Preparation method of boron nitride fiber reinforced ceramic matrix composite material

Abstract

The invention provides a preparation method of a boron nitride fiber reinforced ceramic-based composite material, and belongs to the technical field of boron nitride fiber reinforced ceramic-based composite materials. The preparation method comprises the steps of mixed slurry preparation, fiber cloth pretreatment, coating curing and sintering. The step of preparing the mixed slurry comprises the steps of preparing silicon-boron-oxygen-nitrogen powder, coating and pulping; the preparation method of the silicon-boron-oxygen-nitrogen powder comprises the following steps: mixing tetraethoxysilane and absolute ethyl alcohol, uniformly stirring, dropwise adding trimethyl borate at a dropwise adding rate of 1-2 mL / min while maintaining a stirring speed of 480-520 r / min, adjusting the pH value to 3-4 after dropwise adding, adding hexamethyldisilazane, stirring at 40-50 DEG C for 2-3 h to obtain sol, standing, aging, drying and roasting to obtain the silicon-boron-oxygen-nitrogen powder. The silicon-boron-oxygen-nitrogen powder is obtained; the composite material prepared through the method is high in mechanical property, good in high temperature resistance and excellent in long-term service performance.

Description

Technical Field

[0001] This invention belongs to the technical field of boron nitride fiber reinforced ceramic matrix composites, and specifically relates to a method for preparing boron nitride fiber reinforced ceramic matrix composites. Background Technology

[0002] Ceramic matrix composites are widely used in aerospace, energy and chemical industries due to their excellent high-temperature stability, wear resistance and oxidation resistance. However, traditional ceramic matrix composites generally have defects such as high brittleness, poor toughness and insufficient thermal shock resistance, which limit their application in high-temperature load-bearing structural components.

[0003] However, traditional ceramic matrix composites (such as alumina-based and silicon carbide-based composites) have the following significant drawbacks: First, it is brittle and has low fracture toughness. It is prone to sudden fracture under external impact or complex stress, which severely limits its application in dynamic service scenarios. Second, high-temperature environments (above 1200℃) are prone to grain boundary oxidation and phase structure transformation, which leads to a sharp decline in mechanical properties and cannot meet the requirements of hypersonic aircraft wave-transparent components, aero-engine hot-end components and other materials for long-term stable service in extreme environments above 1600℃.

[0004] To address the aforementioned issues, existing technologies introduce boron nitride (BN) fibers as reinforcements to prepare boron nitride fiber-reinforced ceramic matrix composites. As a high-performance, wave-transparent ceramic matrix, boron nitride fibers exhibit high temperature resistance and stable dielectric properties at high temperatures. Furthermore, boron nitride fibers possess excellent chemical stability, strong thermal shock resistance, and corrosion resistance, effectively resisting the harsh service environment of hypersonic vehicles. Therefore, boron nitride fiber reinforced ceramic matrix composites are a new generation of wave-transparent materials that can meet the requirements of long-term stable operation of wave-transparent components for hypersonic aircraft in ultra-high temperature environments above 1600℃, following quartz fiber composites with a temperature resistance of 1200℃ and silicon nitride / silicon boron nitride fiber composites with a temperature resistance of 1400℃.

[0005] However, existing technologies for preparing boron nitride fiber-reinforced ceramic matrix composites still face the following key bottlenecks: On the one hand, the interfacial bonding strength between the fiber and the matrix is ​​mismatched. The surface of boron nitride fiber is chemically inert and has poor wettability with the ceramic matrix, making it difficult to form an ideal bonding interface. If the bonding is too weak, stress transfer will fail. If the bonding is too strong, the fiber will not be able to effectively consume fracture energy through mechanisms such as "fiber bridging" and "fiber pull-out" during crack propagation. Ultimately, the improvement of the material's bending strength and fracture toughness is limited. On the other hand, insufficient densification of the matrix can easily lead to defects such as pores and cracks during the preparation process. These defects can become stress concentration sources and oxidation channels in high-temperature environments, resulting in a decrease in the material's high-temperature resistance and long-term service stability. In addition, existing processes have poor adaptability to fiber morphology and cannot achieve uniform composite of different fiber morphologies with the matrix, which further restricts the consistency of product performance and large-scale application. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a method for preparing boron nitride fiber reinforced ceramic matrix composite materials, which improves the product's mechanical properties such as bending strength and fracture toughness, and enhances its high-temperature resistance and long-term service stability.

