阅读说明：本技术 一种氮化硅陶瓷材料及其制备方法 (Silicon nitride ceramic material and preparation method thereof ) 是由 刘学建 张辉 黄政仁 姚秀敏 蒋金弟 陈忠明 于 2021-01-20 设计创作，主要内容包括：本发明涉及一种氮化硅陶瓷材料及其制备方法,所述氮化硅陶瓷材料包括氮化硅相和晶界相；所述氮化硅相的含量≥95wt%；所述晶界相为至少含有Y、Mg、O三种元素的混合物；所述晶界相的含量≤5wt%,且晶界相中结晶相的含量≥40vol%。(The invention relates to a silicon nitride ceramic material and a preparation method thereof, wherein the silicon nitride ceramic material comprises a silicon nitride phase and a grain boundary phase; the content of the silicon nitride phase is more than or equal to 95 wt%; the grain boundary phase is a mixture at least containing Y, Mg and O; the content of the grain boundary phase is less than or equal to 5wt%, and the content of a crystalline phase in the grain boundary phase is more than or equal to 40 vol%.)

1. a silicon nitride ceramic material, wherein the silicon nitride ceramic material comprises a silicon nitride phase and a grain boundary phase; the content of the silicon nitride phase is more than or equal to 95 wt%; the grain boundary phase is a mixture at least containing Y, Mg and O; the content of the grain boundary phase is less than or equal to 5wt%, and the content of a crystalline phase in the grain boundary phase is more than or equal to 40 vol%.

2. The silicon nitride ceramic material of claim 1, wherein the total amount of impurities in the silicon nitride ceramic material is less than or equal to 1.0 wt%; the impurities comprise at least one of lattice oxygen, metal impurity ions and impurity carbon.

3. Silicon nitride ceramic material according to claim 1 or 2, characterized in that it has a thermal conductivity of 90W-m^-1·K^-1Above, the breakdown field strength is above 30 kV/mm.

4. A method of preparing a silicon nitride ceramic material according to any one of claims 1 to 3, comprising:

(1) at least one of silicon powder and silicon nitride powder is used as original powder, and Y is used₂O₃Mixing and forming the powder and MgO powder serving as sintering aids in a protective atmosphere to obtain a biscuit;

(2) placing the obtained biscuit in a reducing atmosphere, and carrying out pretreatment at 500-800 ℃ to obtain a biscuit body;

(3) and placing the obtained blank in a nitrogen atmosphere, performing low-temperature heat treatment at 1600-1800 ℃, and performing high-temperature heat treatment at 1800-2000 ℃ to obtain the silicon nitride ceramic material.

5. A method of preparing a silicon nitride ceramic material according to any one of claims 1 to 3, comprising:

(1) at least one of silicon powder and silicon nitride powder is used as original powder, and Y is used₂O₃The powder and MgO powder are used as sintering aids, and then organic solvent and binder are added and mixed in protective atmosphere to obtain mixed slurry;

(2) subjecting the mixed slurry to casting forming in a protective atmosphere to obtain a biscuit;

(3) placing the obtained biscuit in a reducing atmosphere, and carrying out pretreatment at 500-800 ℃ to obtain a biscuit body;

(4) and placing the obtained blank in a nitrogen atmosphere, performing low-temperature heat treatment at 1600-1800 ℃, and performing high-temperature heat treatment at 1800-2000 ℃ to obtain the silicon nitride ceramic material.

6. A production method according to claim 4 or 5, characterized in that, when the original powder contains silicon powder, the mass of the silicon powder is not less than 75wt% of the mass of the original powder; the protective atmosphere is inert atmosphere or nitrogen atmosphere, preferably nitrogen atmosphere; said Y is₂O₃The molar ratio of the powder to the MgO powder is (1.0-1.4): (2.5-2.9) in an amount of not more than 5wt% of the sum of the mass of the original powder and the mass of the sintering aid; wherein the mass of the original powder is the sum of the mass of the silicon nitride generated after the silicon nitride powder and the silicon powder are completely nitrided.

7. The production method according to claim 4 or 5, characterized in that the protective atmosphere is an inert atmosphere or a nitrogen atmosphere; the reducing atmosphere is a hydrogen/nitrogen mixed atmosphere with the hydrogen content not higher than 5%; the pretreatment time is 1-3 hours.

