducing the possibility of further oxidation.

[0003] Currently, the main methods for preparing coatings on carbon fibers include chemical vapor deposition (CVD), sol-gel method, molten salt method, and embedding method. CVD is the most widely used coating preparation method. Ouyang Haibo et al. prepared a PyC / SiC composite coating by using gaseous SiO generated from Si / SiO2 mixed powder at 1400-1600℃ to undergo a chemical vapor reaction on the surface of PyC-coated carbon fibers. However, the prepared coating surface was rough, with a large number of nano-SiC particles growing on it. Furthermore, both the gaseous SiO generation process and the carbothermic reduction process required high temperatures, which easily damaged the carbon fibers and disrupted their structure.

[0004] The molten salt method is an emerging approach for preparing carbide coatings. It involves melting a mixed salt (typically NaCl, KCl, or NaF) at high temperatures to promote the diffusion of Si, Ti, Ta, and other minerals on the material surface, allowing them to react with the carbon matrix to form a carbide coating. Xie et al. used NaCl and NaF as molten salts to prepare SiC coatings at 1250-1300℃, and controlled the coating thickness by adjusting the reaction temperature and the Si / C ratio. By using different Si / C ratios, they prepared both thick (300-350 nm) and thin (130 nm) SiC coatings. However, the molten salt method is a process that sacrifices the substrate template, using carbon as the reaction matrix, which can damage the substrate material.

[0005] The embedding method involves embedding carbon fibers in oxide or metal powder, and then preparing a carbide coating on the fiber surface through a carbothermic reduction reaction. Lee et al. embedded carbon fibers in SiO2 and Si powder, reacting at 1800℃ to prepare a SiC coating. Their study found that at 1500℃, the carbon fibers completely transformed into SiC fibers, while XRD results at 1300℃ showed no SiC formation. The embedding method for preparing carbide coatings requires very high processing temperatures, but high-temperature treatment reduces the mechanical properties of the carbon fibers.

[0006] Chinese patent CN105350294A discloses a method for manufacturing short-cut carbon fibers coated with a silicon carbide layer. It uses nanocrystalline silicon carbide with a coating thickness between 100 and 500 nanometers. The method involves mixing short-cut carbon fibers with the surface adhesive layer removed with nano-silicon powder at a mass ratio of 8–20:100, filling the mixture into a graphite mold, and placing it in an electro-plasma sintering apparatus. The temperature is raised to 1150°C at a rate of 100°C / min, then raised to 1250–1300°C at a rate of 20°C / min, and held for 5 minutes. The temperature is then lowered to 1200°C at a rate of 20°C / min, held for 10 minutes, and allowed to cool naturally in the furnace. After removing the sintered block, it is ground for 15 minutes to obtain the short-cut carbon fibers with the silicon carbide coating. However, the patent requires spark plasma sintering and high-temperature treatment during the preparation process. The high temperature and spark plasma sintering treatment will cause the carbon fiber itself to oxidize and react with the silicon powder, which will generate microcracks on the surface of the carbon fiber, thus greatly affecting the mechanical properties of the carbon fiber itself.

[0007] Chinese patent CN110158309B discloses a method for preparing carbon fibers with a silicon carbide coating. The method involves pretreating 1mm long, 7µm diameter carbon fibers in a muffle furnace at 400℃ for 1 hour, followed by furnace cooling to room temperature. SiC powder with a particle size of 50nm and a purity of 99.99wt% is mixed with dimethyl silicone rubber with a viscosity of 5000mpa·s at a mass ratio of 5:100 to obtain a slurry, which is then mechanically stirred at 300r / min for 12 hours. The carbon fibers are then thoroughly mixed with the SiC slurry and mechanically stirred at 300r / min for 12 hours, with a carbon fiber to slurry mass ratio of 3:100. The thoroughly impregnated carbon fibers are then placed in a muffle furnace at 400℃ for 1 hour, followed by furnace cooling to room temperature to obtain carbon fibers with a silicon carbide coating. However, the silicon carbide coating prepared by this patent is uneven, and a large number of silicon carbide grains are generated on the carbon fiber surface, which affects the mechanical properties of the carbon fiber itself. Summary of the Invention

