Method for improving oxidation ablation resistance of Cf / HfB2-SiC composite material through active cooling and application

Abstract

The invention discloses a method for improving the oxidation ablation resistance of a Cf / HfB2-SiC composite material through active cooling and application, and relates to the field of composite material preparation and thermal protection. The invention aims to solve the technical problems of oxidation ablation, non-uniform cooling, poor structural stability and the like in the prior art. The method comprises the following steps: preparing a carbon fiber woven body, and covering the carbon fiber surface with a coating; preparing HfB2 ceramic slurry; preparing a green body; the low open porosity Cf / HfB2-SiC composite material is obtained; and a directional micropore channel is prepared by adopting a micro electric spark machining method. Through the directional hole channel structure, the low open porosity Cf / HfB2-SiC composite material is adopted, and an active cooling strategy is combined, so that the oxidation ablation resistance and the cooling efficiency of the material in a high heat flow environment are remarkably improved. The prepared composite material serves as a thermal protection material to be applied to a cooling channel of a thermal protection system.

Description

Technical Field

[0001] The present invention relates to the fields of composite material preparation and thermal protection. Background Art

[0002] Hypersonic vehicles pose unprecedented challenges to thermal protection systems in extreme service environments. Especially for critical components such as the leading edge and combustion chamber of the vehicle, they need to withstand a dynamic high-temperature environment exceeding 2000 °C and the erosion of strongly oxidizing gas flows simultaneously. Although traditional ceramic matrix composites represented by HfB2-SiC exhibit good temperature resistance under static high-temperature conditions, their protective performance degrades significantly under the coupled action of transient ultra-high temperature and strong oxidation generated during actual high Mach number flight. This performance degradation is mainly manifested as severe oxidation ablation on the material surface and structural failure of the protective layer due to the accumulation of thermal stress.

[0003] To address this technical problem, current research mainly explores from two directions: improving the intrinsic properties of materials and optimizing the cooling structure. In terms of the material system, although introducing ultra-high temperature ceramic phases such as HfB2 can improve the antioxidant performance to a certain extent, the improvement of the intrinsic properties of the material has approached the theoretical limit. In terms of cooling technology, the porous cooling structure prepared by traditional sintering has inherent defects such as insufficient pore connectivity and uneven pore size distribution, resulting in blocked flow of the cooling medium and severe local heat accumulation, leading to thermal protection failure. In the active thermal protection design of some high-temperature materials, optimizing the pore structure is often used to improve the cooling performance. The directional pore channel structure has been proposed to improve the heat conduction efficiency, but most existing designs have not fully optimized the cooperation between the pore structure and the cooling channel, resulting in unsatisfactory cooling effects and still unable to effectively solve the fundamental problem of the coordinated optimization of oxidation ablation control and thermal management.

[0004] In-depth analysis shows that there are still challenges in how to reduce the surface response temperature and improve the antioxidant ablation ability of materials by optimizing the cooling channel design in extreme thermal environments. Especially under non-uniform heat flux load conditions, how the cooling channel can achieve adaptive matching with the dynamic thermal environment and how to ensure the structural integrity of the cooling channel in a high-temperature oxidation environment are still core issues to be solved. Most current research focuses on optimizing material components or improving cooling structures in isolation, lacking systematic consideration of the integrated design of material-structure-function, which severely restricts the performance breakthrough of the new generation of thermal protection systems. Summary of the Invention

[0005] The present invention provides a method and application for improving the antioxidant ablation performance of C f / HfB2-SiC composite materials by active cooling to solve the technical problems such as oxidation ablation, uneven cooling, and poor structural stability existing in the prior art.

[0006] Method for improving oxidation and ablation resistance of C f / HfB2-SiC composite material by active cooling, which is specifically carried out according to the following steps:

[0007] I. Prepare a carbon fiber braid using carbon fibers, and cover a coating on the surface of the carbon fibers through a chemical vapor deposition process;

[0008] II. Put HfB2 powder, polyethyleneimine, and an ethanol solution into a ball mill for mixing to prepare an HfB2 ceramic slurry;

[0009] III. Use a high-pressure pump to extract the HfB2 ceramic slurry prepared in step II and inject it into a container. At the same time, use a vacuum pump to evacuate the air below the filter element, control the relative pressure difference on both sides of the filter element to be greater than 0.5 MPa, immerse the carbon fiber braid prepared in step I in the HfB2 ceramic slurry, and then dry to obtain a green body;

[0010] IV. Put the green body into liquid polycarbosilane for ultra-high pressure impregnation, then cure it at low temperature, and then put it into a vacuum furnace for sintering;

[0011] Repeat the impregnation with liquid polycarbosilane - low-temperature curing - vacuum sintering process multiple times to obtain a low open porosity C f / HfB2-SiC composite material;

[0012] V. Use a micro electrical discharge machining method to prepare a directional microchannel in the low open porosity C f / HfB2-SiC composite material to obtain a directional microchannel low open porosity C f / HfB2-SiC composite material, and the process is completed.

