Low-temperature sintered (SiC-BN) / BAS composite ceramic and preparation method thereof

Abstract

The invention discloses a low-temperature sintered (SiC-BN) / BAS composite ceramic and a preparation method thereof, and the composite ceramic is prepared from the following components in percentage by mass: 20-40% of BAS, 53-67% of SiC and 3-17% of BN. The (SiC-BN) / BAS composite ceramic is synthesized by adopting a solid-phase reaction method, the (SiC-BN) / BAS composite ceramic with different components and different microstructures can be prepared by regulating and controlling the raw materials and the molar ratio of the raw materials, and the composite ceramic has good mechanical properties, the density is 2.8-3.2 g / cm < 3 >, the bending strength is 170-220 MPa, the elastic modulus is 70-100 MPa, the fracture toughness is 2.5-4.0 MPa.m < 1 / 2 >, and the thermal conductivity is 4.5-5.5 W / (m.K) (T = 1000 DEG C). The material is especially suitable for high-temperature wear-resistant parts and nuclear industry cladding materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature structural ceramics and relates to a high-temperature multiphase structural ceramic, in particular to a low-temperature sintered (SiC-BN) / BAS multiphase ceramic and a preparation method thereof. Background Art

[0002] The rapid development of the aviation industry has placed increasingly stringent demands on the performance and fabrication technologies of high-temperature heat-resistant structural materials. Silicon carbide (SiC) possesses excellent mechanical properties (high strength, high modulus, and high hardness), thermal properties (high temperature resistance, low thermal expansion coefficient, high thermal conductivity, and thermal shock resistance), and chemical stability, making it an important class of high-temperature structural ceramics. However, the inherent brittleness and high sintering temperature of single SiC ceramics severely limit their application in this field.

[0003] Hexagonal boron nitride (BN) has a layered hexagonal crystal structure and is characterized by a high melting point, low thermal expansion, high thermal conductivity, and excellent processing properties. It is a widely used advanced ceramic material. However, due to its relatively low mechanical properties and poor rain erosion resistance, h-BN is rarely used as a single-phase ceramic and is generally used as a second phase in composite ceramics. Composites of SiC and BN have the potential to complement each other's performance. However, both are covalently bonded compounds, and the strong bonding forces result in low atomic diffusion coefficients. Furthermore, the lamellar structure of BN grains easily causes overlapping layers during sintering, resulting in pores. This makes it difficult to sinter dense composite ceramics and results in low mechanical properties.

[0004] Barium aluminosilicate glass (BaO-Al2O3-2SiO2, BAS) is an important inorganic non-metallic material, due to its high melting point (~1760 o C), strong mechanical properties, excellent antioxidant properties and good physical properties and are widely used. Barium aluminosilicate glass has a relatively low softening temperature and can act as a flux to promote the densification of composite ceramics, thereby improving the mechanical properties of composite ceramics. There are already methods of compounding BN and BAS in the prior art. The comprehensive performance of BN / BAS composite ceramics is significantly better than that of single-phase BN ceramics and BAS ceramics. However, the content of BAS glass phase in the composite ceramics is relatively high, and a higher glass phase content will significantly reduce the high-temperature mechanical properties of the composite ceramics. Therefore, introducing a high modulus third phase on the basis of the composite of BN and BAS, and appropriately reducing the content of the BAS glass phase, is expected to further improve the comprehensive performance of the composite ceramics. Summary of the Invention

[0005] The present invention uses BAS glass ceramics as a sintering aid and optimizes the composition ratio of SiC-BN to provide a low-temperature sintered (SiC-BN) / BAS composite ceramic with excellent mechanical properties, high-temperature performance and environmental friendliness, and a preparation method thereof, so as to achieve low-temperature sintering of the composite ceramic and improve its comprehensive performance.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A low-temperature sintered (SiC-BN) / BAS composite ceramic is made of 20-40% BAS, 53-67% SiC and 3-17% BN in terms of mass percentage.

