CN111892415A - A kind of silicon carbide whisker/alumina ceramic composite material and preparation method thereof - Google Patents

Abstract

The invention relates to a silicon carbide whisker/alumina ceramic composite material and a preparation method thereof, belonging to the technical field of alumina ceramic. The preparation method of the silicon carbide whisker/alumina ceramic composite material comprises the following steps: carrying out oscillating pressure sintering on the composite powder to obtain the composite powder; the composite powder consists of silicon carbide whiskers and alumina powder. According to the preparation method of the silicon carbide whisker/alumina ceramic composite material, dynamic pressure sintering is realized by utilizing oscillating pressure sintering, the densification process of a blank is accelerated through mechanisms such as rearrangement, diffusion and migration, the discharge of closed pores at a grain boundary in the later sintering stage is accelerated, the relative density of the composite ceramic material is favorably improved, and the mechanical property of the composite ceramic material is improved.

Description

A kind of silicon carbide whisker/alumina ceramic composite material and preparation method thereof

technical field

The invention relates to a silicon carbide whisker/alumina ceramic composite material and a preparation method thereof, belonging to the technical field of alumina ceramics.

Background technique

Alumina ceramic has the characteristics of high melting point, high hardness, wear resistance, corrosion resistance and low cost. It is the industrial ceramic material with the widest application and largest output in the world. Broad application prospects. However, alumina ceramics have low toughness and high brittleness. In order to continuously expand their application fields, it is often necessary to add reinforcing phases to improve toughness. At present, the main toughening principle is to add different energy dispersion factors, such as fibers, whiskers, particles, etc., into the microstructure of Al ₂ O ₃ ceramics. The principle of improving fracture toughness is that the reinforcement introduced when the material is fractured can consume more energy. At present, the main toughening methods are: ZrO ₂ toughening, nanotechnology toughening, whisker and fiber toughening, particle dispersion toughening Wait.

Whisker toughening mainly improves the toughness of Al ₂ O ₃ -based ceramics through the bridging, pinning or deflecting of cracks and the pulling out of whiskers in ceramics. The pull-out effect for whiskers means that when the crack propagation encounters high-strength whiskers, there is a large shear stress on the interface between the whiskers and the substrate near the crack tip, which can easily cause the whiskers to separate from the interface. , the whiskers can be pulled out from the matrix, and the energy of the external load is consumed by the interface friction to achieve the purpose of toughening. At the same time, the whiskers are pulled out from the matrix to create microcracks to absorb more energy. For crack bridging, it is a kind of crack tip tail effect. That is, when a whisker is encountered in the process of crack propagation, the crack may undergo transgranular failure, or interlocking may occur, that is, the crack bypasses the whisker and forms a friction bridge. The research shows that the existence of crack bridges is found in whisker reinforced ceramic materials and microcrystalline Al ₂ O ₃ ceramics. Toughening for crack deflection is a toughening method for the non-planar fracture effect of cracks. When the crack propagates to the whisker, it is forced to deflect along the whisker, which means that the forward path of the crack is longer, and the stress intensity at the crack tip is reduced. The better, the higher the fracture toughness.

Silicon carbide whisker is a highly oriented single crystal fiber, the composition of the crystalline phase is uniform, and it also has the characteristics of corrosion resistance, high temperature oxidation resistance and wear resistance. Silicon carbide whiskers, as an excellent reinforcing and toughening agent, can strengthen a variety of ceramic matrix composites. However, the use of silicon carbide whiskers to strengthen alumina-based ceramics by conventional preparation methods will also reduce the density of ceramic materials, and increase defects such as pores and microcracks, resulting in a decrease in mechanical properties such as flexural strength of the material.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a preparation method of a silicon carbide whisker/alumina ceramic composite material, which can significantly improve the flexural strength of the material.

The present invention also provides a silicon carbide whisker/alumina ceramic composite material prepared by the above preparation method.

In order to achieve the above purpose, the technical scheme adopted in the preparation method of the silicon carbide whisker/alumina ceramic composite material of the present invention is:

A method for preparing a silicon carbide whisker/alumina ceramic composite material comprises the following steps: sintering a composite powder under oscillating pressure to obtain; the composite powder is composed of a silicon carbide whisker and an alumina powder.

The preparation method of the silicon carbide whisker/alumina ceramic composite material of the present invention utilizes oscillating pressure sintering to realize dynamic pressure sintering, and can accelerate the discharge of closed pores at the grain boundary during sintering and accelerate the blank through mechanisms such as rearrangement, diffusion and migration. The densification process of the body can reduce the sintering temperature, shorten the sintering time and improve the hardness and bending strength of the material. At the same time, the oscillating pressure sintering can also suppress the abnormal growth of the grains, making the size and shape of the grains more uniform, and further improving the material. The hardness and flexural strength of the composite ceramic materials made can meet the needs of high-performance ceramic materials in extreme application environments.

