CN113248263A - Si3N4wSi preform and preparation of Si using the same3N4w/Si3N4Method for compounding materials - Google Patents

Abstract

The invention relates to Si₃N_4wSi preform and preparation of Si using the same₃N_4w/Si₃N₄The method of the composite material takes hydrochloric acid as a pH regulator, and introduces Si powder and Si under the acidic condition₃N₄The forming of the whisker preform is combined, so that the stability of micron-sized Si powder with higher specific surface area in water-based slurry is improved; simultaneously, the polyvinyl alcohol is taken as a dispersant, thereby realizing the Si₃N₄Stable dispersion of whiskers in acidic slurry to obtain Si₃N_4wthe/Si complex phase high volume fraction synergetic stable suspension slurry. The volume of the Si powder expands in the nitridation reaction process, so that the pores in the prefabricated body can be effectively occupied; porous Si₃N_4wPutting the/Si prefabricated body into a nitriding furnace, and introducing N₂Nitriding the Si powder in the preform to form a reaction mixture with Si₃N₄In-situ forming silicon nitride on the whisker to obtain Si₃N_4w/Si₃N₄A composite material. The method developed by the invention is suitable for preparing large-size components with complex shapes, and the high-performance ceramic matrix composite material with isotropy and small residual stress can be obtained by combining gel casting with in-situ reaction.

Description

Si3N4wSi preform and preparation of Si using the same3N4w/Si3N4Method for compounding materials

Technical Field

The invention belongs to the preparation of whisker reinforced composite materials, and relates to Si₃N_4wSi preform and preparation of Si using the same₃N_4w/Si₃N₄A method of compounding a material. In particular to gel injection molding Si₃N_4wSi preform, by nitridation of Si₃N₄In situ preparation of Si on whiskers₃N₄Matrix, thereby obtaining Si₃N_4w/Si₃N₄The preparation method of the composite material is mainly applied to the technical field of wave-transparent ceramic manufacturing.

Background

The wave-transparent composite material can protect a radar antenna system from the influence of the external severe environment, provides an electromagnetic window for the transmission and the reception of electromagnetic waves of the antenna, and ensures the long-term high-efficiency operation of the antenna. The wave-transmitting material for the antenna housing generally has low dielectric constant, low loss and high electromagnetic wave transmittance, and simultaneously has certain mechanical properties such as high strength, high temperature resistance, stable structure and the like, and structural designability.

Silicon nitride (Si)₃N₄) The ceramic is combined by covalent bonds, has excellent mechanical properties, higher thermal stability, low thermal expansion coefficient, good thermal shock resistance and moderate dielectric constant, and can be applied to the field of high-temperature wave-transparent ceramics. The silicon nitride ceramic prepared by the traditional sintering and forming process has high density and high strength, but the high density leads the dielectric constant of the ceramic to be higher, which is not beneficial to improving the wave-transmitting performance; meanwhile, the added sintering aid has certain adverse effects on the high-temperature performance and the wave-transmitting performance of the material; in addition, large-scale shrinkage exists in the sintering process, which results in the preparation of large-size complex-shaped structuresThe component is difficult to be manufactured, and the prepared component has large residual stress, so that the component is not beneficial to long-term use. Researchers put forward the design idea of the porous silicon nitride ceramic, and the dielectric constant of the ceramic is obviously reduced by introducing pores, so that the wave-transparent performance of the ceramic is improved. However, the preparation process of the porous silicon nitride ceramic still mainly takes sintering as a main part at present, and the adverse effects of volume shrinkage of the sintering aid and the ceramic in the sintering process on the material performance and the forming control are still not effectively eliminated.

