Method for improving high-temperature mechanical properties of c / si bcn ceramic matrix composite

Abstract

The application provides a method for improving high-temperature mechanical properties of C / SiBCN ceramic matrix composites, adopts a SiBCN precursor with high ceramic yield and low nitrogen content as a matrix, and carries out an impregnation and pyrolysis process by taking the precursor as the matrix; a PyC-SiC-BN composite interface layer is designed between the fiber and the matrix, and the disordered layered t-BN phase can effectively avoid corrosion of the carbon fiber by Si3N4, and meanwhile, the SiC-BN interface layer is similar in chemical element composition to the SiBCN matrix and has good physical and chemical compatibility. The C / SiBCN composite material obtained through the above preparation method can improve the mechanical and oxidation resistance properties of the composite material. The C / SiBCN composite material obtained through the application has excellent high-temperature mechanical properties, the tensile property at 1700 DEG C can reach the order of magnitude of 300MPa, can realize high-temperature self-oxidation resistance, does not need an oxidation resistance coating, and has excellent high-temperature oxidation resistance.

Description

Technical Field

[0001] This invention belongs to the field of high-performance ceramic matrix composite manufacturing technology, and specifically relates to a method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites. Background Technology

[0002] Carbon fiber reinforced silicon boron carbon nitride ceramic matrix composites (hereinafter referred to as C / SiBCN) use carbon fiber as reinforcement and SiBCN matrix as the main phase obtained by SiBCN liquid-phase precursor conversion method. This combination integrates the superior high-temperature mechanical and physical properties of carbon fiber with the good chemical and thermal stability of the silicon boron carbon nitride ceramic matrix. SiBCN liquid-phase precursors are a type of ceramic precursor with room-temperature liquid properties. They have Si-NBN as the main chain, with the main chain or side chains having silicon-hydrogen bonds, unsaturated groups, or boron-nitrogen bonds. They undergo cross-linking and solidification after relatively low-temperature heat treatment, maintaining a high ceramic yield during further pyrolysis, which can significantly improve impregnation-pyrolysis efficiency and reduce the cost of composite material preparation.

[0003] Compared to commonly used thermal structural composites, namely carbon / carbon materials, C / SiBCN exhibits superior oxidation resistance and load-bearing capacity. Simultaneously, this material overcomes the brittleness of single ceramic materials, representing a new type of high-temperature resistant structural composite material that integrates thermal protection, structural load-bearing, and oxidation resistance. It also possesses characteristics such as high fracture toughness, high strength, large specific heat capacity, thermal shock resistance, light weight, and excellent oxidation resistance. Compared to another commonly used C / SiC ceramic matrix composite, it also has significant advantages in cost, composite mechanical properties, and oxidation resistance: C / SiC composites experience rapid strength and modulus decay at 1400℃, while C / SiBCN, due to the matrix's minimal creep above 1600℃, effectively maintains the mechanical properties of carbon fibers, retaining over 80% of its mechanical properties at 1400℃. Combined with excellent oxidation resistance, it possesses unparalleled advantages over other ceramic matrix composites, making it an important candidate material system for thermal structural components in new weapon systems.

[0004] Although the SiBCN matrix in C / SiBCN composites exhibits high structural stability and oxidation resistance, remaining non-crystallizing, non-decomposing, and non-oxidizing above 1500℃; it also possesses excellent high-temperature mechanical properties and superior high-temperature creep resistance, remaining stable up to 2000℃ in an inert atmosphere and showing minimal mass change up to 1700℃ in air. However, the mechanical property retention rate of C / SiBCN composites at 1600℃ is less than 50%, making it difficult to meet the higher operating temperature requirements of thermal structural components in new weapon models. Research indicates that the main reason for the decline in the high-temperature mechanical properties of C / SiBCN composites is that during high-temperature (~1700℃) processes, in localized areas within the matrix, Si-N bonds and Si-C react with free carbon and residual oxygen in the matrix—including the oxygen content within the original precursor and oxygen introduced during hydrolysis in the process—further increasing and growing microcracks and microporosities within the matrix. Simultaneously, in highly reactive localized areas, Si-N bonds in the matrix begin to react with C elements at the pyrolytic carbon (PyC) interface, leading to interface erosion. Figure 1 In the scanning electron microscope images, the PyC interface was severely eroded and no clear interface was visible. In some areas, the erosion broke through the interface and damaged the carbon fiber, resulting in obvious micropores on the fiber surface, which weakened its performance and led to a significant decrease in the performance of the composite material. In addition, the mismatch of the thermal expansion coefficients between the C fiber and the SiBCN matrix made it difficult to release residual stress during mechanical load-bearing, which also led to a decrease in the mechanical properties of the composite material. In order to give full play to the role of the interface phase in CMC-SiC, the interface phase needs to meet the following requirements: (1) The interface phase has a low modulus to alleviate the thermal mismatch between the fiber and the matrix; (2) The interface phase needs to have good physicochemical compatibility with the matrix and the fiber; (3) The interface needs to have good chemical stability to maintain its high-temperature oxidation resistance and structural stability at high matrix preparation temperatures.

