A core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, its rapid preparation method, and its applications.

Abstract

This invention discloses a core-shell nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, its rapid preparation method, and its applications, belonging to the field of carbon-carbon composite matrix modification technology. The method is as follows: A mixed organic precursor formed by silicon carbide precursor and ultra-high temperature ceramic polymer precursor is dissolved in an organic solvent to form a mixed organic precursor solution. A carbon fiber preform is then subjected to chemical liquid-phase vapor deposition in the mixed organic precursor solution, followed by cooling to obtain the deposited composite material. Heat treatment is then performed to obtain the silicon carbide nanowire-reinforced ceramic matrix modified composite material. Chemical liquid-phase vapor deposition is then performed in an organic solvent, followed by cooling to deposit pyrolytic carbon on the surface of the silicon carbide nanowires to form a core-shell structure, obtaining the core-shell nanowire-reinforced ceramic matrix modified composite material. Vapor-phase silicon infiltration is then performed to seal pores and form a free silicon coating, resulting in a core-shell nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface. This invention uses a combined chemical liquid-phase vapor deposition and chemical vapor infiltration process to rapidly prepare a ceramic matrix modified composite material with low surface porosity.

Description

Technical Field

[0001] This invention belongs to the field of carbon-carbon composite matrix modification technology, specifically relating to a core-shell structure nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, its rapid preparation method, and its application. Background Technology

[0002] Ultra-high temperature ceramic-modified carbon-carbon composites combine the excellent high-temperature resistance of ultra-high temperature ceramics (UHTC) with the superior high-temperature mechanical properties of C / C composites, and are considered one of the most promising structural materials for extreme environments. Matrix modification is a common method for preparing UHTC-modified carbon-carbon composites, and common methods include reactive infiltration (RMI), precursor impregnation pyrolysis (PIP), and chemical vapor deposition (CVI / CVD). The RMI process utilizes capillary forces to infiltrate the molten material into a porous preform, and through its chemical reaction with carbon, generates a modified UHTC ceramic phase. Although it has high densification efficiency and a short production cycle, it inevitably causes damage to the carbon fibers during the infiltration process, leading to a decrease in the mechanical properties of the composite material. PIP involves infiltrating a polymeric organic ceramic precursor into the interior of a carbon fiber preform, and then pyrolyzing it through a high-temperature carbothermal reduction reaction to convert it into modified ceramic. It has the advantage of simple process, but requires multiple cycles of impregnation and pyrolysis, resulting in a long preparation cycle. CVI (Chemical Vapor Impregnation) is a chemical reaction process that transforms gaseous feedstock into solid products. It allows for precise control of material microstructure and minimizes fiber damage, but it suffers from long preparation cycles, high costs, and demanding equipment requirements. Chemical liquid phase vapor deposition (CLVI / CLVD), an improved version of chemical vapor deposition (CVI / CVD), offers a densification rate more than two orders of magnitude faster than reported isothermal CVI, significantly reducing preparation costs and shortening the preparation cycle. However, CLVD faces challenges in depositing large pores and preparing high-density composites, and the inherent brittleness of ultra-high temperature ceramics greatly limits its application. Therefore, a combined approach utilizing the advantages of different processes can be considered to rapidly prepare modified composite materials, while simultaneously introducing nano-reinforcements with good chemical stability and excellent mechanical properties to achieve reinforcement effects on ceramic matrix composites.

[0003] Hou et al. (Ablation behaviors and mechanisms of C f / HfC PIP -SiC CVIComposites: From SiO2 nanowires film to HfO2 skeleton [J]. Corrosion Science, 2022, 209.) Ceramic preparation via the CVI process can fill cracks and pores formed by gaseous products from the carbothermic reduction reaction during PIP heat treatment, and connect HfC ceramic particles prepared by the PIP method. However, the introduction of the CVI process in this combined process further increases the overall preparation cycle and makes the process relatively complex.

[0004] Zhang et al. (Ablation behavior of C / C-HfC-SiC composites prepared by joint route of precursor infiltration and pyrolysis and gaseous silicon infiltration[J]. Chinese Journal of Aeronautics, 2023, 36(9): 426-436.) used vapor-phase silicon infiltration (GSI, using fumed silicon to infiltrate porous C / C in a high-temperature environment) to fill the defects formed by the heat treatment reaction in PIP, and the Si-rich layer on the surface increased its ablation resistance. However, although the GSI process was introduced and the heat treatment temperature was increased, PIP is still the main process for preparing composite materials, and the overall preparation cycle has not been significantly reduced. Moreover, the introduced reinforcing phase SiC nanowires are difficult to maintain the nanowire morphology stably above 1800℃, and their reinforcing effect is weakened.

[0005] He et al. (Microstructure and ablation property of C / C-ZrC-SiC composites fabricated by chemical liquid-vapor deposition combined with precursor infiltration and pyrolysis[J].Ceramics International,2019,45(3):3767-3781) found that the CLVD process preferentially fills small pores within the bundle, while the PIP process preferentially deposits large pores between bundles and layers. The combined CLVD and PIP process reduces the porosity of the composite material and increases the ceramic content, resulting in improved mechanical and ablation properties. However, the intrinsic defects of the surface pores generated by high-temperature pyrolysis, due to both CLVD and PIP, are not effectively filled, and the ablation and mechanical properties of the modified composite material need further improvement.

[0006] Therefore, developing a new combined process to achieve rapid preparation of ceramic-based modified composite materials and reduce the large porosity defect structure on their surface to obtain high-density, high-performance composite materials is an urgent problem to be solved. Summary of the Invention

[0007] To overcome the shortcomings of the existing technologies, and addressing the inherent defects of brittleness in ultra-high temperature ceramics, the presence of numerous pore defects on the surface after high-temperature heat treatment, and the long preparation cycle, this invention provides a core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, along with its rapid preparation method and applications. The ceramic matrix modified composite material with low surface porosity is rapidly prepared using a combined CLVD and GSI process.

[0008] To achieve the above objectives, the present invention employs the following technical solution:

[0009] This invention provides a rapid preparation method for a core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, comprising the following steps:

[0010] S1: A mixed organic precursor formed by silicon carbide precursor and ultra-high temperature ceramic polymer precursor is dissolved in an organic solvent to form a mixed organic precursor solution. The carbon fiber preform is subjected to the first chemical liquid phase vaporization deposition in the mixed organic precursor solution, followed by cooling and then cooling to obtain the deposited composite material.

[0011] S2: The deposited composite material is heat-treated and then cooled to form silicon carbide nanowires, ceramic phase and pyrolytic carbon, thus obtaining silicon carbide nanowire reinforced ceramic matrix modified composite material.

