Method for preparing silicon carbide fiber silicon carbide-based composite ceramic through nano transient eutectic

Abstract

The invention discloses a method for preparing silicon carbide fiber silicon carbide-based composite ceramic by nano transient eutectic, and belongs to the field of silicon carbide composite ceramic preparation. The invention aims to solve the problem of poor mechanical properties of the silicon carbide composite ceramic prepared by the prior art. The method comprises the following steps: 1, preparing mixed powder slurry; 2, treating silicon carbide fibers; 3, alternately laying the prepreg sheets and the ceramic powder; and 4, sintering. The method is used for preparing the silicon carbide fiber silicon carbide-based composite ceramic through nano transient eutectic.

Description

Technical Field

[0001] The invention belongs to the field of preparation of silicon carbide composite ceramics. Background Art

[0002] Silicon carbide fiber reinforced silicon carbide-based composite ceramics are an advanced composite material with high strength, high temperature stability and antioxidant properties. They are widely used in aerospace, hypersonic aircraft, nuclear reactor structures and other fields. Traditional preparation methods have some difficult-to-overcome technical bottlenecks. For example, chemical vapor infiltration and precursor impregnation pyrolysis methods have long process cycles and high costs, and the prepared silicon carbide fiber / silicon carbide composite materials have high porosity; the melt infiltration method will make the matrix and fiber interface easy to react, resulting in degradation of interface performance. There is a certain amount of free silicon in the composite material, which may react or volatilize at high temperatures to reduce the strength of the material. Therefore, it is urgent to provide a new method for preparing silicon carbide fiber / silicon carbide-based composite ceramics. Summary of the invention

[0003] The present invention aims to solve the problem that the silicon carbide composite ceramics prepared by the prior art have poor mechanical properties, and further provides a method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic.

[0004] A method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic is carried out according to the following steps:

[0005] 1. Preparation of mixed powder slurry:

[0006] The silicon carbide, sintering aid and water are ball-milled to obtain a mixed powder slurry;

[0007] The average particle size of the silicon carbide is 40nm to 100nm;

[0008] 2. Processing of silicon carbide fiber:

[0009] The silicon carbide fiber cloth is cleaned and dried, and then calcined at a temperature of 600° C. to 800° C. for 1 h to 2 h to obtain treated silicon carbide fiber;

[0010] Alternatively, the silicon carbide fiber cloth is cleaned and dried, and then immersed in tetrabutyl titanate for 10 to 50 minutes, taken out after immersion, and calcined at a temperature of 500 to 700° C. for 1 to 3 hours to obtain the treated silicon carbide fiber;

[0011] 3. Alternate laying of prepreg and ceramic powder:

[0012] ① The treated silicon carbide fibers are placed in the mixed powder slurry and then dried to obtain a prepreg;

[0013] ② Drying, grinding and sieving the mixed powder slurry to obtain ceramic powder;

[0014] ③ Alternately lay multiple prepreg sheets and ceramic powder to obtain a stacked material;

[0015] 4. Sintering:

[0016] The stacked material is placed in a graphite mold for pre-pressing, and then placed in a spark plasma sintering furnace. Under the conditions of a vacuum environment, a current of 5kA to 7kA, a temperature of 1800°C to 1950°C, and a pressure of 30MPa to 70MPa, the material is sintered for 10min to 30min, and finally cooled to room temperature to obtain silicon carbide fiber / silicon carbide-based composite ceramics.

[0017] The beneficial effects of the present invention are:

[0018] 1. The present invention adopts a spark plasma rapid sintering process, which can achieve rapid sintering of silicon carbide fiber / silicon carbide ceramics in a short time by rapidly heating up and combining with the effect of external pressure.

[0019] 2. The cross-stacking process adopted in the present invention is conducive to superimposing the performance advantages of silicon carbide fibers in a specific direction, while modifying the silicon carbide fibers to further achieve the enhancement and toughening of the composite material.

