Matrix modification-surface coating gradient integrated C / C composite material and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of modified C / C composite materials, and discloses a matrix modification-surface coating gradient integrated C / C composite material and a preparation method thereof.Silicide powder and a low-density C / C composite material are subjected to reactive infiltration under the vacuum condition, after reactive infiltration and heat preservation are finished, a nitrogen atmosphere is switched, heat preservation continues to be conducted, and then the matrix modification-surface coating gradient integrated C / C composite material is obtained; and after the air pressure sintering is finished, the matrix modification-surface coating gradient integrated C / C composite material is obtained. Atmosphere pressure sintering and reactive infiltration technologies are combined, and in the vacuum stage, part of silicide enters a low-density C / C matrix through infiltration and reacts with pyrolytic carbon to generate carbide ceramic; and then N2 with a certain pressure is introduced to react with the residual silicide, and the ultra-high-temperature ceramic coating is generated on the surface of the C / C composite material. By changing the atmosphere mode in the heat preservation process, the whole technological process is simple, and the preparation period is greatly shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of modified C / C composite materials, and in particular relates to a matrix modification-surface coating gradient integrated C / C composite material and a preparation method thereof. Background Art

[0002] Carbon / carbon (C / C) composites use carbon fibers as reinforcements and have many advantages, such as low density, low thermal expansion coefficient, high thermal conductivity, electrical conductivity, excellent thermal shock resistance, ablation resistance and friction resistance. However, C / C composites begin to oxidize in an air atmosphere at 450°C. The mass loss caused by oxidation has a significant impact on the various properties of the composites, especially the mechanical properties, which greatly limits the application of C / C composites in high-temperature environments. Improving the anti-oxidation and anti-ablation protection properties of C / C composites is a prerequisite for their application in high-temperature environments. There are currently two main solutions: coating protection technology and matrix modification technology.

[0003] Reference 1 “Zheng J, He P, Jiang F, et al. Thick and dense nitrogen-doped hafnium carbide ultra-high temperature thermal protection coating for outstanding ablation resistance up to 2600 °C[J]. Journal of Alloys and Compounds, 1010(2025), 177379” successfully synthesized a single-phase solid solution HfCN coating by spray granulation of HfC-HfN composite powder using the dual solid solution effect of radio frequency inductively coupled plasma spheroidization and supersonic atmospheric pressure plasma spraying process. 2 After 200 s of plasma ablation under high heat flux, the HfCN coating exhibits a surface temperature as high as 2600 °C, which can firmly protect the substrate from oxidation damage.

[0004] Reference 2 “Xu C, Jia C, LiuQ, et al. Microstructure and ablation behaviorof C / C-HfC-SiC composites fabricated by reactive melt infiltration with Hf–Sialloy[J]. Journal of the American Ceramic Society, 108(2024)e20215” prepared C / C-HfC-SiC composites by reactive melt infiltration. C / C-HfC-SiC composites exhibited excellent ablation resistance, with a linear ablation rate of 8.9×10 −3 mm / s and keep the surface temperature above 2925 ℃ during the ablation process.

[0005] Among them, the matrix modification method is difficult to form a dense oxygen barrier layer, and the thermal mismatch between the coating and the carbon matrix is ​​also prone to cracking or even falling off, which cannot meet the requirements of strong maneuverability, long flight time, and ultra-high temperature of aircraft. The matrix modification-surface coating gradient integration method is an effective means to solve this problem.

[0006] CN112624801B reports a method for preparing a (SiCNW) / (ZrC matrix-coating integration) modified C / C composite material, which prepares a SiC nanowire skeleton in advance, so that a ZrC (SiC) ceramic coating can be formed on the surface of the matrix while preparing a ZrC ceramic doped matrix by the PIP method. This method first prepares a SiC nanowire skeleton, and then introduces a ceramic component by PIP. The preparation process is complicated and requires multiple impregnation-cracking processes, and the preparation cycle is too long.

