Silicon nitride ceramic material and preparation method and application thereof

Abstract

The invention belongs to the technical field of silicon nitride ceramic materials, and particularly relates to a silicon nitride ceramic material and a preparation method and application thereof.The preparation method comprises the following steps that alpha-Si3N4 powder, ternary nitride powder and rare earth oxide powder are mixed with absolute ethyl alcohol according to the mass ratio of (80-92): (4-10): (2-6) and subjected to ball milling; drying, grinding and sieving the ball-milled slurry; and pre-pressing and sintering the sieved fine powder to obtain the composite material. The rare earth oxide / ternary nitride composite material is composed of one or more of a rare earth oxide and a ternary nitride according to a certain ratio. According to the synergistic combined sintering aid system, through the synergistic effect of multi-element ions, the phase change rate of Si3N4 in the sintering process, the length-diameter ratio of Si3N4 crystal grains and the components of intercrystalline glass phases are regulated and controlled, and the problems that a traditional oxide sintering aid has residual glass phases, the grain boundary is unstable and the like are solved; and comprehensive improvement of the comprehensive performance of the silicon nitride ceramic is realized through a microstructure regulation and control means.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon nitride ceramic materials, and specifically relates to a silicon nitride ceramic material and its preparation method and application. Through this method, the densification of silicon nitride ceramics is successfully achieved, so that the silicon nitride ceramics have the advantages of high bending strength, high fracture toughness and high hardness. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Silicon nitride is a high-performance structural ceramic characterized by high strength, high hardness, low thermal expansion, excellent thermal shock resistance, and oxidation resistance. It is widely used in the fields of machinery, aerospace, automotive, electronics, electric power, and new energy. For example, it can be used to manufacture bearings, turbine blades, seals, molds, ceramic cutting tools, and pump components. Silicon nitride ceramics produced by conventional atmospheric pressure sintering have low density, resulting in insufficient flexural strength and fracture toughness, making them difficult to withstand demanding operating conditions such as high loads and strong impacts.

[0004] Although the strength and density of silicon nitride can be significantly improved through processes such as hot pressing and hot isostatic pressing, the following problems still exist: Oxide sintering aids, such as Y2O3 and Al2O3, are commonly added during the sintering process of silicon nitride ceramics. However, these additives tend to remain within the material, forming alkaline earth metal or aluminum glass phases at grain boundaries. These components are prone to decomposition or reaction in high-temperature, oxidizing, or corrosive environments, affecting the ceramic's service life and exhibiting significant performance degradation, particularly under extreme operating conditions. While these additives promote the formation of a liquid phase, they can also lead to excessive grain growth, resulting in an uneven microstructure, anisotropy in material properties, and the risk of microcrack formation.

[0005] Traditional oxide sintering aids also have the problem of limited selectivity. For example, Al2O3, CaO and other additives have a narrow adaptability range to sintering temperature, making it difficult to achieve dense sintering at lower temperatures. At the same time, they are not suitable for certain special process conditions.

[0006] In addition, the content of sintering aids is also crucial to the sintering process. Sintering aids are directly involved in the formation of the liquid phase. Too little liquid phase will make the densification of Si3N4 ceramics more difficult, and too much liquid phase will eventually lead to an increase in the glass phase content and a decrease in mechanical properties.

[0007] Si3N4 consists of two common crystal forms: α-Si3N4 and β-Si3N4. α-Si3N4 is a low-temperature stable form with high hardness but low toughness; β-Si3N4 is a high-temperature stable form with high flexural strength and fracture toughness, but low hardness. Existing Si3N4 preparation processes often struggle to leverage the advantages of both crystal forms, meaning it's difficult to simultaneously optimize the toughness and hardness of Si3N4 ceramics.

[0008] Furthermore, while current high-end Si3N4 ceramics reinforced with oriented whiskers or fibers can achieve ultra-high axial performance, they present a risk of systemic failure when subjected to complex operating conditions such as multi-directional spatial stress and thermal-mechanical coupling. Finally, existing Si3N4 ceramics are typically produced using methods such as hot pressing and hot isostatic pressing. These processes require prolonged exposure to high temperatures and pressures, resulting in complex and costly processes. Furthermore, prolonged exposure to high temperatures and pressures can lead to abnormal growth of Si3N4 grains, ultimately resulting in a reduction in mechanical properties. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the present invention aims to provide a silicon nitride ceramic material and a preparation method and application thereof.

