A near-zero expansion C / Si3N4-SiC composite material, its preparation method and application

Abstract

This invention discloses a near-zero expansion C / Si3N4-SiC composite material, its preparation method, and its applications, relating to the field of ceramic matrix composite technology. The composite material includes a carbon fiber reinforced silicon nitride-based porous composite material and a silicon carbide matrix coated on the surface of the carbon fiber reinforced silicon nitride-based porous composite material. The carbon fiber reinforced silicon nitride-based porous composite material includes a carbon fiber preform woven from carbon fiber bundles. A pyrolytic carbon interface layer is deposited on the carbon fiber bundles in the carbon fiber preform, and the pyrolytic carbon interface layer is further coated with a silicon nitride matrix. This invention achieves near-zero expansion by controlling the deposition time of the silicon nitride matrix, allowing the silicon nitride matrix to completely encapsulate the carbon fiber bundles, forming diffusely distributed microcracks within the fiber bundles.

Description

Technical Field

[0001] This invention relates to the field of ceramic matrix composites, specifically to a near-zero expansion C / Si3N4-SiC composite material, its preparation method, and its applications. Background Technology

[0002] With the continuous development of science and technology, countries around the world are investing human and material resources in the development of scientific exploration satellites. Space exploration satellites mainly consist of optical elements and the space optomechanical structural components that carry them. To achieve ultra-high detection accuracy, these components must possess high structural and thermal stability, meaning that the absolute value of the material's coefficient of thermal expansion must reach 10 within its service temperature range. -7 K -1 The requirements are even lower. Simultaneously, the materials used must withstand rocket launch vibrations, demanding excellent mechanical properties. To reduce launch costs for space exploration satellites, the materials used in space optomechanical structural components must have low density. Facing the complex space environment, the materials must be resistant to space radiation and atomic impacts. Therefore, the materials used in space optomechanical structural components must possess near-zero coefficient of thermal expansion, excellent mechanical properties, low density, and good environmental stability.

[0003] Carbon fiber reinforced ceramic matrix composites possess advantages such as low density, excellent mechanical properties, low coefficient of thermal expansion, and good environmental stability, making them an ideal choice for next-generation space optomechanical materials. Existing technology discloses a near-zero expansion carbon fiber reinforced multi-element multilayer matrix composite material. This is achieved by controlling the cycle number and layer thickness ratio of the multi-element multilayer matrix, significantly reducing the coefficient of thermal expansion of current ceramic matrix composites. The average coefficient of thermal expansion of the prepared composite material is 0.12 × 10⁻⁶. -6 K -1 This has reached an advanced level. However, when introducing a low-expansion phase into C / SiC, the carbon fiber reinforced multi-element multilayer composite material requires alternating deposition of silicon carbide and silicon nitride, which requires at least 9 furnaces, resulting in a material preparation cycle of 4-5 months. Moreover, the complex process is not conducive to large-scale production. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technologies, this invention primarily solves the problems of long preparation cycles and complex manufacturing processes in carbon fiber reinforced multi-element multilayer matrix composites. This invention provides a near-zero expansion C / Si3N4-SiC composite material, its preparation method, and its applications. This method employs a chemical vapor infiltration process, controlling the deposition time of the silicon nitride matrix to ensure complete encapsulation of the carbon fiber bundles by the Si3N4 matrix. Utilizing the amorphous properties of silicon nitride, numerous diffusely distributed microcracks are formed within the fiber bundles. The high degree of crystallinity of the outer silicon carbide layer constrains the internal fibers and silicon nitride matrix, thereby achieving near-zero expansion.

[0005] The first objective of this invention is to provide a near-zero expansion C / Si3N4-SiC composite material, characterized in that the composite material comprises a carbon fiber reinforced silicon nitride-based porous composite material, and a silicon carbide matrix coated on the surface of the carbon fiber reinforced silicon nitride-based porous composite material;

[0006] The carbon fiber reinforced silicon nitride-based porous composite material includes a carbon fiber preform woven from carbon fiber bundles; a pyrolytic carbon interface layer is deposited on the carbon fiber bundles in the carbon fiber preform, and a silicon nitride matrix is ​​also coated on the pyrolytic carbon interface layer.

[0007] The carbon fiber bundle contains a silicon nitride matrix between the individual fibers inside; the carbon fiber bundle at its edge contains a silicon nitride matrix with a thickness of 0.5~5μm between the individual fibers and the silicon carbide matrix.

[0008] Preferably, the thickness of the pyrolytic carbon interface layer is 100~500nm; and the thickness of the silicon carbide matrix layer outside the carbon fiber bundle is 0.02~0.3mm.

[0009] Preferably, the diameter of the single filament in the carbon fiber bundle is 4~8μm; the number of single filaments in the carbon fiber bundle is 1K, 3K, 6K or 12K; and the carbon fibers in the carbon fiber bundle are T-series fibers.

