Compounding method and application of high-strength graphite and Si3N4 ceramic

Abstract

The invention discloses a high-strength graphite and Si3N4 ceramic compounding method and application thereof.The method comprises the steps that firstly, high-purity silicon nitride powder and a sintering aid are subjected to ball milling, and composite powder is obtained; then preparing a connection active agent containing silicon whiskers through high-energy ball milling; then uniformly spraying a connecting active agent containing silicon whiskers on the surface of the inner cavity of the high-strength graphite, and filling the composite powder into the inner cavity of the high-strength graphite; and finally, applying oscillation pressure to the surface of the composite powder, and sintering in an inert atmosphere to realize the compounding of the high-strength graphite and the Si3N4 ceramic.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic materials, and particularly relates to a method for compounding high-strength graphite and Si 3 N 4 ceramics and its application. Background Art

[0002] Silicon nitride ceramics have high thermal conductivity, low expansion coefficient, and excellent mechanical properties. They are widely used in semiconductor device substrates, and are also used to manufacture sleeves, bearings, etc. in high-temperature gas turbines, and are promoted in the field of automotive engines. In the prior art, agate tanks and ceramic tanks are mainly used to prepare silicon nitride composite powders. However, the costs of agate tanks and ceramic tanks are high, and the tanks are prone to cracking due to their high brittleness. There is an urgent need for a new material that can replace agate tanks and ceramic tanks.

[0003] High-strength graphite has characteristics such as high strength, high thermal conductivity, high density, high temperature resistance, and corrosion resistance, and also has relatively good machining performance. If high-strength graphite and silicon nitride ceramics can be compounded, the heat dissipation performance of the tank during the preparation of materials can be increased, and at the same time, the Si 3 N 4 ceramic tank can be effectively protected. How to combine the two and apply them to prepare a container that can replace agate tanks and ceramic tanks is particularly important. Summary of the Invention

[0004] In order to overcome the problems in the prior art, the present invention provides a method for compounding high-strength graphite and Si 3 N 4 ceramics and its application, realizing the tight and high-strength combination of the interface between Si 3 N 4 and high-strength graphite, and preparing a composite part with Si 3 N 4 ceramics as the inner lining and high-strength graphite as the outer layer, solving the problems of high price, high brittleness, and easy breakage of existing ceramic or agate tanks.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is as follows: The present invention provides a method for compounding high-strength graphite and Si 3 N 4 ceramics, including the following steps: S1. Ball-mill high-purity silicon nitride powder and a sintering aid to obtain a composite powder.

[0006] S2. Prepare the connection activity containing silicon whiskers by high-energy ball milling, and the connection activator containing silicon whiskers is SiC whiskers and / or Si 3 N 4The whiskers and the mixture of nano-Si powder and / or nano-SiO 2 .

[0007] S3. Uniformly spray the connecting activator containing silicon whiskers obtained in step S2 on the surface of the inner cavity of the high-strength graphite, and load the composite powder in S1 into the inner cavity of the high-strength graphite. After applying a positive pressure on the surface of the composite powder, sintering is carried out under a nitrogen atmosphere.

[0008] In the present invention, silicon nitride, the connecting activator containing silicon whiskers are in contact with the high-strength graphite. By using the interfacial reaction, through the intermediate transition of the silicide and Si 3 N 4 and the high-strength graphite, a reaction layer is formed. Specifically, Si reacts with C and N 2 to form SiC and Si 3 N 4 respectively, forming a reaction layer to promote connection. At the same time, whiskers are added to improve the connection strength, and SiO 2 is added to promote the interfacial fusion during the sintering process, ultimately achieving the improvement of the bonding strength of the interface. The silicon nitride powder becomes silicon nitride ceramic after high-temperature sintering, realizing the composite of high-strength graphite and Si 3 N 4 ceramics.

[0009] In the present invention, the connecting activator containing silicon whiskers contains whiskers and other substances, where the whiskers are selected from one or two of SiC whiskers or Si 3 N 4 whiskers, and the other substances are selected from one or two of Si powder or nano-SiO 2 .

[0010] As an alternative embodiment, in the composite method provided by the present invention, the connecting activator containing silicon whiskers is a mixture of Si, SiC whiskers and nano-SiO 2 .

[0011] In the present invention, using whiskers for strengthening can further improve the bonding strength of the interface.

