Silicon carbide ceramic material based on gradient activated sintering and nano composite reinforcement as well as preparation method and application of silicon carbide ceramic material

Abstract

The invention provides a silicon carbide ceramic material based on gradient activated sintering and nano composite reinforcement and a preparation method and application thereof.The preparation method comprises the steps that silicon carbide raw materials are mixed and subjected to ball milling, sintering raw materials are obtained, and the sintering raw materials are sequentially subjected to magnetic field reinforced sintering, pressure sintering and microwave sintering, siC nanowires grow in the pressure sintering process, and finally the silicon carbide ceramic material is obtained. According to the preparation method provided by the invention, sectional sintering is carried out under magnetic field, pressure and microwave strengthening, and specific strengthening means are adopted in different sintering stages, so that activation of sintering powder and arrangement and growth of particles are promoted, the densification of the silicon carbide ceramic is improved, and SiC nanowires grow in the sintering process, so that the performance of the silicon carbide ceramic is improved. Therefore, the mechanical property and the thermal property of the silicon carbide ceramic material are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic materials and relates to a silicon carbide ceramic material, in particular to a silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement, and a preparation method and application thereof. Background Art

[0002] As a representative of the third generation of advanced ceramic materials, silicon carbide ceramics exhibit excellent high-temperature mechanical properties, ultra-high hardness, excellent thermal shock resistance and chemical inertness due to their covalent bond crystal structure. They are irreplaceable in extreme environment fields such as aerospace thermal protection systems, nuclear reactor cladding materials, and semiconductor manufacturing equipment.

[0003] However, the industrial application of silicon carbide ceramics has long been limited by the technical constraints of traditional solid-phase sintering processes. First, pressureless sintering requires ultra-high temperatures exceeding 2000°C, which is not only extremely energy-intensive but also prone to abnormal grain growth and structural defects. Second, the high diffusion activation energy of micron-sized silicon carbide powders makes further increases in material density difficult. Furthermore, to promote material densification, sintering aids such as Al2O3-Y2O3 must be added. These sintering aids tend to form a glassy phase at grain boundaries, which softens at high temperatures and reduces the material's high-temperature performance.

[0004] In recent years, researchers have made various innovations in silicon carbide ceramic preparation technology.

[0005] For example, CN109592984A discloses a method for preparing liquid-phase sintered silicon carbide ceramics. The method uses SiC powder as the raw material, an aluminum oxide precursor, and an ytterbium oxide precursor as sintering aids, and produces the silicon carbide ceramics through hot pressing and sintering. This method optimizes the formulation of the sintering aids, but optimizing the sintering aids alone has limited benefits in improving the performance of the silicon carbide material.

[0006] CN119504275A discloses a silicon carbide ceramic material and its preparation method. Silicon carbide composite nanowires are first prepared and modified with praseodymium. The resulting material is then sintered and annealed using a spark plasma sintering method using liquid polycarbosilane and a modification agent. However, spark plasma sintering is limited by mold size and plasma uniformity control, and the equipment investment cost is high.

[0007] CN115594513A discloses a kind of in-situ generation carbon fiber reinforced silicon carbide ceramic matrix composite material and its preparation method, this method uses silicon carbide powder, sintering aid, binder and catalyst, by compression molding and segmented sintering, part of silicon carbide decomposes in-situ generation carbon fiber, strengthens the strength of silicon carbide ceramic material. The flexural strength of silicon carbide ceramic is improved by carbon fiber, but other properties such as material density need to be improved. In addition, there is also by using nano powder sintering technology, reducing sintering activation energy, improving the density of silicon carbide ceramic, but nano particles have large specific surface area and are prone to hard agglomeration.

[0008] In summary, the current preparation process for silicon carbide ceramics is difficult to significantly improve material properties, and the sintering process is extremely costly, which restricts the large-scale application of silicon carbide ceramics. Therefore, the development of new preparation processes is the core direction for breaking through the large-scale production of high-performance silicon carbide ceramics. Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a silicon carbide ceramic material based on gradient activation sintering and nano-composite reinforcement, as well as its preparation method and application, to optimize the preparation process of silicon carbide ceramic material, reduce the sintering temperature of the material, and improve the performance of the material.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a method for preparing a silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement, the preparation method comprising the following steps:

[0012] Silicon carbide raw materials are mixed and ball-milled to obtain sintering raw materials, and the sintering raw materials are sequentially subjected to magnetic field enhanced sintering, pressure sintering and microwave sintering. SiC nanowires are grown during the pressure sintering to finally obtain silicon carbide ceramic materials.

