CN113121242B - A kind of chopped carbon fiber toughened silicon carbide composite material and preparation method thereof - Google Patents

Abstract

The invention relates to a chopped carbon fiber toughened silicon carbide composite material and a preparation method thereof, wherein the preparation method comprises the following steps: reacting the chopped carbon fibers, a silane coupling agent, absolute ethyl alcohol and deionized water to obtain coupling agent grafted chopped carbon fibers; mixing the coupling agent grafted chopped carbon fibers with an organic solution of a high-carbon-residue-rate binder to obtain high-carbon-residue-rate binder-coated chopped carbon fibers; mixing the chopped carbon fibers coated with the binder with the high carbon residue rate with silicon carbide powder to obtain mixed powder; dry-pressing the mixed powder to obtain a biscuit, and degreasing to obtain a preform; and carrying out reaction infiltration on the prefabricated body to obtain the chopped carbon fiber toughened silicon carbide composite material.

Description

A kind of chopped carbon fiber toughened silicon carbide composite material and preparation method thereof

technical field

The invention specifically relates to a chopped carbon fiber toughened silicon carbide (C _f /SiC) composite material and a preparation method thereof, belonging to the field of fiber toughened composite materials.

Background technique

Silicon carbide ceramics have excellent properties such as high hardness, high strength, oxidation resistance, corrosion resistance and good thermal stability, so they are widely used in petrochemical, aerospace and other fields. However, the brittle fracture of silicon carbide ceramics is currently the biggest obstacle to its application as high-temperature structural ceramics. Carbon fiber toughened silicon carbide (C _f /SiC) composites have the advantages of high specific strength, high specific stiffness, high specific modulus, and low density of carbon fibers. Fracture mechanisms such as matrix cracking have greatly improved its fracture toughness, making carbon fiber toughened silicon carbide (C _f /SiC) composites exhibit ductile fracture, improving their reliability and broadening the field of engineering applications.

Continuous fiber toughened silicon carbide composites are mainly prepared by methods such as chemical vapor infiltration (CVI) and precursor impregnation pyrolysis (PIP), which have high preparation costs and high energy consumption. The preparation of chopped carbon fiber toughened silicon carbide composite materials has low energy consumption, short cycle time, low cost, and the material is isotropic, so it has more engineering application value.

At present, the main methods for preparing chopped carbon fiber toughened silicon carbide composites are: slip casting-reaction infiltration method, gel injection molding-reaction infiltration method, hot press sintering (HP) method, discharge plasma (SPS )Law. Grouting molding has the problem of uneven density of the grouting body and cracking of the product. At the same time, due to the limitation of wet molding, it is necessary to use toxic dispersants such as tetramethylammonium hydroxide (TMAH) to prevent fiber flocculation and molding. Components with low solid content and low strength. Gel injection molding is formed by in-situ reaction crosslinking and curing of organic monomers. During the molding process, a large amount of toxic and harmful organic substances need to be used, which will cause great harm to the human body and the environment. In the process of hot pressing sintering, the sintering temperature and sintering pressure are high, and because of the high pressure, the fibers show obvious orientation, and the sintered parts show anisotropy. During the spark plasma sintering process, the thermal stress is significant due to the effect of sudden cooling and sudden heating. The presence of cracks in the resulting material and the inability to form large-scale parts limit its engineering applications.

Contents of the invention

For the existing chopped carbon fiber toughened silicon carbide composite materials, the slip casting has low solid content, high toxicity of gel casting, significant anisotropy of hot pressing and sintering, and many cracks in spark plasma sintered parts, so it is impossible to realize large size To solve problems such as the preparation of parts, the present invention provides a chopped carbon fiber toughened silicon carbide (C _f /SiC) composite material and a preparation method thereof.

In a first aspect, the present invention provides a method for preparing a chopped carbon fiber toughened silicon carbide ( _Cf /SiC) composite material, comprising: reacting chopped carbon fibers, a silane coupling agent, absolute ethanol, and deionized water to obtain Chopped carbon fibers grafted by a coupling agent; the chopped carbon fibers grafted by the coupling agent are mixed with an organic solution of a high carbon residue rate binder to obtain chopped carbon fibers coated with a high carbon residue rate binder; The chopped carbon fiber coated with a binder with a high residual carbon rate is mixed with silicon carbide powder to obtain a mixed powder; the mixed powder is formed by dry pressing to obtain a biscuit, and a preform is obtained through degreasing treatment; the The preform is subjected to reactive infiltration to obtain the chopped carbon fiber toughened silicon carbide composite material.

The silane coupling agent used in the present invention has amphiphilic molecules and is used as an intermediate interface layer to improve the polarity and interfacial compatibility between the carbon fiber of the inorganic phase and the silicon carbide of the organic phase, which is beneficial to the spreading of the phenolic resin on the surface of the fiber. Since the grafting of silane coupling agent on the surface of carbon fiber is a chemical reaction, the reaction mechanism: that is, the coupling agent first undergoes a hydrolysis reaction to form a silanol bond, and then connects with the fiber surface in the form of a chemical bond. Moreover, the hydrolysis of the silane coupling agent is a reversible reaction, which requires a certain temperature reaction temperature (60-85° C.), and it is difficult to achieve hydrolysis at normal temperature. Therefore, the method of directly mixing and ball milling in one step is not adopted in this patent. Furthermore, the one-step method directly mixes phenolic resin, carbon fiber and silicon carbide powder. The presence of silicon carbide will form a competitive reaction with the phenolic resin coating process of carbon fiber, which is not conducive to the coating of phenolic resin on the surface of carbon fiber.

