Silicon carbide ceramic material, method for producing the same, and use thereof

Abstract

This invention discloses a silicon carbide ceramic material, its preparation method, and its applications, belonging to the field of silicon carbide ceramic preparation technology. The preparation method involves sintering silicon carbide fibers under a vacuum atmosphere using discharge plasma. During the sintering process, a three-dimensional interlocking structure forms between the silicon carbide fibers, and the graphite carbon inside the fibers forms a conductive network, resulting in the silicon carbide ceramic material. This silicon carbide ceramic material exhibits high electrical conductivity, high fracture toughness, and excellent high-temperature stability.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramic preparation technology, and more specifically to a silicon carbide ceramic material, its preparation method, and its application. Background Technology

[0002] Silicon carbide (SiC) ceramics are widely used in high-temperature structural applications such as aerospace, nuclear energy, and military industries due to their excellent high-temperature strength, outstanding oxidation resistance, corrosion resistance, and good radiation resistance. However, intrinsic SiC, as a covalent compound, also exhibits high brittleness and low electrical conductivity, which severely limits its application in scenarios requiring both electrical conductivity and structural functionality, such as high-temperature electrodes, electromagnetic windows, and high-performance heating elements.

[0003] Currently, the main technical approaches for preparing conductive SiC ceramics both domestically and internationally include: second-phase composite reinforcement, doping modification, and traditional powder sintering. Second-phase composite reinforcement involves introducing free carbon, carbon nanotubes, graphene, or metallic phases to construct conductive pathways. For example, polymer precursor infiltration and pyrolysis (PIP) or chemical vapor infiltration (CVI) processes can be used to introduce a carbon phase into the SiC matrix. However, these methods are often complex, time-consuming, and costly, and the second phase is prone to agglomeration and uneven distribution, making it difficult to maintain excellent high-temperature mechanical properties and structural uniformity while achieving high conductivity. Doping modification involves introducing elements such as boron, aluminum, and nitrogen to alter the band structure of SiC and improve its intrinsic conductivity. While this method effectively improves conductivity, it typically requires extremely high sintering temperatures or special atmospheres, and excessive dopants can introduce lattice defects, leading to grain boundary phase formation and consequently degrading the material's high-temperature strength, creep resistance, and oxidation resistance. Traditional powder sintering involves preparing bulk SiC ceramics using processes such as hot pressing (HP) or hot isostatic pressing (HIP). This method yields materials with high density, but generally low fracture toughness (typically 3 MPa·m). 1 / 2 ~4MPa·m 1 / 2 Furthermore, the improvement in electrical conductivity depends on the introduction of the aforementioned second phase or dopant, which faces the same problem. In addition, the high strength of covalent bonds makes SiC densification extremely difficult during sintering, often requiring the addition of sintering aids, which in turn introduces low-melting-point phases and impairs the high-temperature performance of the material.

[0004] While pursuing high electrical conductivity, how to balance or even improve the fracture toughness of materials is the core challenge for their engineering applications. Most existing technical solutions involve performance trade-offs, with improvements in electrical conductivity often at the expense of mechanical properties or high-temperature stability. Summary of the Invention

[0005] To address the above problems, this invention provides a silicon carbide ceramic material, its preparation method, and its application. This silicon carbide ceramic material exhibits high electrical conductivity, high fracture toughness, and excellent high-temperature stability.

[0006] The first objective of this invention is to provide a method for preparing silicon carbide ceramic materials, characterized by comprising the following steps:

[0007] Silicon carbide fibers are subjected to discharge plasma sintering in a vacuum atmosphere. During the sintering process, a three-dimensional interlocking structure is formed between the silicon carbide fibers, and a conductive network is formed between the graphite carbon inside the silicon carbide fibers, thus obtaining silicon carbide ceramic materials.

[0008] In the preparation of silicon carbide fibers using the discharge plasma sintering method, the synergistic effect of plasma spark discharge and axial pressure is utilized to achieve densification.

[0009] In a preferred embodiment of the present invention, the sintering temperature during discharge plasma sintering is 1600℃~1900℃.

[0010] In a preferred embodiment of the present invention, the sintering time during discharge plasma sintering is 8 min to 15 min.