[0013] The said directional microchannel low open porosity C f / HfB2-SiC composite material is applied as a thermal protection material to the cooling channel of a thermal protection system.

[0014] The composite material of the present invention is composed of C f (carbon fiber), HfB2, SiC, and PyC; where C f (carbon fiber): serves as a reinforcing phase to improve the mechanical properties of the material; HfB2: serves as a high-temperature resistant matrix material to provide high thermal stability and oxidation resistance; SiC: enhances the oxidation resistance and mechanical properties of the material; PyC: deposits a PyC intermediate interface layer on the surface of the carbon fiber through a chemical vapor deposition (CVD) technique to enhance the interfacial bonding force between the carbon fiber and the matrix material, and plays a role in improving the interfacial strength and the strength and toughness of the material.

[0015] Liquid water (as a coolant): is used in the cooling channel, and the flow rate is controlled to be 0.1 - 1.0 g / s, and the specific flow rate can be adjusted according to actual needs.

[0016] The present invention adopts micro-EDM technology to produce a low open porosity C f Directional hole channels are manufactured in HfB2-SiC composites. By optimizing the micro-EDM parameters, the aperture and directionality of the channels are precisely controlled to achieve the best cooling effect.

[0017] The present invention uses chemical vapor deposition (CVD) technology to deposit a PyC intermediate phase layer on the surface of the carbon fiber to enhance the interface bonding force between the carbon fiber and the matrix material.

[0018] The present invention combines the coolant circulation system with the material structure to ensure that the coolant can flow evenly in the directional hole channel, thereby achieving a good cooling effect.

[0019] The present invention uses ultra-high pressure precursor impregnation and cracking technology for sintering, and further optimizes the mechanical properties and density of the material through cyclic low-temperature pressureless sintering.

[0020] Working principle:

[0021] Heat load conduction and cooling: The material surface absorbs ambient heat, the surface temperature rises, the surface thermal effect is enhanced, the material radiates heat to the environment to reduce the surface temperature, and the heat that enters the material is transferred to the inside through heat conduction.

[0022] Convective heat transfer:

[0023] Due to the large temperature difference between the material and the fluid, the fluid then flows in the channel, and the relatively cooler fluid carries away the heat by convection, thereby reducing the material temperature.

[0024] Oxidation control: Under conditions of high heat flux density, the core-shell structure oxide film (HfO2 and SiO2) formed on the surface of the material effectively inhibits further oxidation reactions and protects the structure of the composite material.

[0025] Through the combination of the directional hole channel design and the cooling strategy proposed in the present invention, the existing technical difficulties are successfully overcome, the material's anti-oxidation and ablation capabilities and thermal protection performance in extreme thermal environments are significantly improved, and it has important practical application value.

[0026] The present invention improves the coolant flow path through the directional hole channel, ensures uniform distribution of the cooling effect, improves the cooling efficiency of the material, and thus reduces the surface response temperature.

[0027] The present invention combines a composite material with low open porosity, and effectively improves the antioxidant performance of the composite material through an oxide layer with a core-shell structure (such as hafnium oxide coating a silicate glass phase, and a dense oxide layer coating an unablated matrix of the composite material), thereby preventing oxidation from extending into the interior of the material, thereby improving the antioxidant ablation capability.

[0028] Enhanced structural stability: The present invention controls the morphology and distribution of the active cooling channels of the composite material, improves the thermal stability and structural integrity of the material, reduces thermal damage under high heat flux density, and ensures long-term stability in high-temperature environments.

[0029] Improved thermal protection ability under high heat flux density and extreme environmental temperatures: By integrating the active cooling strategy with the optimization of the composite material structure, not only the cooling effect is effectively improved, but also the oxidation ablation resistance and thermal protection performance of the material in extreme environments are enhanced.

[0030] Advantages of the present invention:

[0031] Through innovative design of the directional hole channel structure and the use of a low open porosity C f / HfB2-SiC composite material, combined with the active cooling strategy, significantly improves the oxidation ablation resistance and cooling efficiency of the material in a high heat flux environment. The C f / HfB2-SiC composite material during oxidation, the element hafnium can combine with oxygen to form HfO2 (with a melting point as high as 2810 °C). At the same time, the oxidation products formed by the combination of boron and silicon in the system can form a molten phase covering the ablation center and diffuse outward in a molten state, thereby improving the oxidation and erosion resistance of the composite material at high temperatures. The molten phase is mainly formed by the high-temperature melting of silicon carbide to form a silicate structure or by combining with boron to form a borosilicate structure. The viscosity characteristics of the glass phase enable it to cover some matrix components, reduce the harm caused by pits and holes formed by the oxidation ablation of carbon fibers, and most of the defects are filled with molten SiO2, promoting the formation and growth of HfO2, forming a continuous and dense structure. A dense oxide layer is formed on the surface, further preventing the penetration of oxygen and serving as an effective barrier during the oxidation ablation process.

