Thermal shock resistant phosphate containing high temperature composite reinforced with alumina fibers and method of making

Abstract

The application discloses an anti-thermal shock alumina fiber reinforced phosphate high-temperature-resistant composite material and a preparation method thereof, and belongs to the technical field of ceramic matrix composites. The material is composed of gradient modified alumina fiber reinforcement, composite phosphate matrix and multi-scale composite filler. The fiber surface is provided with a nano yttrium oxide-yttrium phosphate gradient interface layer, and the matrix is an aluminum phosphate-zirconium phosphate-yttrium oxide composite system. The preparation method comprises fiber degumming, gradient interface modification, slurry preparation, impregnation and curing and microwave sintering. Through gradient interface regulation and composite matrix design, the application solves the problems of poor thermal shock resistance and insufficient high-temperature stability of the existing materials. Tests show that the material has no macroscopic cracking after 10 times of water cooling at 1300 DEG C, the strength retention rate is greater than or equal to 88%, the room temperature bending strength is greater than or equal to 280 MPa, and the material has excellent high-temperature mechanical properties and thermal shock stability, and is suitable for aerospace thermal protection and high-temperature structural parts.

Description

Technical Field

[0001] This invention belongs to the field of ceramic matrix composite technology, specifically relating to an alumina fiber reinforced phosphate matrix composite material, which is particularly suitable for high-temperature resistant structural components, thermal protection components, and aerospace wave-transparent components under extreme high temperature and rapid cooling and heating conditions below 1400℃. Background Technology

[0002] Extensive research has been conducted both domestically and internationally on alumina fiber-reinforced phosphate composites.

[0003] The core existing technology is as follows. Chinese Patent CN120056581A (application date 2025.01.16, publication date 2025.05.30): discloses an alumina fiber reinforced aluminum phosphate composite material with an organoaluminum phosphate interface layer, which inhibits fiber corrosion through organosol pretreatment, and has a room temperature flexural strength ≥210MPa and a 1000℃ flexural strength ≥180MPa.

[0004] Chinese Patent CN117756517A (Application Date: 2023.11.21, Publication Date: 2024.03.26): discloses a process for pre-treating alumina fibers and then combining them with a low-viscosity phosphate matrix, which solves the problem of uneven matrix dispersion.

[0005] Chinese Patent CN103086691B (authorization announcement date: October 15, 2014): discloses a method for preparing fiber preforms impregnated with phosphate solution, achieving high temperature resistance and load-bearing capacity of the material.

[0006] EP 0336044 B1 (Publication date 1992.08.12): Discloses a scheme to improve the thermal shock resistance of ceramic materials by controlling microcracks, and clarifies the relationship between the coefficient of thermal expansion and thermal shock resistance.

[0007] USPTO related patents: Focusing on zirconium phosphate-based high-temperature resistant composite materials, achieving short-term ablation resistance at 2500℃, but not involving the thermal shock gradient interface design of alumina fiber reinforced systems.

[0008] The CNKI-indexed paper "Preparation and Performance Study of Alumina Fiber Reinforced Ceramic Matrix Wave-Transparent Composite Material Containing LaPO4 Interface Phase" (2024) states that a lanthanum phosphate interface layer was used to improve the interface matching between the fiber and the matrix, achieving a room temperature tensile strength of 148.3 MPa. However, the performance degraded significantly after thermal cycling above 1200℃.

[0009] Google Scholar has included related research: The upper limit of the long-term service temperature of alumina fiber reinforced phosphate system is concentrated at 1200℃. After water quenching and heating cycles above 1200℃, the material is prone to matrix cracking, fiber-matrix interface debonding failure, strength retention rate is generally less than 70%, and thermal shock resistance is insufficient.

[0010] The existing technology still has the following core defects: 1) Insufficient interface control: Existing single interface layers (organoaluminum phosphate, lanthanum phosphate) only solve the problem of corrosion of fibers by acidic matrix, and cannot achieve gradient control of interface bonding strength. During thermal cycling, brittle fracture caused by strong interface bonding or load transfer failure caused by weak bonding may occur, resulting in poor thermal shock cycle stability.

[0011] 2) Insufficient high-temperature stability of the matrix: Existing single aluminum phosphate matrix is ​​prone to crystal transformation above 1300℃, resulting in volume expansion and microcracks. The thermal expansion coefficient is poorly matched with alumina fiber. Under high-temperature rapid cooling and heating conditions, the material is prone to overall cracking and cannot meet the requirements for long-term service above 1300℃.

