Double-phase silicon nitride ceramic as well as preparation method and application thereof

Abstract

The invention discloses a double-phase silicon nitride ceramic as well as a preparation method and application thereof. The double-phase silicon nitride ceramic comprises equiaxial alpha-Si3N4 and columnar beta-Si3N4 in a two-phase ratio of 1: (0.5-4), the preparation method comprises the following steps: in a protective atmosphere, mixing alpha-Si3N4 pure powder and a sintering aid, carrying out plasma ball milling, and sieving to obtain nano mixed powder; pre-sintering the nano mixed powder in a reducing atmosphere, and sieving to obtain pre-treated powder; and in an oxygen-free atmosphere, axially applying pressure to the pretreated powder, carrying out spark plasma sintering, and cooling to obtain the dual-phase silicon nitride ceramic. Alpha-phase and beta-phase silicon nitride with a certain proportion is prepared through one-time sintering forming, the silicon nitride has a fine and uniform microstructure, two crystal grains are uniformly distributed, and the hardness and the obdurability are high.

Description

Technical Field

[0001] The present invention relates to the technical field of structural ceramics, and in particular to a dual-phase silicon nitride ceramic and a preparation method and application thereof. Background Art

[0002] Silicon nitride ceramics, due to their excellent mechanical properties, thermal shock resistance, corrosion resistance, and high dielectric properties, have become the most widely used structural ceramic material in applications such as cutting tools, high-precision structural parts, smelting and metallurgy, nuclear industry seals, and aerospace components. However, harsh sintering conditions are often required to produce dense silicon nitride ceramic blocks, which limits their microstructure and properties.

[0003] At present, silicon nitride ceramics are single-phase silicon nitride, which usually has two crystal phases, one is the equiaxed α phase, and the other is the columnar β phase. After sintering and densification, silicon nitride is often dominated by β phase grains, and silicon nitride dominated by β phase has excellent toughness and strength, but low hardness. The reason for this performance is that the β phase grain morphology is usually long columnar. However, under the introduction of high pressure, dense silicon nitride can be sintered at a lower temperature, avoiding the occurrence of phase change and thus preparing pure α phase silicon nitride ceramics. Pure α phase silicon nitride with an equiaxed shape has very high hardness, but low strength and toughness. Therefore, for traditional single-phase silicon nitride ceramics, the simultaneous acquisition of hardness and toughness is contradictory.

[0004] Therefore, it is necessary to provide a technical solution for dual-phase silicon nitride to simultaneously improve the hardness and toughness of silicon nitride. Summary of the Invention

[0005] In view of this, the present application provides a dual-phase silicon nitride ceramic and its preparation method and application, which are used to solve the problem of how to simultaneously improve the hardness and toughness of silicon nitride.

[0006] In order to achieve the above technical objectives, this application adopts the following technical solutions: In a first aspect, the present application provides a dual-phase silicon nitride ceramic comprising equiaxed α-Si3N4 and columnar β-Si3N4 with a two-phase ratio of 1:0.5-4.

[0007] Preferably, the average diameter of the crystal grains is 80-300 nm.

[0008] In a second aspect, the present application provides a method for preparing a dual-phase silicon nitride ceramic, comprising the following steps: Under a protective atmosphere, pure α-Si3N4 powder and sintering aid are mixed, subjected to plasma ball milling, and sieved to obtain nano-mixed powder; Pre-sintering the nano-mixed powder in a reducing atmosphere and obtaining pre-treated powder after sieving; In an oxygen-free atmosphere, the pretreated powder is axially pressed and subjected to spark plasma sintering. After cooling, dual-phase silicon nitride ceramics are obtained.

[0009] Preferably, the axial pressure is 50-600 MPa; the oxygen-free atmosphere is a vacuum atmosphere with an absolute pressure of less than or equal to 50 Pa or an inert atmosphere with an absolute pressure of 0.01-10 MPa.

[0010] Preferably, the spark plasma sintering temperature is 1200-1700° C.; the heating rate is 5-500° C. / min; and the sintering time is 1-180 min.

[0011] Preferably, the ball-to-material ratio of plasma ball milling is (20-60):1, the ball milling time is 1-100 hours, and the protective atmosphere is a vacuum atmosphere or an inert atmosphere of 0.2-0.8 MPa.