The present invention adopts short-cut carbon fiber and silicon carbide powder coated with a binder with a high residual carbon rate as raw materials through dry ball milling, dry pressing molding, vacuum degreasing, reaction infiltration and other processes, and the preparation cost is low, non-toxic and harmless, A chopped carbon fiber toughened silicon carbide composite material with light weight, high strength and excellent mechanical properties.

Preferably, the carbon residue rate of the high carbon residue rate binder is 50% to 65%. Preferably, the high carbon residue rate binder is at least one of phenolic resin, epoxy resin, and asphalt resin A kind; In the organic solution of the high carbon residue rate binder, the organic solvent is selected from at least one of acetone, toluene and ethanol (but considering that solvents such as acetone and toluene are toxic, so ethanol is preferably used as a solvent); The chopped carbon fiber coated with high carbon residue rate adhesive is the chopped carbon fiber coated with phenolic resin, the length of the chopped carbon fiber is 10-130 μm, and the diameter is 6-8 μm; the silane coupling agent is ammonia Propyltriethoxysilane (KH550), 3-Aminopropyltrimethoxysilane (KH540), Epoxysilane (KH560), Triaminopropylmethyldiethoxysilane (A-2100), N - at least one of (β-aminoethyl-γ-aminopropyl)methyldimethoxysilanes (A2120).

The present invention adopts the phenolic resin as the binder and mainly has the following advantages: (1) The residual carbon rate after pyrolysis of the phenolic resin is high (50%-65%), which can provide sufficient carbon source for the subsequent reaction infiltration process. (2) Phenolic resin is a rigid molecular chain with excellent bonding performance.

Preferably, the added amount of the chopped carbon fiber, silane coupling agent, absolute ethanol and deionized water is 50g: (0.5-3) g: (60-90) mL: (40-10) mL.

Preferably, the temperature of the reaction is 60-85° C., and the time is 2-4.5 hours.

Preferably, the high carbon residual rate binder accounts for 10 vol% to 30 vol% of the total volume of the chopped carbon fibers coated with the high carbon residual rate binder.

Preferably, the addition amount of the ethanol solvent and the addition amount of the carbon fiber grafted by the coupling agent may be (1-4) g: 1 g.

The invention uses phenolic resin-coated chopped carbon fibers as raw materials, wherein the phenolic resin with excellent bonding performance is used as a binder during dry pressing to facilitate molding, and at the same time, the phenolic resin coating can effectively reduce the amount of binder used. Furthermore, the phenolic resin-coated carbon fiber/silicon carbide biscuit will be transformed into a pyrolytic carbon-coated carbon fiber/silicon carbide preform during the vacuum degreasing process. Pyrolytic carbon provides a sufficient carbon source for reaction infiltration. In addition, pyrolytic carbon-coated chopped carbon fibers will form silicon carbide-coated carbon fibers during the reaction infiltration process, which protects the fibers to a certain extent. Function, prevent carbon fiber from reacting with liquid silicon.

Preferably, the average particle diameter of the silicon carbide powder is 0.5-50 μm.

Preferably, the mass ratio of the high carbon residue rate binder-coated chopped carbon fiber to silicon carbide powder is (10-90) g: (90-10) g.

Preferably, the pressure of the dry pressing is 5-60 MPa.

Using dry pressing molding, the carbon fibers have no obvious orientation, and the molded parts are isotropic; the degreased preform is subjected to reaction infiltration, which can realize rapid densification at low temperature (1450 ° C ~ 1650 ° C), and obtain low-cost and excellent performance. _f /SiC composites. The prepared C _f /SiC composite material has low apparent porosity and low density, and has excellent mechanical, thermal, oxidation resistance, wear resistance and other properties, and is isotropic due to the introduction of chopped carbon fibers, which can meet the requirements of near net shape. , Lightweight and high-strength requirements, it can be used in aerospace, military energy and other fields.

Preferably, the temperature of the degreasing treatment is 700-1100° C., the holding time is 0.5-2 hours, and the vacuum degree is 20-80 Pa; preferably, the heating rate is 1-3° C./min.

Preferably, the reaction infiltration is as follows: placing the preform in silicon powder and sintering at 1450-1650° C. for 0.5-2 hours under vacuum conditions to obtain the chopped carbon fiber toughened silicon carbide composite material.

In a second aspect, the present invention provides the chopped carbon fiber toughened silicon carbide composite material obtained by the above preparation method, the C _f /SiC composite material includes a uniformly dispersed chopped carbon fiber toughened body and a silicon carbide matrix; preferably, the The volume density of the chopped carbon fiber toughened silicon carbide composite material is 2.7g/cm3-2.9g/ ^cm3 , and the bending strength is 200MPa-470MPa.

