Preparation method of carbon-ceramic composite material

Abstract

The invention relates to the technical field of preparation of ceramic-based composite materials, and discloses a preparation method of a carbon-ceramic composite material, which comprises the following steps: placing a colloidal suspension containing chopped carbon fibers and ceramic precursor nanoparticles in an ultrasonic standing wave field to directionally arrange a fiber network, synchronously triggering sol-gel transformation to realize in-situ curing of the fiber network, and drying to obtain the carbon-ceramic composite material. And drying and sintering to obtain the composite material. According to the method, zero-stress combination of a fiber-matrix interface is realized in a liquid phase environment through space-time coordination of sound field dynamic arrangement and gel static curing, so that microcracks caused by thermal mismatch in a traditional process are fundamentally avoided; and a direct-current electric field generation trigger mechanism is combined, so that the global consistency of large-size component gelation is ensured, and the material has microstructure programmability and macroscopic performance stability.

Description

Technical Field

[0001] The present invention relates to a preparation method of a carbon-ceramic composite material, belonging to the technical field of the preparation of ceramic matrix composite materials. Background Art

[0002] In the field of ceramic matrix composite materials, especially in the preparation of carbon-ceramic composite materials, chemical vapor infiltration (CVI) and polymer impregnation pyrolysis (PIP) have long been the mainstream processes. Such technologies usually require prefabricating a carbon fiber preform, and then forcing ceramic precursors to fill the fiber gaps through multiple high-temperature cycles; when applied to scenarios such as aircraft brake discs that need to withstand complex alternating stresses, this paradigm of first forming a skeleton and then filling gradually exposes deep-seated contradictions: in each high-temperature infiltration or pyrolysis process, while increasing the density, a thermal shock is applied to the fiber-matrix interface, and cumulative damage leads to the initiation of microcracks and even delamination failure during the service of the material.

[0003] Although the industry has tried to alleviate the problems by optimizing the preform weaving or reducing the single-treatment temperature, two fundamental limitations have always been unable to be avoided: First, the physical weaving process is difficult to achieve the complex gradient orientation design of fibers, limiting the performance optimization space of components under non-uniform loads; Second, to compensate for the insufficient densification of the low-temperature process, it is necessary to increase the number of cycles, further amplifying the risk of interface damage and the energy consumption burden.

[0004] Specifically, the existing technologies mainly have three bottlenecks: 1. There is an inherent conflict between the high-temperature densification process and the protection of structural integrity, and multiple thermal cycles induce irreversible interface damage; 2. The static physical structure of the fiber preform is difficult to adapt to the requirements of the dynamic stress field, and the microstructural designability is limited; 3. Multiple high-temperature treatments lead to high energy consumption, and the process complexity and material performance show an inverted relationship; the above contradictions are particularly prominent in high-end application scenarios such as aerospace and nuclear energy equipment, becoming the key obstacles restricting the expansion of carbon-ceramic composite materials to more severe working conditions. Therefore, how to synchronously achieve the precise and controllable arrangement of the fiber network and the uniform densification of the matrix under mild conditions, fundamentally avoid thermal stress damage, and obtain carbon-ceramic composite materials with designable properties has become the technical problem to be solved by the present invention. Summary of the Invention

[0005] The present invention provides a preparation method of a carbon-ceramic composite material, and its main purpose is to solve the technical problems of difficult to balance high-temperature densification and structural integrity, limited microstructural designability, and excessive energy consumption during the preparation process of carbon-ceramic materials.

[0006] To achieve the above object, a preparation method of a carbon-ceramic composite material provided by the present invention includes the following steps: Step a, providing a colloidal suspension, the colloidal suspension containing chopped carbon fibers and ceramic matrix precursor nanoparticles; Step b: Place the colloidal suspension in an ultrasonic standing wave field. The ultrasonic standing wave field drives the short carbon fibers to align directionally in the colloidal suspension through acoustic radiation force, forming an ordered fiber network. Step c: Under the condition that the ordered fiber network remains directionally aligned, trigger the sol-gel transition of the colloidal suspension to form a gel solid that in-situ cures the ordered fiber network. The sol-gel transition is completed within the temperature range of zero degrees Celsius to sixty degrees Celsius. Step d: Dry and sinter the gel solid to obtain a carbon-ceramic composite material. The sintering temperature is controlled within the temperature control range of 1000 degrees Celsius to 1400 degrees Celsius.

[0007] Preferably, in step b, by adjusting the frequency, phase of the ultrasonic standing wave field or the layout of the ultrasonic transducers, control the alignment direction of the short carbon fibers to achieve at least one of the fiber orientations of zero-degree orthogonality, ninety-degree orthogonality or quasi-isotropy, or a gradient orientation distributed along a specific function curve.

[0008] Preferably, in step c, the way to trigger the sol-gel transition of the colloidal suspension is: introduce a chemical reagent that can change its pH value into the colloidal suspension.

[0009] Preferably, the chemical reagent is ammonia water.

[0010] Preferably, in step a, the ceramic matrix precursor nanoparticles are silica sol or alumina sol.

[0011] Preferably, in step a, the short carbon fibers and the ceramic matrix precursor nanoparticles are co-dispersed in a low-viscosity liquid medium, and the low-viscosity liquid medium is water or ethanol.

[0012] Preferably, it further includes: during the process of step b, real-time monitor the acoustic transmission characteristics when the sound wave passes through the colloidal suspension; and when the change rate ( ) of the acoustic transmission characteristics is lower than a preset threshold ( ), stop applying the ultrasonic standing wave field and execute step c, where the acoustic transmission characteristics include acoustic impedance or sound velocity.

[0013] Preferably, the acoustic transmission characteristics when the sound wave passes through the colloidal suspension are obtained through the electrical response parameters of the ultrasonic transducer or by the pick-up on the opposite side of the mold receiving the sound wave detection signal.

