High-strength silicon nitride ceramic, method for preparing same, and use thereof

Abstract

The application relates to a high-strength silicon nitride ceramic, a preparation method and application thereof, and belongs to the technical field of advanced structural ceramic materials. The silicon nitride ceramic has a radial and axial double gradient structure. The radial gradient structure is that the content of an intergranular amorphous phase is gradually decreased from 8-15 vol% to 1-5 vol% from the central axis to the outer profile surface. The axial gradient structure is that the content of an intergranular crystalline phase is gradually increased from 2-6 vol% to 10-18 vol% from the first end surface to the second end surface. The high-strength silicon nitride ceramic has excellent bending strength and fracture toughness. The high-strength silicon nitride ceramic is suitable for fields such as high-performance bearings, gas turbine blades and armor protection materials.

Description

Technical Field

[0001] This application belongs to the field of ceramic materials, specifically relating to a high-strength silicon nitride ceramic, its preparation method, its application, and its application. Background Technology

[0002] Traditional homogeneous silicon nitride ceramics have certain limitations in terms of overall mechanical properties, reliability, and lifespan. The mechanical properties of silicon nitride ceramics are mainly determined by their microstructure, especially grain size, type, content, and distribution of grain boundary phases. Studies have shown that the presence of intergranular amorphous phases significantly reduces the high-temperature strength and creep resistance of materials, while the formation of crystalline phases helps to improve the thermal conductivity and fracture toughness of materials. However, in existing technologies, the control of grain boundary phases usually depends on the selection of sintering aids and subsequent heat treatment processes, making it difficult to achieve a spatial gradient distribution of grain boundary phases. Summary of the Invention

[0003] This application addresses the technical problems of existing silicon nitride ceramics in terms of grain boundary phase control and performance uniformity, and provides a high-strength silicon nitride ceramic with radial and axial gradient structures, its preparation method and application. By utilizing the differentiated migration behavior of sintering aids, the spatial distribution of intergranular amorphous phase and crystalline phase is controlled, thereby synergistically improving the strength of the material.

[0004] The objective of this application can be achieved through the following technical solutions.

[0005] In a first aspect of this application, a high-strength silicon nitride ceramic is provided, the high-strength silicon nitride ceramic having a radial gradient structure and an axial gradient structure: The radial gradient structure is characterized by a gradient decrease in the content of intergranular amorphous phase from 8-15 vol% of the total volume to 1-5 vol% from the central axis towards the outer contour surface. The axial gradient structure is such that, from the first end face to the second end face, the content of the intergranular crystalline phase gradually increases from 2-6 vol% of the total volume to 10-18 vol%.

[0006] In some embodiments, the mass ratio of alkaline earth elements to rare earth elements increases continuously from the geometric central axis toward the outer contour surface; wherein, the mass ratio of alkaline earth elements to rare earth elements at the geometric central axis is 0.1 to 0.5, and the mass ratio of alkaline earth elements to rare earth elements at the outer contour surface is 1.5 to 4.0.

[0007] In some embodiments, the high-strength silicon nitride ceramic satisfies at least one of the following conditions: The high-strength silicon nitride ceramic has a Weibull modulus ≥ 20; The high-strength silicon nitride ceramic has a flexural strength of 1300 MPa to 1500 MPa; The high-strength silicon nitride ceramic has a fracture toughness of 7 MPa·m. 1 / 2 ~12 MPa·m 1 / 2 ; The diameter of the β-phase grains in the high-strength silicon nitride ceramic is 800 nm to 2 μm, and the length is 5 μm to 10 μm.

[0008] In some embodiments, the intercrystalline amorphous phase includes a silicate glass phase, and the intercrystalline crystalline phase includes at least one crystalline compound selected from Y2Si3O3N4, Y4Si2O7N2, and MgSiN2.

[0009] In a second aspect of this application, a method for preparing the aforementioned high-strength silicon nitride ceramic is provided, comprising the following steps: α-Si3N4 powder, a first sintering aid, and a second sintering aid are mixed to obtain a mixed raw material; After the mixed raw materials are shaped, they are subjected to gas pressure sintering under a nitrogen atmosphere to obtain high-strength silicon nitride ceramics. The first sintering aid includes alkaline earth oxides, and the second sintering aid includes alumina and rare earth oxides; the gas pressure sintering temperature is 1700~1900 ℃, the heating rate is 20~50℃ / min, the gas pressure sintering pressure is 6~10 MPa, and the gas pressure sintering time is 1~3h.