[0032] 1. Significantly improve the oxidation ablation resistance:

[0033] Problems of the prior art: In the prior art, traditional ceramic matrix composites are prone to oxidation ablation under high heat flux density and extreme environmental temperatures, resulting in serious damage to the material surface and reducing the structural stability and thermal protection performance of the material.

[0034] Advantages of the invention: The present invention uses a low open porosity C f / HfB2-SiC composite material. HfB2 has a high melting point and stronger oxidation ablation resistance, enabling it to still have serviceability under extreme temperature conditions. At the same time, through the design of the directional hole channel and the flow of the coolant, the surface temperature of the material is effectively reduced, inhibiting the occurrence of material ablation. At a high heat flux density (4 MW / m 2) In the ablation test, the surface temperature of the material decreased by 524 °C; meanwhile, in the high-temperature ablation test at 2800 °C, the surface temperature could be reduced by more than 1300 °C, which verified that the present invention could significantly improve the anti-oxidation and ablation resistance of the composite material.

[0035] Quantitative effect: In the ablation test, 4 MW / m 2 In the ablation test, the temperature in the central region remained at 1490 °C, and in the high-temperature ablation test at 2800 °C, the temperature in the central region remained at 1453 °C. Compared with the prior art, the surface response temperature was reduced, and the stability in the extreme thermal environment was enhanced.

[0036] 2. Improve the cooling efficiency:

[0037] Problems of the prior art: In traditional composite materials, the design of the cooling channels fails to be effectively optimized, the cooling effect is often uneven, and the heat load in some areas is too large, resulting in thermal damage to the material.

[0038] Advantages of the invention: Through the design of the directional hole channels, the present invention enables the coolant to flow along a specific direction, improving the flow efficiency of the coolant. Compared with the prior art, the structural optimization of the cooling channels effectively enhances the heat exchange between the coolant and the material surface, improving the cooling efficiency.

[0039] Quantitative effect: At a high heat flux density, the coolant flow rate is 0.17 g / s. By optimizing the flow path of the coolant, the cooling efficiency is significantly improved, ensuring a more uniform cooling effect.

[0040] 3. Enhance the structural stability of the material:

[0041] Problems of the prior art: In a high-temperature and high-pressure environment, the composite materials in the prior art are prone to structural instability due to oxidation ablation and thermal expansion, reducing the service life and performance of the materials.

[0042] Advantages of the invention: Through the preparation of materials with a low open porosity rate and the design of directional hole channels, the present invention not only optimizes the thermal conductivity of the material but also effectively avoids structural damage to the material in a high heat flux environment. By depositing a PyC intermediate phase layer on the surface of the carbon fiber, the interfacial bonding force between the carbon fiber and the matrix material is enhanced, improving the structural stability of the material.

[0043] Qualitative effect: In the long-term (400 seconds) high-temperature ablation test of the composite material prepared by the present invention, the surface response temperature of the material remained stable, and no thermal blockage effect occurred, ensuring the long-term stability of the structure.

[0044] 4. Improve the thermal protection efficiency:

[0045] Prior art problem: Existing thermal protection materials lack effective cooling strategies when facing high-temperature environments such as hypersonic aircraft, resulting in excessive heat loads and affecting the thermal protection effect.

[0046] Advantages of the invention: By integrating the design of directional pore channels with an active cooling strategy, the present invention significantly improves the thermal protection performance of materials in extreme thermal environments. The interaction between the coolant and the composite material effectively removes heat and reduces the heat accumulation on the material surface.

[0047] Quantitative effect: In the ablation test, the cooling channels effectively reduce the surface response temperature, avoiding the overheating problems and ablation damage commonly seen in traditional materials under high heat flux densities, and enhancing the thermal protection ability of the materials.

[0048] 5. Improvement of production efficiency and material saving:

[0049] Prior art problem: The preparation process of traditional composite materials is complex, and the consumption of raw materials is relatively high, resulting in high costs.

[0050] Advantages of the invention: The preparation method of the present invention simplifies the manufacturing process by optimizing the micro-EDM technology and the design of the coolant flow path, while reducing unnecessary waste of raw materials. By adjusting the processing parameters and electrode sizes, the dimensions of the micro-channels are precisely controlled, ensuring the maximum material usage efficiency while meeting the performance requirements, and reducing the production cost.

