A high fracture toughness silicon nitride-based composite ceramic material and a method of making the same

Abstract

This invention relates to the field of structural ceramic materials technology, and discloses a silicon nitride-based composite ceramic material with high fracture toughness and its preparation method. The silicon nitride-based composite ceramic material with high fracture toughness comprises, by mass, the following raw materials: α‑Si3N4 70-82 parts fine powder α‑Si3N4 10-20 parts coarse flour β‑Si3N4 Seed crystals 1-4 parts Y2O3 2 ~5 parts, MgO 0.5~2.0 parts, Al2O3 0 ~1.5 parts. The preparation method includes preparing silicon nitride slurry, preparing silicon nitride composite powder with surface-loaded composite sintering aid, preparing composite particles, preparing ceramic green body, degreasing treatment, and two-stage gas pressure sintering. This invention utilizes... α‑Si3N4 fine powder and α‑Si3N4 The bimodal particle size distribution of coarse powder is beneficial to improving the packing state of raw material powder and enhancing the uniformity during molding and sintering.

Description

Technical Field

[0001] This invention relates to the field of structural ceramic materials technology, specifically to a silicon nitride-based composite ceramic material with high fracture toughness and its preparation method. Background Technology

[0002] Silicon nitride-based ceramic materials possess high strength, hardness, wear resistance, corrosion resistance, and good high-temperature stability, making them widely used in the field of structural ceramics. In existing technologies, silicon nitride-based ceramic materials typically use α-Si3N4 powder as raw material, achieving densification through the addition of sintering aids and appropriate sintering processes. Regarding raw material selection, silicon nitride powder systems with a single particle size or narrow particle size distribution are often employed to obtain more uniform forming properties and sintering behavior.

[0003] However, when using a single-size silicon nitride powder system, the pore distribution of the powder is not easily optimized during the stacking process, and the powder filling density is relatively low. This can easily lead to uneven shrinkage during subsequent sintering, which is not conducive to obtaining high density. At the same time, this type of powder system has limited ability to coordinate and control grain growth and densification behavior during sintering, making it difficult to ensure high density while taking into account the fracture toughness of the material, thus affecting the comprehensive mechanical properties of silicon nitride-based ceramic materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a silicon nitride-based composite ceramic material with high fracture toughness and its preparation method, solving the problem that when using a single-particle-size silicon nitride powder system, the pore distribution of the powder is not easily optimized during the stacking process, and uneven shrinkage is easily generated during the subsequent sintering process.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a silicon nitride-based composite ceramic material with high fracture toughness, wherein the raw materials for preparation comprise, by mass, 70-82 parts of α-Si3N4 fine powder, 10-20 parts of α-Si3N4 coarse powder, 1-4 parts of β-Si3N4 seed crystals, 2-5 parts of Y2O3, 0.5-2.0 parts of MgO, and 0-1.5 parts of Al2O3; wherein the Y2O3, MgO, and Al2O3 are derived from a composite sintering aid precursor loaded on the surface of the α-Si3N4 fine powder and the α-Si3N4 coarse powder.

[0006] Preferably, the average particle size D50 of the α-Si3N4 fine powder is 0.3 to 0.8 μm, and the average particle size D50 of the α-Si3N4 coarse powder is 1.0 to 3.0 μm.

[0007] Preferably, the mass ratio of the α-Si3N4 fine powder to the α-Si3N4 coarse powder is 4:1 to 8:1.

[0008] Preferably, the average grain size of the β-Si3N4 seed crystals is 0.5–2.0 μm, and the aspect ratio is 3–8.

[0009] Preferably, the high fracture toughness silicon nitride-based composite ceramic material comprises, by mass, the following raw materials: 74-78 parts of fine α-Si3N4 powder, 12-16 parts of coarse α-Si3N4 powder, 1.5-3 parts of β-Si3N4 seed crystals, 3-4.5 parts of Y2O3, 0.8-1.5 parts of MgO, and 0.3-1.0 parts of Al2O3.

[0010] Preferably, a method for preparing a silicon nitride-based composite ceramic material with high fracture toughness includes the following steps: S1. Add α-Si3N4 fine powder and α-Si3N4 coarse powder to an alcohol-water mixed solvent, add a dispersant and ball mill to disperse, to obtain silicon nitride slurry; S2. Dissolve the Y source, Mg source and optional Al source in deionized water or alcohol-water mixed solvent to prepare a composite sintering aid precursor. Add the composite sintering aid precursor to the silicon nitride slurry to allow the composite sintering aid precursor to be adsorbed or deposited on the surface of the α-Si3N4 fine powder and the α-Si3N4 coarse powder. Dry to obtain silicon nitride composite powder with surface-loaded composite sintering aid. S3. The silicon nitride composite powder with surface-loaded composite sintering aid is mixed evenly with β-Si3N4 seed crystals, binder and lubricant, and then spray granulation is performed to obtain composite particles. S4. The composite particles are dry-pressed and then subjected to cold isostatic pressing to obtain a ceramic blank. S5. The ceramic green body is degreased under a nitrogen protective atmosphere. The degreasing temperature is 400-700℃ and the temperature is maintained for 1-4 hours. S6. The degreased ceramic green body is subjected to two-stage gas pressure sintering. In the first stage of the two-stage gas pressure sintering, the temperature is raised to 1600-1720℃ and held for 0.5-2 hours. In the second stage of the two-stage gas pressure sintering, the temperature is raised to 1720-1800℃ and held for 1-4 hours. The nitrogen pressure in the two-stage gas pressure sintering is 0.5-10 MPa, thereby obtaining the silicon nitride-based composite ceramic material with high fracture toughness.

