CN113754442A

CN113754442A - High-density multilayer matrix of SiC/SiC composite material and preparation method

Info

Publication number: CN113754442A
Application number: CN202111065251.4A
Authority: CN
Inventors: 成来飞; 叶昉; 郭广达; 宋超坤; 张立同
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2021-09-11
Filing date: 2021-09-11
Publication date: 2021-12-07
Anticipated expiration: 2041-09-11
Also published as: CN113754442B

Abstract

The invention relates to a high-density multilayer matrix of a SiC/SiC composite material and a preparation method thereof, which prepares SiC particles (SiC)_p) Introducing the slurry into the porous SiC/SiC composite material by vacuum impregnation and pressure impregnation, preparing pyrolytic carbon with a certain content in the porous SiC/SiC composite material by adopting a CVI method to uniformly wrap SiC particles, and finally completing the densification of the SiC/SiC composite material by adopting an RMI method through the reaction of the pyrolytic carbon and molten silicon. SiC particles with different particle sizes are introduced in sequence to form a layered structure, so that genetic effect is generated on subsequent preparation of PyC and SiC matrixes, a uniform SiC matrix phase with high volume fraction is obtained, the density of the composite material is increased, the energy of crack propagation is increased, and the mechanical property of the composite material is effectively improved. The composite material prepared by the method has high volume fraction uniform distributionThe SiC matrix phase has high mechanical property and low open porosity, and solves the problems of low SiC phase content, uneven distribution and insufficient toughness in the SiC/SiC matrix prepared by the prior RMI process method.

Description

High-density multilayer matrix of SiC/SiC composite material and preparation method

Technical Field

The invention belongs to a preparation method of a composite material, and relates to a high-density multilayer matrix of a SiC/SiC composite material and a preparation method thereof.

Background

The SiC/SiC composite material has great application prospect in the fields of aerospace thermal structure parts and the like due to the advantages of high temperature resistance, wear resistance, corrosion resistance, high specific strength, high specific modulus, high toughness, creep resistance and the like. With the continuous development of aerospace industry in China, the thrust-weight ratio of an engine is gradually improved, the bypass ratio and the total pressure ratio are continuously improved, the service temperature is higher, the stress requirement is higher, the corrosive environment is higher, and the SiC/SiC composite material for the hot-end structural part of the engine has higher strength and toughness, higher damage tolerance and higher density requirement. The preparation process of the material determines the microstructure and the performance of the material, and an advanced process method needs to be developed to prepare the high-density high-toughness SiC/SiC composite material to meet new challenges.

The preparation method of SiC/SiC comprises CVI (chemical vapor infiltration), PIP (precursor impregnation cracking), MI (melt infiltration), RMI (reactive melt infiltration) and combined processes. The composite material prepared by the CVI method and the PIP method has large open porosity (10-15 percent), is volatile in effect in a high-temperature corrosive environment, and does not meet the requirement of high compactness; the composite material prepared by MI has a large amount of residual silicon (13 percent) and has poor mechanical property, and the performance is sharply reduced when the temperature exceeds the melting point of Si, so that the composite material is difficult to adapt to the high-temperature complex stress working condition of an aeroengine; the RMI process has the characteristics of short period, high density of the composite material, excellent mechanical property and the like, and is a preferred method for preparing high-density SiC/SiC. In the RMI process, the problem of corrosion of the Si melt to the interface and the fiber can exist, and a protective layer with a certain thickness is generally deposited on the surface of the interface by adopting a CVI method to isolate the corrosion of the Si melt to the interface and the fiber. Therefore, the SiC/SiC with compactness and good performance is hopeful to be obtained by the combined process of CVI and RMI.

Although laminated SiC can be deposited on the interface surface by the CVI process, the CVI SiC mainly plays a role in protection, and the matrix phase prepared by the RMI process is the key factor influencing the performance of the final SiC/SiC. The matrix prepared by the RMI method is generally a homogeneous or doped modified phase, has a single structure, cannot realize good crack deflection, consumes crack energy, and realizes a high-toughness matrix to meet the requirements of thermal shock resistance of an aeroengine, for example, a compact SiC/SiC composite material prepared by Wang et al by adopting a Reaction Melt Infiltration (RMI) technology has the bending strength of 288.2 +/-0.88 MPa and the fracture toughness of 16.0 +/-0.25 GPa, and is difficult to meet the requirements of high-toughness stress of the aeroengine. Therefore, the composite material matrix prepared by the RMI method must be structurally designed.