[0010] The carbon fiber preform structure includes a 2D carbon fiber preform, a 2.5D carbon fiber preform, or a 3D woven carbon fiber preform.

[0011] Preferably, the density of the composite material is 1.9~2.1 g / cm³. 3 The porosity is 8~15 vol.%; the absolute value of the coefficient of thermal expansion of this composite material is less than 0.1×10⁻⁶ in the temperature range of -100~100℃. -6 K -1 .

[0012] The second objective of this invention is to provide a method for preparing a near-zero expansion C / Si3N4-SiC composite material, comprising the following steps:

[0013] Continuous carbon fiber bundles are woven into carbon fiber preforms with different structures and a fiber volume fraction of ≥38%.

[0014] The carbon fiber preform is placed in a vacuum furnace with a pressure of <300Pa and a temperature of 800~900℃. Argon and propylene are introduced and the temperature is maintained for 45~200h to deposit a pyrolytic carbon interface layer on the surface of the carbon fiber preform. Then, heat treatment is carried out at 1200~1900℃ for 1~2h.

[0015] The carbon fiber preform after deposition of pyrolytic carbon interface layer and heat treatment is set with pressure <300Pa and temperature 800~1100℃, and argon, hydrogen, silicon tetrachloride and ammonia are introduced. By adjusting the deposition time, the carbon fiber bundle is completely wrapped by the silicon nitride matrix to obtain carbon fiber reinforced silicon nitride-based porous composite material.

[0016] Carbon fiber reinforced silicon nitride-based porous composite material is placed in a deposition furnace with a pressure of <300 Pa and a temperature of 1000~1100 °C. Argon, hydrogen and trichloromethylsilane are introduced to generate silicon carbide matrix on the surface of silicon nitride matrix through reaction, and fill the pores between carbon fiber bundles to obtain near-zero expansion C / Si3N4-SiC composite material.

[0017] Preferably, when depositing the pyrolytic carbon interface layer on the surface of the carbon fiber preform, the flow rate of argon gas is 2~4 L / min, and the flow rate of propylene gas is 2~4 L / min.

[0018] Preferably, when preparing the porous C / Si3N4 composite material, the flow rate of argon is 2~4 L / min, the flow rate of hydrogen is 7~9 L / min, the flow rate of silicon tetrachloride is 3~5 L / min, and the flow rate of ammonia is 2~4 L / min.

[0019] Preferably, when generating a silicon carbide matrix by reaction on the surface of a silicon nitride matrix, the flow rate of argon gas is 2-4 L / min; the flow rate of hydrogen gas is 4-6 L / min; and the molar mass ratio of hydrogen gas to trichloromethylsilane is 10:1.

[0020] The third objective of this invention is to provide an application of near-zero expansion C / Si3N4-SiC composite material in space optomechanical structural components.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention provides a near-zero expansion C / Si3N4-SiC composite material, its preparation method, and its applications. By controlling the deposition time of the silicon nitride matrix to completely encapsulate the fiber bundles, the near-zero expansion C / Si3N4-SiC composite material prepared exhibits an average coefficient of thermal expansion of 0.03 × 10⁻⁶ within a temperature range of -80 to 50 °C. -6 K -1 Its coefficient of thermal expansion has an absolute value of less than 0.1 × 10⁻⁶. -6 K -1 This achieved the goal of near-zero inflation;

[0023] The expansion properties of the carbon fiber ceramic matrix composite provided by this invention depend not only on the expansion coefficients of each component but also on the interaction between the fiber and the matrix. In traditional carbon fiber reinforced ceramic matrix composites, the matrix and fiber are strongly bonded within the bundle, preventing the fibers from fully utilizing their negative expansion properties. Furthermore, most cracks generated are transverse cracks between fiber bundles, failing to effectively mitigate the thermal mismatch between the fiber and the matrix. Research has revealed that the matrix within the fiber bundle significantly influences the expansion properties of the composite material.

[0024] This invention employs a chemical vapor infiltration process to control the deposition time of the silicon nitride matrix, allowing the silicon nitride matrix to completely encapsulate the carbon fiber bundles, thus preparing a C / Si3N4-SiC composite material. This process controls the generated cracks within the fiber bundles, better mitigating the thermal mismatch between the fibers and the matrix, significantly reducing the coefficient of thermal expansion of the carbon fiber reinforced ceramic matrix composite material, and distributing the silicon carbide matrix with good modulus between the fiber bundles, ensuring good mechanical properties while reducing the coefficient of thermal expansion. Attached Figure Description

[0025] Figure 1 The images shown are scanning electron microscope (SEM) images and EDS images of the C / Si3N4-SiC composite material prepared in Example 1.