[0011] Preferably, the volume ratio of ethanol to deionized water in the alcohol-water mixed solvent is 1:1 to 4:1, the ball milling dispersion time is 4 to 24 hours, and the dispersant is ammonium polyacrylate, polyvinylpyrrolidone, or a combination thereof.

[0012] Preferably, the Y source is one or more of yttrium nitrate, yttrium acetate, or yttrium chloride; the Mg source is one or more of magnesium nitrate, magnesium acetate, or magnesium chloride; and the optional Al source is one or more of aluminum nitrate, aluminum isopropoxide, or alumina sol. The pH value of the composite sintering aid precursor after being added to the silicon nitride slurry is 7-10. The dried powder is kept at 400-800°C for 0.5-2 hours under a nitrogen atmosphere.

[0013] Preferably, the particle size of the composite particles obtained by spray granulation is 30-120 μm; the pressure of dry pressing is 50-200 MPa; and the pressure of cold isostatic pressing is 150-300 MPa.

[0014] Preferably, in the first stage of the two-stage gas pressure sintering, the temperature is raised to 1660-1700℃ and held for 0.8-1.5h, and in the second stage of the two-stage gas pressure sintering, the temperature is raised to 1740-1780℃ and held for 1.5-3h, and the nitrogen pressure in the two-stage gas pressure sintering is 2-5MPa.

[0015] This invention provides a silicon nitride-based composite ceramic material with high fracture toughness and its preparation method. It possesses the following beneficial effects: 1. The present invention adopts a bimodal particle size combination of α-Si3N4 fine powder and α-Si3N4 coarse powder, which is beneficial to improve the packing state of the raw material powder and improve the uniformity during the molding and sintering process.

[0016] 2. In this invention, Y2O3, MgO and Al2O3 are introduced by a composite sintering aid precursor, and the composite sintering aid precursor is adsorbed or deposited on the surface of α-Si3N4 fine powder and α-Si3N4 coarse powder, which is beneficial to improving the uniformity of sintering aid distribution.

[0017] 3. By introducing β-Si3N4 seed crystals and combining them with a two-stage gas pressure sintering process, this invention is beneficial to simultaneously achieve material densification and improved fracture toughness during the sintering process.

[0018] 4. Without employing a complex external strengthening phase system, this invention obtains a silicon nitride-based composite ceramic material with high fracture toughness, while also achieving high three-point bending strength and high relative density. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for preparing a silicon nitride-based composite ceramic material with high fracture toughness according to the present invention. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Technical Concept: While existing silicon nitride-based ceramic materials possess high strength, hardness, wear resistance, and high-temperature stability, they still suffer from insufficient fracture toughness and difficulties in achieving a balance of comprehensive mechanical properties in practical applications. Current techniques for improving fracture toughness often employ external strengthening phases, adjustments to the sintering aid system, or changes to sintering process parameters. While these methods can improve material properties to some extent, they still present challenges such as difficulty in controlling the uniformity of sintering aid distribution, difficulty in optimizing powder packing, and insufficient stability during the preparation process.

[0022] Based on this, the present invention provides a silicon nitride-based composite ceramic material with high fracture toughness and its preparation method. The present invention uses a bimodal particle size combination of α-Si3N4 fine powder and α-Si3N4 coarse powder to construct a basic powder system. Y2O3, MgO, and Al2O3 are introduced using a composite sintering aid precursor, which is then adsorbed or deposited on the surface of the α-Si3N4 fine powder and α-Si3N4 coarse powder to form a silicon nitride composite powder with a surface-loaded composite sintering aid. Simultaneously, β-Si3N4 seed crystals are added, and two-stage gas pressure sintering is performed to obtain a silicon nitride-based composite ceramic material with high fracture toughness.

[0023] The raw materials and reagents used in this invention are as follows.

[0024] α-Si3N4 fine powder: average particle size D50 is 0.3-0.8 μm, purity is not less than 98.0%, and oxygen content is not higher than 2.0 wt%. In the embodiments of the present invention, α-Si3N4 fine powder with an average particle size D50 of 0.5 μm is preferably selected.

[0025] α-Si3N4 coarse powder: average particle size D50 is 1.0-3.0 μm, purity is not less than 98.0%, and oxygen content is not higher than 2.0 wt%. In the embodiments of the present invention, α-Si3N4 coarse powder with an average particle size D50 of 1.8 μm is preferably selected.

[0026] β-Si3N4 seed crystals: average particle size of 0.5–2.0 μm, aspect ratio of 3–8, and purity of not less than 97.0%. In the embodiments of the present invention, β-Si3N4 seed crystals with an average particle size of 1.0 μm and an aspect ratio of 5 are preferably selected.

