Preparation method of high-toughness beta-SiC nano ceramic

Abstract

The invention discloses a preparation method of high-toughness beta-SiC nano ceramic, and relates to a preparation method of nano ceramic. The invention aims to solve the problem that the beta-SiC nano ceramic is difficult to prepare in the prior art. The method comprises the following steps: 1, ball milling; 2, drying; 3, sintering; and 4, post-processing. The method is used for preparing the high-toughness beta-SiC nano ceramic.

Description

Technical Field

[0001] The invention relates to a method for preparing nano ceramics. Background Art

[0002] SiC ceramics are ceramics with good thermal and mechanical properties, so they are widely used in many fields. Due to the crystal structure characteristics of its cubic phase, β-SiC has isotropic swelling under long-term irradiation conditions. At the same time, due to some unique properties of β-SiC, it has a wider range of applications in semiconductors, electronics, optics and other fields. However, due to the low mobility of carbon and silicon atoms in SiC, a higher temperature is required for sintering, and β-SiC belongs to a low-temperature phase. At the commonly used sintering temperature (above 2000°C), a crystal transformation will occur. Therefore, β-SiC ceramics are difficult to prepare. At the same time, compared with traditional ceramics, nanoceramics have higher hardness and strength, and higher sintering temperatures and longer sintering times will lead to grain growth. Therefore, compared with traditional ceramics, nanoceramics are more difficult to prepare. Summary of the invention

[0003] The present invention aims to solve the problem that it is difficult to prepare β-SiC nano-ceramics in the prior art, and further provide a method for preparing high-toughness β-SiC nano-ceramics.

[0004] A method for preparing high-toughness β-SiC nano-ceramic is carried out according to the following steps:

[0005] 1. Ball milling:

[0006] Ball milling β-SiC nanopowder, sintering aid and deionized water to obtain slurry;

[0007] 2. Drying:

[0008] The slurry is stirred and evaporated to dryness, and then dried and ground to obtain a dry powder;

[0009] 3. Sintering:

[0010] The dried powder is placed in a boron nitride bushing in a graphite mold, and mechanical pressure and electric field are applied to the upper and lower planes of the powder. Under the mechanical pressure and electric field, the powder is heated to the breakdown temperature, then flash-burned, and finally cooled to room temperature and demolded to obtain a sintered sample.

[0011] 4. Post-processing:

[0012] The sintered sample is cut, ground and polished to complete the preparation method of high-toughness β-SiC nano-ceramics.

[0013] The beneficial effects of the present invention are:

[0014] 1. The present invention has developed a method for preparing high-toughness β-SiC nano-ceramics with simple operation and rapidity, using high-purity nano-scale β-SiC as raw material, and adopting the flash sintering (FS) process, which is carried out at a sintering temperature (the traditional sintering temperature is 1800℃~2300℃) and sintering time (the traditional sintering time is tens of minutes to several hours) far lower than the sintering temperature required by the traditional silicon carbide sintering process. The prepared ceramics can suppress the growth of grains while keeping the β-SiC crystal phase unchanged, maintain the nano-scale grain size, and promote the densification process of the ceramic powder, so as to quickly and simply prepare high-toughness β-SiC nano-ceramics.

[0015] Second, the present invention adjusts the microstructure of the obtained β-SiC nanoceramics by adjusting factors such as sintering aids (including addition amount and mixing ratio, etc.), sintering process (applied mechanical pressure, electric field strength, etc.), etc., so as to further adjust the properties of the obtained ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the XRD pattern of the β-SiC nanoceramic prepared in Example 1;

[0017] Figure 2 TEM image of the β-SiC nanoceramic prepared in Example 1;

[0018] Figure 3 The β-SiC nanoceramic prepared in Example 1 was 1×10 15 cm -2 Mechanical properties results before and after fluence irradiation;

[0019] Figure 4 This is a SEM image of the fracture surface of the β-SiC nano-ceramic prepared in Example 1;

[0020] Figure 5 This is a statistical diagram of the grain size of the β-SiC nanoceramic prepared in Example 1;

[0021] Figure 6 The β-SiC nanoceramic prepared in Example 1 was 1×10 15 cm -2 High-resolution transmission (HR-TEM) image after fluence irradiation;

[0022] Figure 7 This is a SEM image of the polished surface of the β-SiC nano-ceramic prepared in Example 1;