In order to further improve the density of the prepared alumina ceramic composite material, the temperature T of the oscillatory pressure sintering is preferably 1400-1800°C, more preferably 1500-1800°C, still more preferably 1600-1700°C.

In order to make the sintering process proceed sufficiently, preferably, the heating rate to the temperature for oscillating pressure sintering is not more than 8°C/min. For example, when the temperature T of the oscillating pressure sintering is less than or equal to 1600° C., the rate of increasing the temperature to the oscillating pressure sintering temperature T is not more than 8° C./min. In another example, when the temperature T of the oscillating pressure sintering is greater than 1600°C, the temperature is first heated to T ₁ at a first heating rate not greater than 8°C/min, and then heated to the temperature of the oscillation pressure sintering at a second heating rate not greater than 5°C. Temperature T, 1550°C≤T ₁ <T, first heating rate>second heating rate. Further preferably, when the temperature T of the oscillating pressure sintering is less than or equal to 1600° C., the rate of increasing the temperature to the oscillating pressure sintering temperature T is 6 to 8° C./min. When the temperature of the oscillating pressure sintering is greater than 1600°C, the temperature is first heated to T ₁ at a rate of 6-8° C./min, and then heated to the temperature T of the oscillating pressure sintering at a rate of 3-5° C. 1550° C.≤T ₁ < T, the first heating rate>the second heating rate. The temperature T ₁ is preferably 1600°C. Rapid heating is beneficial to the progress of densification and inhibition of grain growth, but due to the short sintering time, material migration and diffusion cannot be fully effected, so that the final densification of the sample is not high; Slow heating in stages can obtain better densification effect and microstructure.

In order to further improve the mechanical properties of the prepared alumina ceramic composite material, preferably, the oscillating pressure sintering pressure is oscillated with an amplitude of 1-10 MPa and an oscillation frequency of 1-10 Hz on the basis of a constant pressure of 20-50 MPa . Further preferably, the pressure of the oscillating hot pressing sintering is oscillated on the basis of a constant pressure of 30-40 MPa. The amplitude of the oscillation hot pressing sintering is 5-10 MPa. The frequency of the oscillation hot pressing sintering is 1-5 Hz.

Silicon carbide whiskers and alumina powders are uniformly dispersed in the composite powder. Preferably, the composite powder is obtained by wet ball milling and drying the mixed powder of the silicon carbide whisker raw material and the alumina raw material. Further preferably, the composite powder is prepared by a method comprising the following steps: ball milling the mixture of the silicon carbide whisker raw material, the alumina powder raw material and the wetting agent, and then drying. The wet ball milling is carried out in a planetary ball mill. The revolution speed of wet ball mill is 90～150r/min, the rotation speed is 180～300r/min, and the time is 180～300min. The material-to-ball ratio of the wet ball mill is 1:1.5-4. The diameter of the silicon carbide whisker raw material is preferably 0.2 to 3 μm, more preferably 1 to 2 μm. The aspect ratio of the silicon carbide whisker raw material is preferably 6 to 48:1, more preferably 9 to 18:1. The average particle diameter of the alumina raw material powder is preferably 0.1 to 2 μm, more preferably 0.2 to 0.5 μm. The drying temperature is preferably 70 to 90°C. The drying time is preferably 10-15 h.

In order to improve the toughness of the alumina ceramic composite material while ensuring that the material has good flexural strength, preferably, the mass ratio of the silicon carbide whiskers to the alumina powder is preferably 1:2 to 25, more preferably 3.5 to 6.5:1. The volume ratio of the silicon carbide whiskers and the alumina powder is 5-30:95-70, more preferably 15-25:75-85.

In order to reduce the energy consumption of oscillating pressure sintering while improving the mechanical properties of the alumina ceramic composite, preferably, the oscillating pressure sintering time is preferably not more than 3 hours, more preferably 0.5-1.5 hours.

Preferably, a pressure of 20-50 MPa is applied to the composite powder before oscillating pressure sintering. Before oscillating pressure sintering, the temperature of the composite powder is started after the pressure is applied, or the temperature of the composite powder is started at the same time as the pressure is applied.

The technical scheme adopted by the silicon carbide whisker/alumina ceramic composite material of the present invention is:

A silicon carbide whisker/alumina ceramic composite material prepared by the above-mentioned preparation method of silicon carbide whisker/alumina ceramic composite material.

