CN114988900A - Method for preparing whisker toughened ceramic matrix composite material by dynamic pressure flash firing - Google Patents
Method for preparing whisker toughened ceramic matrix composite material by dynamic pressure flash firing Download PDFInfo
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- 239000011153 ceramic matrix composite Substances 0.000 title claims abstract description 35
- 239000000463 material Substances 0.000 title claims abstract description 33
- 238000000034 method Methods 0.000 title claims abstract description 30
- 238000010304 firing Methods 0.000 title claims abstract description 27
- 239000000919 ceramic Substances 0.000 claims abstract description 101
- 230000005684 electric field Effects 0.000 claims abstract description 30
- 239000000843 powder Substances 0.000 claims abstract description 25
- 238000003825 pressing Methods 0.000 claims abstract description 19
- 238000005245 sintering Methods 0.000 claims abstract description 12
- 238000001816 cooling Methods 0.000 claims abstract description 9
- 239000013078 crystal Substances 0.000 claims abstract description 6
- 238000005242 forging Methods 0.000 claims abstract description 4
- 239000011812 mixed powder Substances 0.000 claims description 20
- 230000010355 oscillation Effects 0.000 claims description 18
- 239000002002 slurry Substances 0.000 claims description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- 239000008367 deionised water Substances 0.000 claims description 10
- 229910021641 deionized water Inorganic materials 0.000 claims description 10
- 238000010438 heat treatment Methods 0.000 claims description 9
- 238000000227 grinding Methods 0.000 claims description 8
- 238000002390 rotary evaporation Methods 0.000 claims description 8
- 238000007873 sieving Methods 0.000 claims description 8
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 5
- 239000002131 composite material Substances 0.000 claims description 5
- 238000004321 preservation Methods 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 2
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 1
- 230000008569 process Effects 0.000 abstract description 12
- 238000000280 densification Methods 0.000 abstract description 9
- 238000002360 preparation method Methods 0.000 abstract description 9
- 230000007547 defect Effects 0.000 abstract description 7
- 229910010293 ceramic material Inorganic materials 0.000 abstract description 2
- 230000001808 coupling effect Effects 0.000 abstract description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 20
- 238000002485 combustion reaction Methods 0.000 description 12
- 238000001514 detection method Methods 0.000 description 12
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- 239000011159 matrix material Substances 0.000 description 2
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Abstract
The invention belongs to the technical field of ceramic material preparation, and particularly relates to a method for preparing a whisker toughened ceramic matrix composite material by dynamic pressure flash firing. The method comprises the steps of preparing mixed ceramic powder from whiskers and ceramic powder, pressing the mixed ceramic powder into a ceramic blank, applying oscillating pressure to the upper end and the lower end of the ceramic blank while flash firing the ceramic blank to realize flash firing, forging, pressing and sintering under the assistance of dynamic force, and finally cooling to obtain the whisker toughened ceramic matrix composite. In the sintering process, the thermal field, the dynamic force field and the electric field are coupled, so that the sintering temperature is reduced under the coupling action, the ceramic densification speed is accelerated, and finally the whisker toughened ceramic matrix composite material with small crystal grain size, less internal defects, stable whisker structure and high density is prepared.
Description
Technical Field
The invention belongs to the technical field of ceramic material preparation, and particularly relates to a method for preparing a whisker toughened ceramic matrix composite material by dynamic pressure flash firing.
Background
The whisker toughened ceramic matrix composite is an effective measure for improving the brittleness of ceramics, and is a research hotspot in the direction of high-performance structural ceramics at home and abroad. However, since the rigid ceramic whiskers hardly shrink during sintering, when the ceramic matrix shrinks, hoop tensile stress and radial tensile stress are generated around the ceramic whiskers, which prevents the ceramic matrix from further shrinking, and makes it difficult to densify the composite material. Therefore, it is urgently needed to develop a new method to solve the problem that the whisker toughened composite material is difficult to sinter.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for preparing a whisker toughened ceramic matrix composite material by dynamic pressure flash firing, so as to solve the problems that the whisker toughened ceramic matrix composite material is difficult to sinter and the composite material is difficult to densify.
