Preparation method of silicon carbide / silicon nitride composite ceramic with high-temperature wave-absorbing and bearing integration

Abstract

The invention discloses a preparation method of silicon carbide / silicon nitride composite ceramic with high-temperature wave-absorbing and bearing integration, and belongs to the field of high-temperature wave-absorbing ceramic. The invention aims to solve the problem that the high-strength silicon carbide-based high-temperature wave-absorbing ceramic cannot be prepared in the prior art. The method comprises the following steps: 1, ball-milling and mixing silicon carbide, silicon nitride, a sintering aid and water, and then drying, crushing, grinding and sieving; and 2, prepressing and sintering. The preparation method is used for preparing the silicon carbide / silicon nitride composite ceramic with high-temperature wave-absorbing and bearing integration.

Description

Technical Field

[0001] The present invention belongs to the field of high-temperature wave-absorbing ceramics. Background Art

[0002] Silicon carbide has various excellent properties, including high-temperature tolerance, high hardness, corrosion resistance, etc. This makes silicon carbide ceramics one of the ideal materials for manufacturing stealth aircraft and missiles. However, a single silicon carbide bulk ceramic has very poor impedance matching and hardly absorbs electromagnetic waves; therefore, the currently studied silicon carbide-based electromagnetic wave absorbing materials are mostly powder coatings or porous structure materials, but their mechanical properties and other functional properties are poor. Silicon nitride, due to its low density, low dielectric constant, good thermal shock resistance and toughness, can not only improve the crack resistance and fracture toughness of silicon carbide ceramics, but also has adjustable dielectric constant and electrical conductivity, and can effectively absorb electromagnetic waves through structural design or doping, realizing the integration of wave absorption and mechanical load-bearing functions. However, there are many problems to be solved at present. For example, the sintering temperature of silicon carbide / silicon nitride composite ceramics is high, the difference in thermal expansion coefficients between different components may cause cracks or defects, and it is difficult to ensure the uniform distribution of silicon carbide and silicon nitride in the matrix, etc. Summary of the Invention

[0003] The present invention aims to solve the problem that the prior art cannot prepare high-strength silicon carbide-based high-temperature wave-absorbing ceramics, and further provides a preparation method of a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorption and load-bearing.

[0004] A preparation method of a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorption and load-bearing is carried out according to the following steps:

[0005] 1. Mix silicon carbide, silicon nitride, sintering aids and water by ball milling to obtain a mixed powder slurry, and then dry, crush, grind and screen the mixed powder slurry to obtain the ground powder;

[0006] The mass ratio of the silicon carbide to the silicon nitride is 1:(1-9); the average particle size of the silicon carbide is 40nm-500nm; the average particle size of the silicon nitride is 350nm-800nm;

[0007] 2. Place the ground powder in a graphite mold for pre-pressing, and then sinter at a temperature of 1700°C-1900°C and a pressure of 30MPa-80MPa in a vacuum environment for 5min-30min, and finally cool down to room temperature to obtain a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorption and load-bearing.

[0008] The beneficial effects of the present invention are:

[0009] The present invention uses silicon carbide and silicon nitride powders with nano-sized particles as raw materials, and realizes the rapid sintering of silicon carbide / silicon nitride composite ceramics through a rapid hot pressing sintering process in a high-temperature vacuum environment. Silicon nitride with a low dielectric constant serves as the matrix, which can reduce the reflection of electromagnetic waves on the surface; nano-sized silicon carbide serves as the loss phase. Due to the large specific surface area of nano-materials, it can interact with electromagnetic waves more effectively, so that more electromagnetic waves entering the material can be absorbed and attenuated. The ceramic interface of silicon nitride-silicon carbide will also enhance the interfacial polarization loss, further improving the electromagnetic wave absorption performance. In addition, the prepared silicon carbide / silicon nitride composite ceramics have reached a very high density and have excellent mechanical properties, which enables it to have more applications in the aerospace field. Description of the Drawings

[0010] Figure 1 XRD pattern of the silicon carbide / silicon nitride composite ceramic prepared in Example 1;

