A cavity carbon-based composite material with densified inner surface and a preparation method and application thereof

Abstract

The application discloses a cavity carbon-based composite material with densified inner surface and a preparation method and application thereof, and relates to the technical field of carbon-based composite materials. The method places the cavity carbon-based composite material in a graphite crucible paved with infiltration powder, then adds a mold in the inner cavity, and further adds the infiltration powder between the mold and the inner surface of the cavity carbon-based composite material; after the infiltration powder is added completely, the graphite paper and the carbon felt are used for sealing treatment in sequence, and then the crucible is sealed; the sealed graphite crucible is treated at 1600-2100 DEG C for 30-180 min under the protection of inert gas, and the cavity carbon-based composite material with the densified inner surface is obtained. The method adds the infiltration powder between the mold and the inner surface of the cavity carbon-based composite material, and realizes the dense distribution of the ceramic phase on the inner surface of the annular carbon-based composite material (special-shaped part) after heat treatment.

Description

Technical Field

[0001] This invention relates to the field of carbon-based composite materials technology, specifically to a cavity carbon-based composite material with internally densified surface, its preparation method, and its application. Background Technology

[0002] As a key component of solid rocket motors, the throat liner's main function is to control the exhaust volume of engine combustion gases, maintaining a certain pressure within the combustion chamber, and accelerating the gases to the speed of sound through the nozzle throat to generate 65%–75% of the thrust. Currently, the operating environment temperature of the throat liner in solid rocket motor nozzles reaches over 3000K, while also being subjected to the erosion of high-speed particle streams. Therefore, the main factors contributing to throat liner erosion are thermochemical ablation and mechanical erosion, requiring materials that are heat-resistant, lightweight, have high ablation heat, and resist thermomechanical shock. Commonly used throat liner materials in China are tungsten-copper infiltrated materials and C / C composite materials. Tungsten-copper infiltrated composite materials are a self-sweating cooling throat liner material, developed based on the principle that tungsten and copper are mutually insoluble and mutually wetting, exhibiting good high-temperature resistance, ablation resistance, and resistance to airflow erosion. However, due to copper leaching at high temperatures, the two materials are prone to bonding under high-temperature conditions, which is not conducive to mass production. Furthermore, tungsten-copper infiltrated materials have a high density, which is detrimental to weight reduction and thrust improvement in throat liner materials. C / C composite materials have low density, but the matrix itself contains some closed pores. These pores provide channels for oxidizing atmospheres, exacerbating the erosion of the matrix by the flame. Simultaneously, under the shear force of the high-temperature combustion gases, fibers are prone to breakage, and large ablation pores form at defect locations. This leads to overall weight and thinning of the throat liner, resulting in a larger throat liner outlet diameter, insufficient pressure, and reduced thrust. Therefore, the development of ablation-resistant carbon-based composite materials is urgently needed. These materials use carbon fiber as reinforcement, chemical vapor deposition of pyrolytic carbon, liquid-phase impregnation of carbonized resin carbon, or pitch carbon as the matrix, and ultra-high temperature ceramics as ablation-resistant modifying phases. They possess characteristics such as lightweight, resistance to oxidation and ablation, ultra-high melting point, and excellent high-temperature mechanical properties, making them the preferred material for next-generation throat liner materials.

[0003] Currently, the main methods for preparing ablation-resistant carbon-based composite materials include coating methods and matrix modification methods. Among these, matrix modification methods can effectively improve the ablation resistance of C / C composite materials. Matrix modification methods mainly include precursor impregnation pyrolysis, slurry infiltration, and reactive melting infiltration. Precursor impregnation pyrolysis has a long preparation cycle, high time cost, and introduces loose ceramic particles. Materials prepared by slurry impregnation have poor ceramic particle bonding. Reactive melting infiltration, on the other hand, has significant advantages such as short preparation time, strong ceramic-matrix bonding, and near-net-shape forming, showing great application potential. However, in existing technologies, it is difficult to achieve ceramic phase densification on the inner surface of irregularly shaped parts with cavities when preparing samples using reactive melting infiltration, which limits the application of reactive melting infiltration in some fields. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology, the main technical problem solved by this invention is that when preparing samples using reactive infiltration processes, it is difficult to achieve ceramic phase densification on the inner surface of cavitary irregular parts, which limits the application of reactive infiltration processes in some fields. This invention provides a cavity carbon-based composite material with densified inner surface, its preparation method, and its applications. This method involves adding infiltration powder between a mold and the inner surface of the cavity carbon-based composite material, followed by heat treatment, to achieve a dense distribution of the ceramic phase on the inner surface of the cyclic carbon-based composite material (irregular part).