[0027] Y source: selected from one or more of yttrium nitrate, yttrium acetate, or yttrium chloride. In the embodiments of the present invention, yttrium nitrate hexahydrate, of analytical grade, is preferred.

[0028] Mg source: selected from one or more of magnesium nitrate, magnesium acetate, or magnesium chloride. In the embodiments of the present invention, magnesium nitrate hexahydrate, analytical grade, is preferred.

[0029] Optional Al source: selected from one or more of aluminum nitrate, aluminum isopropoxide, or alumina sol. In embodiments of the invention, aluminum nitrate nonahydrate, analytical grade, is preferred.

[0030] Dispersant: Selected from ammonium polyacrylate, polyvinylpyrrolidone, or combinations thereof. In the embodiments of the present invention, ammonium polyacrylate is preferably used, with a solid content of 40 wt%.

[0031] Binder: Selected from one or more of polyvinyl alcohol, polyethylene glycol, or methylcellulose. In embodiments of the present invention, polyvinyl alcohol with a degree of alcoholysis of 87% to 89% is preferred.

[0032] Lubricant: Preferably, one or more of polyethylene glycol, stearic acid, or zinc stearate are used. In embodiments of the present invention, polyethylene glycol with a number average molecular weight of 4000 to 6000 is preferred.

[0033] Alcohol-water mixed solvent: composed of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 1:1 to 4:1. In embodiments of the present invention, an alcohol-water mixed solvent with a volume ratio of ethanol to deionized water of 3:1 is preferably used.

[0034] pH adjuster: Ammonia is preferably used to adjust the pH of the system containing a Y source, a Mg source, and optionally an Al source to 7–10. In embodiments of the present invention, it is preferably adjusted to 8.5–9.0.

[0035] Unless otherwise specified, the amounts of Y2O3, MgO and Al2O3 added in this invention are all calculated as oxides; when using Y source, Mg source and optional Al source to prepare composite sintering aid precursor, the amount of Y source, Mg source and optional Al source to be weighed shall be converted according to the molar amount of the corresponding oxide.

[0036] Unless otherwise specified, "parts" in this invention refer to parts by weight.

[0037] Please see the appendix Figure 1 The following is a description with reference to specific embodiments: Example 1 In this embodiment, the high fracture toughness silicon nitride-based composite ceramic material comprises, by mass, the following raw materials: 76 parts of α-Si3N4 fine powder, 14 parts of α-Si3N4 coarse powder, 2 parts of β-Si3N4 seed crystals, 4 parts of Y2O3, 1.2 parts of MgO, and 0.8 parts of Al2O3.

[0038] Based on the above-mentioned mass proportions, weigh out 760g of fine α-Si3N4 powder, 140g of coarse α-Si3N4 powder, and 20g of β-Si3N4 seed crystals. Calculate and weigh out 135.7g of yttrium nitrate hexahydrate, 76.3g of magnesium nitrate hexahydrate, and 58.9g of aluminum nitrate nonahydrate, respectively, based on their respective oxide content.

[0039] A 3:1 volume ratio of ethanol and deionized water was mixed to prepare 1350 mL of an alcohol-water mixed solvent, comprising 1012.5 mL of ethanol and 337.5 mL of deionized water. 13.5 g of a 40 wt% ammonium polyacrylate solution was added to the alcohol-water mixed solvent, followed by fine and coarse α-Si3N4 powder. Using silicon nitride balls as the ball milling medium, with a ball-to-powder mass ratio controlled at 3:1, the mixture was ball-milled at 180 rpm for 12 h to obtain a silicon nitride slurry.

[0040] A composite sintering aid precursor was prepared by dissolving 135.7 g of yttrium nitrate hexahydrate, 76.3 g of magnesium nitrate hexahydrate, and 58.9 g of aluminum nitrate nonahydrate in 300 mL of deionized water. The composite sintering aid precursor was slowly added to a silicon nitride slurry, and the mixture was stirred at 500 rpm for 1 h. The pH of the system was then adjusted to 8.8 using ammonia, and stirring continued for another 1.5 h.

[0041] Subsequently, spray drying was performed with an inlet temperature of 190℃ and an outlet temperature of 95℃. After spray drying, the resulting powder was placed in a nitrogen atmosphere and held at 650℃ for 1 hour to obtain silicon nitride composite powder with surface-loaded composite sintering aids.

[0042] Silicon nitride composite powder with surface-loaded composite sintering aid was mixed with 20g of β-Si3N4 seed crystals and ball-milled for 2h using silicon nitride balls. Then, 24g of polyvinyl alcohol and 6g of polyethylene glycol were added, and deionized water was added to adjust the slurry solid content to 58wt%. After stirring again until homogeneous, spray granulation was performed. The spray granulation inlet temperature was 185℃ and the outlet temperature was 90℃, yielding composite particles with a particle size of 50–90μm.

[0043] The composite particles are passed through a 60-mesh sieve and then placed into a mold for dry pressing at a pressure of 120 MPa to obtain a preform. The preform is then subjected to cold isostatic pressing at a pressure of 220 MPa for 3 minutes to obtain a ceramic body.

[0044] The ceramic blank was degreased under a nitrogen protective atmosphere. Specifically, the temperature was increased to 220℃ at 2℃ / min and held for 1 hour, then increased to 600℃ at 1.5℃ / min and held for 2 hours, with the nitrogen flow rate controlled at 1.5L / min.