[0023] Figure 8 This is a SEM image of the fracture surface of the β-SiC nano-ceramic prepared in Example 2;

[0024] Fig. 9This is a statistical diagram of the grain size of the β-SiC nano-ceramic prepared in Example 2;

[0025] Fig.10 The β-SiC nanoceramic prepared in Example 2 was 1×10 15 cm -2 High-resolution transmission (HR-TEM) image after fluence irradiation;

[0026] Fig.11 This is a SEM image of the polished surface of the β-SiC nanoceramic prepared in Example 3. DETAILED DESCRIPTION

[0027] Specific implementation method 1: This implementation method is a method for preparing a high-toughness β-SiC nanoceramic, which is carried out according to the following steps:

[0028] 1. Ball milling:

[0029] Ball milling β-SiC nanopowder, sintering aid and deionized water to obtain slurry;

[0030] 2. Drying:

[0031] The slurry is stirred and evaporated to dryness, and then dried and ground to obtain a dry powder;

[0032] 3. Sintering:

[0033] The dried powder is placed in a boron nitride bushing in a graphite mold, and mechanical pressure and electric field are applied to the upper and lower planes of the powder. Under the mechanical pressure and electric field, the powder is heated to the breakdown temperature, then flash-burned, and finally cooled to room temperature and demolded to obtain a sintered sample.

[0034] 4. Post-processing:

[0035] The sintered sample is cut, ground and polished to complete the preparation method of high-toughness β-SiC nano-ceramics.

[0036] Step three of this specific implementation method adopts the FS process, first applying a certain mechanical pressure and electric field strength on the upper and lower planes of the sample, and heating it through the resistance wire in the furnace chamber until the breakdown temperature is reached. The electric field breaks down the ceramic powder at the breakdown temperature. Under severe Joule heat, the sample is rapidly heated to the critical flash temperature in a short time, and after sintering at the critical flash temperature, it is cooled to room temperature.

[0037] In step three of this specific implementation method, during demoulding, a tablet press is used to press the ceramic sheet out of the boron nitride bushing.

[0038] The beneficial effects of this embodiment are:

[0039] 1. This embodiment develops a method for preparing high-toughness β-SiC nanoceramics with simple operation and rapidity, using high-purity nano-scale β-SiC as raw material, adopting FS process, and carrying out the sintering process at a sintering temperature (traditional sintering temperature is 1800℃~2300℃) and sintering time (traditional sintering time is tens of minutes to several hours) far lower than the sintering temperature required by the traditional silicon carbide sintering process. The prepared ceramics can suppress grain growth while keeping the β-SiC crystal phase unchanged, maintain the nano-scale grain size, and promote the densification process of the ceramic powder, so as to quickly and simply prepare high-toughness β-SiC nanoceramics.

[0040] Second, this embodiment adjusts the microstructure of the obtained β-SiC nanoceramics by adjusting factors such as sintering aids (including addition amount and mixing ratio, etc.), sintering process (applied mechanical pressure, electric field strength, etc.), etc., so as to further adjust the performance of the obtained ceramics.

[0041] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that the sintering aid described in step 1 is Al 2 O 3 and Y 2 O 3 Mixed, and Al 2 O 3 With Y 2 O 3 The mass ratio is (5-7): 3. The rest is the same as the first embodiment.

[0042] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the average particle size of the β-SiC nanopowder in step 1 is 55 nm to 65 nm. The rest is the same as specific embodiment 1 or 2.

[0043] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the mass of the sintering aid described in step 1 is 0% to 20% of the mass of the β-SiC nanopowder. The rest is the same as specific embodiment 3.

[0044] Specific implementation method 5: This implementation method is different from specific implementation methods 1 to 4 in that the mass of the deionized water in step 1 is 1 to 4 times the mass of the β-SiC nanopowder. The rest is the same as specific implementation methods 1 to 4.

[0045] Specific embodiment 6: This embodiment is different from the specific embodiments 1 to 5 in that: in step 1, β-SiC nanopowder, sintering aid and deionized water are added to a polytetrafluoroethylene ball mill. 2 O 3The small balls are used as grinding media. The ball milling is carried out for 3 hours to 20 hours under the conditions of a ball-to-material mass ratio of (9 to 15):1 and a ball milling speed of 150 r / min to 400 r / min. The grinding media is composed of Al2O3 with diameters of 5.5 mm to 6.5 mm, 9 mm to 11 mm and 14 mm to 16 mm. 2 O 3 The small balls are mixed in a mass ratio of 3:(2-5):(4-8). The rest is the same as the first to fifth embodiments.