The matrix of the high-toughness ceramic matrix composite material generally has a multilayer structure, and crack propagation energy can be effectively consumed through the deflection of cracks among layers, so that the toughness of the material is improved. The multilayer matrix structure design mostly appears in CVI matrix and MAX phase modified matrix, such as Xuyongdong, Chengdei and the like, SiC/SiC composite material with the multilayer matrix structure can be prepared by adopting the CVI process, and the toughness is as high as 41.5MPa.m 1/2. However, the multilayer matrix structure is not reported in the RMI process, slurry is adopted in the work to dip (SI) submicron SiC particles to coat a CVI SiC protective layer, the SI micron SiC particles fill pores, then CVI PyC is attached to the surface of the SiC particles, interparticle liquid silicon permeation channels are reserved, and a high-density multilayer matrix is obtained after RMI.

Disclosure of Invention

Technical problem to be solved

In order to avoid the defects of the prior art, the invention provides a high-density multilayer matrix of a SiC/SiC composite material and a preparation method thereof, and provides a method for preparing the high-density SiC/SiC composite material with a multilayer matrix structure by Slurry Impregnation (SI) in combination with Chemical Vapor Infiltration (CVI) and Reaction Melt Infiltration (RMI).

Technical scheme

A SiC/SiC composite material high-density multilayer matrix comprises SiC fibers, BN and CVI SiC; the method is characterized in that: the SiC particle layer is of a first layer structure outside CVI SiC, a SiC reaction barrier layer is obtained by a dissolution-precipitation mechanism and a SiC reaction diffusion layer is formed by diffusion mechanism control outside the SiC particle layer, then a Si thin layer consisting of SiC nanocrystals is used for wrapping the SiC particle layer, the barrier layer and the diffusion layer in sequence, and the outermost layer is a SiC coarse crystal layer; the layer of SiC particles being obtained by impregnationThe obtained SiC with adherent distribution_PLaminated SiC produced by PyC reaction of CVI deposited on the surface of CVI SiC_RAnd PyC dissolves and precipitates SiC nanocrystalline and Si formed; the SiC coarse crystal layer is obtained by filling pores with micron-sized particles.

A preparation method of the SiC/SiC composite material high-density multilayer matrix is characterized by comprising the following steps:

step 1, preparing a porous SiC/SiC composite material: adopting a CVI (chemical vapor infiltration) process to deposit a BN interface on the braided SiC fibers, and then adopting the CVI process to deposit a SiC matrix to a semi-densification state to obtain a porous SiC/SiC composite material;

step 2, preparing 300-500 nm SiC particle water-based slurry: adding TMAH (tetramethylammonium hydroxide) with the mass fraction of 0.5-1.0 wt.% and SiC particles with the volume fraction of 3-5 vol.% into deionized water, and performing ball milling to obtain uniformly dispersed slurry;

step 3, dipping 300-500 nmSiC particle water-based slurry:

vacuum impregnation: placing the porous SiC/SiC composite material into a glass drying vessel, vacuumizing until the pressure in the glass vessel is lower than 0.09Mpa, and after keeping for 10-20 min, soaking the SiC/SiC composite material into the slurry obtained in the step 2 and keeping for 10-15 min;

pressure impregnation: putting the porous SiC/SiC composite material and the slurry into a closed container, pressurizing to 0.8Mpa, keeping for 20-30 min, taking out, and drying;

step 4, preparing SiC particle water-based slurry with the particle size of 3-5 microns: adding TMAH (tetramethylammonium hydroxide) with the mass fraction of 0.1-0.3 wt.% and SiC particles with the volume fraction of 3-10 vol.% into deionized water, and performing ball milling to obtain uniformly dispersed slurry;

step 5, dipping the SiC particle water-based slurry with the particle size of 3-5 microns:

vacuum impregnation: placing the porous SiC/SiC composite material into a glass drying vessel, vacuumizing until the pressure in the glass vessel is lower than 0.09Mpa, and soaking the SiC/SiC composite material into the slurry obtained in the step (4) for 20-30 min after keeping for 20-30 min;