[0011] In a preferred embodiment of the present invention, the sintering time during discharge plasma sintering is 10 minutes.

[0012] In a preferred embodiment of the present invention, the pressure during discharge plasma sintering is 45MPa~55MPa.

[0013] In a preferred embodiment of the present invention, the pressure during discharge plasma sintering is 50 MPa.

[0014] The temperature, pressure, and holding time during the SPS process need to be precisely controlled. Insufficient temperature or pressure will limit the densification kinetics, while excessively high parameters will directly damage the fiber's microstructure. Secondly, too short a holding time will not achieve a strong bond between fibers, while too long a holding time will induce abnormal growth of SiC grains and a sharp degradation of fiber properties. Therefore, an optimal balance must be struck between "interfacial bonding strength" and "fiber property retention."

[0015] A second objective of this invention is to provide a silicon carbide ceramic material prepared by the above-described method. The silicon carbide ceramic material prepared by this invention possesses both high mechanical properties and high electrical conductivity. The superior properties of this material stem from its unique microstructure: graphitized carbon and silicon carbide grains together form a continuous conductive network, and the fiber monomers are in close contact and bonded together.

[0016] The third objective of this invention is to provide the application of the aforementioned silicon carbide ceramic material in the field of electrothermal materials, specifically in high-temperature electrothermal materials with high electrical conductivity, high thermal conductivity, and good fracture toughness.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention successfully prepared a novel SiC ceramic material using silicon carbide fiber as raw material via spark plasma sintering (SPS). It successfully sintered pure fiber into a dense SiC ceramic, achieving significant technical advantages. This process integrates the high fracture toughness of the fiber with the high electrical conductivity based on a graphite network, overcoming the limitations of traditional SiC ceramics such as brittleness, difficulty in processing, and low electrical conductivity. The material exhibits excellent comprehensive properties including high fracture toughness, high electrical conductivity, good thermal conductivity, and high-temperature stability. The fracture surface displays a typical serrated crack deflection path, indicating that it inherits the toughening mechanism of the fiber, and its fracture toughness is far superior to that of traditional bulk SiC ceramics. At 700°C, the electrical conductivity reaches 1510 S / m, far exceeding that of traditional SiC ceramics (~537 S / m), meeting the requirements for efficient electrical transport. The thermal conductivity remains at 39 W·m at the highest test temperature. -1 ·K -1 It possesses both excellent heat transfer and thermal shock stability. The material uses SiC fiber as a matrix, inheriting its superior high-temperature oxidation resistance and chemical stability.

[0019] This invention adopts a pure fiber sintering path and uses SPS technology to achieve spot welding of fibers, forming a unique three-dimensional interlocking structure, thereby simultaneously obtaining high toughness and high conductivity that are not available in traditional powder-sintered SiC ceramics. Therefore, the raw materials and preparation process have good innovation. (1) The material uses a single component (pure SiC fiber) as raw material, avoiding complex multiphase batching, simplifying the process flow, and reducing the uncertainty caused by the introduction of the second phase. (2) The material has the characteristics of high toughness, high conductivity, and high temperature resistance, which makes it show great application potential in the fields of high temperature electrodes, special heating elements, aerospace thermal structural components, and nuclear industry cladding materials. Attached Figure Description

[0020] Figure 1XRD patterns and Raman diagrams of different SiC fiber ceramics are shown, where (a) is the XRD pattern of SiC fiber ceramics at different sintering temperatures and (b) is the Raman diagram of SiC fiber ceramics at different sintering temperatures.

[0021] Figure 2 The images show the crack propagation paths and fracture modes of SiC fiber ceramics sintered at 1900℃. (a) is a scan image with a scale bar of 50μm, (b) is a scan image with a scale bar of 20μm, (c) is a scan image with a scale bar of 10μm, and (d) is a scan image with a scale bar of 2μm.

[0022] Figure 3 The stress-strain curve of SiC fiber ceramics at a sintering temperature of 1900℃ is shown.