[0012] Preferably, the particle size of the pure α-Si3N4 powder is 600-900 nm, and the particle size of the nano-mixed powder is 100-300 nm.

[0013] Preferably, the sintering aid comprises a mixture of Al2O3 and Y2O3; the mass ratio of α-Si3N4, Al2O3, and Y2O3 is (84-98): (1-8): (1-8).

[0014] Preferably, the pre-sintering temperature is 1200-1400° C.; the reducing atmosphere comprises an inert gas and hydrogen in a volume ratio of (90-95): (5-10).

[0015] In a third aspect, the present application provides an application of a dual-phase silicon nitride ceramic in the precision manufacturing of ceramic structural parts.

[0016] The beneficial effects of this application are as follows: First, the present invention utilizes plasma milling composite ball processing technology to produce particles with a finer and more evenly distributed particle size. Plasma further activates the particle surface, effectively improving the sintering performance of silicon nitride powder while preventing powder agglomeration, and enabling densification within the silicon nitride phase transition temperature range. Second, the present invention further improves powder quality by processing the powder at high temperatures in conjunction with plasma milling. After plasma milling, an amorphous phase and free silicon appear on the powder surface. The introduction of nitrogen at high temperatures removes these free silicon and amorphous phases, thereby suppressing the imbalance of silicon-oxygen ions in the liquid phase formed by the sintering aid and promoting the formation and growth of columnar grains.

[0017] Third, the present invention synergistically prepares dual-phase silicon nitride ceramics with equiaxed α-Si3N4 and columnar β-Si3N4 two-phase particles through the liquid-phase sintering mechanism formed by the solid phase under high pressure and the sintering aid. By adjusting the pressure and temperature process, the sintering window period of the eutectic microstructure can be obtained. The prepared silicon nitride ceramic block not only has high hardness, but also has excellent bending strength and fracture toughness.

[0018] Fourth, compared with the prior art, the present invention has lower requirements on the particle size of the original powder. The nano silicon nitride powder after plasma treatment has a large surface area and is not easy to agglomerate, which is conducive to the sintering and densification of silicon nitride ceramics, and provides a new way to prepare high-performance silicon nitride ceramics; compared with the prior art, the preparation method of the present invention is easy to implement, and the sintering equipment used is all general equipment.

[0019] Fifth, the high-performance dual-phase silicon nitride ceramics with both equiaxed and columnar crystal forms prepared in the present invention are made by one-step in-situ sintering, which is a simple process. The density, hardness, fracture toughness and strength of the silicon nitride ceramic material obtained in the present invention are all improved at the same time, with the hardness reaching up to 26GPa and the fracture toughness reaching up to 12 MPa·m 1 / 2 , the maximum flexural strength reaches 1450 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the α-Si3N4 powder after plasma ball milling used in Example 1; Figure 2 This is a scanning electron microscope morphology image of the dual-phase eutectic silicon nitride obtained in Example 1 after etching; Figure 3 This is a scanning electron microscope image of the cross section of the dual-phase eutectic silicon nitride prepared in Example 1; Figure 4 This is a scanning electron microscope morphology image of the high α-phase silicon nitride prepared in Comparative Example 2. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] The present application provides a dual-phase silicon nitride ceramic, comprising equiaxed α-Si3N4 and columnar β-Si3N4 with a two-phase ratio of 1:0.5-4.

[0023] α-Si3N4 belongs to the hexagonal system (P3 1cSpace group), its atomic arrangement is periodic stacking of Si-N tetrahedral chains along the c-axis direction. In the eutectic system, under rapid cooling or high-activity sintering conditions, the α phase tends to form equiaxed grains (approximately spherical) to minimize surface energy; β-Si3N4 also belongs to the hexagonal crystal system (P42 / nmc space group), but its atomic arrangement is that Si-N tetrahedrons form a three-dimensional network by sharing vertices, and the layers are connected by weak bonds. Unlike the α phase, the layered structure of the β phase is highly anisotropic, and the bonds along the c-axis direction (perpendicular to the basal plane) are weak, resulting in preferential growth along this direction. In the eutectic system, the β phase tends to form slender columnar grains through a dissolution-recrystallization mechanism to optimize the interfacial energy. In the dual-phase silicon nitride ceramic of the present application, both α phase and β phase silicon nitride exist, and a two-phase coexistence structure is formed by coordinated growth. The equiaxed morphology of the α phase provides mechanical stability, and the columnar morphology of the β phase enhances thermal conductivity and toughness, ultimately achieving a simultaneous improvement in the hardness and toughness of silicon nitride.

