Normal-pressure low-temperature liquid-phase sintered silicon carbide ceramic material and preparation method thereof

Abstract

The invention relates to a normal-pressure low-temperature liquid-phase sintered silicon carbide ceramic material and a preparation method thereof. The preparation method of the normal-pressure low-temperature liquid-phase sintered silicon carbide ceramic material comprises the following steps: (1) mixing aluminum isopropoxide, ytterbium acetate tetrahydrate, silicon carbide raw material powder and a dispersing agent in water to form slurry, drying and sieving to obtain raw material mixed powder; (2) carrying out compression molding on the raw material mixed powder to obtain a biscuit; and (3) carrying out heat treatment on the biscuit, and carrying out normal-pressure powder burying sintering to obtain the normal-pressure low-temperature liquid-phase sintered silicon carbide ceramic material.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic material preparation, and in particular relates to a normal pressure low temperature liquid phase sintered silicon carbide ceramic material and a preparation method thereof. Background Art

[0002] Silicon carbide (SiC) is a strongly covalently bonded compound with numerous excellent properties, including high strength, high hardness, corrosion resistance, wear resistance, oxidation resistance, low thermal expansion coefficient, and high thermal conductivity. Therefore, it holds significant application value and potential in numerous industrial fields. Among these, atmospheric pressure liquid-phase sintered SiC ceramics exhibit higher flexural strength and fracture toughness than atmospheric pressure solid-phase sintered SiC ceramics and reaction-bonded SiC ceramics, resulting in their widespread use in high-speed, heavy-load mechanical seals.

[0003] Traditional liquid phase sintered silicon carbide (LPS SiC) generally uses Al2O3 and Y2O3 as sintering aids. High-strength and high-toughness SiC ceramics are prepared by directly adding Al2O3 and Y2O3 powders and sintering at high temperature. However, this method has a high sintering temperature, usually greater than 1930°C, high energy consumption and easy grain growth. At present, there are several main methods to reduce the sintering temperature of LPS SiC: 1) Adding low-temperature eutectic sintering aids: For example, adding low-melting-point aids (such as Al2O3-SiO2, Y-Al-ON, etc.) further reduces the eutectic point and inhibits grain growth. The aids can generate a liquid phase at around 1550°C (much lower than the 1760°C of Al2O3-Y2O3); 2) Using nano-raw material powders: By using nano-scale SiC powders, the sintering driving force is increased, and nano-SiC powders (<100nm) are used to achieve densification at 1650°C; 3) Precursor conversion method: Active SiC is generated by the decomposition of polymer precursors (such as polycarbosilane) at low temperature, and densification can be achieved at 1500°C when combined with a small amount of aids; 4) Field-assisted sintering technology (FAST / SPS): Spark plasma sintering (SPS) or hot pressing (HP) promotes diffusion through an external field (current / pressure), which can achieve densification at lower temperatures.

[0004] However, in method 1), a glass phase is generated in the ceramic, and the presence of the glass phase reduces the strength and corrosion resistance of the ceramic; in methods 2) and 3), the nanopowders and polymer precursors are expensive; and method 4) is not conducive to the preparation of ceramic materials with complex shapes. Summary of the Invention

[0005] In response to the above-mentioned problem that low-temperature sintering of liquid-phase sintered silicon carbide ceramics is incompatible with high performance or low cost, the present invention introduces a sintering aid by adopting a sintering aid precursor. The precursor is dissolved in an aqueous solution and can achieve uniform coating on the surface of the SiC powder. The Al2O3 and Yb2O3 nanoparticles generated by the in-situ cracking of the precursor can significantly reduce the sintering temperature of the ceramic due to its unique surface effect and diffusion kinetics advantages, thereby realizing low-temperature sintering of liquid-phase sintered silicon carbide ceramics at normal pressure.

