A strong and tough silicon nitride ceramic with a homogeneous network structure and a preparation method and application thereof

Abstract

The application provides a toughened silicon nitride ceramic with a homogeneous network structure and a preparation method and application thereof, and belongs to the technical field of ceramic materials. The application introduces beta-Si3N4 as a toughening phase through spark plasma sintering, and constructs a continuous homogeneous network structure in the silicon nitride ceramic matrix. Since the homogeneous network phase and the matrix phase have completely consistent chemical composition and thermal expansion coefficients, the interface residual stress and microcrack defects caused by the mismatch of thermophysical properties in the traditional heterogeneous composite system are fundamentally avoided, and the network / matrix interface is highly dense and has strong chemical bond. While improving the fracture toughness, the application does not introduce a heterogeneous weak interface, so the bending strength of the material is not sacrificed. The application successfully breaks through the technical bottleneck that strength and toughness are difficult to be considered in the traditional toughening strategy, and realizes the synergistic optimization of high strength and high toughness.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a toughened silicon nitride ceramic with a homogeneous network structure, its preparation method, and its application. Background Technology

[0002] In recent years, with the leapfrog progress of industries such as aerospace, defense, and high-precision equipment manufacturing, more stringent standards have been set for the comprehensive mechanical life of ceramic materials, which are core structural components, under extreme working conditions. Silicon nitride (Si3N4) ceramics, with their high strength, excellent thermal shock resistance, and thermochemical stability, have been widely used in many key components such as engine rotors and high-temperature precision bearings. However, as a typical covalent compound, the inherent brittleness of silicon nitride ceramics limits their reliable application under extremely complex stress environments. How to synergistically improve the strength and fracture toughness of silicon nitride ceramics remains a key scientific problem that urgently needs to be solved in this field.

[0003] To address this toughening challenge, traditional research has focused on introducing a second phase (such as carbon nanotubes, whiskers, metal particles, or even heterogeneous ceramic phases) for composite toughening. However, this toughening strategy involving the addition of heterogeneous phases faces a significant physical drawback: the mismatch between the coefficient of thermal expansion (CTE) and the elastic modulus. This typically leads to substantial residual stress and severe interface defects at the interface during cooling after high-temperature sintering, thereby weakening the intrinsic strength of the matrix and making it difficult to achieve both high strength and high toughness. In contrast, utilizing the phase transformation and microstructure control of silicon nitride for "self-toughening" is considered the most reliable approach. β-Si3N4 grains possess a unique elongated columnar morphology, capable of producing whisker-like pull-out and bridging effects. However, conventional processes often result in a random, disordered grain distribution, making it difficult to specifically prevent crack propagation. If a special microstructure can be designed that retains the homogeneity of silicon nitride ceramics to eliminate thermal mismatch stress, while also allowing long columnar grains to be concentrated and distributed in a specific region to form a network, it is hoped that the bottleneck of existing toughening technologies can be broken. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a toughened silicon nitride ceramic with a homogeneous network structure, its preparation method, and its application. This invention introduces β-Si3N4 through a double-shell coating process and constructs a three-dimensional isolation network, which not only eliminates heterogeneous interface defects but also fully utilizes the self-toughening mechanism of β-Si3N4, achieving a simultaneous and significant improvement in both the material's strength and toughness.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing strong and tough silicon nitride ceramics with a homogeneous network structure, comprising the following steps: Spherical silicon nitride powder, Al2O3 powder and Y2O3 powder are mixed by a first dry method to obtain silicon nitride powder containing a first coating layer; The silicon nitride powder containing the first coating layer is pre-sintered to obtain pre-sintered powder; The pre-sintered powder is mixed with β-Si3N4 powder by a second dry method to obtain a composite powder with a double coating layer. The composite powder with double coating layers is subjected to cold pressing and spark plasma sintering in sequence to obtain a toughened silicon nitride ceramic with a homogeneous network structure.

[0006] Preferably, the median particle size of the spherical silicon nitride powder is 30~100μm; the median particle size of the Al2O3 powder is 0.2μm; and the median particle size of the Y2O3 powder is 0.2μm.