[0012] As an alternative embodiment, in the composite method provided by the present invention, the connecting activator containing silicon whiskers is a uniformly stable suspension, and the volume fraction of the connecting activator containing silicon whiskers in the suspension is 10%-30%.

[0013] In the present invention, the connecting activator containing silicon whiskers is configured as a uniformly stable suspension, which is beneficial to uniformly spraying it on the roughened graphite surface.

[0014] As an alternative embodiment, in the composite method provided by the present invention, the method for preparing the suspension of the silicon-containing whisker connecting activator is as follows: Add the silicon-containing whisker connecting activator and alcohol into a ball mill, and after ball milling, a uniform and stable suspension is obtained.

[0015] As an alternative embodiment, in the composite method provided by the present invention, the mass ratio of the high-purity silicon nitride powder to the sintering aid is (8.8 - 9):(1 - 1.2).

[0016] As an alternative embodiment, in the composite method provided by the present invention, the spraying thickness of the silicon-containing whisker connecting activator is 0.1 - 0.5 mm.

[0017] As an alternative embodiment, in the composite method provided by the present invention, the sintering aid is selected from one or more of Al 2 O 3 、Y 2 O 3 and MgO.

[0018] In the present invention, the role of the sintering aid is to promote the densification of Si 3 N 4 ceramics during sintering.

[0019] As an alternative embodiment, in the composite method provided by the present invention, the sintering aid is selected as a mixture of Al 2 O 3 and MgO.

[0020] As an alternative embodiment, in the composite method provided by the present invention, the sintering aid is selected as a mixture of Al 2 O 3 、Y 2 O 3 and MgO, and the mass ratio of Al 2 O 3 、Y 2 O 3 and MgO is 2:3:5.

[0021] In the present invention, by controlling the mass ratio of Al 2 O 3 、Y 2 O 3 and MgO to be 2:3:5, the densification of the silicon nitride ceramics is ensured.

[0022] As an alternative embodiment, in the composite method provided by the present invention, the sintering process is completed in a sintering furnace, the sintering temperature is 1800 - 2000 °C, the sintering time is greater than 3 h, the positive pressure applied is 15 - 30 MPa, and the oscillating pressure is 0.5 - 10 MPa.

[0023] In the present invention, the use of oscillating pressure can achieve high densification of high-strength graphite and Si 3 N 4 bulk, and at the same time facilitate the combination of silicon nitride and high-strength graphite. The sintering temperature is controlled at 1800 - 2000 °C. Lower than the high temperature will reduce the densification of Si 3 N 4 ceramics, and too high temperature will lead to poor connection effect between graphite and Si 3 N 4 ceramics.

[0024] Based on the same technical concept, the present invention also provides the application of the above-mentioned method for compounding high-strength graphite and Si 3 N 4 ceramics in the preparation of graphite and Si 3 N 4 ceramic composite parts.

[0025] As an alternative embodiment, in the application provided by the present invention, the method for preparing graphite and Si 3 N 4 ceramic composite parts includes the following steps: (1) Make a cavity from high-strength graphite, set an inwardly concave receiving cavity inside the cavity, and roughen the inner wall of the cavity.

[0026] (2) Spray a silicon-containing connecting active agent on the inner wall of the roughened high-strength graphite cavity in step (1), then load the composite powder composed of high-purity silicon nitride powder and sintering aid into the inner cavity of the high-strength graphite cavity, and after applying pressure on the top of the composite powder, place the high-strength graphite cavity in a sintering furnace for oscillating hot pressing sintering to obtain a primary composite part.

[0027] (3) Process the excess graphite in the primary composite part to obtain a graphite and Si 3 N 4 ceramic composite part.

[0028] In the present invention, an inwardly concave receiving cavity is provided inside the cavity. The specific shape of the receiving cavity is not limited and can be triangular, trapezoidal, etc. After setting the receiving cavity, the high-strength graphite and silicon nitride powder interlock with each other, forming a structure similar to inlay, further realizing the tight combination of high-strength graphite and silicon nitride powder.

[0029] As an alternative embodiment, in the application provided by the present invention, in step (1), the inner cavity of the graphite is processed by mechanical processing method to prepare an inwardly concave receiving cavity.

