Short-cut fiber reinforced carbon / silicon carbide matrix composites and their preparation methods

Abstract

This invention relates to the field of fiber-reinforced ceramic matrix composite material preparation technology, and more particularly to a short-fiber reinforced carbon / silicon carbide matrix composite material and its preparation method. This invention uses short-fibers as the reinforcing phase and Si powder and SiO2 powder as the composite Si source. The above components are uniformly dispersed in a phenolic resin solution through a composite process of "mechanical stirring + ultrasonic dispersion." A short-fiber-SiC skeleton with controllable porosity is prepared by precise molding curing and two-stage high-temperature pyrolysis. Finally, a densification process is performed to achieve the target density, resulting in a high-performance short-fiber reinforced carbon / silicon carbide matrix composite material with good dispersibility. The entire process features precise and coordinated process parameters, simple operation, strong controllability, and low cost.

Description

Technical Field

[0001] This invention relates to the field of fiber-reinforced ceramic matrix composite material preparation technology, and in particular to a short-cut fiber-reinforced carbon / silicon carbide matrix composite material and its preparation method. Background Technology

[0002] Carbon / silicon carbide-based composites possess excellent high-temperature resistance, thermal shock resistance, and mechanical properties. Currently, chopped fiber reinforced C / SiC composites have become a research hotspot due to their flexible molding and low cost. However, existing chopped fiber reinforced C / SiC composite preparation technologies generally suffer from several core defects, including a single Si source system, uneven component dispersion, imprecise pyrolysis processes (low temperature, simple curves), uncontrollable pore structure of the skeleton, low densification efficiency, and insufficient performance indicators. These shortcomings make it difficult to meet the demands of high-end equipment for high-performance, low-cost, and large-scale production of materials.

[0003] The core technical route of patent application CN111662091A (Cut Carbon Fiber Reinforced Csf / SiC Ceramic Matrix Composites and Their Preparation Method) is 3D printing of cut carbon fiber + phenolic resin + single Si powder → curing → pyrolysis at 1400~1500℃ → PIP densification. This existing technology has significant technical bottlenecks: First, the use of a single Si source leads to insufficient SiC formation and weak interfacial bonding between the fiber and matrix; second, the process cost is high, with CVI preparation of the SiC matrix and the PIP raw material polycarbosilane being expensive and cost-effective; third, the lack of a targeted dispersion process makes the cut fibers prone to agglomeration, resulting in large fluctuations in product performance. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a short-cut fiber reinforced carbon / silicon carbide-based composite material and a method for preparing the same, which can prepare high-performance short-cut fiber reinforced carbon / silicon carbide-based composite materials.

[0005] This invention provides a method for preparing short-cut fiber reinforced carbon / silicon carbide-based composite materials, comprising the following steps:

[0006] A. Short-cut fibers, composite Si source, and resin solution are mixed, mechanically stirred, and then ultrasonically dispersed to obtain a uniform slurry; the composite Si source includes Si powder and SiO2 powder.

[0007] B. The uniform slurry is molded and cured to obtain a cured blank;

[0008] C. The solidified preform is subjected to two-stage high-temperature pyrolysis under protective gas conditions to obtain a short fiber-SiC skeleton;

[0009] The two-stage high-temperature pyrolysis includes:

[0010] First, heat to 400~600℃ and hold for a period of time; then heat to 1600~1800℃ and hold for a period of time again.

[0011] D. Empty the pores of the short fiber-SiC skeleton, impregnate it in liquid phenolic resin at 2~3 MPa and 70~90℃. After impregnation, cure and heat pyrolysis to obtain short fiber reinforced carbon / silicon carbide-based composite material.

[0012] Preferably, in step A, the mass ratio of Si powder to SiO2 powder is 1:0.5~2.

[0013] Preferably, in step A, the chopped fiber includes at least one of carbon fiber, silicon carbide fiber, and quartz fiber; the chopped fiber has a length of 1-5 mm and a diameter of 5-20 μm.

[0014] The resin includes a thermosetting phenolic resin; the solvent of the resin solution includes ethanol or acetone; the mass concentration of the resin solution is 40% to 60%.

[0015] Preferably, in step A, the mass ratio of the chopped fiber, the composite Si source, and the resin solution is 10~30:20~40:40~70.