Beneficial effect:

First of all, the present invention uses phenolic resin with excellent bonding performance and high carbon residue rate (50% to 65%) as a binder, which can effectively ensure dry pressing, and at the same time, the carbon generated by pyrolysis provides a solid foundation for the reaction infiltration process. adequate carbon source.

Secondly, the present invention uses phenolic resin-coated chopped carbon fibers as raw materials, and the phenolic resin coating on the carbon fiber surface will form a pyrolytic carbon coating in the process of vacuum degreasing, and the pyrolytic carbon coating will form a pyrolytic carbon coating in the process of reaction infiltration. It will react with liquid silicon to form a silicon carbide coating on the surface of the carbon fiber, which can protect the carbon fiber to a certain extent.

Furthermore, the present invention adopts the method of dry pressing, the content of fibers is not limited, no toxic dispersant is required, and the fibers in the molded green body have no obvious orientation, showing typical isotropy, which can meet the needs of industrial applications .

Finally, the present invention performs reaction infiltration on C _f /C/SiC preforms, which can realize near-net shape and rapid densification at low temperature, thereby obtaining high-performance C _f / SiC composite materials.

Description of drawings

Fig. 1 is a flow chart of the preparation of the chopped carbon fiber toughened silicon carbide (C _f /SiC) composite material of the present invention.

Figure 2 is the SEM image of the chopped carbon fiber raw material in Example 1. It can be seen from the figure that the surface of the fiber is rough, and there are wire grooves introduced by the fiber precursor paralleling process. At the same time, there are a large amount of fiber debris on the surface of the fiber. crumbs.

Fig. 3 is the SEM image of the preform in Example 3, wherein the length of the carbon fiber is 10-130 μm, and the particle size of the SiC powder is about 10 μm. It can be seen from the figure that the carbon fiber and silicon carbide can be uniformly mixed together, Moreover, the carbon fiber has no obvious orientation and is isotropic. At the same time, there are a large number of pores in the preform, which is beneficial to the reaction infiltration process.

Fig. 4 is an SEM image of the C _f /SiC composite material in Example 1, showing a typical fiber pulling out toughening mechanism.

FIG. 5 is an XRD pattern of the C _f /SiC composite material after reaction infiltration in Example 2. FIG. According to the analysis of the XRD pattern, the composite material is composed of three phases of residual Si, α-SiC originally added and β-SiC generated by the reaction, and no residual carbon was detected. The possible reasons are: (1) The content of residual carbon is lower than that detected by XRD (2) The residual carbon is amorphous, with low intensity, so it was not detected.

Fig. 6 is a graph showing the flexural strength and elastic modulus of C _f /SiC composites prepared from silicon carbide powders with different particle sizes (5 μm, 10 μm, 20 μm) in Examples 2, 3, and 4. It can be seen from the figure that the flexural strength of the C _f /SiC composite material prepared from 5 μm silicon carbide powder is 448.26±22.86Mpa, and the elastic modulus is 329.67±8.52GPa.

(a) in Figure 7 is the SEM image of the chopped carbon fiber raw material; (b) in Figure 7 is the SEM image of the C _f @30vol%PR composite powder prepared in Example 6, it can be seen from the figure that the phenolic resin evenly distributed.

FIG. 8 is an SEM image of chopped carbon fibers coated with phenolic resin prepared in Comparative Example 1. FIG.

Detailed ways

The specific implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the following figures and embodiments are used to illustrate the present invention, but not to limit the present invention.

The invention relates to a preparation method of chopped carbon fiber toughened silicon carbide (C _f /SiC) composite material. The _Cf /SiC composite material includes a uniformly dispersed chopped carbon fiber reinforcement and a silicon carbide matrix. Chopped carbon fiber and silicon carbide coated with high carbon residual rate binder are used as raw materials, mixed by dry ball milling, dry pressing, vacuum degreasing (700-1100 °C, 0.5-2h), vacuum reaction infiltration (1450 °C) ~1650°C, 0.5~2h) and other processes to prepare the above C _f /SiC composite material. The length of the chopped carbon fiber is 10-130 μm, the diameter is 6-8 μm, and the particle size of the silicon carbide powder is 0.5-50 μm. The high carbon residual rate binder may be phenolic resin, and the chopped carbon fibers coated with the high carbon residual rate binder may be chopped carbon fibers coated with phenolic resin. Wherein, the content of the phenolic resin in the total volume of the chopped carbon fibers coated with the phenolic resin is 10vol% to 30vol%, and the _Cf /SiC composite material prepared by the present invention has low apparent porosity (≤6%) and low density (2.7～ 2.9g/cm ³ ), has excellent mechanical properties (bending strength 200-500MPa), thermal, oxidation resistance, wear resistance and other properties, and isotropic due to the introduction of chopped carbon fibers, which can meet the requirements of near-net shape, light High quality and high strength requirements, can be used in aerospace, military energy and other fields. The present invention optimizes the preparation process of the C _f /SiC composite material, strictly controls the process parameters, so as to realize the improvement of the structure and performance of the C _f /SiC composite material, and prepares a kind of isotropic and excellent mechanical properties _Cf /SiC composites.