[0005] In order to improve the high-temperature mechanical properties of C / SiBCN composite materials, the present invention adopts the following methods: (1) Using low-nitrogen SiBCN precursor as matrix, matrix composition design is carried out. Chemically, through in-depth optimization of the precursor element composition, the content ratio of elements such as Si, B, C, and N is adjusted to reduce the Si3N4 content, so as to exert the inhibitory effect of BCN on the erosion reaction of Si3N4 and carbon fiber, thereby reducing the reaction activity and reaction rate; (2) Interface optimization design is carried out to design and prepare a new composite interface to inhibit or reduce the erosion of the interface and carbon fiber by related reactions under high temperature conditions, so as to ensure that the interface and fiber are not damaged or weakened under high temperature conditions, and obtain C / SiBCN composite material with good high-temperature mechanical properties, and the tensile properties at 1700℃ can reach the order of 300MPa. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the inventors conducted intensive research and provided a method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites. This method uses chlorosilane, boron trichloride, an aminolysis reagent, and a reducing agent as reactants, sequentially completing incomplete aminolysis and reduction reactions in an organic solvent to prepare a high-ceramic-yield, low-nitrogen-content SiBCN precursor. This precursor is then used as the matrix for an impregnation and pyrolysis process. A SiC-BN composite interface layer is designed between the fiber and the matrix. The disordered layered t-BN phase effectively prevents the carbon fibers from being corroded by Si3N4. Simultaneously, the SiC-BN interface layer has a similar chemical elemental composition to the SiBCN matrix, exhibiting good physicochemical compatibility. The C / SiBCN composite material obtained through this preparation method demonstrates improved mechanical and oxidation resistance properties.

[0007] The technical solution provided by this invention is as follows: In a first aspect, a method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites includes the following steps: Using chlorosilane, boron trichloride, aminolysis reagent and reducing agent as reaction raw materials, the aminolysis reaction and reduction reaction were carried out sequentially in an organic solvent to obtain the SiBCN precursor; The carbon fiber woven intermediate is filled into a graphite tooling, heat-treated, and the sizing agent on the surface of the carbon fiber intermediate is removed to form a carbon fiber preform. The carbon fiber preform was removed from the graphite tooling and carbon deposition was performed on the carbon fiber preform under an atmosphere of argon and alkane. The carbon fiber preform after carbon deposition is introduced into an MTS-Ar mixture with H2 as the carrier gas, or into a BCl3-NH3-H2-N2 mixture, or first into an MTS-Ar mixture with H2 as the carrier gas and then into a BCl3-NH3-H2-N2 mixture to perform SiC and / or BN interface treatment on the carbon fiber preform after carbon deposition. The carbon fiber preform that has undergone gradient interface treatment is placed back into the graphite tooling for SiBCN precursor impregnation treatment, followed by curing and high-temperature pyrolysis. The precursor impregnation, curing and high-temperature pyrolysis steps were repeated until the material density reached the required level. The graphite tooling was then removed to obtain the C / SiBCN ceramic matrix composite material.

[0008] In a second aspect, a C / SiBCN ceramic matrix composite material is prepared by the method described in the first aspect for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composite materials.

