A method for preparing lightweight silicon carbide-boron carbide composite ceramics by reaction sintering, the composite ceramics prepared by the method and applications thereof

Abstract

The application belongs to the technical field of ceramic materials, and discloses a method for preparing lightweight silicon carbide-boron carbide composite ceramics by reaction sintering, the composite ceramics prepared by the method and application. The method comprises the following steps: mixing a carbon source and SiB6 powder, adding a solvent and ball milling medium, mixing, drying and sieving to obtain ceramic precursor powder; brushing a layer of BN on the inner surface of a graphite mold, then loading the ceramic precursor powder into the graphite mold, and performing discharge plasma sintering under the conditions of a temperature of 1650-2050 DEG C, a pressure of 20-35 MPa and an argon environment to prepare the composite ceramics. The composite ceramics have good mechanical properties, the hardness at room temperature is 30-35 GPa, the fracture toughness is 5-8 MPa·m 1 / 2 , and the bending strength is 500-800 MPa; the bending strength at a high temperature of 1200 DEG C is 300-500 MPa, and the composite ceramics can be used as mechanical parts of aircraft and in extreme environments.

Description

Technical Field

[0001] This invention belongs to the field of ceramic material preparation technology, and specifically relates to a method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering, the multiphase ceramics prepared therefrom, and their applications. Background Technology

[0002] With the rapid development of aerospace, high-speed transportation, and energy fields, structural materials are subject to multiple performance requirements, including high specific strength, high specific stiffness, high temperature resistance, corrosion resistance, and lightweight. Traditional metallic materials (such as steel and nickel-based alloys), while possessing good toughness and machinability, are prone to softening, oxidation, or creep at high temperatures, making them unsuitable for long-term service under extreme conditions. Compared to metallic materials, ultra-high temperature ceramic materials offer advantages such as high temperature resistance and strong oxidation resistance. With industrial development, increasingly stringent requirements are being placed on ultra-high temperature ceramics, with lightweight design being a crucial element. Lightweight high-performance ceramic materials are gradually becoming an important research direction for next-generation structural materials.

[0003] Silicon carbide (SiC) and boron carbide (B4C) are both covalently bond-dominated ultrahard ceramic materials, characterized by low density, high hardness, and high melting point, making them typical lightweight, high-performance structural materials. When combined, the overall density of the system is approximately 2.7-2.9 g·cm³. -3 It is significantly lower than the density of common metals (such as steel, which has a density of approximately 7.8 g·cm³). -3 ) and ultra-high temperature ceramics (such as ZrB2, with a density of approximately 6.1 g·cm³) -3 This composite design significantly reduces weight while maintaining high strength, making it an ideal system for achieving both lightweight and high performance. Furthermore, SiC possesses high modulus, high strength, and good thermal shock resistance, maintaining structural integrity at high temperatures; B4C has extremely high hardness and wear resistance, but relatively low toughness. Through SiC-B4C composite design, a mutually compensating microstructure can be formed: SiC provides strength and thermal shock resistance, while B4C provides hardness and lightweight characteristics. Both SiC and B4C exhibit excellent high-temperature chemical stability, especially with synergistic protective effects in oxidizing environments: SiC forms a dense SiO2 protective film at high temperatures; B4C oxidizes to form B2O3, which, after melting in the mid-temperature range, can form a glassy composite oxide film with SiO2, effectively preventing oxygen diffusion.

[0004] However, there are currently limited methods for preparing SiC-B4C multiphase ceramics. Most of them are obtained by direct mixing and sintering of powders. The SiC-B4C multiphase ceramics obtained by this direct sintering method require high-temperature sintering, which leads to abnormal grain growth and reduces the mechanical properties of the material. Summary of the Invention

[0005] To address the shortcomings and deficiencies in the existing technologies, the primary objective of this invention is to provide a method for preparing lightweight silicon carbide-boron carbide (SiC-B4C) multiphase ceramics by reaction sintering. This method employs reaction sintering, which lowers the sintering temperature, achieves sufficient densification, and produces fine and uniform grains, thereby obtaining SiC-B4C multiphase ceramics with excellent mechanical properties.

[0006] Another object of the present invention is to provide a lightweight silicon carbide-boron carbide multiphase ceramic prepared by the above preparation method.

[0007] Another object of the present invention is to provide the application of the above-mentioned lightweight silicon carbide-boron carbide multiphase ceramics.