[0007] Preferably, the mass ratio of the spherical silicon nitride powder, Al2O3 powder, and Y2O3 powder is 95:1.5:3.5; The pre-sintering temperature is 1400~1500℃, and the holding time is 0.5~1h.

[0008] Preferably, the median particle size of the β-Si3N4 powder is 40 nm; The mass ratio of the pre-sintered powder to the β-Si3N4 powder is 85~95:5~15.

[0009] Preferably, the rotation speed of the first dry mixing and the second dry mixing are independently 60~85 rpm, and the time is independently 6~10 h.

[0010] Preferably, the cold pressing pressure is 15~18MPa and the time is 5min.

[0011] Preferably, the discharge plasma sintering pressure is 40 MPa, the temperature is 1650~1750℃, and the holding time is 10 min.

[0012] The present invention provides a toughened silicon nitride ceramic with a homogeneous network structure prepared by the above preparation method, comprising a silicon nitride ceramic matrix and a β-Si3N4 network phase distributed between the silicon nitride ceramic matrix.

[0013] This invention provides the application of the above-mentioned strong and tough silicon nitride ceramics with homogeneous network structure in aerospace hot-end structural components, precision bearings, cutting tools or semiconductor support components.

[0014] This invention provides a method for preparing toughened silicon nitride ceramics with a homogeneous network structure. The method employs a double-shell coating process, where the first coating layer is a sintering aid powder and the second coating layer is β-Si3N4 powder. β-Si3N4 is introduced as a toughening phase through spark plasma sintering, constructing a continuous homogeneous network structure within the silicon nitride ceramic matrix. Because the homogeneous network phase and the matrix phase have completely identical chemical composition and thermal expansion coefficient, the residual stress and microcrack defects induced by thermophysical property mismatch in traditional heterogeneous composite systems are fundamentally avoided, ensuring a highly dense network / matrix interface and strong chemical bonding. Compared to traditional disordered self-toughened silicon nitride ceramics, the β-Si3N4 network introduced in this invention constructs a continuous and concentrated energy dissipation barrier in three-dimensional space. This homogeneous network can significantly enhance the deflection, bridging, and shielding energy dissipation effects on crack tips. The homogeneous network structure constructed in this invention improves fracture toughness without introducing heterogeneous weak interfaces, thus preserving the flexural strength of the material and successfully overcoming the technical bottleneck of traditional toughening strategies that struggle to balance strength and toughness. Example results show that the toughened silicon nitride ceramics obtained by this invention exhibit a flexural strength of 580.5~804.5 MPa and a fracture toughness of 4.7~10.0 MPa·m. 1 / 2 This achieves a synergistic optimization of high strength and high toughness.

[0015] Furthermore, the preparation method provided by this invention is simple and efficient, employing dry mixing and physical coating technology throughout the process. This not only avoids the defects such as solvent residue, powder agglomeration, and drying shrinkage that are prone to occur in traditional wet processes, but also has low requirements for production equipment and has extremely high feasibility for industrial scale-up. Attached Figure Description

[0016] Figure 1 Here is a scanning electron microscope image of the toughened silicon nitride ceramic obtained in Example 3; Figure 2 This is a magnified scanning electron microscope image of the toughened silicon nitride ceramic obtained in Example 3; Figure 3 Here is a scanning electron microscope image of the toughened silicon nitride ceramic obtained in Example 4; Figure 4 This is a magnified scanning electron microscope image of the toughened silicon nitride ceramic obtained in Example 4. Detailed Implementation

[0017] This invention provides a method for preparing strong and tough silicon nitride ceramics with a homogeneous network structure, comprising the following steps: Spherical silicon nitride powder, Al2O3 powder and Y2O3 powder are mixed by a first dry method to obtain silicon nitride powder containing a first coating layer; The silicon nitride powder containing the first coating layer is pre-sintered to obtain pre-sintered powder; The pre-sintered powder is mixed with β-Si3N4 powder by a second dry method to obtain a composite powder with a double coating layer. The composite powder with double coating layers is subjected to cold pressing and spark plasma sintering in sequence to obtain a toughened silicon nitride ceramic with a homogeneous network structure.