[0009] The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites provided by the present invention has the following beneficial effects: (1) The present invention uses chlorosilane, boron trichloride, amination reagent and reducing agent as reaction raw materials to complete the incomplete amination reaction and reduction reaction in an organic solvent in sequence to obtain a low nitrogen and high silicon hydrogen content SiBCN precursor, which can effectively reduce the Si3N4 content in the composite matrix and reduce the corrosion of carbon fiber by Si3N4, thereby improving the mechanical and antioxidant properties of the composite material; the tensile properties of C / SiBCN ceramic matrix composite material can reach 300MPa at 1700℃, which can achieve high temperature self-oxidation without the need for an antioxidant coating, demonstrating excellent high temperature antioxidant properties.

[0010] (2) The present invention designs a multi-gradient interface layer (PyC / SiC, PyC / BN or PyC / SiC / BN, especially PyC / SiC / BN) between the fiber and the matrix, which can effectively prevent the fiber from being corroded by Si3N4 and has a similar chemical element composition to the SiBCN matrix, thus having good physicochemical compatibility, thereby improving the mechanical and antioxidant properties of the composite material. Attached Figure Description

[0011] Figure 1 The interface and fiber morphology of traditional C / SiBCN ceramic matrix composites after treatment at 1700℃; Figure 2 This is an electron microscope image of the high-temperature (1700℃) tensile strength of the C / SiBCN ceramic matrix composite material in Example 1; Figure 3 The tensile stress-strain curve of the C / SiBCN ceramic matrix composite material in Example 1 is shown. Detailed Implementation

[0012] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0013] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0014] This invention provides a method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites, comprising the following steps: Step 1: Using chlorosilane, boron trichloride, aminolysis reagent and reducing agent as reaction raw materials, the aminolysis reaction and reduction reaction are carried out sequentially in an organic solvent to obtain the SiBCN precursor.

[0015] In this step, the chlorosilane is selected from at least one of chloromethyltrichlorosilane, methyldichlorosilane, methylvinyldichlorosilane, dimethyldichlorosilane, or dichlorodichlorosilane.

[0016] In this step, the amination reagent is at least one of ammonia, methylamine, ethylamine, or hexamethyldisilazane.

[0017] In this step, the reducing agent is at least one of sodium aluminum hydride and sodium dihydrobis(2-methoxyethoxy)aluminate (hereinafter referred to as red aluminum) in toluene solution, wherein the mass percentage of the red aluminum in toluene solution is 20% to 80%. The reducing agent of the present invention avoids the traditional highly reactive reducing agent systems such as lithium aluminum hydride and lithium hydride, and adopts a mild reducing agent, especially the red aluminum reducing agent system.

[0018] In this step, the organic solvent is at least one of n-hexane, petroleum ether, tetrahydrofuran, toluene, or xylene.

[0019] In this step, the specific implementation steps of the aminolysis reaction and reduction reaction are as follows: chlorosilane monomer, boron trichloride solution, and organic solvent are added to a purified and dried container. Under stirring conditions, the dried aminolysis reagent is introduced into the container. The container is heated to -30~100℃ and stirred for 5~20 hours. After standing for 0.5~20 hours, solid byproducts are removed by filtration, and a supernatant is obtained. A reducing agent is added to the supernatant, and the mixture is stirred at 40~100℃ for 5~20 hours. After acidic treatment, standing for layering, and organic phase separation, the separated organic phase is subjected to rotary evaporation and vacuum distillation to obtain the SiBCN precursor.

[0020] In this step, the molar ratio of chlorosilane to boron trichloride is 1:0.5 to 1:10, and the molar ratio of the total molar amount of boron trichloride and chlorosilane to the molar ratio of the aminolysis reagent is 1:1 to 1:4. The molar ratio of the reducing agent to chlorosilane is 0.5:1 to 2:1.

[0021] This invention obtains a polymer of main-chain Si-NBN through partial aminolysis of the Si-Cl bond of chlorosilane and boron trichloride, and the unreacted Si-Cl is reduced to obtain Si-H, thus preparing a low-nitrogen SiBCN precursor containing Si-H active groups.

[0022] Step 2: The carbon fiber woven intermediate is filled into a graphite tooling and heat-treated to remove the sizing agent from the surface of the carbon fiber intermediate, thus forming a carbon fiber preform.

[0023] In this step, the carbon fiber used in the carbon fiber woven fabric includes one or more of T300 carbon fiber, T700 carbon fiber, T800 carbon fiber, T1000 carbon fiber or M40J carbon fiber; the weaving form of the carbon fiber woven fabric includes one or more of two-dimensional fiber cloth lay-up stitching, two-dimensional half-weaving, orthogonal three-dimensional, three-dimensional yarn wrapping or three-dimensional five-dimensional.

