Synergistic reinforced silicon nitride composite ceramic as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of composite ceramics, and discloses a synergistically reinforced silicon nitride composite ceramic, and a preparation method and application thereof, the raw materials comprise the following components by mass: 40-90 parts of alpha-Si3N4; 8-15 parts of a sintering aid; 0.1 to 15 parts of nano TiN; 0.1 to 12 parts of SiCw (silicon carbide w); in the sintering aid, the mass ratio of Al2O3 to Y2O3 to CaF2 is (5-10): (1-5): (0.5-3). According to the invention, the nano TiN particles and directionally arranged SiCw are creatively added, and freeze drying and hot pressed sintering technologies are combined, so that the problem that strength and toughness of Si3N4 ceramic are difficult to synchronously improve in the prior art is solved, and the defect of poor toughening effect caused by random distribution of a whisker toughening phase in a matrix is overcome. By accurately regulating and controlling the microstructure, uniform dispersion and directional arrangement of a reinforcement phase are realized, the toughening potential of the whisker is fully exerted, and the comprehensive mechanical property of the Si3N4 ceramic is remarkably improved.

Description

Technical Field

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

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

[0003] Si3N4 ceramics are regarded as a key high-performance engineering material with excellent high-temperature strength, wear resistance, thermal shock resistance and chemical stability, and are widely used in various fields. However, its inherent brittle characteristics pose an application bottleneck under high-load and high-friction working conditions. Therefore, it is crucial to develop effective strengthening and toughening technologies to improve its comprehensive performance.

[0004] Current strategies for improving the performance of Si3N4 ceramics often rely on adding sintering aids (such as Al2O3, Y2O3) to optimize the sintering process and increase the density. Although such methods are helpful for densification, they have limited effects on significantly improving the fracture toughness and tribological properties of the material. In contrast, introducing second-phase reinforcements, such as nanoparticle (TiC), silicon carbide whiskers (SiCw) or fibers, has been proven to be a more effective approach. These reinforcements can simultaneously strengthen 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 only focus on improving either bending strength or fracture toughness alone, and it is difficult to synergistically optimize the strength and toughness of Si3N4 ceramics. In addition, commonly used toughening phases such as whiskers usually show a random distribution state in the matrix. This disordered distribution pattern greatly limits the exertion of the toughening efficiency of the toughening phase. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a synergistically strengthened silicon nitride composite ceramic and its preparation method and application. By innovatively adding nano-TiN particles and directionally arranged SiCw, and combining freeze-drying and hot-pressing sintering technologies, the present invention not only solves the problem that it is difficult to simultaneously improve the strength and toughness of Si3N4 ceramics in the existing technology, but also overcomes the defect that the toughening effect is poor due to the random distribution of whisker-like toughening phases in the matrix. By precisely controlling the microstructure, the uniform dispersion and directional arrangement of the reinforcing phases are achieved, the toughening potential of the whiskers is fully exerted, and the comprehensive mechanical properties of Si3N4 ceramics are significantly improved.

[0007] To achieve the above object, the present invention is realized by the following technical solutions: In the first aspect, the present invention provides a synergistically strengthened silicon nitride composite ceramic, and its raw materials by mass parts include the following components: 40 - 90 parts of α-Si3N4; 8 - 15 parts of sintering aids; 0.1 - 15 parts of nano-TiN; 0.1 - 12 parts of SiCw; In the sintering aids, the mass ratio of Al2O3, Y2O3 and CaF2 is 5 - 10:1 - 5:0.5 - 3.

[0008] Al2O3 and Y2O3 as composite sintering aids can significantly improve the liquid phase 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 liquid phase, thus hindering the formation of lattice oxygen and reducing the 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.

[0009] When nano-TiN is introduced as a reinforcing phase into the Si3N4 ceramic matrix, it can play a role in refining grains, hindering dislocations and cracks, and thus effectively improve the flexural strength and fracture toughness of Si3N4.

[0010] Nano-TiN has certain self-lubricity, which can reduce surface adhesive wear; high-hardness nano-TiN particles support the load, which can reduce abrasive particle embedding and effectively reduce the wear rate; nano-TiN has excellent oxidation resistance under high-temperature conditions, which is beneficial to maintaining the high-temperature wear resistance of ceramic materials.

[0011] SiCw has the effects of crack deflection, crack bridging, etc., which can effectively improve the flexural strength and fracture toughness of ceramic materials and has a certain promoting effect on the improvement of the hardness and elastic modulus of ceramic materials. In addition, SiCw has good high-temperature stability and can maintain a good toughening effect under high-temperature conditions.

[0012] In some embodiments, the synergistically strengthened silicon nitride composite ceramic, its raw materials by mass parts include the following components: 50 - 90 parts of α-Si3N4; 8 - 15 parts of sintering aids; 1 - 15 parts of nano-TiN; 1 - 12 parts of SiCw; In the sintering aids, the mass ratio of Al2O3, Y2O3 and CaF2 is 5 - 8:2 - 4:0.5 - 2.

