Composite silicon carbide material and preparation method thereof

Abstract

The invention provides a composite silicon carbide material and a preparation method thereof. The composite silicon carbide material comprises N functional layers and N-1 interface layers, the N-1 interface layer is located between the Nth functional layer and the N-1 functional layer, N is a positive integer of 3-5, the functional layers comprise silicon carbide materials and functional sintering aids, the particle size Dv90 of the silicon carbide material in the Nth functional layer is 2-4 times of the particle size Dv90 of the silicon carbide material in the N-1 functional layer, and the particle size Dv90 of the silicon carbide material in the N-1 functional layer is 2-4 times of the particle size Dv90 of the silicon carbide material in the N-1 functional layer. Each interface layer comprises nano silicon carbide with the particle size of 50-200 nm, a toughening agent and an interface sintering aid, and the particle size Dv90 of the nano silicon carbide in the (N-1) th interface layer is 2-4 times of the particle size Dv90 of the nano silicon carbide in the (N-2) th interface layer. The composite silicon carbide material is high in structural integrity, and the defects such as high-temperature layering and cracks can be reduced or even avoided. The composite silicon carbide material disclosed by the invention is prepared by adopting the preparation method disclosed by the invention.

Description

Technical Field

[0001] This invention relates to the technical field of silicon carbide materials, and specifically to a composite silicon carbide material and its preparation method. Background Technology

[0002] Silicon carbide (SiC) materials are widely used in aerospace, nuclear energy, and chemical industries due to their high hardness, high temperature resistance, corrosion resistance, and excellent thermal conductivity. Traditional single-layer SiC materials are prone to cracking under extreme environments due to thermal stress concentration, while multilayer composite structures can improve the overall performance of SiC materials through flexible and differentiated design of each layer. However, current technologies for preparing multilayer SiC materials often employ separate molding followed by bonding or mechanical assembly. This results in multilayer composite SiC materials with problems such as low interfacial bonding strength, mismatched interlayer thermal expansion coefficients, and easy delamination at high temperatures. Furthermore, during the high-temperature sintering process in the preparation of composite SiC materials, differences in shrinkage rates between the multilayer composite SiC layers can lead to product deformation or cracking, reducing the yield. Summary of the Invention

[0003] To overcome the problems of mismatched thermal expansion coefficients, low interfacial bonding strength, easy delamination at high temperatures, and low sintering yield in existing multilayer composite silicon carbide materials, the composite silicon carbide material of this invention meets the different performance requirements of high-end fields for composite silicon carbide materials through differentiated design of each layer material. It also reduces the difference in thermal expansion coefficients of each silicon carbide layer and reduces the difference in thermal shrinkage rate of each layer at high temperatures. At the same time, the silicon carbide layers have strong interfacial bonding force, so the multilayer composite silicon carbide material is not easy to delaminate at high temperatures, enhances the structural integrity of the multilayer composite silicon carbide material, and improves its high-temperature performance. In addition, the preparation method of integrated molding of multilayer silicon carbide material improves the overall performance of multilayer composite silicon carbide material, effectively reduces the sintering defect rate, and simplifies the production process.

[0004] To achieve the above objectives, the first aspect of the present invention provides a composite silicon carbide material, the composite silicon carbide material comprising N functional layers and N-1 interface layers, wherein the N-1 interface layer is located between the N functional layers and the N-1 functional layers, and N is a positive integer from 3 to 5; The functional layer includes silicon carbide material and functional sintering aid. The particle size Dv90 of the silicon carbide material in the Nth functional layer is 2 to 4 times that of the silicon carbide material in the N-1th functional layer. The interface layer includes nano-silicon carbide, toughening agent, and interface sintering aid. The particle size of the nano-silicon carbide is 50nm-200nm. The particle size Dv90 of the nano-silicon carbide in the (N-1)th interface layer is 2 to 4 times that of the particle size Dv90 of the nano-silicon carbide in the (N-2)th interface layer.

[0005] A second aspect of the present invention provides a method for preparing the above-mentioned composite silicon carbide material.

[0006] The present invention, employing the above-described technical solution, has the following advantages: In the composite silicon carbide material provided by this invention, the particle size Dv90 of the silicon carbide material in the Nth functional layer is 2 to 4 times that in the (N-1)th functional layer. Thus, the particle size Dv90 of the silicon carbide material increases from the first functional layer to the Nth functional layer, and the thermal expansion coefficients of each functional layer are matched, effectively reducing the difference in shrinkage rate of each functional layer at high temperatures and reducing delamination and defects in the composite silicon carbide material at high temperatures. Furthermore, the particle size of the nano-silicon carbide in the interface layer matches the particle size of adjacent functional layers, effectively filling the gaps between functional layers, reducing porosity, and increasing the density of the composite silicon carbide material. There is a chemical bond between the functional sintering aids in the functional layers and the interface sintering aids in the interface layer. The interface layer also includes a toughening agent, which acts as a bridge, thereby improving the interfacial bonding strength between each functional layer. Therefore, the multilayer composite silicon carbide material has good structural integrity and performance, is not prone to delamination or failure at high temperatures, and can meet the needs of use under different working conditions.

[0007] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In this document, unless otherwise specified, data ranges include endpoints. Attached Figure Description

[0008] Figure 1 The diagram shown is a schematic of a cylindrical mold. Detailed Implementation

[0009] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0010] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0011] The first aspect of the present invention provides a composite silicon carbide material, the composite silicon carbide material comprising N functional layers and N-1 interface layers, wherein the N-1 interface layer is located between the N functional layers and the N-1 functional layers, wherein N is a positive integer from 3 to 5 (e.g., 3, 4 or 5). The functional layer includes silicon carbide material and functional sintering aid. The particle size Dv90 of the silicon carbide material in the Nth functional layer is 2 to 4 times (e.g., 2 times, 3 times, 4 times or within any two of the above values) of the silicon carbide material in the (N-1)th functional layer. The interface layer includes nano-silicon carbide, toughening agent, and interface sintering aid. The particle size of the nano-silicon carbide is 50nm-200nm. The particle size Dv90 of the nano-silicon carbide in the (N-1)th interface layer is 2 to 4 times (for example, 2 times, 3 times, 4 times, or within any two of the above values) of the nano-silicon carbide in the (N-2)th interface layer.

