A method for preparing silicon carbide composite material based on optimizing CVI deposition rate and silicon carbide fiber reinforced silicon carbide composite material
By optimizing the CVI deposition rate and process parameters, and controlling the hydrogen carrier gas flow rate at 9–11 L/min⁻¹, the problem of uniform densification of SiCf/SiC composite materials was solved, achieving an efficient and uniform deposition process and improving the density and mechanical properties of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANG HAI RUI HUA SHENG XIN CAI LIAO YOU XIAN GONG SI
- Filing Date
- 2026-05-12
- Publication Date
- 2026-06-09
AI Technical Summary
In existing technologies, the CVI process has difficulty in achieving uniform densification of SiCf/SiC composite materials while ensuring high deposition efficiency, resulting in surface pores and internal porosity, which affects mechanical properties.
By optimizing the CVI deposition rate and controlling the hydrogen carrier gas flow rate at 9–11 L/min⁻¹, combined with specific process parameters including BN interface deposition and MI densification, uniform penetration and efficient deposition of reactive gases are achieved, forming a dense and uniform SiC matrix.
It significantly improves the overall density and structural uniformity of composite materials, enhances mechanical properties, and ensures process stability and the fabrication quality of large-size components.
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Figure CN122167182A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of manufacturing high-performance ceramic matrix composites, and more specifically to a method for preparing silicon carbide composites based on optimized CVI deposition rate and silicon carbide fiber reinforced silicon carbide composites. Background Technology
[0002] Silicon carbide fiber reinforced silicon carbide (SiC) f SiC composites have become key candidate materials for next-generation aero-engines, nuclear energy systems, and spacecraft thermal structural components due to their excellent high-temperature mechanical properties, thermal shock resistance, and oxidation resistance. Chemical vapor infiltration (CVI) is one of the most crucial processes for preparing such composites. It achieves material densification by decomposing and depositing a gaseous precursor within a high-temperature porous fiber preform to form a solid matrix.
[0003] In CVI processes, the deposition rate is a key factor affecting the final material properties, and it is directly related to the precursor supply rate. Existing technologies generally face a dilemma: a deposition rate that is too low leads to insufficient precursor supply, excessively long process cycles, high production costs, and may result in overly porous deposits due to excessive diffusion of reactant gases within the preform; conversely, a deposition rate that is too high easily leads to rapid deposition at the pore inlets on the preform surface and premature pore sealing, severely hindering the diffusion of reactant gases inward and causing an inhomogeneous structure of "dense surface, porous interior," significantly deteriorating the overall mechanical properties of the material. Therefore, finding an optimal deposition rate window for a specific material system to achieve efficient and uniform densification has been a long-standing technical challenge in this field.
[0004] Traditional process theories and practices generally hold that in CVI (Continuous Vibration Injection) processes, excessively high carrier gas flow rates can lead to premature deposition of precursors on the preform surface, causing premature closure of pore inlets and forming a "crust" effect, which severely hinders the uniform densification of the material's interior. Therefore, in process design, the art typically tends to conservatively select lower flow rates to prioritize penetration depth. This often results in long process cycles, limited deposition efficiency, and difficulty in balancing deposition efficiency with dense uniformity.
[0005] Currently, existing technologies have not yet achieved a solution for SiC. f Precise optimization of the carrier gas flow rate in the CVI process of SiC composite materials cannot guarantee a high deposition efficiency while obtaining a uniform and dense material structure, thus limiting the further improvement of the comprehensive performance and preparation stability of the composite materials. Summary of the Invention
[0006] To address the problems in the existing CVI process, such as difficulty in achieving both deposition rate and uniformity, surface pore formation, insufficient internal densification, and low mechanical properties, this invention aims to provide a method for preparing silicon carbide composite materials based on optimized CVI deposition rate, as well as silicon carbide fiber-reinforced silicon carbide composite materials.
