A high-density silicon nitride bearing ball and its preparation method

Abstract

The present invention describes a highly dense silicon nitride bearing ball and its preparation method, belonging to the technical field of ceramic products. High-α-phase Si3N4 powder is the main material of the silicon nitride bearing ball. ALN is used to further improve the wear resistance of the material, Y2O3 is used to improve the density of the silicon nitride bearing ball, pores can be seen under the electron microscope of 0.5 μm after adding Y2O3, MgO is used to promote the transformation of α-phase Si3N4 powder to β-phase, and Li2O and La2O3 form a high-temperature liquid phase to promote the densification of the bearing ball. By virtue of the solubility of organic solvents in silicon nitride, part of the silicon nitride is dissolved in the solution to further soften the performance of the surface layer of the silicon nitride powder. By means of pumping negative pressure, the tiny air bubbles in the silicon nitride powder are removed; by means of evaporating the solvent, the silicon nitride precipitates on the surface of the silicon nitride powder, and further realizes the improvement and adjustment of the shape of the silicon nitride powder itself, and finally a bearing ball with higher densification is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic products, and particularly relates to a highly dense silicon nitride bearing ball and a preparation method thereof. Background Art

[0002] In the fields of modern industry and technology, as a key component, the performance of bearing balls directly affects the operating efficiency and service life of mechanical equipment. As an advanced ceramic material, silicon nitride exhibits significant performance advantages in the application of bearing balls due to its excellent physical and chemical properties. Silicon nitride bearing balls, with their high hardness, high-temperature stability, corrosion resistance, light weight, low friction, and quietness, show broad application prospects in the fields of modern industry and technology. With the continuous progress of technology and the expansion of the market, silicon nitride bearing balls will play an important role in more fields, providing strong support for the technological progress and equipment upgrading of various industries.

[0003] With the continuous progress of technology and the development of the market, the demand for high-performance silicon nitride ceramic bearing balls is increasing day by day. During the preparation process of silicon nitride ceramic bearing balls, more micro-pores and crack sources may be formed, and these defects will reduce the hardness and wear resistance of the material. The development of densification technology can optimize the sintering process, reduce these defects, and thus improve the hardness and wear resistance of the material. The development of densification technology will help improve the performance and quality of products and meet the needs of high-end application fields. Summary of the Invention

[0004] The purpose of the present invention is to provide a highly dense silicon nitride bearing ball and a preparation method thereof. In the present invention, part of the silicon nitride powder is dissolved in a solvent in a solution, and the solvent brings extremely fine powder particles into the pores of the powder, and the solvent is slowly evaporated to achieve the effect of reducing the porosity of the silicon nitride powder.

[0005] A highly dense silicon nitride bearing ball and a preparation method thereof are characterized in that the steps are as follows:

[0006] S1. Put Si powder with an α-phase content higher than 70%, 3 N 4 AlN, Y 2 O 3 MgO, Li 2 O, La 2 O 3 and sintering aids into a ball mill for ball milling until the particle size of all particles is <0.5 μm to prepare a mixed powder. In this step, the high-α-phase Si 3 N 4 powder is the main material of the silicon nitride bearing ball, ALN is used to further improve the wear resistance of the material, Y 2 O 3To improve the density of silicon nitride bearing balls, add Y 2 O 3 After adding 1μm of it, pores can be seen under the electron microscope. MgO is used to promote the transformation of α-phase Si 3 N 4 powder to β-phase. Li 2 O, La 2 O 3 forms a liquid phase at high temperature to promote the densification of bearing balls.

[0007] S2: Take out the mixed powder and put it into a container. Pour an organic solvent exceeding the mass of the mixed powder into the container, stir evenly, put the container into a vacuum furnace for vacuum treatment, and let the container stand in a vacuum state for more than 12 hours. In this step, by means of the solubility of the organic solvent in silicon nitride, part of the silicon nitride is dissolved in the solution to further soften the performance of the surface layer of the silicon nitride powder.