[0006] In a first aspect, the present invention provides a method for preparing a silicon carbide ceramic material by liquid phase sintering at normal pressure and low temperature, the preparation method comprising the following steps: (1) mixing aluminum isopropoxide, ytterbium acetate tetrahydrate, silicon carbide raw material powder, and a dispersant in water to form a slurry, drying, and sieving to obtain a raw material mixed powder; (2) pressing the raw material mixed powder into a shape to obtain a green body; (3) The green body is subjected to heat treatment and powder embedding sintering at normal pressure to obtain the normal pressure low temperature liquid phase sintered silicon carbide ceramic material.

[0007] Preferably, in step (1), based on the total mass of aluminum isopropoxide, ytterbium acetate tetrahydrate and silicon carbide raw material powder as 100wt%, the aluminum isopropoxide and ytterbium acetate tetrahydrate account for 8-10wt% of the total mass of the powder, and the aluminum oxide and ytterbium oxide generated by their decomposition account for 3.21-4.27wt% of the total mass of the powder, preferably 3.21-4.08wt%.

[0008] Preferably, in step (1), the dispersant is tetramethylammonium hydroxide, and the added amount is 0.5-0.8 wt % of the total mass of the powder.

[0009] Preferably, in step (3), the heat treatment process includes: keeping the blank at 200°C in a vacuum sintering furnace for 1 hour, then heating it to 760°C at a rate of 0.5-1.0°C / min and keeping it at that temperature for 1 hour, and finally continuing to heat it to 900°C at a rate of 2.0-5.0°C / min and keeping it at that temperature for 0.5-1 hour.

[0010] Preferably, in step (3), the embedding material used in the atmospheric pressure embedded powder sintering is composed of silicon carbide, aluminum oxide and ytterbium oxide powder; wherein the content of silicon carbide embedding material is 95.73-96.79wt%, preferably 95.92-96.79wt%, and the content of aluminum oxide and ytterbium oxide is 3.21-4.27wt%, preferably 3.21-4.08wt%.

[0011] Preferably, in step (3), the atmospheric pressure buried powder sintering is carried out in an Ar atmosphere, and the sintering process is: first, the temperature is raised to 900°C at a rate of 10.0°C / min, and then the temperature is continued to be raised to 1400°C at a rate of 5.0°C / min, and then the temperature is raised to 1550°C at a rate of 0.5-1.0°C / min and kept warm for 0.5h, and finally the temperature is raised to 1700-1800°C at a rate of 2.0-3.0°C / min and kept warm for 0.5-1.0h.

[0012] In a second aspect, the present invention provides a normal pressure low temperature liquid phase sintered silicon carbide ceramic material obtained according to the above preparation method.

[0013] Beneficial effects (1) The present invention uses water-soluble aluminum isopropoxide and ytterbium acetate tetrahydrate as sintering aid precursors to prepare liquid-phase sintered silicon carbide ceramic materials. Compared with the traditional method of directly adding oxide powder, the sintering aid precursor in the material is decomposed to form a nanophase. The specific surface area of ​​the nanopowder is significantly increased, resulting in an increase in the total surface energy of the system, thereby reducing the surface energy during sintering and initiating material migration at a lower temperature, reducing the sintering temperature by about 200°C. (2) The sintering aid precursor of the present invention is soluble in the solvent, and a relatively small amount of additives can achieve uniform coating on the surface of the SiC powder and achieve densification, thereby reducing the content of the grain boundary phase and facilitating the improvement of high-temperature strength. At the same time, its preparation process is consistent with that of traditional liquid-phase sintered silicon carbide materials, and also has the characteristics of simple process. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The surface microstructure of LPSSiC prepared by adding 8 wt% of sintering aid precursor in Example 1; Figure 2 The surface microstructure of LPSSiC prepared by adding 10 wt% of sintering aid precursor in Example 2; Figure 3 The surface microstructure of LPSSiC prepared by adding 9 wt% of sintering aid precursor in Example 3; Figure 4 The fracture microstructure of LPSSiC prepared by adding 9 wt% of sintering aid precursor in Example 4; Figure 5 The fracture microstructure of LPSSiC prepared by adding 5 wt% sintering aid precursor in Comparative Example 1; Figure 6 This is the surface microstructure of LPSSiC prepared by adding 8 wt% oxide sintering aid powder in Comparative Example 3. DETAILED DESCRIPTION

[0015] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0016] The following is an exemplary description of the method for preparing the atmospheric low-temperature liquid phase sintered silicon carbide ceramic material provided by the present invention. The preparation method may include the following steps: (1) mixing aluminum isopropoxide, ytterbium acetate tetrahydrate, silicon carbide raw material powder, and a dispersant in water to form a slurry, drying, and sieving to obtain a raw material mixed powder; (2) pressing the raw material mixed powder into a shape to obtain a green body; (3) The green body is subjected to heat treatment and powder embedding sintering at normal pressure to obtain the normal pressure low temperature liquid phase sintered silicon carbide ceramic material.