[0051] Qualitative effect: The innovative design of the present invention optimizes the preparation process, reduces the consumption of raw materials and energy consumption during the production process, and improves the production efficiency.

[0052] 6. Wide range of application fields:

[0053] Prior art problem: The application scope of existing composite materials is limited. Especially in extreme environments of high temperature and high pressure, their thermal protection performance and structural stability fail to meet the requirements of hypersonic aircraft.

[0054] Advantages of the invention: The composite material of the present invention has broad application prospects in the thermal protection systems of aerospace, hypersonic aircraft and other high-temperature and high-pressure environments, especially showing excellent performance in terms of cooling performance and antioxidant ability.

[0055] Qualitative effect: The composite material of the present invention can effectively meet the thermal protection requirements in extreme environments, and is widely applied to engineering fields with extremely high temperature and high heat flux density, meeting the needs of cutting-edge technologies such as hypersonic aircraft.

[0056] The present invention adopts an innovative directional pore channel design and a low open porosity C fThe combination of the / HfB2-SiC composite material not only solves the problems of uneven cooling effect and unstable material structure in the prior art, but also significantly improves the oxidation and ablation resistance and thermal protection performance of the material, having significant technical advantages and application values.

[0057] The composite material prepared by the present invention can be widely applied to the thermal protection system in the aerospace field under high temperature and high pressure environments. In addition, the directional pore channel design and active cooling strategy of the composite material can be used in other thermal management systems under high temperature environments and provide more efficient thermal protection solutions. Brief Description of the Drawings

[0058] Figure 1 It is the schematic diagram of the preparation and processing of the directional microchannel and the pictures of the material before and after processing, where Figure a is the processing drawing, Figure b is the schematic processing diagram, and Figure c is the prepared C with low open porosity f Top view of the / HfB2-SiC composite material, and Figure d is the prepared C with low open porosity f Side view of the / HfB2-SiC composite material, and Figure e is the directional microchannel C with low open porosity f Top view of the / HfB2-SiC composite material;

[0059] Figure 2 It is the physical picture of the C with low open porosity f / HfB2-SiC composite material prepared in Example 1:

[0060] Figure 3 It is the C with low open porosity f Porosity diagram of the / HfB2-SiC composite material prepared in Example 1;

[0061] Figure 4 It is the physical picture of the directional microchannel C with low open porosity f / HfB2-SiC composite material prepared in Example 2;

[0062] Figure 5 It is the top view of the directional microchannel C with low open porosity f / HfB2-SiC composite material prepared in Example 3;

[0063] Figure 6 It is the directional microchannel C with low open porosity f Active cooling process diagram of the / HfB2-SiC composite material during the oxyacetylene ablation test;

[0064] Figure 7 It is the macroscopic photos of the composite materials prepared in Example 1 and Example 4 after passive ablation after being detected at different heat flux densities;

[0065] Figure 8The C with a low open porosity and an oriented microchannel prepared in Example 4 f / HfB2-SiC composite material, test chart of the response temperature on the material surface under two ablation states (coolant introduced and coolant not introduced);

[0066] Figure 9 Schematic diagram and macroscopic view of the distribution of oriented straight through holes with different pore diameters prepared on a stepped sample by electrodes with different diameters in Example 5;

[0067] Figure 10 The C with a low open porosity and an oriented microchannel prepared in Example 5 f / HfB2-SiC composite material, macroscopic view of the material before and after the oxyacetylene ablation test;

[0068] Figure 11 The C with a low open porosity and an oriented microchannel prepared in Example 5 f / HfB2-SiC composite material, temperature rise curve graph of the oxyacetylene ablation test;

[0069] Figure 12 The C with a low open porosity prepared in Example 1 f / HfB2-SiC composite material, ablation photo after the oxyacetylene ablation test;

[0070] Figure 13 The C with a low open porosity prepared in Example 1 f / HfB2-SiC composite material, temperature rise curve graph after the oxyacetylene ablation test;

[0071] Figure 14 The C with a low open porosity and an oriented microchannel with different pore diameters prepared in Example 5 f / HfB2-SiC composite material, columnar chart of the cooling effect after introducing coolant. Detailed implementation manners

[0072] Detailed implementation manner 1: The method for improving the oxidation and ablation resistance performance of the C f / HfB2-SiC composite material by active cooling is carried out according to the following steps:

[0073] 1. Prepare a carbon fiber braid using carbon fiber, and cover a coating on the surface of the carbon fiber through a chemical vapor deposition process;

[0074] 2. Put HfB2 powder, polyethyleneimine and an ethanol solution into a ball mill and mix them to prepare an HfB2 ceramic slurry;