[0008] To address the aforementioned problems in existing technologies, reduce interfacial reactions in carbon fiber composites with other materials, and meet the performance requirements of carbon fiber composite materials, this application provides a silicon carbide coating, its preparation method, and a carbon fiber-ceramic matrix composite material with a silicon carbide coating. This silicon carbide coating formation process involves fewer production steps, a simpler production process, and a shorter process flow, making it suitable for large-scale industrial production. Specifically, this method utilizes a silicon vapor deposition process, which to a certain extent reduces damage during carbon fiber preparation and ensures the performance of the prepared carbon fiber composite silicon carbide coating.

[0009] The specific technical solution of this application is as follows:

[0010] A method for preparing a silicon carbide coating includes the following steps:

[0011] (1) Prepare a mixture of carbohydrates and water;

[0012] (2) Impregnate the carbon fiber in the mixed slurry of step (1) and then perform pretreatment;

[0013] (3) The carbon fibers pretreated in step (2) are placed under oxygen-free conditions for high-temperature pyrolysis reaction to obtain carbon fibers with pyrolysis carbon layers.

[0014] (4) The carbon fibers with the cracked carbon layer are subjected to silicon vapor deposition reaction to obtain carbon fibers with silicon carbide coating on the surface.

[0015] The mass ratio of carbohydrates to water in the mixed slurry of step (1) above is (5-20):(40-80).

[0016] The mixed slurry in step (1) above also contains silicon powder, and the mass ratio of carbohydrates to silicon powder is 1:(0.3-0.5).

[0017] In step (1) above, the carbohydrates are selected from any one of glucose, sucrose, citric acid or stearic acid as the carbon source.

[0018] The specific operation of the pretreatment in step (2) above is as follows: first, dry for 3.0 to 5.0 hours, then heat up to 150 to 400°C at a rate of 4 to 10°C / min and keep warm for 1.0 to 4.0 hours.

[0019] The specific conditions for the high-temperature pyrolysis reaction in step (3) above are: vacuum degree 5~50Pa, then heat up to 1000~1300℃ at a rate of 4~10℃ / min and hold for 1.0~4.0h; the carbon layer thickness in step (3) above is 200nm~1200nm.

[0020] The silicon vapor deposition reaction conditions in step (4) above are: silicon vapor vacuum degree 1.0 × 10⁻⁶. -3 ~1.0×10 -2Pa, heat to 1300-1600℃ at a rate of 4-10℃ / min and hold for 1.0-4.0h; the thickness of the silicon carbide coating in step (4) is 200nm-600nm.

[0021] Specifically, the preparation process of the silicon carbide coating is as follows:

[0022] Carbon fibers are impregnated in a slurry with a carbohydrate-to-water ratio of 5–20:40–80 (if silicon powder is present, the mass ratio of carbohydrate to silicon powder is 1:(0.3–0.5)). After drying for 3.0–5.0 hours, the slurry is placed in a box furnace and heated to 150–400°C at a rate of 4–10°C / min, and held for 1.0–4.0 hours. The pretreated carbon fibers are then cut into suitable shapes and placed in a vacuum furnace with a vacuum degree of 5–50 Pa. The temperature is then increased to 1000–1300°C at a rate of 4–10°C / min, and held for 1.0–4.0 hours.

[0023] Carbon fibers with a pyrolysis carbon layer are placed in a vacuum furnace, and silicon vapor deposition is carried out by maintaining a silicon vapor vacuum of 1.0×10-3 to 1.0×10-2 Pa, heating to 1300 to 1600℃ at a rate of 4 to 10℃ / min, and then holding at that temperature for 1.0 to 4.0 hours.

[0024] A carbon fiber with a silicon carbide coating includes carbon fiber and a silicon carbide coating, wherein the silicon carbide coating completely covers the carbon fiber.

[0025] Ceramic matrix composites include ceramic matrix raw materials and carbon fibers, with carbon fibers accounting for 12-15%; the ceramic matrix raw materials include silicon nitride, boric acid, fused silica, silicon powder, carbon black, flake graphite and zirconium boride in a mass ratio of (12-15):(20-25):(2-3):(21-24):(16-18):(14-15):(3-5).

