CN113292344A

CN113292344A - Preparation method of mullite whisker reinforced silicon carbide ceramic matrix composite material with in-situ growth

Info

Publication number: CN113292344A
Application number: CN202110586353.4A
Authority: CN
Inventors: 张景德; 李子禾; 常籽萱; 韩桂芳
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2021-05-27
Filing date: 2021-05-27
Publication date: 2021-08-24
Anticipated expiration: 2041-05-27
Also published as: CN113292344B

Abstract

The invention provides a preparation method of an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite, which comprises the following steps: adding a substrate raw material into a ball milling tank, adding a dispersant aqueous solution and a ball milling medium, carrying out primary ball milling, adding a binder solution, and continuing secondary ball milling to obtain slurry, wherein the substrate raw material comprises silicon carbide powder, aluminum hydroxide powder, metal oxide powder and fluoride powder; step two, drying and dehydrating the slurry obtained in the step one to obtain a solid; granulating the solid obtained in the step two, and then sieving; step four, dry-pressing and molding the undersize obtained in the step three by using a mold to obtain a green body; step five, vacuum drying the green body obtained in the step four; and step six, sintering the green body subjected to vacuum drying in the step five at 1500-1550 ℃, and preserving heat for 2-4 h to obtain the silicon carbide ceramic-based composite material reinforced by the in-situ grown mullite whiskers.

Description

Preparation method of mullite whisker reinforced silicon carbide ceramic matrix composite material with in-situ growth

Technical Field

The disclosure relates to the field of ceramic materials, in particular to a preparation method of an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite.

Background

The silicon carbide ceramic matrix composite material serving as a structural material has very important significance in the aerospace field due to excellent high temperature resistance, corrosion resistance, low density, high strength, high hardness and high modulus. Currently, the reinforcement used to reinforce silicon carbide ceramic substrates mainly comprises: granules, chopped fibers, continuous fibers, and whiskers. Among them, the reinforcing effect of the continuous fiber and the whisker is most remarkable in the aspect of mechanical property. However, the anisotropy of the weave structure of the continuous fibers can cause the problems of low compressive strength, low shear strength between woven layers, short tensile fatigue life and the like of the material. In contrast, the whisker reinforced silicon carbide ceramic matrix composite material can effectively solve the problems due to the isotropy, and has great development potential.

Introduction of whisker reinforcement into ceramic substrates has generally been carried out by an external addition method, for example, in chinese patent application CN105884388A published in 2016, 8, and 24, a modified silicon carbide whisker reinforced ceramic material and a method for preparing the same ", in which antimony trichloride, urea, and a borate ester are added in order to disperse whiskers in a raw material, and stirring is carried out for different periods of time and at different heating temperatures, respectively. In foreign countries, the introduction of whiskers is usually realized by external addition for whisker reinforced silicon carbide-based composite materials. For example Lv et al (Xinyuan Lv et al, simulation of SiC white-re-expressed SiC Ceramic whiskers based on 3D printing and chemical vapor deposition technology [ J ]. Journal of the European Ceramic Society, 2019, 39(11):3380-3386.) first granulate the silicon carbide whiskers by spray drying, then preform the resulting powder by means of binder spray forming technique, and finally achieve the compounding of the silicon carbide Ceramic matrix with the whisker reinforcement by means of chemical vapor infiltration. Therefore, the introduction of the whiskers through the external addition method not only increases the complexity of the preparation process, but also puts more strict requirements on raw materials and process equipment, and greatly increases the production cost of the materials.

Disclosure of Invention

In view of the problems in the background art, the present disclosure aims to provide a method for preparing an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite, which can realize in-situ growth of whiskers to overcome the defect of introducing whiskers by an addition method in the background art.