[0010] In order to achieve the above object, the present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a method for preparing a silicon nitride ceramic material, comprising the following steps: mixing α-Si3N4 powder, ternary nitride powder, and rare earth oxide powder with anhydrous ethanol in a mass ratio of 80-92:4-10:2-6 and ball milling; The slurry after ball milling is dried, ground and sieved; the sieved fine powder is pre-pressed and sintered to obtain the product.

[0011] In a second aspect, the present invention provides a silicon nitride ceramic material prepared by the preparation method.

[0012] In a third aspect, the present invention provides applications of the silicon nitride ceramic material in the fields of aerospace, automobiles, electricity, electronics and / or new energy.

[0013] The beneficial effects achieved by one or more embodiments of the present invention are as follows: The present invention provides a composite sintering aid system for Si3N4 ceramics, comprising rare earth oxides (such as Y2O3 and Lu2O3) and ternary nitrides (such as Ti2AlN and Sr2Si5N8). This synergistic sintering aid system, through the synergistic action of multiple ions, regulates the phase transformation rate, aspect ratio of Si3N4 grains, and composition of the intercrystalline glass phase during sintering. This overcomes the problems of residual glass phase and grain boundary instability associated with traditional oxide sintering aids. Furthermore, through microstructural manipulation, it achieves comprehensive improvements in the overall performance of silicon nitride ceramics, demonstrating promising prospects for widespread application.

[0014] The present invention achieves a multi-faceted improvement in the mechanical properties of Si3N4 ceramics by combining rapid hot pressing sintering technology with a synergistic sintering aid system of ternary nitrides and rare earth oxides. X-ray diffraction (XRD) results and microstructural analysis show that the introduction of ternary nitrides significantly promotes the α / β phase transformation of Si3N4 ceramics during the sintering process and greatly improves the aspect ratio of Si3N4 grains.

[0015] In addition, the Si3N4 ceramic preparation method of the present invention has a fast production speed and a shorter heating time than hot pressing sintering. Under the premise of ensuring the densification of Si3N4 ceramics, it avoids the degradation of mechanical properties caused by abnormal growth of Si3N4 grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0017] Figure 1 3 is a comparison chart of the mechanical properties of Si3N4 ceramic materials prepared in Examples 1-3 of the present invention and Comparative Example 1; Figure 2 XRD diffraction patterns of the Si3N4 ceramic materials prepared in Example 1 and Comparative Example 1 of the present invention; Figure 3 4000x SEM images of the fracture surface of Si3N4 ceramics of the present invention, (a) Si3N4 ceramic material D1 prepared in Comparative Example 1; (b) Si3N4 ceramic material W2 prepared in Example 2; Figure 4 This is an EDS image of a curved cross section of the Si3N4 ceramic material prepared in Example 2 of the present invention; Figure 52000x SEM images of Si3N4 ceramic corrosion samples prepared in Example 2 of the present invention and Comparative Example 1 and comparison diagram of their aspect ratios, (a) SEM image of D1; (b) SEM image of W2; (a1) grain length distribution diagram of D1; (a2) grain diameter distribution diagram of D1; (b1) grain length distribution diagram of W2; (b2) grain diameter distribution diagram of W2. DETAILED DESCRIPTION

[0018] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0019] In a first aspect, the present invention provides a method for preparing a silicon nitride ceramic material, comprising the following steps: mixing α-Si3N4 powder, ternary nitride powder, and rare earth oxide powder with anhydrous ethanol in a mass ratio of 80-95:3-10:2-10 and ball milling; The slurry after ball milling is dried, ground and sieved; the sieved fine powder is pre-pressed and sintered to obtain the product.

[0020] This system should be able to effectively form a liquid phase to promote sintering, and even with the introduction of only a small amount of additives, it can achieve high densification of Si3N4 ceramics at a relatively low temperature. At the same time, the additive system formed by ternary nitrides and rare earth oxides should be able to effectively control the composition of the intergranular phase during sintering, optimize the grain boundary structure, inhibit the formation of a low-melting glass phase, and enhance the thermal stability and mechanical strength of the grain boundaries.