[0030] Compared with the prior art, the beneficial effects of the present invention are: (1) In the present invention, the graphite surface is roughened and then sprayed with a connecting active agent, and then silicon nitride composite powder is added and calcined in an inert atmosphere under pressure to achieve Si 3 N 4 Tight, high-strength interface bonding between ceramics and high-strength graphite.

[0031] (2) In the present invention, Si 3 N 4 Composite powder high temperature oscillation hot pressing sintering realizes Si 3 N 4 High densification of ceramics, while Si 3 N 4 Ceramics and high-strength graphite interface reaction sintering and structural design to achieve Si 3 N 4 The high-strength bond with the high-strength graphite interface is used to prepare Si 3 N 4 The composite part with ceramic as inner lining and high-strength graphite as outer layer solves the problems of high price, high brittleness and easy breakage of existing ceramic or agate tanks. 3 N 4 The density of ceramic is over 97%, the bending strength of the joint is over 20MPa, and the joints of the parts are dense and seamless. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 Schematic diagram of the structure of the cross section of the graphite inner cavity; Figure 2 It is a structural schematic diagram of the cross section of the graphite inner cavity after the indenter is placed; Figure 3 The graphite and Si prepared in Example 1 3 N 4 Interface diagram of the joint of the composite parts. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0035] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present invention.

[0036] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or prepared by existing methods.

[0037] Example 1 Graphite and Si 3 N 4 Preparation of a ceramic composite part, specifically a powder-making tank body with an outer diameter of 100 mm and an inner diameter of 50 mm. The preparation method is as follows: (1) Design and processing of the inner cavity structure of high-strength graphite: A graphite cavity with a diameter of 60 mm is processed from high-strength graphite with an outer diameter of 100 mm, and three alternating trapezoidal structures are ground out on the inner cavity surface using a grinder, and the inner cavity surface is roughened by grinding with a grinding wheel.

[0038] (2) Composite of silicon nitride powder: The silicon nitride powder is compounded with a sintering aid, where Y 2 O 3 and Al 2 O 3 and MgO are combined in a ratio of 2:3:5, and the silicon nitride powder and the sintering aid are ball-milled, where the mass ratio of silicon nitride is 90%, and the remainder is the sintering aid.

[0039] (3) Spraying of the graphite inner cavity binder: The spray gun is placed into the processed graphite cavity, and a silicon-containing connecting activator is sprayed on the inner wall of the graphite, with a spraying thickness of 0.2 mm. The silicon-containing connecting activator is composed of Si, SiC whiskers, and nano-SiO 2 , where the mass ratio of Si is 80%; the mass ratio of SiC whiskers is 15%, and the mass ratio of nano-SiO 2 is 5%, and it is obtained as a uniformly stable suspension with a content of 30% after being ball-milled by a planetary ball mill in an alcohol medium.

[0040] (4) The silicon nitride composite powder prepared in (2) is loaded into the inner cavity of the high-strength graphite, and then a pressure head with a diameter of 50 mm is placed, and the periphery of the pressure head is filled with the composite silicon nitride powder.

[0041] (5) The above-mentioned mold filled with powder is placed in a furnace, an oscillating pressure is applied, and then it is vacuum-pumped and oscillatingly sintered to form a composite part. The sintering temperature is 1850 °C, the sintering time is 6 h, the sintering atmosphere is N 2 atmosphere, the positive pressure applied is 20 MPa, and the oscillating pressure is 3 MPa.

[0042] (6)Composite part processing and treatment: Process the protruding part in the graphite mold, and process the stainless steel cover plate and the stress-bearing part to prepare a ceramic powder tank body.

[0043] The schematic structural diagram of the cross-section of the graphite inner cavity prepared in the present invention is as Figure 1 shown, and the schematic structural diagram after placing the pressure head is as Figure 2 shown, including a pressure head 1, a silicon-containing connecting activator 2, a silicon nitride and sintering aid composite powder 3, and a high-strength graphite cavity 4. The graphite and Si in the present invention 3 N 4 composite part, the density of Si 3 N 4 ceramics is more than 98.5%, the bending strength at the joint reaches 25 MPa, the joint of the manufactured part is dense and seamless, and the joint interface is as Figure 3 shown.

