A high-strength, high-temperature-resistant wave-absorbing ceramic matrix composite material with a bionic structure of a leaf of a sandpaper willow and a preparation method and application thereof

Abstract

The application discloses a high-strength and high-temperature-resistant wave-absorbing ceramic matrix composite material with a bionic structure of a leaf of a saw palmetto and a preparation method and application thereof, and belongs to the technical field of wave-absorbing materials. 3f @BN-SiOC-multiple boride ceramic composite material; the wave-absorbing ceramic matrix composite material has a double-embedded structure composed of a wave-absorbing component, a wave-transparent ceramic matrix and a fiber framework, the wave-absorbing component is embedded in the wave-transparent ceramic matrix, and the wave-transparent ceramic matrix is embedded in the fiber framework. To solve the inherent contradiction between CMC mechanics and EMW absorption performance, meet the demand of high-performance radar stealth materials for the hot end part of a modern high-speed aircraft.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a high-strength, high-temperature resistant microwave absorbing ceramic matrix composite material with a biomimetic structure of Ilex chinensis leaf, its preparation method, and its application. Background Technology

[0002] Currently, materials used in hot-end components of modern high-speed aircraft (such as engine nozzles and wing leading edges) must simultaneously withstand extreme thermo-mechanical loads and maintain stable high-temperature radar wave absorption capabilities over long flight times to evade radar detection. However, the mechanical properties and electromagnetic wave (EMW) absorption performance of existing ceramic matrix composites (CMCs) are both affected by porosity, creating an inherent contradiction: high density is beneficial to mechanical properties but leads to an abnormal increase in CMC dielectric, impedance mismatch, and EMW reflection at the material surface; appropriately introducing porosity can optimize impedance matching but reduces mechanical properties because these pores often become the initiation and propagation points of cracks under external loads. Furthermore, long-term exposure to high-temperature environments leads to CMC oxidation, resulting in a decline in both mechanical properties and EMW absorption performance. Therefore, achieving a multi-functional integrated solution that combines high-temperature oxidation resistance, high load-bearing capacity, and stable radar absorption is a key technological bottleneck in this field.

[0003] Reference 1, "Mo R, Yin X, Ye F, et al. Electromagnetic wave absorption and mechanical properties of silicon carbide fibers reinforced silicon nitride matrix composites[J]. Journal of the European Ceramic Society, 2019, 39(4):743-754." This reference systematically studies the mechanical and electromagnetic properties of silicon carbide (SiC) fiber-reinforced silicon nitride (Si3N4) ceramic composites. The study shows that as the Si3N4 deposition time increases, the pores in the ceramic composite are gradually replaced, and the mechanical properties of the material are significantly improved. However, with the increase of densification, the impedance mismatch between the material and air and the excessively high conductivity cause EMW to be reflected rather than absorbed when it reaches the material surface. Therefore, how to balance the relationship between the mechanical properties of CMC and the EMW absorption performance is a key problem that needs to be solved. Reference 2, "Wei H, Yang S, Feng P, et al. Construction of Si3N4 / SiO2 / SiC–Y2Si2O7 composite ceramics with gradual impedance matching structure for high-temperature electromagnetic wave." This paper systematically studies the dielectric and EMW absorption properties of Si3N4 / SiO2 / SiC–Y2Si2O7 ceramic composites in the range from room temperature to high temperature of 600 °C. The study shows that the material can achieve effective absorption of X-band EMW in the room temperature range of 25 °C–300 °C, with an EAB of 4.2 GHz. However, as the temperature continues to rise to 600 °C, the material is gradually oxidized, the dielectric changes abnormally, impedance mismatch occurs, and the EMW absorption performance drops to 3.2 GHz. Therefore, achieving stable EMW absorption at high temperatures using CMC is a key problem that needs to be solved.

[0004] In summary, existing ceramic matrix composites struggle to balance high mechanical strength with stable broadband electromagnetic wave (EMW) absorption performance under extreme environments. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure of *Ilex chinensis* blades, its preparation method and application, so as to solve the inherent contradiction between CMC mechanics and EMW absorption performance and meet the demand of modern high-speed aircraft for high-performance radar stealth materials in the hot end.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis*, comprising the microwave-absorbing ceramic matrix composite material and an anti-oxidation coating applied to the surface of the microwave-absorbing ceramic matrix composite material, wherein the microwave-absorbing ceramic matrix composite material is Al2O3. 3f @BN-SiOC-Multi-component boride ceramic composite material; The microwave absorbing ceramic matrix composite material has a double embedded structure consisting of a microwave absorbing component, a microwave transparent ceramic matrix, and a fiber skeleton, wherein the microwave absorbing component is embedded in the microwave transparent ceramic matrix, and the microwave transparent ceramic matrix is ​​embedded in the fiber skeleton.

[0007] In one embodiment, the absorbing component is a multi-element ultra-high temperature boride ceramic, which is prepared by uniformly ball-milling and mixing five ceramic powders, namely ZrB2, TiB2, NbB2, HfB2 and TaB2, in a volume ratio of 1:2:1:1:3.

[0008] In one embodiment, the microwave-transparent ceramic substrate is PDC-SiOC ceramic; the fiber skeleton is an alumina fiber preform; and the anti-oxidation coating is prepared by mixing deionized water, silica sol, Al2O3, B2O3, and SiO2 in a mass ratio of 3:1:(0.05~0.1):(0.1~0.2):(0.8~1).

