Alumina-based thermal shock resistant composite material and process for preparing the same

Abstract

This invention discloses an alumina-based thermal shock resistant composite material and its preparation process, belonging to the field of composite material technology. The process includes gradient preform preparation, reinforcement interface modification, directional arrangement of thermal stress buffer units, in-situ reaction electric field-assisted sintering, and steam pre-oxidation post-treatment steps. This invention employs a three-layer micro-gradient structure design. The surface layer relies on nano-alumina and SiC whiskers, possessing both high hardness and wear resistance. The middle layer, through phase transformation toughening, effectively absorbs crack propagation energy and inhibits crack extension. The core layer uses porous mullite composite, whose low coefficient of thermal expansion significantly buffers thermal stress. Structurally, this design balances high strength and high toughness, improving the material's flexural strength, fracture toughness, and thermal shock resistance, and preventing through-crack formation under thermal shock.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to an alumina-based thermal shock resistant composite material and its preparation process, which is particularly suitable for applications with stringent requirements for high-temperature thermal shock resistance and mechanical properties, such as aerospace hot-end components, high-temperature kiln furniture, metallurgical linings, and engine thermal insulation components. Background Technology

[0002] Alumina ceramics possess high temperature resistance, corrosion resistance, high hardness, excellent chemical stability, and insulation properties, making them one of the most widely used ceramic materials in high-temperature structural applications. They have irreplaceable application value in industries such as metallurgy, chemical engineering, aerospace, and machinery manufacturing, and are often used to manufacture high-temperature load-bearing components, thermal insulation bushings, wear-resistant parts, and other devices.

[0003] Traditional alumina-based ceramic materials are mostly homogeneous structures, typically prepared using conventional pressureless sintering or hot-pressing processes. To ensure material strength, a high-density, fine-grained microstructure is often desired. Some existing technologies involve external additives... Reinforcing phases such as SiC and carbon fiber can improve the toughness of materials. There are also technical solutions that improve the overall performance of ceramics by adjusting sintering parameters, in an attempt to balance high-temperature mechanical properties and structural stability.

[0004] However, existing alumina-based ceramic materials have insurmountable technical drawbacks: 1. A single homogeneous structure cannot simultaneously achieve high strength and high toughness. While high density ensures strength, internal stress cannot be effectively released, making it prone to penetrating cracks under thermal shock conditions, resulting in extremely poor thermal shock resistance. 2. The bonding strength between the enhanced phase and the matrix is ​​difficult to control. If the bonding is too tight, thermal stress cannot be released. If the bonding is too loose, the load transfer efficiency is low. The interface is prone to failure at high temperatures and has no self-healing ability. 3. The material can only passively resist thermal stress and lacks active buffering and temperature control mechanisms. After thermal shock cycling, the strength retention rate is extremely low, the critical temperature difference is small, and the service life is short. 4. Adding an external reinforcing phase can easily introduce interfacial impurities, contaminate the matrix, and result in numerous interfacial bonding defects, low sintering density, and limited improvement in mechanical properties. 5. Conventional sintering processes involve high temperatures and high energy consumption, and tend to produce coarse grains, which further exacerbates the brittleness of the material and makes it difficult to meet the requirements of high-temperature rapid cooling and heating conditions. Summary of the Invention

[0005] To overcome the above problems, this invention aims to propose an alumina-based thermal shock resistant composite material and its preparation process, in order to solve the defects of the prior art as mentioned in the background.