[0046] Specific embodiment 7: This embodiment is different from specific embodiments 1 to 6 in that: in step 2, the slurry is stirred and evaporated to dryness at a temperature of 80°C to 100°C and a stirring speed of 200r / min to 400r / min until there is no flowing liquid, and then the heating is stopped, and the stirring speed is 200r / min to 400r / min, and the residual heat is used to continue stirring and evaporating to dryness, and then at a temperature of 60°C to 100°C, it is dried for 8h to 24h, and finally ground and passed through a 360-mesh sieve to obtain a dried powder. The rest is the same as specific embodiments 1 to 6.

[0047] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that in step 3, the temperature is raised to the breakdown temperature in a vacuum or Ar environment, then flashed, and finally cooled to room temperature. The rest is the same as specific embodiments 1 to 7.

[0048] Specific embodiment 9: This embodiment is different from specific embodiments 1 to 8 in that: in step 3, under the conditions of mechanical pressure of 10MPa to 70MPa and electric field strength of 10V / cm to 50V / cm, the temperature is increased at a heating rate of 2℃ / min to 10℃ / min until the breakdown temperature reaches 700℃ to 1300℃, the electric field breaks down the powder at the breakdown temperature, the powder is rapidly heated to the critical flash temperature, and under the conditions of mechanical pressure of 10MPa to 70MPa and electric field strength of 10V / cm to 50V / cm, the powder is flashed for 5s to 80s, the electric field is removed after flashing, and under the conditions of mechanical pressure of 10MPa to 70MPa, the temperature is reduced to room temperature at a cooling rate of 2℃ / min to 10℃ / min. The rest is the same as specific embodiments 1 to 8.

[0049] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that: in step 4, diamond outer circle cutting is used, and then a diamond grinding tool with meshes of 80 to 3000 is used to remove surface scratches from coarse to fine, and finally a diamond polishing liquid is used for polishing. The rest is the same as specific embodiments 1 to 9.

[0050] The following examples are used to verify the beneficial effects of the present invention:

[0051] Embodiment 1:

[0052] A method for preparing high-toughness β-SiC nanoceramic is carried out according to the following steps:

[0053] 1. Ball milling:

[0054] β-SiC nanopowder, sintering aid and deionized water were added into a polytetrafluoroethylene ball mill. 2 O 3 The small balls were used as grinding media. Under the conditions of ball-to-material mass ratio of 10:1 and ball milling speed of 300 r / min, the slurry was obtained by ball milling for 10 h.

[0055] The grinding media are made of Al2O3 with diameters of 6 mm, 10 mm and 15 mm. 2 O 3 The pellets are mixed in a mass ratio of 3:4:6;

[0056] The sintering aid is composed of Al 2 O 3 and Y 2 O 3 Mixed, and Al 2 O 3 With Y 2 O 3 The mass ratio is 5:3;

[0057] The average particle size of the β-SiC nanopowder is 62nm;

[0058] The mass of the sintering aid is 6% of the mass of the β-SiC nanopowder;

[0059] The mass of the deionized water is 4 times the mass of the β-SiC nanopowder;

[0060] 2. Drying:

[0061] Under the conditions of a temperature of 100°C and a stirring speed of 250 r / min, the slurry is stirred and evaporated until there is no flowing liquid, and then the heating is stopped. Under the condition of a stirring speed of 250 r / min, the slurry is stirred and evaporated using the residual heat, and then dried at a temperature of 60°C for 24 hours, and finally ground and passed through a 360-mesh sieve to obtain a dried powder;

[0062] 3. Sintering:

[0063] The dried powder is placed in a boron nitride bushing in a graphite mold, and mechanical pressure and electric field are applied to the upper and lower planes of the powder. Under the conditions of vacuum, mechanical pressure of 30MPa and electric field strength of 30V / cm, the temperature is increased at a heating rate of 10℃ / min until the breakdown temperature reaches 900℃. The electric field breaks down the powder at the breakdown temperature, and the powder is rapidly heated to the critical flash temperature. Under the conditions of vacuum, mechanical pressure of 30MPa and electric field strength of 30V / cm, the powder is flashed for 15s. After flashing, the electric field is removed, and under the conditions of vacuum and mechanical pressure of 30MPa, the temperature is lowered at a rate of 10℃ / min to room temperature and demolded to obtain a sintered sample.