[0021] Furthermore, the additive system should also be able to inhibit abnormal grain growth and promote grain homogenization, thereby achieving a fine and dense microstructure. Through the action of these multiple synergistic mechanisms, the ultimate goal is to achieve comprehensive improvements in the flexural strength, fracture toughness, hardness, and high-temperature stability of Si3N4 ceramics, thereby meeting the high-performance requirements of advanced ceramic materials in high-end equipment manufacturing and extreme environment applications.

[0022] In some embodiments, the mass ratio of α-Si3N4 powder, ternary nitride powder and rare earth oxide powder is 85-92:3-10:2-8.

[0023] Preferably, the mass ratio of α-Si3N4 powder, ternary nitride powder and rare earth oxide powder is 87-92:3-5:2-8.

[0024] In some embodiments, the ternary nitride powder is selected from Ti2AlN, Sr2Si5N8, CaSiN2, Ba2Si5N8, SrSi7N 10 , Ti4AlN3 or at least one of them.

[0025] In some embodiments, the rare earth oxide is Y2O3, Lu2O3, Yb2O3, CeO2 or Eu2O3.

[0026] Preferably, the rare earth oxides are Y2O3 and Lu2O3, and the ternary nitride powder is selected from Ti2AlN and / or Sr2Si5N8; the mass ratio of Y2O3 to Lu2O3 is 1-2:1-2.

[0027] More preferably, the mass ratio of Y2O3 to Lu2O3 is 1.5-2:1.

[0028] Preferably, the ternary nitride powder is Ti2AlN and Sr2Si5N8, the rare earth oxide is Y2O3 and / or Lu2O3, and the mass ratio of Ti2AlN and Sr2Si5N8 is 0.8-1.5:0.8-1.5.

[0029] In some embodiments, the sintering procedure is: 20-30°C to 750-850°C, heating time 8-12 min; 750-850°C to 1600-1700°C, heating time 15-20 min; 1600-1700°C to 1740-1760°C, heating time 2-5 min; keeping at 1740-1760°C, heating time 150-200 min; after the insulation is completed, naturally cool.

[0030] In a second aspect, the present invention provides a silicon nitride ceramic material prepared by the preparation method.

[0031] In a third aspect, the present invention provides applications of the silicon nitride ceramic material in the fields of aerospace, automobiles, electricity, electronics and / or new energy.

[0032] The present invention will be further described below with reference to the embodiments.

[0033] Example 1 In this embodiment, Si3N4 ceramic W1 is prepared: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 90 wt% (purity ≥ 99.9%, particle size D 50=0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), 2.5 wt% layered Ti2AlN (purity ≥95%, 200 mesh), and 2.5 wt% Lu2O3 powder (purity ≥99.9%, particle size 1μm). An appropriate amount of anhydrous ethanol was used as the dispersion solvent. To avoid the introduction of impurities, Si3N4 balls were used as milling balls. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0034] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0035] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-pressing the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0036] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the Si3N4 ceramic W1 was sintered in a rapid hot-pressing furnace. The sintering schedule was room temperature to 800°C (10 minutes, 6 MPa pressure); 800°C to 1650°C (17 minutes, 30 MPa pressure); 1650°C to 1750°C (3 minutes, 30 MPa pressure); a hold at 1750°C (170 minutes, 30 MPa pressure); and a natural cooling cycle from 1750°C to room temperature. The entire sintering process for the Si3N4 ceramic W1 was performed in a vacuum environment (less than 10 Pa).

[0037] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic W1 can be obtained by natural cooling and demoulding.

[0038] In this embodiment, the mechanical properties of Si3N4 ceramic W1 are as follows: Figure 1 As shown, the bending strength reaches 976 MPa and the fracture toughness reaches 9.5 MPa·m 1 / 2 , hardness reaches 15.1 GPa and density is 95.2%.

[0039] Example 2 In this embodiment, Si3N4 ceramic W2: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 90 wt% (purity ≥ 99.9%, particle size D50 =0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), 2.5 wt% layered Ti2AlN (95% purity, 200 mesh), and 2.5 wt% Sr2Si5N8 powder (particle size 660 nm). An appropriate amount of anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as milling balls to avoid the introduction of impurities. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0040] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0041] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-loading the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0042] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the material is sintered in a rapid hot-pressing sintering furnace. The sintering schedule is room temperature to 800°C (10 minutes, 6 MPa pressure); 800°C to 1650°C (17 minutes, 30 MPa pressure); 1650°C to 1750°C (3 minutes, 30 MPa pressure); hold at 1750°C (170 minutes, 30 MPa pressure); and then naturally cool from 1750°C to room temperature. The entire sintering process for Si3N4 ceramic W2 is performed in a vacuum environment.