[0018] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0019] This invention involves a first dry mixing of spherical silicon nitride powder, Al₂O₃ powder, and Y₂O₃ powder to obtain silicon nitride powder containing a first coating layer. In this invention, the spherical silicon nitride powder is preferably a spherical granulated powder prepared by spray drying, and the median particle size of the spherical silicon nitride powder is preferably 30-100 μm, more preferably 50 μm. In this invention, the median particle size of the Al₂O₃ powder is preferably 0.2 μm; the median particle size of the Y₂O₃ powder is also preferably 0.2 μm. This invention uses Al₂O₃ powder and Y₂O₃ powder as sintering aids; their combined action can form a low-melting-point eutectic liquid phase, promoting densification and optimizing interfacial wettability.

[0020] In this invention, the preferred mass ratio of the spherical silicon nitride powder, Al2O3 powder, and Y2O3 powder is 95:1.5:3.5. By controlling the particle size and dosage ratio of the spherical silicon nitride powder, Al2O3 powder, and Y2O3 powder, this invention facilitates the subsequent introduction of the β-Si3N4 toughening phase.

[0021] In this invention, the first dry mixing is preferably carried out in a mixer, the mixing speed is preferably 60-85 rpm, more preferably 70-85 rpm, and the mixing time is preferably 6-10 h, more preferably 8-10 h. No liquid mixing medium is used throughout the first dry mixing process. This invention, through the first dry mixing, enables the sintering aid to uniformly adhere to the surface of the spherical silicon nitride powder, obtaining a first layer of coated powder.

[0022] This invention involves pre-sintering silicon nitride powder containing a first coating layer to obtain pre-sintered powder. In this invention, the pre-sintering is preferably pressureless sintering, and preferably carried out under a nitrogen atmosphere. In this invention, the pre-sintering temperature is preferably 1400~1500℃, and the heating rate to the pre-sintering temperature is preferably 50~100℃ / min. In this invention, during the pre-sintering process, a slight positive pressure (gauge pressure relative to atmospheric pressure) of 0.7~0.9 kPa is maintained inside the furnace cavity. This invention, through pre-sintering, fixes the sintering aid to the surface of the silicon nitride microspheres, ensuring the smooth progress of the subsequent second coating process.

[0023] This invention involves a second dry mixing process between the pre-sintered powder and β-Si3N4 powder to obtain a composite powder with a double coating layer. In this invention, the median particle size of the β-Si3N4 powder is preferably 40 nm; the mass ratio of the pre-sintered powder to the β-Si3N4 powder is preferably 85-95:5-15, more preferably 90:10. By controlling the mass ratio of the pre-sintered powder to the β-Si3N4 powder, this invention regulates the thickness of the network phase and its spatial distribution in the substrate. Simultaneously, a suitable ratio avoids difficulties in sintering densification and porosity defects caused by nanoparticle agglomeration.

[0024] In this invention, the second dry mixing is preferably carried out in a mixer, the mixing speed is preferably 60-85 rpm, more preferably 70-85 rpm, and the mixing time is preferably 6-10 h, more preferably 8-10 h. No liquid mixing medium is used throughout the second dry mixing process. Through the second dry mixing, this invention enables β-Si3N4 powder to uniformly coat the outer layer of silicon nitride microspheres with fixed sintering aids, ultimately obtaining a composite powder with a double-shell structure.

[0025] This invention involves sequentially cold-pressing and spark plasma sintering the composite powder with a double coating layer to obtain a strong and toughened silicon nitride ceramic with a homogeneous network structure. Preferably, the composite powder with the double coating layer is loaded into a graphite mold for cold pressing and spark plasma sintering. In this invention, the cold pressing is preferably performed in a hydraulic press, with a pressure preferably of 13-20 MPa, more preferably 15-18 MPa, and a time preferably of 3-5 min, more preferably 4-5 min.

