Ceramic ball with controllable growth of long columnar beta-Si3N4 crystal grains and preparation method of ceramic ball

Abstract

The invention relates to a long-column-shaped beta-Si3N4 crystal grain controllable growth ceramic ball material and a preparation method of the long-column-shaped beta-Si3N4 crystal grain controllable growth ceramic ball material. The material is prepared by taking alpha-Si3N4 powder as a matrix and adding beta-Si3N4 seed crystal and a composite sintering aid in a specific proportion through a multi-stage air pressure sintering process. The formula comprises the following components in parts by weight: 80-95 parts of alpha-Si3N4 powder, 1-20 parts of beta-Si3N4 seed crystal and 3-10 parts of a composite sintering aid, wherein the composite sintering aid consists of R2O3 (R is at least one of Y, Ce and Lu) and Al2O3. Through seed crystal induction and sintering process control, controllable growth of the size, the length-diameter ratio and the spatial distribution of long columnar beta-Si3N4 crystal grains in the ceramic ball is realized, and the prepared silicon nitride ceramic ball has excellent performances of high toughness, high strength, long service life and the like; and the method is suitable for high-end equipment fields such as high-speed bearings, precision machine tools and wind power generation equipment.

Description

Technical Field

[0001] This invention belongs to the field of high-performance structural ceramics technology, specifically relating to a ceramic ball with controllable growth of long columnar β-Si3N4 grains and its formulation, which is particularly suitable for manufacturing high-performance silicon nitride ceramic bearing balls. Background Technology

[0002] Silicon nitride ceramics, due to their excellent properties such as low density, high strength, high temperature resistance, corrosion resistance, and fatigue resistance, have become an ideal material for manufacturing high-speed precision bearing balls. Of the two crystal phases in silicon nitride ceramics, the α phase is equiaxed, and the β phase is long columnar. Studies have shown that long columnar β-Si3N4 grains can significantly improve the fracture toughness of ceramics through bridging, crack deflection, and pull-out mechanisms, creating a so-called "self-toughening" effect.

[0003] Currently, various technologies have been explored to optimize the microstructure and properties of silicon nitride ceramics. For example, patent CN201510992624.0 proposes a method for preparing high-performance Si3N4 gradient ceramic spheres with a hard surface and tough core. This method involves adding β-Si3N4 seed crystals and Al2O3-R2O3 as sintering aids to the core, and adding AlN and Al2O3-R2O3 as sintering aids to the surface, thus preparing ceramic spheres with a gradient structure. Another study used β-Si3N4 as seed crystals, α-Si3N4 as raw material, and the MgO-Al2O3-SiO2 system as sintering aids to prepare porous silicon nitride ceramics with a porosity of approximately 30%. It was found that adding β-Si3N4 seed crystals effectively promotes the conversion of α-Si3N4 to β-Si3N4.

[0004] However, existing technologies still have the following problems: (1) Uncontrollable grain structure: The size, aspect ratio and spatial distribution of β-Si3N4 grains are difficult to control precisely, resulting in unstable material properties; (2) Insufficient mechanical properties: The toughness, strength and hardness of ceramic balls are difficult to optimize at the same time, which limits their application in high-end equipment; (3) Imperfect sintering process: Traditional sintering process cannot effectively promote the full growth and directional arrangement of long columnar β-Si3N4 grains.

[0005] Therefore, developing a high-performance silicon nitride ceramic ball material capable of achieving controllable growth of long columnar β-Si3N4 grains has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a ceramic ball with controllable growth of long columnar β-Si3N4 grains and its preparation method, which solves the problems of uncontrollable microstructure and insufficient mechanical properties of silicon nitride ceramic balls in the prior art.