In order to achieve the above objects, in some embodiments, the present disclosure provides a method for preparing an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite, comprising the steps of: adding a substrate raw material into a ball milling tank, adding a dispersant aqueous solution and a ball milling medium, carrying out primary ball milling, adding a binder solution after the primary ball milling, and continuing secondary ball milling to obtain slurry, wherein the substrate raw material comprises silicon carbide powder, aluminum hydroxide powder, metal oxide powder and fluoride powder; step two, drying and dehydrating the slurry obtained in the step one to obtain a solid; granulating the solid obtained in the step two, and then sieving; step four, dry-pressing and molding the undersize obtained in the step three by using a mold to obtain a green body; step five, vacuum drying the green body obtained in the step four; and step six, sintering the green body subjected to vacuum drying in the step five at 1500-1550 ℃, and preserving heat for 2-4 h, wherein the lower the sintering temperature is, the longer the heat preservation time is, so as to obtain the silicon carbide ceramic-based composite material enhanced by the mullite whisker grown in situ.

In some embodiments, in step one, the particle size of the silicon carbide powder is 100nm to 1 μm; the particle size of the aluminum hydroxide powder is 100nm-1 mu m; the particle size of the metal oxide powder is 100nm-1 μm; the particle size of the fluoride powder is 100nm-1 μm.

In some embodiments, in step one, the metal oxide of the metal oxide powder is selected from one or more of yttrium oxide, cerium oxide, molybdenum oxide, and vanadium oxide; the fluoride of the fluoride powder is selected from one or more of calcium fluoride, aluminum fluoride and ammonium fluoride; the dispersant in the dispersant aqueous solution is tetramethyl ammonium hydroxide or sodium silicate; the ball milling medium is deionized water or absolute ethyl alcohol; the binder solution is composed of polyvinyl alcohol and deionized water or polyvinyl butyral and absolute ethyl alcohol.

In some embodiments, in the first step, the mass ratio of the silicon carbide powder, the aluminum hydroxide powder, the metal oxide powder and the fluoride powder is (35-80): 15-55): 0.5-15): 0.2-10; the mass of the dispersant aqueous solution is 0.05-2% of that of the matrix raw material, and the dispersant accounts for 10-25% of the mass ratio of the dispersant aqueous solution; the mass of the ball milling medium is 0.5-5 times of that of the matrix raw material; the mass of the binder solution is 0.1-10% of that of the matrix raw material, and the mass ratio of the binder to the binder solution is 5-10%.

In some embodiments, in the step one, the time for one ball milling is 2h to 12 h; the time of the secondary ball milling is 1h-6 h.

In some embodiments, in step two, the temperature for drying and dehydration is 50 ℃ to 150 ℃, and the time for drying and dehydration is 2h to 48 h.

In some embodiments, in step three, the granulation is performed by grinding, and the mesh number of the sieved mesh is 40-200.

In some embodiments, in the fourth step, the dry pressing is performed by two unidirectional pressing, the undersize obtained in the third step is subjected to unidirectional pressure maintaining at a pressure of 80Mpa to 100Mpa for a pressure maintaining time of 1min to 3min, and then the mold is inverted and the unidirectional pressing is performed again at a pressure of 80Mpa to 100Mpa for a pressure maintaining time of 1min to 3 min.

In some embodiments, in step five, the temperature of vacuum drying is 50 ℃ to 120 ℃, the time of vacuum drying is 12h to 36h, and the vacuum degree of vacuum drying is less than 200 Pa.

The beneficial effects of this disclosure are as follows: the generation of the whisker and the sintering of the silicon carbide substrate are carried out simultaneously without additional process, thereby overcoming the defect that the whisker is introduced by adopting an additional method in the background technology.

Drawings

Fig. 1 is an XRD spectrum of the in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 1 of the present disclosure.

FIG. 2 is an SEM photograph of an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 1 of the present disclosure.

Fig. 3 is an XRD spectrum of the in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 2 of the present disclosure.

FIG. 4 is an SEM photograph of an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 2 of the present disclosure.

Fig. 5 is an XRD spectrum of the in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 3 of the present disclosure.

FIG. 6 is an SEM photograph of an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 3 of the present disclosure.

Fig. 7 is an XRD spectrum of in situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 4 of the present disclosure.

FIG. 8 is an SEM photograph of an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 4 of the present disclosure.

Fig. 9 is an XRD spectrum of in situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 5 of the present disclosure.

FIG. 10 is an SEM photograph of an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite of example 5 of the present disclosure.

FIG. 11 is an XRD spectrum of the silicon carbide ceramic matrix composite of comparative example 1 of the present disclosure.

