CN117658641B - Method for preparing high-density SiC ceramic based on selective laser 3D printing and two-step sintering - Google Patents

Abstract

The invention belongs to the technical field of additive manufacturing, and relates to a method for preparing high-density SiC ceramic based on selective laser 3D printing and two-step sintering. The method comprises the following steps: s1, weighing raw materials: weighing raw materials comprising silicon carbide, a carbon source and a binder according to the following proportion, wherein the content of silicon carbide powder is 35-65 vol%, the content of the carbon source is 30-60 vol% and the content of the binder is 5-25 vol% based on 100vol% of the total volume fraction of the silicon carbide, the carbon source and the binder; s2, forming: the mixture fully mixed by the raw materials is 3D printed into a biscuit by selective laser; s3, glue discharging: performing glue discharging on the biscuit to obtain a preform; s4, under-silicon reaction sintering: carrying out under-silicon reaction sintering on the buried silicon of the preform, wherein the mass of silicon used for the buried silicon is 40% -95% of the mass of silicon required by complete reaction between the silicon and carbon of the preform during theoretical calculation, so as to obtain a first sintered body; s5, solid phase sintering under normal pressure: and carrying out normal-pressure solid-phase sintering on the first sintered body to obtain the high-density SiC ceramic.

Description

A method for preparing high-density SiC ceramics based on selective laser 3D printing and two-step sintering

Technical Field

The present invention belongs to the technical field of additive manufacturing, and specifically relates to a method for preparing high-density SiC ceramics based on selective laser 3D printing and two-step sintering.

Background Art

SiC ceramics are considered to be ideal candidate materials for use in extreme environments due to their excellent properties such as low density, high strength, high temperature resistance, radiation resistance, high chemical stability, and corrosion resistance. They are widely used in major defense and industrial fields such as aerospace, armor, space reflectors, nuclear energy, chemicals, and semiconductors. However, now defense and industrial applications often require the use of complex-shaped SiC ceramics, but the strong covalent bond characteristics of SiC ceramics have brought great difficulties and challenges to the molding and manufacturing of SiC ceramic products.

For ceramic components with complex structures, traditional machining methods have long processing cycles and high costs, and the surface quality and dimensional accuracy of the final parts are difficult to guarantee. Although ceramic near-net-shape forming processes such as gel casting or direct solidification injection molding can simplify or eliminate secondary machining, they are highly dependent on molds and often have problems such as pores, warping and cracks when manufacturing large-sized integral parts. 3D printing, also known as additive manufacturing, is a cumulative manufacturing technology that first builds the required three-dimensional model through computer modeling software, and then "partitions" the built three-dimensional model into layer-by-layer cross-sections (i.e. slices) to guide the printer to print layer by layer. The emergence of 3D printing effectively solves these problems, and it has a natural advantage in the preparation of special-shaped components.

Selective laser printing (SLS) is a powder bed rapid manufacturing process. The working principle is as follows: first, the powder bed is preheated, which can reduce thermal stress and help prevent the formation of cracks in sintered components. After preheating, a roller or scraper spreads powder on the powder bed, and the powder is selectively sintered by a high-energy laser beam (such as a _CO2 laser), and the first layer is manufactured. Then the powder supply cylinder and the forming cylinder each rise and fall one layer to cooperate with powder spreading and forming. This construction is repeated until the required three-dimensional component is manufactured. SLS has the advantages of being able to prepare large-sized and complex-shaped components, no support required, high material utilization, and high processing efficiency. It can quickly form complex structural parts to achieve near-net shape manufacturing. At present, SLS is mainly used in the preparation of ceramic material parts in two ways: direct and indirect molding. Direct SLS molding is to irradiate powder with high-energy density laser to achieve molding and sintering-bodying. Ceramic parts manufactured by direct SLS molding are very prone to cracks, which leads to poor mechanical properties of the final product. Indirect SLS molding is to irradiate the polymer powder bonded ceramic powder with a laser to achieve the molding of complex ceramic parts, and then sinter them into ceramic products by heat treatment. The indirect SLS method can be used as a suitable way to form crack-free samples by sintering the low melting point polymer binder in the composition and then removing the binder with a slow heating rate followed by furnace sintering to increase the final density and avoid cracks in the product.