[0023] Figure 4 The images show the scanning image, optical photograph, and indentation image of SiC fiber ceramics sintered at 1900℃. Among them, (a) is the scanning image of the polished surface of SiC fiber ceramics sintered at 1900℃, (b) is the optical photograph of the polished surface of SiC fiber ceramics sintered at 1900℃, (c) is a two-dimensional image of the prismatic indentation area produced by the diamond indenter on the polished surface of SiC fiber ceramics sintered at 1900℃, and (d) is a three-dimensional image of the prismatic indentation area produced by the diamond indenter on the polished surface of SiC fiber ceramics sintered at 1900℃.

[0024] Figure 5 The graph shows a comparison of the conductivity and resistance of SiC fiber ceramics and traditional SiC ceramics. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] High electrical conductivity in ceramic materials requires high density and a large number of free charge carriers. However, pure SiC powder is strongly covalently bonded with an extremely low self-diffusion coefficient, making it almost impossible to densify through solid-state sintering even at extremely high temperatures (>2000°C). Liquid-phase sintering aids are often introduced, and these aids (usually oxides) often remain as glassy phases at the grain boundaries after sintering. These glassy phases severely degrade the high-temperature properties of ceramics: at high temperatures, the glassy phase softens, leading to a sharp decrease in material strength and compromised high-temperature stability. Secondly, the synthesized glassy phase is an insulator, blocking conductive pathways and significantly reducing the overall electrical conductivity of the material. Furthermore, the fracture toughness (K0.05) of highly covalently bonded pure SiC ceramics is also affected. IC Very low (approximately 3 MPa·m) 1 / 2 ~4MPa·m 1 / 2 Achieving high fracture toughness is also a major challenge. The main toughening mechanisms include fiber / whisker toughening, where the introduction of SiC fibers or whiskers consumes a large amount of energy through crack deflection, bridging, and pull-out mechanisms; this is the most effective toughening method. Alternatively, self-toughening can be achieved by growing long columnar or plate-like SiC grains through process control. However, this, in turn, disrupts the uniformity of electrical conductivity in the SiC matrix, reducing the overall conductivity. Therefore, it is often difficult to simultaneously achieve high conductivity, high fracture toughness, and excellent high-temperature stability. Special sintering methods or optimized material composition and microstructure design are required. Therefore, developing a novel SiC ceramic material preparation technology with a relatively simple process that can simultaneously achieve high conductivity, high fracture toughness, and excellent high-temperature stability has become an urgent need in this field.

[0027] This invention innovatively utilizes single-component pure SiC fibers as raw materials and successfully prepares novel SiC fiber ceramics with high density, high fracture toughness, high electrical conductivity, and good thermal conductivity through spark plasma sintering (SPS) technology, demonstrating significant application potential in the field of high-temperature electrode materials.

[0028] The main technical problems to be solved in the preparation of this invention include: the difficulty of densification of SiC fibers during sintering, and how to effectively retain the reinforcing and toughening effects of the fibers while improving density, and achieving synergistic optimization of the material's electrical and thermal properties. Specifically, how to achieve a strong bond between fibers without damaging the fiber structure. SiC fibers themselves have low sintering activity and are prone to grain growth and phase transformation from β-SiC to α-SiC under high-temperature conditions, leading to fiber strength degradation and the loss of the toughening effect of the fibers in the final material. At the same time, excessively high temperatures or pressures can cause the fibers to collapse, losing their high aspect ratio morphological advantages, thus failing to induce subsequent toughening mechanisms such as crack deflection and fiber pull-out. How to eliminate residual porosity and obtain high density while maintaining the fiber network structure. Pure fiber stacked blanks contain a large number of macroscopic pores, and traditional sintering methods are difficult to effectively eliminate pores without damaging the fibers. Low density will seriously affect the material's electrical conductivity, thermal conductivity, and mechanical strength.

[0029] To address the aforementioned technical problems, the core innovation of this invention lies in employing spark plasma sintering (SPS) technology as a solution. SPS technology, through rapid heating generated by pulsed high current, the electric field diffusion effect, and the discharge activation between particles, can preferentially induce localized high temperatures and surface activation at the contact points between fibers at relatively low sintering temperatures and within a short time. This greatly promotes surface diffusion and grain boundary diffusion between fibers, thereby achieving "spot welding" of the fibers. This method can form a robust neck connection between fibers while avoiding excessively high overall temperatures that could degrade fiber performance, ultimately sintering into a dense, three-dimensionally interlocked SiC fiber ceramic. This material retains the high strength and high aspect ratio characteristics of the original fibers, thus possessing excellent fracture toughness (crack propagation path is serrated); and because the SPS process may promote carbon segregation or graphitization on the fiber surface, forming a continuous conductive network, it also endows the material with a significantly higher electrical conductivity than traditional SiC ceramics.

