Silicon carbide ceramics and their preparation methods

Abstract

The application discloses a silicon carbide ceramic and a preparation method thereof. The bending strength of the silicon carbide ceramic is not less than 600 MPa, and the fracture toughness of the silicon carbide ceramic is not less than 10 MPa·m 1 / 2 The silicon carbide ceramic not only has high strength, but also has high toughness, and can be applied to many fields such as aerospace, mechanical industry and electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide ceramic sintering, and specifically relates to a silicon carbide ceramic and its preparation method. Background Technology

[0002] Silicon carbide ceramics possess excellent high-temperature mechanical properties, high hardness, strong thermal shock resistance, high thermal conductivity, and resistance to oxidation and chemical corrosion, making them crucial high-temperature structural materials with broad application prospects in aerospace, machinery, electronic devices, and nuclear reactors. However, the main obstacle hindering the widespread application of silicon carbide ceramics is their brittleness, leading to sudden fractures during use. The brittleness of ceramic materials is primarily determined by their structural characteristics. Structurally, ceramic materials are polycrystalline structures composed of strong ionic and covalent bonds, lacking a slip system to induce deformation. Therefore, existing silicon carbide ceramics require further improvement. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one objective of this invention is to provide a silicon carbide ceramic and its preparation method. The silicon carbide ceramic has a flexural strength of not less than 600 MPa and a fracture toughness of not less than 10 MPa·m. 1 / 2 .

[0004] In one aspect of the invention, a silicon carbide ceramic is provided. According to an embodiment of the invention, the silicon carbide ceramic has a flexural strength of not less than 600 MPa and a fracture toughness of not less than 10 MPa·m. 1 / 2 Therefore, this silicon carbide ceramic not only has high strength but also high toughness, and can be applied in many fields such as aerospace, machinery industry, and electronic devices.

[0005] In addition, the silicon carbide ceramics according to the above embodiments of the present invention may also have the following additional technical features:

[0006] According to an embodiment of the present invention, the density of the silicon carbide ceramic is not less than 98%. Therefore, the silicon carbide ceramic has the advantages of high density and low porosity.

[0007] In another aspect, the present invention provides a method for preparing the above-described silicon carbide ceramic. According to an embodiment of the present invention, the method includes:

[0008] (1) Mix silicon carbide powder and sintering aid to obtain raw material powder;

[0009] (2) An insulating ceramic layer is adjacent to the inner wall of the sintering mold of the spark plasma sintering furnace. The raw material powder is placed into the sintering mold for spark plasma sintering in order to obtain silicon carbide ceramic.

[0010] According to the above-described method for preparing silicon carbide ceramics of the present invention, firstly, silicon carbide powder and sintering aid are mixed to obtain raw material powder. The sintering aid is ionized under an alternating electric field and moves along the current direction, and can be rapidly and uniformly dispersed. At the same time, the sintering aid can react with silicon carbide to generate carbides or silicides, and then form a solid solution with silicon carbide. It then gradually diffuses into the interior of the silicon carbide lattice, promoting solid-phase sintering dominated by deformation, and constructing a nanotwin structure inside the silicon carbide grains, thereby improving the strength and toughness of silicon carbide ceramics. The inner wall of the sintering mold in the spark plasma sintering furnace is adjacent to an insulating ceramic layer. The raw material powder is placed into the sintering mold for spark plasma sintering. Due to the presence of the insulating ceramic layer, it can incorporate the characteristics of flash sintering, where the pulsed current generated during sintering directly acts on the raw material powder. The generated Joule heat and plasma directly heat the raw material powder, resulting in a faster heating rate. This allows for effective temperature regulation of the raw material powder by controlling the pulsed current path, thereby improving the strength and toughness of silicon carbide ceramics. Furthermore, the presence of the insulating ceramic layer facilitates control of the solid-state sintering process. This control promotes the formation of high-density nanotwin structures within the silicon carbide ceramic grains, increasing the slip system that promotes material deformation and improving the silicon carbide ceramic's resistance to crack propagation, thus enhancing its fracture toughness while maintaining its excellent flexural strength and hardness. Compared to traditional spark plasma sintering furnaces that use sintering molds to heat raw material powders, the method described in this application not only significantly increases the heating rate of the raw material powder, promoting the formation of high-density nanotwin structures, but also requires less sintering time and lower voltage and current, greatly reducing power consumption and offering advantages such as energy saving and speed. Therefore, silicon carbide ceramics prepared using this method possess both high strength and high toughness, and the method can significantly reduce energy consumption and save production costs.

