Carbon fiber reinforced carbon / silicon carbide composite material as well as preparation method and application thereof

Abstract

The invention relates to a carbon fiber reinforced carbon / silicon carbide composite material as well as a preparation method and application thereof. The method comprises the following steps: arranging carbon layer interface phases on the surface of a carbon fiber woven body and the inner walls of pores; soaking in a solution containing a carbon element; performing curing; performing carbonization; depositing carbon on the surface of the carbon fiber woven body and in pores by adopting a CVI (Chemical Vapor Infiltration) process; measuring the density of the carbon fiber woven body; if the density is smaller than a preset threshold value, executing the previous steps; if the density is larger than or equal to the preset threshold value, generated carbon is calculated, silicon powder with the stoichiometric ratio is added for fusion siliconizing, the generated carbon is converted into silicon carbide, and the carbon fiber reinforced carbon / silicon carbide composite material is obtained. The technical problem to be solved is how to prepare the carbon fiber reinforced carbon / silicon carbide composite material, so that the carbon fiber reinforced carbon / silicon carbide composite material is good in mechanical property, the bending strength is greater than or equal to 280 MPa, and the tensile strength is greater than or equal to 100 MPa; according to the carbon fiber reinforced carbon / silicon carbide composite material prepared by the preferable technical scheme, the bending strength is greater than or equal to 360 MPa, and the tensile strength is greater than or equal to 180 MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide ceramic-based composite materials, and in particular relates to a carbon fiber reinforced carbon / silicon carbide composite material and a preparation method and application thereof. Background Art

[0002] Carbon fiber reinforced silicon carbide composite materials have high strength, oxidation resistance, high temperature resistance and corrosion resistance, and have become the new generation of thermal protection materials for aerospace vehicles.

[0003] At present, the preparation of carbon fiber reinforced silicon carbide composites mainly adopts the reactive melt infiltration (RMI) method. The RMI method mostly uses a carbon fiber braid as a preform, prepares an interface phase on the fiber surface through a CVD process or a PIP process, and then prepares a carbon source by impregnation and cracking of a phenolic resin, or directly uses a CVI process to pyrolyze the carbon source; finally, the carbon source is converted into silicon carbide by melt infiltration of molten silicon, so that the silicon carbide is filled on the surface and pores of the carbon fiber. RMI has the advantages of short preparation cycle, low residual porosity, and the ability to prepare workpieces of complex shapes. It is a reliable process for low-cost preparation of carbon fiber reinforced silicon carbide composites. However, the RMI process has obvious defects: in the RMI process of preparing the carbon source by impregnation and cracking of phenolic resin, due to the high viscosity of phenolic resin, it is difficult for the phenolic resin to penetrate into the carbon fiber braid after two or three impregnation and cracking, resulting in insufficient carbon source in the carbon fiber braid, less residual carbon in the carbon fiber braid during pyrolysis, and lack of residual carbon to react after molten silicon infiltrates, thereby affecting the distribution of silicon carbide and further affecting the performance of the final product; and in the RMI process of directly pyrolyzing the carbon source using the CVI process, due to the denser carbon deposition, it is difficult for molten silicon to penetrate into the carbon fiber braid, resulting in insufficient reaction between Si and C, and a large amount of residual carbon inside the material, which affects the distribution of silicon carbide and further affects the performance of the final product.

[0004] As can be seen from the above, the performance of carbon fiber reinforced silicon carbide composite materials prepared by the RMI process in the prior art is poor, especially the bending strength and tensile strength of the final carbon fiber reinforced silicon carbide composite materials are low, which is difficult to meet the application in aerospace and other fields. Summary of the Invention

[0005] The main purpose of the present invention is to provide a carbon fiber reinforced carbon / silicon carbide composite material and its preparation method and application. The technical problem to be solved is how to provide a method for preparing a carbon fiber reinforced carbon / silicon carbide composite material so that the mechanical properties of the carbon fiber reinforced carbon / silicon carbide composite material prepared thereby are significantly improved, and its bending strength is ≥280Mpa and its tensile strength is ≥100MPa; the carbon fiber reinforced carbon / silicon carbide composite material prepared by the further preferred technical scheme has a bending strength ≥360Mpa and a tensile strength ≥180MPa.

[0006] The purpose of the present invention and the solution to its technical problems are also achieved by adopting the following technical solutions. According to the present invention, a method for preparing a carbon fiber reinforced carbon / silicon carbide composite material comprises the following steps:

[0007] S11 provides a carbon layer interface phase on the surface of the first carbon fiber braid and the inner wall of the pores to obtain a second carbon fiber braid;

[0008] S12: dipping the second carbon fiber braid into a solution containing a carbon element to obtain a third carbon fiber braid;

[0009] S13 solidifies the solute on the surface and inside the pores of the third carbon fiber braid; carbonizes the solute solidified on the surface and inside the pores of the third carbon fiber braid to pyrolyze into carbon, thereby obtaining a fourth carbon fiber braid;

[0010] S14 uses a CVI process to deposit carbon on the surface and inside the pores of the fourth carbon fiber braid to obtain a fifth carbon fiber braid;

[0011] S15 measures the density of the fifth carbon fiber braid; if the density is greater than or equal to a preset threshold, executes step S16; if the density is less than the preset threshold, uses the fifth carbon fiber braid as a new second carbon fiber braid, and executes steps S12 to S14 in sequence;

[0012] S16 calculates the generated carbon based on the weight difference between the second carbon fiber braided body obtained by executing steps S12 to S14 for the first time and the fifth carbon fiber braided body obtained by executing steps S12 to S14 for the last time, adds a stoichiometric ratio of silicon powder for melt siliconization treatment, and converts the generated carbon into silicon carbide to obtain a carbon fiber reinforced carbon / silicon carbide composite material.

[0013] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0014] Preferably, in the above method, the residual carbon rate of the solute in the solution is ≥40%; the mass concentration of the solution is ≥40%; the viscosity of the solution is ≤300mPa·s; the preset threshold is 1.3g / cm 3 .