[0012] The particle size of the silicon carbide material in this invention has a significant impact on the thermal expansion coefficient of the functional layers. The particle size Dv90 of the silicon carbide material in the Nth functional layer is 2 to 4 times that in the (N-1)th functional layer. This shows that the particle size distribution of the silicon carbide material exhibits an overall increasing trend from the first to the Nth functional layer. Consequently, the thermal expansion coefficient gradually increases from the first to the Nth functional layer, resulting in a continuous change in the thermal expansion coefficient distribution of the multilayer composite silicon carbide material from the first to the Nth functional layer. This matching of thermal expansion coefficients among the functional layers effectively reduces the difference in shrinkage rates at high temperatures, improves the structural integrity of the multilayer composite silicon carbide material, and effectively reduces delamination and failure at high temperatures. Simultaneously, the particle size Dv90 of the nano-silicon carbide in the (N-1)th interface layer is 2 times that in the (N-2)th interface layer. The particle size of silicon carbide nanoparticles increases from the first interface layer to the (N-1)th interface layer, reaching 1-4 times the density of the first functional layer. As the particle size of the silicon carbide material increases from the first functional layer to the Nth functional layer, the inter-particle size gap in the functional layers increases accordingly. The increasing particle size of silicon carbide nanoparticles in the interface layer from the first layer to the (N-1)th layer matches the gaps between adjacent functional layers, effectively filling the micropores in the functional layers and increasing the density of the composite silicon carbide material. Furthermore, the functional layers include functional sintering aids, and the interface layers include interface sintering aids, enabling chemical bonding between adjacent functional layers and the interface layers. The interface layers also include toughening agents, which act as bridges, improving the toughness of the interface layer and enhancing the interfacial bonding force of the functional layers. This effectively reduces or even avoids delamination failure of the composite silicon carbide material at high temperatures, enhancing its high-temperature resistance and giving the composite silicon carbide material good structural integrity and maintaining good performance at different temperatures.

[0013] It is understood that in this invention, the main body of the multilayer composite silicon carbide material is composed of functional layers. The thermal expansion coefficients of each functional layer are kept matched, which can reduce the overall thermal shrinkage difference of the multilayer composite silicon carbide material. The interface layer only plays a bonding role and does not affect the overall thermal shrinkage of the multilayer composite silicon carbide material.

[0014] In this invention, the particle size Dv90 of the silicon carbide material in the functional layer refers to the particle size corresponding to the cumulative volumetric particle size distribution percentage of the silicon carbide material when the silicon carbide material in the functional layer is arranged from smallest to largest. The particle size Dv90 of the silicon carbide material in the functional layer can be obtained by testing with a laser particle size analyzer. Before preparation, the silicon carbide material raw material for preparing the corresponding functional layer is placed in the laser particle size analyzer to test the volumetric particle size distribution curve of the silicon carbide material. The particle size corresponding to the cumulative volumetric particle size distribution percentage of the silicon carbide material reaching 90% is the particle size Dv90.

[0015] By controlling the particle size Dv90 of silicon carbide material in the Nth functional layer to be 2 to 4 times that of silicon carbide material in the N-1th functional layer, and the particle size Dv90 of nano-silicon carbide in the N-1th interface layer to be 2 to 4 times that of nano-silicon carbide in the N-2th interface layer, and by adding sintering aids and toughening agents, compared with the prior art, it is possible to enhance the comprehensive performance of composite silicon carbide materials, keep the thermal expansion coefficients of each functional layer of multilayer composite silicon carbide materials matched, reduce the difference in thermal shrinkage rate at high temperature, and enhance the interfacial bonding force between functional layers. In order to further improve the effect, one or more of the technical features can be further optimized.

[0016] In some embodiments, the composite silicon carbide material is a silicon carbide cylinder. The silicon carbide cylinder, from the outer layer to the inner layer, sequentially includes a first functional layer, a second functional layer to an Nth functional layer. That is, the particle size of the silicon carbide material in the functional layers increases sequentially from the outer layer to the inner layer. It has a complex shape and a multi-layered silicon carbide cylinder with uniform interlayer stress distribution, strong interlayer bonding force, and is not prone to delamination or failure at high temperatures. It can maintain good performance at different temperatures, and its overall comprehensive performance is effectively improved, enabling its long-term stable operation under complex working conditions (such as nuclear reactors and spacecraft thermal protection). When the outer layer to the inner layer includes an Nth functional layer, an N-1th functional layer to the first functional layer, that is, the particle size of the silicon carbide material in the functional layers decreases sequentially from the outer layer to the inner layer, the huge expansion tendency generated by the outer functional layer will be constrained by the inner functional layer when heated, resulting in extremely high stress in the outer functional layer, thereby producing cracks and delamination.

[0017] In some embodiments, the diameter of the silicon carbide cylinder is 150mm-500mm (e.g., 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, 450mm, 500mm or within any two of the above values).

[0018] In some embodiments, the length of the silicon carbide cylinder is less than or equal to 800 mm (e.g., 100 mm, 200 mm, 300 mm, 400 mm, 500 mm, 600 mm, 700 mm, 800 mm, or within any two of the above values). The length of the silicon carbide cylinder is within the above range, which can prevent the silicon carbide cylinder from bending and deforming, and ensure that the coefficients of thermal expansion of each function of the silicon carbide cylinder are matched.

[0019] In some embodiments, the composite silicon carbide material is in the shape of a cuboid, and from one end face of the cuboid to the other end face, it sequentially includes a first functional layer, a second functional layer to an Nth functional layer.

[0020] In some embodiments, the particle size of the silicon carbide material in any functional layer is 0.5 μm-8 μm (e.g., 0.5 μm, 1 μm, 2 μm, 2.5 μm, 3 μm, 4.5 μm, 6 μm, 8 μm or within any two of the above values).

[0021] In some embodiments, the weight ratio of functional sintering aid to silicon carbide material in any functional layer is 1:(8-47.5) (e.g., 1:8, 1:12, 1:18, 1:25, 1:32, 1:40, 1:45, 1:47.5 or within any two of the above values).

[0022] In some embodiments, the weight ratio of functional sintering aid to silicon carbide material in any functional layer is 1:(15-30).

[0023] In some embodiments, any functional layer includes 80wt%-95wt% (e.g., 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 95wt%, or within any two of the above values) of silicon carbide material and 2wt%-20wt% (e.g., 82wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, or within any two of the above values) of functional sintering aid.

[0024] In some embodiments, the functional sintering aids include Al2O3, Y2O3, MgO, CeO2, La2O3, B4C, SiC-B, AlN, and Y3Al5O. 12 At least one of Al2O3-Y2O3, silicon powder, carbon powder, nano-SiC-C composite, and graphene sheet.

[0025] In some embodiments, the weight ratio of toughening agent, interface sintering aid and nano-silicon carbide in any interface layer is 1:(2.5-13.3):(25-100) (e.g., 1:2.5:25, 1:4:40, 1:6:55, 1:8:70, 1:10:85, 1:12:95, 1:13.3:100 or within any two of the above values).

[0026] In some embodiments, any interface layer includes 60wt%-90wt% (e.g., 60wt%, 63wt%, 67wt%, 70wt%, 74wt%, 78wt%, 82wt%, 86wt%, 90wt%, or within any two of the above values) of nano-silicon carbide, 0.9wt%-24wt% (e.g., 0.9wt%, 2wt%, 5wt%, 8wt%, 12wt%, 16wt%, 20wt%, 24wt%, or within any two of the above values) of toughening agent, and 6wt%-20wt% (e.g., 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%, or within any two of the above values) of interface sintering aid.