[0011] In addition, the method for preparing silicon carbide ceramics according to the above embodiments of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, in step (1), the particle size of the silicon carbide powder is 1 μm to 5 μm. This improves the strength and toughness of the silicon carbide ceramic.

[0013] In some embodiments of the present invention, in step (1), the mass percentage of the sintering aid is 1 wt% to 10 wt% based on the total mass of the raw material powder. This can improve the strength and toughness of silicon carbide ceramics.

[0014] In some embodiments of the present invention, the sintering aid includes elemental metal sintering aids and metal oxide sintering aids. This can improve the strength and toughness of silicon carbide ceramics.

[0015] In some embodiments of the present invention, the elemental metal sintering aid includes at least one of aluminum, iron, silver, and magnesium. This can improve the strength and toughness of silicon carbide ceramics.

[0016] In some embodiments of the present invention, the metal oxide sintering aid includes at least one of alumina, yttrium oxide, boron oxide, magnesium oxide, and calcium oxide. This can improve the strength and toughness of silicon carbide ceramics.

[0017] In some embodiments of the present invention, in step (2), the thickness of the insulating ceramic layer is 1 mm to 2.5 mm. This improves the strength and toughness of the silicon carbide ceramic.

[0018] In some embodiments of the present invention, the insulating ceramic layer comprises boron nitride ceramic, zirconium oxide ceramic, or alumina ceramic. This improves the strength and toughness of the silicon carbide ceramic.

[0019] In some embodiments of the present invention, in step (2), the inner diameter of the sintering mold is 10 mm to 150 mm, and the height of the sintering mold is 1 cm to 20 cm. This improves the strength and toughness of silicon carbide ceramics.

[0020] In some embodiments of the present invention, in step (2), the temperature of the spark plasma sintering is 1500℃~1750℃, the pressure of the spark plasma sintering is 30MPa~60MPa, and the holding time is 0.5min~20min. This improves the strength and toughness of silicon carbide ceramics.

[0021] In some embodiments of the present invention, during the heating process of the spark plasma sintering, the sintering temperature is less than 600°C and the heating rate is 180°C / min to 220°C / min, and the sintering temperature is greater than 600°C and the heating rate is 90°C / min to 120°C / min.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0024] Figure 1This is a schematic diagram of a sintering mold structure according to an embodiment of the present invention;

[0025] Figure 2 This is a TEM image of silicon carbide ceramic grains in Embodiment 1 of the present invention;

[0026] Figure 3 This is a SEM image of the cross-section of silicon carbide ceramic in Embodiment 2 of the present invention;

[0027] Figure 4 These are TEM images and energy dispersive spectroscopy (EDS) surface scans of silicon carbide ceramics from Example 3 of this invention.

[0028] In the attached diagram, 10 is a stainless steel electrode, 20 is a graphite base, 30 is a graphite pressure head, 40 is an insulating ceramic layer, 50 is a graphite sintering mold, 60 is raw material powder, 70 is graphite paper, 80 is a pulse current path, and 90 is an infrared temperature measurement hole. Detailed Implementation

[0029] The embodiments of the present invention are described in detail below, and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0030] In one aspect of the invention, a silicon carbide ceramic is provided. According to an embodiment of the invention, the silicon carbide ceramic has a flexural strength of not less than 600 MPa and a fracture toughness of not less than 10 MPa·m. 1 / 2 Therefore, this silicon carbide ceramic not only has high strength but also high toughness, and can be applied in many fields such as aerospace, machinery industry, and electronic devices.