[0026] Preferably, the mass ratio of silicon nitride, boric acid, fused silica, silicon powder, carbon black, flake graphite, and zirconium boride is 14.8:23.9:2.4:22.3:17.6:14.1:4.9.

[0027] The preparation method of ceramic matrix composite material is as follows: silicon nitride, boric acid, fused silica, silicon powder, carbon black, flake graphite and zirconium boride are mixed into powder raw materials. The powder raw materials and carbon fibers with silicon carbide coating prepared in this application are ball-milled and reactive hot-pressed to finally prepare carbon fiber composite SiBCN ceramic matrix composite material.

[0028] The ball milling conditions are: dry milling, speed 100-300 rpm, time 3-5 h, zirconia milling balls (preferably Φ5mm and Φ10mm mixed in a 1:1 ratio), and ball-to-material ratio (2-3):1.

[0029] The reactive hot pressing sintering conditions are as follows: A vacuum environment (34 Pa) is maintained inside the furnace throughout the entire reactive hot pressing sintering process. After loading the furnace, a pre-pressurization of 5 MPa is first applied at room temperature. Then, the furnace temperature is raised to 1200°C at a heating rate of 10°C / min, followed by a further increase to 1600°C at a heating rate of 5°C / min, and held at this temperature for 1 hour. Pressurization begins when the temperature reaches 1200°C, with an increase of 5 MPa for every 100°C increase, until a pressure of 25 MPa is applied at 1600°C, at which point the pressure is maintained. After the holding period, the furnace body cools naturally while the pressure is maintained. All pressure is released when the furnace temperature cools to 1200°C.

[0030] This application has the following advantages over the prior art:

[0031] (1) Compared with the existing technology, this application utilizes the characteristic of carbohydrates decomposing into carbon at high temperature and uses it as a carbon source to first generate a thermally decomposed carbon layer on carbon fiber, and then converts the thermally decomposed carbon layer into a silicon carbide coating through silicon vapor reaction, thereby achieving a new technology of obtaining carbon fiber containing silicon carbide coating without damaging the carbon fiber and under short cycle conditions; compared with directly generating silicon carbide coating on carbon fiber, this technology can reduce the reaction between silicon vapor and carbon fiber when generating silicon carbide coating, thereby reducing damage to carbon fiber; compared with chemical vapor deposition, this invention has the advantages of simple process, low production cost and high bonding strength with the substrate;

[0032] (2) The process of this application is short, the production efficiency is high, the materials are simple, and the equipment requirements in the whole process are low, making it suitable for large-scale production in industry. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the silicon carbide coating of this application;

[0034] Figure 2 This is a scanning electron microscope image of a glucose layer attached to the surface of a continuous carbon fiber in Example 1.

[0035] Figure 3 This is a scanning electron microscope image of the surface of the carbon fiber after pre-carbonization of continuous carbon fiber in Example 1, which is then subjected to carbonization treatment to form an amorphous carbon layer.

[0036] Figure 4 This is a scanning electron microscope image of the carbon fiber silicon vapor deposition reaction in Example 1.

[0037] Figure 5 This is a surface scan selection diagram of the EDS energy dispersive spectroscopy of carbon fiber after silicon vapor deposition reaction in Example 1.

[0038] Figure 6This is an EDS energy dispersive spectroscopy (EDS) data graph of the carbon fiber after silicon vapor deposition reaction in Example 1. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0041] In all embodiments and comparative examples, the weight of carbon fiber used is 100g.

[0042] Example 1

[0043] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 10:45:5. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 200°C at a rate of 6°C / min and holding at that temperature for 2.0 hours. Then, the temperature was increased to 1200°C at a rate of 6°C / min and held at that temperature for 2.0 hours to prepare a pyrolysis carbon layer (average carbon layer thickness 676 nm). After completion, the carbon was subjected to a vacuum autoclave while maintaining a silicon vapor vacuum of 1.0 × 10⁻⁶. -3 The silicon vapor deposition reaction was carried out by heating the carbon fiber to 1500℃ at a rate of 7℃ / min and holding it at that temperature for 2.0 hours, and finally carbon fiber with silicon carbide coating (average thickness of silicon carbide coating is 311nm) was obtained.