pressure impregnation: putting the SiC/SiC composite material and the slurry into a closed container, pressurizing to 0.8Mpa, keeping for 10-20 min, taking out, and drying;

step 6, CVI pyrolytic carbon: putting the impregnated SiC/SiC-SiCp into a CVI pyrolytic carbon deposition furnace to deposit pyrolytic carbon for 30-80 hours;

step 7, liquid silicon infiltration: wrapping the SiC/SiC-SiCp-PyC composite material deposited with the pyrolytic carbon by using Si powder, wrapping the outermost layer by using graphite paper, putting the composite material wrapped with the Si powder into a siliconizing furnace, and performing liquid silicon infiltration for 20-60 min at 1430-1550 ℃ in a vacuum environment to complete the preparation of the SiC/SiC composite material.

Ball milling in the step 2: adding zirconia balls into the ball milling tank, and wet milling for 20-24 hours at a ball milling rotation speed of 100-300 r/min.

Ball milling in the step 2: and adding zirconia balls into the ball milling tank, and carrying out wet milling for 10-12 hours at a ball milling rotating speed of 80-120 r/min.

Advantageous effects

The invention provides a high-density multilayer matrix of SiC/SiC composite material and a preparation method thereof, which comprises the steps of firstly preparing small-size and large-size SiC particles (SiC)_p) The slurry is sequentially introduced into the porous SiC/SiC composite material by vacuum impregnation and pressure impregnation, then pyrolytic carbon (PyC) with a certain content is prepared in the porous SiC/SiC composite material by a CVI method, SiC particles are uniformly wrapped by the pyrolytic carbon (PyC), and finally the densification of the SiC/SiC composite material is completed by the reaction of the pyrolytic carbon and the molten silicon by an RMI method. The SiC particles with different particle sizes are introduced in sequence to form a layered structure, so that a genetic effect is generated on the subsequent preparation of PyC and SiC matrixes, a uniform SiC matrix phase with high volume fraction is obtained, the density of the composite material is effectively increased, the energy of crack propagation is increased, and the mechanical property of the composite material is effectively improved. The composite material prepared by the method has a SiC matrix phase with high volume fraction and uniform distribution, high mechanical property and low open porosity, and solves the problems of low SiC phase content, uneven distribution and insufficient toughness in the SiC/SiC matrix prepared by the prior RMI process method.

Controlling the thickness of the SiC particle layer and a pore structure formed by stacking the SiC particles by adjusting the volume fraction and the dipping times in the SiC slurry; controlling the thickness of a pyrolytic carbon coating outside the SiC particles and the form of a siliconizing pore channel by adjusting the temperature and time of the CVI pyrolytic carbon; the penetration depth of the liquid silicon and the reaction degree of the carbon and the silicon are controlled by adjusting the penetration temperature and the penetration time of the liquid silicon, so that the compactness and the mechanical property of the composite material are optimized.

The invention has the beneficial effects that:

1. the small-size SiC particles and the large-size SiC particles are sequentially introduced (3-5 mu m SiC, 300-500 nmSiC), so that a structure that the small-size particles cover the CVI SiC and the large-size particles fill the pores is formed. The small-size particle coated CVI SiC effectively hinders silicon melt erosion and provides possibility for the design of a multilayer matrix structure; the large particles fill the pores, so that the volume fraction of the SiC phase in the final composite material is increased, and the open porosity of the composite material is reduced.

2. Due to the introduction of the micron/submicron SiC particles, the specific surface area of the material is increased, the deposition speed of the CVI pyrolytic carbon is accelerated, a structure induction effect is generated on the CVI pyrolytic carbon, the ordered degree of the pyrolytic carbon is improved, and the siliconizing reaction is facilitated.

And 3, the SiC particles coated by the CVI pyrolytic carbon are uniformly distributed, and the SiC particles coated by the SiC matrix generated by the reaction of the RMI pyrolytic carbon and the liquid silicon can also be uniformly distributed, so that the phase composition of the composite material can be controlled.

4. The pyrolytic carbon wraps the SiC particles and fills pores inside the fiber bundle. After siliconizing, SiC-coated SiC particles generated by RMI reaction outside the fiber bundle and SiC generated by RMI reaction inside the fiber bundle are formed, and the high SiC phase matrix component characteristic is beneficial to improving the density of the material and can obviously improve the mechanical property of the material.