[0009] In one embodiment, the microwave absorbing ceramic matrix composite material has an effective absorption bandwidth of not less than 8 GHz over a wide temperature range from room temperature to 1473 K; the absorption performance of the microwave absorbing ceramic matrix composite material increases after oxidation at 1473 K for 600 h.

[0010] This invention also provides a method for preparing a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis*, comprising the following steps: The multi-component microwave absorbing agents ZrB2, TiB2, NbB2, HfB2 and TaB2 were pretreated at high temperature in an inert atmosphere and then uniformly mixed to obtain MB mixed powder; The MB mixed powder is uniformly mixed with liquid polysiloxane solution and anhydrous ethanol to obtain an impregnation solution; An alumina fiber preform is placed in an impregnation solution and impregnated under atmospheric pressure of -0.1 MPa to obtain an impregnated preform material. The impregnated preform material is dried and then placed in an oven for crosslinking to obtain a crosslinked material. The above impregnation-crosslinking operation is repeated multiple times. The crosslinked material is then placed in an inert atmosphere for high-temperature heat treatment to obtain an ASM ceramic composite material. The above process is one cycle. After repeating the above operation multiple times, a densified ASM ceramic composite material is obtained. An antioxidant coating was prepared by mixing deionized water, silica sol, Al2O3, B2O3, and SiO2 powders and coating them onto the surface of the densified ASM ceramic composite material, thus obtaining a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure of Ilex chinensis leaves.

[0011] In one embodiment, the volume ratio of ZrB2, TiB2, NbB2, HfB2 and TaB2 is 1:2:1:1:3; the high-temperature inert atmosphere pretreatment is carried out at a temperature of 600 °C for 3 h, and the inert atmosphere is Ar.

[0012] In one embodiment, the mass ratio of the MB mixed powder, the liquid polysiloxane solution, and the anhydrous ethanol is (1~3):(1~3):(1~3).

[0013] In one embodiment, the drying temperature is 80 °C and the drying time is 2-4 h; The crosslinking process involves holding the temperature at 100~200 ℃ for 1~3 h, followed by natural cooling to room temperature; The high-temperature heat treatment process involves heating the temperature to 850~1100℃ at a heating rate of 5℃ / min under an inert atmosphere, holding the temperature for 1~4 hours, and then naturally cooling it to room temperature.

[0014] In one embodiment, the mass ratio of the deionized water, silica sol, Al2O3, B2O3, and SiO2 is 3:1:(0.05~0.1):(0.1~0.2):(0.8~1); and the thickness of the antioxidant coating is 100~200 μm.

[0015] This invention also provides an application of a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure of *Ilex chinensis* blades in the hot-end region of a high-speed aircraft.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a high-strength, high-temperature absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex shamiana*. Inspired by the unique structure (thick cuticle, well-developed palisade tissue, and high-density chloroplasts) and excellent environmental adaptability of the leaves of the ultra-xerophytic plant *Ilex shamiana*, a biomimetic design strategy of "functional decoupling and synergistic integration" is proposed. The CMC of this invention includes a three-dimensional fiber-reinforced skeleton (mechanical load-bearing capacity), a wave-transparent ceramic matrix, and multi-element absorbing components (EMW dissipation) uniformly dispersed in the wave-transparent matrix. An anti-oxidation coating (thermal protection) is applied to the surface of the ceramic composite material, thereby spatially constructing functional zones for "mechanical load-bearing capacity," "EMW dissipation," and "thermal protection." This functional decoupling and integrated material fabrication achieves multifunctional compatibility of long-term thermal protection, load-bearing capacity, and high-temperature stable EMW absorption, meeting the high-temperature broadband stealth requirements of modern high-speed aircraft.

[0017] This invention, through biomimetic structural design, fundamentally breaks the mutually restrictive relationship between mechanical properties and wave absorption performance in traditional CMCs. The material exhibits excellent comprehensive mechanical properties, with a flexural strength of 419.47 ± 69.90 MPa, a Z-axis compressive strength of 403.11 ± 24.54 MPa, a Y-axis compressive strength of 253.68 ± 12.07 MPa, and a fracture toughness of 8.12 ± 0.05 MPa·m. 1 / 2 Furthermore, the material exhibits ultra-stable EMW absorption performance over a wide temperature range from room temperature to 1473 K, with an effective absorption bandwidth remaining above 8 GHz. Notably, after 600 h of oxidation in air at 1473 K, the material's absorption performance did not decrease but rather increased, highlighting its unique long-term high-temperature stealth advantage.

[0018] In summary, the ASM ceramic composite material prepared by this invention has high strength, high toughness, high temperature resistance, stable broadband EMW absorption and long-term oxidation resistance. It is an ideal candidate material for high Mach number hot-end parts (such as engine exhaust nozzles and wing leading edges), meeting their structural load-bearing and long-term stealth requirements in extreme environments. Attached Figure Description