[0012] S3: The silicon carbide nanowire reinforced ceramic matrix modified composite material is subjected to a second chemical liquid phase vaporization deposition in an organic solvent, followed by cooling and then cooling. Pyrolytic carbon is deposited on the surface of silicon carbide nanowires to form a core-shell structure, thus obtaining a core-shell structured nanowire reinforced ceramic matrix modified composite material.

[0013] S4: Vapor phase infiltration and pore sealing treatment is performed on the core-shell nanowire reinforced ceramic matrix modified composite material to form a free silicon coating, thereby obtaining a core-shell nanowire reinforced ceramic matrix modified composite material with a silicon-rich coating on the surface.

[0014] In one embodiment, in step S1, the density of the carbon fiber preform is 0.4–1.2 g / cm³. 3 The carbon fiber preform has a size of Cylindrical carbon fiber preforms.

[0015] In one embodiment, in S1, the ultra-high temperature ceramic polymer precursor is any one of hafnium carbide precursor, zirconium carbide precursor, and tantalum carbide precursor.

[0016] In one embodiment, in S1 and S3, the organic solvent is any one of xylene, toluene, cyclohexane, and kerosene.

[0017] In one embodiment, in S1, the mass ratio of the silicon carbide precursor, the ultra-high temperature ceramic polymer precursor, and the organic solvent is 1:(5-10):(1-10).

[0018] In one embodiment, the first chemical liquid phase vaporization deposition process in S1 is as follows:

[0019] The carbon fiber preform was placed in a liquid phase furnace containing a mixed organic precursor solution and heated to 800–1200°C at a rate of 10–20°C / min. Chemical liquid phase vaporization deposition was carried out for 16–24 h, and then cooled to 600°C at a rate of 10–20°C / min.

[0020] In step S3, the second chemical liquid phase vaporization deposition process is as follows:

[0021] The silicon carbide nanowire-reinforced ceramic matrix modified composite material was placed in a liquid phase furnace containing organic solvent and heated to 800–1200 °C at a rate of 10–20 °C / min. The chemical liquid phase vaporization deposition was carried out for 5–15 h, and then cooled to 600 °C at a rate of 10–20 °C / min.

[0022] In one embodiment, the heat treatment process in S2 is as follows:

[0023] Under the protection of argon atmosphere, the temperature is increased to 1500-1800℃ at a rate of 2-5℃ / min and held for 2-4 hours;

[0024] In step S4, the vapor phase silicon infiltration sealing process is as follows:

[0025] Keep warm at 1800–2150℃ for 10–30 minutes.

[0026] The present invention also provides a core-shell structured nanowire reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, prepared by the aforementioned method, comprising a core-shell structured nanowire reinforced ceramic matrix modified composite material and a free silicon coating; the core-shell structured nanowire reinforced ceramic matrix modified composite material comprises a ceramic phase, carbon fibers, silicon carbide nanowires and pyrolytic carbon;

[0027] The ceramic phase and pyrolytic carbon are co-deposited around the carbon fibers. The silicon carbide nanowires grow extensively in the internal voids and on the surface of the core-shell structure nanowire-reinforced ceramic matrix modified composite material. Pyrolytic carbon is deposited on the surface of the silicon carbide nanowires to form a core-shell structure. The free silicon coating is deposited on the core-shell structure nanowire-reinforced ceramic matrix modified composite material.

[0028] In one embodiment, the core-shell structure divides the large pore defect structure on the surface of the core-shell nanowire-reinforced ceramic matrix modified composite material, and constructs a small mesh structure to form a three-dimensional network; a free silicon coating fills and covers the small mesh structure.

[0029] The present invention also provides the application of the core-shell structured nanowire reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface in the field of thermal protection.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention provides a rapid preparation method for core-shell nanowire-reinforced ceramic matrix modified composite materials with a silicon-rich coating on the surface. This method employs a combined chemical liquid phase vapor deposition (CLPV) and vapor phase silicate infiltration process to rapidly prepare high-performance ceramic matrix modified composite materials with low surface porosity. The main method utilizes CLPV to simultaneously prepare ultra-high temperature ceramic components and form silicon carbide nanowires in one step. Subsequently, pyrolytic carbon is deposited on the nanowire surface to form a stable core-shell reinforcement. This structure is used to construct a three-dimensional network space, effectively dividing the large pores on the composite material surface into a small mesh structure, thereby promoting the rapid deposition of free silicon during vapor phase silicate infiltration and achieving rapid surface densification. This method can effectively shorten the preparation cycle, reduce surface porosity, and the core-shell structure can effectively strengthen the matrix and improve thermal conductivity, resulting in a significant improvement in the mechanical and ablation properties of the composite material. It has good industrial application prospects and economic benefits.

[0032] This invention provides a core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, prepared by the above-described method. Through a one-step process, ultra-high temperature ceramics and nanowire reinforcing phases are introduced, and pyrolytic carbon is deposited on the surface of SiC nanowires to form a core-shell structure. The deposited pyrolytic carbon constructs a highly stable core-shell structure, effectively dividing the large-pore defect structure and forming a small mesh structure. This improves the high-temperature stability of SiC nanowires, reduces structural changes caused by the high-temperature treatment of the vapor-phase silicon infiltration process, and assists in the rapid densification of the composite material surface using vapor-phase silicon infiltration technology. This structure exhibits excellent performance in terms of load-bearing capacity, heat transfer, and ablation resistance.

[0033] Furthermore, this core-shell structured nanowire-reinforced ceramic matrix modified composite material utilizes the core-shell structure to divide the large pores on the surface into a small mesh structure, thereby achieving the filling of surface pores by free silicon and ultimately depositing a dense silicon-rich coating.

[0034] The present invention also provides a core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, which has excellent mechanical properties and anti-oxidation and ablation properties and can be widely used in the field of thermal protection. Attached Figure Description

[0035] Figure 1 Figure (a) is a flowchart of the rapid preparation method of the present invention, and Figure (b) is a schematic diagram of the corresponding equipment;

[0036] Figure 2 Figure (a) shows the macroscopic morphology of the SiC nanowire-reinforced C / C-HfC-SiC composite material prepared in Example 1; Figure (b) shows the macroscopic morphology of the SiC nanowire-reinforced ceramic matrix modified composite material prepared in Comparative Example 1.

[0037] Figure 3 Figures (a) and (b) show the microstructure of the SiC nanowire-reinforced C / C-HfC-SiC composite material before and after polishing; Figures (c) and (d) show the microstructure of the core-shell structure formed by pyrolytic carbon deposition on the surface of SiC nanowires after a second chemical liquid phase vaporization deposition process.