[0043] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic W2 can be obtained by natural cooling and demoulding.

[0044] In this embodiment, the mechanical properties of Si3N4 ceramic W2 are as follows: Figure 1 As shown, the bending strength reaches 818 MPa and the fracture toughness reaches 8.1 MPa·m 1 / 2 , hardness reaches 17.5 GPa and density is 97.3%.

[0045] Example 3 In this embodiment, Si3N4 ceramic W3: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, including 90 wt% of α-Si3N4 powder (purity ≥ 99.9%, particle size D50 =0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), 2.5 wt% Lu2O3 powder (purity ≥99.9%, particle size 1μm), and 2.5 wt% Sr2Si5N8 powder (particle size 660 nm). An appropriate amount of anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as milling balls to avoid the introduction of impurities. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0046] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0047] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-loading the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0048] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the material is sintered in a rapid hot-pressing sintering furnace. The sintering schedule is room temperature to 800°C (10 minutes, pressure 6 MPa); 800°C to 1650°C (17 minutes, pressure 30 MPa); 1650°C to 1750°C (3 minutes, pressure 30 MPa); hold at 1750°C (170 minutes, pressure 30 MPa); then cool naturally from 1750°C to room temperature. The entire sintering process for Si3N4 ceramic W3 is performed in a vacuum environment.

[0049] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic W3 can be obtained by natural cooling and demoulding.

[0050] In this embodiment, the mechanical properties of Si3N4 ceramic W3 are as follows: Figure 1 As shown, the bending strength reaches 992 MPa and the fracture toughness reaches 9.0 MPa·m 1 / 2 , hardness reaches 16.1 GPa and density is 93.6%.

[0051] Example 4 This example prepares Si3N4 ceramic W4: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 91 wt% (purity ≥ 99.9%, particle size D50 =0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), 2 wt% Sr2Si5N8 powder (particle size 660 nm), and 2 wt% layered Ti2AlN (95% purity, 200 mesh). An appropriate amount of anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as milling balls to avoid the introduction of impurities. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0052] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0053] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-pressing the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0054] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the material is sintered in a rapid hot-pressing sintering furnace. The sintering schedule is room temperature to 800°C (10 minutes ramp time, 6 MPa pressure); 800°C to 1650°C (17 minutes ramp time, 30 MPa pressure); 1650°C to 1750°C (3 minutes ramp time, 30 MPa pressure); hold at 1750°C (170 minutes hold time, 30 MPa pressure); and finally, from 1750°C to room temperature, followed by natural cooling. The entire sintering process for Si3N4 ceramic W4 is performed in a vacuum environment.

[0055] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic W4 can be obtained by natural cooling and demoulding.

[0056] In this embodiment, the mechanical properties of Si3N4 ceramic W4 are bending strength of 890 MPa and fracture toughness of 9.1 MPa·m 1 / 2 , hardness reaches 16.9 GPa and density is 95.6%.

[0057] Example 5 In this embodiment, Si3N4 ceramic W5 is prepared: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 87.5 wt% (purity ≥ 99.9%, particle size D 50=0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), 2.5 wt% Lu2O3 powder (purity ≥99.9%, particle size 1μm), 2.5 wt% Sr2Si5N8 powder (particle size 660 nm), and 2.5 wt% layered Ti2AlN (95% purity, 200 mesh). An appropriate amount of anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as milling balls to avoid the introduction of impurities. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0058] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0059] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-pressing the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0060] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the material is sintered in a rapid hot-pressing sintering furnace. The sintering schedule is room temperature to 800°C (10 minutes, pressure 6 MPa); 800°C to 1650°C (17 minutes, pressure 30 MPa); 1650°C to 1750°C (3 minutes, pressure 30 MPa); hold at 1750°C (170 minutes, pressure 30 MPa); then cool naturally from 1750°C to room temperature. The entire sintering process for Si3N4 ceramic W5 is performed in a vacuum environment.

[0061] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic W5 can be obtained by natural cooling and demoulding.