[0013] The preparation method provided by the present invention designs a specific three-stage sintering method. During the first stage of sintering, magnetic field strengthening is applied. The alternating magnetic field can destroy the binding force between the particles in the initial sintering state, so that the sintered powder is evenly dispersed, the formation of uneven agglomerates is avoided, and the powder surface is activated. During the second stage of sintering, pressure is applied to drive the Si-CO gas phase material to migrate along the grain boundaries through air pressure, which can promote particle rearrangement and "neck" formation in the middle stage of sintering, fill the pores, and at the same time, grow β-SiC nanowires during grain formation and growth, so that the nanowires can bridge the grains and significantly improve the fracture toughness. Microwave strengthening is used in the third stage of sintering, and the particles are finally densified in the final sintering stage. Microwaves can achieve selective heating of the grain boundary area, thereby accelerating bulk diffusion, significantly improving the densification effect, and reducing the sintering temperature.

[0014] Preferably, the silicon carbide raw material comprises: silicon carbide powder and a sintering additive, and the sintering additive comprises at least one of a sintering aid, a binder, a dispersing aid, a solvent, a dispersant, a release agent or a defoaming agent.

[0015] Preferably, the sintering aid includes carbon powder and / or boron carbide.

[0016] Preferably, the mass ratio of the carbon powder to boron carbide is (1-10):1, for example, 1:1, 3:1, 5:1, 8:1 or 10:1, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0017] Preferably, the binder comprises polyvinyl alcohol and / or polyacrylic acid.

[0018] Preferably, the mass ratio of polyvinyl alcohol to polyacrylic acid is (0.1-2):1, for example, 0.1:1, 0.5:1, 1:1, 1.5:1 or 2:1, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0019] Preferably, the dispersing aid includes at least one of polyethylene glycol, ammonia water or glycerol.

[0020] Preferably, the solvent comprises deionized water.

[0021] Preferably, the composition of the silicon carbide raw material includes, by mass: 100 parts of silicon carbide powder, 100-120 parts of deionized water, 2-5 parts of carbon powder, 0.6-1.5 parts of boron carbide, 0.8-2 parts of polyvinyl alcohol, 0.8-2 parts of polyethylene glycol, 0.5-2 parts of ammonia water, 0.5-4 parts of glycerol, 0.5-1.5 parts of dispersant, 1-5 parts of polyacrylic acid, 0.5-1.5 parts of release agent, and 0.3-1 part of defoaming agent.

[0022] In the silicon carbide raw material, the mass fraction of deionized water is 100-120 parts, for example, it can be 100 parts, 105 parts, 110 parts, 115 parts or 120 parts, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0023] In the silicon carbide raw material, the mass fraction of carbon powder is 2-5 parts, for example, it can be 2 parts, 3 parts, 4 parts or 5 parts, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0024] In the silicon carbide raw material, the mass fraction of boron carbide is 0.6-1.5 parts, for example, it can be 0.6 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.4 parts or 1.5 parts, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0025] In the silicon carbide raw material, the mass fraction of polyvinyl alcohol is 0.8-2 parts, for example, it can be 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0026] In the silicon carbide raw material, the mass fraction of polyethylene glycol is 0.8-2 parts, for example, it can be 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0027] In the silicon carbide raw material, the mass fraction of ammonia water is 0.5-2 parts, for example, it can be 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0028] In the silicon carbide raw material, the mass fraction of glycerol is 0.5-4 parts, for example, it can be 0.5 parts, 1 parts, 2 parts, 3 parts or 4 parts, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0029] In the silicon carbide raw material, the mass fraction of the dispersant is 0.5-1.5 parts, for example, it can be 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts or 1.5 parts, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0030] In the silicon carbide raw material, the mass fraction of polyacrylic acid is 1-5 parts, for example, it can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0031] In the silicon carbide raw material, the mass fraction of the release agent is 0.5-1.5 parts, for example, it can be 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts or 1.5 parts, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0032] In the silicon carbide raw material, the mass fraction of the defoaming agent is 0.3-1 part, for example, it can be 0.3 part, 0.5 part, 0.8 part or 1 part, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0033] Preferably, the dispersant comprises polyethyleneimine.

[0034] Preferably, the release agent comprises sodium tripolyphosphate.

[0035] Preferably, the defoaming agent comprises emulsified silicone oil.

[0036] Preferably, the ball milling speed is 20-70 rpm, for example, 20 rpm, 30 rpm, 35 rpm, 40 rpm, 50 rpm, 60 rpm or 70 rpm, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0037] Preferably, the ball milling time is 12-48 h, for example, 12 h, 18 h, 24 h, 30 h, 36 h, 42 h or 48 h, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0038] Preferably, the sintering temperature of the magnetic field enhanced sintering is 800-1200°C, for example, it can be 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0039] Preferably, the holding time of the magnetic field enhanced sintering is 30-60 min, for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0040] Preferably, the magnetic field enhanced sintering method includes applying a pulsed electromagnetic field during the sintering process.