[0027] In some embodiments, the toughening agent in any interface layer includes at least one of chopped carbon fibers, organic nanoparticles, inorganic nanoparticles, thermoplastic particles, core-shell structured particles, micro-nano hybrid particles, toughening films, and ex-situ toughening.

[0028] In some embodiments, the toughening agent is chopped carbon fiber with a length of 50 μm to 200 μm (e.g., 50 μm, 70 μm, 90 μm, 120 μm, 150 μm, 180 μm, 200 μm or within any two of the above values).

[0029] In some embodiments, the interface sintering aid includes Al2O3, Y2O3, MgO, CeO2, La2O3, B4C, SiC-B, AlN, and Y3Al5O. 12 At least one of Al2O3-Y2O3, silicon powder, carbon powder, nano-SiC-C composite, and graphene sheet.

[0030] In this invention, the functional sintering aids between functional layers can be the same or different, and the interface sintering aids and toughening agents between interface layers can be the same or different.

[0031] In some embodiments, the composite silicon carbide material comprises three functional layers and two interface layers. The three functional layers are a first functional layer, a second functional layer, and a third functional layer, respectively. The two interface layers are a first interface layer and a second interface layer, respectively. In the first functional layer, the particle size Dv90 of the silicon carbide material is 0.5 μm-1.5 μm (e.g., 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, or within any two of the above values). The smaller particle size Dv90 of the silicon carbide material in the first functional layer results in higher hardness.

[0032] In some embodiments, the particle size Dv90 of the silicon carbide material in the second functional layer is 2μm-4μm (e.g., 2μm, 2.5μm, 3μm, 3.5μm, 4μm, or within any two of the above values). When the particle size Dv90 of the silicon carbide material in the second functional layer is moderate, it has good thermal shock resistance.

[0033] In some embodiments, the particle size Dv90 of the silicon carbide material in the third functional layer is 5μm-8μm (e.g., 5μm, 6μm, 7μm, 8μm, or within any two of the above values). A larger particle size Dv90 in the silicon carbide material of the third functional layer results in stronger thermal conductivity.

[0034] In some embodiments, in the first interface layer, the particle size Dv90 of the nano-silicon carbide is 50nm-120nm (e.g., 50nm, 65nm, 80nm, 95nm, 110nm, 120nm, or any two of the above values). In some embodiments, in the second interface layer, the particle size Dv90 of the nano-silicon carbide is 160nm-200nm (e.g., 160nm, 170nm, 180nm, 190nm, 200nm, or any two of the above values).

[0035] In some embodiments, the first functional layer comprises 90wt%-95wt% (e.g., 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt% or within any two of the above values) of silicon carbide material and 2wt%-10wt% (e.g., 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% or within any two of the above values) of functional sintering aid.

[0036] In some embodiments, the second functional layer comprises 85wt%-90wt% (e.g., 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt% or within any two of the above values) of a second silicon carbide material, and 2wt%-10wt% (e.g., 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% or within any two of the above values) of a functional sintering aid.

[0037] In some embodiments, the third functional layer comprises 80wt%-88wt% (e.g., 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, or within any two of the above values) of silicon carbide material and 2wt%-10wt% (e.g., 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or within any two of the above values) of functional sintering aid.

[0038] In some embodiments, the first interface layer comprises 60wt%-90wt% (e.g., 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 88wt%, 90wt%, or within any two of the above values) of nano-silicon carbide, 0.9wt%-24wt% (e.g., 0.9wt%, 4wt%, 7wt%, 10wt%, 13wt%, 16wt%, 20wt%, 24wt%, or within any two of the above values) of toughening agent, and 6wt%-20wt% (e.g., 6wt%, 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, 17wt%, 20wt%, or within any two of the above values) of interface sintering aid; In some embodiments, the second interface layer comprises 60wt%-90wt% (e.g., 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 88wt%, 90wt%, or within any two of the above values) of nano-silicon carbide, 0.9wt%-24wt% (e.g., 0.9wt%, 4wt%, 7wt%, 10wt%, 13wt%, 16wt%, 20wt%, 24wt%, or within any two of the above values) of toughening agent, and 6wt%-20wt% (e.g., 6wt%, 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, 17wt%, 20wt%, or within any two of the above values) of interface sintering aid.

[0039] In some embodiments, the thickness of the first functional layer is 1mm-5mm (e.g., 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4.5mm, 5mm or within any two of the above values).

[0040] In some embodiments, the thickness of the second functional layer is 1mm-5mm (e.g., 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4.5mm, 5mm or within any two of the above values).

[0041] In some embodiments, the thickness of the third functional layer is 1mm-5mm (e.g., 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4.5mm, 5mm or within any two of the above values).

[0042] In some embodiments, the thickness of the first interface layer is 10μm-50μm (e.g., 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 45μm, 50μm or within any two of the above values).

[0043] In some embodiments, the thickness of the second interface layer is 10μm-50μm (e.g., 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 45μm, 50μm or within any two of the above values).

[0044] In some embodiments, the difference in the coefficient of thermal expansion between the Nth functional layer and the (N-1)th functional layer is less than 0.3 × 10⁻⁶. -6 / ℃ (e.g., 0.05×10) -6 / ℃, 0.10×10 -6 / ℃, 0.15×10 -6 / ℃, 0.20×10 -6 / ℃, 0.25×10 -6 / ℃, 0.29×10 -6 / ℃ or within the range of any two of the above values).

[0045] In this invention, the particle size Dv90 of the silicon carbide material in the Nth functional layer is 2 to 4 times that of the silicon carbide material in the (N-1)th functional layer. The particle size of the silicon carbide material in the Nth functional layer is larger than that in the (N-1)th functional layer. The silicon carbide material in the Nth functional layer has a higher degree of disorder, which relatively weakens the constraint on thermal expansion. Therefore, the coefficient of thermal expansion of the Nth functional layer is greater than that of the (N-1)th functional layer. The difference in the coefficient of thermal expansion between the Nth and (N-1)th functional layers is obtained by subtracting the coefficient of thermal expansion of the (N-1)th functional layer from the coefficient of thermal expansion of the Nth functional layer.

[0046] The difference in the coefficient of thermal expansion between the Nth functional layer and the (N-1)th functional layer is less than 0.3 × 10⁻⁶. -6 / ℃, the thermal shrinkage rate of each functional layer remains consistent under high temperature conditions, reducing the risk of delamination failure and improving its heat resistance.