The preparation method of the chopped carbon fiber toughened silicon carbide (C _f /SiC) composite material of the present invention is exemplarily described below using phenolic resin as a high carbon residue rate binder.

Carbon fiber grafted silane coupling agent. The chopped carbon fiber, silane coupling agent, absolute ethanol, and deionized water are reacted at 60-85° C. for 2-4.5 hours to obtain the chopped carbon fiber grafted by the coupling agent. The reaction is as follows: the silane coupling agent first undergoes a hydrolysis reaction, and the silanol produced by the hydrolysis reacts with the hydroxyl group (-OH) on the surface of the fiber to realize grafting. The specific reaction equation is as follows:

RSiX ₃ +H ₂ O→RSi(OH) ₃ +3HX, RSi(OH) ₃ +HO-M→R(OH) ₂ SiOM+2H ₂ O.

Where X represents the alkoxy group in the silane coupling agent that can undergo hydrolysis reaction, and M represents the surface of the carbon fiber.

The silane coupling agent can be aminopropyltriethoxysilane (KH550), 3-aminopropyltrimethoxysilane (KH540), epoxysilane (KH560), triaminopropylmethyldiethoxy At least one of base silane (A-2100), N-(β-aminoethyl-γ-aminopropyl)methyldimethoxysilane (A2120), the content of the silane coupling agent can be carbon fiber 1wt% ~ 6wt%. The proportions of the chopped carbon fiber, silane coupling agent, absolute ethanol and deionized water may be 50g: 0.5-3g: 60-90ml: 40-10ml. The length of the chopped carbon fiber may be 10-130 μm, and the diameter may be 6-8 μm.

Phenolic resin coated chopped carbon fiber. The chopped carbon fiber grafted with the coupling agent and the ethanol solution of the phenolic resin are ball milled, dried, and sieved to obtain the chopped carbon fiber coated with the phenolic resin. The densities of the phenolic resin and chopped carbon fiber are 1.22g/cm ³ and 1.76g/cm ³ respectively. The content of the phenolic resin in the total volume of the chopped carbon fibers coated with the phenolic resin is 10vol%-30vol%. Wherein the addition amount of the ethanol solvent and the addition amount of the carbon fiber grafted by the coupling agent may be (1-4) g: 1 g. The ball milling speed may be 100-300 rpm, and the ball milling time may be 0.5-2 hours. Silicon carbide balls are used as the grinding medium, and the ball-to-material ratio can be (1-6):1, dried at 40-70°C, ground in an agate mortar, and passed through a 40-100 mesh sieve to obtain chopped carbon fibers coated with phenolic resin. The thickness of the phenolic resin film may be 0.2 μm˜0.8 μm. In the present invention, the phenolic resin is not only used as a binder, which is beneficial to dry pressing molding, but also as a carbon source, and the phenolic resin with a high residual carbon rate (50% to 65%) is converted into inorganic carbon in the process of vacuum degreasing, which is the next step. The reactive infiltration process provides the carbon source.

Dry blend. The chopped carbon fiber coated with phenolic resin and silicon carbide powder were mixed to obtain a C _f /SiC composite powder. Among them, the particle size of silicon carbide powder can be 0.5-50 μm. Silicon carbide with this particle size can be packed closely and can be formed by dry pressing. At the same time, the C _f /SiC composite material obtained by sintering has low apparent porosity and high bulk density. The phenolic resin with high residual carbon rate (50%-65%) can be used as a binder for dry pressing, and the pyrolytic carbon of phenolic resin can provide sufficient carbon source for the reaction infiltration process. The ratio of chopped carbon fiber and silicon carbide powder of the phenolic resin coating may be (10-90):(90-10). The mixing method can be dry ball milling, planetary ball milling can be used, the chopped carbon fiber and silicon carbide powder coated with phenolic resin are put into the ball milling tank, and the silicon carbide ball is used as the grinding medium, and the ball-to-material ratio can be ( 1~6): 1, the rotation speed can be 100~300rpm, and the ball milling time can be 0.5~2h. The powder for molding is prepared by dry ball milling to obtain powder with uniform distribution of chopped carbon fibers, which effectively avoids the use of toxic dispersants. At the same time, dry ball milling does not cause fiber flocculation like wet molding, and the fibers High content. After ball milling, the silicon carbide balls are separated to obtain powder for dry pressing.

Dry pressing. The obtained powder is dry-pressed to obtain a green body of C _f /SiC composite material. The dry pressing may include: putting the powder into a metal mold of 8 mm x 40 mm, and performing dry pressing under a pressure of 5-60 MPa to obtain a C _f /SiC composite green body.

Vacuum degrease. Degreasing treatment means that the organic binder phenolic resin is cracked and uniformly converted into inorganic carbon and certain pores in a vacuum atmosphere, while maintaining a certain dimensional accuracy of the green body, and providing a carbon source for the subsequent reaction infiltration process. The green body is degreased at 700-1100° C. for 0.5-2 hours under vacuum conditions to obtain a preform. The heating rate of the degreasing treatment may be 1-3° C./min, and the degree of vacuum may be 20-80 Pa.