[0041] Preferably, the frequency of the pulsed electromagnetic field is 10-50kHz, for example, it can be 10kHz, 15kHz, 20kHz, 25kHz, 30kHz, 35kHz, 40kHz, 45kHz or 50kHz, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0042] Preferably, the power of the pulsed electromagnetic field is 5-10kW, for example, 5kW, 6kW, 7kW, 8kW, 9kW or 10kW, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0043] Preferably, the pressure sintering temperature is 1400-1600°C, for example, it can be 1400°C, 1425°C, 1450°C, 1475°C, 1500°C, 1525°C, 1550°C, 1575°C or 1600°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0044] Preferably, the pressure sintering method includes three-stage pressure sintering, and the three-stage pressure sintering is divided into a first pressure sintering, a second pressure sintering and a third pressure sintering.

[0045] Preferably, the pressure of the first pressure sintering is 4-6 MPa, for example, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa or 6 MPa, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0046] Preferably, the holding time of the first pressure sintering is 8-12 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0047] Preferably, the pressure of the second pressure sintering is 18-22 MPa, for example, 18 MPa, 19 MPa, 20 MPa, 21 MPa or 22 MPa, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0048] Preferably, the holding time of the second pressure sintering is 8-12 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0049] Preferably, the pressure of the third pressure sintering is 48-52 MPa, for example, 48 MPa, 49 MPa, 50 MPa, 51 MPa or 52 MPa, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0050] Preferably, the holding time of the third pressure sintering is 8-12 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0051] Preferably, the method for growing SiC nanowires comprises: introducing a carbon silicon source for vapor deposition.

[0052] Preferably, the carbon silicon source comprises methyltrichlorosilane.

[0053] Preferably, the flow rate of the carbon silicon source is 45-55 mL / min, for example, it can be 45 mL / min, 48 mL / min, 50 mL / min, 52 mL / min or 55 mL / min, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0054] Preferably, the diameter of the SiC nanowire is 50-100 nm, for example, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0055] Preferably, the microwave sintering temperature is 1600-1700°C, for example, 1600°C, 1620°C, 1640°C, 1650°C, 1660°C, 1680°C or 1700°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0056] Preferably, the holding time of the microwave sintering is 30-60 min, for example, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0057] Preferably, the microwave frequency of the microwave sintering is 2.4-2.5 GHz, for example, 2.4 GHz, 2.42 GHz, 2.45 GHz, 2.48 GHz or 2.5 GHz, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0058] Preferably, the microwave power of the microwave sintering is 3-5 kW, for example, 3 kW, 3.5 kW, 4 kW, 4.5 kW or 5 kW, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0059] Preferably, after the microwave sintering, the preparation method further comprises: a cooling treatment.

[0060] Preferably, a mixture of argon and hydrogen is introduced during the cooling treatment.

[0061] Preferably, the volume ratio of argon to hydrogen is (0.1-10):1, for example, it can be 0.1:1, 1:1, 3:1, 5:1, 8:1 or 10:1, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0062] In the present invention, argon and hydrogen are introduced during the cooling stage, and the gas atmosphere is controlled to inhibit material oxidation, promote surface atomic migration, and promote microcrack healing, with a healing rate of more than 85%.

[0063] As a preferred technical solution of the preparation method provided by the present invention, the preparation method comprises the following steps:

[0064] (1) mixing silicon carbide raw materials and ball milling them, wherein the composition of the silicon carbide raw materials, by mass, includes: 100 parts of silicon carbide powder, 100-120 parts of deionized water, 2-5 parts of carbon powder, 0.6-1.5 parts of boron carbide, 0.8-2 parts of polyvinyl alcohol, 0.8-2 parts of polyethylene glycol, 0.5-2 parts of ammonia water, 0.5-4 parts of glycerol, 0.5-1.5 parts of a dispersant, 1-5 parts of polyacrylic acid, 0.5-1.5 parts of a release agent, and 0.3-1 parts of a defoaming agent, the rotation speed of the ball mill is 20-70 rpm, and the ball milling time is 12-48 hours to obtain a sintering raw material;

[0065] (2) subjecting the sintering raw material to magnetic field enhanced sintering, wherein the magnetic field enhanced sintering method includes applying a pulse electromagnetic field during the sintering process, wherein the frequency of the pulse electromagnetic field is 10-50 kHz, the generating power of the pulse electromagnetic field is 5-10 kW, the sintering temperature of the magnetic field enhanced sintering is 800-1200° C., and the holding time of the magnetic field enhanced sintering is 30-60 min, to obtain a first sintered green body;