[0010] The preparation method described in this application utilizes the high migration rate of alkaline earth oxides during sintering, combined with the relatively stable distribution behavior of rare earth oxides. Under the synergistic effect of temperature and pressure fields, the sintering aids are directionally migrated from the interior of the material to the outer contour surface and end face, thereby forming a gradient distribution of grain boundary phase structure in the radial and axial directions.

[0011] In some embodiments, the preparation method satisfies at least one of the following conditions: The first sintering aid includes MgO and / or CaO; The mass ratio of rare earth oxides to Al2O3 in the second sintering aid is 1:1 to 3:1; The oxygen content of the α-Si3N4 powder is ≤1.2 wt%; The average particle size of the α-Si3N4 powder is 0.3 μm to 0.6 μm; Preferably, the first sintering aid accounts for 1 to 5 wt% of the total mass of the mixed raw materials, and the second sintering aid accounts for 3 to 8 wt% of the total mass of the mixed raw materials.

[0012] Preferably, the particle size D of the α-Si3N4 is... 50 The particle size D of the first sintering aid is 100~500 nm. 50 The particle size D of the second sintering aid is 30~50 nm. 50 The wavelength is 30~50nm.

[0013] This application employs a pressure furnace for sintering, ensuring that the silicon nitride ceramic is subjected to the same pressure in all directions under dense conditions. This allows the sintering aid to diffuse freely according to its own migration rate, without being hindered by sudden forces in any direction. Simultaneously, the relatively large silicon nitride raw material and the relatively small sintering aid raw material facilitate the diffusive diffusion of the sintering aid after it forms a liquid phase.

[0014] In a third aspect of this application, the above-mentioned high-strength silicon nitride ceramic is provided for use in high-performance bearings and gas turbine blades.

[0015] In a fourth aspect of this application, the application of the aforementioned high-strength silicon nitride ceramic in armor protection materials is provided.

[0016] The beneficial effects of this application include: (1) For the first time, a dual-gradient microstructure design with radial and axial gradients was simultaneously achieved in silicon nitride ceramics, forming a spatial complementary distribution of intercrystalline amorphous phase and crystalline phase, which significantly improves the comprehensive mechanical properties of silicon nitride ceramic materials.

[0017] (2) By utilizing the difference in migration rate of sintering aids, the gradient structure can be constructed in one step through the gas pressure sintering process. No complicated multi-step processing is required. The process is highly controllable and suitable for industrial production.

[0018] (3) The obtained silicon nitride ceramic has high strength, high fracture toughness and good microstructure uniformity, which meets the stringent requirements of high reliability of structural ceramic materials for high-end equipment. Attached Figure Description

[0019] Figure 1 The images are XRD patterns of Examples 1-5 and Comparative Example 2 in this application. Detailed Implementation

[0020] The following detailed description, with appropriate reference to the accompanying drawings, discloses a high-strength silicon nitride ceramic, its preparation method, and embodiments of its application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0021] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. The range defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range.

[0022] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0023] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0024] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0025] Traditional sintering processes, such as pressureless sintering, hot pressing, or gas-pressure sintering, can achieve material densification, but they still have limitations in controlling sintering aid migration, grain boundary phase distribution, and grain growth solely by regulating the sintering process. Especially in large-sized or complex-shaped components, the uneven distribution of sintering aids often leads to inconsistencies in material properties, affecting the overall structural reliability. This application achieves a silicon nitride ceramic material with a spatial gradient distribution of grain boundary phases, balancing high strength, toughness, and high reliability, and its efficient preparation method.

[0026] α-Si3N4 powder, a first sintering aid, and a second sintering aid are mixed to obtain a mixed raw material; After the mixed raw materials are shaped, they are subjected to gas pressure sintering under a nitrogen atmosphere to obtain high-strength silicon nitride ceramics. The sintering temperature is 1700~1900 ℃, the heating rate is 20~50℃ / min, the sintering pressure is 6~10 MPa, and the sintering time is 1~3h; The first sintering aid includes alkaline earth oxides, and the second sintering aid includes alumina and rare earth oxides; The migration rate of the first sintering aid during the sintering process is greater than that of the second sintering aid.

[0027] The first sintering aid accounts for 1 to 5 wt% of the total mass of the mixed raw materials, and the second sintering aid accounts for 3 to 8 wt% of the total mass of the mixed raw materials.

[0028] The particle size D of the α-silicon nitride 50 The particle size D of the sintering aid is 100~500 nm. 50 The wavelength is 30~50nm.