[0005] The first objective of this invention is to provide a method for preparing a cavity carbon-based composite material with a densified inner surface, comprising the following steps:

[0006] The hollow carbon-based composite material is placed in a graphite crucible with a thickness of 4-10 mm of melt-infiltrating powder. Then, a mold is added to the inner cavity, and melt-infiltrating powder is added between the mold and the inner surface of the hollow carbon-based composite material. When adding melt-infiltrating powder, after covering the upper surface of the hollow carbon-based composite material, powder is added until the thickness of the upper surface is 5-20 mm.

[0007] After the melt-infiltrating powder is added, the crucible is sealed in sequence using graphite paper and carbon felt, and then sealed.

[0008] The sealed graphite crucible is then treated at 1600–2100℃ for 30–180 min under the protection of an inert gas to obtain a cavity carbon-based composite material with a denser inner surface.

[0009] Preferably, the melt-infiltrating powder is prepared according to the following steps:

[0010] HfSi2 and Al2O3 are mixed in a certain molar ratio. The mixed powder is poured into a ball mill jar, and zirconia grinding balls are added at a ball-to-powder ratio of 2:1. After ball milling, melt-infiltrated powder is obtained.

[0011] Preferably, the molar ratio of HfSi2 to Al2O3 is 50 to 200:1.

[0012] Preferably, the ball milling is performed using a planetary ball mill, with the milling time set to 300-400 r / min for 3-8 hours.

[0013] Preferably, the hollow carbon-based composite material includes a cyclic 2.5DC / C composite material with an inner cavity that is cylindrical and placed vertically in a graphite crucible.

[0014] Preferably, the mold includes a conical mold, a cylindrical mold, or a frustum mold.

[0015] Preferably, the height of the mold is the same as the height of the annular 2.5DC / C composite material.

[0016] Preferably, under the protection of an inert gas, the heating rate during heat treatment is 5–10 °C / min.

[0017] The second objective of this invention is to provide a cavity carbon-based composite material with a denser inner surface.

[0018] The third objective of this invention is to provide an application of a cavity carbon-based composite material with a denser inner surface in rocket engine nozzles.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention provides a cavity carbon-based composite material with a denser inner surface, its preparation method, and its applications. Compared with traditional reactive melting infiltration processes, this process can save 30-50% of the melting infiltration powder, significantly reducing preparation costs. Compared with the partitioned modification reactive melting infiltration process, this invention achieves a dense distribution of the ceramic phase on the inner surface of the cyclic carbon-based composite material (irregularly shaped parts). The porosity of the cyclic carbon-based composite material is reduced by approximately 30-60%, further improving the oxidation and ablation resistance of the carbon-based composite material. Based on this invention, further mold design can be carried out for ablation-resistant carbon-based composite material irregularly shaped parts; the preparation of ablation-resistant carbon-based composite material irregularly shaped parts can be realized. The development prospects of this invention are very promising, with significant economic and social benefits.