[0015] Preferably, in the aforementioned method, the solute is selected from at least one of sucrose, glucose, fructose, maltose, oligofructose, modified starch, phenolic resin and asphalt.

[0016] Preferably, in the aforementioned method, the solute is selected from at least one of sucrose, glucose, fructose, maltose, oligofructose and modified starch.

[0017] Preferably, in the aforementioned method, the solution further comprises an organic monomer and an initiator; the initiator can initiate polymerization of the organic monomer to form a polymer; and the polymer wraps the substances in the solution except the organic monomer and the initiator into a plurality of liquid packets.

[0018] Preferably, in the aforementioned method, the method for preparing the carbon layer interface phase in step S11 includes: depositing a carbon layer on the surface of the first carbon fiber braid and the inner wall of the pores by a CVI method; the process conditions of CVI are: using propane as the raw gas, hydrogen as the carrier gas, the molar ratio of propane to hydrogen is 1:4-6, and the flow rate is 1.9-2.0 L / min / m 3 , temperature is 950~1050℃, pressure is 4~6KPa, and deposition time is 2~4h.

[0019] Preferably, in the aforementioned method, the first carbon fiber braid is made by wrapping needle-punched carbon felt with a mesh; the first carbon fiber braid comprises a plurality of parallel arranged carbon fiber bundles; the density of the first carbon fiber braid is 0.5 to 0.7 g / cm 3 .

[0020] Preferably, in the aforementioned method, the impregnation in step S12 comprises the following steps:

[0021] S81 evacuates the solution containing the second carbon fiber braid to remove air bubbles;

[0022] S82 breaks the vacuum; introduces gas into the environment where the solution is located, and maintains the pressure at 2-5 MPa to allow the solute to adhere to the surface of the second carbon fiber braid and penetrate into the interior of the second carbon fiber braid.

[0023] The purpose of the present invention and the technical problem solved are achieved by adopting the following technical solutions. According to the present invention, a carbon fiber reinforced carbon / silicon carbide composite material is proposed, which comprises:

[0024] a first carbon fiber braid;

[0025] a carbon layer interface phase, disposed on the surface of the first carbon fiber braid and the inner wall of the pores;

[0026] Silicon carbide is arranged on the surface of the carbon layer interface phase; the carbon fiber reinforced carbon / silicon carbide composite material is prepared by the above method.

[0027] The purpose of the present invention and the technical problem solved are achieved by adopting the following technical solutions: The present invention proposes the application of a carbon fiber reinforced carbon / silicon carbide composite material as described above in the aerospace, automotive, or military fields.

[0028] By means of the above technical solution, the carbon fiber reinforced carbon / silicon carbide composite material of the present invention and its preparation method and application have at least the following advantages:

[0029] The carbon fiber-reinforced carbon / silicon carbide composite material proposed in the present invention, as well as its preparation method and application, is obtained by providing a carbon layer as an interface phase on the surface and inner wall of the pores of a first carbon fiber braid to form a second carbon fiber braid, thereby forming a fiber protective film to protect the carbon fibers, thereby preventing high-temperature silicon vapor from eroding the carbon fibers during the subsequent siliconization treatment of molten silicon. It also improves the interfacial bonding performance between the carbon fiber surface and the subsequently formed silicon carbide material, thereby obtaining a suitable interfacial bonding energy and improving the toughness of the carbon fiber-reinforced carbon / silicon carbide composite material. Then, the processes of impregnation pyrolysis to form residual carbon and CVI carbon deposition are alternately performed to generate carbon on the surface of the interface phase, which is used to react with silicon to form silicon carbide during the subsequent siliconization of molten silicon, thereby obtaining a carbon fiber-reinforced carbon / silicon carbide composite material. Among them, the impregnation pyrolysis to form residual carbon is sequentially impregnated, solidified and carbonized by a solution containing carbon elements, so that the solute is pyrolyzed into carbon and is located on the surface and inside the pores of the fourth carbon fiber braid, forming a porous body; the porous body serves as the skeleton of the CVI carbon source, which can make the C infiltrated by CVI cracking adhere to the surface and internal pore walls of the porous body, thereby enhancing the strength of the porous carbon and further improving the mechanical properties of the C / SiC composite material formed after siliconization. Finally, by calculating the total amount of carbon generated by the alternating process of impregnation pyrolysis to form residual carbon and CVI deposition carbon, the silicon powder is melt-siliconized according to the stoichiometric ratio, so that after the generated carbon and silicon are converted into silicon carbide, there is as little or no unreacted carbon and silicon in the material as possible, thereby avoiding the unreacted carbon and silicon from having an adverse effect on the performance of the composite material, ensuring its mechanical properties, and enabling it to be used in the aerospace field.

[0030] The carbon fiber reinforced porous carbon composite material obtained by the technical solution of the present invention has a flexural strength ≥280Mpa and a tensile strength ≥100MPa; the carbon fiber reinforced carbon / silicon carbide composite material prepared by the further preferred technical solution has a flexural strength ≥360Mpa and a tensile strength ≥180MPa.

[0031] It should be noted that in the present invention, almost all of the carbon generated by the alternating process of impregnation pyrolysis to form residual carbon and CVI deposition carbon reacts with molten silicon; the "carbon" in the composite material refers to the carbon in the interface phase of the carbon layer. By controlling the proportion of molten silicon, this part of the carbon does not participate in the reaction to ensure that the carbon fiber itself is not destroyed, thereby ensuring the performance of the final carbon fiber reinforced carbon / silicon carbide composite material.

[0032] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1is a SEM image of carbon produced by pyrolysis of sucrose in Example 1 of the present invention.