[0047] In this invention, the difference in the thermal expansion coefficients between the Nth functional layer and the (N-1)th functional layer is obtained by high-temperature diffraction. Specifically, the composite silicon carbide material sample is placed on a temperature-controlled high-temperature diffraction sample stage, and the Nth and (N-1)th functional layers of the sample are irradiated with monochromatic X-rays. The diffraction signals generated by the crystal lattice are converted into diffraction patterns by a detector. The lattice constants at different temperatures are analyzed according to the Bragg equation. By calculating the change of the lattice constant with temperature, the thermal expansion coefficients of the two functional layers are obtained, and then the difference between them is calculated.

[0048] In some embodiments, the porosity of the composite silicon carbide material is less than 5% (e.g., 1%, 2%, 3%, 4%, 4.5%, or within any two of the above values). The composite silicon carbide has a porosity of less than 5%, high density, and strong high-temperature resistance, ensuring its performance under complex working conditions and facilitating its effective application in high-end fields such as aerospace, nuclear energy, and chemical engineering.

[0049] In this invention, the porosity of the composite silicon carbide material is measured by the following method: First, the sample is completely dried and weighed. Then, the sample is immersed in distilled water, boiled for several hours or vacuumed to allow the pores to fully absorb water, removed, wiped clean, and weighed (m2). Finally, the sample is suspended in water and weighed (m3). The apparent bulk density is calculated using the formula ρv = m1 / (m2-m3) × ρw (where ρw is the density of water). Combined with the theoretical density (ρt) calculated proportionally from the material composition, the total porosity can be calculated using the formula porosity = [1 - (ρv / ρt)] × 100%.

[0050] In some embodiments, the shear strength between the Nth functional layer and the (N-1)th functional layer is greater than or equal to 40 MPa (e.g., 40 MPa, 42 MPa, 44 MPa, 46 MPa, 48 MPa, 50 MPa, 52 MPa, 54 MPa, 56 MPa, or within any two of the above values).

[0051] In this invention, the shear strength between the Nth functional layer and the (N-1)th functional layer is measured by the following method: A composite silicon carbide material sample is clamped in a universal testing machine, and a shear load is applied between the Nth and (N-1)th functional layers until fracture. The load data at fracture is recorded, which is the shear strength between the Nth and (N-1)th functional layers. Furthermore, after the shear strength test, the fracture surface is observed using a scanning electron microscope, revealing a mixed fracture mode. This characteristic indicates good interfacial bonding between the outer and middle layers.

[0052] A second aspect of the present invention provides a method for preparing the composite silicon carbide material provided in the first aspect of the present invention, the method comprising the following steps: (1) Preparation of functional layer slurry: The functional layer slurry includes N types of functional layer slurry, namely, first functional layer slurry, second functional layer slurry, ..., Nth functional layer slurry, where N is a positive integer of 3-5 (e.g., 3, 4 or 5). Any one of the functional layer slurries includes silicon carbide material and functional sintering aid. The particle size Dv90 of silicon carbide material in the Nth functional layer slurry is 2 to 4 times (e.g., 2 times, 3 times, 4 times or within the range of any two of the above values) of the particle size Dv90 of silicon carbide material in the N-1th functional layer slurry. (2) Preparation of interface layer slurry: The interface layer slurry includes N-1 types of interface layer slurry, namely the first interface layer slurry, the second interface layer slurry, ..., the N-1th interface layer slurry, where N is a positive integer from 3 to 5. Any one of the interface layer slurries includes nano-silicon carbide, toughening agent and interface sintering aid. The particle size Dv90 of nano-silicon carbide in the N-1th interface layer slurry is 2 to 4 times (e.g., 2 times, 3 times, 4 times or within the range of any two of the above values) of nano-silicon carbide.

[0053] (3) Layer-by-layer grouting: The first functional layer grout, the second functional layer grout and the Nth functional layer grout are injected into the mold in sequence to form the first functional layer, the second functional layer and the Nth functional layer respectively. Before injecting the second functional layer grout, the first interface layer grout is sprayed on the surface of the first functional layer; ...; before injecting the Nth functional layer grout, the N-1th interface layer grout is sprayed on the surface of the N-1th functional layer to obtain the green body; (4) The blank is subjected to cold isostatic pressing, degreasing, gas pressure sintering and gradient cooling in sequence.

[0054] The method for preparing composite silicon carbide materials provided by this invention adopts an integrated molding technology of layer-by-layer slurry casting-cold isostatic pressing-debinding-sintering, which prepares multi-layer composite silicon carbide materials into a single integral form in one go. This reduces the complex process of separate molding and reassembly in traditional processes, simplifies the production process, and effectively reduces or even avoids defects such as delamination, cracks, and weak interfacial bonding in multi-layer composite silicon carbide materials. It also lowers the sintering defect rate, improves the yield and product performance, and allows for the preparation of complex-shaped multi-layer silicon carbide cylinders, solving the problem of uneven interlayer stress distribution and making it less prone to delamination at high temperatures. This integrated molding technology not only improves production efficiency and ensures product quality consistency, but also meets the quality requirements of high-end application fields for composite silicon carbide materials.

[0055] In some embodiments, the viscosity of any functional layer slurry is 1000 mPa·s-1500 mPa·s, for example, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, 1500 mPa·s, or within any two of the above values.

[0056] By controlling the viscosity of the functional layer slurry within the above range, the fluidity of the functional layer slurry is moderate, avoiding stratification or sedimentation during grouting, ensuring uniform distribution of silicon carbide material in the slurry, reducing the difference in expansion coefficient between functional layers, and also facilitating the removal of air bubbles in the slurry, thus avoiding defects such as pores during sintering.

[0057] In this invention, the viscosity of the functional layer slurry is measured by a rotational viscometer.

[0058] In some embodiments, any functional layer slurry further includes an organic binder, a dispersant, and water.

[0059] In some embodiments, in any functional layer slurry, the silicon carbide material comprises 80%-95% by weight (e.g., 80%, 82%, 85%, 87%, 90%, 92%, 94%, 95%, or any two of the above values), the functional sintering aid comprises 2%-10% by weight (e.g., 2%, 3%, 4%, 5%, 6%, 7%, 9%, 10%, or any two of the above values), and the organic binder comprises 1%-5% by weight (e.g., 1%, 1.5%, 2%). The weight percentage of the dispersant is 0.5%-2% (e.g., 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.7%, 1.9%, 2% or within any two of the above values), and the weight percentage of the water is 0%-3% (e.g., 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 2.8%, 3% or within any two of the above values).

[0060] In some embodiments, the dispersant comprises ammonium polyacrylate.

[0061] In some embodiments, the viscosity of any interface layer slurry is 200 mPa·s-500 mPa·s (e.g., 200 mPa·s, 250 mPa·s, 300 mPa·s, 350 mPa·s, 400 mPa·s, 450 mPa·s, 500 mPa·s, or within any two of the above values). Controlling the viscosity of the interface layer slurry within the above range is beneficial for uniform spraying of the interface layer, improving the adhesion of the interface layer, ensuring the consistency of the adhesion of the functional layers at the interface, and improving the bonding force between the functional layers.