[0017] In some embodiments, in step (1), based on the total mass of aluminum isopropoxide, ytterbium acetate tetrahydrate and silicon carbide raw material powder as 100wt%, the aluminum isopropoxide and ytterbium acetate tetrahydrate can account for 8-10wt% of the total mass of the powder, and the aluminum oxide and ytterbium oxide generated by their decomposition can account for 3.21-4.27wt% of the total mass of the powder, preferably 3.21-4.08wt%. The molar ratio of the aluminum isopropoxide and ytterbium acetate tetrahydrate can be adjusted according to the sintering conditions, for example, it can be 5:3.

[0018] It should be noted that the present invention adopts aluminum isopropylate, ytterbium acetate tetrahydrate as sintering aid organic precursor, both are soluble in water, are conducive to it and disperse evenly in the middle of silicon carbide powder, realize the uniform package of sintering aid at SiC powder surface, promote material uniform densification, thus realize the addition of a small amount of sintering aid, avoid the difficult problem that conventional mechanical mixing particle auxiliary agent is unevenly dispersed and causes local liquid phase excessive, mechanical property decline. Moreover, aluminum isopropylate and ytterbium acetate tetrahydrate are hydrolyzed-condensed in solvent to form nanocomposite auxiliary agent, can generate uniform Yb-Al-O liquid phase at low temperatures, liquid phase formation temperature is down to 1550 ℃ (lower about 200 ℃ than traditional system), and simultaneously acetate radical decomposes and produces reducing atmosphere (CO / H2) can remove SiC surface SiO2 layer, promotes sintering.

[0019] At the same time, the mechanism of the precursor sintering aid used in the present invention to reduce the sintering temperature is that it decomposes at low temperature to generate a nano sintering aid phase, which significantly increases the specific surface area of ​​the nano powder, resulting in an increase in the total surface energy of the system, thereby sintering to reduce the surface energy and start the material migration at a lower temperature; at the same time, the nanoparticles significantly shorten the atomic diffusion distance. According to the diffusion equation (t∝d 3 ), when the particle size is reduced to 1 / 10, the diffusion rate increases by 1000 times, the proportion of grain boundary diffusion increases, and the sintering mechanism of micron powder sintering, which is mainly based on volume diffusion, is improved.

[0020] It should also be noted that if the content of aluminum oxide and ytterbium oxide generated by the decomposition of aluminum isopropoxide and ytterbium acetate tetrahydrate is too low, the generated liquid phase will be insufficient to wet the surface of the silicon carbide powder, making it difficult to promote the densification of liquid-phase sintered silicon carbide ceramics, resulting in the prepared ceramic material containing more pores; if the content of aluminum oxide and ytterbium oxide generated by the decomposition of aluminum isopropoxide and ytterbium acetate tetrahydrate is too high, the generated liquid phase will be excessive, easy to agglomerate and form more second phases and thicker grain boundary layers, thereby reducing the mechanical properties of the prepared ceramic material.

[0021] The existing technology usually adopts the method of directly adding oxide powder to prepare liquid-phase sintered silicon carbide ceramic materials. Compared with the water-soluble sintering aid used in the present invention, its dispersion uniformity in SiC powder is poor, and thus the encapsulation performance of silicon carbide powder is also poor. Under normal pressure sintering conditions, in order to achieve sufficient liquid phase wetting and high-temperature densification sintering, its addition amount is usually above 5wt%, which easily leads to the aggregation of the second phase generated by the sintering aid, reducing the high-temperature performance of the material. The sintering aid used in the present invention has a lower addition amount, reduces the content of the grain boundary phase, and reduces the thickness of the grain boundary phase, which is beneficial to the improvement of the high-temperature strength of the ceramic material.