[0034] Figure 2 1 is a SEM image of carbon produced by pyrolysis of propane by CVI in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] To further illustrate the technical means and effectiveness of the present invention in achieving its intended objectives, the following, in conjunction with the accompanying drawings and preferred embodiments, provides a detailed description of the carbon fiber-reinforced carbon / silicon carbide composite material, its preparation method, and its specific embodiments, structures, features, and effectiveness. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0036] The inventors found that when preparing carbon fiber reinforced carbon / silicon carbide composites by reactive melt infiltration (RMI), the structure of the matrix carbon produced by pyrolysis of a solution containing carbon elements is relatively loose and porous. Although it is conducive to the infiltration of molten silicon, the matrix carbon layer produced by pyrolysis of the solute is too loose and porous, resulting in a discontinuous carbon layer, resulting in very low strength of the composite material after silicon infiltration; and although the matrix carbon produced by CVI pyrolysis is easy to obtain a dense and continuous carbon layer, the carbon layer is too dense, resulting in difficulty for subsequent molten silicon to infiltrate the matrix carbon layer produced by CVI pyrolysis, and no composite material with good performance can be obtained; the present invention cleverly controls the structure and distribution of the generated carbon by alternatingly impregnating carbon with pyrolysis of a solution containing carbon elements and generating carbon by pyrolysis of a carbon source by CVI pyrolysis. The prepared carbon fiber reinforced porous carbon composite material is not only conducive to the silicon infiltration reaction between it and molten silicon to generate silicon carbide, but also can greatly improve the mechanical properties of the composite material.

[0037] A first aspect of the present invention provides a method for preparing a carbon fiber reinforced carbon / silicon carbide composite material, comprising the following steps:

[0038] First, a carbon layer interface phase is formed on the surface and pore inner walls of the first carbon fiber braid to obtain a second carbon fiber braid. The technical purpose of the carbon layer interface phase is to form a fiber protective film on the carbon fiber surface to protect the carbon fiber, thereby preventing the high-temperature silicon vapor from eroding the carbon fiber during the subsequent siliconization treatment of molten silicon. It also improves the interfacial bonding performance between the carbon fiber surface and the subsequently formed silicon carbide material, thereby obtaining suitable interfacial bonding energy and improving the toughness of the carbon fiber reinforced carbon / silicon carbide composite material.

[0039] The carbon layer interface phase can be formed on the surface of the first carbon fiber braid and the inner wall of the pores by using conventional carbon layer formation methods in the art. The present invention preferably uses the CVI method to deposit the carbon layer on the surface of the first carbon fiber braid and the inner wall of the pores; the CVI process conditions are: propane as the raw gas, hydrogen as the carrier gas, the molar ratio of propane to hydrogen is 1:4-6, and the flow rate is 1.9-2.0 L / min / m 3 The temperature is 950-1050°C, the pressure is 4-6KPa, and the deposition is 2-4h to prepare an interface layer with a thickness of 80-100nm. The temperature, pressure and time of the CVI pyrolysis-generated carbon layer interface phase are controlled within the above ranges to ensure that the carbon layer interface phase generated by CVI pyrolysis grows continuously around the surface of the carbon fiber bundle and is more evenly coated on the surface of the carbon fiber bundle, so that the carbon fiber bundle and the carbon generated by CVI pyrolysis are more tightly combined.

[0040] In some specific embodiments of the present invention, the first carbon fiber braid is made by wrapping needle-punched carbon felt with a web, which includes a plurality of parallel carbon fiber bundles with a density of 0.5 to 0.7 g / cm 3 , thickness is 4mm; due to the slight difference in density and thickness of different parts of the braid within the tolerance range, the density of 0.65g / cm is used in the subsequent specific embodiments. 3 A braid with a thickness of about 4 mm serves as the first carbon fiber braid.

[0041] In some specific embodiments of the present invention, the interfacial phase is prepared in a cylindrical pyrolysis furnace with a diameter of 1200 mm and a height of 900 mm. Propane is used as the feed gas, hydrogen as the carrier gas, with a propane:hydrogen molar ratio of 1:5, a flow rate of 2 L / min, a temperature of 1050°C, and a pressure of 4 kPa. Deposition is performed for 2 to 4 hours. The deposition time can be adjusted based on the desired thickness of the interfacial phase.

[0042] Next, matrix carbon is generated on the surface of the carbon layer interface phase. This portion of carbon is evenly distributed on the surface of the carbon fibers and the inner walls of the pores, and is isolated from the carbon fibers by the carbon layer interface phase. This portion of matrix carbon will react with molten silicon in subsequent steps and be completely converted into silicon carbide matrix material. In this step, the processes of impregnation pyrolysis to form residual carbon and CVI deposition of carbon are alternated to ensure that the density of the fiber braid is ≥ the preset threshold. The specific steps are as follows:

[0043] The first step, solution impregnation, involves impregnating the second carbon fiber braid in a solution containing a carbon element to obtain a third carbon fiber braid. It should be noted that the term "solution" as used herein is broad and includes liquid substances that are solid at room temperature and can be converted to liquid upon heating.

[0044] In order to prevent the introduction of other elements from affecting the properties of the final composite material, the present invention preferably includes no or less other elements in the solute of the carbon-containing solution except carbon, hydrogen and oxygen.

[0045] In order to ensure that the solute can generate more carbon after the subsequent pyrolysis process to improve the efficiency of carbon setting, a smaller number of impregnations can introduce a larger amount of carbon; through a large number of experiments, it is verified that the residual carbon rate of the solute in the solution is preferably ≥40%.

[0046] In order to ensure that the solution can be smoothly impregnated and penetrated into the pores of the carbon fiber, the viscosity of the solution should not be too high; in order to ensure that each impregnation can generate more carbon after the subsequent pyrolysis process to improve the efficiency of carbon setting, a smaller number of impregnations can introduce a larger amount of carbon, and the concentration of the solution should not be too low; through a large number of experiments, it is verified that the mass concentration of the solution of the present invention is preferably ≥40%, and the viscosity of the solution is ≤300mPa·s.