[0013] Preferably, the synergistically strengthened silicon nitride composite ceramic, its raw materials by mass parts include the following components: 60 - 90 parts of α-Si3N4; 8 - 15 parts of sintering aids; 1 - 15 parts of nano-TiN; 1 - 12 parts of SiCw; In the sintering aids, the mass ratio of Al2O3, Y2O3 and CaF2 is 5 - 7:2 - 4:0.5 - 1.

[0014] More preferably, in the sintering aid, the mass ratio of Al2O3, Y2O3 and CaF2 is 6:3:1.

[0015] In some embodiments, the raw materials of the synergistically reinforced silicon nitride composite ceramic further include a slurry dispersant and a slurry binder.

[0016] Preferably, the slurry dispersant is sodium dodecyl sulfate; the slurry binder is polyvinylpyrrolidone.

[0017] More 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.

[0018] In a second aspect, the present invention provides a method for preparing the synergistically reinforced silicon nitride composite ceramic, comprising the following steps: Mix the raw materials in proportion and perform wet ball milling with water; Perform directional freeze-drying on the suspension after wet ball milling. Water will freeze and sublime in a set direction, prompting the SiCw in the suspension to be arranged orderly along the ice crystal growth direction. Subsequently, after debinding treatment and hot press sintering, the product is obtained.

[0019] The Si3N4 ceramic prepared by the present invention has the dispersion strengthening effect of nano-TiN and the directional structure of SiCw. The directional structure is obvious, enabling the Si3N4 ceramic to have a high fracture toughness in a certain direction, realizing the dual improvement of the bending strength and fracture toughness of the Si3N4 ceramic.

[0020] In the freeze-drying stage, after cooling the mold with liquid nitrogen, using the temperature difference brought by the upper and lower sides of the mold, the ceramic slurry will form a temperature gradient in the vertical direction, and heat will transfer along the direction opposite to the temperature gradient, thereby achieving the effect of directional solidification of SiCw. During the hot press sintering process, the phase transformation of Si3N4 will not change the directional effect of SiCw, so that the original directional structure is maintained.

[0021] 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 again while retaining the original Si3N4 ceramic matrix, thereby comprehensively improving the mechanical properties.

[0022] Among them, SiCw still maintains a good orientation arrangement 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 helps the crack deflection and the toughening mechanism to play.

[0023] The present invention can realize the matrix structure and directional structure of the Si3N4 ceramic by controlling the raw material ratio, debinding time, hot press sintering time and heating rate.

[0024] In some embodiments, the lyophilization is as follows: the mixture after wet ball milling is directionally frozen in a mold, wherein the heat conduction rates of the materials of the top wall and the bottom wall of the mold are different; then, the temperature is slowly raised under the condition that the vacuum degree is lower than 10 Pa, so that the interlayer ice crystals sublimate into gas and are discharged.

[0025] Preferably, the materials of the top wall and the bottom wall of the mold are polytetrafluoroethylene and stainless steel respectively.

[0026] The temperature difference brought by the upper and lower surfaces of the mold causes the slurry to form a temperature gradient in the vertical direction, and heat is transferred along the direction opposite to the temperature gradient, thereby achieving the effect of directional solidification.

[0027] Preferably, the mixture after wet ball milling is directionally frozen in liquid nitrogen.

[0028] Preferably, during the process of sublimating the interlayer ice crystals into gas, after 100 - 140 h, the temperature is slowly raised from -50 °C to room temperature. Room temperature refers to the ambient temperature, generally 20 - 30 °C. The purpose of slowly raising the temperature is to ensure the uniform sublimation of ice crystals and the integrity of the directional arrangement structure of SiCw. If the heating rate is too fast, the ice crystals may sublimate non-uniformly and rapidly, resulting in the destruction of the directional arrangement of SiCw, the occurrence of structural collapse or disordered distribution, and thus affecting the microstructure and mechanical properties of the composite ceramics.

[0029] In some embodiments, the product after lyophilization is heated at a gradient to remove the binder, and the heating program is as follows: it is heated to 180 - 220 °C at a rate of 1.5 - 2.5 °C / min, and then heated to 580 - 620 °C at a rate of 0.8 - 1.2 °C / min, and maintained at this temperature for 1.5 - 2.5 h.

[0030] Preferably, the heating program during the binder removal process is as follows: it is heated to 200 °C at a rate of 2 °C / min, and then heated to 600 °C at a rate of 1 °C / min, and maintained at this temperature for 2 h. 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 is beneficial to quickly remove the bound water and reduce the binder removal time; while in the high-temperature stage (200 °C to 600 °C), a slower heating rate can prevent the generation of internal residual stress and thermal cracks in the material, and at the same time ensure the full decomposition of organic matter and impurities, and avoid structural damage during the binder removal process.

[0031] 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 keep the pressure between -0.02 MPa and 0.02 MPa. Using a high-vacuum environment in the low-temperature stage 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 decompose significantly. At this time, introducing a small amount of nitrogen can, on the one hand, inhibit the violent oxidative decomposition of the organic matter at high temperatures, and on the other hand, nitrogen, as an inert protective atmosphere, helps to maintain the stability of the sample composition.