[0044] Example 2

[0045] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 20:110:9. After drying for 3.0 hours, the continuous carbon fibers were pretreated by heating to 350℃ at a rate of 6℃ / min and holding at that temperature for 1.0 hour. Then, the temperature was increased to 1200℃ at a rate of 4℃ / min and held at that temperature for 2.0 hours to prepare a pyrolysis carbon layer (average carbon layer thickness 742nm). After completion, the carbon was subjected to a vacuum autoclave while maintaining a silicon vapor vacuum of 1.0×10⁻⁶. -3 The process parameters were as follows: heating to 1500℃ at a rate of 7℃ / min and holding for 2.0 hours to carry out silicon vapor deposition reaction, finally obtaining carbon fiber with silicon carbide coating (average thickness of silicon carbide coating is 352nm).

[0046] Example 3

[0047] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 9:47:3. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 400℃ at a rate of 6℃ / min and holding at that temperature for 1.0 hour. Then, the temperature was increased to 1200℃ at a rate of 5℃ / min and held at that temperature for 2.0 hours to prepare a pyrolysis carbon layer (average carbon layer thickness 924nm). After completion, the carbon was subjected to a vacuum autoclave while maintaining a silicon vapor vacuum of 5.0 × 10⁻⁶. -3 The process parameters were as follows: heating to 1500℃ at a rate of 6℃ / min and holding for 2.0 hours to carry out silicon vapor deposition reaction, finally obtaining carbon fiber with silicon carbide coating (average thickness of silicon carbide coating 421nm).

[0048] Example 4

[0049] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 12:48:4. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 320℃ at a rate of 4℃ / min and holding for 2.0 hours. Then, the temperature was increased to 1100℃ at a rate of 6℃ / min and held for 3.0 hours to prepare a pyrolysis carbon layer (average carbon layer thickness 1053 nm). After completion, the carbon was subjected to a vacuum autoclave with a silicon vapor vacuum of 5.0 × 10⁻⁶. -3 The process parameters were as follows: heating to 1400℃ at a rate of 7℃ / min and holding for 3.0 hours to carry out silicon vapor deposition reaction, finally obtaining carbon fiber with silicon carbide coating (average thickness of silicon carbide coating is 493nm).

[0050] Example 5

[0051] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 20:50:6. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 300℃ at a rate of 5℃ / min and holding for 4.0 hours. Then, the temperature was increased to 1300℃ at a rate of 5℃ / min and held for 1.5 hours to prepare a pyrolysis carbon layer (average carbon layer thickness 1021 nm). After completion, the carbon was subjected to a vacuum autoclave while maintaining a silicon vapor vacuum of 1.0 × 10⁻⁶. -2 The silicon vapor deposition reaction was carried out using process parameters of heating to 1500℃ at a rate of 5℃ / min and holding for 2.0 hours, finally obtaining carbon fibers with a silicon carbide coating (average thickness of silicon carbide coating is 331nm).

[0052] Example 6

[0053] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 8:48:3. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 400℃ at a rate of 8℃ / min and holding at that temperature for 2.0 hours. Then, the temperature was further increased to 1200℃ at a rate of 8℃ / min and held at that temperature for 1.0 hour to prepare a pyrolysis carbon layer (average carbon layer thickness 681nm). After completion, the carbon was subjected to a vacuum autoclave with a silicon vapor vacuum of 7.0×10⁻⁶. -3 The silicon vapor deposition reaction was carried out using process parameters of heating to 1500℃ at a rate of 5℃ / min and holding for 2.0 hours, finally obtaining carbon fibers with a silicon carbide coating (average thickness of silicon carbide coating is 291nm).