[0024] In this step, the heat treatment method is as follows: the carbon fiber woven fabric is placed in an inert atmosphere pyrolysis furnace, heated freely to 1000~1300℃ and held for 1~2 hours, and then cooled freely to room temperature.

[0025] Step 3: Remove the carbon fiber preform from the graphite fixture and perform carbon deposition on the carbon fiber preform in an atmosphere of argon and alkane.

[0026] In this step, the parameters for carbon deposition treatment of carbon fiber preforms include: deposition temperature of 1000~1100℃, heating rate of 1~5℃ / min, alkane gas flow rate of 5~15L / min, deposition chamber pressure of 1~2kPa, and holding time of more than 1h; the deposition weight gain rate of carbon fiber preforms is 5%~30%.

[0027] Step 4: The carbon fiber preform after carbon deposition is passed through MTS (methyltrichlorosilane)-Ar (H2 as carrier gas), or through a BCl3-NH3-H2-N2 mixed gas, or first through MTS-Ar (H2 as carrier gas) and then through a BCl3-NH3-H2-N2 mixed gas to perform SiC and / or BN interface treatment on the carbon fiber preform after carbon deposition.

[0028] In this step, the carbon fiber preform after carbon deposition treatment is introduced into MTS-Ar (H2 as carrier gas) to obtain a PyC / SiC gradient deposition interface layer; the carbon fiber preform after carbon deposition treatment is introduced into a BCl3-NH3-H2-N2 mixed gas to obtain a PyC / BN gradient deposition interface layer; the carbon fiber preform after carbon deposition treatment is first introduced into MTS-Ar (H2 as carrier gas) and then into a BCl3-NH3-H2-N2 mixed gas to obtain a PyC / SiC / BN gradient deposition interface layer.

[0029] In this step, SiC interface preparation is performed on the carbon fiber preform after carbon deposition. The specific method is as follows: MTS-Ar (H2 as carrier gas) is introduced into a chemical vapor deposition furnace, the interface preparation temperature is 1000~1100℃, the heating rate is 1~5℃ / min, the deposition chamber pressure is 1~2kPa, and the thickness of the interface is controlled by controlling the deposition time, thereby introducing a SiC interface layer into the carbon fiber preform.

[0030] In this step, a BN interface is prepared on the carbon fiber preform after carbon deposition. The specific method is as follows: under the conditions of deposition temperature of 600~850℃, system pressure of 3~12kPa, and residence time of 0.5~3s, a BCl3-NH3-H2-N2 mixed gas is introduced into the chemical vapor deposition furnace to prepare a BN interface layer on the surface of the carbon fiber preform.

[0031] This invention designs and prepares a novel composite interface using a PyC / SiC / BN gradient composite interface layer. This is attributed to two factors: firstly, PyC is beneficial for matching the thermal expansion coefficient of C fibers; secondly, a SiC-BN composite interface layer is designed between the fiber and the matrix. The disordered layered t-BN phase effectively prevents the carbon fibers from being corroded by Si3N4. Simultaneously, the SiC-BN interface layer has a similar chemical elemental composition to the SiBCN matrix, exhibiting good physicochemical compatibility and effective bonding. The C / SiBCN composite material obtained through this preparation method improves the mechanical and oxidation resistance properties of the composite material.

[0032] Step 5: The carbon fiber preform that has undergone gradient interface treatment is placed back into the graphite tooling for SiBCN precursor impregnation treatment, and then cured and pyrolyzed in sequence. Step 6: Repeat step 5 until the material density reaches 1.60 g / cm³. 3 The graphite tooling was removed, and the C / SiBCN ceramic matrix composite material was obtained.

[0033] In this step, the specific parameters for impregnation, curing and high-temperature pyrolysis include: impregnation pressure of 0.5~1MPa and temperature of 20~80℃; curing temperature of 180~200℃ and time of 2~4h; and pyrolysis temperature of 1000~1500℃ and time of 2~4h.