[0045] The degreased ceramic green body was placed in a gas pressure sintering furnace for two-stage gas pressure sintering. In the first stage, the temperature was raised to 1680℃ and held for 1 hour; in the second stage, the temperature was raised to 1760℃ and held for 2 hours. The nitrogen pressure was controlled at 3 MPa during the sintering process. After sintering, the green body was cooled to room temperature with the furnace to obtain a silicon nitride-based composite ceramic material with high fracture toughness, which was designated as the sample of Example 1.

[0046] Example 2 In this embodiment, the high fracture toughness silicon nitride-based composite ceramic material comprises, by mass, the following raw materials: 74 parts of α-Si3N4 fine powder, 16 parts of α-Si3N4 coarse powder, 1.8 parts of β-Si3N4 seed crystals, 3.5 parts of Y2O3, 1.0 part of MgO, and 0.5 parts of Al2O3.

[0047] Based on the above-mentioned mass proportions, weigh out 740g of fine α-Si3N4 powder, 160g of coarse α-Si3N4 powder, and 18g of β-Si3N4 seed crystals. Calculate and weigh out 118.7g of yttrium nitrate hexahydrate, 63.6g of magnesium nitrate hexahydrate, and 36.8g of aluminum nitrate nonahydrate, respectively, based on their respective oxide content.

[0048] A 3:1 volume ratio of ethanol and deionized water was mixed to prepare 1450 mL of an alcohol-water mixed solvent, comprising 1087.5 mL of ethanol and 362.5 mL of deionized water. 12.0 g of a 40 wt% ammonium polyacrylate solution was added to the alcohol-water mixed solvent, followed by fine and coarse α-Si3N4 powder. Using silicon nitride balls as the ball milling medium, with a ball-to-powder mass ratio controlled at 3:1, the mixture was ball-milled at 170 rpm for 10 h to obtain a silicon nitride slurry.

[0049] 118.7 g of yttrium nitrate hexahydrate, 63.6 g of magnesium nitrate hexahydrate, and 36.8 g of aluminum nitrate nonahydrate were dissolved in 280 mL of deionized water to prepare a composite sintering aid precursor. The composite sintering aid precursor was slowly added to silicon nitride slurry, and stirred at 450 rpm for 1 h. The pH of the system was then adjusted to 8.6 with ammonia water, and stirring was continued for another 1 h.

[0050] Subsequently, spray drying was performed with an inlet temperature of 180℃ and an outlet temperature of 90℃. After spray drying, the resulting powder was placed in a nitrogen atmosphere and held at 600℃ for 1 hour to obtain silicon nitride composite powder with surface-loaded composite sintering aids.

[0051] Silicon nitride composite powder with surface-loaded composite sintering aid was mixed with 18g of β-Si3N4 seed crystals and stirred at high speed for 2 hours. Then, 20g of polyvinyl alcohol and 5g of polyethylene glycol were added, and deionized water was added to adjust the slurry solid content to 56wt%. After stirring again until homogeneous, spray granulation was performed. The spray granulation inlet temperature was 180℃ and the outlet temperature was 88℃, yielding composite particles with a particle size of 45–85μm.

[0052] The composite particles are dry-pressed at a pressure of 100 MPa to obtain a preform. The preform is then subjected to cold isostatic pressing at a pressure of 200 MPa for 3 minutes to obtain a ceramic green body.

[0053] The ceramic blank was degreased under a nitrogen protective atmosphere. Specifically, the temperature was increased to 200℃ at 2℃ / min and held for 1 hour, then increased to 580℃ at 1℃ / min and held for 2 hours, with the nitrogen flow rate controlled at 1.2L / min.

[0054] The degreased ceramic green body was placed in a gas pressure sintering furnace for two-stage gas pressure sintering. In the first stage, the temperature was raised to 1660℃ and held for 1 hour; in the second stage, the temperature was raised to 1745℃ and held for 2 hours. The nitrogen pressure was controlled at 2.5 MPa during the sintering process. After sintering, the green body was cooled to room temperature with the furnace to obtain a silicon nitride-based composite ceramic material with high fracture toughness, which was designated as the sample of Example 2.

[0055] Example 3 In this embodiment, the high fracture toughness silicon nitride-based composite ceramic material comprises, by mass, the following raw materials: 78 parts of α-Si3N4 fine powder, 12 parts of α-Si3N4 coarse powder, 3 parts of β-Si3N4 seed crystals, 4.2 parts of Y2O3, 1.4 parts of MgO, and 0.6 parts of Al2O3.

[0056] Based on the above-mentioned mass proportions, weigh out 780g of fine α-Si3N4 powder, 120g of coarse α-Si3N4 powder, and 30g of β-Si3N4 seed crystals. Calculate and weigh out 142.5g of yttrium nitrate hexahydrate, 89.1g of magnesium nitrate hexahydrate, and 44.1g of aluminum nitrate nonahydrate, respectively, based on their respective oxide content.