[0032] In some embodiments, hot-press sintering is carried out by gradually heating to 1800 - 1900°C, holding for 0.5 - 2 h, and the hot-press sintering is carried out in a nitrogen atmosphere of 0.05 - 0.15 MPa.

[0033] Preferably, during the hot-press sintering process, the temperature is raised to 1000 - 1300°C at a rate of 15 - 25°C / min, and then raised to 1800 - 1900°C at a rate of 8 - 12°C / min.

[0034] In a third aspect, the present invention provides the application of the synergistically strengthened silicon nitride composite ceramic in the preparation of high-temperature structural components, cutting tools, or wear-resistant parts.

[0035] The beneficial effects obtained by one or more of the above embodiments of the present invention are as follows: By adding nano-TiN particles and directionally arranged SiCw, and combining freeze-drying and hot-press sintering techniques, the present invention realizes the uniform dispersion and directional arrangement of the reinforcing phases, significantly improving the flexural strength and fracture toughness of the Si3N4 ceramic. Experimental data show that for the sample with 5 wt% nano-TiN and 9 wt% directionally arranged SiCw, its flexural strength reaches 879.2 MPa, and the fracture toughness reaches 10.2 MPa·m 1 / 2 , which are respectively increased by about 35% and 40% compared with the sample without adding the reinforcing phase.

[0036] By controlling the content and distribution of the reinforcing phases, the microstructure of the Si3N4 ceramic is regulated, realizing the uniform growth of β-Si3N4 grains and the uniform dispersion of the reinforcing phases, reducing the porosity, and improving the densification of the material. Experimental data show that the relative density of the optimized sample reaches 98.8%, which is significantly higher than that of the sample without adding the reinforcing phase (95.8%). BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The schematic drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0038] Figure 1In the technical solution provided in Embodiment 5 of the present invention, the XRD comparison pattern of the N5C9 sample; Figure 2 In the technical solution provided in Embodiment 5 of the present invention, the fracture surface morphology diagrams of the Si3N4 ceramic of the N5C9 sample: (a) perpendicular to the hot pressing direction; (b) parallel to the hot pressing direction; Figure 3 In the technical solution provided in Embodiment 1, Embodiment 3, Embodiment 5 and Embodiment 7 of the present invention, the mechanical property comparison diagrams of the prepared Si3N4 ceramic: (a) flexural strength; (b) fracture toughness. Detailed implementation manners

[0039] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations for 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 of ordinary skill in the technical field to which the present invention belongs.

[0040] The following is the preparation of Si3N4 ceramic according to a preparation method of a low-dimensional material synergistic texture strengthening silicon nitride composite ceramic provided by the present application: Embodiment 1 This embodiment is a specific embodiment for preparing the Si3N4 ceramic product N5C3.

[0041] 1) Slurry preparation The raw materials for preparing the ceramic product, by mass parts, include the following components: 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; Among them, the purity of the Si3N4 powder is ≥99.9%, and the particle size D 50 = 0.5 μm; the purity of the Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1 μm; the particle size of the nano-TiN is 40 nm; the length of the SiCw is 10 - 50 μm, and the diameter is 0.5 μm; the average molecular weight of PVP is 1300000 g / mol.

[0042] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%; and deionized water is added thereto to make the solid-liquid ratio 2:3. After mixing evenly, a mixed slurry is obtained.

[0043] 2) Freeze drying Place a polytetrafluoroethylene mold with a customized stainless-steel base in a heat-insulating bucket. Pour an appropriate amount of liquid nitrogen into the heat-insulating bucket. After the liquid nitrogen completely cools the mold, pour the mixed slurry prepared in step 1) into the customized mold, and keep the liquid nitrogen present for 15 min to ensure that the internal slurry can be completely frozen until the solvent deionized water is completely frozen into ice crystals.

[0044] Subsequently, place the frozen product together with the mold in a freeze dryer. Preset the temperature to -50 °C, and under an environment with a vacuum degree lower than 10 Pa, after 120 h, raise the temperature to room temperature (25 °C) to sublime the ice crystals between layers into gas and discharge them. After demolding, a directional Si3N4 ceramic with directionally arranged SiCw is obtained.

[0045] 3) Binder burnout treatment Place the directional Si3N4 ceramic prepared in step 2) in an Al2O3 ceramic crucible and transfer it to a binder burnout furnace. Heat it from room temperature to 200 °C at a rate of 2 °C / min, and then heat it to 600 °C at a rate of 1 °C / min and hold it at this temperature for 2 h. During the whole process, when the temperature is lower than 300 °C, keep the vacuum degree lower than 10 Pa, and then introduce nitrogen gas with the air pressure controlled within the range of 0.01 MPa.

[0046] Through the above heat treatment, the removal treatment of SDS and PVP is carried out to obtain a binder burnout product.

[0047] 4) Hot pressing sintering Place the binder burnout product obtained in step 3) in a graphite mold for hot pressing sintering. The specific process is as follows: Heat it from room temperature (25 °C) to 1200 °C at a rate of 20 °C / min, and then heat it to 1850 °C at a rate of 10 °C / min and hold it at this temperature for 1 h. The whole hot pressing sintering process is carried out under a nitrogen atmosphere of 0.1 MPa to obtain a ceramic product N5C3.