[0054] Example 7

[0055] Carbon fibers were impregnated in a slurry made of carbohydrates and water at a mass ratio of 10:45. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 200°C at a rate of 6°C / min and holding for 2.0 hours. Then, the temperature was increased to 1200°C at a rate of 6°C / min and held for 2.0 hours to prepare a pyrolysis carbon layer (average carbon layer thickness 903 nm). After completion, the carbon was subjected to a vacuum autoclave while maintaining a silicon vapor vacuum of 1.0 × 10⁻⁶. -3 The silicon vapor deposition reaction was carried out using process parameters of heating to 1500℃ at a rate of 7℃ / min and holding for 2.0 hours, finally obtaining carbon fibers with a silicon carbide coating (average thickness of silicon carbide coating is 256nm).

[0056] Comparative Example 1

[0057] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 10:45:5. After drying for 4.0 hours, the pyrolysis carbon layer was prepared by heating the slurry to 1200℃ at a rate of 6℃ / min and holding it at that temperature for 2.0 hours. Afterward, the carbon layer was prepared by maintaining a silicon vapor vacuum of 1.0 × 10⁻⁶ in a vacuum hot press furnace. -3 The silicon vapor deposition reaction was carried out by heating the carbon fiber to 1500℃ at a rate of 7℃ / min and holding it at that temperature for 2.0 hours, and finally carbon fiber containing silicon carbide coating was obtained.

[0058] Comparative Example 2

[0059] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 10:45:5. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 500℃ at a rate of 6℃ / min and holding for 2.0 hours. Then, the temperature was increased to 1200℃ at a rate of 6℃ / min and held for 2.0 hours to prepare the pyrolysis carbon layer. After completion, the carbon was placed in a vacuum autoclave, maintaining a silicon vapor vacuum of 1.0 × 10⁻⁶. -3 The silicon vapor deposition reaction was carried out by heating the carbon fiber to 1500℃ at a rate of 7℃ / min and holding it at that temperature for 2.0 hours, and finally carbon fiber containing silicon carbide coating was obtained.

[0060] Comparative Example 3

[0061] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 2:45:1. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 200°C at a rate of 6°C / min and holding at that temperature for 2.0 hours. Then, the temperature was increased to 1200°C at a rate of 6°C / min and held at that temperature for 2.0 hours to prepare the pyrolysis carbon layer. After completion, the carbon was subjected to a vacuum autoclave with a silicon vapor vacuum of 1.0 × 10⁻⁶. -3 The silicon vapor deposition reaction was carried out by heating the carbon fiber to 1500℃ at a rate of 7℃ / min and holding it at that temperature for 2.0 hours, and finally carbon fiber containing silicon carbide coating was obtained.

[0062] Comparative Example 4

[0063] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 20:40:5. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 200℃ at a rate of 6℃ / min and holding at that temperature for 2.0 hours. Then, the temperature was increased to 1200℃ at a rate of 6℃ / min and held at that temperature for 2.0 hours to prepare the pyrolysis carbon layer. After completion, the carbon was placed in a vacuum hot press furnace, maintaining a silicon vapor vacuum of 1.0 × 10⁻⁶. -3 The silicon vapor deposition reaction was carried out by heating the carbon fiber to 1500℃ at a rate of 7℃ / min and holding it at that temperature for 2.0 hours, and finally carbon fiber containing silicon carbide coating was obtained.

[0064] Comparative Example 5

[0065] Carbon fibers were impregnated in a slurry made of carbohydrates, water, and silicon powder in a mass ratio of 10:45:8. After drying for 4.0 hours, the continuous carbon fibers were pretreated by heating to 200℃ at a rate of 6℃ / min and holding at that temperature for 2.0 hours. Then, the temperature was increased to 1200℃ at a rate of 6℃ / min and held at that temperature for 2.0 hours to prepare the pyrolysis carbon layer. After completion, the carbon was placed in a vacuum hot press furnace, maintaining a silicon vapor vacuum of 1.0 × 10⁻⁶. -3The silicon vapor deposition reaction was carried out by heating the carbon fiber to 1500℃ at a rate of 7℃ / min and holding it at that temperature for 2.0 hours, and finally carbon fiber containing silicon carbide coating was obtained.