8. The preparation method according to claim 4 or 5, characterized in that, when the raw powder contains silicon powder, after the pretreatment and before the low-temperature heat treatment, the obtained blank is subjected to nitriding treatment in a reducing atmosphere; the parameters of the nitridation treatment comprise: the nitrogen atmosphere is a hydrogen/nitrogen mixed atmosphere with the hydrogen content not higher than 5%, the pressure is 0.1-0.2 MPa, the temperature is 1350-1450 ℃, and the heat preservation time is 3-6 hours.

9. The production method according to claim 4 or 5, wherein the pressure of the nitrogen atmosphere is 0.5 to 10 MPa; the time of the low-temperature heat treatment is 1.5-2.5 hours; the time of the high-temperature heat treatment is 4-12 hours.

10. The production method according to claim 5, wherein the obtained mixed slurry is subjected to vacuum degassing treatment before the casting molding; the binder is polyvinyl butyral, and the addition amount of the binder is 5-9 wt% of the sum of the mass of the original powder and the mass of the sintering aid; wherein the mass of the original powder is the sum of the mass of the silicon nitride generated after the silicon nitride powder and the silicon powder are completely nitrided.

Technical Field

The invention relates to a silicon nitride ceramic material and a preparation method thereof, belonging to the field of silicon nitride ceramics.

Background

In recent years, semiconductor devices have been rapidly developed in the direction of high power, high frequency, and integration. The heat generated by the operation of the semiconductor device is a critical factor causing the failure of the semiconductor device, and the thermal conductivity of the insulating substrate is critical to affect the heat dissipation of the whole semiconductor device. In addition, in the fields of electric automobiles, high-speed railways, rail transit and the like, the semiconductor device is often subjected to complex mechanical environments such as jolt, vibration and the like in the use process, which puts severe requirements on the reliability of the used materials.

High thermal conductivity silicon nitride (Si)₃N₄) Due to excellent mechanical and thermal properties, the ceramic is considered to be an optimal semiconductor insulating substrate material with high strength and high thermal conductivity, and has great potential in the aspect of heat dissipation application of high-power Insulated Gate Bipolar Transistors (IGBTs). The theoretical thermal conductivity of the silicon nitride crystal can reach 400 W.m^-1·K^-1Thus, the substrate has a potential to be a highly thermally conductive substrate. The silicon nitride ceramic has excellent mechanical properties and good high heat conduction potential, is expected to make up the defects of the existing ceramic substrate materials such as aluminum oxide, aluminum nitride and the like, and has great potential in the application aspect of high-end semiconductor devices, particularly high-power IGBT heat dissipation substrates. However, the thermal conductivity of the traditional silicon nitride ceramic material is only 20-30 W.m^-1·K^-1And the application requirement of heat dissipation of the substrate of the high-power semiconductor device cannot be met at all.

On the other hand, silicon nitride is a compound with strong covalent bond, and is difficult to sinter and compact by solid phase diffusion, and a proper amount (usually more than 5wt percent) of rare earth oxide and/or metal oxide must be added as a sintering aid (such as Y)₂O₃、La₂O₃、MgO、Al₂O₃CaO, etc.), the addition of the sintering aid can significantly reduce the thermal conductivity of the silicon nitride ceramic, and the low content of the sintering aid helps to obtain high thermal conductivity, while the low content of the sintering aid brings the problem of sintering densification of the silicon nitride ceramic.

Disclosure of Invention

In view of the above technical problems, the present invention provides a silicon nitride ceramic material and a method for preparing the same.

In one aspect, the present invention provides a silicon nitride ceramic material comprising a silicon nitride phase and a grain boundary phase; the content of the silicon nitride phase is more than or equal to 95 wt%; the grain boundary phase is a mixture at least containing Y, Mg and O; the content of the grain boundary phase is less than or equal to 5wt%, and the content of a crystalline phase in the grain boundary phase is more than or equal to 40 vol%.

In the method, the silicon nitride phase has high composition content, the volume content of the crystal phase in the grain boundary phase is more than or equal to 40%, and the high silicon nitride crystal phase and the grain boundary phase of the crystal are favorable for reducing the scattering of phonons and improving the thermal conductivity and breakdown field strength of the silicon nitride ceramic material. Generally, the sintering aid oxide (e.g. Y)₂O₃MgO, etc.) and silicon nitride powder surface small amount of native oxide (SiO)₂、SiO_xEtc.) form eutectic liquid phases (i.e., liquid phase sintering mechanism) during the high temperature sintering of the silicon nitride ceramic material, and as the sintering temperature is lowered, these eutectic liquid phases tend to be present in the prepared silicon nitride ceramic material in the form of amorphous glass phase converted into solid state (i.e., grain boundary phase). The grain boundary phase has a lower thermal conductivity and breakdown field strength than silicon nitride crystal grains, and the higher the content of the amorphous glass phase in the grain boundary phase, the lower its corresponding thermal conductivity and breakdown field strength.