[0014] Preferably, in step c, the way to trigger the sol-gel transition of the colloidal suspension is: apply a direct current electric field to the colloidal suspension, and in-situ generate ions that change its pH value inside the colloidal suspension through electrolysis, and the ions achieve the synchronous gelation of the colloidal suspension.

[0015] Preferably, a DC electric field is applied by designing the mold carrying the colloidal suspension as an electrode. Under the action of electrolysis, hydroxide ions are generated at the cathode and hydrogen ions are generated at the anode, and the hydroxide ions adjust the pH value of the colloidal suspension to trigger the sol-gel transition.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. While the ultrasonic standing wave field drives the short carbon fibers to be oriented and arranged to form an ordered network, the sol-gel transition is synchronously triggered in the liquid phase environment. This instant synergy between the dynamic arrangement process and the static curing mechanism avoids the structural disturbance caused by the transfer of the fiber preform in the traditional process, enabling the fiber-matrix interface to form a complete bond in a zero-stress state, and essentially avoiding the microcrack initiation path caused by the thermal expansion mismatch.

[0017] 2. By using the mold carrying the colloidal suspension as an electrolysis electrode to apply a DC electric field, hydroxide / hydrogen ions are in-situ generated inside the colloidal suspension to adjust the pH value. This endogenous triggering mechanism enables the gelation reaction to be synchronously initiated within the volume of the component, avoiding the concentration gradient effect of the external catalyst diffusion, and ensuring that the spatial orientation fidelity of the fiber network and the matrix curing uniformity in the thick-section component reach a self-consistent balance at the molecular scale. At the same time, by utilizing the dual functions of the ultrasonic transducer for both transmitting and receiving, and analyzing the inflection point of the impedance spectrum characteristics of the sound wave propagating in the suspension, the phase transition process of the fiber orientation state from disorder to order is real-time sensed. This criterion based on the evolution of the intrinsic physical quantity of the medium replaces the empirical time control mode, enabling the acoustic field removal timing and the gel triggering node to form an adaptive match, and avoiding the cavitation damage caused by energy overload or the structural defect of insufficient arrangement.

[0018] 3. The suspension dispersion system of short carbon fibers in the nano-ceramic sol, combined with the acoustic radiation force manipulation and the room-temperature sol-gel transition, decouples the traditional high-temperature pyrolysis densification process into mild physical-chemical sequential reactions. This path reconstruction that replaces the gas-phase infiltration with the liquid-phase environment and the mechanical weaving with the field-controlled arrangement enables the preparation of ceramic matrix composites to achieve a synergistic leap in the sintering temperature window shift and the single-forming efficiency while maintaining the programmability of the microstructure. Description of the Drawings

[0019] Figure 1 It is a functional flowchart of the preparation process of the carbon-ceramic composite material of the present invention; Figure 2 It is a temperature control curve graph of the drying stage and the sintering stage of the present invention; Figure 3 It is a real-time monitoring and control timing diagram of fiber arrangement driven by the ultrasonic field of the present invention; Figure 4 It is a temperature-time curve graph of different process stages of the present invention; Figure 5It is a comparison chart of sintering temperatures.

[0020] The realization of the purpose, functional features, and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Specific Embodiments

[0021] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] The embodiments of the present application provide a method for preparing a carbon-ceramic composite material, and the method includes the following steps: Step a: Provide a colloidal suspension, which includes chopped carbon fibers and ceramic matrix precursor nanoparticles; Step b: Place the colloidal suspension in an ultrasonic standing wave field, and the ultrasonic standing wave field drives the chopped carbon fibers to align directionally in the colloidal suspension through acoustic radiation force to form an ordered fiber network; Step c: Under the condition that the ordered fiber network maintains its directional arrangement, trigger the sol-gel transition of the colloidal suspension to form a gel solidified body that in-situ cures the ordered fiber network. The sol-gel transition is completed within the temperature range from zero degrees Celsius to sixty degrees Celsius; Step d: Dry and sinter the gel solidified body to obtain a carbon-ceramic composite material, and the sintering temperature is controlled within the temperature control range of 1000 degrees Celsius to 1400 degrees Celsius.

[0023] Preferably, in step b, by regulating the frequency, phase of the ultrasonic standing wave field or the layout of the ultrasonic transducers, control the arrangement direction of the chopped carbon fibers to achieve at least one of the fiber orientations of zero-degree orthogonality, ninety-degree orthogonality, or quasi-isotropic, or a gradient orientation distributed along a specific function curve.

[0024] Preferably, in step c, the way to trigger the sol-gel transition of the colloidal suspension is: introduce a chemical reagent that can change its pH value into the colloidal suspension.

[0025] Preferably, the chemical reagent is ammonia water.

[0026] Preferably, in step a, the ceramic matrix precursor nanoparticles are silica sol or alumina sol.

[0027] Preferably, in step a, the chopped carbon fibers and the ceramic matrix precursor nanoparticles are jointly dispersed in a low-viscosity liquid medium, and the low-viscosity liquid medium is water or ethanol.

[0028] Preferably, it further includes: during the process of step b, real-time monitoring of the acoustic transmission characteristics when the sound wave passes through the colloidal suspension; and when the change rate ( ) is lower than a preset threshold ( When it reaches ( ), stop applying the ultrasonic standing wave field and perform step c, where the acoustic transmission characteristics include acoustic impedance or sound velocity.

[0029] Preferably, the acoustic transmission characteristics when the sound wave passes through the colloidal suspension are obtained through the electrical response parameters of the ultrasonic transducer or through the acoustic wave detection signal received by the pickup on the opposite side of the mold.

[0030] Preferably, in step c, the way to trigger the sol-gel transition of the colloidal suspension is: apply a direct current electric field to the colloidal suspension, and in-situ generate ions that change its pH value inside the colloidal suspension through electrolysis, and the ions achieve the synchronous gelation of the colloidal suspension.