[0030] In summary, this invention achieves a strong bond between fibers through material selection and a short-time, high-efficiency SPS preparation process, while maximizing the preservation of the fibers' inherent superior properties. It effectively solves the technical challenges of sintering densification and synergistic control of multiple properties in SiC fiber ceramics, providing a new approach for the preparation of high-performance SiC-based high-temperature structural-functional integrated ceramics.

[0031] This invention selects pure SiC fibers as raw materials and achieves densification through spark plasma sintering. By forming a continuous conductive network within the SiC fiber ceramic through high-temperature sintering, the compatibility problems common in multiphase composites are avoided, achieving a synergistic improvement in high conductivity and high toughness. The process has a short cycle time, low energy consumption, and eliminates the need for complex subsequent silicon infiltration treatments. This patent has outstanding advantages in terms of material system simplicity, conductivity stability, process controllability, and environmental friendliness, making it particularly suitable for applications with extremely high requirements for synergistic electro-thermal-mechanical performance, such as high-temperature electrodes, aerospace thermal structural components, and nuclear industry cladding.

[0032] The silicon carbide fibers used in this invention have a diameter of 10-20 μm and were purchased from Fujian Liya New Materials Co., Ltd. They belong to the third generation of silicon carbide fibers, with a C / Si atomic ratio close to 1:1. They are mainly composed of equiaxed β-SiC nanocrystals (grain size typically between 50-500 nm). These nanocrystals are not completely randomly arranged, but exhibit a certain degree of preferred orientation, with the <111> crystal orientation tending to align along the fiber axis. This orientation structure significantly contributes to the fiber's high modulus. The fiber contains relatively little free carbon.

[0033] If high-oxygen-content SiC fibers are selected, a decomposition reaction will occur at high temperatures (>1200°C): SiC + O2 → SiO2 + CO, accompanied by rapid grain growth. This leads to a sharp decrease in fiber strength, making it impossible to guarantee the mechanical properties of the fiber ceramics during sintering. If low-oxygen, carbon-rich SiC fibers are selected, the thermal stability is improved compared to high-oxygen-content SiC fibers by reducing the oxygen content during the preparation of SiC fiber ceramics, but the overall high-temperature stability is still low. The Cansas-3301 high-crystallinity SiC fiber produced by Fujian Liya New Materials Co., Ltd., used in this invention, is almost pure SiC with extremely low oxygen and free carbon content. This allows it to maintain excellent mechanical properties and structural stability even above 1600°C. Its microstructure consists of coarse, stable β-SiC grains, inhibiting recrystallization and performance degradation at high temperatures. In the high-purity matrix of the high-crystallinity SiC fiber, there are no impurities such as oxygen to interfere with this process. These displaced carbon atoms can migrate and aggregate freely, self-assembling along the boundaries of SiC grains into a continuous, nanoscale network. Before high-temperature heat treatment (e.g., 1900°C), this excess carbon may be "locked" in the amorphous SiCx structure in an amorphous form or exist as amorphous carbon at grain boundaries, but in very small amounts, insufficient to form a continuous conductive network. At the high temperature of 1900°C, these newly formed continuous carbon networks rapidly undergo structural ordering, transforming from a disordered layered structure into a highly crystalline graphitic carbon structure.

[0034] Example 1

[0035] Continuous silicon carbide fibers were cut to a length of 1-2 mm and poured into a graphite mold. Graphite paper was used to isolate the mold and powder to prevent direct contact between them. Under a vacuum atmosphere, the sample was placed in a spark plasma sintering furnace and sintered at 1600°C for 10 min with an axial pressure of 50 MPa to obtain SiC fiber ceramics.