[0031] According to an embodiment of the present invention, the density of the silicon carbide ceramic is not less than 98%. This silicon carbide ceramic has the advantages of high density and low porosity. Therefore, the silicon carbide ceramic of this application not only has high strength but also high toughness.

[0032] In another aspect, the present invention provides a method for preparing the above-described silicon carbide ceramic. According to an embodiment of the present invention, the method includes:

[0033] S100: Mixing silicon carbide powder and sintering aids

[0034] In this step, silicon carbide powder and sintering aids are mixed to obtain raw material powder. The sintering aids are ionized under an alternating electric field and move along the current direction, enabling rapid and uniform dispersion. Simultaneously, the sintering aids react with silicon carbide to form carbides or silicides, which then form a solid solution with silicon carbide. This solution gradually diffuses into the silicon carbide lattice, promoting deformation-driven solid-phase sintering and constructing nanotwin structures within the silicon carbide grains, thereby improving the strength and toughness of the silicon carbide ceramic. Furthermore, the particle size of the silicon carbide powder is 1μm to 5μm, which further enhances the strength and toughness of the silicon carbide ceramic. Those skilled in the art will understand that mixing is a conventional operation in the field; for example, mechanical stirring can be used for mixing, and the mixing environment is an inert atmosphere such as anhydrous argon or nitrogen.

[0035] According to an embodiment of the present invention, the mass percentage of the sintering aid is 1 wt% to 10 wt% based on the total mass of the raw material powder. The inventors have found that a mass percentage of 1 wt% to 10 wt% for the sintering aid can promote the dense sintering of the raw material powder without generating too many low-strength intergranular phases due to excessive sintering aid content, thereby maintaining the good mechanical properties of silicon carbide ceramics.

[0036] According to embodiments of the present invention, the sintering aid includes elemental metallic sintering aids and metal oxide sintering aids. Further, the elemental metallic sintering aid includes at least one of aluminum, iron, silver, and magnesium; the metal oxide sintering aid includes at least one of alumina, yttrium oxide, boron oxide, magnesium oxide, and calcium oxide. The inventors have discovered that by using the above-mentioned sintering aids, carbides or silicides can be generated by reacting with silicon carbide to form carbides or silicides, which then form a solid solution with silicon carbide and gradually diffuse into the silicon carbide lattice, promoting deformation-dominated solid-phase sintering. This can induce the formation of nanotwin structures within the silicon carbide grains, thereby improving the strength and toughness of silicon carbide ceramics.

[0037] S200: The inner wall of the sintering mold in the spark plasma sintering furnace is adjacent to an insulating ceramic layer. The raw material powder is placed into the sintering mold for spark plasma sintering.

[0038] In this step, the inner wall of the sintering mold in the spark plasma sintering furnace is adjacent to an insulating ceramic layer. The raw material powder is placed into the sintering mold for spark plasma sintering. Due to the presence of the insulating ceramic layer, it can incorporate the technical characteristics of flash sintering, where the pulsed current generated during sintering directly acts on the raw material powder. The Joule heating generated in the raw material powder, along with the plasma, directly heats the powder, resulting in a faster heating rate. This allows for effective temperature regulation of the raw material powder by controlling the pulsed current path, thereby improving the strength and toughness of silicon carbide ceramics. On the other hand, the presence of the insulating ceramic layer facilitates control of the solid-state sintering process. By controlling solid-state sintering, it promotes the formation of high-density nanotwin structures within the silicon carbide ceramic grains, increasing the slip system that promotes material deformation and improving the silicon carbide ceramic's resistance to crack propagation, i.e., improving its fracture toughness, while maintaining its excellent flexural strength and hardness. Compared to traditional spark plasma sintering furnaces that use sintering molds to heat raw material powders, the method of this application not only significantly increases the heating rate of the raw material powder, promoting the formation of high-density nanotwin structures, but also requires less sintering time and lower voltage and current, greatly reducing power consumption and offering advantages such as energy saving and speed. It should be noted that spark plasma sintering furnaces are conventional equipment in the art, and those skilled in the art can select the specific model of spark plasma sintering furnace according to actual needs.