[0006] Therefore, the specific technical solution adopted by the present invention is as follows: According to one aspect of the present invention, a process for preparing an alumina-based thermal shock resistant composite material is provided, comprising the following steps: S1: Prepare a three-layer slurry according to the following mass proportions: the surface slurry consists of 100 parts of nano-alumina with a particle size ≤50nm, 10 parts of SiC whiskers, 1.5-2% ammonium polyacrylate dispersant, 3-5% polyvinyl alcohol binder, and deionized water; the SiC whiskers have an aspect ratio of 15-25. The middle layer slurry consists of 100 parts of alumina and 20 parts of nano-alumina with a particle size of 0.5-1μm. The toughening particles are mixed with an equal amount of dispersant, an equal amount of binder, and deionized water. The core layer slurry is mixed with 100 parts alumina, 30 parts porous mullite with a porosity of 30-40%, an equal amount of dispersant, an equal amount of binder, and deionized water. The three slurries are ball-milled until they are uniformly dispersed and free of agglomeration, then cast into films in sequence, and then pressed at a pressure of 15-20 MPa for 10-15 minutes to obtain a three-layer gradient composite preform. S2: Deposited on the surface of carbon fiber using chemical vapor deposition process. The composite gradient coating is deposited at a temperature of 850-900℃ and a pressure of 500-800Pa. Argon is introduced as the carrier gas with a flow rate of 80-120mL / min. The coating is deposited to a thickness of 200nm, and the interfacial shear strength is adjusted to 20-80MPa. Modified carbon fibers are incorporated into the gradient composite preform. S3: Select hollow alumina microspheres with a diameter of 50-200μm, pre-fill the microspheres with Sn-Bi low melting point alloy with a melting point of 139℃, add the filled hollow alumina microspheres to the core layer slurry at a dosage of 8-12% of the solid phase mass of the core layer slurry, apply a directional pressure of 5-10MPa during the slurry curing stage to make the microspheres uniformly distributed inside the core layer without agglomeration; S4: Add Al powder and... according to a molar ratio of 4:3 The powder is thoroughly mixed with each layer of slurry, and then sintered using spark plasma sintering. The pulse current is set to 1000A, the pulse frequency to 10Hz, and the sintering pressure to 30MPa. The temperature is increased to 1300℃ at a rate of 80-100℃ / min, and held for 15-20 minutes to achieve in-situ generation. The whisker-toughened phase was cooled to room temperature in the furnace. S5: The sintered green body is placed in a steam atmosphere, the processing temperature is controlled at 1200℃, the steam flow rate is 50-60mL / min, and the temperature is maintained for 2h to generate a 1μm thick boehmite coating on the surface of the green body, thus obtaining an alumina-based thermal shock resistant composite material.

[0007] Optionally, in S1, the ball milling speed is 300-400 r / min, the ball milling time is 4-6 h, the solid content of the slurry is controlled at 65-70%, and zirconia grinding balls are used for the ball milling with a material-to-ball mass ratio of 1:3.

[0008] Optionally, in S2, the heating rate of chemical vapor deposition is 10-15℃ / min, the entire deposition process is isolated from air, and the furnace is cooled to room temperature after deposition.

[0009] Optionally, in S3, the wall thickness of the hollow alumina microspheres is 2-5 μm; the alloy filling adopts a vacuum impregnation process with a vacuum degree of 0.06-0.08 MPa, an impregnation temperature of 150-160℃, an impregnation time of 20-30 min, and repeated impregnation 1-2 times to ensure that there are no voids or bubbles inside the microspheres.

[0010] Optionally, in S4, the entire process of spark plasma sintering is evacuated, with the vacuum level controlled at 5-10 Pa. After sintering, the furnace is cooled at a rate of 50-60 °C / min.

[0011] Optionally, in S4, after in-situ reaction sintering, a diameter of 50 nm and an aspect ratio greater than 20 are formed in the composite matrix. Whiskers.

[0012] Optionally, in S5, the steam pre-oxidation treatment uses saturated steam, and the heating rate during the treatment stage is 20-30℃ / min.

[0013] Optionally, in the three-layer gradient composite preform, the surface layer thickness accounts for 20-25% of the total thickness, the intermediate layer thickness accounts for 30-35% of the total thickness, and the core layer thickness accounts for 40-50% of the total thickness.

[0014] An alumina-based thermal shock resistant composite material, wherein the composite material has a three-layer gradient structure of surface layer-intermediate layer-core layer, and a reinforcing phase is provided between the reinforcing phase and the matrix. The self-healing interface layer contains hollow alumina microspheres filled with Sn-Bi alloy embedded in the core layer, and in-situ grown substrates... Whisker toughening phase, with boehmite anti-oxidation buffer layer covering the material surface.

[0015] To address the various shortcomings of existing alumina-based ceramic materials, this invention overcomes these technical limitations through a synergistic approach of structural design, interface control, and process optimization. Specific beneficial effects are as follows: 1. To address the shortcomings of a single homogeneous structure in simultaneously achieving high strength and high toughness, and in the difficulty of releasing thermal stress, this invention employs a three-layer micro-gradient structure design. The surface layer relies on nano-alumina and SiC whiskers, possessing both high hardness and wear resistance; the middle layer... Phase transformation toughening effectively absorbs crack propagation energy and prevents crack extension; the core layer uses porous mullite composite, and its low coefficient of thermal expansion can significantly buffer thermal stress. Structurally, it balances high strength and high toughness, and the material's bending strength, fracture toughness, and thermal shock resistance are all improved, preventing the generation of through cracks under thermal shock.