[0031] Preferably, the direct current electric field is applied by designing the mold carrying the colloidal suspension as an electrode. Under the action of electrolysis, hydroxide ions are generated at the cathode and hydrogen ions are generated at the anode, and the hydroxide ions adjust the pH value of the colloidal suspension to trigger the sol-gel transition.

[0032] Example 1: In this example, a colloidal suspension composed of short carbon fibers and ceramic matrix precursor nanoparticles is used. An ultrasonic standing wave field is introduced in the liquid phase environment to achieve the directional arrangement of the fibers. Then, immediately after the formation of this ordered structure, the sol-gel transition process is triggered to in-situ cure the fiber network, so as to construct the bonding structure between the fiber and the matrix under the condition of no interfacial residual stress; in the specific implementation process, first prepare a colloidal suspension, which includes short carbon fibers and ceramic matrix precursor nanoparticles, and disperse it in a low-viscosity liquid medium. The liquid medium can be water or ethanol. The setting of this dispersion system, on the one hand, is beneficial to enhancing the response sensitivity of the short carbon fibers under the action of the sound field, so as to achieve rapid directional arrangement; on the other hand, the nanoparticle-type ceramic precursor (such as silica sol or alumina sol) has good dispersibility and reactivity, and can quickly complete the transition from the sol state to the gel state under the triggering conditions to achieve the in-situ locking of the arranged fiber structure; place the above colloidal suspension in the ultrasonic standing wave field. Under the action of the acoustic radiation force, the short carbon fibers are directionally aggregated along the nodes or anti-nodes of the standing wave field to form an ordered fiber network structure. By controlling the standing wave frequency, phase and the spatial layout of the ultrasonic transducer, the arrangement mode of the fibers can be controlled, including zero-degree orthogonal arrangement, ninety-degree orthogonal arrangement, quasi-isotropic arrangement, or gradient orientation arrangement that satisfies a specific function distribution. For non-uniformly loaded components, the fiber orientation mode distributed along the function curve can be preferably selected to improve the stress adaptation ability of the local structure.

[0033] In the fiber alignment stage, to achieve an accurate judgment of the dynamic state, the present invention introduces a monitoring mechanism based on acoustic transmission characteristics as the judgment criterion. Specifically, through the electrical response parameters of ultrasonic transducers, or by using a pickup arranged on the opposite side of the mold to receive the acoustic detection signal after passing through the colloidal suspension, the acoustic transmission characteristics are monitored in real time, including acoustic impedance or sound velocity. When the change rate of the acoustic transmission characteristics is lower than a preset threshold, that is, the absolute value of the change rate does not exceed a certain threshold it is determined that the fiber alignment has tended to be stable. At this time, the application of the ultrasonic standing wave field is stopped, and the process proceeds to the next gelation treatment step. The setting of this real-time criterion avoids the errors brought by the traditional experience-based time control mode and improves the consistency and controllability of the fiber alignment stage. When the ordered fiber network is still in a stable alignment state, the sol-gel transition process is immediately triggered to complete the in-situ curing of the fiber network. The specific triggering method can be achieved through two means: one is to introduce a chemical reagent (such as ammonia water) that can adjust the pH value of the colloidal suspension into the colloidal suspension, and the polymerization reaction of the sol system is triggered by increasing the system pH value to form a three-dimensional cross-linked structure; the other is to trigger by electrolysis, that is, by designing the mold carrying the colloidal suspension as an electrolysis electrode and applying a direct current electric field, so that hydroxide ions are in-situ generated inside the liquid to adjust the pH value, thereby triggering the sol-gel transition reaction. This electrolysis method can ensure synchronous gelation reactions throughout the component, effectively avoiding the structural gradient phenomenon caused by uneven diffusion of externally added catalysts and improving the structural consistency of thick-section components.

[0034] After the gelation process is completed, the formed gel solid needs to be dried and sintered to obtain the target carbon-ceramic composite material. The temperature during the sintering process is controlled at a temperature significantly lower than the highest temperature required for densification treatment in traditional chemical vapor infiltration or polymer impregnation pyrolysis processes, at least reduced by more than one hundred degrees Celsius. The realization of this temperature reduction benefits from the interface construction and structural curing completed in the previous operations, thus avoiding thermal shock to the fibers, reducing process energy consumption, and simplifying the process complexity. In actual operation, it is recommended to adopt a staged heating method during the drying process to avoid cracking of the gel structure due to rapid dehydration; during the sintering process, according to the thermal decomposition and crystallization behavior of the selected precursor, a constant temperature treatment can be carried out within the temperature control range of 1000 to 1400 degrees Celsius to achieve the closure of micropores and further improve the material density.

[0035] Example 2: In practical applications, for example, when used to manufacture a thermal shock-bearing carbon-ceramic component with a thick cross-section and complex geometric structure, such as the thermal protection module of a hypersonic aircraft, a chopped carbon fiber and ceramic matrix precursor nanoparticle (silica sol) can be used to jointly form an initial colloidal suspension system. This system uses deionized water as the liquid phase medium. After being fully stirred and mixed at room temperature, it is further processed through a multi-stage ultrasonic dispersion process to ensure that the chopped carbon fibers are dispersed in a monomer state and avoid agglomeration. Moreover, the apparent viscosity of the resulting suspension is controlled at a level not higher than 10 mPa·s to ensure good fiber responsiveness under subsequent acoustic radiation. Inject the above colloidal suspension into a prefabricated reaction mold. This mold is a composite structure composed of a non-metallic inert material and an embedded metal electrode, with a cavity inside that defines the morphology corresponding to the forming shape of the target component. An ultrasonic transducer array facing the liquid region is arranged at the bottom and top of the mold respectively. This array has an adjustable spacing structure to flexibly control the spatial distribution parameters of the standing wave field. After the colloidal suspension is injected into the cavity, start the ultrasonic transducer system, initially set the frequency to 1.5 MHz, and form a stable standing wave field through phase adjustment. In this sound field, the chopped carbon fibers migrate and agglomerate along the direction of the standing wave nodes under the action of the acoustic radiation force, gradually forming a regular ordered network structure. The fiber migration speed is jointly affected by factors such as its length, the viscosity of the suspension medium, and the acoustic intensity amplitude. A higher arrangement efficiency can be achieved by optimizing the above conditions.

