Silicon nitride ceramic with high thermal conductivity and high mechanical property and preparation method thereof

Abstract

The application relates to the technical field of ceramic materials, in particular to a silicon nitride ceramic with high thermal conductivity and high mechanical property and a preparation method thereof. By adding a crystal phase inducer RE4Si2O7N2 in the preparation process of the silicon nitride ceramic, the crystal phase inducer can induce directional conversion of intercrystalline glass phase in the silicon nitride ceramic as a nucleation site, effectively eliminates the adverse effect of amorphous glass phase on the material property, simultaneously constructs a microstructure with synergistic crystal boundary strengthening and heat conduction optimization, and finally prepares the silicon nitride ceramic with excellent mechanical property, high thermal conductivity and uniform microstructure.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a silicon nitride ceramic with both high thermal conductivity and high mechanical properties, and its preparation method. Background Technology

[0002] Silicon nitride ceramic materials have long been used in aerospace, automotive, chemical and civilian fields due to their high strength, high toughness, corrosion resistance, high hardness, wear resistance and chemical stability.

[0003] While silicon nitride ceramics possess excellent theoretical thermal conductivity, their densification requires the use of sintering aids (such as rare earth oxides and MgO) to form a liquid phase, due to their strong covalent bonds. However, these sintering aids typically remain as an amorphous glassy phase within the silicon nitride ceramic after cooling. These glassy phases severely scatter phonons, becoming a major obstacle to heat conduction and significantly reducing the thermal conductivity of silicon nitride ceramics.

[0004] Therefore, while ensuring the excellent mechanical properties of silicon nitride ceramics, improving the thermal conductivity of silicon nitride ceramics is one of the key aspects of current silicon nitride ceramic research. Summary of the Invention

[0005] To overcome the above problems, the present invention provides a silicon nitride ceramic with both high thermal conductivity and high mechanical properties, and a method for preparing the same.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing silicon nitride ceramics that possess both high thermal conductivity and high mechanical properties, comprising the following steps: α-Si3N4 powder, sintering aid and crystal phase inducer RE4Si2O7N2 were mixed, wet ball milled, dried, ground and sieved to obtain precursor powder; Precursor powder is processed into a green body; Silicon nitride ceramics with both high thermal conductivity and high mechanical properties are obtained by hot pressing and sintering the green blank. In the crystal phase inducer RE4Si2O7N2, RE is selected from one or more of Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb or Lu.

[0007] In one or more embodiments, the sintering aid is one or more of rare earth oxides, MgO, or MgSiN2; the rare earth elements in the rare earth oxides are the same as the RE types in the crystal phase inducer RE4Si2O7N2, and the rare earth elements are selected from one or more of Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb, or Lu.

[0008] In one or more embodiments, the preparation method of the crystal phase inducer RE4Si2O7N2 includes the following steps: α-Si3N4 powder, RE2O3 and SiO2 were mixed and then heat-treated in an oxygen-free atmosphere to obtain the crystal phase inducer RE4Si2O7N2. In RE2O3, RE is selected from one or more of Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb, or Lu.

[0009] Preferably, the molar ratio of the α-Si3N4 powder, RE2O3, and SiO2 is 1:4:1.

[0010] Preferably, the heat treatment temperature is 1600~1700℃ and the heat treatment time is 6~12 h.

[0011] Preferably, the oxygen-free atmosphere includes nitrogen or a rare gas.

[0012] In one or more embodiments, the mass ratio of α-Si3N4 powder, sintering aid and crystal phase inducer RE4Si2O7N2 is (80~95):(5-10):(0.5~10).

[0013] In one or more embodiments, anhydrous ethanol is used as the dispersion solvent during the wet ball milling process.

[0014] In one or more embodiments, hot pressing sintering includes a first stage and a second stage; The parameters for the first stage are: heat preservation at 1200~1600℃ and 10~50 MPa for 1~4 h. The second stage parameters are: heat preservation at 1600~1900℃ and 10~50 MPa for 2~6 h.

[0015] In a second aspect, the present invention provides a silicon nitride ceramic that combines high thermal conductivity and high mechanical properties, prepared by the preparation method described in the first aspect.