At present, the ceramic samples manufactured by indirect selective laser 3D printing have low density, many pores and low mechanical properties, which are far from the performance required for service. Subsequent heat treatment is necessary to improve the performance. The main sintering densification methods are reactive sintering (LSI), chemical vapor phase method (CVI) and precursor impregnation pyrolysis (PIP). However, the process of indirect selective laser printing combined with LSI has the problem of high free silicon content (>10vol%) in the silicon carbide matrix, and the presence of free silicon easily leads to low bending strength (≤100MPa) and high brittleness (fracture toughness ≤1MPa·m1/2) of silicon carbide ceramic products. When the service temperature exceeds 1400℃, the strength of the sintered body decreases rapidly with the melting of free silicon. The presence of free silicon also makes the acid and alkali corrosion resistance of the matrix worse. Both CVI and PIP methods have problems such as long process repetition cycle and easy to produce closed inner pores.

Summary of the invention

In view of the above problems in the prior art, the present invention provides a method for preparing high-density SiC ceramics based on a two-step sintering process of selective laser 3D printing combined with "under-siliconized" reaction sintering and atmospheric solid phase sintering. Compared with the reaction sintering densification method, the high-density SiC ceramics obtained by the method of the present invention have no free silicon residue in the finished product, which is beneficial to improving the high-temperature mechanical properties and acid and alkali corrosion resistance of SiC ceramic products. The present invention achieves the above purpose through the following technical solutions:

The present invention provides a method for preparing high-density SiC ceramics based on selective laser 3D printing and two-step sintering. The method comprises the following steps:

S1 weighing raw materials: weighing raw materials including silicon carbide, carbon source and binder according to the following proportions, wherein, based on the total volume fraction of silicon carbide, carbon source and binder as 100 vol%, the content of silicon carbide powder is 35-65 vol%, the content of carbon source is 30-60 vol%, and the content of binder is 5-25 vol%;

S2 molding: the mixture of the above raw materials is fully mixed into a blank by selective laser 3D printing;

S3 debinding: debinding the green blank to obtain a preform;

S4: silicon-deficient reaction sintering: the preform is buried with silicon for silicon-deficient reaction sintering, the mass of silicon used for the buried silicon is 40% to 95% of the mass of silicon required for complete reaction between the silicon and the carbon of the preform in theoretical calculation, to obtain a first sintered body;

S5 normal pressure solid phase sintering: the first sintered body is subjected to normal pressure solid phase sintering to obtain a high-density SiC ceramic.

Preferably, in step S4, the parameters of the silicon-deficient reaction sintering are: the sintering atmosphere is vacuum, the sintering temperature is 1500-1800° C., and the sintering time is 0.5-3 hours.

Preferably, in step S5, the parameters of the atmospheric pressure solid phase sintering are: the sintering atmosphere is an inert atmosphere, the (maximum) sintering temperature is 2000-2300° C., and the holding time of the (maximum) sintering temperature is 0.5-2 h.

Preferably, the carbon source is carbon black, carbon microspheres or graphite; the binder is a polymer, preferably a thermoplastic resin and/or a thermosetting resin; more preferably, the binder is a phenolic resin.

Preferably, the raw materials include boron carbide in addition to silicon carbide, a carbon source and a binder, wherein the amount of boron carbide is 0.5-8wt% of the silicon carbide.

Preferably, in step S3, the debinding temperature is 800-1000° C., and the debinding time is 0.5-1 hour.

Preferably, the method further comprises: before the under-silicon reaction sintering, vacuum impregnating or pressure impregnating the debinded preform in a precursor solution, followed by high-temperature pyrolysis; preferably, the precursor impregnation solution is an organic solution of phenolic resin with a mass fraction of 30 to 70%.

Preferably, the main phases of the high-density SiC ceramic are 2H-C and 6H-SiC.

Preferably, the high-density SiC ceramic has an open porosity of 1% to 2% and a density of 3.0 to 3.1 g/cm ³ .

Preferably, the high-density SiC ceramic has a flexural strength of 280 MPa or more and an elastic modulus of 300 GPa or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an XRD pattern of SiC ceramics prepared by “silicon-deficient” reaction sintering and pressureless solid phase sintering in Example 1;

FIG2 is a SEM image of SiC ceramics prepared by “silicon-deficient” reaction sintering and pressureless solid phase sintering in Example 1;

FIG3 is a backscattered SEM image (a) of the first sintered body of Comparative Example 1 through silicon reaction sintering and a secondary electron SEM image (b) of SiC ceramics prepared through silicon reaction sintering and atmospheric pressure solid phase sintering;

FIG4 is a secondary electron SEM image of SiC ceramics prepared by solid phase sintering at normal pressure only in Comparative Example 2;

FIG5 is an XRD pattern of SiC ceramics prepared in Comparative Example 3;

FIG6 is a backscattered SEM image (a) and a secondary electron SEM image (b) of the SiC ceramic prepared in Comparative Example 3.