[0075] III. Use a high-pressure pump to extract the HfB2 ceramic slurry prepared in Step II and inject it into a container. At the same time, use a vacuum pump to evacuate the air below the filter element, control the relative pressure difference on both sides of the filter element to be greater than 0.5 MPa, immerse the carbon fiber braid prepared in Step I in the HfB2 ceramic slurry, and then dry it to obtain a green body;

[0076] IV. Put the green body into liquid polycarbosilane for ultra-high pressure impregnation, then cure it at low temperature, and then put it into a vacuum furnace for sintering;

[0077] Repeat the impregnation with liquid polycarbosilane - low-temperature curing - vacuum sintering process multiple times to obtain a low open porosity C f / HfB2 - SiC composite material;

[0078] V. Use micro electrical discharge machining to prepare oriented micro pore channels from the low open porosity C f / HfB2 - SiC composite material to obtain an oriented microchannel low open porosity C f / HfB2 - SiC composite material, and the process is completed.

[0079] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the volume concentration of the ethanol solution is 70%. Others are the same as Specific Embodiment 1.

[0080] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the rotation speed of the ball mill in Step II is 250 r / min and the mixing time is 2 h. Others are the same as Specific Embodiment 1 or 2.

[0081] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the impregnation time in the HfB2 ceramic slurry in Step III is 1 - 6 h. Others are the same as any one of Specific Embodiments 1 to 3.

[0082] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that the impregnation time in liquid polycarbosilane in Step IV is 1 - 8 h and the pressure is 30 - 200 MPa. Others are the same as any one of Specific Embodiments 1 to 4.

[0083] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that the low-temperature curing temperature in Step IV is 200 °C. Others are the same as any one of Specific Embodiments 1 to 5.

[0084] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that in Step V, using micro electrical discharge machining technology, through an instantaneously high-energy current, the low open porosity C for making micropores fThe / HfB2-SiC composite material burns through to form directional microchannels for the flow of coolant during the active cooling process. The rest is the same as any one of the first to sixth specific embodiments.

[0085] Specific Embodiment Eight: The difference between this embodiment and any one of the first to seventh specific embodiments is that in step five, during micro-EDM, a copper tube electrode with a size of Ф0.1mm-Ф3.0mm is used, and the processing parameters are as follows: the pulse width of the pulse power supply is in the range of 1-13 gears, the pulse interval is in the range of 1-10 gears, the power amplifier is in the range of 1-3 gears, the processing voltage is 50V or 100V, and the processing current is 6A-10A. The rest is the same as any one of the first to seventh specific embodiments.

[0086] Specific Embodiment Nine: The difference between this embodiment and any one of the first to eighth specific embodiments is that in step five, the aperture of the directional micro-pore channels is controlled to be 0.2-1.0mm. The rest is the same as any one of the first to eighth specific embodiments.

[0087] Specific Embodiment Ten: This embodiment improves the oxidation and ablation resistance performance of C f / HfB2-SiC composite material by preparing a directional microchannel low-porosity C f / HfB2-SiC composite material, and the application of the directional microchannel low-porosity C f / HfB2-SiC composite material is used as a thermal protection material in the cooling channels of a thermal protection system.

[0088] The content of the present invention is not limited to the content of the above embodiments. The combination of one or several specific embodiments can also achieve the purpose of the invention.

[0089] Example 1:

[0090] The preparation of the low-porosity C f / HfB2-SiC composite material is specifically carried out according to the following steps:

[0091] One, a carbon fiber braided body is prepared using carbon fiber, with a braided body size of 100×100×10mm 3 , and the volume content is 10%, and a coating is covered on the surface of the carbon fiber through a chemical vapor deposition process;

[0092] Two, 600g of HfB2 powder after particle size grading, 6g of polyethyleneimine (CH2CH2NH) n and 1100g of an ethanol solution with a concentration of 70vol.% are put into a ball mill (the ball-to-material ratio is 10:1), and stirred at a rate of 250r / min for 2h for mixing to prepare an HfB2 ceramic slurry;

[0093] III. Use a high-pressure pump to extract the HfB2 ceramic slurry prepared in Step II and inject it into a container. At the same time, use a vacuum pump to evacuate the air below the filter element, control the relative pressure difference on both sides of the filter element to be greater than 0.5 MPa, immerse the 18 g carbon fiber braid prepared in Step I in the HfB2 ceramic slurry for 5 h, and then dry to obtain a green body;

[0094] IV. Place the green body in liquid polycarbosilane for ultra-high pressure impregnation for 8 h, control the pressure to be 200 MPa, then cure at a low temperature of 200 °C to obtain a preform. Sinter the preform in a vacuum furnace, with a sintering temperature of 1300 °C and a sintering time of 1 h;

[0095] Repeat the impregnation with liquid polycarbosilane - low-temperature curing - vacuum sintering process 8 times to obtain a low open porosity C f / HfB2 - SiC composite material.