[0008] A method for preparing the above-mentioned low-temperature sintered (SiC-BN) / BAS composite ceramic comprises the following steps:

[0009] Step S1: BAS, SiC powder (β-SiC) and BN powder are mixed, anhydrous ethanol and ball milling media are added, and the mixture is ball milled in a mixer to obtain a uniform mixed slurry, wherein the SiC powder and BN powder are ultrasonically dispersed before mixing, the solvent is anhydrous ethanol, and the dispersion time is 10-60 minutes; the ball milling media is Al2O3 balls, the ball-to-material ratio is 4-8:1, and the ball milling time is 20-30 hours;

[0010] Step S2: drying and sieving the mixed slurry to obtain a mixed powder;

[0011] Step S3: Place the mixed powder into a graphite mold and sinter in a hot pressing sintering furnace under inert gas protection, controlling the sintering temperature to 1450~1550 o C, sintering pressure is 10~30MPa, heat preservation and pressure holding is 60~120min, after heat preservation and pressure holding, cooling with furnace, demoulding, (SiC-BN) / BAS composite ceramics are obtained, and the temperature is controlled from room temperature to 1200 o The heating rate is 10~30 o C / min, from 1200 o C to sintering temperature 1450~1550 o The heating rate is 10~25 o C / min.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1. The present invention adopts a solid-phase reaction method to synthesize (SiC-BN) / BAS composite ceramics. By regulating the raw materials and their molar ratios, (SiC-BN) / BAS composite ceramics with different compositions and different microstructures can be prepared, providing the possibility of preparing composite ceramic materials with special uses or excellent performance.

[0014] 2. The present invention uses BAS liquid-phase sintering to regulate the composition of SiC-BN, and then combines it with hot pressing technology to obtain (SiC-BN) / BAS composite ceramics with a dense structure and uniform composition at a relatively low sintering temperature, achieving a simultaneous improvement in fracture toughness and thermal conductivity, meeting the load-bearing and heat dissipation requirements of aviation equipment.

[0015] 3. The present invention realizes the preparation of (SiC-BN) / BAS composite ceramics by low temperature sintering. The composite ceramics have good mechanical properties and a density of 2.8~3.2g / cm 3 , flexural strength is 170~220MPa, elastic modulus is 70~100MPa, fracture toughness is 2.5~4.0MPa·m 1 / 2 , thermal conductivity is 4.5~5.5W / (m·K)(T=1000 o C), especially suitable for high temperature wear-resistant parts and nuclear industry cladding materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a process flow chart for the preparation of low-temperature sintered (SiC-BN) / BAS composite ceramics;

[0017] Figure 2 XRD pattern of (SiC-BN) / BAS composite ceramic prepared in Example 2;

[0018] Figure 3 XRD pattern of the (SiC-BN) / BAS composite ceramic prepared in Example 4;

[0019] Figure 4 XRD pattern of the SiC / BAS composite ceramic prepared in Comparative Example 1;

[0020] Figure 5 This is an electron microscope image of the fracture morphology of the (SiC-BN) / BAS composite ceramic prepared in Example 2;

[0021] Figure 6 This is an electron microscope image of the fracture morphology of the (SiC-BN) / BAS composite ceramic prepared in Example 4;

[0022] Figure 7 This is an electron microscope image of the fracture morphology of the SiC / BAS composite ceramic prepared in Comparative Example 1;

[0023] Figure 8 Graphs showing the flexural strength and fracture toughness of (SiC-BN) / BAS composite ceramics prepared in Examples 1, 2, 3, 4 and Comparative Example 1;

[0024] Figure 9This is a crack growth diagram of the (SiC-BN) / BAS composite ceramic prepared in Example 2, where a is a low-magnification image, and b and c are high-magnification images of the marked areas B and C shown in a, respectively. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0026] Example 1:

[0027] This embodiment provides a method for preparing low temperature sintered (SiC-BN) / BAS composite ceramics, such as Figure 1 As shown, the specific steps of the method are as follows:

[0028] Step 1. Calculate the mass of the required raw materials by mass percentage. The BAS matrix accounts for 30%, β-SiC accounts for 66.5%, and BN accounts for 3.5%. The chemical formula of BAS is BaO·Al2O3·2SiO2, that is, BaO:Al2O3:SiO2=1:1:2. To reduce costs, part of the Al2O3 and all of the SiO2 in BAS are provided by fly ash (CFA).