[0016] 2. To address the shortcomings of difficult-to-control interfacial bonding strength between the reinforcing phase and the matrix, easy failure at high temperatures, and lack of self-healing ability, this invention sets at the interface... The composite self-healing coating, at low temperatures, uses BN as a lubricant, allowing interface slippage to release thermal stress; at high temperatures (>800℃)... The softening process forms a glassy phase, which can seal internal microcracks and achieve interface self-healing. The interface shear strength can be controlled between 20-80 MPa, balancing interface load transfer efficiency and stress release effect, and avoiding interface debonding and failure problems.

[0017] 3. To address the shortcomings of materials that can only passively resist thermal stress and lack an active buffering mechanism, this invention introduces hollow alumina microspheres filled with Sn-Bi alloy into the core layer as an active thermal stress buffering unit. Under rapid heating conditions, the alloy melts and absorbs heat, slowing down the heating rate of the matrix. Under rapid cooling conditions, the alloy solidifies and expands, compensating for the shrinkage stress of the matrix, significantly reducing thermal stress damage and extending service life.

[0018] 4. To address the shortcomings of added reinforcing phases, such as the easy introduction of interfacial impurities and low sintering density, this invention employs in-situ reaction sintering to generate in-situ... The whisker-toughened phase has a clean and impurity-free interface with the matrix, is tightly bonded, and has no interface defects. At the same time, the heat released by the reaction can assist sintering, reduce sintering temperature, reduce energy consumption, inhibit grain coarsening, increase material density, and significantly improve mechanical properties.

[0019] 5. To address the drawbacks of conventional sintering processes, such as high energy consumption and low strength retention after thermal shock, this invention employs electric field-assisted discharge plasma sintering to refine grains and reduce sintering energy consumption. Combined with steam pre-oxidation post-treatment, a boehmite coating is generated on the material surface. During thermal shock, the coating dehydrates and absorbs heat to form a microporous buffer layer, further releasing stress and improving the strength retention after thermal shock, thus adapting to harsh working conditions of high temperature and rapid cooling and heating. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. Specific conditions not specified in the embodiments shall be performed according to conventional conditions or manufacturer's recommended conditions. Reagents or instruments whose manufacturers are not specified are commercially available products. All quantities mentioned in the present invention are parts by weight, and performance tests shall be performed using national standard methods.

[0021] Example 1 Preparation process (1) Gradient green body forming: Prepare the surface slurry: 100 parts of nano-alumina with a particle size of 40nm, 10 parts of SiC whiskers with an aspect ratio of 20, 1.8% ammonium polyacrylate dispersant, 4% polyvinyl alcohol binder, and deionized water, and ball mill and mix them; Prepare the intermediate layer slurry: 100 parts of alumina, 20 parts of SiC whiskers with a particle size of 0.8μm Particles, equal amounts of dispersant and binder are ball-milled and mixed; core layer slurry is prepared: 100 parts alumina, 30 parts porous mullite with a porosity of 35%, equal amounts of dispersant and binder are ball-milled and mixed; sequentially cast and molded, held under 18MPa pressure for 12min, and stacked to obtain a gradient composite preform.

[0022] (2) Interface modification treatment: A 200 nm thick layer was deposited on the carbon fiber surface by chemical vapor deposition. Composite coating, deposition temperature 880℃, deposition pressure 600Pa, argon flow rate 100mL / min, and interfacial shear strength adjusted to 50MPa.

[0023] (3) Directional arrangement of thermal stress buffer units: Hollow alumina microspheres with a diameter of 100 μm are selected and filled with Sn-Bi alloy with a melting point of 139℃. The amount of microspheres added is 10% of the mass of the core solid phase. They are incorporated into the core slurry and arranged uniformly under a directional pressure of 8 MPa. The alloy filling inside the hollow alumina microspheres is carried out by vacuum impregnation process: The hollow alumina microspheres are placed in a vacuum impregnation tank and the vacuum degree is evacuated to 0.06~0.08 MPa and held for 30~40 min. Then, molten Sn-Bi alloy is injected and the impregnation temperature is 150~160℃. The impregnation is held for 20~30 min and the vacuum impregnation is repeated 1~2 times to ensure that the microspheres are fully filled, without gaps or bubbles.