[0038] Figure 4 Figure (a) is a TEM image of SiC nanowires in the SiC nanowire-reinforced C / C-HfC-SiC composite material prepared after the first chemical liquid-phase vaporization process in Example 1. Figure (b) is a TEM image of the core-shell structure in the core-shell structure nanowire-reinforced C / C-HfC-SiC composite material prepared after the second chemical liquid-phase vaporization process in Example 1.

[0039] Figure 5 Figures (a) and (c) show the cross-section, surface microstructure, and corresponding energy dispersive spectroscopy (EDS) and XRD results of the SiC nanowire-reinforced ceramic matrix modified composite material with a silicon carbide-rich coating on the surface obtained in Comparative Example 2 after vapor-phase silicon infiltration; Figures (b) and (d) show the cross-section, surface microstructure, and corresponding EDS and XRD results of the core-shell structure nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on the surface obtained in Example 1.

[0040] Figure 6 The thermal diffusivity and thermal conductivity of the composite material prepared by chemical liquid-phase vaporization deposition according to this invention are obtained through testing. Figure 6HS0 is the SiC nanowire-reinforced C / C-HfC-SiC composite material obtained in Comparative Example 1 through the first chemical liquid phase vaporization deposition process; HS1 is the SiC nanowire-reinforced C / C-HfC-SiC composite material obtained in Comparative Example 2 through the first chemical liquid phase vaporization deposition process; and HS2 is the core-shell structured nanowire-reinforced C / C-HfC-SiC composite material obtained in Example 1 through two chemical liquid phase vaporization deposition processes.

[0041] Figure 7 For a heat flux density of 2.38 MW / m 2 Macroscopic morphology of oxyacetylene flame ablation after 60 seconds; among which Figure 7 (a) The sample is a SiC-free nanowire-reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating on the surface, obtained by vapor-phase silicon infiltration in Comparative Example 1. Figure 7 (b) The sample is a SiC nanowire reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating on the surface, obtained by vapor phase silicon infiltration in Comparative Example 2. Figure 7 (c) The sample is a C / C-HfC-SiC composite material with a core-shell structure and silicon-rich coating on the surface, obtained by vapor-phase silicon infiltration in Example 1.

[0042] Figure 8 This is a microscopic morphology image of the ablation center of the sample after oxyacetylene ablation; among which... Figure 8 (a) is a SiC nanowire-reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating on the surface, obtained by vapor-phase silicon infiltration in Comparative Example 1. Figure 8 (b) is the SiC nanowire-reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating on the surface, obtained by vapor-phase silicon infiltration in Comparative Example 2. Figure 8 (c) is the core-shell structured nanowire reinforced C / C-HfC-SiC composite material obtained by vapor phase silicon infiltration in Example 1, which has a silicon-rich coating on the surface. Detailed Implementation

[0043] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0044] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0045] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0046] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0047] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0048] This invention provides a core-shell nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, along with its rapid preparation method and applications. The preparation method employs a chemical liquid phase vapor deposition process to introduce ultra-high temperature ceramics and construct a core-shell structure, which strengthens the matrix, fills voids, and improves thermal conductivity. Secondly, a combined vapor-phase silicate infiltration process is used for surface sealing, rapidly preparing a core-shell nanowire-reinforced ceramic matrix modified composite material with low surface porosity. The chemical liquid phase vapor deposition process regulates the core-shell structure by adjusting the deposition temperature, precursor solution composition, and heat treatment temperature. Furthermore, the strong penetrating power of fumed silica in the vapor-phase silicate infiltration process controls the composition and microstructure of the coating formed on the surface of the ceramic matrix modified composite material, improving the density, mechanical properties, and oxidation and ablation resistance of the composite material.

[0049] like Figure 1 As shown, this invention provides a rapid preparation method for a core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, comprising the following steps:

[0050] S1: A mixed organic precursor formed by silicon carbide precursor and ultra-high temperature ceramic polymer precursor is dissolved in an organic solvent to form a mixed organic precursor solution. The mass ratio of silicon carbide precursor, ultra-high temperature ceramic polymer precursor and organic solvent is 1:(5~10):(1~10). The carbon fiber preform is subjected to the first chemical liquid phase vaporization deposition in the mixed organic precursor solution, followed by cooling and then cooling to obtain the deposited composite material.

[0051] Specifically, the process of the first chemical liquid-phase vaporization deposition is as follows:

[0052] The carbon fiber preform is placed in a liquid phase furnace containing a mixed organic precursor solution and heated to 800–1200°C at a rate of 10–20°C / min. Chemical liquid phase vaporization deposition is carried out for 16–24 h, and then cooled to 600°C at a rate of 10–20°C / min. By adjusting the chemical liquid phase vaporization deposition process parameters, ultra-high temperature ceramics and nanowire reinforcing phases can be introduced simultaneously, reducing the time required for additional reinforcing phase introduction or matrix densification.

[0053] More specifically, the density of the carbon fiber preform is 0.4–1.2 g / cm³. 3 The carbon fiber preform has a size of The cylindrical carbon fiber preform is preferred. More preferably, the ultra-high temperature ceramic polymer precursor is any one of hafnium carbide, zirconium carbide, and tantalum carbide precursors. The organic solvent is any one of xylene, toluene, cyclohexane, and kerosene.

[0054] S2: The deposited composite material is heat-treated and then cooled to form silicon carbide nanowires, ceramic phase and pyrolytic carbon, thus obtaining silicon carbide nanowire reinforced ceramic matrix modified composite material.

[0055] Specifically, the heat treatment process is as follows:

[0056] Under an argon atmosphere, the temperature was increased to 1500–1800℃ at a rate of 2–5℃ / min and held for 2–4 hours. The heat treatment temperature of 1500–1800℃ avoids the agglomeration or coarsening of the prepared silicon carbide nanowires caused by excessively high temperatures.

[0057] S3: The silicon carbide nanowire reinforced ceramic matrix modified composite material is subjected to a second chemical liquid phase vaporization deposition in an organic solvent, followed by cooling and then cooling. Pyrolytic carbon is deposited on the surface of silicon carbide nanowires to form a core-shell structure, thus obtaining a core-shell structured nanowire reinforced ceramic matrix modified composite material.