[0019] Figure 1 The images show macroscopic photographs of *Ilex shamiana*, corresponding microscopic structures of leaf tissues, and schematic diagrams of the microstructure of the ASM ceramic composite material prepared in this invention. Figure 2 The XRD patterns are corresponding to the embodiments of the present invention; wherein, (a) is the XRD pattern of the ASM-1 ceramic composite material in Example 1; (b) is the XRD pattern of the ASM-2 ceramic composite material in Example 2; (c) is the XRD pattern of the ASM-3 ceramic composite material in Example 3; and (d) is the XRD pattern of the ASM-4 ceramic composite material in Example 4. Figure 3These are microscopic electron scanning images of Examples 1-4 of the present invention; wherein (a1-a3) are microscopic morphology images of the ASM-1 ceramic composite material in Example 1; (b1-b3) are microscopic morphology images of the ASM-2 ceramic composite material in Example 2; (c1-c3) are microscopic morphology images of the ASM-3 ceramic composite material in Example 3; and (d1-d3) are microscopic morphology images of the ASM-4 ceramic composite material in Example 4. Figure 4 The figures are for mechanical property testing; (a) shows the room temperature bending properties of the ASM ceramic composites prepared in Examples (1)-(4); (b) shows the Z-direction compressive properties of the ASM ceramic composites prepared in Examples (1)-(4); (c) shows the Y-direction compressive properties of the ASM ceramic composites prepared in Examples (1)-(4); and (d) shows the fracture toughness of the ASM ceramic composites prepared in Examples (1)-(4). Figure 5 The dielectric constant test curves are shown in the frequency range of 8.2-40 GHz; where (a) is the real dielectric part of the ASM ceramic composite material prepared in Examples (1)-(4); (b) is the imaginary dielectric part of the ASM ceramic composite material prepared in Examples (1)-(4); and (c) is the loss tangent of the ASM ceramic composite material prepared in Examples (1)-(4). Figure 6 The graphs show the EMW absorption performance in the frequency range of 8.2-40 GHz; where (a) is the EMW absorption performance of the ASM-1 ceramic composite material prepared in Example 1; (b) is the EMW absorption performance of the ASM-2 ceramic composite material prepared in Example 2; (c) is the EMW absorption performance of the ASM-3 ceramic composite material prepared in Example 3; and (d) is the EMW absorption performance of the ASM-4 ceramic composite material prepared in Example 4. Figure 7 The high-temperature EMW absorption performance of the ASM-4 ceramic composite material prepared in Example 5 from room temperature to high temperature of 1473 K. Detailed Implementation

[0020] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0022] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0023] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0024] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0025] This study investigated the drought resistance mechanism of *Haloxylon ammodendron*, a hyperxerophyte found in the desert regions of Northwest China. The study revealed that *Haloxylon ammodendron* leaves possess a thick cuticle and dense epidermal hairs, which inhibit transpiration and water loss, representing an adaptation to drought and heat. Furthermore, its mesophyll tissue contains abundant palisade tissue, significantly enhancing mechanical strength and compressive strength to resist perennial wind, sandstorms, and snow pressure. The palisade tissue contains numerous chloroplasts, which enhance photosynthesis and store energy-rich organic matter, improving the survival ability of *Haloxylon ammodendron*. These unique biological tissues exhibit different functions, providing a guarantee for *Haloxylon ammodendron*'s long-term adaptation to summer drought and winter cold. The study also found that the MoSi2 / SiO2-B2O3-Al2O3 coating exhibits excellent antioxidant and thermal cycling properties. Specifically, the coating demonstrates superior antioxidant performance, effectively protecting C / C composite materials from almost no mass loss after 200 hours at 1073 K in air, and only a 0.7% mass loss after 200 hours at 1773 K. The formation of the B2O3 glass phase at low temperatures and the borosilicate glass at high temperatures are the main reasons for the coating's excellent oxidation resistance. Furthermore, PDC-SiOC ceramics exhibit excellent thermal stability due to their unique anionic silica network. PDC-SiOC, which undergoes low-temperature (<1200℃) pyrolysis, displays amorphous wave transmission characteristics, improving impedance matching and making it suitable as a matrix material for CMCs used in harsh high-temperature environments. Research has proposed an approximate method for controlling the multivariable dielectric dispersion characteristics under the protection of anti-oxidation coatings, revealing the relationship between the material's dielectric dispersion characteristics and broadband absorption characteristics, achieving high-temperature electromagnetic wave absorption at 1473 K. Studies have shown that multi-component boride ultra-high-temperature ceramics possess unique dielectric properties and high conductivity loss capability, which can synergistically enhance the EMW attenuation capability of composite materials and improve absorption performance.

[0026] This study decouples and partitions the functional characteristics of materials, aiming to resolve previously contradictory material properties and achieve synergistic enhancement of multiple functions. Based on this, this invention proposes an alumina fiber-reinforced multi-element ultra-high temperature boride ceramic composite material to enhance mechanical properties, EMW attenuation, and oxidation resistance, meeting the urgent need for high-performance stealth materials in modern high-speed aircraft.

[0027] This invention provides a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure of Ilex chinensis leaf, its preparation method, and its application.

[0028] The present invention provides a high-strength, high-temperature resistant ceramic matrix composite material with a biomimetic structure of Ilex chinensis leaf. The ceramic matrix composite material has a double embedded structure, wherein the absorbing component is embedded in the wave-transparent ceramic matrix, and the wave-transparent ceramic matrix is ​​embedded in the fiber skeleton. The surface of the ceramic matrix composite material is coated with an anti-oxidation coating.

[0029] The microwave absorbing components are multi-element ultra-high temperature boride ceramics, including ZrB2, TiB2, NbB2, HfB2, and TaB2; the microwave-transparent ceramic matrix is ​​PDC-SiOC ceramic; and the fiber skeleton is an alumina fiber preform. The anti-oxidation coating is composed of Al2O3, B2O3, and SiO2.