[0026] Figure 2 This is a schematic diagram of the expansion properties of the C / Si3N4-SiC composite material prepared in Example 1 in the temperature range of -80~50℃, where a is the linear expansion curve and b is the expansion coefficient curve as a function of temperature.

[0027] Figure 3 The mechanical property curves of the C / Si3N4-SiC composite material prepared in Example 1 are shown, where a is the bending stress-strain curve and b is the fracture toughness-displacement curve.

[0028] Figure 4 This is a schematic diagram of the expansion properties of the C / SiC composite material prepared in Comparative Example 1 in the temperature range of -80~50℃, where a is the linear expansion curve and b is the expansion coefficient curve as a function of temperature.

[0029] Figure 5 The mechanical property curves of the C / SiC composite material prepared in Comparative Example 1 are shown, where a is the bending stress-strain curve and b is the fracture toughness-displacement curve. Detailed Implementation

[0030] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0031] The first aspect of the present invention provides a near-zero expansion C / Si3N4-SiC composite material, the composite material comprising a carbon fiber reinforced silicon nitride-based porous composite material, and a silicon carbide matrix coated on the surface of the carbon fiber reinforced silicon nitride-based porous composite material;

[0032] The carbon fiber reinforced silicon nitride-based porous composite material includes a carbon fiber preform woven from carbon fiber bundles; a pyrolytic carbon interface layer is deposited on the carbon fiber bundles in the carbon fiber preform, and a silicon nitride matrix is ​​also coated on the pyrolytic carbon interface layer.

[0033] The carbon fiber bundle contains a silicon nitride matrix between the individual fibers inside; the carbon fiber bundle at its edge contains a silicon nitride matrix with a thickness of 0.5~5μm between the individual fibers and the silicon carbide matrix.

[0034] The thickness of the pyrolytic carbon interface layer is 100~500nm; the thickness of the silicon carbide matrix layer outside the carbon fiber bundle is 0.02~0.3mm.

[0035] The diameter of the single filaments in the carbon fiber bundle is 4~8μm; the number of single filaments in the carbon fiber bundle is 1K, 3K, 6K or 12K; the carbon fibers in the carbon fiber bundle are T-series fibers;

[0036] The carbon fiber preform structure includes a 2D carbon fiber preform, a 2.5D carbon fiber preform, or a 3D woven carbon fiber preform.

[0037] The density of the composite material is 1.9~2.1 g / cm³. 3 The porosity is 8~15 vol.%; the absolute value of the coefficient of thermal expansion of this composite material is less than 0.1×10⁻⁶ in the temperature range of -100~100℃. -6 K -1 .

[0038] In one embodiment, a near-zero expansion C / Si3N4-SiC composite material is provided, the composite material comprising carbon fiber bundles, a pyrolytic carbon interface layer on the surface of the carbon fiber bundles, a silicon nitride matrix layer that completely encapsulates the carbon fiber bundles, and a silicon carbide matrix layer outside the carbon fiber bundles.

[0039] The carbon fiber uses T-series fibers: T300, T700, and T800, etc.

[0040] The silicon nitride matrix layer that completely encapsulates the carbon fiber bundle is as follows: only the silicon nitride matrix exists between the individual fibers inside the carbon fiber bundle, and a silicon nitride matrix with a thickness of 0.5~5μm exists between the individual fibers at the edge of the carbon fiber bundle and the silicon carbide matrix.

[0041] The thickness of the silicon carbide matrix layer outside the carbon fiber bundle is 0.02~0.3mm.

[0042] Preferably, the absolute value of the coefficient of thermal expansion of the near-zero expansion C / Si3N4-SiC composite material is less than 0.1×10⁻⁶ in the temperature range of -80 to 50°C. -6 K -1 .

[0043] A second aspect of this invention provides a method for preparing a near-zero expansion C / Si3N4-SiC composite material, comprising the following steps:

[0044] Continuous carbon fiber bundles are woven into carbon fiber preforms with different structures and a fiber volume fraction of ≥38%.

[0045] The carbon fiber preform is placed in a vacuum furnace with a pressure of <300 Pa and a temperature of 800~900℃. Argon and propylene are introduced and the temperature is maintained for 45~200h to deposit a pyrolytic carbon interface layer on the surface of the carbon fiber preform. Then, a heat treatment is performed at 1200~1900℃ for 1~2h.

[0046] The carbon fiber preform after deposition of pyrolytic carbon interface layer and heat treatment is subjected to a pressure of <300Pa and a temperature of 800~1100℃. Argon, hydrogen, silicon tetrachloride and ammonia are introduced. By adjusting the deposition time, the carbon fiber bundle is completely wrapped by the silicon nitride matrix to obtain carbon fiber reinforced silicon nitride-based porous composite material (porous C / Si3N4 composite material).