The silicon nitride crystal whisker is a single crystal material, has excellent mechanical property, can keep stable at high temperature, and is not easy to grow crystal grains or generate other defects. In the early period of the team, the silicon nitride whisker is used as a raw material, and a silicon nitride whisker preform with porous structure characteristics, certain bearing capacity and excellent wave-transmitting performance is formed by adopting a gel casting process. Because the combination of the whiskers in the whisker preform formed by gel casting is weaker, in order to improve the strength and the rigidity of the material, a silicon nitride substrate is prepared in the silicon nitride whisker preform by adopting the processes of precursor impregnation cracking (PIP), Chemical Vapor Infiltration (CVI) and the like, and finally the silicon nitride whisker reinforced silicon nitride ceramic matrix composite (Si-based composite) with good mechanical property and wave-transmitting property is obtained₃N_4w/Si₃N₄). The gel casting is combined with the PIP/CVI combined process, and impurities such as sintering aids and the like are not introduced into the material; meanwhile, the gel casting process has the advantages of simple operation, low cost, near net size and the like; compared with PIP and CVI methods, the PIP and CVI methods have lower preparation temperature and smaller material size change in the process of preparing the substrate by the two methods. Therefore, the combined process of gel casting combined with PIP/CVI solves the problems of the conventional sintering process to some extent. However, specific analysis shows that when a substrate is prepared in a silicon nitride whisker preform by a PIP process, the substrate produced usually has defects such as hole cracks and the like due to certain shrinkage in the process of converting a liquid polymer precursor into ceramic, and the inside of the material still has certain stress; when the matrix is prepared by adopting the CVI process, micron-sized pores in the whisker preform are not beneficial to the full diffusion of the gaseous precursor, the pores are easy to nucleate at the pore diameter to seal the pores, and the prepared matrix is in gradient distributionI.e. more surface and less interior, which is not beneficial to the bearing of the crystal whisker. Therefore, there is still a need to find a new silicon nitride substrate preparation process matched with the gel injection molding preparation of silicon nitride whisker preform to solve the above problems and further improve Si₃N_4w/Si₃N₄The comprehensive performance of the composite material.

The invention provides a method for preparing a silicon nitride substrate by adopting Si powder nitridation, and the method fills the pores of the prefabricated body by using the volume expansion in the process of Si powder nitridation reaction and avoids the problem of shrinkage stress generated by other processes. It is worth proposing that in the invention, the Si powder is not introduced in a dipping mode by preparing Si powder slurry after the silicon nitride whisker preform is formed, but the Si powder and the silicon nitride whisker are mixed to prepare slurry and are introduced together by a gel injection molding process when the whisker preform is formed. The invention adopts micron-sized Si powder to ensure that the matrix generated by the subsequent nitridation reaction is uniformly distributed. Stable dispersion of micron-sized Si powder in gel casting process slurry and Si in acidic slurry₃N_4wAnd the synergistic stable dispersion of the Si powder will be the key to the realization of the technical idea proposed by the present invention.

The gel casting process is to form a three-dimensional network structure by reacting a monomer and a cross-linking agent at a certain temperature, and fix ceramic powder in the three-dimensional network structure to realize low-temperature ceramic molding. When the slurry is prepared, the dispersant, the pH regulator and the like are added to realize uniform mixing of the slurry. Due to the surface charge characteristics of the silicon nitride powder, the dispersibility of the silicon nitride powder in the slurry is closely related to the pH value of the slurry. Studies have shown that when the slurry pH is adjusted>7, the silicon nitride surface groups will adsorb [ OH-]The surface of the particles is negatively charged to form an electric double layer. Along with the increase of the pH value, the thickness of the double electric layers on the surfaces of the particles is increased, the interparticle repulsion force is increased, the dispersibility of the silicon nitride particles is improved, the viscosity of the slurry is reduced, and the system stability can be realized. However, aiming at the technical assumption provided by the invention, Si is easy to hydrolyze in an alkaline environment to generate bubbles due to the difference of the properties of the original powder; meanwhile, although the activity of the large-particle-size Si powder is low and the large-particle-size Si powder can be kept stable in the alkaline slurry under the condition of low volume fraction, the size of a matrix formed after the large-particle-size Si powder is nitrided is large, the matrix is not easy to be uniformly distributed, and the reinforcing effect is limited; however, it is not limited toThe Si powder with the particle size of less than 10 microns has large specific surface area and higher reaction activity, cannot realize stable dispersion in alkaline slurry, and is not beneficial to the performance control of the final material; although SiO is formed by surface modification of Si powder, e.g. oxidation₂And the method of layer and the like can realize the stability of the oxide layer in the alkaline slurry, but the oxide layer has a barrier effect on the subsequent nitridation reaction and is not beneficial to the regulation and control of material performance.