Reactive infiltration. The obtained prefabricated body is placed in silicon powder, and sintered at 1450-1650° C. for 0.5-2 hours under vacuum conditions to obtain a C _f /SiC composite material. The process of reactive infiltration is at temperatures above the melting point of silicon. Liquid silicon enters the material through capillary force, and reacts with carbon in the material to form silicon carbide in situ to achieve densification. The melting point of silicon is 1414°C. Therefore, the preferred sintering temperature in the present invention is 1450-1650°C. Because the reaction temperature is too low to reach the melting point of silicon, it is impossible to form a liquid phase and proceed to the reaction infiltration process, and the reaction temperature is too high. Liquid silicon will evaporate and consume more energy. The silicon powder used is high-purity silicon powder (99.99%). The heating rate of the sintering may be 3-10° C./min, and the holding time may be 0.5-2 hours. After the sintering process is completed, it is cooled to room temperature with the furnace under argon or nitrogen or vacuum atmosphere.

As shown above, C _f /SiC composite materials are prepared from phenolic resin-coated chopped carbon fibers, silicon carbide powder, silicon powder, etc. Excellent performance. The invention uses chopped carbon fiber as the toughening phase to give full play to the toughening effect of the fiber, obtains a powder with uniform distribution of fiber and silicon carbide, and adopts a dry pressing method to obtain a required sample. The prefabricated body is subjected to reactive infiltration and rapid densification at low temperature to obtain a high-performance C _f /SiC composite material. The _Cf /SiC composite material prepared by the invention is light, high-strength, isotropic, and has excellent mechanical properties, and can meet the needs of aerospace, military energy and other fields.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Example 1

This example provides a method for preparing a C _f /SiC composite material. The C _f /SiC composite material uses chopped carbon fibers coated with phenolic resin, silicon carbide powder, and high-purity silicon powder as raw materials, and is formed by dry pressing- Obtained by reaction infiltration.

Include the following steps:

(1) Carbon fiber grafted silane coupling agent: chopped carbon fiber (50g), aminopropyltriethoxysilane (KH550) (0.5g), absolute ethanol (70mL), deionized water (30mL) in 60 React at ℃ for 2 hours to obtain chopped carbon fibers grafted by coupling agent, wherein the content of KH550 is 1 wt% of the carbon fibers. The chopped carbon fiber has a length of 10 to 130 μm and a diameter of 6 μm.

(2) Phenolic resin coated chopped carbon fiber: the ethanol solution of the chopped carbon fiber grafted by the coupling agent of 50g and 50mL phenolic resin (the content of phenolic resin accounts for 25vol of the composite powder of the chopped carbon fiber of phenolic resin coated film) %) through ball milling, drying and sieving to obtain chopped carbon fibers coated with phenolic resin. Among them, the ball milling speed is 100rpm, the ball milling time is 0.5h, the silicon carbide ball is used as the grinding medium, the ball-to-material ratio is 2:1, dried at 40°C, ground in an agate mortar, and passed through a 40-mesh sieve to obtain phenolic resin-coated short Cut carbon fiber.

(3) Dry mixing: put phenolic resin-coated chopped carbon fibers (20 g) and silicon carbide powder (80 g) into a ball mill jar, and the particle size of the silicon carbide powder is 0.5 μm. Using silicon carbide balls as the grinding medium, the ball-to-material ratio is 6:1, the rotational speed is 100 rpm, and the ball milling time is 0.5 h. After ball milling, the silicon carbide balls are separated to obtain powder for dry pressing.

(4) Dry pressing molding: put the powder into a metal mold of 8 mm x 40 mm, and dry press molding under a pressure of 5 MPa to obtain a C _f /SiC composite material green body.

(5) Vacuum degreasing: Heating the C _f /SiC biscuit under a vacuum degree of 30 Pa to 700 ° C at 1 ° C / min, keeping it for 0.5 h, and cooling it to room temperature with the furnace in an argon atmosphere to obtain C _f / C / SiC preform.

(6) Reaction infiltration: place the preform in high-purity silicon powder with a particle size of 1 μm, sinter it under a vacuum of 40 Pa, heat it at 10°C/min to 1400°C, and then heat it at 5°C/min to 1650°C, keep the temperature for 2 hours, and cool down to room temperature with the furnace under an argon atmosphere to obtain a C _f /SiC composite material.

Example 2

This example provides a method for preparing a C _f /SiC composite material. The C _f /SiC composite material uses chopped carbon fibers coated with phenolic resin, silicon carbide powder, and high-purity silicon powder as raw materials, and is formed by dry pressing- Obtained by reaction infiltration.

Include the following steps:

(1) Carbon fiber grafted silane coupling agent: chopped carbon fiber (50g), aminopropyltriethoxysilane (KH550) (3g), absolute ethanol (70mL), deionized water (30mL) at 70 ° C The reaction was carried out for 2.5 hours to obtain chopped carbon fibers grafted by the coupling agent, wherein the content of KH550 was 6 wt% of the carbon fibers. The chopped carbon fiber has a length of 10 to 130 μm and a diameter of 7 μm.