[0047] Through a large number of experiments, it has been verified that the solute in the solution is selected from at least one of sucrose, glucose, fructose, maltose, oligofructose, modified starch, phenolic resin and asphalt; the above raw materials are used as solutes to prepare a solution or are heated to become a liquid and then impregnated into the first carbon fiber braid, and combined with the subsequent CVI carbon deposition process, the composite material formed has good mechanical properties, as shown in Examples 1 to 6, its bending strength is ≥280MPa, and its tensile strength is ≥100MPa.

[0048] Through a large number of experiments, it has been verified that the solute in the solution is selected from at least one of sucrose, glucose, fructose, maltose, oligofructose and modified starch; after preparing a solution with the above raw materials as solutes, the first carbon fiber braid is impregnated, and combined with the subsequent CVI carbon deposition process, the mechanical properties of the composite material formed are further improved. As shown in Examples 1 to 4, its bending strength is ≥360 MPa and its tensile strength is ≥180 MPa.

[0049] When a solution is prepared using at least one of sucrose, glucose, fructose, maltose, oligofructose and modified starch as a solute, the solution preferably also includes an organic monomer and an initiator, and a catalyst may also be added; the organic monomer and initiator are conventional choices in the field, as long as they can initiate the polymerization reaction of the organic monomer under the immersion conditions; the present invention does not specifically limit the types of organic monomers and initiators. In some specific embodiments of the present invention, acrylamide and NN bisacrylamide are used as organic monomers, ammonium persulfate is used as an initiator, and ferric chloride is used as a catalyst. The initiator can induce the polymerization of organic monomers to form polymers; the polymer can wrap the substances in the solution except the organic monomer and the initiator to form a plurality of smaller liquid packages; then in the subsequent solidification step, the liquid in the liquid package is dried, leaving only the solute; in the subsequent carbonization step, the polymer is pyrolyzed and the solute is also decomposed, thereby forming a porous and loose deposited carbon.

[0050] In order to remove bubbles in the solution, the present invention also includes vacuuming the solution containing the second carbon fiber braid to remove bubbles during the impregnation step; when vacuuming, the impregnation environment is at negative pressure, and the gauge pressure is displayed as -0.1 to -1 MPa; after the bubbles in the solution are removed, the vacuum is broken.

[0051] In order to ensure the impregnation effect of the solution, so that the solution can not only adhere to the surface of the carbon fiber, but also fully penetrate into the pores of the carbon fiber, the present invention preferably uses pressure impregnation, specifically: compressed air or other gases are introduced into the environment where the solution is located, so that the pressure is maintained at 2 to 5 MPa for 0.1 to 3 hours, so that the solute adheres to the surface of the second carbon fiber braid and fully penetrates into the interior of the second carbon fiber braid.

[0052] The second step is to solidify the solute so that the solute is solidified on the surface and inside the pores of the third carbon fiber braid.

[0053] For liquids at room temperature, they can be dried by heating. As the liquid evaporates, only the solute will remain on the surface of the carbon layer interface phase. If organic monomers and initiators are added to the solution, only the solute wrapped in the polymer will remain on the surface of the carbon layer interface phase. In some embodiments, curing is to remove the braid from the solution, let it stand, scrape off the excess gel after the solute is completely solidified inside the braid, and then place the braid in an oven at 200-300°C for curing reaction for 2-4 hours. In some embodiments, curing is to place the braid impregnated with the solution in an oven below 100°C for 0.5-3 hours to solidify the solute inside the braid, then remove the excess gel, and then place it in an oven at 200-300°C for 2-4 hours.

[0054] For the precursor that is solid at room temperature, the impregnation step is to heat it to make it liquid and then impregnate the braid. At this time, solidification is to take out the braid impregnated with the autogenous solution and cool it so that the carbon-containing raw material solidifies and remains inside the braid.

[0055] The third step is carbonization, which thermally decomposes the solute solidified on the surface and inside the pores of the third carbon fiber braid into carbon, thereby obtaining a fourth carbon fiber braid.

[0056] The process conditions of carbonization can be adjusted according to the type of raw materials containing carbon elements. Generally, the carbonization reaction is carried out at 1100-1200℃ for 1.5-3h. The technical purpose of carbonization is, on the one hand, to open the cross-linking of the raw material molecules, and the raw materials coated with polymers also include pyrolysis of the polymers. On the other hand, it is to pyrolyze the raw materials into elemental carbon, generate 2-3μm dispersed elemental carbon particles and form a porous matrix carbon. The dense carbon particles in the matrix carbon are connected together and coated on the interface phase of the carbon fiber surface and the inner wall of the pore. Due to the pyrolysis of the polymer and the solidification and carbonization of the solute raw materials, the volume shrinks when hydrogen and oxygen elements are released, resulting in gaps between the carbon particles, and the carbon particles are randomly arranged on the surface of the carbon fiber bundle and the inside of the carbon fiber braid. The carbon wrapped on the surface of the carbon fiber bundle is not smooth and continuous enough, and cannot form a dense barrier on the surface of the carbon fiber bundle, such as the attached Figure 1 shown.

[0057] In the fourth step, carbon is deposited on the surface and inside the pores of the fourth carbon fiber braid using a CVI process to obtain a fifth carbon fiber braid.

[0058] The generation of matrix carbon by CVI pyrolysis of carbon sources can be carried out by conventional methods in the art. In some embodiments, the temperature for generating carbon by CVI pyrolysis is 1050-1200°C. At this temperature, the carbon generated by pyrolysis is dense and continuous, and the deposited carbon grows continuously around the surface of the carbon fiber bundle and the inner wall of the pores of the carbon fiber braid, forming a tubular carbon layer to relatively evenly wrap the carbon fiber bundle. The carbon fiber bundle is tightly combined with the matrix carbon generated by CVI pyrolysis, and the carbon generated by CVI pyrolysis is filled on the surface and / or pores of the porous matrix carbon; the general deposition time is 60-100h; the carbon fiber reinforced porous carbon composite material obtained in this way is more conducive to subsequent siliconization treatment. In the present invention, the raw material gas for CVI pyrolysis is a conventional choice in the art, as long as the CVI process can be used to generate carbon by pyrolysis, for example, it can be propane, butane, natural gas, etc., and the present invention does not limit it.