[0007] CN119350048A reports a high-temperature structural load-bearing / anti-ablation integrated ceramic-based composite material and its preparation method, which uses chemical vapor deposition to obtain a gradient density C / C matrix, solidifies and cracks phenolic resin to obtain a C / C intermediate, then obtains an ultra-high temperature ceramic modified matrix through reactive infiltration, and finally prepares a coating. The preparation process is long and the cost is high. Summary of the invention

[0008] In order to solve the problems of long preparation technology cycle and complicated process flow of existing matrix modification-surface coating gradient integrated C / C composite materials, the present invention proposes a matrix modification-surface coating gradient integrated C / C composite material and a preparation method thereof. The whole process flow of the present invention is simple and the preparation cycle is relatively short.

[0009] To solve the above problems, the present invention adopts the following technical solutions: A method for preparing a matrix modification-surface coating gradient integrated C / C composite material, comprising: Silicide powder and low-density C / C composite material are reacted and infiltrated under vacuum conditions. After the reaction and infiltration are completed, the atmosphere is switched to nitrogen and the heat preservation is continued to perform gas pressure sintering. After the gas pressure sintering is completed, the matrix modification-surface coating gradient integrated C / C composite material is obtained.

[0010] Preferably, the density of the low-density C / C composite material is 1.1-1.5 g / cm 3 .

[0011] Preferably, the silicide powder comprises HfSi 2 powder.

[0012] Preferably, the silicide powder further comprises other silicide powders, wherein the other silicide powders include ZrSi 2 Powder, TiSi 2 Powder, TaSi 2 Powder and NbSi 2 at least one of powders; Before the reaction infiltration of silicide powder and low-density C / C composite material under vacuum conditions, the following process is also included: Using anhydrous ethanol as dispersant, other silicide powders were mixed with HfSi 2 The powder is wet-milled, and during the wet-milling, the mass ratio of the volatile dispersant to the powder is 1: (4-6), the ball milling speed is 300-650 rpm, and the ball milling time is 6-12 h. After ball milling, the volatile dispersant is dried, and then sieved with a sieve of 200 mesh or more, and the sieved material is reacted and infiltrated with a low-density C / C composite material under vacuum conditions.

[0013] Preferably, the HfSi 2 The particle size of the powder is 1-10 μm, and the particle size of the other silicide powder is 1-10 μm.

[0014] Preferably, the parameters for the reaction infiltration of silicide powder and low-density C / C composite material under vacuum conditions are as follows: The heating rate is 5~10 ℃ / min, the holding temperature is 1600~1900 ℃, the holding time is 0.5~1 h, and the vacuum degree is 1~10 Pa.

[0015] Preferably, after the reaction, dissolution and heat preservation are completed, the nitrogen atmosphere is switched and the heat preservation is continued to perform gas pressure sintering, which includes the following process: The holding time in nitrogen atmosphere is 1.5~3 h, then the temperature is lowered to 1400 ℃ at a rate of 5~10 ℃ / min, and then cooled with the furnace to complete gas pressure sintering; the nitrogen pressure is 0.5~2 MPa.

[0016] Preferably, the silicide powder and the low-density C / C composite material are reacted and infiltrated under vacuum conditions, and after the reaction and infiltration are completed, the atmosphere is switched to nitrogen and the heat preservation is continued to perform gas pressure sintering, including: A thin carbon felt is laid on the bottom and side wall of the gas pressure sintering mold, and then a layer of graphite paper is stacked; the silicide powder is poured into the gas pressure sintering mold, the thickness of the silicide powder is 0.8-1.0 times the thickness of the low-density C / C composite material, and then the low-density C / C composite material is placed on top of the silicide powder, and the silicide powder is continued to be poured, so that the thickness of the silicide powder above the low-density C / C composite material is 1.0-1.2 times the thickness of the low-density C / C composite material, and finally a layer of graphite paper and carbon felt is placed on top of the silicide powder; the gas pressure sintering mold is then placed in a gas pressure sintering furnace, and reaction infiltration is carried out under vacuum conditions. When the reaction infiltration and heat preservation are completed, N is introduced into the gas pressure sintering furnace. 2 , and maintain the preset pressure and continue to keep warm to carry out gas pressure sintering.