[0026] In this invention, the spark plasma sintering is preferably carried out under a nitrogen atmosphere. The preferred pressure for spark plasma sintering is 40 MPa, and the preferred temperature is 1650~1750℃, more preferably 1700℃. The preferred holding time is 10 min, and the preferred heating rate to the spark plasma sintering temperature is 100~200℃ / min, more preferably 150℃ / min. In this invention, a slight positive pressure (gauge pressure relative to the external atmospheric pressure) of 0.7~0.9 kPa is maintained inside the furnace cavity during the spark plasma sintering process. By controlling the conditions and parameters of spark plasma sintering, this invention promotes the densification process of the ceramic material and the phase transformation process of the silicon nitride matrix. After sintering, this invention cools down at a rate of 100℃ / min to promote densification and prevent the formation of microcracks inside due to rapid cooling.

[0027] The present invention provides a toughened silicon nitride ceramic with a homogeneous network structure prepared by the above preparation method, comprising a silicon nitride ceramic matrix and a β-Si3N4 network phase distributed between the silicon nitride ceramic matrix.

[0028] This invention provides the application of the aforementioned strong and toughened silicon nitride ceramics with a homogeneous network structure in aerospace hot-end structural components, precision bearings, cutting tools, or semiconductor support components. In this invention, the aerospace hot-end structural components preferably include turbine blades or rotors; the precision bearings preferably include engine bearings, machine tool spindle bearings, or high-speed train bearings.

[0029] The following detailed description, in conjunction with embodiments, illustrates the toughened silicon nitride ceramics with a homogeneous network structure provided by the present invention, their preparation methods, and applications. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1 A toughened silicon nitride ceramic with a homogeneous network structure and its preparation method are disclosed, comprising the following steps: (1) Weigh out spherical silicon nitride powder (median particle size 50 μm), Al2O3 powder (median particle size 0.2 μm) and Y2O3 powder (median particle size 0.2 μm) in a mass ratio of 95:1.5:3.5, and put the powders into a plastic container. Then place the plastic container in a mixer for dry mixing and coating treatment. The mixing time is 10 h and the rotation speed is 85 rpm. No liquid mixing medium is used throughout the process to obtain the first layer of coated powder.

[0031] (2) The first layer of coating powder obtained in step (1) is sintered at 1400°C under nitrogen atmosphere for 30 minutes without pressure, so that the sintering aid is fixed on the surface of silicon nitride microspheres.

[0032] (3) The β-Si3N4 powder (median particle size 40nm) with a mass ratio of 5:95 and the mixed powder obtained in step (2) are further mixed and coated in a mixer for 10h at a speed of 85rpm, and finally coated powder with a double shell structure is obtained.

[0033] (4) The coated powder obtained in step (3) is loaded into a graphite mold with an inner diameter of 30 mm and pre-pressed for 5 min under a hydraulic press to set the shape. Then the mold is transferred to a spark plasma sintering equipment and sintered at a sintering temperature of 1700℃ (heating rate of 100℃ / min), a sintering pressure of 40 MPa, a holding time of 10 min, a nitrogen atmosphere, and a gauge pressure of 0.7 kPa. The cooling rate is 100℃ / min. After sintering, the mixture is cooled in the furnace and demolded to obtain silicon nitride ceramic with a homogeneous network structure.

[0034] The bending strength, fracture toughness, and β-Si3N4 phase content of the obtained silicon nitride ceramics with homogeneous network structure were determined. Bending strength was tested using the three-point bending method; fracture toughness was tested using the single-sided notched beam SENB method, with the testing standard being ASTM-1820a; the β-Si3N4 phase was tested using X-ray diffraction, specifically: for the β-Si3N4 phase, diffraction peaks at 27.1° and 36.1° were selected, corresponding to the (200) and (120) planes, respectively; for the α-Si3N4 phase, diffraction peaks at 31.0° and 35.4° were selected, corresponding to the (201) and (210) planes, respectively. ω (β) = ( I β(200) + I β(120) ) / ( I α(210) + I α(201) + I β(200) + I β(120) ) × 100%.