[0036] To realize the dynamic monitoring of the fiber orientation process, this solution sets a piezoelectric acoustic wave sensing unit embedded in the mold side wall to receive the response signal after the standing wave signal passes through the suspension. At the same time, combined with the electrical impedance spectrum response parameters of the ultrasonic transducer itself, a monitoring mechanism for real-time judging the evolution of the system structure state is established. By analyzing the sound velocity change rate, when the absolute value of this value continuously drops below a preset threshold (for example, 0.2 m / s²) for a specified time period, the system determines that the fiber arrangement state tends to be stable, and at this time, the ultrasonic system is turned off. Immediately start the sol-gel transition triggering mechanism, preferably using the electrolysis method. By embedding metal electrodes in the mold and applying a DC voltage, the recommended initial value is 6 V, and the electrode spacing is 15 mm, to in-situ generate hydroxide ions inside the liquid phase system to adjust the pH value. To ensure that the formed fiber network structure is not disturbed, the pH value change rate is controlled at no more than 0.5 units per minute, and finally the pH value is stabilized between 8.5 and 9.5, so that the silica sol system enters the gel transition interval and undergoes a three-dimensional cross-linking reaction to achieve the spatial locking of the fiber network structure.

[0037] After the gel is formed, it is left standing at room temperature for 48 hours for preliminary stabilization, and then enters the staged drying process. First, it is naturally dried at 35 °C for 12 hours, then transferred to an incubator and continuously dried at 55 °C for 12 hours, then raised to 80 °C and maintained for 6 hours, and finally placed in a vacuum drying oven and continuously treated at 100 °C for 4 hours to ensure that the internal residual liquid is fully volatilized and prevent structural cracks caused by rapid dehydration; after drying, the obtained gel body is transferred to a high-temperature sintering furnace for sintering treatment. In the heating stage, the initial heating rate is 3 °C per minute. After rising to 300 °C, it is held at a constant temperature for 2 hours to remove organic residues. Subsequently, it is raised to 1200 °C at a rate of 5 °C per minute and held at a constant temperature for 3 hours. This temperature control strategy is set according to the crystallization characteristics of the silica precursor, aiming to achieve microstructural densification and avoid structural cracks caused by high-temperature thermal stress at the fiber-matrix interface. After sintering, a programmed cooling method is adopted, and the cooling rate per minute is not higher than 2 °C until it returns to room temperature to control the uniform shrinkage of the overall structure. The carbon-ceramic composite material obtained through the above process steps has its fiber arrangement orientation determined by the standing wave node spacing. In this implementation, the node spacing is controlled between 1.2 and 1.5 mm, forming a spatial structure layout mainly composed of layered and orderly superposition. This arrangement makes the direction of the principal stress have good consistency with the load path during the service process of the component, which helps to improve the material fracture delay performance and toughness retention ability under thermal shock conditions; at the same time, relying on the spatial synchrony of the gel reaction brought about by electrolytic triggering, the pH distribution in thick sections and complex components is uniform and remains within a reasonable fluctuation range, which helps to improve the matrix curing consistency, and the overall structure density control can meet the service strength requirements in practical applications.

[0038] Example 3: In the verification of this example, a colloidal suspension containing short carbon fibers and ceramic matrix precursor nanoparticles was first prepared. The average length of the short carbon fibers was controlled at 200 microns, and the diameter was 7 microns. This selection was based on an engineering trade-off to ensure good response sensitivity of the fibers under the action of the sound field, while avoiding entanglement caused by excessive length or reduced reinforcement effect due to excessive shortness. The ceramic matrix precursor nanoparticles were selected as silica sol with an average particle size of 30 nanometers. Its dispersibility and reactivity were pre-evaluated to ensure a rapid transition from the sol state to the gel state under triggering conditions. The low-viscosity liquid medium was deionized water with a viscosity of 0.89 millipascal seconds (at 25 degrees Celsius). This choice was based on the universality of water as a common solvent, environmental friendliness, and good adaptability to sound wave transmission. The mass ratio of the short carbon fibers to the ceramic matrix precursor nanoparticles was determined to be 1:15 through preliminary exploration. The entire preparation process was carried out under strict control of temperature (25 degrees Celsius) and stirring rate (300 revolutions per minute for 30 minutes) to ensure a highly uniform suspension and dispersion of the fibers and nanoparticles in the liquid medium. The apparent viscosity of the resulting colloidal suspension was controlled at no higher than 10 millipascal seconds to ensure good fiber responsiveness under subsequent acoustic radiation. The prepared colloidal suspension was injected into a transparent rectangular quartz mold with dimensions of 100×50×10 millimeters. An array of piezoelectric ceramic ultrasonic transducers was arranged at the bottom and top of the mold. This array had an adjustable spacing structure to achieve flexible control of the spatial distribution parameters of the standing wave field.