[0066] The carbon fibers containing silicon carbide coatings obtained in the various embodiments and comparative examples were used to prepare ceramic matrix composites, and the performance of the obtained composites was tested. The preparation process of the ceramic matrix composites is as follows:

[0067] Silicon nitride, boric acid, fused silica, silicon powder, carbon black, flake graphite, and zirconium boride are mixed into powder raw materials. The powder raw materials are then ball-milled and reactive hot-pressed with carbon fibers coated with silicon carbide to finally prepare carbon fiber composite SiBCN ceramic matrix composite material.

[0068] The ball milling conditions are: dry milling, speed 200 rpm, time 3 h, zirconia milling balls (preferably Φ5mm and Φ10mm mixed in a 1:1 ratio), and ball-to-material ratio 2:1.

[0069] The reaction hot pressing sintering conditions are: inert gas protection, heating rate of 10℃ / min, holding at 1500℃ for 60min, and 20MPa.

[0070] Carbon fiber accounts for 15%; the mass ratio of silicon nitride, boric acid, fused silica, silicon powder, carbon black, flake graphite, and zirconium boride is 14.8:23.9:2.4:22.3:17.6:14.1:4.9.

[0071] Test example:

[0072] The residual flexural strength (MPa), elastic modulus (GPa), flexural strength (MPa), and fracture toughness (MPa·m) of the obtained ceramic composite material after thermal shock at 900℃ were determined. 1 / 2 Density / g / cm 3 test.

[0073] Mechanical properties were measured using a WD-P electronic universal testing machine manufactured by Jinan Test Instrument Co., Ltd. For measuring the elastic modulus and flexural strength: a fine ceramic universal testing machine was used with the three-point bending method to test the flexural strength of the material. The indenter loading rate was 0.5 mm / min, and the specimen span was 30 mm. The composite material samples were machined to the standard dimensions required for testing: 3 mm × 4 mm × 36 mm.

[0074] For fracture toughness measurement: The fracture toughness of the material was tested using the single-sided notched beam method on a precision ceramic universal testing machine. The fracture toughness specimen dimensions were 20mm × 2mm × 4mm, with a pre-supported crack of 2mm depth and 0.2mm width in the middle of the specimen. During the fracture toughness measurement, the indenter loading rate was 0.05mm / min, and the specimen span was 16mm.

[0075] Thermal shock resistance test: The ceramic sample was processed into a standard flexural strength specimen of 3mm×4mm×36mm with a span of 30mm. A box-type resistance furnace was used for heating. After reaching the programmed temperature, the sample was held at that temperature for 10 minutes to ensure it reached the predetermined temperature. The heated specimen was then quickly removed and immersed in an ice-water mixture. After complete cooling, the specimen was removed and dried. The residual flexural strength of the thermally shocked specimen was measured on a precision ceramic universal testing machine according to the flexural strength test standard, and compared with the original flexural strength. The thermal shock resistance of the composite material was evaluated based on the residual strength rate.

[0076] Density is achieved using the Archimedes' method of water displacement.

[0077] The specific test results are shown in Table 1 below:

[0078] Table 1

[0079]

[0080] As can be seen from the data in Table 1, in Comparative Example 1, the lack of pretreatment resulted in a reduction in the thickness, uniformity, and density of the pyrolytic carbon coating formed on the carbon fiber surface. The fiber was subjected to greater damage during the silicon vapor deposition reaction, leading to a decrease in the performance of the resulting ceramic matrix composite material.

[0081] In Comparative Example 2, the excessively high pretreatment temperature severely damaged the carbon fibers, causing them to become brittle. At this point, the carbon fibers had lost their toughness, leading to the introduction of numerous defects during the preparation of the ceramic matrix composite material, which resulted in a significant reduction in the mechanical properties of the final composite material.

[0082] In Comparative Example 3, due to the low slurry concentration, the impregnation effect of carbon fiber is poor, and the thickness of the thermally decomposed carbon layer generated on the surface of carbon fiber is small. In the subsequent silicon evaporation process, it may react with the carbon fiber, damage the carbon fiber, and ultimately reduce the performance of the ceramic matrix composite material.