[0017] Preferably, the preparation method of the matrix modification-surface coating gradient integrated C / C composite material of the present invention further comprises the following process: The low-density C / C composite material is pretreated: the low-density C / C composite material is ultrasonically cleaned in anhydrous ethanol, and then placed in an oven for drying, and the pretreatment of the low-density C / C composite material is completed; the pretreated low-density C / C composite material is used to react and melt-infiltrate with silicate powder under vacuum conditions.

[0018] The present invention also provides a matrix modification-surface coating gradient integrated C / C composite material, and the matrix modification-surface coating gradient integrated C / C composite material is prepared by the preparation method of the present invention as described above.

[0019] The present invention has the following beneficial effects: The preparation method of the matrix modification-surface coating gradient integrated C / C composite material of the present invention combines atmosphere pressure sintering with reactive infiltration technology. In the vacuum stage, part of the silicide enters the low-density C / C matrix through infiltration and reacts with pyrolytic carbon to form carbide ceramics. Subsequently, N2 at a certain pressure is introduced. 2 , reacting with the remaining silicide to form an ultra-high temperature ceramic coating on the surface of the C / C composite material. The present invention simplifies the entire process and greatly shortens the preparation cycle by changing the atmosphere mode of the heat preservation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 HfC in Example 1 of the present invention x N y -SEM images of HfC-SiC-C / C composite materials. (a) is the SEM image of the composite surface, (b) is a local enlarged image of (a), and (c) is the point scanning data of A and B in (a); (d) is the SEM image of the composite cross section, (e) is a local enlarged image of (d), and (f) is the point scanning data of C and D in (d).

[0021] Figure 2 For the SiC nanowire toughening HfC in Example 2 of the present invention x N y -XRD spectrum of HfC-SiC-C / C composite material. (a) is the XRD spectrum of the composite material surface, (b) is the local enlarged view of the highest peak in (a), and (c) is the XRD spectrum of the composite material cross section.

[0022] Figure 3 For the SiC nanowire toughening HfC in Example 2 of the present invention x N y -Cross-sectional SEM image of HfC-SiC-C / C composite material.

[0023] Figure 4 is (Hf, Ti, Ta)C in Example 3 of the present invention x N y -Surface SEM images of (Hf, Ti, Ta)C-SiC-C / C composite materials. (a) is the surface SEM image of the composite material, (b) is a local enlarged image of (a), and (c) is the point scanning data of A and B in (a).

[0024] Figure 5 is (Hf, Ti, Ta)C in Example 4 of the present invention x N y -Macroscopic photographs of the surface of (Hf, Ti, Ta)C-SiC-C / C composite material before and after ablation, where (a) is the macroscopic photograph of the surface before ablation, and (b) is the macroscopic photograph of the surface after ablation.

[0025] Figure 6 These are macroscopic photographs of the samples after the experiment in Comparative Example 1 of the present invention was completed, wherein (a) is a macroscopic photograph of the sample after it was taken out of the gas pressure furnace, and (b) is a macroscopic photograph after the sintered block around the sample was knocked open. DETAILED DESCRIPTION

[0026] The present invention is described clearly and completely below in conjunction with the accompanying drawings and embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, not all embodiments.

[0027] The invention provides a method for preparing a C / C composite material with integrated matrix modification and surface coating gradient. The method comprises the following steps: placing silicide powder and C / C composite material into a gas pressure sintering mold, allowing the powder to coat the C / C composite material, placing the mold in an atmosphere pressure sintering furnace, setting a heating program and an atmosphere mode of the gas pressure furnace for high temperature treatment, and polishing with sandpaper to obtain the C / C composite material with integrated matrix modification and surface coating gradient.

[0028] Specifically, the present invention controls the atmosphere change during the high temperature heat treatment process to achieve Hf-based carbide ultra-high temperature ceramics to modify the C / C matrix while generating SiC on the surface. x N y Doped (M,Hf)C x N y Coating; where (M, Hf) C x N y M may not be contained in the solution. In this case, (M, Hf)C x N y HfC x N y ; When M is contained, M includes one or more of Zr, Ti, Ta and Nb.

[0029] Specifically, the preparation method of the matrix modification-surface coating gradient integrated C / C composite material of the present invention comprises the following steps: Step 1: Pretreat the low-density C / C composite material; wherein the density of the low-density C / C composite material is 1.1-1.5 g / cm 3 The density is measured by an intelligent graphite density porosity analyzer; the pretreatment includes: ultrasonic cleaning the C / C composite material in anhydrous ethanol and then drying it in an oven.