(2) Phenolic resin coated chopped carbon fiber: 50mL ethanol solution of the chopped carbon fiber grafted with 50g described coupling agent and phenolic resin (the content of phenolic resin is 1% of the composite powder of the chopped carbon fiber of phenolic resin coated film) 25vol%) through ball milling, drying, and sieving to obtain chopped carbon fibers coated with phenolic resin. Among them, the ball milling speed is 150rpm, the ball milling time is 1.5h, the silicon carbide ball is used as the grinding medium, the ball-to-material ratio is 4:1, dried at 60°C, ground in an agate mortar, and passed through a 80-mesh sieve to obtain a phenolic resin-coated short Cut carbon fiber.

(3) Dry mixing: phenolic resin-coated chopped carbon fibers (30 g) and silicon carbide powder (70 g) were put into a ball mill jar, and the particle size of the silicon carbide powder was 5 μm. Using silicon carbide balls as the grinding medium, the ball-to-material ratio is 2:1, the rotational speed is 300rpm, and the ball milling time is 2h. After ball milling, the silicon carbide balls are separated to obtain powder for dry pressing.

(4) Dry pressing molding: put the powder into a metal mold of 8 mm x 40 mm, and dry press molding under a pressure of 15 MPa to obtain a green body of C _f /SiC composite material.

(5) Vacuum degreasing: Heating the C _f /SiC biscuit under a vacuum of 60 Pa at 1.5 °C/min to 900 °C, keeping it for 1.5 h, and cooling it to room temperature with the furnace under a nitrogen atmosphere to obtain the C _f /C/ SiC preform.

(6) Reaction infiltration: place the preform in high-purity silicon powder with a particle size of 50 μm, sinter it under a vacuum of 70 Pa, heat it at 5°C/min to 1400°C, and then heat it at 3°C/min to 1550°C, keep it warm for 1.5h, and cool down to room temperature with the furnace under a nitrogen atmosphere to obtain a C _f /SiC composite material.

Example 3

This example provides a method for preparing a C _f /SiC composite material. The C _f /SiC composite material uses chopped carbon fibers coated with phenolic resin, silicon carbide powder, and high-purity silicon powder as raw materials, and is formed by dry pressing- Obtained by reaction infiltration.

Include the following steps:

(1) Carbon fiber grafted silane coupling agent: chopped carbon fiber (50g), aminopropyltriethoxysilane (KH550) (1.5g), absolute ethanol (70mL), deionized water (30mL) in 80 React at ℃ for 3 hours to obtain chopped carbon fibers grafted by the coupling agent, wherein the content of KH550 is 3 wt% of the carbon fibers. The chopped carbon fiber has a length of 10 to 130 μm and a diameter of 8 μm.

(2) phenolic resin coated chopped carbon fiber: the ethanol solution of the chopped carbon fiber grafted with 50g of the coupling agent and 50mL phenolic resin (the content of the phenolic resin accounts for 25vol of the composite powder of the chopped carbon fiber of the phenolic resin coated film) %) through ball milling, drying and sieving to obtain chopped carbon fibers coated with phenolic resin. Among them, the ball milling speed is 200rpm, the ball milling time is 1.5h, the silicon carbide ball is used as the grinding medium, the ball-to-material ratio is 3:1, dried at 65°C, ground in an agate mortar, and passed through a 100-mesh sieve to obtain phenolic resin-coated short Cut carbon fiber.

(3) Dry mixing: phenolic resin-coated chopped carbon fibers (30 g) and silicon carbide powder (70 g) were put into a ball mill jar, and the particle size of the silicon carbide powder was 10 μm. Using silicon carbide balls as the grinding medium, the ball-to-material ratio is 4:1, the rotational speed is 250rpm, and the ball milling time is 2h. After ball milling, the silicon carbide balls are separated to obtain powder for dry pressing.

(4) Dry pressing molding: put the powder into a metal mold of 8 mm x 40 mm, and dry press molding under a pressure of 10 MPa to obtain a green body of C _f /SiC composite material.

(5) Vacuum degreasing: Heating the C _f /SiC biscuit to 1100 °C at 3 °C/min under a vacuum of 50 Pa, holding it for 0.5 h, and cooling it to room temperature with the furnace in a vacuum atmosphere to obtain the C _f /C/ SiC preform.

(6) Reaction infiltration: place the preform in high-purity silicon powder with a particle size of 1 μm, sinter it under a vacuum of 80 Pa, heat it at 10°C/min to 1400°C, and then heat it at 3.5°C/min To 1450°C, keep it warm for 2h, and cool down to room temperature with the furnace in a vacuum atmosphere to obtain a C _f /SiC composite material.

Example 4

This example provides a method for preparing a C _f /SiC composite material. The C _f /SiC composite material uses chopped carbon fibers coated with phenolic resin, silicon carbide powder, and high-purity silicon powder as raw materials, and is formed by dry pressing~ Obtained by reaction infiltration.

Include the following steps:

(1) Carbon fiber grafted silane coupling agent: chopped carbon fiber (50g), aminopropyltriethoxysilane (KH550) (2.5g), absolute ethanol (70mL), deionized water (30mL) in 80 React at ℃ for 3.5 h to obtain chopped carbon fibers grafted by coupling agent, wherein the content of KH550 is 5 wt% of the carbon fibers. The chopped carbon fiber has a length of 10 to 130 μm and a diameter of 6 μm.