[0062] In this invention, the viscosity of the functional layer slurry is measured by a rotational viscometer.

[0063] In some embodiments, any interface layer slurry further includes an organic binder and a solvent (such as ethanol), the organic binder providing temporary adhesion to facilitate the coating and molding of the interface layer slurry.

[0064] In some embodiments, in any interface layer slurry, the toughening agent accounts for 0.3%-0.8% by weight (e.g., 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or within any two of the above values), the nano-silicon carbide accounts for 20%-30% by weight (e.g., 20%, 22%, 24%, 26%, 28%, 30%, or within any two of the above values), the interface sintering aid accounts for 2%-4% by weight (e.g., 2%, 2.5%, 3.0%, 3.5%, 4%, or within any two of the above values), the organic binder accounts for 4%-6% by weight (e.g., 4%, 4.5%, 5%, 5.5%, 6%, or within any two of the above values), and the solvent accounts for 60%-70% by weight (e.g., 60%, 62%, 64%, 66%, 68%, 70%, or within any two of the above values).

[0065] In some embodiments, the organic binder includes polyvinyl alcohol and / or phenolic resin.

[0066] In some embodiments, the mold is made of metal (such as stainless steel) or high-temperature resistant resin, and the inner wall of the mold is polished to a mirror finish, which can effectively prevent the slurry from sticking together.

[0067] In some embodiments, in step (3), the mold is preheated to 50°C-80°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 78°C, 80°C, or within any two of the above values). Preheating the mold to the above temperature can reduce the temperature difference between the slurry and the mold, reduce bubble formation, and accelerate the initial curing speed of the slurry.

[0068] In some embodiments, in step (3), a low-speed constant flow pump is used to inject at a flow rate of 5 mL / min to 20 mL / min (e.g., 5 mL / min, 7.5 mL / min, 10 mL / min, 12.5 mL / min, 15 mL / min, 17.5 mL / min, 20 mL / min or within any two of the above values), which can effectively avoid the deformation of the solidified functional layer caused by the impact of the injected slurry.

[0069] In some embodiments, in step (3), after the functional layer slurry is injected into the mold, it is homogenized, vacuum defoamed, and dried in sequence. After drying, the surface is polished (for example, polished with 600-grit sandpaper) to increase the interlayer roughness.

[0070] In some embodiments, homogenization includes centrifugation, sonication, etc., wherein the centrifugation conditions include: a rotation speed of 300 rpm to 800 rpm (e.g., 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, or any two of the above values), and a centrifugation time of 3 minutes to 5 minutes (e.g., 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, or any two of the above values). Homogenization removes air bubbles and improves density.

[0071] In some embodiments, the conditions for vacuum degassing include: a vacuum degree ≤ 0.1 MPa, maintained for 5-10 minutes (e.g., 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, or within any two of the above values) to eliminate micropores.

[0072] In some embodiments, the drying is carried out in a hot air circulating drying oven at 40°C-60°C (e.g., 40°C, 45°C, 50°C, 55°C, 60°C or within any two of the above values) until the surface is cured (moisture content <5%), for 1 hour to 2 hours (e.g., 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours or within any two of the above values).

[0073] In some embodiments, the conditions for cold isostatic pressing include: a pressure of 100 MPa-200 MPa, for example, 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 200 MPa, or any two of the above values, and a duration of 1 hour-2 hours (for example, 1 hour, 1.2 hours, 1.5 hours, 2 hours, or any two of the above values). Cold isostatic pressing under these conditions can eliminate interlayer gaps, enhance the bonding between functional layers, increase the density of the green body, and uniformly compress each layer, reducing the difference in sintering shrinkage rates between functional layers.

[0074] In some embodiments, the billet is subjected to cold isostatic pressing, then demolded, and subsequently precision machined using a CNC machine tool.

[0075] In some embodiments, the degreasing conditions include: heating to 600°C at a rate of 1°C / min to 3°C / min (e.g., 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, or any two of the above values) under an inert atmosphere, and holding at that temperature for 1 hour to 4 hours (e.g., 1 hour, 2 hours, 3 hours, 4 hours, or any two of the above values). Degreasing under these conditions effectively removes organic binders from the green body, avoids residual carbides or pores, and further reduces the sintering defect rate.

[0076] In some embodiments, the conditions for gas pressure sintering include: in an argon and / or vacuum environment, at a pressure of 5 MPa-20 MPa, raising the temperature to a temperature of 1950℃-2100℃ (e.g., 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min or within any two of the above values) at a heating rate of 10℃ / min-15℃ / min (e.g., 1950℃, 1975℃, 2000℃, 2025℃, 2050℃, 2075℃, 2100℃ or within any two of the above values), and holding the temperature for 1h-4h (e.g., 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or within any two of the above values). Sintering at the above temperature can further improve the densification of the composite silicon carbide material through atomic diffusion. At the same time, maintaining the above pressure can effectively suppress the decomposition of silicon carbide and ensure the good performance of the composite silicon carbide material.

[0077] In some embodiments, the gradient cooling conditions include: slow cooling to 800°C at 2°C / min-5°C / min (e.g., 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 4°C / min, 4.5°C / min, 5°C / min or within any two of the above values).

[0078] In some embodiments, in step (3), the functional layer slurry is injected into the cylindrical mold in the order of the first functional layer slurry, the second functional layer slurry to the Nth functional layer slurry. The cylindrical mold is located in a centrifuge, and a cylindrical blank is obtained by centrifugation.

[0079] like Figure 1As shown, the cylindrical mold 2 includes a grouting port 1 and a centrifugal turntable 3. Functional layer slurry is injected into the mold in the order of first functional layer slurry, second functional layer slurry to Nth functional layer slurry to obtain a cylindrical blank. The cylindrical blank includes first functional layer slurry, second functional layer slurry to Nth functional layer slurry from the outer layer to the inner layer.

[0080] Unless otherwise specified, the raw materials and methods for preparing the lithium-ion batteries described in this invention are all conventional choices in the art.