The silicon carbide whisker/alumina ceramic composite material of the present invention is prepared by the above-mentioned preparation method of silicon carbide whisker/alumina ceramic composite material, the relative density is above 97.71%, the bending strength is above 447MPa, and the Vickers The hardness is above 12.47GPa, and it is a high-performance alumina ceramic composite material.

Description of drawings

Fig. 1 is the XRD pattern of the silicon carbide whisker/alumina ceramic composite material prepared in Examples 1-3;

Fig. 2 is the fracture SEM image of the silicon carbide whisker/alumina ceramic composite material obtained in Example 1;

Fig. 3 is the fracture SEM image of the silicon carbide whisker/alumina ceramic composite material obtained in Example 2;

FIG. 4 is a SEM image of the fracture surface of the silicon carbide whisker/alumina ceramic composite material prepared in Example 3. FIG.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

The planetary ball mills used in the preparation methods of silicon carbide whiskers/alumina ceramic composites in Examples 1 to 3 and Comparative Examples are the QM-QX-2L planetary ball mills produced by Miqi Instruments Co., Ltd.; Examples 1 to 3 The alumina raw material powder used in this product is a product of type AKP-30 produced by Sumitomo Corporation of Japan, and the purity of the silicon carbide whisker raw material used is above 99%.

Examples of preparation methods of silicon carbide whiskers/alumina ceramic composites

Example 1

The preparation method of the silicon carbide whisker/alumina ceramic composite material of the present embodiment includes the following steps:

1) Weigh 41.9 g of alumina raw material powder, 9.05 g of silicon carbide whisker raw material (the mass ratio of alumina raw material powder and silicon carbide whisker raw material is about 4.6:1, and the volume ratio is 80:20), and put into In the two ball mill jars, add 100ml of absolute ethanol to each ball mill jar, stir evenly, seal and fix it in the planetary ball mill, put in agate balls to control the ratio of material to ball to 1:2, and control the revolution speed of the planetary ball mill to be 120r/ min, the rotation speed is 240r/min, and the ball milling is 256min; the average particle size of the alumina raw material powder used is 0.3 μm, the diameter of the silicon carbide whisker is 1.5 μm, and the aspect ratio is 12:1;

2) After the ball milling, take out the material from the ball mill tank and filter out the agate balls with a sieve, then place it in a rectangular enamel pan and put it in a bellows to dry for 12 hours, then take it out and put it in a heating porcelain pan and place it in an electric heating constant temperature drying The oven was dried at 80 °C for 12 h, and after drying, it was taken out and sieved for several times to obtain dry and fine SiC _w /Al ₂ O ₃ composite powder;

3) Take 11g of SiC _w /Al ₂ O ₃ composite powder and put it into a graphite mold with an inner diameter of 30 mm, then put the graphite mold loaded with the composite powder into the oscillating pressure sintering furnace, apply a constant pressure of 30 MPa, and control the temperature rise. The rate is 8°C/min and the temperature is raised to 1600°C to start oscillating pressure sintering. After the oscillating pressure sintering is over, close the oscillating pressure sintering furnace, slowly cool down to room temperature, and then take out;

The temperature of oscillating pressure sintering is 1600℃, the pressure of oscillating pressure sintering is 30MPa constant pressure, the amplitude is 5MPa, the oscillation frequency is 1Hz, and the time of oscillating pressure sintering is 1h.

Example 2

The preparation method of the silicon carbide whisker/alumina ceramic composite material of the present embodiment includes the following steps:

1) Weigh 39.3 g of alumina raw material powder, 11.32 g of silicon carbide whisker raw material (the mass ratio of alumina raw material powder and silicon carbide whisker raw material is about 3.47:1, and the volume ratio is 75:25), and put into In the two ball mill jars, add 100ml of absolute ethanol to each ball mill jar, stir evenly, seal and fix it in the planetary ball mill, put in agate balls to control the ratio of material to ball to 1:2, and control the revolution speed of the planetary ball mill to be 120r/ min, the rotation speed is 240 r/min, and the ball milling is 256 min; the average particle size of the alumina raw material powder used is 0.2 μm, the diameter of the silicon carbide whiskers is 1 μm, and the aspect ratio is 9:1;

2) After the ball milling, take out the material from the ball mill tank and filter out the agate balls with a sieve, then place it in a rectangular enamel pan and put it in a bellows to dry for 12 hours, then take it out and put it in a heating porcelain pan and place it in an electric heating constant temperature drying The oven was dried at 80 °C for 12 h, and after drying, it was taken out and sieved for several times to obtain dry and fine SiC _w /Al ₂ O ₃ composite powder;

