High-density alumina fiber reinforced alumina ceramic matrix composite and low-temperature preparation method thereof

Abstract

The application provides a high-density preparation method of an alumina fiber reinforced alumina ceramic matrix composite material and a low-temperature preparation method thereof. The method comprises the following steps: pretreating and degumming an alumina fiber preform; preparing a lanthanum phosphate interface solution; vacuum impregnating the pretreated alumina fiber preform in the lanthanum phosphate interface solution, and then taking out the preform to be placed and dried at low temperature, pre-sintered at low temperature, and cycled for multiple times until the interface layer reaches a set thickness, so that a preform containing a lanthanum phosphate interface layer is obtained; preparing an aluminum sol containing lithium fluoride; vacuum impregnating the preform containing the lanthanum phosphate interface layer in the aluminum sol containing lithium fluoride, and then taking out the preform to be placed and dried at low temperature, pre-sintered at low temperature, and cycled for multiple times until the weight gain is less than 1 wt%, and then performing normal pressure sintering in an air atmosphere, so that the alumina fiber reinforced alumina ceramic matrix composite material containing the lanthanum phosphate interface layer is obtained.

Description

Technical Field

[0001] This invention belongs to the technical field of fiber-reinforced ceramic matrix composites, specifically relating to a high-density alumina fiber-reinforced alumina ceramic matrix composite and its low-temperature preparation method. Background Technology

[0002] With the development of aerospace technology, the requirements for aerospace wave-transparent materials are becoming increasingly stringent. These materials must possess properties such as light weight, high strength, high temperature resistance, corrosion resistance, and electrical insulation. Furthermore, they must exhibit excellent wave-transmitting properties, capable of transmitting electromagnetic waves across various wavelengths to meet the communication, navigation, and reconnaissance requirements of aerospace vehicles. Aerospace wave-transparent materials have been widely used in the aerospace field. For example, satellite communication antennas are typically made of wave-transparent materials to ensure that satellites can penetrate the Earth's atmosphere to communicate with other satellites or ground stations. In addition, aerospace wave-transparent materials are also used to manufacture antenna windows or radomes for components such as aircraft, missiles, and satellites, protecting the materials from high temperatures and corrosion while ensuring the normal operation of communication and detection systems.

[0003] As structural materials, ceramic matrix composites not only meet physical properties such as wave transmission requirements but also possess excellent mechanical properties, avoiding problems like cracking and peeling of wave-transmitting coatings. This makes them promising for development and research in the field of high-temperature wave-transmitting materials. Continuous fiber-reinforced ceramic matrix composites retain the advantages of the matrix ceramic, such as high-temperature resistance, oxidation resistance, high hardness, high strength, and good high-temperature stability. The introduction of fiber reinforcement improves the toughness of the matrix ceramic through interfacial debonding, crack deflection, and bridging between the fiber and the matrix. This reduces the harmful effects of the high brittleness of the individual ceramic particles on practical applications. Furthermore, compared to dispersed reinforcement with particulate reinforcement, continuous fiber reinforcement has a more significant toughening effect, further improving the material's mechanical properties.

[0004] In the field of continuous fiber ceramic matrix composite microwave-transparent materials, current research mainly focuses on oxides and nitrides. For oxides, although silica fiber-reinforced silica has mature processing, stable performance, and good mechanical properties, its low operating temperature limits its application in high-temperature applications. Meanwhile, expensive nitride precursors and environmentally unfriendly solvents limit the application of nitride matrices in practical production. Alumina fiber-reinforced alumina matrix, due to its excellent high-temperature thermal stability, low dielectric constant, low coefficient of thermal expansion, environmental friendliness, and low cost, has become one of the most promising materials for research. However, due to the extremely similar composition of the reinforcement and matrix, a solid-state reaction occurs between the matrix and fibers during sintering, easily forming a strong interface. This reduces the matrix's ability to deflect cracks at the fiber-matrix interface and restricts fiber pull-out and bridging effects, thus reducing the toughness of the composite material and making it prone to brittle fracture (i.e., the bonding strength between the fiber and matrix is ​​equal to or even exceeds the internal fracture strength of the fiber, leading to brittle fracture of the composite material). However, the service temperature of alumina fibers is much lower than the sintering temperature for alumina matrix densification, making it difficult to balance the retained strength of the fibers and the sintering density of the matrix. Currently, porous matrices are used to reduce the bonding strength between the matrix and fibers in the composite material, causing the fiber fracture point to be far from the crack plateau in the matrix. Toughness is improved by using fiber bridging to hinder crack propagation and fiber pull-out, thereby generating frictional stress. While porous matrices improve the fracture toughness of the composite material, the porous structure reduces the contribution of the matrix to the mechanical properties of the composite sample, thus reducing the material's strength. A suitable interface layer primarily functions to modify the fiber surface, transfer loads, prevent crack propagation, deflect cracks, and inhibit diffusion, dissolution, reaction, and oxidation between the matrix and fiber at high temperatures. This ensures that the stress on the fiber itself is much greater than the stress introduced by the interface, promoting fiber pull-out and bridging, and improving toughening effects against brittle fracture. Common interface layers include pyrolytic carbon (PyC), boron nitride (BN), and monazite (LaPO4). However, PyC and BN have poor oxidation resistance at high temperatures; BN reacts with O2 in the air above 800℃ to generate B2O3 gas, which damages the internal structure of the material. The LaPO4 interface layer not only has a low dielectric constant, but the addition of LaPO4 further improves the thermal stability of the fiber. La has the largest ionic radius and is most effective in improving thermal stability; LaPO4 exhibits high thermal stability in both reducing and oxidizing environments. Meanwhile, LaPO4 and Al2O3 have good chemical compatibility and can form a sufficiently weak interface. This interface can prevent crack propagation through debonding and crack deflection, thereby improving fiber pull-out ability, ensuring the toughness of the composite material, and increasing the service life of the material.However, the preparation of the LaPO4 interface layer still has some shortcomings. In the preparation of 2.5D fiber composites, the LaPO4 interface layer is mainly synthesized through the reaction of precursors. Due to the relatively close arrangement between fibers, it is difficult to uniformly generate the multiphase mixed liquid phase on the fiber surface. Furthermore, the synthesized interface layer is prone to detachment and has poor adhesion. Additionally, for alumina fibers, another problem exists: excessively high sintering temperatures can cause abnormal grain growth during dynamic recrystallization, thus reducing the fiber's strength and toughness. Therefore, the alumina fibers prepared generally have a maximum operating temperature. Currently, the application of LaPO4 also includes adding LaPO4 during the preparation of alumina fibers. LaPO4 exists at the grain boundaries inside the fiber, and by inhibiting grain growth, it increases the service temperature of the fiber. However, the LaPO4 interface layer has little effect on inhibiting the growth of Al2O3 grains inside the fiber. At the same time, due to the limitation of the coefficient of thermal expansion, the coefficient of thermal expansion of LaPO4 is about 25% higher than that of alumina fibers. A thicker interface layer will lead to poor thermal shock resistance of the material. Therefore, the thickness of the interface layer should generally not exceed 500nm. The low content and location limit the effect of LaPO4 on inhibiting grain growth. Therefore, it is still necessary to lower the sintering temperature of the matrix to achieve higher density and crystallinity at a lower sintering temperature. Higher density and crystallinity, in turn, ensure its higher mechanical properties.