[0062] In this embodiment, the mechanical properties of Si3N4 ceramic W5 are bending strength up to 951 MPa and fracture toughness up to 8.8 MPa·m 1 / 2 , hardness reaches 15.9 GPa and density is 96.3%.

[0063] Example 6 This example prepares Si3N4 ceramic W6: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, including 80 wt% of α-Si3N4 powder (purity ≥ 99.9%, particle size D50 =0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), 5 wt% Lu2O3 powder (purity ≥99.9%, particle size 1μm), 5 wt% Sr2Si5N8 powder (particle size 660 nm), and 5 wt% layered Ti2AlN (95% purity, 200 mesh). An appropriate amount of anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as milling balls to avoid the introduction of impurities. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0064] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0065] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-pressing the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0066] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the material is sintered in a rapid hot-pressing sintering furnace. The sintering schedule is room temperature to 800°C (10 minutes, pressure 6 MPa); 800°C to 1650°C (17 minutes, pressure 30 MPa); 1650°C to 1750°C (3 minutes, pressure 30 MPa); hold at 1750°C (170 minutes, pressure 30 MPa); then naturally cool from 1750°C to room temperature. The entire sintering process for Si3N4 ceramic W6 is performed in a vacuum environment.

[0067] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic W6 can be obtained by natural cooling and demoulding.

[0068] In this embodiment, the mechanical properties of Si3N4 ceramic W6 are bending strength of 832 MPa and fracture toughness of 9.1 MPa·m 1 / 2 , hardness reaches 16.4 GPa and density is 94.6%.

[0069] Comparative Example 1 In this comparative example, Si3N4 ceramic D1 was prepared, and the sintering aid was only Y2O3 powder: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 95 wt% (purity ≥ 99.9%, particle size D 50 =0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), and an appropriate amount of anhydrous ethanol as the dispersion solvent. To avoid the introduction of impurities, Si3N4 balls were used as milling balls. The milling process was carried out in a planetary ball mill at a speed of 300 rpm for 8 hours.

[0070] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0071] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-pressing the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0072] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the ceramic was sintered in a rapid hot-pressing furnace. The sintering schedule was room temperature to 800°C (10 minutes, 6 MPa pressure); 800°C to 1650°C (17 minutes, 30 MPa pressure); 1650°C to 1750°C (3 minutes, 30 MPa pressure); a hold at 1750°C (170 minutes, 30 MPa pressure); and finally, a natural cooling cycle from 1750°C to room temperature. The entire sintering process for Si3N4 ceramic D1 was performed in a vacuum environment.

[0073] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic D1 can be obtained by natural cooling and demoulding.

[0074] In this comparative example, the mechanical properties of Si3N4 ceramic D1 are as follows: Figure 1 As shown, the bending strength reaches 788 MPa and the fracture toughness reaches 8.9 MPa·m 1 / 2 , hardness reaches 15.6 GPa and density is 98.6%.

[0075] Comparative Example 2 In this comparative example, Si3N4 ceramic D2 was prepared, and the sintering aids were only Y2O3 powder and Lu2O3 powder, without ternary nitride: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 92.5 wt% (purity ≥ 99.9%, particle size D 50 =0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), and 2.5 wt% Lu2O3 powder (purity ≥99.9%, particle size 1μm). An appropriate amount of anhydrous ethanol was used as the dispersion solvent. To avoid the introduction of impurities, Si3N4 balls were used as milling balls. The milling process was performed in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0076] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0077] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-loading the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0078] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the material is sintered in a rapid hot-pressing sintering furnace. The sintering schedule is room temperature to 800°C (10 minutes, 6 MPa pressure); 800°C to 1650°C (17 minutes, 30 MPa pressure); 1650°C to 1750°C (3 minutes, 30 MPa pressure); a hold at 1750°C (170 minutes, 30 MPa pressure); and finally, a natural cooling cycle from 1750°C to room temperature. The entire sintering process for Si3N4 ceramic D2 is performed in a vacuum environment.

[0079] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic D2 can be obtained by natural cooling and demoulding.

[0080] In this comparative example, the bending strength of Si3N4 ceramic D2 reaches 856 MPa and the fracture toughness reaches 9.1 MPa·m 1 / 2 , hardness reaches 16.1 GPa and density is 97.2%.

