Surface coating preparation method of boron nitride fiber reinforced ceramic matrix composite material and product prepared by surface coating preparation method

Abstract

The invention provides a surface coating preparation method of a boron nitride fiber reinforced ceramic matrix composite material and a product prepared by the surface coating preparation method, and relates to the field of ceramic materials. The preparation method of the surface coating of the boron nitride fiber reinforced ceramic-based composite material comprises the following steps: sintering to prepare a ceramic repair layer, vapor deposition to prepare a ceramic compact layer, and spraying and curing to prepare a surface smooth layer. According to the preparation method of the surface coating of the boron nitride fiber reinforced ceramic matrix composite material, on the premise that the wave-transparent performance of the composite material is not affected, the matching performance of the surface coating and the composite material is good, and the surface coating and the composite material can be effectively combined; the surface coating can uniformly form a film on the surface of the composite material, surface defects of the composite material are effectively filled, and the air tightness of the composite material is good; and meanwhile, the surface coating also has anti-pollution performance.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials, and in particular to a method for preparing a surface coating of a boron nitride fiber-reinforced ceramic matrix composite material and the product obtained therefrom. Background Technology

[0002] BN fiber-reinforced ceramic matrix composites possess excellent high-temperature mechanical properties, superior wave transmission characteristics, and near-zero ablation resistance at ultra-high temperatures. Following Si3N4 fiber-reinforced ceramic matrix composites, they represent a new generation of high-temperature wave-transmitting materials for high-Mach aircraft radomes / antenna windows. Similar to the preparation methods for Si3N4 fiber-reinforced ceramic matrix composites, the mainstream preparation method for BN fiber-reinforced ceramic matrix composites is the PIP (impregnation-pyrolysis) process. This involves weaving BN fibers into fiber preforms with different structural designs and volume fractions, pretreating them, and then combining them with different types of ceramic precursors. Then, based on the physical and chemical properties of the precursors, pyrolysis is performed under a nitrogen or ammonia atmosphere to complete the ceramization transformation. This process is repeated to finally obtain BN fiber-reinforced ceramic matrix composites of a predetermined density. Commonly used ceramic matrices include Si3N4, SiBN, and BN.

[0003] However, during the preparation of BN fiber-reinforced ceramic matrix composites, the pyrolysis of the ceramic precursor generates numerous micropores with pore sizes ranging from hundreds of nanometers to tens of micrometers. These micropores readily absorb surrounding moisture during subsequent application, leading to moisture absorption, especially since boron-containing ceramic materials such as BN and SiBN are inherently hygroscopic. For high-Mach aircraft radomes / antenna windows made of BN fiber-reinforced ceramic matrix composites, moisture absorption is a significant factor affecting their mechanical and electrical properties during use and storage. Therefore, effective coating protection is essential for BN fiber-reinforced ceramic matrix composites to prevent moisture absorption.

[0004] Generally speaking, the surface coating of BN fiber-reinforced ceramic matrix composites used for radomes / antenna windows must meet the following basic requirements: First, it must have low dielectric and low loss characteristics and not affect the wave transmission performance of the radome / antenna window; second, the surface coating must have good adhesion to the substrate and must not delaminate or peel off; third, the surface coating must have good airtightness to the substrate and be able to withstand moisture erosion in the long-term storage environment; and fourth, the surface coating must have certain anti-fouling properties to avoid pollution of the composite material by the external environment.

[0005] In existing technologies, moisture-proofing measures for BN fiber-reinforced ceramic matrix composites used in radomes / antenna windows typically employ spraying or brushing with silicone resin. However, this method is not well-suited for BN fiber-reinforced ceramic matrix composites. Specifically, directly applying silicone resin to BN fiber-reinforced ceramic matrix composites for moisture protection has the following technical drawbacks: First, due to the structural design and manufacturing process of BN fiber-reinforced ceramic matrix composites, it is difficult to achieve uniform preparation. Furthermore, a considerable number of micropores / macropores (pore sizes ranging from tens to hundreds of micrometers) exist within the composite material. Machining the composite material exposes these surface defects, resulting in a material surface that combines micropores and macropores. Silicone resin is difficult to uniformly form a film on such a surface, failing to meet the airtightness requirements of the surface coating. Second, the numerous defects on the surface of BN fiber-reinforced ceramic matrix composites prevent silicone resin from effectively filling the macropore defects, directly affecting the bonding performance between the surface coating and the composite material, the composite material's resistance to airflow erosion, and the product's appearance quality. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a method for preparing a surface coating on boron nitride fiber-reinforced ceramic matrix composites. Without affecting the wave transmission performance of the composite material, the surface coating exhibits good compatibility with the composite material and can effectively bond with it. The surface coating can form a uniform film on the surface of the composite material, effectively filling surface defects and improving the airtightness of the composite material. Simultaneously, the surface coating also possesses anti-fouling properties. This invention also provides products prepared using the aforementioned surface coating preparation method.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a surface coating of a boron nitride fiber reinforced ceramic matrix composite material includes the following steps: sintering to prepare a ceramic repair layer, vapor deposition to prepare a dense ceramic layer, and spraying and curing to prepare a smooth surface layer. The method for preparing the ceramic repair layer by sintering is as follows: adding high-temperature resistant ceramic powder to an ethyl acetate solution of polysilazane and mixing it evenly to obtain a coating slurry; brushing the coating slurry onto the outer surface of the boron nitride fiber reinforced ceramic matrix composite material, and then drying and sintering to obtain a composite material with a ceramic repair layer. The method for preparing a dense ceramic layer by vapor deposition is as follows: placing the composite material with the ceramic repair layer in a chemical vapor deposition furnace, continuously evacuating and heating to 850-950°C, and holding at that temperature; continuously introducing reactive gas to perform chemical vapor deposition; and obtaining a composite material with a dense ceramic layer deposited on its surface. The reaction gas consists of silicon source gas, ammonia gas, and hydrogen gas; The method for preparing a smooth surface layer by spraying and curing involves spraying a coating liquid containing organosilicon resin onto the outer surface of a composite material on which a dense ceramic layer has been deposited, and then heating and curing to form a smooth surface layer, thereby completing the preparation of the surface coating of the boron nitride fiber reinforced ceramic matrix composite material.