Aiming at the problems, the invention provides a method for adjusting the pH of slurry by using hydrochloric acid as a pH regulator<7, forming a positive ion layer on the surfaces of the silicon nitride and the Si, and realizing the stability of the Si powder; meanwhile, a certain amount of dispersant polyvinyl alcohol (PVA) is added, hydrophobic groups in molecules of the PVA can be adsorbed on the surfaces of the solid particles, and hydroxyl groups in the molecules have hydrophilic characteristics, so that a potential barrier layer can be formed on the surfaces of the solid particles, particle aggregation and gravity settling are hindered, and uniform dispersion of the mixed powder is realized. After the mixed slurry of the silicon nitride crystal whisker and the Si powder with proper viscosity is obtained by adjusting the pH value, the content of a dispersant, the volume fraction of a solid phase and the like of the slurry, the gelation is carried out at low temperature to realize the gelation of Si₃N_4wAnd forming a Si blank. Then, Si is converted into a silicon nitride matrix by high-temperature nitridation, thereby obtaining a silicon nitride whisker reinforced silicon nitride composite material (Si)₃N_4w/Si₃N₄)。

Disclosure of Invention

Technical problem to be solved

In order to avoid the defects of the prior art, the invention provides Si₃N_4wSi preform and preparation of Si using the same₃N_4w/Si₃N₄The composite material is prepared through compounding silicon nitride crystal whisker and Si powder to form homogeneous, isotropic and near-net-size three-dimensional netted Si structure₃N_4wIntroducing nitrogen into the preform to cause nitridation reaction of Si powder, and forming a silicon nitride matrix on the silicon nitride whisker in situ, thereby obtaining Si₃N_4w/Si₃N₄A composite material.

Technical scheme

Si₃N_4wa/Si preform, characterized in thatThe components are Si powder and Si with the volume ratio of 1: 2-10₃N₄A whisker, wherein: the grain size of the Si powder is 1-10 mu m, and the length-diameter ratio of the crystal whisker is 5-20.

By using the Si₃N_4wPreparation of Si from Si preform₃N_4w/Si₃N₄A method of compounding a material, characterized by the steps of:

step 1, preparing slurry: 40 to 55 wt.% of Si₃N₄Dissolving whisker, 5-15 wt.% of Si powder, 0.5-0.8 wt.% of dispersing agent polyvinyl alcohol PVA and 1.2-1.7 wt.% of wetting agent polyethylene glycol-400 into deionized water, adding 2.5-4.5 wt.% of hydrochloric acid HCl, adjusting the pH value to 1-3, and performing ball milling dispersion for 1-6 hours; adding 5-8 wt.% of acrylamide AM and 0.3-0.5 wt.% of N, N-methylene bisacrylamide MBAM, and performing ball milling and dispersion for 0.5-4 hours to obtain slurry;

step 2, injection molding and curing: adding 0.3-0.45 wt.% of ammonium persulfate APS (ammonium persulfate per second) serving as an initiator into the slurry, removing bubbles in vacuum for 5-10 min, stirring, then carrying out injection molding, vibrating to remove bubbles, and then crosslinking and curing the slurry at 60-90 ℃ to obtain a ceramic wet blank;

step 3, demolding and drying: demoulding the cured ceramic wet blank, and naturally drying at room temperature;

step 4, glue discharging treatment: placing the dried ceramic biscuit in a muffle furnace, heating to 400-600 ℃ at the speed of 0.5-2 ℃/min, and preserving heat for 1-4 h to obtain porous Si₃N_4wa/Si preform;

step 5, in-situ nitridation: porous Si₃N_4wthe/Si preform is placed in a nitriding furnace in N₂Heating to 1400-1500 ℃ at the speed of 1-5 ℃/min in the atmosphere, preserving heat for 1-4 h to enable the Si powder to react fully to generate a silicon nitride substrate, filling pores, and obtaining Si₃N_4w/Si₃N₄A composite material.