[0016] The beneficial effects of this invention are as follows: The silicon nitride ceramic provided by this invention possesses both high thermal conductivity and high mechanical properties, with a room temperature thermal conductivity ≥65 W / (m·K), flexural strength ≥900 MPa, and fracture toughness ≥10 MPa·m. 1 / 2By adding the crystal phase inducer RE4Si2O7N2 during the preparation of silicon nitride ceramics, it can act as a nucleation site to induce the directional transformation of the intergranular glass phase inside the silicon nitride ceramics, effectively eliminating the adverse effects of amorphous glass phase on material properties. At the same time, it constructs a microstructure that synergistically strengthens grain boundaries and optimizes thermal conductivity, ultimately preparing silicon nitride ceramics with excellent mechanical properties, high thermal conductivity, and uniform microstructure. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 The powder diffraction (XRD) patterns of the powders prepared in Examples 1-3 and Comparative Example 1 are shown below. Figure 2 The XRD patterns of the powders prepared in Examples 4-6 are shown. Figure 3 The XRD patterns of the silicon nitride ceramics prepared in Example 7 and Comparative Example 2 are shown below. Figure 4 The XRD patterns of the silicon nitride ceramics prepared in Example 8 and Comparative Example 3 are shown below. Figure 5 The XRD patterns of the silicon nitride ceramics prepared in Example 9 and Comparative Example 4 are shown. Figure 6 The XRD patterns of the silicon nitride ceramics prepared in Example 10 and Comparative Example 5 are shown below. Figure 7 The mechanical properties of the silicon nitride ceramics prepared in Examples 7-8 and Comparative Examples 2-3 are shown in the figure. Figure 8 The graph shows the thermal conductivity test results of the silicon nitride ceramics prepared in Examples 7-8 and Comparative Examples 2-3; Figure 9 The mechanical properties of the silicon nitride ceramics prepared in Examples 9-10 and Comparative Examples 4-5 are shown in the figure. Figure 10 The graph shows the thermal conductivity test results of the silicon nitride ceramics prepared in Examples 9-10 and Comparative Examples 4-5. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] Although silicon nitride ceramics possess excellent theoretical thermal conductivity, their densification requires the use of sintering aids (such as rare earth oxides and MgO) to form a liquid phase, due to their strong covalent bonds. However, these sintering aids typically remain as an amorphous glassy phase within the silicon nitride ceramic after cooling. These glassy phases severely scatter phonons, becoming a major obstacle to heat conduction and significantly reducing the thermal conductivity of silicon nitride ceramics.

[0022] To eliminate or crystallize the glassy phase at grain boundaries, current research often employs subsequent heat treatment processes. However, for conventional silicate glassy phases, their own crystallization ability is limited, often requiring high heat treatment temperatures or long holding times, and the type of precipitated crystalline phase is difficult to control precisely. Insufficient crystallization or a mismatch between the thermal conductivity and coefficient of thermal expansion of the precipitated crystalline phase and the silicon nitride matrix can introduce microcracks or new interfacial thermal resistance at grain boundaries, weakening the toughening effect or even impairing thermal conductivity.

[0023] To overcome the above problems, the present invention provides a silicon nitride ceramic with both high thermal conductivity and high mechanical properties, and a method for preparing the same.

[0024] This invention adds a crystal phase inducer, RE4Si2O7N2, during the preparation of silicon nitride ceramics. RE4Si2O7N2 acts as a nucleation site, inducing the in-situ precipitation of a controllable crystalline second phase from the glassy phase at grain boundaries. This not only transforms the poorly thermally conductive and high-temperature-softening glassy phase into a crystalline phase with high thermal conductivity and good bonding with the matrix, significantly improving the thermal conductivity of the material, but also improves the grain boundary bonding strength by controlling the type and distribution of the grain boundary phase, and synergistically optimizes the morphology and arrangement of β-Si3N4 grains, thereby increasing the density of silicon nitride ceramics. Ultimately, this invention achieves a dual breakthrough in the mechanical and thermal conductivity properties of silicon nitride ceramics.

[0025] The silicon nitride ceramic provided by this invention has a room temperature thermal conductivity ≥65 W / (m·K), a flexural strength ≥900 MPa, and a fracture toughness ≥10 MPa·m. 1 / 2 .

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0027] Example 1 Preparation of the crystal phase inducer Lu4Si2O7N2: (1) Mix 1 mol α-Si3N4 powder, 4 mol Lu2O3 and 1 mol SiO2 and add them to a planetary ball mill. Add anhydrous ethanol as a dispersion solvent. The amount of anhydrous ethanol added is 2 / 3 of the volume of the ball mill jar. Perform wet ball milling. To avoid introducing impurities, use Si3N4 balls as grinding balls. The ball milling speed is 300 r / min. To ensure uniform mixing, the ball milling time is 12 h.