[0016] Preferably, in step A, the mechanical stirring speed is 300~500 r / min, and the time is 1~2 h;

[0017] The ultrasonic dispersion power is 220~280 W, the temperature is ≤40℃, and the time is 30~60 min.

[0018] Preferably, in step B, molding and curing the uniform slurry includes:

[0019] The uniform slurry is injected into a mold, kept under pressure at 20~30℃ and 5~10 MPa, and then heated to 150~200℃ for curing.

[0020] Preferably, in step C, the heating rate to 400~600℃ is 2.5~3.5℃ / min; after heating to 400~600℃, the holding time is 0.5~1.5 h;

[0021] The heating rate to 1600~1800℃ is 4~8℃ / min, and the holding time is 1~3 h;

[0022] After the two-stage high-temperature pyrolysis, the process also includes: cooling the furnace to 700~900℃;

[0023] The porosity of the short fiber-SiC skeleton is 35%~40%.

[0024] Preferably, in step D, the method for emptying the pores of the short fiber-SiC skeleton is as follows:

[0025] First, evacuate the short fiber-SiC skeleton to ≤-0.095 MPa and hold the pressure for 30~60 min;

[0026] The soaking time is 1-3 hours;

[0027] The heating rate for the pyrolysis is 4~6℃ / min, the pyrolysis temperature is 1600~2200℃, and the time is 1~2h.

[0028] Preferably, in step D, the pores of the short fiber-SiC skeleton are emptied, and the fiber is impregnated in liquid phenolic resin at 2~3 MPa and 70~90℃. After impregnation, the fiber is cured and then pyrolyzed, which is recorded as one densification cycle.

[0029] After one densification cycle, the process further includes: repeating the densification cycle; the number of repetitions is 3 to 4 times;

[0030] The density of the chopped fiber reinforced carbon / silicon carbide-based composite material is 1.8~2.2 g / cm³. 3 .

[0031] The present invention also provides a short-cut fiber reinforced carbon / silicon carbide-based composite material prepared by the preparation method described above.

[0032] This invention uses chopped fibers as the reinforcing phase and Si powder and SiO2 powder as the composite Si source. The above components are uniformly dispersed in a phenolic resin solution using a "mechanical stirring + ultrasonic dispersion" composite process. A short-fiber-SiC skeleton with controllable porosity is prepared through precise molding curing and two-stage high-temperature pyrolysis. Finally, a densification process is used to achieve the target density, resulting in a high-performance chopped fiber reinforced carbon / silicon carbide-based composite material with good dispersibility. The entire process features precise and coordinated process parameters, simple operation, strong controllability, and low cost. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a method for preparing short-cut fiber reinforced carbon / silicon carbide-based composite materials, comprising the following steps:

[0035] A. Short-cut fibers, composite Si source, and resin solution are mixed, mechanically stirred, and then ultrasonically dispersed to obtain a uniform slurry; the composite Si source includes Si powder and SiO2 powder.

[0036] B. The uniform slurry is molded and cured to obtain a cured blank;

[0037] C. The solidified preform is subjected to two-stage high-temperature pyrolysis under protective gas conditions to obtain a short fiber-SiC skeleton;

[0038] The two-stage high-temperature pyrolysis includes:

[0039] First, heat to 400~600℃ and hold for a period of time; then heat to 1600~1800℃ and hold for a period of time again.

[0040] D. Empty the pores of the short fiber-SiC skeleton, impregnate it in liquid phenolic resin at 2~3 MPa and 70~90℃. After impregnation, cure and heat pyrolysis to obtain short fiber reinforced carbon / silicon carbide-based composite material.

[0041] Regarding step A:

[0042] Short-cut fibers, composite Si source, and resin solution are mixed, mechanically stirred, and then ultrasonically dispersed to obtain a uniform slurry; the composite Si source includes Si powder and SiO2 powder.

[0043] In some embodiments of the present invention, the chopped fibers are at least one of carbon fiber, silicon carbide fiber, and quartz fiber. The length of the chopped fibers is 1 to 5 mm, such as 3 mm or 2 mm; the diameter is 5 to 20 μm, such as 5 to 10 μm, 15 to 20 μm, or 5 to 9 μm.