[0034] Example Example 1 A method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites includes the following steps: (1) A 500ml dry three-necked flask is equipped with an N2 inlet stopcock, a condenser, a nitrogen outlet stopcock, a constant pressure dropping funnel, and an electromagnetic stirrer. The flask is evacuated, and nitrogen is passed through to replace the air in the system. Adsorbed water is removed by heating with an alcohol lamp. 50ml of tetrahydrofuran is added to the reaction flask using a syringe. 10.8mL of methyldichlorosilane monomer, 12mL of methylvinyldichlorosilane, and 250mL of 1mol / L boron trichloride solution are added to the purified and dried tetrahydrofuran using a syringe. Under stirring, 120mL of dried hexamethyldisilazane is added dropwise to the reaction flask. The container is heated to 60℃ and stirred for 12 hours. After standing for 2 hours, the solid byproducts are removed by filtration, yielding the supernatant. 140g of a toluene solution of red aluminum (70% by mass) is added in 5 portions. After adding the toluene solution of red aluminum, the mixture is stirred for 1 hour. The oil bath temperature is then raised to 62℃ and stirred for 13 hours. The oil bath was then removed, and the reaction mixture was allowed to cool naturally. With stirring, the resulting reactant was slowly added to 500 mL of a petroleum ether / hydrochloric acid mixed pickling solution. The temperature was raised to 15°C, and the mixture was stirred for 15 minutes, followed by standing for 30 minutes. At this point, the mixture in the container separated into layers: a brown organic phase on top and an aqueous phase on the bottom. The organic phase was separated. The organic phase was collected and subjected to rotary evaporation and vacuum distillation to remove the solvent petroleum ether, yielding a relatively viscous, light yellow, transparent oily product, a novel low-nitrogen, high-silicon-hydrogen content SiBCN precursor, which can be used as an impregnation matrix for carbon fiber reinforced composites.

[0035] (2) Using T300·1K carbon fiber layup and stitching as reinforcement, a 100mm×200mm flat sample was made, with the fiber volume fraction of the fabric in the sample being 35%; the flat sample was placed in an inert atmosphere pyrolysis furnace, and the temperature was raised to 1000℃ and kept for 2 hours, and then cooled to room temperature. A carbon interface layer was deposited on the heat-treated carbon fiber fabric using chemical vapor deposition (CVD). The deposition temperature was 1000℃, the heating rate was 3℃ / min, the propylene gas flow rate was 8L / min, the deposition chamber pressure was 1kPa, the deposition time was 130h, and the deposition weight gain was 15wt%, resulting in a carbon fiber preform. A SiC coating was then prepared on the surface of the carbon fiber preform by introducing MTS-Ar (H2 as carrier gas) into a CVD furnace, with an interface preparation temperature of 1000℃, a heating rate of 3℃ / min, and a deposition chamber pressure of 1.5kPa. Finally, a BN coating was prepared on the surface of the carbon fiber preform by introducing a BCl3-NH3-H2-N2 mixed gas as a precursor at a deposition temperature of 700℃, a system pressure of 5kPa, and a residence time of 2s.

[0036] (3) The SiBCN precursor impregnation liquid obtained in (1) is introduced into the composite preform after step (2) by pressure impregnation. The impregnation liquid is impregnated into the fabric at 25°C and -0.1MPa pressure. Then, pressure is applied at 1MPa for 1 hour. After the impregnation is complete, the preform is taken out.

[0037] (4) Place the blank obtained in step (3) into an argon atmosphere furnace for curing at a curing temperature of 200°C for 2 hours, and then lower the furnace temperature to room temperature. The solidified preform was placed in a high-temperature pyrolysis furnace and pyrolyzed under an argon atmosphere at a temperature of 1200℃ for 2 hours to allow the SiBCN precursor to complete its ceramic transformation.

[0038] (5) Repeat steps (3) and (4) 8 times to finally obtain 1.60 g / cm³. 3 The above are dense C / SiBCN ceramic matrix composites.

[0039] The cross-section of the composite material prepared by the above method was observed using a scanning electron microscope. The gradient interface morphology was clearly visible. Figure 2 The measured tensile strength of the composite material at room temperature was 383 MPa, and the tensile strength at 1700℃ was 352 MPa. (See attached data.) Figure 3 .