[0096] Example 2:

[0097] The preparation of the low open porosity C f / HfB2 - SiC composite material is carried out specifically according to the following steps:

[0098] I. Prepare a carbon fiber braid using carbon fiber, with a braid size of 100×100×10 mm 3 , with a volume content of 15%, and cover a coating on the carbon fiber surface through chemical vapor deposition process;

[0099] II. Put 630 g of particle - sized HfB2 powder, 6.3 g of polyethyleneimine (CH2CH2NH) n and 1200 g of ethanol solution with a concentration of 70 vol.% into a ball mill (the ball - to - material ratio is 10:1), and stir at a rate of 250 r / min for 2 h for mixing to prepare an HfB2 ceramic slurry;

[0100] III. Use a high - pressure pump to extract the HfB2 ceramic slurry prepared in Step II and inject it into a container. At the same time, use a vacuum pump to evacuate the air below the filter element, control the relative pressure difference on both sides of the filter element to be greater than 0.5 MPa, immerse the 26 g carbon fiber braid prepared in Step I in the HfB2 ceramic slurry for 6 h, and then dry to obtain a green body;

[0101] IV. Place the green body in liquid polycarbosilane for ultra - high pressure impregnation for 2 h, control the pressure to be 180 MPa, then cure at a low temperature of 200 °C to obtain a preform. Sinter the preform in a vacuum furnace, with a sintering temperature of 1300 °C and a sintering time of 1 h;

[0102] Repeat the impregnation with liquid polycarbosilane - low - temperature curing - vacuum sintering process 8 times to obtain a low open porosity C f / HfB2 - SiC composite material.

[0103] Example 3:

[0104] Preparation of the low open porosity C f / HfB2-SiC composite material is carried out specifically according to the following steps:

[0105] I. Carbon fiber braids are prepared using carbon fibers, with the braid size of 100×100×10 mm 3 , and the volume content is 25%, and a coating is covered on the surface of the carbon fibers through a chemical vapor deposition process;

[0106] II. 600 g of HfB2 powder after particle size grading, 6 g of polyethyleneimine (CH2CH2NH) n and 1100 g of ethanol solution with a concentration of 70 vol.% are put into a ball mill (the ball-to-material ratio is 10:1), and stirred at a rate of 250 r / min for 2 h for mixing to prepare an HfB2 ceramic slurry;

[0107] III. A high-pressure pump is used to extract the HfB2 ceramic slurry prepared in step II and inject it into a container. At the same time, a vacuum pump is used to evacuate the air below the filter element, and the relative pressure difference on both sides of the filter element is controlled to be greater than 0.5 MPa. 40 g of the carbon fiber braid prepared in step I is impregnated in the HfB2 ceramic slurry for 5 h, and then dried to obtain a green body;

[0108] IV. The green body is put into liquid polycarbosilane for ultra-high pressure impregnation for 2 h, and the pressure is controlled to be 200 MPa, and then low-temperature cured at 200 °C to obtain a blank body. The blank body is sintered in a vacuum furnace, the sintering temperature is 1300 °C, and the sintering time is 1 h;

[0109] The impregnation of liquid polycarbosilane - low-temperature curing - vacuum sintering process is cycled 8 times to obtain the low open porosity C f / HfB2-SiC composite material.

[0110] Example 4:

[0111] This example uses the low open porosity C f / HfB2-SiC composite material obtained in Example 1, and an active cooling directional microchannel is constructed on this composite material to improve the C f / HfB2-SiC composite material's oxidation and ablation resistance performance, which is specifically carried out according to the following steps:

[0112] I. Using the micro-EDM method, the low open porosity C prepared in step IV of Example 1 fOriented micro-pore channels are prepared in the / HfB2-SiC composite material for micro-EDM. The process and parameters are as follows: The pulse width has 6 gears, the pulse interval has 6 gears, the power amplifier has 3 gears, and the electrode size is 0.2 mm. An oriented micro-channel with a low open porosity C is obtained. f The / HfB2-SiC composite material is completed.

[0113] The prepared / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C f The / HfB2-SiC composite material has good thermal stability, oxidation resistance, and cooling efficiency, and is suitable for medium / high heat flux density environments. The surface response temperature is significantly reduced, and the anti-oxidation and ablation ability is enhanced.