[0036] Example 2

[0037] Continuous silicon carbide fibers were cut to a length of 1-2 mm and poured into a graphite mold. Graphite paper was used to isolate the mold and powder to prevent direct contact between them. Under a vacuum atmosphere, the sample was placed in a spark plasma sintering furnace and sintered at 1800°C for 10 min with an axial pressure of 50 MPa to obtain SiC fiber ceramics.

[0038] Example 3

[0039] Continuous silicon carbide fibers were cut to a length of 1-2 mm and poured into a graphite mold. Graphite paper was used to isolate the mold and powder to prevent direct contact between them. Under a vacuum atmosphere, the sample was placed in a spark plasma sintering furnace and sintered at 1900°C for 10 min with an axial pressure of 50 MPa to obtain SiC fiber ceramics.

[0040] Comparative Example 1

[0041] Silicon carbide powder was poured into a graphite mold, and the sample was placed in a spark plasma sintering furnace under a vacuum atmosphere. The sintering temperature was 1900°C, the temperature was held for 10 min, and an axial pressure of 50 MPa was applied to perform SPS sintering to obtain SiC ceramics.

[0042] Using an electrical discharge machining (EDM) CNC cutting machine (Beijing Ninghua Technology Co., Ltd., NH400), the voltage was set to 120 V, the current to 2.4 A, the pulse duration to 64 μs, the pulse gap to 7 μs, and the servo feed rate to 8 m / min. The sample was then cut to the dimensions specified for testing, and then the mechanical, electrical, and thermal properties were tested.

[0043] The bulk density and porosity of the samples were tested using mercury intrusion porosimetry. The flexural strength of the samples was tested using a ceramic universal testing machine. The fracture toughness of the samples was tested using indentation. The phase composition of the samples was characterized by X-ray diffraction and Raman spectroscopy. The surface morphology of the samples was observed using a super depth-of-field 3D microscope. The electrical conductivity (σ) of the samples was tested using a CTA-3 (Beijing, Creo) instrument under low-pressure helium atmosphere using the standard four-probe method. The test samples were cuboids with dimensions of approximately 3 mm × 3 mm × 10 mm. The thermal diffusivity of the material was obtained using a Netzsch LFA 457 instrument. Then, the thermal conductivity of the material at the test temperature is obtained according to the formula. (T), sample size is approximately 10×10×2 mm 3 .

[0044] ;

[0045] in, (T) is the thermal diffusivity at the test temperature. ρ The sample density is C, which is measured using the Archimedes method. p (T) represents the heat capacity at the test temperature, which is calculated using the Dulong-Petit law.

[0046] from Figure 1 As can be seen from (a) in the figure, the main crystalline phases in SiC fiber ceramics are SiC and graphite C. With increasing sintering temperature, the diffraction peaks of graphite C in SiC fiber ceramics gradually increase. According to... Figure 1 The Raman spectrum in (b) shows that at 1350 cm⁻¹ -1 and 1580 cm -1 Distinct absorption peaks appeared nearby, corresponding to the D and G peaks of carbon materials, respectively. Only the TO peak of SiC was observed in the spectrum; no other characteristic peaks were detected. This is mainly because the Raman excitation efficiency of the C-C bond is significantly higher than that of the Si-C bond, causing the dominant C-C bond response to potentially mask the Si-C signal. The D peak represents the degree of defects or disorder in the carbon structure, while the G peak reflects the ordered graphite structure of sp² hybridized carbon. With increasing sintering temperature, the intensity of the G peak significantly increased, and the I... D / I G The ratio gradually decreases, indicating that the degree of ordering of graphitic carbon in the material increases and defects decrease, further confirming the trend of graphitization degree with increasing temperature observed in XRD. Figure 1 In this context, 2θ is denoted as 2 theta, and intensity is denoted as Intensity. Raman shift is denoted as Raman shift.

[0047] Figure 2The crack propagation path and fracture morphology of SiC fiber ceramic fracture surfaces are shown. It is evident that the high aspect ratio and high strength of SiC fibers effectively promote crack deflection at the fiber-matrix interface or within the fiber's own fracture surface, forming a typical serrated propagation trajectory. This tortuous crack path significantly prolongs the crack propagation distance, consumes more fracture energy, and thus significantly improves the overall fracture toughness of the material.