[0030] Step 2: wet ball milling, drying and sieving the silicide powder; wherein the silicide powder is HfSi 2 Powder or HfSi 2 The powder is mixed with other silicide powders, and the particle size of all powders is 1-10 μm and the purity is ≥99.9%. The other silicide powders include ZrSi 2 Powder, TiSi 2 Powder, TaSi 2 Powder and NbSi 2 At least one of the powders. When the silicide powder is HfSi 2When the silicide powder is HfSi 2 When the powder is a mixture of HfSiO2 and other silicides, the wet ball milling, drying and sieving pretreatment mentioned above is required. The wet ball milling includes: using anhydrous ethanol as a dispersant to ball mill the powder; anhydrous ethanol and the powder (i.e., HfSi 2 The mass ratio of the powder to the mixture of other silicates) is 1: (4~6), the ball mill speed is 300~500 rpm, and the ball milling time is 6~8 h; after ball milling, it is placed in an oven to dry, and then sieved with a sieve of 200 mesh or more.

[0031] Step 3: Put the powder obtained in step 2 and the C / C composite material obtained in step 1 into a gas pressure sintering mold, so that the powder covers the C / C composite material, and then place the mold in an atmosphere pressure sintering furnace, set the heating program and atmosphere mode for high temperature treatment, take out the sample, polish it with sandpaper and clean it to obtain a matrix modification-surface coating gradient integrated C / C composite material. The specific process of this step is as follows: first, lay a thin carbon felt on the bottom and side wall of the gas pressure sintering mold, and then stack a layer of graphite paper; pour the powder obtained in step 2 into the mold, the powder thickness is 0.8~1.0 times the thickness of the C / C composite material, and then place the C / C composite material obtained in step 1 on top of the powder, continue to pour powder, so that the powder thickness on the C / C composite material is 1.0~1.2 times the thickness of the C / C composite material, and finally place a layer of graphite paper and carbon felt on top of the powder. The mold was then placed in an atmosphere pressure sintering furnace, which was evacuated to 1-10 Pa. The temperature of the atmosphere pressure sintering furnace was raised to 1600-1900 °C at a heating rate of 5-10 °C / min for 0.5-1 h, and N was introduced into the atmosphere pressure sintering furnace. 2 , and maintain the pressure in the atmosphere pressure sintering furnace at 0.5~2 MPa. After keeping warm for 1.5~3 h, cool down to 1400 ℃ at a rate of 5~10 ℃ / min, and then cool to room temperature with the furnace. After taking out the sample, polish it with sandpaper and clean it to obtain the matrix modification-surface coating gradient integrated C / C composite material.

[0032] In the above scheme of the present invention, atmosphere pressure sintering is combined with reactive infiltration technology. In the vacuum stage, part of the silicide is infiltrated into the low-density C / C matrix and reacts with pyrolytic carbon to form carbide ceramics. Subsequently, a certain pressure of N is introduced. 2 , reacts with the remaining silicide to form an ultra-high temperature ceramic coating on the surface of the C / C composite material. 2 , then N 2Directly react with silicide powder and sinter into blocks, silicide powder cannot enter the interior through infiltration to modify the C / C composite material. The complex process flow of matrix modification-surface coating gradient integration is solved by changing the atmosphere mode during high temperature treatment.

[0033] The method provided by the present invention is to infiltrate the interior of the C / C composite material through silicide. Because the Gibbs free energy of the reaction between the transition metal and pyrolytic carbon is much smaller than that of the Si element, the reaction ability is stronger. Therefore, when the silicide infiltrates the outside of the pores of the C / C composite material, a large amount of carbide ultra-high temperature ceramics will be generated, and then the Si-rich melt infiltrates the inside of the pores to generate more SiC ceramics. The prepared modified C / C composite material matrix is ​​rich in Hf-based carbide ultra-high temperature ceramics on the outside, which has excellent ablation resistance. The matrix is ​​rich in SiC, which plays a vital role in alleviating the thermal mismatch between Hf-based carbides and PyC. This gradient distribution is conducive to heat transfer and can greatly improve the ultra-high temperature protection performance of carbon-based composite materials.