[0114] Figure 1 It is the processing drawing of the oriented micro-channel and the pictures of the material before and after processing. Among them, Figure a is the processing drawing, Figure b is the enlarged partial processing drawing, and Figure c is the top view of the prepared / HfB2-SiC composite material with a low open porosity C. f The top view of the / HfB2-SiC composite material with a low open porosity C, and Figure d is the top view of the prepared / HfB2-SiC composite material with a low open porosity C. f The side view of the / HfB2-SiC composite material with a low open porosity C, and Figure e is the top view of the / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C. f The top view of the / HfB2-SiC composite material with a low open porosity C;

[0115] Figure 2 It is the physical picture of the / HfB2-SiC composite material with a low open porosity C prepared in Example 1: f The physical picture of the / HfB2-SiC composite material with a low open porosity C prepared in Example 1:

[0116] Figure 3 It is the porosity diagram of the / HfB2-SiC composite material with a low open porosity C prepared in Example 1: f The porosity diagram of the / HfB2-SiC composite material with a low open porosity C;

[0117] Figure 4 It is the physical picture of the / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C prepared in Example 2: f The physical picture of the / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C prepared in Example 2;

[0118] Figure 5 It is the top view of the / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C prepared in Example 3: f The top view of the / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C prepared in Example 3;

[0119] Figure 6 It is the top view of the / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C prepared in Example 4: f The active cooling process diagram of the / HfB2-SiC composite material with an oriented micro-channel and a low open porosity C during the oxyacetylene ablation test;

[0120] Figure 7Macrophotographs of the composites prepared in Example 1 and Example 4 after passive ablation detection at different heat flux densities; it can be proved from the figure that the ablation state of the material becomes better after introducing active cooling, and there is no ablation but only surface oxidation, which proves that this method is effective.

[0121] Figure 8 The oriented microchannel low open porosity C prepared for Example 4 f Response temperature test diagrams of the surface of the / HfB2 - SiC composite material in Example 4 under two ablation states (with and without coolant), which proves that introducing coolant by the method of the present invention can reduce the surface temperature of the material, and the maximum temperature can be reduced by 524 °C. At this time, the coolant consumption is only 0.17 g / s, and the cooling efficiency is high, and the scheme is feasible.

[0122] Example 5:

[0123] This example uses the low open porosity C obtained in Example 1 f / HfB2 - SiC composite material, and constructs an active cooling oriented microchannel on this composite material to improve the anti - oxidation and ablation performance of the C f / HfB2 - SiC composite material. The specific steps are as follows:

[0124] I. Use the micro - electrical discharge machining method to prepare oriented micro - pores channels on the low open porosity C f / HfB2 - SiC composite material prepared in Step 4 of Example 1. Carry out micro - electrical discharge machining, and the process and parameters are: pulse width is at gear 2, pulse interval is at gear 3, power amplifier is at gear 2. 19 through - holes are prepared on the stepped sample using electrodes with different diameters. The pore distribution is as Figure 9 (In the left a - figure, 3 mm, 6 mm, and 7.5 mm represent the distance of the oriented microchannel from the center of the circle. The right b - figure is the 4 - kind pore - diameter oriented microchannel low open porosity C f / HfB2 - SiC composite material) shown. The figure shows the macroscopic view of the surface of the porous sample prepared by micro - electrical discharge machining using different electrode diameters. Measured at randomly selected positions using an optical microscope, when the electrode diameters are 0.2 mm, 0.3 mm, 0.4 mm, and 0.5 mm, the actual average pore diameters are 0.3 ± 0.05 mm, 0.4 ± 0.05 mm, 0.5 ± 0.05 mm, and 0.6 ± 0.05 mm respectively.

[0125] The composite material of this example is suitable for applications that require anti - oxidation and ablation resistance in extreme environments (2800 °C). The stability of the material under high - temperature and high - heat flux density is improved, and at the same time, a good cooling effect is maintained.

[0126] The oriented microchannel low open porosity C prepared in the example fThe / HfB2-SiC composite material is applied as a cooling element into the cooling channels of a cooling thermal management system; the flow rate of the coolant is controlled to be 0.1 - 1.0 g / s.

[0127] Under an oxygen-rich environment, an oxy-acetylene ablation test was carried out on the directionally microchanneled low-porosity C f / HfB2-SiC composite material as shown Figure 10 below, and the temperature rise curve is as shown Figure 11 below. Through the macroscopic images of the material before and after ablation, it is shown that exposure to the oxy-acetylene flame caused a white oxide layer to form on the sample surface, accompanied by ablation damage to varying degrees, and there were ablation pits; however, compared with the C f / HfB2-SiC composite material (Example 1) without constructing an actively cooled microchannel pore after the oxy-acetylene ablation test, the ablation photos ( Figure 12 ) and the temperature rise curve ( Figure 13 ) have been significantly improved.

[0128] The porous sample prepared by the present invention has directionally through-hole cooling channels, and during the whole test process, the flow rate of the liquid coolant is maintained at 0.75 g / s.