FIG. 12 is an SEM photograph of the silicon carbide ceramic matrix composite of comparative example 1 of the present disclosure.

FIG. 13 is an XRD spectrum of the silicon carbide ceramic matrix composite of comparative example 2 of the present disclosure.

FIG. 14 is an SEM photograph of a silicon carbide ceramic matrix composite of comparative example 2 of the present disclosure.

FIG. 15 is an XRD spectrum of the silicon carbide ceramic matrix composite of comparative example 3 of the present disclosure.

FIG. 16 is an SEM photograph of a silicon carbide ceramic matrix composite of comparative example 3 of the present disclosure.

FIG. 17 is an XRD spectrum of the silicon carbide ceramic matrix composite of comparative example 4 of the present disclosure.

FIG. 18 is an SEM photograph of a silicon carbide ceramic matrix composite of comparative example 4 of the present disclosure.

FIG. 19 is an XRD spectrum of the silicon carbide ceramic matrix composite of comparative example 5 of the present disclosure.

FIG. 20 is an SEM photograph of a silicon carbide ceramic matrix composite of comparative example 5 of the present disclosure.

Detailed Description

The preparation method of the mullite whisker reinforced silicon carbide ceramic matrix composite material with in-situ growth according to the disclosure is explained in detail below.

The preparation method of the mullite whisker reinforced silicon carbide ceramic matrix composite material with in-situ growth according to the disclosure comprises the following steps: adding a substrate raw material into a ball milling tank, adding a dispersant aqueous solution and a ball milling medium, carrying out primary ball milling, adding a binder solution after the primary ball milling, and continuing secondary ball milling to obtain slurry, wherein the substrate raw material comprises silicon carbide powder, aluminum hydroxide powder, metal oxide powder and fluoride powder; step two, drying and dehydrating the slurry obtained in the step one to obtain a solid; granulating the solid obtained in the step two, and then sieving; step four, dry-pressing and molding the undersize obtained in the step three by using a mold to obtain a green body; step five, vacuum drying the green body obtained in the step four; and step six, sintering the green body subjected to vacuum drying in the step five at 1500-1550 ℃, and preserving heat for 2-4 h, wherein the lower the sintering temperature is, the longer the heat preservation time is, so as to obtain the silicon carbide ceramic-based composite material enhanced by the mullite whisker grown in situ.

The mullite-combined silicon carbide sintering method is combined with the mullite whisker gas-solid/gas-liquid-solid growth process to prepare the mullite whisker reinforced silicon carbide ceramic matrix composite material in situ, and the generation of the whisker and the sintering of the silicon carbide matrix are carried out simultaneously without additional processes, so that the defect of introducing the whisker by an additional method in the background art is overcome. The prepared ceramic matrix composite does not contain impurity phases (namely cristobalite phases) except silicon carbide and mullite, the whiskers in the prepared ceramic matrix composite are disorderly and uniformly distributed and form a bird nest structure in a criss-cross mode, and the prepared ceramic matrix composite has the characteristics of high bending strength and the like. In addition, the preparation method disclosed by the invention is simple and efficient in process and easy to control in operation.

In some embodiments, in step one, the particle size of the silicon carbide powder is 100nm to 1 μm; the particle size of the aluminum hydroxide powder is 100nm-1 mu m; the particle size of the metal oxide powder is 100nm-1 μm; the particle size of the fluoride powder is 100nm-1 μm. The particle size of all the powder is smaller than 1 mu m, so that on one hand, the raw material powder has larger specific surface area, and the sintering activity is favorably improved; in addition, the aluminum hydroxide particles can be used as pore-forming agents, so that the size of the aluminum hydroxide particles cannot exceed 1 mu m, large-size pores are prevented from being formed in the product, the distribution uniformity of whiskers in the product is influenced, and the product performance is reduced; the particle size of the powder is larger than 100nm, because the nano powder is easy to agglomerate in the process of preparing the slurry to form large-size particles, the method is not beneficial to the subsequent process.