[0064] 4. Post-processing:

[0065] The sintered sample was cut using a diamond outer circle, and then repeatedly polished using 80 mesh, 250 mesh, 500 mesh, 800 mesh, 1500 mesh and 3000 mesh diamond grinding discs in sequence to remove surface scratches. Finally, it was polished using diamond polishing liquid to obtain β-SiC nanoceramics.

[0066] Embodiment 2: This embodiment is different from Embodiment 1 in that the use of sintering aid is eliminated in step 1. The rest is the same as Embodiment 1.

[0067] Embodiment 3: This embodiment is different from Embodiment 1 in that: in step 3, the temperature is increased at a heating rate of 10°C / min until the breakdown temperature reaches 1200°C; and in step 3, the flash burning is performed for 30s. The rest is the same as in Embodiment 1.

[0068] Figure 1 This is the XRD diagram of the β-SiC nanoceramic prepared in Example 1; it can be seen from the figure that only the diffraction peak of β-SiC exists in the β-SiC nanoceramic prepared in this example, and the diffraction peak near 33.6° means that there is a stacking fault in the sample.

[0069] Figure 2 This is a TEM image of the β-SiC nanoceramic prepared in Example 1; it can be seen from the figure that there are a large number of nano-sized grains in the β-SiC nanoceramic prepared in this example, and a large number of black lines are observed inside the nano-grains, indicating that the rapid heating and cooling leads to the generation of a large number of stacking faults inside the grains.

[0070] Figure 3 The β-SiC nanoceramic prepared in Example 1 was 1×10 15 cm -2 Mechanical properties before and after injection irradiation; As can be seen from the figure, the fracture toughness of the obtained β-SiC nanoceramics reaches 6.54±0.49MPa·m 1 / 2(Based on the test standard GB / T 23806-2009 "Fine Ceramics Fracture Toughness Test Method Single Edge Precracked Beam (SEPB) Method"), compared with the traditional SiC ceramic fracture toughness of 2-4MPa·m 1 / 2 , the fracture toughness of the β-SiC nanoceramic obtained in this embodiment is significantly improved; in addition, the compressive strength of the obtained β-SiC nanoceramic reaches 2.83±0.13GPa (according to the test standard GB / T8489-2006 "Fine Ceramics Compression Strength Test Method"), the Vickers hardness is 20.42±0.43GPa (1kg load, 15s, according to the test standard GB / T 16534-2009 "Fine Ceramics Room Temperature Hardness Test Method"), the elastic modulus is 367.9±6GPa (according to the test standard ASTM E384-17 "Standard Test Method for Microindentation Hardness of Materials"), and the nanohardness is 25.74±0.86GPa (according to the test standard ASTM E384-17 "Standard Test Method for Microindentation Hardness of Materials"), and the mechanical properties are excellent. After irradiation, the fracture toughness, compressive strength, Vickers hardness, elastic modulus and nanohardness are reduced to 4.05±0.91MPa·m 1 / 2 , 2.07±0.27GPa, 18.76±1.03GPa, 307.4±9.3GPa and 22.91±1.34GPa.

[0071] Figure 4 This is a SEM image of the fracture surface of the β-SiC nano-ceramic prepared in Example 1; as can be seen from the image, the fracture surface presents a typical intergranular fracture morphology.

[0072] Figure 5 The grain size statistics of the β-SiC nanoceramic prepared in Example 1 are obtained by measuring the grain size of more than 1500 particles in TEM. 10 =37.32nm (10% grain size ≤38.07nm), D 50 =58.31nm (50% grain size ≤ 60.48nm), D 90 =94.72nm (90% of the grain size ≤98.41nm), D ave =63.57nm (average grain size 65.97nm).

[0073] Figure 6 The β-SiC nanoceramic prepared in Example 1 was 1×10 15 cm -2 High-resolution transmission (HR-TEM) image after injection irradiation; after irradiation, a large number of stacking faults appeared inside the β-SiC grains.

[0074] Figure 7This is a SEM image of the polished surface of the β-SiC nano-ceramic prepared in Example 1; it can be seen from the figure that there are open pores on the surface of the sample. According to BS EN 1389:2004 "Advanced industrial ceramics. Ceramic composites. Physical properties. Determination of density and apparent porosity", its open porosity is measured to be 3.1%.