[0022] In some embodiments, in step (1), the dispersant may be tetramethylammonium hydroxide, and the added amount may be 0.5-0.8 wt % of the total mass of the powder.

[0023] In some embodiments, in step (1), the drying temperature may be 80-100°C, and the mesh size of the sieve may be 60-100. Too low a drying temperature may result in incomplete evaporation of the powder moisture; too high a drying temperature may easily cause the added organic additives to form a crust, which is not conducive to uniform dispersion of the powder.

[0024] In some embodiments, in step (2), the pressing method can be to first put the raw material mixed powder into a steel mold and press it at a pressure of 20-40 MPa, and then isostatically press it at 150-200 MPa (for example, 200 MPa).

[0025] In some embodiments, in step (3), the heat treatment process may include: keeping the green billet at 200°C in a vacuum sintering furnace for 1 hour, then heating it to 760°C at a rate of 0.5-1.0°C / min and keeping it at that temperature for 1 hour, and finally continuing to heat it to 900°C at a rate of 2.0-5.0°C / min and keeping it at that temperature for 0.5-1 hour.

[0026] By controlling the heating rate and temperature, aluminum isopropoxide and ytterbium acetate tetrahydrate can be fully decomposed and the chemical water can be removed to generate nano-active alumina and ytterbium oxide respectively. At the same time, the added organic additives can be decomposed, which is beneficial to the generation of liquid phase in the subsequent sintering process and realize densified sintering.

[0027] In some embodiments, in step (3), the embedding material used in the atmospheric pressure embedded powder sintering can be composed of silicon carbide, aluminum oxide and ytterbium oxide powder; wherein the content of silicon carbide embedding material can be 95.73-96.79wt%, preferably 95.92-96.79wt%, and the content of aluminum oxide and ytterbium oxide can be 3.21-4.27wt%, preferably 3.21-4.08wt%.

[0028] The buried powder's composition is consistent with that of the sample. This preferential loss of additives from the buried powder inhibits the volatilization of low-melting-point sintering aid components in the sample, maintaining sample composition stability. Furthermore, the buried powder fills the voids surrounding the sintered body. At high temperatures, the liquid phase formed balances the liquid distribution through capillary forces, inhibiting the downward migration of the liquid phase formed at high temperatures due to gravity, promoting uniform densification of the sample. Using buried powder in liquid-phase sintering can increase sample density by 5-15% while reducing defects (e.g., porosity down to <0.5%).

[0029] In some embodiments, in step (3), the atmospheric pressure buried powder sintering can be carried out in an Ar atmosphere, and the sintering process can be: first heating to 900°C at a rate of 10.0°C / min, then continuing to heat to 1400°C at a rate of 5.0°C / min, then heating to 1550°C at a rate of 0.5-1.0°C / min and keeping warm for 0.5h, and finally heating to (sintering temperature) 1700-1800°C at a rate of 2.0-3.0°C / min and keeping warm for 0.5-1.0h.

[0030] It should be noted that since the temperature range for liquid-phase sintering to generate the liquid phase is relatively narrow, slowly heating up the temperature in this area (0.5-1.0°C / min) can avoid local overheating that causes premature or uneven generation of the liquid phase, and avoid unreacted oxide residues caused by too rapid heating. By keeping the temperature in the liquid-phase generation temperature range (keeping it at 1550°C for 0.5h), the liquid phase can fully penetrate the gaps between the particles, cover the SiC surface, form a continuous liquid phase network, reduce the density unevenness caused by local enrichment of the liquid phase, and make the material have a uniform microstructure.