[0047] The C / Si3N4 composite material was placed in a deposition furnace with a pressure of <300 Pa and a temperature of 1000~1100 °C. Argon, hydrogen and trichloromethylsilane were introduced to generate a silicon carbide matrix on the surface of the silicon nitride matrix through reaction, and the pores between the carbon fiber bundles were filled to obtain the near-zero expansion C / Si3N4-SiC composite material.

[0048] When depositing a pyrolytic carbon interface layer on the surface of the carbon fiber preform, the flow rate of argon gas is 2~4 L / min and the flow rate of propylene gas is 2~4 L / min; preferably, the flow rate of argon gas is 3 L / min and the flow rate of propylene gas is 3 L / min.

[0049] When preparing porous C / Si3N4 composite materials, the flow rate of argon is 2~4 L / min, the flow rate of hydrogen is 7~9 L / min, the flow rate of silicon tetrachloride is 3~5 L / min, and the flow rate of ammonia is 2~4 L / min; preferably, the flow rate of argon is 3 L / min, the flow rate of hydrogen is 8 L / min, the flow rate of silicon tetrachloride is 4 L / min, and the flow rate of ammonia is 3 L / min.

[0050] When a silicon carbide matrix is ​​generated on the surface of a silicon nitride matrix through a reaction, the flow rate of argon gas is 2-4 L / min; the flow rate of hydrogen gas is 4-6 L / min, preferably 3 L / min for argon gas and 5 L / min for hydrogen gas; the molar mass ratio of hydrogen gas to trichloromethylsilane is 10:1.

[0051] In one embodiment, a method for preparing a near-zero expansion C / Si3N4-SiC composite material includes the following steps:

[0052] Step 1: Lay up plain weave carbon fiber fabric woven from continuous carbon fiber bundles, and then sew them together along the thickness direction with continuous carbon fiber bundles to obtain a carbon fiber preform with a fiber volume fraction ≥38%.

[0053] Step 2: Place the carbon fiber preform prepared in Step 1 in a vacuum furnace with a pressure of <300Pa and a temperature of 800~900℃, introduce argon as a dilution gas and propylene as a carbon source, and keep it at the temperature for 45~200h to deposit a pyrolytic carbon interface layer with a thickness of 100~500nm on the surface of the carbon fiber.

[0054] Step 3: Place the carbon fiber preform with completed pyrolytic carbon interface layer deposition prepared in Step 2 in an environment with pressure <300Pa for high temperature heat treatment at 1200~1900℃ and hold for 1-2 hours.

[0055] Step 4: Place the heat-treated carbon fiber preform prepared in Step 3 into a deposition furnace, evacuate to a pressure <300Pa and heat to 800~1100℃, then introduce argon as a carrier gas, hydrogen as a dilution gas, silicon tetrachloride as a silicon source, and ammonia as a nitrogen source. By adjusting the deposition time, the carbon fiber bundles are completely wrapped by the silicon nitride matrix to obtain C / Si3N4 porous composite material.

[0056] Step 5: Place the C / Si3N4 composite material prepared in Step 4 in a deposition furnace, evacuate to a pressure <300 Pa and heat to 1000~1100℃, then introduce argon as a carrier gas, hydrogen as a dilution gas, and trichloromethylsilane as a carbon source. A silicon carbide matrix is ​​generated on the surface of the silicon nitride matrix through a reaction, filling the pores between the carbon fiber bundles in the composite material, resulting in a density of 1.9~2.1 g / cm³. 3 And near-zero expansion C / Si3N4-SiC composite materials with an open porosity of 8~15 vol.%.

[0057] The number of single filaments in the continuous carbon fiber bundle described in step 1 includes, but is not limited to, 1K, 3K, 6K, or 12K. When the number of single filaments in the continuous carbon fiber bundle is 1K, 3K, 6K, or 12K, the fiber bundle is completely wrapped by adjusting the deposition time of the silicon nitride matrix.

[0058] In step 1, the plain weave carbon fiber cloth woven from continuous carbon fiber bundles is laminated and then sewn together along the thickness direction with continuous carbon fiber bundles to obtain 2D lay-up, 2.5D weaving and 3D weaving shaped structures.

[0059] Carbon fiber preform structures include, but are not limited to, 2D carbon fiber preforms, 2.5D carbon fiber preforms, and 3D woven carbon fiber preforms.

[0060] Among them, the 2D carbon fiber preform is made by weaving continuous carbon fiber bundles into plain weave carbon fiber cloth, then cutting the fiber cloth into a certain size and stacking it, then clamping it with a mold and sewing it with carbon fiber bundles along the stacking direction of the carbon fiber cloth to finally obtain the 2D carbon fiber preform.

[0061] The 2.5D carbon fiber preform and the 3D woven carbon fiber preform are made by machine weaving.

[0062] When the carbon fiber preform is a 2D carbon fiber preform, a 2.5D carbon fiber preform, or a 3D three-dimensional woven carbon fiber preform, the fiber bundles are completely wrapped by adjusting the deposition time of the silicon nitride matrix.