In some embodiments, in step one, the metal oxide of the metal oxide powder is selected from one or more of yttrium oxide, cerium oxide, molybdenum oxide, and vanadium oxide; the fluoride of the fluoride powder is selected from one or more of calcium fluoride, aluminum fluoride and ammonium fluoride; the dispersant in the dispersant aqueous solution is tetramethyl ammonium hydroxide or sodium silicate; the ball milling medium is deionized water or absolute ethyl alcohol; the binder solution is composed of polyvinyl alcohol and deionized water or polyvinyl butyral and absolute ethyl alcohol. One or more of yttrium oxide, cerium oxide, molybdenum oxide and vanadium oxide powder used in the first step can promote the generation of a liquid phase in the green body in the sintering process, so that mullite crystal nuclei are uniformly formed at all positions of the green body; one or more of calcium fluoride, aluminum fluoride and ammonium fluoride used in the method can promote the preferential growth of mullite crystal nucleus in the [001] direction through gas phase reaction, thereby forming the whisker. The reasonable sintering aid system can promote the generation of whiskers in the sintering process and serve as a reinforcement to improve the bending strength of a product, and in the whisker generation process, fluoride is added to introduce fluorine element which can serve as a catalyst in the process of sintering to generate whiskers so as to promote the gas phase reaction of mullite whiskers; the reasonable sintering aid system can promote the densification of a blank in the sintering process, fluoride also serves as fluxing agent in the sintering densification process, and due to the characteristic of fluoride ions, the addition of fluoride can greatly reduce the viscosity of a generated liquid phase, improve the fluidity and further promote the effect of the liquid phase on the densification process. By "reasonable sintering aid system" is meant: the metal oxide and the fluoride are added simultaneously, and the metal oxide and the fluoride act synergistically to promote the generation of the whisker. Therefore, at least one should be added to each of the two. Among them, the metal oxide is added for the purpose of lowering the generation temperature of the liquid phase during sintering. The formation of the liquid phase is effective to promote the contact and reaction of the fluoride with other substances.

In some embodiments, in the first step, the mass ratio of the silicon carbide powder, the aluminum hydroxide powder, the metal oxide powder and the fluoride powder is (35-80): 15-55): 0.5-15): 0.2-10; the mass of the dispersant aqueous solution is 0.05-2% of the mass of the matrix raw material, and the dispersant accounts for 10-25% of the mass ratio of the dispersant aqueous solution; the mass of the ball milling medium is 0.5-5 times of that of the matrix raw material; the mass of the binder solution is 0.1-10% of the mass of the matrix raw material, and the mass ratio of the binder to the binder solution is 5-10%.

In some embodiments, in the step one, the time for one ball milling is 2h to 12 h; the time of the secondary ball milling is 1h-6 h. The ball milling time is less than 2 hours, so that the raw material powder is not fully mixed, and the components of the green blank are not uniformly distributed to influence the product performance; the high ball milling time and the 12h time can cause a large amount of raw material powder to be crushed by ball milling, resulting in the change of the particle size of the raw material powder, and the particle size of the powder used for dry pressing after the control is difficult.

In some embodiments, in step two, the temperature for drying and dehydration is 50 ℃ to 150 ℃, and the time for drying and dehydration is 2h to 48 h. Too low drying temperature and drying time can cause the moisture in the slurry to be removed incompletely, thereby causing the moisture in the powder to be unable to be quantitatively regulated in the next granulation process, causing granulation difficulty and influencing the subsequent process. Too high a drying temperature may result in ingredients other than moisture such as: the binder is pyrolyzed to influence the product performance; too long drying time results in longer cycle time and reduced production efficiency.

In some embodiments, in step three, the granulation is performed by grinding, and the mesh number of the sieved mesh is 40-200. The mesh number is less than 40, so that the particle size of the sieved powder is too large, and the powder cannot be tightly stacked in the dry pressing process; the mesh number higher than 200 meshes can cause the undersize of the screened powder, the poor powder flowability and the arch bridge effect in the dry pressing process. The two conditions can cause the density of the green body obtained by dry pressing to be greatly reduced, even the phenomenon of spalling occurs, and the defective rate is greatly improved.

In some embodiments, in step four, the mold is a stainless steel mold.

