High-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material and preparation method thereof

Abstract

The invention relates to a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material and a preparation method thereof. The method comprises the following steps: preparing a carbon fiber preform of which the fiber volume density is gradually increased along the thickness and length directions by adopting two-dimensional carbon fiber cloth and carbon fibers; immersing the carbon fiber preform in a solvent, heating, drying and carrying out heat treatment; the sealed container is vacuumized, low-viscosity liquid polycarbosilane is sucked into the sealed container, the liquid polycarbosilane submerges the carbon fiber preform, and a pretreated part is obtained after impregnation; drying the pretreated part at room temperature, and preserving heat for 4-24 hours at 400 DEG C and 1-20 MPa to obtain a first intermediate; placing the first intermediate in a vacuum or inert atmosphere, and sintering at 800-2000 DEG C for 2-10 h to obtain a second intermediate; and slowly cracking the second intermediate at the temperature of 200-800 DEG C for 1-5 hours to obtain the variable-density carbon fiber reinforced silicon carbide ceramic-based composite material with high density.

Description

Technical Field

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

[0002] With the further development of new hypersonic aircraft, there is an urgent need for high-performance and lightweight materials for wing leading edge, nose cone, windward surface of fuselage, nozzle and other parts that serve in extremely harsh environments such as long-term flight, high-altitude flight and engine propulsion system. f / SiC) composites have shown great advantages in high-performance thermal protection. Variable-density silicon carbide ceramic-based composites are a type of strong covalent bond compound that fully combines the advantages of carbon fiber and matrix, and has 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 composites, compared with the existing carbon fiber reinforced carbon-based composites, variable-density carbon fiber reinforced silicon carbide composites have good high-temperature ablation resistance. By changing the density of carbon fiber reinforced silicon carbide composites, it has higher thermal protection, ablation and good mechanical properties, and meets the requirements of lightweight materials. It has become a research hotspot for new high-performance thermal protection composites at home and abroad.

[0003] 201110131837.6 discloses a method for preparing a carbon fiber reinforced silicon carbide composite material, which uses a carbon fiber woven piece and a polycarbosilane precursor to obtain a continuous carbon fiber reinforced silicon carbide composite material through multiple rounds of compound production cycles of impregnation, drying and cracking. 201610277281.4 discloses a method for preparing a carbon fiber reinforced silicon carbide composite material, which uses 3-30mm short-cut carbon fiber 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 a carbon fiber reinforced silicon carbide composite material. However, the above-mentioned carbon fiber reinforced silicon carbide composite materials are all uniform density materials, which cannot meet the requirements of high-performance thermal protection composite materials in terms of thermal protection, ablation 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-based 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 high-density variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material and a preparation method thereof, and to solve the problem of existing uniform-density carbon fiber reinforced silicon carbide ceramic matrix composite material by proposing a high-density variable-density carbon fiber reinforced silicon carbide ceramic matrix composite material. f / C-SiC) composites cannot meet the technical requirements of high-performance thermal protection composites in terms of thermal protection, ablation and good mechanical properties.

[0006] The present invention provides a method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material, comprising the following steps:

[0007] 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;

[0008] 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;

[0009] 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;

[0010] 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;

[0011] 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;

[0012] 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.

[0013] Preferably, in step S3, the low-viscosity liquid polycarbosilane is first heated to 30-80°C, kept warm for 30min-2h, and sucked into a sealed container so that the liquid polycarbosilane covers 1 / 6-5 / 6 of the carbon fiber preform in the thickness direction, and the preform is kept warm for 1h-5h; then the low-viscosity liquid polycarbosilane is heated to 80-120°C, kept warm for 30min-2h, and sucked into a sealed container so that the liquid polycarbosilane completely covers the carbon fiber preform, and the preform is kept warm for 1h-5h.

[0014] Preferably, the fiber volume density of the variable density fabric is 0.2-1.0 g / cm 3The 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.

[0015] Preferably, 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.

[0016] Preferably, 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.

[0017] Preferably, the molecular structure of 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-based composite material with a high degree of densification.

[0021] Preferably, the carbon fiber preform has a thickness of 3 mm to 80 mm.

[0022] Preferably, the inert gas includes one or more mixed atmospheres of nitrogen, ammonia and argon.