[0063] The third aspect of this invention provides an application of near-zero expansion C / Si3N4-SiC composite material in space optomechanical structural components.

[0064] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0065] Example 1

[0066] This embodiment uses T300 carbon fibers with a fiber bundle size of 1K to prepare a near-zero expansion C / Si3N4-SiC composite material, specifically including the following steps:

[0067] (1) Preparation of carbon fiber preform: T300 carbon fiber bundles with a fiber monofilament quantity of 1K are woven into plain weave fiber cloth, and then cut into dimensions of length × width = 170mm × 110mm. 20 layers are stacked, and then 1K T300 continuous carbon fiber bundles are sewn along the thickness direction of the stack. Finally, graphite clamps are used to fix it to obtain a 2D carbon fiber preform.

[0068] (2) Preparation of pyrolytic carbon interface layer: The 2D carbon fiber preform prepared in step (1) is placed in a deposition furnace with a pressure of 5 kPa and a temperature of 900 °C. Argon gas with a flow rate of 3 L / min and propylene gas with a flow rate of 3 L / min are introduced. The deposition time is 3 h, and a pyrolytic carbon interface layer of 200 nm is obtained on the surface of the fiber bundle. Then, it is heat-treated at 1800 °C for 2 h.

[0069] (3) Preparation of the matrix: The heat-treated carbon fiber preform prepared in step (2) was placed in a deposition furnace, evacuated to a pressure of 5 kPa and heated to 850 °C, and then argon gas with a flow rate of 3 L / min, hydrogen gas with a flow rate of 8 L / min, silicon tetrachloride gas with a flow rate of 4 L / min and ammonia gas with a flow rate of 3 L / min were introduced. The deposition time was 80 h to prepare a porous C / Si3N4 composite material; then the porous C / Si3N4 composite material was applied. The composite material was placed in a deposition furnace, evacuated to a pressure of 5 kPa, and heated to 1100 °C. Argon gas was then introduced at a flow rate of 3 L / min, followed by hydrogen gas at a flow rate of 5 L / min. Trichloromethylsilane was also introduced, with a molar ratio of trichloromethylsilane to hydrogen of 1:10. The deposition time was 320 h. A silicon carbide matrix was formed on the surface of the silicon nitride matrix through a reaction, filling the pores between the fiber bundles in the composite material, resulting in a density of 2.06 ± 0.80 g / cm³. 3 C / Si3N4-SiC composite material with an open porosity of 9±1%.

[0070] It should be noted that the C / Si3N4-SiC composite material prepared according to Example 1 has an average coefficient of thermal expansion of 0.03 × 10⁻⁶ in the temperature range of -80 to 50 °C. -6 K -1 The absolute value of the thermal expansion coefficient of the composite material is less than 0.1 × 10⁻⁶. -6 K -1 This achieved the goal of near-zero inflation.

[0071] Example 2

[0072] This embodiment uses T700 carbon fibers with a fiber bundle size of 3K to prepare a near-zero expansion C / Si3N4-SiC composite material, specifically including the following steps:

[0073] (1) Preparation of fiber preform: T700 carbon fiber bundles with a fiber monofilament quantity of 3K are woven into plain weave fiber cloth, then cut into length × width = 150mm × 100mm, and stacked in 16 layers. Then, T300 continuous carbon fiber bundles with 1K are sewn along the thickness direction of the stack. Finally, graphite clamps are used to fix it to obtain 2D carbon fiber preform.

[0074] (2) Interface preparation: The 2D carbon fiber preform prepared in step (1) was placed in a deposition furnace with a pressure of 5 kPa and a temperature of 900 °C. Argon gas with a flow rate of 3 L / min and propylene gas with a flow rate of 3 L / min were introduced. The deposition time was 3 h. A pyrolytic carbon interface layer of 200 nm was obtained on the surface of the fiber bundle. Then, it was heat-treated at 1900 °C for 1 h.

[0075] (3) Si3N4 matrix layer deposition: The carbon fiber preform prepared in step (2) is placed in a deposition furnace, vacuumed to a pressure of 5KPa and heated to 850℃, and then argon gas with a flow rate of 3L / min, hydrogen gas with a flow rate of 8L / min, silicon tetrachloride gas with a flow rate of 4L / min and ammonia gas with a flow rate of 3L / min are introduced. The deposition time is 120h to prepare C / Si3N4 porous composite material.

[0076] (4) SiC matrix deposition: The porous C / Si3N4 composite material prepared in step (3) was placed in a deposition furnace, evacuated to a pressure of 5 kPa and heated to 1100 °C, and then argon gas with a flow rate of 3 L / min and hydrogen gas with a flow rate of 5 L / min were introduced. Trichloromethylsilane was introduced, and the molar mass ratio of trichloromethylsilane to hydrogen was 1:10. The deposition time was 280 h. A silicon carbide matrix was generated on the surface of the silicon nitride matrix through reaction, which filled the pores between the fiber bundles in the composite material, resulting in a density of 2.01 ± 0.42 g / cm³. 3 C / Si3N4-SiC composite material with an open porosity of 10±1%.