[0044] In some embodiments of the present invention, the chopped fibers are pretreated chopped fibers. The pretreated chopped fibers are prepared by degumming and drying. The drying temperature is 100~120℃, for example 110℃, 105℃, or 120℃; the drying time is 2~4 h, for example 3 h, 3.5 h, or 2 h. Pretreatment removes surface impurities from the chopped fibers, improves the bonding strength between the chopped fibers and the matrix, and prevents interfacial delamination.

[0045] The composite Si source comprises Si powder and SiO2 powder. The purity of the Si powder is ≥99%, for example, 99%; the particle size is 1~5 μm, for example, 3 μm or 2 μm. The purity of the SiO2 powder is ≥99.5%, for example, 99.5%; the particle size is 0.5~2 μm, for example, 1 μm, 0.5 μm or 0.8 μm. The mass ratio of Si powder to SiO2 powder is 1:0.5~2, for example, 1:1, 1:0.8, or 1:1.2. The composite Si source can promote the continuous formation of the SiC phase through reactions (Si+C→SiC, SiO2+3C→SiC+2CO↑), optimize interfacial bonding, and solve the defect of insufficient SiC formation from a single Si source.

[0046] In some embodiments of the present invention, the resin is a thermosetting phenolic resin with a softening point of 80-100°C. The solvent for the resin solution is ethanol or acetone. The mass concentration of the resin solution is 40%-60%, such as 50%, 55%, or 45%. The viscosity of the resin solution is 600-700 mPa·s, such as 650 mPa·s, 700 mPa·s, or 600 mPa·s.

[0047] In some embodiments of the present invention, the resin solution is a degassed resin solution. The degassed resin solution is prepared by mixing the resin and solvent, followed by allowing it to stand for degassed purposes. The standing time for degassed purposes is 30-60 minutes, for example, 40 minutes. A degassed resin solution helps to prevent the formation of internal defects in the green body.

[0048] In some embodiments of the present invention, the mass ratio of chopped fibers, composite Si source and resin solution is 10~30:20~40:40~70, for example 15:30:55, 20:35:45, 12:28:60.

[0049] In some embodiments of the present invention, the mechanical stirring speed is 300~500 r / min, such as 400 r / min, 450 r / min, or 350 r / min; and the time is 1~2 h, such as 1.5 h, 2 h, or 1 h.

[0050] In some embodiments of the present invention, the ultrasonic dispersion power is 220~280 W, such as 250 W, 280 W, 220 W; the temperature is ≤40℃, such as 35~40℃; and the time is 30~60 min, such as 45 min, 35 min, 50 min.

[0051] This invention employs a mechanical stirring combined with ultrasonic dispersion process, which can achieve uniform dispersion of components and avoid defects such as uneven internal structure and large performance fluctuations in the product.

[0052] Regarding step B:

[0053] The uniform slurry is molded and cured to obtain a cured blank.

[0054] In some embodiments of the present invention, the mold used for compression molding is a graphite mold or a stainless steel mold; when a stainless steel mold is used, a layer of graphite release agent is coated on the inner surface of the stainless steel mold.

[0055] In some embodiments of the present invention, the uniform slurry is specifically subjected to molding and curing as follows:

[0056] The uniform slurry is injected into a mold, kept under pressure at 20~30℃ and 5~10 MPa, and then heated to 150~200℃ for curing.

[0057] The holding temperature is 25℃. The holding pressure is 8 MPa, 10 MPa, or 6 MPa. The holding time is 30~60 min, e.g., 40 min, 30 min, or 50 min. The heating rate is 4~6℃ / min, e.g., 5℃ / min. The curing temperature is 180℃; the curing time is 2~4 h, e.g., 3 h or 4 h.

[0058] After molding and curing, the process also includes cooling and demolding. The cooling rate is 1~3℃ / min, for example, 2℃ / min.

[0059] The molding and curing method in this invention can avoid cracking and deformation of the preform and improve the structural integrity of the subsequent pyrolysis skeleton.

[0060] Regarding step C:

[0061] The solidified preform was subjected to two-stage high-temperature pyrolysis under protective gas conditions to obtain a short-fiber-SiC skeleton.

[0062] In some embodiments of the present invention, the protective gas is an inert gas, such as argon or nitrogen. The flow rate of the protective gas is 50-100 mL / min, for example, 80 mL / min, 100 mL / min, or 60 mL / min.