The technical scheme adopted by the invention is as follows:
a method for preparing a whisker toughened ceramic matrix composite material by dynamic pressure flash firing comprises the following steps:
1) uniformly mixing the crystal whisker and the ceramic powder to prepare ceramic mixed powder;
2) pressing the ceramic mixed powder into a ceramic green body;
3) placing the ceramic blank body in a furnace body, heating the furnace body to a certain temperature, applying an electric field to the ceramic blank body for flash firing, applying oscillating pressure to the upper end and the lower end of the ceramic blank body while the flash firing is carried out, and carrying out dynamic pressure-assisted flash firing, forging and pressure sintering;
4) and after keeping the temperature for a certain time, stopping oscillating the pressure and the electric field, and cooling to obtain the whisker toughened ceramic matrix composite material.
Heating the furnace body to 500-1200 ℃ in the step 3); the electric field intensity is 50-300V/cm, and the current density is 60-200 mA/mm 2 。
The median value of the oscillation pressure in the step 3) is 10-150 MPa according to the area calculation, the amplitude value is 5-50 MPa, the frequency value is 0.5-20 Hz, and the power value of the product of the amplitude value and the frequency is not more than 200.
The application of the oscillating pressure in the step 3) may be performed before the flash combustion starts or after the flash combustion starts, but not later than the flash combustion stabilization phase.
The specific steps of the step 1) are as follows: the crystal whisker and the ceramic powder are ultrasonically dispersed in water to obtain ceramic slurry, and the ceramic slurry is subjected to rotary evaporation, grinding and sieving to obtain ceramic mixed powder, wherein the grain size of the ceramic mixed powder is 150 microns.
The whisker is as follows: the proportion of the ceramic powder is 5-30%: 70-95% of deionized water, wherein the amount of the deionized water is more than the total amount of the whiskers and the ceramic powder; the ultrasonic dispersion time is 6-48 h.
The whisker is SiC whisker and Al 2 O 3 Whisker and ZrO 2 One of the whiskers; the ceramic powder is ZrO 2 Powder of Al 2 O 3 One kind of powder.
And the heat preservation time in the step 4) is 5-30 min.
When the ceramic body is pressed in the step 2), the pressed ceramic body can be in various shapes, such as dog bone shape, cylindrical shape, strip shape and the like, and the shape can be selected according to the requirement.
And 3) after an electric field is applied to the ceramic blank, slowly increasing the current of the blank to a set value, then converting voltage control into current control, rapidly decreasing the voltage, entering a flash combustion stabilization stage, completely flash-combusting in the state, and preserving the heat under a preset current density.
The whisker toughened ceramic matrix composite material prepared by the method is adopted. The density of the composite material ranges from 96 percent to 99.8 percent, and the hardness is 17.5 to 23.5 GPa.
When an electric field and oscillation pressure are applied to a ceramic blank, the electric field and the oscillation pressure can be simultaneously applied to the upper pressing head and the lower pressing head at the upper end and the lower end of the ceramic blank, and the electric field is connected to the upper pressing head and the lower pressing head in two stages; oscillation pressure can be applied to the upper end and the lower end of the ceramic blank through upper and lower pressure, an electric field is applied to the ceramic blank in other directions, such as the left and right directions, the specific direction of the electric field can be adjusted according to the shape of the ceramic blank, and no fixed limitation exists.
In the present invention, it is well known that high strength structural ceramics are brittle and have limited plastic deformability, requiring higher temperatures to effect deformation. According to the invention, flash firing is selected during preparation, the flash firing process is about 3-30min, and the whisker toughened ceramic matrix composite material can realize large-degree plastic deformation at a lower temperature, so that low-temperature rapid sintering, rapid substance transmission and low-temperature superplastic deformation of the material are realized. Pure flash firing overcomes the problem of difficult sintering, but still does not overcome the problem of difficult material densification.