And the oscillation defoaming time of the step 2 is 5-10 min.

And (4) naturally drying for 24-72 h at room temperature in the step (3).

Advantageous effects

The invention provides Si₃N_4wSi preform and preparation of Si using the same₃N_4w/Si₃N₄Method of making a composite material, Si₃N₄Preparing the crystal whisker and the Si powder into a ceramic wet blank by gel casting one-step molding, drying and then adopting low-temperature air firing to discharge gel to obtain porous Si₃N_4wa/Si preform; porous Si₃N_4wPutting the/Si prefabricated body into a nitriding furnace, and introducing N₂Nitriding the Si powder in the preform to form a reaction mixture with Si₃N₄In-situ forming silicon nitride on the whisker to obtain Si₃N_4w/Si₃N₄A composite material. The invention takes hydrochloric acid as a pH regulator, innovatively introduces Si powder and Si under acidic condition₃N₄The forming of the whisker preform is combined, so that the stability of micron-sized Si powder with higher specific surface area in water-based slurry is improved; simultaneously, the polyvinyl alcohol (PVA) is taken as a dispersant, thereby realizing the Si₃N₄Stable dispersion of whiskers in acidic slurry to obtain Si₃N_4wthe/Si complex phase high volume fraction synergetic stable suspension slurry. The volume of the Si powder expands in the nitridation reaction process, so that the pores in the prefabricated body can be effectively occupied, and the shrinkage of the blank body is reduced; and the in-situ reaction does not change the distribution of Si, so that a silicon nitride substrate with uniform distribution can be obtained, and the crystal whisker bearing is facilitated. The method developed by the invention is suitable for preparing large-size components with complex shapes, and the high-performance ceramic matrix composite material with isotropy and small residual stress can be obtained by combining gel casting with in-situ reaction.

In order to solve the problem that the low-particle-size Si powder cannot be stably dispersed in the conventional gel-casting alkaline slurry, the invention provides an acidic slurry with the pH value less than 7, and polyvinyl alcohol (PVA) is used as a dispersing agent, so that the suspension stable dispersion of the high-volume-fraction silicon nitride whiskers and the low-particle-size Si powder multiphase particles with the particle size of less than 10 mu m is realized.

In order to solve the problems of more holes and cracks, uneven distribution and the like of a PIP/CVI silicon nitride substrate when a composite material is prepared by combining a gel casting process with a PIP/CVI process, the method utilizes Si powder in-situ nitridation reaction to uniformly occupy the holes of a ceramic blank and effectively reduces the stress in the composite material.

In order to solve the problems of complex process flow and the like caused by that when a composite material is prepared by combining gel casting with PIP/CVI technology, firstly, a whisker preform is formed, and then a substrate is prepared step by step and for many times by a CVI or PIP method, the invention provides that Si powder is added in the forming process of the silicon nitride whisker preform, and the two processes of forming the preform and preparing the substrate are highly combined, so that the process steps of the composite material are obviously simplified, and the manufacturing period is shortened.

Si provided by the invention₃N_4w/Si₃N₄The preparation method of the composite material has the beneficial effects that:

1. si prepared by the invention₃N_4w/Si₃N₄The composite material has excellent mechanical, wave-transparent, high-temperature and environmental properties and good comprehensive performance, and can meet the high-performance requirements of high-temperature wave-transparent components such as a hypersonic aircraft radome on the material.