[0029] Step 2: Weigh 6.3g BaCO3 powder, 1.21g Al2O3 powder, 8.93g CFA powder, 1.4g BN, and 26.6g β-SiC; the particle size of the BaCO3 powder is 0.3~2.0μm, the particle size of the Al2O3 powder is 0.3~0.8μm, the particle size of the CFA powder is 0.9~8.0μm, the particle size of the β-SiC powder is 0.4~2.4μm, and the particle size of the BN powder is 0.1~0.4μm.

[0030] Step 3: Before mixing, β-SiC and BN were pre-dispersed using anhydrous ethanol as a dispersion medium and ultrasonically treated for 30 minutes.

[0031] Step 4: Place BaCO3 powder, Al2O3 powder, CFA powder, and the dispersed β-SiC and BN into a mixing bottle. The grinding medium is Al2O3 balls, and the solvent is anhydrous ethanol. The Al2O3 balls and the mixed powders are mixed in a mixer at a mass ratio of 5:1 for 24 hours.

[0032] Step 5: Stir-fry the mixed slurry quickly and put it into 100 o Dry in oven C for 12 hours, and after drying, pass through a 120-mesh sieve to obtain a uniform mixed powder.

[0033] Step 6: Put the mixed powder into graphite mold and put it into hot pressing sintering furnace under nitrogen protection.o The heating rate was from room temperature to 1200 °C / min. o C, then 15 o The heating rate was increased to 1500 °C / min. o C, the sintering pressure is 10MPa, and the temperature and pressure are kept for 60min. After the temperature is kept, the furnace is cooled and the mold is demolded to obtain (SiC-BN) / BAS composite ceramics.

[0034] The density and mechanical properties of the (SiC-BN) / BAS composite ceramics prepared in this embodiment are shown in Tables 1 and 3, and the average thermal expansion coefficient is shown in Table 3.

[0035] The flexural strength and fracture toughness of the (SiC-BN) / BAS phase ceramics prepared in this embodiment are shown in Figure 2. Figure 8 As shown in Table 1 and Figure 8 It can be seen that the flexural strength is 207.5±2.8MPa and the fracture toughness is 3.44±0.08MPa·m 1 / 2 .

[0036] Example 2:

[0037] This embodiment provides a method for preparing low temperature sintered (SiC-BN) / BAS composite ceramics, such as Figure 1 As shown, the specific steps of the method are as follows:

[0038] Step 1: Calculate the mass of the required raw materials by mass percentage: BAS matrix accounts for 30%, β-SiC accounts for 63%, and BN accounts for 7%.

[0039] Step 2: Weigh 6.3g BaCO3 powder, 1.21g Al2O3 powder, 8.93g CFA powder, 2.8g BN, and 25.2g β-SiC.

[0040] Step 3: Before mixing, β-SiC and BN were pre-dispersed using anhydrous ethanol as a dispersion medium and ultrasonically treated for 30 minutes.

[0041] Step 4: Place BaCO3 powder, Al2O3 powder, CFA powder, and the dispersed β-SiC and BN into a mixing bottle. The grinding medium is Al2O3 balls, and the solvent is anhydrous ethanol. The Al2O3 balls and the mixed powders are mixed in a mixer at a mass ratio of 5:1 for 24 hours.

[0042] Step 5: Stir-fry the mixed slurry quickly and put it into 100 o Dry in oven C for 12 hours, and after drying, pass through a 120-mesh sieve to obtain a uniform mixed powder.

[0043] Step 6: Put the mixed powder into graphite mold and put it into hot pressing sintering furnace under nitrogen protection. oThe heating rate was from room temperature to 1200 °C / min. o C, then 15 o The heating rate was increased to 1500 °C / min. o C, the sintering pressure is 10MPa, and the temperature and pressure are kept for 60min. After the temperature is kept, the furnace is cooled and the mold is demolded to obtain (SiC-BN) / BAS composite ceramics.

[0044] The density and mechanical properties of the (SiC-BN) / BAS composite ceramics prepared in this example are shown in Table 1, the thermal conductivity is shown in Table 2, and the average thermal expansion coefficient is shown in Table 3.