[0008] Preferably, in the sintering preparation of the ceramic repair layer, the concentration of the ethyl acetate solution of polysilazane is 45-50 wt%. The high-temperature resistant ceramic powder is silicon nitride powder and / or boron nitride powder; the particle size of silicon nitride powder is 1-10 μm, and the particle size of boron nitride powder is 1-10 μm; The weight of high-temperature resistant ceramic powder added to the coating slurry is 15-30% of the weight of polysilazane.

[0009] Preferably, in the sintering preparation of the ceramic repair layer, anhydrous air or synthetic air is used as the sintering atmosphere, the sintering temperature is 550-650℃, and the sintering time is 0.5-1h. The thickness of the ceramic repair layer is 10-30μm.

[0010] Furthermore, in the preparation of the ceramic dense layer by chemical vapor deposition, when the thickness of the deposited ceramic dense layer is less than or equal to 50-60% of the predetermined thickness, the total flow rate of the reaction gas is controlled at 5-8 L / min; when the thickness of the deposited ceramic dense layer is greater than 50-60% of the predetermined thickness, the total flow rate of the reaction gas is controlled at 2-3 L / min. Preferably, the predetermined thickness is 50-150 μm.

[0011] Preferably, in the preparation of the dense ceramic layer by vapor deposition, the silicon source gas is silane or chlorosilane; the chlorosilane is one of the following: HSiCl3, H2SiCl2, SiCl4; The volumetric flow rate ratio of silicon source gas, ammonia, and hydrogen in the reaction gas is 1-1.2:1.5-2.5:2-4.

[0012] Preferably, in the process of preparing the smooth surface layer by spraying and curing, the curing temperature is 80-120℃ and the curing time is 2-5h; The spraying liquid consists of silicone resin, curing agent, antifouling agent and solvent; The thickness of the smooth surface layer is 20-50 μm.

[0013] Preferably, the organosilicon resin is one of the following: epoxy-modified organosilicon resin, methylphenyl silicone resin, or phenyl silicone resin; The solvent is at least one of the following: ethyl acetate, toluene, xylene, or isopropanol; The curing agent is an organotin curing agent or an amine curing agent; The antifouling agent is 1H,1H,2H,2H-perfluorodecyltriethoxysilane and / or heptadecafluorodecyltrimethoxysilane.

[0014] Preferably, in the spraying liquid, the weight ratio of solvent to silicone resin is 1.5-2.5:1; The curing agent should be added at a weight of 5-7% of the total weight of the silicone resin. The antifouling agent should be added at a weight of 3-5% of the total weight of the silicone resin.

[0015] A product prepared by the aforementioned method, wherein the surface coating of the product comprises, in sequence: a ceramic repair layer, a ceramic dense layer, and a surface smoothing layer; The thickness of the ceramic repair layer is 10-30 μm; the thickness of the ceramic dense layer is 50-150 μm; and the thickness of the surface smoothing layer is 20-50 μm.

[0016] Application of the aforementioned product in the fabrication of radomes or antenna windows for high-Mach aircraft.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The surface coating preparation method of boron nitride fiber reinforced ceramic matrix composite material of the present invention is based on the characteristics of composite material, ceramic dense layer and their bonding characteristics. First, ceramic precursor combined with ceramic powder is used as ceramic repair component to construct ceramic repair layer on the surface of composite material. The ceramic repair component has similar properties to the composite matrix component and good matching. It not only effectively repairs the surface pore defects of composite material and makes up for the defects caused by conventional PIP process, but also provides the basic conditions for the uniform preparation of ceramic dense layer in the subsequent process, realizing the effective transition between composite material and ceramic dense layer. Then, on the basis of ceramic repair layer, ceramic dense layer is prepared by chemical vapor deposition. It is not limited by the shape and size of composite component. The coating preparation is uniform and has good micro and macro consistency. It can be effectively bonded to composite matrix through ceramic repair layer. Finally, an organosilicon coating containing antifouling agent is used to protect the outermost layer of composite material. While improving the moisture resistance of composite material, it reduces or avoids the contamination of products by oil, dust, fingerprints and other impurities during storage or transfer. Through the effective combination of each coating and composite material, the functions of air tightness, moisture resistance and antifouling are integrated. The aforementioned technologies work together synergistically to achieve good compatibility between the surface coating and the composite material without affecting the wave transmission performance of the composite material, and the two materials can be effectively bonded together. The surface coating can form a uniform film on the surface of the composite material, effectively filling the surface defects of the composite material and improving the air tightness of the composite material. At the same time, the surface coating also has anti-fouling properties.