[0039] During the fiber orientation stage, the frequency of the ultrasonic standing wave field was set at 1.5 megahertz. This frequency was selected mainly considering ensuring effective driving of the migration of short carbon fibers by the acoustic radiation force while minimizing the possible cavitation effect in the water medium, thus avoiding damage to the fibers. The sound field intensity was finely controlled by adjusting the input voltage of the ultrasonic transducers and set at 20 volts peak-to-peak to ensure sufficient driving force for rapid orientation. By adjusting the phase difference of the ultrasonic transducer array, the verification of two typical fiber orientation modes was achieved: The first was a zero-degree orthogonal arrangement. By adjusting the phase of the ultrasonic transducer array, the sound pressure nodes were regularly distributed along the length direction of the mold, guiding the short carbon fibers to agglomerate and arrange along this direction. The second was a ninety-degree orthogonal arrangement. By adjusting the phase, the sound pressure nodes were regularly distributed along the width direction of the mold, achieving the directional arrangement of short carbon fibers along the width direction. To enable dynamic monitoring of the fiber orientation process, a piezoelectric acoustic sensing unit was embedded in the side wall of the mold to receive the response signal of the standing wave signal passing through the colloidal suspension. At the same time, combined with the electrical impedance spectrum response parameters of the ultrasonic transducers themselves, a monitoring mechanism for real-time judgment of the evolution of the system structure state was established. Through real-time monitoring of the change rate of the acoustic wave transmission characteristics, when its absolute value continuously dropped below the preset threshold After 60 seconds, the system automatically determines that the fiber arrangement state tends to be stable, and at this time, the application of the ultrasonic standing wave field is stopped. The fundamental technical consideration for setting this criterion is to achieve a technical optimization balance between the speed of fiber network formation and stability. If the threshold of this change rate is set too high, the sound field may stop before the fibers are fully arranged in an orderly manner, resulting in insufficient arrangement. On the contrary, if it is set too low, it may lead to too long a sound field action time, increasing energy consumption and possibly causing unnecessary medium disturbances. Therefore, the determination of this threshold needs to be based on the intrinsic characteristics such as the geometric properties of the short carbon fibers, the viscosity of the suspension medium, and the intensity of the ultrasonic field, and combined with the fiber arrangement accuracy that must be achieved in a specific application scenario, to set it within a reasonable engineering range that can optimize the overall technical effect.

[0040] Under the condition that the ordered fiber network maintains an oriented arrangement, a sol-gel transition of the colloidal suspension is randomly induced to form a gel solidified body that in-situ cures the ordered fiber network. In this embodiment, a direct current electric field-induced gelation method is mainly used to verify its ability to achieve global uniform curing in large-sized components. By embedding high-purity graphite electrodes inside a quartz mold that holds the colloidal suspension and applying a direct current voltage, with a recommended initial value of 6 volts and an electrode spacing of 15 mm, under the action of electrolysis, hydroxide ions are generated at the cathode and hydrogen ions are generated at the anode. The hydroxide ions are generated and diffuse in-situ inside the colloidal suspension, gradually adjusting the pH value of the colloidal suspension. To ensure that the formed fiber network structure is not disturbed, the rate of change of the pH value is strictly controlled to not exceed 0.5 unit per minute. The fundamental technical consideration for controlling this rate is to achieve a technical optimization balance between the uniformity of gel curing and the avoidance of structural stress accumulation. If the rate of change of the pH value is too fast, it may cause a sudden increase in the pH value in a local area, leading to rapid gelation, and then generating internal stress and even causing microcracks; conversely, if the rate is too slow, it will prolong the gelation time, reduce production efficiency, and may introduce unnecessary disturbances under the long-term action of the electric field. Therefore, the determination of this rate needs to be set within a reasonable engineering range that can optimize the overall gelation effect based on the reaction kinetic characteristics of the ceramic matrix precursor, the size of the component, and the requirements of the final product for the internal stress state; finally, the pH value is stabilized between 8.5 and 9.5, enabling the silica sol system to enter the gel transition range and undergo a three-dimensional cross-linking reaction, achieving the spatial locking of the fiber network structure. The sol-gel transition is completed at room temperature (25 °C) and takes about 2 hours. After the gel solidified body is formed, it is first left standing at room temperature (25 °C) for 48 hours for preliminary stabilization treatment to allow the gel network to fully shrink and strengthen, and then a staged drying treatment is carried out to avoid cracking of the gel structure due to rapid dehydration. The drying process includes: the first stage is natural drying at 35 °C for 12 hours to promote the evaporation of free water and reduce the stress caused by capillary action; the second stage is transferred to an incubator and dried continuously at 55 °C for 12 hours to further remove the physically adsorbed water in the gel pores; the third stage is raised to 80 °C and maintained for 6 hours to treat the bound water in preparation for subsequent vacuum drying; the fourth stage is finally placed in a vacuum drying oven and continuously treated at 100 °C for 4 hours, with the vacuum degree maintained below 10 Pa to completely remove the residual adsorbed water and part of the chemically bound water and prevent structural cracks caused by rapid dehydration.

[0041] After drying is completed, the obtained gel solid is transferred to a high-temperature sintering furnace for sintering treatment. The sintering process strictly follows the programmed heating and cooling curve to achieve microstructure densification and avoid structural cracks caused by high-temperature thermal stress at the fiber-matrix interface. In the heating stage of sintering: the initial heating rate is 3 degrees Celsius per minute. After heating to 300 degrees Celsius, it is held at a constant temperature for 2 hours to remove organic residues. Subsequently, it continues to heat at a rate of 5 degrees Celsius per minute to 1200 degrees Celsius and is held at a constant temperature for 3 hours. This temperature control strategy is set based on the crystallization characteristics of the silica precursor, and its fundamental lies in achieving a technical optimization balance between material densification and avoiding interfacial thermal stress. If the sintering temperature is too high or the heating rate is too fast, it may lead to carbon fiber oxidation or excessive reaction with the matrix, and at the same time cause severe interfacial thermal stress, resulting in microcracks; conversely, if the sintering temperature is too low or the holding time is insufficient, it may lead to incomplete densification and too high porosity of the material, affecting the final mechanical properties. Therefore, the determination of these sintering parameters needs to be based on the thermal decomposition and crystallization behavior of the ceramic matrix precursor, the thermal stability of the chopped carbon fiber, and the mechanical properties required for the final composite material, and set within a reasonable engineering range that can optimize the overall material properties. In the cooling stage of sintering: after sintering, a programmed cooling method is adopted, and the cooling rate per minute is not higher than 2 degrees Celsius until it returns to room temperature to control the uniform shrinkage of the overall structure and further reduce the thermal stress generated during the cooling process.