[0028] (2) The ball mill slurry was placed in a drying oven to evaporate and remove anhydrous ethanol. After grinding and sieving, a composite powder was obtained. The composite powder was loaded into a mold and pressed into round tablets at 10 MPa using a tablet press to obtain a pre-pressed product.

[0029] (3) The pre-pressed product was placed in a tube furnace and heated to 1600°C at a heating rate of 5°C / min under a nitrogen atmosphere. The temperature was held for 12 h and then ground and sieved after natural cooling to obtain the crystal phase inducer Lu4Si2O7N2.

[0030] Example 2 Compared with Example 1, the heat preservation time in step (3) was adjusted to 8 h, and the other methods were the same as in Example 1.

[0031] Example 3 Compared with Example 1, the heat preservation time in step (3) was adjusted to 6 h, and the other methods were the same as in Example 1.

[0032] Comparative Example 1 Compared with Example 1, the temperature of heat treatment in step (3) was adjusted to 1550℃ and held for 6 h, while the other methods were the same as in Example 1.

[0033] Figure 1 The XRD patterns of the powders prepared in Examples 1-3 and Comparative Example 1 are shown below. Figure 1 As can be seen, when the heat treatment temperature is 1600℃, the main crystalline phase of the powders prepared in Examples 1-3 is Lu4Si2O7N2. However, when the heat treatment temperature is reduced to 1550℃, only the diffraction peak of Lu2SiO5 can be detected in the powder, indicating that temperature affects the phase evolution. Therefore, the synthesis temperature of the crystal phase inducer RE4Si2O7N2 is determined to be 1600℃.

[0034] Example 4 Preparation of crystal phase inducer Yb4Si2O7N2: (1) Mix 1 mol α-Si3N4 powder, 4 mol Yb2O3 and 1 mol SiO2 and add them to a planetary ball mill. Add anhydrous ethanol as a dispersion solvent. The amount of anhydrous ethanol added is 2 / 3 of the volume of the ball mill jar. Perform wet ball milling. To avoid introducing impurities, use Si3N4 balls as grinding balls. The ball milling speed is 300 r / min. To ensure uniform mixing, the ball milling time is 12 h.

[0035] (2) The ball mill slurry was placed in a drying oven to evaporate and remove anhydrous ethanol. After grinding and sieving, a composite powder was obtained. The composite powder was loaded into a mold and pressed into round tablets at 10 MPa using a tablet press to obtain a pre-pressed product.

[0036] (3) The pre-pressed product was placed in a tube furnace and heated to 1600°C at a heating rate of 5°C / min under a nitrogen atmosphere. The temperature was held for 12 h and then ground and sieved after natural cooling to obtain the crystal phase inducer Yb4Si2O7N2.

[0037] Example 5 Compared with Example 4, the heat preservation time in step (3) was adjusted to 8 h, and the other methods were the same as in Example 4.

[0038] Example 6 Compared with Example 4, the heat preservation time in step (3) was adjusted to 6 h, and the other methods were the same as in Example 4.

[0039] Figure 2 The XRD patterns of the powders prepared in Examples 4-6 are shown below. Figure 2 As can be seen from the data, when the heat treatment temperature is 1600℃, the main crystalline phase of the powder prepared in Examples 4 to 6 is Yb4Si2O7N2.

[0040] Example 7 Preparation of silicon nitride ceramics: (1) Mix 91 parts of α-Si3N4 powder, 5 parts of Lu2O3 powder, 2 parts of crystal phase inducer Lu4Si2O7N2 and 2 parts of MgO powder and add them into a planetary ball mill. Add anhydrous ethanol as a dispersion solvent. The amount of anhydrous ethanol added is 2 / 3 of the volume of the ball milling jar. Wet ball milling is performed. To avoid introducing impurities, Si3N4 balls are used as grinding balls. The ball milling speed is 300 r / min. To ensure uniform mixing, the ball milling time is 12 h.

[0041] (2) Place the ball mill slurry in a drying oven, evaporate to remove anhydrous ethanol, and then grind and sieve to obtain precursor powder.

[0042] The precursor powder is loaded into a mold and pressed into a disc using a tablet press at 10 MPa to obtain a preform.