[0058] Because SiC nanowires suffer from poor high-temperature structural stability, easy agglomeration, and easy decomposition in practical preparation and application, pyrolytic carbon is deposited on their surface to form a core-shell structure. This serves several purposes: first, it improves their thermal stability; second, this structure enhances the connection between the nanowires and the matrix, leveraging the high elasticity and high modulus advantages of SiC nanowires, while the multi-stage pull-out phenomenon during fracture further consumes energy, improving the mechanical properties of the ceramic material; and third, the shell pyrolytic carbon has a high intrinsic thermal conductivity, and by connecting the nanowires to each other, it constructs a three-dimensional thermally conductive network, improving the thermal conductivity of the composite material.

[0059] Specifically, the second chemical liquid-phase vaporization deposition process is as follows:

[0060] The silicon carbide nanowire-reinforced ceramic matrix modified composite material was placed in a liquid phase furnace containing organic solvent and heated to 800–1200 °C at a rate of 10–20 °C / min for chemical liquid phase vaporization deposition for 5–15 h. Then, the temperature was cooled to 600 °C at a rate of 10–20 °C / min. This process can grow SiC nanowires under catalytic conditions using chemical liquid phase vaporization deposition technology and rapidly deposit pyrolytic carbon to construct a core-shell structure.

[0061] More preferably, the organic solvent is any one of xylene, toluene, cyclohexane and kerosene.

[0062] S4: Vapor phase infiltration and pore sealing treatment is performed on the core-shell structured nanowire reinforced ceramic matrix modified composite material to form a free silicon coating, thereby obtaining a core-shell structured nanowire reinforced ceramic matrix modified composite material with a silicon-rich coating on the surface.

[0063] Specifically, the process of vapor phase silicon infiltration sealing is as follows:

[0064] Keep warm at 1800–2150℃ for 10–30 minutes.

[0065] The present invention also provides a core-shell structured nanowire reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, prepared by the above preparation method, comprising a core-shell structured nanowire reinforced ceramic matrix modified composite material and a free silicon coating deposited on the surface of the core-shell structured nanowire reinforced ceramic matrix modified composite material.

[0066] The core-shell structured nanowire-reinforced ceramic matrix modified composite material includes a ceramic phase, carbon fibers, silicon carbide nanowires, and pyrolytic carbon.

[0067] The ceramic phase and pyrolytic carbon are co-deposited around the carbon fibers. The silicon carbide nanowires grow extensively in the internal voids and on the surface of the core-shell structure nanowire-reinforced ceramic matrix modified composite material. Pyrolytic carbon is deposited on the surface of the silicon carbide nanowires to form a core-shell structure. The free silicon coating is deposited on the core-shell structure nanowire-reinforced ceramic matrix modified composite material.

[0068] The core-shell structure divides the large-pore defect structure on the surface of the core-shell nanowire-reinforced ceramic matrix modified composite material, constructing a small mesh structure that forms a three-dimensional network; a free silicon coating fills and covers the small mesh structure. Specifically, the core of the core-shell structure is silicon carbide nanowires, and the outer shell is pyrolytic carbon.

[0069] By employing a combined process for rapidly preparing nanowire-reinforced ceramic matrix modified composites, pyrolytic carbon is deposited on the surface of SiC nanowires to form a core-shell structure, thereby improving the high-temperature stability of SiC nanowires and reducing structural changes caused by the high-temperature treatment of the vapor-phase silicon infiltration process.

[0070] After constructing the core-shell structure, the large porosity defect structure on the surface of the composite material was effectively divided, and a small mesh structure of a three-dimensional network was constructed (e.g. Figure 3 As shown in (c), this facilitates rapid surface sealing by vapor-phase silicon infiltration (e.g., Figure 5 As shown in Table 1, a dense coating is formed, reducing porosity. Simultaneously, the nanomaterials themselves have a large specific surface area. The pyrolytic carbon in the shell of the nanowires can react fully with silicon vapor, rapidly forming a high-quality, uniformly distributed SiC coating. Subsequently, due to the low diffusion rate of silicon in the SiC coating, silicon vapor cannot continue to diffuse into the internal matrix. Unreacted free silicon can only condense on the already formed SiC coating on the surface. Therefore, the sealing coating on the surface of the core-shell structured nanowire-reinforced composite material contains a large amount of free silicon, resulting in low porosity.

[0071] The core-shell nanowire-reinforced composite material with a silicon-rich coating exhibited a flexural strength of 138.35 MPa and a flexural modulus of 18.50 GPa, representing increases of 29.5% and 19.4% respectively compared to the silicon carbide nanowire-reinforced modified composite material with a silicon carbide-rich coating, as shown in Table 2. This was achieved at a heat flux density of 2.38 MW / m². 2 After 60 s of ablation under an oxyacetylene flame, the core-shell structured nanowire-reinforced composite material with a silicon-rich coating exhibited good ablation performance, with linear ablation rate of 1.02 μm / s and mass ablation rate of 0.25 mg / s. This is attributed to the surface coating being rich in free silicon (e.g., ...). Figure 5 The evaporative endothermic effect (as shown) and the improved thermal conductivity due to the core-shell structure (e.g.) Figure 6 (As shown) This leads to a decrease in the surface temperature at the ablation center, promoting the formation of a dense oxide layer on the surface (such as...). Figure 8 (As shown).

[0072] This invention employs a combined CLVD and GSI process to rapidly prepare ceramic-based modified composite materials with low surface porosity. CLVD deposition of pyrolytic carbon on the surface of silicon carbide nanowires forms a core-shell structure, which strengthens the matrix. Simultaneously, the filling of internal voids and the heat transfer pathways provided by the deposited pyrolytic carbon enhance the thermal conductivity. Furthermore, the network structure formed by the core-shell structure divides the large pores on the composite surface into smaller mesh structures. Combined with chemical vapor infiltration (CVIS), the sealing coating deposited on the composite surface contains a large amount of free silicon. The evaporation and oxidation of free silicon during ablation reduces the surface temperature, thus improving the ablation performance of the composite material. In addition, the preparation method provided by this invention has a short preparation cycle, fast deposition rate, uniform ceramic product distribution, and minimal fiber damage during the preparation process.

[0073] The present invention also provides the above-mentioned core-shell structured nanowire reinforced ceramic matrix modified composite material with silicon-rich coating on the surface, which has excellent mechanical properties and anti-oxidation and ablation properties, and can be widely used in the field of thermal protection.

[0074] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0075] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0076] Example 1:

[0077] (1) Weigh a certain amount of polycarbosilane and ultra-high temperature ceramic hafnium carbide polymer precursor and dissolve them in 10L xylene (the mass ratio of polycarbosilane, ultra-high temperature ceramic hafnium carbide polymer precursor and xylene is 1:5:5), and after 2 hours of ultrasonic vibration, a uniformly dispersed mixed organic precursor solution is obtained.