[0066] (3) subjecting the first sintered green body to three-stage pressure sintering, wherein the temperature of the three-stage pressure sintering is 1400-1600° C., and the process of the three-stage pressure sintering comprises: first increasing the pressure to 4-6 MPa and holding the pressure for 8-12 min, then increasing the pressure to 18-22 MPa and holding the pressure for 8-12 min, and finally increasing the pressure to 48-52 MPa and holding the pressure for 8-12 min. During the three-stage pressure sintering process, methyltrichlorosilane is introduced at a flow rate of 45-55 mL / min to decompose and grow SiC nanowires with a diameter of 50-100 nm, thereby obtaining a second sintered green body;

[0067] (4) The second sintered green body is subjected to microwave sintering, wherein the microwave frequency of the microwave sintering is 2.4-2.5 GHz, the microwave power of the microwave sintering is 3-5 kW, the temperature of the microwave sintering is 1600-1700° C., and the holding time of the microwave sintering is 30-60 min. The cooling process after the sintering is carried out in a mixed gas atmosphere of argon and hydrogen, and the volume ratio of argon to hydrogen is (0.1-10):1. After the cooling is completed, a silicon carbide ceramic material is obtained.

[0068] In a second aspect, the present invention provides a silicon carbide ceramic material, which is prepared by the preparation method described in the first aspect.

[0069] The silicon carbide ceramic material provided by the present invention has a uniform microscopic grain size of 1-2 μm, wherein the β-SiC nanowires are distributed in a network-like manner, the material has a high density, a porosity of ≤1.3%, and excellent mechanical and thermal properties, with a flexural strength of ≥576 MPa and a fracture toughness of ≥5.9 MPa·m 1 / 2, thermal conductivity ≥ 150W / m·K, thermal expansion coefficient ≤ 4×10 -6 / K.

[0070] In a third aspect, the present invention provides an application of the silicon carbide ceramic material described in the second aspect, wherein the silicon carbide ceramic material is applied to at least one of a spacecraft thermal protection device, a nuclear reactor cladding material, or a semiconductor device.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] (1) The preparation method provided by the present invention performs segmented sintering under magnetic field, pressure and microwave strengthening respectively. By adopting specific strengthening means at different sintering stages, the electromagnetic field is used to promote powder dispersion and surface activation, the pressure is used to drive the migration of substances in the tissue to fill the pores, and the microwave is used to achieve selective heating of the grain boundaries, thereby significantly improving the homogenization and densification effect of the silicon carbide ceramic material and significantly reducing the sintering temperature.

[0073] (2) During the pressure sintering process, the growth of SiC nanowires is promoted by pressure matching, and the nanowires bridge the grains, significantly improving the fracture toughness of silicon carbide ceramic materials;

[0074] (3) The obtained silicon carbide ceramic material has excellent mechanical and thermal properties, with a flexural strength of ≥576MPa and a fracture toughness of ≥5.9MPa·m 1 / 2 , thermal conductivity ≥ 150W / m·K, thermal expansion coefficient ≤ 4×10 -6 / K. DETAILED DESCRIPTION

[0075] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0076] In order to clearly illustrate the technical solution of the present invention, in a specific embodiment, the dispersant is polyethyleneimine, which is a commercially available product with a CAS number of 9002-98-6, an Mn of 10,000, and a PDI of ≤1.3; the release agent is sodium tripolyphosphate with a CAS number of 7758-29-4, which is a commercially available product; and the defoaming agent is emulsified silicone oil, which is a commercially available product.

[0077] Example 1

[0078] This embodiment provides a method for preparing a silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement, the preparation method comprising the following steps:

[0079] (1) mixing silicon carbide raw materials and ball milling them, wherein the composition of the silicon carbide raw materials, by mass, includes: 100 parts of silicon carbide powder, 110 parts of deionized water, 3 parts of carbon powder, 1 part of boron carbide, 1 part of polyvinyl alcohol, 1 part of polyethylene glycol, 1 part of ammonia water, 2 parts of glycerol, 1 part of dispersant, 3 parts of polyacrylic acid, 1 part of release agent, and 0.6 part of defoaming agent, the ball milling speed is 50 rpm, and the ball milling time is 30 hours to obtain a sintering raw material;

[0080] (2) using an electromagnetic generator to generate a pulsed electromagnetic field, and subjecting the sintering raw material to magnetic field enhanced sintering under the pulsed electromagnetic field, wherein the generating power of the pulsed electromagnetic field is 8 kW, the frequency of the pulsed electromagnetic field is 30 kHz, the temperature of the magnetic field enhanced sintering is 1000° C., and the holding time is 45 min, to obtain a first sintered green body;

[0081] (3) The first sintered green body was pressure-sintered at a temperature of 1500° C. The pressure was increased by a high-pressure air pump to 5 MPa, 20 MPa, and 50 MPa, respectively. The holding time of each pressure stage was 10 min. During the pressure sintering process, CH3SiCl3 gas was introduced at a flow rate of 50 mL / min. The CH3SiCl3 gas was decomposed and grown into SiC nanowires during the sintering process. After the pressure sintering was completed, a second sintered green body was obtained.