[0005] Therefore, the research team of this invention believes it is necessary to explore a preparation method that can produce composite materials that meet the performance requirements of aerospace wave-transparent materials. Summary of the Invention

[0006] The purpose of this invention is to address the defects or deficiencies in existing continuous fiber reinforced ceramic matrix composite material preparation technologies, and to provide a high-density alumina fiber reinforced alumina ceramic matrix composite material and its low-temperature preparation method.

[0007] The concept and principle of this invention:

[0008] In the fields of aerospace hot-end components and wave-transparent materials, oxide continuous fiber reinforced oxide matrix composites, in addition to possessing the advantages common to most ceramic matrix composites such as lightweight and high strength, exhibit excellent high-temperature oxidation resistance (especially air oxidation and water vapor oxidation) and good mechanical properties, making them promising for broad applications and high research potential. Alumina fiber reinforced alumina matrix is ​​one of the most promising materials among oxide continuous fiber reinforced oxide matrix composites. Therefore, our research team continues to explore the existing problems of alumina fiber reinforced alumina matrix.

[0009] Since the introduction of an interface layer is currently the most suitable measure, our research team has modified the existing process to address some of the problems in the preparation of LaPO4 interface layers. By improving the raw materials of the precursor, we have used lanthanum dihydrogen phosphate to prepare the LaPO4 interface layer, in order to solve the problems of easy detachment and poor adhesion of the interface layer.

[0010] Currently, the main methods for preparing 2.5D continuous fiber ceramic matrix composites include slurry method, precursor impregnation pyrolysis (PIP), sol-gel method, and chemical vapor infiltration (CVI). The slurry method, as a solid-state method, has a short molding cycle, but it requires high particle size control during the initial impregnation stage. Smaller particle sizes result in more uniform distribution within the fiber preform, but this also increases surface energy. Even with different surface properties, smaller particle sizes tend to lead to particle agglomeration, reducing surface energy and causing defects in the material. The precursors in the precursor impregnation pyrolysis method are generally organic polymers, which are toxic and pollute the environment. Furthermore, the precursor synthesis steps in the PIP method are cumbersome and costly, limiting its widespread use in industrial production. The chemical vapor infiltration method is not only more complex to operate but also requires more sophisticated experimental equipment, further increasing production costs. Sol-gel synthesis, as a liquid-phase synthesis method, not only boasts advantages such as simple process, environmental friendliness, and low cost, but also solves the uniformity problem caused by particle size in the liquid phase, where solutes exist in the form of ions and molecules, compared to the solid phase. Through drying and gelation, small solute particles precipitate from the liquid phase and adhere to the fiber surface, improving reactivity and lowering the reaction temperature. Combined with the assistance of matrix sintering aids, this allows for the production of relatively dense materials at lower temperatures. The numerous advantages of sol-gel synthesis also partially compensate for the long preparation cycle, making it suitable for practical production processes. Common sintering aids include MgO and SiO2, which mainly generate new phases by adding materials that can react with the matrix in the solid phase. However, while the formation of new phases lowers the sintering temperature, it also affects the properties of the raw materials. For example, the mullite phase (3Al2O3·2SiO2) formed by the solid-phase reaction of SiO2 and Al2O3, although improving high-temperature creep resistance compared to Al2O3, has worse mechanical properties at room temperature. Therefore, the research team of this invention hopes to reduce the sintering temperature while preserving the original phase.

[0011] After extensive research, the research team of this invention found that lithium fluoride best meets the expected requirements. Firstly, lithium fluoride has a melting point of 848℃, which allows it to be used as a sintering aid for oxide ceramics, lowering the sintering temperature or promoting the transformation of the material from an amorphous to a crystalline state at a lower sintering temperature, thereby increasing the density and crystallinity of the ceramic. This increased density and crystallinity improves the material's strength, and the load is transferred more effectively under stress. For continuous fiber ceramic matrix composites, stress diffusion tends to occur between interfacial layers, which also plays a positive role in fiber pull-out and maintaining toughness. Secondly, as a microwave dielectric ceramic additive, lithium fluoride can achieve a quality factor of 10. 6 The quantity is also sufficient to ensure that it will not affect the wave transmission performance of the product when used as an additive in wave-transparent materials. In addition, lithium fluoride has a low melting point and good stability. Therefore, the research team believes that it can be used as an additive that can both preserve the original phase and reduce the sintering temperature as desired in this invention.