[0044] Example 2 (1)Design and processing of the high-strength graphite inner cavity structure: Process a graphite cavity with a diameter of 140 mm from high-strength graphite with an outer diameter of 200 mm, and use a grinder to grind out 5 alternating trapezoidal structures on the inner cavity, and perform roughening treatment on the inner cavity surface with a grinding wheel.

[0045] (2)Silicon nitride powder compounding: Compound silicon nitride powder with a sintering aid, where Y in the sintering aid 2 O 3 and Al 2 O 3 are combined in a ratio of 2:3, and the silicon nitride powder and the sintering aid are ball-milled, where the proportion of silicon nitride is 88%, and the rest is the sintering aid.

[0046] (3)Spraying of the graphite inner cavity connector: Place the spray gun into the processed graphite cavity, and spray a silicon-containing connecting activator on the inner wall of the graphite, with a spraying thickness of 0.3 mm. The silicon-containing connecting activator is composed of Si and SiC whiskers, where the mass proportion of Si is 85%; the mass proportion of SiC whiskers is 15%, and it is obtained as a uniform and stable suspension with a content of 20% after ball-milling treatment in an alcohol medium by a planetary ball mill.

[0047] (4)Load the silicon nitride composite powder prepared in 2 into the high-strength graphite inner cavity, place the upper pressure head, the diameter of the pressure head is 120 mm, and at the same time fill the periphery of the pressure head with the composite silicon nitride powder.

[0048] (5)Place the above-mentioned mold filled with powder in the furnace, apply an oscillating pressure, and then make a composite part through vacuum pumping and oscillating sintering. Among them, the sintering temperature is 1880 °C, the sintering time is 7 h, the sintering atmosphere is N 2 atmosphere, the applied positive pressure is 25 MPa, and the oscillating pressure is 5 MPa.

[0049] (6) Composite part processing and treatment: Process the protruding part in the graphite mold, and process the stainless steel cover plate and the stress part to prepare a ceramic powder tank.

[0050] The schematic structural diagram of the cross-section of the graphite inner cavity prepared in the present invention is as Figure 1 shown, and the schematic structural diagram after putting the pressure head is as Figure 2 shown, including a pressure head 1, a silicon-containing connecting activator 2, a silicon nitride and sintering aid composite powder 3, and a high-strength graphite cavity 4. The graphite and Si 3 N 4 composite part prepared in the present invention has a Si 3 N 4 ceramic density of more than 98%, the bending strength at the joint reaches 23 MPa, and the joint of the workpiece is dense and seamless.

[0051] Example 3 (1) Design and processing of the high-strength graphite inner cavity structure: Process a graphite cavity with a diameter of 100 mm from high-strength graphite with an outer diameter of 200 mm, and use a grinder to grind out 5 alternating trapezoidal structures on the inner cavity, and perform roughening treatment on the inner cavity surface with a grinding wheel.

[0052] (2) Silicon nitride powder compounding: Compound silicon nitride powder with a sintering aid, where the ratio of Y 2 O 3 and Al 2 O 3 and MgO is 2:3:5. Ball mill the silicon nitride powder and the sintering aid, where the proportion of silicon nitride is 90%, and the rest is the sintering aid.

[0053] (3) Spraying of the graphite inner cavity connector: Place the spray gun in the processed graphite cavity, spray the silicon-containing connecting activator on the inner wall of the graphite, with a spraying thickness of 0.3 mm, where the mass proportion of Si is 80%; the mass proportion of SiC whiskers is 20%, and it is ball milled in an alcohol medium by a planetary ball mill to obtain a uniform and stable suspension with a content of 10%.

[0054] (4) Load the silicon nitride composite powder prepared in (2) into the high-strength graphite inner cavity, put in a pressure head with a diameter of 80 mm, and fill the periphery of the pressure head with the composite silicon nitride powder.

[0055] (5) Place the above-mentioned mold filled with powder in the furnace, apply an oscillating pressure, and then vacuum pump and oscillating sinter to make a composite part. Among them, the sintering temperature is 2000 °C, the sintering time is 4 h, the sintering atmosphere is N 2 atmosphere, the applied positive pressure is 28 MPa, and the oscillating pressure is 2 MPa.

[0056] (6) Composite part processing and treatment: Process the protruding part in the graphite mold, and process the stainless steel cover plate and the stress-bearing part to prepare a ceramic powder-making tank body.