[0048] from Figure 3 As shown in the stress-strain curve, during the main stress increase phase, the curve exhibits a multi-step growth characteristic. This unique deformation behavior indicates that the material does not undergo sudden overall fracture during loading, but rather achieves phased energy dissipation through the gradual fracture of internal SiC fibers. The fracture of each fiber requires additional strain energy consumption, thus macroscopically manifesting as multiple step-like increases in stress. This fracture mechanism significantly improves the material's fracture toughness and damage tolerance, enabling it to exhibit non-brittle fracture characteristics during load-bearing, demonstrating a good synergistic effect of strength and toughness. Its fracture toughness reaches 6.11 MPa·m. 1 / 2 It is significantly superior to traditional SiC ceramics. Figure 3 In this context, deformation is denoted as Deformation, and force is denoted as Force.

[0049] Figure 4 (a) and Figure 4 Image (b) shows the SEM and optical images of the polished surface of SiC fiber ceramics sintered at 1900°C. The silicon carbide fiber ceramics sintered at 1900°C exhibit a highly dense textured microstructure. The fiber alignment is mainly perpendicular to the sintering pressure direction. Although the increased sintering temperature leads to grain growth within the silicon carbide fibers, the applied sintering pressure effectively suppresses surface roughening, and the overall fiber diameter remains essentially unchanged. This morphological and structural stability maintained under high-temperature conditions helps mitigate the degradation of the material's mechanical properties. Figure 4 Images (c) and (d) show the two-dimensional and three-dimensional morphologies of the rhomboid indentations produced by Vickers hardness testing on the polished surface of silicon carbide fiber ceramic sintered at 1900°C. The clear and complete indentation outlines indicate that the silicon carbide fiber ceramic possesses good plastic deformation capacity and fracture toughness. The three-dimensional morphology further reveals the height variations in the indentation area and its surroundings: the interior of the indentation is relatively flat with slight bulges at the edges, and obvious crack deflection is visible near the indentation. These characteristics indicate that the ceramic material can effectively resist brittle fracture.

[0050] Figure 5The electrical conductivity and resistivity of SiC fiber ceramics and conventional SiC ceramics were compared. The electrical conductivity of both types of ceramics increased with increasing test temperature, while the resistivity decreased. The room temperature electrical conductivity of pure SiC fiber ceramics was approximately 183 S / m, higher than the 57 S / m of conventional SiC ceramics. At 700℃, the electrical conductivity of SiC whisker ceramics reached 1510 S / m, significantly higher than the 537 S / m of conventional SiC ceramics at the same temperature. Furthermore, the rate of increase in electrical conductivity with increasing temperature was higher for SiC fiber ceramics than for conventional SiC ceramics. Figure 5 In this context, temperature is denoted as Temperature and electrical conductivity as Electrical conductivity.

[0051] Although traditional SiC ceramics possess semiconductor properties, their wire cutting process still faces challenges such as low processing efficiency, high surface roughness, and difficulty in subsequent grinding and polishing. The SiC fiber ceramics prepared in this invention, with their high electrical conductivity, ensure a faster material removal rate during processing, facilitating the fabrication of complex structures of various shapes and sizes. The high electrical conductivity of SiC fiber ceramics is primarily due to the high graphite carbon content in pure SiC fiber ceramics. Furthermore, with increasing sintering temperature, the amount of graphitized carbon significantly increases, forming a continuous conductive permeation network within the SiC fibers, which significantly improves the overall conductivity of the sample. In contrast, if silicon carbide powder is used as the raw material and additional graphite carbon is added, while this will improve conductivity to some extent, the increase will be significantly lower than that achieved by the formation of high-temperature graphite carbon within the silicon carbide fibers. Firstly, the conductive network formed by graphite carbon within the fibers of silicon carbide fiber ceramics is embedded, three-dimensionally continuous, and symbiotic with the structural framework. This process readily forms a conductive permeation network with high efficiency, achieving a significant leap in overall conductivity with minimal graphite carbon. In contrast, the SiC powder with added graphite carbon powder, after mechanical mixing and sintering, exhibits conductivity dependent on the pathways formed by the contact between graphite particles. To form a conductive network, a high volume fraction of graphite is typically required, far exceeding the amount of graphite carbon formed in situ at high temperatures within the fiber ceramic. Furthermore, the conductive network composed of graphite particles is random and unstable. Secondly, the interface between the graphite carbon precipitated in situ in the fiber ceramic and the SiC grains is atomically tight, formed through phase separation into a coherent or semi-coherent interface. Phonons and electrons can transport efficiently between the interfaces, contributing to the maintenance of high thermal and electrical conductivity. In the SiC powder with added graphite system, the graphite particles and SiC powder are in physical contact, resulting in poor interfacial bonding. Phonons are severely scattered upon reaching this weak interface, and the graphite particles have limited effect on improving the fracture toughness of silicon carbide ceramics. Finally, the graphite carbon generated in situ at high temperatures within SiC fibers is nanoscale, possesses high intrinsic conductivity, and its distribution is determined by the SiC grain boundary network, exhibiting uniformity and continuity. The graphite powder added to SiC powder is typically micron or submicron in size, and it is prone to agglomeration during mixing, resulting in uneven distribution within the matrix. Even when using carbon nanotubes or graphene, dispersion remains a significant challenge. Therefore, directly adding graphite carbon to SiC powder cannot replicate the superior overall performance resulting from in-situ graphite carbon generation within SiC fibers.