[0043] (3) The green blank was hot-pressed and sintered to obtain silicon nitride ceramics with both high thermal conductivity and high mechanical properties. The sintering parameters were as follows: room temperature to 900℃, heating time 1 h, pressure in vacuum environment; 900℃ to 1200℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1200℃ to 1400℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1400℃ to 1600℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1600℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere; 1600℃ to 1700℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1700℃ to 1800℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1800℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere. The sintering process of silicon nitride ceramics was carried out under a nitrogen atmosphere at 1800℃ to 1600℃ for 1 hour, with a pressure of 30 MPa under nitrogen atmosphere; the sintering process was carried out from 1600℃ to 1200℃ for 2 hours, with a pressure of 30 MPa under nitrogen atmosphere; and the sintering process was carried out from 1200℃ to room temperature for 3 hours, with no pressure maintained.

[0044] Comparative Example 2 Compared with Example 7, the crystal phase inducer Lu4Si2O7N2 is not added in step (1).

[0045] 93 parts of α-Si3N4 powder, 5 parts of Lu2O3 powder and 2 parts of MgO powder were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent, and the amount of anhydrous ethanol added was 2 / 3 of the volume of the ball mill jar. Wet ball milling was carried out. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling speed was 300 r / min. To ensure uniform mixing, the ball milling time was 12 h.

[0046] The remaining methods are the same as in Example 7, to obtain silicon nitride ceramic, denoted as LM.

[0047] Example 8 Preparation of silicon nitride ceramics: (1) 91 parts of α-Si3N4 powder, 5 parts of Lu2O3 powder, 2 parts of crystal phase inducer Lu4Si2O7N2 and 2 parts of MgSiN2 powder were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent. The amount of anhydrous ethanol added was 2 / 3 of the volume of the ball mill jar. Wet ball milling was carried out. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling speed was 300 r / min. To ensure uniform mixing, the ball milling time was 12 h.

[0048] (2) Place the ball mill slurry in a drying oven, evaporate to remove anhydrous ethanol, and then grind and sieve to obtain precursor powder.

[0049] The precursor powder is loaded into a mold and pressed into a disc using a tablet press at 10 MPa to obtain a preform.

[0050] (3) The green blank was hot-pressed and sintered to obtain silicon nitride ceramics with both high thermal conductivity and high mechanical properties. The sintering parameters were as follows: room temperature to 900℃, heating time 1 h, pressure in vacuum environment; 900℃ to 1200℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1200℃ to 1400℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1400℃ to 1600℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1600℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere; 1600℃ to 1700℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1700℃ to 1800℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1800℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere. The sintering process of silicon nitride ceramics was carried out under a nitrogen atmosphere at 1800℃ to 1600℃ for 1 hour, with a pressure of 30 MPa under nitrogen atmosphere; the sintering process was carried out from 1600℃ to 1200℃ for 2 hours, with a pressure of 30 MPa under nitrogen atmosphere; and the sintering process was carried out from 1200℃ to room temperature for 3 hours, with no pressure maintained.

[0051] Comparative Example 3 Compared with Example 8, the crystal phase inducer Lu4Si2O7N2 is not added in step (1).

[0052] 93 parts of α-Si3N4 powder, 5 parts of Lu2O3 powder and 2 parts of MgSiN2 powder were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent, and the amount of anhydrous ethanol added was 2 / 3 of the volume of the ball mill jar. Wet ball milling was carried out. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling speed was 300 r / min. To ensure uniform mixing, the ball milling time was 12 h.

[0053] The remaining methods are the same as in Example 8, to obtain silicon nitride ceramic, denoted as LMN.

[0054] Example 9 Preparation of silicon nitride ceramics: (1) 91 parts of α-Si3N4 powder, 5 parts of Yb2O3 powder, 2 parts of crystal phase inducer Yb4Si2O7N2 and 2 parts of MgO powder were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent. The amount of anhydrous ethanol added was 2 / 3 of the volume of the ball mill jar. Wet ball milling was carried out. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling speed was 300 r / min. To ensure uniform mixing, the ball milling time was 12 h.

[0055] (2) Place the ball mill slurry in a drying oven, evaporate to remove anhydrous ethanol, and then grind and sieve to obtain precursor powder.

[0056] The precursor powder is loaded into a mold and pressed into a disc using a tablet press at 10 MPa to obtain a preform.

[0057] (3) The green blank was hot-pressed and sintered to obtain silicon nitride ceramics with both high thermal conductivity and high mechanical properties. The sintering parameters were as follows: room temperature to 900℃, heating time 1 h, pressure in vacuum environment; 900℃ to 1200℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1200℃ to 1400℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1400℃ to 1600℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1600℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere; 1600℃ to 1700℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1700℃ to 1800℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1800℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere. The sintering process of silicon nitride ceramics was carried out under a nitrogen atmosphere at 1800℃ to 1600℃ for 1 hour, with a pressure of 30 MPa under nitrogen atmosphere; the sintering process was carried out from 1600℃ to 1200℃ for 2 hours, with a pressure of 30 MPa under nitrogen atmosphere; and the sintering process was carried out from 1200℃ to room temperature for 3 hours, with no pressure.