Preferably, the total amount of impurities in the silicon nitride ceramic material is less than or equal to 1.0 wt%.

Preferably, the impurities include at least one of lattice oxygen, metal impurity ions, and impurity carbon.

Preferably, the thermal conductivity of the silicon nitride ceramic material is 90 W.m^-1·K^-1Above, the breakdown field strength is above 30 kV/mm.

During the previous research process, the inventor finds that: silicon nitride ceramics are a phonon heat transfer mechanism, and the mean free path of phonons is large and the thermal conductivity is high only when a silicon nitride crystal lattice is complete and has no defects. However, during the preparation of silicon nitride ceramic materials, lattice oxygen, metal impurity ions, carbon impurities and the like tend to enter silicon nitride lattices to different degrees, so that structural defects such as vacancies, dislocations and the like are formed, and the mean free path of phonons is significantly reduced, thereby reducing the thermal conductivity of the materials. Therefore, how to reduce the contents of lattice oxygen, metal impurity ions, carbon impurities and the like is the key to improve the thermal conductivity of the silicon nitride ceramic material.

Moreover, the present inventors have also found that: during the process of sintering the silicon nitride ceramic material at high temperature, although the added sintering aid can form eutectic liquid phase and is easy to be mixed with a small amount of native oxide (SiO) on the surface of silicon nitride powder₂、SiO_xEtc.) to form a low-melting-point liquid phase, thereby promoting the liquid-phase mass transfer of silicon nitride crystal grains to realize high-temperature sintering densification (namely a liquid-phase sintering mechanism). However, as the sintering temperature is lowered, these liquid phases form grain boundary phases mainly composed of an amorphous glass phase among silicon nitride crystal grains, and the grain boundary phases mainly composed of the amorphous glass phase have a low influence on thermal conductivity (generally, several to ten and several W · m · s)^-1·K^-1) Is critical. Therefore, how to change the amorphous grain boundary phase into the crystallized grain boundary phase (i.e. increase the content of the crystalline phase in the grain boundary phase) is the key to increase the thermal conductivity of the silicon nitride ceramic material.

In addition, the inventor, earlier research also shows that: the thermal conductivity of the silicon nitride ceramic tends to decrease with the increase of the ionic radius of the rare earth element serving as the sintering aid; compared with MgO sintering aid, the CaO sintering aid is not beneficial to the growth of silicon nitride columnar grains, and the thermal conductivity and the strength are generally lower.

In summary, how to select a proper kind of sintering aid, how to control the content of the sintering aid, and how to control the crystallization degree of the grain boundary phase is a key way to improve the thermal conductivity of the silicon nitride ceramic material.

Therefore, the invention also provides a preparation method of the silicon nitride ceramic material, which comprises the following steps:

(1) at least one of silicon powder and silicon nitride powder is used as original powder, and Y is used₂O₃The powder and MgO powder are used as sintering aids, and then organic solvent and binder are added and mixed in protective atmosphere to obtain mixed slurry;

(2) subjecting the mixed slurry to casting forming in a protective atmosphere to obtain a biscuit;

(3) placing the obtained biscuit in a reducing atmosphere, and carrying out pretreatment at 500-800 ℃ to obtain a biscuit body;

(4) and placing the obtained blank in a nitrogen atmosphere, performing low-temperature heat treatment at 1600-1800 ℃, and performing high-temperature heat treatment at 1800-2000 ℃ to obtain the silicon nitride ceramic material.

Preferably, the resulting mixed slurry is subjected to vacuum degassing treatment before casting.

Preferably, the binder is polyvinyl butyral (PVB), and the addition amount is 5-9 wt% of the sum of the original powder mass and the sintering aid mass. Wherein the mass of the original powder is the sum of the mass of the silicon nitride generated after the silicon nitride powder and the silicon powder are completely nitrided.

Preferably, the organic solvent is absolute ethyl alcohol; the solid content of the obtained mixed slurry (the ratio of the mass of the original powder and the total mass of the sintering aid to the total mass of the slurry) is 50-70 wt%.

Therefore, the invention also provides another preparation method of the silicon nitride ceramic material, which comprises the following steps:

(1) at least one of silicon powder and silicon nitride powder is used as original powder, and Y is used₂O₃Mixing and forming the powder and MgO powder serving as sintering aids in a protective atmosphere to obtain a biscuit;

(2) placing the obtained biscuit in a reducing atmosphere, and carrying out pretreatment at 500-800 ℃ to obtain a biscuit body;

(3) and placing the obtained blank in a nitrogen atmosphere, performing low-temperature heat treatment at 1600-1800 ℃, and performing high-temperature heat treatment at 1800-2000 ℃ to obtain the silicon nitride ceramic material.