The invention applies pressure while flash burning is carried out, the pressure is selected not to be constant pressure but to be oscillating pressure, and the progress is not smooth while the oscillating pressure is applied, because the flash burning result directly influences whether the oscillating pressure can be applied or not. When the defects generated in the material by flash firing are too small, rapid deformation and densification cannot be achieved even if an oscillating pressure is applied. When the number of defects generated in the material by flash firing is too large, the defects are aggregated to form microscopic pores, and at this time, the pores cannot be removed even if an oscillating pressure is applied, thereby greatly reducing the performance of the material.
In the sintering process, the thermal field, the dynamic force field and the electric field are coupled, so that the sintering temperature is reduced under the coupling action, the densification speed is accelerated, and the ceramic matrix composite material with small grain size, less internal defects, stable whisker structure and high density is finally prepared.
Drawings
FIG. 1 is a scanned (500 times) view of a whisker toughened ceramic matrix composite made in example 1;
FIG. 2 is a scanned graph (10000 times) of the whisker toughened ceramic matrix composite material prepared in example 1;
FIG. 3 is a scanned graph (500 times) of the ceramic matrix composite made in example 5;
FIG. 4 is a scanned graph (15000 times) of the ceramic matrix composite prepared in example 5;
FIG. 5 is a scanned graph of the ceramic matrix composite made in example 6.
Detailed Description
The following examples are given to illustrate specific embodiments of the present invention, but the following examples are only intended to illustrate the present invention in detail and do not limit the scope of the present invention in any way.
Example 1:
the preparation method of the whisker toughened ceramic matrix composite material comprises the following steps:
(1) al is stirred by ultrasonic for 10h 2 O 3 Fully dispersing 2g of whiskers and 28g of zirconia powder in 100g of deionized water to obtain ceramic slurry with uniformly distributed whiskers, and then sequentially performing rotary evaporation, grinding and sieving on the ceramic slurry to obtain 150-micron ceramic mixed powder;
(2) pressing 4g of the ceramic mixed powder obtained in the step (1), and obtaining a dog-bone-shaped ceramic blank A after pressing and forming;
(3) placing the ceramic blank A obtained in the step (2) between an upper pressure head and a lower pressure head, heating to a preset temperature of 800 ℃, applying a preset electric field strength on the upper pressure head and the lower pressure head of the ceramic blank, and starting flash burning until the materials are completely flash burned; wherein the electric field intensity is 100V/cm, and the current density is 100 mA/mm 2 。
(4) And after the ceramic body A is subjected to flash combustion stably, applying oscillation pressure with the median value of 30 MPa, the amplitude value of 5MPa and the frequency of 1Hz by controlling the upper pressure head and the lower pressure head, preserving the temperature for 10 min, stopping oscillation force and flash combustion, and cooling to obtain the whisker toughened zirconia ceramic matrix composite.
Through detection, the density of the final sample reaches 99.1%, and the hardness reaches 17.5 GPa.
Example 2:
the preparation method of the whisker toughened ceramic matrix composite material comprises the following steps:
(1) 2g of SiC whisker and Al are stirred by ultrasound for 10h 2 O 3 Fully dispersing 10g of powder in 50g of deionized water to obtain the crystal whiskerUniformly distributing ceramic slurry, and then sequentially performing rotary evaporation, grinding and sieving on the ceramic slurry to obtain ceramic mixed powder of 150 micrometers;
(2) 3g of the ceramic mixed powder obtained in the step (1) is pressed, and a dog-bone-shaped ceramic blank body A is obtained after pressing and forming;
(3) placing the ceramic blank A obtained in the step (2) between an upper pressure head and a lower pressure head, heating to a preset temperature of 1000 ℃, applying a preset electric field strength on the upper pressure head and the lower pressure head of the ceramic blank, and starting flash burning until the materials are completely flash burned; wherein the electric field intensity is 200V/cm, and the current density is 8mA/mm 2 。
(4) And when the ceramic blank A starts to flash, applying oscillation pressure with the median value of 50MPa, the amplitude value of 10MPa and the frequency of 2Hz by controlling the upper pressure head and the lower pressure head, preserving the temperature for 1.5min, stopping oscillation force and flash combustion, and cooling to obtain the whisker toughened zirconia ceramic matrix composite.
Through detection, the density of the final sample reaches 99.3%, and the hardness reaches 23.5 GPa.