[0030] This invention also provides a method for preparing a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis*, comprising the following steps: S1: After pretreating the multi-component microwave absorbing agents ZrB2, TiB2, NbB2, HfB2 and TaB2 in a high-temperature inert atmosphere, they are uniformly mixed in a certain mass ratio to obtain MB mixed powder; S2: Mix MB mixed powder with liquid polysiloxane solution and anhydrous ethanol uniformly according to the preset mass ratio to obtain impregnation solution; S3: The alumina fiber preform is placed in the impregnation solution and impregnated under atmospheric pressure of -0.1 MPa to obtain the impregnated preform material; the impregnated preform material is dried and placed in an oven for crosslinking to obtain the crosslinked material; the above impregnation-crosslinking operation is repeated 3 times, and the crosslinked material is placed in an inert atmosphere for high-temperature heat treatment to obtain the ASM ceramic composite material. This process is 1 cycle. S4: Repeat the above S3 operation multiple times to obtain the densified ASM ceramic composite material; S5: An anti-oxidation coating of a certain thickness is prepared on the surface of the densified ASM ceramic composite material by mixing deionized water, silica sol, Al2O3, B2O3, and SiO2 powder in a certain proportion and then using a brushing process.

[0031] The volume ratio of the ZrB2, TiB2, NbB2, HfB2, and TaB2 powders is 1:2:1:1:3.

[0032] The high-temperature inert atmosphere pretreatment is carried out at a temperature of 600 °C for 3 h, and the inert atmosphere is Ar.

[0033] The mass ratio of the MB mixed powder, liquid polysiloxane solution, and anhydrous ethanol is (1~3):(1~3):(1~3).

[0034] The drying temperature is 80 ℃ and the time is 2~4 h.

[0035] The crosslinking temperature of the oven is 100~200 ℃, and the oven is kept at this temperature for 1~3 h, followed by natural cooling to room temperature.

[0036] Specifically, the high-temperature heat treatment in the inert atmosphere is as follows: Heating was carried out at a rate of 5 °C / min to 850-1100 °C, held for 1-4 h, and then allowed to cool naturally to room temperature.

[0037] After repeating the cycle 1 to 5 times, the densified ASM ceramic composite material is obtained.

[0038] The mass ratio of deionized water, silica sol, Al2O3, B2O3, and SiO2 in the antioxidant coating is 3:1:(0.05~0.1):(0.1~0.2):(0.8~1).

[0039] The prepared antioxidant coating has a thickness of 100~200 μm.

[0040] Another aspect of the present invention provides the application of a high-strength, high-temperature resistant radar-absorbing ceramic matrix composite material with a biomimetic structure of *Ilex chinensis* blades in the hot-end region of a high-speed aircraft, meeting the demand of modern high-speed aircraft for high-performance radar stealth materials in the hot-end region.

[0041] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0042] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0043] Example 1: Step 1: Five ultra-high temperature boride ceramic powders—ZrB2, TiB2, NbB2, HfB2, and TaB2—were subjected to high-temperature pretreatment. Each of the five ceramic powders was placed in an alumina crucible and then transferred to a resistance wire heated heat treatment furnace. In a flowing Ar atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, held for 3 hours, and then cooled to room temperature with the furnace to obtain the pretreated ceramic powders.

[0044] Step 2: Weigh the ZrB2, TiB2, NbB2, HfB2 and TaB2 after high temperature pretreatment in Step 1 in a volume ratio of 1:2:1:1:3 and ball mill them for 2 hours to make the five ceramic powders evenly mixed to obtain MB mixed powder.

[0045] Step 3: Weigh MB mixed powder, liquid polysiloxane solution and anhydrous ethanol at a mass ratio of 1:1:1, and then strongly ultrasonically disperse for 12 h to obtain a uniformly mixed impregnation solution.

[0046] Step 4: Place the pre-woven alumina fiber preform into the impregnation solution in Step 3 and put it into a vacuum impregnation chamber. After maintaining the pressure at -0.1 MPa atmospheric pressure for 0.5 h, the impregnated preform material is obtained.

[0047] Step 5: Place the preform material impregnated in Step 4 in an 80 ℃ oven and keep it at that temperature for 4 h until the anhydrous ethanol is completely dried. Then, raise the oven temperature to 160 ℃ at a rate of 5 ℃ / min, keep it at that temperature for 2 h, and then let it cool naturally to room temperature to complete the crosslinking reaction and obtain the crosslinked material.

[0048] Step 6: Repeat steps 4 and 5 three times, then place the cross-linked material into a heat treatment chamber with a resistance wire as the heating element. In a flowing Ar atmosphere, raise the temperature from room temperature to 1000 ℃ at a heating rate of 5 ℃ / min, hold for 2 h, and then allow it to cool naturally to room temperature to complete the high-temperature heat treatment and obtain the ASM-1 ceramic composite material after one densification.

[0049] Step 7: The ASM-1 ceramic composite material after densification in step 6 is processed into the corresponding size according to the standard for dielectric constant and reflectivity testing. The required samples include: (1) Waveguide test sample: X-band (22.86 mm × 10.16 mm × 2 mm), Ku-band (15.80 mm × 7.90 mm × 2 mm), K-band (10.668 mm × 4.318 mm × 2 mm), Ka-band (7.112 mm × 3.556 mm × 2 mm); High temperature reflection test sample: 180 mm × 180 mm × 3 mm.

[0050] Step 8: Mix deionized water, silica sol, Al2O3, B2O3, and SiO2 powder in a mass ratio of 3:1:0.05:0.1:1 until homogeneous, and then apply an antioxidant coating with a thickness of 150 μm to the surface of the sample processed in Step 7 using a brushing method.

