An anisotropic SiC (B4C) / h-BN composite ceramic sealing ring and a preparation method thereof

Abstract

The application discloses an anisotropic SiC (B4C) / h-BN composite ceramic sealing ring and a preparation method thereof, and relates to the technical field of high-temperature sealing materials. The sealing ring comprises a heat-conducting framework composed of h-BN flaky particles arranged along the ring plane, and a SiC-B4C composite binding phase generated by in-situ conversion of polycarbosilane and trimethyl borate. The preparation method comprises the following steps: coating a precursor interface on the h-BN; mixing the h-BN with a thermoplastic bonding system to obtain a high-solid-content slurry; performing stage-by-stage progressive pressure loading and die forming to arrange the flaky particles in a directional manner; performing segmented thermal debinding; performing reaction sintering to generate the SiC-B4C composite phase; and finally performing hot isostatic pressing. Through the construction of an orientation structure and the cooperative conversion of double precursors, the radial thermal conductivity of the sealing ring is significantly higher than the axial thermal conductivity, the mechanical properties can be adjusted and controlled, the interface bonding is strengthened, the sealing ring with high compactness, high thermal conductivity, anisotropy and excellent mechanical properties is obtained, and the sealing ring is suitable for high-temperature rotating equipment.

Description

Technical Field

[0001] This invention relates to the field of high-temperature sealing ceramic materials technology, specifically to an anisotropic SiC(B4C) / h-BN composite ceramic sealing ring and its preparation method. Background Technology

[0002] As high-end power equipment and high-temperature rotating machinery develop towards higher power density, higher speeds, and harsher service environments, sealing rings are subjected to high temperatures, friction and wear, cyclic thermal shocks, and complex stress coupling during long-term use. These conditions not only require materials to possess excellent high-temperature strength, wear resistance, and dimensional stability, but also to achieve a coordinated match between heat conduction and load-bearing capacity in different directions to reduce the risk of seal failure caused by heat accumulation and localized stress concentration. Among existing high-temperature sealing materials, carbon-based materials, while possessing certain self-lubricating properties, are prone to oxidation, ablation, and structural degradation in oxidizing environments. Metallic materials, under long-term high-temperature service conditions, are susceptible to thermal softening, creep deformation, and thermal fatigue damage, making it difficult to meet the requirements for dimensional stability and long-term reliability under high-temperature and high-load conditions. Therefore, advanced ceramic materials that combine high-temperature stability, high wear resistance, and structural stability are gradually becoming an important development direction for high-temperature sealing components.

[0003] In ceramic material systems, SiC(B4C) / h-BN composite ceramics combine the high thermal conductivity and high-temperature strength of silicon carbide, the high hardness and lightweight of boron carbide, and the layered self-lubricating properties of hexagonal boron nitride, exhibiting potential advantages in the synergistic effect of high thermal conductivity, wear resistance, and self-lubrication. However, if the component powders are directly mixed, molded, and sintered, physical contact interfaces are mainly formed between the phases. The degree of interfacial bonding and phase distribution are difficult to control effectively, easily introducing interface defects and residual porosity during sintering. The discontinuity of the interface structure not only increases the interfacial thermal resistance but may also form localized stress concentration areas during thermal cycling, affecting the long-term service stability of the material.

[0004] Furthermore, sealing rings exhibit significant directional performance requirements in actual service: they need to rapidly dissipate frictional heat in the radial direction, while bearing the main load in the axial direction. When the internal structure of the material is randomly distributed, it is difficult to achieve coordinated control of thermal conductivity and mechanical properties in different directions, thus limiting its performance under complex operating conditions.

[0005] Therefore, there is an urgent need to provide a SiC-B4C-h-BN composite ceramic sealing ring and its preparation method that can simultaneously achieve interface structure regulation, microstructure orientation construction and densification strengthening, so as to achieve directional regulation and synergistic optimization of thermal and mechanical properties while ensuring structural compactness, thereby meeting the application requirements of high-temperature sealing components in extreme service environments. Summary of the Invention

[0006] In view of the problems mentioned in the background art, the purpose of this invention is to provide an anisotropic SiC(B4C) / h-BN composite ceramic sealing ring and its preparation method, so as to solve the problems in the prior art of difficult control of composite ceramic interface structure, random microstructure orientation, difficulty in achieving directional matching of thermal and mechanical properties, and insufficient high-temperature service stability.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution: An anisotropic SiC(B4C) / h-BN composite ceramic sealing ring is provided, comprising: The thermally conductive framework structure formed by h-BN sheet-like particles; A SiC-B4C composite phase formed by high-temperature in-situ conversion of silicon-containing and boron-containing precursors; The h-BN flake particles are oriented along the plane of the sealing ring and form a continuous in-plane thermally conductive network structure, which makes the thermal conductivity of the sealing ring in the radial direction higher than that in the axial direction. The SiC-B4C composite bonding phase is distributed between and at the interface of the lamellar boron nitride, which enhances the interfacial bonding strength and improves the overall density.

[0008] As a further technical solution of the present invention, the silicon-containing precursor is polycarbosilane, and the boron-containing precursor is trimethyl borate.

[0009] As a further technical solution of the present invention, the aspect ratio of the h-BN flake particles is 5 to 10, and the volume fraction is 30% to 70%.

[0010] As a further technical solution of the present invention, the relative density of the composite ceramic sealing ring is not less than 95%.