[0008] S3: Take out the container after the vacuum standing is completed, stir evenly, put it into a distillation device with negative pressure and heating functions, heat the distillation device, and the organic solvent distills out slowly. At the same time, keep the negative pressure state in the distillation device until the mass fraction of the organic solvent accounts for 10%-40%. In this step, by means of pumping negative pressure, the tiny air bubbles in the silicon nitride powder are removed; by means of evaporating the solvent, the silicon nitride is deposited on the surface of the silicon nitride powder, and further the improvement and adjustment of the shape of the silicon nitride powder itself are realized, laying a good foundation for further densification.

[0009] S4: Take out the wet powder containing the organic solvent in the container, pour the wet powder into two hemispherical molds, apply pressure to mold it into a spherical blank; while keeping the pressure applied, put the spherical blank into the distillation device for negative pressure heating until the spherical blank is dried and then stop the negative pressure heating. In this step, the remaining organic solvent is extruded by physical pressure. By keeping the high-temperature negative pressure state, while removing the organic solvent, a negative pressure is formed inside the powder and a positive pressure is applied outside to realize the densification of the whole material.

[0010] S5: Perform cold isostatic pressing on the spherical blank;

[0011] S6: Sinter the spherical blank. The sintering process is carried out in a nitrogen atmosphere, the sintering temperature is 1700°C - 1900°C, the sintering pressure is 4 atm - 30 atm, the sintering time is 48h - 96h, and after sintering, it is a silicon nitride blank;

[0012] S7: Machine the silicon nitride blank to prepare bearing balls of the required size.

[0013] Furthermore, Si 3 N 4 powder, AlN, Y 2 O3 , MgO, Li 2 O, La 2 O 3 、The mass fraction ratio of the sintering aid is (80 - 88):(3 - 7.0):(3 - 7):(1 - 5):(1 - 5):(1 - 5):(1 - 3).

[0014] Further, the organic solvent described in step S2 is one or two or three combinations of toluene-based solution, acetone, and methyl ethyl ketone.

[0015] Further, in step S2, the distillation temperature is 60°C - 200°C, and the distillation time is more than 12 hours per kilogram of the organic solvent.

[0016] Further, the edge area of the hemispherical mold described in step S4 has a toothed structure.

[0017] Further, in step S4, the negative pressure heating temperature is 120°C - 300°C, and the distillation time is 0.5h - 2h. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art.

[0019] Figure 1 SEM image of the cross-section of the bearing ball prepared by the present invention;

[0020] Figure 2 SEM image of the cross-section of the bearing ball prepared by the original process. SPECIFIC EMBODIMENTS

[0021] The following embodiments are provided to better further understand the present invention, which is not limited to the best embodiment, and does not limit the content and protection scope of the present invention. Any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other prior arts and being the same or similar to the present invention falls within the protection scope of the present invention. Embodiment

[0022] Put Si 3 N 4 powder with an α-phase content higher than 70%, AlN, Y 2 O 3 , MgO, Li 2 O, La 2 O 3 , and the sintering aid into a ball mill according to the mass fraction ratio of 80:4:5:5:3:1:1:1 for ball milling until the particle size of all particles < 0.5 μm to prepare 0.8 kg of mixed powder.

[0023] Take out the mixed powder and put it into a container. Pour 1.2 kg of methyl ethyl ketone into the container, stir evenly, put the container into a vacuum furnace for vacuum treatment, and let the container stand still in a vacuum state for 24 hours.

[0024] Take out the container after the vacuum standing is completed, stir evenly, put it into a distillation device with negative pressure and heating functions, heat the distillation device, and the organic solvent distills out slowly. At the same time, maintain the negative pressure state inside the distillation device and distill until the mass fraction of the organic solvent accounts for 10%.

[0025] Take out the wet powder containing the organic solvent in the container, pour the wet powder into two hemispherical molds. The hemispherical molds are claw-shaped, and the claw shape protects the powder from being scattered when extruded, and pressure can be continuously applied after the solvent is extruded. Apply pressure to mold into a spherical blank; while maintaining the applied pressure, put the spherical blank into the distillation device for negative pressure heating until the spherical blank is dried and then stop the negative pressure heating.

[0026] Perform cold isostatic pressing on the spherical blank.

