A silicon nitride ceramic material, its preparation method and application

Abstract

This invention belongs to the technical field of silicon nitride ceramic materials, specifically relating to a silicon nitride ceramic material, its preparation method, and its application. The preparation method includes 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; drying, grinding, and sieving the ball-milled slurry; pre-pressing and sintering the sieved fine powder to obtain the final product. The material is composed of one or more rare earth oxides and ternary nitrides in a certain proportion. This synergistic sintering aid system, through the synergistic effect of multiple ions, regulates the phase transformation rate of Si3N4 during sintering, the aspect ratio of Si3N4 grains, and the composition of the glassy phase between crystals, overcoming the problems of residual glassy phase and grain boundary instability in traditional oxide sintering aids. Furthermore, it achieves a comprehensive improvement in the overall performance of silicon nitride ceramics through microstructure control.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride ceramic materials technology, specifically relating to a silicon nitride ceramic material, its preparation method and application. The method successfully achieves densification of silicon nitride ceramics, giving them advantages such as high bending strength, high fracture toughness and high hardness. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Silicon nitride is a high-performance structural ceramic with high strength, high hardness, low thermal expansion, excellent thermal shock resistance, and oxidation resistance. It is widely used in machinery, aerospace, automotive, electronics, power, and new energy fields, for example, in the manufacture of bearings, turbine blades, seals, molds, ceramic cutting tools, and pump components. However, silicon nitride ceramics prepared by traditional atmospheric pressure sintering have low density, resulting in insufficient flexural strength and fracture toughness, making them unsuitable for demanding conditions such as high loads and strong impacts.

[0004] Although processes such as hot pressing and hot isostatic pressing can significantly improve the strength and density of silicon nitride, the following problems still exist:

[0005] During the sintering process of silicon nitride ceramics, oxide sintering aids such as Y₂O₃ and Al₂O₃ are generally added. However, these aids tend to remain within the material, forming alkaline earth metals or aluminum glassy phases at grain boundaries. These components are prone to decomposition or reaction under high-temperature, oxidizing, or corrosive environments, affecting the service life of the ceramics, especially exhibiting significant performance degradation under extreme conditions. While these aids promote liquid phase formation, they can also lead to excessive grain growth, resulting in inhomogeneous microstructure and consequently increasing the risk of anisotropy in material properties and microcrack formation.

[0006] Traditional oxide sintering aids also suffer from limited selectivity. For example, aids such as Al2O3 and CaO have a narrow range of adaptability to sintering temperatures, making it difficult to achieve dense sintering at lower temperatures. They are also not suitable for certain special process conditions.

[0007] In addition, the content of sintering aids is also crucial to the sintering process. Sintering aids directly participate in the formation of the liquid phase. Too little liquid phase will make it more difficult to densify Si3N4 ceramics, while too much liquid phase will eventually lead to an increase in the glass phase content and a decrease in mechanical properties.

[0008] Si3N4 comprises two common crystal forms: α-Si3N4 and β-Si3N4. α-Si3N4 is a low-temperature stable crystal form with high hardness but low toughness; β-Si3N4 is a high-temperature stable crystal form with high flexural strength and fracture toughness but low hardness. Existing Si3N4 preparation processes often struggle to combine the advantages of both crystal forms, meaning it is difficult to simultaneously optimize the toughness and hardness of Si3N4 ceramics.

[0009] Furthermore, while current high-end Si3N4 ceramics reinforced with oriented whiskers or fibers can achieve ultra-high axial performance, they pose a risk of systemic failure when subjected to complex conditions such as multi-directional spatial stress and thermo-mechanical coupling loads. Finally, existing Si3N4 ceramics are generally prepared using methods such as hot pressing sintering and hot isostatic pressing sintering. These processes require prolonged exposure to high temperatures and pressures, resulting in complex processes and high costs. Moreover, prolonged exposure to high temperatures and pressures can lead to abnormal growth of Si3N4 grains, ultimately causing a decrease in mechanical properties. Summary of the Invention

[0010] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a silicon nitride ceramic material, its preparation method and application.

[0011] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0012] In a first aspect, the present invention provides a method for preparing 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 them;

[0013] The slurry after ball milling is dried, ground, and sieved; the sieved fine powder is then pre-pressed and sintered to obtain the final product.

[0014] Secondly, the present invention provides a silicon nitride ceramic material prepared by the aforementioned preparation method.

[0015] Thirdly, the present invention provides the application of the silicon nitride ceramic material in the fields of aerospace, automotive, power, electronics and / or new energy.

[0016] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0017] This invention provides a composite sintering aid system for Si3N4 ceramics, comprising rare earth oxides (Y2O3, Lu2O3, etc.) and ternary nitrides (Ti2AlN, Sr2Si5N8, etc.). This synergistic sintering aid system, through the synergistic effect of multiple ions, regulates the phase transformation rate of Si3N4 during sintering, the aspect ratio of Si3N4 grains, and the composition of the glassy phase between crystals. It overcomes the problems of residual glassy phase and grain boundary instability associated with traditional oxide sintering aids. Furthermore, it achieves a comprehensive improvement in the overall performance of silicon nitride ceramics through microstructure control, demonstrating promising application prospects.

[0018] This invention achieves multifaceted improvements in the mechanical properties of Si3N4 ceramics through the combination of rapid hot pressing sintering technology and a synergistic combination of ternary nitrides and rare earth oxides as sintering aids. X-ray diffraction (XRD) results and microstructure analysis show that the introduction of ternary nitrides significantly promotes the α / β phase transformation of Si3N4 ceramics during sintering and greatly improves the aspect ratio of Si3N4 grains.

[0019] Furthermore, the Si3N4 ceramic preparation method of the present invention has a fast production speed and a shorter heating time compared to hot pressing sintering. Under the premise of ensuring the densification of Si3N4 ceramic, it avoids the decline in mechanical properties caused by abnormal growth of Si3N4 grains. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a comparison diagram of the mechanical properties of Si3N4 ceramic materials prepared in Examples 1-3 and Comparative Example 1 of the present invention;

[0022] Figure 2 The XRD diffraction patterns of the Si3N4 ceramic materials prepared in Example 1 and Comparative Example 1 of this invention are shown below.

[0023] Figure 3 The images are SEM images of the damaged surface of the Si3N4 ceramic of the present invention at 4000x magnification. (a) Si3N4 ceramic material D1 prepared in Comparative Example 1; (b) Si3N4 ceramic material W2 prepared in Example 2.

[0024] Figure 4 This is an EDS image of the bent cross-section of the Si3N4 ceramic material prepared in Example 2 of this invention;

[0025] Figure 5The images show SEM images of the Si3N4 ceramic corrosion samples prepared in Example 2 and Comparative Example 1 of this invention at 2000x magnification and their aspect ratio comparisons. (a) SEM image of D1; (b) SEM image of W2; (a1) Grain length distribution of D1; (a2) Grain diameter distribution of D1; (b1) Grain length distribution of W2; (b2) Grain diameter distribution of W2. Detailed Implementation

[0026] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] In a first aspect, the present invention provides a method for preparing silicon nitride ceramic material, comprising the following steps: mixing and ball-milling 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;

[0028] The slurry after ball milling is dried, ground, and sieved; the sieved fine powder is then pre-pressed and sintered to obtain the final product.

[0029] This system should be able to effectively form a liquid phase to promote sintering, and even with only a small amount of additives, it should be able to achieve high densification of Si3N4 ceramics at relatively low temperatures. Simultaneously, 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, suppress the formation of low-melting-point glass phases, and enhance the thermal stability and mechanical strength of the grain boundaries.

[0030] Furthermore, this additive system should also possess the ability to inhibit abnormal grain growth and promote grain homogenization, thereby obtaining a fine and dense microstructure. Under the combined effect of these multiple synergistic mechanisms, the overall performance of Si3N4 ceramics is ultimately improved in terms of flexural strength, fracture toughness, hardness, and high-temperature stability, meeting the high-performance requirements of advanced ceramic materials in fields such as high-end equipment manufacturing and extreme environment applications.

[0031] 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.

[0032] Preferably, the mass ratio of α-Si3N4 powder, ternary nitride powder and rare earth oxide powder is 87-92:3-5:2-8.

[0033] In some embodiments, the ternary nitride powder is selected from Ti2AlN, Sr2Si5N8, CaSiN2, Ba2Si5N8, and SrSi7N. 10 At least one of Ti4AlN3.

[0034] In some embodiments, the rare earth oxide is Y2O3, Lu2O3, Yb2O3, CeO2, or Eu2O3.

[0035] 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.

[0036] More preferably, the mass ratio of Y2O3 to Lu2O3 is 1.5-2:1.

[0037] Preferably, 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.

[0038] In some embodiments, the sintering process is as follows: 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 2-5 min; holding at 1740-1760℃, heating time 150-200 min; after holding, natural cooling.

[0039] Secondly, the present invention provides a silicon nitride ceramic material prepared by the aforementioned preparation method.

[0040] Thirdly, the present invention provides the application of the silicon nitride ceramic material in the fields of aerospace, automotive, power, electronics and / or new energy.

[0041] The present invention will be further described below with reference to the embodiments.

[0042] Example 1

[0043] In this embodiment, Si3N4 ceramic W1 is prepared:

[0044] Step 1 - Mixing Raw Materials

[0045] The raw material powder was weighed strictly according to the component ratio, of which 90 wt% was α-Si3N4 powder (purity ≥99.9%, particle size D). 50The composition of the powder consisted of 0.5 μm of Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 2.5 wt% of layered Ti₂AlN powder (purity 95%, 200 mesh), and 2.5 wt% of Lu₂O₃ powder (purity ≥ 99.9%, particle size 1 μm). Anhydrous ethanol was used as the dispersion solvent. To avoid introducing impurities, Si₃N₄ balls were used as grinding balls. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0046] Step 2 - Slurry Drying

[0047] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C to dry completely, thereby evaporating the anhydrous ethanol and obtaining coarse powder.

[0048] Step 3 - Grinding and Sieving

[0049] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0050] Step 4 - Mold Installation and Pre-pressing

[0051] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0052] Step 5 - Rapid Hot Pressing and Sintering

[0053] After pre-pressing, the ceramic was sintered in a rapid hot-pressing sintering furnace. The sintering regime was as follows: room temperature to 800 ℃, heating time 10 min, pressure 6 MPa; 800 ℃ to 1650 ℃, heating time 17 min, pressure 30 MPa; 1650 ℃ to 1750 ℃, heating time 3 min, pressure 30 MPa; holding at 1750 ℃ ​​for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The sintering process of Si3N4 ceramic W1 was carried out entirely in a vacuum environment (below 10 Pa).

[0054] Step Six - Cooling and Demolding

[0055] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic W1.

[0056] 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 It has a hardness of 15.1 GPa and a density of 95.2%.

[0057] Example 2

[0058] In this embodiment, Si3N4 ceramic W2:

[0059] Step 1 - Mixing Raw Materials

[0060] The raw material powder was weighed strictly according to the component ratio, of which 90 wt% was α-Si3N4 powder (purity ≥99.9%, particle size D). 50 The composition of the powder consisted of 0.5 μm of Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 2.5 wt% of layered Ti₂AlN powder (purity 95%, 200 mesh), and 2.5 wt% of Sr₂Si₅N₈ powder (particle size 660 nm). Anhydrous ethanol was used as the dispersion solvent, and Si₃N₄ balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0061] Step 2 - Slurry Drying

[0062] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0063] Step 3 - Grinding and Sieving

[0064] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0065] Step 4 - Mold Installation and Pre-pressing

[0066] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0067] Step 5 - Rapid Hot Pressing and Sintering

[0068] After pre-pressing, the material is placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime is as follows: room temperature to 800 ℃, heating time 10 min, pressure 6 MPa; 800 ℃ to 1650 ℃, heating time 17 min, pressure 30 MPa; 1650 ℃ to 1750 ℃, heating time 3 min, pressure 30 MPa; holding at 1750 ℃ ​​for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The entire sintering process of Si3N4 ceramic W2 is carried out in a vacuum environment.

[0069] Step Six - Cooling and Demolding

[0070] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic W2.

[0071] In this embodiment, the mechanical properties of Si3N4 ceramic W2 are as follows: Figure 1As shown, the bending strength reaches 818 MPa, and the fracture toughness reaches 8.1 MPa·m. 1 / 2 It has a hardness of 17.5 GPa and a density of 97.3%.

[0072] Example 3

[0073] In this embodiment, Si3N4 ceramic W3 is:

[0074] Step 1 - Mixing Raw Materials

[0075] The raw material powder was weighed strictly according to the component ratio, of which 90 wt% was α-Si3N4 powder (purity ≥99.9%, particle size D). 50 The grinding media included 0.5 μm of Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 2.5 wt% of Lu₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), and 2.5 wt% of Sr₂Si₅N₈ powder (particle size 660 nm). Anhydrous ethanol was used as the dispersion solvent, and Si₃N₄ balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0076] Step 2 - Slurry Drying

[0077] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0078] Step 3 - Grinding and Sieving

[0079] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0080] Step 4 - Mold Installation and Pre-pressing

[0081] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0082] Step 5 - Rapid Hot Pressing and Sintering

[0083] After pre-pressing, the ceramic was placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime was as follows: room temperature to 800 ℃, heating time 10 min, pressure 6 MPa; 800 ℃ to 1650 ℃, heating time 17 min, pressure 30 MPa; 1650 ℃ to 1750 ℃, heating time 3 min, pressure 30 MPa; holding at 1750 ℃ ​​for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The sintering process of Si3N4 ceramic W3 was carried out entirely in a vacuum environment.

[0084] Step Six - Cooling and Demolding

[0085] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic W3.

[0086] 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 It has a hardness of 16.1 GPa and a density of 93.6%.

[0087] Example 4

[0088] In this embodiment, Si3N4 ceramic W4 is prepared:

[0089] Step 1 - Mixing Raw Materials

[0090] The raw material powder was weighed strictly according to the component ratio, of which α-Si3N4 powder accounted for 91 wt% (purity ≥99.9%, particle size D). 50 The grinding media included: 0.5 μm particle size, 5 wt% Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 2 wt% Sr₂Si₅N₈ powder (particle size 660 nm), and 2 wt% layered Ti₂AlN (purity 95%, 200 mesh). Anhydrous ethanol was used as the dispersion solvent, and Si₃N₄ balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0091] Step 2 - Slurry Drying

[0092] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0093] Step 3 - Grinding and Sieving

[0094] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0095] Step 4 - Mold Installation and Pre-pressing

[0096] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0097] Step 5 - Rapid Hot Pressing and Sintering

[0098] After pre-pressing, the ceramic was placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime was as follows: room temperature to 800 ℃, heating time 10 min, pressure 6 MPa; 800 ℃ to 1650 ℃, heating time 17 min, pressure 30 MPa; 1650 ℃ to 1750 ℃, heating time 3 min, pressure 30 MPa; holding at 1750 ℃ ​​for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The sintering process of Si3N4 ceramic W4 was carried out entirely in a vacuum environment.

[0099] Step Six - Cooling and Demolding

[0100] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic W4.

[0101] In this embodiment, the Si3N4 ceramic W4 exhibits a flexural strength of 890 MPa and a fracture toughness of 9.1 MPa·m. 1 / 2 It has a hardness of 16.9 GPa and a density of 95.6%.

[0102] Example 5

[0103] In this embodiment, Si3N4 ceramic W5 is prepared:

[0104] Step 1 - Mixing Raw Materials

[0105] The raw material powder was weighed strictly according to the component ratio, of which α-Si3N4 powder accounted for 87.5 wt% (purity ≥99.9%, particle size D). 50 The grinding media included: 0.5 μm of Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 2.5 wt% of Lu₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 2.5 wt% of Sr₂Si₅N₈ powder (particle size 660 nm), and 2.5 wt% of layered Ti₂AlN (purity 95%, 200 mesh). Anhydrous ethanol was used as the dispersion solvent, and Si₃N₄ balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0106] Step 2 - Slurry Drying

[0107] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0108] Step 3 - Grinding and Sieving

[0109] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0110] Step 4 - Mold Installation and Pre-pressing

[0111] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0112] Step 5 - Rapid Hot Pressing and Sintering

[0113] After pre-pressing, the ceramic was placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime was as follows: room temperature to 800 °C, heating time 10 min, pressure 6 MPa; 800 °C to 1650 °C, heating time 17 min, pressure 30 MPa; 1650 °C to 1750 °C, heating time 3 min, pressure 30 MPa; holding at 1750 °C for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The sintering process of Si3N4 ceramic W5 was carried out entirely in a vacuum environment.

[0114] Step Six - Cooling and Demolding

[0115] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic W5.

[0116] In this embodiment, the Si3N4 ceramic W5 exhibits a flexural strength of 951 MPa and a fracture toughness of 8.8 MPa·m. 1 / 2 It has a hardness of 15.9 GPa and a density of 96.3%.

[0117] Example 6

[0118] In this embodiment, Si3N4 ceramic W6 is prepared:

[0119] Step 1 - Mixing Raw Materials

[0120] The raw material powder was weighed strictly according to the component ratio, of which 80 wt% was α-Si3N4 powder (purity ≥99.9%, particle size D). 50 The grinding media included: 0.5 μm of Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 5 wt% of Lu₂O₃ powder (purity ≥ 99.9%, particle size 1 μm), 5 wt% of Sr₂Si₅N₈ powder (particle size 660 nm), and 5 wt% of layered Ti₂AlN (purity 95%, 200 mesh). Anhydrous ethanol was used as the dispersion solvent, and Si₃N₄ balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0121] Step 2 - Slurry Drying

[0122] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0123] Step 3 - Grinding and Sieving

[0124] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0125] Step 4 - Mold Installation and Pre-pressing

[0126] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0127] Step 5 - Rapid Hot Pressing and Sintering

[0128] After pre-pressing, the ceramic was placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime was as follows: room temperature to 800 °C, heating time 10 min, pressure 6 MPa; 800 °C to 1650 °C, heating time 17 min, pressure 30 MPa; 1650 °C to 1750 °C, heating time 3 min, pressure 30 MPa; holding at 1750 °C for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The sintering process of Si3N4 ceramic W6 was carried out entirely in a vacuum environment.

[0129] Step Six - Cooling and Demolding

[0130] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic W6.

[0131] In this embodiment, the Si3N4 ceramic W6 exhibits a flexural strength of 832 MPa and a fracture toughness of 9.1 MPa·m. 1 / 2 It has a hardness of 16.4 GPa and a density of 94.6%.

[0132] Comparative Example 1

[0133] In this comparative example, Si3N4 ceramic D1 was prepared using only Y2O3 powder as a sintering aid.

[0134] Step 1 - Mixing Raw Materials

[0135] The raw material powder was weighed strictly according to the component ratio, of which α-Si3N4 powder accounted for 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 introducing impurities, Si3N4 balls were used as grinding balls. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0136] Step 2 - Slurry Drying

[0137] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0138] Step 3 - Grinding and Sieving

[0139] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0140] Step 4 - Mold Installation and Pre-pressing

[0141] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0142] Step 5 - Rapid Hot Pressing and Sintering

[0143] After pre-pressing, the ceramic was placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime was as follows: room temperature to 800 °C, heating time 10 min, pressure 6 MPa; 800 °C to 1650 °C, heating time 17 min, pressure 30 MPa; 1650 °C to 1750 °C, heating time 3 min, pressure 30 MPa; holding at 1750 °C for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The entire sintering process of Si3N4 ceramic D1 was carried out in a vacuum environment.

[0144] Step Six - Cooling and Demolding

[0145] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic D1.

[0146] 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 It has a hardness of 15.6 GPa and a density of 98.6%.

[0147] Comparative Example 2

[0148] In this comparative example, Si3N4 ceramic D2 was prepared using only Y2O3 and Lu2O3 powders as sintering aids, without any ternary nitrides.

[0149] Step 1 - Mixing Raw Materials

[0150] The raw material powder was weighed strictly according to the component ratio, of which α-Si3N4 powder accounted for 92.5 wt% (purity ≥99.9%, particle size D). 50The grinding media included 0.5 μm of Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm) and 2.5 wt% of Lu₂O₃ powder (purity ≥ 99.9%, particle size 1 μm). Anhydrous ethanol was used as the dispersion solvent, and Si₃N₄ balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0151] Step 2 - Slurry Drying

[0152] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0153] Step 3 - Grinding and Sieving

[0154] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0155] Step 4 - Mold Installation and Pre-pressing

[0156] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0157] Step 5 - Rapid Hot Pressing and Sintering

[0158] After pre-pressing, the ceramic is placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime is as follows: room temperature to 800 ℃, heating time 10 min, pressure 6 MPa; 800 ℃ to 1650 ℃, heating time 17 min, pressure 30 MPa; 1650 ℃ to 1750 ℃, heating time 3 min, pressure 30 MPa; holding at 1750 ℃ ​​for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The entire sintering process of Si3N4 ceramic D2 is carried out in a vacuum environment.

[0159] Step Six - Cooling and Demolding

[0160] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic D2.

[0161] In this comparative example, the Si3N4 ceramic D2 exhibits a flexural strength of 856 MPa and a fracture toughness of 9.1 MPa·m. 1 / 2 It has a hardness of 16.1 GPa and a density of 97.2%.

[0162] Comparative Example 3

[0163] In this comparative example, Si3N4 ceramic D3 was prepared using only Y2O3 and Lu2O3 powders as sintering aids, without any ternary nitrides.

[0164] Step 1 - Mixing Raw Materials

[0165] The raw material powder was weighed strictly according to the component ratio, of which 90 wt% was α-Si3N4 powder (purity ≥99.9%, particle size D). 50 The grinding media included 0.5 μm of Y₂O₃ powder (purity ≥ 99.9%, particle size 1 μm) and 5 wt% of Lu₂O₃ powder (purity ≥ 99.9%, particle size 1 μm). Anhydrous ethanol was used as the dispersion solvent, and Si₃N₄ balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0166] Step 2 - Slurry Drying

[0167] The well-mixed slurry was poured into a petri dish and placed in a vacuum drying oven at 80 °C for one day to completely evaporate the anhydrous ethanol and obtain coarse powder.

[0168] Step 3 - Grinding and Sieving

[0169] After grinding the coarse powder with uniform composition multiple times, it is passed through a 60-mesh sieve to obtain fine powder with relatively uniform particle size.

[0170] Step 4 - Mold Installation and Pre-pressing

[0171] After grinding and sieving, the fine powder is loaded into a mold and pre-compressed on a tablet press at a pressure of 10 MPa.

[0172] Step 5 - Rapid Hot Pressing and Sintering

[0173] After pre-pressing, the ceramic is placed in a rapid hot-pressing sintering furnace for sintering. The sintering regime is as follows: room temperature to 800 ℃, heating time 10 min, pressure 6 MPa; 800 ℃ to 1650 ℃, heating time 17 min, pressure 30 MPa; 1650 ℃ to 1750 ℃, heating time 3 min, pressure 30 MPa; holding at 1750 ℃ ​​for 170 min, pressure 30 MPa; and then cooling naturally to room temperature. The entire sintering process of Si3N4 ceramic D3 is carried out in a vacuum environment.

[0174] Step Six - Cooling and Demolding

[0175] After sintering, allow it to cool naturally and then demold to obtain Si3N4 ceramic D3.

[0176] In this comparative example, the Si3N4 ceramic D3 exhibits a flexural strength of 844 MPa and a fracture toughness of 8.9 MPa·m. 1 / 2 It has a hardness of 15.8 GPa and a density of 96.6%.

[0177] Comparative Example 4

[0178] In this comparative example, Si3N4 ceramic D4 was prepared using only layered Ti2AlN and Sr2Si5N8 as sintering aids, without rare earth oxides.

[0179] Step 1 - Mixing Raw Materials

[0180] The raw material powder was weighed strictly according to the component ratio, of which 90 wt% was α-Si3N4 powder (purity ≥99.9%, particle size D). 50 The powder consisted of 0.5 μm thick Ti2AlN (95% purity, 200 mesh) and 5 wt% Sr2Si5N8 powder (660 nm particle size). Anhydrous ethanol was used as the dispersion solvent, and Si3N4 balls were used as grinding balls to avoid introducing impurities. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0181] Everything else is the same as in Example 1.

[0182] In this comparative example, the Si3N4 ceramic D4 exhibits a flexural strength of 857 MPa and a fracture toughness of 8.7 MPa·m. 1 / 2 It has a hardness of 16.8 GPa and a density of 96.2%.

[0183] Comparative Example 5

[0184] In this comparative example, Si3N4 ceramic D5 was prepared using only layered Ti2AlN as a sintering aid, without any rare earth oxides.

[0185] Step 1 - Mixing Raw Materials

[0186] The raw material powder was weighed strictly according to the component ratio, of which α-Si3N4 powder accounted for 95 wt% (purity ≥99.9%, particle size D). 50 =0.5μm), layered Ti2AlN content 5 wt% (purity 95%, 200 mesh); and an appropriate amount of anhydrous ethanol as the dispersion solvent. To avoid introducing impurities, Si3N4 balls were used as grinding balls. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0187] Everything else is the same as in Example 1.

[0188] In this comparative example, the Si3N4 ceramic D5 exhibits a flexural strength of 901 MPa and a fracture toughness of 8.4 MPa·m. 1 / 2 It has a hardness of 17.1 GPa and a density of 95.7%.

[0189] Comparative Example 6

[0190] In this comparative example, Si3N4 ceramic D6 was prepared using only Sr2Si5N8 as a sintering aid, without any rare earth oxides.

[0191] Step 1 - Mixing Raw Materials

[0192] The raw material powder was weighed strictly according to the component ratio, of which α-Si3N4 powder accounted for 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 introducing impurities, Si3N4 balls were used as grinding balls. The ball milling process was carried out in a planetary ball mill at a speed of 300 r / min for 8 h.

[0193] Everything else is the same as in Example 1.

[0194] In this comparative example, the Si3N4 ceramic D6 exhibits a flexural strength of 842 MPa and a fracture toughness of 8.8 MPa·m. 1 / 2 It has a hardness of 16.3 GPa and a density of 96.8%.

[0195] The relevant properties of Si3N4 ceramics prepared in Examples 1-6 and Comparative Examples 1-6 are summarized in Table 1.

[0196] Table 1. Relevant properties of Si3N4 ceramics prepared in Examples 1-6 and Comparative Examples 1-6

[0197]

[0198] As shown in Table 1, with the synergistic introduction of 2.5 wt% rare earth oxide Lu2O3 and layered Ti2AlN, although the density decreased slightly, the flexural strength increased by 23.8% and the fracture toughness increased by 5.6%. After the synergistic introduction of 2.5 wt% layered Ti2AlN and Sr2Si5N8, the flexural strength increased by 12%; after the synergistic introduction of 2.5 wt% Sr2Si5N8 and 2.5 wt% Lu2O3, the flexural strength increased by nearly 26% with minimal change in toughness, and the hardness also improved. Simultaneous introduction of Y2O3, Sr2Si5N8, Lu2O3, and layered Ti2AlN also resulted in a simultaneous increase in both flexural strength and hardness.

[0199] Combination Figure 1Analysis revealed that, compared to the blank sample D1 with only Y2O3 added, sample W1, with the synergistic introduction of rare earth oxides Lu2O3 and layered Ti2AlN (both at 2.5 wt%), decreased in density from 98.6% to 95.2%, but increased in Si3N4 flexural strength from 788 MPa to 976 MPa, an increase of nearly 24%; and increased in fracture toughness from 8.9 MPa·m. 1 / 2 Increased to 9.5 MPa·m 1 / 2 This represents an increase of 5.6%.

[0200] After synergistically introducing 2.5 wt% layered Ti2AlN and 2.5 wt% Sr2Si5N8 into W2, the hardness increased from 15.6 GPa to 17.5 GPa, an improvement of 12%. In W3, synergistically introducing 2.5 wt% Sr2Si5N8 and 2.5 wt% Lu2O3 as sintering aids, the flexural strength of Si3N4 ceramic was the largest increase, reaching 992 MPa, with a performance improvement of nearly 26%.

[0201] To verify the test results in Table 1, a series of analyses and 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 below. Figure 2 As shown, Si3N4 in W2 is almost entirely β-Si3N4, while D1 contains a small amount of α-Si3N4. This indicates that the synergistic introduction of Lu2O3, Sr2Si5N8 and layered Ti2AlN promotes the α / β phase transformation during the liquid-phase sintering of Si3N4.

[0202] After the Si3N4 ceramic fractured by bending, the fracture surface was sputter-coated with gold, and SEM images of the fracture surface were taken using a scanning electron microscope. Figure 3 Tables (a) and (b) show 4000x SEM images of the cross-sections 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 columnar β-Si3N4 grains have grown in all Si3N4 ceramics, such as Figure 3 The area highlighted by the red dashed box in the image. In addition, there are many long, narrow indentations left by the pull-out of columnar crystals during the fracture process, such as... Figure 3 The area highlighted by the yellow dashed line in (b) is shown. Compared to whisker-toughened Si3N4 ceramic materials, the Si3N4 ceramic prepared in this embodiment of the invention achieves improved toughness entirely through the self-toughening of columnar β-Si3N4 grains. This results in lower costs and more uniform performance in all directions, making the Si3N4 ceramic material isotropic.

[0203] Simultaneously, cross-sectional elemental distribution analysis was performed using an energy dispersive spectroscopy (EDS) instrument mounted on a scanning electron microscope. The EDS results for the cross-section of the Si3N4 ceramic W2 prepared in Example 2 are as follows: Figure 4 As shown, the synergistic sintering aids are well and uniformly distributed in the Si3N4 ceramic matrix. Only titanium elements show partial aggregation. Combined with XRD pattern analysis, this is because the layered nitrides have high stability and do not participate in the formation of the liquid phase during the Si3N4 sintering process, but remain in their original positions. Al elements are lost during the liquid phase sintering process and eventually form intergranular TiN.

[0204] To statistically analyze the grain size of the samples and determine their aspect ratio variations, the sample surfaces were polished and then etched using a sodium hydroxide (NaOH) solution at 400 °C for 1 min. A 2000x magnification image of the surface was then captured using a scanning electron microscope, and the length and diameter distribution data of β-Si3N4 grains were obtained by analyzing 100 grains. The grain size statistics for Si3N4 ceramic D1 prepared in Comparative Example 1 and Si3N4 ceramic W2 prepared in Example 2 are shown below. Figure 5 As shown. From Figure 5 The data shows 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 Si3N4 ceramic W2 sample prepared in Example 2, which combines layered Ti2AlN and Sr2Si5N8, achieved an aspect ratio of 8.9. Figure 5 As shown in (b), (b1) and (b2).

[0205] In summary, the Si3N4 ceramic sintering aid system designed in this invention has significant technical advantages. By introducing a small amount of ternary nitrides and rare earth oxides in a synergistic combination, high densification of Si3N4 ceramics can be achieved during sintering, effectively overcoming the problems of grain boundary glass phase residue and performance bottlenecks caused by traditional aid systems. This composite aid system achieves a synergistic improvement in mechanical properties while maintaining excellent toughness, including simultaneous enhancement of flexural strength and hardness. As shown in Example W3, its flexural strength and hardness are significantly better than those of Control Example D1, and no decrease in toughness is observed, fully verifying the optimization effect of this system. In terms of process implementation, the method provided in this application has the characteristics of reasonable temperature and pressure control, and a simple and efficient process route, which can significantly shorten the sintering cycle, reduce energy consumption and material loss, and facilitate the subsequent industrialization, large-scale production and application promotion of the product.

[0206] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon nitride ceramic material, characterized in that: The process includes the following steps: mixing and ball-milling α-Si3N4 powder, ternary nitride powder, and rare earth oxide powder with anhydrous ethanol at a mass ratio of 80-95:3-10:2-10; the ternary nitride powder is selected from Ti2AlN and / or Sr2Si5N8; the rare earth oxide is Y2O3 and / or Lu2O3; the mass ratio of Y2O3 to Lu2O3 is 1-2:1-2; The slurry after ball milling is dried, ground, and sieved; the sieved fine powder is pre-pressed and sintered to obtain the final product. The sintering process is as follows: 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 2-5 min; hold at 1740-1760℃, heating time 150-200 min; after holding, cool.

2. The method for preparing silicon nitride ceramic material according to claim 1, characterized in that: 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 silicon nitride ceramic material according to claim 2, characterized in that: 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 silicon nitride ceramic material according to claim 1, characterized in that: The rare earth oxides are Y2O3 and Lu2O3.

5. The method for preparing silicon nitride ceramic material according to claim 1, characterized in that: The mass ratio of Y2O3 to Lu2O3 is 1.5-2:

1.

6. The method for preparing silicon nitride ceramic material according to claim 1, characterized in that: The ternary nitride powder is Ti2AlN and Sr2Si5N8, with a mass ratio of Ti2AlN to Sr2Si5N8 of 0.8-1.5:0.8-1.

5.

7. A silicon nitride ceramic material, characterized in that: It is prepared by any one of the preparation methods described in claims 1-6.

8. The application of the silicon nitride ceramic material of claim 7 in the fields of aerospace, automotive, power, electronics and / or new energy.

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