[0007] To address the aforementioned technical problems, the present invention adopts the following technical solution: A method for preparing boron nitride fiber-reinforced ceramic matrix composite material includes the steps of preparing a mixed slurry, pretreating the fiber cloth, coating and curing, and sintering. The specific operations are as follows: 1. Preparation of mixed slurry (1) Preparation of silicon boron oxynitride powder Mix tetraethyl orthosilicate with anhydrous ethanol and stir at 240-260 rpm for 10-15 min. Add trimethyl borate dropwise at a rate of 1-2 mL / min while maintaining a stirring speed of 480-520 rpm. After the addition is complete, stir for 30-35 min. Add 0.10-0.13 mol / L hydrochloric acid solution to adjust the pH to 3-4. Add hexamethyldisilazane and heat to 40-50℃. Keep warm and stir for 2-3 h to obtain a sol. The mass ratio of tetraethyl orthosilicate, anhydrous ethanol, trimethyl borate, and hexamethyldisilazane is 37-38:95-100:7.0-7.3:4.8-5.0. Pour the sol into a sealed container and allow it to age at room temperature for 24-48 hours. Then, dry it at 58-62℃ for 6.0-6.3 hours and at 100-105℃ for 11-12 hours. Finally, calcine it under a nitrogen atmosphere by heating it to 600-610℃ at a rate of 4.5-5.5℃ / min and holding it at that temperature for 1.5-2.0 hours. Then, heat it to 1200-1400℃ at a rate of 8-10℃ / min and hold it at that temperature for 3-4 hours. After naturally cooling to room temperature, silicon boron oxynitride powder is obtained. (2) Covering The silicon boron oxynitride powder was placed in anhydrous ethanol and stirred evenly. Then, alumina sol was added at a rate of 1.5-2.0 g / min. After addition, the powder was ultrasonically dispersed for 30-40 min at a power of 110-120 W and a frequency of 36-40 kHz. After ultrasonication, the temperature was increased to 46-52℃ and stirred at 480-520 rpm for 2.5-3.0 h. After stirring, the powder was aged at room temperature for 24-26 h. After drying, the powder was calcined in a nitrogen atmosphere. The temperature was increased to 400-420℃ at a rate of 3.5-4.0℃ / min and held for 1.3-1.5 h. Then, the temperature was increased to 850-900℃ at a rate of 7.5-8.0℃ / min and held for 2.0-2.2 h. The powder was then naturally cooled to room temperature to obtain alumina-coated silicon boron oxynitride powder. The mass ratio of the silicon boron oxygen nitrogen powder, anhydrous ethanol, and alumina sol is 10-12:100:60-65; The alumina sol is prepared by adding aluminum isopropoxide to anhydrous ethanol, stirring at 280-320 rpm for 25-30 min, adding glacial acetic acid, and continuing to stir at room temperature for 25-30 min. After stirring, the temperature is raised to 42-47℃, deionized water is added, and the addition time is controlled to be 10-15 min. Stirring is continued at 42-47℃ for 1.5-2.0 h to obtain alumina sol. The volume-to-mass ratio of the anhydrous ethanol, aluminum isopropoxide, glacial acetic acid, and deionized water is 50-55 mL: 1.8-2.2 g: 0.58-0.62 g: 0.52-0.56 g; (3) Pulping Add deionized water to anhydrous ethanol and stir until homogeneous. Then add KH560 silane coupling agent, heat to 40-45℃, and stir for 25-30 minutes. Add polyvinylpyrrolidone and stir at 250-280 rpm for 20-25 minutes. Add alumina-coated silicon boron oxygen nitrogen powder and yttrium oxide and ball milling is performed. The ball-to-material ratio is 3-5:1, the ball milling time is 15-20 minutes, and the ball milling speed is 200-230 rpm. After ball milling, stir at 40-45℃ for 1.5-2.0 hours. Add 6-8g of glycerol and stir for 30-35 minutes. Then lower the temperature to 30-32℃ and stir at 250-270 rpm for 1.0-1.2 hours to obtain a mixed slurry. The mass ratio of anhydrous ethanol, deionized water, kH560 silane coupling agent, polyvinylpyrrolidone, alumina-coated silicon boron oxygen nitrogen powder, and yttrium oxide is 40:5-7:1.4-1.7:2.0-2.4:45-50:0.8-1.0.

[0008] 2. Fiber cloth pretreatment Boron nitride fibers were placed in a plasma device for etching. Argon gas was introduced and the argon gas flow rate was controlled at 20-25 sccm, the vacuum degree was -0.07 to -0.075 MPa, the etching power was 120-130 W, and the etching time was 7-10 min to obtain the pretreated fiber cloth. The boron nitride fiber cloth has a weaving density of 20-23 threads / 10mm in the warp and 20-23 threads / 10mm in the weft, and the areal density of the fiber cloth is 120-130 g / m². 2 The thickness is 280-300μm.