[0008] The objective of this invention is achieved through the following technical solution: A method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering includes the following steps: mixing a carbon source with SiB6 powder, adding ball milling media and solvent, mixing, drying, and sieving to obtain ceramic precursor powder, wherein the carbon source is graphite or carbon black; brushing a layer of BN onto the inner surface of a graphite mold, then loading the ceramic precursor powder into the graphite mold, heating to 1650~2050℃, setting the pressure to 20~35MPa, and performing spark plasma sintering in an argon atmosphere to prepare lightweight silicon carbide-boron carbide multiphase ceramics.

[0009] The carbon source or SiB6 powder has a particle size of 1~3µm and a purity of ≥99.999wt%.

[0010] The molar ratio of the carbon source to SiB6 powder is 5:2; the sum of the masses of the carbon source and SiB6 powder is in the mass ratio of the milling media and the solvent to 1:5:3.

[0011] The heating rate is 50~150℃ / min, and the discharge plasma sintering time is 5~10min.

[0012] The temperature is raised to 1650°C; the preferred time for the discharge plasma sintering is 10 minutes.

[0013] The ball milling media are Si3N4 balls; the solvent is anhydrous ethanol; and the sieving is performed through an 80-1000 mesh sieve.

[0014] The preparation method is carried out according to the following chemical equation: 2SiB6 + 5C = 2SiC + 3B4C.

[0015] A lightweight silicon carbide-boron carbide multiphase ceramic prepared by the above method has a Vickers hardness of 30-35 GPa and a fracture toughness of 5-8 MPa·m at room temperature.1 / 2 The bending strength is 500~800MPa; the bending strength at 1200℃ is 300~500MPa.

[0016] The above-mentioned lightweight silicon carbide-boron carbide multiphase ceramics are used in ultra-high temperature environments.

[0017] The term "ultra-high temperature" refers to temperatures above 1200℃.

[0018] The aforementioned lightweight silicon carbide-boron carbide multiphase ceramics are used in the field of mechanical components for aircraft.

[0019] The present invention has the following advantages and beneficial effects compared with the prior art: Compared to traditional direct sintering methods, the reaction sintering method used in this invention has its own thermal driving force, which can reduce the sintering temperature, thereby obtaining SiC-B4C multiphase ceramics with good interfacial bonding strength and excellent mechanical properties. These ceramics exhibit a Vickers hardness of 30-35 GPa and a fracture toughness of 5-8 MPa·m at room temperature. 1 / 2 With a bending strength of 500~800MPa and a bending strength of 300~500MPa at 1200℃, SiC-B4C can be well applied in ultra-high temperature environments. It is lightweight, meets the load-bearing capacity requirements in industry, and is very suitable for mechanical parts of aircraft. Attached Figure Description

[0020] Figure 1 This is a phase equilibrium diagram of SiC-B4C ceramics at temperatures ranging from 25 to 2000℃. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0022] The carbon black and SiB6 powders used in the following examples all have a particle size of 1~3µm and a purity of ≥99.999wt%.

[0023] Example 1

[0024] (1) Weigh 1.25 mol of carbon black and 0.5 mol of SiB6 powder and mix them together. Then add anhydrous ethanol as solvent and Si3N4 grinding media. The total mass of carbon black and SiB6 powder is in the mass ratio of Si3N4 grinding media and anhydrous ethanol to 1:5:3. After mixing, drying and passing through an 80-mesh sieve, ceramic precursor powder is obtained. (2) A layer of BN is brushed onto the inner surface of the graphite mold. The ceramic precursor powder is placed into the graphite mold and heated to 1650℃ at a rate of 100℃ / min. The pressure is set to 30MPa, and discharge plasma sintering is performed in an argon atmosphere for 10 min to obtain lightweight SiC-B4C multiphase ceramic. Figure 1 As shown, at 1650℃, the phase equilibrium products are SiC and B4C.

[0025] The SiC-B4C multiphase ceramic prepared in this embodiment was tested and found to have a Vickers hardness of 35 GPa (Hv0.2) and a fracture toughness of 7 MPa·m at room temperature. 1 / 2 Its bending strength is 700 MPa; its bending strength at 1200℃ is 500 MPa.

[0026] Example 2

[0027] (1) Weigh 1.25 mol of carbon black and mix it with 0.6 SiB6 powder, then add anhydrous ethanol as solvent and Si3N4 grinding media. The total mass of carbon black and SiB6 powder is 1:5:3 in mass ratio with Si3N4 grinding media and anhydrous ethanol. After mixing, drying and passing through an 80-mesh sieve, ceramic precursor powder is obtained. (2) A layer of BN is brushed onto the inner surface of the graphite mold. The ceramic precursor powder is placed into the graphite mold and heated to 1950℃ at a rate of 100℃ / min. The pressure is set to 30MPa, and discharge plasma sintering is performed in an argon atmosphere for 10 min to obtain lightweight SiC-B4C multiphase ceramic. Figure 1 As shown, at 1950℃, the phase equilibrium products are SiC and B4C.