[0024] In some embodiments, the average diameter of the grains is 80-300 nm.

[0025] The present application provides a method for preparing a dual-phase silicon nitride ceramic, comprising the following steps: S1. Under a protective atmosphere, the α-Si3N4 pure powder and the sintering aid were mixed, plasma milled, and sieved to obtain a nano-mixed powder; S2. Pre-sintering the nano-mixed powder under a reducing atmosphere and sieving to obtain a pretreated powder; S3. In an oxygen-free atmosphere, the pretreated powder is axially pressed and subjected to spark plasma sintering. After cooling, a dual-phase silicon nitride ceramic is obtained.

[0026] The present invention prepares silicon nitride with a certain ratio of α-phase and β-phase by one-time sintering. The silicon nitride has a fine and uniform microstructure, uniform distribution of two-crystal grains, high density, high hardness, high strength and toughness. The hardness of the obtained silicon nitride ceramic is 21-26 GPa, and the fracture toughness of the silicon nitride ceramic is 9-12 MPa·m 1 / 2 , the flexural strength is 1100-1450 MPa.

[0027] In this application, a plasma ball mill is used to mix and ball-mill α-Si3N4 powder and sintering aids Al2O3 and Y2O3 to obtain a nano-mixed powder of Si3N4, Al2O3 and Y2O3 with uniform particle size. The mixed powder of Si3N4, Al2O3 and Y2O3 is then pretreated at high temperature to reduce the content of free silicon, and then spark plasma sintering is carried out under high pressure to perform partial phase transformation to obtain dual-phase silicon nitride ceramics.

[0028] In some embodiments, the axial pressure is 50-600 MPa; the oxygen-free atmosphere is a vacuum atmosphere with an absolute pressure of less than or equal to 50 Pa or an inert atmosphere with an absolute pressure of 0.01-10 MPa.

[0029] In some embodiments, the spark plasma sintering temperature is 1200-1700° C., the heating rate is 5-500° C. / min, and the sintering time is 1-180 min.

[0030] In this application, the pretreated powder is loaded into a high-strength mold for spark plasma sintering. The mold used can be the conventional SPS sintering mold type in the prior art, or various improved mold shapes. The present invention prepares eutectic high-hardness and high-toughness silicon nitride ceramics under higher axial pressure. The material of the mold can be adjusted according to the required pressure. For example, high-strength graphite, carbon fiber and other materials can be used to prepare a mold that can withstand greater pressure. It can be processed by itself or entrusted to a mold manufacturer for customization.

[0031] By adjusting the pressure and temperature process, the present invention can obtain a sintering window period of eutectic microstructure. The prepared silicon nitride ceramic block not only has high hardness, but also has excellent bending strength and fracture toughness.

[0032] In some embodiments, the ball-to-material ratio of plasma ball milling is (20-60):1, the ball milling time is 1-100 hours, and the protective atmosphere is a vacuum atmosphere or an inert atmosphere of 0.2-0.8 MPa.

[0033] During the sintering process, the selected powder particle size has low requirements for particle size and uniformity. After plasma ball milling, a nano-mixed powder with uniform particle size can be obtained. The plasma ball mill is produced by Guangdong Huaxin Materials Innovation Co., Ltd. The plasma vacuum ball milling tank is made of cemented carbide, and the ball milling medium used is cemented carbide balls.

[0034] The inert gas of the present application includes but is not limited to one or more of nitrogen, helium, argon and neon. The protective atmosphere, reducing atmosphere and oxygen-free atmosphere of the present application are beneficial to prevent oxidation of silicon nitride ceramics.

[0035] In some embodiments, the particle size of the pure α-Si 3 N 4 powder is 600-900 nm, and the particle size of the nano-mixed powder is 100-300 nm.

[0036] In some embodiments, the sintering aid includes a mixture of Al2O3 and Y2O3; the mass ratio of α-Si3N4, Al2O3, and Y2O3 is (84-98): (1-8): (1-8).

