A variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density and its preparation method

Abstract

The present invention relates to a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density and a preparation method thereof; the steps are as follows: a carbon fiber preform with an increasing fiber volume density in the thickness and length directions is prepared by using two-dimensional carbon fiber cloth and carbon fibers; the carbon fiber preform is immersed in a solvent, heated, dried and heat-treated; the sealed container is evacuated, low-viscosity liquid polycarbosilane is sucked into the sealed container, and the liquid polycarbosilane covers the carbon fiber preform, and a pretreated part is obtained after impregnation; the pretreated part is dried at room temperature and kept at 400 °C under 1-20 MPa for 4-24 h to obtain a first intermediate; the first intermediate is placed in a vacuum or inert atmosphere and sintered at a temperature of 800-2000 °C for 2-10 h to obtain a second intermediate; the second intermediate is slowly pyrolyzed at a temperature of 200-800 °C for 1-5 h to obtain a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic matrix composite material preparation, and particularly to a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density and a preparation method thereof. Background Art

[0002] With the further development of new hypersonic aircraft, under the urgent demand for high-performance and lightweight materials for components such as the leading edge of the wing, nose cone, windward side of the fuselage, and nozzle that serve in extremely harsh environments such as long-term flight, high-altitude flight, and engine propulsion systems of the aircraft, variable-density carbon fiber reinforced silicon carbide (C f / SiC) composite materials have shown great advantages in high-performance thermal protection. Variable-density silicon carbide ceramic matrix composite materials are a type of strong covalent bond compound, which fully combines the advantages of carbon fibers and the matrix, and have excellent properties such as low density, corrosion resistance, ablation resistance, high temperature resistance, high strength, and high wear resistance. In the field of high-performance thermal protection composite materials, compared with the existing carbon fiber reinforced carbon matrix composite materials, variable-density carbon fiber reinforced silicon carbide composite materials have good high-temperature ablation resistance. By changing the density of carbon fiber reinforced silicon carbide composite materials, they can have higher thermal protection, ablation resistance, and good mechanical properties, meeting the requirement of material lightweighting. It has become a research hotspot of new high-performance thermal protection composite materials at home and abroad.

[0003] CN201110131837.6 discloses a preparation method of carbon fiber reinforced silicon carbide composite materials, which uses a carbon fiber woven part and a polycarbosilane precursor to carry out multi-round composite production through the production cycle of impregnation, drying, and pyrolysis to obtain continuous carbon fiber reinforced silicon carbide composite materials. A preparation method of carbon fiber reinforced silicon carbide composite materials disclosed in CN201610277281.4 uses 3-30 mm short-cut carbon fibers to be strongly dispersed in a dimethyl sulfoxide solution, and then mixed with a silicon carbide suspension, stirred evenly, and the mixed slurry is placed in a mold for shaping - hot pressing and sintering to obtain carbon fiber reinforced silicon carbide composite materials. However, the above-mentioned carbon fiber reinforced silicon carbide composite materials used are all uniform density materials, which cannot meet the requirements for high-performance thermal protection composite materials in terms of thermal protection, ablation resistance, and good mechanical properties.

[0004] Therefore, in view of the above problems, the present invention urgently needs to provide a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density and a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density and a preparation method thereof. By proposing a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density, the problems of the existing uniform-density carbon fiber reinforced silicon carbide (C fThe technical problem that the (C-SiC) composite material cannot meet the requirements of high-performance thermal protection composite materials in terms of thermal protection, ablation resistance, and good mechanical properties.