Example 3:
the preparation method of the whisker toughened ceramic matrix composite material comprises the following steps:
(1) 2g of SiC whiskers and ZrO were ultrasonically stirred for 10 hours 2 Fully dispersing 18g of powder in 100g of deionized water to obtain ceramic slurry with uniformly distributed whiskers, and then sequentially performing rotary evaporation, grinding and sieving on the ceramic slurry to obtain 150-micron ceramic mixed powder;
(2) pressing 4g of the ceramic mixed powder obtained in the step (1), and obtaining a dog-bone-shaped ceramic blank A after pressing and forming;
(3) placing the ceramic body A obtained in the step (2) between an upper pressure head and a lower pressure head, heating to a preset temperature of 1000 ℃, then applying a preset electric field strength to the upper pressure head and the lower pressure head of the ceramic body, and starting flash burning until the materials are completely flash-burned; wherein the electric field intensity is 100V/cm, and the current density is 200mA/mm 2 。
(4) And after the ceramic body A is subjected to flash combustion stably, applying oscillation pressure with the median value of 150MPa, the amplitude value of 50MPa and the frequency of 2Hz by controlling an upper pressure head and a lower pressure head, preserving the temperature for 10 min, stopping oscillation force and flash combustion, and cooling to obtain the whisker toughened zirconia ceramic matrix composite.
Through detection, the density of the final sample reaches 99.6%, and the hardness reaches 18.5 GPa.
Example 4:
the preparation method of the whisker toughened ceramic matrix composite material comprises the following steps:
(1) al is stirred by ultrasonic for 10h 2 O 3 Whisker 3g and Al 2 O 3 Fully dispersing 7g of powder in 40g of deionized water to obtain ceramic slurry with uniformly distributed whiskers, and then sequentially performing rotary evaporation, grinding and sieving on the ceramic slurry to obtain 150-micron ceramic mixed powder;
(2) pressing 4g of the ceramic mixed powder obtained in the step (1), and obtaining a dog-bone-shaped ceramic blank A after pressing and forming;
(3) placing the ceramic blank A obtained in the step (2) between an upper pressure head and a lower pressure head, heating to a preset temperature of 1000 ℃, applying a preset electric field strength on the upper pressure head and the lower pressure head of the ceramic blank, and starting flash burning until the materials are completely flash burned; wherein the electric field intensity is 200V/cm, and the current density is 5 mA/mm 2 。
(4) And when the ceramic blank A starts to flash, applying oscillation pressure with the median value of 150MPa, the amplitude value of 20MPa and the frequency of 5Hz by controlling the upper pressure head and the lower pressure head, preserving the temperature for 1 min, stopping oscillation force and flash combustion, and cooling to obtain the whisker toughened zirconia ceramic matrix composite.
Through detection, the density of the final sample reaches 99.8%, and the hardness reaches 22 GPa.
Example 5:
the preparation method of the whisker toughened ceramic matrix composite material comprises the following steps:
(1) al is stirred by ultrasonic for 10h 2 O 3 Fully dispersing 2g of whiskers and 28g of zirconia powder in 100g of deionized water to obtain ceramic slurry with uniformly distributed whiskers, and then sequentially performing rotary evaporation, grinding and sieving on the ceramic slurry to obtain 150-micron ceramic mixed powder;
(2) pressing 4g of the ceramic mixed powder obtained in the step (1), and obtaining a dog-bone-shaped ceramic blank A after pressing and forming;
(3) sintering the ceramic blank A obtained in the step (2) at 900 ℃ for 2h to obtain a prepressing sample B with the relative density of 67%;
(4) and (3) placing the prepressing sample B in a furnace body, raising the temperature of the furnace body to 1230 ℃ of black body radiation temperature, applying oscillation pressure with the median value of 30 MPa, the amplitude value of 5MPa and the frequency of 1Hz on the prepressing sample B by controlling an upper pressure head and a lower pressure head, stopping oscillation force, and cooling to obtain the whisker toughened zirconia ceramic matrix composite material.
Through detection, the density of the final sample reaches 96%, and the hardness reaches 14.7 GPa.