[0009] 3. Coating and curing The pretreated fiber cloth is laid flat on a vacuum adsorption worktable, and the vacuum degree is adjusted to -0.08 to -0.09 MPa. The mixed slurry is added, and the cloth is coated with a scraper. The scraping speed is controlled at 20-25 mm / s. After the scraping is completed, the cloth is left to stand for 15-20 minutes, and the coating thickness is controlled at 24-28 μm. After drying, the cloth is placed in the mold of a hot press molding machine. Nitrogen gas is introduced and the flow rate is maintained at 200-210 mL / min. The pressure is controlled at 0.50-0.52 MPa. The cloth is left to stand at room temperature for 5-7 minutes. The temperature is then increased to 80-82℃ and held at 1.0-1.2 MPa for 28-32 minutes. The temperature is then increased to 118-123℃ and held at 1.4-1.7 MPa for 28-32 minutes. The temperature is then increased to 180-183℃ and held at 1.4-1.7 MPa for 1.5-2.0 hours. The cloth is then cooled to room temperature to obtain the composite boron nitride fiber cloth.

[0010] 4. Sintering The composite boron nitride fiber cloth is placed in a sintering furnace, nitrogen gas is introduced, and the temperature is increased to 580-600℃ at a rate of 4.0-5.0℃ / min, and held for 25-30 min. The atmosphere is then switched to argon gas, and the temperature is increased to 1300-1330℃ at a rate of 2.5-3.0℃ / min, and the pressure is increased to 2.5-3.0 MPa. The temperature is held for 3.0-3.3 h. After the holding period, the temperature is decreased to 580-600℃ at a rate of 4.0-5.0℃ / min, the argon gas is turned off, and the material is allowed to cool naturally to room temperature to obtain the boron nitride fiber reinforced ceramic matrix composite material.

[0011] The present invention discloses a method for preparing boron nitride fiber-reinforced ceramic matrix composites. Boron nitride fiber cloth is used as the reinforcing phase, and silicon boron oxynitride (SiO2) and alumina coating are used as the ceramic matrix. This method ultimately enhances the mechanical properties of the product, ensures high-temperature resistance, and effectively improves long-term service stability. Specifically, tetraethyl orthosilicate (TEO2) provides the silicon source, trimethyl borate (TBO) provides the boron source, and hexamethyldisilazane (DIS) provides the nitrogen source. TEO and TBO are hydrolyzed to generate a Si-OB network, which, combined with the hexamethyldisilazane component, forms Si-OBN ceramic powder. This powder exhibits high high-temperature strength, excellent oxidation resistance, and a thermal expansion coefficient that matches that of boron nitride fibers, minimizing fiber damage and ensuring product stability. Aluminum isopropoxide is then used as the aluminum source, hydrolyzed and dehydrated to form an aluminum sol. This aluminum sol is used to coat the SiO2 powder, with alumina sol particles deposited on the surface to form a coating layer. This ensures fiber reinforcement, improves product density and strength, and enhances high-temperature stability. In the pulping step, a stable and fluid slurry is formed through ball milling and stirring. The plasma treatment of boron nitride fiber cloth significantly improves the wettability of the fiber surface, making it easier for the slurry to penetrate into the fiber bundle, thereby enhancing the mechanical properties of the composite material. Combined with the coating and sintering steps, the reinforcing properties of boron nitride fiber are effectively utilized, improving the toughness and flexural strength of the product, enhancing the fiber's service performance in long-term high-temperature environments, and improving product stability.

[0012] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. The boron nitride fiber-reinforced ceramic matrix composite material prepared by the method of the present invention has a fracture toughness of 8.14-8.51 MPa·m. 1 / 2 The flexural strength is 314.3-323.5 MPa, and the linear ablation rate after oxyacetylene ablation at 2500℃ for 400 s is 5.01-5.17 × 10⁻⁶. -3 The coefficient of thermal expansion is 2.53-2.67×10 mm / s at room temperature and below 1000℃. -6 / ℃; 2. The boron nitride fiber-reinforced ceramic matrix composite material prepared by the method of the present invention was placed in an air environment at 1200℃ and kept at that temperature for 120 hours. The fracture toughness was measured again to be 7.82-8.31 MPa·m. 1 / 2 Its flexural strength is 298.6-314.1 MPa; 3. The boron nitride fiber-reinforced ceramic matrix composite material prepared by the method of the present invention was placed in an air atmosphere at 1000°C for 12 hours, and then immediately placed in deionized water at 24°C for 12 hours, with the deionized water completely immersing the composite material. This treatment constitutes one thermal shock cycle, and seven consecutive thermal shock cycles were performed. The fracture toughness was then measured again to be 7.68-8.15 MPa·m. 1 / 2 Its flexural strength is 292.6-306.0 MPa. Detailed Implementation