[0081] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0082] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0083] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0084] Preparation Example 1 (1) Preparation of functional layer slurry First functional layer slurry: 92wt% silicon carbide material (particle size Dv90 is 1μm), 5wt% Al2O3-Y2O3 (functional sintering aid), and 5wt% polyvinyl alcohol (organic binder) are added to water in sequence, and finally 0.5wt% ammonium polyacrylate (dispersant) is added to adjust the slurry viscosity to 1200mPa·s to obtain the first functional layer slurry; Second functional layer slurry: 88wt% silicon carbide material (particle size Dv90 of 4μm), 5wt% Al2O3-Y2O3 and B4C (mass ratio of 3:2) (functional sintering aid), and 4wt% polyvinyl alcohol (organic binder) are added to water in sequence. Finally, 1wt% ammonium polyacrylate (dispersant) is added to adjust the slurry viscosity to 1200mPa·s to obtain the second functional layer slurry. Third functional layer slurry: 85wt% silicon carbide material (particle size Dv90 of 8μm), 10wt% B4C and AlN (mass ratio of 8:2) (functional sintering aid), and 10wt% polyvinyl alcohol (organic binder) are added to water in sequence. Finally, 2wt% ammonium polyacrylate (dispersant) is added to adjust the slurry viscosity to 1200mPa·s to obtain the third functional layer slurry. In the second functional layer slurry, the particle size Dv90 of silicon carbide material is 4 times that of silicon carbide material in the first functional layer slurry, and the particle size Dv90 of silicon carbide material in the third functional layer slurry is 2 times that of silicon carbide material in the second functional layer slurry.

[0085] (2) Preparation of interface layer slurry First interface layer slurry: 25wt% of nano-silicon carbide (particle size Dv90 is 90nm) and 3wt% of Al2O3-Y2O3 (interface sintering aid) are added to ethanol and ultrasonically dispersed. Then, 0.5wt% of short-cut carbon fibers are added and mechanically stirred until the fibers are uniformly dispersed. Finally, 5wt% of phenolic resin (organic binder) is added and the slurry viscosity is adjusted to 300mPa·s to obtain the first interface layer slurry. Second interface layer slurry: 25wt% of nano-silicon carbide (particle size Dv90 is 180nm) and 3wt% of Al2O3-Y2O3 (interface sintering aid) are added to ethanol and ultrasonically dispersed. Then, 0.5wt% of short-cut carbon fibers are added and mechanically stirred until the fibers are uniformly dispersed. Finally, 5wt% of phenolic resin (organic binder) is added, and the slurry viscosity is adjusted to 300mPa·s to obtain the second interface layer slurry. In the second interface layer slurry, the particle size Dv90 of nano-silicon carbide is twice that of nano-silicon carbide in the first interface layer slurry.

[0086] (3) Grouting layer by layer Preheat the mold to 60℃ to reduce the temperature difference between the slurry and the mold, reduce bubble formation, and accelerate the initial curing speed of the slurry. Using a low-speed constant flow pump at a flow rate of 15 mL / min, the first functional layer slurry, the second functional layer slurry, and the third functional layer slurry are sequentially injected into a cylindrical mold located in a centrifuge. After injecting any one of the functional layer slurries, the mold is centrifuged at 500 rpm for 5 hours, followed by vacuum degassing (vacuum degree ≤ 0.1 MPa) and drying in a 50℃ hot air circulating drying oven until the surface is cured (moisture content < 5%). After drying, the surface is lightly sanded with 600-grit sandpaper to increase the interlayer roughness, forming the first functional layer, the second functional layer, and the third functional layer sequentially from the outside to the inside. Before injecting the second functional layer slurry, the first interface layer slurry is sprayed onto the surface of the first functional layer to form the first interface layer. Before injecting the third functional layer slurry, the second interface layer slurry is sprayed onto the surface of the second functional layer to form the second interface layer, finally obtaining a cylindrical preform.

[0087] (4) Cold isostatic pressing, degreasing, and gas pressure sintering Cold isostatic pressing: The preform is encapsulated in a rubber mold and subjected to cold isostatic pressing at 150MPa pressure for 2 hours; Degreasing: Under a nitrogen atmosphere, the temperature is increased to 600℃ at a rate of 2℃ / min and held for 3 hours; Gas pressure sintering: In an argon atmosphere, the temperature is increased to 2000℃ at a rate of 10℃ / min, a gas pressure of 15MPa is applied, and the temperature is held for 3 hours.

[0088] Preparation Example 2 (1) Preparation of functional layer slurry: Refer to Preparation Example 1; (2) Grouting was used to prepare the first functional layer, the second functional layer and the third functional layer respectively: Preheat the mold to 60℃ to reduce the temperature difference between the slurry and the mold, reduce bubble formation, and accelerate the initial curing speed of the slurry. The first functional layer slurry was injected into a cylindrical mold in a centrifuge at a flow rate of 15 mL / min using a low-speed constant flow pump. After centrifugation at 500 rpm for 5 h, vacuum degassing (vacuum degree ≤ 0.1 MPa) was performed, followed by drying in a 50℃ hot air circulating drying oven until the surface was cured (moisture content < 5%). Then, the first functional layer was obtained by cold isostatic pressing, degreasing, and gas pressure sintering, with the cold isostatic pressing, degreasing, and gas pressure sintering performed as in Preparation Example 1. The preparation of the second and third functional layers is carried out in accordance with the preparation of the first functional layer; (3) Assemble the silicon carbide cylinder. The first functional layer, the second functional layer, and the third functional layer are assembled by bonding to form a silicon carbide cylinder, wherein the first functional layer is located on the outermost side, the third functional layer is located on the innermost side, and the second functional layer is located between the first functional layer and the third functional layer.

[0089] Example 1 The composite silicon carbide material prepared by Preparation Example 1 is a silicon carbide cylinder. The composite silicon carbide material includes three functional layers and two interface layers. From the outer layer to the inner layer, the three functional layers are a first functional layer, a second functional layer and a third functional layer. The two interface layers are a first interface layer and a second interface layer. The first interface layer is located between the second functional layer and the first functional layer, and the second interface layer is located between the third functional layer and the second functional layer. In the first functional layer, the particle size Dv90 of the silicon carbide material is 1 μm; in the second functional layer, the particle size Dv90 of the silicon carbide material is 4 μm; in the third functional layer, the particle size Dv90 of the silicon carbide material is 8 μm; the particle size Dv90 of the silicon carbide material in the second functional layer is 4 times that of the silicon carbide material in the first functional layer; the particle size Dv90 of the silicon carbide material in the third functional layer is 2 times that of the silicon carbide material in the second functional layer. In the first interface layer, the particle size Dv90 of the nano-silicon carbide is 90 nm; in the second interface layer, the particle size Dv90 of the nano-silicon carbide is 180 nm, and the particle size Dv90 of the nano-silicon carbide in the second interface layer is twice that of the nano-silicon carbide in the first interface layer. The first functional layer comprises 94.8 wt% silicon carbide material and 5.2 wt% Al2O3-Y2O3 (functional sintering aid); the second functional layer comprises 94.6 wt% silicon carbide material, 5.4 wt% Al2O3-Y2O3 and B4C (mass ratio 3:2, functional sintering aid); the third functional layer comprises 89.5 wt% silicon carbide material, 10.5 wt% B4C and AlN (mass ratio 8:2, functional sintering aid). The thickness of the first functional layer, the second functional layer and the third functional layer is 2mm.