[0051] Example 2: Step 1: Five ultra-high temperature boride ceramic powders—ZrB2, TiB2, NbB2, HfB2, and TaB2—were subjected to high-temperature pretreatment. Each of the five ceramic powders was placed in an alumina crucible and then transferred to a resistance wire heated heat treatment furnace. In a flowing Ar atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, held for 3 hours, and then cooled to room temperature with the furnace to obtain the pretreated ceramic powders.

[0052] Step 2: Weigh the ZrB2, TiB2, NbB2, HfB2 and TaB2 after high temperature pretreatment in Step 1 in a volume ratio of 1:2:1:1:3 and ball mill them for 2 hours to make the five ceramic powders evenly mixed to obtain MB mixed powder.

[0053] Step 3: Weigh MB mixed powder, liquid polysiloxane solution and anhydrous ethanol in a mass ratio of 1:1.5:1.5, and then strongly ultrasonically disperse for 12 h to obtain a uniformly mixed impregnation solution.

[0054] Step 4: Place the pre-woven alumina fiber preform into the impregnation solution in Step 3 and put it into a vacuum impregnation chamber. After maintaining the pressure at -0.1 MPa atmospheric pressure for 0.5 h, the impregnated preform material is obtained.

[0055] Step 5: Place the preform material impregnated in Step 4 in an 80 ℃ oven and keep it at that temperature for 4 h until the anhydrous ethanol is completely dried. Then, raise the temperature of the oven to 150 ℃ at a rate of 5 ℃ / min, keep it at that temperature for 2 h, and then let it cool naturally to room temperature to complete the crosslinking reaction and obtain the crosslinked material.

[0056] Step 6: Repeat steps 4 and 5 three times, then place the cross-linked material into a heat treatment chamber with a resistance wire as the heating element. In a flowing Ar atmosphere, raise the temperature from room temperature to 1000 ℃ at a heating rate of 5 ℃ / min, hold for 2 h, and then allow it to cool naturally to room temperature to complete the high-temperature heat treatment and obtain the densified ASM ceramic composite material.

[0057] Step 7: Repeat step 6 twice to obtain the ASM-2 ceramic composite material after two densifications.

[0058] Step 8: The ASM-2 ceramic composite material after densification in step 7 is processed into the corresponding size according to the standard for dielectric constant and reflectivity testing. The required samples include: (1) Waveguide test sample: X-band (22.86 mm × 10.16 mm × 2 mm), Ku-band (15.80 mm × 7.90 mm × 2 mm), K-band (10.668 mm × 4.318 mm × 2 mm), Ka-band (7.112 mm × 3.556 mm × 2 mm); High temperature reflection test sample: 180 mm × 180 mm × 3 mm.

[0059] Step 9: Mix deionized water, silica sol, Al2O3, B2O3, and SiO2 powder in a mass ratio of 3:1:0.05:0.1:1 until homogeneous, and then apply an antioxidant coating with a thickness of 150 μm to the surface of the sample processed in Step 8 using a brushing method.

[0060] Example 3: Step 1: Five ultra-high temperature boride ceramic powders—ZrB2, TiB2, NbB2, HfB2, and TaB2—were subjected to high-temperature pretreatment. Each of the five ceramic powders was placed in an alumina crucible and then transferred to a resistance wire heated heat treatment furnace. In a flowing Ar atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, held for 3 hours, and then cooled to room temperature with the furnace to obtain the pretreated ceramic powders.

[0061] Step 2: Weigh the ZrB2, TiB2, NbB2, HfB2 and TaB2 after high temperature pretreatment in Step 1 in a volume ratio of 1:2:1:1:3 and ball mill them for 2 hours to make the five ceramic powders evenly mixed to obtain MB mixed powder.

[0062] Step 3: Weigh MB mixed powder, liquid polysiloxane solution and anhydrous ethanol in a mass ratio of 1:1:2 and then strongly ultrasonically disperse for 12 h to obtain a uniformly mixed impregnation solution.

[0063] Step 4: Place the pre-woven alumina fiber preform into the impregnation solution in Step 3 and put it into a vacuum impregnation chamber. After maintaining the pressure at -0.1 MPa atmospheric pressure for 0.5 h, the impregnated preform material is obtained.

[0064] Step 5: Place the preform material impregnated in Step 4 in an 80 ℃ oven and keep it at that temperature for 4 h until the anhydrous ethanol is completely dried. Then, raise the temperature of the oven to 150 ℃ at a rate of 5 ℃ / min, keep it at that temperature for 2 h, and then let it cool naturally to room temperature to complete the crosslinking reaction and obtain the crosslinked material.

[0065] Step 6: Repeat steps 4 and 5 three times, then place the cross-linked material into a heat treatment chamber with a resistance wire as the heating element. In a flowing Ar atmosphere, raise the temperature from room temperature to 900 ℃ at a heating rate of 5 ℃ / min, hold for 2 h, and then allow it to cool naturally to room temperature to complete the high-temperature heat treatment and obtain the densified ASM ceramic composite material.

[0066] Step 7: Repeat step 6 three times to obtain the ASM-3 ceramic composite material after three densification processes.