[0083] In Comparative Examples 1-3, since the flexural strength and elastic modulus of the samples were much smaller than the average standard values, and during the sample preparation process for fracture toughness and thermal shock resistance tests, the samples experienced natural fractures, resulting in large errors in the measured data, none of which reached the average standard. Therefore, there is no specific experimental data.

[0084] Comparative Example 4: If the slurry concentration is high, the fluidity of the slurry will decrease, and the impregnation effect of the carbon fiber filaments in the internal region of the carbon fiber bundle will be reduced during the impregnation process. If the impregnation effect is guaranteed, repeated impregnation is required, which will increase costs.

[0085] The technical solution of this application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention, including the best mode, and also to enable any person skilled in the art to practice this invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the textual description of the claims, or if they include equivalent structural elements that are not substantially different from the textual description of the claims, then these other embodiments should also be included within the scope of the claims. For those skilled in the art, it is understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of this invention, and the scope of this invention is defined by the appended claims and their equivalents.

Claims

1. A method of producing a silicon carbide coating, characterized by, The method comprises the following steps: (1) preparing a mixed slurry of carbohydrates and water; (2) immersing carbon fibers in the mixed slurry of step (1) and then performing pretreatment; (3) performing a high-temperature pyrolysis reaction on the pretreated carbon fibers of step (2) under an oxygen-free condition to obtain carbon fibers with a pyrolytic carbon layer; (4) performing a silicon vapor deposition reaction on the carbon fibers with a pyrolytic carbon layer to obtain carbon fibers with a silicon carbide coating.

2. The method of claim 1, wherein: The mass ratio of carbohydrates to water in the mixed slurry of step (1) is (5-20):(40-80).

3. The method of claim 1, wherein: The mixed slurry of step (1) further contains silicon powder, and the mass ratio of carbohydrates to silicon powder is 1:(0.3-0.5).

4. The method of claim 1, wherein: The carbohydrates of step (1) are selected from any one of glucose, sucrose, citric acid, or stearic acid.

5. The method of claim 1, wherein the silicon carbide coating is formed by a process comprising: The pretreatment of step (2) is specifically performed by first airing for 3.0-5.0 h, then heating at a rate of 4-10 ℃ / min to 150-400 ℃ and maintaining the temperature for 1.0-4.0 h.

6. The method of claim 1, wherein the silicon carbide coating is formed by a process comprising: The high-temperature pyrolysis reaction of step (3) is specifically performed by heating at a rate of 4-10 ℃ / min to 1000-1300 ℃ under a vacuum degree of 5-50 Pa and maintaining the temperature for 1.0-4.0 h; the thickness of the carbon layer of step (3) is 200 nm-1200 nm.

7. The method of claim 1, wherein the silicon carbide coating is formed by a process comprising: The step (4) silicon evaporation reaction conditions are: silicon vapor vacuum degree 1.0×10 -3 ~1.0×10 -2 Pa, temperature rising rate 4~10 ℃ / min, temperature 1300~1600 ℃, holding time 1.0~4.0 h; the step (4) silicon carbide coating thickness 200 nm~600 nm.

8. A carbon fiber with a silicon carbide coating, characterized by, The ceramic matrix composite material comprises carbon fibers and a silicon carbide coating prepared by the method of any one of claims 1-7, and the silicon carbide coating completely covers the carbon fibers.

9. A ceramic matrix composite material, characterized by: The ceramic matrix composite material comprises a ceramic matrix raw material and carbon fibers, and the proportion of the carbon fibers is 12-15%; the ceramic matrix composite material is prepared by mixing the ceramic matrix raw material and the carbon fibers, ball milling, and reaction hot-pressing sintering; the carbon fibers are the carbon fibers with a silicon carbide coating of claim 8.

10. The ceramic matrix composite of claim 9, wherein: The ceramic matrix raw material comprises a mass ratio of (12-15):(20-25):(2-3):(21-24):(16-18):(14-15). (3-5) of silicon nitride, boric acid, fused quartz, silicon powder, carbon black, flaky graphite, and zirconium boride.

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