[0057] A 1500 mL alcohol-water mixed solvent was prepared by mixing ethanol and deionized water in a volume ratio of 3:1, comprising 1125 mL of ethanol and 375 mL of deionized water. 15.0 g of ammonium polyacrylate solution with a solid content of 40 wt% was added to the alcohol-water mixed solvent, followed by fine and coarse α-Si3N4 powder. Using silicon nitride balls as the ball milling medium, with a ball-to-powder mass ratio controlled at 4:1, the mixture was ball-milled at 200 rpm for 14 h to obtain a silicon nitride slurry.

[0058] A composite sintering aid precursor was prepared by dissolving 142.5 g of yttrium nitrate hexahydrate, 89.1 g of magnesium nitrate hexahydrate, and 44.1 g of aluminum nitrate nonahydrate in 320 mL of deionized water. The composite sintering aid precursor was slowly added to a silicon nitride slurry, and the mixture was stirred at 600 rpm for 1 h. The pH of the system was then adjusted to 9.0 using ammonia, and stirring continued for another 2 h.

[0059] Subsequently, spray drying was performed with an inlet temperature of 200℃ and an outlet temperature of 100℃. After spray drying, the resulting powder was placed in a nitrogen atmosphere and held at 700℃ for 1 hour to obtain silicon nitride composite powder with surface-loaded composite sintering aids.

[0060] Silicon nitride composite powder with surface-loaded composite sintering aid was mixed with 30g of β-Si3N4 seed crystals and ball-milled for 3h using silicon nitride balls. Then, 28g of polyvinyl alcohol and 7g of polyethylene glycol were added, and deionized water was added to adjust the slurry solid content to 60wt%. After stirring again until homogeneous, spray granulation was performed. The spray granulation inlet temperature was 190℃ and the outlet temperature was 92℃, yielding composite particles with a particle size of 60–100μm.

[0061] The composite particles were dry-pressed at a pressure of 140 MPa to obtain a preform. The preform was then subjected to cold isostatic pressing at a pressure of 240 MPa for 4 minutes to obtain a ceramic green body.

[0062] The ceramic blank was degreased under a nitrogen protective atmosphere. Specifically, the temperature was increased to 220℃ at 2℃ / min and held for 1 hour, then increased to 620℃ at 1.5℃ / min and held for 2 hours, with the nitrogen flow rate controlled at 1.5L / min.

[0063] The degreased ceramic green body was placed in a gas pressure sintering furnace for two-stage gas pressure sintering. In the first stage, the temperature was raised to 1695℃ and held for 1.2 hours; in the second stage, the temperature was raised to 1775℃ and held for 2.5 hours. The nitrogen pressure was controlled at 4 MPa during the sintering process. After sintering, the green body was cooled to room temperature with the furnace to obtain a silicon nitride-based composite ceramic material with high fracture toughness, which was designated as the sample of Example 3.

[0064] Comparative Example 1 In this comparative example, except that Y2O3, MgO and Al2O3 are not introduced through composite sintering aid precursors and silicon nitride composite powder with surface-loaded composite sintering aids is not prepared, the composition of other raw materials is the same as in Example 1.

[0065] In this comparative example, the raw materials for preparing the high fracture toughness silicon nitride-based composite ceramic material include, by mass, 76 parts of α-Si3N4 fine powder, 14 parts of α-Si3N4 coarse powder, 2 parts of β-Si3N4 seed crystals, 4 parts of Y2O3, 1.2 parts of MgO, and 0.8 parts of Al2O3.

[0066] Weigh out 760g of fine α-Si3N4 powder, 140g of coarse α-Si3N4 powder, 20g of β-Si3N4 seed crystals, 40g of Y2O3 powder, 12g of MgO powder, and 8g of Al2O3 powder according to the above mass proportions.

[0067] A 3:1 volume ratio of ethanol and deionized water was mixed to prepare 1350 mL of an alcohol-water mixed solvent, comprising 1012.5 mL of ethanol and 337.5 mL of deionized water. 13.5 g of a 40 wt% ammonium polyacrylate solution was added to the alcohol-water mixed solvent, followed by fine and coarse α-Si3N4 powder. Using silicon nitride balls as the ball milling medium, with a ball-to-powder mass ratio controlled at 3:1, the mixture was ball-milled at 180 rpm for 12 h to obtain a silicon nitride slurry.

[0068] Y2O3 powder, MgO powder and Al2O3 powder were directly added to the silicon nitride slurry and stirred at 500 rpm for 2 hours to ensure that the Y2O3 powder, MgO powder and Al2O3 powder were mixed evenly with the silicon nitride slurry.

[0069] The powder was then dried using a spray drying method, with an inlet temperature of 190℃ and an outlet temperature of 95℃. After spray drying, the resulting powder was placed under a nitrogen atmosphere and held at 650℃ for 1 hour to obtain the final powder.

[0070] The powder was mixed with 20g of β-Si3N4 seed crystals and ball-milled with silicon nitride balls for 2 hours. Then, 24g of polyvinyl alcohol and 6g of polyethylene glycol were added, and deionized water was added to adjust the slurry solid content to 58wt%. After stirring again until homogeneous, spray granulation was performed. The inlet temperature of the spray granulation was 185℃, and the outlet temperature was 90℃, yielding composite particles with a particle size of 50–90μm.