2. Si according to the invention₃N_4w/Si₃N₄The preparation method of the composite material can obtain the high-performance ceramic matrix composite material with isotropy and small residual stress, and is suitable for manufacturing large-size components with complex shapes.

3. Si according to the invention₃N_4w/Si₃N₄The preparation method of the composite material comprises the step of introducing reaction source Si powder of a silicon nitride substrate in the composite material into Si in advance₃N₄In the whisker preform, the preparation process of the composite material matrix is simplified, the process complexity is reduced, and the preparation period is greatly shortened.

4. Si according to the invention₃N_4w/Si₃N₄The slurry of the composite material preparation method takes HCl as a pH regulator, thereby realizing the stable dispersion of Si powder with the particle size of less than 10 mu m, improving the volume fraction of solid phase in gel casting slurry, not only effectively improving the strength of a blank body and ensuring the integrity of the blank body, but also reducing the volume shrinkage and residual stress in the drying process of the blank body and being beneficial to the mechanical property of the composite material.

5. The inventionInvolving Si₃N_4w/Si₃N₄The preparation method of the composite material can adjust Si in the slurry₃N₄The proportion of the crystal whiskers and the Si powder realizes the design of a pore structure of the prefabricated body, the content and the distribution of two phases can be regulated, more space is provided for the collaborative design of the mechanics and the wave-transmitting performance of the composite material, the requirements under different conditions can be met, and the customized design is hopeful to be realized.

6. Si according to the invention₃N_4w/Si₃N₄According to the preparation method of the composite material, the Si powder is subjected to nitridation reaction to increase weight, and the volume is expanded in the reaction process. The generated silicon nitride substrate can replicate the distribution of Si powder in a preform, or uniformly grow on the lap joint of the whisker to play a role in strengthening the preform, or form holes among the whiskers and the surface of the whisker, effectively fill ceramic pores to play a role in densification, and is favorable for improving the material performance.

Drawings

FIG. 1 is a process flow diagram of the present invention

FIG. 2 is Si prepared according to example 1 of the present invention₃N_4wMacroscopic photograph of/Si preform

FIG. 3 is Si prepared according to example 1 of the present invention₃N_4wScanning Electron Microscope (SEM) picture of/Si preform degumming rear section

FIG. 4 shows Si prepared in example 1 of the present invention₃N_4w/Si₃N₄Scanning Electron Microscope (SEM) photograph of composite section

FIG. 5 shows Si prepared in example 1 of the present invention₃N_4wSi preform and Si₃N_4w/Si₃N₄X-ray diffraction (XRD) patterns of composite materials

Detailed Description

The invention will now be further described with reference to the following examples and drawings:

si provided by the invention₃N_4w/Si₃N₄A preparation method of a composite material, in particular to gel casting Si₃N_4wAfter the/Si preform, at high temperature N₂Nitriding reaction of Si in atmosphereIn-situ formation of a silicon nitride matrix, thereby obtaining Si₃N_4w/Si₃N₄A method of compounding a material. The invention can prepare Si with isotropic characteristic, excellent mechanical property and wave-transmitting property₃N_4w/Si₃N₄The composite material solves the problems of complex preparation process, large residual stress, more defects of prepared matrix and uneven distribution of the existing whisker reinforced ceramic matrix composite material.

Example 1.

Step one, preparing slurry:

in this embodiment, Si having a diameter of 0.5 to 1 μm and an aspect ratio of about 5 to 10 is used₃N₄Whiskers and Si powder with the particle size of 1-10 mu m. Adding Si into a ball milling tank₃N₄25.27g of whisker and 2.10g of Si powder, then adding 0.28g of polyethylene glycol-4000.6 g of polyvinyl alcohol, 1.5g of concentrated hydrochloric acid and 16.79g of deionized water, and ball-milling for 4 hours. 2.72g of acrylamide and 0.18g of N, N-methylenebisacrylamide were then added, and ball milling was continued for 1 hour.