[0075] Figure 8 This is the SEM image of the fracture surface of the β-SiC nano-ceramic prepared in Example 2; there is no obvious difference from the SEM image of the fracture surface of the ceramic in Example 1.

[0076] Fig. 9 This is a statistical diagram of the grain size of the β-SiC nanoceramic prepared in Example 2; the statistical diagram is obtained by measuring the grain size of more than 1500 particles in TEM, D 10 =38.07nm, D 50 =60.48nm, D 90 =98.41nm, D ave =65.97nm.

[0077] Fig.10 The β-SiC nanoceramic prepared in Example 2 was 1×10 15 cm -2 High-resolution transmission (HR-TEM) image after injection irradiation; after irradiation, a large number of stacking faults appeared inside the β-SiC grains.

[0078] Fig.11 This is a SEM image of the polished surface of the β-SiC nano-ceramic prepared in Example 3; as can be seen from the image, there are a small number of open pores on the surface of the sample, and its open porosity is measured to be 0.86%.

Claims

1. A method for preparing high-toughness β-SiC nanoceramics, characterized in that It is carried out in the following steps:

1. Ball milling: Ball milling β-SiC nanopowder, sintering aid and deionized water to obtain slurry; 2. Drying: The slurry is stirred and evaporated to dryness, and then dried and ground to obtain a dry powder; 3. Sintering: The dried powder is placed in a boron nitride bushing in a graphite mold, and mechanical pressure and electric field are applied to the upper and lower planes of the powder. Under the mechanical pressure and electric field, the powder is heated to the breakdown temperature, then flash-burned, and finally cooled to room temperature and demolded to obtain a sintered sample.

4. Post-processing: The sintered sample is cut, ground and polished to complete the preparation method of high-toughness β-SiC nano-ceramics.

2. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that The sintering aid described in step 1 is a mixture of Al2O3 and Y2O3, and the mass ratio of Al2O3 to Y2O3 is (5-7):

3.

3. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that The average particle size of the β-SiC nanopowder described in step 1 is 55nm to 65nm.

4. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that The mass of the sintering aid described in step 1 is 0% to 20% of the mass of the β-SiC nanopowder.

5. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that The mass of the deionized water in step 1 is 1 to 4 times the mass of the β-SiC nanopowder.

6. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that In step 1, β-SiC nanopowder, sintering aid and deionized water are added to a polytetrafluoroethylene ball mill, and Al2O3 balls are used as grinding media. The grinding process is performed for 3 hours to 20 hours at a ball-to-material mass ratio of (9 to 15):1 and a ball mill speed of 150 r / min to 400 r / min. The grinding media is formed by mixing Al2O3 balls with diameters of 5.5 mm to 6.5 mm, 9 mm to 11 mm and 14 mm to 16 mm in a mass ratio of 3:(2 to 5):(4 to 8).

7. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that In step 2, the slurry is stirred and evaporated until there is no flowing liquid at a temperature of 80°C to 100°C and a stirring speed of 200r / min to 400r / min, and then the heating is stopped. At a stirring speed of 200r / min to 400r / min, the residual heat is used to continue stirring and evaporating to dryness, and then at a temperature of 60°C to 100°C, it is dried for 8h to 24h, and finally ground and passed through a 360-mesh sieve to obtain a dried powder.

8. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that In step 3, the temperature is raised to the breakdown temperature in a vacuum or Ar environment, then flashed, and finally cooled to room temperature.

9. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that In step three, under the conditions of mechanical pressure of 10MPa~70MPa and electric field strength of 10V / cm~50V / cm, the temperature is increased at a heating rate of 2℃ / min~10℃ / min until the breakdown temperature is 700℃~1300℃. The electric field breaks down the powder at the breakdown temperature, and the powder is rapidly heated to the critical flash temperature. Under the conditions of mechanical pressure of 10MPa~70MPa and electric field strength of 10V / cm~50V / cm, it flashes for 5s~80s. After flashing, the electric field is removed, and under the conditions of mechanical pressure of 10MPa~70MPa, the temperature is reduced to room temperature at a cooling rate of 2℃ / min~10℃ / min.

10. The method for preparing a high-toughness β-SiC nanoceramic according to claim 1, characterized in that In step 4, diamond outer circle cutting is used, and then a diamond grinding tool with mesh size of 80 to 3000 is used to remove surface scratches from coarse to fine, and finally polishing is performed using diamond polishing liquid.

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