[0006] A method for preparing a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density provided by the present invention includes the following steps:

[0007] S1) Using two-dimensional carbon fiber cloth and carbon fiber to prepare a carbon fiber preform with an increasing fiber volume density along the thickness and length directions;

[0008] S2) Immerse the carbon fiber preform in one or a mixture of two solvents of anhydrous ethanol or acetone, keep the pressure and temperature at 0.1 - 10 MPa and 45 - 150 °C for 2 - 24 h, transfer it to an oven, dry it at 50 - 120 °C for 2 - 24 hours, and heat-treat the dried carbon fiber preform at 200 - 800 °C in a vacuum or inert gas atmosphere for 2 - 12 hours;

[0009] S3) Put the heat-treated carbon fiber preform into a sealed container, perform a vacuum treatment on the sealed container to evacuate the air in the sealed container, suck low-viscosity liquid polycarbosilane into the sealed container, and immerse the carbon fiber preform with the liquid polycarbosilane to obtain a pre-treated part;

[0010] S4) Dry the pre-treated part at room temperature for 1 - 48 h, transfer the dried pre-treated part to a curing container, and keep it at 400 °C and 1 - 20 MPa for 4 - 24 h to obtain a first intermediate;

[0011] S5) Place the first intermediate in a vacuum or inert atmosphere and sinter it at a temperature of 800 - 2000 °C for 2 - 10 h to obtain a second intermediate;

[0012] S6) Slowly pyrolyze the second intermediate at a temperature of 200 - 800 °C for 1 - 5 h to obtain a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density.

[0013] Preferably, in step S3, first heat the low-viscosity liquid polycarbosilane to 30 - 80 °C, keep it warm for 30 min - 2 h, suck it into the sealed container, and in the thickness direction, make the liquid polycarbosilane cover 1 / 6 - 5 / 6 of the carbon fiber preform, keep it warm and impregnate for 1 h - 5 h; then heat the low-viscosity liquid polycarbosilane to 80 - 120 °C, keep it warm for 30 min - 2 h, suck it into the sealed container, and make the liquid polycarbosilane completely cover the carbon fiber preform, keep it warm and impregnate for 1 h - 5 h.

[0014] Preferably, the fiber volume density of the variable-density fabric is 0.2 - 1.0 g / cm along the thickness direction 3varies within the range; the fiber volume density of the variable density fabric varies within the range of 0.1-0.7 g / cm at intervals of 20-100 mm along the length direction. 3 varies within the range.

[0015] Preferably, the carbon fiber preform is a two-dimensional carbon fiber cloth and 2-10 strands of carbon fiber, and the variable density carbon fiber preform is woven by mixing any two of the 2.5D weaving, three-dimensional weaving, and needle-punched stitching weaving processes.

[0016] Preferably, at 25 °C, the viscosity of the liquid polycarbosilane is 15-120 mPa·s; the carbon residue rate of the liquid polycarbosilane is 75-81%, and the molecular weight is 1000-2000 g / mol.

[0017] Preferably, the molecular structural formula of the liquid polycarbosilane is

[0018]

[0019] X = 0.1.

[0020] Preferably, steps S3 to S5 are repeated for 8-25 cycles to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite with a high degree of densification.

[0021] Preferably, the thickness of the carbon fiber preform is 3 mm - 80 mm.

[0022] Preferably, the inert gas includes one or more mixed atmosphere environments such as nitrogen, ammonia, and argon.

[0023] The present invention also provides a high-density variable density carbon fiber reinforced silicon carbide ceramic matrix composite obtained by the preparation method of the high-density variable density carbon fiber reinforced silicon carbide ceramic composite as described in any one of the above.

[0024] The high-density variable density carbon fiber reinforced silicon carbide ceramic matrix composite and its preparation method provided by the present invention have the following advantages compared with the prior art:

[0025] 1. The present invention provides a preparation method of a high-density variable density carbon fiber reinforced silicon carbide ceramic matrix composite. The carbon fiber preform is treated with an organic solvent, and then impregnated with a low-viscosity liquid polycarbosilane solution, the carbon fiber preform is cured, the first intermediate is sintered, and the second intermediate is slowly cracked to obtain a high-density carbon fiber reinforced silicon carbide ceramic matrix composite. The obtained ceramic matrix composite has the characteristics of high densification degree, high temperature resistance, ablation resistance, variable density, and light weight, and has excellent application value in the field of new high-performance thermal protection composite materials.