[0063] The two-stage high-temperature pyrolysis includes:

[0064] First, heat from room temperature to 400~600℃ and hold for a period of time; then heat to 1600~1800℃ and hold for a period of time again.

[0065] The heating rate to 400~600℃ (e.g., 500℃) is 2.5~3.5℃ / min, e.g., 3℃ / min. After heating to 400~600℃ (e.g., 500℃), the holding time is 0.5~1.5 h, e.g., 1 h. Heating from room temperature to 400~600℃ and holding at that temperature can remove small molecules (e.g., CH4, CO, H2, C2H2, and some phenolic derivatives) from the solidified preform.

[0066] The heating rate to 1600~1800℃ (e.g., 1700℃, 1800℃, 1600℃) is 4~8℃ / min, e.g., 7℃ / min, 5℃ / min, 4℃ / min. The holding time after heating is 1~3 h, e.g., 2.5 h, 2 h, 1 h.

[0067] After the two-stage high-temperature pyrolysis, the process further includes cooling the furnace to 700-900℃. Specifically, the temperature can be reduced to 800℃. The cooling rate is 10-20℃ / min, such as 20℃ / min, 13℃ / min, or 10℃ / min.

[0068] In some embodiments of the present invention, the porosity of the short fiber-SiC skeleton is 35% to 40%, such as 38%, 36%, or 37%.

[0069] Unlike existing patents that employ low-temperature pyrolysis at 1200~1500℃ and have simple heating curves, this invention uses two-stage high-temperature pyrolysis, which can promote the full reaction of the composite Si source to generate a continuous SiC phase. At the same time, it can precisely control the porosity of the framework, providing the optimal penetration channel for subsequent PIP densification and solving the problem of difficult densification caused by disordered framework pores in existing technologies.

[0070] Regarding step D:

[0071] The pores of the short fiber-SiC skeleton are emptied, and the fiber is impregnated in liquid phenolic resin at 2~3 MPa and 70~90℃. After impregnation, the fiber is cured and pyrolyzed to obtain a short fiber reinforced carbon / silicon carbide-based composite material.

[0072] In some embodiments of the present invention, the method for purging the pores of the short fiber-SiC skeleton is as follows:

[0073] Place the short fiber-SiC skeleton into the densification equipment, first evacuate to ≤-0.095 MPa, and hold the pressure for 30~60 min to fully empty the pores of the skeleton.

[0074] Specifically, first evacuate to -0.098 MPa, -0.1125 MPa, and -0.096 MPa, and hold the pressure for 40 minutes.

[0075] The densification equipment can be a pressure impregnation tank.

[0076] In some embodiments of the present invention, the soaking time is 1 to 3 hours, such as 1.5 hours or 2 hours.

[0077] Immersion in liquid phenolic resin at 2-3 MPa and 70-90℃ helps the liquid phenolic resin to fully penetrate all the pores of the skeleton. Specifically, the impregnation pressures are 2.8 MPa, 3 MPa, and 2.5 MPa, and the temperatures are 90℃, 75℃, and 70℃.

[0078] In some embodiments of the present invention, the curing temperature is 150~200℃, for example 180℃; and the curing time is 2~3 h, for example 3 h or 2 h.

[0079] In some embodiments of the present invention, the heating rate for pyrolysis is 4~6℃ / min, for example 5℃ / min. The pyrolysis temperature is 1600~2200℃, for example 1800℃, 1950℃, or 1600℃; and the time is 1~2 h, for example 1.5 h.

[0080] In this invention, the pores of the short fiber-SiC skeleton are emptied, and the fiber is impregnated in liquid phenolic resin at 2-3 MPa and 70-90°C. After impregnation, it is cured and then pyrolyzed, which is recorded as one densification cycle. After one densification cycle, the process further includes repeating the densification cycle. The number of repetitions is 3-4 times, for example, 3 or 4 times.

[0081] In some embodiments of the present invention, the density of the short-cut fiber reinforced carbon / silicon carbide-based composite material is 1.8~2.2 g / cm³. 3 For example, 2.02 g / cm³ 3 2.15 g / cm 3 1.95 g / cm 3 .

[0082] This invention employs a composite Si source system, overcoming the limitations of existing single Si source technologies. By synergistically reacting Si powder and SiO2 powder at a mass ratio of 1:0.5~2, the defects of insufficient SiC formation and weak fiber-matrix interface bonding caused by single Si sources are resolved.