[0021] This invention involved comparative experiments with three different molds—conical, frustum, and cylindrical—without a mold. The results showed that a cylindrical mold significantly aided in the preparation of cyclic carbon-based composite materials, substantially improving the ceramic densification of the inner surface of the sample. The main reason is that the driving force for melt infiltration during the reaction process is primarily capillary force, which, influenced by gravity, provides a higher driving force. However, the inner cavity surface deviates from the direction of gravity, resulting in a relatively insufficient driving force for melt infiltration. Simultaneously, the powder itself tends to spontaneously sinter at high temperatures, spontaneously agglomerating towards the center, further reducing the contact between the sidewalls and the melt. These factors all contribute to a decrease in the infiltration depth and surface density of the inner wall. By using tooling molds that match the cavity size, the melt distribution after melting can be restricted, increasing the contact area between the melt and the inner wall, improving the infiltration contact time and release area, while mitigating the negative effects of powder sintering. Based on this, ablation tests were conducted on samples prepared using molds of different shapes and without molds, and their ablation resistance was compared and analyzed. It was found that after adding a cylindrical mold, the mass ablation rate of the material increased by 93.66%, the linear ablation rate changed from 3.65 μm / s to -4.47 μm / s, and the sample thickness changed from thinning to thickening. The reason for the thickening was that an oxide film was formed on the sample surface. Attached Figure Description

[0022] Figure 1 This is a process effect diagram of the present invention;

[0023] Figure 2 The density-open porosity bar chart shows the cyclic C / C-HfC-SiC composite materials prepared by the present invention using different molds.

[0024] Figure 3 Low-magnification SEM images of the inner surface of the cyclic C / C-HfC-SiC composite material prepared by the present invention using different molds;

[0025] Figure 4 Images of the ablation process of the cyclic carbon-based composite material of the present invention;

[0026] Figure 5 Macroscopic morphology images of the cyclic C / C-HfC-SiC composite materials prepared by the present invention after ablation using different molds. Detailed Implementation

[0027] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0028] The purpose of this invention is to provide a mold that achieves better melting and infiltration effect during the reaction melting and infiltration process, while reducing the preparation cost, significantly improving the ablation resistance of the resulting composite material, and providing more ideas for the preparation of carbon-based composite materials for subsequent irregular parts.

[0029] The first aspect of this invention provides a method for preparing a cavity carbon-based composite material with a densified inner surface, comprising the following steps:

[0030] The hollow carbon-based composite material is placed in a graphite crucible with a thickness of 4-10 mm of melt-infiltrating powder. Then, a mold is added to the inner cavity, and melt-infiltrating powder is added between the mold and the inner surface of the hollow carbon-based composite material. When adding melt-infiltrating powder, after covering the upper surface of the hollow carbon-based composite material, powder is added until the thickness of the upper surface is 5-20 mm.

[0031] After the melt-infiltrating powder is added, the crucible is sealed in sequence using graphite paper and carbon felt, and then sealed.

[0032] The sealed graphite crucible is then treated at 1600–2100℃ for 30–180 min under the protection of an inert gas to obtain a cavity carbon-based composite material with a denser inner surface.

[0033] The hollow carbon-based composite material includes a cyclic 2.5DC / C composite material with a cylindrical inner cavity, which is placed vertically in a graphite crucible. The mold includes a conical mold, a cylindrical mold, or a frustum mold. The height of the mold is set to be equal to the height of the cyclic 2.5DC / C composite material. It should be noted that the mold configuration corresponds to the cavity configuration in the hollow carbon-based composite material.

[0034] This invention achieves a dense distribution of ceramic phase on the inner surface of a cyclic carbon-based composite material (irregularly shaped part) by adding melt-infiltrating powder between the mold and the inner surface of the hollow carbon-based composite material, followed by heat treatment.

[0035] Based on this invention, further mold design can be carried out for ablation-resistant carbon-based composite irregular parts; thus realizing the preparation of ablation-resistant carbon-based composite irregular parts.

[0036] Compared with traditional reactive melt infiltration processes, the method provided by this invention can save 30-50% of the melt infiltration powder, greatly reducing the preparation cost.

[0037] According to the present invention, the melt-infiltrating powder is prepared according to the following steps:

[0038] HfSi2 and Al2O3 are mixed in a certain molar ratio. The mixed powder is poured into a ball mill jar, and zirconia grinding balls are added at a ball-to-powder ratio of 2:1. After ball milling, melt-infiltrated powder is obtained.