[0026] 2. The present invention provides a method for preparing a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density. By using low-viscosity, liquid polycarbosilane as the silicon carbide precursor, compared with solid polycarbosilane, there is no need to dissolve solid polycarbosilane with organic solvents, which can significantly reduce the porosity of the carbon fiber preform to be processed.

[0027] 3. The present invention provides a method for preparing a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density. By pre-heat treating the carbon fiber preform, the interfacial bonding between the silicon carbide matrix and the carbon fiber can be enhanced, thereby improving the mechanical properties of the composite material.

[0028] 4. The present invention provides a method for preparing a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density. Heat the liquid polycarbosilane, and change the viscosity of the liquid polycarbosilane by temperature, so as to better achieve the impregnation effect on the variable-density carbon fiber preform, and enable the final material to exhibit a significant density gradient, making the high-temperature ablation-resistant material further improved compared with the material with uniform density. Specific Embodiments

[0029] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] A method for preparing a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density provided by the present invention includes the following steps:

[0031] S1) Use two-dimensional carbon fiber cloth and carbon fiber to prepare a carbon fiber preform with an increasing fiber volume density in the thickness and length directions;

[0032] S2) Immerse the carbon fiber preform in one or a mixture of two of anhydrous ethanol or acetone, keep the pressure and temperature at 0.1 - 10 MPa and 45 - 150 °C for 2 - 24 h, transfer it to an oven, dry it at 50 - 120 °C for 2 - 24 hours, and heat-treat the dried carbon fiber preform at 200 - 800 °C in a vacuum or inert gas atmosphere for 2 - 12 hours;

[0033] S3) Put the heat-treated carbon fiber preform into a sealed container, evacuate the sealed container to remove the air inside, suck the low-viscosity liquid polycarbosilane into the sealed container, submerge the carbon fiber preform with the liquid polycarbosilane, and obtain a pre-treated part after impregnation;

[0034] S4) The pre-treated part is dried at room temperature for 1 - 48 h, and the dried pre-treated part is transferred to a curing container, and is heat-insulated at 400 °C under 1 - 20 MPa for 4 - 24 h to obtain a first intermediate;

[0035] S5) The first intermediate is placed in a vacuum or inert atmosphere and sintered at a temperature of 800 - 2000 °C for 2 - 10 h to obtain a second intermediate;

[0036] S6) The second intermediate is slowly pyrolyzed at a temperature of 200 - 800 °C for 1 - 5 h to obtain a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite with high density.

[0037] Specifically, in step S3, first, the low-viscosity liquid polycarbosilane is heated to 30 - 80 °C, heat-insulated for 30 min - 2 h, sucked into a sealed container, and in the thickness direction, the liquid polycarbosilane submerges 1 / 6 - 5 / 6 of the carbon fiber preform, and after heat-insulated impregnation for 1 h - 5 h; then the low-viscosity liquid polycarbosilane is heated to 80 - 120 °C, heat-insulated for 30 min - 2 h, sucked into a sealed container, and the liquid polycarbosilane completely submerges the carbon fiber preform, and heat-insulated impregnation is carried out for 1 h - 5 h.

[0038] Specifically, the fiber volume density of the variable-density fabric varies in the range of 0.2 - 1.0 g / cm 3 in the thickness direction; the fiber volume density of the variable-density fabric varies in the range of 0.1 - 0.7 g / cm 3 every 20 - 100 mm in the length direction.

[0039] Specifically, the carbon fiber preform is a variable-density carbon fiber preform obtained by mixing and weaving a two-dimensional carbon fiber cloth and 2 - 10 strands of carbon fiber by any two of the 2.5D weaving, three-dimensional weaving, and needle stitching weaving processes.

[0040] Specifically, at 25 °C, the viscosity of the liquid polycarbosilane is 15 - 120 mPa·s; the residual carbon rate of the liquid polycarbosilane is 75 - 81%, and the molecular weight is 1000 - 2000 g / mol.