In the invention, the preparation of the powder and the blank is completed in a protective atmosphere, impurities such as oxygen content, metal impurity ions, impurity carbon atoms and the like in the original powder are controlled, and the blank is pretreated in a reducing atmosphere to inhibit the further oxidation of the original powder in the preparation process, so that the concentrations of oxygen and other defects in the crystal lattice of the silicon nitride ceramic are finally reduced. On the basis, the inventor also regulates and controls the components and the content of a grain boundary phase in the silicon nitride ceramic material in a step-by-step sintering mode, improves the content of a crystalline phase in the grain boundary phase, and finally obtains the silicon nitride ceramic material with high heat conductivity and high breakdown field strength.

In the following description, the present method refers to the above two methods unless otherwise specified.

In the method, preferably, when the original powder contains silicon powder, the mass percentage of the silicon powder in the original powder is not less than 75 wt%. When the original powder is silicon powder or mixed powder of silicon powder and silicon nitride powder, the quality of the original powder refers to the sum of the quality of the silicon nitride in the original powder and the quality of the silicon nitride generated after the silicon powder in the original powder is nitrided.

In the method, preferably, said Y is₂O₃The molar ratio of the powder to the MgO powder is (1.0-1.4): (2.5-2.9) in an amount of not more than 5wt% based on the total mass of the raw material powder and the sintering aid. When the original powder is a mixed powder of silicon powder and silicon nitride powder, the mass of the original powder is the sum of the mass of silicon nitride in the original powder and the mass of silicon nitride generated after the silicon powder in the original powder is nitrided.

In the method, preferably, the protective atmosphere is an inert atmosphere or a nitrogen atmosphere, and preferably a nitrogen atmosphere.

In the method, preferably, the reducing atmosphere is a hydrogen/nitrogen mixed atmosphere with the hydrogen content not higher than 5%; the pretreatment time is 1-3 hours.

In the method, preferably, when the original powder contains silicon powder, after the pretreatment and before the low-temperature heat treatment, the obtained blank is subjected to nitriding treatment in a nitrogen atmosphere; the parameters of the nitridation treatment process include: the nitrogen atmosphere is a hydrogen/nitrogen mixed atmosphere with the hydrogen content not higher than 5%, the pressure is 0.1-0.2 MPa, the temperature is 1350-1450 ℃, and the heat preservation time is 3-6 hours.

In the method, preferably, the pressure of the nitrogen atmosphere (preferably, without hydrogen) is 0.5 to 10 MPa; the time of the low-temperature heat treatment is 1.5-2.5 hours; the time of the high-temperature heat treatment is 4-12 hours.

Has the advantages that:

the invention reduces the amount of crystal lattice vacancy, dislocation and other structural defects by controlling the oxygen content (including avoiding raw material oxidation and reducing atmosphere pretreatment in the processes of material mixing and biscuit forming), the metal impurity ion content and the carbon content in the preparation process, and achieves the purposes of improving the thermal conductivity and the breakdown field strength of the silicon nitride ceramic material. Meanwhile, the components and the content of a grain boundary phase are regulated and controlled through a two-step sintering process, and a sintering aid is promoted to generate a liquid phase in a low-temperature sintering stage, so that densification is promoted; and at the high temperature stage, the residual MgO sintering aid is partially volatilized, and simultaneously, the content of a glass phase in a grain boundary phase is further reduced, so that the aims of reducing the content of the grain boundary phase, increasing the crystallization degree of the grain boundary phase and further improving the thermal conductivity of the silicon nitride ceramic material are fulfilled. Meanwhile, the high breakdown field strength of the material is beneficial to application in high-power devices, and is beneficial to reducing the thickness of the substrate material and reducing the thermal resistance, so that the copper-clad plate made of the material has the typical characteristics of thermal shock resistance, high reliability and long service life.