[0007] The present invention provides a method for preparing silicon carbide composite materials based on optimized CVI deposition rate, comprising silicon carbide fiber preform weaving, preform forming and drying, BN interface deposition, CVI densification, and MI densification; wherein, the CVI densification uses methyltrichlorosilane as a precursor, hydrogen as a carrier gas and reducing agent, and the total hydrogen supply flow rate is controlled at 9–11 L / min. -1 The reaction temperature is 1000–1300℃, the system pressure is 20–25kPa, and the deposition time is 50–80 hours.
[0008] In a preferred embodiment, the silicon carbide fiber preform is made by two-dimensional, 2.5D or three-dimensional weaving, and the fiber volume fraction is 40%–45%.
[0009] In a preferred embodiment, the molding and drying steps are as follows: after wetting the preform with deionized water, it is heat-treated at 140–180°C for 2–6 hours.
[0010] In a preferred embodiment, the BN interface deposition uses boron trichloride as the boron source, ammonia as the nitrogen source, and hydrogen as the carrier gas, with a boron trichloride-ammonia-hydrogen molar ratio of 1:3:1, a deposition temperature of 550–950℃, and a deposition time of 25–50 hours.
[0011] In a preferred embodiment, during the CVI densification, methyltrichlorosilane is stored in a liquid state at a storage temperature of 20–40°C and is introduced into the reaction chamber via hydrogen bubbling.
[0012] In a preferred embodiment, the MI densification is performed by heating to 1480–1550°C in a vacuum environment to allow for molten silicon infiltration.
[0013] In a preferred embodiment, before the MI densification, the CVI-densified preform is first immersed in a carbon source and subjected to solidification and pyrolysis treatment, and then vacuum melt infiltration is performed together with silicon material.
[0014] In a preferred embodiment, the carbon source is selected from any one of phenolic resin, asphalt, and polycarbosilane.
[0015] The silicon carbide fiber-reinforced silicon carbide composite material according to the present invention is prepared by the above-described preparation method.
[0016] In a preferred embodiment, the bulk density of the silicon carbide fiber-reinforced silicon carbide composite material is 2.80–2.82 g / cm³. 3 .
[0017] This invention employs a specific process flow and controls the hydrogen carrier gas flow rate within an optimized range during the CVI densification process. This ensures sufficient precursor supply and high deposition efficiency while effectively preventing premature pore sealing on the preform surface. It allows the reactive gas to fully penetrate into the preform and achieve uniform deposition, significantly improving the shortcomings of traditional processes where deposition rate and uniformity are difficult to balance, and the material surface is dense while the interior is porous. This effectively enhances the overall density and structural uniformity of the composite material, thereby greatly improving its mechanical properties. At the same time, it improves process stability and repeatability, meeting the needs for efficient and stable fabrication of large-size components. Attached Figure Description
[0018] Figure 1 This is a complete process flow diagram of the silicon carbide composite material preparation method based on the optimized CVI deposition rate according to the present invention. Detailed Implementation
[0019] The present invention will be further described in detail below with reference to embodiments, comparative examples and accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments.
[0020] Traditional CVI processes have limitations in their understanding of carrier gas flow rates, generally believing that high flow rates inevitably lead to surface pore sealing. Therefore, they have long used relatively low flow rates, sacrificing deposition efficiency. Through extensive system experiments and synergistic optimization of the complete process system (including the preform structure, BN interface layer, CVI densification parameters, and subsequent MI densification process), this invention reveals a relatively high optimal window for hydrogen carrier gas flow rates (9–11 L / min) under specific process conditions. -1 Within this flow rate range, the rapid surface sealing phenomenon expected by traditional theory will not occur. Instead, it ensures a sufficient supply of reactants and a reasonable deposition rate, while effectively renewing the reactive gas and penetrating deep into the preform. This results in excellent penetration uniformity at a high deposition efficiency, ultimately yielding SiC with more uniform densification and superior overall mechanical properties. f / SiC composite material. Thus, this invention breaks through the traditional understanding that "high flow rate inevitably leads to surface sealing", and provides a brand-new technical path to solve the problem of CVI densification uniformity.