[0071] The composite particles are passed through a 60-mesh sieve and then placed into a mold for dry pressing at a pressure of 120 MPa to obtain a preform. The preform is then subjected to cold isostatic pressing at a pressure of 220 MPa for 3 minutes to obtain a ceramic body.

[0072] The ceramic blank was degreased under a nitrogen protective atmosphere. Specifically, the temperature was increased to 220℃ at 2℃ / min and held for 1 hour, then increased to 600℃ at 1.5℃ / min and held for 2 hours, with the nitrogen flow rate controlled at 1.5L / min.

[0073] The degreased ceramic green body was placed in a gas pressure sintering furnace for two-stage gas pressure sintering. In the first stage, the temperature was raised to 1680℃ and held for 1 hour; in the second stage, the temperature was raised to 1760℃ and held for 2 hours. The nitrogen pressure was controlled at 3 MPa during the sintering process. After sintering, the green body was cooled to room temperature with the furnace to obtain the sintered body, which was designated as Comparative Example 1 sample.

[0074] Comparative Example 2 In this comparative example, except for the absence of β-Si3N4 seed crystals, the composition of the raw materials and the preparation conditions are the same as in Example 1.

[0075] In this comparative example, the raw materials for preparing the high fracture toughness silicon nitride-based composite ceramic material include, by mass, 76 parts of fine α-Si3N4 powder, 14 parts of coarse α-Si3N4 powder, 4 parts of Y2O3, 1.2 parts of MgO, and 0.8 parts of Al2O3.

[0076] Based on the above-mentioned mass proportions, weigh out 760g of fine α-Si3N4 powder and 140g of coarse α-Si3N4 powder. As oxides, weigh out 135.7g of yttrium nitrate hexahydrate, 76.3g of magnesium nitrate hexahydrate, and 58.9g of aluminum nitrate nonahydrate.

[0077] A 3:1 volume ratio of ethanol and deionized water was mixed to prepare 1350 mL of an alcohol-water mixed solvent, comprising 1012.5 mL of ethanol and 337.5 mL of deionized water. 13.5 g of a 40 wt% ammonium polyacrylate solution was added to the alcohol-water mixed solvent, followed by fine and coarse α-Si3N4 powder. Using silicon nitride balls as the ball milling medium, with a ball-to-powder mass ratio controlled at 3:1, the mixture was ball-milled at 180 rpm for 12 h to obtain a silicon nitride slurry.

[0078] A composite sintering aid precursor was prepared by dissolving 135.7 g of yttrium nitrate hexahydrate, 76.3 g of magnesium nitrate hexahydrate, and 58.9 g of aluminum nitrate nonahydrate in 300 mL of deionized water. The composite sintering aid precursor was slowly added to a silicon nitride slurry, and the mixture was stirred at 500 rpm for 1 h. The pH of the system was then adjusted to 8.8 using ammonia, and stirring continued for another 1.5 h.

[0079] Subsequently, spray drying was performed with an inlet temperature of 190℃ and an outlet temperature of 95℃. After spray drying, the resulting powder was placed in a nitrogen atmosphere and held at 650℃ for 1 hour to obtain silicon nitride composite powder with surface-loaded composite sintering aids.

[0080] Silicon nitride composite powder with surface-loaded composite sintering aid was mixed with 24g of polyvinyl alcohol and 6g of polyethylene glycol, and deionized water was added to adjust the solid content of the slurry to 58wt%. After stirring evenly again, spray granulation was performed. The inlet temperature of spray granulation was 185℃ and the outlet temperature was 90℃, resulting in composite particles with a particle size of 50-90μm.

[0081] The composite particles are passed through a 60-mesh sieve and then placed into a mold for dry pressing at a pressure of 120 MPa to obtain a preform. The preform is then subjected to cold isostatic pressing at a pressure of 220 MPa for 3 minutes to obtain a ceramic body.

[0082] The ceramic blank was degreased under a nitrogen protective atmosphere. Specifically, the temperature was increased to 220℃ at 2℃ / min and held for 1 hour, then increased to 600℃ at 1.5℃ / min and held for 2 hours, with the nitrogen flow rate controlled at 1.5L / min.

[0083] The degreased ceramic green body was placed in a gas pressure sintering furnace for two-stage gas pressure sintering. In the first stage, the temperature was raised to 1680℃ and held for 1 hour; in the second stage, the temperature was raised to 1760℃ and held for 2 hours. The nitrogen pressure was controlled at 3 MPa during the sintering process. After sintering, the green body was cooled to room temperature with the furnace to obtain the sintered body, which was designated as Comparative Example 2 sample.

[0084] Comparative Example 3 In this comparative example, except that the bimodal particle size combination of α-Si3N4 fine powder and α-Si3N4 coarse powder was not used, and only α-Si3N4 fine powder was used, the other raw material composition and preparation conditions were the same as in Example 1.

[0085] In this comparative example, the raw materials for preparing the high fracture toughness silicon nitride-based composite ceramic material include, by mass, 90 parts of α-Si3N4 fine powder, 2 parts of β-Si3N4 seed crystals, 4 parts of Y2O3, 1.2 parts of MgO, and 0.8 parts of Al2O3.