[0034] The method provided by the present invention introduces N at a certain pressure during the subsequent heat preservation process. 2 , promoting N 2 Reaction with silicides produces high melting point (M, Hf)C that is tightly bonded to the C / C composite material. x N y The coating effectively reduces the content of residual silicide after infiltration.

[0035] In the matrix modification-surface coating gradient integrated C / C composite material prepared by the above preparation method of the present invention, the matrix is ​​rich in Hf-based carbide ultra-high temperature ceramics on the outside and rich in SiC on the inside; and when the silicide raw material is only HfSi 2 When the surface of the modified C / C composite material contains SiC x N y Doped HfC x N y Coating, when the silicide raw material except HfSi 2 When other silicides are included, the surface of the modified C / C composite material contains SiC x N y Doped (M,Hf)C x N y The coating, wherein M comprises one or more of Zr, Ti, Ta and Nb.

[0036] Example 1 The preparation method of the matrix modification-surface coating gradient integrated C / C composite material of this embodiment comprises the following steps: Step 1. Prepare a 10×10×10 mm thick plate with a density of 1.18 g / cm 3The C / C composites were ultrasonically cleaned in anhydrous ethanol for 30 min and then dried in a drying oven at 70 ℃ for 12 h.

[0037] Step 2. HfSi 2 The powder was placed in a 70 °C drying oven and dried for 12 h, and then sieved using a 200-mesh sieve.

[0038] Step 3. Lay thin carbon felt on the bottom and side walls of the air pressure furnace mold, and then stack a layer of graphite paper; pour the powder into the mold with a thickness of 8 mm, then place the C / C composite material on top of the powder, continue to pour 10 mm thick powder, and finally place a layer of graphite paper and carbon felt on top of the powder.

[0039] Step 4. Place the prepared mold into a gas pressure sintering furnace. The holding temperature of the gas pressure sintering furnace is 1700 °C, the heating rate is 8 °C / min, and the holding time is set to 2 h. The heating and the first 1 h of the holding process are in a vacuum environment with a vacuum degree of 5 Pa. This process is a reactive infiltration process. N is introduced into the subsequent holding and cooling process. 2 The pressure is 1 MPa. The temperature is lowered to 1400 °C at a rate of 8 °C / min, and finally the furnace is cooled to room temperature and taken out. This process is a gas pressure sintering process under nitrogen atmosphere.

[0040] Step 5. Use 240-grit sandpaper to smooth the surface of the sample, clean it, and dry it to obtain the surface containing SiC x N y Doped HfC x N y Coating, matrix modification-surface coating gradient integrated C / C composite material with HfC-rich matrix outside and SiC-rich matrix inside. Figure 1 As shown in Figure (a), Figure 1 Figure (b) is Figure 1 A partial enlarged view of Figure (a). Figure 1 Figure (c) is Figure 1 In the EDS point scanning data in Figure (a), it can be seen that the white phase on the surface is HfC x N y , the gray rod-like structure is SiC x N y , embedded in HfC x N y The cross-sectional SEM images are shown in Figure 1. Figure 1 As shown in Figure (d), Figure 1 Figure (e) is Figure 1 A partial enlarged view of Figure (d). Figure 1 Figure (f) in the figure is Figure 1From the EDS point scanning data in Figure (d), it can be seen that the ceramics are distributed in a gradient within the C / C matrix, with HfC ceramics on the outside and SiC ceramics on the inside.

[0041] Example 2 The preparation method of the matrix modification-surface coating gradient integrated C / C composite material of this embodiment comprises the following steps: Step 1. Prepare a 10×10×8 mm thick plate with a density of 1.16 g / cm 3 The C / C composites were ultrasonically cleaned in anhydrous ethanol for 30 min and then dried in a drying oven at 70 ℃ for 12 h.

[0042] Step 2. HfSi 2 The powder was placed in a drying oven at 70 °C and dried for 12 h. 2 Mix well with nickel powder in a mortar at a mass ratio of 300:1, and sieve the powder using a 300-mesh sieve.