[0035] The material prepared in Example 1 was tested and found to have a flexural strength of 703.4 MPa and a fracture toughness of 4.7 MPa·m. 1 / 2 The β-Si3N4 phase after sintering accounts for 36.6% of the total Si3N4 content.

[0036] Example 2 A toughened silicon nitride ceramic with a homogeneous network structure and its preparation method are disclosed, comprising the following steps: (1) Weigh out spherical silicon nitride powder (median particle size 50 μm), Al2O3 powder (median particle size 0.2 μm) and Y2O3 powder (median particle size 0.2 μm) in a mass ratio of 95:1.5:3.5, and put the powders into a plastic container. Then place the plastic container in a mixer for dry mixing and coating treatment. The mixing time is 10 h and the rotation speed is 85 rpm. No liquid mixing medium is used throughout the process to obtain the first layer of coated powder.

[0037] (2) The first layer of coating powder obtained in step (1) is sintered at 1400°C under nitrogen atmosphere for 30 minutes without pressure, so that the sintering aid is fixed on the surface of silicon nitride microspheres.

[0038] (3) The β-Si3N4 powder (median particle size 40nm) with a mass ratio of 10:90 and the mixed powder obtained in step (2) are further mixed and coated in a mixer for 10h at a speed of 85rpm, and finally coated powder with a double shell structure is obtained.

[0039] (4) The coated powder obtained in step (3) is loaded into a graphite mold with an inner diameter of 30 mm and pre-pressed for 5 min under a hydraulic press to set the shape. Then the mold is transferred to a spark plasma sintering equipment and sintered at a sintering temperature of 1650℃ (heating rate of 100℃ / min), a sintering pressure of 40 MPa, a holding time of 10 min, a nitrogen atmosphere, and a gauge pressure of 0.7 kPa. The cooling rate is 100℃ / min. After sintering, the mixture is cooled in the furnace and demolded to obtain silicon nitride ceramic with a homogeneous network structure.

[0040] The material prepared in Example 2 was tested and found to have a flexural strength of 804.5 MPa and a fracture toughness of 6.4 MPa·m. 1 / 2 The β-Si3N4 phase after sintering accounts for 42.5% of the total Si3N4 content.

[0041] Example 3 A toughened silicon nitride ceramic with a homogeneous network structure and its preparation method are disclosed, comprising the following steps: (1) Weigh out spherical silicon nitride powder (median particle size 50 μm), Al2O3 powder (median particle size 0.2 μm) and Y2O3 powder (median particle size 0.2 μm) in a mass ratio of 95:1.5:3.5, and put the powders into a plastic container. Then place the plastic container in a mixer for dry mixing and coating treatment. The mixing time is 10 h and the rotation speed is 85 rpm. No liquid mixing medium is used throughout the process to obtain the first layer of coated powder.

[0042] (2) The first layer of coating powder obtained in step (1) is sintered at 1400°C under nitrogen atmosphere for 30 minutes without pressure, so that the sintering aid is fixed on the surface of silicon nitride microspheres.

[0043] (3) The β-Si3N4 powder (median particle size 40nm) with a mass ratio of 10:90 and the mixed powder obtained in step (2) are further mixed and coated in a mixer for 10h at a speed of 85rpm, and finally coated powder with a double shell structure is obtained.

[0044] (4) The coated powder obtained in step (3) is loaded into a graphite mold with an inner diameter of 30 mm and pre-pressed for 5 min under a hydraulic press to set the shape. Then the mold is transferred to a spark plasma sintering equipment and sintered at a sintering temperature of 1700℃ (heating rate of 100℃ / min), a sintering pressure of 40 MPa, a holding time of 10 min, a nitrogen atmosphere, and a gauge pressure of 0.7 kPa. The cooling rate is 100℃ / min. After sintering, the mixture is cooled in the furnace and demolded to obtain silicon nitride ceramic with a homogeneous network structure.

[0045] Figure 1 This is a scanning electron microscope image of the hardened silicon nitride ceramic obtained in Example 3 after polishing; Figure 2 for Figure 1 A magnified image of a section is shown. Electron microscopy reveals significant contrast differences and network morphology, with the darker areas representing the isolation network formed by β-Si3N4. The network boundaries formed by the introduced β-Si3N4 are clearly visible in the magnified image.