Drawings

FIG. 1 is an XRD pattern of a silicon nitride ceramic material prepared in example 1;

FIG. 2 is a typical SEM microstructure for the silicon nitride ceramic material prepared in example 1;

FIG. 3 is a typical TEM microstructure of a silicon nitride ceramic material prepared in example 1;

FIG. 4 is an XRD pattern of the material prepared after the nitriding treatment of example 6;

FIG. 5 is an XRD pattern of the material prepared after high temperature sintering of example 6;

FIG. 6 is a typical SEM microstructure for the preparation of a silicon nitride ceramic material of example 6.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

In the present disclosure, the silicon nitride ceramic material contains a silicon nitride phase of not less than 95% and a grain boundary phase having a crystal phase content of not less than 40%. Moreover, the obtained silicon nitride ceramic material has low contents of lattice oxygen, metal impurity ions, carbon impurities and the like, and the total content is below 1.0 wt%. Therefore, the silicon nitride ceramic material of the present invention has high thermal conductivity and breakdown field strength.

In one embodiment of the invention, the preparation process under clean and protective atmosphere is adopted, so that air or hot air is prevented from contacting the material, and the impurity content and oxygen content in the prepared ceramic are controlled, thereby achieving the purpose of improving the thermal conductivity and breakdown field strength of the material on the premise of not reducing the bending strength of the material. The following is an exemplary description of the method for preparing the silicon nitride ceramic material provided by the present invention.

The preparation method of the silicon nitride ceramic material specifically comprises the following steps: mixing materials and biscuit molding under a protective atmosphere, pretreating under a reducing atmosphere, sintering under a nitrogen atmosphere and controlling a sintering system.

And (5) mixing materials under a protective atmosphere. Mixing the original powder and sintering aid Y₂O₃Adding absolute ethyl alcohol into the powder and MgO powder in a closed container as a solvent, uniformly mixing under the protection of protective atmosphere, and drying to obtain mixed powder. Or, the original powder and the sintering aid Y are mixed₂O₃Putting the powder and MgO powder in a closed container, adding absolute ethyl alcohol as an organic solvent and PVB as a binder, and then uniformly mixing under the protection of a protective atmosphere to obtain mixed slurry. Wherein, the binder can be 5-9 wt% of the total mass of the original powder and the sintering aid. The solid content of the obtained mixed slurry is 50-70 wt%.

In an alternative embodiment, the protective atmosphere used for mixing is an inert atmosphere or a nitrogen atmosphere, preferably a nitrogen atmosphere. Preferably, a closed container with a polyurethane or nylon lining is used for mixing, and nitrogen is introduced into the container to avoid air entering.

In an alternative embodiment, the raw powder is silicon nitride powder, silicon powder, or a mixture of silicon nitride powder and silicon powder. Wherein, the mass percent of the silicon powder in the mixed powder of silicon nitride and silicon is not less than 75 percent, namely the silicon nitride generated after the silicon powder is nitrided accounts for more than 80 percent of the mass percent of the whole silicon nitride phase.

In an alternative embodiment, the sintering aid (Y)₂O₃Powder and MgO powder) does not exceed 5wt% of the total mass of the original powder and the sintering aid. If the sintering aid is too much, the grain boundary phase content in the prepared silicon nitride ceramic material is increasedThe thermal conductivity and the breakdown field strength of the material are reduced. If the sintering aid is too little, densification cannot be sufficiently promoted, so that the prepared silicon nitride ceramic material has low density and increased air holes, and the thermal conductivity and breakdown field strength of the material are reduced. Further preferably, Y is contained in the sintering aid₂O₃The molar ratio of MgO to MgO can be 1.0-1.4: 2.5-2.9. If the MgO is excessive, the temperature of the liquid phase eutectic point formed by the sintering aid is relatively low, and the MgO is seriously volatilized at high temperature, so that the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are relatively low. If a small amount of MgO is used, the proportion of MgO in the sintering aid is low, the temperature of the eutectic point of the liquid phase formed by the sintering aid is relatively high, and the densification effect of the material is relatively poor, so that the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are obviously reduced.

And (5) forming the biscuit in a protective atmosphere. And directly pressing and molding the mixed powder in a protective atmosphere to obtain a biscuit. The compression molding method includes, but is not limited to, dry compression molding, isostatic pressing, etc. Or directly casting the mixed slurry in a protective atmosphere to obtain a biscuit (sheet biscuit). Preferably, the mixed slurry is subjected to vacuum degassing treatment (the degree of vacuum is generally-0.1 to-10 kPa, and the time is 4 to 24 hours) before casting molding. More preferably, the thickness of the sheet biscuit is adjusted by controlling the height of the doctor blade of the casting. In alternative embodiments, the protective atmosphere used for greenbody formation may be an inert atmosphere or a nitrogen atmosphere, preferably a nitrogen atmosphere. Generally, nitrogen is directly introduced for protection in the molding process.