[0028] The SiC-B4C multiphase ceramic prepared in this embodiment was tested and found to have a Vickers hardness of 30 GPa (Hv0.2) and a fracture toughness of 5 MPa·m at room temperature. 1 / 2 Its bending strength is 400 MPa; its bending strength at 1200℃ is 500 MPa.

[0029] Example 3

[0030] (1) Weigh 1.25 mol of carbon black and 0.4 mol of SiB6 powder and mix them together. Then add anhydrous ethanol as solvent and Si3N4 grinding media. The total mass of carbon black and SiB6 powder is 1:5:3 in mass ratio with Si3N4 grinding media and anhydrous ethanol. After mixing, drying and passing through an 80-mesh sieve, ceramic precursor powder is obtained. (2) A layer of BN was brushed onto the inner surface of the graphite mold. The ceramic precursor powder was placed into the graphite mold and heated to 2050℃ at a rate of 100℃ / min. The pressure was set to 30MPa, and spark plasma sintering was performed in an argon atmosphere for 10 min to obtain lightweight SiC-B4C multiphase ceramic. Figure 1 As shown, at 2050℃, the phase equilibrium products are SiC and B4C.

[0031] The SiC-B4C multiphase ceramic prepared in this embodiment was tested and found to have a Vickers hardness of 24 GPa (Hv0.2) and a fracture toughness of 4.5 MPa·m at room temperature. 1 / 2 The bending strength is 400 MPa; the bending strength at 1200℃ is 300 MPa.

[0032] In summary, the lightweight SiC-B4C multiphase ceramics prepared by the reaction sintering method of this invention exhibit good mechanical properties, with a Vickers hardness of 24-35 GPa and a fracture toughness of 4.5-7 MPa·m at room temperature. 1 / 2 Its bending strength is 400~700MPa; its bending strength at 1200℃ is 300~500MPa, making it well-suited for ultra-high temperature extreme environments. Furthermore, due to its lightweight characteristics, it is very suitable for use in the mechanical components of aircraft.

[0033] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering, characterized in that... The process includes the following steps: mixing a carbon source with SiB6 powder, adding ball milling media and solvent, mixing, drying, and sieving to obtain ceramic precursor powder, wherein the carbon source is graphite or carbon black; brushing a layer of BN onto the inner surface of a graphite mold, then loading the ceramic precursor powder into the graphite mold, heating to 1650~2050℃, setting the pressure to 20~35MPa, and performing spark plasma sintering in an argon atmosphere to prepare lightweight silicon carbide-boron carbide multiphase ceramics.

2. The method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering according to claim 1, characterized in that: The carbon source or SiB6 powder has a particle size of 1~3µm and a purity of ≥99.999wt%.

3. The method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering according to claim 1, characterized in that: The molar ratio of the carbon source to SiB6 powder is 5:2; the sum of the masses of the carbon source and SiB6 powder is in the mass ratio of the milling media and the solvent to 1:5:

3.

4. The method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering according to claim 1, characterized in that: The heating rate is 50~150℃ / min, and the discharge plasma sintering time is 5~10min.

5. The method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering according to claim 1, characterized in that: The temperature is raised to 1650°C; the discharge plasma sintering time is 10 minutes.

6. The method for preparing lightweight silicon carbide-boron carbide multiphase ceramics by reaction sintering according to claim 1, characterized in that: The ball milling media are Si3N4 balls; the solvent is anhydrous ethanol; and the sieving is performed through an 80-1000 mesh sieve.

7. A lightweight silicon carbide-boron carbide multiphase ceramic prepared by the method according to any one of claims 1 to 6, characterized in that: The lightweight silicon carbide-boron carbide multiphase ceramic has a hardness of 24~35 GPa and a fracture toughness of 4.5~7 MPa·m at room temperature. 1 / 2 The bending strength is 400~700MPa; the bending strength at 1200℃ is 300~500MPa.

8. The application of the lightweight silicon carbide-boron carbide multiphase ceramic according to claim 7 in the field of ultra-high temperature environment.

9. The application according to claim 8, characterized in that: The term "ultra-high temperature" refers to temperatures above 1200℃.

10. The application of the lightweight silicon carbide-boron carbide multiphase ceramic according to claim 7 in the field of mechanical components of aircraft.

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