[0013] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0014] Example 1 1. Preparation of mixed slurry (1) Preparation of silicon boron oxynitride powder Mix 38g of tetraethyl orthosilicate with 100g of anhydrous ethanol, stir at 260rpm for 15min, add 7.3g of trimethyl borate dropwise at a rate of 2mL / min, and maintain a stirring speed of 520r / min during the dropwise addition. After the dropwise addition is complete, stir for 35min, add 0.13mol / L hydrochloric acid solution to adjust the pH value to 4, add 5.0g of hexamethyldisilazane, heat to 50℃, and stir for 3h to obtain a sol. The sol was poured into a sealed container and allowed to stand at room temperature for 28 hours. It was then dried at 62°C for 6.3 hours and at 105°C for 11 hours. After that, it was calcined under a nitrogen atmosphere. The temperature was increased to 610°C at a rate of 5.5°C / min and held for 2.0 hours. The temperature was then increased to 1400°C at a rate of 10°C / min and held for 4 hours. After naturally cooling to room temperature, silicon boron oxynitride powder was obtained. (2) Covering 12g of silicon boron oxynitride powder was added to 100g of anhydrous ethanol and stirred evenly. Then, 65g of alumina sol was added at a rate of 2.0g / min. After addition, the mixture was ultrasonically dispersed for 40min at a power of 120W and a frequency of 40kHz. After ultrasonication, the temperature was increased to 52℃ and stirred at 520rpm for 3.0h. After stirring, the mixture was aged at room temperature for 26h. After drying, the mixture was calcined in a nitrogen atmosphere. The temperature was increased to 420℃ at a rate of 4.0℃ / min and held for 1.5h. Then, the temperature was increased to 900℃ at a rate of 8.0℃ / min and held for 2.2h. The mixture was then naturally cooled to room temperature to obtain alumina-coated silicon boron oxynitride powder. The alumina sol was prepared by adding 2.2 g of aluminum isopropoxide to 55 mL of anhydrous ethanol, stirring at 320 rpm for 30 min, adding 0.62 g of glacial acetic acid, stirring at room temperature for another 30 min, raising the temperature to 47 °C, adding 0.56 g of deionized water, controlling the addition time to 15 min, and stirring at 47 °C for another 2.0 h to obtain the alumina sol. (3) Pulping Add 7g of deionized water to 40g of anhydrous ethanol, stir well, then add 1.7g of KH560 silane coupling agent, heat to 45℃, keep warm and stir for 30min, add 2.4g of polyvinylpyrrolidone, stir at 280rpm for 25min, add 50g of alumina-coated silicon boron oxygen nitrogen powder and 1.0g of yttrium oxide for ball milling, with a ball-to-material ratio of 5:1, ball milling time of 20min, and ball milling speed of 230rpm. After ball milling, keep warm and stir at 45℃ for 2.0h, add 8g of glycerol, stir for 35min, then lower the temperature to 32℃ and stir at 270rpm for 1.2h to obtain a mixed slurry.

[0015] 2. Fiber cloth pretreatment Boron nitride fibers were placed in a plasma device for etching. Argon gas was introduced and the argon gas flow rate was controlled at 25 sccm, the vacuum degree was -0.075 MPa, the etching power was 130 W, and the etching time was 10 min to obtain the pretreated fiber cloth. The boron nitride fiber cloth has a weaving density of 23 threads / 10mm in the warp and 23 threads / 10mm in the weft, and the areal density of the fiber cloth is 130g / m². 2 The thickness is 280μm.

[0016] 3. Coating and curing The pretreated fiber cloth was laid flat on a vacuum adsorption worktable, and the vacuum degree was adjusted to -0.09MPa. The mixed slurry was added, and the cloth was coated with a scraper at a speed of 25mm / s. After the coating was completed, it was left to stand for 20 minutes, and the coating thickness was controlled to be 28μm. After drying, it was placed in the mold of a hot press molding machine, and nitrogen was introduced. The nitrogen flow rate was maintained at 210mL / min, and the pressure was controlled at 0.52MPa. The cloth was left to stand at room temperature for 7 minutes, then the temperature was increased to 82℃ and held at 1.2MPa for 32 minutes. The temperature was increased to 123℃ and held at 1.7MPa for 32 minutes. The temperature was then increased to 183℃ and held at 1.7MPa for 2.0h. The cloth was then cooled to room temperature to obtain the composite boron nitride fiber cloth.

[0017] 4. Sintering The composite boron nitride fiber cloth was placed in a sintering furnace, nitrogen gas was introduced, and the temperature was increased to 600℃ at a rate of 5.0℃ / min and held for 30 min. The atmosphere was then switched to argon gas, and the temperature was increased to 1330℃ at a rate of 3.0℃ / min and pressurized to 3.0 MPa. The temperature was held for 3.3 h. After the holding period, the temperature was decreased to 600℃ at a rate of 5.0℃ / min, the argon gas was turned off, and the mixture was allowed to cool naturally to room temperature to obtain the boron nitride fiber reinforced ceramic matrix composite material.