[0081] Comparative Example 3 In this comparative example, Si3N4 ceramic D3 was prepared, and the sintering aids were only Y2O3 powder and Lu2O3 powder, without ternary nitride: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, including 90 wt% of α-Si3N4 powder (purity ≥ 99.9%, particle size D 50 =0.5μm), 5 wt% Y2O3 powder (purity ≥99.9%, particle size 1μm), and 5 wt% Lu2O3 powder (purity ≥99.9%, particle size 1μm). An appropriate amount of anhydrous ethanol was used as the dispersion solvent. To avoid the introduction of impurities, Si3N4 balls were used as milling balls. The milling process was performed in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0082] Step 2 - Slurry Drying The uniformly mixed slurry was poured into a Petri dish, placed in a vacuum drying oven at a drying temperature of 80°C for one day, and the anhydrous ethanol was completely evaporated to obtain a coarse powder.

[0083] Step 3 - Grind and sieve Grind the coarse powder with uniform composition several times and then pass it through a 60-mesh sieve to obtain fine powder with relatively uniform and fine particle size; Step 4 - Pre-loading the mold The fine powder after grinding and screening is loaded into a mold and pre-compressed on a tablet press with a pre-compression pressure of 10 MPa.

[0084] Step 5 - Rapid Hot Pressing Sintering After pre-pressing, the ceramic is sintered in a rapid hot-pressing furnace. The sintering cycle is as follows: room temperature to 800°C (10 minutes, pressure 6 MPa); 800°C to 1650°C (17 minutes, pressure 30 MPa); 1650°C to 1750°C (3 minutes, pressure 30 MPa); hold at 1750°C (170 minutes, pressure 30 MPa); then cool from 1750°C to room temperature. The entire sintering process for Si3N4 ceramic D3 is performed in a vacuum environment.

[0085] Step 6 - Cooling and demoulding After sintering, Si3N4 ceramic D3 can be obtained by natural cooling and demoulding.

[0086] In this comparative example, the bending strength of Si3N4 ceramic D3 reaches 844 MPa and the fracture toughness reaches 8.9 MPa·m 1 / 2 , hardness reaches 15.8 GPa and density is 96.6%.

[0087] Comparative Example 4 In this comparative example, Si3N4 ceramic D4 was prepared, and the sintering aids were only layered Ti2AlN and Sr2Si5N8, without rare earth oxides: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 90 wt% (purity ≥ 99.9%, particle size D 50 =0.5μm), 5 wt% layered Ti2AlN (95% purity, 200 mesh), and 5 wt% Sr2Si5N8 powder (660 nm particle size). An appropriate amount of anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as milling balls to avoid the introduction of impurities. The milling process was carried out in a planetary ball mill at a speed of 300 rpm for 8 hours.

[0088] The rest are the same as in Example 1.

[0089] In this comparative example, the bending strength of Si3N4 ceramic D4 reaches 857MPa and the fracture toughness reaches 8.7MPa·m 1 / 2 , hardness reaches 16.8 GPa and density is 96.2%.

[0090] Comparative Example 5 In this comparative example, Si3N4 ceramic D5 was prepared, and the sintering aid was only layered Ti2AlN, without rare earth oxides: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 95 wt% (purity ≥ 99.9%, particle size D 50 =0.5μm), layered Ti2AlN with a content of 5 wt% (95% purity, 200 mesh); an appropriate amount of anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as milling balls to avoid the introduction of impurities. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0091] The rest are the same as in Example 1.

[0092] In this comparative example, the bending strength of Si3N4 ceramic D5 reaches 901 MPa and the fracture toughness reaches 8.4 MPa·m 1 / 2 , hardness reaches 17.1 GPa and density is 95.7%.

[0093] Comparative Example 6 In this comparative example, Si3N4 ceramic D6 was prepared, and the sintering aid was only Sr2Si5N8, without rare earth oxides: Step 1 - Mixing the ingredients The raw material powders were weighed strictly according to the composition ratio, of which α-Si3N4 powder was 95 wt% (purity ≥ 99.9%, particle size D 50=0.5μm), 5wt% Sr2Si5N8 powder (particle size 660 nm), and an appropriate amount of anhydrous ethanol as the dispersion solvent. To avoid the introduction of impurities, Si3N4 balls were used as milling balls. The milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 hours.

[0094] The rest are the same as in Example 1.

[0095] In this comparative example, the bending strength of Si3N4 ceramic D6 reaches 842 MPa and the fracture toughness reaches 8.8 MPa·m 1 / 2 , hardness reaches 16.3 GPa and density is 96.8%.

[0096] The relevant properties of the Si3N4 ceramics prepared in Examples 1-6 and Comparative Examples 1-6 are summarized in Table 1.

[0097] Table 1 Relevant properties of Si3N4 ceramics prepared in Examples 1-6 and Comparative Examples 1-6

[0098] Table 1 shows that the synergistic introduction of 2.5 wt% rare earth oxide Lu2O3 and layered Ti2AlN resulted in a slight decrease in density but an increase in flexural strength by 23.8% and fracture toughness by 5.6%. The synergistic introduction of 2.5 wt% layered Ti2AlN and Sr2Si5N8 resulted in a 12% increase in both flexural strength and hardness. The synergistic introduction of 2.5 wt% Sr2Si5N8 and 2.5 wt% Lu2O3 resulted in a maximum increase in flexural strength of nearly 26%, with little change in toughness. The simultaneous introduction of Y2O3, Sr2Si5N8, Lu2O3, and layered Ti2AlN also resulted in a simultaneous increase in flexural strength and hardness.

[0099] Combine Figure 1 Analysis shows that compared with the blank sample D1 with only Y2O3 added, the density of sample W1 decreased from 98.6% to 95.2% with the synergistic introduction of rare earth oxide Lu2O3 and layered Ti2AlN, both of which were introduced in an amount of 2.5 wt%. However, the flexural strength of Si3N4 increased from 788 MPa to 976 MPa, an increase of nearly 24%; the fracture toughness increased from 8.9 MPa·m 1 / 2 Increased to 9.5 MPa·m 1 / 2 , an increase of 5.6%.

[0100] After the synergistic introduction of 2.5 wt% layered Ti2AlN and 2.5 wt% Sr2Si5N8 into W2, the hardness increased from 15.6 GPa to 17.5 GPa, an increase of 12%; after the synergistic introduction of 2.5 wt% Sr2Si5N8 and 2.5 wt% Lu2O3 as sintering aids into W3, the bending strength of Si3N4 ceramics increased the most, reaching 992 MPa, with a performance improvement of nearly 26%.

[0101] In order to verify the test results in Table 1, a series of analytical characterizations were performed on the prepared Si3N4 ceramics. The XRD patterns of the Si3N4 ceramics prepared in Example 2 (W2) and Comparative Example 1 (D1) are shown in Figure 1. Figure 2 As shown, Si3N4 in W2 almost exists in the form of β-Si3N4, and D1 contains a small amount of α-Si3N4, which indicates that the synergistically introduced Lu2O3, Sr2Si5N8 and layered Ti2AlN promote the α / β phase transformation during the liquid phase sintering of Si3N4.

[0102] The cross section of Si3N4 ceramic was subjected to gold spraying after bending and fracture, and the SEM image of the cross section was taken using a scanning electron microscope. Figure 3 (a) and (b) show 4000 times SEM images of the cross section of Si3N4 ceramic D1 prepared in comparative example 1 and Si3N4 ceramic W2 prepared in example 2. Figure 3 It is not difficult to see that Si3N4 ceramics have grown columnar β-Si3N4 grains, such as Figure 3 In addition, there are many long strip-shaped indentations left by the extraction of columnar crystals during the fracture process, such as Figure 3 The area selected by the yellow dashed line in (b) is shown. Compared to whisker-toughened Si3N4 ceramics, the Si3N4 ceramics prepared in this embodiment rely entirely on the self-toughening of columnar β-Si3N4 grains to achieve enhanced toughness. This reduces costs while also providing more uniform properties in all directions, making the Si3N4 ceramics isotropic.

[0103] At the same time, the cross-section element distribution analysis was carried out using the energy dispersive spectrometer (EDS) equipped with a scanning electron microscope. The cross-section EDS results of the Si3N4 ceramic W2 prepared in Example 2 are as follows: Figure 4 As shown in the figure, the synergistic combination of sintering aids is well and evenly distributed in the Si3N4 ceramic matrix, with only titanium element partially aggregated. Combined with XRD pattern analysis, this is because the layered nitrides are highly stable and do not participate in the formation of the liquid phase during the Si3N4 sintering process, but remain in their original position. The Al element is lost during the liquid phase sintering process and finally forms intergranular TiN.

[0104] In order to calculate the grain size of the samples and understand the changes in their aspect ratio, the sample surface was polished and then etched with a 400°C sodium hydroxide (NaOH) solution for 1 minute. A scanning electron microscope was then used to capture a 2000x image of the surface, and 100 grains were counted to obtain the length and diameter distribution data of the β-Si3N4 grains. The grain statistics of the Si3N4 ceramic D1 prepared in Comparative Example 1 and the Si3N4 ceramic W2 prepared in Example 2 are shown in Figure 2. Figure 5 As shown. Figure 5 The data show that the aspect ratio of the Si3N4 ceramic D1 prepared in Comparative Example 1 is 3.6. Figure 5 As shown in (a), (a1) and (a2), the aspect ratio of the Si3N4 ceramic W2 sample prepared in Example 2 with the synergistic layered Ti2AlN and Sr2Si5N8 reaches 8.9, as shown in Figure 5 As shown in (b), (b1) and (b2).

[0105] In summary, the Si3N4 ceramic sintering aid system designed by the present invention has significant technical advantages. By introducing a small amount of ternary nitride and rare earth oxide synergistic combination, high densification of Si3N4 ceramics can be achieved during the sintering process, effectively overcoming the problems of residual grain boundary glass phase and performance bottlenecks brought about by traditional additive systems. This composite additive system achieves a synergistic improvement in mechanical properties, including simultaneous enhancement of flexural strength and hardness, while maintaining excellent toughness. As shown in Example W3, its flexural strength and hardness are significantly better than those of Reference Example D1, and there is no decrease in toughness, which fully verifies the optimization effect of the system. In terms of process implementation, the method provided by the present application has the characteristics of reasonable temperature and pressure control, simple and efficient process route, etc., can significantly shorten the sintering cycle, reduce energy consumption and material loss, and is conducive to the subsequent industrialization, large-scale production and application promotion of the product.

[0106] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon nitride ceramic material, characterized in that: The method comprises the following steps: mixing α-Si3N4 powder, ternary nitride powder and rare earth oxide powder with anhydrous ethanol in a mass ratio of 80-95:3-10:2-10 and ball milling; the ternary nitride powder is selected from Ti2AlN, Sr2Si5N8, CaSiN2, Ba2Si5N8, SrSi7N 10 , Ti4AlN3; the rare earth oxide is Y2O3, Lu2O3, Yb2O3, CeO2 or Eu2O3; The slurry after ball milling is dried, ground and sieved; the sieved fine powder is pre-pressed and sintered to obtain the product.

2. The method for preparing a silicon nitride ceramic material according to claim 1, wherein: The mass ratio of α-Si3N4 powder, ternary nitride powder and rare earth oxide powder is 85-92:3-10:2-8.

3. The method for preparing the silicon nitride ceramic material according to claim 2, wherein: The mass ratio of α-Si3N4 powder, ternary nitride powder and rare earth oxide powder is 87-92:3-5:2-8.

4. The method for preparing a silicon nitride ceramic material according to claim 1, wherein: The rare earth oxides are Y2O3 and Lu2O3, and the ternary nitride powder is selected from Ti2AlN and / or Sr2Si5N8.

5. The method for preparing the silicon nitride ceramic material according to claim 4, wherein: The mass ratio of Y2O3 and Lu2O3 is 1-2:1-2.

6. The method for preparing the silicon nitride ceramic material according to claim 5, wherein: The mass ratio of Y2O3 to Lu2O3 is 1.5-2:

1.

7. The method for preparing a silicon nitride ceramic material according to claim 1, wherein: The ternary nitride powder is Ti2AlN and Sr2Si5N8, the rare earth oxide is Y2O3 and / or Lu2O3, and the mass ratio of Ti2AlN to Sr2Si5N8 is 0.8-1.5:0.8-1.

5.

8. The method for preparing a silicon nitride ceramic material according to claim 1, wherein: The sintering procedure is: 20-30℃ to 750-850℃, heating time 8-12 min; 750-850℃ to 1600-1700℃, heating time 15-20 min; 1600-1700℃ to 1740-1760℃, heating time 2-5min; keep warm at 1740-1760℃, heating time 150-200min; after the insulation is completed, cool.

9. A silicon nitride ceramic material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Application of the silicon nitride ceramic material according to claim 9 in the fields of aerospace, automobile, electric power, electronics and / or new energy.

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