[0043] Step 3. Lay thin carbon felt on the bottom and side walls of the air pressure furnace mold, and then stack a layer of graphite paper; pour powder into the mold with a thickness of 5 mm, then place the C / C composite material on top of the powder, continue to pour 8 mm thick powder, and finally place a layer of graphite paper and carbon felt on top of the powder.

[0044] Step 4. Place the prepared mold into a gas pressure sintering furnace. The holding temperature of the gas pressure sintering furnace is 1700 °C, the heating rate is 8 °C / min, and the holding time is set to 4 h. The heating and the first 1 h of the holding process are in a vacuum environment with a vacuum degree of 10 Pa. This process is a reactive infiltration process. N is introduced into the subsequent holding and cooling process. 2 The pressure is 0.5 MPa. The temperature is lowered to 1400 °C at a rate of 5 °C / min, and finally the furnace is cooled to room temperature and taken out. This process is a gas pressure sintering process under nitrogen atmosphere.

[0045] Step 5. Use 240-grit sandpaper to smooth the surface of the sample, clean it, and dry it to obtain the surface containing SiC x N y Doped HfC x N y Coating, matrix modification-surface coating gradient integrated C / C composite material with HfC-rich matrix outside and SiC-rich matrix inside. Its surface XRD spectrum is as follows Figure 2 As shown in Figure (a), Figure 2 Figure (b) is Figure 2 The partial enlarged view of Figure (a) shows that the diffraction peak of the surface is between the HfC peak and the HfN peak. The XRD spectrum of the cross section is shown in Figure 2As shown in Figure (c), carbon peaks, HfC peaks and SiC peaks were detected. Figure 3 , it can be seen that nanowires are generated around the ceramic phase in the C / C matrix.

[0046] Example 3 The preparation method of the matrix modification-surface coating gradient integrated C / C composite material of this embodiment comprises the following steps: Step 1. Prepare a 12×10×10 mm thick plate with a density of 1.25 g / cm 3 The C / C composites were ultrasonically cleaned in anhydrous ethanol for 30 min and then dried in a drying oven at 70 ℃ for 12 h.

[0047] Step 2. HfSi 2 Powder and TiSi 2 、TaSi 2 The mixed solution was ball-milled at a ratio of 8:2:1, the mass ratio of anhydrous ethanol to powder was 1:5, the ball mill speed was 300-500 rpm, and the ball milling time was 8 h. The ball-milled solution was placed in an oven to dry for 12 h to evaporate the anhydrous ethanol. The dried powder was then sieved using a 200-mesh screen.

[0048] Step 3. Lay thin carbon felt on the bottom and side walls of the air pressure furnace mold, and then stack a layer of graphite paper; pour powder into the mold with a thickness of 10 mm, then place the C / C composite material on top of the powder, continue to pour 12 mm thick powder, and finally place a layer of graphite paper and carbon felt on top of the powder.

[0049] Step 4. Place the prepared mold into a gas pressure sintering furnace. The holding temperature of the gas pressure sintering furnace is 1700 °C, the heating rate is 5 °C / min, and the holding time is set to 2 h. The heating and the first 1 h of the holding process are in a vacuum environment with a vacuum degree of 8 Pa. This process is a reactive infiltration process. N is introduced into the subsequent holding and cooling process. 2 The pressure is 0.5 MPa. The temperature is lowered to 1400 °C at a rate of 5 °C / min, and finally the furnace is cooled to room temperature and taken out. This process is a gas pressure sintering process under nitrogen atmosphere.

[0050] Step 5. Use 240-grit sandpaper to smooth the surface of the sample, clean it, and dry it to obtain the surface containing SiC x N y Doped (Hf, Ti, Ta)C x N y Coating, matrix modification-surface coating gradient integrated C / C composite material with (Hf, Ti, Ta)C-rich matrix outside and SiC-rich matrix inside. Figure 4 As shown in Figure (a), Figure 4 Figure (b) is Figure 4 A partial enlarged view of Figure (a). Figure 4 Figure (c) shows the EDS point scanning data. It can be seen that the white phase is (Hf, Ti, Ta)C x N y , the gray rod-like structure is SiC x N y .