[0039] The molar ratio of HfSi2 to Al2O3 is 50 to 200:1.

[0040] The ball milling process uses a planetary ball mill, and the milling time is 3-8 hours with a rotation speed set at 300-400 r / min.

[0041] According to the present invention, under the protection of an inert gas, the heating rate during heat treatment is 5 to 10 °C / min.

[0042] In one embodiment, a method for preparing a cavity carbon-based composite material with a densified inner surface includes the following steps:

[0043] Step 1: Select a density of 1.0–1.4 g / cm³ 3 The cyclic 2.5DC / C composite material was polished with 50-mesh, 400-mesh and 1000-mesh sandpaper in sequence to keep the sample surface smooth. Then, it was ultrasonically cleaned with deionized water for 20-70 minutes and dried at 50-80℃ for 3-8 hours.

[0044] Step 2: Mix HfSi2 and Al2O3 at a certain molar ratio, pour the mixed powder into a ball mill jar, and add zirconia grinding balls at a ball-to-powder ratio of 2:1. Use a planetary ball mill to ball mill the mixed powder for 3-8 hours at a speed of 300-400 r / min, and then place it in an oven to dry for 6-12 hours.

[0045] Step 3: Place the annular porous C / C composite material parallel to each other in a graphite crucible with a bottom layer of melt-infiltrating powder of 4–10 mm thickness. Then, add a mold into the internal cavity, followed by adding melt-infiltrating powder, ensuring the powder remains loose during addition. After the powder completely covers the upper surface of the sample, continue adding powder until the upper surface thickness is 5–20 mm. See [link / reference] Figure 1 The image shows the effect of placing the mold inside the annular porous C / C composite material cavity.

[0046] It should be noted that when the annular porous C / C composite material is placed in parallel, it means that the annular porous C / C composite material is placed vertically in the graphite crucible, and the axis of the annular porous C / C composite material is perpendicular to the graphite crucible.

[0047] Step 4: After the powder is added, seal the crucible with graphite paper and carbon felt in sequence, and then seal the crucible.

[0048] Step 5: Place the sealed graphite crucible in a heat treatment furnace. Under Ar atmosphere protection, heat to 1600-2100℃ at a rate of 5-10℃ / min, hold for 30-180min, then turn off the power and cool down. After the sample cools to room temperature, remove it and use sandpaper to polish away any residual powder adhering to the sample surface to obtain a C / C-HfC-SiC composite material with a dense inner surface.

[0049] A second aspect of the present invention provides a cavity carbon-based composite material with a densified inner surface.

[0050] A third aspect of the present invention provides the application of a cavity carbon-based composite material with an inner surface densified in a rocket engine nozzle.

[0051] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0052] Example 1

[0053] Step 1: Select a density of 1.4 g / cm³ 3 The cyclic 2.5DC / C composite material was polished with 50-mesh, 400-mesh and 1000-mesh sandpaper in sequence to keep the sample surface smooth. Then, it was ultrasonically cleaned with deionized water for 40 minutes and dried at 60°C for 8 hours.

[0054] Step 2: Mix HfSi2 and Al2O3 at a certain molar ratio, pour the mixed powder into a ball mill jar, and add zirconia grinding balls at a ball-to-powder ratio of 2:1. Use a planetary ball mill to ball mill the mixed powder for 3–8 hours at a speed of 300 r / min. Then place it in an oven to dry for 6 hours.

[0055] Step 3: Place the annular porous C / C composite material parallel to each other in a graphite crucible with a 4mm thick layer of melt infiltration powder at the bottom. Then add melt infiltration powder, ensuring that the powder is in a loose state during the addition process. After the powder completely covers the upper surface of the sample, continue to add powder until the upper surface thickness is 5mm.

[0056] Step 4: After the powder is added, seal the crucible with graphite paper and carbon felt in sequence, and then seal the crucible.