[0018] (2) The ceramic repair layer formed on the surface of the boron nitride fiber reinforced ceramic matrix composite material by the preparation method described in this invention is divided into grids by cross-cutting method to control the grid cut to penetrate the entire coating and reach the composite matrix. After gridding, 3M Scotch 600 test tape is used for adhesion and peeling. No grids fall off in the grid area, indicating that the ceramic repair layer has good bonding performance with the composite matrix.

[0019] (3) The ceramic dense layer obtained by the preparation method described in this invention is heated to 1200°C in 30s under the radiation of a quartz lamp, and kept at 1200°C for 100s before being cooled to room temperature. After repeating the aforementioned quartz lamp thermal shock test 5 times, no cracking or peeling occurred in the ceramic dense layer.

[0020] (4) The product prepared by the preparation method described in this invention has excellent airtightness. In the airtightness test, the vacuum degree on one side of the product is evacuated to 0.099 MPa and kept in vacuum for 2 hours. The vacuum degree on that side of the product is only reduced by 5-7 kPa.

[0021] (5) The product prepared by the method described in this invention is placed in a constant temperature and humidity environment of 42°C and 95% relative humidity for 96 hours. The increase rate of mass after the test compared with the mass before the test (i.e., moisture absorption rate) is 0.5-0.8%.

[0022] (6) After the surface coating is prepared by the preparation method described in this invention, the dielectric loss tangent of the product is only increased by 0.001-0.003 compared with boron nitride fiber reinforced ceramic matrix composite material (i.e. matrix material).

[0023] (7) The method for preparing the surface coating of boron nitride fiber reinforced ceramic matrix composite material of the present invention is not limited by the shape and size of the composite material component, the raw materials are easy to obtain, the process is simple, the preparation process is easy to control, and it is conducive to large-scale industrial production. Detailed Implementation

[0024] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] This invention provides a method for preparing a surface coating of boron nitride fiber reinforced ceramic matrix composite material, comprising the following steps: sintering to prepare a ceramic repair layer, vapor deposition to prepare a dense ceramic layer, and spraying and curing to prepare a smooth surface layer.

[0027] The method for preparing the ceramic repair layer by sintering is as follows: the weight of the added high-temperature resistant ceramic powder is controlled to be 15-30% of the weight of polysilazane. The high-temperature resistant ceramic powder is added to the ethyl acetate solution of polysilazane and mixed evenly to obtain a coating slurry. Then, the coating slurry is brushed onto the outer surface of the BN fiber reinforced ceramic matrix composite material. After drying at 120-150℃ for 0.5-2 hours, it is polished with sandpaper. Then, it is placed in a muffle furnace with anhydrous air or synthetic air as the sintering atmosphere, heated to 550-650℃, and sintered at that temperature for 0.5-1 hours to complete the surface pore defect repair of the BN fiber reinforced ceramic matrix composite material, and a composite material with a ceramic repair layer (thickness of 10-30μm) is obtained.

[0028] In the sintering preparation of the ceramic repair layer, the concentration of the ethyl acetate solution of polysilazane is 45-50 wt%. The high-temperature resistant ceramic powder is silicon nitride powder and / or boron nitride powder; the particle size of silicon nitride powder is 1-10 μm, and the particle size of boron nitride powder is 1-10 μm.

[0029] The method for preparing a dense ceramic layer by chemical vapor deposition involves suspending a composite material with a ceramic repair layer in a chemical vapor deposition furnace, continuously evacuating and heating it to the reaction temperature (850-950℃), and maintaining the temperature. Then, according to a predetermined ratio and gas flow rate, silicon source gas, ammonia, and hydrogen are simultaneously introduced as reaction gases for chemical vapor deposition. During the chemical vapor deposition process, when the thickness of the deposited dense ceramic layer is less than or equal to 50-60% of the predetermined thickness, the total flow rate of the reaction gas is controlled at 5-8 L / min; when the thickness of the deposited dense ceramic layer is greater than 50-60% of the predetermined thickness, the total flow rate of the reaction gas is controlled at 2-3 L / min. After the chemical vapor deposition is completed, the furnace is cooled and nitrogen is used for purging to obtain a composite material with a dense ceramic layer (thickness of 50-150 μm, material of silicon nitride) deposited on the surface.

[0030] In the preparation of the dense ceramic layer by vapor deposition, the silicon source gas is silane or chlorosilane; the chlorosilane is one of the following: HSiCl3, H2SiCl2, SiCl4; The volumetric flow rate ratio of silicon source gas, ammonia, and hydrogen is 1-1.2:1.5-2.5:2-4.