(2) Phenolic resin coated chopped carbon fiber: the ethanol solution of the chopped carbon fiber grafted with 50g of the coupling agent and 50mL phenolic resin (the content of the phenolic resin is 2% of the composite powder of the chopped carbon fiber of the phenolic resin coated film) 25vol%) through ball milling, drying, and sieving to obtain chopped carbon fibers coated with phenolic resin. Among them, the ball milling speed is 100rpm, the ball milling time is 1.5h, the silicon carbide balls are used as the grinding medium, the ball-to-material ratio is 1:1, dried at 60°C, ground in an agate mortar, and passed through a 80-mesh sieve to obtain phenolic resin-coated short Cut carbon fiber.

(3) Dry mixing: phenolic resin-coated chopped carbon fibers (30 g) and silicon carbide powder (70 g) were put into a ball mill jar, and the particle size of the silicon carbide powder was 20 μm. Using silicon carbide balls as the grinding medium, the ball-to-material ratio is 1:1, the rotation speed is 250rpm, and the ball milling time is 1.5h. After ball milling, the silicon carbide balls are separated to obtain powder for dry pressing.

(4) Dry pressing molding: put the powder into a metal mold of 8 mm x 40 mm, and dry press molding under a pressure of 30 MPa to obtain a green body of C _f /SiC composite material.

(5) Vacuum degreasing: Heating the C _f /SiC biscuit under a vacuum of 45 Pa at 1.5 °C/min to 1000 °C, keeping it warm for 0.5 h, and cooling it to room temperature with the furnace in an argon atmosphere to obtain C _f /C / SiC preform.

(6) Reaction infiltration: place the preform in high-purity silicon powder with a particle size of 1 μm, sinter it under a vacuum of 80 Pa, heat it at 10°C/min to 1400°C, and then heat it at 3°C/min to 1600°C, keep it warm for 1.5h, and cool down to room temperature with the furnace under an argon atmosphere to obtain a C _f /SiC composite material.

Example 5

This example provides a method for preparing a C _f /SiC composite material. The C _f /SiC composite material uses chopped carbon fibers coated with phenolic resin, silicon carbide powder, and high-purity silicon powder as raw materials, and is formed by dry pressing- Obtained by reaction infiltration.

Include the following steps:

(1) Chopped carbon fiber (50g), aminopropyltriethoxysilane (KH550) (2g), absolute ethanol (70mL) and deionized water (30mL) were reacted at 80°C for 4h to obtain the coupling agent Branched chopped carbon fibers, wherein the content of KH550 is 4wt% of the carbon fibers. The chopped carbon fiber has a length of 10 to 130 μm and a diameter of 7 μm.

(2) Phenolic resin coated chopped carbon fiber: the ethanol solution of the chopped carbon fiber grafted with 50g of the coupling agent and 50mL phenolic resin (the content of the phenolic resin is 2% of the composite powder of the chopped carbon fiber of the phenolic resin coated film) 25vol%) through ball milling, drying, and sieving to obtain chopped carbon fibers coated with phenolic resin. Among them, the ball milling speed is 250rpm, the ball milling time is 2h, silicon carbide balls are used as the grinding medium, the ball-to-material ratio is 5:1, dried at 55°C, ground in an agate mortar, and passed through a 80-mesh sieve to obtain phenolic resin-coated chopped strands. carbon fiber.

(3) Dry mixing: phenolic resin-coated chopped carbon fibers (20 g) and silicon carbide powder (80 g) were put into a ball mill jar, and the particle size of the silicon carbide powder was 10 μm. Using silicon carbide balls as the grinding medium, the ball-to-material ratio is 2:1, the rotational speed is 150rpm, and the ball milling time is 1.5h. After ball milling, the silicon carbide balls are separated to obtain powder for dry pressing.

(4) Dry pressing molding: put the powder into a metal mold of 8 mm x 40 mm, and dry press molding under a pressure of 25 MPa to obtain a green body of C _f /SiC composite material.

(5) Vacuum degreasing: Heat the C _f /SiC green body at 2°C/min to 900°C under a vacuum of 75Pa, keep it warm for 1.5h, and cool it to room temperature with the furnace in a vacuum atmosphere to obtain C _f /C/ SiC preform.

(6) Reaction infiltration: place the preform in high-purity silicon powder with a particle size of 50 μm, sinter it under a vacuum of 40 Pa, heat it at 10°C/min to 1400°C, and then heat it at 5°C/min to 1550°C, keep it warm for 1h, and cool down to room temperature with the furnace under vacuum atmosphere to obtain a C _f /SiC composite material.

Example 6

This embodiment provides a C _f @30vol% PR composite powder, the C _f @30vol% PR composite powder includes chopped carbon fiber, silane coupling agent, and phenolic resin, wherein the phenolic resin accounts for the short portion of the phenolic resin coating. The content of the total volume of cut carbon fiber is 30vol%, and it is obtained by coupling agent grafting-ball milling method.