[0090] The first interface layer comprises 87.7 wt% nano-silicon carbide, 1.8 wt% chopped carbon fibers, and 10.5 wt% Al2O3-Y2O3 (interface sintering aid); the second interface layer comprises 87.7 wt% nano-silicon carbide, 1.8 wt% chopped carbon fibers, and 10.5% Al2O3-Y2O3 (interface sintering aid).

[0091] The thickness of the first interface layer, the second interface layer and the third interface layer is 30 μm.

[0092] Example 2 This embodiment is based on Embodiment 1, except that neither the first interface layer nor the second interface layer includes short-cut carbon fibers.

[0093] Example 3 This embodiment is based on Embodiment 1, except that neither the first interface layer nor the second interface layer contains an interface sintering aid.

[0094] Example 4 This embodiment is based on Embodiment 1, except that the first functional layer, the second functional layer and the third functional layer all include 11wt% functional sintering aid and 77wt% silicon carbide material.

[0095] Example 5 This embodiment is based on Embodiment 1, except that the silicon carbide cylinder, from the outer layer to the inner layer, has three functional layers: a third functional layer, a second functional layer, and a first functional layer.

[0096] Example 6 This embodiment is based on Embodiment 1, except that the composite silicon carbide material is not a silicon carbide cylinder.

[0097] Comparative Example 1 This embodiment is based on Embodiment 1, except that the particle size Dv90 of the silicon carbide material in the first functional layer is 1 μm; the particle size Dv90 of the silicon carbide material in the second functional layer is 5 μm; and the particle size Dv90 of the silicon carbide material in the third functional layer is 25 μm. The particle size Dv90 of the silicon carbide material in the third functional layer is 5 times that of the silicon carbide material in the second functional layer.

[0098] Comparative Example 2 This embodiment is based on Embodiment 1, except that the particle size Dv90 of the silicon carbide material in the first functional layer is 2 μm; the particle size Dv90 of the silicon carbide material in the second functional layer is 2 μm; the particle size Dv90 of the silicon carbide material in the third functional layer is 2 μm; the particle size Dv90 of the silicon carbide material in the third functional layer is twice that of the silicon carbide material in the second functional layer; and the particle size Dv90 of the silicon carbide material in the second functional layer is twice that of the silicon carbide material in the second functional layer.

[0099] Comparative Example 3 This embodiment is based on Embodiment 1, except that the particle size Dv90 of the nano-silicon carbide in the first interface layer is 90 nm; the particle size Dv90 of the nano-silicon carbide in the second interface layer is 90 nm, and the particle size Dv90 of the nano-silicon carbide in the second interface layer is 1 times that of the nano-silicon carbide in the first interface layer.

[0100] Comparative Example 4 The silicon carbide cylinder prepared by Preparation Example 2.

[0101] Test case The performance of the silicon carbide composite materials prepared in the examples and comparative examples was tested. The specific test methods are as follows, and the test results are shown in Table 1.

[0102] (1) Sintering defect rate Ultrasonic testing was used to test the delamination and cracking of the composite silicon carbide material obtained by the preparation example of the present invention. A total of 20 pieces were tested. Those with delamination or cracking were recorded as defective pieces. The defect rate was calculated as: (number of defective pieces / 20) × 100%.

[0103] (2) The difference in thermal expansion coefficient between the Nth functional layer and the (N-1)th functional layer A composite silicon carbide material sample was placed on a temperature-controlled high-temperature diffraction stage. The Nth and (N-1)th functional layers of the sample were irradiated with monochromatic X-rays, and the diffraction signals generated by the crystal lattice were converted into diffraction patterns by a detector. The lattice constants at different temperatures were analyzed according to the Bragg equation. By calculating the change of the lattice constants with temperature, the thermal expansion coefficients of the two functional layers were obtained, and the difference between them was then calculated.

[0104] (3) Porosity of composite silicon carbide materials During testing, the sample was first completely dried and weighed. The dry weight (m1) was then measured. The sample was then immersed in distilled water and boiled for several hours or vacuumed to allow the pores to fully absorb water. After removing the sample and wiping off the surface moisture, the wet weight (m2) was measured. Finally, the sample was suspended in water and weighed (m3). The apparent bulk density was calculated using the formula ρv = m1 / (m2-m3) × ρw (where ρw is the density of water). Combined with the theoretical density (ρt) calculated proportionally based on the material composition, the total porosity was calculated using the formula porosity = [1 - (ρv / ρt)] × 100%.

[0105] (4) Shear strength between the Nth functional layer and the (N-1)th functional layer The composite silicon carbide material sample is clamped on a universal testing machine, and a shear load is applied between the Nth functional layer and the (N-1)th functional layer until fracture. The load data at fracture is recorded, which is the shear strength between the Nth functional layer and the (N-1)th functional layer.

[0106] Table 1 The " / " indicates that the data does not exist here.

[0107] As can be seen from the test results of the comparative examples and embodiments in Table 1, compared with the composite silicon carbide material in the comparative examples, the difference in the coefficient of thermal expansion between the third functional layer and the second functional layer, and between the second functional layer and the first functional layer, is reduced. The porosity of the composite silicon carbide material is also reduced. As a result, the shear strength between the third functional layer and the second functional layer, and between the second functional layer and the first functional layer, is significantly improved, and the bonding strength between the functional layers is enhanced. This indicates that by controlling the particle size Dv90 of the silicon carbide material in the Nth functional layer to be 2 to 4 times that of the silicon carbide material in the N-1th functional layer, and the particle size Dv90 of the nano-silicon carbide in the N-1th interface layer to be 2 to 4 times that of the nano-silicon carbide in the N-2th interface layer, and by adding sintering aids and toughening agents, the coefficients of thermal expansion of each functional layer of the multilayer composite silicon carbide material can be kept matched, the difference in thermal shrinkage rate at high temperature is reduced, and the porosity is reduced. This enhances the shear strength and bonding force between the functional layers and reduces the delamination and failure of the silicon carbide material at high temperatures.

[0108] The comparison between Preparation Example 1 and Preparation Example 2 in Table 1 shows that the sintering defect rate of Preparation Example 1 is lower than that of Preparation Example 2. The integrated molding preparation method of composite silicon carbide material provided by the present invention can effectively reduce or even avoid defects such as delamination, cracks, and weak interfacial bonding in multilayer composite silicon carbide materials, thereby reducing the sintering defect rate.

[0109] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite silicon carbide material, characterized in that, The composite silicon carbide material includes N functional layers and N-1 interface layers, wherein the N-1th interface layer is located between the Nth functional layer and the N-1th functional layer, and N is a positive integer from 3 to 5. The functional layer includes silicon carbide material and functional sintering aid. The particle size Dv90 of the silicon carbide material in the Nth functional layer is 2 to 4 times that of the silicon carbide material in the N-1th functional layer. The interface layer includes nano-silicon carbide, toughening agent, and interface sintering aid. The particle size of the nano-silicon carbide is 50nm-200nm. The particle size Dv90 of the nano-silicon carbide in the (N-1)th interface layer is 2 to 4 times that of the particle size Dv90 of the nano-silicon carbide in the (N-2)th interface layer.