[0018] Example 2 1. Preparation of mixed slurry (1) Preparation of silicon boron oxynitride powder Mix 38g of tetraethyl orthosilicate with 98g of anhydrous ethanol, stir at 250rpm for 13min, add 7.2g of trimethyl borate dropwise at a rate of 1.5mL / min, and maintain a stirring speed of 500r / min during the dropwise addition. After the dropwise addition is complete, stir for 33min, add 0.12mol / L hydrochloric acid solution to adjust the pH to 3.5, add 5.0g of hexamethyldisilazane, heat to 45℃, and stir for 2.5h to obtain a sol. The sol was poured into a sealed container and allowed to stand at room temperature for 26 hours. It was then dried at 60°C for 6.2 hours and at 102°C for 12 hours. After that, it was calcined under a nitrogen atmosphere. The temperature was increased to 606°C at a rate of 5.0°C / min and held for 1.8 hours. The temperature was then increased to 1300°C at a rate of 9°C / min and held for 3.5 hours. After naturally cooling to room temperature, silicon boron oxynitride powder was obtained. (2) Covering 12g of silicon boron oxynitride powder was added to 100g of anhydrous ethanol and stirred evenly. Then, 63g of alumina sol was added at a rate of 1.8g / min. After addition, the mixture was ultrasonically dispersed for 35min at a power of 115W and a frequency of 38kHz. After ultrasonication, the temperature was increased to 48℃ and stirred at 500rpm for 2.8h. After stirring, the mixture was aged at room temperature for 25h. After drying, the mixture was calcined in a nitrogen atmosphere. The temperature was increased to 410℃ at a rate of 3.8℃ / min and held for 1.4h. Then, the temperature was increased to 880℃ at a rate of 7.7℃ / min and held for 2.1h. The mixture was then naturally cooled to room temperature to obtain alumina-coated silicon boron oxynitride powder. The alumina sol was prepared by adding 2.0 g of aluminum isopropoxide to 53 mL of anhydrous ethanol, stirring at 300 rpm for 27 min, adding 0.60 g of glacial acetic acid, and stirring at room temperature for another 27 min. After stirring, the temperature was raised to 45 °C, and 0.54 g of deionized water was added, with the addition time controlled at 13 min. Stirring was continued at 45 °C for 1.8 h to obtain the alumina sol. (3) Pulping Add 6g of deionized water to 40g of anhydrous ethanol and stir until homogeneous. Then add 1.5g of KH560 silane coupling agent, heat to 42℃, and stir for 27min. Add 2.2g of polyvinylpyrrolidone and stir at 270rpm for 23min. Add 48g of alumina-coated silicon boron oxygen nitrogen powder and 0.9g of yttrium oxide for ball milling. The ball-to-material ratio is 4:1, the ball milling time is 18min, and the ball milling speed is 220rpm. After ball milling, stir at 43℃ for 1.7h, add 7g of glycerol, stir for 32min, then lower the temperature to 32℃ and stir at 260rpm for 1.2h to obtain a mixed slurry.

[0019] 2. Fiber cloth pretreatment Boron nitride fibers were placed in a plasma device for etching. Argon gas was introduced and the argon gas flow rate was controlled at 23 sccm, the vacuum degree was -0.072 MPa, the etching power was 125 W, and the etching time was 8 min to obtain the pretreated fiber cloth. The boron nitride fiber cloth has a weaving density of 22 threads / 10mm in the warp and 22 threads / 10mm in the weft, and the areal density of the fiber cloth is 126g / m². 2 The thickness is 290μm.

[0020] 3. Coating and curing The pretreated fiber cloth was laid flat on a vacuum adsorption worktable, and the vacuum degree was adjusted to -0.085MPa. The mixed slurry was added, and the cloth was coated with a scraper at a speed of 23mm / s. After the coating was completed, it was left to stand for 17 minutes, and the coating thickness was controlled to be 26μm. After drying, it was placed in the mold of a hot press molding machine, and nitrogen gas was introduced. The nitrogen flow rate was maintained at 205mL / min, and the pressure was controlled at 0.52MPa. The cloth was left to stand at room temperature for 6 minutes, and then the temperature was increased to 82℃ and held at 1.1MPa for 30 minutes. The temperature was increased to 120℃ and held at 1.6MPa for 30 minutes. The temperature was then increased to 182℃ and held at 1.6MPa for 1.8 hours. The cloth was then cooled to room temperature to obtain the composite boron nitride fiber cloth.

[0021] 4. Sintering The composite boron nitride fiber cloth was placed in a sintering furnace, nitrogen gas was introduced, and the temperature was increased to 590℃ at a rate of 4.5℃ / min and held for 28 min. The atmosphere was then switched to argon gas, and the temperature was increased to 1320℃ at a rate of 2.7℃ / min and pressurized to 2.7 MPa. The temperature was held for 3.2 h. After the holding period, the temperature was decreased to 590℃ at a rate of 4.5℃ / min, the argon gas was turned off, and the mixture was allowed to cool naturally to room temperature to obtain the boron nitride fiber reinforced ceramic matrix composite material.