[0012] To achieve the above objectives based on the above inventive concept, the technical solution provided by this invention is as follows:

[0013] A low-temperature preparation method for a high-density alumina fiber-reinforced alumina ceramic matrix composite material, characterized by the following steps:

[0014] 1) The pretreated alumina fiber preform (the pretreatment here is to remove the surface gel-like protective layer) is placed in a lanthanum phosphate interface solution for vacuum impregnation. After removal, it is dried at 60-200℃ and pre-sintered at 400-700℃ in sequence (i.e., low-temperature drying and low-temperature pre-sintering are performed in sequence). The impregnation-drying-pre-sintering process is repeated multiple times until the interface layer reaches the target thickness, and a preform containing a lanthanum phosphate interface layer is obtained.

[0015] The lanthanum phosphate interface solution is prepared by lanthanum dihydrogen phosphate solution and anhydrous ethanol;

[0016] 2) The preform containing the lanthanum phosphate interface layer obtained in step 1) is placed in an aluminum sol containing lithium fluoride for vacuum impregnation. After removal, it is dried at 60-200℃ and pre-sintered at 400-700℃ in sequence (i.e., low-temperature drying and low-temperature pre-sintering are performed in sequence). The impregnation-drying-pre-sintering process is repeated multiple times until the weight gain is less than 1wt%, and an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer is obtained.

[0017] 3) The alumina fiber reinforced alumina ceramic preform containing the lanthanum phosphate interface layer obtained in step 2) is sintered under normal pressure in an air atmosphere to finally obtain a high-density alumina fiber reinforced alumina ceramic matrix composite material, namely, the alumina fiber reinforced alumina ceramic matrix composite material containing the lanthanum phosphate interface layer.

[0018] The solid content of lithium fluoride in the alumina ceramic matrix is ​​0.01-5 wt%.

[0019] Furthermore, step 1) specifically involves:

[0020] 1.1) The pretreated alumina fiber preform was placed in a lanthanum phosphate interfacial solution for vacuum impregnation. The vacuum degree was 80-4000 Pa and the impregnation time was 0.5-24 h.

[0021] The solid content of lanthanum dihydrogen phosphate is 15-120 g / L, and the pH is 0.5-3; correspondingly, the content of lanthanum dihydrogen phosphate in the lanthanum phosphate interface solution is 0.4-3.2 wt%.

[0022] 1.2) After removal, perform low-temperature graded drying. First, dry at a temperature range of 60-78℃ for 3-6 hours to remove non-bound water. Then, dry at a temperature range of 150-200℃ for gelation for 3-10 hours.

[0023] 1.3) Continue with low-temperature pre-sintering at a temperature of 400-700℃ and a holding time of 1-6 hours;

[0024] 1.4) Repeat the impregnation-drying-pre-sintering process of steps 1.1)-1.3) until the interface layer reaches the target thickness, and a preform containing a lanthanum phosphate interface layer is obtained.

[0025] Furthermore, step 2) specifically involves:

[0026] 2.1) The preform containing the lanthanum phosphate interface layer was placed in an aluminum sol containing lithium fluoride for vacuum impregnation. The vacuum degree was 80-4000 Pa and the impregnation time was 0.5-24 h.

[0027] The lithium fluoride-containing aluminum sol is formed by uniformly mixing aluminum sol and lithium fluoride solution; wherein, in the lithium fluoride-containing aluminum sol, the mass ratio of lithium fluoride to aluminum oxide in the aluminum sol is 1:5-1:600.

[0028] In commonly used aluminum sol, the aluminum oxide content is 10-40%; the lithium fluoride solution is obtained by thoroughly stirring lithium fluoride powder and deionized water, and the solid content of lithium fluoride powder in the lithium fluoride solution is 1-30 g / L; during preparation, the aluminum sol and lithium fluoride solution are mixed in equal volumes.

[0029] 2.2) After removal, perform low-temperature graded drying. First, dry at a temperature range of 80-99℃ for 3-6 hours to remove non-bound water. Then, dry at a temperature of 150-200℃ for gelation for 3-10 hours.

[0030] 2.3) Continue with low-temperature pre-sintering at a temperature of 400-700℃ and a holding time of 1-6 hours;

[0031] 2.4) Repeat the impregnation-drying-pre-sintering process of steps 2.1)-2.3) until the weight gain is less than 1 wt%, to obtain an alumina fiber-reinforced alumina ceramic preform containing a lanthanum phosphate interface layer.

[0032] Furthermore, in step 3), the sintering temperature is 800-1000℃ and the sintering time is 1-6h.

[0033] Further, in step 1), the alumina fiber preform is a 2.5D fabric woven from alumina fiber bundles, the weaving method is shallow cross-linking, the volume fraction is 30%-50%, the pretreatment temperature is 400-700℃, and the time is 1-6h.

[0034] Furthermore, in step 1.4), repeat 1-6 times.

[0035] Further, in step 2.4), repeat 12-26 times.

[0036] Meanwhile, the present invention also provides a high-density alumina fiber-reinforced alumina ceramic matrix composite material prepared by the above-mentioned low-temperature preparation method, and an aerospace wave-transparent material product based on the material.