The introduction of the SiC particles not only improves the content of the SiC phase in the matrix, but also can be used as a reinforcing phase, improve crack cracking energy and increase crack propagation paths. The small-size SiC particles and PyC are used for coating CVI SiC, and a multilayer structure RMI matrix is formed after siliconizing, so that the toughness of the material is improved. The large-size SiC particles are distributed in the center of the pores of the porous SiC/SiC composite material, and a compact matrix in which the SiC particles are connected is formed after the surface is subjected to pyrolysis, carbonization and siliconizing, so that the strength of the material is improved.

Drawings

FIG. 1 is a process flow diagram of a preparation method related to the present invention.

FIG. 2 is a schematic view of the microstructure and composition of the SiC/SiC composite material prepared by the present invention.

It can be seen in the figure that: the SiC particle layer is a first layer structure outside CVI SiC and mainly comprises SiC with adherence distribution obtained by dipping_PLaminated SiC produced by PyC reaction of CVI deposited on the surface of CVI SiC_RAnd PyC dissolves out SiC nanocrystals and a small portion of Si. The layer structure effectively prevents the erosion of the Si melt. And a SiC reaction barrier layer is obtained by a dissolution-precipitation mechanism and a SiC reaction diffusion layer is formed by a diffusion mechanism. The SiC particle layer, the barrier layer and the diffusion layer are wrapped by a Si thin layer consisting of a large amount of Si and SiC nanocrystals formed by a small amount of reaction. The SiC coarse crystal layer is an outermost layer wrapping structure and is characterized in that: the SiC homogeneous nucleation grows, the growth obstruction is small, the crystal grains are large, the growth stops after the adjacent crystal grains contact, and the SiC homogeneous nucleation grows to form an irregular layer. The multilayer matrix structure can effectively improve the fracture toughness of the material, and the fracture toughness is 37.77 +/-2.03.

The outermost SiC particle layer is mainly obtained by pore-filling with micron-sized particles. The layer mainly has the function of increasing the content of the SiC phase in the matrix phase of the composite material. In addition, SiC particles can deflect matrix cracks, the material strength is improved, and the room-temperature bending strength of the composite material is 577.59 +/-9.55.

FIG. 3 is a photograph of the polished cross-sectional morphology back-scattered (BSE) of the SiC/SiC composite prepared in example 3.

FIG. 4 is an X-ray diffraction (XRD) pattern of the SiC/SiC composites prepared in examples 1, 2 and 3.

Detailed Description

The invention will now be further described with reference to the following examples and drawings:

the Slurry Impregnation (SI) is combined with Chemical Vapor Infiltration (CVI) and Reaction Melt Infiltration (RMI) to prepare SiC/SiC composite materials by the following steps:

step 1, preparing a SiC/SiC prefabricated body:

step 1.1, preparing a Boron Nitride (BN) interface phase on the surface of a SiC fiber braided body, wherein the thickness of the interface phase is 300-500 nm.

Step 1.2, preparing a SiC matrix with a certain volume fraction in the SiC fiber preform obtained in step 1.1 by adopting a CVI process. Trichloromethylsilane (MTS) is used as a precursor, hydrogen is used as a carrier gas, argon is used as a diluent gas, the flow ratio of the trichloromethylsilane (MTS) to the carrier gas to the argon is 1: 5-50: 2-20, the total pressure is 0.5-5 kPa, the deposition temperature is 873-1773K, and the deposition time is about 600 hours. The obtained porous ceramic material has a porosity of 28 to 36% and a density of 1.7 to 2.1g/cm³The porous SiC/SiC composite material is used for subsequent slurry impregnation.

Step 2, preparing 300-500 nm SiC particle water-based slurry:

step 2.1, adding SiC particles with the particle size of 300-500 nm and the volume fraction of 10 vol.% into HF acid, and magnetically stirring for 24 hours at room temperature. Respectively centrifuging the acid-washed SiC particles for 2 times by using deionized water and absolute ethyl alcohol at the rotating speed of 5000r/min to obtain the SiC particles with the SiO on the surfaces removed₂SiC particles of (1).

And 2.2, dispersing 0.5-1.0 wt.% of tetramethylammonium hydroxide (TMAH) in deionized water, and magnetically stirring at room temperature to prepare a uniform solution.