DETAILED DESCRIPTION

The present invention is further described by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention. Unless otherwise specified, each percentage refers to the percentage by mass. The following is an exemplary description of the method for preparing high-density SiC ceramics based on selective laser 3D printing and two-step sintering according to the present invention.

Weigh the raw materials. Weigh the raw materials including silicon carbide, carbon source and binder according to the following proportions, wherein, based on the total volume fraction of silicon carbide, carbon source and binder as 100 vol%, the content of silicon carbide powder is 35-65 vol%, the content of carbon source is 30-60 vol%, and the content of binder is 5-25 vol%.

The average particle size of the silicon carbide powder may be 0.5 to 100 μm.

The carbon source includes but is not limited to carbon black, carbon microbeads (MCMB) or other carbon sources such as graphite. The particle size of the carbon source powder can be 5 to 50 μm.

The binder may be a polymer, such as a thermoplastic resin and/or a thermosetting resin. Specifically, a phenolic resin may be used as the binder.

In some technical solutions, the raw materials include boron carbide in addition to silicon carbide, carbon source and binder. Boron carbide can increase the sintering driving force during the pressureless solid phase sintering process. For example, the amount of boron carbide can be 0.5-8wt% of silicon carbide.

Mixing. The above raw materials are mixed evenly to obtain a mixture. Mixing can be performed by ball milling. Ball milling is a routine operation in the art, and those skilled in the art can adjust the corresponding parameters as needed. The ball milling time and the ball milling speed can be changed as needed. For example, the ball milling speed is 50 to 100 rpm, and the ball milling time is controlled at 1 to 4 hours. During the ball milling process, the mass ratio of the material and the ball milling medium (grinding balls) can be changed as needed. For example, the mass ratio of the material and the ball milling medium can be 1:1.5. Ball milling can be performed in a ball milling jar. For example, grinding balls with SiC media are used.

During the ball milling process, the above raw materials and grinding balls are added to a ball milling jar and then ball milled. Phenolic resin is preferably added in batches. This is conducive to better bonding of the solid phenolic resin to the raw material powder and avoiding agglomeration during laser printing, so that the green blank has higher strength. The phenolic resin powder can be added in two times.

As an example, silicon carbide, a carbon source, boron carbide, about 40-60 wt% of phenolic resin and grinding balls are added to a ball mill. After ball milling for 2.5 hours, the remaining phenolic resin is added and the ball milling is continued until all the materials are evenly mixed.

Sieve. The mixed material can be sieved through a 50-70 mesh sieve. Sieve can prevent the agglomerates produced by the agglomeration of particles during the ball milling process from affecting the laser printing quality.

Molding. Use laser printing to form a blank of the required model (shape). Laser printing is a routine operation in this field, and those skilled in the art can adjust the corresponding parameters as needed. For example, for three-dimensional modeling of silicon carbide parts, the design file is kept in STL format, and the graphic samples displayed in the STL format file are laser printed into high-precision physical samples. A _CO2 laser can be used for laser printing. In some embodiments, the complex phase powder is laid to a certain thickness and preheated, and then the powder is laid layer by layer for laser printing. The powder laying thickness can be 0.05 to 0.3 mm. The preheating temperature can be 60 to 110°C. The laser power can be 15 to 120W.

Debinding. The debinding temperature can be 800-1000°C, and the debinding time can be 0.5-1 hour. For example, the green blank is heated to 200-300°C at a heating rate of 2-3°C/min, and then heated to 600-700°C at a heating rate of 1-2°C/min, and then heated to 800-1000°C at a heating rate of 1-3°C/min and kept at 800-1000°C for 0.5-1h.