[0040] Example 2 A method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites includes the following steps: (1) A 500ml dry three-necked flask is equipped with an N2 inlet stopcock, a condenser, a nitrogen outlet stopcock, a constant pressure dropping funnel, and an electromagnetic stirrer. The flask is evacuated, and nitrogen is passed through to replace the air in the system. Adsorbed water is removed by heating with an alcohol lamp. 50ml of tetrahydrofuran is added to the reaction flask using a syringe. 10.8mL of methyldichlorosilane monomer, 12mL of methylvinyldichlorosilane, and 250mL of 1mol / L boron trichloride solution are added to the purified and dried tetrahydrofuran using a syringe. Under stirring, 120mL of dried hexamethyldisilazane is added dropwise to the reaction flask. The container is heated to 60℃ and stirred for 12 hours. After standing for 2 hours, the solid byproducts are removed by filtration, yielding the supernatant. 140g of a toluene solution of red aluminum (70% by mass) is added in 5 portions. After adding the toluene solution of red aluminum, the mixture is stirred for 1 hour. The oil bath temperature is then raised to 62℃ and stirred for 13 hours. The oil bath was then removed, and the reaction mixture was allowed to cool naturally. With stirring, the resulting reactant was slowly added to 500 mL of a petroleum ether / hydrochloric acid mixed pickling solution. The temperature was raised to 15°C, and the mixture was stirred for 15 minutes, followed by standing for 30 minutes. At this point, the mixture in the container separated into layers: a brown organic phase on top and an aqueous phase on the bottom. The organic phase was separated. The organic phase was collected and subjected to rotary evaporation and vacuum distillation to remove the solvent petroleum ether, yielding a relatively viscous, light yellow, transparent oily product, a novel low-nitrogen, high-silicon-hydrogen content SiBCN precursor, which can be used as an impregnation matrix for carbon fiber reinforced composites.

[0041] (2) Using T700·12K carbon fiber three-dimensional five-dimensional braided fabric as reinforcement, a 100mm×200mm flat sample was made, and the fiber volume fraction of the fabric in the sample was 35%; the flat sample was placed in an inert atmosphere pyrolysis furnace, and the temperature was raised to 1300℃ and kept for 1h, and then cooled to room temperature. A carbon interface layer was deposited on the heat-treated carbon fiber fabric using chemical vapor deposition (CVD). The deposition temperature was 1000℃, the heating rate was 5℃ / min, the propylene gas flow rate was 8L / min, the deposition chamber pressure was 1kPa, the deposition time was 130h, and the deposition weight gain was 15wt%, resulting in a carbon fiber preform. A SiC coating was then prepared on the surface of the carbon fiber preform by introducing MTS-Ar (H2 as carrier gas) into a CVD furnace, with an interface preparation temperature of 1000℃, a heating rate of 3℃ / min, and a deposition chamber pressure of 1.5kPa. Finally, a BN coating was prepared on the surface of the carbon fiber preform by introducing a BCl3-NH3-H2-N2 mixed gas as a precursor system at a deposition temperature of 700℃, a system pressure of 5kPa, and a residence time of 2s.

[0042] (3) The SiBCN precursor impregnation liquid obtained in (1) is introduced into the composite preform after step (2) by pressure impregnation. The impregnation liquid is impregnated into the fabric at 25°C and -0.1MPa pressure. Then, pressure is applied at 1MPa for 1 hour. After the impregnation is complete, the preform is taken out.

[0043] (4) Place the blank obtained in step (3) into an argon atmosphere furnace for curing at a curing temperature of 200°C for 2 hours, and then lower the furnace temperature to room temperature. The solidified preform was placed in a high-temperature pyrolysis furnace and pyrolyzed under an argon atmosphere at a temperature of 1200℃ for 2 hours to allow the SiBCN precursor to complete its ceramic transformation.

[0044] (5) Repeat steps (3) and (4) 8 times to finally obtain 1.60 g / cm³. 3 The above are dense C / SiBCN ceramic matrix composites.

[0045] The cross-section of the composite material prepared by the above method was observed using a scanning electron microscope, and a gradient interface morphology was clearly observed. The tensile strength of the composite material at room temperature was measured to be 342 MPa, and the tensile strength at 1700℃ was 323 MPa.