[0031] The method for preparing the surface smooth layer by spraying and curing is as follows: after diluting the silicone resin with a solvent, a curing agent and an antifouling agent are added sequentially and mixed evenly to obtain a spraying liquid; the spraying liquid is evenly sprayed onto the surface of the composite material with a dense ceramic layer deposited on the surface, the temperature is raised to 80-120℃, and after heat preservation and curing for 2-5 hours, a surface smooth layer with a thickness of 20-50μm is formed, thus completing the preparation of the surface coating of the boron nitride fiber reinforced ceramic matrix composite material.

[0032] In the preparation of the smooth surface layer by spraying and curing, the silicone resin is one of the following: epoxy-modified silicone resin, methylphenyl silicone resin, or phenyl silicone resin; The solvent is at least one of the following: ethyl acetate, toluene, xylene, isopropanol; the weight ratio of solvent to silicone resin is 1.5-2.5:1.

[0033] In the process of preparing the smooth surface layer by spraying and curing, the curing agent is an organotin curing agent (dibutyltin dilaurate, stannous octoate) or an amine curing agent. When the organosilicon resin is epoxy-modified organosilicon resin, an amine curing agent is preferred. When the organosilicon resin is methylphenyl silicone resin or phenyl silicone resin, an organotin curing agent is preferred. The weight of the curing agent added is 5-7% of the total weight of the organosilicon resin.

[0034] In the preparation of the smooth surface layer by spraying and curing, the antifouling agent is 1H,1H,2H,2H-perfluorodecyltriethoxysilane or heptadecafluorodecyltrimethoxysilane, and the weight of the antifouling agent added is 3-5% of the total weight of the silicone resin.

[0035] The surface coating preparation method for boron nitride fiber-reinforced ceramic matrix composites of this invention addresses the characteristics of the composite material, the ceramic dense layer, and their bonding properties. First, a ceramic repair layer is constructed on the surface of the composite material to repair surface pore defects and provide the foundation for the uniform preparation of the subsequent ceramic dense layer, achieving an effective transition between the composite material and the ceramic dense layer. Then, based on the ceramic repair layer, a ceramic dense layer and a surface smoothing layer are constructed sequentially. Through the effective combination of each coating with the composite material, functions such as airtightness, moisture resistance, and stain resistance are integrated. Specifically, the organic smoothing coating can provide moisture resistance and stain resistance at room temperature and low temperatures; after the organic smoothing coating ablates and fails at high temperatures, the ceramic dense coating immediately provides airtightness and temperature resistance.

[0036] This invention also provides a product prepared using the aforementioned method, wherein the surface coating of the boron nitride fiber-reinforced ceramic matrix composite material comprises a three-layer coating structure: a ceramic repair layer, a ceramic dense layer, and a surface smoothing layer. The ceramic repair layer repairs surface pore defects in the composite material and provides a transitional base between the composite material and the ceramic dense layer; the ceramic dense layer provides reinforcement, airtightness, and temperature resistance; and the surface smoothing layer provides moisture resistance, stain resistance, and surface protection.

[0037] The present invention also provides the application of the aforementioned product in the fabrication of radomes or antenna windows for high Mach aircraft.

[0038] The present invention will be further described below with reference to some specific embodiments.

[0039] Example 1 This embodiment provides a method for preparing a surface coating of a boron nitride fiber-reinforced ceramic matrix composite material, specifically as follows: 1. Sintering preparation of ceramic repair layer The weight of the added high-temperature resistant ceramic powder was controlled to be 20% of the weight of polysilazane. The high-temperature resistant ceramic powder was added to the ethyl acetate solution of polysilazane and mixed evenly to obtain a coating slurry. The coating slurry was then brushed onto the outer surface of the BN fiber reinforced ceramic matrix composite. After drying at 120℃ for 1 hour, it was sanded with sandpaper and then placed in a muffle furnace. Anhydrous air or synthetic air was used as the sintering atmosphere, and the temperature was raised to 600℃ and held for sintering for 0.5 hours to complete the surface pore defect repair of the BN fiber reinforced ceramic matrix composite, thus obtaining a composite material with a ceramic repair layer (thickness of 20 μm).

[0040] The concentration of the ethyl acetate solution of polysilazane is 50 wt%.

[0041] The high-temperature resistant ceramic powder consists of silicon nitride powder and boron nitride powder, with a mass ratio of 1:1. The particle size of both the silicon nitride powder and the boron nitride powder is 2 μm.

[0042] 2. Preparation of dense ceramic layers by vapor deposition The composite material with the ceramic repair layer was hoisted into a chemical vapor deposition furnace, continuously evacuated and heated to the reaction temperature (850℃), and held at that temperature. Then, silicon source gas, ammonia, and hydrogen were simultaneously introduced as reaction gases according to a predetermined ratio and gas flow rate for chemical vapor deposition. During the chemical vapor deposition process, when the thickness of the deposited dense ceramic layer was less than or equal to 50% of the predetermined thickness, the total flow rate of the reaction gas was controlled at 6 L / min; when the thickness of the deposited dense ceramic layer was greater than 50% of the predetermined thickness, the total flow rate of the reaction gas was controlled at 2.5 L / min. After the chemical vapor deposition was completed, the furnace was cooled and nitrogen was used for purging to obtain a composite material with a dense ceramic layer (100 μm thick, made of silicon nitride) deposited on the surface.