Include the following steps:

(1) Carbon fiber grafted silane coupling agent: chopped carbon fiber (50g), aminopropyltriethoxysilane (KH550) (1.5g), absolute ethanol (70mL), deionized water (30mL) at 75 The reaction was carried out at ℃ for 4 hours to obtain chopped carbon fibers grafted by the coupling agent, wherein the content of KH550 was 3wt% of the carbon fibers. The chopped carbon fiber has a length of 10 to 130 μm and a diameter of 6 μm.

(2) phenolic resin coated chopped carbon fiber: the ethanol solution of the chopped carbon fiber grafted with 50g described coupling agent and 50mL phenolic resin (the content of phenolic resin accounts for 30vol of the composite powder of the chopped carbon fiber of phenolic resin coated film) %) through ball milling, drying and sieving to obtain chopped carbon fibers coated with phenolic resin. Among them, the ball milling speed is 300rpm, the ball milling time is 1h, the silicon carbide ball is the grinding medium, the ball-to-material ratio is 2:1, dried at 40°C, ground in an agate mortar, and passed through a 40-mesh sieve to obtain phenolic resin-coated chopped strands. carbon fiber.

Comparative example 1

With reference to the implementation of Example 2, the only difference between Comparative Example 1 and Implementation 2 is that no silane coupling agent (aminopropyltriethoxysilane) is added in step (1).

Since the silane coupling agent aims to improve the polarity and interfacial compatibility between the carbon fiber of the inorganic phase and the phenolic resin of the organic phase, the ethanol solution of the carbon fiber and the phenolic resin is directly ball-milled without adding the silane coupling agent, and the phenolic resin is The surface of the fibers is balled and cannot be spread, see Figure 8.

Table 1:

sample Open porosity Bulk density g/cm³ Elastic modulus GPa Bending strength MPa Example 2 0.6%±0.002 2.86±0.02 329.67±8.52 448.26±22.86 Example 3 0.56%±0.003 2.82±0.02 324.46±6.53 387.27±25.45 Example 4 0.83%±0.01 2.85±0.03 297.10±18.73 325.91±11.58

Claims (3)

1. A preparation method of a short carbon fiber toughened silicon carbide composite material is characterized by comprising the following steps:

reacting the chopped carbon fibers, a silane coupling agent, absolute ethyl alcohol and deionized water to obtain coupling agent grafted chopped carbon fibers, wherein the addition amounts of the chopped carbon fibers, the silane coupling agent, the absolute ethyl alcohol and the deionized water are 50g: (0.5-3) g: (60-90) mL: (40-10) mL, wherein the reaction temperature is 60-85 ℃, and the reaction time is 2-4.5 h; the length of the short carbon fiber is 10-130 μm, and the diameter is 6-8 μm;

ball-milling, drying and sieving the coupling agent grafted chopped carbon fibers and an ethanol solution of phenolic resin with the carbon residue rate of 50% -65% to obtain phenolic resin coated chopped carbon fibers, wherein the phenolic resin accounts for 10-30 vol% of the total volume of the phenolic resin coated chopped carbon fibers, and the thickness of the phenolic resin coated film is 0.2-0.8 mu m;

carrying out dry ball milling mixing on the phenolic resin coated chopped carbon fibers and silicon carbide powder with the average particle size of 0.5-50 mu m to obtain mixed powder; the mass ratio of the phenolic resin coated chopped carbon fibers to the silicon carbide powder is (10-90) g: (90-10) g; taking silicon carbide balls as grinding media, wherein the ball material ratio is (1-6) to 1, the rotating speed is 100-300 rpm, and the ball milling time is 0.5-2 h;

carrying out dry pressing on the mixed powder to obtain a carbon fiber/silicon carbide biscuit coated with phenolic resin, and carrying out degreasing treatment to obtain a carbon fiber/silicon carbide preform coated with pyrolytic carbon, wherein the pressure of the dry pressing is 5-60 MPa;

the temperature of the degreasing treatment is 700-1100 ℃, the heat preservation time is 0.5-2 h, the vacuum degree is 20-80 Pa, and the heating rate is 1-3 ℃/min;

placing the carbon fiber/silicon carbide prefabricated body coated with the pyrolytic carbon into silicon powder, sintering for 0.5-2 h at 1450-1650 ℃ under vacuum condition for reaction infiltration, and converting the carbon fiber coated with the pyrolytic carbon into the carbon fiber coated with the silicon carbide to obtain the chopped carbon fiber toughened silicon carbide composite material;

the chopped carbon fiber toughened silicon carbide composite material comprises a uniformly dispersed chopped carbon fiber toughened body and a silicon carbide substrate; the volume density of the chopped carbon fiber toughened silicon carbide composite material is 2.7g/cm ³ ～2.9 g/cm ³ The bending strength is 200MPa to 470MPa.

2. The method according to claim 1, wherein the silane coupling agent is at least one selected from the group consisting of aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, epoxysilane, triaminopropylmethyldiethoxysilane, and N- (β -aminoethyl- γ -aminopropyl) methyldimethoxysilane.

3. The chopped carbon fiber toughened silicon carbide composite material prepared by the preparation method according to claim 1.

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