[0078] (2) The density is 0.4 g / cm³ 3 The preform with dimensions of φ80mm×10mm, the heating elements H1 and H2, and other components are fully assembled, and a uniformly dispersed mixed organic precursor solution is poured into the reaction vessel, so that the upper surface of the heating element H1 is immersed in the mixed organic precursor solution.

[0079] (3) Start the equipment power supply, adjust the power, and raise the temperature of the heating element H2 to 800℃ at a rate of 10℃ / min, and keep it at that temperature for 24 hours; when cooling down, lower the temperature to 600℃ at a rate of 10℃ / min, then turn off the power supply and let it cool down with the furnace.

[0080] (4) The composite material obtained in (3) was placed in an isothermal furnace in a flowing argon atmosphere for heat treatment. The temperature was increased to 1500℃ at a heating rate of 2℃ / min, and the temperature was held for 2 hours. The power was then turned off and the furnace was cooled to obtain SiC nanowire reinforced C / C-HfC-SiC composite material.

[0081] (5) The composite material obtained in (4) was placed in a liquid phase furnace containing organic solvent and heated to 800°C at a rate of 10°C / min, and chemical liquid phase vaporization deposition was performed for 5 h. Then the temperature was lowered to 600°C at a rate of 10°C / min, the power was turned off and the furnace was cooled to obtain a core-shell structured nanowire reinforced C / C-HfC-SiC composite material;

[0082] (6) The core-shell nanowire reinforced C / C-HfC-SiC composite material was subjected to vapor phase silicon infiltration and pore sealing treatment. Under argon protection, the silicon infiltration temperature was 1800℃ and the holding time was 10min, resulting in a core-shell nanowire reinforced C / C-HfC-SiC composite material with a silicon-rich coating on the surface.

[0083] After introducing SiC nanowires and depositing pyrolytic carbon on the surface, the following advantages are achieved: First, it enhances the thermal stability of the nanowires, resulting in minimal structural changes after vapor-phase silicon infiltration. Second, it strengthens the connection between the nanowires and the matrix, as the multi-stage pull-out of the pyrolytic carbon and SiC nanowires during fracture further consumes energy and improves the mechanical properties of the composite material. Third, the shell pyrolytic carbon has a high intrinsic thermal conductivity and connects the nanowires to form a three-dimensional thermally conductive network, improving the thermal conductivity of the composite material. Fourth, the core-shell structure reduces the size of large pore defects, which is beneficial for surface sealing after vapor-phase silicon infiltration and for the rapid deposition of silicon-rich coatings, significantly reducing the ablation surface temperature. Therefore, the C / C-HfC-SiC composite material with a core-shell nanowire-reinforced structure containing a silicon-rich coating obtained in Example 1 has a porosity of 3.93%, and its mechanical properties are significantly improved. The flexural strength and flexural modulus are 138.35 MPa and 18.50 GPa, respectively. Secondly, the improved thermal conductivity, coupled with the large amount of free silicon in the surface sealing coating, plays a significant role in cooling the surface during ablation (ablation center temperature is 1885℃), resulting in the formation of a dense oxide layer. The ablation performance is significantly improved, and the linear ablation rate is 1.02 μm / s (see Table 2 for details).

[0084] Example 2:

[0085] (1) Weigh a certain amount of polycarbosilane and ultra-high temperature ceramic zirconium carbide and tantalum carbide polymer precursor and dissolve them in 10L of toluene (the mass ratio of polycarbosilane, ultra-high temperature ceramic zirconium carbide and tantalum carbide polymer precursor and toluene is 1:5:1), and after 2 hours of ultrasonic vibration, a uniformly dispersed mixed organic precursor solution is obtained.

[0086] (2) The density is 0.6 g / cm³ 3 The preform with dimensions of φ80mm×15mm, the heating elements H1 and H2, and other components are fully assembled, and a uniformly dispersed mixed organic precursor solution is poured into the reaction vessel, so that the upper surface of the heating element H1 is immersed in the mixed organic precursor solution.

[0087] (3) Start the equipment power supply, adjust the power, and raise the temperature of the heating element H2 to 900℃ at a rate of 15℃ / min, and keep it at that temperature for 20h; when cooling down, lower the temperature to 600℃ at a rate of 15℃ / min, then turn off the power supply and let it cool down with the furnace.

[0088] (4) The composite material obtained in (3) was placed in an isothermal furnace in a flowing argon atmosphere for heat treatment. The temperature was raised to 1600℃ at a rate of 3℃ / min and held for 2 hours. The power was then turned off and the furnace was cooled to obtain SiC nanowire reinforced C / C-ZrC-TaC-SiC modified composite material.

[0089] (5) The SiC nanowire-reinforced C / C-ZrC-TaC-SiC modified composite material obtained in (4) was placed in a liquid phase furnace containing organic solvent and heated to 900℃ at a rate of 15℃ / min, and chemical liquid phase vaporization deposition was performed for 10h. Then, the temperature was lowered to 600℃ at a rate of 15℃ / min, the power was turned off and the furnace was cooled to obtain the core-shell structured nanowire-reinforced C / C-ZrC-TaC-SiC composite material;

[0090] (6) The core-shell nanowire reinforced C / C-ZrC-TaC-SiC composite material was subjected to vapor phase silicon infiltration and sealing treatment. Under argon protection, the silicon infiltration temperature was 1900℃ and the holding time was 15min, resulting in a core-shell nanowire reinforced C / C-ZrC-TaC-SiC composite material with a silicon-rich coating on the surface.

[0091] Example 3:

[0092] (1) Weigh a certain amount of polycarbosilane and ultra-high temperature ceramic hafnium carbide and tantalum carbide polymer precursor and dissolve them in 10L of cyclohexane (the mass ratio of polycarbosilane, ultra-high temperature ceramic hafnium carbide and tantalum carbide polymer precursor and cyclohexane is 1:10:10), and after 2 hours of ultrasonic vibration, a uniformly dispersed mixed organic precursor solution is obtained.

[0093] (2) The density is 0.9 g / cm³ 3 The preform with dimensions of φ100mm×20mm, the heating elements H1 and H2, and other components are fully assembled, and a uniformly dispersed mixed organic precursor solution is poured into the reaction vessel, so that the upper surface of the heating element H1 is immersed in the mixed organic precursor solution.

[0094] (3) Start the equipment power supply, adjust the power, and raise the temperature of the heating element H2 to 1000℃ at a rate of 20℃ / min, and keep it at that temperature for 16 hours; when cooling down, lower the temperature to 600℃ at a rate of 20℃ / min, then turn off the power supply and let it cool down with the furnace.