[0059] The fifth step is to measure the density of the fifth carbon fiber braid; if the density is ≥ the preset threshold, subsequent siliconization treatment is carried out; if the density is < the preset threshold, the fifth carbon fiber braid is used as the new second carbon fiber braid, and the steps of solution impregnation, solute solidification, carbonization and CVI deposition are carried out in sequence, and then the density of the new fifth carbon fiber braid is measured.

[0060] In some embodiments of the present invention, the preset threshold is 1.3 g / cm 3 The higher the preset threshold, the more conducive it is to improving the mechanical properties of the composite material. In order to obtain a composite material with higher mechanical properties, the present invention preferably sets the preset threshold to 1.35 g / cm 3 ; Further preferably, the preset threshold is 1.40g / cm 3 ; Further, the preset threshold is 1.45g / cm 3 ; Further, the preset threshold is 1.50g / cm 3 .

[0061] Finally, there is the siliconization step; the carbon generated, that is, the weight gain of the matrix carbon, is calculated by the weight difference between the second carbon fiber braid when the "solution impregnation, solute solidification, carbonization and CVI deposition" process is performed for the first time and the fifth carbon fiber braid when the "solution impregnation, solute solidification, carbonization and CVI deposition" process is performed for the last time, and it is converted into moles. Then, a stoichiometric ratio of silicon powder is added thereto, and the siliconization treatment is carried out at 1450-1680°C. At this temperature, the molten silicon first wets the surface of the carbon fiber reinforced porous carbon composite material, and then the molten silicon penetrates into the matrix carbon of the carbon fiber reinforced porous carbon composite material through capillary action, and reacts with the matrix carbon in situ to generate silicon carbide. During the siliconization process, as the molten silicon reacts with the matrix carbon, the reaction gradually weakens, and the generated carbon fiber reinforced carbon / silicon carbide composite material may contain some residual matrix carbon, and the surface pores may be filled with residual silicon. In this step, the most ideal state is that the molar ratio of the generated carbon and the molten silicon is 1:1, and there is as little or no unreacted carbon and unreacted silicon as possible after the reaction, so as to avoid the adverse effects of unreacted carbon or silicon on the properties of the composite material; in some embodiments, the siliconizing reaction time is preferably 2 to 5 hours.

[0062] The present invention adopts the above technical solution to prepare carbon fiber reinforced carbon / silicon carbide composite materials with high density and good mechanical properties, and the bending strength is ≥280Mpa, the tensile strength is ≥100MPa, and the density is ≥1.8g / cm 3 Further preferably, when at least one of sucrose, glucose, fructose, maltose, oligofructose and modified starch is used as the solute of the carbon element solution, its flexural strength is ≥360Mpa, tensile strength is ≥180MPa, and density is ≥1.96g / cm 3The reason for its good mechanical properties is that, on the one hand, two carbon deposition processes of solution impregnation, curing, carbonization and CVI carbon source pyrolysis to generate matrix carbon are alternately carried out to obtain a carbon fiber reinforced porous carbon composite material that is beneficial to both siliconization treatment and the reaction of carbon and silicon to generate silicon carbide; on the other hand, the present invention provides a carbon layer as an interface phase on the surface of the carbon fiber, which serves as a bridge between the carbon fiber and the silicon carbide material, thereby protecting the carbon fiber and playing a major load-bearing role in the carbon fiber reinforced carbon / silicon carbide composite material, thereby improving the strength of the carbon fiber reinforced carbon / silicon carbide composite material.

[0063] A second aspect of the present invention provides a carbon fiber reinforced carbon / silicon carbide composite material prepared by the aforementioned method, comprising:

[0064] The first carbon fiber braid is made by wrapping needle-punched carbon felt with a mesh; the first carbon fiber braid includes a plurality of parallel arranged carbon fiber bundles; the density of the first carbon fiber braid is 0.5 to 0.7 g / cm 3 ;

[0065] a carbon layer interface phase, disposed on the surface of the first carbon fiber braid and the inner wall of the pores;

[0066] Silicon carbide is arranged on the carbon layer interface phase surface, including both the carbon layer interface phase surface covering the carbon fiber side surface and the carbon layer interface phase surface covering the carbon fiber pore inner wall.

[0067] A third aspect of the present invention provides an application of the carbon fiber reinforced carbon / silicon carbide composite material as described above in the aerospace, automotive, or military fields.

[0068] The present invention will be further described below with reference to specific embodiments, but this should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0069] Unless otherwise specified, the materials and reagents mentioned below are commercially available products familiar to those skilled in the art. Unless otherwise specified, the methods described are all well-known methods in the art. Unless otherwise defined, technical or scientific terms used shall have the same meanings as those commonly understood by those skilled in the art.

[0070] Example 1

[0071] (1) The density of the needle-punched carbon felt combined with the mesh tire was 0.65g / cm 3 , carbon fiber braid with a thickness of 4mm.

[0072] (2) A carbon layer interface phase was prepared on the surface of the carbon fiber braid in a pyrolysis furnace, specifically as follows: propane was used as the raw gas, hydrogen was used as the carrier gas, the molar ratio of propane to hydrogen was 1:5, and the furnace chamber specification of the pyrolysis furnace was a cylindrical furnace chamber with a diameter of 1200 mm and a height of 900 mm; the mixed gas was introduced into the pyrolysis furnace at a flow rate of 2 L / min, the temperature of the pyrolysis furnace was 1050°C, the pressure was 4 kPa, and the deposition was carried out for 2 h.

[0073] (3) Sucrose (theoretical residual carbon rate 42%) was prepared into a 40 wt% sucrose aqueous solution, 2 wt% of sucrose amount of acrylamide and 0.2 wt% of sucrose amount of NN bisacrylamide monomer were added to the sucrose aqueous solution, 0.1 wt% of monomer amount of ammonium persulfate was used as the initiator, and the solution viscosity was 13 mPa.s.