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

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

[0025] 1. The present invention provides a method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material, wherein a carbon fiber preform is treated with an organic solvent, and then the carbon fiber preform is 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, thereby obtaining a high-density carbon fiber reinforced silicon carbide ceramic-based composite material. The obtained ceramic-based composite material has the characteristics of high densification, 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 high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material. By selecting low-viscosity, liquid polycarbosilane as a silicon carbide precursor, compared with solid polycarbosilane, there is no need to use an organic solvent to dissolve the solid polycarbosilane, 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 high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material. By pre-heat treating the carbon fiber preform, the interface 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 high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material. Liquid polycarbosilane is heated and the viscosity of the liquid polycarbosilane is changed by temperature, so as to better achieve the impregnation effect of the variable-density carbon fiber preform, and the final material can present a significant density gradient, so that the high-temperature ablation-resistant material is further improved compared to the material with uniform density. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The present invention provides a method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material, comprising the following steps:

[0031] 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;

[0032] 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;

[0033] 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;

[0034] 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;

[0035] 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;

[0036] 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.

[0037] Specifically, in step S3, the low-viscosity liquid polycarbosilane is first heated to 30-80°C, kept warm for 30min-2h, and sucked into a sealed container, so that the liquid polycarbosilane covers 1 / 6-5 / 6 of the carbon fiber preform in the thickness direction, and kept warm for 1h-5h; then the low-viscosity liquid polycarbosilane is heated to 80-120°C, kept warm for 30min-2h, and sucked into a sealed container, so that the liquid polycarbosilane completely covers the carbon fiber preform, and kept warm for 1h-5h.

[0038] Specifically, the fiber volume density of the variable density fabric is 0.2-1.0 g / 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.

[0039] Specifically, 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.

[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 structure of liquid polycarbosilane is

[0042]

[0043] X=0.1.

[0044] Specifically, step S3 to step S5 are repeated for 8-25 times to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite material with a high degree of densification.

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

[0046] Specifically, the inert gas includes one or more mixed atmospheres of nitrogen, ammonia, and argon.

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

[0048] The present invention provides a method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material, which comprises the following steps: using two-dimensional carbon fiber cloth and carbon fiber to prepare a carbon fiber preform with increasing fiber volume density along the thickness and length directions, using an organic solvent to pretreat the carbon fiber preform, and then using a liquid polycarbosilane solution to impregnate and cure the carbon fiber preform, subjecting an intermediate 1 to high-temperature sintering, and subjecting an intermediate 2 to low-temperature cracking, thereby obtaining a variable-density carbon fiber reinforced silicon carbide ceramic-based composite material; the obtained variable-density carbon fiber reinforced silicon carbide ceramic-based composite material has the characteristics of high densification, high-temperature resistance, ablation resistance, variable density, light weight, etc., 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 on 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 temperature, which is beneficial to the densification of the composite material, reduces the number of composite production rounds, and reduces production costs.

[0050] Embodiment 1

[0051] A method for preparing a high-density variable-density carbon fiber reinforced silicon carbide ceramic-based composite material comprises the following steps:

[0052] 101) A carbon fiber preform with increasing fiber volume density along the thickness and length directions is prepared using two-dimensional carbon fiber cloth and carbon fiber; wherein the carbon fiber preform is a variable density carbon fiber preform made by mixing two-dimensional carbon fiber cloth and two strands of carbon fiber through two weaving processes of 2.5D and needle stitching;

[0053] 102) The carbon fiber preform is immersed in anhydrous ethanol, maintained at 0.1 MPa and 45° C. for 2 hours, transferred to an oven, and dried at 50° C. for 2 hours, and the dried carbon fiber preform is heat treated at 500° C. in a vacuum or inert gas atmosphere for 2 hours;

[0054] 103) 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 part is obtained after impregnation;

[0055] 104) drying the pretreated article at room temperature for 1 hour, transferring the dried pretreated article to a curing container, and keeping the temperature at 400° C. and 1 MPa for 4 hours to obtain a first intermediate;

[0056] 105) placing the first intermediate in a vacuum or inert atmosphere and sintering at 800° C. for 2 h to obtain a second intermediate;

[0057] 106) The second intermediate is slowly cracked at 500° C. for 1 hour 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 is 0.2 g / cm 3 The fiber volume density of the variable density fabric changes gradually within the range of 0.2g / cm2 every 20mm along the length direction. 3 changes within the range of.

[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, step 103 to step 105 are repeated for 15 times to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite material with a high degree of densification.

[0061] Specifically, the inert gas is nitrogen.