[0057] The schematic structural diagram of the cross-section of the graphite inner cavity prepared in the present invention is as Figure 1 shown, and the schematic structural diagram after putting in the pressure head is as Figure 2 shown, including a pressure head 1, a silicon-containing connecting activator 2, a composite powder of silicon nitride and a sintering aid 3, and a high-strength graphite cavity 4. The graphite and Si 3 N 4 composite part prepared in the present invention has a Si 3 N 4 ceramic density of more than 98.3%, a flexural strength at the joint reaching 22 MPa, and the joint of the manufactured part is dense and seamless.

[0058] Comparative Example 1 (1) Design and processing of the high-strength graphite inner cavity structure: Process a graphite cavity with a diameter of 60 mm from high-strength graphite with an outer diameter of 100 mm, and use a grinder to grind 3 alternating trapezoidal structures on the inner cavity, and perform roughening treatment on the inner cavity surface with a grinding wheel.

[0059] (2) Do not use a sintering aid, that is, do not compound the silicon nitride powder, and use pure silicon nitride powder.

[0060] (3) Spraying of the graphite inner cavity connector: Place the spray gun in the processed graphite cavity, and spray a silicon-containing connecting activator on the inner wall of the graphite, with a spraying thickness of 0.2 mm. The silicon-containing connecting activator is composed of Si, SiC whiskers and nano-SiO 2 and the mass ratio of Si is 80%; the mass ratio of SiC whiskers is 15%, and the mass ratio of nano-SiO 2 is 5%, and it is obtained as a uniform and stable suspension with a content of 30% after ball milling treatment in an alcohol medium by a planetary ball mill.

[0061] (4) Load the silicon nitride powder in (2) into the high-strength graphite inner cavity, then put in a pressure head with a diameter of 50 mm, and at the same time fill the periphery of the pressure head with the compounded silicon nitride powder.

[0062] (5) Place the above-mentioned mold filled with powder in the furnace, apply an oscillating pressure, and then make a composite part through vacuum pumping and oscillating sintering. Among them, the sintering temperature is 1850 °C, the sintering time is 6 h, the sintering atmosphere is N 2 atmosphere, the applied positive pressure is 20 MPa, and the oscillating pressure is 3 MPa.

[0063] (6) Composite part processing and treatment: Process the protruding part in the graphite mold, and process the stainless steel cover plate and the stress-bearing part to prepare a ceramic powder-making tank body.

[0064] In the composite prepared in the present invention, Si 3 N 4 The density of the ceramic is 91.5%, there are many pores, and the flexural strength at the joint is 20 MPa. The porosity of silicon nitride will make the ball milling effect worse.

[0065] Comparative Example 2 (1) Design and processing of the high-strength graphite inner cavity structure: A graphite cavity with a diameter of 100 mm was processed from high-strength graphite with an outer diameter of 200 mm, and 5 alternating trapezoidal structures were polished out of the inner cavity using a grinder, and the inner cavity surface was roughened by grinding wheel.

[0066] (2) Silicon nitride powder compounding: The silicon nitride powder was compounded with a sintering aid. The ratio of Y 2 O 3 and Al 2 O 3 and MgO in the sintering aid is 2:3:5. The silicon nitride powder and the sintering aid were ball milled, with silicon nitride accounting for 90% and the rest being the sintering aid.

[0067] (3) No binder was sprayed on the graphite inner cavity.

[0068] (4) The silicon nitride composite powder prepared in (2) was loaded into the high-strength graphite inner cavity, and a pressure head with a diameter of 80 mm was placed, and the surrounding of the pressure head was filled with the composite silicon nitride powder.

[0069] (5) The above mold filled with powder was placed in a furnace, an oscillating pressure was applied, and then vacuum pumping and oscillating sintering were carried out to make a composite. The sintering temperature was 1850 °C, the sintering time was 6 h, the sintering atmosphere was N 2 atmosphere, the positive pressure applied was 28 MPa, and the oscillating pressure was 2 MPa.

[0070] (6) Processing and treatment of the composite: The excess part in the graphite mold was processed, and a stainless steel cover plate and a stress member were processed to prepare a ceramic powder-making tank body.

[0071] In the composite prepared in the present invention, Si 3 N 4 The density of the ceramic is above 98.3%, the flexural strength at the joint reaches 5 MPa, the joint of the part is not tight, and there are many cracks.