[0048] In this embodiment, the mechanical properties of the prepared ceramic product N5C3 are as Figure 3 shown, in which the flexural strength reaches 745.42 MPa, the fracture toughness reaches 8.83 MPa·m 1 / 2 , and the hardness reaches 16.1 GPa.

[0049] Example 2 This embodiment is a specific example for preparing a Si3N4 ceramic product N10C3.

[0050] 1) Slurry preparation The raw materials for preparing the ceramic product, by mass, include the following components: 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; Among them, the purity of Si3N4 powder is ≥99.9%, and the particle size D 50 =0.5μm; the purity of Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1μm; the particle size of nano-TiN is 40nm; the length of SiCw is 10 - 50μm, and the diameter is 0.5μm; the average molecular weight of PVP is 1300000g / mol.

[0051] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%; deionized water is added to make the solid-liquid ratio 2:3. After mixing evenly, a mixed slurry is obtained.

[0052] 2) Freeze-drying Pour the mixed slurry prepared in step 1) into a customized mold, cool it with liquid nitrogen, freeze it directionally, and keep it for 10 min until the deionized water is completely frozen.

[0053] Subsequently, place the frozen product together with the mold in a freeze-dryer. Preset the temperature to -50°C, and in an environment with a vacuum degree lower than 10 Pa, after 120 h, raise the temperature to room temperature (25°C) to sublime the interlayer ice crystals into gas and discharge them. After demolding, a directional Si3N4 ceramic containing directionally arranged SiCw is obtained.

[0054] 3) Debinding treatment Place the directional Si3N4 ceramic prepared in step 2) in an Al2O3 ceramic crucible, transfer it to a debinding furnace, heat it from room temperature to 200°C at a rate of 2°C / min, and then heat it to 600°C at a rate of 1°C / min and hold it at this temperature for 2 h. During the whole process, when the temperature is lower than 300°C, keep the vacuum degree lower than 10 Pa, and then introduce nitrogen gas with the air pressure controlled within the range of 0.01 MPa.

[0055] Through the above heat treatment, SDS and PVP are removed to obtain a debound product.

[0056] 4) Hot pressing and sintering Place the debound product obtained in step 3) in a graphite mold for hot pressing and sintering. The specific process is as follows: heat it from room temperature (25°C) to 1200°C at a rate of 20°C / min, and then heat it to 1850°C at a rate of 10°C / min and hold it at this temperature for 1 h. The whole hot pressing and sintering process is carried out in a nitrogen atmosphere of 0.1 MPa to obtain a ceramic product N10C3.

[0057] 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 15.9 GPa.

[0058] Example 3 This example is a specific example for preparing the Si3N4 ceramic product N5C6.

[0059] 1) Slurry preparation The raw materials for preparing the ceramic product, by mass parts, include the following components: 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; Among them, the purity of the Si3N4 powder is ≥99.9%, and the particle size D 50 = 0.5 μm; the purity of the Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1 μm; the particle size of the nano-TiN is 40 nm; the length of the SiCw is 10 - 50 μm, and the diameter is 0.5 μm; the average molecular weight of the PVP is 1300000 g / mol.

[0060] After mixing the above raw materials according to the set mass ratio, then add SDS and PVP to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%; and add deionized water to it so that the solid-liquid ratio is 2:3. After mixing evenly, a mixed slurry is obtained.

[0061] 2) Freeze-drying Pour the mixed slurry prepared in step 1) into a customized mold, use liquid nitrogen for cooling, and freeze directionally for 12 min until the deionized water is completely frozen.

[0062] Subsequently, place the frozen product together with the mold in a freeze-dryer, pre-set at -50°C, in an environment with a vacuum degree lower than 10 Pa, and after 120 h, raise the temperature to room temperature (25°C) to sublime the interlayer ice crystals into gas and discharge them. After demolding, an oriented Si3N4 ceramic containing oriented SiCw is obtained.

[0063] 3) Binder burnout treatment Place the oriented Si3N4 ceramic prepared in step 2) in an Al2O3 ceramic crucible, transfer it to a binder burnout furnace, heat it from room temperature to 200°C at a rate of 2°C / min, and then heat it to 600°C at a rate of 1°C / min and hold it at this temperature for 2 h. During the whole process, when the temperature is lower than 300°C, keep the vacuum degree lower than 10 Pa, and then introduce nitrogen, and control the air pressure within the range of 0.02 MPa. Through the above heat treatment, the removal treatment of SDS and PVP is carried out to obtain a binder burnout product.

[0064] 4) Hot pressing and sintering Place the debinding product obtained in step 3) in a graphite mold and perform hot pressing sintering. The specific process is as follows: Heat from room temperature to 1200 °C at a rate of 20 °C / min, and then heat to 1850 °C at a rate of 10 °C / min, and hold at this temperature for 1 h. The entire hot pressing sintering process is carried out in a nitrogen atmosphere of 0.1 MPa to obtain the ceramic product N5C6.