[0021] like Figure 1As shown, the method for preparing silicon carbide composite materials based on optimized CVI deposition rate according to the present invention first includes weaving a silicon carbide fiber preform. Using silicon carbide fiber bundles, a porous fiber preform with a fiber volume fraction of 40%–45% is prepared through two-dimensional, 2.5D, or three-dimensional weaving. It should be understood that this fiber volume fraction is beneficial for ensuring the effective transport and permeation of reactant gases in the subsequent CVI process.
[0022] like Figure 1 As shown, the method for preparing silicon carbide composite materials based on optimized CVI deposition rate according to the present invention further includes preform molding and drying. The woven preform is placed in a molding mold, and the woven material is wetted with deionized water to improve its formability; subsequently, it is heat-treated at 140–180°C for 2–6 hours to remove internal moisture and fix the shape.
[0023] like Figure 1 As shown, the method for preparing silicon carbide composite materials based on optimized CVI deposition rate according to the present invention further includes BN interface deposition. The dried preform is placed in a chemical vapor deposition furnace, using boron trichloride (BCl3) as the boron source, ammonia (NH3) as the nitrogen source, and hydrogen as the carrier gas, controlling the BCl3–NH3–H2 molar ratio to be 1:3:1; deposition is carried out at a temperature of 550–950°C for 25–50 hours to form a boron nitride (BN) interface layer on the surface of the silicon carbide fibers, which is used to adjust the bonding strength between the silicon carbide fibers and the silicon carbide matrix.
[0024] like Figure 1 As shown, the method for preparing silicon carbide composite materials based on optimized CVI deposition rate according to the present invention further includes CVI densification. The preform with completed BN interface deposition is transferred to a CVI reactor, using methyltrichlorosilane (MTS) as the reaction precursor, and high-purity hydrogen with a purity ≥99.999% as the carrier gas and reducing agent. The MTS precursor is stored in liquid form at a temperature controlled at 20–40°C, and the MTS is loaded into the reaction chamber via hydrogen bubbling. The reaction chamber temperature is raised to 1000–1300°C, and the system pressure is maintained at 20–25 kPa; the total hydrogen supply flow rate is precisely controlled at 9–11 L / min. -1 Chemical vapor infiltration deposition is carried out continuously for 50–80 hours; MTS decomposes at high temperature to generate silicon- and carbon-containing active species, which react on the surface of the preform pores and deposit to form a solid SiC matrix, gradually filling the pores inside the preform.
[0025] like Figure 1As shown, the method for preparing silicon carbide composite materials based on optimized CVI deposition rate according to the present invention further includes MI densification. The CVI-densified preform is impregnated with a carbon source, allowing the carbon source to fully penetrate the residual pores of the preform. Subsequently, the preform impregnated with the carbon source is subjected to solidification and pyrolysis treatment. The treated preform and an equal weight of silicon material are placed together in a graphite mold or crucible, heated to 1480–1550°C under vacuum and held at this temperature. This allows molten silicon to penetrate the residual pores of the preform by capillary force and react to form SiC, completing the filling of the residual pores and finally obtaining dense SiC. f / SiC composite material.
[0026] Example 1
[0027] Weaving: 2.5D weaving technology is used to weave domestically produced third-generation silicon carbide fibers into a flat preform with a fiber volume fraction of approximately 40%.
[0028] Molding and drying: Place the preform in the molding mold, wet it with deionized water, and put it together with the mold into a forced-air drying oven to dry at a constant temperature of 160℃ for 4 hours.
[0029] BN interface deposition: The dried preform was placed in a chemical vapor deposition furnace, and BCl3 and NH3 were introduced with Ar as diluent gas. The deposition was carried out at 650°C and atmospheric pressure for 40 hours to obtain the BN interface layer.
[0030] CVI densification: The preform is transferred to a low-pressure CVI furnace, and the MTS container temperature is set to 27°C; high-purity hydrogen is introduced, and the total flow rate is precisely stabilized at 9 L / min. -1 The furnace temperature was raised to 1150℃, the system pressure was adjusted to 25kPa, the MTS container valve was opened, and CVI was introduced into the reaction chamber in a bubbling manner for 60 hours.