[0012] 3) Single toughening mechanism: It only relies on fiber pull-out toughening and does not achieve multi-scale synergistic toughening. The resistance to microcrack propagation is low and the mechanical properties of the material deteriorate rapidly after thermal shock.

[0013] 4) Limitations of the preparation process: Existing hot pressing and high-temperature sintering processes are prone to high-temperature damage to alumina fibers, and vacuum impregnation has a long cycle and poor density uniformity, making it impossible to balance production efficiency and material performance.

[0014] Therefore, there is an urgent need to develop a composite material that combines excellent thermal shock resistance, high temperature stability, and high mechanical properties. Summary of the Invention

[0015] To address the aforementioned problems, this invention provides a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material and its preparation method.

[0016] Specifically, a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material is composed of the following components in the indicated mass percentages.

[0017] Specifically, the gradient-modified alumina fiber reinforcement is 30%-55%. The composite phosphate matrix is ​​35%-60%. (Multi-scale composite filler) is 5%-15%.

[0018] Specifically, the surface of the gradient-modified alumina fiber reinforcement has a gradient structure of nano-yttrium oxide transition layer-in-situ generated yttrium phosphate interface layer.

[0019] Specifically, the composite phosphate matrix is ​​an aluminum phosphate-zirconium phosphate-yttrium oxide composite system with a molar ratio of n(aluminum phosphate):n(zirconium phosphate):n(yttrium oxide)=100:(15-35):(2-8) and n(aluminum phosphate):n(zirconium phosphate):n(yttrium oxide)=100:(15-35):(2-8).

[0020] Specifically, the multi-scale composite filler is composed of hexagonal boron nitride nanosheets (h-BNNS) and mullite whiskers.

[0021] Specifically, the gradient-modified alumina fiber reinforcement uses continuous polycrystalline αα-alumina fibers with an Al2O3 content ≥99% and a single filament diameter of 7-12 μm. The thickness of the nano-yttrium oxide transition layer is 10-30 nm, and the thickness of the yttrium phosphate interface layer is 40-170 nm.

[0022] Specifically, in the multi-scale composite filler, the mass ratio of hexagonal boron nitride nanosheets (h-BNNS) to mullite whiskers is 1:(2-4).

[0023] Specifically, the h-BNNS flakes have a diameter of 500-800 nm and a thickness of 5-15 nm. The mullite whiskers have a diameter of 1-3 μm and an aspect ratio of 15-30.

[0024] A method for preparing a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material includes the following steps: S1 Fiber Degumming: Keep the alumina fiber fabric at 500-550℃ for 1-2 hours to remove the surface organic sizing agent.

[0025] S2 fiber gradient interface modification: The degummed fiber is immersed in yttrium nitrate ethanol solution, dried, and kept at 800-900℃ to generate a nano-yttrium oxide transition layer. The immersion is repeated 2-4 times. Then the fiber is immersed in ammonium dihydrogen phosphate aqueous solution, reacted in situ, and dried to generate a yttrium phosphate interface layer.

[0026] S3 matrix slurry preparation: Aluminum dihydrogen phosphate, zirconium oxychloride, yttrium oxide nanopowder and multi-scale composite filler are added to deionized water and ball-milled to obtain a slurry with a solid content of 55%-70%.

[0027] S4 Preforming and Curing: The modified fiber layup is preformed, immersed in the matrix slurry under normal pressure and ultrasonically impregnated, and then subjected to gradient curing (80℃→120℃→180℃→250℃).

[0028] S5 Microwave Sintering: The solidified green blank is heated to 1100-1250℃ in air at a rate of 5-10℃ / min, held for 30-90min, and then cooled in the furnace.

[0029] Specifically, in step S2, the concentration of the yttrium nitrate ethanol solution is 0.05-0.2 mol / L. The pH value of the ammonium dihydrogen phosphate aqueous solution is 2-3, and the water bath immersion temperature is 60-80℃.

[0030] Specifically, in step S3, the viscosity of the slurry after ball milling is 200-500 mPa·s; in step S4, the pressure of cold pressing preforming is 5-10 MPa.

[0031] Specifically, in step S4, the fiber layup method is 0° / 90° alternating layup.

[0032] Specifically, in step S4, the ultrasonic impregnation power is 100-200W; the gradient curing is specifically: 80℃ for 1 hour, 120℃ for 2 hours, 180℃ for 3 hours, and 250℃ for 2 hours.

[0033] Specifically, in step S5, the heating rate of microwave sintering is 8℃ / min, the holding temperature is 1200℃, and the holding time is 60min.