[0051] Example 4 The preparation method of the matrix modification-surface coating gradient integrated C / C composite material of this embodiment comprises the following steps: Step 1. Prepare a 28×5 mm thick plate with a density of 1.31 g / cm 3 The C / C composites were ultrasonically cleaned in anhydrous ethanol for 30 min and then dried in a drying oven at 70 ℃ for 12 h.

[0052] Step 2. HfSi 2 Powder and TiSi 2 、TaSi 2 The mixed solution was ball-milled at a ratio of 12:2:1, the mass ratio of anhydrous ethanol to powder was 1:5, the ball mill speed was 300-500 rpm, and the ball milling time was 7 h. The ball-milled solution was placed in an oven to dry for 12 h to evaporate the anhydrous ethanol. The dried powder was then sieved using a 200-mesh screen.

[0053] Step 3. Lay thin carbon felt on the bottom and side walls of the air pressure furnace mold, and then stack a layer of graphite paper; pour powder into the mold with a thickness of 5 mm, then place the C / C composite material on top of the powder, continue to pour 5 mm thick powder, and finally place a layer of graphite paper and carbon felt on top of the powder.

[0054] Step 4. Place the prepared mold into a gas pressure sintering furnace. The holding temperature of the gas pressure sintering furnace is 1800 °C, the heating rate is 8 °C / min, the holding time is set to 2 h, the heating process is in a vacuum environment, and the vacuum degree is 5 Pa. This process is a reactive infiltration process; N2 is introduced during the holding and cooling process. 2 The pressure is 1.5 MPa. The temperature is lowered to 1400 °C at a rate of 10 °C / min, and finally the furnace is cooled to room temperature and taken out. This process is a gas pressure sintering process under nitrogen atmosphere.

[0055] Step 5. Use 240-grit sandpaper to smooth the surface of the sample, clean it, and dry it to obtain the surface containing SiC x N yDoped (Hf, Ti, Ta)C x N y Coating, matrix modification with (Hf, Ti, Ta)C-rich outside and SiC-rich inside - surface coating gradient integrated C / C composite material. 2 The prepared composite material was subjected to a 60 s ablation test under a heat flux density of , and the macroscopic photographs before and after ablation are shown in Figure 5 As shown in Figures (a) and (b), the oxide film on the surface after ablation is dense and has no obvious peeling. The mass ablation rate is only 0.22 mg / s.

[0056] Comparative Example 1 This comparative example comprises the following steps: Step 1. Prepare a 12×8×9 mm thick plate with a density of 1.20 g / cm 3 The C / C composites were ultrasonically cleaned in anhydrous ethanol for 30 min and then dried in a drying oven at 70 ℃ for 12 h.

[0057] Step 2. HfSi 2 The powder was placed in a 70 °C drying oven and dried for 12 h, and then sieved using a 200-mesh sieve.

[0058] Step 3. Lay thin carbon felt on the bottom and side walls of the air pressure furnace mold, and then stack a layer of graphite paper; pour the powder into the mold with a thickness of 8 mm, then place the C / C composite material on top of the powder, continue to pour 9 mm thick powder, and finally place a layer of graphite paper and carbon felt on top of the powder.

[0059] Step 4. Place the prepared mold into a gas pressure sintering furnace. The holding temperature of the gas pressure sintering furnace is 1700 °C, the heating rate is 8 °C / min, and the holding time is set to 2 h. N2 is introduced during the entire process of heating, holding, and cooling. 2 , the pressure is 1 MPa. The temperature is lowered to 1400 ℃ at a rate of 8 ℃ / min, and finally cooled to room temperature with the furnace and taken out. Figure 6 Figure (a) is a photo of the sample after it was taken out. It can be seen that the powder is sintered around the sample. The sintered block around the sample is knocked open. Figure 6 In Figure (b), the powder is around the sample and N 2 No reaction, no penetration into the substrate, and no coating was formed.

[0060] It can be seen from the above scheme of the present invention that the method combines gas pressure sintering technology with reactive infiltration technology, and by changing the atmosphere mode of the heat preservation process, Hf-based carbide ultra-high temperature ceramics can be used to modify the C / C matrix while generating SiC on the surface. x N yDoped (M,Hf)C x N y The coating process is simple and the preparation cycle is greatly shortened.