[0043] The silicon source gas is silane.

[0044] The volumetric flow rate ratio of silicon source gas, ammonia, and hydrogen is 1.1:2:3.

[0045] 3. Spraying and curing to prepare a smooth surface layer After diluting the silicone resin with a solvent, a curing agent and an antifouling agent were added sequentially and mixed evenly to obtain a spraying liquid. The spraying liquid was evenly sprayed onto the surface of the composite material with a dense ceramic layer deposited on the surface. The temperature was raised to 110℃ and kept warm for 3 hours to form a smooth surface layer with a thickness of 40μm, thus completing the preparation of the surface coating of the boron nitride fiber reinforced ceramic matrix composite material.

[0046] The organosilicon resin is methylphenyl silicone resin.

[0047] The solvent is toluene; the weight ratio of solvent to silicone resin is 2:1.

[0048] The curing agent is dibutyltin dilaurate; the weight of the curing agent added is 5.5% of the total weight of the silicone resin.

[0049] The antifouling agent is 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and the weight of the antifouling agent added is 3.5% of the total weight of the organosilicon resin.

[0050] This embodiment also provides a product prepared by the aforementioned method, wherein the surface coating of the boron nitride fiber reinforced ceramic matrix composite material comprises, in sequence: a ceramic repair layer, a ceramic dense layer, and a surface smoothing layer.

[0051] This embodiment also provides the application of the aforementioned product in the fabrication of radomes or antenna windows for high-Mach aircraft.

[0052] The surface coating preparation method for boron nitride fiber-reinforced ceramic matrix composites in this embodiment involves forming a ceramic repair layer on the surface of the composite material using a cross-cut method. The cuts are controlled to penetrate the entire coating and reach the composite matrix. After cross-cutting, 3M Scotch 600 test tape is used for adhesion and removal; no grid cells fall off within the grid area, indicating good adhesion between the ceramic repair layer and the composite matrix. The dense ceramic layer deposited on the surface of the ceramic repair layer is heated to 1200°C in 30 seconds under quartz lamp radiation, held at 1200°C for 100 seconds, and then cooled to room temperature. After repeating this quartz lamp thermal shock test five times, no cracking or peeling of the dense ceramic layer occurred. In the airtightness test, the product prepared using this surface coating preparation method exhibits excellent airtightness. A vacuum of 0.099 MPa is applied to one side of the product, and after maintaining this vacuum for 2 hours, the vacuum level on that side decreases by 6 kPa (i.e., to 0.093 MPa), indicating excellent airtightness. The product prepared using the surface coating method of this embodiment was placed in a constant temperature and humidity environment of 42°C and 95% for 96 hours. After standing, the increase in mass (i.e., moisture absorption rate) after the test was found to be 0.5% compared to the mass before the test. After the surface coating was prepared using the method of this embodiment, the dielectric loss tangent of the product increased by only 0.003 compared to the boron nitride fiber reinforced ceramic matrix composite material (i.e., the matrix material).

[0053] Example 2 This embodiment provides a method for preparing a surface coating of a boron nitride fiber-reinforced ceramic matrix composite material, specifically as follows: 1. Sintering preparation of ceramic repair layer The addition weight of high-temperature resistant ceramic powder was controlled to be 18% of the weight of polysilazane. The high-temperature resistant ceramic powder was added to the ethyl acetate solution of polysilazane and mixed evenly to obtain a coating slurry. The coating slurry was then brushed onto the outer surface of the BN fiber-reinforced ceramic matrix composite. After drying at 130℃ for 0.75h, it was sanded with sandpaper and then placed in a muffle furnace. Anhydrous air or synthetic air was used as the sintering atmosphere, and the temperature was raised to 580℃ and held for sintering for 0.8h to complete the surface pore defect repair of the BN fiber-reinforced ceramic matrix composite, thus obtaining a composite material with a ceramic repair layer (thickness of 20μm).

[0054] The concentration of the ethyl acetate solution of polysilazane is 48 wt%.

[0055] The high-temperature resistant ceramic powder is silicon nitride powder; the particle size of silicon nitride powder is 2μm.

[0056] 2. Preparation of dense ceramic layers by vapor deposition The composite material with the ceramic repair layer was hoisted into a chemical vapor deposition furnace, continuously evacuated and heated to the reaction temperature (870℃), and held at that temperature. Then, silicon source gas, ammonia, and hydrogen were simultaneously introduced as reaction gases according to a predetermined ratio and gas flow rate for chemical vapor deposition. During the chemical vapor deposition process, when the thickness of the deposited dense ceramic layer was less than or equal to 55% of the predetermined thickness, the total flow rate of the reaction gas was controlled at 6.5 L / min; when the thickness of the deposited dense ceramic layer was greater than 55% of the predetermined thickness, the total flow rate of the reaction gas was controlled at 2 L / min. After the chemical vapor deposition was completed, the furnace was cooled and nitrogen was used for purging to obtain a composite material with a dense ceramic layer (100 μm thick, made of silicon nitride) deposited on the surface.