[0074] (4) Immersing the carbon fiber braid containing the interfacial phase in a 40 wt% sucrose aqueous solution containing monomers; evacuating to -0.1 MPa and maintaining the pressure for 20 minutes, then breaking the vacuum. Compressed air is introduced into the pyrolysis furnace to a pressure of 2 MPa, and the pressure is maintained for 20 minutes to allow the sucrose solution to fully penetrate the braid.

[0075] (5) The braid is taken out from the solution. After the sucrose is completely solidified inside the braid, the excess gel is scraped off and the braid is placed in an oven at 280°C for curing reaction for 3 hours.

[0076] (6) Then it was carbonized in a pyrolysis furnace at 1200℃ for 3h. Figure 1 As shown, the carbon produced by pyrolysis of sucrose is granular, and the carbon layer structure is relatively loose and porous, resulting in a discontinuous carbon layer.

[0077] (7) Matrix carbon was deposited on the surface and inner wall of the pores of the carbon fiber braid in a pyrolysis furnace as follows: propane was used as the raw gas, hydrogen was used as the carrier gas, the molar ratio of propane to hydrogen was 1:8, the furnace chamber of the pyrolysis furnace was a cylindrical furnace chamber with a diameter of 1200 mm and a height of 900 mm; the mixed gas was introduced into the pyrolysis furnace at a flow rate of 2 L / min, the temperature of the pyrolysis furnace was 1200 ° C, and the carburizing was carried out for 60 hours. The results are as follows: Figure 2 As shown, the carbon produced by CVI pyrolysis is tubular, and the carbon layer structure is relatively dense and continuous.

[0078] (8) After steps (3) to (7) were performed three times, the density of the composite material increased to 1.4 g / cm 3 , calculate the amount of carbon generated, add stoichiometric silicon powder, and perform siliconization treatment with molten silicon at 1550°C for 2h to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0079] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 1.95 g / cm3 , the bending strength reaches 361.9MPa and the tensile strength reaches 182MPa.

[0080] Example 2

[0081] (1) Same as Example 1.

[0082] (2) Same as Example 1, except that the deposition time is 3 h.

[0083] (3) The same as Example 1, except that the concentration of the sucrose aqueous solution is 70 wt %, 2 wt % of sucrose-based acrylamide, 0.2 wt % of sucrose-based NN bisacrylamide, and 0.1 wt % of monomer ammonium persulfate are added to the sucrose aqueous solution, and the solution viscosity is 125 mPa·s.

[0084] (4) Soak the carbon fiber braid in 0.5 mol / L FeCl3·6H2O for 12 h ， To ensure uniform FeCl₃ adhesion to the carbon fiber surface, the carbon fiber braid was then immersed in a 70wt% sucrose solution for 10 minutes. The pressure was then evacuated to -0.1 MPa and held for 20 minutes before breaking the vacuum. Compressed air was introduced into the pyrolysis furnace to a pressure of 3 MPa and maintained for 20 minutes to ensure the sucrose solution fully penetrated the braid.

[0085] (5) The solution containing the braid is placed in a reactor and reacted in an oven at 80°C for 2 hours and solidified inside the braid. The braid is then placed in an oven at 280°C for 3 hours.

[0086] (6) Same as Example 1.

[0087] (7) Same as Example 1, except that the carburizing time at 1200°C is 80 h.

[0088] (8) Same as Example 1. The difference is that steps (3) to (7) are performed twice, and the density of the composite material increases to 1.42 g / cm 3 , siliconized for 3 hours to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0089] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 1.95 g / cm 3 , the bending strength reaches 362.7MPa and the tensile strength reaches 183MPa.

[0090] Example 3

[0091] (1) Same as Example 1.

[0092] (2) Same as Example 1.

[0093] (3) Same as Example 1. The difference is that the solute is glucose (theoretical residual carbon content of glucose is 40%); the concentration of the glucose aqueous solution is 40 wt %, 2 wt % of glucose-based acrylamide, 0.2 wt % of glucose-based NN bisacrylamide, and 0.1 wt % of monomer ammonium persulfate are added to the glucose aqueous solution, and the solution viscosity is 8 mPa·s.

[0094] (4) Soak the carbon fiber braid in 0.5 mol / L FeCl3·6H2O for 12 h ， To ensure uniform FeCl₃ adhesion to the carbon fiber surface, the carbon fiber braid was then immersed in a 40wt% glucose solution. The pressure was evacuated to -0.1 MPa and maintained for 20 minutes, then the vacuum was broken. Compressed air was introduced into the pyrolysis furnace to a pressure of 2 MPa and maintained for 20 minutes to ensure that the glucose solution fully permeated the braid.

[0095] (5) The solution containing the braid was placed in a reactor and reacted in an oven at 80°C for 1 hour and solidified inside the braid. The braid was then placed in an oven at 280°C for 3 hours.

[0096] (6) Same as Example 1.

[0097] (7) Same as Example 1, except that the carburizing time at 1200°C is 80 h.

[0098] (8) Same as Example 1. The difference is that steps (3) to (7) are performed three times, and the density of the composite material is 1.45 g / cm 3 , siliconized for 3 hours to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0099] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 1.96 g / cm 3 , the bending strength reaches 363.4MPa and the tensile strength reaches 183MPa.

[0100] Example 4

[0101] (1) Same as Example 1.

[0102] (2) Same as Example 1.

[0103] (3) Same as Example 1. The difference is that the solute is glucose; the concentration of the glucose aqueous solution is 70 wt %, 2 wt % of glucose in acrylamide, 2 wt % of glucose in NN bisacrylamide, and 0.1 wt % of elastomer in ammonium persulfate are added to the glucose aqueous solution, and the solution viscosity is 33 mPa·s.