[0022] Example 3 1. Preparation of mixed slurry (1) Preparation of silicon boron oxynitride powder Mix 37g of tetraethyl orthosilicate with 95g of anhydrous ethanol, stir at 240rpm for 10min, add 7.0g of trimethyl borate dropwise at a rate of 1mL / min, and maintain a stirring speed of 480r / min during the dropwise addition. After the dropwise addition is complete, stir for 30min, add 0.10mol / L hydrochloric acid solution to adjust the pH value to 3, add 4.8g of hexamethyldisilazane, heat to 40℃, and stir for 2h to obtain a sol. The sol was poured into a sealed container and allowed to stand at room temperature for 24 hours. It was then dried at 58°C for 6.0 hours and at 100°C for 12 hours. After that, it was calcined under a nitrogen atmosphere, heated to 600°C at a rate of 4.5°C / min and held for 1.5 hours. Then, it was heated to 1200°C at a rate of 8°C / min and held for 3 hours. After naturally cooling to room temperature, silicon boron oxynitride powder was obtained. (2) Covering 10g of silicon boron oxynitride powder was added to 100g of anhydrous ethanol and stirred evenly. Then, 60g of alumina sol was added at a rate of 1.5g / min. After addition, the mixture was ultrasonically dispersed for 30min at a power of 110W and a frequency of 36kHz. After ultrasonication, the temperature was increased to 46℃ and stirred at 480rpm for 2.5h. After stirring, the mixture was aged at room temperature for 24h. After drying, the mixture was calcined in a nitrogen atmosphere. The temperature was increased to 400℃ at a rate of 3.5℃ / min and held for 1.3h. Then, the temperature was increased to 850℃ at a rate of 7.5℃ / min and held for 2.0h. The mixture was then naturally cooled to room temperature to obtain alumina-coated silicon boron oxynitride powder. The alumina sol is prepared by adding 1.8g of aluminum isopropoxide to 50mL of anhydrous ethanol, stirring at 280rpm for 25min, adding 0.58g of glacial acetic acid, stirring at room temperature for another 25min, raising the temperature to 42℃, adding 0.52g of deionized water, controlling the addition time to 10min, and stirring at 42℃ for another 1.5h to obtain the alumina sol. (3) Pulping Add 5g of deionized water to 40g of anhydrous ethanol and stir until homogeneous. Then add 1.4g of KH560 silane coupling agent, heat to 40℃, and stir for 25min. Add 2.0g of polyvinylpyrrolidone and stir at 250rpm for 20min. Add 45g of alumina-coated silicon boron oxygen nitrogen powder and 0.8g of yttrium oxide for ball milling. The ball-to-material ratio is 3:1, the ball milling time is 15min, and the ball milling speed is 200rpm. After ball milling, stir at 40℃ for 1.5h, add 6g of glycerol, stir for 30min, then lower the temperature to 30℃ and stir at 250rpm for 1.0h to obtain a mixed slurry.

[0023] 2. Fiber cloth pretreatment Boron nitride fibers were placed in a plasma device for etching. Argon gas was introduced and the argon gas flow rate was controlled at 20 sccm, the vacuum degree was -0.07 MPa, the etching power was 120 W, and the etching time was 7 min to obtain the pretreated fiber cloth. The boron nitride fiber cloth has a weaving density of 20 threads / 10mm in the warp and 20 threads / 10mm in the weft, and the areal density of the fiber cloth is 120g / m². 2 The thickness is 300μm.

[0024] 3. Coating and curing The pretreated fiber cloth was laid flat on a vacuum adsorption worktable, and the vacuum degree was adjusted to -0.08MPa. The mixed slurry was added, and the cloth was coated with a scraper at a speed of 20mm / s. After the coating was completed, it was left to stand for 15 minutes, and the coating thickness was controlled to be 24μm. After drying, it was placed in the mold of a hot press molding machine, and nitrogen gas was introduced. The nitrogen flow rate was maintained at 200mL / min, and the pressure was controlled at 0.50MPa. The cloth was left to stand at room temperature for 5 minutes, and the temperature was increased to 80℃ and held at 1.0MPa for 28 minutes. The temperature was increased to 118℃ and held at 1.4MPa for 28 minutes. The temperature was further increased to 180℃ and held at 1.4MPa for 1.5 hours. The cloth was then cooled to room temperature to obtain the composite boron nitride fiber cloth.

[0025] 4. Sintering The composite boron nitride fiber cloth was placed in a sintering furnace, nitrogen gas was introduced, and the temperature was increased to 580℃ at a rate of 4.0℃ / min and held for 25 min. The atmosphere was then switched to argon gas, and the temperature was increased to 1300℃ at a rate of 2.5℃ / min and pressurized to 2.5 MPa. The temperature was held for 3.0 h. After the holding period, the temperature was decreased to 580℃ at a rate of 4.0℃ / min, the argon gas was turned off, and the mixture was allowed to cool naturally to room temperature to obtain the boron nitride fiber reinforced ceramic matrix composite material.