[0046] The material prepared in Example 3 was tested and found to have a flexural strength of 580.5 MPa and a fracture toughness of 7.4 MPa·m. 1 / 2 The β-Si3N4 phase after sintering accounts for 40.3% of the total Si3N4 content.

[0047] Example 4 A toughened silicon nitride ceramic with a homogeneous network structure and its preparation method are disclosed, comprising the following steps: (1) Weigh out spherical silicon nitride powder (median particle size 50 μm), Al2O3 powder (median particle size 0.2 μm) and Y2O3 powder (median particle size 0.2 μm) in a mass ratio of 95:1.5:3.5, and put the powders into a plastic container. Then place the plastic container in a mixer for dry mixing and coating treatment. The mixing time is 10 h and the rotation speed is 85 rpm. No liquid mixing medium is used throughout the process to obtain the first layer of coated powder.

[0048] (2) The first layer of coating powder obtained in step (1) is sintered at 1400°C under nitrogen atmosphere for 30 minutes without pressure, so that the sintering aid is fixed on the surface of silicon nitride microspheres.

[0049] (3) The β-Si3N4 powder (median particle size 40nm) with a mass ratio of 10:90 and the mixed powder obtained in step (2) are further mixed and coated in a mixer for 10h at a speed of 85rpm, and finally coated powder with a double shell structure is obtained.

[0050] (4) The coated powder obtained in step (3) is loaded into a graphite mold with an inner diameter of 30 mm and pre-pressed for 5 min under a hydraulic press to set the shape. Then the mold is transferred to a spark plasma sintering equipment and sintered at a sintering temperature of 1750℃ (heating rate of 100℃ / min), a sintering pressure of 40 MPa, a holding time of 10 min, a nitrogen atmosphere, and a gauge pressure of 0.7 kPa. The cooling rate is 100℃ / min. After sintering, the mixture is cooled in the furnace and demolded to obtain silicon nitride ceramic with a homogeneous network structure.

[0051] Figure 3 This is a scanning electron microscope image of the hardened silicon nitride ceramic obtained in Example 4 after polishing. Figure 4 for Figure 3 A magnified view of a portion of the image. For example... Figure 3As shown in the low-magnification SEM image, a continuous three-dimensional network skeleton morphology can be clearly observed inside the material. Figure 3 The darker, slightly rounded cellular regions represent the silicon nitride matrix phase (i.e., the morphological core retained from the original spherical powder), while the regions surrounding the cellular matrix and forming a continuous network distribution are the homogeneous network matrix introduced through the double-shell coating process. For example... Figure 4 The high-magnification SEM detail image is shown. Figure 4 The channel region defined by the yellow dashed lines represents the constructed homogeneous isolation network layer, while the region outside the dashed lines represents the silicon nitride matrix phase. Observing the interface between the network phase and the matrix phase shown by the yellow dashed lines, the interface bonding is extremely tight, dense, and coherent, with no separation defects such as micropores or microcracks observed. This fully demonstrates that this method eliminates the thermal expansion coefficient mismatch problem caused by traditional heterogeneous phase toughening, greatly alleviates the residual stress at the interface during sintering and cooling, and ensures extremely high bonding strength between the matrix and the network structure and the integrity of the overall mechanical structure.

[0052] The material prepared in Example 4 was tested and found to have a flexural strength of 701.8 MPa and a fracture toughness of 10.0 MPa·m. 1 / 2 After sintering, the β-Si3N4 phase accounts for 80.3% of the total Si3N4 content. In this embodiment, in addition to the added β-silicon nitride, the α-silicon nitride in the matrix itself will spontaneously transform from the α phase to the β phase during high-temperature sintering. In this embodiment, 10% β-silicon nitride was added, and after sintering, it became 80.3%, which indicates that 70.3% of the α-silicon nitride was transformed into β-silicon nitride during the sintering process.