[0020] 3. Compared with the traditional preparation method of ceramic-based composite materials, the present invention has a simpler preparation process and has the advantages of short reaction time and high product quality. It not only significantly reduces the production cost, but also realizes the reinforcement and toughening of silicon carbide ceramics, and has excellent electromagnetic shielding performance. It has broad application prospects in high-tech fields such as aerospace hot end components and nuclear reactors. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The XRD spectrum of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1;

[0022] Figure 2 This is a microscopic morphology of the fracture surface of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1;

[0023] Figure 3 This is a comparison chart of the flexural strength of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1 and the silicon carbide ceramic prepared in the comparative experiment;

[0024] Figure 4 A comparison chart of the fracture toughness of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1 and the silicon carbide ceramic prepared in the comparative experiment;

[0025] Figure 5This is an electromagnetic shielding diagram of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1. DETAILED DESCRIPTION

[0026] Specific implementation method 1: This implementation method is a method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic, which is carried out according to the following steps:

[0027] 1. Preparation of mixed powder slurry:

[0028] The silicon carbide, sintering aid and water are ball-milled to obtain a mixed powder slurry;

[0029] The average particle size of the silicon carbide is 40nm to 100nm;

[0030] 2. Processing of silicon carbide fiber:

[0031] The silicon carbide fiber cloth is cleaned and dried, and then calcined at a temperature of 600° C. to 800° C. for 1 h to 2 h to obtain treated silicon carbide fiber;

[0032] Alternatively, the silicon carbide fiber cloth is cleaned and dried, and then immersed in tetrabutyl titanate for 10 to 50 minutes, taken out after immersion, and calcined at a temperature of 500 to 700° C. for 1 to 3 hours to obtain the treated silicon carbide fiber;

[0033] 3. Alternate laying of prepreg and ceramic powder:

[0034] ① The treated silicon carbide fibers are placed in the mixed powder slurry and then dried to obtain a prepreg;

[0035] ② Drying, grinding and sieving the mixed powder slurry to obtain ceramic powder;

[0036] ③ Alternately lay multiple prepreg sheets and ceramic powder to obtain a stacked material;

[0037] 4. Sintering:

[0038] The stacked material is placed in a graphite mold for pre-pressing, and then placed in a spark plasma sintering furnace. Under the conditions of a vacuum environment, a current of 5kA to 7kA, a temperature of 1800°C to 1950°C, and a pressure of 30MPa to 70MPa, the material is sintered for 10min to 30min, and finally cooled to room temperature to obtain silicon carbide fiber / silicon carbide-based composite ceramics.

[0039] The beneficial effects of this embodiment are:

[0040] 1. This embodiment adopts a spark plasma rapid sintering process, which can achieve rapid sintering of silicon carbide fiber / silicon carbide ceramics in a short time by rapidly increasing the temperature and combining it with the effect of external pressure.

[0041] 2. The cross-stacking process adopted in this embodiment is conducive to superimposing the performance advantages of silicon carbide fibers in a specific direction, while modifying the silicon carbide fibers to further achieve the enhancement and toughening of the composite material.

[0042] 3. Compared with the traditional ceramic-based composite material preparation method, the present embodiment has a simpler preparation process and has the advantages of short reaction time and high product quality. It not only significantly reduces the production cost, but also realizes the reinforcement and toughening of silicon carbide ceramics, and has excellent electromagnetic shielding performance. It has broad application prospects in high-tech fields such as aerospace hot end components and nuclear reactors.

[0043] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that the sintering aid described in step 1 is one or a combination of aluminum oxide and yttrium oxide. The rest is the same as specific embodiment 1.

[0044] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that: the mass of the sintering aid described in step 1 is 2% to 8% of the mass of silicon carbide; the mass ratio of the total mass of silicon carbide and sintering aid described in step 1 to water is 1:(3 to 8). Other aspects are the same as specific implementation method 1 or 2.

[0045] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the ball milling mixing described in step 1 is specifically performed for 6 hours to 20 hours at a rotation speed of 200 r / min to 600 r / min and a ball-to-material mass ratio of (2 to 6):1. The rest is the same as specific embodiment 3.