[0082] (4) The second sintered green body is subjected to microwave sintering in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.45 GHz, the microwave power is 4 kW, the temperature of the microwave sintering is 1650°C, and the holding time is 45 min. The cooling process after microwave sintering is carried out in a mixed gas atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1), and finally a silicon carbide ceramic material is obtained.

[0083] Example 2

[0084] This embodiment provides a method for preparing a silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement, the preparation method comprising the following steps:

[0085] (1) mixing silicon carbide raw materials and ball milling them, wherein the composition of the silicon carbide raw materials, by mass, includes: 100 parts of silicon carbide powder, 110 parts of deionized water, 3 parts of carbon powder, 1 part of boron carbide, 1 part of polyvinyl alcohol, 1 part of polyethylene glycol, 1 part of ammonia water, 2 parts of glycerol, 1 part of dispersant, 3 parts of polyacrylic acid, 1 part of release agent, and 0.6 part of defoaming agent, the ball milling speed is 20 rpm, and the ball milling time is 48 hours to obtain a sintering raw material;

[0086] (2) using an electromagnetic generator to generate a pulsed electromagnetic field, and subjecting the sintering raw material to magnetic field enhanced sintering under the pulsed electromagnetic field, wherein the generating power of the pulsed electromagnetic field is 10 kW, the frequency of the pulsed electromagnetic field is 10 kHz, the temperature of the magnetic field enhanced sintering is 1200° C., and the holding time is 30 min, to obtain a first sintered green body;

[0087] (3) The first sintered green body was pressure-sintered at a temperature of 1600° C. The pressure was increased by a high-pressure air pump to 4 MPa, 18 MPa, and 48 MPa, respectively. The holding time of each pressure stage was 12 min. During the pressure sintering process, CH3SiCl3 gas was introduced at a flow rate of 55 mL / min. The CH3SiCl3 gas was decomposed and grown into SiC nanowires during the sintering process. After the pressure sintering was completed, a second sintered green body was obtained.

[0088] (4) The second sintered green body is subjected to microwave sintering in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.5 GHz, the microwave power is 3 kW, the microwave sintering temperature is 1600°C, and the holding time is 60 min. The cooling process after microwave sintering is carried out in a mixed gas atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1), and finally a silicon carbide ceramic material is obtained.

[0089] Example 3

[0090] This embodiment provides a method for preparing a silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement, the preparation method comprising the following steps:

[0091] (1) mixing silicon carbide raw materials and ball milling them, wherein the composition of the silicon carbide raw materials, by mass, includes: 100 parts of silicon carbide powder, 110 parts of deionized water, 3 parts of carbon powder, 1 part of boron carbide, 1 part of polyvinyl alcohol, 1 part of polyethylene glycol, 1 part of ammonia water, 2 parts of glycerol, 1 part of dispersant, 3 parts of polyacrylic acid, 1 part of release agent, and 0.6 part of defoaming agent, the ball milling speed is 70 rpm, and the ball milling time is 12 hours to obtain a sintering raw material;

[0092] (2) using an electromagnetic generator to generate a pulsed electromagnetic field, and subjecting the sintering raw material to magnetic field enhanced sintering under the pulsed electromagnetic field, wherein the generating power of the pulsed electromagnetic field is 5 kW, the frequency of the pulsed electromagnetic field is 50 kHz, the temperature of the magnetic field enhanced sintering is 800° C., and the holding time is 60 min, to obtain a first sintered green body;

[0093] (3) The first sintered green body was pressure-sintered at a temperature of 1400° C. The pressure was increased by a high-pressure air pump to 6 MPa, 22 MPa, and 52 MPa, respectively. The holding time of each pressure stage was 8 min. During the pressure sintering process, CH3SiCl3 gas was introduced at a flow rate of 45 mL / min. The CH3SiCl3 gas was decomposed and grown into SiC nanowires during the sintering process. After the pressure sintering was completed, a second sintered green body was obtained.

[0094] (4) The second sintered green body is subjected to microwave sintering in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.4 GHz, the microwave power is 5 kW, the temperature of the microwave sintering is 1700°C, and the holding time is 30 min. The cooling process after microwave sintering is carried out in a mixed gas atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1), and finally a silicon carbide ceramic material is obtained.

[0095] Example 4

[0096] This embodiment provides a preparation method of a silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement. Compared with Example 1, the pressure of the pressure sintering in step (3) is controlled to remain unchanged at 50 MPa, and the holding time is 30 minutes. The rest is the same as Example 1.