[0065] In this example, the mechanical properties of the prepared ceramic product N5C6 are as Figure 3 shown. Compared with the product N5C3, the fracture toughness has been further improved. The fracture toughness reaches 9.77 MPa·m 1 / 2 , the flexural strength reaches 772.05 MPa, and the hardness reaches 16.4 GPa.

[0066] Example 4 This example is a specific example for preparing the Si3N4 ceramic product N10C6.

[0067] 1) Slurry preparation The raw materials for preparing the ceramic product, by mass, include the following components: 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; Among them, the purity of the Si3N4 powder is ≥99.9%, and the particle size D 50 = 0.5 μm; the purity of the Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1 μm; the particle size of the nano-TiN is 40 nm; the length of the SiCw is 10 - 50 μm, and the diameter is 0.5 μm; the average molecular weight of PVP is 1300000 g / mol.

[0068] After mixing the above raw materials according to the set mass ratio, add SDS and PVP to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%; and add deionized water to make the solid-liquid ratio 2:3, and after mixing evenly, obtain a mixed slurry.

[0069] 2) Freeze drying Pour the mixed slurry prepared in step 1) into a customized mold, use liquid nitrogen for cooling, directionally freeze, and hold for 15 min until the deionized water is completely frozen.

[0070] Subsequently, place the frozen product together with the mold in a freeze dryer, pre-set at -50 °C, and in an environment with a vacuum degree lower than 10 Pa, after 120 h, heat to room temperature to sublimate the interlayer ice crystals into gas and discharge them. After demolding, obtain a directional Si3N4 ceramic containing directionally arranged SiCw.

[0071] 3) Debinding treatment Place the oriented Si3N4 ceramic prepared in step 2) in an Al2O3 ceramic crucible, transfer it to a debinding furnace, heat it from room temperature to 200 °C at a rate of 2 °C / min, then heat it to 600 °C at a rate of 1 °C / min, and hold it at this temperature for 2 h. During the whole process, when the temperature is below 300 °C, keep the vacuum degree below 10 Pa, and then introduce nitrogen gas, and control the air pressure within the range of 0.015 MPa. Through the above heat treatment, the removal treatment of SDS and PVP is carried out to obtain a debound product.

[0072] 4) Hot pressing and sintering Place the debound product obtained in step 3) in a graphite mold for hot pressing and sintering. The specific process is as follows: heat it from room temperature to 1200 °C at a rate of 20 °C / min, then heat it to 1850 °C at a rate of 10 °C / min, and hold it at this temperature for 1 h. The whole hot pressing and sintering process is carried out under a nitrogen atmosphere of 0.1 MPa to obtain the ceramic product N10C6.

[0073] In this embodiment, compared with the product N5C6, the mechanical properties of the prepared ceramic product N10C6 show that the flexural strength drops to 704.23 MPa, and the fracture toughness reaches 9.32 MPa·m 1 / 2 , and the hardness reaches 16.2 GPa.

[0074] Example 5 This embodiment is a specific example for preparing the Si3N4 ceramic product N5C9.

[0075] 1) Slurry preparation The raw materials for preparing the ceramic product, by mass, include the following components: 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; Among them, the purity of the Si3N4 powder is ≥99.9%, and the particle size D 50 = 0.5 μm; the purity of the Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1 μm; the particle size of the nano-TiN is 40 nm; the length of the SiCw is 10 - 50 μm, and the diameter is 0.5 μm; the average molecular weight of PVP is 1300000 g / mol.

[0076] After mixing the above raw materials according to the set mass ratio, then add SDS and PVP to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%; and add deionized water to it to make the solid-liquid ratio 2:3, and after mixing evenly, obtain a mixed slurry.

[0077] 2) Freeze drying Pour the mixed slurry prepared in step 1) into a customized mold, cool it with liquid nitrogen, freeze it directionally, and maintain for 12 min until the deionized water is completely frozen.

[0078] Subsequently, place the frozen product together with the mold in a freeze dryer, pre-set at -50 °C, in an environment with a vacuum degree lower than 10 Pa, and after 120 h, raise the temperature to room temperature to sublime the interlayer ice crystals into gas and discharge them. After demolding, a directional Si3N4 ceramic containing directionally arranged SiCw is obtained.

[0079] 3) Debinding treatment Place the directional Si3N4 ceramic prepared in step 2) in an Al2O3 ceramic crucible, transfer it to a debinding furnace, heat it from room temperature to 200 °C at a rate of 2 °C / min, and then heat it to 600 °C at a rate of 1 °C / min and hold for 2 h at this temperature. During the whole process, when the temperature is lower than 300 °C, maintain the vacuum degree lower than 10 Pa, and then introduce nitrogen with the air pressure controlled within the range of 0.005 MPa.

[0080] 4) Hot pressing sintering Place the debinding product obtained in step 3) in a graphite mold for hot pressing sintering. The specific process is as follows: heat it from room temperature to 1200 °C at a rate of 20 °C / min, and then heat it to 1850 °C at a rate of 10 °C / min and hold for 1 h at this temperature. The whole hot pressing sintering process is carried out in a nitrogen atmosphere of 0.1 MPa to obtain the ceramic product N5C9.