[0027] Sinter the spherical blank. The sintering process is carried out in a nitrogen atmosphere, the sintering temperature is 1750 °C, the sintering pressure is 20 atm, and the sintering time is 72 h. After sintering, it is a silicon nitride blank.

[0028] Cut the silicon nitride blank prepared in Example 1 with a silicon carbide wire, and scan it with a scanning electron microscope to obtain an image as shown in Figure 1 , and the porosity of the cut surface is about 0.12%. Example

[0029] Si powder with an α-phase content higher than 70% 3 N 4 , AlN, Y 2 O 3 , MgO, Li 2 O, La 2 O 3 , sintering aids, with a mass fraction ratio of 80:4:5:5:3:1:1:1 are put into a ball mill for ball milling until the particle size of all particles < 0.5 μm, and 0.8 kg of mixed powder is prepared.

[0030] Pour the mixed powder into two hemispherical molds and mold into a spherical blank by pressing.

[0031] Perform cold isostatic pressing on the spherical blank.

[0032] Debind the spherical blank.

[0033] The spherical green body is sintered. The sintering process is carried out in a nitrogen atmosphere. The sintering temperature is 1750 °C, the sintering pressure is 20 atm, and the sintering time is 72 h. After sintering, it is a silicon nitride blank.

[0034] The silicon nitride blank obtained in Example 2 is cut with a silicon carbide wire and scanned by a scanning electron microscope to obtain an image as Figure 2 shown. The porosity of the cut surface is about 0.76%.

Claims

1. A high-density silicon nitride bearing ball and a preparation method thereof, characterized in that: The steps are: S1. Put Si3N4 powder with an α-phase content higher than 70%, AlN, Y2O3, MgO, Li2O, La2O3 and sintering aid into a ball mill for ball milling until all particles have a particle size of less than 0.5 μm to prepare a mixed powder; S2, take out the mixed powder and put it into a container, pour an organic solvent in an amount exceeding the mass of the mixed powder into the container, stir evenly, put the container into a vacuum furnace for vacuum treatment, and let the container stand in a vacuum state for more than 12 hours; S3, taking out the container after vacuum standing, stirring evenly, putting it into a distillation device with negative pressure and heating functions, heating the distillation device, slowly distilling the organic solvent out, while maintaining the negative pressure state in the distillation device, and distilling until the mass fraction of the organic solvent accounts for 10%-40%; S4, taking out the wet powder containing the organic solvent in the container, pouring the wet powder into two hemispherical molds, applying pressure to mold into a spherical body; while maintaining the pressure, placing the spherical body in a distillation device for negative pressure heating until the spherical body is dry and then stopping the negative pressure heating; S5, cold isostatic pressing the spherical green body; S6, sintering the spherical blank, the sintering process is carried out in a nitrogen atmosphere, the sintering temperature is 1700° C.-1900° C., the sintering pressure is 4 atm-30 atm, the sintering time is 48h-96h, and the sintered blank is a silicon nitride blank; S7. Machining the silicon nitride blank to prepare bearing balls of required sizes.

2. A high-density silicon nitride bearing ball and a preparation method thereof according to claim 1, characterized in that: In step S1, the mass fraction ratio of Si3N4 powder, AlN, Y2O3, MgO, Li2O, La2O3 and sintering aid is (80-88): (3-7.0): (3-7): (1-5): (1-5): (1-5): (1-3).

3. A high-density silicon nitride bearing ball and a preparation method thereof according to claim 1, characterized in that: The organic solvent in step S2 is one or a combination of two or three of toluene-based solution, acetone and butanone.

4. A high-density silicon nitride bearing ball and a preparation method thereof according to claim 1, characterized in that: In step S2, the distillation temperature is 60° C.-200° C., and the distillation time is greater than 12 hours per kilogram of organic solvent.

5. The high-density silicon nitride bearing ball and the preparation method thereof according to claim 1, characterized in that: In step S4, the edge area of ​​the hemispherical mold has a toothed structure.

6. The high-density silicon nitride bearing ball and the preparation method thereof according to claim 1, characterized in that: In step S4, the negative pressure heating temperature is 120° C.-300° C., and the distillation time is 0.5 h-2 h.

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