[0057] Step 5: Place the sealed graphite crucible in a heat treatment furnace. Under Ar atmosphere protection, heat to 2100℃ at a rate of 10℃ / min and hold for 30min. Then turn off the power and cool down. After the sample cools to room temperature, take it out and use sandpaper to polish away the residual powder adhering to the sample surface to obtain C / C-HfC-SiC composite material.

[0058] The cyclic C / C-HfC-SiC composite material obtained in this embodiment has an open porosity of 15.14% and a density of 3.92 g / cm³. 3 The ceramic layer on the inner surface of the composite material tends to detach. The cyclic C / C-HfC-SiC composite material obtained in this example exhibits a heat flux density of 4.18 MW / m³. 2 After 40 s of ablation under an oxyacetylene flame, the mass ablation rate and the linear ablation rate were 0.079 g / s and 3.65 μm / s, respectively.

[0059] Example 2

[0060] Step 1: Select a density of 1.0 g / cm³ 3 The cyclic 2.5DC / C composite material was polished with 50-mesh, 400-mesh and 1000-mesh sandpaper in sequence to keep the sample surface smooth. Then, it was ultrasonically cleaned with deionized water for 40 minutes and dried at 70°C for 8 hours.

[0061] Step 2: Mix HfSi2 and Al2O3 at a certain molar ratio, pour the mixed powder into a ball mill jar, and add zirconia grinding balls at a ball-to-powder ratio of 2:1. Use a planetary ball mill to ball mill the mixed powder for 3 hours at a speed of 300 r / min. Then place it in an oven to dry for 7 hours.

[0062] Step 3: Place the annular porous C / C composite material parallel to each other in a graphite crucible with a 4mm thick layer of melt-infiltrating powder at the bottom. Add a cylindrical high-strength graphite mold into the cavity, and then add melt-infiltrating powder, ensuring that the powder is in a loose state during the addition process. After the powder completely covers the upper surface of the sample, continue to add powder until the upper surface thickness is 5mm.

[0063] Step 4: After the powder is added, seal the crucible with graphite paper and carbon felt in sequence, and then seal the crucible.

[0064] Step 5: Place the sealed graphite crucible in a heat treatment furnace. Under Ar atmosphere protection, heat to 2100℃ at a rate of 10℃ / min and hold for 30min. Then turn off the power and cool down. After the sample cools to room temperature, take it out and use sandpaper to polish away the residual powder adhering to the sample surface to obtain C / C-HfC-SiC composite material.

[0065] The cyclic C / C-HfC-SiC composite material obtained in this embodiment has an open porosity of 9.74% and a density of 4.03 g / cm³. 3 The ceramic layer on the inner surface of the composite material is dense. The cyclic C / C-HfC-SiC composite material obtained in this example has a heat flux density of 4.18 MW / m³.2 After 40 s of ablation under an oxyacetylene flame, the mass ablation rate and linear ablation rate were 0.005 g / s and -4.47 μm / s, respectively. Compared with the unmodified version, the ablation performance of the cyclic C / C-HfC-SiC composite material was significantly improved.

[0066] Example 3

[0067] Step 1: Select a density of 1.0 g / cm³ 3 The cyclic 2.5DC / C composite material was polished with 50-mesh, 400-mesh and 1000-mesh sandpaper in sequence to keep the sample surface smooth. Then, it was ultrasonically cleaned with deionized water for 60 minutes and dried at 80°C for 6 hours.

[0068] Step 2: Mix HfSi2 and Al2O3 at a certain molar ratio, pour the mixed powder into a ball mill jar, and add zirconia grinding balls at a ball-to-powder ratio of 2:1. Use a planetary ball mill to ball mill the mixed powder for 3 hours at a speed of 300 r / min. Then place it in an oven to dry for 6 hours.