[0095] (4) The composite material obtained in (3) was placed in an isothermal furnace in a flowing argon atmosphere for heat treatment. The temperature was raised to 1700℃ at a rate of 4℃ / min and held for 3 hours. The power was then cut off and the furnace was cooled to obtain SiC nanowire reinforced C / C-HfC-TaC-SiC composite material.

[0096] (5) The composite material obtained in (4) was placed in a liquid phase furnace containing organic solvent and heated to 1000℃ at a rate of 20℃ / min, and chemical liquid phase vaporization deposition was carried out for 15h. Then, the temperature was lowered to 600℃ at a rate of 20℃ / min, the power was turned off and the furnace was cooled to obtain a core-shell structured nanowire reinforced C / C-HfC-TaC-SiC composite material;

[0097] (6) The core-shell nanowire reinforced C / C-HfC-TaC-SiC composite material was subjected to vapor phase silicon infiltration and sealing treatment. Under argon protection, the silicon infiltration temperature was 1900℃ and the holding time was 30min, resulting in a core-shell nanowire reinforced C / C-HfC-TaC-SiC composite material with a silicon-rich coating on the surface.

[0098] Example 4:

[0099] (1) Weigh a certain amount of polycarbosilane and ultra-high temperature hafnium carbide, zirconium carbide and tantalum carbide polymer precursor and dissolve them in 10L of kerosene (the mass ratio of the ultra-high temperature ceramic polymer precursor composed of polycarbosilane, ultra-high temperature hafnium carbide, zirconium carbide and tantalum carbide polymer precursor and kerosene is 1:10:5), and after ultrasonic vibration for 2 hours, a uniformly dispersed mixed organic precursor solution is obtained.

[0100] (2) The density is 1.2 g / cm³ 3 The preform with dimensions of φ120mm×30mm, the heating elements H1 and H2, and other components are fully assembled, and a uniformly dispersed mixed organic precursor solution is poured into the reaction vessel, so that the upper surface of the heating element H1 is immersed in the mixed organic precursor solution.

[0101] (3) Start the equipment power supply, adjust the power, and raise the temperature of the heating element H2 to 1200℃ at a rate of 20℃ / min, and keep it at that temperature for 16h; when cooling down, lower the temperature to 600℃ at a rate of 20℃ / min, then turn off the power supply and let it cool down with the furnace.

[0102] (4) The composite material obtained in (3) was placed in an isothermal furnace with a flowing argon atmosphere for heat treatment. The temperature was increased to 1800℃ at a heating rate of 5℃ / min, and the temperature was held for 4 hours. The power was then turned off and the furnace was cooled to obtain SiC nanowire reinforced C / C-HfC-ZrC-TaC-SiC composite material.

[0103] (5) The composite material obtained in (4) was placed in a liquid phase furnace containing organic solvent and heated to 1200℃ at a rate of 20℃ / min, and chemical liquid phase vaporization deposition was carried out for 15h. Then, the temperature was lowered to 600℃ at a rate of 20℃ / min, the power was turned off and the furnace was cooled to obtain a core-shell structured nanowire reinforced C / C-HfC-ZrC-TaC-SiC composite material;

[0104] (6) The core-shell nanowire reinforced C / C-HfC-ZrC-TaC-SiC composite material was subjected to vapor phase silicon infiltration and pore sealing treatment. Under argon protection, the silicon infiltration temperature was 2150℃ and the holding time was 30min, resulting in a core-shell nanowire reinforced C / C-HfC-ZrC-TaC-SiC composite material with a silicon-rich coating on the surface.

[0105] Comparative Example 1:

[0106] (1) Weigh a certain amount of polycarbosilane and ultra-high temperature hafnium carbide polymer precursor and dissolve them in 10L xylene (the mass ratio of polycarbosilane, ultra-high temperature hafnium carbide polymer precursor and xylene is 1:5:5), and after 2 hours of ultrasonic vibration, a uniformly dispersed mixed organic precursor solution is obtained.

[0107] (2) The density is 0.4 g / cm³ 3 The preform with dimensions of φ80mm×10mm, the heating elements H1 and H2, and other components are fully assembled, and a uniformly dispersed mixed organic precursor solution is poured into the reaction vessel, so that the upper surface of the heating element H1 is immersed in the mixed organic precursor solution.

[0108] (3) Start the equipment power supply, adjust the power, and raise the temperature of the heating element H2 to 1000℃ at a rate of 10℃ / min, and keep it at that temperature for 24 hours; when cooling down, lower the temperature to 600℃ at a rate of 10℃ / min, then turn off the power supply and let it cool down with the furnace.

[0109] (4) The composite material obtained in (3) was placed in an isothermal furnace in a flowing argon atmosphere for heat treatment. The temperature was raised to 1850℃ at a heating rate of 2℃ / min, and held for 2 hours. The power was then turned off and the furnace was cooled to obtain a SiC nanowire-reinforced ceramic matrix modified composite material.

[0110] (5) The composite material obtained in (4) is placed in a liquid phase furnace containing organic solvent and heated to 800°C at a rate of 10°C / min, and chemical liquid phase vaporization deposition is carried out for 5 hours. Then the temperature is reduced to 600°C at a rate of 10°C / min, the power is turned off and the furnace is cooled.

[0111] (6) The composite material was subjected to vapor phase silicon infiltration and sealing treatment. Under argon protection, the silicon infiltration temperature was 1800℃ and the holding time was 10min to obtain a SiC nanowire-reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating on the surface.

[0112] Because the heat treatment temperature was high, SiC nanowires were not introduced. Due to the lack of a highly elastic and high-modulus SiC nanowire reinforcing phase, energy could not be further dissipated through pull-out during fracture, resulting in decreased mechanical properties. Furthermore, the coating formed by surface deposition after vapor-phase silicon infiltration was predominantly SiC, and did not significantly reduce the ablation temperature. Compared to the C / C-HfC-SiC composite material with a silicon carbide-rich coating but without nanowire reinforcement obtained in Comparative Example 1, the C / C-HfC-SiC composite material with a silicon-rich coating and core-shell nanowire reinforcement obtained in Example 1 exhibited a 64.3% reduction in porosity, a 62.7% increase in flexural strength, a 121.0% increase in flexural modulus, a 397°C reduction in ablation center temperature, an 85.0% reduction in linear ablation rate, and a 70.9% reduction in mass ablation rate (see Table 2).

[0113] Comparative Example 2:

[0114] (1) Weigh a certain amount of polycarbosilane and ultra-high temperature ceramic hafnium carbide polymer precursor and dissolve them in 10L xylene (the mass ratio of polycarbosilane, ultra-high temperature ceramic hafnium carbide polymer precursor and xylene is 1:5:5), and after 2 hours of ultrasonic vibration, a uniformly dispersed mixed organic precursor solution is obtained.