[0061] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a matrix modification-surface coating gradient integrated C / C composite material, characterized in that: include: Silicide powder and low-density C / C composite material are reacted and infiltrated under vacuum conditions. After the reaction and infiltration are completed, the atmosphere is switched to nitrogen and the heat preservation is continued to perform gas pressure sintering. After the gas pressure sintering is completed, the matrix modification-surface coating gradient integrated C / C composite material is obtained.

2. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 1, characterized in that: The density of the low-density C / C composite material is 1.1-1.5 g / cm 3 .

3. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 1, characterized in that: The silicide powder includes HfSi2 powder.

4. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 3, characterized in that: The silicide powder material further includes other silicide powders, wherein the other silicide powders include at least one of ZrSi2 powder, TiSi2 powder, TaSi2 powder and NbSi2 powder; Before the reaction infiltration of silicide powder and low-density C / C composite material under vacuum conditions, the following process is also included: Using anhydrous ethanol as a dispersant, other silicate powders and HfSi2 powder are wet ball-milled. During wet ball milling, the mass ratio of volatile dispersant to powder is 1: (4~6), the ball milling speed is 300~650 rpm, and the ball milling time is 6~12 h. After ball milling, the volatile dispersant is dried and then sieved with a sieve of 200 mesh or more. The sieved material is reacted and infiltrated with a low-density C / C composite material under vacuum conditions.

5. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 4, characterized in that: The particle size of the HfSi2 powder is 1-10 μm, and the particle size of the other silicide powder is 1-10 μm.

6. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 1, characterized in that: The parameters for reactive infiltration of silicide powder and low-density C / C composite materials under vacuum conditions are as follows: The heating rate is 5~10 ℃ / min, the holding temperature is 1600~1900 ℃, the holding time is 0.5~1 h, and the vacuum degree is 1~10 Pa.

7. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 1, characterized in that: When the reaction, dissolution and heat preservation are completed, the nitrogen atmosphere is switched and the heat preservation is continued to carry out gas pressure sintering, which includes the following process: The holding time in nitrogen atmosphere is 1.5~3 h, then the temperature is lowered to 1400 ℃ at a rate of 5~10 ℃ / min, and then cooled with the furnace to complete gas pressure sintering; the nitrogen pressure is 0.5~2 MPa.

8. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 1, characterized in that: The reaction infiltration of silicide powder and low-density C / C composite materials is carried out under vacuum conditions. When the reaction infiltration and heat preservation are completed, the nitrogen atmosphere is switched and the heat preservation is continued to carry out gas pressure sintering, including: A thin carbon felt is laid on the bottom and side wall of the gas pressure sintering mold, and then a layer of graphite paper is stacked; the silicide powder is poured into the gas pressure sintering mold, the thickness of the silicide powder is 0.8~1.0 times the thickness of the low-density C / C composite material, and then the low-density C / C composite material is placed on top of the silicide powder, and the silicide powder is continued to be poured, so that the thickness of the silicide powder above the low-density C / C composite material is 1.0~1.2 times the thickness of the low-density C / C composite material, and finally a layer of graphite paper and carbon felt is placed on top of the silicide powder; the gas pressure sintering mold is then placed in a gas pressure sintering furnace, and reaction infiltration is carried out under vacuum conditions. When the reaction infiltration insulation is completed, N2 is introduced into the gas pressure sintering furnace, and the preset pressure is maintained, and insulation is continued to carry out gas pressure sintering.

9. The method for preparing a matrix modification-surface coating gradient integrated C / C composite material according to claim 1, characterized in that: It also includes the following processes: The low-density C / C composite material is pretreated: the low-density C / C composite material is ultrasonically cleaned in anhydrous ethanol, and then placed in an oven for drying, and the pretreatment of the low-density C / C composite material is completed; the pretreated low-density C / C composite material is used to react and melt-infiltrate with silicate powder under vacuum conditions.

10. A matrix modification-surface coating gradient integrated C / C composite material, characterized in that: The matrix modification-surface coating gradient integrated C / C composite material is prepared by the preparation method according to any one of claims 1-9.

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