[0058] Comparative Example 4 Compared with Example 9, the crystal phase inducer Yb4Si2O7N2 is not added in step (1).

[0059] 93 parts of α-Si3N4 powder, 5 parts of Yb2O3 powder and 2 parts of MgO powder were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent, and the amount of anhydrous ethanol added was 2 / 3 of the volume of the ball mill jar. Wet ball milling was carried out. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling speed was 300 r / min. To ensure uniform mixing, the ball milling time was 12 h.

[0060] The remaining methods are the same as in Example 9, to obtain silicon nitride ceramic, denoted as YbM.

[0061] Example 10 Preparation of silicon nitride ceramics: (1) 91 parts of α-Si3N4 powder, 5 parts of Yb2O3 powder, 2 parts of crystal phase inducer Yb4Si2O7N2 and 2 parts of MgSiN2 powder were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent. The amount of anhydrous ethanol added was 2 / 3 of the volume of the ball mill jar. Wet ball milling was carried out. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling speed was 300 r / min. To ensure uniform mixing, the ball milling time was 12 h.

[0062] (2) Place the ball mill slurry in a drying oven, evaporate to remove anhydrous ethanol, and then grind and sieve to obtain precursor powder.

[0063] The precursor powder is loaded into a mold and pressed into a disc using a tablet press at 10 MPa to obtain a preform.

[0064] (3) The green blank was hot-pressed and sintered to obtain silicon nitride ceramics with both high thermal conductivity and high mechanical properties. The sintering parameters were as follows: room temperature to 900℃, heating time 1 h, pressure in vacuum environment; 900℃ to 1200℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1200℃ to 1400℃, heating time 40 min, pressure 30 MPa, nitrogen atmosphere; 1400℃ to 1600℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1600℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere; 1600℃ to 1700℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1700℃ to 1800℃, heating time 1 h, pressure 30 MPa, nitrogen atmosphere; 1800℃, holding for 3 h, pressure 30 MPa, nitrogen atmosphere. The sintering process of silicon nitride ceramics was carried out under a nitrogen atmosphere at 1800℃ to 1600℃ for 1 hour, with a pressure of 30 MPa under nitrogen atmosphere; the sintering process was carried out from 1600℃ to 1200℃ for 2 hours, with a pressure of 30 MPa under nitrogen atmosphere; and the sintering process was carried out from 1200℃ to room temperature for 3 hours, with no pressure. The entire process was conducted under a nitrogen atmosphere, with a vacuum stage below 900℃ to ensure complete removal of impurities. After sintering, the ceramics were ground and sieved to obtain silicon nitride ceramics, denoted as YbMNYb.

[0065] Comparative Example 5 Compared with Example 10, the crystal phase inducer Yb4Si2O7N2 is not added in step (1).

[0066] 93 parts of α-Si3N4 powder, 5 parts of Yb2O3 powder and 2 parts of MgSiN2 powder were mixed and added to a planetary ball mill. Anhydrous ethanol was added as a dispersion solvent, and the amount of anhydrous ethanol added was 2 / 3 of the volume of the ball mill jar. Wet ball milling was carried out. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling speed was 300 r / min. To ensure uniform mixing, the ball milling time was 12 h.

[0067] The remaining methods are the same as in Example 10, to obtain silicon nitride ceramic, denoted as YbMN.

[0068] Figure 3 The XRD patterns of the silicon nitride ceramics prepared in Example 7 and Comparative Example 2 are shown below. Figure 4 The XRD patterns of the silicon nitride ceramics prepared in Example 8 and Comparative Example 3 are shown below. Figure 5 The XRD patterns of the silicon nitride ceramics prepared in Example 9 and Comparative Example 4 are shown. Figure 6 The XRD patterns of the silicon nitride ceramics prepared in Example 10 and Comparative Example 5 are shown below. from Figures 3-6 As can be seen, compared with silicon nitride ceramics prepared without the addition of crystal phase inducer RE4Si2O7N2, the diffraction peak positions and relative intensities of silicon nitride ceramics prepared with the addition of crystal phase inducer RE4Si2O7N2 are highly consistent with the standard phase data of RE4Si2O7N2, and no other impurity phase characteristic peaks appear. This comparison result shows that the addition of crystal phase inducer RE4Si2O7N2 has achieved the directional crystallization of the glass phase inside silicon nitride ceramics.