[0007] The technical solution of the present invention is as follows: 1. Formulation Design The ceramic ball material of this invention is composed of the following raw materials: a. α-Si3N4 powder: 80-95 parts by weight, used as a matrix material, with an α phase content greater than 95% and an average particle size of 0.5-1.5 μm; b. β-Si3N4 seed crystal: 1-20 parts by weight, as a nucleation center, to induce α→β phase transformation and control grain growth, with β phase content greater than 98%, exhibiting a long columnar single crystal structure, with a diameter of 0.5-2 μm, a length of 3-10 μm, and an aspect ratio of 3:1 to 20:1; c. Composite sintering aid: 3-10 parts by weight, composed of R2O3 (R is at least one of Y, Ce, Lu), Al2O3 and Fe2O3, in a mass ratio of (20-80):(20-80):(5-40).

[0008] 2. Raw materials, parts by weight, and performance requirements a. 80-95 parts by weight of α-Si3N4 powder, α phase content >95%, average particle size 0.5-1.5 μm; b. 1-20 parts by weight of β-Si3N4 seed crystals, β phase content >98%, diameter 0.5-2 μm, length 3-10 μm; c. 3-10 parts by weight of composite sintering aid, R2O3:Al2O3:Fe2O3=(20-80):(20-80):(0.1-5).

[0009] 3. Preparation method The method for preparing the ceramic ball material of the present invention includes the following steps: a. Mixing: Place α-Si3N4 powder, β-Si3N4 seed crystals and composite sintering aid into a planetary ball mill in proportion, use silicon nitride balls as the ball milling medium, and ball mill in anhydrous ethanol solvent for 8-24 h to make the raw materials uniformly mixed; b. Molding: The mixed powder is formed by hydraulic pressing at a pressure of 3-10 MPa, and then made uniform and dense by cold isostatic pressing at a pressure of 150-300 MPa; c. Sintering: The spherical blank is subjected to multi-stage gas pressure sintering: First stage: Under vacuum, the temperature is increased to 1400-1500 ℃ at 5-10 ℃ / min and held for 0.5-2 h to complete degreasing and partial α→β ​​phase transformation; Second stage: Under nitrogen atmosphere, the temperature is increased to 1600-1700 ℃ at 3-8 ℃ / min and held for 1-3 h to promote α→β phase transformation and grain growth; Third stage: Under nitrogen atmosphere, the temperature is increased to 1750-1850 ℃ at 2-5 ℃ / min and held for 2-6 h to allow the long columnar β-Si3N4 grains to grow fully and form an interlocking structure; d. Machining: Precision machining of the sintered ceramic balls to achieve the required dimensional accuracy and surface finish.

[0010] 4. Microstructure control Through the above formula and process, this invention achieves the controllable growth of long columnar β-Si3N4 grains inside ceramic spheres: a. Seed induction: The added β-Si3N4 seed crystals serve as nucleation centers, inducing the α→β phase transformation to grow along a specific crystal orientation; b. Liquid phase sintering: The composite sintering aid forms a liquid phase at high temperature, which promotes material transport and grain growth; c. Process control: Multi-stage sintering process precisely controls phase transformation and grain growth.

[0011] In the final obtained ceramic sphere material, the average diameter of the long columnar β-Si3N4 grains is 0.5-3 μm, the average length is 5-25 μm, and the aspect ratio is 5:1 to 25:1, forming a dense interlocking network structure.

[0012] Advantages of this invention: Compared with the prior art, the present invention has the following advantages: 1. Controllable microstructure: Through the synergistic effect of β-Si3N4 seed crystals and sintering process, the size, aspect ratio and spatial distribution of long columnar β-Si3N4 grains were controlled. 2. Excellent mechanical properties: The interlocking structure formed by the long columnar β-Si3N4 grains significantly improves the fracture toughness of the material (7-12 MPa·m¹ / ²), while maintaining high hardness (14-16 GPa) and bending strength (800-1200 MPa). 3. Stable and reliable process: The multi-stage gas pressure sintering process is conducive to the full growth of long columnar β-Si3N4 grains, which improves the consistency and reliability of the product; 4. Wide range of applications: The prepared ceramic ball materials are particularly suitable for high-end equipment fields such as high-speed bearings, precision machine tool spindle bearings, and wind power equipment bearings. Attached Figure Description

[0013] Figure 1 This is a SEM image of the microstructure of the ceramic spheres prepared in Example 1 of this invention. Detailed Implementation