Under-silicon reaction sintering. The preform obtained by debinding is buried in silicon for under-silicon reaction sintering. In the above reaction sintering process, the mass of silicon used for burying silicon is 40% to 95% of the mass of silicon required for the complete reaction of the silicon and the carbon of the preform in theoretical calculation. It is generally believed that 1 mol of carbon requires 1 mol of silicon to react to generate SiC in theoretical calculation. If the mass of silicon used for burying silicon is lower than 40% of the mass of silicon required for the complete reaction of the silicon and the carbon of the preform in theoretical calculation, it will cause the sintered body to have too many pores, and it will be difficult to densify even if normal pressure solid phase sintering is performed later. If the mass of silicon used for burying silicon is higher than 95% of the mass of silicon required for the complete reaction of the silicon and the carbon of the preform in theoretical calculation, free silicon will exist in the first sintered body after reaction sintering, and the free silicon will continue to remain in the finished silicon carbide ceramic after normal pressure solid phase sintering. The present invention adopts "under-silicon" reaction sintering, which can ensure that the density of the sintered body is greatly improved while no free silicon exists, which helps the subsequent normal pressure solid phase sintering to achieve further densification. The inventors have used silicon reaction sintering and found that the sintered body produced by silicon reaction sintering has a high content of free silicon, which forms silicon vapor and then evaporates during the atmospheric pressure solid phase sintering process, resulting in an increase in the porosity of the silicon carbide ceramic product and an inability to sinter to densify.

The sintering atmosphere of the silicon-deficient reaction sintering is vacuum, the sintering temperature is 1500-1800° C., and the sintering time is 0.5-3 hours. For example, the vacuum degree is -10 to -100 Pa.

The first sintered body after the silicon-deficient reaction sintering is subjected to pressureless solid phase sintering. The parameters of pressureless solid phase sintering are: the sintering atmosphere is an inert atmosphere (such as argon atmosphere), the (maximum) sintering temperature is 2000-2300°C, and the (maximum) sintering temperature holding time is 0.5-2h. For example, the temperature is raised to 1200°C at a heating rate of 5-10°C/min, and the temperature is directly raised to 1800°C at a heating rate of 3-5°C/min, and then the temperature is directly raised to 2000-2300°C at a heating rate of 1-3°C/min and kept at 2000-2300°C for 0.5-2h.

The first sintered body after the silicon-deficient reaction sintering is usually not completely densified. The porosity of the first sintered body is about 5-15%. Therefore, it is preferred to perform normal pressure solid phase sintering on the first sintered body after the silicon-deficient reaction sintering to further densify it.

As an optional technical solution, the preform after debinding can also be vacuum impregnated or pressurized impregnated in a precursor solution, and then pyrolyzed at high temperature. This is conducive to further improving the density of the green body. The impregnation and pyrolysis are conventional steps. The process conditions of impregnation and pyrolysis can be adjusted by those skilled in the art as needed. The precursor solution can be a phenolic resin solution or other precursor solutions. As an example, the solvent of the phenolic resin solution is ethanol, with a mass fraction of 30 to 70%.

The main phases of the high-density SiC ceramics of the present invention are 2H-C and 6H-SiC.

The open porosity and density of SiC ceramics were tested according to the Archimedean drainage method. In some technical solutions, the open porosity of the SiC ceramics of the present invention is 1% to 2%, and the density is 3.0 to 3.1 g/cm ³ .

The bending strength and elastic modulus of SiC ceramics are tested according to the standard ceramic three-point bending strength test. In some technical solutions, the three-point bending strength of the SiC ceramics of the present invention is above 280 MPa, and the elastic modulus is above 300 GPa.

Test of linear shrinkage: shrinkage = (sample length before sintering - sample length after sintering) / sample length before sintering. In some technical solutions, the shrinkage of the SiC ceramics of the present invention is 3% to 4%.

In summary, the method for preparing SiC ceramics based on selective laser 3D printing and two-step sintering described in the present invention obtains highly dense SiC ceramics, without the presence of a second phase or a glass phase at the grain boundaries, with clean grain boundaries and no free silicon residue, excellent mechanical strength, low sintering shrinkage, good high temperature performance, and excellent acid and alkali corrosion resistance.

The following examples are further listed to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood 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 belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Example 1

The method for preparing high-density SiC ceramics based on selective laser 3D printing and two-step sintering specifically includes the following steps:

(1) Weigh 1442g of silicon carbide, 1420g of carbon microspheres, 22g of boron carbide and 230g of phenolic resin respectively. Wherein, based on the total volume fraction of silicon carbide, carbon source and binder as 100vol%, the content of silicon carbide is 35vol%, the content of boron carbide is 50vol%, and the content of binder is 15vol%. The amount of boron carbide used is 1.5wt% of silicon carbide. The above raw materials are ball-milled to obtain a mixture. The specific ball-milling process is: add all silicon carbide, all carbon microspheres, all boron carbide, 40wt% of phenolic resin, silicon carbide grinding balls (accounting for 1.5 times the sum of the mass of all raw materials of silicon carbide ceramics) into a ball mill, after ball milling for 0.5h, add the remaining phenolic resin, and continue ball milling for 1.5 hours. The ball milling speed is 75 rpm.

