A method for producing a self-growing densified silicon nitride ceramic structure

Abstract

The application discloses a preparation method of a self-growth densification silicon nitride ceramic structure, and belongs to the technical field of ceramic products. In the application, rare earth metal elements replace rare earth metal oxides in composition, a frame mainly composed of beta-phase silicon nitride is sintered in one step, oxygen is introduced to oxidize the rare earth metal elements, the rare earth metal elements are oxidized after capturing oxygen to realize self-growth, internal stress of the rare earth metal oxides is generated, the rare earth metal elements after oxidation are melted in a second sintering step to form a liquid phase, and the internal stress of the rare earth metal oxides is released, and the melted rare earth metal oxides flow into pores of the ceramic to promote the ceramic to realize further densification.

Description

Technical Field

[0001] This invention relates to the field of ceramic products technology, and in particular to a method for preparing a self-grown, densified silicon nitride ceramic structural component. Background Technology

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

[0003] With continuous technological advancements and market development, the demand for high-performance silicon nitride ceramic bearing balls is increasing. During the manufacturing process, silicon nitride ceramic bearing balls may form more micropores and crack initiations, which can reduce the material's hardness and wear resistance. The development of densification technology can optimize the sintering process, reduce these defects, and thus improve the material's hardness and wear resistance. The development of densification technology will help improve product performance and quality, meeting the needs of high-end applications. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing self-growing and densified silicon nitride ceramic structural parts. In this invention, a framework mainly composed of β-phase silicon nitride is first sintered, and then oxygen is introduced to oxidize rare earth metal elements. The rare earth metal elements capture oxygen and are oxidized to achieve self-growth. In the second sintering, the molten and oxidized rare earth metal elements form a liquid phase, which promotes further densification of the ceramic.

[0005] A method for preparing a self-grown, densified silicon nitride ceramic structural component, characterized by the following steps:

[0006] S1. Si3N4 powder with an α-phase content higher than 70%, AlN, elemental Y, MgO, elemental Li, elemental La, and sintering aids are placed in a ball mill and ball-milled in an oxygen-free air atmosphere until all particles have a diameter <0.5 μm, preparing a mixed powder. In this step, the high α-phase Si3N4 powder is the main material of silicon nitride ceramics. AlN is used to further improve the wear resistance of the material. Elemental Y, after oxidation, forms Y2O3, which is used to improve the density of silicon nitride ceramic structures. After adding Y2O3, pores are visible under a 1 μm electron microscope. MgO is used to promote the transformation of the α-phase Si3N4 powder to the β-phase. Elemental Li and La, after oxidation, form Li2O and La2O3, which form a liquid phase at high temperature, promoting the densification of ceramic structures. Ball milling in an oxygen-free environment prevents the elemental metals from increasing their activity and oxidizing after grinding.

[0007] S2. The mixed powder is molded into a green body; the green body is then sintered once at a temperature of 1550-1650℃, a pressure of 3-20 atm, and a time of 30-72 hours. The sintering air atmosphere is an inert gas atmosphere. After the first sintering, the pressure is released and the temperature is slowly lowered. The sintered product is silicon nitride green body 1. In this step, the silicon nitride ceramic sintered will have countless micropores invisible to the naked eye because most of the α-phase silicon nitride has been converted into β-phase silicon nitride, and there is no Li2O or La2O3 forming a liquid phase at high temperature to promote the densification of the ceramic structure.

[0008] S3. After cooling to room temperature, evacuate the environment of the silicon nitride blank 1 and introduce oxygen at a pressure greater than atmospheric pressure, then let it stand for 7-30 days. This step is to ensure that oxygen penetrates into the silicon nitride blank 1 as much as possible, ensuring that the contact with rare earth metal elements reaches more than 90%.

[0009] S4. After the silicon nitride blank 1 has settled, slowly heat it to 100-300℃ in an oxygen atmosphere above atmospheric pressure, and hold it at 100-300℃ for 0.5-5 hours. This step is crucial for the complete reaction of rare earth metals with oxygen. The reaction releases some heat, so it needs to be held at a lower temperature. After reacting with oxygen, the rare earth metals capture oxygen atoms, increasing their volume and achieving a self-growth effect.

[0010] S5. Vacuum the oxygen atmosphere surrounding the silicon nitride blank 1, introduce inert gas, and perform a second sintering on the silicon nitride blank 1. The sintering temperature is 1700-1850℃, the sintering pressure is 3-20 atm, and the sintering time is 30-72h. The sintered blank is silicon nitride blank 2. In this step, the rare earth metal elements themselves have certain internal stress after oxidation. Under high temperature, the rare earth metal oxides melt into liquid. In order to release their internal stress, the liquid will flow into the various pores of the silicon nitride blank 1, achieving a higher degree of density.

[0011] S6. Machining the silicon nitride blank 2 to prepare a ceramic structural part of the required size.

[0012] Furthermore, in step S1, the mass fraction ratio of Si3N4 powder, AlN, elemental Y, MgO, elemental Li, elemental La, and sintering aid is (80-88):(3-7.0):(2-5):(1-5):(1-3):(1-3):(1-3).

[0013] Furthermore, in step S1, the air atmosphere in the ball mill is an oxygen-free air atmosphere.

[0014] Furthermore, in step S2, the sintering air atmosphere is a nitrogen air atmosphere or an argon air atmosphere.

[0015] Furthermore, in step S3, the pressure of the oxygen introduced is 1-10 atm.

[0016] Furthermore, the pressure of the oxygen atmosphere in step S4 is 1-10 atm.