[0115] (2) The density is 0.4 g / cm³ 3 The preform with dimensions of φ80mm×10mm, the heating elements H1 and H2, and other components are fully assembled, and a uniformly dispersed mixed organic precursor solution is poured into the reaction vessel, so that the upper surface of the heating element H1 is immersed in the mixed organic precursor solution.

[0116] (3) Start the equipment power supply, adjust the power, and raise the temperature of the heating element H2 to 900℃ at a rate of 10℃ / min, and keep it at that temperature for 24 hours; when cooling down, lower the temperature to 600℃ at a rate of 10℃ / min, then turn off the power supply and let it cool down with the furnace.

[0117] (4) The composite material obtained in (3) was placed in an isothermal furnace in a flowing argon atmosphere for heat treatment. The temperature was increased to 1800℃ at a heating rate of 2℃ / min, and the temperature was held for 2 hours. The power was then turned off and the furnace was cooled to obtain the SiC nanowire reinforced ceramic matrix modified composite material.

[0118] (5) The composite material was subjected to vapor phase silicon infiltration and sealing treatment. Under the protection of argon, the silicon infiltration temperature was 1800℃ and the holding time was 10min, resulting in a SiC nanowire reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating on the surface.

[0119] After introducing SiC nanowires, the grain size of the SiC nanowires coarsens during subsequent vapor-phase silicon infiltration to form a core-shell structure for further deposition of pyrolytic carbon, thus weakening the reinforcing effect. Furthermore, since there is no core-shell structure for meshing on the surface, the coating deposited after vapor-phase silicon infiltration is predominantly SiC, without a significant effect on reducing the ablation temperature. Therefore, compared to the silicon carbide-rich coating-reinforced C / C-HfC-SiC composite material with silicon carbide nanowires, obtained in Comparative Example 2, the silicon-rich coating-reinforced core-shell nanowire-reinforced C / C-HfC-SiC composite material obtained in Example 1 exhibits a 59.7% reduction in porosity, a 29.5% increase in flexural strength, a 19.4% increase in flexural modulus, a 105°C reduction in ablation center temperature, an 80.7% reduction in linear ablation rate, and a 49.0% reduction in mass ablation rate (see Table 2).

[0120] Table 1. Changes in density and porosity before and after vapor-phase silica infiltration.

[0121]

[0122] Table 2. Results of mechanical tests and ablation performance tests

[0123]

[0124]

[0125] As shown in Table 1 above, the density of the composite material is significantly increased and the porosity is significantly reduced after the chemical vapor infiltration process. Compared with the silicon carbide nanowire reinforced ceramic matrix modified composite material with silicon carbide-rich coating on the surface obtained in Comparative Example 2, the porosity of the core-shell structure nanowire reinforced ceramic matrix modified composite material obtained in Example 1 is reduced by 59.7% to only 3.93%, indicating that the vapor infiltration process has a significant pore-sealing effect.

[0126] As can be seen from the comparison of Comparative Examples 1, 2 and 1 in Table 2 above, after vapor-phase silicon infiltration, the flexural strength and modulus of the core-shell nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on the surface are significantly improved, the surface temperature is reduced, and the ablation performance is improved. This indicates that the core-shell nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating rapidly prepared by this combined process has both excellent mechanical and ablation properties.

[0127] like Figure 2A comparison of Figures (a) and (b) shows that in Example 1, the sample that underwent the first chemical liquid phase vaporization deposition process formed a large number of SiC nanowires on its surface after high-temperature treatment, while in Comparative Example 1, the sample that underwent the first chemical liquid phase vaporization deposition process did not form SiC nanowires on its surface after high-temperature treatment.

[0128] like Figure 3 As shown, see Figure 3 (a) and (b) show the microstructure of the SiC nanowire-reinforced C / C-HfC-SiC composite material surface after the first chemical liquid phase vaporization deposition process. (See also...) Figure 3 (a) shows the surface morphology before polishing, while also incorporating a large number of SiC nanowires and bulk ceramic phases. See [link to relevant documentation]. Figure 3 (b) shows the backscattering morphology of the surface after polishing. The white area represents the ultra-high temperature ceramic phase, the gray area represents the SiC phase, and the black area represents pyrolytic carbon fibers. Figure 3 The small image in (b) shows the co-deposition of the ceramic phase and pyrolytic carbon around the carbon fibers; see also Figure 3 (c) and (d) show the microstructure of the surface and core-shell structure after the second chemical liquid phase vaporization deposition process. Figure 3 (c) shows the morphology of the core-shell structure on the surface, which divides the large pores on the surface into small pores, which is beneficial for the rapid deposition of silicon-rich coatings on the surface. Figure 3 (d) The high-magnification morphology image shows that a ring of pyrolytic carbon is uniformly formed around the SiC nanowire, thus forming a core-shell structure with SiC nanowire as the core and PyC as the outer shell.

[0129] like Figure 4 As shown in Figures (a) and (b), the SiC nanowires formed after the first chemical liquid phase vaporization deposition process exhibit a bamboo-like morphology. After the second chemical liquid phase vaporization deposition process, a core-shell structure is formed, and the surface of the SiC nanowires is uniformly covered with pyrolytic carbon. The two are closely connected and have a good interface.

[0130] like Figure 5 As shown, cross-sectional image ( Figure 5 As shown in (a, b), macroscopically, a coating layer is deposited on the substrate surface after vapor phase silicon infiltration, and the coating layer is well bonded to the substrate with a thickness of about 50 μm. Figure 5 (c) shows that the coating formed on the surface of the nanowire-reinforced ceramic matrix modified composite material of Comparative Example 2 after vapor-phase silicon infiltration is dominated by hexagonal SiC crystals. Figure 5 (d) shows that the coating formed on the surface of the core-shell nanowire reinforced C / C-HfC-SiC composite material of Example 1 after vapor phase silicon infiltration is mainly composed of white free silicon phase.

[0131] Figure 6 HS0 is the SiC nanowire-reinforced C / C-HfC-SiC composite material obtained in Example 1 without SiC, HS1 is the SiC nanowire-reinforced C / C-HfC-SiC composite material obtained in Example 2, and HS2 is the core-shell structured nanowire-reinforced C / C-HfC-SiC composite material obtained in Example 1. The comparison shows that the thermal conductivity of the ceramic matrix modified composite material is improved after constructing the core-shell structure, which contributes to the reduction of the surface ablation temperature during the subsequent ablation process.