[0077] It should be noted that the C / Si3N4-SiC composite material prepared according to Example 2 has an average coefficient of thermal expansion of 0.07 × 10⁻⁶ in the temperature range of -80 to 50 °C. -6 K -1 The absolute value of the thermal expansion coefficient of the composite material is less than 0.1 × 10⁻⁶. -6 K -1 This achieved the goal of near-zero inflation.

[0078] Example 3

[0079] This embodiment uses a 3D 4d carbon fiber preform to prepare a near-zero expansion C / Si3N4-SiC composite material, specifically including the following steps:

[0080] (1) Preparation of fiber preform: T300 carbon fiber bundles with a fiber monofilament quantity of 1K are interwoven in space by machine to form a three-dimensional four-way (3D4d) carbon fiber preform with the following dimensions: length × width × height = 100mm × 100mm × 5mm.

[0081] (2) Preparation of pyrolytic carbon interface layer: The 3D4d carbon fiber preform prepared in step (1) was placed in a deposition furnace with a pressure of 5KPa and a temperature of 900℃. Argon gas with a flow rate of 3L / min and propylene gas with a flow rate of 3L / min were introduced. The deposition time was 1.5h, and a 100nm pyrolytic carbon interface layer was obtained on the surface of the fiber bundle. Then, it was heat-treated at 1800℃ for 2h.

[0082] (3) Preparation of the matrix: The heat-treated carbon fiber preform prepared in step (2) was placed in a deposition furnace, evacuated to a pressure of 5 kPa and heated to 800 °C, and then argon gas with a flow rate of 3 L / min, hydrogen gas with a flow rate of 8 L / min, silicon tetrachloride gas with a flow rate of 4 L / min and ammonia gas with a flow rate of 3 L / min were introduced. The deposition time was 160 h to prepare a porous C / Si3N4 composite material; then the porous C / Si3N4 composite material was applied. The composite material was placed in a deposition furnace, evacuated to a pressure of 5 kPa, and heated to 1100 °C. Argon gas was then introduced at a flow rate of 3 L / min, followed by hydrogen gas at a flow rate of 5 L / min. Trichloromethylsilane was also introduced, with a molar ratio of trichloromethylsilane to hydrogen of 1:10. The deposition time was 300 h. A silicon carbide matrix was formed on the surface of the silicon nitride matrix through a reaction, filling the pores between the fiber bundles in the composite material, resulting in a density of 2.10 ± 0.80 g / cm³. 3 C / Si3N4-SiC composite material with an open porosity of 9±1%.

[0083] It should be noted that the C / Si3N4-SiC composite material prepared according to Example 3 has an average coefficient of thermal expansion of 0.02 × 10⁻⁶ in the temperature range of -80 to 50 °C. -6 K -1 The absolute value of the thermal expansion coefficient of the composite material is less than 0.1 × 10⁻⁶. -6 K -1 This achieved the goal of near-zero inflation.

[0084] Compare with Example 1

[0085] This comparative example uses T300 carbon fibers with a fiber bundle size of 1K to prepare a near-zero expansion C / SiC composite material, specifically including the following steps:

[0086] (1) Preparation of carbon fiber preform: T300 carbon fiber bundles with a fiber monofilament quantity of 1K are woven into plain fiber cloth, then cut into a size of 170mm×110mm, and 20 layers are stacked. Then, 1K T300 continuous carbon fiber bundles are sewn along the thickness direction of the stack. Finally, graphite clamps are used to fix it to obtain 2D carbon fiber preform.

[0087] (2) Preparation of pyrolytic carbon interface layer: The 2D carbon fiber preform prepared in step (1) is placed in a deposition furnace with a pressure of 5 kPa and a temperature of 900 °C. Argon gas with a flow rate of 3 L / min and propylene gas with a flow rate of 3 L / min are introduced. The deposition time is 3 h, and a pyrolytic carbon interface layer of 200 nm is obtained on the surface of the fiber bundle. Then, it is heat-treated at 1800 °C for 2 h.

[0088] (3) Preparation of the matrix: The heat-treated carbon fiber preform prepared in step (2) was placed in a deposition furnace, evacuated to a pressure of 5 kPa and heated to 1100 °C, and then argon gas with a flow rate of 3 L / min and hydrogen gas with a flow rate of 5 L / min were introduced. Trichloromethylsilane was also introduced, with a molar mass ratio of trichloromethylsilane to hydrogen of 1:10. The deposition time was 400 h. A silicon carbide matrix was generated on the surface of the fiber bundle through reaction, resulting in a density of 2.12 ± 0.50 g / cm³. 3 C / Si3N4-SiC composite material with an open porosity of 10±1%.