[0037] In the present application, the α-Si3N4 content of the Si3N4 powder is greater than or equal to 90%, and the purity of the sintering aids Al2O3 and Y2O3 is greater than or equal to 90%.

[0038] In some embodiments, the pre-sintering temperature is 1200-1400° C.; the reducing atmosphere includes an inert gas and hydrogen in a volume ratio of (90-95): (5-10).

[0039] The pre-sintering process is carried out in a tubular furnace. After pre-sintering, α-Si3N4-Al2O3-Y2O3 mixed powder is obtained. During pre-sintering, the pressure of the protective gas can be appropriately increased to prevent the decomposition of silicon nitride ceramics.

[0040] The present application provides an application of a dual-phase silicon nitride ceramic in the precision manufacturing of ceramic structural parts.

[0041] The present invention is further described below through specific examples.

[0042] Example 1 A dual-phase silicon nitride ceramic comprises equiaxed α-Si3N4 and columnar β-Si3N4 with a two-phase ratio of 1:2.

[0043] The preparation method of dual-phase silicon nitride ceramics is as follows: S1. Using α-Si3N4 powder (synthesized by silicon powder nitridation, particle size 800 nm, purity 95%) as the matrix raw material, Al2O3 and Y2O3 powders (purity 99.9%, particle size less than 800 nm) as sintering aids, the sintering process was carried out using a plasma ball mill with a ball-to-particle ratio of 30:1, with a mass fraction of 90% α-Si3N4 powder, 5% Al2O3 powder, and 5% Y2O3 powder. The mixture was milled using cemented carbide balls (6 mm in diameter) at a ball-to-particle ratio of 30:1. The mixture was sieved after 8 h in a plasma ball mill to obtain a nano-mixed powder. Figure 1 This is a scanning electron microscope image of the α-Si3N4 powder after plasma ball milling used in Example 1; S2. Place the nanocomposite powder in a tube furnace and introduce a nitrogen mixture into the furnace at 1300°C for 2 hours. After treatment, pass the powder through a 200-mesh sieve to obtain a uniform powder of Si₃N₄, Al₂O₃, and Y₂O₃, which is the pretreated powder. S3. The pre-sintered α-Si3N4-Al2O3-Y2O3 body was placed in a high-strength SPS mold. The mold was made of carbon fiber and consisted of a sleeve, an upper punch, and a lower punch. The sleeve had a diameter of 20 mm. Graphite paper was placed between the mold and the powder to facilitate demolding. Under an axial pressure of 200 MPa and a nitrogen atmosphere of 0.1 MPa, the temperature was raised to 1550°C at a rate of 150°C / min and maintained for 30 min. After cooling, the mold was removed to obtain a dual-phase silicon nitride ceramic. After sampling and testing, the relative density of the obtained dual-phase silicon nitride ceramics is 99.5% (relative to the theoretical density of 3.20 g / cm 3 The average grain diameter of the obtained dual-phase silicon nitride ceramics is 180 nm, the hardness of Si3N4 ceramics is 22 GPa, and the fracture toughness of Si3N4 is 12 MPa·m 1 / 2 , the flexural strength is 1450 MPa.

[0044] Example 2 A dual-phase silicon nitride ceramic comprises equiaxed α-Si3N4 and columnar β-Si3N4 with a two-phase ratio of 1:0.5.

[0045] The preparation method of dual-phase silicon nitride ceramics is as follows: S1. α-Si3N4 powder (synthesized by silicon nitridation, 900 nm particle size, 95% purity) was used as the matrix raw material, along with MgO and Y2O3 powders (99% purity, particle size less than 800 nm) as sintering aids. The Si3N4 powder mass fraction was 92%, the MgO and Y2O3 powder mass fractions were 5% and 3%, respectively, and cemented carbide balls (6 mm diameter) were used as the milling media, with a ball-to-powder mass ratio of 40:1. The mixture was milled in a plasma ball mill for 12 hours, and the resulting nanocomposite powder was sieved. S2. The nano-mixed powder was subjected to rotary evaporation and then introduced into a mixed gas (95% nitrogen, 5% hydrogen) in a 1300°C tube furnace. The treated powder was passed through a 200-mesh sieve to obtain a uniform powder of Si3N4, MgO, and Y2O3, i.e., the pretreated powder; S3. Place the pretreated powder into the SPS mold. The mold is made of carbon fiber material and includes a sleeve, an upper pressure head, and a lower pressure head. The diameter of the sleeve is 20 mm. Graphite paper is placed between the mold and the powder to facilitate demolding. Under the conditions of axial pressure of 260 MPa and nitrogen of 0.1 MPa, the temperature is raised to 1500 °C at a rate of 100 °C / min and kept warm for 40 min to produce dual-phase silicon nitride ceramics.