And 2.3, adding the SiC particles obtained in the step 2.1 into the dispersion liquid obtained in the step 2.2, adding the dispersion liquid and a proper amount of zirconia ball milling beads into a ball milling tank, and carrying out wet milling in the ball milling tank for 20-24 hours at a ball milling speed of 100-300r/min to obtain uniformly dispersed SiC slurry with the volume fraction of 3-5 vol.%.

Step 3, dipping 300-500 nmSiC particle water-based slurry:

and 3.1, putting the porous SiC/SiC composite material and the SiC particle slurry prepared in the step 2.3 into a glass drying dish, vacuumizing until the pressure in the glass dish is lower than 0.09MPa, and soaking the porous SiC/SiC composite material into the slurry for 10-15 min after keeping for 10-20 min.

And 3.2, putting the porous SiC/SiC composite material and the slurry into a closed container, pressurizing to 0.8MPa, keeping for 20-30 min, taking out, and drying for 3 hours at 150 ℃.

Step 4, preparing SiC particle water-based slurry with the particle size of 3-5 microns:

step 4.1 particle size reductionSiC particles with the volume fraction of 20 vol.% and the particle diameter of 3-5 mu m are added into HF acid, and the mixture is magnetically stirred for 12 hours at room temperature. Respectively centrifuging the acid-washed SiC particles for 2 times by using deionized water and absolute ethyl alcohol at the rotating speed of 5000r/min to obtain the SiC particles with the SiO on the surfaces removed₂SiC particles of (1).

And 4.2, dispersing 0.1-0.3 wt.% of tetramethylammonium hydroxide (TMAH) in deionized water, and magnetically stirring at room temperature to prepare a uniform solution.

And 4.3, adding the SiC particles obtained in the step 4.1 into the dispersion liquid obtained in the step 4.2, then adding the dispersion liquid and a proper amount of zirconia ball milling beads into a ball milling tank, carrying out wet milling in the ball milling tank for 10-12 hours at a ball milling speed of 80-120r/min, and obtaining uniformly dispersed SiC slurry with the volume fraction of 3-10 vol.%.

and 5.1, putting the porous SiC/SiC composite material obtained in the step 3.2 and the SiC particle slurry obtained in the step 4.3 into a glass drying dish, vacuumizing until the pressure in the glass dish is lower than 0.09MPa, and soaking the porous SiC/SiC composite material into the slurry for 20-30 min after the pressure is kept for 20-30 min.

And 5.2, putting the porous SiC/SiC composite material obtained in the step 5.1 and the slurry into a closed container, pressurizing to 0.8MPa, keeping for 10-20 min, taking out, and drying for 3 hours at 150 ℃.

Repeating the step 5, and circularly dipping for many times to obtain SiC/SiC-SiC meeting the content requirement of large-size SiC particles_PA composite material.

Step 6, CVI pyrolytic carbon:

SiC/SiC-SiC to be impregnated_pThe composite material is placed in a pyrolytic carbon deposition furnace and propylene (C)₃H₆) And depositing pyrolytic carbon as a precursor gas source at 870 ℃ and 5kPa for 30-80 hours.

Step 7, liquid silicon infiltration:

SiC/SiC-SiC of deposited pyrolytic carbon_pWrapping the-PyC composite material with Si powder, wrapping the outermost layer with graphite paper, placing the Si powder-wrapped composite material into a siliconizing furnace, and heating at 1430And (3) carrying out liquid silicon infiltration for 20-60 min at the temperature of 1550 ℃ in a vacuum environment to complete the preparation of the SiC/SiC composite material.

The specific embodiment is as follows:

example 1

Step 1, preparing a SiC/SiC prefabricated body:

Step 2, preparing 300-500 nm SiC particle water-based slurry:

Step 3, dipping 300-500 nmSiC particle water-based slurry:

step 4.1, adding SiC particles with the particle size of 3-5 mu m and the volume fraction of 20 vol.% into HF acid, and magnetically stirring for 12 hours at room temperature. Respectively centrifuging the acid-washed SiC particles for 2 times by using deionized water and absolute ethyl alcohol at the rotating speed of 5000r/min to obtain the SiC particles with the SiO on the surfaces removed₂SiC particles of (1).