[0034] It has the following beneficial effects: (1) Significantly improved thermal shock resistance: The gradient interface layer achieves precise control of the fiber-matrix interface bonding strength, which avoids the corrosion of the fiber by the acid matrix and achieves fiber pull-out toughening through the weak interface effect; After 10 cycles of water cooling at 1300℃ to room temperature, the material retains ≥88% of its bending strength and has no macroscopic cracking, which is far superior to the retention rate of less than 70% in the existing technology.

[0035] (2) Excellent high temperature stability: The composite phosphate matrix suppresses the high temperature crystal transformation of aluminum phosphate through the doping of zirconium phosphate and yttrium oxide. There is no obvious volume change at 1400℃. The coefficient of thermal expansion is highly matched with that of alumina fiber. The long-term service temperature can reach 1350℃ and the short-term temperature resistance can reach 1450℃.

[0036] (3) Comprehensive optimization of mechanical properties: Multi-scale composite fillers and fibers form a synergistic toughening effect, h-BNNS induces crack deflection, mullite whiskers bridge cracks and hinder crack propagation; the material has a room temperature bending strength ≥280MPa, a bending strength at 1300℃ in air atmosphere ≥240MPa, and a high temperature performance retention rate ≥85%, which is better than existing materials of the same system.

[0037] (4) Low damage and high efficiency of process: The maximum sintering temperature throughout the process does not exceed 1250℃. Combined with microwave sintering, it avoids high-temperature grain growth and performance damage of alumina fibers. The gradient curing + atmospheric pressure ultrasonic impregnation process does not require hot pressing or high pressure vessel equipment. The production cycle is shortened by more than 60% compared with the existing technology, which is suitable for industrial mass production.

[0038] (5) High practicality: The material has the characteristics of high temperature resistance, thermal shock resistance, high mechanical properties and adjustable dielectric properties, and can be widely used in aerospace thermal protection, high temperature furnace and kiln structural parts, engine high temperature resistant parts, hypersonic aircraft wave-transparent components and other fields. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0040] Figure 1 This is a partially enlarged cross-sectional schematic diagram of a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to the present invention; Figure 2 This is a flowchart of the preparation method of a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to the present invention; Figure reference numerals: 1-Nano yttrium oxide (Y2O3) transition layer, 2-Yttrium phosphate (YPO4) interface layer, 3-Multi-scale composite filler. Detailed Implementation

[0041] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0042] The following detailed description of the implementation method of the present invention is in conjunction with the accompanying drawings. The description is only a partial embodiment and not all embodiments. For clarity, representations and descriptions unrelated to the present invention are omitted in the drawings and description.

[0043] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the following detailed description of the technical solution is provided. Obviously, the described embodiments are only a portion of the embodiments of this invention, not all of them, and should not be construed as limiting the scope of implementation of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0044] Example 1 This embodiment is a preferred implementation of the present invention.

[0045] In this embodiment, the specific mass proportions of the composite material components are as follows: 40% gradient modified alumina fiber, 50% composite phosphate matrix, and 10% multi-scale composite filler 3.

[0046] In this embodiment, the mass ratio of h-BNNS to mullite whiskers in the multi-scale composite filler 3 is 1:3; the molar ratio of the composite phosphate matrix n(aluminum phosphate):n(zirconium phosphate):n(yttrium oxide) = 100:25:5.

[0047] In this embodiment, the preparation steps are as follows: S1 alumina fiber degumming: Continuous α-alumina fiber fabric (Al2O3 content 99.5%, single filament diameter 10μm, tensile strength 1.8GPa), heat-preserved in air atmosphere at 520℃ for 1.5h, and then cooled to room temperature after degumming.

[0048] S2 fiber gradient modification: Prepare a 0.1 mol / L yttrium nitrate ethanol solution, vacuum impregnate for 15 min, dry at 90℃ for 30 min, repeat 3 times; keep warm at 850℃ for 45 min to generate nano-yttrium oxide transition layer 1 (thickness 20 nm); then immerse in an aqueous solution of ammonium dihydrogen phosphate at pH=2.5, impregnate in a water bath at 70℃ for 45 min to generate yttrium phosphate interface layer 2 (thickness 100 nm) in situ, rinse and dry at 110℃ for 1.5 h.

[0049] S3 matrix slurry preparation: Aluminum dihydrogen phosphate, zirconium oxychloride, and yttrium oxide nanopowder were added to deionized water according to the formula, multi-scale composite filler 3 was added, and ball milling was carried out for 3 hours to obtain a slurry with a solid content of 65% and a viscosity of 350 mPa·s, with a ball-to-material ratio of 3:1.