[0052] CN100457683C discloses a conductive silicon carbide foam ceramic material with controllable resistivity and its preparation method. The silicon carbide foam ceramic uses polygonal closed rings as basic units, and the basic units are interconnected to form a three-dimensional connected network. The relative density of the ceramic ribs constituting the polygonal closed ring units is ≥99%. By weight fraction, its composition consists of 80% to 96% silicon carbide, 10% to 2% metallic phase, and 10% to 2% silicon. The resistivity ranges from 5 Ω·cm to 0.01 Ω·cm.

[0053] CN119410992A discloses a silicon carbide-based composite material with high conductivity and high toughness, its preparation method, and its application. This silicon carbide-based composite material consists of a SiC matrix containing an α-phase and β-phase dual-phase structure and a eutectic high-entropy alloy distributed in a network pattern. The two components work synergistically, effectively balancing high conductivity and high toughness, while also reducing the sintering temperature and increasing the material's density, thereby achieving comprehensive optimization of the material's properties.

[0054] CN118359440A discloses a high thermal conductivity spark plasma sintered silicon carbide ceramic material and its preparation method. The raw materials for this high thermal conductivity spark plasma sintered silicon carbide ceramic material, by mass percentage, include 85-98 wt.% submicron-sized silicon carbide powder, 0.01-2 wt.% micron-sized silicon carbide powder, 1-10 wt.% rare earth oxides, 0.5-3 wt.% magnesium oxide, 0.01-2 wt.% carbon, and 0.5-2 wt.% dispersant. This invention patent, based on a raw material system using submicron-sized silicon carbide powder as raw material and rare earth oxides as sintering aids, adds magnesium oxide as a second sintering aid, significantly reducing the eutectic point and viscosity of the liquid phase. This effectively promotes mass transfer efficiency during sintering, improves densification and grain growth efficiency, thereby enhancing the thermal conductivity of SiC ceramics.

[0055] Compared with the aforementioned invention patents, this invention uses silicon carbide fiber as the reinforcing phase and matrix raw material; the conductive reinforcing phase is in-situ generated graphitized carbon; the material is integrally and densely formed through a spark plasma sintering process. Compared with the prior art, the beneficial effects of this invention are: by synergistically controlling the sintering temperature, pressure, and holding time, a functional-structural integrated material with a room temperature conductivity of not less than 180 S / m and a high-temperature (700℃) conductivity of not less than 1500 S / m, while exhibiting significantly higher fracture toughness than traditional silicon carbide ceramics, has been successfully prepared. This material exhibits typical ductile fracture behavior and uniform spark processing characteristics, and can meet the requirements for conductivity, structure, and weather resistance under extreme environments such as high temperature and strong corrosion.