[0069] Step 3: Place the annular porous C / C composite material parallel to each other in a graphite crucible with a 4mm thick layer of melt-infiltrating powder at the bottom. Add a frustum-shaped high-strength graphite mold into the cavity, and then add melt-infiltrating powder, ensuring that the powder is in a loose state during the addition process. After the powder completely covers the upper surface of the sample, continue to add powder until the upper surface thickness is 6mm.

[0070] Step 4: After the powder is added, seal the crucible with graphite paper and carbon felt in sequence, and then seal the crucible.

[0071] Step 5: Place the sealed graphite crucible in a heat treatment furnace. Under Ar atmosphere protection, heat to 2000℃ at a rate of 10℃ / min and hold for 60min. Then turn off the power and cool down. After the sample cools to room temperature, take it out and use sandpaper to polish away the residual powder adhering to the sample surface to obtain C / C-HfC-SiC composite material.

[0072] The cyclic C / C-HfC-SiC composite material obtained in this embodiment has an open porosity of 11.54% and a density of 3.57 g / cm³. 3 The ceramic layer on the inner surface of the composite material is porous and discontinuous. The cyclic C / C-HfC-SiC composite material obtained in this example operates at a heat flux density of 4.18 MW / m³. 2 After 40 s of ablation under an oxyacetylene flame, the mass ablation rate and linear ablation rate were 0.039 g / s and 2.80 μm / s, respectively. Compared with the unmodified version, the ablation performance of the cyclic C / C-HfC-SiC composite material was improved.

[0073] Example 4

[0074] Step 1: Select a density of 1.0 g / cm³ 3 The cyclic 2.5DC / C composite material was polished with 50-mesh, 400-mesh and 1000-mesh sandpaper in sequence to keep the sample surface smooth. Then, it was ultrasonically cleaned with deionized water for 60 minutes and dried at 80°C for 6 hours.

[0075] Step 2: Mix HfSi2 and Al2O3 at a certain molar ratio, pour the mixed powder into a ball mill jar, and add zirconia grinding balls at a ball-to-powder ratio of 2:1. Use a planetary ball mill to ball mill the mixed powder for 3 hours at a speed of 300 r / min. Then place it in an oven to dry for 7 hours.

[0076] Step 3: Place the annular porous C / C composite material parallel to each other in a graphite crucible with a 4mm thick layer of melt-infiltrating powder at the bottom. Add a conical high-strength graphite mold into the cavity, and then add melt-infiltrating powder, ensuring that the powder is in a loose state during the addition process. After the powder completely covers the upper surface of the sample, continue to add powder until the upper surface thickness is 5mm.

[0077] Step 4: After the powder is added, seal the crucible with graphite paper and carbon felt in sequence, and then seal the crucible.

[0078] Step 5: Place the sealed graphite crucible in a heat treatment furnace. Under Ar atmosphere protection, heat to 2000℃ at a rate of 10℃ / min and hold for 60min. Then turn off the power and cool down. After the sample cools to room temperature, take it out and use sandpaper to polish away the residual powder adhering to the sample surface to obtain C / C-HfC-SiC composite material.

[0079] The cyclic C / C-HfC-SiC composite material obtained in this embodiment has an open porosity of 17.60% and a density of 3.36 g / cm³. 3 The ceramic layer on the inner surface of the composite material is porous and discontinuous. The cyclic C / C-HfC-SiC composite material obtained in this example operates at a heat flux density of 4.18 MW / m³. 2 After 40 s of ablation under an oxyacetylene flame, the mass ablation rate and linear ablation rate were 0.052 g / s and 5.70 μm / s, respectively. Compared with the unmodified version, the ablation performance of the cyclic C / C-HfC-SiC composite material was slightly reduced.

[0080] Comparative experiments were conducted with and without three different molds (conical, frustum-shaped, and cylindrical). The results showed that the cylindrical mold played a significant auxiliary role in preparing cyclic carbon-based composite materials, substantially improving the ceramic densification of the inner surface of the sample. Compared with the absence of a mold, the addition of a cylindrical mold increased the mass ablation rate of the material by 93.66%, changed the linear ablation rate from 3.65 μm / s to -4.47 μm / s, and altered the sample thickness from thinning to thickening. The thickening was attributed to the formation of an oxide film on the sample surface.