[0104] (4) Soak the carbon fiber braid in 0.5 mol / L FeCl3·6H2O for 12 h， To ensure uniform FeCl₃ adhesion to the carbon fiber surface, the carbon fiber braid was then immersed in a 70wt% glucose solution for 10 minutes. The pressure was then evacuated to -0.1 MPa and held for 20 minutes, then the vacuum was broken. Compressed air was introduced into the pyrolysis furnace to a pressure of 2 MPa (first press) or 5 MPa (second press), and maintained for 20 minutes to ensure the glucose solution fully penetrated the braid.

[0105] (5) The solution containing the braid is placed in a reactor and reacted in an oven at 80°C for 1 hour, and solidified inside the braid. Then, the excess gel is removed and placed in an oven at 280°C for curing reaction for 3 hours.

[0106] (6) Same as Example 1, except that the carbonization time is 1.5 h.

[0107] (7) Same as Example 1.

[0108] (8) Same as Example 1. The difference is that steps (3) to (7) are performed twice, and the density of the composite material increases to 1.52 g / cm 3 , siliconizing treatment for 1h to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0109] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 2.01 g / cm 3 , the bending strength reaches 367MPa and the tensile strength reaches 209MPa.

[0110] Example 5

[0111] (1) Same as Example 1.

[0112] (2) Same as Example 1, except that the deposition time is 3 h.

[0113] (3) Same as Example 1, except that the solution is an ethanol solution of phenolic resin with a mass concentration of 50 wt % and a solution viscosity of 300 mPa·s.

[0114] (4) Immerse the carbon fiber braid in a 50 wt% ethanol solution of phenolic resin for 30 minutes. Evacuate to -0.1 MPa and maintain for 20 minutes, then break the vacuum. Introduce compressed air into the pyrolysis furnace to a pressure of 5 MPa and maintain this pressure for 20 minutes to allow the phenolic solution to fully penetrate the braid.

[0115] (5) The solution containing the braid is placed in a reactor and reacted in an oven at 90°C for 2 hours, and solidified inside the braid. Then, excess phenolic resin is removed and the braid is placed in an oven at 280°C for curing reaction for 3 hours.

[0116] (6) Same as Example 1.

[0117] (7) Same as Example 1, except that the carburizing time at 1200°C is 80 h.

[0118] (8) Same as Example 1. The difference is that steps (3) to (7) are performed once, and the density of the composite material increases to 1.4 g / cm 3 , siliconizing treatment for 1h to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0119] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 1.8 g / cm 3 , the bending strength reaches 280.6MPa and the tensile strength reaches 102.4MPa.

[0120] Example 6

[0121] (1) Same as Example 1.

[0122] (2) Same as Example 1, except that the deposition time is 3 h.

[0123] (3) Same as Example 1. The difference is that the raw material containing carbon elements is asphalt, which is melted at 80°C to produce liquid asphalt with a viscosity of about 300 mPa·s (due to the high temperature, viscosity measurement is difficult to operate, and the viscosity value here is an estimate).

[0124] (4) Immerse the carbon fiber braid in liquid asphalt for 30 minutes. Evacuate to -0.1 MPa and maintain for 20 minutes, then break the vacuum. Introduce compressed air into the pyrolysis furnace to a pressure of 5 MPa and maintain this pressure for 20 minutes to allow the liquid asphalt to fully penetrate the braid.

[0125] (5) Cool to room temperature to allow the asphalt to solidify and remain inside the fiber braid.

[0126] (6) Same as Example 1, except that the carbonization time is 2 h.

[0127] (7) Same as Example 1, except that the carburizing time at 1200°C is 80 h.

[0128] (8) Same as Example 1. The difference is that steps (3) to (7) are performed twice, and the density of the composite material increases to 1.37 g / cm 3 , siliconizing treatment for 1h to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0129] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 1.85 g / cm 3 , the bending strength reaches 285.6MPa and the tensile strength reaches 109.4MPa.

[0130] Comparative Example 1

[0131] (1) to (6) are the same as in Example 1.

[0132] (7) None.

[0133] (8) Repeat steps (3) to (6) five times until the density of the composite material increases to 1.4 g / cm 3 , calculate the amount of carbon generated, add stoichiometric silicon powder, and perform siliconization treatment with molten silicon at 1550°C for 2h to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0134] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 1.98 g / cm 3 , the bending strength reaches 87.6MPa and the tensile strength reaches 96.4MPa.

[0135] Comparative Example 2

[0136] (1) to (2) are the same as in Example 1.

[0137] (3)~(6)None.

[0138] (7) Same as Example 1, except that the carburizing time at 1200°C is 80 h.

[0139] (8) Repeat step (7) three times, and the density of the composite material is 1.4 g / cm 3 , calculate the amount of carbon generated, add stoichiometric silicon, and perform siliconizing treatment at 1550℃ for 1h to obtain carbon fiber reinforced carbon / silicon carbide composite materials.

[0140] The carbon fiber reinforced carbon / silicon carbide composite material prepared in this embodiment has a density of 1.59 g / cm 3 , the bending strength reaches 229.6MPa and the tensile strength reaches 103.8MPa.