[0031] MI densification: The preform after CVI is impregnated with any carbon source, such as phenolic resin, asphalt, or polycarbosilane, and then cured and pyrolyzed; the preform and silicon raw material are placed together in a vacuum furnace and heated at 10℃ / min. -1 The temperature was raised to 1550℃ and held for 1 hour before being cooled in the furnace to obtain the final composite material.
[0032] Performance testing: The obtained composite material was processed into standard tensile specimens, and the average tensile strength at room temperature was 382.34 MPa.
[0033] Example 2
[0034] Except for adjusting the total hydrogen flow rate in the CVI step to 11 L / min -1 Except for adjusting the system pressure to 20 kPa, the other steps, equipment, and parameters are exactly the same as in Example 1.
[0035] The average room temperature tensile strength of the obtained composite material was 389.15 MPa, according to the test results.
[0036] Example 3
[0037] Except for adjusting the precast body size to an engineering-scale plate-shaped component of 700mm in length and 500mm in width, the other steps, equipment and process parameters are exactly the same as in Example 1.
[0038] After preparation, samples were taken from the center and edges of the component for performance testing. The average room temperature tensile strength was 381.01 MPa, and the bulk density was 2.80 g / cm³. 3 The core mechanical properties and densification level are in the same excellent range as the small-sized sample in Example 1, and the data fluctuation range is small.
[0039] Comparative Example 1
[0040] Except for adjusting the total hydrogen flow rate in the CVI step to 12 L / min -1 Except for the steps, equipment and parameters, all other steps, equipment and parameters are exactly the same as in Example 1.
[0041] The average room temperature tensile strength of the obtained composite material was 360.45 MPa, which is lower than that of Examples 1 and 2. This indicates that when the flow rate exceeds 11 L / min... -1 During deposition, phenomena such as obstructed gas transport and excessively rapid local deposition rates can easily occur, hindering uniform densification and leading to a decline in material properties. Therefore, a flow rate of 11 L / min is clearly defined. -1 The critical point for significant performance improvement is not necessarily the case that higher flow rates always lead to better performance.
[0042] Comparative Example 2
[0043] Except for adjusting the total hydrogen flow rate in the CVI step to 8 L / min -1 Except for the steps, equipment and parameters, all other steps, equipment and parameters are exactly the same as in Example 1.
[0044] The average room temperature tensile strength of the obtained composite material was only 344.23 MPa, significantly lower than that of Examples 1 and 2. This indicates that when the flow rate is below 9 L / min... -1 At that time, the precursor supply was relatively insufficient, and the matrix densification could not reach the optimal level, thus limiting the improvement of the overall material performance. Therefore, a flow rate of 9 L / min was determined. -1 This is the critical point for a significant performance improvement.
[0045] Performance test results
[0046] The room temperature mechanical properties of Examples 1–3 and Comparative Examples 1–2 were tested, and the results are shown in the table below:
[0047]
[0048] A higher bulk density indicates more complete densification of CVI+MI and fewer internal pores. The bulk density of the embodiments of this invention can reach 2.80–2.82 g / cm³. 3 The comparative ratio was only 2.76–2.78 g / cm³. 3 The densification levels differed significantly.
[0049] The proportional limit represents the maximum load-bearing stress of a material without permanent deformation; the fewer the internal pores of the material, the higher the proportional limit. The proportional limit of the embodiments of this invention is 148.14–149.36 MPa, while the comparative examples are only 136.72–143.55 MPa, indicating superior elastic load-bearing capacity.
[0050] Tensile strength is the core mechanical property of composite materials. The tensile strength of the examples is concentrated in 381.02–389.15 MPa, while that of the comparative examples is only 344.23–360.45 MPa, showing a very significant performance improvement.