3) Take 11g of SiC _w /Al ₂ O ₃ composite powder and put it into a graphite mold with an inner diameter of 30mm, then put the graphite mold loaded with the powder into an oscillating pressure sintering furnace, apply a constant pressure of 40MPa, and control the heating rate The oscillating pressure sintering was started by heating up to 1500 ℃ at 8 ℃/min. After the oscillating pressure sintering was completed, the oscillating pressure sintering furnace was closed, and the oscillating pressure sintering furnace was slowly cooled to room temperature, and then taken out;

The temperature of oscillating pressure sintering is 1500℃, the pressure of oscillating pressure sintering is 40MPa constant pressure, the amplitude is 10MPa, the oscillation frequency is 5Hz, and the time of oscillating pressure sintering is 1h.

Example 3

The preparation method of the silicon carbide whisker/alumina ceramic composite material of the present embodiment includes the following steps:

1) Weigh 44.5g of alumina raw material powder and 6.8g of silicon carbide whisker raw material (the mass ratio of the alumina raw material powder and the silicon carbide whisker raw material is about 6.5:1, and the volume ratio is 85:15), and put into In the two ball mill jars, add 100ml of absolute ethanol to each ball mill jar, stir evenly, seal and fix it in the planetary ball mill, put in agate balls to control the ratio of material to ball to 1:2, and control the revolution speed of the planetary ball mill to be 120r/ min, the rotation speed is 240 r/min, and the ball milling is 256 min; the average particle size of the alumina raw material powder used is 0.5 μm, the diameter of the silicon carbide whiskers is 2 μm, and the aspect ratio is 18:1;

2) After the ball milling, take out the material from the ball mill tank and filter out the agate balls with a sieve, then place it in a rectangular enamel pan and put it in a bellows to dry for 12 hours, then take it out and put it in a heating porcelain pan and place it in an electric heating constant temperature drying The oven was dried at 80 °C for 12 h, and after drying, it was taken out and sieved for several times to obtain dry and fine SiC _w /Al ₂ O ₃ composite powder;

3) Take 11g of SiC _w /Al ₂ O ₃ composite powder and put it into a graphite mold with an inner diameter of 30mm, then put the graphite mold loaded with the powder into the oscillating pressure sintering furnace, apply a constant pressure of 30MPa, and control the heating rate Heat up to 1600°C at 8°C/min, and then adjust the heating rate to 5°C/min and heat up to 1800°C to start oscillating pressure sintering. After the oscillating pressure sintering is over, close the oscillating pressure sintering furnace, slowly cool to room temperature, and take it out, that is, have to;

The temperature of oscillating pressure sintering is 1800℃, the pressure of oscillating pressure sintering is 30MPa constant pressure, the amplitude is 5MPa, the oscillation frequency is 2Hz, and the time of oscillating pressure sintering is 1h.

Examples of Silicon Carbide Whisker/Alumina Ceramic Composites

Example 4

The silicon carbide whisker/alumina ceramic composite material of this embodiment is prepared by the preparation method in any one of the foregoing Embodiments 1 to 3, and will not be repeated here.

Comparative ratio

The preparation method of the silicon carbide whisker/alumina ceramic composite material of the present comparative example comprises the following steps:

1) Prepare SiC _w /Al ₂ O ₃ composite powder according to steps 1) to 2) of Example 1;

2) Take 11g of SiC _w /Al ₂ O ₃ composite powder and put it into a graphite mold with an inner diameter of 30mm, then put the graphite mold loaded with the composite powder into the oscillating pressure sintering furnace, apply a constant pressure of 50MPa, and control the temperature rise. The rate is 8°C/min and the temperature is raised to 1600°C to start hot pressing sintering. After sintering, the oscillating pressure sintering furnace is closed, slowly cooled to room temperature and taken out. The constant is 50MPa, and the pressure sintering time is 1h.

Experimental example

1) Using an X-ray diffraction analyzer (XRD) to characterize the phases of the silicon carbide whiskers/alumina ceramic composites prepared in Examples 1 to 3, respectively, and then analyze the raw materials and their phase changes in the preparation process and The phase composition of the final ceramic composite is shown in Figure 1. It can be seen from the figure that after oscillating pressure sintering, the main crystal phases of the sample are Al ₂ O ₃ and SiC, and no other diffraction peaks appear. It also shows that no other impurities were introduced during the preparation of the composite powder.