[0050] S4 Preforming and Curing: 10 layers of fiber fabric are laid at 0° / 90° and preformed by cold pressing at 8MPa; impregnation at normal pressure for 30min, supplemented by ultrasonic vibration at 150W; gradient curing: 80℃ for 1h → 120℃ for 2h → 180℃ for 3h → 250℃ for 2h to obtain the green body.

[0051] S5 Microwave Sintering: Under air atmosphere, heat to 1200℃ at 8℃ / min, hold for 60min, and cool with the furnace to obtain the finished product.

[0052] In this embodiment, the performance test results show that the thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material of this embodiment has a room temperature flexural strength of 312 MPa; a flexural strength of 268 MPa at 1300℃, with a high temperature retention rate of 85.9%; after 10 cycles of water cooling from 1300℃ to room temperature, the flexural strength is 278 MPa, with a strength retention rate of 89.1%, and no macroscopic cracks; after holding at 1400℃ for 2 hours, the volume change rate is ≤0.2%, and there is no crystal transformation.

[0053] Example 2 In this embodiment, the specific mass percentage of the composite material components is as follows: 35% gradient modified alumina fiber, 55% composite phosphate matrix, and 10% multi-scale composite filler.

[0054] In this embodiment, the mass ratio of h-BNNS to mullite whiskers in the multi-scale composite filler 3 is 1:2; the molar ratio of the composite phosphate matrix n(aluminum phosphate):n(zirconium phosphate):n(yttrium oxide) = 100:15:2.

[0055] In this embodiment, the preparation steps are as follows: S1 alumina fiber adhesive removal: heat treatment at 500℃ for 2 hours, followed by cooling after adhesive removal.

[0056] S2 fiber gradient modification: 0.05 mol / L yttrium nitrate ethanol solution, vacuum impregnation for 20 min, drying at 80℃ for 30 min, repeated twice; heat treatment at 800℃ for 60 min to generate yttrium oxide transition layer (thickness 12 nm); ammonium dihydrogen phosphate solution at pH=2, water bath impregnation at 60℃ for 60 min to generate yttrium phosphate interface layer 2 (thickness 50 nm), rinsed and dried at 100℃ for 2 h.

[0057] S3 matrix slurry preparation: ball milling for 2 hours, solid content 55%, viscosity 200 mPa·s.

[0058] S4 Pre-forming and Curing: 5MPa cold pressing pre-forming, immersion for 40min, 100W ultrasonication; gradient curing as in Example 1.

[0059] S5 microwave sintering: Heat to 1100℃ at 5℃ / min, hold for 90min, and cool with the furnace.

[0060] In this embodiment, the performance test results show that the thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material of this embodiment has a room temperature flexural strength of 286 MPa; a flexural strength of 245 MPa at 1300℃, and a high temperature retention rate of 85.7%; after 10 cycles of water cooling from 1300℃ to room temperature, the strength retention rate is 88.2%, and there are no macroscopic cracks.

[0061] Example 3 In this embodiment, the specific mass percentage of the composite material components is as follows: 50% gradient modified alumina fiber, 42% composite phosphate matrix, and 8% multi-scale composite filler.

[0062] In this embodiment, the mass ratio of h-BNNS to mullite whiskers in the multi-scale composite filler 3 is 1:4; the molar ratio of the composite phosphate matrix n(aluminum phosphate):n(zirconium phosphate):n(yttrium oxide) = 100:35:8.

[0063] In this embodiment, the preparation steps are as follows: S1 alumina fiber adhesive removal: heat at 550℃ for 1 hour, then cool after adhesive removal.

[0064] S2 fiber gradient modification: 0.2 mol / L yttrium nitrate ethanol solution, vacuum impregnation for 10 min, drying at 100℃ for 30 min, repeated 4 times; heat treatment at 900℃ for 30 min to generate yttrium oxide transition layer (thickness 28 nm); ammonium dihydrogen phosphate solution at pH=3, water bath impregnation at 80℃ for 30 min to generate yttrium phosphate interface layer 2 (thickness 170 nm), rinsed and dried at 120℃ for 1 h.

[0065] S3 matrix slurry preparation: ball milling for 4 hours, solid content 70%, viscosity 500 mPa·s.

[0066] S4 Pre-forming and Curing: 10MPa cold pressing pre-forming, immersion for 20min, 200W ultrasonication; gradient curing as in Example 1.