[0014] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0015] Example 1: A ceramic sphere material with controllable growth of long columnar β-Si3N4 grains, the preparation steps are as follows: (1) Mixing: 90 parts by weight of α-Si3N4 powder (α phase content 96%, average particle size 1.0 μm), 5 parts by weight of β-Si3N4 seed crystals (β phase content 99%, diameter 1.0-1.5 μm, length 5-8 μm, aspect ratio 5:1 to 8:1) and 5 parts by weight of composite sintering aid (Y2O3:Al2O3:Fe2O3=45:45:10) were placed in a planetary ball mill and milled for 12 h in anhydrous ethanol solvent with silicon nitride balls as the ball milling medium at a speed of 200 rpm.

[0016] (2) Molding: The mixed powder is formed into a spherical blank by cold isostatic pressing at a pressure of 200 MPa.

[0017] (3) Sintering: The spherical blank is subjected to multi-stage gas pressure sintering: First stage: Under vacuum, the temperature is increased to 1450 ℃ at 8 ℃ / min and held for 1 h; Second stage: Under nitrogen atmosphere, the temperature is increased to 1650 ℃ at 5 ℃ / min and held for 2 h; Third stage: Under nitrogen atmosphere, the temperature is increased to 1800 ℃ at 3 ℃ / min and held for 4 h.

[0018] (4) Processing: The sintered ceramic balls are precision machined to achieve G10 level precision.

[0019] Testing revealed that the ceramic spheres prepared in this embodiment contained elongated columnar β-Si3N4 grains with an average diameter of 1.5 μm, an average length of 15 μm, and an aspect ratio of 10:1. The mechanical properties were: fracture toughness 9.5 MPa·m¹ / ², flexural strength 1050 MPa, and Vickers hardness 15.2 GPa. Example

[0020] A high-performance silicon nitride ceramic bearing ball is prepared according to the following steps: (1) Mixing: 85 parts by weight of α-Si3N4 powder (α phase content 97%, average particle size 0.8 μm), 10 parts by weight of β-Si3N4 seed crystals (β phase content 99%, diameter 0.5-1 μm, length 8-10 μm, aspect ratio 10:1 to 15:1) and 5 parts by weight of composite sintering aid (Y2O3:Al2O3:Fe2O3=50:30:20) were placed in a planetary ball mill and milled for 20 h in anhydrous ethanol solvent with silicon nitride balls as the ball milling medium at a speed of 200 rpm.

[0021] (2) Molding: The mixed powder is formed into a spherical blank by cold isostatic pressing at a pressure of 250 MPa.

[0022] (3) Sintering: The spherical blank is subjected to multi-stage gas pressure sintering: First stage: Under vacuum, the temperature is increased to 1500 ℃ at 10 ℃ / min and held for 0.5 h; Second stage: Under nitrogen atmosphere, the temperature is increased to 1700 ℃ at 8 ℃ / min and held for 1 h; Third stage: Under nitrogen atmosphere, the temperature is increased to 1850 ℃ at 5 ℃ / min and held for 2 h.

[0023] (4) Processing: The sintered ceramic balls are precision machined to achieve G5 level precision.

[0024] Testing revealed that the ceramic spheres prepared in this embodiment contained elongated columnar β-Si3N4 grains with an average diameter of 1.0 μm, an average length of 20 μm, and an aspect ratio of 20:1. The mechanical properties were: fracture toughness 11.5 MPa·m¹ / ², flexural strength 980 MPa, and Vickers hardness 15.8 GPa.

[0025] Comparative Example The traditional silicon nitride ceramic sphere preparation method was adopted: only α-Si3N4 powder was used, without adding β-Si3N4 seed crystals, and a one-stage sintering process was adopted (directly heated to 1750 ℃ ​​and held for 2 h). Other process conditions were the same as in Example 1.

[0026] Testing revealed that the β-Si3N4 grains in the comparative-prepared ceramic spheres exhibited non-uniform grain size, with an average aspect ratio of only 8:1. The mechanical properties were: fracture toughness 6.2 MPa·m¹ / ², flexural strength 750 MPa, and Vickers hardness 14.5 GPa.