[0045] The XRD pattern of the (SiC-BN) / BAS composite ceramic prepared in this example is as follows: Figure 3 Shown by Figure 3 It can be seen that BaCO3 powder, Al2O3 powder and CFA powder are completely reacted to form BAS after hot pressing and sintering, in which the main crystal phase is hexagonal BAS and the secondary crystal phase is monoclinic BAS.

[0046] The fracture morphology of the (SiC-BN) / BAS composite ceramic prepared in this example is as follows: Figure 5 As shown by Figure 5 It can be seen that the main failure mode of composite ceramics is intergranular fracture.

[0047] The flexural strength and fracture toughness of the (SiC-BN) / BAS composite ceramics prepared in this embodiment are shown in Figure 2. Figure 8 As shown in Table 1 and Figure 8 It can be seen that the flexural strength is 194.9±4.6MPa and the fracture toughness is 3.74±0.10MPa·m 1 / 2 .

[0048] The crack propagation of the (SiC-BN) / BAS composite ceramic prepared in this embodiment is shown in Figure 9. Figure 9 The pull-out of the BN layer structure, the deflection of the crack and the bridging of the crack can be observed.

[0049] Example 3:

[0050] This embodiment provides a method for preparing low temperature sintered (SiC-BN) / BAS composite ceramics, such as Figure 1 As shown, the specific steps of the method are as follows:

[0051] Step 1: Calculate the mass of the required raw materials by mass percentage: BAS matrix accounts for 30%, β-SiC accounts for 59.5%, and BN accounts for 10.5%.

[0052] Step 2: Weigh 6.3g BaCO3 powder, 1.21g Al2O3 powder, 8.93g CFA powder, 4.2g BN, and 23.8g β-SiC.

[0053] Step 3: Before mixing, β-SiC and BN were pre-dispersed using anhydrous ethanol as a dispersion medium and ultrasonically treated for 30 minutes.

[0054] Step 4: Place BaCO3 powder, Al2O3 powder, CFA powder, and the dispersed β-SiC and BN into a mixing bottle. The grinding medium is Al2O3 balls, and the solvent is anhydrous ethanol. The Al2O3 balls and the mixed powders are mixed in a mixer at a mass ratio of 5:1 for 24 hours.

[0055] Step 5: Stir-fry the mixed slurry quickly and put it into 100 o Dry in oven C for 12 hours, and after drying, pass through a 120-mesh sieve to obtain a uniform mixed powder.

[0056] Step 6: Put the mixed powder into graphite mold and put it into hot pressing sintering furnace under nitrogen protection. o The heating rate was from room temperature to 1200 °C / min. o C, then 15 o The heating rate was increased to 1500 °C / min. o C, the sintering pressure is 10MPa, and the temperature and pressure are kept for 60min. After the temperature is kept, the furnace is cooled and the mold is demolded to obtain (SiC-BN) / BAS composite ceramics.

[0057] The density and mechanical properties of the (SiC-BN) / BAS composite ceramics prepared in this example are shown in Table 1, and the average thermal expansion coefficient is shown in Table 3.

[0058] The flexural strength and fracture toughness of the (SiC-BN) / BAS composite ceramics prepared in this embodiment are shown in Figure 2. Figure 8 As shown in Table 1 and Figure 8 It can be seen that the flexural strength is 183.3±1.1MPa and the fracture toughness is 3.29±0.12MPa·m 1 / 2 .

[0059] Example 4:

[0060] This embodiment provides a method for preparing low temperature sintered (SiC-BN) / BAS composite ceramics, such as Figure 1 As shown, the specific steps of the method are as follows:

[0061] Step 1: Calculate the mass of the required raw materials by mass percentage: BAS matrix accounts for 30%, β-SiC accounts for 56%, and BN accounts for 14%.

[0062] Step 2: Weigh 6.3g BaCO3 powder, 1.21g Al2O3 powder, 8.93g CFA powder, 5.60g BN, and 22.4g β-SiC.

[0063] Step 3: Before mixing, β-SiC and BN were pre-dispersed using anhydrous ethanol as a dispersion medium and ultrasonically treated for 30 minutes.

[0064] Step 4: Place BaCO3 powder, Al2O3 powder, CFA powder, and the dispersed β-SiC and BN into a mixing bottle. The grinding medium is Al2O3 balls, and the solvent is anhydrous ethanol. The Al2O3 balls and the mixed powders are mixed in a mixer at a mass ratio of 5:1 for 24 hours.