Example 6:
the preparation method of the whisker toughened ceramic matrix composite material comprises the following steps:
(1) al is stirred by ultrasonic for 10h 2 O 3 Fully dispersing 2g of whiskers and 28g of zirconia powder in 100g of deionized water to obtain ceramic slurry with uniformly distributed whiskers, and then sequentially performing rotary evaporation, grinding and sieving on the ceramic slurry to obtain 150-micron ceramic mixed powder;
(2) pressing 4g of the ceramic mixed powder obtained in the step (1), and obtaining a dog-bone-shaped ceramic blank A after pressing and forming;
(3) placing the ceramic blank A obtained in the step (2) between an upper pressure head and a lower pressure head, heating to a preset temperature of 800 ℃, applying a preset electric field strength on the upper pressure head and the lower pressure head of the ceramic blank, and starting flash burning until the materials are completely flash burned; wherein the electric field intensity is 100V/cm, and the current density is 100 mA/mm 2 。
(4) And after the ceramic body A is subjected to flash firing stably, applying a constant pressure of 30 MPa by controlling the upper pressure head and the lower pressure head, preserving the temperature for 10 min, stopping applying the pressure and performing flash firing, and cooling to obtain the whisker toughened zirconia ceramic matrix composite.
Through detection, the density of the final sample reaches 97.8%, and the hardness reaches 15.6 GPa.
Example 7: over-high electric field strength 400
The difference from example 1 is that the electric field strength used in step 3) was 400V/cm.
Through detection, the density of the final sample reaches 98.5%, and the hardness reaches 16.7 GPa.
Example 8: electric field intensity is too small 30
The difference from example 1 is that the electric field strength used in step 3) was 30V/cm.
Through detection, the sample is not subjected to flash combustion, and the density is not changed and is still 63%.
Example 9: current density too low 40
The difference from example 1 is that the current density used in step 3) was 20mA/mm 2 。
Through detection, the density of the final sample reaches 94%, and the hardness reaches 12.7 GPa.
Example 10: current density 300 deg.C too high
The difference from example 1 is that the current density used in step 3) was 300mA/mm 2 。
Through detection, the density of the final sample reaches 90%, and the hardness reaches 11.4 GPa.
Example 11:
the difference from example 1 is that the median value of the oscillation pressure was calculated in terms of area at 200MPa, the amplitude at 5MPa and the frequency at 1 Hz.
Through detection, the density of the final sample reaches 97.5%, and the hardness reaches 15.2 GPa.
Example 12:
the difference from example 1 is that the median value of the oscillation pressure is 5MPa, the amplitude value is 2MPa and the frequency value is 1Hz, calculated according to the area.
Through detection, the density of the final sample reaches 96.8%, and the hardness reaches 15 GPa.
Example 13:
the difference from example 1 is that the zirconia powder was replaced with SiC powder.
Under the same conditions, no flash combustion occurs and no change occurs in the density, which indicates that the method of the invention is not applicable to all raw material types.
As seen from FIG. 1, the scanned image of the whisker toughened ceramic sample prepared in example 1 has no pores, which proves that the sample has higher density under the condition; as can be seen from fig. 2, the grain size is 230 nm. The presence of pores in the low power scan of the whisker toughened ceramic sample prepared in example 5, as seen in figure 3, demonstrates the lower density of the sample from this condition and the grain size is 350nm as seen in figure 4. From fig. 5, it can also be seen that there are still pores in the scanned image of the whisker toughened ceramic sample prepared in example 6, but the number of pores is less than that of fig. 3, demonstrating that the density is improved, but still less than that of fig. 1. Thus demonstrating the effectiveness of flash combined oscillatory forging.
The experiment shows that when the sintering process is finished at the temperature corresponding to the blackbody radiation temperature without flash burning, the required furnace temperature can be greatly improved, and the final sample has very low relative density and hardness within the same heat preservation time.
When the oscillating pressure is not applied and the constant pressure is used, it can be seen that the density of the synthesized sample is lower than that of the sample synthesized under the oscillating pressure in the same time, because the oscillating pressure accelerates the densification process, i.e. accelerates the sliding process or plastic deformation process of the grain boundary. The change is similar to the fatigue process in the metal material, and has great promotion effect on the improvement of compactness and performance.