In some embodiments, in the fourth step, the dry pressing is performed by two unidirectional pressing steps, the undersize obtained in the third step is firstly subjected to unidirectional pressing at a pressure of 80Mpa to 100Mpa for a pressure holding time of 1min to 3min, and then the mold is turned upside down and is subjected to unidirectional pressing again at a pressure of 80Mpa to 100Mpa for a pressure holding time of 1min to 3 min. The forming pressure is low, so that the powder in the die can not overcome the friction force between particles and the friction force of the die to the powder, and further can not flow and rearrange fully; too high a forming pressure can cause damage to the mold and can also lead to difficulties in demolding and cracking of the green edge. The dwell time is usually more than 30s and not less than 10s, and the dwell time is prolonged to effectively improve the density of the green body and the uniformity degree of the internal density distribution, so that the dwell time is increased to 1min-3min in the invention. However, excessively prolonging the pressure maintaining time will prolong the production cycle and affect the production efficiency. The density distribution of the upper part and the lower part of the green body in the pressure direction can be ensured to be more uniform by adopting two times of unidirectional pressurization in opposite directions. Typically, the green part distal to the indenter end will have a lower density than the near indenter part after a single press.

In some embodiments, in step five, the temperature of vacuum drying is 50 ℃ to 120 ℃, the time of vacuum drying is 12h to 36h, and the vacuum degree of vacuum drying is less than 200 Pa. When the drying temperature and time do not meet the conditions, the moisture in the green body cannot be sufficiently removed, the sintering process of the green body is seriously influenced, the product performance is reduced, and even the product is scrapped. The lower the vacuum level, the better the drying effect, but is limited by the equipment, and generally the vacuum drying oven can reduce the vacuum level to less than 200 Pa.

The test procedure of the embodiments of the present disclosure is explained next.

Example 1

The mullite whisker reinforced silicon carbide ceramic matrix composite material with in-situ growth is prepared according to the following method.

Step one, adding 62.6% of silicon carbide powder (with the particle size of 1 micrometer), 35.0% of aluminum hydroxide powder (with the particle size of 100nm), 1.5% of yttrium oxide powder (with the particle size of 1 micrometer) and 0.9% of calcium fluoride powder (with the particle size of 1 micrometer) as base raw materials into a ball milling tank, adding a dispersing agent aqueous solution (the dispersing agent is tetramethylammonium hydroxide, the mass ratio of the dispersing agent to the dispersing agent aqueous solution is 25%) with the mass ratio of 0.6% of the base raw material mass and deionized water with the mass ratio of 1.5 times of the base raw material mass, carrying out primary ball milling for 4 hours, adding a 0.5% adhesive solution (formed by polyvinyl alcohol and deionized water, the mass ratio of the polyvinyl alcohol to the adhesive solution is 10%) after primary ball milling, and continuing secondary ball milling for 1 hour to obtain slurry;

step two, putting the slurry obtained in the step one into a heat preservation box, and drying for 48 hours at 95 ℃ to obtain a solid;

grinding and granulating the solid obtained in the step two, and then sieving the solid, wherein the mesh number of a sieved screen is 100 meshes;

step four, performing dry pressing molding on the undersize product obtained in the step three by using a stainless steel mold to obtain a green body, wherein the dry pressing adopts two times of unidirectional pressurization, firstly the undersize product obtained in the step three is subjected to unidirectional pressurization at the pressure of 80MPa for 2min, then the mold is reversed, and unidirectional pressurization is performed again at the pressure of 80MPa for 2 min;

step five, vacuum drying the green body obtained in the step four at 95 ℃ for 36 hours, wherein the vacuum degree of the vacuum drying is about 130 Pa;

and step six, sintering the green body subjected to vacuum drying in the step five at 1550 ℃, and preserving heat for 2 hours to obtain the silicon carbide ceramic-based composite material 1 reinforced by the in-situ grown mullite whiskers.

The test and the result of the mullite whisker reinforced silicon carbide ceramic matrix composite material 1 in the in-situ growth are as follows:

(1) the product is characterized by X-ray diffraction analysis (XRD) and a Scanning Electron Microscope (SEM), and the observation results are shown in figure 1 and figure 2, the product only contains silicon carbide and mullite phases, the whisker distribution is disordered and uniform, and the whiskers are crisscrossed to form a bird nest structure.