Repeating the step 5, circularly dipping for 2 times to obtain SiC/SiC-SiC meeting the content requirement of large-size SiC particles_PA composite material.

Step 6, CVI pyrolytic carbon:

SiC/SiC-SiC to be impregnated_pThe composite material is placed in a pyrolytic carbon deposition furnace and propylene (C)₃H₆) And depositing pyrolytic carbon as a precursor gas source at 870 ℃ and 5kPa for 30-50 hours.

Step 7, liquid silicon infiltration:

SiC/SiC-SiC of deposited pyrolytic carbon_pAnd (2) wrapping the PyC composite material with Si powder, wrapping the outermost layer with graphite paper, putting the composite material wrapped with the Si powder into a siliconizing furnace, and performing liquid silicon infiltration for 20-60 min at 1430-1550 ℃ in a vacuum environment to complete the preparation of the SiC/SiC composite material.

As can be seen from FIG. 4, the matrix of the SiC/SiC composite material obtained in example 1 was mainly SiC, containing only a small amount of Si, and the flexural strength of the tested material was 511.46. + -. 6.90 MPa.

Example 2

Step 1, preparing a SiC/SiC prefabricated body:

Step 2, preparing 300-500 nm SiC particle water-based slurry:

Step 3, dipping 300-500 nmSiC particle water-based slurry:

Repeating the step 5, circularly dipping for 3 times to obtain SiC/SiC-SiC meeting the content requirement of large-size SiC particles_PA composite material.

Step 6, CVI pyrolytic carbon:

Step 7, liquid silicon infiltration:

As can be seen from FIG. 4, the matrix of the SiC/SiC composite material obtained in example 2 is mainly SiC, a more obvious layered structure appears at the periphery of CVI SiC, and the bending strength of the tested material is 542.73 + -25.68 MPa, and the fracture toughness is 37.77 + -2.03 MPa.m ^ 1/2.

Example 3

Step 1, preparing a SiC/SiC prefabricated body:

Step 2, preparing 300-500 nm SiC particle water-based slurry:

Step 3, dipping 300-500 nmSiC particle water-based slurry:

Step 6, CVI pyrolytic carbon:

SiC/SiC-SiC to be impregnated_pThe composite material is placed in a pyrolytic carbon deposition furnace and propylene (C)₃H₆) And depositing pyrolytic carbon as a precursor gas source at 870 ℃ and 5kPa for 50-80 hours.

Step 7, liquid silicon infiltration:

As can be seen from FIGS. 3 and 4, the matrix of the SiC/SiC composite material obtained in example 3 was mainly SiC and contained only a small amount of Si, and the bending strength of the material obtained by the test was 577.59. + -. 9.55 and the density was 2.48g/cm³The open porosity was 7.61%, and the residual silicon content was 4.32 vol.%.

Claims

1. A high-density multi-layer SiC/SiC matrix is prepared from SiC fibresBN and CVI SiC; the method is characterized in that: the SiC particle layer is of a first layer structure outside CVI SiC, a SiC reaction barrier layer is obtained by a dissolution-precipitation mechanism and a SiC reaction diffusion layer is formed by diffusion mechanism control outside the SiC particle layer, then a Si thin layer consisting of SiC nanocrystals is used for wrapping the SiC particle layer, the barrier layer and the diffusion layer in sequence, and the outermost layer is a SiC coarse crystal layer; the layer of SiC particles comprising an adherent distribution of SiC obtained by impregnation_PLaminated SiC produced by PyC reaction of CVI deposited on the surface of CVI SiC_RAnd PyC dissolves and precipitates SiC nanocrystalline and Si formed; the SiC coarse crystal layer is obtained by filling pores with micron-sized particles.

2. A method for preparing the SiC/SiC composite material high-density multilayer matrix of claim 1, which is characterized by comprising the following steps:

step 3, dipping 300-500 nmSiC particle water-based slurry:

3. The method of claim 2, wherein: ball milling in the step 2: adding zirconia balls into the ball milling tank, and wet milling for 20-24 hours at a ball milling rotation speed of 100-300 r/min.

4. The method of claim 2, wherein: ball milling in the step 2: and adding zirconia balls into the ball milling tank, and carrying out wet milling for 10-12 hours at a ball milling rotating speed of 80-120 r/min.