[0097] Example 5

[0098] This embodiment provides a preparation method of a silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement. Compared with Example 1, the mixture of argon and hydrogen is not introduced into the cooling process in step (4), that is, the cooling process is carried out in an air atmosphere. The rest is the same as Example 1.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing a silicon carbide ceramic material, which comprises the following steps:

[0101] The silicon carbide raw materials were mixed and ball-milled, wherein the composition and ball-milling process of the silicon carbide raw materials were the same as those in Example 1 to obtain sintered raw materials, which were sintered in a sintering furnace at a sintering temperature of 2050° C. and a sintering time of 2 h to obtain a silicon carbide ceramic material.

[0102] Comparative Example 2

[0103] This comparative example provides a method for preparing a silicon carbide ceramic material, which comprises the following steps:

[0104] (1) mixing silicon carbide raw materials and ball milling them, wherein the composition and ball milling process of the silicon carbide raw materials are the same as those in Example 1, to obtain a sintered raw material;

[0105] (2) The sintering raw materials are sintered, and a pulsed electromagnetic field, pressure and microwaves are applied simultaneously during the sintering process. During the sintering process, CH3SiCl3 gas is introduced at a flow rate of 50 mL / min. The CH3SiCl3 gas is cracked and grown into SiC nanowires during the sintering process. The sintering temperature is 1650°C and the sintering time is 2 hours. The power of the pulsed electromagnetic field is 8 kW and the frequency is 30 kHz. The pressure is sequentially increased to 5 MPa, 20 MPa and 50 MPa, and the holding time of each pressure section is 40 minutes. The frequency of the microwave is 2.45 GHz and the power is 4 kW. The cooling process after sintering is carried out in a mixed gas atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1), and finally a silicon carbide ceramic material is obtained.

[0106] Comparative Example 3

[0107] This comparative example provides a method for preparing a silicon carbide ceramic material. Compared with Example 1, no pulsed electromagnetic field is applied in step (2), no pressurization is performed in step (3), and no microwave is applied in step (4). The rest is the same as Example 1.

[0108] Comparative Example 4

[0109] This comparative example provides a method for preparing a silicon carbide ceramic material. Compared with Example 1, no pulsed electromagnetic field is applied in step (2), and the rest is the same as Example 1.

[0110] Comparative Example 5

[0111] This comparative example provides a method for preparing a silicon carbide ceramic material. Compared with Example 1, no pressurization is performed in step (3), and the rest is the same as Example 1.

[0112] Comparative Example 6

[0113] This comparative example provides a method for preparing a silicon carbide ceramic material. Compared with Example 1, CH3SiCl3 gas is not introduced in step (3) to grow SiC nanowires, and the rest is the same as Example 1.

[0114] Comparative Example 7

[0115] This comparative example provides a method for preparing a silicon carbide ceramic material, which comprises the following steps:

[0116] (1) mixing silicon carbide raw materials and ball milling them, wherein the silicon carbide raw materials and ball milling parameters are the same as those in Example 1, to obtain a sintered raw material;

[0117] (2) pressure sintering the sintering raw material at a temperature of 1000° C., pressurizing the raw material to 5 MPa, 20 MPa, and 50 MPa, respectively, with a holding time of 10 min for each pressure range, to obtain a first sintered green body;

[0118] (3) The first sintered green body is subjected to microwave sintering in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.45 GHz, the microwave power is 4 kW, the temperature of the microwave sintering is 1500° C., and the holding time is 45 min. During the microwave sintering process, CH3SiCl3 gas is introduced at a flow rate of 50 mL / min. The CH3SiCl3 gas is cracked and grown into SiC nanowires during the sintering process, and a second sintered green body is obtained after the completion of the sintering process.

[0119] (4) An electromagnetic generator is used to generate a pulsed electromagnetic field, and the second sintered blank is subjected to magnetic field enhanced sintering under the pulsed electromagnetic field. The generating power of the pulsed electromagnetic field is 8 kW, the frequency of the pulsed electromagnetic field is 30 kHz, the temperature of the magnetic field enhanced sintering is 1650°C, and the holding time is 45 minutes. The cooling process after sintering is carried out in a mixed gas atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1), and finally a silicon carbide ceramic material is obtained.

[0120] Performance Testing

[0121] The silicon carbide ceramic materials provided in the examples and comparative examples were tested for density, mechanical properties, and thermal properties. The results are listed in Table 1.

[0122] The bulk density was determined by the Archimedes drainage method, the flexural strength was determined by the three-point bending method, the fracture toughness was determined by the single-edge notched beam (SENB) method, and the thermal conductivity at 25 °C was determined by the laser flash method.

[0123] Table 1

[0124]

[0125]

[0126] As can be seen from Table 1:

[0127] (1) The preparation method provided by the present invention adopts a gradient activation sintering method and a three-stage sintering process in combination with a specific strengthening method, which effectively reduces the sintering temperature of the ceramic material, reduces the process difficulty and cost, and effectively improves and strengthens the microstructure of the material, and grows nanowires in the material to strengthen the strength of the material. The resulting ceramic material has a high density and a volume density of 3.16g / cm 3, the porosity is only below 1.3%; it has excellent mechanical properties, with a bending strength of more than 576MPa, especially more than 650MPa, and a fracture toughness of 5.9MPa·m 1 / 2 At the same time, it has excellent thermal properties, with a thermal conductivity of more than 150W / m·K and a thermal expansion coefficient of 3.7×10 -6 / K or above.