2. The composite silicon carbide material according to claim 1, characterized in that, The composite silicon carbide material is a silicon carbide cylinder, which includes a first functional layer, a second functional layer, and an Nth functional layer from the outer layer to the inner layer; the diameter of the silicon carbide cylinder is 150mm-500mm; and the length of the silicon carbide cylinder is less than or equal to 800mm.

3. The composite silicon carbide material according to claim 1 or 2, characterized in that, The particle size Dv90 of silicon carbide material in any functional layer is 0.5μm-8μm; And / or, the weight ratio of functional sintering aid to silicon carbide material in any functional layer is 1:(8-47.5); the weight ratio of toughening agent, interface sintering aid, and nano-silicon carbide in any interface layer is 1:(2.5-13.3):(25-100); the functional sintering aid includes Al2O3, Y2O3, MgO, CeO2, La2O3, B4C, SiC-B, AlN, Y3Al5O 12 The toughening agent comprises at least one of Al2O3-Y2O3, silicon powder, carbon powder, nano-SiC-C composite, and graphene sheets; the toughening agent comprises at least one of short-cut carbon fibers, organic nanoparticles, inorganic nanoparticles, thermoplastic particles, core-shell structured particles, micro-nano hybrid particles, toughening films, and in-situ toughening; the interface sintering aid comprises Al2O3, Y2O3, MgO, CeO2, La2O3, B4C, SiC-B, AlN, and Y3Al5O3. 12 At least one of Al2O3-Y2O3, silicon powder, carbon powder, nano-SiC-C composite, and graphene sheet.

4. The composite silicon carbide material according to claim 3, characterized in that, The composite silicon carbide material comprises three functional layers and two interface layers. The three functional layers are a first functional layer, a second functional layer, and a third functional layer. The two interface layers are a first interface layer and a second interface layer. In the first functional layer, the particle size Dv90 of the silicon carbide material is 0.5 μm-1.5 μm; in the second functional layer, the particle size Dv90 of the silicon carbide material is 2 μm-4 μm; in the third functional layer, the particle size Dv90 of the silicon carbide material is 5 μm-8 μm. In the first interface layer, the particle size Dv90 of the nano-silicon carbide is 50 nm-120 nm; in the second interface layer, the particle size Dv90 of the nano-silicon carbide is 160 nm-200 nm.

5. The composite silicon carbide material according to claim 4, characterized in that, The first functional layer comprises 90wt%-95wt% silicon carbide material and 2wt%-10wt% functional sintering aid; the thickness of the first functional layer is 1mm-5mm; And / or, the second functional layer comprises 85wt%-90wt% of a second silicon carbide material and 2wt%-15wt% of a functional sintering aid; the thickness of the second functional layer is 1mm-5mm; And / or, the third functional layer comprises 80wt%-88wt% silicon carbide material and 2wt%-20wt% functional sintering aid; the thickness of the third functional layer is 1mm-5mm.

6. The composite silicon carbide material according to claim 4, characterized in that, The first interface layer comprises 60wt%-90wt% nano-silicon carbide, 0.9wt%-24wt% toughening agent, and 6wt%-20wt% interface sintering aid; the thickness of the first interface layer is 10μm-50μm. And / or, the second interface layer comprises 60wt%-90wt% nano-silicon carbide, 0.9wt%-24wt% toughening agent, and 6wt%-20wt% interface sintering aid; the thickness of the second interface layer is 10μm-50μm.

7. The composite silicon carbide material according to claim 1 or 2, characterized in that, The absolute value of the difference in the coefficient of thermal expansion between the Nth functional layer and the (N-1)th functional layer is less than 0.3 × 10⁻⁶. -6 / ℃; And / or, the porosity of the composite silicon carbide material is less than 5%; And / or, the shear strength between the Nth functional layer and the (N-1)th functional layer is greater than or equal to 40 MPa.

8. A method for preparing the composite silicon carbide material according to any one of claims 1-7, characterized in that, The method includes the following steps: (1) Preparation of functional layer slurry: The functional layer slurry includes N kinds of functional layer slurry, namely the first functional layer slurry, the second functional layer slurry and the Nth functional layer slurry, where N is a positive integer from 3 to 5. Any kind of functional layer slurry includes silicon carbide material and functional sintering aid. The particle size Dv90 of silicon carbide material in the Nth functional layer slurry is 2 to 4 times that of silicon carbide material in the N-1th functional layer slurry. (2) Preparation of interface layer slurry: The interface layer slurry includes N-1 types of interface layer slurry, namely the first interface layer slurry, the second interface layer slurry and the N-1th interface layer slurry, where N is a positive integer from 3 to 5. Any one of the interface layer slurries includes nano-silicon carbide, toughening agent and interface sintering aid. The particle size Dv90 of nano-silicon carbide in the N-1th interface layer slurry is 2 to 4 times that of nano-silicon carbide in the N-2th interface layer slurry. (3) Layer-by-layer grouting: The first functional layer grout, the second functional layer grout and the Nth functional layer grout are sequentially injected into the mold to form the first functional layer, the second functional layer and the Nth functional layer respectively. Before injecting the second functional layer grout, the first interface layer grout is sprayed on the surface of the first functional layer. Until the Nth functional layer grout is injected, the N-1th interface layer grout is sprayed on the surface of the N-1th functional layer to obtain the green body. (4) The blank is subjected to cold isostatic pressing, degreasing, gas pressure sintering and gradient cooling in sequence.

9. The method for preparing the composite silicon carbide material according to claim 8, characterized in that, The conditions for cold isostatic pressing include: a pressure of 100MPa-200MPa and a duration of 1h-2h; the conditions for degreasing include: heating to 600℃ at a heating rate of 1℃ / min-3℃ / min under an inert atmosphere and holding for 1h-4h; the conditions for gas pressure sintering include: heating to 1950℃-2100℃ at a heating rate of 10℃ / min-15℃ / min under an argon and / or vacuum environment and a pressure of 5MPa-20MPa and a holding time of 1h-4h. And / or, the viscosity of any functional layer slurry is 1000 mPa·s-1500 mPa·s; the viscosity of any interface layer slurry is 200 mPa·s-500 mPa·s.

10. The method for preparing the composite silicon carbide material according to claim 8 or 9, characterized in that, In step (3), the functional layer slurry is injected into the cylindrical mold in the order of the first functional layer slurry, the second functional layer slurry to the Nth functional layer slurry. The cylindrical mold is located in a centrifuge, and a cylindrical blank is obtained by centrifugation.

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