[0024] (4) In-situ reaction sintering: Add Al powder and... The powder was mixed with each layer of slurry and sintered using spark plasma sintering at a pulse current of 1000A, a frequency of 10Hz, a pressure of 30MPa, a heating rate of 90℃ / min, and a holding temperature of 1300℃ for 18min, followed by furnace cooling. Characterization using scanning electron microscopy (SEM) showed that the above in-situ reaction and sintering process could generate a uniformly distributed powder in situ within the alumina matrix. whiskers, obtained The whiskers have a diameter of approximately 50 nm and an aspect ratio greater than 20. The whiskers do not exhibit significant agglomeration and are densely bonded to the matrix interface, effectively playing a role in crack deflection and bridging toughening.

[0025] (5) Post-treatment: Water vapor is introduced at 1200℃ and kept at the temperature for 2 hours. The water vapor flow rate is 55 mL / min to obtain the finished composite material.

[0026] Comparative Example 1 Conventional single homogeneous alumina ceramic was used, without gradient structure, self-healing interface, or thermal stress buffer unit. It was conventionally sintered at 1600℃ without pressure and held for 2 hours without water vapor pre-oxidation treatment. The proportions of other raw materials were the same as in Example 1.

[0027] Comparative Example 2 Using conventional external addition The reinforced alumina ceramic has no gradient structure, no self-healing interface, and no in-situ toughening. It is conventionally hot-pressed and sintered without electric field-assisted sintering or steam treatment. The proportions of other raw materials are the same as in Example 1.

[0028] Performance test results In this invention The diameter and aspect ratio of the whiskers were characterized using scanning electron microscopy (SEM). Ten fields of view were randomly selected for statistical analysis. The results showed that the whisker diameter was concentrated around 50 nm, and the aspect ratios were all greater than 20. The data reproducibility was good. The test data shows that the alumina-based thermal shock resistant composite material prepared by this invention has a density, mechanical properties, and thermal shock resistance that are far superior to conventional alumina ceramics. All properties are improved in a synergistic way, which completely solves the defects of the prior art and is suitable for the use requirements of high temperature thermal shock resistant conditions.

[0029] Example 2 Adjust process parameters: in step (1), the surface layer thickness accounts for 22% of the total thickness, the intermediate layer accounts for 33%, and the core layer accounts for 45%; in step (2), the deposition temperature is adjusted to 870℃ and the interface shear strength is adjusted to 60MPa; in step (4), the sintering holding time is adjusted to 20min, and the remaining raw material ratios and preparation steps are exactly the same as in Example 1.

[0030] Testing showed that the composite material prepared in this embodiment had a density of 98.8%, a flexural strength of 790 MPa, and a fracture toughness of [missing information]. It has undergone 50 thermal shock cycles at 800℃, and its strength retention rate after thermal shock is 85%, with all performance parameters meeting the standards.

[0031] Example 3 Adjusting process parameters: In step (3), the diameter of the hollow alumina microspheres is selected as 150 μm, and the alloy content is adjusted to 11%; in step (5), the water vapor flow rate is adjusted to 60 mL / min, and the remaining raw material ratios and preparation steps are exactly the same as in Example 1.

[0032] Testing showed that the composite material prepared in this embodiment had a density of 99.0%, a flexural strength of 800 MPa, and a fracture toughness of [missing information]. It has undergone 51 thermal shock cycles at 800℃, and its strength retention rate after thermal shock is 86%, demonstrating stable and compliant performance.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

[0034] Although the present invention has been disclosed above with reference to preferred embodiments, the embodiments are merely examples for illustrative purposes and are not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. The scope of protection claimed by the present invention should be determined by the claims.

Claims

1. A process for the preparation of an alumina-based thermal shock resistant composite material, characterized in that, The steps are as follows: S1: Prepare a three-layer structure slurry according to the mass fraction, including a surface slurry, an intermediate slurry, and a core slurry; ball mill the three slurries separately until they are evenly dispersed and free of agglomeration, then cast them into films in sequence, and then press and stack them to obtain a three-layer gradient composite preform; S2: using chemical vapor deposition process, depositing on the surface of carbon fiber Composite gradient coating, argon gas as carrier gas, depositing to the coating thickness of 200 nm, regulating the interface shear strength to 20-80 MPa, and incorporating the modified carbon fiber into the gradient composite blank. S3: Select hollow alumina microspheres with a diameter of 50-200μm, pre-fill the microspheres with Sn-Bi low melting point alloy with a melting point of 139℃, add the filled hollow alumina microspheres to the core layer slurry at a dosage of 8-12% of the solid phase mass of the core layer slurry, apply a directional pressure of 5-10MPa during the slurry curing stage to make the microspheres uniformly distributed inside the core layer without agglomeration; S4: Add Al powder and... according to a molar ratio of 4:3 The powder is thoroughly and evenly mixed with each layer of slurry, and then sintered using spark plasma sintering. S5: The sintered green body is placed in a steam atmosphere, the processing temperature is controlled at 1200℃, the steam flow rate is 50-60mL / min, and the temperature is maintained for 2h to generate a 1μm thick boehmite coating on the surface of the green body, thus obtaining an alumina-based thermal shock resistant composite material.

2. The alumina-based thermal shock resistant composite material and its preparation process according to claim 1, characterized in that, The surface slurry is composed of 100 parts of nano-alumina with a particle size ≤50nm, 10 parts of SiC whiskers, 1.5-2% ammonium polyacrylate dispersant, 3-5% polyvinyl alcohol binder, and deionized water, with the SiC whiskers having an aspect ratio of 15-25; the intermediate layer slurry is composed of 100 parts of alumina and 20 parts of nano-alumina with a particle size of 0.5-1μm. The toughening particles are mixed with an equal amount of dispersant, an equal amount of binder, and deionized water; the core layer slurry is mixed with 100 parts alumina, 30 parts porous mullite with a porosity of 30-40%, an equal amount of dispersant, an equal amount of binder, and deionized water.

3. The alumina-based thermal shock resistant composite material and its preparation process according to claim 2, characterized in that, In S1, the ball milling speed is 300-400 r / min, the ball milling time is 4-6 h, the solid content of the slurry is controlled at 65-70%, the ball milling uses zirconia grinding balls, the material-to-ball mass ratio is 1:3, and the holding pressure in S1 is 15-20 MPa, the holding time is 10-15 min.

4. The alumina-based thermal shock resistant composite material and its preparation process according to claim 1, characterized in that, In S2, the heating rate of chemical vapor deposition is 10-15℃ / min. Air is isolated throughout the deposition process. After deposition, the furnace is cooled to room temperature. The deposition temperature in S2 is 850-900℃, the deposition pressure is 500-800Pa, and the carrier gas flow rate is 80-120mL / min.

5. The alumina-based thermal shock resistant composite material and its preparation process according to claim 1, characterized in that, In S3, the wall thickness of the hollow alumina microspheres is 2-5 μm; the alloy filling adopts a vacuum impregnation process with a vacuum degree of 0.06-0.08 MPa, an impregnation temperature of 150-160℃, an impregnation time of 20-30 min, and repeated impregnation 1-2 times to ensure that there are no voids or bubbles inside the microspheres.

6. The alumina-based thermal shock resistant composite material and its preparation process according to claim 1, characterized in that, In S4, the entire spark plasma sintering process is carried out under vacuum, with the vacuum level controlled at 5-10 Pa. After sintering, the furnace is cooled at a rate of 50-60℃ / min. In S4, the pulse current is set to 1000A, the pulse frequency to 10Hz, and the sintering pressure to 30MPa. The temperature is increased to 1300℃ at a rate of 80-100℃ / min and held for 15-20 minutes, resulting in in-situ generation. The whisker-toughened phase was cooled to room temperature in the furnace.

7. The alumina-based thermal shock resistant composite material and its preparation process according to claim 1, characterized in that, In S4, after in-situ reaction sintering, a diameter of 50 nm and an aspect ratio greater than 20 are formed within the composite matrix. Whiskers.

8. The alumina-based thermal shock resistant composite material and its preparation process according to claim 1, characterized in that, In S5, the steam pre-oxidation treatment uses saturated steam, and the heating rate during the treatment stage is 20-30℃ / min.

9. The alumina-based thermal shock resistant composite material and its preparation process according to claim 1, characterized in that, In a three-layer gradient composite preform, the surface layer accounts for 20-25% of the total thickness, the middle layer accounts for 30-35% of the total thickness, and the core layer accounts for 40-50% of the total thickness.

10. An alumina-based thermal shock resistant composite material, characterized in that, The composite material is prepared by the preparation process described in any one of claims 1-9; the composite material has a three-layer gradient structure of surface layer-intermediate layer-core layer, and a reinforcing phase is provided between the matrix and the matrix. The self-healing interface layer contains hollow alumina microspheres filled with Sn-Bi alloy embedded in the core layer, and in-situ grown substrates... Whisker toughening phase, with boehmite anti-oxidation buffer layer covering the material surface.

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