[0011] Figure 2 Microscopic morphology and element distribution maps of the silicon carbide / silicon nitride composite ceramic prepared in Example 1;

[0012] Figure 3 Mechanical property comparison chart of the silicon carbide / silicon nitride composite ceramic prepared in Example 1 and the silicon carbide ceramic prepared in the comparative experiment;

[0013] Figure 4 Electromagnetic wave absorption performance chart of the silicon carbide / silicon nitride composite ceramic prepared in Example 1 at different temperatures. Detailed Embodiments

[0014] Detailed Embodiment 1: A preparation method of a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorption and load-bearing is carried out according to the following steps:

[0015] 1. Mix silicon carbide, silicon nitride, sintering aids and water by ball milling to obtain a mixed powder slurry, then dry, crush, grind and screen the mixed powder slurry to obtain the ground powder;

[0016] The mass ratio of silicon carbide to silicon nitride is 1:(1-9); the average particle size of silicon carbide is 40nm-500nm; the average particle size of silicon nitride is 350nm-800nm;

[0017] 2. Place the ground powder in a graphite mold for pre-pressing, and then sinter at 1700°C-1900°C and a pressure of 30MPa-80MPa in a vacuum environment for 5min-30min, and finally cool down to room temperature to obtain a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorption and load-bearing.

[0018] The beneficial effects of this embodiment are as follows:

[0019] In this embodiment, silicon carbide and silicon nitride powders with nano-sized particles are used as raw materials. In a high-temperature vacuum environment, rapid sintering of silicon carbide / silicon nitride composite ceramics is achieved through a rapid hot pressing sintering process. Silicon nitride with a low dielectric constant serves as the matrix, which can reduce the reflection of electromagnetic waves on the surface; nano-sized silicon carbide serves as the loss phase. Due to the large specific surface area of nano-materials, it can interact with electromagnetic waves more effectively, so that more electromagnetic waves entering the material can be absorbed and attenuated. The ceramic interface of silicon nitride - silicon carbide will also enhance the interfacial polarization loss, further improving the electromagnetic wave absorption performance. In addition, the prepared silicon carbide / silicon nitride composite ceramics reach a very high density and have excellent mechanical properties, which enables it to have more applications in the aerospace field.

[0020] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the sintering aid described in Step 1 is one or a mixture of two of alumina and yttrium oxide. Others are the same as Specific Embodiment 1.

[0021] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that the mass of the sintering aid described in Step 1 is 2% - 8% of the total mass of silicon carbide and silicon nitride. Others are the same as Specific Embodiment 1 or 2.

[0022] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that the mass ratio of the total mass of silicon carbide, silicon nitride, and the sintering aid to the mass of water in Step 1 is 1:(2 - 7). Others are the same as Specific Embodiment 3.

[0023] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that the ball milling and mixing in Step 1 is specifically carried out under the conditions of a rotation speed of 200 r / min - 500 r / min and a ball-to-material mass ratio of (2 - 6):1 for 6 h - 18 h. Others are the same as Specific Embodiments 1 to 4.

[0024] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that the sieving in Step 1 is through a sieve mesh of 20 - 80 meshes. Others are the same as Specific Embodiments 1 to 5.

[0025] Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is that the pre-pressing in Step 2 is specifically carried out under the condition of a pressure of 20 MPa - 100 MPa for 20 min - 50 min. Others are the same as Specific Embodiments 1 to 6.

[0026] Embodiment VIII: The difference between this embodiment and any one of Embodiments I - VII is that: the vacuum degree of the vacuum environment described in Step 2 is 0.1 Pa - 1 Pa. Others are the same as those in Embodiments I - VII.

[0027] Embodiment IX: The difference between this embodiment and any one of Embodiments I - VIII is that: in Step 2, under the conditions of a vacuum environment and a pressure of 30 MPa - 80 MPa, first, at a heating rate of 50 °C / min - 150 °C / min, heat up to 900 °C - 1050 °C, then at a heating rate of 50 °C / min - 120 °C / min, heat up to 1400 °C - 1650 °C, and finally at a heating rate of 50 °C / min - 100 °C / min, heat up to 1700 °C - 1900 °C. Others are the same as those in Embodiments I - VIII.