[0046] The relative density of the spherical grain high-strength and tough silicon nitride ceramics prepared in this example is 99.4% (relative to the theoretical density of 3.20 g / cm 3 The average grain diameter is 190 nm, the hardness of Si3N4 ceramics is 24 GPa, and the fracture toughness is 10 MPa·m 1 / 2 , the flexural strength is 1350MPa.

[0047] Example 3 A dual-phase silicon nitride ceramic comprises equiaxed α-Si3N4 and columnar β-Si3N4 with a two-phase ratio of 1:1.

[0048] The preparation method of dual-phase silicon nitride ceramics is as follows: S1. Si3N4, Al2O3, and Y2O3 powders were prepared from the same sources as in Example 1, with α-Si3N4 powder as the matrix raw material. The average particle size of the Si3N4 powder was 700 nm. Al2O3 and Y2O3 powders were used as sintering aids, with particle sizes less than 800 nm. The Si3N4 powder was milled at a mass fraction of 92%, Al2O3 at 5%, and Y2O3 at 3%, respectively. Carbide balls (6 mm diameter) were used as the milling media, with a ball-to-material ratio of 40:1. The mixed powders were milled in a plasma ball mill for 8 hours and then sieved to obtain a nano-mixed powder. S2. The mixed powder is introduced into a 1300°C tube furnace through a mixed gas (95% nitrogen, 5% hydrogen). After treatment, the powder is passed through a 200-mesh sieve to obtain a uniform powder of Si₃N₄, Al₂O₃, and Y₂O₃, i.e., the pretreated powder. S3. Place the pretreated powder into the SPS mold. The mold is made of carbon fiber material and includes a sleeve, an upper pressure head, and a lower pressure head. The diameter of the sleeve is 20 mm. Graphite paper is placed between the mold and the powder to facilitate demolding. Under the conditions of axial pressure of 200 MPa and nitrogen of 0.1 MPa, the temperature is raised to 1580 °C at a rate of 100 °C / min and kept warm for 30 min to produce dual-phase silicon nitride ceramics.

[0049] The relative density of the Si3N4 ceramic prepared in this example is 99.6% (relative to the theoretical density of 3.20 g / cm3). The average grain diameter is 300 nm, the hardness of the Si3N4 ceramic is 23 GPa, and the fracture toughness is 9 MPa·m 1 / 2 , the flexural strength is 1300MPa.

[0050] Comparative Example 1 A method for preparing silicon nitride ceramics is the same as that of Example 1 except that the pre-sintering temperature is 650° C. and the holding time is 2 h.

[0051] Comparative Example 2 A method for preparing silicon nitride ceramics, the other contents of which are the same as those of Example 1, except that step S2 is not included.

[0052] Comparative Examples 3-4 A method for preparing silicon nitride ceramics, the other contents are the same as those of Example 1, except that the axial pressure in step S3 is 20 MPa and 700 MPa respectively.

[0053] Comparative Examples 5-6 A method for preparing silicon nitride ceramics is the same as that of Example 1 except that, in step S3, the spark plasma sintering temperatures are 1000° C. and 1800° C., respectively.

[0054] Testing and Evaluation The microscopic morphologies of the silicon nitride ceramics obtained in the examples and comparative examples were identified. Figure 2 The microscopic morphology of the eutectic high-performance silicon nitride ceramic obtained in Example 1 after etching is shown in FIG. Figure 3 The cross-sectional microstructure of the eutectic high performance silicon nitride ceramic prepared in Example 1 is shown in FIG. Figure 2 and Figure 3 It can be seen that the black spherical grains in the photo are α-Si3N4, and the columnar and rod-shaped grains are β-Si3N4.