[0067] Step 8: The ASM-3 ceramic composite material after densification in step 7 is processed into the corresponding size according to the standard for dielectric constant and reflectivity testing. The required samples include: (1) Waveguide test sample: X-band (22.86 mm × 10.16 mm × 2 mm), Ku-band (15.80 mm × 7.90 mm × 2 mm), K-band (10.668 mm × 4.318 mm × 2 mm), Ka-band (7.112 mm × 3.556 mm × 2 mm); High temperature reflection test sample: 180 mm × 180 mm × 3 mm.

[0068] Step 9: Mix deionized water, silica sol, Al2O3, B2O3, and SiO2 powder in a mass ratio of 3:1:0.1:0.1:1 until homogeneous, and then apply an antioxidant coating with a thickness of 150 μm to the surface of the sample processed in Step 8 using a brushing method.

[0069] Example 4: Step 1: Five ultra-high temperature boride ceramic powders—ZrB2, TiB2, NbB2, HfB2, and TaB2—were subjected to high-temperature pretreatment. Each of the five ceramic powders was placed in an alumina crucible and then transferred to a resistance wire heated heat treatment furnace. In a flowing Ar atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, held for 3 hours, and then cooled to room temperature with the furnace to obtain the pretreated ceramic powders.

[0070] Step 2: Weigh the ZrB2, TiB2, NbB2, HfB2 and TaB2 after high temperature pretreatment in Step 1 in a volume ratio of 1:2:1:1:3 and ball mill them for 2 hours to make the five ceramic powders evenly mixed to obtain MB mixed powder.

[0071] Step 3: Weigh MB mixed powder, liquid polysiloxane solution and anhydrous ethanol in a mass ratio of 1:2:2 and then strongly ultrasonically disperse for 12 h to obtain a uniformly mixed impregnation solution.

[0072] Step 4: Place the pre-woven alumina fiber preform into the impregnation solution in Step 3 and put it into a vacuum impregnation chamber. After maintaining the pressure at -0.1 MPa atmospheric pressure for 0.5 h, the impregnated preform material is obtained.

[0073] Step 5: Place the preform material impregnated in Step 4 in an 80 ℃ oven and keep it at that temperature for 4 h until the anhydrous ethanol is completely dried. Then, raise the oven temperature to 160 ℃ at a rate of 5 ℃ / min, keep it at that temperature for 2 h, and then let it cool naturally to room temperature to complete the crosslinking reaction and obtain the crosslinked material.

[0074] Step 6: Repeat steps 4 and 5 three times, then place the cross-linked material into a heat treatment chamber with a resistance wire as the heating element. In a flowing Ar atmosphere, raise the temperature from room temperature to 1000 ℃ at a heating rate of 5 ℃ / min, hold for 2 h, and then allow it to cool naturally to room temperature to complete the high-temperature heat treatment and obtain the densified ASM ceramic composite material.

[0075] Step 7: Repeat step 6 four times to obtain the ASM-4 ceramic composite material after four densification processes.

[0076] Step 8: The ASM-4 ceramic composite material after densification in step 7 is processed into the corresponding size according to the standard for dielectric constant and reflectivity testing. The required samples include: (1) Waveguide test sample: X-band (22.86 mm × 10.16 mm × 2 mm), Ku-band (15.80 mm × 7.90 mm × 2 mm), K-band (10.668 mm × 4.318 mm × 2 mm), Ka-band (7.112 mm × 3.556 mm × 2 mm); High temperature reflection test sample: 180 mm × 180 mm × 3 mm.

[0077] Step 9: Mix deionized water, silica sol, Al2O3, B2O3, and SiO2 powder in a mass ratio of 3:1:0.05:0.2:1 until homogeneous, and then apply an antioxidant coating with a thickness of 200 μm to the surface of the sample processed in Step 8 using a brushing method.

[0078] Example 5: Step 1: Five ultra-high temperature boride ceramic powders—ZrB2, TiB2, NbB2, HfB2, and TaB2—were subjected to high-temperature pretreatment. Each of the five ceramic powders was placed in an alumina crucible and then transferred to a resistance wire heated heat treatment furnace. In a flowing Ar atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, held for 3 hours, and then cooled to room temperature with the furnace to obtain the pretreated ceramic powders.

[0079] Step 2: Weigh the ZrB2, TiB2, NbB2, HfB2 and TaB2 after high temperature pretreatment in Step 1 in a volume ratio of 1:2:1:1:3 and ball mill them for 2 hours to make the five ceramic powders evenly mixed to obtain MB mixed powder.

[0080] Step 3: Weigh MB mixed powder, liquid polysiloxane solution and anhydrous ethanol at a mass ratio of 1:1:1, and then strongly ultrasonically disperse for 12 h to obtain a uniformly mixed impregnation solution.

[0081] Step 4: Place the pre-woven alumina fiber preform into the impregnation solution in Step 3 and put it into a vacuum impregnation chamber. After maintaining the pressure at -0.1 MPa atmospheric pressure for 0.5 h, the impregnated preform material is obtained.

[0082] Step 5: Place the preform material impregnated in Step 4 in an 80 ℃ oven and keep it at that temperature for 4 h until the anhydrous ethanol is completely dried. Then, raise the oven temperature to 180 ℃ at a rate of 5 ℃ / min, keep it at that temperature for 2 h, and then let it cool naturally to room temperature to complete the crosslinking reaction and obtain the crosslinked material.

[0083] Step 6: Repeat steps 4 and 5 three times, then place the cross-linked material into a heat treatment chamber with a resistance wire as the heating element. In a flowing Ar atmosphere, raise the temperature from room temperature to 1100 ℃ at a heating rate of 5 ℃ / min, hold for 2 h, and then allow it to cool naturally to room temperature to complete the high-temperature heat treatment and obtain the densified ASM ceramic composite material.