[0083] This invention employs a precise dispersion process that combines mechanical stirring and ultrasonic dispersion. The ultrasonic dispersion power is controlled at 220~280W, and the temperature is precisely controlled at ≤40℃, which completely solves the problem of agglomeration of short-cut fibers and Si source, and greatly improves the uniformity of component dispersion.

[0084] This invention breaks through the limitations of traditional low-temperature pyrolysis by adopting a two-stage high-temperature pyrolysis process. It precisely controls the heating, holding, and cooling curves to prepare a high-performance short fiber-SiC skeleton with a porosity of 35%~40%. The pore structure is regular and has good connectivity, providing optimal permeation channels for subsequent densification treatment and significantly improving densification efficiency.

[0085] This invention achieves synergistic optimization of parameters throughout the entire process, from raw material pretreatment, mixing and dispersion, molding and curing, high-temperature pyrolysis to densification. It has strong process adaptability and can be compatible with various reinforcing phases such as carbon fiber, silicon carbide fiber, and quartz fiber. There are no restrictions on the shape of the product, and the production cycle is short and the cost is low. Only 3 to 4 densification cycles are needed to achieve the target density, which fully meets the requirements of large-scale industrial production.

[0086] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0087] The present invention also provides a short-cut fiber reinforced carbon / silicon carbide-based composite material prepared by the preparation method described above.

[0088] This invention overcomes many industry pain points of traditional preparation technology, and achieves significant improvements in both overall performance and production efficiency, demonstrating remarkable technological innovation, industrial applicability, and market competitiveness.

[0089] To further illustrate the present invention, the following detailed description of the short-cut fiber reinforced carbon / silicon carbide-based composite material and its preparation method provided by the present invention is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0090] Example 1

[0091] Raw material preparation:

[0092] After degumming, the short-cut fibers (carbon fibers with a length of 3 mm and a diameter of 5~10 μm) were dried at 110℃ for 3 h to obtain pretreated short-cut fibers.

[0093] The composite Si source consists of Si powder (99% purity, 3 μm particle size) and SiO2 powder (99.5% purity, 1 μm particle size) in a mass ratio of 1:1.

[0094] After mixing thermosetting phenolic resin and ethanol, the mixture was allowed to stand for 40 min to remove bubbles, resulting in a degassed resin solution with a mass concentration of 50% and a viscosity of 650 mPa·s.

[0095] Preparation of chopped fiber reinforced carbon / silicon carbide-based composites:

[0096] 1. The pretreated short-cut fibers, composite Si source and degassed resin solution are mixed at a mass ratio of 15:30:55, mechanically stirred (400 r / min, 1.5h), and then ultrasonically dispersed (250W, temperature controlled at 35~40℃, 45min) to obtain a uniform slurry.

[0097] 2. The uniform slurry is injected into a graphite mold and held under pressure at 25℃ and 8 MPa for 40 min. Then, the temperature is increased to 180℃ at 5℃ / min and cured for 3 h. After molding, the mold is cooled at 2℃ / min and demolded (dimensional deviation ±0.15%) to obtain the cured green body.

[0098] 3. The solidified preform is subjected to a two-stage high-temperature pyrolysis under a protective gas (argon, flow rate of 80 mL / min): first, it is heated from room temperature (rate of 3℃ / min) to 500℃ and held for 1 h; then it is heated (rate of 7℃ / min) to 1700℃ and held for 2.5 h.

[0099] After two-stage high-temperature pyrolysis, the temperature was reduced to 800℃ at 20℃ / min and then cooled in the furnace to obtain a short fiber-SiC skeleton (the skeleton porosity was 38%).

[0100] 4. Place the short fiber-SiC skeleton into a pressure impregnation tank, first evacuate to -0.098MPa, and hold the pressure for 40 minutes to fully empty the pores of the skeleton;

[0101] The sample was impregnated in liquid phenolic resin at 2.8 MPa and 90 °C for 1.5 h. After impregnation, it was cured at 180 °C for 3 h, then heated to 1800 °C at 5 °C / min and pyrolyzed for 2 h, which was recorded as one densification cycle. After repeating the cycle 3 times, a density of 2.02 g / cm³ was obtained. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 102.4 MPa and a flexural modulus of 18.7 GPa.