[0081] To further illustrate the performance of the method provided by this invention, the accompanying drawings are provided.

[0082] Figure 2 This is a density-open porosity histogram of the cyclic C / C-HfC-SiC composite material prepared using different molds according to the present invention; from Figure 2 It can be seen that the sample prepared using the cylindrical mold has the highest density and the lowest porosity, indicating that the sample density is significantly improved.

[0083] Figure 3 Low-magnification SEM images of the inner surface of the annular C / C-HfC-SiC composite material prepared by this invention using different molds; from Figure 3 It can be seen that the ceramic layer on the surface of the sample prepared without using a mold has obvious peeling and insufficient bonding force. The inner wall surface of the sample prepared with a conical and frustum mold does not have the required ceramic layer. The inner surface of the sample prepared with a cylindrical mold is dense and the ceramic layer is tightly bonded to the sample.

[0084] Figure 4 Images of the ablation process of the cyclic carbon-based composite material of the present invention; from Figure 4 This is a photograph of the sample at a certain moment during the oxyacetylene flame test.

[0085] Figure 5 Macroscopic morphology images of the annular C / C-HfC-SiC composite materials prepared by this invention after ablation using different molds; from Figure 5 It can be seen that the oxide film on the surface of the sample prepared without the use of a mold is loose and there is obvious peeling after the oxyacetylene test. In contrast, the inner wall surface of the sample prepared with a conical and frustum mold does not form a dense film, while the inner surface oxide film of the sample prepared with a cylindrical mold is dense.

[0086] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cavity carbon-based composite material with a densified inner surface, characterized in that, Includes the following steps: The hollow carbon-based composite material is placed in a graphite crucible with a thickness of 4-10 mm of melt-infiltrating powder. Then, a mold is added to the inner cavity, and melt-infiltrating powder is added between the mold and the inner surface of the hollow carbon-based composite material. When adding melt-infiltrating powder, after covering the upper surface of the hollow carbon-based composite material, powder is added until the thickness of the upper surface is 5-20 mm. After the melt-infiltrating powder is added, the crucible is sealed in sequence using graphite paper and carbon felt, and then sealed. The sealed graphite crucible is treated at 1600~2100℃ for 30~180 min under the protection of inert gas to obtain a cavity carbon-based composite material with a dense inner surface. The melt-infiltrating powder is prepared according to the following steps: HfSi2 and Al2O3 are mixed in a certain molar ratio. The mixed powder is poured into a ball mill jar, and zirconia grinding balls are added at a ball-to-powder ratio of 2:

1. After ball milling, melt-infiltrated powder is obtained. The molar ratio of HfSi2 to Al2O3 is 50~200:1; The hollow carbon-based composite material includes a cyclic 2.5 DC / C composite material with a cylindrical inner cavity, which is placed vertically in a graphite crucible.

2. The method for preparing the cavity carbon-based composite material with internal surface densification according to claim 1, characterized in that, The ball milling process uses a planetary ball mill, and the milling time is 3-8 hours with a rotation speed of 300-400 r / min.

3. The method for preparing the cavity carbon-based composite material with internal surface densification according to claim 1, characterized in that, Molds include conical molds, cylindrical molds, or frustum molds.

4. The method for preparing the cavity carbon-based composite material with internal surface densification according to claim 3, characterized in that, The height of the mold is the same as the height of the annular 2.5 DC / C composite material.

5. The method for preparing the cavity carbon-based composite material with internal surface densification according to claim 1, characterized in that, Under the protection of inert gas, the heating rate during heat treatment is 5~10℃ / min.

6. A cavity carbon-based composite material with an internally densified surface obtained by the method of any one of claims 1 to 5.

7. The application of the cavity carbon-based composite material with internally densified structure as described in claim 6 in a rocket engine nozzle.

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