[0067] S5 microwave sintering: Heat to 1250℃ at 10℃ / min, hold for 30min, and cool with the furnace.

[0068] In this embodiment, the performance test results show that the thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material of this embodiment has a room temperature flexural strength of 325 MPa; a flexural strength of 279 MPa at 1300℃, and a high temperature retention rate of 85.8%; after 10 cycles of water cooling from 1300℃ to room temperature, the strength retention rate is 88.7%, and there are no macroscopic cracks.

[0069] In summary, Examples 1-3 showed that after 10 cycles of water cooling from 1300℃ to room temperature, the materials exhibited no macroscopic cracks, and the strength retention rate remained above 88%. The gradient-modified interface layer (nano-yttrium oxide transition layer 1 - yttrium phosphate interface layer 2) effectively controlled the bonding strength between the fiber and the matrix, acting as a stress buffer and preventing rapid crack propagation along the interface during thermal shock, thereby significantly improving the material's thermal shock resistance. The introduction of zirconium phosphate and yttrium oxide to construct the composite matrix not only optimized the thermal expansion matching but also significantly improved the high-temperature crystal stability of the matrix, avoiding performance degradation during high-temperature service. The multi-scale composite filler 3 effectively consumed fracture energy through crack deflection and bridging mechanisms, compensating for the high brittleness of the ceramic matrix and achieving a simultaneous improvement in room temperature strength and high-temperature toughness.

[0070] Comparative Example 1 This comparative example is a prior art solution without a gradient interface layer.

[0071] In this comparative example, except that the alumina fibers were not subjected to gradient interface modification and were directly used without adhesive, the other components and processes were completely consistent with those in Example 1.

[0072] In this comparative example, the performance test results show that the product has a room temperature flexural strength of 195 MPa, a flexural strength of 122 MPa at 1300℃, and a high temperature retention rate of 62.6%. After three cycles of water cooling from 1300℃ to room temperature, the material exhibits macroscopic cracking, and the strength retention rate is 41.2%.

[0073] Therefore, compared with the performance test data of Examples 1-3, Comparative Example 1 (without gradient interface layer) showed macroscopic cracking after only 3 thermal shock cycles, and the strength retention rate dropped sharply to 41.2%. This indicates that the gradient modified interface layer (nano-yttrium oxide transition layer 1-yttrium phosphate interface layer 2) can effectively regulate the bonding strength between the fiber and the matrix, play a stress buffering role, prevent cracks from rapidly propagating along the interface during thermal shock, and thus significantly improve the thermal shock resistance of the material.

[0074] Comparative Example 2 This comparative example uses a single aluminum phosphate matrix without composite doping.

[0075] In this comparative example, except that the matrix is ​​made of pure aluminum phosphate and is free of zirconium phosphate and yttrium oxide doping, the other components and processes are completely the same as in Example 1.

[0076] In this comparative example, the performance test results show that the product has a room temperature flexural strength of 265 MPa; a flexural strength of 178 MPa at 1300℃, and a high temperature retention rate of 67.2%; after 10 cycles of water cooling from 1300℃ to room temperature, the strength retention rate is 65.3%, and microcracks appear in the matrix.

[0077] Therefore, compared with the performance test data of Examples 1-3, Comparative Example 2 (single aluminum phosphate matrix) showed a flexural strength retention rate of only 67.2% at 1300℃, and microcracks appeared in the matrix after thermal shock, indicating that the single matrix has insufficient stability at high temperatures and poor thermal compatibility with the fiber. Examples 1-3 maintained a flexural strength retention rate of over 85% at high temperature (1300℃), and their microstructure remained intact. This indicates that the introduction of zirconium phosphate and yttrium oxide to construct the composite matrix not only optimized the thermal expansion matching but also significantly improved the high-temperature crystal stability of the matrix, avoiding performance degradation of the material during high-temperature service.

[0078] Comparative Example 3 This comparative example is without multi-scale composite filler 3.

[0079] In this comparative example, except for the absence of multi-scale composite filler 3, the other components and processes are completely consistent with those in Example 1.

[0080] In this comparative example, the performance test results show that the product has a room temperature flexural strength of 242 MPa, a flexural strength of 196 MPa at 1300℃, a high temperature retention rate of 81.0%, and a strength retention rate of 78.5% after 10 cycles of water cooling from 1300℃ to room temperature.