[0102] Example 2

[0103] Raw material preparation:

[0104] After degumming, the chopped fibers (silicon carbide fibers with a length of 2 mm and a diameter of 15~20 μm) were dried at 105℃ for 3.5 h to obtain pretreated chopped fibers.

[0105] The composite Si source consists of Si powder (99% purity, 2 μm particle size) and SiO2 powder (99.5% purity, 0.5 μm particle size) in a mass ratio of 1:0.8.

[0106] After mixing thermosetting phenolic resin and acetone, the mixture was allowed to stand for 40 minutes to remove bubbles, resulting in a degassed resin solution with a mass concentration of 55% and a viscosity of 700 mPa·s.

[0107] Preparation of chopped fiber reinforced carbon / silicon carbide-based composites:

[0108] 1. The pretreated short-cut fibers, composite Si source and degassed resin solution are mixed at a mass ratio of 20:35:45, mechanically stirred (450 r / min, 2h), and then ultrasonically dispersed (280W, temperature controlled at 35~40℃, 35min) to obtain a uniform slurry.

[0109] 2. The uniform slurry is injected into a graphite mold and held under pressure at 25℃ and 10 MPa for 30 min. Then, the temperature is increased to 180℃ at 5℃ / min and cured for 4 h. After molding, the mold is cooled at 2℃ / min and demolded (dimensional deviation ±0.18%) to obtain the cured green body.

[0110] 3. The solidified preform is subjected to a two-stage high-temperature pyrolysis under a protective gas (nitrogen, flow rate of 100 mL / min): first, it is heated from room temperature (rate of 3℃ / min) to 500℃ and held for 1 h; then it is heated (rate of 5℃ / min) to 1800℃ and held for 2 h.

[0111] After two-stage high-temperature pyrolysis, the temperature was reduced to 800℃ at 13℃ / min and then cooled in the furnace to obtain a short fiber-SiC skeleton (the skeleton porosity was 36%).

[0112] 4. Place the short fiber-SiC skeleton into a pressure impregnation tank, first evacuate to -0.1125MPa, and hold the pressure for 40 minutes to fully empty the pores of the skeleton;

[0113] The sample was impregnated in liquid phenolic resin at 3 MPa and 75 °C for 2 h. After impregnation, it was cured at 180 °C for 2 h, then heated to 1950 °C at 5 °C / min and pyrolyzed for 1.5 h, which was recorded as one densification cycle. After repeating the cycle 4 times, a density of 2.15 g / cm³ was obtained. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 145.8 MPa and a flexural modulus of 23.6 GPa.

[0114] Example 3

[0115] Raw material preparation:

[0116] After degumming, the short-cut fibers (quartz fibers, 2 mm in length and 5-9 μm in diameter) were dried at 120℃ for 2 h to obtain pretreated short-cut fibers.

[0117] The composite Si source consists of Si powder (99% purity, 2 μm particle size) and SiO2 powder (99.5% purity, 0.8 μm particle size) in a mass ratio of 1:1.2.

[0118] After mixing thermosetting phenolic resin and acetone, the mixture was allowed to stand for 40 minutes to remove bubbles, resulting in a degassed resin solution with a mass concentration of 45% and a viscosity of 600 mPa·s.

[0119] Preparation of chopped fiber reinforced carbon / silicon carbide-based composites:

[0120] 1. The pretreated short-cut fibers, composite Si source and degassed resin solution are mixed at a mass ratio of 12:28:60, mechanically stirred (350 r / min, 1h), and then ultrasonically dispersed (220W, temperature controlled at 35~40℃, 50min) to obtain a uniform slurry.

[0121] 2. The uniform slurry is injected into a graphite mold and held under pressure at 25℃ and 6 MPa for 50 min. Then, the temperature is increased to 180℃ at 5℃ / min and cured for 4 h. After molding, the mold is cooled at 2℃ / min and demolded (dimensional deviation ±0.2%) to obtain the cured green body.

[0122] 3. The solidified preform is subjected to a two-stage high-temperature pyrolysis under a protective gas (nitrogen, flow rate of 60 mL / min): first, it is heated from room temperature (rate of 3℃ / min) to 500℃ and held for 1 h; then it is heated (rate of 4℃ / min) to 1600℃ and held for 1 h.