[0039] According to embodiments of the present invention, the thickness of the insulating ceramic layer is 1 mm to 2.5 mm. For example, the thickness is 1 mm, 1.5 mm, 1.8 mm, 2 mm, 2.5 mm, etc. The inventors have found that by controlling the thickness of the insulating ceramic layer within the above range, the pulse current can be controlled to flow from the graphite pressure head to the raw material powder, rather than the graphite sintering mold. This allows the flash firing technology to be integrated, thereby improving the strength and toughness of silicon carbide ceramics.

[0040] According to embodiments of the present invention, the insulating ceramic layer comprises boron nitride ceramic, zirconia ceramic, or alumina ceramic. The inventors have discovered that boron nitride ceramic, zirconia ceramic, or alumina ceramic possesses excellent insulation and thermal conductivity properties, thereby controlling the pulse current path and promptly transferring the heat generated by the raw material powder, reflecting the temperature changes of the raw material powder, which is beneficial for controlling the sintering process and can further improve the strength and toughness of silicon carbide ceramics.

[0041] According to embodiments of the present invention, the inner diameter of the sintering mold is 10mm to 150mm, and the height of the sintering mold is 1cm to 20cm. For example, the inner diameter of the sintering mold is 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 120mm, 150mm, etc.; and the height of the sintering mold is 1cm, 2cm, 4cm, 6cm, 8cm, 10cm, 12cm, 14cm, 16cm, 18cm, 20cm, etc. The inventors have found that controlling the inner diameter of the sintering mold to be 10mm to 150mm and the height of the sintering mold to be 1cm to 20cm can ensure a high heating rate of the raw material powder, promote the formation of a high-density nanotwinned structure, and thus improve the strength and toughness of silicon carbide ceramics.

[0042] According to an embodiment of the present invention, reference Figure 1 The sintering mold of the spark plasma sintering furnace includes a stainless steel electrode 10, a graphite base 20, a graphite pressure head 30, an insulating ceramic layer 40, a graphite sintering mold 50, graphite paper 70, and an infrared temperature measuring hole 90. An insulating ceramic layer 40 is provided on the inner wall of the graphite sintering mold 50, and graphite paper 70 is provided on the side of the insulating ceramic layer 40 away from the graphite sintering mold 50. The raw material powder 60 is placed inside the graphite sintering mold 50. When the power is turned on, under the action of the insulating ceramic layer 40, a pulsed current forms a pulsed current path 80 flowing through the raw material powder, thus acting on the raw material powder 60, significantly increasing the heating rate of the raw material powder 60 and causing solid-state sintering, thereby promoting the formation of a high-density nanotwin structure and improving the strength and toughness of silicon carbide ceramics.

[0043] According to embodiments of the present invention, the temperature of spark plasma sintering is 1500℃~1750℃, the pressure of spark plasma sintering is 30MPa~60MPa, and the holding time is 0.5min~20min. For example, the spark plasma sintering temperature is 1500℃, 1550℃, 1600℃, 1650℃, 1700℃, 1750℃, etc., the spark plasma sintering pressure is 30MPa, 35MPa, 40MPa, 45MPa, 50MPa, 60MPa, etc., and the holding time is 0.5min, 1min, 3min, 5min, 10min, 12min, 15min, 20min, etc. The inventors discovered that controlling the conditions of spark plasma sintering within the aforementioned range can ensure both the dense sintering of the raw material powder and the saving of sintering time, preventing the disappearance of the nanotwin structure within the silicon carbide grains, thereby improving the strength and toughness of silicon carbide ceramics, increasing the preparation efficiency of silicon carbide ceramics, and reducing the energy consumption in the preparation of silicon carbide ceramics. Furthermore, during the heating process of spark plasma sintering, the sintering temperature is below 600℃ with a heating rate of 180℃ / min to 220℃ / min, and the sintering temperature is above 600℃ with a heating rate of 90℃ / min to 120℃ / min.