[0051] The trend of bending strength and tensile strength is completely consistent, indicating that the optimized process of the present invention has achieved comprehensive optimization of overall mechanical properties. The material has better resistance to deformation and cracking under tensile and bending loads, which is a comprehensive performance upgrade rather than a local improvement.
[0052] Therefore, the total hydrogen flow rate during the CVI densification step is controlled at 9–11 L / min. -1 Within the range, the prepared SiC f / SiC composites have higher bulk density and fewer internal pores, and their core mechanical properties, such as proportional limit, tensile strength, and flexural strength, are significantly better than those with flow rates below 8 L / min. -1 or higher than 12 L / min -1 The samples were excellent, and the performance uniformity and stability of the large-sized components were outstanding.
[0053] In summary, the hydrogen carrier gas flow rate in the CVI step was optimized to 9–11 L / min. -1 This invention achieves a highly efficient and uniform deposition range beyond traditional experience. The bulk density of the material prepared within this flow rate range is >2.78 g / cm³. 3 The mechanical properties of the composite material prepared using the optimized flow rate of this invention are significantly superior to those of the comparative example, and the performance data are concentrated, achieving a good balance between deposition efficiency and internal uniformity. Comparative experiments show that the composite material prepared using the optimized flow rate of this invention exhibits significantly better tensile strength than other flow rate ranges, with a marked improvement in mechanical properties. The parameter window of this invention is clearly defined, and the synergistic effect of each parameter is evident, making it easy to precisely control and stably implement on industrial equipment, providing a reliable process foundation for the fabrication of large-size, high-performance, and consistent components.
[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims. All aspects not described in detail in this invention are conventional technical content.
Claims
1. A method for preparing silicon carbide composite materials based on optimized CVI deposition rate, characterized in that, It includes silicon carbide fiber preform weaving, preform forming and drying, BN interface deposition, CVI densification, and MI densification; wherein, the CVI densification uses methyltrichlorosilane as a precursor and hydrogen as a carrier gas and reducing agent, and the total hydrogen supply flow rate is controlled at 9–11 L / min. -1 The reaction temperature is 1000–1300℃, the system pressure is 20–25kPa, and the deposition time is 50–80 hours.
2. The method for preparing silicon carbide composite material according to claim 1, characterized in that, The silicon carbide fiber preform is made by two-dimensional, 2.5D or three-dimensional weaving, with a fiber volume fraction of 40%–45%.
3. The method for preparing silicon carbide composite materials according to claim 1, characterized in that, The molding and drying steps are as follows: after wetting the preform with deionized water, it is heat-treated at 140–180°C for 2–6 hours.
4. The method for preparing silicon carbide composite material according to claim 1, characterized in that, The BN interface deposition uses boron trichloride as the boron source, ammonia as the nitrogen source, and hydrogen as the carrier gas, with a boron trichloride-ammonia-hydrogen molar ratio of 1:3:1, a deposition temperature of 550–950℃, and a deposition time of 25–50 hours.
5. The method for preparing silicon carbide composite material according to claim 1, characterized in that, In the CVI densification process, methyltrichlorosilane is stored in liquid form at a storage temperature of 20–40°C and is introduced into the reaction chamber via hydrogen bubbling.
6. The method for preparing silicon carbide composite material according to claim 1, characterized in that, The MI densification is carried out by heating to 1480–1550°C in a vacuum environment to achieve molten silicon infiltration.
7. The method for preparing silicon carbide composite material according to claim 6, characterized in that, Before densification of MI, the CVI-densified preform is first immersed in a carbon source and then subjected to solidification and pyrolysis treatment, and then vacuum melt infiltration is carried out together with silicon material.
8. The method for preparing silicon carbide composite material according to claim 7, characterized in that, The carbon source is selected from any one of phenolic resin, asphalt, and polycarbosilane.
9. A silicon carbide fiber-reinforced silicon carbide composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1–8.
10. The silicon carbide fiber-reinforced silicon carbide composite material according to claim 9, characterized in that, The bulk density of the silicon carbide fiber-reinforced silicon carbide composite material is 2.80–2.82 g / cm³. 3 .