And (3) pre-treating the formed biscuit in a reducing atmosphere. Pre-treating the formed biscuit in a reducing atmosphere at a certain temperature to remove oxygen in the original powder and remove organic matters in the formed biscuit. In an alternative embodiment, when the raw powder is silicon powder or a mixed powder of silicon nitride and silicon, the molded biscuit is pretreated at a certain temperature in a reducing atmosphere, and then further nitrided in the reducing atmosphere.

In an alternative embodiment, the pretreatment may be performed in a reducing nitrogen atmosphere having a hydrogen content of not more than 5%, and the gas pressure of the reducing atmosphere is 0.1 to 0.2 MPa. The pretreatment temperature can be 500-800 ℃, and the heat preservation time can be 1-3 hours.

In an alternative embodiment, the nitriding treatment can be performed in a nitrogen atmosphere with a hydrogen content of not more than 5%, and the atmosphere pressure is 0.1 to 0.2 MPa. The nitriding treatment temperature is 1350-1450 ℃, and the heat preservation time is 3-6 hours.

And sintering the blank, including low-temperature heat treatment and high-temperature heat treatment. Specifically, sintering densification is performed under high nitrogen pressure by a step-by-step sintering process, wherein the step-by-step sintering process comprises low-temperature heat treatment for inhibiting volatilization of low-melting-point substances in a sintering aid and further high-temperature sintering for densification. In the invention, the sintering treatment adopts air pressure sintering under the condition of high nitrogen pressure, and the atmosphere pressure can be 0.5-10 MPa. The green body can be placed in a BN crucible for sintering treatment. Wherein, the temperature of the low-temperature heat treatment (low-temperature sintering) can be 1600-1800 ℃, and the heat preservation time can be 1.5-2.5 hours. The temperature of the high-temperature heat treatment (high-temperature sintering) can be 1800-2000 ℃, and the heat preservation time can be 4-12 hours.

In the invention, the prepared silicon nitride ceramic has low contents of lattice oxygen, metal impurity ions, impurity carbon and the like, has the characteristics of high thermal conductivity and high breakdown field intensity, and the thermal conductivity is 90 W.m^-1·K^-1And the breakdown field strength reaches more than 30 KV/mm.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1

First, 95g of Si was mixed₃N₄Powder, 5g sintering aid powder (Y)₂O₃:MgO1.2:2.5, mol ratio), 1g of castor oil, 1g of PEG, 70g of absolute ethyl alcohol and 200g of silicon nitride grinding balls are put into a lining polyurethane ball-milling tank with an atmosphere protection function, the cover of the ball-milling tank is sealed, vacuum pumping is performed in sequence, and N is introduced₂Under protective atmosphere, ball-milling and mixing for 6h to obtain slurry; a further 5g of PVB and 3g of DBP were added to the above slurry, continuing on at N₂Ball milling for 6 hours under the protection of atmosphere to obtain uniform slurry; next, the slurry was degassed under vacuum for 6h at N₂Carrying out tape casting on a substrate biscuit under the protection of atmosphere, wherein the thickness d +/-0.05 mm (d is 0.2-2.0); thirdly, cutting the formed substrate biscuit into a required shape, putting the cut substrate biscuit into a BN crucible, and putting the crucible into a carbon tube furnace; then, the heat treatment is carried out according to the following process sequence: (1) at 0.15MPa N₂(containing 5% of H)₂) Heating to 600 ℃ at the speed of 5 ℃/min under the protection of atmosphere, and then performing debonding pretreatment for 2 h; (2) at 2MPa N₂Heating to 1650 ℃ at the speed of 5 ℃/min under the protection of atmosphere, and then carrying out low-temperature heat treatment for 2 h; (3) at 8MPa N₂Heating to 1950 ℃ at the speed of 3 ℃/min under the protection of atmosphere, and then sintering at high temperature for 8 hours; (4) cooling to room temperature along with the furnace.