[0081] In this embodiment, a Si3N4 ceramic product N5C9 with high density is obtained after sintering; after testing, the XRD pattern of the product N5C9 is as Figure 1 shown, and the diffraction peak intensity of SiCw perpendicular to the hot pressing direction is stronger than that parallel to the hot pressing direction. The micro-morphology diagram of the product N5C9 is as Figure 2 shown, and the side and end faces of SiCw are well directionally arranged in different directions, fully confirming the excellent effect of freeze drying.

[0082] After testing, the mechanical property comparison diagram of the Si3N4 ceramic prepared in the embodiment of the present invention is as Figure 3 shown in (a) and (b) therein. Compared with the product N5C6, the fracture toughness of the product N5C9 has further improved, and the fracture toughness reaches 10.2 MPa·m 1 / 2 , the flexural strength reaches 879.22 MPa, and the hardness reaches 16.7 GPa. The SEM morphology of the product N5C9 is as Figure 2 shown, and the texture degree in both directions is obvious. Through Figure 2 observing the end face of the whiskers in (a) therein, and in Figure 2In (b), observing the sides of many whiskers further proves that a certain amount of whiskers results in good freeze-drying effect and significant orientation.

[0083] For the prepared Si3N4 ceramic, β-Si3N4, nano-TiN, and SiCw in it do not conflict with each other, and can significantly improve the fracture toughness of the ceramic again on the basis of retaining the original Si3N4 ceramic matrix, thereby comprehensively improving the mechanical properties. To verify the above analysis conclusion, the product N5C9 was cut, polished, and ion-thinned, and then the microscopic morphology of the grains was observed under TEM. Among them, SiCw still maintains good orientation arrangement 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 helps the crack deflection and the play of the toughening mechanism.

[0084] Example 6 This example is a specific example for preparing the Si3N4 ceramic product N10C9.

[0085] Slurry preparation The raw materials for preparing the ceramic product, by mass, include the following components: 72 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; 10 parts of nano-TiN; 9 parts of SiCw; Among them, the purity of the Si3N4 powder is ≥99.9%, and the particle size D 50 = 0.5μm; the purity of the Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1μm; the particle size of the nano-TiN is 40nm; the length of the SiCw is 10 - 50μm, and the diameter is 0.5μm; the average molecular weight of PVP is 1300000 g / mol.

[0086] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%; and deionized water is added to make the solid-liquid ratio 2:3. After mixing evenly, a mixed slurry is obtained.

[0087] 2) Freeze-drying Pour the mixed slurry prepared in step 1) into a customized mold, use liquid nitrogen for cooling, directionally freeze, and keep it for 10 min until the deionized water is completely frozen.

[0088] Subsequently, place the frozen product together with the mold in a freeze-dryer, pre-set at -50°C, in an environment with a vacuum degree lower than 10 Pa, and after 120 h, raise the temperature to room temperature to sublime the interlayer ice crystals into gas and discharge them. After demolding, a directional Si3N4 ceramic containing directionally arranged SiCw is obtained.

[0089] 3) Debinding treatment Place the oriented Si3N4 ceramic obtained in step 2) in an Al2O3 ceramic crucible, transfer it to a debinding furnace, heat it from room temperature to 200 °C at a rate of 2 °C / min, and then heat it to 600 °C at a rate of 1 °C / min, and hold it at this temperature for 2 h. During the whole process, when the temperature is below 300 °C, keep the vacuum degree below 10 Pa, and then introduce nitrogen, and control the air pressure within the range of 0.01 MPa.

[0090] 4) Hot press sintering Place the debinding product obtained in step 3) in a graphite mold for hot press sintering. The specific process is as follows: heat it from room temperature to 1200 °C at a rate of 20 °C / min, and then heat it to 1850 °C at a rate of 10 °C / min, and hold it at this temperature for 1 h. The whole hot press sintering process is carried out in a nitrogen atmosphere of 0.1 MPa to obtain the ceramic product N10C9.

[0091] In this embodiment, the fracture toughness of the N10C9 sample reaches 9.7 MPa·m 1 / 2 , the flexural strength reaches 823.89 MPa, and the hardness reaches 16.3 GPa.

[0092] Example 7 This embodiment is a specific embodiment for preparing the Si3N4 ceramic product N5C12.

[0093] 1) Slurry preparation The raw materials for preparing the ceramic product, by mass, include the following components: 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; Among them, the purity of the Si3N4 powder is ≥99.9%, and the particle size D 50 = 0.5 μm; the purity of the Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1 μm; the particle size of the nano-TiN is 40 nm; the length of the SiCw is 10 - 50 μm, and the diameter is 0.5 μm; the average molecular weight of PVP is 1300000 g / mol.

[0094] After mixing the above raw materials according to the set mass ratio, add SDS and PVP to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%; and add deionized water to it so that the solid-liquid ratio is 2:3, and after mixing evenly, obtain a mixed slurry.

[0095] 2) Freeze drying Pour the mixed slurry obtained in step 1) into a customized mold, use liquid nitrogen for cooling, directionally freeze, and hold for 10 min until the deionized water is completely frozen.