[0123] After two-stage high-temperature pyrolysis, the temperature was reduced to 800℃ at 10℃ / min and then cooled in the furnace to obtain a short fiber-SiC skeleton (the skeleton porosity was 37%).

[0124] 4. Place the short fiber-SiC skeleton into a pressure impregnation tank, first evacuate to -0.096MPa, and hold the pressure for 40 minutes to fully empty the pores of the skeleton;

[0125] The material was impregnated in liquid phenolic resin at 2.5 MPa and 70℃ for 2 h. After impregnation, it was cured at 180℃ for 2 h, then heated to 1600℃ at 5℃ / min and pyrolyzed for 1.5 h, which was recorded as one densification cycle. After repeating the cycle 3 times, a density of 1.95 g / cm³ was obtained. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 92.2 MPa and a flexural modulus of 18.3 GPa.

[0126] Comparative Example 1

[0127] The difference from Example 1 is that the Si source is not a composite Si source, but Si powder;

[0128] That is, replace the SiO2 powder (purity of 99.5% and particle size of 1 μm) in Example 1 with Si powder (purity of 99% and particle size of 3 μm).

[0129] The dimensional deviation during cooling and demolding is ±0.32%.

[0130] The remaining steps were the same as in Example 1, yielding a product with a density of 1.78 g / cm³. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 68.3 MPa and a flexural modulus of 14.1 GPa.

[0131] Comparative Example 2

[0132] The difference from Example 1 is that the mass ratio of Si powder to SiO2 powder in the composite Si source is different;

[0133] That is, the composite Si source is Si powder (purity 99%, particle size 3 μm) and SiO2 powder (purity 99.5%, particle size 1 μm), with a mass ratio of 6:1.

[0134] The dimensional deviation during cooling and demolding is ±0.28%.

[0135] The remaining steps were the same as in Example 1, yielding a product with a density of 1.85 g / cm³. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 75.8 MPa and a flexural modulus of 15.6 GPa.

[0136] Comparative Example 3

[0137] The difference from Example 1 is as follows:

[0138] In the preparation of chopped fiber reinforced carbon / silicon carbide-based composite materials, step 1 is as follows:

[0139] The pretreated chopped fibers, composite Si source, and degassed resin solution were mixed at a mass ratio of 15:30:55 and mechanically stirred (400 r / min, 135 min) to obtain a uniform slurry.

[0140] The dimensional deviation during cooling and demolding is ±0.35%.

[0141] The remaining steps were the same as in Example 1, yielding a product with a density of 1.93 g / cm³. 3The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 79.9 MPa and a flexural modulus of 16.4 GPa.

[0142] Comparative Example 4

[0143] The difference from Example 1 is as follows:

[0144] In the preparation of chopped fiber reinforced carbon / silicon carbide-based composite materials, step 1 is as follows:

[0145] The pretreated short-cut fibers, composite Si source, and degassed resin solution were mixed at a mass ratio of 15:30:55 and ultrasonically dispersed (250W, temperature control 35~40℃, 135 min) to obtain a uniform slurry.

[0146] The dimensional deviation during cooling and demolding is ±0.38%.

[0147] The remaining steps were the same as in Example 1, yielding a product with a density of 1.86 g / cm³. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 71.4 MPa and a flexural modulus of 14.9 GPa.

[0148] Comparative Example 5

[0149] The difference from Example 1 is as follows:

[0150] Replace the two-stage high-temperature pyrolysis in step 3 with traditional low-temperature pyrolysis;

[0151] That is: Step 3 is:

[0152] The solidified preform was subjected to conventional low-temperature pyrolysis under a protective gas (argon, flow rate of 80 mL / min): heated from room temperature to 1400℃ at a rate of 2℃ / min and held for 4 h without segmented holding steps; after pyrolysis, it was cooled to 800℃ at a rate of 20℃ / min and then cooled with the furnace to obtain a short fiber-SiC skeleton (skeleton porosity of 28%).

[0153] The remaining steps were the same as in Example 1, yielding a product with a density of 1.69 g / cm³. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 56.4 MPa and a flexural modulus of 11.9 GPa.