Step two, injection molding and curing:

and (3) fully dissolving 0.15g of ammonium persulfate in 1.5g of deionized water, adding the solution into the slurry obtained in the step one, removing bubbles in vacuum for 3min, circulating for 3 times, uniformly stirring, then carrying out injection molding, vibrating for 5min to remove bubbles, and then crosslinking and curing the slurry at 80 ℃.

Step three, demolding and drying:

and (3) after the slurry is completely gelatinized, demolding to obtain a ceramic wet blank, and naturally drying the obtained wet blank in the air for 48 hours to obtain a ceramic biscuit.

Step four, glue discharging treatment:

putting the ceramic biscuit obtained in the third step into a muffle furnace, heating to 600 ℃ at the speed of 1 ℃/min, and preserving heat for 2h to obtain Si shown in figure 2₃N_4wThe surface of the/Si prefabricated body is smooth and complete and has no crack; as shown in FIG. 3, the Si powder can be observed to be uniformly distributed on the lapping part of the whisker, the hole between the whiskers and the surface of the whisker on the section of the crystal under a scanning electron microscope.

Step five, in-situ nitridation:

placing the preform obtained in the fourth step in nitridingIn a furnace, in N₂Heating to 1450 deg.C at a rate of 5 deg.C/min in atmosphere, and maintaining for 2h to allow Si powder in the preform to react sufficiently to obtain Si₃N_4w/Si₃N₄The fracture of the composite material is observed, and as shown in fig. 4, the generated silicon nitride matrix duplicates the distribution of Si powder in the prefabricated body, uniformly grows at the lap joint of the whisker, reinforces the prefabricated body of the whisker, and simultaneously plays a certain role in densifying the matrix distributed in the holes among the whiskers and the surface of the whisker. Comparative analysis of XRD results of the materials before and after the reaction in FIG. 5 revealed that Si was completely converted to Si₃N₄。

Example 2.

Step one, preparing slurry:

in this embodiment, Si having a diameter of 0.5 to 1 μm and an aspect ratio of about 5 to 10 is used₃N₄Whiskers and Si powder with the particle size of 1-10 mu m. Adding Si into a ball milling tank₃N₄23.40g of whisker and 3.50g of Si powder, then adding 0.28g of polyethylene glycol-4000.6 g of polyvinyl alcohol, 1.5g of concentrated hydrochloric acid and 16.79g of deionized water, and ball-milling for 4 hours. 2.72g of acrylamide and 0.18g of N, N-methylenebisacrylamide were then added, and ball milling was continued for 1 hour.

Step two, injection molding and curing:

and (3) fully dissolving 0.15g of ammonium persulfate in 1.5g of deionized water, adding the solution into the slurry obtained in the step one, removing bubbles in vacuum for 3min, circulating for 3 times, uniformly stirring, then carrying out injection molding, vibrating for 5min to remove bubbles, and then crosslinking and curing the slurry at 80 ℃.

Step three, demolding and drying:

and (3) after the slurry is completely gelatinized, demolding to obtain a ceramic wet blank, and naturally drying the obtained wet blank in the air for 48 hours to obtain a ceramic biscuit.

Step four, glue discharging treatment:

putting the ceramic biscuit obtained in the step three into a muffle furnace, heating to 600 ℃ at the speed of 1 ℃/min, and preserving heat for 2h to obtain Si₃N_4wa/Si preform.

Step five, in-situ nitridation:

placing the preform obtained in the fourth step in a nitriding furnace in N₂Heating to 1450 deg.C at a rate of 5 deg.C/min in atmosphere, and maintaining for 2h to allow Si powder in the preform to react sufficiently to obtain Si₃N_4w/Si₃N₄A composite material.

Example 3.