[0046] Example 3 A method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites includes the following steps: (1) A 500ml dry three-necked flask is equipped with an N2 inlet stopcock, a condenser, a nitrogen outlet stopcock, a constant pressure dropping funnel, and an electromagnetic stirrer. The flask is evacuated, and nitrogen is passed through to replace the air in the system. Adsorbed water is removed by heating with an alcohol lamp. 50ml of tetrahydrofuran is added to the reaction flask using a syringe. 10.8mL of methyldichlorosilane monomer, 12mL of methylvinyldichlorosilane, and 250mL of 1mol / L boron trichloride solution are added to the purified and dried tetrahydrofuran using a syringe. Under stirring, 120mL of dried hexamethyldisilazane is added dropwise to the reaction flask. The container is heated to 60℃ and stirred for 12 hours. After standing for 2 hours, the solid byproducts are removed by filtration, yielding the supernatant. 140g of a 70% toluene solution of red aluminum is added in 5 portions. After adding the toluene solution of red aluminum, the mixture is stirred for 1 hour. The oil bath temperature is then raised to 62℃ and stirred for 13 hours. The oil bath was then removed, and the reaction mixture was allowed to cool naturally. With stirring, the resulting reactant was slowly added to 500 mL of a petroleum ether / hydrochloric acid mixed pickling solution. The temperature was raised to 15°C, and the mixture was stirred for 15 minutes, followed by standing for 30 minutes. At this point, the mixture in the container separated into layers: a brown organic phase on top and an aqueous phase on the bottom. The organic phase was separated. The organic phase was collected and subjected to rotary evaporation and vacuum distillation to remove the solvent petroleum ether, yielding a relatively viscous, light yellow, transparent oily product, a novel low-nitrogen, high-silicon-hydrogen content SiBCN precursor, which can be used as an impregnation matrix for carbon fiber reinforced composites.

[0047] (2) Using T300·1K carbon fiber three-dimensional five-dimensional braided fabric as reinforcement, a 100mm×200mm flat sample was made, and the fiber volume fraction of the fabric in the sample was 35%; the flat sample was placed in an inert atmosphere pyrolysis furnace, and the temperature was raised to 1000℃ and kept for 2 hours, and then cooled to room temperature. A carbon interface layer was deposited on the heat-treated carbon fiber fabric using chemical vapor deposition (CVD). The deposition temperature was 1000℃, the heating rate was 5℃ / min, the propylene gas flow rate was 8L / min, the deposition chamber pressure was 1kPa, the deposition time was 215h, and the deposition weight gain was 20wt%, resulting in a carbon fiber preform. A SiC coating was then prepared on the surface of the carbon fiber preform by introducing MTS-Ar (H2 as carrier gas) into a CVD furnace, with an interface preparation temperature of 1000℃, a heating rate of 3℃ / min, and a deposition chamber pressure of 1.5kPa. Finally, a BN coating was prepared on the surface of the carbon fiber preform by introducing a BCl3-NH3-H2-N2 mixed gas as a precursor system at a deposition temperature of 700℃, a system pressure of 5kPa, and a residence time of 2s.

[0048] (3) The SiBCN precursor impregnation liquid obtained in (1) is introduced into the composite preform after step (2) by pressure impregnation. The impregnation liquid is impregnated into the fabric at 25°C and -0.1MPa pressure. Then, pressure is applied at 1MPa for 1 hour. After the impregnation is complete, the preform is taken out.

[0049] (4) Place the blank obtained in step (3) into an argon atmosphere furnace for curing at a curing temperature of 200°C for 2 hours, and then lower the furnace temperature to room temperature. The solidified preform was placed in a high-temperature pyrolysis furnace and pyrolyzed under an argon atmosphere at a temperature of 1200℃ for 2 hours to allow the SiBCN precursor to complete its ceramic transformation.

[0050] (5) Repeat steps (3) and (4) 8 times to finally obtain 1.60 g / cm³. 3 The above are dense C / SiBCN ceramic matrix composites.

[0051] The cross-section of the composite material prepared by the above method was observed using a scanning electron microscope, and a gradient interface morphology was clearly observed. The tensile strength of the composite material at room temperature was measured to be 405 MPa, and the tensile strength at 1700℃ was 374 MPa.