[0042] In addition, under the action of an ultrasonic standing wave field, short carbon fibers exhibit significant directional migration and aggregation behaviors in the colloidal suspension. Through the acoustic wave sensing unit on the side wall of the mold and the electrical impedance spectrum response of the ultrasonic transducer itself, the change rate of the sound velocity in the colloidal suspension was monitored in real time to evaluate the dynamic process of fiber alignment. The typical curve of the change rate of the sound velocity in the colloidal suspension shows that in the initial stage of the curve, the change rate of the sound velocity is large, indicating that the short carbon fibers are rapidly responding to the acoustic radiation force for directional alignment. As time goes by, the short carbon fibers gradually form an ordered network, and the change rate of the sound velocity tends to be flat until its absolute value continuously drops below the preset threshold for a specific time. Then the system automatically determines that the alignment is stable and stops the sound field, which verifies the effectiveness of the acoustic transmission characteristics as a real-time criterion, avoids the possible errors caused by the traditional empirical time control mode, and significantly improves the consistency and controllability of the fiber alignment stage. By slicing the gel solidified body and observing it through a scanning electron microscope, it is clearly confirmed that the short carbon fibers form a highly ordered fiber network structure under the action of the sound field. In the specimen with a zero-degree orthogonal arrangement, the short carbon fibers are parallelly distributed along a specific direction, with a dense arrangement and clear directionality. In the specimen with a ninety-degree orthogonal arrangement, the short carbon fibers show an ordered structure in the vertical direction. These results strongly support the ability of the present invention to achieve controllable directional alignment of fibers through the sound field. At the same time, to verify the uniformity of the direct current electric field-induced gelation in large-sized components, micro pH sensors were set at different positions (center, edge) inside the gel reaction mold to monitor the change of the pH value in real time. During the electrolytic triggering gelation process, the pH values at the center and edge positions almost rise synchronously, and the difference in pH values is always controlled within a small range, which fully shows that the in-situ triggering mechanism of the direct current electric field can effectively avoid the concentration gradient effect caused by uneven diffusion of external catalysts in the gelation reaction, ensuring the spatial orientation fidelity of the fiber network and the matrix curing uniformity in thick-section components, which is crucial for maintaining the structural consistency of complex components.

[0043] After the staged drying and sintering treatments, density measurement and microscopic pore structure analysis were carried out on the obtained carbon-ceramic composite materials, and they were compared with the same type of materials prepared by traditional processes. The results show that under the condition of significantly reducing the maximum sintering temperature (at least 100 degrees Celsius lower than the traditional process), the present invention process can still obtain a final density and an average porosity similar to those of the traditional process. This confirms that the present invention has successfully achieved a downward shift of the sintering temperature window through the interface construction and structure curing completed in the previous operations, fundamentally avoiding the thermal shock to the fibers during the traditional high-temperature pyrolysis process, significantly reducing the process energy consumption, and simplifying the process complexity. Microscopic structure analysis shows that for the composite materials prepared by the present invention, the fiber-matrix interface is tightly bonded, and no microcrack initiation caused by thermal stress is observed.

[0044] Example 4: This example combinesFigures 1 to 3 , an implementation description of a preparation method for a carbon-ceramic composite material is given. As Figure 1 shown, starting from raw material preparation, it successively includes the preparation of short carbon fibers, ceramic precursor sol, and low-viscosity medium to form a colloidal suspension system suitable for the action of the sound field; in the ultrasonic treatment step, the suspension is placed in a 1.5 MHz standing wave field, and the short carbon fibers are driven to align directionally by the acoustic radiation force, and a real-time acoustic monitoring means is used to track the orderly aggregation state of the fibers to ensure the formation of a stable ordered network structure; then it enters the electrolysis-triggered gelation link, and by applying a 6 V DC electric field and combining an in-situ pH adjustment mechanism, room temperature curing is achieved, that is, the sol-gel transition is triggered while the fibers remain aligned, and the obtained gel solid is cured. After 48 h of curing, the composite structure enters the heat treatment stage, including a program-controlled process of staged drying and sintering at 1200 °C to further improve the density and avoid crack generation. Finally, the obtained carbon-ceramic composite material has comprehensive performance advantages such as a zero-stress interface, no heat treatment cracks, and programmable structure.

[0045] As Figure 2 shown, the horizontal axis is the process time (hours), and the vertical axis is the temperature (°C), covering two process stages, the drying stage and the sintering stage. In the figure, the drying stage is represented by a solid line, and the corresponding temperature control curve shows a slow temperature rise and staged temperature holding to ensure the stability of the gel solid structure and no cracks occur; after the drying is completed, it enters the sintering stage, represented by a dotted line. In this stage, the temperature is first rapidly raised to about 300 °C and held at a constant temperature to remove organic residues, and then the temperature is continued to be raised to about 1200 °C and held at a constant temperature to achieve microstructural densification to complete the sintering densification process of the ceramic matrix and improve the strength and stability of the material.

[0046] As Figure 3 shown, at the starting stage of the process, the ultrasonic control system starts the standing wave field (1.5 MHz), applies the acoustic radiation force to the colloidal suspension through the transducer array, drives the short carbon fibers to migrate directionally, and the monitoring module collects real-time acoustic signals. The system executes a loop cycle at a sampling frequency of 100 ms, and calculates in the monitoring module, that is, the acoustic feature change rate. When the condition is satisfied, it triggers the alt branch judgment process, the system issues a compliance signal and closes the sound field, and continuously optimizes the parameters to finally form a stable fiber network. The whole process adopts key timing parameter control, including sampling frequency: 10 Hz, stability criterion: continuous compliance 5 times, response delay: <50 ms, to ensure that the control logic responds in time and stops the sound field when the fiber structure tends to be stable, avoiding cavitation damage caused by excessive energy input, so as to achieve precise ordered arrangement control.