[0128] (2) Compared with Example 1, in Example 4, the pressure is kept constant during the pressure sintering process, and there is no gradient gas pressure. The mechanical strength of the silicon carbide material decreases slightly, the thermal conductivity decreases, and the porosity increases significantly. The strengthening of the gradient gas pressure helps to rearrange the particles during the sintering process, thereby improving the material microstructure and enhancing the mechanical strength. It also drives the Si-CO gas phase to migrate along the grain boundaries, filling the pores, effectively reducing the material porosity and improving the density. In Example 5, the cooling process is completed in an air atmosphere, and the mechanical strength of the material decreases. The use of an argon-hydrogen mixture during the cooling process helps to repair the microcracks on the surface of the ceramic material, thereby improving the material strength.

[0129] (3) In Comparative Example 1, the traditional one-stage sintering method was adopted, and the performance and density of the ceramic material were difficult to meet the high quality requirements. In Comparative Example 3, only three-stage sintering was adopted, and there was a lack of strengthening means. The corresponding temperature could not reach the sintering temperature, the material could not be densified, and silicon carbide ceramic material could not be obtained. Combining the results of Comparative Example 2 and Comparative Example 7, in Comparative Example 2, multiple strengthening means were applied simultaneously during the one-stage sintering process, and in Comparative Example 7, pressure sintering, microwave sintering and magnetic field strengthening sintering were used in turn. Although multiple strengthening means were used, the performance of the material was not significantly improved. It can be seen that the strengthening means need to be combined with a specific sintering process in order to significantly enhance the material performance. Compared with Example 1, in Comparative Examples 4-6, in Comparative Example 4, no pulsed electromagnetic field is applied, uneven agglomeration is easily generated during sintering, and the powder activation effect is lacking, which affects the sintering effect, resulting in a significant decrease in all aspects of material performance; in Comparative Example 5, no pressure sintering is performed. On the one hand, the migration-promoting effect of pressure is lacking, and on the other hand, in the absence of pressure means, the growth effect of nanowires is also poor, resulting in material performance failing to meet the standards; in Comparative Example 6, in the absence of composite reinforcement of nanowires, material performance also deteriorates significantly.

[0130] In summary, the preparation method provided by the present invention significantly improves the homogenization and densification effects of silicon carbide ceramic materials through gradient activation sintering and nanowire composite reinforcement, and significantly reduces the sintering temperature required. The obtained silicon carbide ceramic material has excellent mechanical and thermal properties.

[0131] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement, characterized in that: The preparation method comprises the following steps: Silicon carbide raw materials are mixed and ball-milled to obtain sintering raw materials, and the sintering raw materials are sequentially subjected to magnetic field enhanced sintering, pressure sintering and microwave sintering. SiC nanowires are grown during the pressure sintering to finally obtain silicon carbide ceramic materials.

2. The preparation method according to claim 1, characterized in that The silicon carbide raw material includes: silicon carbide powder and sintering additives, wherein the sintering additives include at least one of a sintering aid, a binder, a dispersing aid, a solvent, a dispersant, a release agent or a defoaming agent; Preferably, the sintering aid comprises carbon powder and / or boron carbide; Preferably, the mass ratio of the carbon powder to boron carbide is (1-10):1; Preferably, the binder comprises polyvinyl alcohol and / or polyacrylic acid; Preferably, the mass ratio of the polyvinyl alcohol to the polyacrylic acid is (0.1-2):1; Preferably, the dispersing aid comprises at least one of polyethylene glycol, ammonia or glycerol; Preferably, the solvent comprises deionized water; Preferably, the composition of the silicon carbide raw material includes, by mass: 100 parts of silicon carbide powder, 100-120 parts of deionized water, 2-5 parts of carbon powder, 0.6-1.5 parts of boron carbide, 0.8-2 parts of polyvinyl alcohol, 1-5 parts of polyacrylic acid, 0.8-2 parts of polyethylene glycol, 0.5-2 parts of ammonia water, 0.5-4 parts of glycerol, 0.5-1.5 parts of dispersant, 0.5-1.5 parts of release agent, and 0.3-1 parts of defoaming agent.