[0096] Subsequently, the frozen product together with the mold was placed in a freeze dryer, pre-set at -50 °C, and in an environment with a vacuum degree lower than 10 Pa. After 120 h, the temperature was raised to room temperature to sublime the interlayer ice crystals into gas and discharge them. After demolding, a directional Si3N4 ceramic containing directionally arranged SiCw was obtained.

[0097] 3) Binder burnout treatment The directional Si3N4 ceramic prepared in step 2) was placed in an Al2O3 ceramic crucible and transferred to a binder burnout furnace. It was heated 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, and held at this temperature for 2 h. Throughout the process, the vacuum degree was kept lower than 10 Pa before 300 °C, and then nitrogen was introduced, and the air pressure was controlled within the range of 0.02 MPa. Through the above heat treatment, the removal treatment of SDS and PVP was carried out to obtain a binder burnout product.

[0098] 4) Hot pressing sintering The binder burnout product obtained in step 3) was placed in a graphite mold for hot pressing sintering. The specific process was as follows: It was heated from room temperature to 1200 °C at a rate of 20 °C / min, and then from 1200 °C to 1850 °C at a rate of 10 °C / min, and held at this temperature for 1 h. The entire hot pressing sintering process was carried out in a nitrogen atmosphere of 0.1 MPa to obtain a ceramic product N5C12.

[0099] In this embodiment, the mechanical properties of the product N5C12 are as Figure 3 shown. Compared with the product N5C9, the mechanical properties decreased. The fracture toughness reached 9.26 MPa·m 1 / 2 , the flexural strength reached 779.09 MPa, and the hardness reached 15.3 GPa.

[0100] Example 8 This embodiment is a specific example for preparing the Si3N4 ceramic product N10C12.

[0101] 1) Slurry preparation The raw materials for preparing the ceramic product, by mass, included the following components: 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; Among them, the purity of the Si3N4 powder was ≥99.9%, and the particle size D 50 = 0.5 μm; the purity of the Al2O3, Y2O3, and CaF2 powders was ≥99.9%, and the particle size was 1 μm; the particle size of the nano-TiN was 40 nm; the length of the SiCw was 10 - 50 μm, and the diameter was 0.5 μm; the average molecular weight of PVP was 1300000 g / mol.

[0102] After mixing the above raw materials according to the set mass ratio, SDS and PVP are added to the mixed powder. The mass percentage of SDS in the mixed powder is 1%, and the mass percentage of PVP in the mixed powder is 1%. Deionized water is added thereto to make the solid-liquid ratio 2:3. After mixing evenly, a mixed slurry is obtained.

[0103] 2) Freeze-drying Pour the mixed slurry prepared in step 1) into a customized mold, cool it with liquid nitrogen, freeze it directionally, and keep it for 10 min until the deionized water is completely frozen.

[0104] Subsequently, place the frozen product together with the mold in a freeze dryer, pre-set at -50 °C, and under an environment with a vacuum degree lower than 10 Pa, after 120 h, raise the temperature to room temperature to sublime the interlayer ice crystals into gas and discharge them. After demolding, a directional Si3N4 ceramic containing directionally arranged SiCw is obtained.

[0105] 3) Debinding treatment Place the directional Si3N4 ceramic prepared in step 2) in an Al2O3 ceramic crucible, transfer it to a debinding furnace, heat it from room temperature to 200 °C at a rate of 2 °C / min, and then heat it to 600 °C at a rate of 1 °C / min and hold it at this temperature for 2 h. During the whole process, when the temperature is lower than 300 °C, keep the vacuum degree lower than 10 Pa, and then introduce nitrogen gas with the air pressure controlled within the range of 0.01 MPa.

[0106] 4) Hot pressing and sintering Place the debinding product obtained in step 3) in a graphite mold for hot pressing and sintering. The specific process is as follows: heat it from room temperature to 1200 °C at a rate of 20 °C / min, and heat it from 1200 °C to 1850 °C at a rate of 10 °C / min and hold it at this temperature for 1 h. The whole hot pressing and sintering process is carried out under a nitrogen atmosphere of 0.1 MPa to obtain a ceramic product N10C12.

[0107] In this embodiment, the mechanical properties of the prepared ceramic product N10C12 decrease. The fracture toughness reaches 8.92 MPa·m 1 / 2 , the flexural strength reaches 743.21 MPa, and the hardness reaches 15.1 GPa.

[0108] Comparative example 1 This embodiment is a specific embodiment for preparing a Si3N4 ceramic product N0C0.

[0109] 1) Raw material mixing The raw materials for preparing the ceramic product, by mass, include the following components: 91 parts of Si3N4; 5 parts of Al2O3; 3 parts of Y2O3; 1 part of CaF2; Among them, the purity of Si3N4 powder is ≥99.9%, and the particle size D 50 =0.5 μm; the purity of Al2O3, Y2O3, and CaF2 powders is ≥99.9%, and the particle size is 1 μm; After mixing the above raw materials according to the set mass ratio, anhydrous ethanol is added as a solvent to make the solid-liquid ratio 1:4. After mixing evenly, a mixed slurry is obtained.