[0047] Example 5: Polyvinyl alcohol was dissolved in deionized water. By continuously stirring and heating until completely dissolved, an aqueous polyvinyl alcohol solution with a mass fraction of 5% was obtained. At room temperature, a silica sol with a volume fraction of 30% was slowly added to the solution as a precursor, and ammonia water with a volume fraction of 2% was simultaneously dropped to preliminarily adjust the pH of the system, making the overall in a weakly alkaline environment to control the gelation rate of the precursor sol and avoid premature reaction. Subsequently, short carbon fibers pretreated by drying were added to the obtained mixed solution. The length of the carbon fibers was controlled within the range of 1 mm to 3 mm. Through ultrasonic treatment, they were uniformly dispersed in the system to form a fibrous colloidal suspension. The setting of the fiber length range was aimed at achieving stable spatial staggered overlapping to construct a three-dimensional network structure, while reducing the risk of sedimentation caused by long fibers or interface discontinuity caused by short fibers; the fibrous colloidal suspension was introduced into a rectangular mold cavity equipped with parallel ultrasonic transducers, filled the mold cavity and removed air bubbles. The working frequency of the transducers was set between 40 kHz and 60 kHz. The specific frequency was determined according to the geometric size of the mold and the sound wave propagation speed in the medium to establish a one-dimensional standing wave field along the axis of the transducers. The initial working phases of the transducers were kept consistent, and the spatial position of the standing wave nodes in the cavity was controlled by means of phase difference adjustment, so that the short carbon fibers tended to and were stably distributed near the nodes under the action of radiation force, thus realizing an orderly arrangement perpendicular to the nodes. The frequency setting formed a balance between maintaining the spatial resolution of the sound field and the fiber response ability. A lower frequency could enhance the radiation driving force but reduce the spatial control accuracy, while a higher frequency could improve the distribution accuracy but might cause fiber response delay. Therefore, the selected range was a reasonable interval for realizing the overall arrangement stability.

[0048] After maintaining the stable action of the ultrasonic standing wave field for 20 minutes, titanium electrodes were respectively set on the side walls at both ends of the mold, and a DC voltage was applied. The voltage value was controlled between 100 V and 150 V. The electrode spacing was set within the range of 5 cm to 15 cm according to the length of the mold. The electric field effect guided the directional migration of charged ions in the solution, causing the pH value to change in a local area, thereby inducing a sol-gel transition in the colloidal system. The voltage setting must ensure the effective electrolysis induction rate while avoiding the interference of bubble generation on the fiber network structure. Insufficient voltage might cause a lag in the gel reaction, while too high voltage might cause gas evolution phenomena to interfere with the gel uniformity. The electrolysis duration was controlled within 10 minutes to ensure that the arrangement structure of the fibers under the action of the standing wave field was solidified and formed before the gel was completed.

[0049] After gelation is completed, the whole together with the mold is transferred to a constant-temperature drying environment. The drying temperature is maintained at 60 °C for 24 hours. During the drying process, it should be avoided that the gel structure is broken or the volume is deformed due to rapid water loss. After drying is completed, the formed component is pre-carbonized under a nitrogen atmosphere. The heating process adopts a staged heating method, and the heating rate does not exceed 5 °C per minute. The pre-carbonization temperature is controlled between 800 °C and 1000 °C to ensure the stability of the interfacial structure between the carbon fiber and the matrix formed by the precursor; Subsequently, it is further heated to 2000 °C in a vacuum or argon atmosphere for final heat treatment, so that the polymer carbon source is fully carbonized and the dense transformation of the ceramic phase is realized, and a carbon-ceramic composite material with stable structure, ordered fiber arrangement and good interfacial bonding is obtained; The above process flow realizes the directional distribution of short carbon fibers in the sol system and quickly locks the formed network structure by constructing a linkage mechanism of sound field induction - electric field curing. Through the synchronous completion of gel curing induced by local pH change during the continuous process of standing wave guidance, the coordination between the three-dimensional space structure and the fiber arrangement is formed.

[0050] Example 6: To prepare an aircraft leading edge component with an asymmetric shape, the preset structure of this component requires that its internal fiber-reinforced network has an orientation distributed along a specific function gradient to cope with the non-uniform heat flow and stress field it bears under the predetermined service conditions. The preparation method starts with the calibration of the raw material system. Short carbon fibers with an average length of 200 μm and an aspect ratio of about 30 are selected and dispersed in deionized water with silica sol with an average particle size of 30 nm at a mass ratio of 1:15 to form a colloidal suspension. To ensure that the subsequent process parameters can be set based on reproducible physical bases, it is necessary to first obtain the actual size distribution of this batch of carbon fibers by laser diffraction method and measure the apparent viscosity of this colloidal suspension at standard room temperature using a falling ball viscometer , and the measurement results of both of them and the reference sound velocity of the initial disordered suspension obtained by an ultrasonic velocity measuring instrument , are all used as input parameters for subsequent calculations.

[0051] Then, this colloidal suspension is injected into a non-metallic mold customized for this leading edge component, with an array of high-purity graphite electrodes embedded in the inner wall. The ultrasonic transducer array outside the mold is activated to generate a standing wave field with a frequency of 1.5 MHz. By independently programming and controlling the phases of each unit in the transducer array, an acoustic potential well with nodal lines arranged along the aforementioned specific function curve is constructed inside the mold. Under the action of acoustic radiation force, the short carbon fibers migrate to the sound pressure node region and complete the directional arrangement. The key to this process lies in the judgment of the fiber network reaching a stable and ordered state; An adaptive control algorithm deployed in the system, through a sound wave sensor built into the mold wall, continuously samples and detects the sound wave signal at a frequency of 10 Hz and calculates the sound velocity in real time The criterion adopted by this algorithm is a dynamic convergence condition, which is related to the physical relaxation time of the system , rather than a fixed empirical threshold. This relaxation time is jointly determined by the medium viscosity and the sound field energy density . According to the pre-established physical model, when the sound speed change rate drops below 5% of its peak change rate and this state lasts stably for more than five sampling periods, the control algorithm determines that the fiber network has reached macroscopic stability and immediately terminates the application of the ultrasonic standing wave field.