[0044] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0045] Example 1

[0046] 95 wt% 1 μm silicon carbide powder and 5 wt% aluminum powder were mechanically mixed for 20 min under an anhydrous argon atmosphere. 0.8 g of the resulting powder was placed into a sintering mold in a specially designed spark plasma sintering furnace with an inner diameter of 15 mm and a height of 6 cm. A 2.5 mm thick layer of boron nitride ceramic was deposited on the inner wall of the mold. The mold was then placed in the furnace for sintering at a temperature of 1700 °C, with heating rates of 200 °C / min (below 600 °C) and 100 °C / min (above 600 °C), a sintering pressure of 45 MPa, a holding time of 10 min, and a sintering vacuum of less than 20 Pa. After sintering, the vacuum was maintained below 20 Pa, and the mixture was allowed to cool naturally to room temperature to obtain silicon carbide ceramic.

[0047] The obtained product is a cylindrical silicon carbide ceramic block with a measured density of 3.27 g / cm³. 3 The theoretical density yields a density of approximately 99.7%, and it possesses a flexural strength as high as 650 MPa and a tensile strength of 10.7 MPa·m. 1 / 2The silicon carbide ceramic exhibits good fracture toughness, with grain sizes greater than 10 μm and a high-density nanotwin structure within the grains. A TEM image of the silicon carbide ceramic grains prepared in Example 1 is shown below. Figure 2 As shown, from Figure 2 It can be seen that the silicon carbide grains have a high-density nanotwin structure, which can improve the strength and toughness of silicon carbide ceramics.

[0048] Example 2

[0049] 95 wt% 1 μm silicon carbide powder and 5 wt% alumina powder were mechanically mixed for 20 min under an anhydrous argon atmosphere. 10 g of the resulting powder was placed into a sintering mold in a specially designed spark plasma sintering furnace with an inner diameter of 50 mm and a height of 2 cm. A 2 mm thick layer of boron nitride ceramic was deposited on the inner wall of the mold. The mold was then placed in the spark plasma sintering furnace for sintering at a temperature of 1750 °C, a heating rate of 200 °C / min (for temperatures below 600 °C) and 100 °C / min (for temperatures above 600 °C), a sintering pressure of 50 MPa, a holding time of 3 min, and a sintering vacuum of less than 20 Pa. After sintering, the vacuum was maintained below 20 Pa, and the mixture was allowed to cool naturally to room temperature to obtain silicon carbide ceramic.

[0050] The obtained product is a cylindrical silicon carbide ceramic block with a measured density of 3.25 g / cm³. 3 The theoretical density yields a density of approximately 99.6%, and it possesses a flexural strength as high as 630 MPa and a tensile strength of 10.6 MPa·m. 1 / 2 The silicon carbide ceramic exhibits good fracture toughness, with a grain size greater than 10 μm and a high-density nanotwin structure within the grains. The SEM image of the cross-section of the silicon carbide ceramic prepared in Example 2 is shown below. Figure 3 As shown, from Figure 3 It can be seen that silicon carbide ceramics exhibit both intergranular and transgranular fractures during fracture. The fracture surface produced by transgranular fracture shows a stepped morphology, which is caused by the crack deflection effect of high-density nanotwins inside the silicon carbide grains. This is the main mechanism by which nanotwins improve the fracture toughness of silicon carbide ceramics.

