Preparation method of self-growing densified silicon nitride ceramic structural member

Abstract

The invention discloses a preparation method of a self-growing densified silicon nitride ceramic structural member, and belongs to the technical field of ceramic products. Rare earth metal oxides are replaced by rare earth metal elementary substances, a frame with beta-phase silicon nitride as a main body is obtained through one-step sintering, then oxygen is introduced to oxidize the rare earth metal elements, the rare earth metal elements are oxidized after capturing the oxygen to achieve self-growth, the rare earth metal oxides generate internal stress, and the beta-phase silicon nitride is obtained. The rare earth metal elements subjected to two-step sintering, melting and oxidation form a liquid phase, the internal stress of the rare earth metal oxide is released, the molten rare earth metal oxide flows into each pore of the ceramic, and further densification of the ceramic is promoted.

Description

Technical Field

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

[0002] In modern industry and technology, bearing balls are key components whose performance directly impacts the operating efficiency and service life of mechanical equipment. Silicon nitride, an advanced ceramic material, exhibits significant performance advantages in bearing balls due to its exceptional physical and chemical properties. Silicon nitride bearing balls, with their high hardness, high-temperature stability, corrosion resistance, lightweight design, low friction, and quiet operation, offer 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 even more areas, providing strong support for technological advancement and equipment upgrades across various industries.

[0003] With the continuous advancement of technology and the development of the market, the demand for high-performance silicon nitride ceramic bearing balls is increasing. The manufacturing process of silicon nitride ceramic bearing balls may form more microscopic pores and crack sources, which 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. This development will help improve product performance and quality, meeting the needs of high-end applications. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a self-growing and densified silicon nitride ceramic structural component. The present invention first sinters to form a framework with β-phase silicon nitride as the main body, then introduces oxygen to oxidize rare earth metal elements. The rare earth metal elements capture oxygen and then oxidize to achieve self-growth. The second sintering melts the oxidized rare earth metal elements to 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 is characterized by the following steps: S1. Place Si3N4 powder with an α-phase content higher than 70%, AlN, elemental Y, MgO, elemental Li, elemental La, and a sintering aid into a ball mill and perform ball milling in an oxygen-free air atmosphere until all particles have a particle size of <0.5 μm to prepare a mixed powder. In this step, the high-α-phase Si3N4 powder is the main material for silicon nitride ceramics, AlN is used to further improve the wear resistance of the material, and elemental Y is oxidized to form Y2O3, which is used to improve the density of silicon nitride ceramic structural parts. After adding Y2O3, pores of 1 μm are visible under an electron microscope. MgO is used to promote the transformation of α-phase Si3N4 powder to β-phase. Elemental Li and La are oxidized to form Li2O and La2O3, which form a liquid phase at high temperature to promote the densification of ceramic structural parts. Ball milling in an oxygen-free environment is to prevent the activity of elemental metals from increasing after grinding and oxidizing and burning.

[0006] S2. The mixed powder is molded into a green body; the green body is subjected to a primary sintering process at a sintering temperature of 1550-1650°C, a sintering pressure of 3-20 atm, and a sintering time of 30-72 hours in an inert gas atmosphere. After the primary sintering process is completed, the pressure is released and the temperature is slowly lowered to produce a silicon nitride green body 1. The silicon nitride ceramic sintered in this step has a large portion of the α-phase silicon nitride converted to β-phase silicon nitride, and no Li2O and La2O3 form a liquid phase at high temperatures, which promotes the densification of the ceramic structure and forms countless microscopic pores that are invisible to the naked eye.

[0007] S3. After cooling to room temperature, the environment surrounding the silicon nitride blank 1 is evacuated and oxygen pressure exceeding atmospheric pressure is introduced. The blank is then allowed to stand for 7-30 days. This step ensures that oxygen penetrates as much as possible into the silicon nitride blank 1, ensuring that the contact rate with the rare earth metal element reaches 90% or more.

[0008] S4. After the silicon nitride blank 1 has been allowed to rest, it is slowly heated to 100-300°C in an oxygen atmosphere above atmospheric pressure and maintained at 100-300°C for 0.5-5 hours. This step is crucial for the complete reaction between the rare earth metal and oxygen. Since some heat is released during the reaction, it is necessary to maintain the temperature at a reduced temperature. The reaction between the rare earth metal and oxygen captures oxygen atoms, increasing its volume and achieving a self-growth effect.

[0009] S5. The oxygen atmosphere surrounding the silicon nitride blank 1 is evacuated, an inert gas is introduced, and the silicon nitride blank 1 is subjected to a secondary sintering process at a sintering temperature of 1700-1850°C, a sintering pressure of 3-20 atm, and a sintering time of 30-72 hours. After sintering, the silicon nitride blank 2 is obtained. In this step, the rare earth metal elements themselves have a certain amount of internal stress after being oxidized. Under the action of high temperature, the rare earth metal oxides melt into a liquid. To release the internal stress, the liquid will flow into the pores of the silicon nitride blank 1, achieving a higher degree of density.

[0010] S6. Machining the silicon nitride blank 2 to prepare a ceramic structural part of a required size.

[0011] 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).

[0012] Furthermore, in step S1, the air atmosphere for ball milling is an oxygen-free air atmosphere.

[0013] Furthermore, in step S2, the sintering air atmosphere is a nitrogen air atmosphere or an argon air atmosphere.