[0086] Based on the above mass proportions, weigh out 900g of α-Si3N4 fine powder and 20g of β-Si3N4 seed crystals. As oxides, weigh out 135.7g of yttrium nitrate hexahydrate, 76.3g of magnesium nitrate hexahydrate, and 58.9g of aluminum nitrate nonahydrate.

[0087] A 3:1 volume ratio of ethanol and deionized water was mixed to prepare 1450 mL of an alcohol-water mixed solvent, comprising 1087.5 mL of ethanol and 362.5 mL of deionized water. 15.0 g of a 40 wt% ammonium polyacrylate solution was added to the alcohol-water mixed solvent, followed by fine α-Si3N4 powder. Using silicon nitride balls as the ball milling medium, with a ball-to-powder mass ratio controlled at 3:1, the mixture was ball-milled at 180 rpm for 12 h to obtain a silicon nitride slurry.

[0088] A composite sintering aid precursor was prepared by dissolving 135.7 g of yttrium nitrate hexahydrate, 76.3 g of magnesium nitrate hexahydrate, and 58.9 g of aluminum nitrate nonahydrate in 300 mL of deionized water. The composite sintering aid precursor was slowly added to a silicon nitride slurry, and the mixture was stirred at 500 rpm for 1 h. The pH of the system was then adjusted to 8.8 using ammonia, and stirring continued for another 1.5 h.

[0089] Subsequently, spray drying was performed with an inlet temperature of 190℃ and an outlet temperature of 95℃. After spray drying, the resulting powder was placed in a nitrogen atmosphere and held at 650℃ for 1 hour to obtain silicon nitride composite powder with surface-loaded composite sintering aids.

[0090] Silicon nitride composite powder with surface-loaded composite sintering aid was mixed with 20g of β-Si3N4 seed crystals and ball-milled for 2h using silicon nitride balls. Then, 24g of polyvinyl alcohol and 6g of polyethylene glycol were added, and deionized water was added to adjust the slurry solid content to 58wt%. After stirring again until homogeneous, spray granulation was performed. The spray granulation inlet temperature was 185℃ and the outlet temperature was 90℃, yielding composite particles with a particle size of 50–90μm.

[0091] The composite particles are passed through a 60-mesh sieve and then placed into a mold for dry pressing at a pressure of 120 MPa to obtain a preform. The preform is then subjected to cold isostatic pressing at a pressure of 220 MPa for 3 minutes to obtain a ceramic body.

[0092] The ceramic blank was degreased under a nitrogen protective atmosphere. Specifically, the temperature was increased to 220℃ at 2℃ / min and held for 1 hour, then increased to 600℃ at 1.5℃ / min and held for 2 hours, with the nitrogen flow rate controlled at 1.5L / min.

[0093] The degreased ceramic green body was placed in a gas pressure sintering furnace for two-stage gas pressure sintering. In the first stage, the temperature was raised to 1680℃ and held for 1 hour; in the second stage, the temperature was raised to 1760℃ and held for 2 hours. The nitrogen pressure was controlled at 3 MPa during the sintering process. After sintering, the green body was cooled to room temperature with the furnace to obtain the sintered body, which was designated as Comparative Example 3 sample.

[0094] Test Example 1 Performance tests were performed on the samples of Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0095] Samples from Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were processed into strip specimens. The specimens used for the three-point bending strength test and fracture toughness test were all 3mm × 4mm × 36mm in size. The specimen surfaces were ground and the edges were chamfered before use.

[0096] Each sample group shall include no fewer than 3 specimens for bulk density testing, no fewer than 5 specimens for three-point bending strength testing, and no fewer than 5 specimens for fracture toughness testing. The test results shall be the average value.

[0097] The bulk density of each group of samples was determined using the Archimedes water displacement method. The test medium was deionized water, and the test temperature was room temperature.

[0098] The relative density is calculated based on the theoretical density and volume density obtained from the conversion of the raw material composition of each group of samples.

[0099] The three-point bending strength of each group of samples was determined by the three-point bending method, with a span of 30 mm, a loading rate of 0.5 mm / min, and a test temperature of room temperature.

[0100] The fracture toughness of each group of samples was determined using the single-sided V-notch beam method. The sample size was 3mm×4mm×36mm, the span was 30mm, the V-notch depth was controlled to be 0.8~1.2mm, the loading rate was 0.05mm / min, and the test temperature was room temperature.

[0101] The test results are shown in Table 1.

[0102] Table 1 Performance test results of each group of samples

[0103] As shown in Table 1, the bulk density, relative density, three-point bending strength and fracture toughness of the samples in Example 1, Example 2 and Example 3 are all higher than those of the samples in Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0104] In the embodiments of the present invention, under the raw material system and process conditions adopted, the fracture toughness of the samples of Example 1, Example 2 and Example 3 is 7.84 to 8.57 MPa·m^1 / 2, and the three-point bending strength is 886 to 946 MPa; the fracture toughness of the samples of Comparative Example 1, Comparative Example 2 and Comparative Example 3 is 6.18 to 6.63 MPa·m^1 / 2, and the three-point bending strength is 742 to 812 MPa.