[0132] Figure 7 For a heat flux density of 2.38 MW / m 2 The macroscopic morphology image after 60 seconds of oxyacetylene flame ablation shows that, compared with Comparative Example 1, the SiC nanowire-reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating obtained by vapor-phase silicon infiltration has a different surface composition. Figure 7 (a) Comparative Example 2: SiC nanowire-reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating on the surface obtained by vapor phase silicon infiltration. Figure 7 (b) In comparison, the core-shell structured nanowire-reinforced C / C-HfC-SiC composite material obtained by vapor-phase silicon infiltration in Example 1, with a silicon-rich coating on the surface, is... Figure 7 The ablation surfaces in (c) are divided into three regions: the central region (region I), the transition region (region II), and the edge region (region III). The difference is that the central region in Figure (c) is more dense and suffers less ablation damage.

[0133] Figure 8 This is a microscopic morphology image of the ablation center of the sample after oxyacetylene ablation. It can be seen that, in Comparative Example 1, the oxide layer surface of the ablation center of the SiC nanowire-reinforced C / C-HfC-SiC composite material with a silicon carbide-rich coating obtained by vapor-phase silicon infiltration is covered on the carbon fiber, resembling a "coral reef" shape. Figure 8 (a)); Comparative Example 2: SiC nanowire-reinforced C / C-HfC-SiC composite material obtained by vapor-phase silicon infiltration with a silicon carbide-rich coating on the surface ( Figure 8 (b) The continuity and smoothness of the oxide layer at the ablation center are further improved, while the core-shell structured nanowire-reinforced C / C-HfC-SiC composite material with a silicon-rich coating obtained by vapor-phase silicon infiltration in Example 1 is further improved. Figure 8 (c) The oxide layer at the ablation center is flat and has no obvious cracks or large pores, exhibiting the best ablation resistance.

[0134] This invention introduces ultra-high temperature ceramics and nanowire reinforcing phases in a one-step process, and uses deposited pyrolytic carbon to construct a highly stable core-shell structure to effectively divide the large pore structure on the surface, forming a small grid structure. The auxiliary vapor phase silicon infiltration technology enables the surface of the composite material to be rapidly densified. This structure exhibits excellent performance in terms of load-bearing, heat transfer and ablation resistance, and has good prospects for industrial application and economic benefits.

[0135] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface, characterized in that, This includes core-shell structured nanowire-reinforced ceramic matrix modified composites and free silicon coatings; The core-shell structured nanowire-reinforced ceramic matrix modified composite material includes a ceramic phase, carbon fibers, silicon carbide nanowires, and pyrolytic carbon. The ceramic phase and pyrolytic carbon are co-deposited around the carbon fibers. The silicon carbide nanowires grow extensively in the internal voids and on the surface of the core-shell structure nanowire-reinforced ceramic matrix modified composite material. Pyrolytic carbon is deposited on the surface of the silicon carbide nanowires to form a core-shell structure. The free silicon coating is deposited on the core-shell structure nanowire-reinforced ceramic matrix modified composite material. The rapid preparation method of the core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface includes the following steps: S1: A mixed organic precursor formed by silicon carbide precursor and ultra-high temperature ceramic polymer precursor is dissolved in an organic solvent to form a mixed organic precursor solution. The carbon fiber preform is subjected to the first chemical liquid phase vaporization deposition in the mixed organic precursor solution, followed by cooling and then cooling to obtain the deposited composite material. S2: The deposited composite material is heat-treated and then cooled to form silicon carbide nanowires, ceramic phase and pyrolytic carbon, thus obtaining silicon carbide nanowire reinforced ceramic matrix modified composite material. S3: The silicon carbide nanowire reinforced ceramic matrix modified composite material is subjected to a second chemical liquid phase vaporization deposition in an organic solvent, followed by cooling and then cooling. Pyrolytic carbon is deposited on the surface of silicon carbide nanowires to form a core-shell structure, thus obtaining a core-shell structured nanowire reinforced ceramic matrix modified composite material. S4: Vapor phase infiltration and pore sealing treatment is performed on the core-shell nanowire reinforced ceramic matrix modified composite material to form a free silicon coating, thereby obtaining a core-shell nanowire reinforced ceramic matrix modified composite material with a silicon-rich coating on the surface.

2. The core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface according to claim 1, characterized in that, In step S1, the density of the carbon fiber preform is 0.4~1.2 g / cm³. 3 The carbon fiber preform is a cylindrical carbon fiber preform with dimensions of φ80~120mm×10~30mm.

3. The core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface according to claim 1, characterized in that, In S1, the ultra-high temperature ceramic polymer precursor is any one of hafnium carbide precursor, zirconium carbide precursor, and tantalum carbide precursor.

4. The core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface according to claim 1, characterized in that, In S1 and S3, the organic solvent is any one of xylene, toluene, cyclohexane, and kerosene.

5. The core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface according to claim 1, characterized in that, In S1, the mass ratio of the silicon carbide precursor, the ultra-high temperature ceramic polymer precursor and the organic solvent is 1:(5~10):(1~10).

6. The core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface according to claim 1, characterized in that, In S1, the first chemical liquid phase vaporization deposition process is as follows: The carbon fiber preform was placed in a liquid phase furnace containing a mixed organic precursor solution and heated to 800-1200°C at a rate of 10-20°C / min. Chemical liquid phase vaporization deposition was carried out for 16-24 hours, and then cooled to 600°C at a rate of 10-20°C / min. In step S3, the second chemical liquid phase vaporization deposition process is as follows: The silicon carbide nanowire-reinforced ceramic matrix modified composite material was placed in a liquid phase furnace containing organic solvent and heated to 800-1200℃ at a rate of 10-20℃ / min. The chemical liquid phase vaporization deposition was carried out for 5-15 hours, and then cooled to 600℃ at a rate of 10-20℃ / min.

7. The core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface according to claim 1, characterized in that, In step S2, the heat treatment process is as follows: Under the protection of argon atmosphere, the temperature is increased to 1500~1800℃ at a rate of 2~5℃ / min and held for 2~4h; In step S4, the vapor phase silicon infiltration sealing process is as follows: Keep warm at 1800~2150℃ for 10~30 minutes.

8. The core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface according to claim 1, characterized in that, The core-shell structure divides the large pore defect structure on the surface of the core-shell nanowire-reinforced ceramic matrix modified composite material, and constructs a small grid structure to form a three-dimensional network; a free silicon coating fills and covers the small grid structure.

9. The application of a core-shell structured nanowire-reinforced ceramic matrix modified composite material with a silicon-rich coating on its surface as described in any one of claims 1 to 8 in the field of thermal protection.

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