[0089] It should be noted that the C / SiC composite material prepared according to Comparative Example 1 has an average coefficient of thermal expansion of 0.93 × 10⁻⁶ in the temperature range of -80 to 50 °C. -6 K -1 Compared to Control Example 1, in Example 1, the coefficient of thermal expansion decreased to 0.03 × 10⁻⁶ after depositing silicon nitride within the fiber bundle for 80 hours. -6 K -1 This means that near-zero inflation has been achieved.

[0090] To illustrate the relevant properties of the C / Si3N4-SiC composite material provided by this invention, the accompanying drawings are provided.

[0091] Figure 1 The images shown are scanning electron microscope (SEM) images and EDS images of the C / Si3N4-SiC composite material prepared in Example 1.

[0092] from Figure 1 The SEM images show that the material consists of carbon fiber bundles, a silicon nitride matrix, and a silicon carbide matrix, with numerous cracks present in the matrix within the fiber bundles; from Figure 1 EDS analysis shows that nitrogen elements encapsulate carbon elements, indicating that the silicon nitride matrix completely encapsulates the carbon fiber bundles, and there is a certain thickness of silicon nitride matrix between the fiber monofilaments outside the fiber bundles and the silicon carbide matrix.

[0093] Figure 2 This is a schematic diagram of the expansion properties of the C / Si3N4-SiC composite material prepared in Example 1 in the temperature range of -80~50℃, where a is the linear expansion curve and b is the expansion coefficient curve as a function of temperature.

[0094] from Figure 2 As can be seen from a, the linear expansion of the composite material first decreases and then increases, with a gradual trend. From Figure 2 As can be seen from b, the material has a low coefficient of thermal expansion. The average coefficient of thermal expansion within the temperature range of -80 to 50℃ is 0.03 × 10⁻⁶. -6 K -1 The absolute value of the thermal expansion coefficient of the composite material is less than 0.1 × 10⁻⁶. -6 K -1 This achieved the goal of near-zero inflation.

[0095] Figure 3 The mechanical property curves of the C / Si3N4-SiC composite material prepared in Example 1 are shown, where a is the bending stress-strain curve and b is the fracture toughness-displacement curve.

[0096] After testing, the C / Si3N4-SiC composite material prepared in Example 1 showed a flexural strength of 329±5 MPa and a fracture toughness of 22.3±1.4 MPa / m. 2 .

[0097] Figure 4 This is a schematic diagram of the expansion properties of the C / SiC composite material prepared in Comparative Example 1 in the temperature range of -80~50℃, where a is the linear expansion curve and b is the expansion coefficient curve as a function of temperature.

[0098] from Figure 4 As can be seen from a, the linear expansion of the C / SiC composite material gradually increases with increasing temperature. From... Figure 4 As shown in b, the coefficient of thermal expansion of the material gradually increases with increasing temperature. The average coefficient of thermal expansion in the temperature range of -80~50℃ is 0.93×10⁻⁶. -6 K -1 .

[0099] Figure 5 The mechanical property curves of the C / SiC composite material prepared in Comparative Example 1 are shown, where a is the bending stress-strain curve and b is the fracture toughness-displacement curve.

[0100] After testing, the flexural strength of the C / SiC composite material prepared in Comparative Example 1 was 338±8 MPa, and the fracture toughness was 20.3±1.1 MPa / m. 2 .

[0101] Compared to Comparative Example 1, Example 1 introduced a silicon nitride matrix into the fiber bundle via chemical vapor deposition, completely encapsulating the fiber bundle and creating numerous diffusely distributed microcracks within it. This significantly mitigated the thermal mismatch between the fiber bundle and the matrix, ultimately reducing the coefficient of thermal expansion to near zero. Depositing a high-modulus silicon carbide matrix outside the fiber bundle not only confined the microcracks within the fiber bundle but also greatly preserved the mechanical properties; the flexural strength decreased only from 338±8 MPa in Comparative Example 1 to 329±5 MPa in Example 1. Compared to a prior art near-zero expansion carbon fiber reinforced multi-element multilayer matrix composite material, the preparation cycle was also reduced from 4-5 months to 2-3 months.

[0102] In summary, the composite material provided by this invention includes a carbon fiber bundle, a pyrolytic carbon interface layer on the surface of the carbon fiber bundle, a silicon nitride matrix layer completely encapsulating the carbon fiber bundle, and a silicon carbide matrix layer outside the carbon fiber bundle. The silicon nitride matrix layer completely encapsulating the carbon fiber bundle is characterized by the presence of only silicon nitride matrix between the individual fibers inside the carbon fiber bundle, and a silicon nitride matrix with a thickness of 0.5~5μm between the individual fibers at the edge of the carbon fiber bundle and the silicon carbide matrix. This invention achieves near-zero expansion by controlling the deposition time of the silicon nitride matrix, allowing the silicon nitride matrix to completely encapsulate the carbon fiber bundle and forming diffusely distributed microcracks within the fiber bundle.