[0031] In addition, 1400-1550℃ is the temperature in the liquid phase generation area, and a low heating rate of 0.5-1.0℃ / min and a holding time of 0.5h ensure the sufficient generation of the liquid phase. From 1550℃ to the sintering temperature, the temperature is raised to the sintering temperature at a faster heating rate of 2.0-3.0℃ / min and held for 0.5-1h. This can minimize the volatilization of the liquid phase while ensuring sample densification and ensuring sample performance. The sintering temperature is 1700-1800℃. Too low a sintering temperature makes it difficult to ensure sample densification; too high a sintering temperature will cause a large amount of volatilization of the generated liquid phase, resulting in the existence of pores and poor material performance.

[0032] The preparation method provided by the present invention provides a silicon carbide ceramic material sintered at low temperature under normal pressure, with a relative density (Archimedes method test) of ≥98.0%, preferably 98.5-99.5%, a bending strength of greater than 500 MPa, preferably 550-650 MPa, and a fracture toughness of 6.8-8.5 MPa·m 1 / 2 .

[0033] The following examples are further given to illustrate the present invention in detail. It should be understood that the following examples are only used to further illustrate the present invention and cannot be interpreted as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, and those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values ​​exemplified below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0034] Example 1

[0035] The method for preparing the silicon carbide ceramic material provided in this embodiment by liquid phase sintering at normal pressure and low temperature comprises the following steps: (1) 2.41 g of aluminum isopropoxide and 5.59 g of ytterbium acetate tetrahydrate were dissolved in 200 g of deionized water, and 92.0 g of SiC powder and 0.8 g of tetramethylammonium hydroxide were added to the mixture. 200 g of silicon carbide grinding balls were added to a ball mill and ball milled for 4 h to obtain a slurry. The slurry was then dried in an oven at 80° C. and passed through a 60-mesh sieve to obtain a raw material mixed powder. (2) dry pressing the sieved powder at 20 MPa, and then isostatically pressing at 200 MPa to obtain a green blank; (3) The formed green body is kept at 200°C in a vacuum sintering furnace for 1 hour, then heated to 760°C at a heating rate of 0.5°C / min, kept warm for 1 hour, and then heated to 900°C at a heating rate of 5°C / min, kept warm for 1 hour; the heat-treated green body is placed in a graphite mold and buried in a buried powder consisting of 96.68wt% silicon carbide, 3.32wt% aluminum oxide and ytterbium oxide powder; under Ar atmosphere, the temperature is raised to 900°C at a heating rate of 10.0°C / min, then raised to 1400°C at a heating rate of 5.0°C / min, then raised to 1550°C at a heating rate of 0.5°C / min, kept warm for 0.5 hour, and then heated to 1800°C at a heating rate of 2.0°C / min, kept warm for 0.5 hour, to obtain the atmospheric pressure low temperature liquid phase sintered silicon carbide ceramic material.

[0036] Figure 1This is the surface microstructure of LPSSiC prepared by adding 8 wt% of the sintering aid precursor in Example 1. The green portion represents 6H silicon carbide, the red portion represents 4H silicon carbide, the white portion represents the sintering aid, and the black portion represents pores. As can be seen from the image, the sample has a uniform microstructure with a small amount of pores.

[0037] The silicon carbide ceramic sample obtained in Example 1 has a relative density of 98.5%, a flexural strength of 559.8±56.8 MPa, and a fracture toughness of 6.80 MPa·m 1 / 2 .

[0038] Example 2

[0039] The preparation method of the atmospheric low-temperature liquid-phase sintered silicon carbide ceramic material provided in this embodiment refers to Example 1, with the main differences being that the addition amounts of aluminum isopropoxide, ytterbium acetate tetrahydrate, and SiC powder are 3.01 g, 6.99 g, and 90.0 g, respectively; the buried powder composition is 95.73 wt% silicon carbide, 4.27 wt% aluminum oxide, and ytterbium oxide powder; the sintering temperature is 1700°C, and the holding time is 1.0 h.

[0040] Figure 2 This is the surface microstructure of LPSSiC prepared by adding 10 wt% of the sintering aid precursor in Example 2. The gray portion represents silicon carbide, and the white portion represents the sintering aid. As can be seen from the figure, the sample's microstructure is uniform and dense, with minimal pores, and the silicon carbide grains are primarily equiaxed.