[0014] Furthermore, in step S3, the pressure of the introduced oxygen is 1-10 atm.

[0015] Furthermore, the pressure of the oxygen atmosphere in step S4 is 1-10 atm.

[0016] Furthermore, the inert air atmosphere in step S5 is a nitrogen air atmosphere or an argon air atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the specific implementation or the description of the prior art.

[0018] Figure 1 This is the SEM image of the cross section after the first sintering of the present invention; Figure 2 This is the SEM image of the cross-section after secondary sintering of the present invention. DETAILED DESCRIPTION

[0019] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0020] The technology of the present invention is actually applied to ceramic bearing balls, so this embodiment is described using bearing balls as an example.

[0021] Si3N4 powder with an α-phase content higher than 70%, AlN, elemental Y, MgO, elemental Li, elemental La, and a sintering aid were placed in a ball mill and ball-milled in an oxygen-free environment until all particles had a particle size of <0.5 μm. The ratio of the above components was 80:4:5:3:3.5:4:0.5, and 2 kg of mixed powder was prepared.

[0022] The mixed powder was molded into a spherical green body, which was then cold isostatically pressed for 15 days. The bearing balls were then debinded. The green bodies were then sintered once at a temperature of 1600°C, a pressure of 8 atm, and a sintering time of 48 hours in an argon atmosphere.

[0023] After the first sintering is completed, the pressure is released to normal pressure and the temperature is slowly lowered to room temperature. At this time, the bearing ball has completed the first rough sintering, and about 90% of the α-phase silicon nitride has been converted into β-phase silicon nitride. Microscopically, a staggered and irregular short fiber skeleton is formed. The rare earth metal is attached to the β-phase silicon nitride crystal rod in the form of particles. Because the rare earth metal elements cannot form a liquid phase to fill the gap, the electron microscope effect is as follows: Figure 1 As shown in the figure, the degree of densification is low and the gaps between the silicon nitride short fiber skeletons are large.

[0024] The environment of the spherical green body that has completed the first sintering is vacuumed and 3atm of oxygen is introduced. It is left to stand for 9 days to ensure that oxygen penetrates into the spherical green body as much as possible and to ensure that the contact between oxygen and rare earth metal elements reaches more than 90%.

[0025] After the static period, the pressure is maintained constant and the temperature is slowly raised to 300°C, where it is then held for 2 hours. During this step, the rare earth metal reacts with oxygen, releasing heat and increasing the activity of the molecules. Simultaneously, the rare earth metal captures oxygen atoms, increasing its volume and achieving a self-growth effect. This squeezes the oxidized rare earth metal into the ceramic voids.

[0026] After the insulation is complete, the spherical blank is evacuated to remove oxygen and introduced with nitrogen for a secondary sintering process at a temperature of 1750°C, a pressure of 8 atm, and a sintering time of 64 hours. The resulting bearing ball blank is a sintered ball. During the sintering process, the rare earth metal oxide melts into a liquid. To release its internal stress, the liquid flows into the pores of the silicon nitride blank 1, achieving a higher degree of density.

[0027] The bearing ball blank is machined to prepare the ceramic bearing ball of the required size. The electron microscope effect is as follows Figure 2 As shown, the silicon nitride crystal pillars are surrounded by various components, achieving a higher densification effect.

Claims

1. A method for preparing a self-grown densified silicon nitride ceramic structure, characterized by: The steps are: S1. Put Si3N4 powder with an α-phase content higher than 70%, AlN, elemental Y, MgO, elemental Li, elemental La, and a sintering aid into a ball mill and mill until all particles have a particle size of less than 0.5 μm to prepare a mixed powder; S2. Molding the mixed powder into a green body; sintering the green body once at a sintering temperature of 1450-1650° C., a sintering pressure of 3-20 atm, and a sintering time of 30-72 h. After the primary sintering is completed, releasing the pressure and slowly cooling the temperature to obtain a silicon nitride green body 1; S3. After cooling to room temperature, the environment of the silicon nitride blank 1 is vacuumed, oxygen is introduced, and the blank is left to stand for 7-30 days; S4. After the silicon nitride blank 1 is allowed to stand, it is slowly heated to 100-300°C in an oxygen atmosphere and kept at 100-300°C for 0.5-5h; S5. The oxygen atmosphere of the silicon nitride blank 1 is vacuumed, an inert gas is introduced, and the silicon nitride blank 1 is subjected to secondary sintering at a sintering temperature of 1700-1850° C., a sintering pressure of 3-20 atm, and a sintering time of 30-72 h. After sintering, a silicon nitride blank 2 is obtained. S6. Machining the silicon nitride blank 2 to prepare a ceramic structural part of a required size.

2. The method for preparing a self-grown densified silicon nitride ceramic structure according to claim 1, characterized in that: The mass fraction ratio of Si3N4 powder, AlN, Y2O3, MgO, Li2O, La2O3 and sintering aid in step S1 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 structure according to claim 1, characterized in that: In step S1 , the air atmosphere during ball milling is an oxygen-free atmosphere.

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

6. The method for preparing a self-grown densified silicon nitride ceramic structure 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 structure according to claim 1, characterized in that: The inert air atmosphere in step S5 is a nitrogen air atmosphere or an argon air atmosphere.

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