[0105] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A silicon nitride-based composite ceramic material with high fracture toughness, characterized in that, The high fracture toughness silicon nitride-based composite ceramic material comprises, by weight, the following raw materials: 70-82 parts of α-Si3N4 fine powder, 10-20 parts of α-Si3N4 coarse powder, 1-4 parts of β-Si3N4 seed crystals, 2-5 parts of Y2O3, 0.5-2.0 parts of MgO, and 0-1.5 parts of Al2O3; wherein, the Y2O3, MgO, and Al2O3 are derived from composite sintering aid precursors loaded on the surfaces of the α-Si3N4 fine powder and the α-Si3N4 coarse powder.

2. The silicon nitride-based composite ceramic material with high fracture toughness according to claim 1, characterized in that, The average particle size D50 of the α-Si3N4 fine powder is 0.3 to 0.8 μm, and the average particle size D50 of the α-Si3N4 coarse powder is 1.0 to 3.0 μm.

3. The silicon nitride-based composite ceramic material with high fracture toughness according to claim 1, characterized in that, The mass ratio of the fine α-Si3N4 powder to the coarse α-Si3N4 powder is 4:1 to 8:

1.

4. The silicon nitride-based composite ceramic material with high fracture toughness according to claim 1, characterized in that, The average grain size of the β-Si3N4 seed crystals is 0.5–2.0 μm, and the aspect ratio is 3–8.

5. The silicon nitride-based composite ceramic material with high fracture toughness according to claim 1, characterized in that, The high fracture toughness silicon nitride-based composite ceramic material comprises, by mass, the following raw materials: 74-78 parts of fine α-Si3N4 powder, 12-16 parts of coarse α-Si3N4 powder, 1.5-3 parts of β-Si3N4 seed crystals, 3-4.5 parts of Y2O3, 0.8-1.5 parts of MgO, and 0.3-1.0 parts of Al2O3.

6. A method for preparing a silicon nitride-based composite ceramic material with high fracture toughness, characterized in that, The high fracture toughness silicon nitride-based composite ceramic material according to any one of claims 1-5 comprises the following steps: S1. Add α-Si3N4 fine powder and α-Si3N4 coarse powder to an alcohol-water mixed solvent, add a dispersant and ball mill to disperse, to obtain silicon nitride slurry; S2. Dissolve the Y source, Mg source and optional Al source in deionized water or alcohol-water mixed solvent to prepare a composite sintering aid precursor. Add the composite sintering aid precursor to the silicon nitride slurry to allow the composite sintering aid precursor to be adsorbed or deposited on the surface of the α-Si3N4 fine powder and the α-Si3N4 coarse powder. Dry to obtain silicon nitride composite powder with surface-loaded composite sintering aid. S3. The silicon nitride composite powder with surface-loaded composite sintering aid is mixed evenly with β-Si3N4 seed crystals, binder and lubricant, and then spray granulation is performed to obtain composite particles. S4. The composite particles are dry-pressed and then subjected to cold isostatic pressing to obtain a ceramic blank. S5. The ceramic green body is degreased under a nitrogen protective atmosphere. The degreasing temperature is 400-700℃ and the temperature is maintained for 1-4 hours. S6. The degreased ceramic green body is subjected to two-stage gas pressure sintering. In the first stage of the two-stage gas pressure sintering, the temperature is raised to 1600-1720℃ and held for 0.5-2 hours. In the second stage of the two-stage gas pressure sintering, the temperature is raised to 1720-1800℃ and held for 1-4 hours. The nitrogen pressure in the two-stage gas pressure sintering is 0.5-10 MPa, thereby obtaining the silicon nitride-based composite ceramic material with high fracture toughness.

7. The method for preparing a silicon nitride-based composite ceramic material with high fracture toughness according to claim 6, characterized in that, The volume ratio of ethanol to deionized water in the alcohol-water mixed solvent is 1:1 to 4:1, the ball milling dispersion time is 4 to 24 hours, and the dispersant is ammonium polyacrylate, polyvinylpyrrolidone, or a combination thereof.

8. The method for preparing a silicon nitride-based composite ceramic material with high fracture toughness according to claim 6, characterized in that, The Y source is one or more of yttrium nitrate, yttrium acetate, or yttrium chloride; the Mg source is one or more of magnesium nitrate, magnesium acetate, or magnesium chloride; the optional Al source is one or more of aluminum nitrate, aluminum isopropoxide, or alumina sol; the pH value of the composite sintering aid precursor after being added to the silicon nitride slurry is 7-10; the dried powder is kept at 400-800℃ for 0.5-2 hours under a nitrogen atmosphere.

9. The method for preparing a silicon nitride-based composite ceramic material with high fracture toughness according to claim 6, characterized in that, The composite particles obtained by spray granulation have a particle size of 30–120 μm; the pressure of dry pressing is 50–200 MPa; and the pressure of cold isostatic pressing is 150–300 MPa.

10. The method for preparing a silicon nitride-based composite ceramic material with high fracture toughness according to claim 6, characterized in that, The first stage of the two-stage gas pressure sintering is heated to 1660-1700℃ and held for 0.8-1.5 hours. The second stage of the two-stage gas pressure sintering is heated to 1740-1780℃ and held for 1.5-3 hours. The nitrogen pressure of the two-stage gas pressure sintering is 2-5 MPa.

Images