[0057] The silicon source gas is HSiCl3.

[0058] The volumetric flow rate ratio of silicon source gas, ammonia, and hydrogen is 1.2:2.5:3.5.

[0059] 3. Spraying and curing to prepare a smooth surface layer After diluting the silicone resin with a solvent, a curing agent and an antifouling agent were added sequentially and mixed evenly to obtain a spraying liquid. The spraying liquid was then evenly sprayed onto the surface of the composite material with a dense ceramic layer deposited on it. The temperature was raised to 100℃ and cured for 2.5 hours to form a smooth surface layer with a thickness of 40μm, thus completing the preparation of the surface coating of the boron nitride fiber reinforced ceramic matrix composite material.

[0060] The organosilicon resin is methylphenyl silicone resin.

[0061] The solvent is ethyl acetate; the weight ratio of solvent to silicone resin is 2.3:1.

[0062] The curing agent is stannous octoate; the weight of the curing agent added is 5% of the total weight of the silicone resin.

[0063] The antifouling agent is heptadecafluorodecyltrimethoxysilane, and the weight of the antifouling agent added is 3% of the total weight of the silicone resin.

[0064] This embodiment also provides a product prepared by the aforementioned method, wherein the surface coating of the boron nitride fiber reinforced ceramic matrix composite material comprises, in sequence: a ceramic repair layer, a ceramic dense layer, and a surface smoothing layer.

[0065] This embodiment also provides the application of the aforementioned product in the fabrication of radomes or antenna windows for high-Mach aircraft.

[0066] The surface coating preparation method for boron nitride fiber-reinforced ceramic matrix composites in this embodiment involves forming a ceramic repair layer on the surface of the boron nitride fiber-reinforced ceramic matrix composite using a cross-cut method. The cross-cut cuts are controlled to penetrate the entire coating and reach the composite matrix. After cross-cutting, 3M Scotch 600 test tape is used for adhesion and removal; no grid cells fall off within the grid area, indicating good adhesion between the ceramic repair layer and the composite matrix. The dense ceramic layer deposited on the surface of the ceramic repair layer is heated to 1200℃ in 30 seconds under quartz lamp radiation, held at 1200℃ for 100 seconds, and then cooled to room temperature. After repeating the aforementioned quartz lamp thermal shock test five times, no cracking or peeling of the dense ceramic layer occurred. In the airtightness test, the product prepared using the surface coating preparation method of this embodiment was evacuated to a vacuum level of 0.099 MPa on one side of the product. After maintaining this vacuum for 2 hours, the vacuum level on that side decreased by 7 kPa (i.e., the vacuum level became 0.092 MPa), indicating excellent airtightness of the product. The product prepared using the surface coating method of this embodiment was placed in a constant temperature and humidity environment of 42°C and 95% for 96 hours. After standing, the increase in mass (i.e., moisture absorption rate) after the test was found to be 0.6% compared to the mass before the test. After the surface coating was prepared using the method of this embodiment, the dielectric loss tangent of the product increased by only 0.002 compared to the boron nitride fiber reinforced ceramic matrix composite material (i.e., the matrix material).

[0067] Example 3 This embodiment provides a method for preparing a surface coating of a boron nitride fiber-reinforced ceramic matrix composite material, specifically as follows: 1. Sintering preparation of ceramic repair layer The weight of the added high-temperature resistant ceramic powder was controlled to be 25% of the weight of polysilazane. The high-temperature resistant ceramic powder was added to the ethyl acetate solution of polysilazane and mixed evenly to obtain a coating slurry. The coating slurry was then brushed onto the outer surface of the BN fiber reinforced ceramic matrix composite. After drying at 135℃ for 1.5h, it was sanded with sandpaper and then placed in a muffle furnace. Anhydrous air or synthetic air was used as the sintering atmosphere, and the temperature was raised to 650℃ and held for sintering for 0.5h to complete the surface pore defect repair of the BN fiber reinforced ceramic matrix composite, thus obtaining a composite material with a ceramic repair layer (thickness of 20μm).

[0068] The concentration of the ethyl acetate solution of polysilazane is 45 wt%.

[0069] The high-temperature resistant ceramic powder is boron nitride powder; the particle size of the boron nitride powder is 2μm.

[0070] 2. Preparation of dense ceramic layers by vapor deposition The composite material with the ceramic repair layer was hoisted into a chemical vapor deposition furnace, continuously evacuated and heated to the reaction temperature (920℃), and held at that temperature. Then, silicon source gas, ammonia, and hydrogen were simultaneously introduced as reaction gases according to a predetermined ratio and gas flow rate for chemical vapor deposition. During the chemical vapor deposition process, when the thickness of the deposited dense ceramic layer was less than or equal to 60% of the predetermined thickness, the total flow rate of the reaction gas was controlled at 7L / min; when the thickness of the deposited dense ceramic layer was greater than 60% of the predetermined thickness, the total flow rate of the reaction gas was controlled at 2.8L / min. After the chemical vapor deposition was completed, the furnace was cooled and nitrogen was used for purging to obtain a composite material with a dense ceramic layer (100μm thick, made of silicon nitride) deposited on the surface.