[0037] The advantages of this invention are:

[0038] 1. This invention utilizes a lanthanum dihydrogen phosphate solution to prepare a lanthanum phosphate interface layer, unlike the current mainstream method of preparing lanthanum phosphate interface layers through synthesis. The 2.5D continuous alumina fiber preform used in this invention has a relatively tight bond between the fibers. Synthetic methods tend to generate lanthanum phosphate particles on the surface of the preform, hindering further reaction within the preform and leading to inhomogeneity of the surface and internal interface layer. This invention avoids the problem of uneven and poor bonding between lanthanum phosphate and fibers generated under vacuum, which can lead to interface detachment due to gas generation during subsequent drying steps. Lanthanum phosphate is directly generated through the thermal decomposition of lanthanum dihydrogen phosphate, simplifying the process and improving the bonding degree and uniformity between the fibers and the interface layer. Furthermore, because lanthanum phosphate does not react with alumina at high temperatures, a weak interface can be formed. This weak interface can promote the formation of bridging sites and improve the fracture toughness of the material.

[0039] 2. In this invention, lithium fluoride is added to aluminum sol as a sol precursor for the impregnation-drying-sintering process of fiber preforms. Under the same impregnation cycle, the addition of lithium fluoride significantly reduces the sintering temperature of the composite matrix, increases the density and crystallinity of the alumina matrix, and prepares a composite material with a higher degree of densification. The increased densification significantly improves the strength of the composite material.

[0040] 3. This invention employs a sol-gel method, utilizing staged drying to reduce bubble generation during the drying process and prevent the formation of internal pores due to untimely gas escape. Since different solvents have different boiling points, different drying times and temperatures need to be set accordingly. The first-stage drying temperature is below the solvent's boiling point, drying the solution through evaporation to remove unbound water and prevent pores from forming inside the material due to solvent boiling. Because oxide continuous fiber reinforced oxide composites are sensitive to pores, the mechanical properties of the composite are highly dependent on the material's density and porosity; reducing internal pores improves the material's mechanical properties. The second-stage drying stage gels the bound water in the solid phase material after the initial drying. Without removing bound water, the gas phase at high temperatures... Escape can disrupt the sintering process, leading to a decrease in the mechanical properties of the sample. Furthermore, the introduction of a pre-sintering-sintering process involves multiple cycles. Due to the difference in thermal expansion coefficients between the matrix, interface layer, and fibers, repeated heating and cooling impregnation cycles introduce residual stress into the solid-phase material. This residual stress is often tensile stress, which promotes crack propagation and reduces the maximum load the material can withstand. Pre-sintering reduces residual tensile stress and also minimizes damage to the fibers caused by the matrix during sintering. Even at lower sintering temperatures, repeated sintering processes can lead to thermal fatigue and creep in the fibers, causing damage. The pre-sintering-sintering process improves fiber retention strength, thereby enhancing the mechanical properties of the composite material.

[0041] 4. By uniformly adding lithium fluoride to the alumina matrix, this invention ensures that the material can obtain a high-performance continuous alumina fiber reinforced alumina composite material with high crystallinity, high density, low porosity, and low fiber damage at a lower sintering temperature. This reduces the sintering and densification temperature of the alumina matrix, avoids the loss of alumina fibers due to high-temperature sintering, improves the mechanical properties of the composite material, and enhances the application potential of this material in actual production. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the preparation process of the present invention;

[0043] Figure 2 This is a schematic XRD pattern of a lithium fluoride-containing matrix sintered at 1000℃ for 2 hours.

[0044] Figure 3 This is a schematic diagram of the XRD pattern of a lithium fluoride-containing matrix sintered at 800℃ for 2 hours.

[0045] Figure 4 Al2O 3f Image of LaPO4 / Al2O3·LiF composite material sample;

[0046] Figure 5 This is a diagram showing the fiber pull-out at the three-point bending fracture section of the composite material.

[0047] Figure 6 This is a schematic diagram of the composite material EDS. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0049] This invention provides a low-temperature preparation method for high-density alumina fiber-reinforced alumina ceramic matrix composites, the preparation process as follows: Figure 1 As shown, the main steps include:

[0050] Pretreatment of fiber preforms:

[0051] The fiber preform used in this invention is a 2.5D fiber fabric woven from alumina fiber bundles using a shallow cross-linking weaving method, with a fiber volume fraction between 30% and 50%. The fiber preform needs to be degummed before use by treating it at 400-700℃ for 1-6 hours to obtain the degummed fiber preform.

[0052] Preparation of lanthanum phosphate interfacial solution (also known as interfacial precursor solution):

[0053] The raw materials used for the lanthanum dihydrogen phosphate interface solution are lanthanum dihydrogen phosphate solution and anhydrous ethanol. The lanthanum dihydrogen phosphate solution is quantitatively mixed in anhydrous ethanol and stirred evenly to form a solution. The solid content of lanthanum dihydrogen phosphate in the lanthanum dihydrogen phosphate interface solution is 15-120 g / L, and the pH is between 0.5 and 3.

[0054] Preform for preparing the lanthanum phosphate interface layer:

[0055] The pretreated alumina fiber preform is vacuum impregnated in a lanthanum phosphate interface solution at a vacuum level of 80-4000 Pa for 0.5-24 h. The preform is then removed and subjected to low-temperature graded drying at a temperature of 60-200℃ for 6-16 h. After that, it is subjected to low-temperature pre-sintering at a temperature of 400-700℃ for 1-6 h. The impregnation-drying-pre-sintering process is repeated 1-6 times until the target thickness is achieved, thus obtaining a preform containing a lanthanum phosphate interface layer.

[0056] Preparation of lithium fluoride-containing aluminum sol (also known as matrix precursor solution):

[0057] The alumina content is 10-40%; lithium fluoride powder is used as solvent, and the solid content in the solution is 1-30 g / L; the lithium fluoride aqueous solution and aluminum sol are mixed evenly and stirred thoroughly to obtain an aluminum sol containing lithium fluoride; the mass ratio of lithium fluoride to alumina in the aluminum sol is 1:5-1:600.