[0065] Step 5: Stir-fry the mixed slurry quickly and put it into 100 o Dry in oven C for 12 hours, and after drying, pass through a 120-mesh sieve to obtain a uniform mixed powder.

[0066] Step 6: Put the mixed powder into graphite mold and put it into hot pressing sintering furnace under nitrogen protection. o The heating rate was from room temperature to 1200 °C / min. o C, then 15 o The heating rate was increased to 1500 °C / min. o C, the sintering pressure is 10MPa, and the temperature and pressure are kept for 60min. After the temperature is kept, the furnace is cooled and the mold is demolded to obtain (SiC-BN) / BAS composite ceramics.

[0067] The density and mechanical properties of the (SiC-BN) / BAS composite ceramics prepared in this example are shown in Table 1, the thermal conductivity is shown in Table 2, and the average thermal expansion coefficient is shown in Table 3.

[0068] The XRD pattern of the (SiC-BN) / BAS composite ceramic prepared in this example is as follows: Figure 3 As shown by Figure 3 It can be seen that BaCO3 powder, Al2O3 powder and CFA powder are completely reacted to form BAS after hot pressing and sintering, in which the main crystal phase is hexagonal BAS and the secondary crystal phase is monoclinic BAS.

[0069] The fracture morphology of the (SiC-BN) / BAS composite ceramic prepared in this example is shown in the electron microscope image. Figure 6 As shown by Figure 6 It can be seen that the main failure mode of composite ceramics is intergranular fracture.

[0070] The flexural strength and fracture toughness of the SiC / BAS composite ceramics prepared in this embodiment are as follows: Figure 8 As shown in Table 1 and Figure 8 It can be seen that the flexural strength is 176.2±2.0MPa and the fracture toughness is 2.85±0.08MPa·m 1 / 2 .

[0071] Comparative Example 1:

[0072] This comparative example provides a method for preparing SiC / BAS composite ceramics, and the specific steps of the method are as follows:

[0073] Step 1: Calculate the required raw material mass by mass percentage, with BAS matrix accounting for 30% and β-SiC accounting for 70%.

[0074] Step 2: Weigh 6.30g BaCO3 powder, 1.21g Al2O3 powder, 8.93g fly ash powder, and 28g β-SiC powder.

[0075] Step 3: Before mixing, β-SiC powder was pre-dispersed using anhydrous ethanol as a dispersion medium by ultrasonic treatment for 30 minutes.

[0076] Step 4: Place BaCO3 powder, Al2O3 powder, CFA powder, and dispersed β-SiC into a mixing bottle. The grinding medium is Al2O3 balls, and the solvent is anhydrous ethanol. The Al2O3 balls and the mixed powders are mixed in a mixer at a mass ratio of 5:1 for 24 hours.

[0077] Step 5: Stir-fry the mixed slurry quickly and put it into 100 o Dry in oven C for 12 hours, and after drying, pass through a 120-mesh sieve to obtain a uniform mixed powder.

[0078] Step 6: Put the mixed powder into graphite mold and put it into hot pressing sintering furnace under nitrogen protection. o The heating rate was from room temperature to 1200 °C / min. o C, then 15 o The heating rate was increased to 1500 °C / min. o C, the sintering pressure is 10 MPa, and the temperature and pressure are kept for 60 minutes. After the temperature is kept, the furnace is cooled and the mold is demolded to obtain SiC / BAS composite ceramics.

[0079] The density and mechanical properties of the SiC / BAS composite ceramics prepared in this comparative example are shown in Table 1, the thermal conductivity is shown in Table 2, and the average thermal expansion coefficient is shown in Table 3.

[0080] The XRD pattern of the SiC / BAS composite ceramic prepared in this comparative example is shown in FIG. Figure 4 As shown by Figure 4 It can be seen that BaCO3 powder, Al2O3 powder and CFA powder are completely reacted to form BAS after hot pressing and sintering, in which the main crystal phase is hexagonal BAS and the secondary crystal phase is monoclinic BAS.