[0026] Comparative Example 2-1 The changes made in Example 2 are as follows: In the process of preparing the mixed slurry, the coating step is omitted; the alumina-coated silicon boron oxy nitrogen powder in the slurry preparation step is replaced with an equal amount of silicon boron oxy nitrogen powder. In the pulping step, the kH560 silane coupling agent component is omitted; The rest of the operations are exactly the same.

[0027] Comparative Example 2-2 The changes made in Example 2 are as follows: In the process of preparing the mixed slurry, the step of preparing silicon boron oxynitride powder is omitted, and the silicon boron oxynitride powder in the coating step is replaced with "5g silicon dioxide powder and 5g boron nitride powder". The fiber cloth pretreatment step is omitted, and the pretreated fiber cloth in the coating and curing step is replaced in equal amounts with untreated boron nitride fiber cloth; the boron nitride fiber cloth has a weave density of 20 threads / 10mm in the warp and 20 threads / 10mm in the weft, and the areal density of the fiber cloth is 120g / m². 2 The thickness is 300μm; The rest of the operations are exactly the same.

[0028] Performance testing The boron nitride fiber-reinforced ceramic matrix composites prepared in Examples 1-3, Comparative Example 2-1, and Comparative Example 2-2 were subjected to mechanical properties, high-temperature resistance, and thermal shock cycle resistance tests, as detailed below: 1. Mechanical properties

[0029] 2. High temperature resistance The boron nitride fiber-reinforced ceramic matrix composites prepared in Examples 1-3, Comparative Example 2-1, and Comparative Example 2-2 were placed in an air environment at 1200℃ and kept static for 120 hours. The fracture toughness and flexural strength were tested again, and the test results are as follows:

[0030] 3. Thermal shock cycling resistance The boron nitride fiber-reinforced ceramic matrix composites prepared in Examples 1-3, Comparative Examples 2-1, and Comparative Examples 2-2 were placed in an air atmosphere at 1000°C for 12 hours, and then immediately placed in deionized water at 24°C for 12 hours, with the deionized water completely immersing the composites. This treatment constituted one thermal shock cycle, and seven consecutive thermal shock cycles were performed. The fracture toughness and flexural strength were then tested again, and the test results are as follows:

[0031] Based on the test results above, it can be seen that Comparative Example 2-1 omits the aluminum sol coating, resulting in the absence of an alumina protective layer on the surface of the silicon boron oxynitride (SiBO) powder. This leads to poor dispersion performance and easy agglomeration of the SiBO powder. Furthermore, the omission of the silane coupling agent in the slurry preparation step affects the penetration of the slurry into the boron nitride fibers, thus reducing the reinforcing properties of the boron nitride fibers. Ultimately, this reduces the high-temperature resistance and mechanical properties of the composite material, shortening its long-term service life under complex environments. Comparative Example 2-2 uses only physically mixed silica boron nitride powder, which has lower high-temperature strength and poor sintering activity. Moreover, the surface of the boron nitride fibers is untreated, resulting in numerous pores and physical gaps between the fibers and the matrix, hindering effective load transfer and weakening the reinforcing and toughening effect of the boron nitride fibers. During sintering, the mismatch in thermal expansion coefficients between the silica powder and the boron nitride fibers leads to numerous cracks during heating, making them prone to oxidation and cracking at high temperatures. This further shortens the service life under complex environments and reduces overall performance.

[0032] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0033] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a boron nitride fiber-reinforced ceramic matrix composite material, characterized in that, This includes the steps of preparing the mixed slurry, pretreatment of the fiber cloth, coating and curing, and sintering. The preparation of the mixed slurry includes the steps of preparing silicon boron oxynitride powder, coating, and slurry preparation; The steps for preparing silicon boron oxynitride powder are as follows: Tetraethyl orthosilicate is mixed with anhydrous ethanol and stirred evenly. Trimethyl borate is then added dropwise at a rate of 1-2 mL / min, while maintaining a stirring speed of 480-520 r / min. After the addition is complete, the pH value is adjusted to 3-4, and hexamethyldisilazane is added. The mixture is stirred at 40-50℃ for 2-3 hours to obtain a sol. After static aging, drying, and calcination, silicon boron oxynitride powder is obtained. The coating step is as follows: the silicon boron oxy nitrogen powder is placed in anhydrous ethanol, stirred evenly, and then alumina sol is added at a rate of 1.5-2.0 g / min. After the addition is complete, the powder is ultrasonically dispersed and stirred at 46-52℃ for 2.5-3.0 h. After stirring, the powder is aged, dried, and calcined to obtain alumina-coated silicon boron oxy nitrogen powder.

2. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the step of preparing silicon boron oxy nitrogen powder, the mass ratio of tetraethyl orthosilicate, anhydrous ethanol, trimethyl borate, and hexamethyldisilazane is 37-38:95-100:7.0-7.3:4.8-5.

0.

3. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the coating step, the mass ratio of the silicon boron oxy nitrogen powder, anhydrous ethanol, and alumina sol is 10-12:100:60-65.

4. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the coating step, the alumina sol is prepared by adding aluminum isopropoxide to anhydrous ethanol, stirring at 280-320 rpm for 25-30 min, adding glacial acetic acid, and continuing to stir at room temperature for 25-30 min. After stirring, the temperature is raised to 42-47℃, deionized water is added, and the addition time is controlled to be 10-15 min. Stirring is continued at 42-47℃ for 1.5-2.0 h to obtain alumina sol. The volume-to-mass ratio of anhydrous ethanol, aluminum isopropoxide, glacial acetic acid, and deionized water is 50-55 mL: 1.8-2.2 g: 0.58-0.62 g: 0.52-0.56 g.

5. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, The pulping steps are as follows: Deionized water is added to anhydrous ethanol and stirred evenly. Then, KH560 silane coupling agent is added, the temperature is raised to 40-45℃, and the mixture is stirred for 25-30 minutes. Polyvinylpyrrolidone is added and stirred at 250-280 rpm for 20-25 minutes. Alumina-coated silicon boron oxygen nitrogen powder and yttrium oxide are added and ball-milled. The ball-to-material ratio is 3-5:1, the ball-milling time is 15-20 minutes, and the ball-milling speed is 200-230 rpm. After ball milling, the mixture is stirred at 40-45℃ for 1.5-2.0 hours. Then, 6-8g of glycerol is added and stirred for 30-35 minutes. The temperature is then lowered to 30-32℃ and stirred at 250-270 rpm for 1.0-1.2 hours to obtain a mixed slurry.

6. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 5, characterized in that, The mass ratio of anhydrous ethanol, deionized water, kH560 silane coupling agent, polyvinylpyrrolidone, alumina-coated silicon boron oxygen nitrogen powder, and yttrium oxide is 40:5-7:1.4-1.7:2.0-2.4:45-50:0.8-1.

0.

7. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, The fiber cloth pretreatment step is as follows: boron nitride fiber cloth is placed in a plasma device for etching, argon gas is introduced, the argon gas flow rate is controlled at 20-25 sccm, the vacuum degree is -0.07 to -0.075 MPa, the etching power is 120-130 W, and the etching time is 7-10 min, to obtain the pretreated fiber cloth. The boron nitride fiber cloth has a weaving density of 20-23 threads / 10mm in the warp and 20-23 threads / 10mm in the weft, and the areal density of the fiber cloth is 120-130 g / m². 2 The thickness is 280-300μm.

8. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, The coating and curing steps are as follows: the pretreated fiber cloth is laid flat on a vacuum adsorption worktable, the vacuum degree is adjusted to -0.08 to -0.09 MPa, the mixed slurry is added, and the cloth is coated with a scraper, with the scraping speed controlled at 20-25 mm / s. After the scraping is completed, it is left to stand for 15-20 minutes, and the coating thickness is controlled at 24-28 μm. After drying, it is placed in the mold of a hot press molding machine, nitrogen is introduced, and the nitrogen flow rate is maintained at 200-210 mL / min. The pressure is controlled at 0.50-0.52 MPa. The cloth is left to stand at room temperature for 5-7 minutes, the temperature is raised to 80-82℃, and the temperature is maintained at 1.0-1.2 MPa for 28-32 minutes. The temperature is raised to 118-123℃, and the temperature is maintained at 1.4-1.7 MPa for 28-32 minutes. The temperature is further raised to 180-183℃, and the temperature is maintained at 1.4-1.7 MPa for 1.5-2.0 hours. The cloth is then cooled to room temperature to obtain the composite boron nitride fiber cloth.

9. The method for preparing a boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, The sintering step is as follows: the composite boron nitride fiber cloth is placed in a sintering furnace, nitrogen gas is introduced, the temperature is increased to 580-600℃ at a rate of 4.0-5.0℃ / min, and held for 25-30min. The atmosphere is then switched to argon gas, the temperature is increased to 1300-1330℃ at a rate of 2.5-3.0℃ / min, and the pressure is increased to 2.5-3.0MPa. The temperature is held for 3.0-3.3h. After the holding period, the temperature is decreased to 580-600℃ at a rate of 4.0-5.0℃ / min, the argon gas is turned off, and the mixture is allowed to cool naturally to room temperature to obtain the boron nitride fiber reinforced ceramic matrix composite material.

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