And testing the prepared SiC porous ceramic by using an X-ray diffractometer to obtain an XRD spectrogram, and further analyzing the phase composition of the sample. The X-ray source is Cu Ka rays, the wavelength lambda is 0.1548nm, the filter plate is made of nickel, the voltage is 40kV, the current is 150mA, the continuous scanning range is 10-90 degrees, and the scanning speed is 10 degrees/min.

And (3) carrying out micro-topography analysis on the product by using a scanning electron microscope (JEOL JSM-7800, Phenom Pro). Before testing, the sample is dried in a vacuum drying oven for 12h in vacuum, and then the bottom surface of the sample is adhered to a sample table by conductive adhesive and placed into an instrument to observe the section. Before scanning, in order to increase the conductivity of the sample, the cross section of the sample is subjected to gold spraying treatment, and the gold spraying time is 30 s.

(2) The bending strength of the product is 125 MPa.

The bending strength of the sample is measured by adopting a microcomputer controlled electronic universal testing machine, and the specific steps are as follows: firstly, processing a sample into a sample strip with the size of 3 multiplied by 4 multiplied by 20mm by a grinding machine and an internal cutting machine, cleaning the sample by ultrasonic, and drying; measuring the actual size of the samples by using a vernier caliper, wherein each group of samples is not less than 5; then, the bending strength of the test piece is measured by using a microcomputer controlled electronic universal testing machine, the test piece is fixed by using a clamp of the testing machine, the middle part of the test piece is aligned with a pressure head, a pressure sensor uniformly pressurizes at a certain pressure speed until the test piece is crushed, the maximum test load numerical value on a stress and strain curve on a computer is recorded, and the compression strength is calculated by using a formula (1).

In the formula: sigma_FIs bending strengthIn MPa; f_FThe maximum load of the bending resistance test is expressed in kN; l is the span of the clamp and is in mm; b. h is the width and thickness of the sample respectively, the unit is mm, the loading speed is 0.2mm/min, and the span is 20 mm.

Example 2

Except for the step one of adding 52.0 percent of silicon carbide, 45.0 percent of aluminum hydroxide, 2.0 percent of yttrium oxide and 1.0 percent of calcium fluoride into a ball milling tank, the rest of the process is the same as the example 1, and the step six obtains the silicon carbide ceramic matrix composite material 2 with in-situ growth mullite whisker reinforcement.

The test result of the mullite whisker reinforced silicon carbide ceramic matrix composite material 2 with the in-situ growth comprises the following steps:

(1) through an X-ray diffraction curve (figure 3) and observation under an electron microscope (figure 4), the product only contains silicon carbide and mullite phases, the whiskers are distributed disorderly and uniformly, and the whiskers are crisscrossed to form a bird nest structure.

(2) The bending strength of the product is 135 MPa.

Example 3

Except for the step one of adding 62.6 percent of silicon carbide, 35.0 percent of aluminum hydroxide, 1.5 percent of cerium oxide and 0.9 percent of calcium fluoride into a ball milling tank, the rest of the process is the same as the step 1, and the step six obtains the silicon carbide ceramic matrix composite material 3 with in-situ growth mullite whisker reinforcement.

The test result of the mullite whisker reinforced silicon carbide ceramic matrix composite 3 in situ growth is as follows:

(1) through an X-ray diffraction curve (figure 5) and observation under an electron microscope (figure 6), the product only contains silicon carbide and mullite phases, the whiskers are distributed disorderly and uniformly, and the whiskers are crisscrossed to form a bird nest structure.

(2) The bending strength of the product is 100 MPa.

Example 4

The process is the same as example 1 except that in the sixth step, the sintering temperature is 1500 ℃, and the silicon carbide ceramic matrix composite 4 reinforced by the mullite whisker in situ growth is obtained in the sixth step.

The test result of the mullite whisker reinforced silicon carbide ceramic matrix composite 4 in situ growth is as follows:

(1) through an X-ray diffraction curve (figure 7) and observation under an electron microscope (figure 8), the product only contains silicon carbide and mullite phases, the whiskers are distributed disorderly and uniformly, and the whiskers are crisscrossed to form a bird nest structure.