[0058] Preparation of alumina fiber-reinforced alumina ceramic preforms with a lanthanum phosphate interface layer:

[0059] The preform containing the lanthanum phosphate interface layer was vacuum impregnated in an aluminum sol containing lithium fluoride at a vacuum level of 80-4000 Pa for 0.5-24 h. The preform was then removed and placed in an oven for low-temperature graded drying at a temperature of 60-200℃ for 6-16 h. The preform was then pre-sintered at a low temperature of 400-700℃ for 1-6 h. The above impregnation-drying-pre-sintering process was repeated 12-26 times until the sample weight gain was less than 1 wt%, thus obtaining an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer.

[0060] Preparation of target composite material:

[0061] The alumina fiber-reinforced alumina ceramic preform containing a lanthanum phosphate interface layer was placed in a high-temperature furnace and sintered under normal pressure air atmosphere. The sintering temperature was 800-1000℃ and the sintering time was 1-6h, finally obtaining alumina fiber-reinforced alumina ceramic matrix composite material samples.

[0062] According to the above preparation process, the present invention has the following specific embodiments:

[0063] Example 1

[0064] 1) Take 30% by volume of 2.5D alumina fiber preform and place it in a muffle furnace for degumming. The degumming temperature is 600℃ and the time is 1h.

[0065] 2) Prepare a lanthanum phosphate interfacial solution with a solid content of 15 g / L and a pH of 1.2, wherein the lanthanum dihydrogen phosphate content is 0.4 wt%.

[0066] 3) The fiber preform obtained in step 1) is fully immersed in the lanthanum phosphate interface solution prepared in step 2), placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level is below 0.4 kPa, timing begins, and evacuation continues for another 30 minutes. The impregnated preform is then placed in an oven and dried at 80°C for 10 hours. After drying, a pre-sintering treatment is performed at 600°C for 2 hours. The impregnation-drying-pre-sintering process is repeated 6 times to obtain a preform containing a lanthanum phosphate interface layer with a thickness of 90 nm.

[0067] 4) Prepare an aluminum sol containing lithium fluoride with a lithium fluoride solid content of 2.9 g / L and deionized water as the solvent. Mix the lithium fluoride aqueous solution and the aluminum sol at a volume ratio of 1:1 (using neutral aluminum sol produced by Xi'an Kequan Laboratory Equipment Co., Ltd., with an alumina content of 20%, an error margin of 1%, and an aluminum-chloride ratio of 1.1:1), and stir thoroughly to obtain the aluminum sol containing lithium fluoride.

[0068] 5) The preform containing the lanthanum phosphate interface layer was fully immersed in an aluminum sol containing lithium fluoride, placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level was below 0.4 kPa, timing was started, and the vacuum was continued for another 30 minutes. The impregnated preform was then removed and placed in an oven for low-temperature drying at 80℃ for 10 hours. After drying, it underwent low-temperature pre-sintering at 700℃ for 1 hour. The impregnation-drying-pre-sintering process was repeated 23 times. The sample weight gain was less than 1 wt%, resulting in an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer.

[0069] 6) Finally, the alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer was placed in a high-temperature furnace and sintered under normal pressure air atmosphere. The sintering temperature was 950℃ and the sintering time was 1h. After sintering, the final alumina fiber-reinforced alumina ceramic matrix composite material sample with a diameter of 50*50*3mm was obtained.

[0070] The solid content of LiF in the matrix was found to be 0.8 wt%, and the density was 2.41 g / cm³. 3 The porosity is 18.2%, the flexural strength is 65.1 MPa, and the fracture displacement is 0.134 mm.

[0071] Example 2

[0072] 1) Take 40% by volume of 2.5D alumina fiber preform and place it in a muffle furnace for degumming. The degumming temperature is 600℃ and the time is 2h.

[0073] 2) Prepare a lanthanum phosphate interfacial solution with a solid content of 30 g / L and a pH of 1.2, and a lanthanum dihydrogen phosphate content of 0.8 wt%.

[0074] 3) The fiber preform obtained in step 1) is thoroughly immersed in the lanthanum phosphate interface solution prepared in step 2), placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level is below 0.4 kPa, timing begins, and evacuation continues for another 30 minutes. The impregnated preform is then placed in an oven and dried at 90°C for 8 hours. After drying, a pre-sintering treatment is performed at 600°C for 2 hours. The impregnation-drying-pre-sintering process is repeated four times to obtain a preform containing a lanthanum phosphate interface layer with a thickness of 120 nm.

[0075] 4) Prepare an aluminum sol containing lithium fluoride with a lithium fluoride solid content of 1 g / L and deionized water as the solvent. Mix the lithium fluoride aqueous solution and the aluminum sol at a volume ratio of 1:1 (using neutral aluminum sol produced by Xi'an Kequan Laboratory Equipment Co., Ltd., with an alumina content of 20%, an error margin of 1%, and an aluminum-chloride ratio of 1.1:1), and stir thoroughly to obtain the aluminum sol containing lithium fluoride.

[0076] 5) The preform containing the lanthanum phosphate interface layer was fully immersed in an aluminum sol containing lithium fluoride, placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level was below 0.4 kPa, timing was started, and the vacuum was continued for 6 hours. The impregnated preform was then removed and placed in an oven for low-temperature drying at 80℃ for 15 hours. After drying, it underwent low-temperature pre-sintering at 700℃ for 1 hour. The impregnation-drying-pre-sintering process was repeated 26 times. The sample weight gain was less than 1 wt%, resulting in an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer.