[0081] The fracture morphology of the SiC / BAS composite ceramic prepared in this comparative example is shown in the electron microscope image. Figure 7 As shown by Figure 7It can be seen that the main failure mode of multiphase ceramics is transgranular fracture.

[0082] The flexural strength and fracture toughness of the SiC / BAS composite ceramics prepared in this comparative example are shown in FIG. Figure 8 As shown by Figure 8 It can be seen that the flexural strength is 215.1±5.0MPa and the fracture toughness is 2.98±0.15MPa·m 1 / 2 .

[0083] From Table 1 and Figure 8 It can be seen that when the BN content is ≤10.5wt.%, the flexural strength of the (SiC-BN) / BAS composite ceramics decreases slightly, while the fracture toughness increases significantly. When the BN content is 7%, the comprehensive mechanical properties are optimal, indicating that the introduction of BN increases the toughness of the composite ceramics. As shown in Tables 2 and 3, the introduction of BN not only increases the thermal conductivity of the (SiC-BN) / BAS composite ceramics but also reduces its thermal expansion coefficient, which will help improve the thermal shock resistance of the (SiC-BN) / BAS composite ceramics.

[0084] Comparative Example 2:

[0085] This comparative example provides a method for preparing a BN / BAS composite ceramic, and the specific steps of the method are as follows:

[0086] Step 1: Calculate the mass of the required raw materials by mass percentage, with BAS matrix accounting for 90% and BN accounting for 10%.

[0087] Step 2: Weigh 16.93g BaCO3 powder, 8.76g Al2O3 powder, 10.31g SiO2 powder, and 4g BN powder.

[0088] Step 3: Before mixing, BN was pre-dispersed using anhydrous ethanol as a dispersion medium and ultrasonically treated for 30 minutes.

[0089] Step 4: Place BaCO3 powder, Al2O3 powder, SiO2 powder, and dispersed BN into a mixing bottle. The grinding medium is Al2O3 balls, and the solvent is anhydrous ethanol. Mix the Al2O3 balls and the mixed powders in a mixer at a mass ratio of 5:1 for 24 hours.

[0090] Step 5: Stir-fry the mixed slurry quickly and put it into 100 o Dry in oven C for 12 hours, and after drying, pass through a 120-mesh sieve to obtain a uniform mixed powder.

[0091] Step 6: Put the mixed powder into graphite mold and put it into hot pressing sintering furnace under nitrogen protection. o The heating rate was from room temperature to 1200 °C / min. o C, then 15 oThe heating rate was increased to 1500 °C / min. o C, the sintering pressure is 10MPa, and the temperature and pressure are kept for 60min. After the temperature is kept, the furnace is cooled and the mold is demolded to obtain BN / BAS composite ceramics.

[0092] The density and mechanical properties of the BN / BAS composite ceramics prepared in this comparative example are shown in Table 4. As shown in Table 4, the density of the BN / BAS composite ceramics is 3.18 g / cm 3 , flexural strength is 160.8±5.4MPa, fracture toughness is 2.45±0.11MPa·m 1 / 2 Comparing the data in Table 1 and Table 4, it can be found that the flexural strength and fracture toughness of BN / BAS composite ceramics are significantly lower than those of (SiC-BN) / BAS composite ceramics, which indicates that the mechanical properties of composite ceramics can be significantly improved by appropriately reducing the content of BAS sintering aid and introducing high modulus SiC phase.

[0093] Table 1 Density and mechanical properties of SiC / BAS composite ceramics and (SiC-BN) / BAS composite ceramics

[0094]

[0095] Table 2 Thermal conductivity of SiC / BAS composite ceramics and (SiC-BN) / BAS composite ceramics

[0096]

[0097] Table 3 Average thermal expansion coefficients of SiC / BAS composite ceramics and (SiC-BN) / BAS composite ceramics

[0098]

[0099] Table 4 Density and mechanical properties of BN / BAS composite ceramics

[0100]

[0101] From the experimental data in Tables 1, 2, 3, and 4, it can be seen that (SiC-BN) / BAS composite ceramics have better comprehensive properties than SiC / BAS and BN / BAS composite ceramics: (1) The fracture toughness value of (SiC-BN) / BAS composite ceramics is significantly higher than that of SiC / BAS composite ceramics; (2) The thermal conductivity of (SiC-BN) / BAS composite ceramics is significantly higher than that of SiC / BAS composite ceramics, and the thermal expansion coefficient is lower; (3) The mechanical properties of (SiC-BN) / BAS composite ceramics are significantly improved compared with those of BN / BAS composite ceramics. It can be seen that SiC, BN, and BAS composites can complement each other to achieve synergistic optimization of mechanical properties and thermophysical properties, forming high-performance composite ceramic materials with excellent comprehensive properties.