The silicon nitride ceramic substrate material obtained in example 1 had a flexural strength of 810MPa and a thermal conductivity of 106 W.m^-1·K^-1The breakdown field strength is 45 KV/mm. The XRD pattern of the material is shown in figure 1, and only high-strength beta-Si exists₃N₄Diffraction peaks and no significant steamed bread peaks, indicating beta-Si in the prepared material₃N₄The content of the phase is more than 95wt%, and the content of the grain boundary phase is less than 5%. The typical SEM microstructure of the material is shown in figure 2, the material has high density and uniform microstructure, and Si₃N₄The grains (grey black areas) typically exhibit a bimodal distribution of fine equiaxed Si₃N₄Grains and large long columnar Si₃N₄Crystal grains are embedded with each other; the grain boundary phase (grey white area) has low content and is uniformly dispersed and distributed in Si₃N₄In a matrix; further, through statistical analysis of at least 10 SEM pictures and by combining that the total introduction amount of the sintering aid in the raw materials is less than or equal to 5wt%, the grain boundary phase containing silicon nitride ceramic material prepared by the embodiment can be obtainedThe amount is less than 5 wt%. A typical TEM microstructure of the material is shown in FIG. 3 (B in FIG. 3 is a partial enlargement of the dashed box area in A in FIG. 3), Si₃N₄Grain boundary phases (grey-white areas) are dispersedly distributed among the crystal grains (grey-black areas), and the grain boundary phases consist of glass phases (light-colored areas) and crystalline phases (dark-colored areas); through statistical analysis of at least 10 TEM pictures, the content of the crystalline phase in the grain boundary phase of the silicon nitride ceramic material prepared in the embodiment is about 54 vol%.

Examples 2 to 5

The raw material ratio, the sintering aid composition, the pretreatment process, the sintering process and other specific parameters are shown in table 1, the process refers to example 1, and the prepared material composition and properties are shown in table 2.

Example 6

First, 3g of Si was mixed₃N₄Powder, 55g of Si powder, 4.5g of sintering aid powder (Y)₂O₃MgO (1.4: 2.6) in a molar ratio), 0.7g of castor oil, 0.6g of PEG, 50g of absolute ethyl alcohol and 130g of silicon nitride grinding balls are put into a lining polyurethane ball milling pot with an atmosphere protection function, the pot cover of the ball milling pot is sealed, vacuum pumping is carried out in sequence, and N is introduced₂Under protective atmosphere, ball-milling and mixing for 8h to obtain slurry; a further 4g of PVB and 2.5g of DBP were added to the above slurry, continuing on at N₂Ball milling for 6 hours under the protection of atmosphere to obtain uniform slurry; next, the slurry was degassed under vacuum for 6h at N₂Carrying out tape casting to form a substrate biscuit under the protection of atmosphere; thirdly, cutting the formed substrate biscuit into a required shape, putting the cut substrate biscuit into a BN crucible, and putting the crucible into a carbon tube furnace; then, the heat treatment is carried out according to the following process sequence: (1) at 0.2MPa N₂(containing 5% of H)₂) Heating to 600 ℃ at the speed of 4 ℃/min under the protection of atmosphere, and then performing debonding pretreatment for 3 h; (2) at 0.2MPa N₂(containing 5% of H)₂) Under the protection of atmosphere, raising the temperature to 1450 ℃ at the speed of 5 ℃/min, and then carrying out nitridation treatment for 6 h; (3) at 3MPa N₂Heating to 1700 ℃ at the speed of 6 ℃/min under the protection of atmosphere, and then carrying out low-temperature heat treatment for 2 h; (4) at 8MPa N₂Heating to 1950 ℃ at the speed of 5 ℃/min under the protection of atmosphere, and then sintering at high temperature for 10 h; (5) cooling to room temperature along with the furnace.

The silicon nitride ceramic substrate material obtained in example 6 had a flexural strength of 710MPa and a thermal conductivity of 110 W.m^-1·K^-1The breakdown field strength is 48 KV/mm. The XRD pattern of the material after the nitridation treatment process (2)) is shown in figure 4, and the main crystal phases are all alpha-Si₃N₄While containing a small amount of beta-Si₃N₄Phase (5-10%). The XRD pattern of the material after the high-temperature sintering process (the process (4)) is shown in figure 5, and only beta-Si exists₃N₄Diffraction peak and no obvious steamed bread peak, which shows that beta-Si in the prepared material₃N₄The content of the phase is more than 95wt%, and the content of the grain boundary phase is less than 5 wt%; further, by using the same method as in example 1 above, it was found that the content of the crystal phase in the grain boundary phase of the material was about 60 vol%. A typical SEM microstructure of the material fracture is shown in FIG. 6, and the material has high density and uniform microstructure and is composed of fine equiaxed Si₃N₄Grains and large long columnar Si₃N₄The crystal grains are embedded with each other.

Examples 7 to 10

The raw material ratio, the sintering aid composition, the pretreatment process, the nitriding process, the sintering process and other specific parameters are shown in table 1, the process refers to example 6, and the prepared material composition and properties are shown in table 2.