[0028] Embodiment X: The difference between this embodiment and any one of Embodiments I - IX is that: in Step 2, under the conditions of a vacuum environment and a pressure of 30 MPa - 80 MPa, cool down to room temperature at a cooling rate of 20 °C / min - 100 °C / min. Others are the same as those in Embodiments I - IX.

[0029] The following examples are used to verify the beneficial effects of the present invention:

[0030] Example 1:

[0031] A preparation method of a silicon carbide / silicon nitride composite ceramic with integrated high - temperature wave absorption and load - bearing properties is carried out according to the following steps:

[0032] I. Under the conditions of a rotation speed of 300 r / min and a ball - to - material mass ratio of 5:1, ball - mill and mix silicon carbide, silicon nitride, sintering aids and water for 10 h to obtain a mixed powder slurry, then dry, crush and grind the mixed powder slurry, and pass it through a 60 - mesh sieve to obtain the ground powder;

[0033] The mass ratio of silicon carbide to silicon nitride is 1:9; the average particle size of silicon carbide is 60 nm; the average particle size of silicon nitride is 500 nm;

[0034] The sintering aids are composed of alumina and yttrium oxide mixed in a mass ratio of 3:4;

[0035] The mass of the sintering aids is 6% of the total mass of silicon carbide and silicon nitride;

[0036] The mass ratio of the total mass of silicon carbide, silicon nitride and sintering aids to the mass of water is 1:4;

[0037] II. Place the ground powder in a graphite mold, pre-press it for 50 min under the condition of a pressure of 70 MPa, and then under the conditions of a vacuum degree of 0.1 Pa and a pressure of 50 MPa, first heat it to 1000 °C at a heating rate of 100 °C / min, then heat it to 1600 °C at a heating rate of 100 °C / min, and finally heat it to 1900 °C at a heating rate of 50 °C / min. Sinter it for 20 min under the conditions of a vacuum degree of 0.1 Pa, a temperature of 1900 °C and a pressure of 50 MPa. Finally, under the conditions of a vacuum degree of 0.1 Pa and a pressure of 50 MPa, cool it to room temperature at a cooling rate of 50 °C / min to obtain the silicon carbide / silicon nitride composite ceramic.

[0038] In Step II, place the ground powder in a graphite mold and lay a layer of graphite paper between the powder and the mold.

[0039] Comparative experiment: The difference between this comparative experiment and Example 1 is that the use of silicon nitride is omitted in Step I. Others are the same as in Example 1.

[0040] It is measured by the Archimedes method that the silicon carbide / silicon nitride composite ceramic prepared in Example 1 has a very high relative density, reaching more than 99%.

[0041] Figure 1 is the XRD pattern of the silicon carbide / silicon nitride composite ceramic prepared in Example 1; as can be seen from the figure, strong diffraction peaks of SiC and Si 3 N 4 appear, indicating that the silicon carbide / silicon nitride composite ceramic is successfully prepared by this method.

[0042] Figure 2 is the microscopic morphology diagram and element distribution diagram of the silicon carbide / silicon nitride composite ceramic prepared in Example 1; as can be seen from the figure, carbon, silicon and nitrogen elements are evenly distributed in the prepared silicon carbide / silicon nitride composite ceramic, indicating that silicon carbide and silicon nitride in the ceramic are dispersedly distributed, and it also further indicates that the silicon carbide / silicon nitride composite ceramic is successfully prepared by the method in the example, and it can be seen from the microscopic morphology that it has no cracks or defects.

[0043] Test according to national standards GB / T 6569-2006 and GB / T 23806-2009; Figure 3 is the mechanical property comparison diagram of the silicon carbide / silicon nitride composite ceramic prepared in Example 1 and the silicon carbide ceramic prepared in the comparative experiment; as can be seen from the figure, the flexural strength of the silicon carbide / silicon nitride composite ceramic is 516 MPa, which is 66% higher than that of the ordinary silicon carbide ceramic; the fracture toughness is 6.4 MPa·m 1 / 2 , which is 15% higher than that of the ordinary silicon carbide ceramic.