(2) The bending strength of the product is 87 MPa.

Example 5

The process is the same as example 1 except that the sintering temperature is 1500 ℃ and the heat preservation time is 4 hours in the sixth step, and the silicon carbide ceramic matrix composite material 5 enhanced by the mullite whiskers growing in situ is obtained in the sixth step.

The test result of the mullite whisker reinforced silicon carbide ceramic matrix composite 5 in situ growth is as follows:

(1) through an X-ray diffraction curve (figure 9) and observation under an electron microscope (figure 10), the product only contains silicon carbide and mullite phases, the whiskers are distributed disorderly and uniformly, and the whiskers are crisscrossed to form a bird nest structure.

(2) The bending strength of the product is 94 MPa.

Comparative example 1

The process is the same as example 1 except that the first step of adding 64.0% of silicon carbide and 36.0% of aluminum hydroxide into the ball milling pot and the sixth step of obtaining the ceramic matrix composite material 6 with silicon carbide are carried out.

Test results of the silicon carbide ceramic matrix composite 6:

(1) the product was free of mullite whiskers and had a cristobalite phase in addition to the silicon carbide and mullite phases, as observed by X-ray diffraction (fig. 11) and electron microscopy (fig. 12).

(2) The bending strength of the product is 11 MPa.

Comparative example 2

The process is the same as example 1 except that the first step is to add 63.5% of silicon carbide, 35.0% of aluminum hydroxide and 1.5% of yttrium oxide into the ball milling pot, and the sixth step is to obtain the silicon carbide ceramic matrix composite 7.

Test results of the silicon carbide ceramic matrix composite 7:

(1) the product was free of mullite whiskers and had a cristobalite phase in addition to the silicon carbide and mullite phases, as observed by X-ray diffraction (fig. 13) and electron microscopy (fig. 14).

(2) The bending strength of the product is 41 MPa.

Comparative example 3

The process is the same as example 1 except that the silicon carbide ceramic matrix composite material 8 is obtained in the sixth step of adding 64.1% of silicon carbide, 35.0% of aluminum hydroxide and 0.9% of calcium fluoride into the ball milling pot in the first step.

Test results of the silicon carbide ceramic matrix composite 8:

(1) according to an X-ray diffraction curve (figure 15) and observation under an electron microscope (figure 16), the product contains a cristobalite phase in addition to silicon carbide and mullite phases, and the generated mullite whiskers are extremely small in quantity.

(2) The bending strength of the product is 35 MPa.

Comparative example 4

The process is the same as example 1 except that in the sixth step, the sintering temperature is 1450 ℃, and the silicon carbide ceramic matrix composite material 9 is obtained in the sixth step.

Test results of the silicon carbide ceramic matrix composite 9:

(1) through an X-ray diffraction curve (figure 17) and observation under an electron microscope (figure 18), the product only contains silicon carbide and mullite phase, and the growth of the mullite phase has certain anisotropy, but the whisker structure is not formed.

(2) The bending strength of the product is 68 MPa.

Comparative example 5

The process is the same as example 1 except that the heat preservation time in the sixth step is 6 hours, and the silicon carbide ceramic matrix composite material 10 is obtained in the sixth step.

Test results for the silicon carbide ceramic matrix composite 10:

(1) the product only contains silicon carbide and mullite phases and does not contain mullite whiskers by the X-ray diffraction curve (figure 19) and the observation under an electron microscope (figure 20).

(2) The bending strength of the product is 84 MPa.

It is clear from examples 1 and 2 that the change in the mixture ratio of the silicon carbide powder, the aluminum hydroxide powder, the metal oxide powder and the fluoride powder has an influence only on the flexural strength of the product.

It is seen from examples 1 and 3 that the material selection of the metal oxide powder has only an effect on the flexural strength of the product.

From example 1 and examples 4-5 it is seen that the appropriate sintering temperature and the appropriate holding time only have an effect on the flexural strength of the product.

As seen from example 1 and comparative examples 4 to 5, improper sintering temperature and improper sintering time affect not only whisker generation but also bending strength of the product.

It is seen from example 1 and comparative examples 1 to 3 that the metal oxide and the fluoride powder together act to eliminate the cristobalite phase and greatly enhance the flexural strength.