[0084] Step 7: Repeat step 6 four times to obtain the ASM-4 ceramic composite material after four densification processes.

[0085] Step 8: The ASM-4 ceramic composite material after densification in step 7 is processed into the corresponding size according to the standard for dielectric constant and reflectivity testing. The required samples include: (1) Waveguide test sample: X-band (22.86 mm × 10.16 mm × 2 mm), Ku-band (15.80 mm × 7.90 mm × 2 mm), K-band (10.668 mm × 4.318 mm × 2 mm), Ka-band (7.112 mm × 3.556 mm × 2 mm); High temperature reflection test sample: 180 mm × 180 mm × 3 mm.

[0086] Step 9: Mix deionized water, silica sol, Al2O3, B2O3, and SiO2 powder in a mass ratio of 3:1:0.1:0.1:1 until homogeneous, and then apply an antioxidant coating with a thickness of 150 μm to the surface of the sample processed in Step 8 using a brushing method.

[0087] like Figure 1 As shown, *Ilex shamiana*, a hyperxerophyte in the arid desert regions of Northwest China, has a leaf structure with three important components: a hard outer epidermis, an internal palisade structure, and abundant chloroplasts. These important biological tissues enable it to withstand long-term wind and sand erosion and survive in the arid, hot desert environment, making it the only evergreen plant in the Northwest desert region. Inspired by this biological structure, this invention prepares an ASM ceramic composite material coated with an antioxidant layer. The antioxidant coating provides excellent thermal protection. In addition, the alumina fibers and multi-component boride ultra-high temperature absorbing components in the ASM ceramic composite material respectively enhance the material's mechanical properties and absorb electromagnetic waves. The ASM ceramic composite material prepared in this invention has a similar microstructure to the leaf tissue of *Ilex shamiana*, both containing an outer protective layer, an internal reinforcing body, and an electromagnetic wave / light absorbing phase.

[0088] like Figure 2 As shown, the XRD patterns demonstrate the successful preparation of ASM ceramic composites. PDC-SiOC ceramics exist as an amorphous phase and do not exhibit obvious characteristic diffraction peaks. ASM ceramic composites with different compositions all show characteristic diffraction peaks of five boride phases.

[0089] Depend on Figure 3 It can be seen that as the densification times increase, the porosity between fiber bundles in ASM ceramic composites gradually decreases and is replaced by PDC-SiOC ceramics and multi-component boride ceramics.

[0090] like Figure 4 As shown, the ASM ceramic composite material exhibits excellent mechanical properties, with the best flexural strength being 419.47 ± 69.90 MPa. Figure 4 a) The optimal compression performance in the Z-axis is 403.11 ± 24.54 MPa ( Figure 4 b), the optimal compression performance in the Y direction is 253.68 ± 12.07 MPa ( Figure 4 c) The optimal fracture toughness is 8.12 ± 0.05 MPa·m. 1 / 2 ( Figure 4 d).

[0091] like Figure 5 As shown, Figure 5 a, Figure 5 b, Figure 5 c represents the real part, imaginary part, and loss tangent of the prepared ASM ceramic composite material, respectively. It can be seen that the dielectric value of the ASM ceramic composite material exhibits obvious dielectric dispersion characteristics (the dielectric value gradually decreases with increasing frequency), which plays an important role in enabling the composite material to achieve broadband EMW absorption. Furthermore, with the increase of densification times, the real part, imaginary part, and loss tangent of the material's dielectric all gradually increase. This is mainly attributed to the increased content of multi-component boride absorbers in the ceramic composite material, thus enhancing its EMW attenuation capability.

[0092] like Figure 6 As shown, Figure 6 a, Figure 6 b, Figure 6 c, Figure 6Figure d shows the EMW absorption performance of ASM ceramic composites after different densification cycles. The ASM-1 sample (Example 1) achieved an EAB of 23.18 GHz at 7.95 mm; the ASM-2 sample (Example 2) achieved EABs of 27.07 GHz and 17.25 GHz at 8.9 mm and 3.7 mm, respectively; the ASM-3 sample (Example 3) achieved EABs of 25.5 GHz and 17.19 GHz at 8.1 mm and 2.8 mm, respectively; finally, the ASM-4 sample (Example 4) achieved an EAB of 13.20 GHz at only 1.3 mm, demonstrating excellent EMW absorption capability. According to the quarter-wavelength theory, materials with higher densification cycles possess larger complex permittivity, meaning they can achieve effective EMW absorption at smaller thicknesses. Therefore, the ASM-4 sample with four densification cycles exhibits excellent absorption performance only at smaller thicknesses, demonstrating its application potential.

[0093] like Figure 7 As shown, the ASM ceramic composite material with four densification cycles (Example 5) exhibits ultra-stable EMW absorption performance at high temperatures. Its EAB remains no less than 8 GHz across a temperature range of 298 K to 1473 K, overcoming the current predicament of declining high-temperature absorption performance in ceramic matrix composites. This characteristic provides significant potential for its practical applications under harsh high-temperature conditions.

[0094] In summary, addressing the critical issue that existing ceramic matrix composites struggle to simultaneously achieve high mechanical strength and stable broadband electromagnetic wave (EMW) absorption performance under extreme environments, this invention, inspired by the multi-tissue functional partitioning structure of *Ilex shamrock* leaves, proposes a design principle of functional decoupling and integrated construction. This material system was prepared using a continuous vacuum impregnation and precursor pyrolysis process to produce Al₂O₃. 3f The @BN-SiOC-multi-component boride ceramic composite material achieves spatial decoupling and synergistic enhancement of mechanical load-bearing capacity, EMW attenuation, and long-term high-temperature thermal protection. This ceramic matrix composite material exhibits excellent mechanical properties; simultaneously, it demonstrates ultra-stable EMW absorption capacity over a wide temperature range from room temperature to 1473 K, with an effective absorption bandwidth (EAB) of no less than 8 GHz; after oxidation at 1473 K for 600 h, the material's absorption performance does not decrease but rather increases, exhibiting long-term stable high-temperature stealth advantages. This invention breaks through the bottleneck of the mutual constraint between the mechanical and microwave absorption properties of traditional ceramic matrix composite materials, providing a multifunctional integrated material solution for the hot-end parts of high-speed aircraft that combines high load-bearing capacity, oxidation resistance, and strong EMW absorption.

[0095] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis*, characterized in that... It includes a microwave-absorbing ceramic matrix composite material and an anti-oxidation coating applied to the surface of the microwave-absorbing ceramic matrix composite material, wherein the microwave-absorbing ceramic matrix composite material is Al2O3. 3f @BN-SiOC-Multi-component boride ceramic composite material; The microwave absorbing ceramic matrix composite material has a double embedded structure consisting of a microwave absorbing component, a microwave transparent ceramic matrix, and a fiber skeleton, wherein the microwave absorbing component is embedded in the microwave transparent ceramic matrix, and the microwave transparent ceramic matrix is ​​embedded in the fiber skeleton.

2. The high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis* as described in claim 1, characterized in that... The microwave absorbing component is a multi-element ultra-high temperature boride ceramic, which is prepared by uniformly ball milling and mixing ZrB2, TiB2, NbB2, HfB2 and TaB2 in a volume ratio of 1:2:1:1:

3.

3. The high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis* as described in claim 1, characterized in that... The microwave-transparent ceramic matrix is ​​PDC-SiOC ceramic; the fiber skeleton is an alumina fiber preform. The antioxidant coating is prepared by mixing deionized water, silica sol, Al2O3, B2O3 and SiO2 in a mass ratio of 3:1:(0.05~0.1):(0.1~0.2):(0.8~1).

4. The high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis* as described in claim 1, characterized in that... The microwave absorbing ceramic matrix composite material has an effective absorption bandwidth of not less than 8 GHz over a wide temperature range from room temperature to 1473 K; the absorption performance of the microwave absorbing ceramic matrix composite material increases after oxidation at 1473 K for 600 h.

5. A method for preparing a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure of *Ilex chinensis* leaf as described in any one of claims 1 to 4, characterized in that, Includes the following steps: The multi-component microwave absorbers ZrB2, TiB2, NbB2, HfB2 and TaB2 were pretreated at high temperature in an inert atmosphere and then uniformly mixed to obtain MB mixed powder. The MB mixed powder is uniformly mixed with liquid polysiloxane solution and anhydrous ethanol to obtain an impregnation solution; The alumina fiber preform was placed in an impregnation solution and impregnated at an atmospheric pressure of -0.1 MPa to obtain the impregnated preform material. After the impregnated preform material is dried, it is placed in an oven for crosslinking to obtain a crosslinked material. After repeating the above impregnation-crosslinking operation multiple times, the crosslinked material is placed in an inert atmosphere for high-temperature heat treatment to obtain an ASM ceramic composite material. The above process is one cycle. After repeating the above operation multiple times, a densified ASM ceramic composite material is obtained. An antioxidant coating was prepared by mixing deionized water, silica sol, Al2O3, B2O3, and SiO2 powders and coating them onto the surface of the densified ASM ceramic composite material, thus obtaining a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure of Ilex chinensis leaves.

6. The method for preparing the high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis* according to claim 5, characterized in that, The volume ratio of ZrB2, TiB2, NbB2, HfB2 and TaB2 is 1:2:1:1:3; the high-temperature inert atmosphere pretreatment is carried out at a temperature of 600 °C for 3 h, and the inert atmosphere is Ar.

7. The method for preparing a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis* according to claim 5, characterized in that, The mass ratio of the MB mixed powder, liquid polysiloxane solution, and anhydrous ethanol is (1~3):(1~3):(1~3).

8. The method for preparing the high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis* according to claim 5, characterized in that, The drying temperature is 80 ℃, and the time is 2~4 h; The crosslinking process involves holding the temperature at 100~200 ℃ for 1~3 h, followed by natural cooling to room temperature; The high-temperature heat treatment process involves heating to 850~1100 ℃ at a heating rate of 5 ℃ / min under an inert atmosphere, holding at that temperature for 1~4 h, and then naturally cooling to room temperature.

9. The method for preparing the high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure resembling the leaves of *Ilex chinensis* according to claim 5, characterized in that, The mass ratio of the deionized water, silica sol, Al2O3, B2O3, and SiO2 is 3:1:(0.05~0.1):(0.1~0.2):(0.8~1); the thickness of the antioxidant coating is 100~200 μm.

10. The application of a high-strength, high-temperature resistant microwave-absorbing ceramic matrix composite material with a biomimetic structure of *Ilex chinensis* blades as described in any one of claims 1 to 4 in the hot-end portion of a high-speed aircraft.

Images