[0055] Figure 4 This is a scanning electron microscope image of the silicon nitride prepared in Comparative Example 2. Due to the lack of high-temperature nitriding treatment of the powder in a tube furnace, Comparative Example 2 results in an imbalance in the silicon-oxygen ion ratio in the liquid phase, which inhibits the growth of β-Si3N4 and significantly reduces the fracture toughness of the product.

[0056] The relative density, average diameter, ceramic hardness, fracture toughness and flexural strength of the silicon nitride ceramics obtained in different embodiments and comparative examples were tested. The results are shown in Table 1.

[0057] Relative density: Determined by ASTM C20 drainage method or ISO 18754 Archimedes principle, expressed as a percentage (relative to the theoretical density of 3.20 g / cm 3 percentage of ); Average grain size: calculated by X-ray diffraction (XRD) combined with Scherrer formula, or by microscope statistics according to ASTM E112 / ISO15743; Hardness: Tested according to ASTM E384 / ISO 6507 Vickers hardness method, loading range 1~120 kgf; fracture toughness (10 MPa·m 1 / 2 ) Using ASTM E1820 single-edge notched beam test (SENB) or indentation method, combined with elastic modulus and crack size calculation; Flexural strength: Complies with ASTM C1161 three-point bending.

[0058] Table 1 Test results

[0059] Test results show that the silicon nitride ceramics prepared in this application achieve both hardness and toughness. However, the lack of a pre-sintering step or improper pressure and temperature control during sintering negatively impacts the hardness or toughness of the silicon nitride ceramics, and the dual-phase silicon nitride ceramics of this application cannot be obtained. Comparative Example 5, in particular, was prepared at too low a temperature to achieve a dense sintering result, and no performance data is available.

[0060] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A dual-phase silicon nitride ceramic, characterized in that: It includes equiaxed α-Si3N4 and columnar β-Si3N4 with a two-phase ratio of 1:0.5-4.

2. The dual-phase silicon nitride ceramic according to claim 1, characterized in that The average diameter of its grains is 80-300nm.

3. A method for preparing the dual-phase silicon nitride ceramic according to any one of claims 1 to 2, characterized in that: The following steps are involved: Under a protective atmosphere, pure α-Si3N4 powder and sintering aid are mixed, subjected to plasma ball milling, and sieved to obtain nano-mixed powder; Pre-sintering the nano-mixed powder under a reducing atmosphere, and sieving to obtain pre-treated powder; In an oxygen-free atmosphere, the pretreated powder is axially pressed and subjected to spark plasma sintering. After cooling, the dual-phase silicon nitride ceramic is obtained.

4. The method for preparing the dual-phase silicon nitride ceramic according to claim 3, wherein: The axial pressure is 50-600 MPa; the oxygen-free atmosphere is a vacuum atmosphere with an absolute pressure less than or equal to 50 Pa or an inert atmosphere with an absolute pressure of 0.01-10 MPa.

5. The method for preparing the dual-phase silicon nitride ceramic according to claim 3, wherein: The spark plasma sintering temperature is 1200-1700° C.; the heating rate is 5-500° C. / min; and the sintering time is 1-180 min.

6. The method for preparing the dual-phase silicon nitride ceramic according to claim 3, wherein: The ball-to-material ratio of the plasma ball mill is (20-60):1, and the ball milling time is 1-100 hours; the protective atmosphere is a vacuum atmosphere or an inert atmosphere of 0.2-0.8 MPa.

7. The method for preparing the dual-phase silicon nitride ceramic according to claim 3, wherein: The particle size of the pure α-Si3N4 powder is 600-900 nm, and the particle size of the nano-mixed powder is 100-300 nm.

8. The method for preparing the dual-phase silicon nitride ceramic according to claim 3, wherein: The sintering aid includes a mixture of Al2O3 and Y2O3; the mass ratio of the α-Si3N4, Al2O3, and Y2O3 is (84-98): (1-8): (1-8).

9. The method for preparing the dual-phase silicon nitride ceramic according to claim 3, wherein: The pre-sintering temperature is 1200-1400° C.; the reducing atmosphere comprises an inert gas and hydrogen in a volume ratio of (90-95): (5-10).

10. Use of the dual-phase silicon nitride ceramic obtained by the preparation method according to any one of claims 3 to 9 in the precision manufacturing of ceramic structural parts.

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