[0052] At the moment when the fiber network structure is locked, the electrolysis-triggered gelation program is immediately started. By applying a direct current electric field to the graphite electrodes embedded in the mold, water is electrolyzed in-situ to generate hydroxide ions, thereby uniformly increasing the value of the entire colloidal system. The applied direct current voltage value is dynamically adjusted through a feedback control logic, and its sole objective is to strictly maintain the rising rate of the value within the range of 0.4 to 0.5 units per minute. This rate range is established based on the experimental data of the specific silica sol-gel kinetics, aiming to ensure that the three-dimensional cross-linking reaction of the gel network occurs uniformly on a sufficient time scale, thus avoiding the generation of internal stress concentration. The control system dynamically adjusts the output voltage according to the value monitored in real time, referring to a preset calibration curve of voltage and change rate, to ensure the synchronism of the gelation reaction throughout the component volume.

[0053] After the gel solid is left standing in the mold for 48 hours, it enters the heat treatment stage. The setting of its temperature control curve is completely based on the physical and chemical transformation data obtained from the thermogravimetric analysis and differential scanning calorimetry of the gel. The first constant temperature platform of the heating curve is set at 300 °C, which corresponds to the end point of the first significant weight loss step caused by the volatilization of organic matter and physically adsorbed water in the thermogravimetric analysis curve. The second constant temperature platform, i.e., the sintering temperature, is set at 1200 °C. This choice is based on the peak of the exothermic peak corresponding to the transformation of amorphous silica to crystal in the differential scanning calorimetry curve, and combined with the density and strength test results of the samples sintered at different temperatures, it is determined that this temperature is the balance point for achieving sufficient densification of the material and avoiding the reaction of carbon fibers. In the final programmed cooling stage, the rate is controlled below 2 °C per minute. This rate is determined based on the measurement of the thermal expansion coefficient and fracture toughness of the sintered material, based on the thermal stress model Calculation shows that this cooling rate ensures that the maximum thermal stress caused by the temperature difference between the inside and outside of the material is always lower than the safety threshold of its fracture toughness. This measure ensures in principle that no microcracks are generated at the interface between the fiber and the matrix due to thermal mismatch after cooling, thus ensuring the structural integrity of the carbon-ceramic composite material.

[0054] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a carbon-ceramic composite material, characterized in that, The method includes the following steps: Step a: Provide a colloidal suspension, which contains short carbon fibers and ceramic matrix precursor nanoparticles; Step b: Place the colloidal suspension in an ultrasonic standing wave field. The ultrasonic standing wave field drives the short carbon fibers to align directionally in the colloidal suspension through acoustic radiation force, forming an ordered fiber network; Step c: Under the condition that the ordered fiber network remains directionally arranged, trigger the sol-gel transition of the colloidal suspension to form a gel solidified body that in-situ cures the ordered fiber network. The sol-gel transition is completed within the temperature range from zero degrees Celsius to sixty degrees Celsius; Step d: Dry and sinter the gel solidified body to obtain a carbon-ceramic composite material. The sintering temperature is controlled within the temperature control range of 1000 degrees Celsius to 1400 degrees Celsius.

2. The preparation method of a carbon-ceramic composite material according to claim 1, characterized in that, In step b, by regulating the frequency, phase of the ultrasonic standing wave field or the layout of the ultrasonic transducers, control the alignment direction of the short carbon fibers to achieve at least one of the fiber orientations of zero-degree orthogonality, ninety-degree orthogonality or quasi-isotropy, or a gradient orientation distributed along a specific function curve.

3. The preparation method of a carbon-ceramic composite material according to claim 1, characterized in that, In step c, the way to trigger the sol-gel transition of the colloidal suspension is: introduce a chemical reagent that can change its pH value into the colloidal suspension.

4. The preparation method of a carbon-ceramic composite material according to claim 3, wherein, The chemical reagent is ammonia water.

5. The preparation method of a carbon-ceramic composite material according to claim 1, wherein, In step a, the ceramic matrix precursor nanoparticles are silica sol or alumina sol.

6. The preparation method of a carbon-ceramic composite material according to claim 1, wherein, In step a, the short carbon fibers and the ceramic matrix precursor nanoparticles are jointly dispersed in a low-viscosity liquid medium, and the low-viscosity liquid medium is water or ethanol.

7. The preparation method of a carbon-ceramic composite material as described in claim 1, characterized in that, It also includes: During the process of step b, the acoustic transmission characteristics when the sound wave passes through the colloidal suspension are monitored in real time; and when the rate of change of the acoustic transmission characteristic is lower than a preset threshold stop applying the ultrasonic standing wave field and perform step c, where the acoustic transmission characteristic includes acoustic impedance or sound velocity.

8. The preparation method of a carbon-ceramic composite material according to claim 7, wherein, The acoustic transmission characteristics when the sound wave passes through the colloidal suspension are obtained through the electrical response parameters of the ultrasonic transducer or through the acoustic wave detection signal received by the pickup on the opposite side of the mold.

9. The preparation method of a carbon-ceramic composite material according to claim 1, wherein, In step c, the way to trigger the sol-gel transition of the colloidal suspension is: apply a direct current electric field to the colloidal suspension, and in-situ generate ions that change its pH value inside the colloidal suspension through electrolysis, and the ions realize the synchronous gelation of the colloidal suspension.

10. The preparation method of a carbon-ceramic composite material according to claim 9, characterized in that, The direct current electric field is applied by designing the mold carrying the colloidal suspension as an electrode. Under the electrolysis effect, hydroxide ions are generated at the cathode and hydrogen ions are generated at the anode, and the hydroxide ions adjust the pH value of the colloidal suspension to trigger the sol-gel transition.

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