Claims

1. A preparation method of an in-situ growth mullite whisker reinforced silicon carbide ceramic matrix composite material comprises the following steps:

adding a substrate raw material into a ball milling tank, adding a dispersant aqueous solution and a ball milling medium, carrying out primary ball milling, adding a binder solution after the primary ball milling, and continuing secondary ball milling to obtain slurry, wherein the substrate raw material comprises silicon carbide powder, aluminum hydroxide powder, metal oxide powder and fluoride powder;

step two, drying and dehydrating the slurry obtained in the step one to obtain a solid;

granulating the solid obtained in the step two, and then sieving;

step four, dry-pressing and molding the undersize obtained in the step three by using a mold to obtain a green body;

step five, vacuum drying the green body obtained in the step four;

and step six, sintering the green body subjected to vacuum drying in the step five at 1500-1550 ℃, and preserving heat for 2-4 h, wherein the lower the sintering temperature is, the longer the heat preservation time is, so as to obtain the silicon carbide ceramic-based composite material enhanced by the mullite whisker grown in situ.

2. The method for preparing an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite material according to claim 1, wherein in the first step,

the particle size of the silicon carbide powder is 100nm-1 mu m;

the particle size of the aluminum hydroxide powder is 100nm-1 mu m;

the particle size of the metal oxide powder is 100nm-1 μm;

the particle size of the fluoride powder is 100nm-1 μm.

3. The method for preparing an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite material according to claim 1, wherein in the first step,

the metal oxide of the metal oxide powder is selected from one or more of yttrium oxide, cerium oxide, molybdenum oxide and vanadium oxide;

the fluoride of the fluoride powder is selected from one or more of calcium fluoride, aluminum fluoride and ammonium fluoride;

the dispersant in the dispersant aqueous solution is tetramethyl ammonium hydroxide or sodium silicate;

the ball milling medium is deionized water or absolute ethyl alcohol;

the binder solution is composed of polyvinyl alcohol and deionized water or polyvinyl butyral and absolute ethyl alcohol.

4. The method for preparing an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite material according to claim 1, wherein in the first step,

the mass ratio of the silicon carbide powder, the aluminum hydroxide powder, the metal oxide powder and the fluoride powder is (35-80): 15-55): 0.5-15): 0.2-10;

the mass of the dispersant aqueous solution is 0.05-2% of that of the matrix raw material, and the dispersant accounts for 10-25% of the mass ratio of the dispersant aqueous solution;

the mass of the ball milling medium is 0.5-5 times of that of the matrix raw material;

the mass of the binder solution is 0.1-10% of that of the matrix raw material, and the mass ratio of the binder to the binder solution is 5-10%.

5. The method for preparing an in-situ grown mullite whisker reinforced silicon carbide ceramic matrix composite material according to claim 1, wherein in the first step,

the time of primary ball milling is 2h-12 h;

the time of the secondary ball milling is 1h-6 h.

6. The method for preparing the mullite whisker reinforced silicon carbide ceramic matrix composite material in situ grown according to claim 1,

in the second step, the temperature of drying and dehydration is 50-150 ℃, and the time of drying and dehydration is 2-48 h.

7. The method for preparing the mullite whisker reinforced silicon carbide ceramic matrix composite material in situ grown according to claim 1,

in the third step, the granulation adopts a grinding mode, and the mesh number of a sieving screen is 40-200 meshes.

8. The method for preparing the mullite whisker reinforced silicon carbide ceramic matrix composite material in situ grown according to claim 1,

in the fourth step, the dry pressing adopts two times of unidirectional pressurization, firstly, the undersize obtained in the third step is subjected to unidirectional pressure maintaining with the pressure of 80-100 Mpa for 1-3 min, then the mould is reversed, and the unidirectional pressurization is carried out again with the pressure of 80-100 Mpa for 1-3 min.

9. The method for preparing the mullite whisker reinforced silicon carbide ceramic matrix composite material in situ grown according to claim 1,

in the fifth step, the temperature of vacuum drying is 50-120 ℃, the time of vacuum drying is 12-36 h, and the vacuum degree of vacuum drying is less than 200 Pa.