[0029] Example 1 Provide α-Si3N4 powder (D 50 =500 nm), MgO (D 50 =50 nm), Y2O3 (D 50 =50 nm) and Al2O3 (D 50 A mixed raw material (with a particle size of 50 nm) was prepared, wherein the content of MgO was 3 wt%, the content of Y2O3 was 5 wt%, and the content of Al2O3 was 2 wt%. The mixed raw material was ball-milled and then the green body was prepared by dry pressing combined with cold isostatic pressing. The green body was placed in a gas pressure sintering furnace and sintered under a nitrogen atmosphere at a sintering temperature of 1800 ℃, a heating rate of 30 ℃ / min, a sintering pressure of 8 MPa, and a holding time of 2 h, to obtain high-strength silicon nitride ceramic.

[0030] The high-strength silicon nitride ceramic prepared in this embodiment (its first end face phase is as follows) Figure 1 The XRD pattern shows that the α and β phases are roughly equal in content. Its radial gradient structure exhibits a decreasing content of intergranular amorphous phase from 12 vol% to 3 vol% from the central axis towards the outer contour surface; the axial gradient structure shows an increasing content of intergranular crystalline phase from 4 vol% to 15 vol% from the first end face to the second end face. The material has a flexural strength of 1420 MPa and a fracture toughness of 9.5 MPa·m. 1 / 2 The β phase grain size is 1.2 μm in diameter and 7.5 μm in length (the performance characteristics are summarized in Table 1).

[0031] Example 2 Provide α-Si3N4 powder (D 50 =500 nm), CaO (D 50 =50 nm) and Yb2O3 (D 50 =50 nm) and Al2O3 (D 50A mixed raw material (with a particle size of 50 nm) containing 2 wt% CaO, 4 wt% Yb₂O₃, and 3 wt% Al₂O₃ was prepared by ball milling. The raw material was then used to prepare a green body by a combination of dry pressing and cold isostatic pressing. The green body was placed in a pneumatic sintering furnace and sintered under a nitrogen atmosphere at a temperature of 1750 ℃, a heating rate of 40 ℃ / min, a sintering pressure of 7 MPa, and a holding time of 2.5 h, yielding high-strength silicon nitride ceramic.

[0032] The high-strength silicon nitride ceramic prepared in this embodiment (its first end face phase is as follows) Figure 1 The XRD pattern shows that the α and β phases are roughly equal in content. Its radial gradient structure exhibits a decreasing content of intergranular amorphous phase from 10 vol% to 2 vol% from the central axis towards the outer contour surface; the axial gradient structure shows an increasing content of intergranular crystalline phase from 3 vol% to 14 vol% from the first end face to the second end face. The material has a flexural strength of 1380 MPa and a fracture toughness of 10.2 MPa·m. 1 / 2 The β phase grain size is 1.0 μm in diameter and 6.8 μm in length (the performance characteristics are summarized in Table 1).

[0033] Example 3 Provide α-Si3N4 powder (D 50 =500 nm), MgO (D 50 =50 nm), Yb2O3 (D 50 =50 nm), Gd2O3 (D 50 =50nm) and Al2O3 (D 50 A mixed raw material (with a particle size of 50 nm) was prepared, wherein the content of MgO was 4 wt%, Yb2O3 was 2 wt%, Gd2O3 was 2 wt%, and Al2O3 was 3.5 wt%. The mixed raw material was ball-milled and then the green body was prepared by dry pressing combined with cold isostatic pressing. The green body was placed in a gas pressure sintering furnace and sintered under a nitrogen atmosphere at a sintering temperature of 1850 ℃, a heating rate of 25 ℃ / min, a sintering pressure of 9 MPa, and a holding time of 1.5 h, to obtain high-strength silicon nitride ceramic.

[0034] The high-strength silicon nitride ceramic prepared in this embodiment (its first end face phase is as follows) Figure 1The XRD pattern shows that the α and β phases are roughly equal in content. Its radial gradient structure exhibits a decreasing content of intergranular amorphous phase from 14 vol% to 4 vol% from the central axis towards the outer contour surface; the axial gradient structure shows an increasing content of intergranular crystalline phase from 5 vol% to 16 vol% from the first end face to the second end face. The material has a flexural strength of 1450 MPa and a fracture toughness of 8.9 MPa·m. 1 / 2 The β phase grain size is 1.5 μm in diameter and 8.2 μm in length (the performance characteristics are summarized in Table 1).