[0027] Table 1: Performance Comparison of Examples and Comparative Examples Test item Example 1 Example 2 Comparative example Fracture toughness (MPa·m¹ / ²) 9.3 11.6 6.2 Bending strength (MPa) 1050 970 750 Vickers hardness (GPa) 15 15.5 14.5 Grain aspect ratio 10:1 20:1 8:1 The above test results show that the present invention significantly improves the microstructure quality and mechanical properties of silicon nitride ceramic balls by adding β-Si3N4 seed crystals and optimizing the sintering process.

[0028] Table 2: Comparison of the performance of the ceramic ball material of the present invention with that of existing technologies Performance index The present application Conventional silicon nitride ceramic Performance improvement Fracture toughness (MPa·m¹ / ²) 7-12 4-7 About 50% Bending strength (MPa) 800-1200 600-900 About 30% Vickers hardness (GPa) 14-16 13-15 About 10% Grain aspect ratio 5:1-25:1 3:1-15:1 Significantly improved 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 ceramic sphere with controllable growth of long columnar β-Si3N4 grains, characterized in that, It is composed of the following raw materials: 80-95 parts by weight of α-Si3N4 powder, 1-20 parts by weight of β-Si3N4 seed crystals, and 3-15 parts by weight of composite sintering aid; the composite sintering aid is composed of R2O3, Al2O3 and Fe2O3, wherein R is at least one of Y, Ce and Lu.

2. The ceramic ball according to claim 1, characterized in that, The α-Si3N4 powder has an α-phase content greater than 95% and an average particle size of 0.5-1.5 μm.

3. The ceramic ball according to claim 1, characterized in that, The β-Si3N4 seed crystal has a long columnar single crystal structure, with a β phase content greater than 98%, a diameter of 0.5-2 μm, a length of 3-10 μm, and an aspect ratio of 3:1 to 20:

1.

4. The ceramic ball according to claim 1, characterized in that, The mass ratio of R2O3, Al2O3 and Fe2O3 in the composite sintering aid is (20-80):(20-80):(0.1-5).

5. The ceramic ball according to claim 1, characterized in that, The average diameter of the long columnar β-Si3N4 grains in the ceramic spheres is 0.5-3 μm, the average length is 5-25 μm, and the aspect ratio is 5:1 to 25:

1.

6. A method for preparing ceramic spheres with controllable growth of long columnar β-Si3N4 grains according to any one of claims 1-5, characterized in that, Includes the following steps: a. Mix α-Si3N4 powder, β-Si3N4 seed crystals and composite sintering aids in a certain proportion to obtain a mixed powder; b. Shape the mixed powder into spherical blanks; c. Perform multi-stage gas pressure sintering on the spherical blank; d. Perform precision machining on the sintered ceramic balls.

7. The method for preparing ceramic spheres with controllable growth of long columnar β-Si3N4 grains according to claim 6, characterized in that, The mixing step employs planetary ball milling, using silicon nitride balls as the milling medium, and is performed in anhydrous ethanol solvent for 8-24 hours.

8. The method for preparing ceramic spheres with controllable growth of long columnar β-Si3N4 grains according to claim 6, characterized in that, The molding process involves hydraulic pressing, with a molding pressure of 3-10 MPa.

9. The method according to claim 6, characterized in that, The molding process is cold isostatic pressing, with a molding pressure of 150-300 MPa.

10. The method for preparing ceramic spheres with controllable growth of long columnar β-Si3N4 grains according to claim 6, characterized in that, The multi-stage gas pressure sintering includes: a. First stage: In a vacuum environment, heat to 1400-1500 ℃ at a rate of 5-10 ℃ / min and hold for 0.5-2 h; b. Second stage: Under a nitrogen atmosphere, the temperature is increased to 1600-1700 ℃ at a rate of 3-8 ℃ / min and held for 1-3 h; c. Third stage: Under a nitrogen atmosphere, heat to 1750-1850 ℃ at a rate of 2-5 ℃ / min and hold for 2-6 h.

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