Example 11

The preparation process of the silicon nitride ceramic material in this example 11 is as follows, referring to example 1, and the main differences are: mixing 95g of Si₃N₄Powder, 5g sintering aid powder (Y)₂O₃MgO (1.2: 2.5) in a molar ratio), 1g of castor oil, 1g of PEG, 70g of absolute ethyl alcohol and 200g of silicon nitride grinding balls are put into a lining polyurethane ball milling pot with an atmosphere protection function, the pot cover of the ball milling pot is sealed, vacuum pumping is performed in sequence, and N is introduced₂And (5) carrying out ball milling and mixing for 6h under the protective atmosphere to obtain slurry. Then drying, sieving, dry pressing (20MPa) and cold isostatic pressing (200MPa) are carried out in nitrogen atmosphere to obtain the biscuit.

Comparative example 1

The specific parameters of the raw material ratio, the composition of the sintering aid, the pretreatment process, the sintering process and the like are the same as those in the embodiment 1 (see table 1), and the process refers to the embodiment 1, and is characterized in that: the technological processes of ball milling, mixing, biscuit forming and the like do not adopt nitrogen atmosphere protection measures. The compositions and properties of the prepared materials are shown in table 1. Because the nitrogen atmosphere protection measure of the invention is not adopted in the material preparation process, the silicon nitride powder in the raw material is oxidized in different degrees, so that the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are obviously reduced, but the bending strength is basically kept unchanged.

Comparative example 2

The specific parameters of the sintering aid, such as composition ratio, pretreatment process, sintering process and the like, are the same as those of example 1 (see table 1), and the differences are that: the total amount of sintering aid increases. The compositions and properties of the prepared materials are shown in table 2. Because the content of the sintering aid is higher, the grain boundary phase with lower thermal conductivity formed by the sintering aid has higher content, so that the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are obviously reduced, but the bending strength is basically kept unchanged.

Comparative example 3

The raw material ratio, the types and total amount of sintering aids, the pretreatment process, the sintering process and other specific parameters are the same as those in example 1 (see table 1), and the differences are as follows: different sintering aid proportions (Y)₂O₃MgO 1.2: 4.0). The compositions and properties of the prepared materials are shown in table 2. Because the proportion of MgO in the sintering aid is higher, the temperature of the liquid phase eutectic point formed by the sintering aid is relatively lower, and the high-temperature volatilization is more serious, the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are obviously reduced.

Comparative example 4

The raw material ratio, the types and total amount of sintering aids, the pretreatment process, the sintering process and other specific parameters are the same as those in example 1 (see table 1), and the differences are as follows: different sintering aid proportions (Y)₂O₃MgO 1.3: 2.0). The compositions and properties of the prepared materials are shown in table 2. Because the proportion of MgO in the sintering aid is low, the temperature of the liquid phase eutectic point formed by the sintering aid is relatively high, and the densification effect of the material is relatively poor, the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are obviousIs significantly reduced.

Comparative example 5

The specific parameters of the raw material ratio, the composition of the sintering aid, the pretreatment process and the like are the same as those in example 1 (see table 1), and the process is similar to that in example 1, except that: the sintering process is one-step sintering. The compositions and properties of the prepared materials are shown in table 2. Because the low-temperature heat treatment process is not included, the MgO volatilization starts to happen seriously under the condition of insufficient densification, the densification effect of the material is relatively poor, and the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are obviously reduced.

Comparative example 6

The specific parameters of the raw material ratio, the composition of the sintering aid, the pretreatment process, the sintering process and the like are the same as those in example 1 (see table 1), and the process is the same as that in example 1, except that: the low-temperature heat treatment temperature is lower. The compositions and properties of the prepared materials are shown in table 2. Because the low-temperature heat treatment temperature is lower, the densification effect of the material is relatively poorer, so that the thermal conductivity and the breakdown field strength of the prepared silicon nitride ceramic material are obviously reduced.

Comparative examples 7 to 8

The specific parameters of the raw material ratio, the composition of the sintering aid, the pretreatment process, the sintering process and the like are the same as those in example 8 (see table 1), and the process is the same as that in example 8, except that: the nitriding temperature was either lower (comparative example 7) or higher (comparative example 8). The compositions and properties of the prepared materials are shown in table 2. Because the nitriding treatment temperature is lower (comparative example 7) or higher (comparative example 8), the Si powder in the material is not fully nitrided (comparative example 7) or a partial silicification phenomenon occurs (comparative example 8), so that the mechanical, thermal and electrical properties of the prepared silicon nitride ceramic material are obviously reduced.

Table 1 shows the composition and preparation process of the silicon nitride ceramic material:

table 2 shows the phase composition and performance parameters of the silicon nitride ceramic material: