A synergistically strengthened silicon nitride composite ceramic and its preparation method and application

Abstract

The present invention belongs to the technical field of composite ceramics, and discloses a synergistically reinforced silicon nitride composite ceramic and its preparation method and application. The raw materials thereof are calculated by mass and include the following components: 40-90 parts of α-Si3N4; 8-15 parts of sintering aid; 0.1-15 parts of nano-TiN; 0.1-12 parts of SiCw; in the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 5-10:1-5:0.5-3. The present invention innovatively adds nano-TiN particles and directional SiCw, combines freeze-drying and hot pressing sintering technology, and not only solves the problem that Si3N4 ceramics in the prior art are difficult to improve strength and toughness simultaneously, but also overcomes the defect that the whisker-like toughening phase is randomly distributed in the matrix, resulting in poor toughening effect. By precisely controlling the microstructure, the uniform dispersion and directional arrangement of the reinforcing phase are achieved, the toughening potential of the whiskers is fully utilized, and the comprehensive mechanical properties of the Si3N4 ceramics are significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite ceramics, and in particular relates to a synergistically reinforced silicon nitride composite ceramic and a preparation method and application thereof. Background Art

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

[0003] Si3N4 ceramics, thanks to their outstanding high-temperature strength, wear resistance, thermal shock resistance, and chemical stability, are considered a key high-performance engineering material for a wide range of applications. However, their inherent brittleness poses a bottleneck in their application under high-load and high-friction conditions. Therefore, the development of effective strengthening and toughening technologies to enhance their overall performance is crucial.

[0004] Current strategies for improving the properties of Si3N4 ceramics often rely on the addition of sintering aids (such as Al2O3 and Y2O3) to optimize the sintering process and increase density. While these approaches facilitate densification, they have limited success in significantly improving the fracture toughness and tribological properties of the material. In contrast, the introduction of second-phase reinforcements, such as nanoparticles (TiC), silicon carbide whiskers (SiCw), or fibers, has proven to be a more effective approach. These reinforcements can simultaneously enhance the mechanical properties of the matrix and improve its wear resistance through mechanisms such as dispersion strengthening, crack deflection, and bridging.

[0005] However, traditional methods often focus solely on improving either flexural strength or fracture toughness, making it difficult to synergistically optimize the strength and toughness of Si3N4 ceramics. Furthermore, commonly used toughening phases, such as whiskers, are typically randomly distributed within the matrix. This disordered distribution significantly limits the toughening effectiveness of the toughening phases. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a synergistically reinforced silicon nitride composite ceramic and its preparation method and application. The present invention innovatively adds nano-TiN particles and directional SiCw, combines freeze-drying and hot pressing sintering technology, not only solving the problem of the difficulty of Si3N4 ceramics in the existing technology in improving strength and toughness simultaneously, but also overcomes the defect that the whisker-like toughening phase is randomly distributed in the matrix, resulting in poor toughening effect. By precisely controlling the microstructure, the uniform dispersion and directional arrangement of the reinforcing phase are achieved, the toughening potential of the whiskers is fully utilized, and the comprehensive mechanical properties of Si3N4 ceramics are significantly improved.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a synergistically reinforced silicon nitride composite ceramic, the raw materials of which, by weight, include the following components: 40-90 parts of α-Si3N4; 8-15 parts of sintering aid; 0.1-15 parts of nano-TiN; 0.1-12 parts of SiCw;

[0009] In the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 5-10:1-5:0.5-3.

[0010] Al2O3 and Y2O3, as composite sintering aids, can significantly improve the liquidus viscosity of Si3N4 ceramics and enhance their high-temperature thermal properties. Non-oxide sintering aids such as CaF2 effectively reduce the oxygen content in the liquidus, thereby hindering the formation of lattice oxygen and reducing defects in the crystal. Fluorine atoms have a significant effect on the grain growth of Si3N4 ceramics. Replacing oxide sintering aids with fluoride sintering aids can improve the mechanical properties of silicon nitride.

[0011] When nano-TiN is introduced into the Si3N4 ceramic matrix as a reinforcement phase, it can refine the grains, hinder dislocations and cracks, and thus effectively improve the bending strength and fracture toughness of Si3N4.

[0012] Nano-TiN has a certain self-lubricating property, which can reduce surface adhesive wear; high-hardness nano-TiN particles support the load, which can reduce the embedding of abrasive particles and effectively reduce the wear rate; nano-TiN has excellent antioxidant properties under high temperature conditions, which is beneficial to maintaining the high-temperature wear resistance of ceramic materials.

[0013] SiCw has crack deflection and crack bridging properties, effectively improving the flexural strength and fracture toughness of ceramic materials, and has a certain promoting effect on the hardness and elastic modulus of ceramic materials. In addition, SiCw has good high-temperature stability and can maintain good toughening effects under high temperature conditions.

[0014] In some embodiments, the raw materials of the synergistically reinforced silicon nitride composite ceramic include the following components by weight: 50-90 parts of α-Si3N4; 8-15 parts of sintering aid; 1-15 parts of nano-TiN; 1-12 parts of SiCw;

[0015] In the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 5-8:2-4:0.5-2.

[0016] Preferably, the raw materials of the synergistically reinforced silicon nitride composite ceramic include the following components by mass: 60-90 parts of α-Si3N4; 8-15 parts of sintering aid; 1-15 parts of nano-TiN; 1-12 parts of SiCw;

[0017] In the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 5-7:2-4:0.5-1.

[0018] Further preferably, in the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 6:3:1.

[0019] In some embodiments, the raw materials for the synergistically reinforced silicon nitride composite ceramic further include a slurry dispersant and a slurry binder.

[0020] Preferably, the slurry dispersant is sodium lauryl sulfate; and the slurry binder is polyvinyl pyrrolidone.

[0021] Further preferably, the slurry dispersant accounts for 0.5-2% of the total mass of the mixed powder; the slurry binder accounts for 0.5-2% of the total mass of the mixed powder.

[0022] In a second aspect, the present invention provides a method for preparing the synergistically reinforced silicon nitride composite ceramic, comprising the following steps:

[0023] Mix the raw materials in proportion and add water for wet ball milling;

[0024] The suspension after wet ball milling is subjected to directional freeze drying, and the water will freeze and sublime in the set direction, prompting the SiCw in the suspension to be arranged in an orderly manner along the growth direction of the ice crystals. Subsequently, it is subjected to debinding treatment and hot pressing sintering to obtain the product.

[0025] The Si3N4 ceramics prepared by the present invention have the dispersion strengthening effect of nano-TiN and the directional structure of SiCw. The obvious directional structure makes the Si3N4 ceramics have higher fracture toughness in a certain direction, thereby achieving a dual improvement in the bending strength and fracture toughness of the Si3N4 ceramics.

[0026] During the freeze-drying stage, the mold is cooled with liquid nitrogen. The temperature difference between the upper and lower sides of the mold creates a vertical temperature gradient in the ceramic slurry. Heat is then transferred in the opposite direction of the temperature gradient, achieving directional solidification of the SiCw. During the hot-pressing sintering process, the phase transition of Si3N4 does not alter the orientation of the SiCw, maintaining its original directional structure.

[0027] The β-Si3N4, nano-TiN and SiCw in the Si3N4 ceramic prepared by the present invention do not conflict with each other, and can significantly improve the fracture toughness of the ceramic while retaining the original Si3N4 ceramic matrix, thereby comprehensively improving the mechanical properties.

[0028] Among them, SiC whiskers still maintain good orientation during the sintering process, which proves that the whiskers can be well embedded in the matrix and play a toughening role, and the stable interface structure is conducive to crack deflection and toughening mechanism.

[0029] The present invention can realize the matrix structure and directional structure of Si3N4 ceramics by controlling the raw material ratio, debinding time, hot pressing sintering time and heating rate.

[0030] In some embodiments, the freeze-drying is as follows: directionally freezing the mixture after wet ball milling in a mold, wherein the thermal conductivity of the materials of the top wall and bottom wall of the mold is different; then slowly heating under a vacuum degree below 10 Pa to allow the ice crystals between the layers to sublime and be discharged into gas.

[0031] Preferably, the materials of the top wall and the bottom wall of the mold are polytetrafluoroethylene and stainless steel respectively.

[0032] The temperature difference between the upper and lower surfaces of the mold causes the slurry to form a temperature gradient in the vertical direction, and the heat is transferred in the direction opposite to the temperature gradient, thereby achieving the effect of directional solidification.

[0033] Preferably, the wet ball-milled mixture is directionally frozen in liquid nitrogen.

[0034] Preferably, during the process of sublimating the interlayer ice crystals into gas, the temperature is slowly raised from -50°C to room temperature over 100-140 hours. Room temperature refers to ambient temperature, generally 20-30°C. The purpose of slow heating is to ensure uniform sublimation of the ice crystals and the integrity of the oriented arrangement structure of SiCw. If the heating rate is too fast, the ice crystals may sublime rapidly and non-uniformly, resulting in the destruction of the oriented arrangement of SiCw, structural collapse or disordered distribution, and thus affecting the microstructure and mechanical properties of the composite ceramic.

[0035] In some embodiments, the freeze-dried product is subjected to gradient heating to remove binder, and the heating program is: heating to 180-220°C at 1.5-2.5°C / min, then heating to 580-620°C at 0.8-1.2°C / min, and maintaining at this temperature for 1.5-2.5h.

[0036] The preferred heating schedule for the debinding process is: heating to 200°C at 2°C / min, then to 600°C at 1°C / min, and maintaining this temperature for 2 hours. The purpose of controlling the heating rate in stages is to adapt to the removal characteristics of different components and moisture in the green body. In the low-temperature stage (room temperature to 200°C), a faster heating rate facilitates the rapid removal of bound water, reducing debinding time. In the high-temperature stage (200°C to 600°C), a slower heating rate prevents the generation of internal residual stress and thermal cracking in the material, while ensuring the complete decomposition of organic matter and impurities, thus avoiding structural damage during the debinding process.

[0037] Preferably, during the debinding process, when the temperature is below 300°C, the system vacuum is maintained below 10 Pa. When the temperature reaches 300°C or above, nitrogen is introduced to maintain the pressure at -0.02 MPa to 0.02 MPa. Using a high vacuum environment at low temperatures is beneficial for effectively removing residual moisture and low-temperature volatile components in the mixture. When the temperature rises above 300°C, the organic additives in the system begin to significantly decompose. At this time, introducing a small amount of nitrogen can not only inhibit the vigorous oxidative decomposition of organic matter at high temperatures, but also help maintain the stability of the sample composition by acting as an inert protective atmosphere.

[0038] In some embodiments, the hot pressing sintering is performed by gradually increasing the temperature to 1800-1900° C. and keeping the temperature for 0.5-2 hours. The hot pressing sintering is performed in a nitrogen atmosphere of 0.05-0.15 MPa.

[0039] Preferably, during the hot pressing sintering process, the temperature is raised to 1000-1300° C. at 15-25° C. / min, and then raised to 1800-1900° C. at 8-12° C. / min.

[0040] In a third aspect, the present invention provides an application of the synergistically reinforced silicon nitride composite ceramic in the preparation of high-temperature structural parts, cutting tools or wear-resistant parts.

[0041] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0042] The present invention achieves uniform dispersion and oriented alignment of the reinforcing phase by adding nano-TiN particles and aligned SiCw, combined with freeze-drying and hot-pressing sintering techniques. This significantly improves the flexural strength and fracture toughness of Si3N4 ceramics. Experimental data show that the sample with 5wt% nano-TiN and 9wt% aligned SiCw has a flexural strength of 879.2MPa and a fracture toughness of 10.2MPa·m. 1 / 2 , which were increased by about 35% and 40% respectively compared with the samples without reinforcement phase.

[0043] By controlling the content and distribution of the reinforcement phase and regulating the microstructure of the Si3N4 ceramic, the uniform growth of β-Si3N4 grains and the uniform dispersion of the reinforcement phase were achieved, reducing porosity and improving the material's density. Experimental data showed that the optimized sample achieved a relative density of 98.8%, significantly higher than the 95.8% of the sample without the reinforcement phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] 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.

[0045] Figure 1 The XRD comparison patterns of the N5C9 sample in the technical solution provided in Example 5 of the present invention;

[0046] Figure 2 In the technical solution provided in Example 5 of the present invention, the fracture morphology of the Si3N4 ceramic of the N5C9 sample is as follows: (a) perpendicular to the hot pressing direction; (b) parallel to the hot pressing direction;

[0047] Figure 3 Comparison of the mechanical properties of Si3N4 ceramics prepared in Example 1, Example 3, Example 5 and Example 7 of the present invention: (a) flexural strength; (b) fracture toughness. DETAILED DESCRIPTION

[0048] 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.

[0049] The following is a preparation method for a low-dimensional material synergistically textured and strengthened silicon nitride composite ceramic provided in this application to prepare Si3N4 ceramic production:

[0050] Example 1

[0051] This embodiment is a specific example of preparing Si3N4 ceramic product N5C3.

[0052] 1) Slurry preparation

[0053] The raw materials for preparing ceramic products include the following components by mass: 83 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 5 parts of nano-TiN; 3 parts of SiCw;

[0054] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0055] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0056] 2) Freeze-drying

[0057] Place a custom PTFE mold with a stainless steel base in an insulated bucket. Pour an appropriate amount of liquid nitrogen into the bucket. Once the mold is completely cooled by the liquid nitrogen, pour the mixed slurry prepared in step 1) into the custom mold. Keep the liquid nitrogen in the presence of liquid nitrogen for 15 minutes to ensure the slurry is completely frozen, until the deionized water solvent is completely frozen into ice crystals.

[0058] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours. The temperature was then raised to room temperature (25°C) to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramics contained aligned SiCw.

[0059] 3) Debinding treatment

[0060] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a binder removal furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, then to 600°C at a rate of 1°C / min, and held at this temperature for 2 hours. Throughout the process, the vacuum was maintained below 10 Pa below 300°C. Nitrogen was then introduced, and the pressure was controlled within 0.01 MPa.

[0061] Through the above heat treatment, SDS and PVP are removed to obtain a debinding product.

[0062] 4) Hot pressing sintering

[0063] The debinding product from step 3) was placed in a graphite mold and hot-pressed. The process involved heating from room temperature (25°C) to 1200°C at a rate of 20°C / min, then to 1850°C at a rate of 10°C / min, and then maintaining this temperature for 1 hour. The entire hot-pressing sintering process was performed in a nitrogen atmosphere at 0.1 MPa to produce the ceramic product, N5C3.

[0064] In this embodiment, the mechanical properties of the prepared ceramic product N5C3 are as follows: Figure 3 As shown, the bending strength reaches 745.42MPa and the fracture toughness reaches 8.83MPa·m 1 / 2 , the hardness reaches 16.1GPa.

[0065] Example 2

[0066] This embodiment is a specific example of preparing Si3N4 ceramic product N10C3.

[0067] 1) Slurry preparation

[0068] The raw materials for preparing ceramic products include the following components by mass: 78 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 10 parts of nano-TiN; 3 parts of SiCw;

[0069] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0070] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0071] 2) Freeze-drying

[0072] The mixed slurry prepared in step 1) was poured into a customized mold, cooled with liquid nitrogen, and directionally frozen for 10 minutes until the deionized water was completely frozen.

[0073] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours. The temperature was then raised to room temperature (25°C) to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramic containing aligned SiCw was obtained.

[0074] 3) Debinding treatment

[0075] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a binder removal furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, then to 600°C at a rate of 1°C / min, and held at this temperature for 2 hours. Throughout the process, the vacuum was maintained below 10 Pa below 300°C. Nitrogen was then introduced, and the pressure was controlled within 0.01 MPa.

[0076] Through the above heat treatment, SDS and PVP are removed to obtain a debinding product.

[0077] 4) Hot pressing sintering

[0078] The debinding product from step 3) was placed in a graphite mold and hot-pressed. The process involved heating from room temperature (25°C) to 1200°C at a rate of 20°C / min, then to 1850°C at a rate of 10°C / min, and then maintaining this temperature for 1 hour. The entire hot-pressing sintering process was performed in a nitrogen atmosphere at 0.1 MPa, yielding the ceramic product, N10C3.

[0079] In this embodiment, the flexural strength of the prepared ceramic product N10C3 reaches 705.36 MPa and the fracture toughness reaches 8.67 MPa·m 1 / 2 , the hardness reaches 15.9GPa.

[0080] Example 3

[0081] This embodiment is a specific example of preparing Si3N4 ceramic product N5C6.

[0082] 1) Slurry preparation

[0083] The raw materials for preparing ceramic products include the following components by mass: 80 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 5 parts of nano-TiN; 6 parts of SiCw;

[0084] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0085] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0086] 2) Freeze-drying

[0087] The mixed slurry prepared in step 1) was poured into a customized mold, cooled with liquid nitrogen, and directionally frozen for 12 minutes until the deionized water was completely frozen.

[0088] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours. The temperature was then raised to room temperature (25°C) to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramic contained aligned SiCw particles.

[0089] 3) Debinding treatment

[0090] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a debinding furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, then to 600°C at a rate of 1°C / min, and held at this temperature for 2 hours. Throughout this process, the vacuum was maintained below 10 Pa below 300°C. Nitrogen was then introduced, with the pressure controlled within 0.02 MPa. This heat treatment removed SDS and PVP, resulting in a debinding product.

[0091] 4) Hot pressing sintering

[0092] The debinding product from step 3) was placed in a graphite mold and hot-pressed. The process involved heating the material from room temperature to 1200°C at a rate of 20°C / min, then to 1850°C at a rate of 10°C / min, and then maintaining this temperature for 1 hour. The entire hot-pressing sintering process was performed in a nitrogen atmosphere at 0.1 MPa to produce the ceramic product, N5C6.

[0093] In this embodiment, the mechanical properties of the prepared ceramic product N5C6 are as follows: Figure 3 Compared with the product N5C3, the fracture toughness is further improved. The fracture toughness reaches 9.77MPa·m 1 / 2 , the bending strength reaches 772.05MPa and the hardness reaches 16.4GPa.

[0094] Example 4

[0095] This embodiment is a specific example of preparing Si3N4 ceramic product N10C6.

[0096] 1) Slurry preparation

[0097] The raw materials for preparing ceramic products include the following components by mass: 75 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 10 parts of nano-TiN; 6 parts of SiCw;

[0098] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0099] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0100] 2) Freeze-drying

[0101] The mixed slurry prepared in step 1) was poured into a customized mold, cooled with liquid nitrogen, and directionally frozen for 15 minutes until the deionized water was completely frozen.

[0102] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours before being warmed to room temperature to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramic containing aligned SiCw was obtained.

[0103] 3) Debinding treatment

[0104] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a debinding furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, then to 600°C at a rate of 1°C / min, and held at this temperature for 2 hours. Throughout this process, the vacuum was maintained below 10 Pa below 300°C. Nitrogen was then introduced, with the pressure controlled within 0.015 MPa. This heat treatment removed SDS and PVP, resulting in a debinding product.

[0105] 4) Hot pressing sintering

[0106] The debinding product from step 3) was placed in a graphite mold and hot-pressed. The process involved heating the material from room temperature to 1200°C at a rate of 20°C / min, then to 1850°C at a rate of 10°C / min, and then maintaining this temperature for 1 hour. The entire hot-pressing sintering process was performed in a nitrogen atmosphere at 0.1 MPa to produce the ceramic product, N10C6.

[0107] In this embodiment, the mechanical properties of the ceramic product N10C6 are compared with those of the product N5C6. The bending strength is reduced to 704.23 MPa, and the fracture toughness is 9.32 MPa·m 1 / 2 , the hardness reaches 16.2GPa.

[0108] Example 5

[0109] This embodiment is a specific example of preparing Si3N4 ceramic product N5C9.

[0110] 1) Slurry preparation

[0111] The raw materials for preparing ceramic products include the following components by mass: 77 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 5 parts of nano-TiN; 9 parts of SiCw;

[0112] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0113] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0114] 2) Freeze-drying

[0115] The mixed slurry prepared in step 1) was poured into a customized mold, cooled with liquid nitrogen, and directionally frozen for 12 minutes until the deionized water was completely frozen.

[0116] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours before being warmed to room temperature to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramic containing aligned SiCw was obtained.

[0117] 3) Debinding treatment

[0118] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a binder removal furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, then to 600°C at a rate of 1°C / min, and held at this temperature for 2 hours. Throughout the process, the vacuum level was maintained below 10 Pa below 300°C. Nitrogen was then introduced, and the pressure was controlled within 0.005 MPa.

[0119] 4) Hot pressing sintering

[0120] The debinding product obtained in step 3) is placed in a graphite mold and subjected to hot pressing and sintering.

[0121] The specific process involves heating from room temperature to 1200°C at a rate of 20°C / min, then to 1850°C at a rate of 10°C / min, and holding at this temperature for 1 hour. The entire hot-pressing sintering process is carried out in a nitrogen atmosphere at 0.1 MPa, resulting in the ceramic product N5C9.

[0122] In this embodiment, after sintering, a Si3N4 ceramic product N5C9 with high density was obtained; after testing, the XRD pattern of the product N5C9 was as follows Figure 1 As shown in Figure 2, the diffraction peak of SiCw perpendicular to the hot pressing direction is stronger than the diffraction peak parallel to the hot pressing direction. Figure 2 As shown in the figure, the side and end faces of SiCw are well oriented in different directions, which fully confirms the excellent effect of freeze drying.

[0123] After testing, the mechanical properties comparison chart of Si3N4 ceramics prepared in the embodiment of the present invention is as follows: Figure 3 As shown in (a) and (b), the fracture toughness of product N5C9 is further improved compared with product N5C6, with the fracture toughness reaching 10.2MPa·m 1 / 2 , the bending strength reaches 879.22MPa, and the hardness reaches 16.7GPa. The SEM morphology of the product N5C9 is as follows Figure 2 As shown, the texture degree in two directions is obvious. Figure 2 In (a), the end face of the whisker is observed. Figure 2 In (b), the side faces of many whiskers were observed, which further proved that a certain amount of whiskers resulted in good freeze-drying effect and significant orientation.

[0124] The Si3N4 ceramics produced, in which β-Si3N4, nano-TiN, and SiCw do not conflict with each other, can significantly improve the fracture toughness of the ceramic while retaining the original Si3N4 ceramic matrix, thereby comprehensively improving the mechanical properties. To verify the above analysis conclusions, the product N5C9 was cut and polished, and the micromorphology of the grains was observed under TEM after ion thinning. Among them, SiCw still maintained a good orientation arrangement during the sintering process, confirming that the whiskers can be well embedded in the matrix and play a toughening role, and the stable interface structure is conducive to crack deflection and the toughening mechanism.

[0125] Example 6

[0126] This embodiment is a specific example of preparing Si3N4 ceramic product N10C9.

[0127] Preparation of slurry The raw materials for preparing ceramic products include the following components by mass: Si3N4 72 parts; Al2O3 5 parts; Y2O3 3 parts; CaF2 1 part; nano-TiN 10 parts; SiCw 9 parts;

[0128] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0129] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0130] 2) Freeze-drying

[0131] The mixed slurry prepared in step 1) was poured into a customized mold, cooled with liquid nitrogen, and directionally frozen for 10 minutes until the deionized water was completely frozen.

[0132] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours before being warmed to room temperature to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramic containing aligned SiCw was obtained.

[0133] 3) Debinding treatment

[0134] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a binder removal furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, then to 600°C at a rate of 1°C / min, and held at this temperature for 2 hours. Throughout the process, the vacuum was maintained below 10 Pa below 300°C. Nitrogen was then introduced, and the pressure was controlled within 0.01 MPa.

[0135] 4) Hot pressing sintering

[0136] The debinding product from step 3) was placed in a graphite mold and hot-pressed. The process involved heating the material from room temperature to 1200°C at a rate of 20°C / min, then to 1850°C at a rate of 10°C / min, and then maintaining this temperature for 1 hour. The entire hot-pressing sintering process was performed in a nitrogen atmosphere at 0.1 MPa to produce the ceramic product, N10C9.

[0137] In this embodiment, the fracture toughness of the N10C9 sample reaches 9.7 MPa·m 1 / 2 The bending strength reaches 823.89MPa, and the hardness reaches 16.3GPa.

[0138] Example 7

[0139] This embodiment is a specific example of preparing Si3N4 ceramic product N5C12.

[0140] 1) Slurry preparation

[0141] The raw materials for preparing ceramic products include the following components by mass: 75 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 5 parts of nano-TiN; 12 parts of SiCw;

[0142] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0143] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0144] 2) Freeze-drying

[0145] The mixed slurry prepared in step 1) was poured into a customized mold, cooled with liquid nitrogen, and directionally frozen for 10 minutes until the deionized water was completely frozen.

[0146] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours before being warmed to room temperature to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramic containing aligned SiCw was obtained.

[0147] 3) Debinding treatment

[0148] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a debinding furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, and then from 200°C to 600°C at a rate of 1°C / min, where it was held at this temperature for 2 hours. Throughout the process, the vacuum was maintained below 10 Pa before 300°C, after which nitrogen was introduced with the pressure controlled within 0.02 MPa. This heat treatment removed SDS and PVP, resulting in a debinding product.

[0149] 4) Hot pressing sintering

[0150] The debinding product from step 3) was placed in a graphite mold and hot-pressed. The process involved heating the material from room temperature to 1200°C at a rate of 20°C / min, then to 1850°C at a rate of 10°C / min, and then maintaining this temperature for 1 hour. The entire hot-pressing sintering process was performed in a nitrogen atmosphere at 0.1 MPa to produce the ceramic product, N5C12.

[0151] In this embodiment, the mechanical properties of product N5C12 are as follows: Figure 3 Compared with the product N5C9, the mechanical properties are reduced and the fracture toughness reaches 9.26MPa·m 1 / 2 The bending strength reaches 779.09MPa, and the hardness reaches 15.3GPa.

[0152] Example 8

[0153] This embodiment is a specific example of preparing Si3N4 ceramic product N10C12.

[0154] 1) Slurry preparation

[0155] The raw materials for preparing ceramic products include the following components by mass: 70 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 10 parts of nano-TiN; 12 parts of SiCw;

[0156] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm; nano-TiN particle size 40nm; SiCw length 10-50μm, diameter 0.5μm; average molecular weight of PVP 1300000g / mol.

[0157] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder, with the mass percentage of SDS in the mixed powder being 1% and the mass percentage of PVP in the mixed powder being 1%. Deionized water is then added thereto to make a solid-liquid ratio of 2:3, and after mixing, a mixed slurry is obtained.

[0158] 2) Freeze-drying

[0159] The mixed slurry prepared in step 1) was poured into a customized mold, cooled with liquid nitrogen, and directionally frozen for 10 minutes until the deionized water was completely frozen.

[0160] The frozen product, along with the mold, was then placed in a freeze dryer set at -50°C under a vacuum of less than 10 Pa for 120 hours before being warmed to room temperature to allow the interlayer ice crystals to sublime and escape as gas. After demolding, the resulting oriented Si3N4 ceramic containing aligned SiCw was obtained.

[0161] 3) Debinding treatment

[0162] The oriented Si3N4 ceramic produced in step 2) was placed in an Al2O3 ceramic crucible and transferred to a binder removal furnace. The temperature was raised from room temperature to 200°C at a rate of 2°C / min, then to 600°C at a rate of 1°C / min, and held at this temperature for 2 hours. Throughout the process, the vacuum was maintained below 10 Pa below 300°C. Nitrogen was then introduced, and the pressure was controlled within 0.01 MPa.

[0163] 4) Hot pressing sintering

[0164] The debinding product from step 3) was placed in a graphite mold and hot-pressed. The specific process involved heating from room temperature to 1200°C at a rate of 20°C / min, then from 1200°C to 1850°C at a rate of 10°C / min, and then maintaining this temperature for 1 hour. The entire hot-pressing sintering process was carried out in a nitrogen atmosphere at 0.1 MPa to obtain the ceramic product, N10C12.

[0165] In this embodiment, the mechanical properties of the prepared ceramic product N10C12 decreased. The fracture toughness reached 8.92 MPa·m 1 / 2 The bending strength reaches 743.21MPa, and the hardness reaches 15.1GPa.

[0166] Comparative Example 1

[0167] This embodiment is a specific example of preparing Si3N4 ceramic product NOC0.

[0168] 1) Raw material mixing

[0169] The raw materials for preparing ceramic products include the following components by mass: 91 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2;

[0170] Among them, the purity of Si3N4 powder is ≥99.9%, the particle size is D 50 =0.5μm; Al2O3, Y2O3, CaF2 powder purity ≥99.9%, particle size 1μm;

[0171] After mixing the above raw materials according to the set mass ratio, anhydrous ethanol was added as a solvent to make the solid-liquid ratio 1:4, and mixed to obtain a mixed slurry.

[0172] 2) Ball mill drying

[0173] Place the mixed slurry obtained in step 1) in a ball mill with a ball-to-material ratio of 3:1 and mill at 300 rpm for 12 hours. After the powders are evenly mixed, pour the slurry into a Petri dish and dry it in an oven at 70°C for 24 hours. Then, mill the powder.

[0174] 3) Grinding and sieving

[0175] The ball-milled powder obtained in step 2) is poured into a mortar, ground into powder, and passed through a 60-mesh sieve to obtain a uniformly mixed powder, thereby obtaining a sieved powder.

[0176] 4) Hot pressing sintering

[0177] The sieved powder was placed in a graphite mold and hot-pressed. The process involved heating from room temperature to 1200°C at a rate of 20°C / min, then to 1800°C at a rate of 10°C / min, and then holding at this temperature for 1 hour. The entire hot-pressing sintering process was carried out in a nitrogen atmosphere at 0.1 MPa.

[0178] In this comparative example, after sintering, a Si3N4 ceramic product N0C0 with high density was obtained; the bending strength reached 630.24MPa, and the fracture toughness reached 6.65MPa·m 1 / 2 , the hardness reaches 14.8GPa.

[0179] Comparative Example 2

[0180] Compared with Example 1, the difference is that in step 2), a polytetrafluoroethylene mold is used for containing and freezing by liquid nitrogen. The rest is the same as Example 1.

[0181] In this comparative example, the mechanical properties of the prepared ceramic product are as follows: bending strength is 720.22 MPa, fracture toughness is 8.15 MPa·m 1 / 2 , with a hardness of 15.8 GPa.

[0182] Comparative Example 3

[0183] Compared with Example 1, the difference is that in step 3), during the entire process of debinding treatment, the atmosphere is nitrogen and the pressure is 0.01 MPa. The rest is the same as in Example 1.

[0184] In this comparative example, the mechanical properties of the prepared ceramic product are as follows: bending strength is 730.15 MPa, fracture toughness is 8.51 MPa·m 1 / 2 , with a hardness of 16.3 GPa.

[0185] 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 shall be included within the scope of protection of the present invention.

Claims

1. A synergistically reinforced silicon nitride composite ceramic, characterized by: The raw materials include the following components by weight: 40-90 parts of α-Si3N4; 8-15 parts of sintering aid; 0.1-15 parts of nano-TiN; 0.1-12 parts of SiCw; In the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 5-10:1-5:0.5-3; Mix the raw materials in proportion and add water for wet ball milling; The suspension after wet ball milling is subjected to directional freeze drying, and the water will freeze and sublime in the set direction, prompting the SiCw in the suspension to be arranged in an orderly manner along the growth direction of the ice crystals. Subsequently, it is subjected to debinding treatment and hot pressing sintering to obtain the product.

2. The synergistically reinforced silicon nitride composite ceramic according to claim 1, characterized in that: The raw materials include the following components by weight: 50-90 parts of α-Si3N4; 8-15 parts of sintering aid; 1-15 parts of nano-TiN; 1-12 parts of SiCw; In the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 5-8:2-4:0.5-2.

3. The synergistically reinforced silicon nitride composite ceramic according to claim 1, characterized in that: The raw materials also include a slurry dispersant and a slurry binder; the slurry dispersant is sodium lauryl sulfate; and the slurry binder is polyvinyl pyrrolidone.

4. The synergistically reinforced silicon nitride composite ceramic according to claim 3, characterized in that: The slurry dispersant accounts for 0.5-2% of the total mass of the raw materials; the slurry binder accounts for 0.5-2% of the total mass of the raw materials.

5. The method for preparing the synergistically reinforced silicon nitride composite ceramic according to any one of claims 1 to 4, characterized in that: The steps include: Mix the raw materials in proportion and add water for wet ball milling; The suspension after wet ball milling is subjected to directional freeze drying, and the water will freeze and sublime in the set direction, prompting the SiCw in the suspension to be arranged in an orderly manner along the growth direction of the ice crystals. Subsequently, it is subjected to debinding treatment and hot pressing sintering to obtain the product.

6. The method for preparing the synergistically reinforced silicon nitride composite ceramic according to claim 5, characterized in that: The freeze drying comprises: directionally freezing the mixture after wet ball milling in a mold, wherein the thermal conductivity of the materials of the top wall and the bottom wall of the mold is different; Then, under the condition of vacuum degree less than 10Pa, the temperature is raised from -50℃ to room temperature over 100-140h to allow the interlayer ice crystals to sublime and be discharged into gas.

7. The method for preparing the synergistically reinforced silicon nitride composite ceramic according to claim 5, characterized in that: The materials of the top wall and bottom wall of the mold are polytetrafluoroethylene and stainless steel respectively.

8. The method for preparing the synergistically reinforced silicon nitride composite ceramic according to claim 5, characterized in that: The freeze-dried product was subjected to gradient heating to remove binder. The heating program was as follows: heating to 180-220°C at 1.5-2.5°C / min, then heating to 580-620°C at 0.8-1.2°C / min, and maintaining at this temperature for 1.5-2.5h. During the debinding process, when the temperature is below 300°C, the system vacuum is maintained below 10Pa. When the temperature reaches 300°C or above, nitrogen is introduced to keep the pressure at -0.02MPa~0.02MPa.

9. The method for preparing the synergistically reinforced silicon nitride composite ceramic according to claim 5, characterized in that: The hot pressing sintering is carried out by gradually increasing the temperature to 1800-1900° C. and keeping the temperature for 0.5-2 hours. The hot pressing sintering is carried out in a nitrogen atmosphere of 0.05-0.15 MPa.

10. Use of the synergistically reinforced silicon nitride composite ceramic according to any one of claims 1 to 4, or the synergistically reinforced silicon nitride composite ceramic prepared by the preparation method according to any one of claims 5 to 9, in the preparation of high-temperature structural parts, cutting tools or wear-resistant parts.

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