[0110] 2) Ball milling and drying Place the mixed slurry obtained in step 1) in a ball mill with a ball-to-material ratio of 3:1 and ball mill for 12 h at a rotational speed of 300 r / min. After the powders are evenly mixed, pour the slurry into a petri dish and dry it in an oven at 70 °C for 24 h to obtain the ball-milled powder.

[0111] 3) Grinding and sieving Pour the ball-milled powder obtained in step 2) into a mortar, grind it into a powder, and pass it through a 60-mesh sieve to obtain a uniformly mixed powder, i.e., the sieved powder.

[0112] 4) Hot pressing and sintering Place the sieved powder in a graphite mold for hot pressing and sintering. The specific process is as follows: heat up from room temperature to 1200 °C at a rate of 20 °C / min, and then heat up to 1800 °C at a rate of 10 °C / min and hold for 1 h at this temperature. The entire hot pressing and sintering process is carried out in a nitrogen atmosphere of 0.1 MPa.

[0113] In this comparative example, a Si3N4 ceramic product N0C0 with high density was obtained after sintering; the flexural strength reached 630.24 MPa, and the fracture toughness reached 6.65 MPa·m 1 / 2 , and the hardness reached 14.8 GPa.

[0114] Comparative Example 2 Compared with Example 1, the difference is that in step 2), a polytetrafluoroethylene mold is used for loading and liquid nitrogen freezing is carried out, and the rest is the same as in Example 1.

[0115] In this comparative example, the mechanical properties of the prepared ceramic product are as follows: the flexural strength is 720.22 MPa, the fracture toughness is 8.15 MPa·m 1 / 2 , and the hardness is 15.8 GPa.

[0116] Comparative Example 3 Compared with Example 1, the difference is that in step 3), during the entire process of debinding treatment, the gas pressure is 0.01 MPa in a nitrogen atmosphere, and the rest is the same as in Example 1.

[0117] In this comparative example, the mechanical properties of the prepared ceramic product are as follows: the flexural strength is 730.15 MPa, the fracture toughness is 8.51 MPa·m1 / 2 , with a hardness of 16.3 GPa.

[0118] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A synergistically reinforced silicon nitride composite ceramic, characterized in that: Its raw materials, by mass, include the following components: 40 - 90 parts of α-Si3N4; 8 - 15 parts of sintering aids; 0.1 - 15 parts of nano-TiN; 0.1 - 12 parts of SiCw; In the sintering aids, the mass ratio of Al2O3, Y2O3 and CaF2 is 5 - 10:1 - 5:0.5 - 3.

2. The synergistically reinforced silicon nitride composite ceramic according to claim 1, wherein: Its raw materials, by mass, include the following components: 50 - 90 parts of α-Si3N4; 8 - 15 parts of sintering aids; 1 - 15 parts of nano-TiN; 1 - 12 parts of SiCw; In the sintering aids, 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, wherein: The raw materials further include a slurry dispersant and a slurry binder; the slurry dispersant is sodium dodecyl sulfate; the slurry binder is polyvinylpyrrolidone.

4. The synergistically reinforced silicon nitride composite ceramic according to claim 3, wherein: 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 preparation method of the synergistically strengthened silicon nitride composite ceramic according to any one of claims 1-4, characterized in that: It includes the following steps: Mix the raw materials in proportion and carry out wet ball milling with water; Perform directional freeze-drying on the suspension after wet ball milling. Water will freeze and sublimate in the set direction, prompting the SiCw in the suspension to be arranged orderly along the ice crystal growth direction. Subsequently, through debinding treatment and hot press sintering, it can be obtained.

6. The preparation method of the synergistically reinforced silicon nitride composite ceramic according to claim 5, wherein: The freeze-drying is: directionally freeze the mixture after wet ball milling in a mold, where the heat conduction rates of the materials of the top wall and the bottom wall of the mold are different; Then, under the condition that the vacuum degree is lower than 10 Pa, after 100 - 140 h, raise the temperature from -50°C to room temperature to sublimate the interlayer ice crystals into gas and discharge them.

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

8. The preparation method of the synergistically reinforced silicon nitride composite ceramic according to claim 5, characterized in that: Gradient heat the product after freeze-drying to carry out debinding. The heating program is: raise the temperature to 180 - 220°C at a rate of 1.5 - 2.5°C / min, and then raise the temperature to 580 - 620°C at a rate of 0.8 - 1.2°C / min, and maintain it at this temperature for 1.5 - 2.5 h; During the debinding process, when the temperature is lower than 300°C, keep the system vacuum degree lower than 10 Pa. When it reaches 300°C and above, introduce nitrogen to keep the air pressure at -0.02 MPa to 0.02 MPa.

9. The preparation method of the synergistically reinforced silicon nitride composite ceramic according to claim 5, wherein: Hot press sintering is to gradient heat to 1800 - 1900°C, keep warm for 0.5 - 2 h, and the hot press sintering is carried out in a nitrogen atmosphere of 0.05 - 0.15 MPa.

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

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