[0071] The silicon source gas is H2SiCl2.

[0072] The volumetric flow rate ratio of silicon source gas, ammonia, and hydrogen is 1.1:2.1:3.2.

[0073] 3. Spraying and curing to prepare a smooth surface layer After diluting the silicone resin with a solvent, a curing agent and an antifouling agent were added sequentially and mixed evenly to obtain a spraying liquid. The spraying liquid was evenly sprayed onto the surface of the composite material with a dense ceramic layer deposited on the surface. The temperature was raised to 105℃ and cured for 4 hours to form a smooth surface layer with a thickness of 40μm, thus completing the preparation of the surface coating of the boron nitride fiber reinforced ceramic matrix composite material.

[0074] The silicone resin is an epoxy-modified silicone resin.

[0075] The solvent is xylene; the weight ratio of solvent to silicone resin is 2.1:1.

[0076] The curing agent is an amine-based curing agent; the weight of the curing agent added is 6.2% of the total weight of the silicone resin.

[0077] The antifouling agent is 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and the weight of the antifouling agent added is 4% of the total weight of the organosilicon resin.

[0078] This embodiment also provides a product prepared by the aforementioned method, wherein the surface coating of the boron nitride fiber reinforced ceramic matrix composite material comprises, in sequence: a ceramic repair layer, a ceramic dense layer, and a surface smoothing layer.

[0079] This embodiment also provides the application of the aforementioned product in the fabrication of radomes or antenna windows for high-Mach aircraft.

[0080] The surface coating preparation method for boron nitride fiber-reinforced ceramic matrix composites in this embodiment involves forming a ceramic repair layer on the surface of the boron nitride fiber-reinforced ceramic matrix composite using a cross-cut method. The cross-cut cuts are controlled to penetrate the entire coating and reach the composite matrix. After cross-cutting, 3M Scotch 600 test tape is used for adhesion and removal; no grid cells fall off within the grid area, indicating good adhesion between the ceramic repair layer and the composite matrix. The dense ceramic layer deposited on the surface of the ceramic repair layer is heated to 1200℃ in 30 seconds under quartz lamp radiation, held at 1200℃ for 100 seconds, and then cooled to room temperature. After repeating the aforementioned quartz lamp thermal shock test five times, no cracking or peeling of the dense ceramic layer occurred. In the airtightness test, the product prepared using the surface coating preparation method of this embodiment was evacuated to a vacuum level of 0.099 MPa on one side of the product. After maintaining this vacuum for 2 hours, the vacuum level on that side decreased by 5 kPa (i.e., the vacuum level became 0.094 MPa), indicating excellent airtightness of the product. The product prepared using the surface coating method of this embodiment was placed in a constant temperature and humidity environment of 42°C and 95% for 96 hours. After standing, the increase in mass (i.e., moisture absorption rate) after the test was found to be 0.8% compared to the initial mass. After the surface coating was prepared using the method of this embodiment, the dielectric loss tangent of the product increased by only 0.001 compared to the boron nitride fiber reinforced ceramic matrix composite material (i.e., the matrix material).

[0081] Comparative Example 1 Comparative Example 1 adopts the scheme of Example 1, except that the step of preparing a dense ceramic layer by vapor deposition is omitted, and a smooth surface layer is directly prepared on the surface of the ceramic repair layer.

[0082] The product prepared using the surface coating method of Comparative Example 1 underwent an airtightness test. A vacuum of 0.099 MPa was applied to one side of the product, and after maintaining this vacuum for 2 hours, the vacuum level on that side decreased by 11 kPa (i.e., the vacuum level became 0.088 MPa). The product prepared using the surface coating method of this embodiment was placed in a constant temperature and humidity environment of 42°C and 95% for 96 hours. The increase in mass after the test compared to before the test (i.e., moisture absorption rate) was 3.1%.

[0083] Comparative Example 2 Comparative Example 2 adopts the scheme of Example 1, except that the sintering preparation of the ceramic repair layer is omitted, and the ceramic repair layer and the surface smoothing layer are prepared directly on the surface of the BN fiber reinforced ceramic matrix composite material in sequence.

[0084] In Comparative Example 2, a dense ceramic layer deposited on the surface of a BN fiber-reinforced ceramic matrix composite was heated to 1200°C in 30 seconds under quartz lamp radiation, held at 1200°C for 100 seconds, and then cooled to room temperature. During the third repetition of the aforementioned quartz lamp thermal shock test, cracks appeared in the dense ceramic layer. In the airtightness test, the product prepared using the surface coating method of Comparative Example 2 was evacuated to a vacuum level of 0.099 MPa on one side of the product. After maintaining this vacuum for 2 hours, the vacuum level on that side decreased by 20 kPa (i.e., to 0.079 MPa). The product prepared using the surface coating method of this embodiment was placed in a constant temperature and humidity environment of 42°C and 95% for 96 hours. The increase in mass after the test compared to before the test (i.e., moisture absorption rate) was 4.2%.