[0102] The performance improvement is mainly attributed to: (1) Fracture toughness enhancement mechanism - the introduction of SiC significantly improves the strength of the composite ceramic, while the layered structure of BN can effectively dissipate fracture energy through mechanisms such as lamellar pull-out, crack deflection and bridging. The synergistic effect of the two makes the (SiC-BN) / BAS composite ceramic significantly better in toughness than the single SiC / BAS and BN / BAS systems while maintaining high strength. The presence of the BAS glass phase further promotes the passivation and bridging effect of cracks. (2) Thermal conductivity improvement and thermal expansion regulation - the high thermal conductivity of SiC and the two-dimensional thermal conduction path of BN jointly construct an efficient heat transfer network, overcoming the low thermal conductivity defect of the BAS glass phase. At the same time, the negative thermal expansion characteristics of BN and the moderate thermal expansion of SiC compensate each other, making the thermal expansion coefficient of the composite ceramic close to the use requirements of the composite material.

Claims

1. A low temperature sintered (SiC-BN) / BAS composite ceramic, characterized in that The composite ceramic is made of 20-40% BAS, 53-67% SiC and 3-17% BN in terms of mass percentage.

2. The low temperature sintered (SiC-BN) / BAS composite ceramic according to claim 1, characterized in that The composite ceramic is made of 30% BAS, 66.5% SiC and 3.5% BN by mass.

3. The low temperature sintered (SiC-BN) / BAS composite ceramic according to claim 1, characterized in that The composite ceramic is made of 30% BAS, 63% SiC and 7% BN by mass.

4. The low temperature sintered (SiC-BN) / BAS composite ceramic according to claim 1, characterized in that The composite ceramic is made of 30% BAS, 59.5% SiC and 10.5% BN by mass.

5. The low temperature sintered (SiC-BN) / BAS composite ceramic according to claim 1, characterized in that The composite ceramic is made of 30% BAS, 56% SiC and 14% BN by mass.

6. The low temperature sintered (SiC-BN) / BAS composite ceramic according to claim 1, 2, 3, 4 or 5, characterized in that The SiC is β-type SiC.

7. A method for preparing the low temperature sintered (SiC-BN) / BAS composite ceramic according to any one of claims 1 to 6, characterized in that The method comprises the following steps: Step S1: BAS, SiC powder and BN powder are mixed, anhydrous ethanol and ball milling medium are added, and ball milling is performed on a mixer to obtain a uniform mixed slurry; Step S2: drying and sieving the mixed slurry to obtain a mixed powder; Step S3: Place the mixed powder into a graphite mold and sinter under inert gas protection, controlling the sintering temperature to be 1450~1550 o C, the sintering pressure is 10~30MPa, the heat preservation and pressure holding time is 60~120min, and after the heat preservation and pressure holding are completed, the furnace is cooled and the mold is demolded to obtain (SiC-BN) / BAS composite ceramics.

8. The method for preparing low temperature sintered (SiC-BN) / BAS composite ceramics according to claim 7, characterized in that In the step S1, the SiC powder and the BN powder are ultrasonically dispersed before mixing, the solvent is anhydrous ethanol, and the dispersion time is 10 to 60 minutes.

9. The method for preparing low temperature sintered (SiC-BN) / BAS composite ceramics according to claim 7, characterized in that In step S1, the ball milling medium is Al2O3 balls, the ball-to-material ratio is 4-8:1, and the ball milling time is 20-30 hours.

10. The method for preparing low temperature sintered (SiC-BN) / BAS composite ceramics according to claim 7, characterized in that In step S3, the temperature is controlled from room temperature to 1200 o The heating rate is 10~30 o C / min, from 1200 o C to sintering temperature 1450~1550 o The heating rate is 10~25 o C / min.

Images