3. The preparation method according to claim 1 or 2, characterized in that The ball milling speed is 20-70 rpm; Preferably, the ball milling time is 12-48 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that The sintering temperature of the magnetic field enhanced sintering is 800-1200°C; Preferably, the holding time of the magnetic field enhanced sintering is 30-60 minutes. Preferably, the magnetic field enhanced sintering method includes applying a pulsed electromagnetic field during the sintering process; Preferably, the frequency of the pulsed electromagnetic field is 10-50 kHz; Preferably, the pulsed electromagnetic field has a generating power of 5-10 kW.

5. The preparation method according to any one of claims 1 to 4, characterized in that The pressure sintering temperature is 1400-1600°C; Preferably, the pressure sintering method includes three-stage pressure sintering, and the three-stage pressure sintering is divided into a first pressure sintering, a second pressure sintering and a third pressure sintering; Preferably, the pressure of the first pressure sintering is 4-6 MPa; Preferably, the holding time of the first pressure sintering is 8-12 minutes; Preferably, the pressure of the second pressure sintering is 18-22 MPa; Preferably, the holding time of the second pressure sintering is 8-12 minutes; Preferably, the pressure of the third pressure sintering is 48-52 MPa; Preferably, the holding time of the third pressure sintering is 8-12 minutes.

6. The preparation method according to any one of claims 1 to 5, characterized in that The method for growing SiC nanowires comprises: introducing a carbon silicon source for vapor deposition; Preferably, the carbon silicon source comprises methyltrichlorosilane; Preferably, the flow rate of the carbon silicon source is 45-55 mL / min; Preferably, the diameter of the SiC nanowire is 50-100 nm.

7. The preparation method according to any one of claims 1 to 6, characterized in that The microwave sintering temperature is 1600-1700°C; Preferably, the holding time of the microwave sintering is 30-60 min; Preferably, the microwave frequency of the microwave sintering is 2.4-2.5 GHz; Preferably, the microwave power of the microwave sintering is 3-5kW; Preferably, after the microwave sintering, the preparation method further comprises: cooling treatment; Preferably, a mixture of argon and hydrogen is introduced during the cooling process; Preferably, the volume ratio of argon to hydrogen is (0.1-10):

1.

8. The preparation method according to any one of claims 1 to 7, characterized in that The preparation method comprises the following steps: (1) mixing silicon carbide raw materials and ball milling them, wherein the composition of the silicon carbide raw materials, by mass, includes: 100 parts of silicon carbide powder, 100-120 parts of deionized water, 2-5 parts of carbon powder, 0.6-1.5 parts of boron carbide, 0.8-2 parts of polyvinyl alcohol, 0.8-2 parts of polyethylene glycol, 0.5-2 parts of ammonia water, 0.5-4 parts of glycerol, 0.5-1.5 parts of a dispersant, 1-5 parts of polyacrylic acid, 0.5-1.5 parts of a release agent, and 0.3-1 parts of a defoaming agent, the rotation speed of the ball mill is 20-70 rpm, and the ball milling time is 12-48 hours to obtain a sintering raw material; (2) subjecting the sintering raw material to magnetic field enhanced sintering, wherein the magnetic field enhanced sintering method includes applying a pulse electromagnetic field during the sintering process, wherein the frequency of the pulse electromagnetic field is 10-50 kHz, the generating power of the pulse electromagnetic field is 5-10 kW, the sintering temperature of the magnetic field enhanced sintering is 800-1200° C., and the holding time of the magnetic field enhanced sintering is 30-60 min, to obtain a first sintered green body; (3) subjecting the first sintered green body to three-stage pressure sintering, wherein the temperature of the three-stage pressure sintering is 1400-1600° C., and the process of the three-stage pressure sintering comprises: first increasing the pressure to 4-6 MPa and holding the pressure for 8-12 min, then increasing the pressure to 18-22 MPa and holding the pressure for 8-12 min, and finally increasing the pressure to 48-52 MPa and holding the pressure for 8-12 min. During the three-stage pressure sintering process, methyltrichlorosilane is introduced at a flow rate of 45-55 mL / min to decompose and grow SiC nanowires with a diameter of 50-100 nm, thereby obtaining a second sintered green body; (4) The second sintered green body is subjected to microwave sintering, wherein the microwave frequency of the microwave sintering is 2.4-2.5 GHz, the microwave power of the microwave sintering is 3-5 kW, the temperature of the microwave sintering is 1600-1700° C., and the holding time of the microwave sintering is 30-60 min. The cooling process after the sintering is carried out in a mixed gas atmosphere of argon and hydrogen, and the volume ratio of argon to hydrogen is (0.1-10):

1. After the cooling is completed, a silicon carbide ceramic material is obtained.

9. A silicon carbide ceramic material, characterized in that: The silicon carbide ceramic material is prepared by the preparation method according to any one of claims 1 to 8.

10. A use of the silicon carbide ceramic material according to claim 9, characterized in that: The silicon carbide ceramic material is applied to at least one of a spacecraft thermal protection device, a nuclear reactor cladding material or a semiconductor device.

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