[0041] Specifically, the molecular structural formula of the liquid polycarbosilane is

[0042]

[0043] X = 0.1.

[0044] Specifically, steps S3 to S5 are repeated, and the number of cycles is 8 - 25 times to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite with a higher densification degree.

[0045] Specifically, the thickness of the carbon fiber preform is 3 mm - 80 mm.

[0046] Specifically, the inert gas includes one or more mixed atmosphere environments such as nitrogen, ammonia, and argon.

[0047] The present invention also provides a high-density variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material obtained by a preparation method of a high-density variable-density carbon fiber reinforced silicon carbide ceramic composite material as described in any one of the above.

[0048] The present invention provides a preparation method of a high-density variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material. A carbon fiber preform with an increasing fiber volume density along the thickness and length directions is prepared by using a two-dimensional carbon fiber cloth and carbon fibers. The carbon fiber preform is pretreated with an organic solvent, and then impregnated, cured, sintered at a high temperature for intermediate 1, and pyrolyzed at a low temperature for intermediate 2 with a liquid polycarbosilane solution to obtain a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material. The obtained variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material has the characteristics of high densification degree, high temperature resistance, ablation resistance, variable density, and light weight, and has excellent application value in the field of new high-performance thermal protection composite materials.

[0049] The liquid polycarbosilane selected in the present invention has a low curing temperature, low energy consumption during the production process, low requirements for the production capacity of equipment, and reduces the production cost of the composite material; the liquid polycarbosilane precursor has a high residual carbon rate at high temperatures, which is beneficial to the densification of the composite material, reduces the number of composite production cycles, and reduces the production cost.

[0050] Example 1

[0051] A preparation method of a high-density variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material includes the following steps:

[0052] 101) Use a two-dimensional carbon fiber cloth and carbon fibers to prepare a carbon fiber preform with an increasing fiber volume density along the thickness and length directions; wherein, the carbon fiber preform is made by mixing and weaving a two-dimensional carbon fiber cloth and 2 strands of carbon fibers through two weaving processes of 2.5D and needle punching stitching to form a variable-density carbon fiber preform.

[0053] 102) Immerse the carbon fiber preform in absolute ethanol, keep the pressure and temperature at 0.1 MPa and 45 °C for 2 h, transfer it to an oven, dry it at 50 °C for 2 hours, and heat-treat the dried carbon fiber preform at 500 °C in a vacuum or inert gas atmosphere for 2 hours.

[0054] 103) Put the heat-treated carbon fiber preform into a sealed container, perform a vacuum treatment on the sealed container to evacuate the air in the sealed container, suck low-viscosity liquid polycarbosilane into the sealed container, and immerse the carbon fiber preform with the liquid polycarbosilane to obtain a pretreated part.

[0055] 104) The pre-treated part is dried at room temperature for 1 h. Then the dried pre-treated part is transferred to a curing container and kept at 400 °C and 1 MPa for 4 h to obtain the first intermediate product.

[0056] 105) The first intermediate product is placed in a vacuum or inert atmosphere and sintered at 800 °C for 2 h to obtain the second intermediate product.

[0057] 106) The second intermediate product is slowly pyrolyzed at 500 °C for 1 h to obtain a variable-density carbon fiber reinforced silicon carbide ceramic composite material with high density.

[0058] Specifically, the fiber volume density of the variable-density fabric varies gradually in the range of 0.2 g / cm 3 along the thickness direction; the fiber volume density of the variable-density fabric varies gradually in the range of 0.2 g / cm 3 every 20 mm along the length direction.

[0059] Specifically, at 25 °C, the viscosity of the liquid polycarbosilane is 15 - 120 mPas; the residual carbon rate of the liquid polycarbosilane is 75 - 81%, and the molecular weight is 1000 - 2000 g / mol.

[0060] Specifically, steps 103 to 105 are repeated for 15 cycles to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite material with a relatively high degree of densification.