[0046] Specific implementation example 5: This implementation example is different from specific implementation examples 1 to 4 in that the thickness of the silicon carbide fiber cloth in step 2 is 0.1 mm to 0.3 mm. The rest is the same as specific implementation examples 1 to 4.

[0047] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that: in step 3①, the treated silicon carbide fiber is placed in the mixed powder slurry and immersed for 10min to 50min under the condition of vacuum degree of 0.1Pa to 5Pa, and the immersion is repeated 3 to 9 times; the drying described in step 3① is specifically dried at a temperature of 40℃ to 80℃ for 2h to 10h. The rest is the same as specific embodiments 1 to 5.

[0048] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that: the sieving described in step 3 ② is specifically through a 20-80 mesh screen; the laying thickness of the ceramic powder described in step 3 ③ is 0.2 mm to 1 mm. The rest is the same as specific embodiments 1 to 6.

[0049] Specific implementation eight: This implementation differs from specific implementations one to seven in that the pre-pressing in step four is performed at a pressure of 20 MPa to 100 MPa for 20 to 50 minutes. The rest is the same as specific implementations one to seven.

[0050] Specific embodiment 9: This embodiment is different from specific embodiments 1 to 8 in that: in step 4, under the conditions of vacuum degree of 0.1Pa to 1Pa and pressure of 30MPa to 70MPa, the current is regulated, and the temperature is first raised to 1000℃ to 1500℃ at a heating rate of 50℃ / min to 150℃ / min, and then raised to 1800℃ to 1950℃ at a heating rate of 30℃ / min to 120℃ / min. The rest is the same as specific embodiments 1 to 8.

[0051] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that: in step 4, under the conditions of vacuum degree of 0.1Pa to 1Pa and pressure of 30MPa to 70MPa, the current is regulated, the temperature is lowered to 900℃ to 1200℃ at a cooling rate of 10℃ / min to 30℃ / min, then to 200℃ to 500℃ at a cooling rate of 20℃ / min to 50℃ / min, and finally to room temperature at a cooling rate of 30℃ / min to 80℃ / min. The rest is the same as specific embodiments 1 to 9.

[0052] The following examples are used to verify the beneficial effects of the present invention:

[0053] Embodiment 1:

[0054] A method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic is carried out according to the following steps:

[0055] 1. Preparation of mixed powder slurry:

[0056] At a rotation speed of 300 r / min and a ball-to-material mass ratio of 5:1, silicon carbide, a sintering aid and water were ball-milled for 20 h to obtain a mixed powder slurry;

[0057] The average particle size of the silicon carbide is 60nm; the sintering aid is a mixture of aluminum oxide and yttrium oxide in a mass ratio of 3:2;

[0058] The mass of the sintering aid is 6% of the mass of silicon carbide.

[0059] The mass ratio of the total mass of the silicon carbide and the sintering aid to the water is 1:3;

[0060] 2. Processing of silicon carbide fiber:

[0061] Under the condition of power of 600W, the silicon carbide fiber cloth was immersed in ethanol and ultrasonically cleaned for 30 minutes, dried after cleaning, and then calcined at a temperature of 700°C for 2 hours to obtain the treated silicon carbide fiber;

[0062] The thickness of the silicon carbide fiber cloth is 0.2 mm;

[0063] 3. Alternate laying of prepreg and ceramic powder:

[0064] ① Under the condition of vacuum degree of 0.1Pa, the treated silicon carbide fiber is arranged in the mixed powder slurry and immersed for 30min, and the immersion is repeated 3 times, and then dried at a temperature of 60°C for 5h to obtain a prepreg;

[0065] ② Dry, grind and pass the mixed powder slurry through a 60-mesh sieve to obtain ceramic powder;

[0066] ③ Alternately lay multiple prepreg sheets and ceramic powder to obtain a stacked material;

[0067] The ceramic powder is laid with a thickness of 0.5 mm; the stacked material has 20 layers of prepreg sheets and 21 layers of ceramic powder;

[0068] 4. Sintering:

[0069] The stacked material is placed in a graphite mold, pre-pressed for 30 minutes at a pressure of 30 MPa, and then placed in a spark plasma sintering furnace. Under the conditions of a vacuum degree of 0.1 Pa and a pressure of 50 MPa, the current is regulated, and the temperature is first increased to 1500°C at a heating rate of 100°C / min, and then increased to 1900°C at a heating rate of 50°C / min. Then, under the conditions of a vacuum degree of 0.1 Pa, a current of 6 kA, a temperature of 1900°C and a pressure of 50 MPa, it is sintered for 20 minutes. Finally, under the conditions of a vacuum degree of 0.1 Pa and a pressure of 50 MPa, the current is regulated, the temperature is cooled to 1000°C at a cooling rate of 20°C / min, then cooled to 300°C at a cooling rate of 30°C / min, and finally cooled to room temperature at a cooling rate of 50°C / min to obtain silicon carbide fiber / silicon carbide-based composite ceramics.

[0070] Embodiment 2: This embodiment is different from Embodiment 1 in that: in step 2, the silicon carbide fiber cloth is immersed in ethanol and ultrasonically cleaned for 30 minutes at a power of 600 W, dried after cleaning, and then immersed in tetrabutyl titanate for 30 minutes, taken out after immersion, and calcined at a temperature of 600° C. for 2 hours to obtain the treated silicon carbide fiber. The rest is the same as Embodiment 1.

[0071] Comparative experiment: The difference between this embodiment and the first embodiment is that the use of the prepreg sheet is omitted in step 3, and the ceramic powder is directly loaded into the graphite mold for pre-pressing and sintering in step 4. The rest is the same as the first embodiment.

[0072] According to tests, the porosity of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1 is only 0.9%.

[0073] Figure 1 This is the XRD spectrum of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1; it can be seen from the figure that the phase of the prepared silicon carbide fiber / silicon carbide composite ceramic is β-SiC, and almost no α-SiC is found. This shows that the silicon carbide ceramic prepared by the method in the example has almost no crystal transformation.

[0074] Figure 2 This is a microscopic morphology of the fracture surface of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1; it can be seen from the figure that the silicon carbide fiber structure in the matrix is ​​well maintained, which shows that the silicon carbide fiber is well bonded to the matrix and has basically no pores, but is not completely sintered into a whole; in addition, some fibers are pulled out of the material, which shows that the silicon carbide fiber can play its toughening role.

[0075] Tested according to GB / T 6569-2006 standard, Figure 3 The figure is a comparison chart of the flexural strength of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1 and the silicon carbide ceramic prepared in the comparative experiment; it can be seen from the figure that the flexural strength of the silicon carbide fiber / silicon carbide composite ceramic is 413.5MPa, which is 26% higher than that of ordinary silicon carbide ceramics. It shows that the method in the embodiment can successfully prepare high-strength silicon carbide fiber / silicon carbide composite ceramics.

[0076] Tested according to GB / T 23806-2009 standard, Figure 4 This is a comparison chart of the fracture toughness of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1 and the silicon carbide ceramic prepared in the comparative experiment; it can be seen from the figure that the fracture toughness of the silicon carbide fiber / silicon carbide composite ceramic is 6.8MPa·m 1 / 2 , which is 38% higher than that of common silicon carbide ceramics. This indicates that the method in the embodiment can successfully prepare high-toughness silicon carbide fiber / silicon carbide composite ceramics.

[0077] According to the national standards GB / T 6569-2006 and GB / T 23806-2009, the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 2 has a flexural strength of 446.8 MPa and a fracture toughness of 7.1 MPa·m 1 / 2 .

[0078] The silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1 was processed into a size of 22.86×10.16×3 mm. 3 The block is tested using a microwave network vector analyzer (waveguide method); Figure 5 This is the electromagnetic shielding diagram of the silicon carbide fiber / silicon carbide-based composite ceramic prepared in Example 1; as can be seen from the figure, the shielding effectiveness SE is greater than 30dB in the entire X-band (8.2GHz~12.4GHz), showing excellent electromagnetic wave shielding performance, which indicates that the silicon carbide fiber / silicon carbide composite ceramic has excellent electromagnetic shielding performance.