[0056] Therefore, this invention differs significantly from the above: In the preparation process, when multiphase composites are used, compatibility issues arise. On one hand, the added conductive phase and the SiC matrix, due to physical or chemical incompatibility, form a weak interface. This easily leads to stress concentration points, and under load, cracks preferentially propagate along this weak interface, reducing the overall mechanical properties of the material. On the other hand, heterogeneous interfaces are typically "high-energy-barrier regions" for electron scattering, resulting in a sharp increase in contact resistance. Poor compatibility leading to interface porosity, defects, or chemical reaction layers can interrupt or hinder the formation of these channels, destroying the conductive pathway. Because the interface state is difficult to precisely control, the final electrical properties are often unstable and have poor repeatability. In terms of raw materials, this invention uses single-component silicon carbide fiber as a precursor, forming a continuous conductive network and reinforcing structure through in-situ conversion, thus avoiding the common compatibility problems of multiphase composites.

[0057] Regarding the conductivity mechanism, this invention relies on the in-situ generation and diffusion connection of graphite carbon within the fibers to construct a continuous conductive network, achieving high conductivity without adding any conductive phase. In terms of process, spark plasma sintering (SPS) is employed to achieve strong bonding and efficient densification of the fiber-fiber interface at a lower temperature and in a shorter time. The process cycle is short, energy consumption is low, and there is no need for subsequent silicon infiltration or complex treatments such as adding sintering aids and conductive phases. In existing technologies, CN109999870A, CN120573707A, and CN119410992A introduce a highly conductive second phase (such as carbon nanotubes, graphene, carbon black, metal particles, etc.) into the SiC matrix. When the content of the second phase exceeds a critical value (percolation threshold), they will contact each other in the matrix, forming a three-dimensional continuous conductive network through which electrons are mainly transported. In CN120504545A, elements such as B, Al, N, and P are introduced during the sintering process. By replacing C or Si atoms in the crystal lattice, impurity energy levels are introduced into the wide bandgap of SiC, thereby increasing the intrinsic carrier concentration and significantly reducing its bulk resistance. In CN108298542A, a continuous ultrathin conductive layer (such as pyrolytic carbon, graphene, or a metal coating) is pre-deposited or formed on the surface of SiC ceramics or fibers, and a conductive path is constructed through the external conductive layer.

[0058] The innovation of this invention lies in avoiding the common interfacial compatibility problems in multiphase composite materials from the source of raw materials and processes. This invention uses single-component silicon carbide fiber as a precursor, and through a precisely controlled SPS process, it transforms in situ during sintering to construct a continuous conductive network. Regarding the conductivity mechanism, unlike the percolation model that relies on an added conductive phase, and unlike the intrinsic conductivity model that alters the band structure through heterogeneous doping, it relies on the in-situ generation and diffusion of graphite carbon on the fiber surface. This achieves a synergistic improvement in high conductivity and excellent mechanical properties without introducing any heterogeneous conductive phase. This "structure-function integration" design effectively avoids problems such as weak bonding, high resistance, and premature performance degradation caused by poor interfacial compatibility, ensuring a high degree of uniformity and reliability in material structure and performance.

[0059] This invention has outstanding advantages in terms of material system simplicity, electrical conductivity stability, high temperature performance retention, and process controllability. It is particularly suitable for applications with extremely high requirements for synergistic electro-thermal-mechanical performance, such as high temperature electrodes, aerospace thermal structural components, and nuclear industry cladding.

[0060] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0061] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing silicon carbide ceramic material, characterized in that, Includes the following steps: Silicon carbide fibers are subjected to discharge plasma sintering in a vacuum atmosphere. During the sintering process, a three-dimensional interlocking structure is formed between the silicon carbide fibers, and a conductive network is formed between the graphite carbon inside the silicon carbide fibers, thus obtaining silicon carbide ceramic materials. During discharge plasma sintering, the sintering temperature is 1600℃~1900℃, the sintering time is 8min~15min, and the pressure is 45MPa~55MPa.

2. The method for preparing a silicon carbide ceramic material according to claim 1, characterized in that, During discharge plasma sintering, the sintering time is 10 minutes.

3. The method for preparing a silicon carbide ceramic material according to claim 1, characterized in that, The pressure during discharge plasma sintering is 50 MPa.

4. A silicon carbide ceramic material prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the silicon carbide ceramic material according to claim 4 as an electrothermal material.

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