[0051] Example 3

[0052] 99 wt% 1 μm silicon carbide powder and 1 wt% aluminum powder were mechanically mixed for 20 min under an anhydrous argon atmosphere. 150 g of the resulting powder was placed into a sintering mold in a specially designed spark plasma sintering furnace with an inner diameter of 100 mm and a height of 4 cm. The inner wall of the mold was lined with a 1 mm thick layer of boron nitride ceramic. The mold was then placed in the spark plasma sintering furnace for sintering at a temperature of 1600 °C, a heating rate of 200 °C / min (for temperatures below 600 °C) and 100 °C / min (for temperatures above 600 °C), a sintering pressure of 45 MPa, a holding time of 20 min, and a sintering vacuum of less than 20 Pa. After sintering, the vacuum was maintained below 20 Pa, and the mixture was allowed to cool naturally to room temperature to obtain silicon carbide ceramic.

[0053] The obtained product is a cylindrical silicon carbide ceramic block with a measured density of 3.25 g / cm³. 3 The theoretical density yields a density of approximately 99.8%, and it possesses a flexural strength as high as 637 MPa and a tensile strength of 11.3 MPa·m. 1 / 2 The fracture toughness of the silicon carbide ceramic is high. The grain size of the silicon carbide ceramic is greater than 10 μm, and the grains contain a high-density nanotwin structure. The atomic TEM image and energy dispersive spectroscopy (EDS) pattern of the silicon carbide ceramic prepared in Example 3 are shown below. Figure 4 As shown, from Figure 4 It can be seen that aluminum atoms replace silicon atoms in silicon carbide and are uniformly dispersed inside the silicon carbide lattice. Since the radii of aluminum atoms and silicon atoms are very similar, the doping of aluminum atoms does not cause obvious lattice distortion in silicon carbide.

[0054] Example 4

[0055] 90 wt% 1 μm silicon carbide powder and 10 wt% aluminum powder were mechanically mixed for 20 min under an anhydrous argon atmosphere. 20 g of the resulting powder was placed into a sintering mold in a specially designed spark plasma sintering furnace with an inner diameter of 50 mm and a height of 10 cm. A 2 mm thick layer of boron nitride ceramic was deposited on the inner wall of the mold. The mold was then placed in the spark plasma sintering furnace for sintering at a temperature of 1700 °C, a heating rate of 200 °C / min (for temperatures below 600 °C) and 100 °C / min (for temperatures above 600 °C), a sintering pressure of 60 MPa, a holding time of 5 min, and a sintering vacuum of less than 20 Pa. After sintering, the vacuum was maintained below 20 Pa, and the mixture was allowed to cool naturally to room temperature to obtain silicon carbide ceramic.

[0056] The obtained product is a cylindrical silicon carbide ceramic block with a measured density of 3.25 g / cm³. 3The theoretical density yields a density of approximately 99.9%, and it possesses a flexural strength as high as 607 MPa and a tensile strength of 11.9 MPa·m. 1 / 2 The fracture toughness of silicon carbide ceramics is high, the grain size is greater than 10 μm, and there is a high-density nanotwin structure inside the grains.

[0057] Example 5

[0058] 95 wt% 1 μm silicon carbide powder was mechanically mixed with 2.5 wt% aluminum powder and 2.5 wt% iron powder under an anhydrous argon atmosphere for 20 min. 25 g of the resulting powder was placed into a sintering mold in a specially designed spark plasma sintering furnace with an inner diameter of 20 mm and a height of 6 cm. A 1 mm thick layer of boron nitride ceramic was deposited on the inner wall of the mold. The mold was then placed in the spark plasma sintering furnace for sintering at a temperature of 1500 °C, a heating rate of 200 °C / min (for temperatures below 600 °C) and 100 °C / min (for temperatures above 600 °C), a sintering pressure of 40 MPa, a holding time of 15 min, and a sintering vacuum of less than 20 Pa. After sintering, the vacuum was maintained below 20 Pa, and the mixture was allowed to cool naturally to room temperature to obtain silicon carbide ceramic.