[0085] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0086] 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 surface coating of a boron nitride fiber-reinforced ceramic matrix composite material, characterized in that, The process includes the following steps: sintering to prepare a ceramic repair layer, vapor deposition to prepare a dense ceramic layer, and spraying and curing to prepare a smooth surface layer; The method for preparing the ceramic repair layer by sintering is as follows: adding high-temperature resistant ceramic powder to an ethyl acetate solution of polysilazane and mixing it evenly to obtain a coating slurry; brushing the coating slurry onto the outer surface of the boron nitride fiber reinforced ceramic matrix composite material, and then drying and sintering to obtain a composite material with a ceramic repair layer. The method for preparing a dense ceramic layer by vapor deposition is as follows: placing the composite material with the ceramic repair layer in a chemical vapor deposition furnace, continuously evacuating and heating to 850-950°C, and holding at that temperature; continuously introducing reactive gas to perform chemical vapor deposition; and obtaining a composite material with a dense ceramic layer deposited on its surface. The reaction gas consists of silicon source gas, ammonia gas, and hydrogen gas; The method for preparing a smooth surface layer by spraying and curing involves spraying a coating liquid containing organosilicon resin onto the outer surface of a composite material on which a dense ceramic layer has been deposited, and then heating and curing to form a smooth surface layer, thereby completing the preparation of the surface coating of the boron nitride fiber reinforced ceramic matrix composite material.

2. The method for preparing a surface coating of boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the sintering preparation of the ceramic repair layer, the concentration of the ethyl acetate solution of polysilazane is 45-50 wt%. The high-temperature resistant ceramic powder is silicon nitride powder and / or boron nitride powder; the particle size of silicon nitride powder is 1-10 μm, and the particle size of boron nitride powder is 1-10 μm; The weight of high-temperature resistant ceramic powder added to the coating slurry is 15-30% of the weight of polysilazane.

3. The method for preparing a surface coating of boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the preparation of the ceramic repair layer by sintering, anhydrous air or synthetic air is used as the sintering atmosphere, the sintering temperature is 550-650℃, and the sintering time is 0.5-1h. The thickness of the ceramic repair layer is 10-30μm.

4. The method for preparing a surface coating of boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the preparation of a dense ceramic layer by chemical vapor deposition, when the thickness of the deposited dense ceramic layer is less than or equal to 50-60% of the predetermined thickness, the total flow rate of the reaction gas is controlled at 5-8 L / min; when the thickness of the deposited dense ceramic layer is greater than 50-60% of the predetermined thickness, the total flow rate of the reaction gas is controlled at 2-3 L / min. The predetermined thickness is 50-150 μm.

5. The method for preparing a surface coating of boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the preparation of the dense ceramic layer by vapor deposition, the silicon source gas is silane or chlorosilane; the chlorosilane is one of the following: HSiCl3, H2SiCl2, SiCl4; The volumetric flow rate ratio of silicon source gas, ammonia, and hydrogen in the reaction gas is 1-1.2:1.5-2.5:2-4.

6. The method for preparing a surface coating of boron nitride fiber-reinforced ceramic matrix composite material according to claim 1, characterized in that, In the process of preparing the smooth surface layer by spraying and curing, the curing temperature is 80-120℃ and the curing time is 2-5h; The spraying liquid consists of silicone resin, curing agent, antifouling agent and solvent; The thickness of the smooth surface layer is 20-50 μm.

7. The method for preparing a surface coating of boron nitride fiber-reinforced ceramic matrix composite material according to claim 6, characterized in that, The organosilicon resin is one of the following: epoxy-modified organosilicon resin, methylphenyl silicone resin, or phenyl silicone resin; The solvent is at least one of the following: ethyl acetate, toluene, xylene, or isopropanol; The curing agent is an organotin curing agent or an amine curing agent; The antifouling agent is 1H,1H,2H,2H-perfluorodecyltriethoxysilane and / or heptadecafluorodecyltrimethoxysilane.

8. The method for preparing a surface coating of boron nitride fiber-reinforced ceramic matrix composite material according to claim 6, characterized in that, In the spraying liquid, the weight ratio of solvent to silicone resin is 1.5-2.5:1; The curing agent should be added at a weight of 5-7% of the total weight of the silicone resin. The antifouling agent should be added at a weight of 3-5% of the total weight of the silicone resin.

9. A product prepared by the method according to any one of claims 1-8, characterized in that, The surface coating of the product comprises, in sequence: a ceramic repair layer, a ceramic dense layer, and a surface smoothing layer; The thickness of the ceramic repair layer is 10-30 μm; the thickness of the ceramic dense layer is 50-150 μm; and the thickness of the surface smoothing layer is 20-50 μm.

10. The application of the product as described in claim 9 in the manufacture of an aircraft radome or antenna window.