Claims

1. A method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic, characterized in that It is carried out in the following steps:

1. Preparation of mixed powder slurry: The silicon carbide, sintering aid and water are ball-milled to obtain a mixed powder slurry; The average particle size of the silicon carbide is 40nm to 100nm; 2. Processing of silicon carbide fiber: The silicon carbide fiber cloth is cleaned and dried, and then calcined at a temperature of 600° C. to 800° C. for 1 h to 2 h to obtain treated silicon carbide fiber; Alternatively, the silicon carbide fiber cloth is cleaned and dried, and then immersed in tetrabutyl titanate for 10 to 50 minutes, taken out after immersion, and calcined at a temperature of 500 to 700° C. for 1 to 3 hours to obtain the treated silicon carbide fiber; 3. Alternate laying of prepreg and ceramic powder: ① The treated silicon carbide fibers are placed in the mixed powder slurry and then dried to obtain a prepreg; ② Drying, grinding and sieving the mixed powder slurry to obtain ceramic powder; ③ Alternately lay multiple prepreg sheets and ceramic powder to obtain a stacked material; 4. Sintering: The stacked material is placed in a graphite mold for pre-pressing, and then placed in a spark plasma sintering furnace. Under the conditions of a vacuum environment, a current of 5kA to 7kA, a temperature of 1800°C to 1950°C, and a pressure of 30MPa to 70MPa, the material is sintered for 10min to 30min, and finally cooled to room temperature to obtain silicon carbide fiber / silicon carbide-based composite ceramics.

2. The method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that The sintering aid described in step 1 is one or a combination of aluminum oxide and yttrium oxide.

3. The method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that The mass of the sintering aid described in step one is 2% to 8% of the mass of silicon carbide; the mass ratio of the total mass of silicon carbide and the sintering aid described in step one to water is 1:(3 to 8).

4. The method for preparing silicon carbide fiber and silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that The ball milling mixing described in step 1 is specifically performed for 6h to 20h at a rotation speed of 200r / min to 600r / min and a ball-to-material mass ratio of (2 to 6):

1.

5. The method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that The thickness of the silicon carbide fiber cloth described in step 2 is 0.1 mm to 0.3 mm.

6. The method for preparing silicon carbide fiber silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that In step 3①, under the condition of vacuum degree of 0.1Pa~5Pa, the treated silicon carbide fiber is arranged in the mixed powder slurry and immersed for 10min~50min, and the immersion is repeated 3 times~9 times; the drying described in step 3① is specifically at the condition of temperature of 40℃~80℃, and is dried for 2h~10h.

7. The method for preparing silicon carbide fiber and silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that The sieving described in step 3② is specifically through a sieve of 20-80 mesh; the laying thickness of the ceramic powder described in step 3③ is 0.2mm-1mm.

8. The method for preparing silicon carbide fiber and silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that The pre-pressing described in step 4 is specifically performed at a pressure of 20 MPa to 100 MPa for 20 min to 50 min.

9. The method for preparing silicon carbide fiber and silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that In step 4, under the conditions of vacuum degree of 0.1Pa~1Pa and pressure of 30MPa~70MPa, the current is regulated, and the temperature is first increased to 1000℃~1500℃ at a heating rate of 50℃ / min~150℃ / min, and then increased to 1800℃~1950℃ at a heating rate of 30℃ / min~120℃ / min.

10. The method for preparing silicon carbide fiber and silicon carbide-based composite ceramics by nano transient eutectic according to claim 1, characterized in that In step 4, under the conditions of vacuum degree of 0.1Pa~1Pa and pressure of 30MPa~70MPa, the current is regulated, the temperature is cooled to 900℃~1200℃ at a cooling rate of 10℃ / min~30℃ / min, then cooled to 200℃~500℃ at a cooling rate of 20℃ / min~50℃ / min, and finally cooled to room temperature at a cooling rate of 30℃ / min~80℃ / min.

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