[0044] The silicon carbide / silicon nitride composite ceramic prepared in Example 1 was processed into a block with dimensions of 22.86×10.16×3 mm 3 and tested using a microwave network vector analyzer (waveguide method) at room temperature to 600 °C. Figure 4 Figure for the electromagnetic wave absorption performance of the silicon carbide / silicon nitride composite ceramic prepared in Example 1 at different temperatures; as can be seen from the figure, the silicon carbide / silicon nitride composite ceramic has good electromagnetic wave absorption performance from 25 °C to 600 °C, and the minimum reflection losses are -10.1 dB (25 °C), -9.2 dB (100 °C), -20.8 dB (200 °C), -35.5 dB (300 °C), -25.5 dB (400 °C), -17.9 dB (500 °C), and -12.8 dB (600 °C) respectively, and the effective absorption bandwidths are 0.2 GHz (25 °C), 0 GHz (100 °C), 0.7 GHz (200 °C), 2.0 GHz (300 °C), 4.0 GHz (400 °C), 2.1 GHz (500 °C), 1.1 GHz (600 °C) respectively, which indicates that the silicon carbide / silicon nitride composite ceramic has excellent high-temperature electromagnetic wave absorption performance. Especially at 300 °C and 400 °C, the minimum reflection loss reaches -35.5 dB (300 °C) and the effective absorption bandwidth is 4.0 GHz (400 °C).

Claims

1. A method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load-bearing properties, characterized in that It is carried out in the following steps:

1. ball-milling silicon carbide, silicon nitride, a sintering aid and water to obtain a mixed powder slurry, and then drying, crushing, grinding and sieving the mixed powder slurry to obtain a ground powder; The mass ratio of silicon carbide to silicon nitride is 1:(1-9); the average particle size of silicon carbide is 40nm-500nm; the average particle size of silicon nitride is 350nm-800nm; 2. Place the ground powder in a graphite mold for pre-compression, then sinter for 5 min to 30 min in a vacuum environment at a temperature of 1700°C to 1900°C and a pressure of 30 MPa to 80 MPa, and finally cool to room temperature to obtain a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorption and load-bearing properties.

2. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load-bearing properties according to claim 1, characterized in that The sintering aid described in step 1 is one or a mixture of aluminum oxide and yttrium oxide.

3. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load bearing properties according to claim 1, characterized in that The mass of the sintering aid described in step 1 is 2% to 8% of the total mass of silicon carbide and silicon nitride.

4. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load bearing properties according to claim 1, characterized in that The mass ratio of the total mass of silicon carbide, silicon nitride and sintering aid described in step 1 to water is 1:(2-7).

5. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load-bearing properties according to claim 1, characterized in that The ball milling mixing described in step 1 is specifically performed for 6h to 18h at a rotation speed of 200r / min to 500r / min and a ball-to-material mass ratio of (2 to 6):

1.

6. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load-bearing properties according to claim 1, characterized in that The sieving described in step 1 is through a sieve of 20 mesh to 80 mesh.

7. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load-bearing properties according to claim 1, characterized in that The pre-pressing in step 2 is specifically performed at a pressure of 20 MPa to 100 MPa for 20 to 50 minutes.

8. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load-bearing properties according to claim 1, characterized in that The vacuum degree of the vacuum environment described in step 2 is 0.1Pa to 1Pa.

9. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load-bearing properties according to claim 1, characterized in that In step 2, under the conditions of a vacuum environment and a pressure of 30 MPa to 80 MPa, the temperature is first increased to 900°C to 1050°C at a heating rate of 50°C / min to 150°C / min, then increased to 1400°C to 1650°C at a heating rate of 50°C / min to 120°C / min, and finally increased to 1700°C to 1900°C at a heating rate of 50°C / min to 100°C / min.

10. The method for preparing a silicon carbide / silicon nitride composite ceramic with integrated high-temperature wave absorbing and load bearing properties according to claim 1, characterized in that In step 2, under the conditions of vacuum environment and pressure of 30 MPa to 80 MPa, the temperature is lowered to room temperature at a cooling rate of 20° C. / min to 100° C. / min.

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