When the electric field intensity is too high, the power in the flash process is increased sharply, so that too high heat is generated at the contact part of the electrode and the sample, and the sample is damaged. Thereby reducing the density and performance of the sample. When the electric field strength is too small, the initial condition of flash firing cannot be reached, and flash firing cannot occur at this time, so that the density of the sample cannot be improved.
When the current density is too high, the current-excited vacancies and defects are greatly increased, and part of the vacancies are gathered in the interior of the grains to generate pores, which cannot be removed by plastic deformation or grain boundary sliding, thereby reducing the compactness and the performance of the sample. When the current density is too small, the density brought by flash firing is lower, and the vacancy excited by the current is smaller, at the moment, even if oscillating pressure is applied, the densification and deformation processes are still controlled by diffusion, while in the densification and deformation processes controlled by diffusion, the oscillating force cannot play a role in promotion, and finally, the density and the deformation degree of the sample are mostly brought by flash firing, so the density and the performance are lower.
When the median value of the oscillating pressure is too small, dislocation or grain boundary slip caused by flash firing cannot be activated, and the densification and deformation processes are still mainly controlled by diffusion, so that the oscillating pressure has little influence on densification and deformation and has low performance.
When the median value of the oscillation pressure is too large, the material is deformed to a large extent, the defect excited by the current is not enough to regulate and control the strain caused by the large pressure, and a large number of air holes are generated in the sample to adapt to the large deformation, so that the density and the performance of the final sample are reduced on the contrary.
In the invention, the density test is carried out by an Archimedes drainage method, and the hardness test is carried out by a microhardness tester.
Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solutions of the present invention by those of ordinary skill in the art should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.
Claims (9)
1. A method for preparing a whisker toughened ceramic matrix composite material by dynamic pressure flash firing is characterized by comprising the following steps:
uniformly mixing the crystal whisker and the ceramic powder to prepare ceramic mixed powder;
pressing the ceramic mixed powder into a ceramic green body;
placing the ceramic blank in a furnace body, heating the furnace body to a certain temperature, applying an electric field to the ceramic blank for flash firing, applying oscillating pressure to the upper end and the lower end of the ceramic blank while the flash firing is carried out, and carrying out dynamic force assisted flash firing, forging and pressure sintering;
4) and (5) after keeping the temperature for a certain time, stopping oscillating the pressure and the electric field, and cooling to obtain the whisker toughened ceramic matrix composite material.
2. The production method according to claim 1, characterized in that: heating the furnace body to 500-1200 ℃ in the step 3); the electric field intensity is 50-300V/cm, and the current density is 60-200 mA/mm 2 。
3. The method of claim 1, wherein: the median value of the oscillation pressure in the step 3) is 10-150 MPa according to the area calculation, the amplitude value is 5-50 MPa, and the frequency value is 0.5-20 Hz.
4. The method of claim 1, wherein: the specific steps of the step 1) are as follows: the crystal whisker and the ceramic powder are ultrasonically dispersed in water to obtain ceramic slurry, and the ceramic slurry is subjected to rotary evaporation, grinding and sieving to obtain ceramic mixed powder, wherein the grain size of the ceramic mixed powder is 150 microns.
5. The method of claim 4, wherein: the whisker: the proportion of the ceramic powder is 5-30%: 70-95% of deionized water, wherein the amount of the deionized water is more than the total amount of the whiskers and the ceramic powder; the ultrasonic dispersion time is 6-48 h.
6. The method of claim 4, wherein: the whisker is SiC whisker and Al 2 O 3 Whisker and ZrO 2 One of the whiskers; the ceramic powder is ZrO 2 Powder of Al 2 O 3 One kind of powder.
7. The method of claim 1, wherein: and the heat preservation time in the step 4) is 5-30 min.
8. A whisker toughened ceramic matrix composite material produced by the method of any one of claims 1 to 7.
9. The whisker toughened ceramic matrix composite according to claim 8, wherein: the density of the composite material ranges from 99 percent to 99.8 percent, and the hardness is 17.5 to 23.5 GPa.
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