[0154] Comparative Example 6

[0155] The difference from Example 1 is as follows:

[0156] Step 3 is as follows: The solidified preform is subjected to high-temperature pyrolysis under a protective gas (argon, flow rate of 80 mL / min): heated from room temperature (rate of 3℃ / min) to 1700℃ and held at that temperature for 3.5 h;

[0157] After high-temperature pyrolysis, the temperature was lowered to 800℃ at 20℃ / min and then cooled in the furnace to obtain a short fiber-SiC skeleton (the skeleton porosity was 25%).

[0158] The remaining steps were the same as in Example 1, yielding a product with a density of 1.64 g / cm³. 3 The chopped fiber reinforced carbon / silicon carbide-based composite material has a room temperature flexural strength of 51.4 MPa and a flexural modulus of 10.3 GPa.

[0159] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a short-fiber reinforced carbon / silicon carbide-based composite material, characterized in that, Includes the following steps: A. Short-cut fibers, composite Si source, and resin solution are mixed, mechanically stirred, and then ultrasonically dispersed to obtain a uniform slurry; the composite Si source includes Si powder and SiO2 powder. B. The uniform slurry is molded and cured to obtain a cured blank; C. The solidified preform is subjected to two-stage high-temperature pyrolysis under protective gas conditions to obtain a short fiber-SiC skeleton; The two-stage high-temperature pyrolysis includes: First, heat to 400~600℃ and hold for a period of time; then heat to 1600~1800℃ and hold for a period of time again. D. Empty the pores of the short fiber-SiC skeleton, impregnate it in liquid phenolic resin, and after impregnation, cure and heat pyrolysis to obtain short fiber reinforced carbon / silicon carbide-based composite material.

2. The preparation method according to claim 1, characterized in that, In step A, the mass ratio of Si powder to SiO2 powder is 1:0.5~2.

3. The preparation method according to claim 1, characterized in that, In step A, the chopped fibers include at least one of carbon fiber, silicon carbide fiber, and quartz fiber; the length of the chopped fibers is 1-5 mm and the diameter is 5-20 μm. The resin includes a thermosetting phenolic resin; the solvent of the resin solution includes ethanol or acetone; the mass concentration of the resin solution is 40% to 60%.

4. The preparation method according to claim 1, characterized in that, In step A, the mass ratio of the chopped fiber, the composite Si source, and the resin solution is 10~30:20~40:40~70.

5. The preparation method according to claim 1, characterized in that, In step A, the mechanical stirring speed is 300~500 r / min, and the time is 1~2 h; The ultrasonic dispersion power is 220~280 W, the temperature is ≤40℃, and the time is 30~60 min.

6. The preparation method according to claim 1, characterized in that, Step B, which involves molding and curing the uniform slurry, includes: The uniform slurry is injected into a mold, kept under pressure at 20~30℃ and 5~10 MPa, and then heated to 150~200℃ for curing.

7. The preparation method according to claim 1, characterized in that, In step C, the heating rate to 400~600℃ is 2.5~3.5℃ / min; after heating to 400~600℃, the holding time is 0.5~1.5 h; The heating rate to 1600~1800℃ is 4~8℃ / min, and the holding time is 1~3 h; After the two-stage high-temperature pyrolysis, the process also includes: cooling the furnace to 700~900℃; The porosity of the short fiber-SiC skeleton is 35%~40%.

8. The preparation method according to claim 1, characterized in that, In step D, the method for emptying the pores of the short fiber-SiC framework is as follows: First, evacuate the short fiber-SiC skeleton to ≤-0.095 MPa and hold the pressure for 30~60 min; The soaking time is 1-3 hours; The heating rate for the pyrolysis is 4~6℃ / min, the pyrolysis temperature is 1600~2200℃, and the time is 1~2 h.

9. The preparation method according to claim 1, characterized in that, In step D, the sample is immersed in liquid phenolic resin at 2~3 MPa and 70~90℃. The pores of the short fiber-SiC skeleton are emptied, and the fiber is impregnated in liquid phenolic resin. After impregnation, the fiber is cured and then pyrolyzed, which is recorded as one densification cycle. After one densification cycle, the process further includes: repeating the densification cycle; the number of repetitions is 3 to 4 times; The short fiber reinforced carbon / silicon carbide based composite material has a density of 1.8-2.2 g / cm 3 .

10. The chopped fiber reinforced carbon / silicon carbide-based composite material prepared by the preparation method according to any one of claims 1 to 9.