[0035] Example 4 Except that the MgO content in the sintering aid is 5 wt% and the Y2O3 content is 3 wt%, the other steps and conditions are the same as in Example 1.

[0036] The high-strength silicon nitride ceramic prepared in this embodiment (its first end face phase is as follows) Figure 1 The XRD pattern shows that the α-phase and β-phase contents are roughly equal. In its radial gradient structure, the content of intergranular amorphous phase decreases from 13 vol% to 2 vol%; in its axial gradient structure, the content of intergranular crystalline phase increases from 3 vol% to 14 vol%. The material has a flexural strength of 1350 MPa and a fracture toughness of 11.0 MPa·m. 1 / 2 The β phase grain size is 0.9 μm in diameter and 6.2 μm in length (the performance characteristics are summarized in Table 1).

[0037] Example 5 Except for the sintering pressure of 10 MPa, the sintering temperature of 1700 ℃, and the holding time of 3 h, the other steps and conditions are the same as in Example 1.

[0038] The high-strength silicon nitride ceramic prepared in this embodiment (its first end face phase is as follows) Figure 1 The XRD pattern shows that the α-phase and β-phase contents are roughly equal. In its radial gradient structure, the content of intergranular amorphous phase decreases from 9 vol% to 1.5 vol%; in its axial gradient structure, the content of intergranular crystalline phase increases from 2.5 vol% to 13 vol%. The material has a flexural strength of 1310 MPa and a fracture toughness of 9.8 MPa·m. 1 / 2 The β phase grain size is 0.8 μm in diameter and 5.5 μm in length (the performance characteristics are summarized in Table 1).

[0039] Comparative Example 1 Except for the use of a single sintering aid Y2O3 (content of 5 wt%), the other steps and conditions are the same as in Example 1.

[0040] The silicon nitride ceramic prepared in this comparative example exhibits no obvious radial and axial gradient structure, a uniform distribution of intergranular amorphous phase (approximately 10 vol%), and a low content of crystalline phase (approximately 3 vol%). The material has a flexural strength of 1100 MPa and a fracture toughness of 6.5 MPa·m. 1 / 2 (The performance characteristics are summarized in Table 1).

[0041] Comparative Example 2 Except for the sintering temperature of 1650 ℃ and the sintering pressure of 3 MPa, the other steps and conditions are the same as in Example 1.

[0042] The silicon nitride ceramic prepared in this comparative example has insufficient density, high and uniformly distributed intergranular amorphous phase content, and fails to form an effective gradient structure (its first end face phase is as follows). Figure 1 The XRD pattern shows that the α-phase and β-phase contents are roughly equal. The material has a flexural strength of 980 MPa and a fracture toughness of 5.8 MPa·m. 1 / 2 This indicates a significant decrease in its mechanical properties (the performance characteristics are summarized in Table 1).

[0043] Performance testing methods The content of intergranular amorphous phase in silicon nitride ceramics; the mass ratio of alkaline earth elements to rare earth elements in silicon nitride ceramics: the content of each element and phase was detected by micro-area XRD from the inner part of the central axis to the outer contour.

[0044] Flexural strength of silicon nitride ceramics: The flexural strength of silicon nitride ceramics was tested using a universal testing machine in accordance with the standard GB / T 6569-2006.

[0045] Fracture toughness of silicon nitride ceramics: A hardness tester was used to pre-create cracks under a load of 1 kgf, and the fracture toughness of silicon nitride ceramics was calculated based on the crack length.

[0046] The diameter of the β-phase grains in silicon nitride ceramics; the length of the β-phase grains in silicon nitride ceramics; the average particle size of α-Si3N4 powder; and the particle size of the sintering aid: their specific dimensions were measured using SEM morphology images.

[0047] Table 1 Summary of performance index data for each embodiment and comparative example

[0048] This application utilizes the difference in migration rates between alkaline earth and rare earth sintering aids during gas pressure sintering, combined with optimized sintering process parameters, to achieve a controllable gradient distribution of intergranular amorphous and crystalline phases in the radial and axial directions. This dual-gradient structure fully leverages the spatial complementary effect of grain boundary phases, improving material strength while maintaining high fracture toughness, and significantly enhancing the mechanical properties and microstructural uniformity of silicon nitride ceramics.