[0061] Specifically, the inert gas is nitrogen.

[0062] The performance of the obtained variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density is shown in Table 1.

[0063] Example 2

[0064] A method for preparing a variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material with high density, comprising the following steps:

[0065] 201) A carbon fiber preform with increasing fiber volume density along the thickness and length directions is prepared by using a two-dimensional carbon fiber cloth and carbon fibers; wherein, the carbon fiber preform is a variable-density carbon fiber preform fabricated by mixing and weaving a two-dimensional carbon fiber cloth and 10-ply carbon fibers through two weaving processes of 2.5D and needle punching and stitching.

[0066] 202) The carbon fiber preform is immersed in acetone, kept under pressure and at a temperature of 10 MPa and 150 °C for 24 h, then transferred to an oven and dried at 120 °C for 24 h. The dried carbon fiber preform is heat-treated at 800 °C in a vacuum or inert gas atmosphere for 2 - 12 h.

[0067] (203) Place the heat-treated carbon fiber preform into a sealed container, evacuate the sealed container to remove the air inside, suck in low-viscosity liquid polycarbosilane into the sealed container until the liquid polycarbosilane covers the carbon fiber preform, and obtain a pre-treated part after impregnation;

[0068] (204) Dry the pre-treated part at room temperature for 48 h, transfer the dried pre-treated part to a curing container, and keep it at 400 °C and 20 MPa for 24 h to obtain a first intermediate;

[0069] (205) Place the first intermediate in a vacuum or inert atmosphere and sinter it at 2000 °C for 2 - 10 h to obtain a second intermediate;

[0070] (206) Slowly pyrolyze the second intermediate at 800 °C for 5 h to obtain a variable-density carbon fiber reinforced silicon carbide ceramic composite with high density.

[0071] Specifically, the fiber volume density of the variable-density fabric varies in the range of 0.2 - 1.0 g / cm 3 along the thickness direction; the fiber volume density of the variable-density fabric varies in the range of 0.1 - 0.7 g / cm 3 every 20 - 100 mm along the length direction.

[0072] Specifically, the carbon fiber preform is fabricated into a variable-density carbon fiber preform by co-weaving a two-dimensional carbon fiber cloth and 2 - 10 strands of carbon fiber using two weaving processes: 2.5D and needle punching and stitching.

[0073] Specifically, at 25 °C, the viscosity of the liquid polycarbosilane is 15 - 120 mPas; the carbon residue rate of the liquid polycarbosilane is 75 - 81%, and the molecular weight is 1000 - 2000 g / mol.

[0074] Specifically, the molecular structure of the liquid polycarbosilane is

[0075]

[0076] X = 0.1.

[0077] Specifically, repeat steps 203 to 205 for 25 cycles to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite with a higher densification degree.

[0078] Specifically, the thickness of the carbon fiber preform is 50 mm.

[0079] Specifically, the inert gas includes nitrogen, ammonia, and argon.

[0080] The properties of the obtained variable-density carbon fiber reinforced silicon carbide ceramic composite with high density are shown in Table 1.

[0081] Example 3

[0082] A method for preparing a variable-density carbon fiber reinforced silicon carbide ceramic composite material with high density includes the following steps:

[0083] 301) Use two-dimensional carbon fiber cloth and carbon fiber to prepare a carbon fiber preform with increasing fiber volume density in the thickness and length directions; among them, the carbon fiber preform is made of two-dimensional carbon fiber cloth and 6-strand carbon fiber by two knitting processes of 2.5D and needle punching and stitching to produce a variable-density carbon fiber preform;

[0084] 302) Immerse the carbon fiber preform in one or a mixture of two of anhydrous ethanol or acetone, keep the pressure and temperature at 5 MPa and 100 °C for 12 h, transfer it to an oven, dry it at 60 °C for 12 hours, and heat-treat the dried carbon fiber preform in a vacuum or inert gas atmosphere at 600 °C for 8 hours;