[0069] Figure 7 The graph shows the mechanical properties of the silicon nitride ceramics prepared in Examples 7-8 and Comparative Examples 2-3. Figure 7 As can be seen, compared with LM, LML's flexural strength, fracture toughness, and hardness are improved by 3.3%, 4.9%, and 2.8%, respectively. In the LMN and LMNL system, the improvement effect brought by adding the crystal phase inducer Lu4Si2O7N2 is more significant, with LMNL's flexural strength, fracture toughness, and hardness increasing by 24.3%, 4.9%, and 3.2% compared with LMN.

[0070] Figure 8 The graph shows the thermal conductivity test results of the silicon nitride ceramics prepared in Examples 7-8 and Comparative Examples 2-3. Figure 8 As can be seen, the addition of the crystal phase inducer Lu4Si2O7N2 can effectively improve the thermal conductivity of silicon nitride ceramics. LML improves by 20.7% compared to LM, and LMNL improves by 8.7% compared to LMN.

[0071] Figure 9 The figures show the mechanical properties of the silicon nitride ceramics prepared in Examples 9-10 and Comparative Examples 4-5. Compared to YbM, the flexural strength, fracture toughness, and hardness of YbMYb were increased by 3.5%, 4%, and 2.6%, respectively. In the YbMN and YbMNYb system, the improvement effect brought by the addition of the crystal phase inducer Yb4Si2O7N2 was more significant, with YbMNYb showing an increase of 14.7%, 2.5%, and 1.5% in flexural strength, fracture toughness, and hardness compared to YbMN.

[0072] Figure 10 The graph shows the thermal conductivity test results of the silicon nitride ceramics prepared in Examples 9-10 and Comparative Examples 4-5. Figure 10 As can be seen, the addition of the crystal phase inducer Yb4Si2O7N2 can effectively improve the thermal conductivity of silicon nitride ceramics. YbMYb improves by 9.8% compared to YbM, and YbMNYb improves by 5.7% compared to YbMN.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing silicon nitride ceramics with both high thermal conductivity and high mechanical properties, characterized in that, Includes the following steps: α-Si3N4 powder, sintering aid and crystal phase inducer RE4Si2O7N2 were mixed, wet ball milled, dried, ground and sieved to obtain precursor powder; Precursor powder is processed into a green body; Silicon nitride ceramics with both high thermal conductivity and high mechanical properties are obtained by hot pressing and sintering the green blank. In the crystal phase inducer RE4Si2O7N2, RE is selected from one or more of Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb or Lu.

2. The preparation method according to claim 1, characterized in that, The sintering aid is one or more of rare earth oxides, MgO, or MgSiN2. The rare earth elements in the rare earth oxides are the same as the REs in the crystal phase inducer RE4Si2O7N2. The rare earth elements are selected from one or more of Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb or Lu.

3. The preparation method according to claim 1, characterized in that, The preparation method of the crystal phase inducer RE4Si2O7N2 includes the following steps: α-Si3N4 powder, RE2O3 and SiO2 were mixed and then heat-treated in an oxygen-free atmosphere to obtain the crystal phase inducer RE4Si2O7N2. In RE2O3, RE is selected from one or more of Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb, or Lu.

4. The preparation method according to claim 3, characterized in that, The molar ratio of α-Si3N4 powder, RE2O3 and SiO2 is 1:4:

1.

5. The preparation method according to claim 3, characterized in that, The heat treatment temperature is 1600~1700℃, and the heat treatment time is 6~12 h.

6. The preparation method according to claim 3, characterized in that, The oxygen-free atmosphere includes nitrogen or rare gases.

7. The preparation method according to claim 1, characterized in that, The mass ratio of α-Si3N4 powder, sintering aid and crystal phase inducer RE4Si2O7N2 is (80~95):(5-10):(0.5~10).

8. The preparation method according to claim 1, characterized in that, Anhydrous ethanol is used as the dispersion solvent in the wet ball milling process.

9. The preparation method according to claim 1, characterized in that, Hot pressing sintering includes a first stage and a second stage; The first stage parameters are: heat preservation at 1200~1600℃ and 10~50 MPa for 1~4 h. The second stage parameters are: heat preservation at 1600~1900℃ and 10~50 MPa for 2~6 h.

10. A silicon nitride ceramic possessing both high thermal conductivity and high mechanical properties, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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