Chopped fiber-reinforced ultrahigh-temperature ceramic matrix composite and method of making

Abstract

The application relates to the technical field of ceramic matrix composite materials, and particularly discloses a chopped fiber reinforced ultrahigh-temperature ceramic matrix composite material and a preparation method thereof, which comprises the following components in parts by mass: 60-75 parts of ZrB2, 8-15 parts of SiC particles, 8-15 parts of modified chopped SiC fibers and 1-3 parts of B4C. The preparation method comprises the following steps: ZrB2, SiC particles and B4C are mixed and ball milled, the modified chopped SiC fibers are added and mixed to obtain a composite powder, and then the composite material is prepared through hot-pressing sintering. In the application, a modified layer of arylalkynyl polyborosilazane is constructed on the surface of the chopped SiC fibers, the dispersion uniformity of the fibers in the ceramic matrix is improved, the interface bonding performance between the fibers and the matrix is improved, and the high-temperature stability and the mechanical properties of the composite material are improved through the synergistic reinforcing effect between ZrB2, SiC particles, B4C and the arylalkynyl polyborosilazane coated chopped SiC fibers.

Description

Technical Field

[0001] This invention relates to the field of ceramic matrix composites, specifically to a short-cut fiber reinforced ultra-high temperature ceramic matrix composite and its preparation method. Background Technology

[0002] Ultra-high temperature ceramics are non-oxide ceramic materials composed of transition metal borides, carbides, etc. They possess properties such as high-temperature oxidation resistance, thermal shock resistance, moderate coefficient of thermal expansion, and high thermal conductivity, and are widely used in heat-resistant protection devices for extreme environments, such as nose cones of hypersonic vehicles, rocket engine nozzles, and thermal protection systems of spacecraft. However, the inherent brittleness and low fracture toughness of single-phase ultra-high temperature ceramics severely limit their engineering applications.

[0003] Introducing fiber materials into ultra-high temperature ceramic matrices is an effective way to solve the above problems. Depending on the morphology, fiber reinforcement methods can be divided into whiskers, chopped fibers, and continuous fibers, among which chopped fibers have attracted much attention due to their simple processing and low cost. Currently, the preparation methods for fiber-reinforced ultra-high temperature ceramic matrix composites mainly include precursor impregnation pyrolysis, chemical vapor infiltration, reactive melting infiltration, and hot pressing / discharge plasma sintering. Among these, precursor impregnation pyrolysis has a low pyrolysis temperature and causes less damage to the fibers, but the material has more pores, a long preparation cycle, and high cost. Chemical vapor infiltration produces products with high purity and complete crystal structure, but the preparation cycle is long and requires sophisticated equipment. Reactive melting infiltration has a shorter preparation cycle, can prepare large-size complex components with high density, but it easily leaves behind low-melting-point metallic phases, affecting high-temperature performance. Hot pressing / discharge plasma sintering can effectively reduce porosity, but the high sintering temperature easily leads to fiber performance degradation and weakens the toughening effect. In addition, the uniformity of fiber dispersion in the matrix and the interfacial bonding state between the fiber and the ceramic matrix are also key factors that determine the final performance of the composite material.

[0004] Chinese patent application CN103964882A discloses a method for preparing fiber-reinforced ultra-high temperature ceramic matrix composites, employing a slurry impregnation combined with reactive infiltration process. The resulting composite material exhibits high densification and low open porosity, but the high reactive infiltration temperature may lead to fiber performance degradation and weakened toughening effect. Chinese patent application CN118666586A discloses a chopped fiber-reinforced ultra-high temperature ceramic matrix composite and its preparation method. Using a mixed powder composed of silicon boron oxynitride, pure silicon powder, zirconium diboride, and a carbon source, along with chopped fibers, as raw materials, a reactive hot-pressing sintering process is employed to obtain a composite material with high density and low porosity. However, the uniformity of chopped fiber dispersion in the matrix and the interfacial bonding state between the fibers and the ceramic matrix still require further optimization.

[0005] Therefore, there is an urgent need to develop a short-fiber reinforced ultra-high temperature ceramic matrix composite material with excellent mechanical properties.

[0006] Summary of the Invention (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a short-fiber reinforced ultra-high temperature ceramic matrix composite material and its preparation method, solving the problem of high brittleness in short-fiber reinforced ultra-high temperature ceramic matrix composite materials.

[0007] (II) Technical Solution To achieve the above objectives, this invention discloses a short-fiber reinforced ultra-high temperature ceramic matrix composite material, comprising the following components by mass: 60-75 parts ZrB2, 8-15 parts SiC particles, 8-15 parts modified short-cut SiC fibers, 1-3 parts B4C; The modified short-cut SiC fiber is an aromatic alkynyl polyborosilazane-coated short-cut SiC fiber, which is obtained by coating activated short-cut SiC fibers with an aromatic alkynyl polyborosilazane precursor.

[0008] Preferably, the method for preparing the modified chopped SiC fibers includes the following steps: S1. Add the chopped SiC fibers to a dilute nitric acid solution, soak at room temperature for 12-24 hours, wash with deionized water until neutral, and dry to obtain activated chopped SiC fibers. S2. Under a nitrogen atmosphere, hexamethyldisilazane was added to anhydrous n-hexane to obtain a hexamethyldisilazane solution. The system was then cooled, and boron trichloride and methyldichlorosilane were added dropwise to the hexamethyldisilazane solution. After reacting for 4-8 hours, the reaction system was heated, distilled under reduced pressure, and cooled to room temperature to obtain the polyborosilicate precursor. S3. The polyborosilazane precursor is added to anhydrous toluene and stirred to dissolve. Under a nitrogen atmosphere, 4-ethynylstyrene, Karstedt catalyst and hydroquinone are added and reacted at 80-100℃ for 6-12h. After the reaction is completed, the mixture is cooled to room temperature to obtain the aromatic ynyl polyborosilazane precursor. S4. The aromatic alkynyl polyborosilazane precursor is dispersed in anhydrous xylene and mixed by stirring to obtain a coating solution. The activated chopped SiC fibers are ultrasonically dispersed into the coating solution, impregnated, and dried to obtain modified chopped SiC fibers.

[0009] Preferably, the length of the chopped SiC fibers in S1 is 5-10 mm.

[0010] Preferably, the dilute nitric acid solution in S1 is a dilute nitric acid aqueous solution with a concentration of 0.1-0.5 mol / L.

[0011] Preferably, the mass ratio of chopped SiC fibers to dilute nitric acid solution in S1 is 1:(20-50).

[0012] Preferably, in the drying process of S1, the drying temperature is 70-90℃ and the drying time is 8-10h.

[0013] Preferably, the temperature for cooling in S2 is from -20°C to 0°C.

[0014] Preferably, the heating process in S2 is carried out in two stages, with a heating rate of 2-3℃ / min in both stages. The first stage heats up to 120-150℃ and is heat-treated for 8-12 hours, while the second stage heats up to 250-300℃ and is heat-treated for 5-15 hours.

[0015] Preferably, the vacuum distillation in S2 is carried out under vacuum conditions at a temperature of 70-100℃ for 1-2 hours.

[0016] Preferably, the mass ratio of hexamethyldisilazane, anhydrous n-hexane, boron trichloride, and methyldichlorosilane in S2 is 100:(300-600):(20-40):(25-45).

[0017] Preferably, the Karstedt catalyst in S3 is a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex.

[0018] Preferably, the mass ratio of polyborosilazane precursor, anhydrous toluene, 4-ethynyl styrene, Karstedt catalyst, and hydroquinone in S3 is 100:(200-300):(5-30):(0.01-0.1):(0.01-0.1).

[0019] Preferably, during the stirring process in step S4, the rotation speed is 300-400 r / min and the time is 30-60 min.

[0020] Preferably, the ultrasonic dispersion time in S4 is 10-30 min.

[0021] Preferably, the immersion treatment time in S4 is 3-6 hours.

[0022] Preferably, in the drying process of S4, the drying temperature is 80-100℃ and the time is 4-6h.

[0023] Preferably, the mass ratio of the aromatic alkynyl polyborosilazane precursor, anhydrous xylene, and activated chopped SiC fibers in S4 is (10-30):(70-90):100.

[0024] A method for preparing the aforementioned chopped fiber reinforced ultra-high temperature ceramic matrix composite material includes the following steps: Step 1: Add ZrB2, SiC particles, and B4C to anhydrous ethanol, ball mill to obtain a slurry, dry the slurry to obtain a ceramic premix, and then mix the ceramic premix with modified chopped SiC fibers at low speed to obtain a composite powder. Step 2: Under an argon protective atmosphere, the composite powder is loaded into a mold and hot-pressed and sintered to obtain a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material.

[0025] Preferably, the particle size of the SiC particles in step one is 0.5-2 μm.

[0026] Preferably, in step one, the ball milling speed is 150-250 r / min and the time is 12-24 h.

[0027] Preferably, the solid content of the slurry in step one is 50%-60%.

[0028] Preferably, in step one, the drying temperature is 60-80℃ and the drying time is 8-12h.

[0029] Preferably, in step one, during the low-speed mixing process, the rotation speed is 20-40 r / min and the mixing time is 1-3 h.

[0030] Preferably, in the hot pressing sintering process of step two, the heating rate is 5-10℃ / min, the sintering temperature is 1600-1800℃, the pressure is 20-40MPa, and the holding time is 1-2h.

[0031] (iii) Beneficial technical effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Short-cut SiC fibers have high strength, excellent high-temperature stability and antioxidant properties, and can be used as a reinforcing phase to improve the brittleness of ceramic materials through mechanisms such as crack deflection, fiber bridging and pull-out energy dissipation. In this invention, the short-cut SiC fibers are first surface activated with dilute nitric acid solution to remove impurities on the fiber surface and generate oxygen-containing active groups on the fiber surface, thereby improving the fiber surface energy and wettability and providing active sites for the subsequent attachment of polyborosilicate precursors. In the preparation of polyborosilicate precursors, hexamethyldisilazane provides N-H active sites and a silicon-nitrogen skeleton, which participates in the substitution reaction as an amine source; boron trichloride introduces boron, whose B-Cl bond has high activity and is easy to be substituted with NH to form B-N bonds; methyldichlorohydrosilane provides hydrogen-containing silicon structural units, in which the Si-Cl bond undergoes condensation substitution with nitrogen-containing active groups to form Si-N bonds, while retaining some Si-H active bonds, providing reaction sites for the subsequent hydrosilylation grafting reaction. Through a condensation reaction, the three components gradually form polyborosilazane segments containing BN and Si-N structural units. Subsequent heating promotes further condensation, increasing the polymer's molecular weight and structural stability, yielding a polyborosilazane precursor. Then, under the action of a Karstedt catalyst, the alkynyl group in 4-ethynylstyrene undergoes a hydrosilylation addition reaction with the Si-H bonds of the polyborosilazane precursor, introducing an aromatic alkynyl structure into the polyborosilazane molecular chain, resulting in an aromatic alkynyl polyborosilazane precursor. Further, the aromatic alkynyl polyborosilazane precursor is dispersed in anhydrous xylene to form a low-viscosity coating system. Ultrasonic treatment promotes thorough wetting of the activated chopped SiC fibers by the coating solution, allowing the precursor molecules to be uniformly adsorbed onto the fiber surface. Because acid-treated SiC fibers possess high surface energy and oxygen-containing active sites, precursor molecules adhere to the fiber surface through surface adsorption, van der Waals interactions, and interfacial interactions between oxygen-containing active sites and polar groups in the precursor. After solvent evaporation, a uniform and continuous precursor coating layer is formed, resulting in modified chopped SiC fibers. This improves the surface state of the chopped SiC fibers and enhances their dispersibility and interfacial bonding in the ceramic matrix. During subsequent hot-pressing sintering, the argon protective atmosphere reduces the degree of fiber oxidation damage, allowing the chopped SiC fiber reinforcement structure to be maintained. Simultaneously, during heat treatment, the aromatic alkyne structure first undergoes cross-linking and solidification, providing a carbon source during subsequent high-temperature pyrolysis. Together with the Si, B, and N elements in polyborosilazane, it forms a Si-BCN ceramic phase, reducing porosity and defect formation caused by precursor pyrolysis shrinkage and improving the density of the fiber-matrix interface. This invention improves the fiber surface condition through an aromatic alkynyl polyborosilazane coating, enhancing the interfacial bonding between the fiber and the matrix, reducing fiber agglomeration, and improving the uniform distribution of fibers in the ZrB2 matrix. Therefore, the modified chopped SiC fibers can effectively hinder crack propagation through mechanisms such as fiber bridging, crack deflection, and pull-out energy dissipation, thereby improving the fracture toughness and impact resistance of the composite material.

[0032] (2) This invention uses ZrB2 as the ultra-high temperature ceramic matrix material, utilizing the high melting point, high strength, high hardness, and excellent thermal stability of ZrB2 to provide high-temperature load-bearing capacity for the composite material. After adding micron-sized SiC particles, the SiC particles are distributed in the ZrB2 matrix as a dispersed reinforcing phase, which has good dispersion stability, can reduce agglomeration during sintering, and is conducive to the formation of a uniform second-phase reinforcing structure. On the one hand, the excellent high-temperature oxidation resistance of SiC is utilized to improve the stability of the composite material in a high-temperature oxidizing environment; on the other hand, SiC particles can inhibit the abnormal growth of ZrB2 grains through grain boundary pinning, refine the ceramic matrix structure, and improve the material density. At the same time, SiC particles can induce crack deflection during crack propagation, prolong the crack propagation path, and improve the crack resistance and fracture toughness of the composite material. The addition of B4C can further improve the hardness and high-temperature stability of the material. Its high strength and thermal stability help to enhance the wear resistance and impact resistance of ZrB2-based composite materials in high-temperature service environments. Meanwhile, B4C can act as a sintering promoter, reacting with oxygen impurities in the system during high-temperature sintering to reduce the adverse effects of oxide impurities on grain boundaries, inhibit abnormal grain growth, promote densification of the ZrB2-based ceramic matrix, and reduce the formation of pore defects, thereby further improving the mechanical properties of the composite material.

[0033] (3) This invention employs a combination of chopped fiber reinforcement and hot-pressing sintering, enabling the aromatic acetylenic polyborosilicate coating layer to undergo in-situ transformation during sintering and form a stable bond with the ZrB2 matrix. Simultaneously, the hot-pressing process promotes contact bonding and interfacial sintering between the components, improving the densification of the composite material and reducing internal porosity and interfacial defects. The prepared chopped fiber reinforced ultra-high temperature ceramic matrix composite material fully utilizes the high-temperature load-bearing capacity of the ZrB2 matrix, the antioxidant and strengthening effects of SiC particles and B4C reinforcing phases, and the interfacial regulation and toughening effects of modified chopped SiC fibers, thereby obtaining an ultra-high temperature ceramic matrix composite material with excellent high-temperature stability and mechanical properties. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] Example 1 A method for preparing modified chopped SiC fibers includes the following steps: S1. Add 1 part of short-cut SiC fiber with a length of 5 mm to 20 parts of dilute nitric acid solution with a concentration of 0.1 mol / L, soak at room temperature for 12 h, wash with deionized water until neutral, and dry at 70℃ for 10 h to obtain activated short-cut SiC fiber. S2. Under a nitrogen atmosphere, 100 parts of hexamethyldisilazane were added to 300 parts of anhydrous n-hexane to obtain a hexamethyldisilazane solution. The system was then cooled to -20°C, and 20 parts of boron trichloride and 25 parts of methyldichlorosilane were added dropwise to the hexamethyldisilazane solution. After reacting for 4 hours, the reaction system was heated at a rate of 2°C / min. The system was first heated to 120°C for 12 hours, then heated to 250°C for 15 hours. The system was then distilled under vacuum at 70°C for 2 hours and cooled to room temperature to obtain a polyborosilicate precursor. S3. Add 100 parts of the polyborosilazane precursor to 200 parts of anhydrous toluene, stir to dissolve, add 5 parts of 4-ethynylstyrene, 0.01 parts of Karstedt catalyst and 0.01 parts of hydroquinone under nitrogen atmosphere, react at 80°C for 12 h, after the reaction is completed, cool to room temperature to obtain the aromatic ynyl polyborosilazane precursor; S4. Disperse the 10 parts of aromatic alkynyl polyborosilazane precursor in 70 parts of anhydrous xylene, stir and mix for 60 min at a speed of 300 r / min to obtain a coating solution, disperse 100 parts of activated chopped SiC fibers into the coating solution by ultrasonication for 10 min, impregnate for 3 h, and then dry at 80 °C for 6 h to obtain modified chopped SiC fibers.

[0036] Example 2 A method for preparing modified chopped SiC fibers includes the following steps: S1. Add 1 part of 7 mm long short-cut SiC fiber to 35 parts of 0.3 mol / L dilute nitric acid solution, soak at room temperature for 18 h, wash with deionized water until neutral, and dry at 80 °C for 9 h to obtain activated short-cut SiC fiber. S2. Under a nitrogen atmosphere, 100 parts of hexamethyldisilazane were added to 450 parts of anhydrous n-hexane to obtain a hexamethyldisilazane solution. The system was then cooled to -10℃, and 30 parts of boron trichloride and 35 parts of methyldichlorosilane were added dropwise to the hexamethyldisilazane solution. After reacting for 6 hours, the reaction system was heated at a rate of 2.5℃ / min. The system was first heated to 135℃ for 10 hours, then heated to 275℃ for 10 hours. The system was then distilled under vacuum at 85℃ for 1.5 hours and cooled to room temperature to obtain a polyborosilicate precursor. S3. Add 100 parts of the polyborosilazane precursor to 250 parts of anhydrous toluene, stir to dissolve, add 18 parts of 4-ethynylstyrene, 0.06 parts of Karstedt catalyst and 0.06 parts of hydroquinone under nitrogen atmosphere, react at 90°C for 9 hours, and after the reaction is completed, cool to room temperature to obtain the aromatic ynyl polyborosilazane precursor. S4. Disperse the 20 parts of aromatic alkynyl polyborosilazane precursor in 80 parts of anhydrous xylene, stir and mix for 45 min at a speed of 350 r / min to obtain a coating solution, disperse 100 parts of activated chopped SiC fibers into the coating solution by ultrasonication for 20 min, impregnate for 4.5 h, and then dry at 90 °C for 5 h to obtain modified chopped SiC fibers.

[0037] Example 3 A method for preparing modified chopped SiC fibers includes the following steps: S1. Add 1 part of 10 mm long short-cut SiC fiber to 50 parts of 0.5 mol / L dilute nitric acid solution, soak at room temperature for 24 h, wash with deionized water until neutral, and dry at 90 °C for 8 h to obtain activated short-cut SiC fiber. S2. Under a nitrogen atmosphere, 100 parts of hexamethyldisilazane were added to 600 parts of anhydrous n-hexane to obtain a hexamethyldisilazane solution. The system was then cooled to 0°C. 40 parts of boron trichloride and 45 parts of methyldichlorosilane were added dropwise to the hexamethyldisilazane solution. After reacting for 8 hours, the reaction system was heated at a rate of 3°C / min. The system was first heated to 150°C for 8 hours, then heated to 300°C for 5 hours. The system was then distilled under vacuum at 100°C for 1 hour and cooled to room temperature to obtain a polyborosilicate precursor. S3. Add 100 parts of the polyborosilazane precursor to 300 parts of anhydrous toluene, stir to dissolve, add 30 parts of 4-ethynylstyrene, 0.1 parts of Karstedt catalyst and 0.1 parts of hydroquinone under nitrogen atmosphere, react at 100℃ for 6 h, after the reaction is completed, cool to room temperature to obtain the aromatic ynyl polyborosilazane precursor. S4. Disperse the 30 parts of aromatic alkynyl polyborosilazane precursor in 90 parts of anhydrous xylene, stir and mix for 30 min at a speed of 400 r / min to obtain a coating solution, disperse 100 parts of activated chopped SiC fibers into the coating solution by ultrasonication for 30 min, impregnate for 6 h, and then dry at 100 °C for 4 h to obtain modified chopped SiC fibers.

[0038] Example 4 A method for preparing a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material includes the following steps: Step 1: Add 60 parts ZrB2, 8 parts SiC particles with a particle size of 0.5μm, and 1 part B4C to anhydrous ethanol, and ball mill at 150 r / min for 24 h to obtain a slurry with a solid content of 50%. Dry the slurry at 60℃ for 12 h to obtain a ceramic premix. Then mix the ceramic premix with 8 parts modified short-cut SiC fibers at a low speed of 20 r / min for 3 h to obtain a composite powder. Step 2: Under an argon protective atmosphere, the composite powder is loaded into a mold, heated to 1600℃ at a heating rate of 5℃ / min, and held at 20MPa for 2 hours for hot pressing sintering to obtain a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material.

[0039] The preparation method of the modified chopped SiC fiber used in this embodiment is exactly the same as that of the modified chopped SiC fiber in Example 1.

[0040] Example 5 A method for preparing a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material includes the following steps: Step 1: Add 64 parts ZrB2, 10 parts SiC particles with a particle size of 1μm, and 1.5 parts B4C to anhydrous ethanol, and ball mill at 175 r / min for 20 h to obtain a slurry with a solid content of 53%. Dry the slurry at 65℃ for 11 h to obtain a ceramic premix. Then mix the ceramic premix with 10 parts modified short-cut SiC fibers at a low speed of 25 r / min for 2.5 h to obtain a composite powder. Step 2: Under an argon protective atmosphere, the composite powder is loaded into a mold, heated to 1650°C at a heating rate of 7°C / min, and held at 25MPa for 1.7 hours for hot pressing sintering to obtain a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material.

[0041] The preparation method of the modified chopped SiC fiber used in this embodiment is exactly the same as that of the modified chopped SiC fiber in Example 2.

[0042] Example 6 A method for preparing a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material includes the following steps: Step 1: Add 71 parts ZrB2, 13 parts SiC particles with a particle size of 1.5 μm, and 2.5 parts B4C to anhydrous ethanol, and ball mill at 225 r / min for 16 h to obtain a slurry with a solid content of 58%. Dry the slurry at 75 °C for 9 h to obtain a ceramic premix. Then mix the ceramic premix with 13 parts modified short-cut SiC fibers at a low speed of 35 r / min for 1.5 h to obtain a composite powder. Step 2: Under an argon protective atmosphere, the composite powder is loaded into a mold, heated to 1750°C at a heating rate of 9°C / min, and held at 35MPa for 1.3 hours for hot pressing sintering to obtain a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material.

[0043] The preparation method of the modified chopped SiC fiber used in this embodiment is exactly the same as that of the modified chopped SiC fiber in Example 2.

[0044] Example 7 A method for preparing a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material includes the following steps: Step 1: Add 75 parts ZrB2, 15 parts SiC particles with a particle size of 2μm and 3 parts B4C to anhydrous ethanol, and ball mill at 250 r / min for 12 h to obtain a slurry with a solid content of 60%. Dry the slurry at 80℃ for 8 h to obtain a ceramic premix. Then mix the ceramic premix with 15 parts modified short-cut SiC fibers at a low speed of 40 r / min for 1 h to obtain a composite powder. Step 2: Under an argon protective atmosphere, the composite powder is loaded into a mold and heated to 1800°C at a heating rate of 10°C / min. The temperature is maintained at 40MPa for 1 hour, and hot pressing sintering is performed to obtain a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material.

[0045] The preparation method of the modified chopped SiC fiber used in this embodiment is exactly the same as that of the modified chopped SiC fiber in Example 3.

[0046] Comparative Example 1 A method for preparing a chopped fiber reinforced ultra-high temperature ceramic matrix composite material is provided. Compared with the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material in Example 6, the main difference is that in this comparative example, the modified chopped SiC fibers in step one are replaced with activated chopped SiC fibers in equal amounts, while the other components and preparation methods are completely consistent with those in Example 6.

[0047] Comparative Example 2 A method for preparing a chopped fiber reinforced ultra-high temperature ceramic matrix composite material is disclosed. Compared with the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material in Example 6, the main difference is that in this comparative example, in the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material, SiC particles in step one are replaced with ZrB2 in equal amounts, while other components and preparation methods are completely consistent with those in Example 6.

[0048] Comparative Example 3 A method for preparing a chopped fiber reinforced ultra-high temperature ceramic matrix composite material is disclosed. Compared with the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material in Example 6, the main difference is that in this comparative example, in the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material, B4C in step one is replaced with ZrB2 in equal amounts, while the other components and preparation methods are completely consistent with those in Example 6.

[0049] Comparative Example 4 A method for preparing a chopped fiber reinforced ultra-high temperature ceramic matrix composite material is provided. Compared with the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material in Example 6, the main difference is that in this comparative example, in the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material, the modified chopped SiC fibers in step one are replaced with ZrB2 in equal amounts, while the other components and preparation methods are completely consistent with those in Example 6.

[0050] Comparative Example 5 A method for preparing a chopped fiber reinforced ultra-high temperature ceramic matrix composite material is disclosed. Compared with the method for preparing the chopped fiber reinforced ultra-high temperature ceramic matrix composite material in Example 6, the main difference is that in this comparative example, the modified chopped SiC fibers in step one are replaced with polyborosilazane modified chopped SiC fibers in equal amounts, while the other components and preparation methods are completely consistent with those in Example 6.

[0051] The short-fiber reinforced ultra-high temperature ceramic matrix composites prepared in Examples 4-7 and Comparative Examples 1-5 were subjected to relevant performance tests, and the test methods are as follows: (1) Fracture toughness test: According to GB / T 23806-2025 "Test method for fracture toughness of fine ceramics - single-sided precracked beam (SEPB) method", the critical load at which the single-sided precracked beam specimen fractures is measured at room temperature. The fracture toughness of the test specimen is calculated based on the crack length, span and specimen size. (2) Bending strength test: According to GB / T 6569-2006 "Test method for bending strength of fine ceramics", the maximum stress of the specimen at the time of fracture is calculated by the critical load, span and specimen size when the specimen breaks, i.e. bending strength. (3) Apparent porosity: According to GB / T 25995-2010 "Test Method for Density and Apparent Porosity of Fine Ceramics", the sample is placed in a drying oven and dried to constant weight. After cooling to room temperature, it is weighed and then placed in a vacuum container. Deionized water is added until the sample is completely submerged. The vacuum is released and the sample is soaked until it is saturated with water. The sample is taken out, the surface liquid is wiped off, and it is weighed. The saturated sample is then immersed in a basket, suspended in deionized water, weighed, and the apparent porosity is calculated. The test results are shown in Table 1: Table 1 Test Project <![CDATA[Fracture toughness (MPa·m 1 / 2 )]]> Bending strength (MPa) Apparent porosity (%) Example 4 6.9 468 2.8 Example 5 7.6 481 2.1 Example 6 8.8 503 1.5 Example 7 8.1 492 1.8 Comparative Example 1 4.3 354 5.0 Comparative Example 2 5.1 420 3.5 Comparative Example 3 5.4 431 3.1 Comparative Example 4 3.7 327 6.4 Comparative Example 5 7.1 452 2.5 As can be seen from the test results in Table 1, the short-fiber reinforced ultra-high temperature ceramic matrix composites prepared in Examples 4-7 have high fracture toughness, flexural strength, and low apparent porosity. Among them, Example 6 has the best overall performance, with a fracture toughness of 8.8 MPa·m. 1 / 2 The flexural strength was 503 MPa, and the apparent porosity was 1.5%. Compared with Example 6, in Comparative Example 1, the modified short-cut SiC fibers were replaced with activated short-cut SiC fibers in equal amounts. The absence of the arylynyl polyborosilazane coating layer weakened the interfacial regulation effect on the fiber surface, leading to a decrease in the bonding ability between the fibers and the ZrB2 matrix, an increase in interfacial defects, and consequently, a decrease in the fracture toughness and flexural strength of the composite material, and an increase in apparent porosity. In Comparative Example 2, the SiC particles were replaced with ZrB2 in equal amounts. Due to the lack of the dispersed reinforcing phase of SiC particles, the grain boundary pinning and crack deflection effects were reduced, weakening the matrix microstructure regulation ability and resulting in a decrease in the mechanical properties of the composite material. In Comparative Example 3, the B4C was replaced with ZrB2 in equal amounts. Due to the lack of the B4C reinforcing phase, the high-temperature strengthening effect and sintering densification effect of the composite material were reduced, leading to a decrease in the fracture toughness and flexural strength, and an increase in apparent porosity. In Comparative Example 4, the modified short-cut SiC fibers were replaced with an equal amount of ZrB2. The lack of reinforcement from the modified short-cut SiC fibers and the interfacial bonding provided by the arylynyl polyborosilazane coating reduced the fiber reinforcement and interfacial regulation effects, weakening the crack propagation inhibition capacity. This resulted in decreased fracture toughness and flexural strength of the composite material, and increased apparent porosity. In Comparative Example 5, the modified short-cut SiC fibers were replaced with an equal amount of polyborosilazane-modified short-cut SiC fibers. The lack of cross-linking reinforcement provided by the arylynyl structure reduced the structural stability and shrinkage resistance of the coating during the ceramization process, making it difficult to form a continuous and dense Si-BCN ceramic network structure. This led to decreased interfacial bonding capacity, increased apparent porosity, and reduced mechanical properties of the composite material.

[0052] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A short-fiber reinforced ultra-high temperature ceramic matrix composite material, characterized in that: By weight, it includes the following components: 60-75 parts ZrB2, 8-15 parts SiC particles, 8-15 parts modified short-cut SiC fibers, 1-3 parts B4C; The modified short-cut SiC fiber is an aromatic alkynyl polyborosilazane-coated short-cut SiC fiber, which is obtained by coating activated short-cut SiC fibers with an aromatic alkynyl polyborosilazane precursor.

2. The short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 1, characterized in that: The method for preparing the modified chopped SiC fibers includes the following steps: S1. Add the chopped SiC fibers to a dilute nitric acid solution, soak at room temperature for 12-24 hours, wash with deionized water until neutral, and dry to obtain activated chopped SiC fibers. The mass ratio of chopped SiC fibers to dilute nitric acid solution is 1:(20-50). S2. Under a nitrogen atmosphere, hexamethyldisilazane was added to anhydrous n-hexane to obtain a hexamethyldisilazane solution. The system was then cooled, and boron trichloride and methyldichlorosilane were added dropwise to the hexamethyldisilazane solution. After reacting for 4-8 hours, the reaction system was heated, distilled under reduced pressure, and cooled to room temperature to obtain a polyborosilicate precursor. The mass ratio of hexamethyldisilazane, anhydrous n-hexane, boron trichloride, and methyldichlorosilane was 100:(300-600):(20-40):(25-45). S3. The polyborosilicate precursor is added to anhydrous toluene and stirred to dissolve. Under a nitrogen atmosphere, 4-ethynylstyrene, Karstedt catalyst, and hydroquinone are added, and the mixture is reacted at 80-100℃ for 6-12 hours. After the reaction is completed, the mixture is cooled to room temperature to obtain an aromatic ynylstyrene polyborosilicate precursor. The mass ratio of the polyborosilicate precursor, anhydrous toluene, 4-ethynylstyrene, Karstedt catalyst, and hydroquinone is 100:(200-300):(5-30):(0.01-0.1):(0.01-0.1). S4. The aromatic alkynyl polyborosilazane precursor is dispersed in anhydrous xylene and mixed by stirring to obtain a coating solution. The activated chopped SiC fibers are ultrasonically dispersed into the coating solution, impregnated, and dried to obtain modified chopped SiC fibers. The mass ratio of aromatic alkynyl polyborosilazane precursor, anhydrous xylene, and activated chopped SiC fibers is (10-30):(70-90):

100.

3. The short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 2, characterized in that: The length of the short-cut SiC fibers in S1 is 5-10 mm.

4. The short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 2, characterized in that: The cooling temperature in S2 is from -20℃ to 0℃; the heating process is carried out in two stages, with a heating rate of 2-3℃ / min for both stages. The first stage heats up to 120-150℃ and is heat-treated for 8-12 hours, while the second stage heats up to 250-300℃ and is heat-treated for 5-15 hours; the vacuum distillation is carried out under vacuum conditions at a temperature of 70-100℃ for 1-2 hours.

5. The short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 2, characterized in that: The immersion treatment time in S4 is 3-6 hours.

6. A method for preparing the short-fiber reinforced ultra-high temperature ceramic matrix composite material as described in any one of claims 1-5, characterized in that: Includes the following steps: Step 1: Add ZrB2, SiC particles, and B4C to anhydrous ethanol, ball mill to obtain a slurry, dry the slurry to obtain a ceramic premix, and then mix the ceramic premix with modified chopped SiC fibers at low speed to obtain a composite powder. Step 2: Under an argon protective atmosphere, the composite powder is loaded into a mold and hot-pressed and sintered to obtain a short-cut fiber reinforced ultra-high temperature ceramic matrix composite material.

7. The method for preparing a short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 6, characterized in that: The particle size of the SiC particles in step one is 0.5-2 μm.

8. The method for preparing a short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 6, characterized in that: In step one, during the low-speed mixing process, the rotation speed is 20-40 r / min, and the mixing time is 1-3 h.

9. The method for preparing a short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 6, characterized in that: The solid content of the slurry in step one is 50%-60%.

10. The method for preparing a short-fiber reinforced ultra-high temperature ceramic matrix composite material according to claim 6, characterized in that: In step two, during the hot pressing sintering process, the heating rate is 5-10℃ / min, the sintering temperature is 1600-1800℃, the pressure is 20-40MPa, and the holding time is 1-2h.