[0103] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0104] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a near-zero expansion C / Si3N4-SiC composite material, characterized in that, The method comprises the following steps: weaving continuous carbon fiber bundles into carbon fiber preforms with a fiber volume fraction of ≥38% in different structures; placing the carbon fiber preform in a vacuum furnace, setting a pressure <300 Pa, a temperature of 800-900℃, and introducing argon and propylene, and holding for 45-200 h to deposit a pyrolytic carbon interface layer on the surface of the carbon fiber preform, and then performing heat treatment at 1200-1900℃ for 1-2 h; placing the carbon fiber preform with the deposited pyrolytic carbon interface layer and after heat treatment, setting a pressure <300 Pa, a temperature of 800-1100℃, and introducing argon, hydrogen, silicon tetrachloride and ammonia, and adjusting the deposition time to completely wrap the carbon fiber bundle with the silicon nitride matrix to obtain a carbon fiber reinforced silicon nitride-based porous composite material; placing the carbon fiber reinforced silicon nitride-based porous composite material in a deposition furnace, setting a pressure <300 Pa, a temperature of 1000-1100℃, and introducing argon, hydrogen and trichloromethylsilane to generate a silicon carbide matrix on the surface of the silicon nitride matrix by reaction, and fill the pores between the carbon fiber bundles, thus obtaining a near-zero expansion C / Si3N4-SiC composite material; the composite material comprises a carbon fiber reinforced silicon nitride-based porous composite material, and a silicon carbide matrix coated on the surface of the carbon fiber reinforced silicon nitride-based porous composite material; the carbon fiber reinforced silicon nitride-based porous composite material comprises a carbon fiber preform woven from carbon fiber bundles; a pyrolytic carbon interface layer is deposited on the carbon fiber bundles in the carbon fiber preform; and a silicon nitride matrix is coated on the pyrolytic carbon interface layer; the carbon fiber bundles contain a silicon nitride matrix between the fiber filaments; the fiber filaments at the edge of the carbon fiber bundle contain a silicon nitride matrix with a thickness of 0.5-5 μm between the silicon carbide matrix; the thickness of the pyrolytic carbon interface layer is 100-500 nm; and the thickness of the silicon carbide matrix layer outside the carbon fiber bundle is 0.02-0.3 mm; the diameter of the fiber filaments in the carbon fiber bundle is 4-8 μm; the number of the fiber filaments in the carbon fiber bundle is 1K, 3K, 6K or 12K; and the carbon fiber in the carbon fiber bundle is a T series fiber; the carbon fiber preform comprises a 2D carbon fiber preform, a 2.5D carbon fiber preform or a 3D woven carbon fiber preform; The density of the composite material is 1.9~2.1g / cm 3 , the open porosity is 8~15vol.%; the absolute value of the thermal expansion coefficient of the composite material in the temperature range of -100~100℃ is less than 0.1×10 -6 K -1 .

2. The method of claim 1, wherein the near-zero expansion C / Si3N4-SiC composite material is prepared by the steps of: mixing a carbon source and a silicon source to form a mixture; and sintering the mixture to form the near-zero expansion C / Si3N4-SiC composite material. when depositing the pyrolytic carbon interface layer on the surface of the carbon fiber preform, the flow rate of the introduced argon is 2-4 L / min, and the flow rate of the introduced propylene is 2-4 L / min.

3. The method of claim 1, wherein the near-zero expansion C / Si3N4-SiC composite material is prepared by the steps of: mixing a carbon source and a silicon source to form a mixture; and sintering the mixture to form the near-zero expansion C / Si3N4-SiC composite material. when preparing the C / Si3N4 porous composite material, the flow rate of the introduced argon is 2-4 L / min, the flow rate of the introduced hydrogen is 7-9 L / min, the flow rate of the introduced silicon tetrachloride is 3-5 L / min, and the flow rate of the introduced ammonia is 2-4 L / min.

4. The method of claim 1, wherein the near-zero expansion C / Si3N4-SiC composite material is prepared by the steps of: mixing a carbon source and a silicon source to form a mixture; and sintering the mixture to form the near-zero expansion C / Si3N4-SiC composite material. when generating the silicon carbide matrix on the surface of the silicon nitride matrix by reaction, the flow rate of the introduced argon is 2-4 L / min; the flow rate of the introduced hydrogen is 4-6 L / min; and the molar mass ratio of the hydrogen to the trichloromethylsilane is 10:

1.

5. Application of a near-zero expansion C / Si3N4-SiC composite material prepared by the method of any one of claims 1-4 to a space optical machine structure.

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