[0041] The silicon carbide ceramic sample obtained in Example 2 has a relative density of 98.0%, a flexural strength of 504±52 MPa, and a fracture toughness of 8.00 MPa·m 1 / 2 .

[0042] Example 3

[0043] The preparation method of the atmospheric low temperature liquid phase sintered silicon carbide ceramic material provided in this embodiment refers to Example 1, with the main differences being that: the addition amounts of aluminum isopropoxide, ytterbium acetate tetrahydrate, and SiC powder are 2.71 g, 6.29 g, and 91.0 g, respectively, and the amount of tetramethylammonium hydroxide is 0.5 g; the heating rate from 200°C to 760°C during heat treatment is 1°C / min, and the temperature is kept at 900°C for 0.5h; the buried powder composition is 96.18wt% silicon carbide, 3.82wt% aluminum oxide, and ytterbium oxide powder; during the sintering process, the heating rate from 1400°C to 1550°C is 1°C / min, the heating rate from 1550°C to the sintering temperature is 3°C / min, the sintering temperature is 1750°C, and the holding time is 1.0h.

[0044] Figure 3This is the surface microstructure of LPSSiC prepared by adding 9 wt% of the sintering aid precursor in Example 3. As can be seen from the figure, the sample microstructure is uniform and dense, with almost no pores.

[0045] The relative density of the silicon carbide ceramic sample of Example 3 is 98.5%, the bending strength is 540±67 MPa, and the fracture toughness is 7.80 MPa·m 1 / 2 .

[0046] Example 4

[0047] The preparation method of the atmospheric low temperature liquid phase sintered silicon carbide ceramic material provided in this embodiment refers to that of Example 3, with the main difference being that the sintering temperature is 1800°C.

[0048] Figure 4 This is the fracture microstructure of LPSSiC prepared by adding 9 wt% of the sintering aid precursor in Example 4. As can be seen from the figure, the silicon carbide grains are small and evenly distributed, the fracture surface is essentially free of pores, the white sintering aid phase uniformly envelops the gray silicon carbide phase, and a large number of silicon carbide grains are pulled out.

[0049] The relative density of the sample prepared in Example 4 is 99.0%, the flexural strength is 595±60 MPa, and the fracture toughness is 8.50 MPa·m 1 / 2 .

[0050] Comparative Example 1

[0051] The preparation method of the silicon carbide ceramic material provided in this comparative example refers to Example 1, with the main differences being that the addition amounts of aluminum isopropoxide, ytterbium acetate tetrahydrate, and SiC powder are 1.50 g, 3.50 g, and 95.0 g, respectively; and the sintering temperature holding time is 1.0 h.

[0052] Figure 5 This is the fracture microstructure of LPSSiC prepared by adding 5 wt% sintering aid precursor in Comparative Example 1. As can be seen from the figure, due to the low amount of sintering aid added, there are a lot of pores in the fracture of the pressureless sintered sample, and the sintering aid content (white part) is low and unevenly distributed.

[0053] The sample prepared in Comparative Example 1 has a relative density of 95.0%, a flexural strength of 434±35 MPa, and a fracture toughness of 6.50 MPa·m 1 / 2 .

[0054] Comparative Example 2

[0055] The preparation method of the silicon carbide ceramic material provided in this comparative example refers to that in Example 1, the main differences are: the addition amounts of aluminum isopropoxide, ytterbium acetate tetrahydrate, and SiC powder are 4.52 g, 10.48 g, and 85.0 g, respectively; and the sintering temperature is 1750°C.

[0056] The relative density of the silicon carbide ceramic sample obtained in this comparative example 2 is 99.2%, the bending strength is 476±21MPa, and the fracture toughness is 7.50MPa·m 1 / 2 .