[0072] The graphite and Si 3 N 4 composites prepared in Examples 1-3 of the present invention, Si 3 N 4The ceramic density is above 98%, the bending strength at the joint is greater than 22 MPa, and the joint of the workpiece is dense and seamless. Compared with Example 1, in Comparative Example 1, no sintering aid was used, and pure silicon nitride powder was used. In the composite prepared, Si 3 N 4 both the ceramic density and the bending strength at the joint are poor. At the same time, the porosity will make the ball milling effect worse. Compared with Example 1, in Comparative Example 2, the inner cavity of the graphite was not sprayed with a binder. In the composite prepared, Si 3 N 4 the ceramic density is poor, the bending strength at the joint is greatly reduced, and there are cracks in many places.

[0073] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is limited only to these descriptions. For those of ordinary skill in the art to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A composite method of high-strength graphite and Si3N4 ceramics, characterized in that: The following steps are involved: S1, ball milling high-purity silicon nitride powder and a sintering aid to obtain a composite powder; S2, preparing a connecting active agent containing silicon whiskers by high-energy ball milling, wherein the connecting active agent containing silicon whiskers is a mixture of SiC whiskers and / or Si3N4 whiskers and nano-Si powder and / or nano-SiO2; S3, spraying the silicon whisker-containing connecting active agent obtained in step S2 uniformly on the surface of the high-strength graphite inner cavity, and loading the composite powder in S1 into the high-strength graphite inner cavity, applying positive pressure on the surface of the composite powder, and sintering it in a nitrogen atmosphere.

2. The composite method of high-strength graphite and Si3N4 ceramics according to claim 1, characterized in that: The connecting active agent containing silicon whiskers is a mixture of Si, SiC whiskers and nano-SiO2.

3. The composite method of high-strength graphite and Si3N4 ceramics according to claim 1, characterized in that: The connecting active agent containing silicon whiskers is a uniform and stable suspension, and the volume fraction of the connecting active agent containing silicon whiskers in the suspension is 10%-30%.

4. The composite method of high-strength graphite and Si3N4 ceramics according to claim 3, characterized in that: The method for preparing the suspension of the connecting active agent containing silicon whiskers is as follows: adding the connecting active agent containing silicon whiskers and alcohol into a ball mill, and obtaining a uniform and stable suspension after ball milling.

5. The composite method of high-strength graphite and Si3N4 ceramics according to claim 1, characterized in that: The mass ratio of the high-purity silicon nitride powder to the sintering aid is (8.8-9):(1-1.2), and the spraying thickness of the connecting activator containing silicon whiskers is 0.1-0.5 mm.

6. The composite method of high-strength graphite and Si3N4 ceramics according to claim 1, characterized in that: The sintering aid is selected from one or more of Al2O3, Y2O3 and MgO.

7. The composite method of high-strength graphite and Si3N4 ceramics according to claim 1, characterized in that: The sintering aid is selected as a mixture of Al2O3 and MgO, or the sintering aid is a mixture of Al2O3, Y2O3 and MgO.

8. The composite method of high-strength graphite and Si3N4 ceramics according to claim 1, characterized in that: The sintering process is completed in a sintering furnace, the sintering temperature is 1800-2000°C, the sintering time is greater than 3 hours, the applied positive pressure is 15-30MPa, and the oscillation pressure is 0.5-10MPa.

9. Use of the composite method of high-strength graphite and Si3N4 ceramics as claimed in any one of claims 1 to 8 in the preparation of graphite and Si3N4 ceramic composite products.

10. The use according to claim 9, characterized in that: The method for preparing a graphite and Si3N4 ceramic composite component comprises the following steps: (1) A cavity is made of high-strength graphite, an inwardly concave receiving cavity is provided inside the cavity, and the inner wall of the cavity is roughened; (2) spraying a connecting activator containing silicon whiskers on the inner wall of the high-strength graphite cavity roughened in step (1), then loading a composite powder consisting of high-purity silicon nitride powder and a sintering aid into the high-strength graphite cavity, and after applying pressure on the top of the composite powder, placing the high-strength graphite cavity in a sintering furnace for oscillating hot pressing sintering to obtain a primary composite product; (3) Processing the excess graphite in the primary composite part to obtain a graphite and Si3N4 ceramic composite part.

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