[0129] The surface of the sample was cooled using an active cooling test device. Taking the temperature difference (ΔT) of the surface response temperature as the evaluation criterion, the active cooling performance of the coolant in the directionally microchanneled low-porosity C f / HfB2-SiC composite material was evaluated as shown Figure 14 below. During the active cooling process, the pore size of the cooling channel is closely related to the cooling performance. When the channel diameter is in the range of 0.4 - 0.5 mm (processing tolerance ±0.05 mm), the cooling performance is the best. Under extreme conditions of about 2800 °C / 400 s, the coolant maintained its function for 400 s and achieved a maximum temperature reduction of 1329 °C. It proves the effectiveness of the method for improving the oxidation and ablation resistance of the C f / HfB2-SiC composite material through active cooling.

[0130] Table 1 shows the comparison of the surface temperatures after active cooling of the directionally microchanneled low-porosity C f / HfB2-SiC composite material.

[0131] Table 1

[0132]

Claims

1. Method for improving oxidation and ablation resistance of C f / HfB2-SiC composite material by active cooling, characterized in that The method is specifically carried out according to the following steps: First, prepare a carbon fiber braid using carbon fiber, and cover a coating on the surface of the carbon fiber through a chemical vapor deposition process; Second, put HfB2 powder, polyethyleneimine, and an ethanol solution into a ball mill for mixing to prepare an HfB2 ceramic slurry; Third, use a high-pressure pump to extract the HfB2 ceramic slurry prepared in the second step and inject it into a container. At the same time, use a vacuum pump to evacuate the air below the filter element, control the relative pressure difference on both sides of the filter element to be greater than 0.5 MPa, immerse the carbon fiber braid prepared in the first step in the HfB2 ceramic slurry, and then dry it to obtain a green body; Fourth, put the green body into liquid polycarbosilane for ultra-high-pressure impregnation, then cure it at a low temperature, and then put it into a vacuum furnace for sintering; The process of impregnating liquid polycarbosilane - low-temperature curing - vacuum sintering is cycled multiple times to obtain a C / HfB2 - SiC composite material with a low open porosity rate; f ​ V. Using the micro-EDM method, fabricate oriented micro-pore channels in the low open porosity C f / HfB2-SiC composite material prepared in Step IV to obtain the low open porosity C f / HfB2-SiC composite material, thus completing the process.

2. Method for improving oxidation and ablation resistance of C f / HfB2 - SiC composite material by active cooling, characterized in that The volume concentration of the ethanol solution described in the second step is 70%.

3. The method for improving the oxidation and ablation resistance performance of C f / HfB2-SiC composite material by active cooling according to claim 1, characterized in that The rotation speed of the ball mill described in the second step is 250 r / min, and the mixing time is 2 h.

4. Method for improving oxidation and ablation resistance performance of C f / HfB2 - SiC composite material by active cooling, characterized in that The impregnation time in the HfB2 ceramic slurry in the third step is 1 to 6 h.

5. Method for improving oxidation and ablation resistance of C f / HfB2 - SiC composite material by active cooling, characterized in that In the fourth step, impregnation in liquid polycarbosilane is carried out for 1 to 8 h, and the pressure is 30 to 200 MPa.

6. The method for improving the oxidation and ablation resistance performance of C f / HfB2-SiC composite materials by active cooling according to claim 1, characterized in that The low-temperature curing temperature described in the fourth step is 200 °C.

7. A method for improving the oxidation and ablation resistance of C f / HfB2-SiC composite materials by active cooling, characterized in that Step 5: Using the micro-EDM technology, burn through the low open porosity C f / HfB2-SiC composite material for making micropores through an instantaneously high-energy current to form a directional microchannel for the coolant to flow through during the active cooling process. f ​ 8. A method for improving the oxidation and ablation resistance of C f / HfB2 - SiC composite materials by active cooling, characterized in that In the micro-EDM process in the fifth step, a copper tube electrode with a size of Ф0.1 mm to Ф3.0 mm is used, and the processing parameters are: the pulse width of the pulse power supply is in the range of 1 to 13 gears, the pulse interval is in the range of 1 to 10 gears, the power amplifier is in the range of 1 to 3 gears, the processing voltage is 50 V or 100 V, and the processing current is 6 A to 10 A.

9. The method for improving the oxidation and ablation resistance of C f / HfB2-SiC composite materials by active cooling, characterized in that In the fifth step, control the pore diameter of the directional micro-pore channels to be 0.2 to 1.0 mm.

10. The method for improving the oxidation and ablation resistance of C f / HfB2-SiC composite material by active cooling as claimed in claim 1 to prepare the directional microchannel low open porosity C f / HfB2-SiC composite material application, characterized in that The directional microchannel low open porosity C f / HfB2-SiC composite material is applied as a thermal protection material to the cooling channels of the thermal protection system.

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