(2) The ball-milled mixture is passed through a 60-mesh sieve and printed into a green blank part of the desired shape using SLS.

(3) The printed green blank parts are placed in a graphite crucible and subjected to a debinding treatment at 900°C for 0.5 hours to obtain a preform.

(4) The preform after debinding is subjected to silicon-depleted reaction sintering in a vacuum sintering furnace to obtain a first sintered body. The sintering temperature is 1550°C, the sintering time is 0.5 hours, and the vacuum degree is -16 Pa. The mass of silicon used for buried silicon is 80% of the mass of silicon required for complete reaction between the silicon and the carbon of the preform in theoretical calculation.

(5) The first sintered body was placed in a graphite crucible for solid-phase sintering at normal pressure in an argon atmosphere. The temperature was raised to 1200°C at a heating rate of 5°C/min, and then directly raised to 1800°C at a heating rate of 3°C/min, and then directly raised to 2000°C at a heating rate of 1°C/min and kept at that temperature for 1 h.

FIG1 is an XRD graph of SiC ceramics prepared by "silicon-deficient" reaction sintering and pressureless solid phase sintering in Example 1. It can be seen that the main phases of the sample are 2H-C and 6H-SiC phases. Since there is no diffraction peak of elemental silicon in the XRD graph, there is no silicon residue in the SiC ceramic product of the present invention.

Figure 2 is a SEM image of SiC ceramics prepared by "silicon-deficient" reaction sintering and pressureless solid phase sintering in Example 1. It can be seen that the SiC particles are tightly combined without obvious pores, indicating that the sintering effect of the method of the present invention is excellent and helps to densify SiC ceramics.

1 and 2 , the high-density SiC ceramic product obtained by the method of the present invention has no free silicon residue, which can fully promote sintering densification.

Example 2

The method is basically the same as Example 1, except that: in step (1), 1648 g of silicon carbide, 1279 g of carbon microspheres, 25 g of boron carbide and 230 g of phenolic resin are weighed. Wherein, based on the total volume fraction of silicon carbide, carbon source and binder being 100 vol%, the content of silicon carbide is 40 vol%, the content of carbon source is 45 vol%, and the content of binder is 15 vol%. The amount of boron carbide is 1.5 wt% of silicon carbide.

Comparative Example 1

The method is basically the same as Example 1, except that in step (3), the mass of silicon used for embedding silicon is 150% of the mass of silicon required for complete reaction between the silicon and the carbon of the preform in theoretical calculation.

Figure 3 is a SEM image (a) of the first sintered body sintered by silicon reaction in comparative example 1 and a SEM image (b) of SiC ceramics prepared by silicon reaction sintering and pressureless solid phase sintering. It can be seen that there is an obvious silicon contrast in Figure (a), which is due to a large amount of free silicon (white) filled between the SiC matrix (gray). Moreover, the first sintered body sintered by silicon reaction has a high content of free silicon, which forms silicon vapor and then volatilizes in the pressureless solid phase sintering process, resulting in an increase in the porosity of the finished silicon carbide ceramic, which cannot be sintered to densify, see Figure (b).

Comparative Example 2

The method is basically the same as Example 1, except that step (4) is omitted, that is, the preform is directly subjected to normal pressure solid phase sintering.

Figure 4 is a SEM image of SiC ceramics sintered only at atmospheric pressure in Comparative Example 2. It can be seen that the sample has many pores, the silicon carbide particles are loosely arranged, and there are many pores. This is because atmospheric pressure solid phase sintering alone cannot achieve sintering densification of the preform.

Comparative Example 3

The method is basically the same as Example 1, except that step (5) is omitted.

Figure 5 is an XRD graph of the SiC ceramic prepared in Comparative Example 3. Figure 6 is a backscattering SEM image (a) and a secondary electron morphology SEM image (b) of the SiC ceramic prepared in Comparative Example 3. It can be seen that there is no obvious silicon contrast in Figure (a), which indicates that there is no free silicon in the SiC ceramic, but Figure (b) shows that there are also many pores in the finished SiC ceramic.