[0057] Comparative Example 3

[0058] The preparation method of the silicon carbide ceramic material provided in this comparative example comprises the following steps: Dissolve 2.41 g of aluminum oxide and 5.59 g of ytterbium oxide in 200 g of deionized water, add 92.0 g of SiC powder, 1.0 g of tetramethylammonium hydroxide, and 200 g of silicon carbide grinding balls into a ball mill, and ball mill for 4 hours to obtain a slurry. Then, place the slurry in an oven at 80°C for drying and then pass it through a 60-mesh sieve. The sieved powder was pressed under a pressure of 20 MPa and then isostatically pressed at 200 MPa. The green body was heated to 200 °C at a rate of 5 °C / min in a vacuum sintering furnace, then heated to 600 °C at a rate of 1 °C / min, kept warm for 1 hour, and then heated to 900 °C at a rate of 5 °C / min, kept warm for 1 hour. The heat-treated sample was heated to 1000 °C at a rate of 5 °C / min under vacuum conditions. Then, argon was introduced and the temperature was increased to 1800 °C at a rate of 2 °C / min, kept warm for 30 minutes. Then, the temperature was increased to 1930 °C at a rate of 2 °C / min, kept warm for 1 hour.

[0059] Figure 6 This is the surface microstructure of LPSSiC prepared with 8 wt% oxide sintering aid powder added in Comparative Example 3. The gray represents the silicon carbide phase, and the white represents the phase generated by the sintering aid. As can be seen from the figure, the sample is dense, but a large amount of sintering aid aggregates, resulting in an uneven microstructure.

[0060] The relative density of the silicon carbide ceramic sample obtained in this comparative example is 99.5%, the flexural strength is 580±45MPa, and the fracture toughness is 8.60MPa·m 1 / 2 .

[0061] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a silicon carbide ceramic material by liquid phase sintering at normal pressure and low temperature, characterized in that: The preparation method comprises the following steps: (1) mixing aluminum isopropoxide, ytterbium acetate tetrahydrate, silicon carbide raw material powder, and a dispersant in water to form a slurry, drying, and sieving to obtain a raw material mixed powder; (2) pressing the raw material mixed powder into a shape to obtain a green blank; (3) The green body is subjected to heat treatment and powder embedding sintering at normal pressure to obtain the normal pressure low temperature liquid phase sintered silicon carbide ceramic material.

2. The preparation method according to claim 1, characterized in that In step (1), based on the total mass of aluminum isopropoxide, ytterbium acetate tetrahydrate and silicon carbide raw material powder as 100wt%, the aluminum isopropoxide and ytterbium acetate tetrahydrate account for 8-10wt% of the total mass of the powder, and the aluminum oxide and ytterbium oxide generated by their decomposition account for 3.21-4.27wt% of the total mass of the powder, preferably 3.21-4.08wt%.

3. The preparation method according to claim 1 or 2, characterized in that In step (1), the dispersant is tetramethylammonium hydroxide, and the added amount is 0.5-0.8 wt % of the total mass of the powder.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step (3), the heat treatment process includes: keeping the green billet at 200°C in a vacuum sintering furnace for 1 hour, then heating it to 760°C at a rate of 0.5-1.0°C / min and keeping it at that temperature for 1 hour, and finally continuing to heat it to 900°C at a rate of 2.0-5.0°C / min and keeping it at that temperature for 0.5-1 hour.

5. The preparation method according to any one of claims 1 to 4, characterized in that In step (3), the embedding material used in the atmospheric pressure embedded powder sintering is composed of silicon carbide, aluminum oxide and ytterbium oxide powder; wherein the content of silicon carbide embedding material is 95.73-96.79wt%, preferably 95.92-96.79wt%, and the content of aluminum oxide and ytterbium oxide is 3.21-4.27wt%, preferably 3.21-4.08wt%.

6. The preparation method according to any one of claims 1 to 5, characterized in that In step (3), the atmospheric pressure buried powder sintering is carried out in an Ar atmosphere, and the sintering process is: first, the temperature is raised to 900°C at a rate of 10.0°C / min, then the temperature is continued to be raised to 1400°C at a rate of 5.0°C / min, then the temperature is raised to 1550°C at a rate of 0.5-1.0°C / min and kept warm for 0.5h, and finally the temperature is raised to 1700-1800°C at a rate of 2.0-3.0°C / min and kept warm for 0.5-1.0h.

7. A silicon carbide ceramic material obtained by the preparation method according to any one of claims 1 to 6 through liquid phase sintering at normal pressure and low temperature.

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