[0081] Therefore, compared with the performance test data of Examples 1-3, Comparative Example 3 (without multi-scale composite filler 3) maintained certain high-temperature performance (retention rate 81.0%), but its comprehensive mechanical properties at room temperature and after thermal shock were significantly lower than those of Examples 1-3. This indicates that the multi-scale composite filler 3 effectively consumed fracture energy through crack deflection, bridging and other mechanisms, making up for the defects of high brittleness in the ceramic matrix, and achieving simultaneous improvement of room temperature strength and high-temperature toughness.

[0082] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A thermal shock resistant alumina fiber-reinforced phosphate high-temperature resistant composite material, characterized in that, Components in the following mass percentages Composition: 30%-55% gradient modified alumina fiber reinforcement; 35%-60% composite phosphate matrix; 5%-15% (multi-scale composite filler); wherein, the surface of the gradient modified alumina fiber reinforcement has a gradient structure of nano-yttrium oxide transition layer (1) - in-situ generated yttrium phosphate interface layer (2); the composite phosphate matrix is ​​an aluminum phosphate-zirconium phosphate-yttrium oxide composite system, and its molar ratio is n(aluminum phosphate):n(zirconium phosphate):n(yttrium oxide)=100:(15-35):(2-8), n(aluminum phosphate):n(zirconium phosphate):n(yttrium oxide)=100:(15-35):(2-8); the multi-scale composite filler (3) is composed of hexagonal boron nitride nanosheets (h-BNNS) and mullite whiskers.

2. The thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to claim 1, characterized in that, The gradient modified alumina fiber reinforcement uses continuous polycrystalline αα-alumina fiber with an Al2O3 content ≥99% and a single filament diameter of 7-12μm; the thickness of the nano-yttrium oxide transition layer (1) is 10-30nm, and the thickness of the yttrium phosphate interface layer (2) is 40-170nm.

3. The thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to claim 1, characterized in that, In the multi-scale composite filler (3), the mass ratio of hexagonal boron nitride nanosheets (h-BNNS) to mullite whiskers is 1:(2-4); wherein the h-BNNS sheet diameter is 500-800nm ​​and the thickness is 5-15nm; the mullite whiskers have a diameter of 1-3μm and an aspect ratio of 15-30.

4. A method for preparing a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material, comprising preparing the thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1 fiber desizing: Keep the alumina fiber fabric at 500-550℃ for 1-2 hours to remove the surface organic sizing agent; S2 fiber gradient interface modification: The degummed fiber was immersed in yttrium ethanol solution, dried, and kept at 800-900℃ to generate a nano-yttrium oxide transition layer (1). The immersion was repeated 2-4 times. Then the fiber was immersed in ammonium dihydrogen phosphate aqueous solution, reacted in situ, and dried to generate a yttrium phosphate interface layer (2). S3 matrix slurry preparation: Aluminum dihydrogen phosphate, zirconium oxychloride, yttrium oxide nanopowder and multi-scale composite filler were added to deionized water and ball-milled to obtain a slurry with a solid content of 55%-70%. S4 Preforming and Curing: The modified fiber layup is preformed, immersed in the matrix slurry under normal pressure and ultrasonically impregnated, and then subjected to gradient curing (80℃→120℃→180℃→250℃). S5 Microwave Sintering: The solidified green blank is heated to 1100-1250℃ in air at a rate of 5-10℃ / min, held for 30-90min, and then cooled in the furnace.

5. The method for preparing a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to claim 4, characterized in that, In step S2, the concentration of the yttrium nitrate ethanol solution is 0.05-0.2 mol / L; the pH value of the ammonium dihydrogen phosphate aqueous solution is 2-3, and the water bath immersion temperature is 60-80℃.

6. The method for preparing a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to claim 4, characterized in that, In step S3, the viscosity of the slurry after ball milling is 200-500 mPa·s; in step S4, the pressure of cold pressing preforming is 5-10 MPa.

7. The method for preparing a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to claim 4, characterized in that, In step S4, the fiber layup method is 0° / 90° alternating layup.

8. The method for preparing a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to claim 4, characterized in that, In step S4, the ultrasonic impregnation power is 100-200W; the gradient curing specifically involves: holding at 80℃ for 1 hour, holding at 120℃ for 2 hours, holding at 180℃ for 3 hours, and holding at 250℃ for 2 hours.

9. The method for preparing a thermal shock resistant alumina fiber reinforced phosphate high-temperature resistant composite material according to claim 4, characterized in that, In step S5, the heating rate of microwave sintering is 8℃ / min, the holding temperature is 1200℃, and the holding time is 60min.

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