[0077] 6) Finally, the alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer was placed in a high-temperature furnace and sintered under normal pressure air atmosphere. The sintering temperature was 900℃ and the sintering time was 4h. After sintering, the final alumina fiber-reinforced alumina ceramic matrix composite material sample with a diameter of 50*50*3mm was obtained.

[0078] The solid content of LiF in the matrix was found to be 0.1 wt%, and the density was 2.36 g / cm³. 3 The porosity is 18.6%, the flexural strength is 60.4 MPa, and the fracture displacement is 0.144 mm.

[0079] Example 3

[0080] 1) Take 50% by volume of 2.5D alumina fiber preform and place it in a muffle furnace for degumming. The degumming temperature is 600℃ and the time is 2h.

[0081] 2) Prepare a lanthanum dihydrogen phosphate interfacial solution with a solid content of 60 g / L and a pH of 1.1, containing 1.2 wt% lanthanum dihydrogen phosphate.

[0082] 3) The fiber preform obtained in step 1) is fully immersed in the lanthanum phosphate interface solution prepared in step 2), placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level is below 0.4 kPa, timing begins, and evacuation continues for 12 hours. The impregnated preform is then placed in an oven and dried at 90°C for 4 hours. The drying temperature is then increased to 150°C, and drying continues for another 8 hours. After drying, a pre-sintering treatment is performed at 400°C for 6 hours. The impregnation-drying-pre-sintering process is repeated three times to obtain a preform containing a lanthanum phosphate interface layer with a thickness of 180 nm.

[0083] 4) Prepare an aluminum sol containing lithium fluoride with a lithium fluoride solid content of 10 g / L and deionized water as the solvent. Mix the lithium fluoride aqueous solution and the aluminum sol at a volume ratio of 1:1 (using neutral aluminum sol produced by Xi'an Kequan Laboratory Equipment Co., Ltd., with an alumina content of 20%, an error margin of 1%, and an aluminum-chloride ratio of 1.1:1), and stir thoroughly to obtain the aluminum sol containing lithium fluoride.

[0084] 5) The preform containing the lanthanum phosphate interface layer was fully immersed in an aluminum sol containing lithium fluoride, placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level was below 0.4 kPa, timing was started, and the vacuum was continued for another 60 minutes. The impregnated preform was then removed and placed in an oven for low-temperature drying at 90℃ for 4 hours. The drying temperature was then increased to 150℃, and drying continued for another 8 hours. After drying, low-temperature pre-sintering was performed at 500℃ for 3 hours. The impregnation-drying-pre-sintering process was repeated 12 times. The sample weight gain was less than 1 wt%, resulting in an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer.

[0085] 6) Finally, the alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer was placed in a high-temperature furnace and sintered under normal pressure and air atmosphere. The sintering temperature was 1000℃ and the sintering time was 2 hours. After sintering, a final alumina fiber-reinforced alumina ceramic matrix composite material sample of 50*50*3mm was obtained. Its XRD pattern is shown in the figure. Figure 2 As shown, after adding LiF, the crystallinity of the α-Al2O3 phase is further improved at a sintering temperature of 1000℃, approaching the crystallinity of pure Al2O3 powder sintered at 1300-1400℃. At the same time, due to the presence of Li, a solid solution is formed with alumina. The presence of Li in the interstitial spaces of alumina causes lattice distortion and the generation of a new phase.

[0086] The solid content of LiF in the matrix was found to be 2.7 wt%, and the density was 2.26 g / cm³. 3The porosity is 19.9%, the flexural strength is 62.7 MPa, and the fracture displacement is 0.126 mm.

[0087] Example 4

[0088] 1) Take 50% by volume of 2.5D alumina fiber preform and place it in a muffle furnace for degumming. The degumming temperature is 600℃ and the time is 2h.

[0089] 2) Prepare a lanthanum phosphate interfacial solution with a solid content of 120 g / L and a pH of 0.8, and a lanthanum dihydrogen phosphate content of 2.4 wt%.

[0090] 3) The fiber preform obtained in step 1) is fully immersed in the lanthanum phosphate interface solution prepared in step 2), placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level is below 0.4 kPa, timing begins, and evacuation continues for 24 hours. The impregnated preform is then placed in an oven and dried at 90°C for 4 hours. The drying temperature is then increased to 200°C, and drying continues for another 8 hours. After drying, a pre-sintering treatment is performed at 500°C for 2 hours. The impregnation-drying-pre-sintering process is repeated twice to obtain a preform containing a lanthanum phosphate interface layer with a thickness of 300 nm.

[0091] 4) Prepare an aluminum sol containing lithium fluoride with a lithium fluoride solid content of 15 g / L and deionized water as the solvent. Mix the lithium fluoride aqueous solution and the aluminum sol at a volume ratio of 1:1 (using neutral aluminum sol produced by Xi'an Kequan Laboratory Equipment Co., Ltd., with an alumina content of 20%, an error margin of 1%, and an aluminum-chloride ratio of 1.1:1), and stir thoroughly to obtain the aluminum sol containing lithium fluoride.

[0092] 5) The preform containing the lanthanum phosphate interface layer was fully immersed in an aluminum sol containing lithium fluoride, placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level was below 0.4 kPa, timing was started, and evacuation continued for 60 minutes. The impregnated preform was then removed and placed in an oven for low-temperature drying at 90℃ for 2 hours. The drying temperature was then increased to 200℃, and drying continued for 4 hours. After drying, low-temperature pre-sintering was performed at 400℃ for 6 hours. The impregnation-drying-pre-sintering process was repeated 16 times. The sample weight gain was less than 1 wt%, resulting in an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer.

[0093] 6) Finally, the alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer was placed in a high-temperature furnace and sintered under normal pressure air atmosphere. The sintering temperature was 800℃ and the sintering time was 6h. After sintering, the final alumina fiber-reinforced alumina ceramic matrix composite material sample with a diameter of 50*50*3mm was obtained.

[0094] The solid content of LiF in the matrix was found to be 5 wt%, and the density was 2.51 g / cm³. 3 The porosity is 16.9%, the flexural strength is 64.5 MPa, and the fracture displacement is 0.129 mm.

[0095] Example 5

[0096] 1) Take 50% by volume of 2.5D alumina fiber preform and place it in a muffle furnace for degumming. The degumming temperature is 600℃ and the time is 2h.

[0097] 2) Prepare a lanthanum phosphate interfacial solution with a solid content of 120 g / L and a pH of 0.8, and a lanthanum dihydrogen phosphate content of 2.4 wt%.

[0098] 3) The fiber preform obtained in step 1) is fully immersed in the lanthanum phosphate interface solution prepared in step 2), placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level is below 0.4 kPa, timing begins, and evacuation continues for 8 hours. The impregnated preform is then placed in an oven and dried at 85°C for 6 hours. The drying temperature is then increased to 200°C, and drying continues for another 10 hours. After drying, a pre-sintering treatment is performed at 600°C for 2 hours. The impregnation-drying-pre-sintering process is repeated once to obtain a preform containing a lanthanum phosphate interface layer with a thickness of 20 nm.

[0099] 4) Prepare an aluminum sol containing lithium fluoride with a lithium fluoride solid content of 10 g / L and deionized water as the solvent. Mix the lithium fluoride aqueous solution and the aluminum sol at a volume ratio of 1:1 (using neutral aluminum sol produced by Xi'an Kequan Laboratory Equipment Co., Ltd., with an alumina content of 20%, an error margin of 1%, and an aluminum-chloride ratio of 1.1:1), and stir thoroughly to obtain the aluminum sol containing lithium fluoride.

[0100] 5) The preform containing the lanthanum phosphate interface layer was fully immersed in an aluminum sol containing lithium fluoride, placed in a vacuum impregnation tank, and evacuated for 10 minutes. When the vacuum level was below 0.4 kPa, timing was started, and evacuation continued for 60 minutes. The impregnated preform was then removed and placed in an oven for low-temperature drying at 90℃ for 2 hours. The drying temperature was then increased to 200℃, and drying continued for 4 hours. After drying, low-temperature pre-sintering was performed at 400℃ for 6 hours. The impregnation-drying-pre-sintering process was repeated 16 times. The sample weight gain was less than 1 wt%, resulting in an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer.

[0101] 6) Finally, the alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer was placed in a high-temperature furnace and sintered under normal pressure and air atmosphere. The sintering temperature was 800℃ and the sintering time was 2 hours. After sintering, a final alumina fiber-reinforced alumina ceramic matrix composite material sample of 50*50*3mm was obtained. Its XRD pattern is shown in the figure. Figure 3 As shown, it is clear that after adding LiF, crystalline alumina has been formed at a sintering temperature of 800℃. Most of it is the stable α-Al2O3 phase, which is also the phase that the research team of this invention expected. At the same time, there is a small amount of transition phase that has not been completely transformed into the stable α-Al2O3 phase.

[0102] The solid content of LiF in the matrix was found to be 3.3 wt%, and the density was 2.44 g / cm³. 3 The porosity is 16.3%, the flexural strength is 67.5 MPa, and the fracture displacement is 0.131 mm.

[0103] Figure 4 The image shows a sample of the composite material of the present invention as described in the foregoing embodiment. It can be seen from the image that the composite material prepared by the method of the present invention has a high degree of densification. Figure 5 The image shows the fiber pull-out section of the composite material at three-point bending fracture. As can be seen from the image, the main advantage of continuous fiber composite materials compared to traditional ceramic sheets is the improvement in toughness due to the introduction of fibers. The main toughening mechanism of fibers is fiber pull-out and bridging. The large amount of fiber pull-out in the SEM image confirms the existence of the sample's toughness from a meso-microscopic perspective. Figure 6 This is a schematic diagram of EDS for the composite material, showing the distribution of P and Si elements in the EDS surface scanning analysis. P is a unique element in the interface layer, reflecting the distribution of the lanthanum phosphate interface layer. In the figure, it is uniformly distributed around the fiber. The fiber specifications used in this embodiment are 72% Al2O3 and 28% SiO2, while silicon only exists inside the fiber, reflecting the distribution of alumina fiber in the material.

[0104] Comparative Example 1

[0105] 1) Take 40% by volume of 2.5D alumina fiber preform and place it in a muffle furnace for degumming. The degumming temperature is 600℃ and the time is 2h.

[0106] 2) Prepare a lanthanum phosphate interfacial solution with a solid content of 15 g / L and a pH of 1.4, and a lanthanum dihydrogen phosphate content of 0.4 wt%.

[0107] 3) Thoroughly immerse the fiber preform obtained in step 1) in the lanthanum phosphate interface solution prepared in step 2), place it in a vacuum impregnation tank, and evacuate for 10 minutes. When the vacuum level is below 0.4 kPa, start timing and continue evacuating for another 30 minutes. Place the impregnated preform in an oven and dry at 80℃ for 10 hours. After drying, perform pre-sintering treatment at 600℃ for 2 hours. Repeat the impregnation-drying-pre-sintering process twice to obtain a preform containing a lanthanum phosphate interface layer with a thickness of 20 nm.

[0108] 4) Prepare aluminum sol using neutral aluminum sol produced by Xi'an Kequan Laboratory Equipment Co., Ltd., with an aluminum oxide content of 20%, a tolerance of 1%, and an aluminum-chlorine ratio of 1.1:1.

[0109] 5) The preform containing the lanthanum phosphate interface layer was fully immersed in alumina sol and placed in a vacuum impregnation tank. Vacuuming was performed for 10 minutes. When the vacuum level was below 0.4 kPa, timing was started, and vacuuming continued for another 30 minutes. The impregnated preform was then removed and placed in an oven for low-temperature drying at 80℃ for 10 hours. After drying, low-temperature pre-sintering was performed at 600℃ for 2 hours. This impregnation-drying-pre-sintering process was repeated 21 times. The sample weight gain was less than 1 wt%, resulting in an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer.

[0110] 6) Finally, the alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer was placed in a high-temperature furnace and sintered under normal pressure air atmosphere. The sintering temperature was 1300℃ and the sintering time was 2h. After sintering, a final alumina fiber-reinforced alumina ceramic matrix composite material sample of 50*50*3mm was obtained.

[0111] The density was measured to be 2.01 g / cm³. 3 The porosity is 23.2%, the flexural strength is 51.5 MPa, and the fracture displacement is 0.098 mm.

[0112] Comparing the performance data of the embodiments and comparative examples, it can be seen that the density of the above-described embodiment samples is higher than that of Comparative Example 1, while the porosity is also lower, indicating that the lithium fluoride-containing matrix has a higher density than the lithium fluoride-free matrix. Furthermore, the flexural strength is higher than that of Comparative Example 1, indicating better strength. The fracture displacement is also higher, indicating a more significant fiber pull-out effect, and the addition of the interface layer improves the toughness of the composite material. Therefore, the method of the present invention improves both strength and toughness, comprehensively enhancing the mechanical properties of the composite material, making it highly promising for practical applications.

[0113] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A low-temperature preparation method for a high-density alumina fiber-reinforced alumina ceramic matrix composite material, characterized in that, Includes the following steps: 1) The pretreated alumina fiber preform is placed in a lanthanum phosphate interface solution for vacuum impregnation. After removal, it is successively dried at 60-200℃ and pre-sintered at 400-700℃. The impregnation-drying-pre-sintering process is repeated multiple times until the interface layer reaches the target thickness, and a preform containing a lanthanum phosphate interface layer is obtained. The lanthanum phosphate interface solution is prepared by lanthanum dihydrogen phosphate solution and anhydrous ethanol; The alumina fiber preform is a 2.5D fabric woven from alumina fiber bundles, using a shallow cross-linking method, with a volume fraction of 30%-50%. 2) The preform containing the lanthanum phosphate interface layer obtained in step 1) is placed in an aluminum sol containing lithium fluoride for vacuum impregnation. After removal, it is successively dried at 60-200℃ and pre-sintered at 400-700℃. The impregnation-drying-pre-sintering process is repeated multiple times until the weight gain is less than 1 wt%, thus obtaining an alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer. 3) The alumina fiber-reinforced alumina ceramic preform containing the lanthanum phosphate interface layer obtained in step 2) is sintered at atmospheric pressure in an air atmosphere at 800-1000℃ to finally obtain a high-density alumina fiber-reinforced alumina ceramic matrix composite material.

2. The low-temperature preparation method according to claim 1, characterized in that, Step 1) Specifically: 1.1) The pretreated alumina fiber preform is placed in a lanthanum phosphate interfacial solution for vacuum impregnation. The vacuum degree is 80-4000 Pa and the impregnation time is 0.5-24 h. In the lanthanum dihydrogen phosphate interfacial solution, the solid content of lanthanum dihydrogen phosphate is 15-120 g / L, and the pH is 0.5-3; 1.2) After removal, perform low-temperature graded drying. First, dry at 60-78℃ for 3-6 hours, and then dry at 150-200℃ for 3-10 hours. 1.3) Perform low-temperature pre-sintering at a temperature of 400-700℃ for 1-6 hours. 1.4) Repeat the impregnation-drying-pre-sintering process of steps 1.1)-1.3) until the interface layer reaches the target thickness, and a preform containing a lanthanum phosphate interface layer is obtained.

3. The low-temperature preparation method according to claim 1 or 2, characterized in that, Step 2) specifically involves: 2.1) The preform containing the lanthanum phosphate interface layer obtained in step 1) is placed in an aluminum sol containing lithium fluoride for vacuum impregnation. The vacuum degree is 80-4000 Pa and the impregnation time is 0.5-24 h. The lithium fluoride-containing aluminum sol is formed by uniformly mixing aluminum sol and lithium fluoride solution; wherein the mass ratio of lithium fluoride to aluminum oxide in the aluminum sol is 1:5-1:

600. 2.2) After removal, perform low-temperature graded drying. First, dry at 80-99℃ for 3-6 hours, and then dry at 150-200℃ for 3-10 hours. 2.3) Perform low-temperature pre-sintering at a temperature of 400-700℃ for 1-6 hours. 2.4) Repeat the impregnation-drying-pre-sintering process of steps 2.1)-2.3) until the weight gain is less than 1 wt%, to obtain an alumina fiber-reinforced alumina ceramic preform containing a lanthanum phosphate interface layer.

4. The low-temperature preparation method according to claim 3, characterized in that: In step 3), the sintering time is 1-6 hours.

5. The low-temperature preparation method according to claim 4, characterized in that: In step 1), the pretreatment temperature of the alumina fiber preform is 400-700℃ and the time is 1-6h.

6. The low-temperature preparation method according to claim 2, characterized in that: In step 1.4), repeat 1-6 times.

7. The low-temperature preparation method according to claim 3, characterized in that: In step 2.4), repeat 12-26 times.

8. A high-density alumina fiber-reinforced alumina ceramic matrix composite material, characterized in that: It is prepared by any of the low-temperature preparation methods described in claims 1-7.

9. A type of aerospace wave-transparent material product, characterized in that: The aerospace wave-transparent material used is prepared by any of the low-temperature preparation methods described in claims 1-7.

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