[0053] Example 5 A toughened silicon nitride ceramic with a homogeneous network structure and its preparation method, comprising the following steps: (1) Weigh out spherical silicon nitride powder (median particle size 50 μm), Al2O3 powder (median particle size 0.2 μm) and Y2O3 powder (median particle size 0.2 μm) in a mass ratio of 95:1.5:3.5, and put the powders into a plastic container. Then place the plastic container in a mixer for dry mixing and coating treatment. The mixing time is 10 h and the rotation speed is 85 rpm. No liquid mixing medium is used throughout the process to obtain the first layer of coated powder.

[0054] (2) The first layer of coating powder obtained in step (1) is sintered at 1400°C under nitrogen atmosphere for 30 minutes without pressure, so that the sintering aid is fixed on the surface of silicon nitride microspheres.

[0055] (3) The β-Si3N4 powder (median particle size 40nm) with a mass ratio of 15:85 and the mixed powder obtained in step (2) are further mixed and coated in a mixer for 10h at a speed of 85rpm, and finally coated powder with a double shell structure is obtained.

[0056] (4) The coated powder obtained in step (3) is loaded into a graphite mold with an inner diameter of 30 mm and pre-pressed for 5 min under a hydraulic press to set the shape. Then the mold is transferred to a spark plasma sintering equipment and sintered at a sintering temperature of 1700℃ (heating rate of 100℃ / min), a sintering pressure of 40 MPa, a holding time of 10 min, a nitrogen atmosphere, and a gauge pressure of 0.7 kPa. The cooling rate is 100℃ / min. After sintering, the mixture is cooled in the furnace and demolded to obtain silicon nitride ceramic with a homogeneous network structure.

[0057] The material prepared in Example 5 was tested and found to have a flexural strength of 694.5 MPa and a fracture toughness of 6.7 MPa·m. 1 / 2 The β-Si3N4 phase after sintering accounts for 52.5% of the total Si3N4 content.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a toughened silicon nitride ceramic with a homogeneous network structure, characterized in that, Includes the following steps: Spherical silicon nitride powder, Al2O3 powder and Y2O3 powder are mixed by a first dry method to obtain silicon nitride powder containing a first coating layer; The silicon nitride powder containing the first coating layer is pre-sintered to obtain pre-sintered powder; The pre-sintered powder is mixed with β-Si3N4 powder by a second dry method to obtain a composite powder with a double coating layer. The composite powder with double coating layers is subjected to cold pressing and spark plasma sintering in sequence to obtain a toughened silicon nitride ceramic with a homogeneous network structure.

2. The preparation method according to claim 1, characterized in that, The median particle size of the spherical silicon nitride powder is 30~100μm; the median particle size of the Al2O3 powder is 0.2μm; and the median particle size of the Y2O3 powder is 0.2μm.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the spherical silicon nitride powder, Al2O3 powder, and Y2O3 powder is 95:1.5:3.

5. The pre-sintering temperature is 1400~1500℃, and the holding time is 0.5~1h.

4. The preparation method according to claim 1, characterized in that, The median particle size of the β-Si3N4 powder is 40 nm; The mass ratio of the pre-sintered powder to the β-Si3N4 powder is 85~95:5~15.

5. The preparation method according to claim 1, characterized in that, The rotation speed of the first dry mixing and the second dry mixing are independently 60~85 rpm, and the time is independently 6~10h.

6. The preparation method according to claim 1, characterized in that, The cold pressing pressure is 13~20MPa, and the holding time is 3~5min.

7. The preparation method according to claim 1 or 6, characterized in that, The discharge plasma sintering pressure is 40 MPa, the temperature is 1650~1750℃, and the holding time is 10 min.

8. The toughened silicon nitride ceramic with a homogeneous network structure prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It includes a silicon nitride ceramic matrix and a β-Si3N4 network phase distributed between the silicon nitride ceramic matrix.

9. The application of the strong and toughened silicon nitride ceramic with homogeneous network structure as described in claim 8 in aerospace hot-end structural components, precision bearings, cutting tools, or semiconductor support components.

Images