[0017] Furthermore, the inert air atmosphere mentioned in step S5 is a nitrogen air atmosphere or an argon air atmosphere. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0019] Figure 1 This is a SEM image of the cross-section after the first sintering of the present invention;

[0020] Figure 2 This is a SEM image of the cross-section after secondary sintering in this invention. Detailed Implementation

[0021] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0022] The technology of this invention is actually applied to ceramic bearing balls, so this embodiment uses bearing balls as an example for explanation.

[0023] Si3N4 powder with an α-phase content higher than 70%, AlN, elemental Y, MgO, elemental Li, elemental La, and sintering aids were placed in a ball mill and ball-milled in an oxygen-free environment until all particles had a particle size of <0.5μm. The ratio of the above components was 80:4:5:3:3.5:4:0.5, and 2kg of mixed powder was prepared.

[0024] The mixed powder was molded into spherical blanks, then subjected to cold isostatic pressing for 15 days, followed by debinding of the bearing balls. The spherical blanks were then sintered once at a temperature of 1600℃, a pressure of 8 atm, and a sintering time of 48 hours in an argon-air atmosphere.

[0025] After the first sintering, the pressure is released to atmospheric pressure, and the temperature is slowly lowered to room temperature. At this point, the bearing ball has completed the first rough sintering, and about 90% of the α-phase silicon nitride has been transformed into β-phase silicon nitride. Microscopically, a staggered and irregular short fiber skeleton has formed. Rare earth metals are attached to the β-phase silicon nitride crystal rod in granular form. Because the rare earth metal elements failed to form a liquid phase to fill the gaps, the electron microscopy image shows... Figure 1 As shown, the densification level is low and the gaps between the silicon nitride short fiber skeletons are large.

[0026] The environment of the spherical blank after one sintering is evacuated and oxygen at 3 atm is introduced. It is then left to stand for 9 days to ensure that oxygen penetrates into the spherical blank as much as possible and that the contact between oxygen and rare earth metal elements reaches more than 90%.

[0027] After settling, maintain constant pressure and slowly raise the temperature to 300℃, then hold at 300℃ for 2 hours. During this step, rare earth metals react with oxygen, releasing heat and increasing molecular activity. Simultaneously, the rare earth metals capture oxygen atoms after reacting with oxygen, increasing their volume and achieving a self-growth effect. This process also forces the oxidized rare earth metals into the ceramic pores.

[0028] After heat preservation, oxygen is removed by vacuuming, and nitrogen is introduced for secondary sintering of the spherical blank. The sintering temperature is 1750℃, the sintering pressure is 8 atm, and the sintering time is 64 hours. The sintered blank is the bearing ball blank. During the sintering process, the rare earth metal oxide melts into a liquid. In order to release its internal stress, the liquid flows into the pores of the silicon nitride blank 1, achieving a higher degree of compactness.

[0029] The bearing ball blank is machined to produce ceramic bearing balls of the required size. Electron microscopy results are shown below. Figure 2 As shown, the silicon nitride crystal pillar is surrounded by various components, achieving a higher degree of densification.

Claims

1. A method for preparing a self-grown, densified silicon nitride ceramic structural component, characterized in that: The steps are as follows: S1. Si3N4 powder with an α phase content higher than 70%, AlN, elemental Y, MgO, elemental Li, elemental La, and sintering aid are placed into a ball mill and ball-milled until all particles have a particle size of <0.5μm to prepare a mixed powder. S2. The mixed powder is molded into a blank; the blank is sintered once at a temperature of 1450-1650℃, a sintering pressure of 3-20 atm, and a sintering time of 30-72h. After the first sintering is completed, the pressure is released and the temperature is slowly lowered. The sintered product is silicon nitride blank 1. S3. After cooling to room temperature, evacuate the environment of the silicon nitride blank 1 and introduce oxygen, and let it stand for 7-30 days. S4. After the silicon nitride blank 1 has been left to stand, slowly heat it to 100-300℃ in an oxygen atmosphere and keep it at 100-300℃ for 0.5-5 hours. S5. Vacuum treatment is performed on the oxygen atmosphere in which the silicon nitride blank 1 is located, and inert gas is introduced. The silicon nitride blank 1 is then sintered twice. The sintering temperature is 1700-1850℃, the sintering pressure is 3-20 atm, and the sintering time is 30-72h. The sintered blank is silicon nitride blank 2. S6. Machining the silicon nitride blank 2 to prepare a ceramic structural part of the required size.

2. The method for preparing a self-grown densified silicon nitride ceramic structural component according to claim 1, characterized in that: In step S1, the mass fraction ratio of Si3N4 powder, AlN, elemental Y, MgO, elemental Li, elemental La and sintering aid is (80-88): (3-7.0): (3-7): (1-5): (1-5): (1-5): (1-3).

3. The method for preparing a self-grown densified silicon nitride ceramic structural component according to claim 1, characterized in that: In step S1, the air atmosphere in the ball mill is an oxygen-free atmosphere.

4. The method for preparing a self-grown densified silicon nitride ceramic structural component according to claim 1, characterized in that: In step S2, the sintering air atmosphere is a nitrogen air atmosphere or an argon air atmosphere.

5. The method for preparing a self-grown densified silicon nitride ceramic structural component according to claim 1, characterized in that: In step S3, the pressure of the oxygen introduced is 1-10 atm.

6. The method for preparing a self-grown densified silicon nitride ceramic structural component according to claim 1, characterized in that: The pressure of the oxygen atmosphere in step S4 is 1-10 atm.

7. The method for preparing a self-grown densified silicon nitride ceramic structural component according to claim 1, characterized in that: The inert gas mentioned in step S5 is nitrogen or argon.

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