Step one, preparing slurry:

in this embodiment, Si having a diameter of 0.5 to 1 μm and an aspect ratio of about 5 to 10 is used₃N₄Whiskers and Si powder with the particle size of 1-10 mu m. Adding Si into a ball milling tank₃N₄18.72g of whisker and 6.99g of Si powder, then adding 4000.6g of polyethylene glycol, 0.28g of polyvinyl alcohol, 1.5g of concentrated hydrochloric acid and 16.79g of deionized water, and ball-milling for 4 hours. 2.72g of acrylamide and 0.18g of N, N-methylenebisacrylamide were then added, and ball milling was continued for 1 hour.

Step two, injection molding and curing:

and (3) fully dissolving 0.15g of ammonium persulfate in 1.5g of deionized water, adding the solution into the slurry obtained in the step one, removing bubbles in vacuum for 3min, circulating for 3 times, uniformly stirring, then carrying out injection molding, vibrating for 5min to remove bubbles, and then crosslinking and curing the slurry at 80 ℃.

Step three, demolding and drying:

and (3) after the slurry is completely gelatinized, demolding to obtain a ceramic wet blank, and naturally drying the obtained wet blank in the air for 48 hours to obtain a ceramic biscuit.

Step four, glue discharging treatment:

putting the ceramic biscuit obtained in the step three into a muffle furnace, heating to 600 ℃ at the speed of 1 ℃/min, and preserving heat for 2h to obtain Si₃N_4wa/Si preform.

Step five, in-situ nitridation:

placing the preform obtained in the fourth step in a nitriding furnace in N₂Heating to 1450 deg.C at a rate of 5 deg.C/min in atmosphere, and maintaining for 2h to allow Si powder in the preform to react sufficiently to obtain Si₃N_4w/Si₃N₄A composite material.

Claims (4)

1. Si₃N_4wthe/Si prefabricated body is characterized by comprising Si powder and Si in a volume ratio of 1: 2-10₃N₄A whisker, wherein: the grain size of the Si powder is 1-10 mu m, and the length-diameter ratio of the crystal whisker is 5-20.

2. Use of Si as described in claim 1₃N_4wPreparation of Si from Si preform₃N_4w/Si₃N₄A method of compounding a material, characterized by the steps of:

step 1, preparing slurry: 40 to 55 wt.% of Si₃N₄Dissolving whisker, 5-15 wt.% of Si powder, 0.5-0.8 wt.% of dispersing agent polyvinyl alcohol PVA and 1.2-1.7 wt.% of wetting agent polyethylene glycol-400 into deionized water, adding 2.5-4.5 wt.% of hydrochloric acid HCl, adjusting the pH value to 1-3, and performing ball milling dispersion for 1-6 hours; adding 5-8 wt.% of acrylamide AM and 0.3-0.5 wt.% of N, N-methylene bisacrylamide MBAM, and performing ball milling and dispersion for 0.5-4 hours to obtain slurry;

step 2, injection molding and curing: adding 0.3-0.45 wt.% of ammonium persulfate APS (ammonium persulfate per second) serving as an initiator into the slurry, removing bubbles in vacuum for 5-10 min, stirring, then carrying out injection molding, vibrating to remove bubbles, and then crosslinking and curing the slurry at 60-90 ℃ to obtain a ceramic wet blank;

step 3, demolding and drying: demoulding the cured ceramic wet blank, and naturally drying at room temperature;

step 4, glue discharging treatment: placing the dried ceramic biscuit in a muffle furnace, heating to 400-600 ℃ at the speed of 0.5-2 ℃/min, and preserving heat for 1-4 h to obtain porous Si₃N_4wa/Si preform;

step 5, in-situ nitridation: porous Si₃N_4wthe/Si preform is placed in a nitriding furnace in N₂Heating to 1400-1500 ℃ at the speed of 1-5 ℃/min in the atmosphere, preserving heat for 1-4 h to enable the Si powder to react fully to generate a silicon nitride substrate, filling pores, and obtaining Si₃N_4w/Si₃N₄A composite material.

3. The method of claim 2, wherein: and the oscillation defoaming time of the step 2 is 5-10 min.

4. The method of claim 2, wherein: and (4) naturally drying for 24-72 h at room temperature in the step (3).

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