[0049] The embodiments herein do not exhaustively cover the points not covered by the technical scope claimed in this application, and new technical solutions formed by equivalent substitutions of one or more technical features in the technical solutions of the embodiments are also within the scope of protection claimed in this application. At the same time, in all the listed or unlisted embodiments of the solution in this application, each parameter in the same embodiment merely represents an instance of its technical solution (i.e., a feasible solution), and there is no strict matching or limiting relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this application, unless otherwise stated.

[0050] The technical means disclosed in this application are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered within the scope of protection of this application.

[0051] The specific embodiments described herein are merely illustrative examples of the spirit of this application. Those skilled in the art to which this application pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of this application or exceeding the scope defined by the appended claims.

Claims

1. A high-strength silicon nitride ceramic, characterized in that, The high-strength silicon nitride ceramic has a radial gradient structure and an axial gradient structure; The radial gradient structure is characterized by a gradient decrease in the content of intergranular amorphous phase from 8-15 vol% of the total volume to 1-5 vol% from the central axis towards the outer contour surface. The axial gradient structure is such that, from the first end face to the second end face, the content of the intergranular crystalline phase gradually increases from 2-6 vol% of the total volume to 10-18 vol%.

2. The high-strength silicon nitride ceramic according to claim 1, characterized in that, From the geometric central axis toward the outer contour surface, the mass ratio of alkaline earth elements to rare earth elements shows a continuous gradient increasing distribution; among them, the mass ratio of alkaline earth elements to rare earth elements at the geometric central axis is 0.1~0.5, and the mass ratio of alkaline earth elements to rare earth elements at the outer contour surface is 1.5~4.

0.

3. The high-strength silicon nitride ceramic according to claim 1, characterized in that, The high-strength silicon nitride ceramic satisfies at least one of the following conditions: The high-strength silicon nitride ceramic has a Weibull modulus ≥ 20; The high-strength silicon nitride ceramic has a flexural strength of 1300 MPa to 1500 MPa; The high-strength silicon nitride ceramic has a fracture toughness of 7 MPa·m. 1 / 2 ~12 MPa·m 1 / 2 ; The diameter of the β-phase grains in the high-strength silicon nitride ceramic is 800 nm to 2 μm, and the length is 5 μm to 10 μm.

4. The high-strength silicon nitride ceramic according to claim 1, characterized in that, The intercrystalline amorphous phase includes a silicate glass phase, and the intercrystalline crystalline phase includes at least one crystalline compound selected from Y2Si3O3N4, Y4Si2O7N2, and MgSiN2.

5. A method for preparing high-strength silicon nitride ceramic as described in any one of claims 1 to 4, characterized in that, Includes the following steps: α-Si3N4 powder, a first sintering aid, and a second sintering aid are mixed to obtain a mixed raw material. After the mixed raw materials are shaped, they are subjected to gas pressure sintering under a nitrogen atmosphere to obtain high-strength silicon nitride ceramics. The first sintering aid includes alkaline earth oxides, and the second sintering aid includes alumina and rare earth oxides; the gas pressure sintering temperature is 1700~1900 ℃, the heating rate is 20~50℃ / min, the gas pressure sintering pressure is 6~10 MPa, and the gas pressure sintering time is 1~3h.

6. The method according to claim 5, characterized in that, At least one of the following conditions must be met: The first sintering aid includes MgO and / or CaO; The mass ratio of rare earth oxides to alumina in the second sintering aid is 1:1 to 3:1; The rare earth oxides include at least one of Yb2O3, Y2O3, and Gd2O3; The oxygen content of the α-Si3N4 powder is ≤1.2 wt%; The average particle size of the α-Si3N4 powder is 0.3 μm to 0.6 μm.

7. The method according to claim 5, characterized in that, At least one of the following conditions must be met: The first sintering aid accounts for 1 to 5 wt% of the total mass of the mixed raw materials; The second sintering aid accounts for 3 to 8 wt% of the total mass of the mixed raw materials.

8. The method according to claim 5, characterized in that, At least one of the following conditions must be met: The particle size D of the α-Si3N4 powder 50 The range is 100~500nm; The particle size D of the first sintering aid 50 30~50nm; The particle size D of the second sintering aid 50 The wavelength is 30~50nm.

9. The application of a high-strength silicon nitride ceramic as described in any one of claims 1-4 or a high-strength silicon nitride ceramic obtained by the preparation method described in any one of claims 5-8 in high-performance bearings and gas turbine blades.

10. The application of a high-strength silicon nitride ceramic as described in any one of claims 1-4 or a high-strength silicon nitride ceramic obtained by the preparation method described in any one of claims 5-8 in armor protection materials.

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