[0059] The obtained product is a cylindrical silicon carbide ceramic block with a measured density of 3.29 g / cm³. 3 The theoretical density yields a density of approximately 99.7%, and it possesses a flexural strength as high as 684 MPa and a tensile strength of 10.3 MPa·m. 1 / 2 The fracture toughness of silicon carbide ceramics is high, the grain size is greater than 10 μm, and there is a high-density nanotwin structure inside the grains.

[0060] Comparative Example 1

[0061] 99 wt% 1 μm silicon carbide powder and 1 wt% aluminum powder were mechanically mixed for 20 min under an anhydrous argon atmosphere. 150 g of the resulting powder was placed into a standard sintering mold in a spark plasma sintering furnace with an inner diameter of 100 mm and a height of 4 cm. The inner wall of the mold did not have an insulating ceramic layer. The mold was then placed in the spark plasma sintering furnace for sintering at a temperature of 1600 °C, a heating rate of 200 °C / min (for temperatures below 600 °C) and 100 °C / min (for temperatures above 600 °C), a sintering pressure of 45 MPa, a holding time of 20 min, and a sintering vacuum of less than 20 Pa. After sintering, the vacuum was maintained below 20 Pa, and the mixture was allowed to cool naturally to room temperature to obtain silicon carbide ceramic.

[0062] The obtained product is a cylindrical silicon carbide ceramic block with a measured density of 2.73 g / cm³. 3It has a density of approximately 82.3% and a flexural strength of only 300 MPa and a tensile strength of 4.8 MPa·m. 1 / 2 The fracture toughness of silicon carbide ceramics is approximately 2 μm, and no high-density nanotwin structures were observed within the grains.

[0063] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0064] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of making a silicon carbide ceramic, characterized by, The bending strength of the silicon carbide ceramic is not less than 600 MPa, the fracture toughness of the silicon carbide ceramic is not less than 10 MPa·m 1 / 2 , the relative density of the silicon carbide ceramic is not less than 98%, and the method comprises: (1) mixing silicon carbide powder and sintering aids to obtain raw material powder; (2) the inner wall of a sintering mold of a spark plasma sintering furnace is adjacent to an insulating ceramic layer, and the raw material powder is placed in the sintering mold for spark plasma sintering to obtain silicon carbide ceramic, wherein the thickness of the insulating ceramic layer is 1mm-2.5mm; the temperature of the spark plasma sintering is 1500℃-1750℃, the pressure of the spark plasma sintering is 30MPa-60MPa, and the holding time is 0.5min-20min; in the temperature rising process of the spark plasma sintering, the sintering temperature is less than 600℃, the heating rate is 180℃ / min-220℃ / min, and the sintering temperature is greater than 600℃, the heating rate is 90℃ / min-120℃ / min.

2. The method of claim 1, wherein, In step (1), the particle size of the silicon carbide powder is 1μm-5μm.

3. The method of claim 1, wherein, In step (1), the mass fraction of the sintering aid is 1wt%-10wt% based on the total mass of the raw material powder.

4. The method of claim 3, wherein, The sintering aid includes a metal element sintering aid and a metal oxide sintering aid.

5. The method of claim 4, wherein, The metal element sintering aid includes at least one of aluminum, iron, silver and magnesium.

6. The method of claim 4, wherein, The metal oxide sintering aid includes at least one of aluminum oxide, yttrium oxide, boron oxide, magnesium oxide and calcium oxide.

7. The method of claim 1, wherein, The insulating ceramic layer includes boron nitride ceramic, zirconium oxide ceramic or aluminum oxide ceramic.

8. The method of claim 1, wherein, In step (2), the inner diameter of the sintering mold is 10mm-150mm, and the height of the sintering mold is 1cm-20cm.

9. The silicon carbide ceramic produced by the method of any one of claims 1 to 8, characterized by The bending strength of the silicon carbide ceramic is not less than 600 MPa, the fracture toughness of the silicon carbide ceramic is not less than 10 MPa·m 1 / 2 , and the density of the silicon carbide ceramic is not less than 98%.

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