2) The JSM-7001F scanning electron microscope (SEM) of JEOL was used to detect and analyze the microscopic morphology of the silicon carbide whiskers/alumina ceramic composites prepared in Examples 1 to 3, as shown in Figures 2 to 2. 4. It can be seen from Figures 2 to 4 that the samples have reached a good density after sintering, and the rod-shaped SiC whiskers are closely combined with Al ₂ O ₃ . Some SiC whiskers penetrate through the Al ₂ O ₃ crystal, and some pass through the Al ₂ O ₃ grain boundary without obvious pores.

3) The bulk density of the silicon carbide whisker/alumina ceramic composite materials prepared in Examples 1 to 3 and the comparative example was measured by the Archimedes densitometry method. Then the ratio of actual density (ie bulk density) to theoretical density was calculated to obtain the relative density. The results are shown in Table 1.

Table 1 Densities and relative densities of silicon carbide whiskers/alumina ceramic composites prepared in Examples 1 to 3 and Comparative Examples

Density/g·cm^-3 Relative density/% Example 1 3.776 98.95 Example 2 3.691 97.71 Example 3 3.802 98.63 Comparative ratio 3.743 98.09

4) The flexural strength of the silicon carbide whisker/alumina ceramic composite materials prepared in Examples 1 to 4 was tested according to "GB/T6569-2006 Test Method for Bending Strength of Fine Ceramics", and the results are shown in Table 2.

Table 2 Bending strength of silicon carbide whiskers/alumina ceramic composites prepared in Examples 1 to 3 and Comparative Example

5) According to "GBT 16534-1996 Vickers Hardness Test Method Standard for Engineering Ceramics", the hardness of the silicon carbide whisker/alumina ceramic composite materials prepared in Examples 1 to 3 and the comparative example was tested, and the results are shown in Table 3.

Table 3 Hardness of alumina ceramic materials prepared in Examples 1 to 3 and Comparative Example

Hardness (unit Gpa) Example 1 17.16 Example 2 16.19 Example 3 12.47 Comparative ratio 16.06

Claims (10)

1. a preparation method of silicon carbide whisker/alumina ceramic composite material, it is characterized in that: comprise the following steps: oscillating pressure sintering of composite powder, to obtain; described composite powder is composed of silicon carbide whisker and alumina Powder composition. 2 . The method for preparing a silicon carbide whisker/alumina ceramic composite material according to claim 1 , wherein the temperature T of the oscillating pressure sintering is 1400-1800° C. 3 . 3. The preparation method of silicon carbide whisker/alumina ceramic composite material according to claim 2, characterized in that: when the temperature T of the oscillating pressure sintering is less than or equal to 1600°C, the rate of heating up to the oscillating pressure sintering temperature T is not constant. greater than 8°C/min; when the temperature T of the oscillating pressure sintering is greater than 1600°C, the temperature is first heated to T 1 at a first temperature increase rate not greater than 8°C/min, and then heated to T ₁ at a second temperature increase rate not greater than 5°C. The temperature T of the oscillating pressure sintering, 1550°C≤T ₁ <T, the first heating rate>the second heating rate. 4 . The preparation method of silicon carbide whisker/alumina ceramic composite material according to claim 1 , wherein the pressure of the oscillating pressure sintering is carried out on the basis of a constant pressure of 20-50 MPa and the amplitude is 1-10 MPa. 5 . , The oscillation frequency is 1~10Hz. 5. The preparation method of silicon carbide whisker/alumina ceramic composite material according to claim 1, characterized in that: the composite powder is a wet method of the mixed powder of silicon carbide whisker raw material and alumina raw material Ball milled and dried. 6 . The preparation method of silicon carbide whisker/alumina ceramic composite material according to claim 1 , wherein: the diameter of the silicon carbide whisker raw material is 0.2-3 μm, and the aspect ratio is 6-48:1 . 7 . The method for preparing a silicon carbide whisker/alumina ceramic composite material according to claim 5 or 6 , wherein the average particle size of the alumina raw material powder is 0.1-2 μm. 8 . 8. The preparation method of the silicon carbide whisker/alumina ceramic composite material according to any one of claims 1 to 6, wherein the mass ratio of the silicon carbide whisker to the alumina powder is 1: 2～25, the volume ratio is 5～30:95～70. 9 . The preparation method of silicon carbide whisker/alumina ceramic composite material according to any one of claims 1 to 6 , wherein the time of the oscillating pressure sintering does not exceed 3 hours. 10 . 10. A silicon carbide whisker/alumina ceramic composite material prepared by the method for preparing a silicon carbide whisker/alumina ceramic composite material according to claim 1.

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