[0085] 303) Put the heat-treated carbon fiber preform into a sealed container, perform a vacuum treatment on the sealed container to evacuate the air in the sealed container, suck low-viscosity liquid polycarbosilane into the sealed container, and let the liquid polycarbosilane cover the carbon fiber preform to obtain a pre-treated part after impregnation;

[0086] 304) Dry the pre-treated part at room temperature for 24 h, transfer the dried pre-treated part to a curing container, and keep it at 400 °C and 10 MPa for 12 h to obtain a first intermediate;

[0087] 305) Place the first intermediate in a vacuum or inert atmosphere and sinter it at 1200 °C for 6 h to obtain a second intermediate;

[0088] 306) Slowly pyrolyze the second intermediate at 600 °C for 3 h to obtain a variable-density carbon fiber reinforced silicon carbide ceramic composite material with high density.

[0089] Specifically, the fiber volume density of the variable-density fabric varies in the range of 0.5 g / cm 3 along the thickness direction; the fiber volume density of the variable-density fabric varies in the range of 0.7 g / cm 3 every 50 mm along the length direction.

[0090] Specifically, at 25 °C, the viscosity of the liquid polycarbosilane is 15 - 120 mPas; the residual carbon rate of the liquid polycarbosilane is 75 - 81%, and the molecular weight is 1000 - 2000 g / mol.

[0091] Specifically, the molecular structure of the liquid polycarbosilane is

[0092]

[0093] X = 0.1.

[0094] Specifically, steps 303 to 305 are repeated 20 times to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite with a high degree of densification.

[0095] Specifically, the thickness of the carbon fiber preform is 80 mm.

[0096] Specifically, the inert gas includes nitrogen and ammonia.

[0097] The properties of the obtained variable density carbon fiber reinforced silicon carbide ceramic composite with a high density are shown in Table 1.

[0098] Comparative Example 1

[0099] The difference between this comparative example and Example 1 is only that in step 103, solid polycarbosilane and low-viscosity liquid polycarbosilane are used in combination, and the mass ratio of solid polycarbosilane to low-viscosity liquid polycarbosilane is 1:1.

[0100] The properties of the obtained variable density carbon fiber reinforced silicon carbide ceramic composite are shown in Table 2.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is only that step 106 is omitted.

[0103] The properties of the obtained variable density carbon fiber reinforced silicon carbide ceramic composite are shown in Table 2.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 1 is only that step 102 is omitted.

[0106] The properties of the obtained variable density carbon fiber reinforced silicon carbide ceramic composite are shown in Table 2.

[0107] Table 1 Properties of the composites obtained in Examples 1 to 3

[0108] Project Name Example 1 Example 2 Example 3 <![CDATA[Density / (g / cm 3 )]]> 1.90 2.30 2.05 Tensile Strength / MPa 225 221 243 Flexural Strength / MPa 351 343 378 Interlaminar Shear Strength / MPa 51.2 51.2 52.5 Linear Ablation Rate / (mm / s) 0.0165 0.0097 0.0130 Mass Ablation Rate / (g / s) 0.0301 0.0152 0.0291 Open-Pore Porosity / % 5.92 5.31 5.45

[0109] Table 2 Properties of the composites obtained in Comparative Examples 1 to 4

[0110] Project Name Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[Density / (g / cm 3 )]]> 1.98 1.90 1.91 Tensile Strength / MPa 219 192 199 Flexural Strength / MPa 309 302 305 Interlaminar Shear Strength / MPa 48.2 47.3 46.6 Linear Ablation Rate / (mm / s) 0.0143 0.0207 0.0191 Mass Ablation Rate / (g / s) 0.0293 0.0352 0.0326 Open-Pore Porosity / % 7.28 6.51 5.12

[0111] Comparing Table 1 and Table 2, in Comparative Example 1, solid polycarbosilane and low-viscosity liquid polycarbosilane are used in combination. Compared with the technical solution of Example 1, the porosity is high. By using low-viscosity liquid polycarbosilane as the silicon carbide precursor instead of solid polycarbosilane, there is no need to dissolve solid polycarbosilane with organic solvents, which can significantly reduce the porosity of the carbon fiber preform to be treated.