[0141] As can be seen from the above examples, the present invention first uses the CVI process to set a carbon layer interface phase on the surface of the carbon fiber and the inner wall of the pores to form a protective film for the carbon fiber; then, a carbon-containing raw material is used as a solute to prepare a solution or the raw material is converted into a liquid state by heating, and the carbon fiber braid is subjected to solution impregnation, curing and carbonization, and porous carbon is deposited on the surface of the carbon fiber and the inner wall of the pores; then, the carbon source is pyrolyzed by CVI to generate matrix carbon, which is coated on the surface of the carbon fiber and filled in the inner wall of the carbon fiber pores; the two carbon generation processes are alternately performed, and the generated carbon is reacted with molten silicon to generate silicon carbide in situ; and a carbon fiber reinforced carbon / silicon carbide composite material is prepared by the above process. The mechanical properties of the carbon fiber reinforced carbon / silicon carbide composite material are good, and its bending strength is ≥280Mpa and its tensile strength is ≥100MPa, as shown in Examples 1 to 6. Furthermore, by preferably selecting the raw material containing carbon elements from at least one of sucrose, glucose, fructose, maltose, oligofructose and modified starch, and adding monomers and initiators to the solution, during the process of impregnation, curing and carbonization to generate carbon, the solution is coated into liquid packets through the polymerization of organic monomers and adhered to the surface of the interface phase, including the surface of the carbon fiber and the inner wall of the pores, so that it is evenly distributed on the carbon fiber, and then the solvent evaporates during the curing stage, so that the solute is evenly distributed on the carbon fiber, so that the carbon residue after carbonization is evenly distributed on the carbon fiber, thereby further optimizing the distribution of the carbon residue, and the resulting carbon fiber reinforced carbon / silicon carbide composite material has better mechanical properties, its flexural strength ≥360 MPa, and its tensile strength ≥180 MPa, as shown in Examples 1 to 4. Among them, because the molecular weight of glucose is lower than that of sucrose, and the residual carbon rate is similar to that of sucrose, when the solution concentration is high, the carbon fiber reinforced carbon / silicon carbide composite material prepared therefrom has better mechanical properties, its flexural strength ≥367 MPa, and its tensile strength ≥209 MPa, as shown in Example 4.

[0142] From the above comparative examples, it can be seen that in comparative example 1, only the process of solution impregnation, curing and carbonization is used to set the matrix carbon, although the amount of carbon generated is the same as that in example 1 (the density is 1.4 g / cm 3 ), and the density is also very high, its mechanical properties are poor, its bending strength can only reach 87.6MPa (about 24% of Example 1), and its tensile strength can only reach 96.4MPa (about 53% of Example 1). In Comparative Example 2, only the CVI process is used for the matrix carbon setting, although the amount of carbon generated is the same as that in Example 1 (the density is 1.4g / cm 3 ), however, its mechanical properties are poor, its bending strength can only reach 229.6MPa (about 63% of Example 1), and its tensile strength can only reach 103.8MPa (about 57% of Example 1).

[0143] The technical features in the claims and / or the specification of the present invention may be combined, and the manner of combination is not limited to the combination obtained by reference in the claims. The technical solutions obtained by combining the technical features in the claims and / or the specification are also within the scope of protection of the present invention.

[0144] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiment based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a carbon fiber reinforced carbon / silicon carbide composite material, characterized in that: It includes the following steps: S11 provides a carbon layer interface phase on the surface of the first carbon fiber braid and the inner wall of the pores to obtain a second carbon fiber braid; S12: dipping the second carbon fiber braid into a solution containing a carbon element to obtain a third carbon fiber braid; S13 solidifies the solute on the surface and inside the pores of the third carbon fiber braid; Carbonization is performed to thermally decompose the solute solidified on the surface and inside the pores of the third carbon fiber braid into carbon, thereby obtaining a fourth carbon fiber braid; S14 uses a CVI process to deposit carbon on the surface and inside the pores of the fourth carbon fiber braid to obtain a fifth carbon fiber braid; S15 measures the density of the fifth carbon fiber braid; If the density is greater than or equal to the preset threshold, step S16 is executed; If the density is less than the preset threshold, the fifth carbon fiber braid is used as a new second carbon fiber braid, and steps S12 to S14 are performed in sequence; S16 calculates the generated carbon based on the weight difference between the second carbon fiber braided body obtained by executing steps S12 to S14 for the first time and the fifth carbon fiber braided body obtained by executing steps S12 to S14 for the last time, adds a stoichiometric ratio of silicon powder for melt siliconization treatment, and converts the generated carbon into silicon carbide to obtain a carbon fiber reinforced carbon / silicon carbide composite material.

2. The method according to claim 1, characterized in that The residual carbon rate of the solute in the solution is ≥40%; the mass concentration of the solution is ≥40%; the viscosity of the solution is ≤300mPa·s; the preset threshold is 1.3g / cm 3 .

3. The method according to claim 1, characterized in that The solute is selected from at least one of sucrose, glucose, fructose, maltose, oligofructose, modified starch, phenolic resin and asphalt.

4. The method according to claim 1, wherein The solute is selected from at least one of sucrose, glucose, fructose, maltose, oligofructose and modified starch.

5. The method according to claim 4, characterized in that The solution also includes an organic monomer and an initiator.

6. The method according to any one of claims 1 to 5, characterized in that The method for preparing the carbon layer interface phase in step S11 includes: depositing a carbon layer on the surface of the first carbon fiber braid and the inner wall of the pores by a CVI method; the process conditions of CVI are: using propane as the raw gas, hydrogen as the carrier gas, the molar ratio of propane to hydrogen is 1:4-6, and the flow rate is 1.9-2.0 L / min / m 3 , temperature is 950~1050℃, pressure is 4~6KPa, and deposition time is 2~4h.

7. The method according to claim 6, characterized in that The first carbon fiber braid is made by wrapping needle-punched carbon felt with a mesh; the first carbon fiber braid includes a plurality of parallel arranged carbon fiber bundles; the density of the first carbon fiber braid is 0.5 to 0.7 g / cm 3 .

8. The method according to any one of claims 1 to 5, characterized in that The impregnation in step S12 includes the following steps: S81 evacuates the solution containing the second carbon fiber braid to remove air bubbles; S82 breaks the vacuum; introduces gas into the environment where the solution is located, and maintains the pressure at 2-5 MPa to allow the solute to adhere to the surface of the second carbon fiber braid and penetrate into the interior of the second carbon fiber braid.

9. A carbon fiber reinforced carbon / silicon carbide composite material, characterized in that: It includes: a first carbon fiber braid; a carbon layer interface phase, disposed on the surface of the first carbon fiber braid and the inner wall of the pores; Silicon carbide, disposed on the interface phase surface of the carbon layer; The carbon fiber reinforced carbon / silicon carbide composite material is prepared by the method according to any one of claims 1 to 8.

10. Use of the carbon fiber reinforced carbon / silicon carbide composite material according to claim 9 in aerospace, automotive industry or military field.

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