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

[0063] Embodiment 2

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

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

[0066] 202) The carbon fiber preform is immersed in acetone, maintained at 10 MPa and 150° C. for 24 hours, transferred to an oven, and dried at 120° C. for 24 hours, and the dried carbon fiber preform is heat treated at 800° C. in a vacuum or inert gas atmosphere for 2-12 hours;

[0067] 203) 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;

[0068] 204) drying the pretreated article at room temperature for 48 hours, transferring the dried pretreated article to a curing container, and keeping the temperature at 400° C. and 20 MPa for 24 hours to obtain a first intermediate;

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

[0070] 206) The second intermediate is slowly cracked at 800°C for 5 hours to obtain a variable density carbon fiber reinforced silicon carbide ceramic composite material with high density.

[0071] Specifically, the fiber volume density of the variable density fabric is 0.2-1.0 g / 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.

[0072] Specifically, the carbon fiber preform is made of two-dimensional carbon fiber cloth and 2-10 strands of carbon fiber through two weaving processes of 2.5D and needle stitching to form a variable density carbon fiber preform.

[0073] 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.

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

[0075]

[0076] X=0.1.

[0077] Specifically, step 203 to step 205 are repeated for 25 times to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite material with a high degree of densification.

[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 high-density variable-density carbon fiber reinforced silicon carbide ceramic composite material are shown in Table 1.

[0081] Embodiment 3

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

[0083] 301) A carbon fiber preform with increasing fiber volume density along the thickness and length directions is prepared using two-dimensional carbon fiber cloth and carbon fiber; wherein the carbon fiber preform is a variable density carbon fiber preform made by mixing two-dimensional carbon fiber cloth and 6-strand carbon fiber through two weaving processes of 2.5D and needle stitching;

[0084] 302) The carbon fiber preform is immersed in one or a mixed solvent of anhydrous ethanol or acetone, maintained at 5 MPa and 100°C for 12 hours, transferred to an oven, and dried at 60°C for 12 hours, and the dried carbon fiber preform is heat treated at 600°C in a vacuum or inert gas atmosphere for 8 hours;

[0085] 303) placing the heat-treated carbon fiber preform into a sealed container, evacuating the sealed container to exhaust the air in the sealed container, and sucking low-viscosity liquid polycarbosilane into the sealed container, so that the liquid polycarbosilane covers the carbon fiber preform, and obtaining a pretreated part after impregnation;

[0086] 304) drying the pretreated article at room temperature for 24 hours, transferring the dried pretreated article to a curing container, and keeping the temperature at 400° C. and 10 MPa for 12 hours to obtain a first intermediate;

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

[0088] 306) The second intermediate is slowly cracked at 600°C for 3 hours 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 is 0.5 g / cm 3 The fiber volume density of the variable density fabric changes gradually within the range of 0.7g / cm2 every 50mm along the length direction. 3 changes within the range of.

[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 liquid polycarbosilane is

[0092]

[0093] X=0.1.

[0094] Specifically, step 303 to step 305 are repeated for 20 cycles to obtain a carbon fiber reinforced silicon carbide ceramic matrix composite material 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 high-density variable-density carbon fiber reinforced silicon carbide ceramic composite material are shown in Table 1.

[0098] Comparative Example 1

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

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

[0101] Comparative Example 2

[0102] The difference between this comparative example and the first embodiment is that step 106 is omitted.

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

[0104] Comparative Example 3

[0105] The difference between this comparative example and the first embodiment is that step 102 is omitted.

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

[0107] Table 1 Properties of the composite materials obtained from 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 Bending strength / MPa 351 343 378 Layer shear strength / MPa 51.2 51.2 52.5 Line ablation rate / (mm / s) 0.0165 0.0097 0.0130 Mass ablation rate / (g / s) 0.0301 0.0152 0.0291 Open porosity / % 5.92 5.31 5.45

[0109] Table 2 Properties of the composite materials obtained from 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 Bending strength / MPa 309 302 305 Layer shear strength / MPa 48.2 47.3 46.6 Line ablation rate / (mm / s) 0.0143 0.0207 0.0191 Mass ablation rate / (g / s) 0.0293 0.0352 0.0326 Open porosity / % 7.28 6.51 5.12

[0111] Comparing Table 1 and Table 2, Comparative Example 1 uses a compound of solid polycarbosilane and low-viscosity liquid polycarbosilane. Compared with the technical solution of Example 1, the porosity is high. By selecting low-viscosity, liquid polycarbosilane as the silicon carbide precursor, compared with solid polycarbosilane, there is no need to use an organic solvent to dissolve the solid polycarbosilane, 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 eliminates the slow cracking process at high temperature, has low density, and reduced 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 are reduced. Example 1 can enhance the interface bonding between the silicon carbide matrix and the carbon fiber by pre-heat treating the carbon fiber preform in advance, thereby improving the mechanical properties of its composite material.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, 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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