[0052] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0053] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites, characterized in that, Includes the following steps: Using chlorosilane, boron trichloride, aminolysis reagent and reducing agent as reaction raw materials, the aminolysis reaction and reduction reaction were carried out sequentially in an organic solvent to obtain the SiBCN precursor; The carbon fiber woven intermediate is filled into a graphite tooling, heat-treated, and the sizing agent on the surface of the carbon fiber intermediate is removed to form a carbon fiber preform. The carbon fiber preform was removed from the graphite tooling and carbon deposition was performed on the carbon fiber preform in an atmosphere of argon and alkane. The carbon fiber preform after carbon deposition is introduced into an MTS-Ar mixture with H2 as the carrier gas, or into a BCl3-NH3-H2-N2 mixture, or first into an MTS-Ar mixture with H2 as the carrier gas and then into a BCl3-NH3-H2-N2 mixture to perform SiC and / or BN interface treatment on the carbon fiber preform after carbon deposition. The carbon fiber preform that has undergone gradient interface treatment is placed back into the graphite tooling for SiBCN precursor impregnation treatment, followed by curing and high-temperature pyrolysis. The precursor impregnation, curing and high-temperature pyrolysis steps were repeated until the material density reached the required level. The graphite tooling was then removed to obtain the C / SiBCN ceramic matrix composite material.

2. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The chlorosilane is selected from at least one of chloromethyltrichlorosilane, methyldichlorosilane, methylvinyldichlorosilane, dimethyldichlorosilane, or dichlorodichlorosilane.

3. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The amine-dissolving reagent is at least one of ammonia, methylamine, ethylamine, or hexamethyldisilazane.

4. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The reducing agent is at least one of sodium aluminum hydride and a toluene solution of red aluminum, wherein the mass concentration of the toluene solution of red aluminum is 20% to 80%.

5. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The specific implementation steps of the aminolysis and reduction reactions are as follows: chlorosilane monomer, boron trichloride solution, and organic solvent are added to a purified and dried container. Under stirring conditions, the dried aminolysis reagent is introduced into the container. The container is heated to -30~100℃ and stirred for 5~20 hours. After standing for 0.5~20 hours, solid byproducts are removed by filtration, and a supernatant is obtained. A reducing agent is added to the supernatant, and the mixture is stirred at 40~100℃ for 5~20 hours. After acidic treatment, standing for layering, and organic phase separation, the separated organic phase is subjected to rotary evaporation and vacuum distillation to obtain the SiBCN precursor.

6. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The molar ratio of the chlorosilane to boron trichloride is 1:0.5 to 1:10; The total molar ratio of boron trichloride and chlorosilane to the aminolysis reagent is 1:1 to 1:

4. The molar ratio of the reducing agent to chlorosilane is 0.5:1 to 2:

1.

7. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The parameters for carbon deposition treatment of carbon fiber preforms include: deposition temperature of 1000~1100℃, heating rate of 1~5℃ / min, alkane gas flow rate of 5~15L / min, deposition chamber pressure of 1~2kPa, and holding time of more than 1h; the deposition weight gain rate of carbon fiber preforms is 5%~30%.

8. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The SiC interface was prepared on the carbon fiber preform after carbon deposition. The specific method is as follows: MTS-Ar mixed gas with H2 as carrier gas was introduced into the chemical vapor deposition furnace. The interface preparation temperature was 1000~1100℃, the heating rate was 1~5℃ / min, the deposition chamber pressure was 1~2kPa, and the thickness of the interface was controlled by controlling the deposition time, so that the SiC interface layer was introduced into the carbon fiber preform. The BN interface was prepared on the carbon fiber preform after carbon deposition using the following method: a BCl3-NH3-H2-N2 mixed gas was introduced into a chemical vapor deposition furnace at a deposition temperature of 600~850℃, a system pressure of 3~12kPa, and a residence time of 0.5~3s to prepare a BN interface layer on the surface of the carbon fiber preform.

9. The method for improving the high-temperature mechanical properties of C / SiBCN ceramic matrix composites according to claim 1, characterized in that, The specific parameters for impregnation, curing and high-temperature pyrolysis include: impregnation pressure of 0.5~1MPa and temperature of 20~80℃; curing temperature of 180~200℃ and time of 2~4h; and pyrolysis temperature of 1000~1500℃ and time of 2~4h.

10. A C / SiBCN ceramic matrix composite material, characterized in that, The C / SiBCN ceramic matrix composite material was prepared by the method for improving the high-temperature mechanical properties as described in any one of claims 1 to 9.

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