Comparative Example 4

The method is basically the same as Example 1, except that in step (3), the mass of silicon used for embedding silicon is 150% of the mass of silicon required for complete reaction between the silicon and the carbon of the preform in theoretical calculation, and step (5) is omitted. The test results show that there is a lot of free silicon in SiC ceramics.

Comparative Example 5

The method is basically the same as Example 1, except that in step (3), the mass of silicon used for embedding silicon is 30% of the mass of silicon required for complete reaction between the silicon and the carbon of the preform in theoretical calculation.

The amount of silicon used in comparative example 5 is relatively small, which will lead to poor reaction between the buried silicon and the carbon in the preform, further resulting in poor expansion and filling effect caused by the above reaction. The reaction sintered body will have a large number of pores, and subsequent solid-phase sintering at normal pressure will be difficult to further densify.

Table 1 Properties of SiC ceramics prepared by two-step sintering of selected area laser 3D printing:

As can be seen from Table 1, the flexural strength and elastic modulus of Comparative Example 1 are relatively low. This is because there is a large amount of free silicon in the SiC ceramic of Comparative Example 1. During the solid-phase sintering stage at normal pressure, the free silicon forms silicon vapor and volatilizes, which causes a large number of pores to form in the silicon carbide matrix, which is not conducive to the densification of solid-phase sintering at normal pressure. Comparative Example 2 has a high porosity and very low flexural strength. This is because direct solid-phase sintering at normal pressure without buried silicon reaction sintering will result in a loose structure of the SiC ceramic. The flexural strength and elastic modulus of Comparative Example 3 are relatively low, and the open porosity is relatively high. This is because only under-silicon reaction sintering is not enough to complete the sintering and densification of SiC ceramics.

Claims (10)

1. A method for preparing high-density SiC ceramic based on selective laser 3D printing and two-step sintering, which is characterized by comprising the following steps:

S1, weighing raw materials: weighing raw materials comprising silicon carbide, a carbon source and a binder according to the following proportion, wherein the content of silicon carbide powder is 35-65 vol%, the content of the carbon source is 30-60 vol% and the content of the binder is 5-25 vol% based on 100vol% of the total volume fraction of the silicon carbide, the carbon source and the binder;

s2, forming: the mixture fully mixed by the raw materials is 3D printed into a biscuit by selective laser;

S3, glue discharging: performing glue discharging on the biscuit to obtain a preform;

S4, under-silicon reaction sintering: carrying out under-silicon reaction sintering on the buried silicon of the preform, wherein the mass of silicon used for the buried silicon is 40% -95% of the mass of silicon required by complete reaction between the silicon and carbon of the preform during theoretical calculation, so as to obtain a first sintered body; the parameters of the under-silicon reaction sintering are as follows: the sintering atmosphere is vacuum, the sintering temperature is 1500-1800 ℃, and the sintering time is 0.5-3 hours;

S5, solid phase sintering under normal pressure: carrying out normal-pressure solid-phase sintering on the first sintered body to obtain high-density SiC ceramic; the parameters of the normal pressure solid phase sintering are as follows: the sintering atmosphere is inert atmosphere, the sintering temperature is 2000-2300 ℃, and the heat preservation time of the sintering temperature is 0.5-2 h.

2. The method of claim 1, wherein the carbon source is carbon black, carbon microspheres, or graphite; the binder is a thermoplastic resin and/or a thermosetting resin.

3. The method of claim 2, wherein the binder is a phenolic resin.

4. The method of claim 1, wherein the feedstock comprises boron carbide in addition to silicon carbide, a carbon source and a binder, wherein the boron carbide is present in an amount of 0.5 to 8wt% of the silicon carbide.

5. The method according to claim 1, wherein in step S3, the temperature of the paste is 800 to 1000 ℃ and the paste discharging time is 0.5 to 1 hour.

6. The method according to claim 1, wherein the method further comprises: before under-silicon reaction sintering, the preform after glue discharge is subjected to vacuum impregnation or pressure impregnation in a precursor solution, and then high-temperature pyrolysis is carried out.

7. The method according to claim 6, wherein the precursor solution is a phenolic resin organic solution with a mass fraction of 30-70%.

8. The method of claim 1, wherein the main phases of the highly dense SiC ceramic are 2H-C and 6H-SiC.

9. The method of claim 1, wherein the high-density SiC ceramic has an open gas porosity of 1% to 2% and a density of 3.0 to 3.1 g/cm ³.

10. The method of claim 1, wherein the high density SiC ceramic has a flexural strength of 280 MPa or more and an elastic modulus of 300GPa or more.