[0112] Comparing Table 1 and Table 2, compared with Example 1, Comparative Example 2 cancels the high-temperature slow pyrolysis process, resulting in low density and a decline in overall mechanical properties.

[0113] Comparing Table 1 and Table 2, compared with Example 1, Comparative Example 3 omits the heat treatment process, and the overall mechanical properties decline. In Example 1, by pre-heat treating the carbon fiber preform, the interfacial bonding between the silicon carbide matrix and the carbon fiber can be enhanced, thereby improving the mechanical properties of the composite material.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material, characterized in that: The steps include: S1) preparing a carbon fiber preform with increasing fiber volume density along thickness and length directions using a two-dimensional carbon fiber cloth and carbon fiber; S2) immersing the carbon fiber preform in one or a mixed solvent of anhydrous ethanol or acetone, maintaining pressure and heat preservation at 0.1-10 MPa and 45-150° C. for 2-24 hours, transferring to an oven, drying at 50-120° C. for 2-24 hours, and heat-treating the dried carbon fiber preform at 200-800° C. in a vacuum or inert gas atmosphere for 2-12 hours; S3) placing the heat-treated carbon fiber preform into a sealed container, performing a vacuum treatment on the sealed container to exhaust the air in the sealed container, and sucking low-viscosity liquid polycarbosilane into the sealed container, wherein the liquid polycarbosilane covers the carbon fiber preform, and a pretreated piece is obtained after impregnation; S4) drying the pretreated part at room temperature for 1-48 hours, transferring the dried pretreated part to a curing container, and keeping the temperature at 400° C. and 1-20 MPa for 4-24 hours to obtain a first intermediate; S5) placing the first intermediate in a vacuum or inert atmosphere and sintering at a temperature of 800-2000° C. for 2-10 h to obtain a second intermediate; S6) slowly pyrolyzing the second intermediate at a temperature of 200-800° C. for 1-5 hours to obtain a variable-density carbon fiber reinforced silicon carbide ceramic-based composite material with high density.

2. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: In step S3, first heat the low-viscosity liquid polycarbosilane to 30-80°C, keep it warm for 30min-2h, and suck it into a sealed container. In the thickness direction, the liquid polycarbosilane is allowed to cover 1 / 6-5 / 6 of the carbon fiber preform, and the preform is kept warm for 1h-5h. Then heat the low-viscosity liquid polycarbosilane to 80-120°C, keep it warm for 30min-2h, and suck it into a sealed container. Make the liquid polycarbosilane completely cover the carbon fiber preform, and keep it warm for 1h-5h.

3. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: The fiber volume density of variable density fabrics is 0.2-1.0g / cm along the thickness direction. 3 The fiber volume density of the variable density fabric varies gradually within the range of 0.1-0.7 g / cm2 every 20-100 mm along the length direction. 3 changes within the range of.

4. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: The carbon fiber preform is a variable density carbon fiber preform obtained by mixing two-dimensional carbon fiber cloth and 2-10 strands of carbon fiber through any two of 2.5D weaving, three-dimensional weaving and needle-punching stitching weaving processes.

5. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: At 25°C, the viscosity of liquid polycarbosilane is 15-120 mPa·s; the residual carbon rate of liquid polycarbosilane is 75-81%, and the molecular weight is 1000-2000 g / mol.

6. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: The molecular structure of liquid polycarbosilane is X＝0.1。 7. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: Repeat step S3 to step S5 for 8-25 times to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite material with a high degree of densification.

8. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: The thickness of the carbon fiber preform is 3mm-80mm.

9. The method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to claim 1, characterized in that: The inert gas includes one or more mixed atmospheres such as nitrogen, ammonia and argon.

10. A high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material obtained based on the method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material according to any one of claims 1 to 9.

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