[0011] A method for preparing an anisotropic SiC(B4C) / h-BN composite ceramic sealing ring is also provided, comprising the following steps: S1. Polycarbosilane is dissolved in an organic solvent to form a precursor solution, and then mixed with flake boron nitride to form a coating layer on the surface of boron nitride; subsequently, trimethyl borate is added for deposition treatment to obtain precursor-modified composite powder. S2. The composite powder is mixed with a thermoplastic binder system composed of paraffin, polyethylene and stearic acid, and sheared and kneaded under heating conditions to prepare a uniform slurry. S3. The slurry is placed in a mold, and thermoplastic molding flow orientation is performed in the molten state of the bonding system. By gradually applying pressure in stages, the sheet boron nitride rotates and rearranges during the melting flow and pressure process, and is oriented along the plane of the sealing ring to form a blank with an orientation structure. S4. Perform hot degreasing treatment on the green body to remove paraffin, polyethylene and stearic acid; S5. High-temperature sintering is carried out under a protective atmosphere to transform polycarbosilane and trimethyl borate in situ to form a composite phase and construct a continuous radial thermally conductive network structure. S6. The sintered body is subjected to hot isostatic pressing treatment. Under the action of high temperature and inert gas pressure, the material is further densified and the interfacial bonding is strengthened to obtain the final composite ceramic sealing ring.

[0012] As a further technical solution of the present invention, in step S1, the mass ratio of polycarbosilane to trimethyl borate is 2.5:1, and the amount of polycarbosilane used is 1.5 to 3.5 parts by weight, and the amount of trimethyl borate used is 0.6 to 1.4 parts by weight.

[0013] As a further technical solution of the present invention, in step S3, the staged progressive pressure loading includes: First, apply a pressure of 3-6 MPa to achieve slurry spreading and preliminary orientation adjustment of h-BN flake particles; Subsequently, a pressure of 8–18 MPa is applied to further induce the h-BN flake particles to rearrange along the plane of the sealing ring and form an oriented arrangement structure.

[0014] As a further technical solution of the present invention, in step S4, the thermal degreasing treatment is carried out by a segmented heating method, with a heating rate of 0.5 to 3°C / min.

[0015] As a further technical solution of the present invention, in step S5, the sintering temperature is 1700-1900℃, and the sintering atmosphere is an inert gas, preferably argon or nitrogen.

[0016] As a further technical solution of the present invention, the hot isostatic pressing treatment temperature is 1600-1750℃, the pressure is 100-150MPa, the holding time is 2-6h, and the hot isostatic pressing treatment atmosphere is argon.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) By constructing a controllable interface transition layer, the present invention achieves effective combination between the reinforcing phase and h-BN, reduces interface defects and interface thermal resistance, and improves the overall density and mechanical properties of the material; at the same time, the reinforcing phase is generated through in-situ reaction, avoiding the problems of uneven distribution of reinforcing phase and weak interface bonding in traditional simple mixing systems, forming a stable reinforcing network structure, thereby improving the structural stability of the material under high temperature friction conditions.

[0018] (2) The present invention constructs a microstructure with directional characteristics by directional molding, so that the material forms a differentiated structure in the radial and axial directions, thereby realizing the directional control of thermal conductivity and mechanical properties; wherein, the radial direction is conducive to the rapid dissipation of frictional heat, and the axial direction can provide a higher load-bearing capacity, thereby improving the service reliability of the sealing ring in high-temperature thermal cycling and complex stress coupling environment.

[0019] (3) By introducing hot isostatic pressing densification treatment, the present invention effectively reduces the residual porosity inside the material and strengthens the interface bonding, significantly improving the bending strength and structural integrity of the material; and through the synergistic effect between interface construction, orientation control and reaction sintering, it realizes the adjustable design of thermal and mechanical properties, providing a new technical path for the structural optimization and performance improvement of high-temperature sealed ceramic components. Attached Figure Description

[0020] Figure 1 This is a flowchart of the anisotropic SiC(B4C) / h-BN composite ceramic sealing ring of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0022] Example 1 like Figure 1 As shown, a method for preparing an anisotropic SiC(B4C) / h-BN composite ceramic sealing ring includes the following steps: S1. Preparation of precursor-modified composite powder Weigh 10 kg of hexagonal boron nitride (h-BN) powder (average particle size 10 μm, aspect ratio 7), 2.5 kg of polycarbosilane (PCS), and 1.0 kg of trimethyl borate (TMB). Dissolve the polycarbosilane in xylene to prepare a polycarbosilane solution with a mass fraction of 10–20 wt%. Stir magnetically for 30 min at room temperature until uniform and transparent. Add the flake-shaped boron nitride powder and continue stirring at 40–60 °C for 2 h to allow the polycarbosilane to be fully adsorbed onto the h-BN surface. The polycarbosilane is in a molecular-level dispersion in the solvent and is deposited on the boron nitride surface through interfacial adsorption. After drying, it forms a continuous precursor coating layer, thereby providing uniform interfacial reaction sites during subsequent sintering. Then, trimethyl borate was added dropwise to the above mixture at a rate of 0.5 to 1 mL / min and stirred continuously for 1 h to promote its uniform deposition on the h-BN surface. The resulting suspension was subjected to solvent evaporation treatment at 80 to 100 °C to obtain precursor-modified composite powder.

[0023] S2. Preparation of high solids content thermoplastic slurry Weigh 0.8 kg of paraffin wax, 0.2 kg of polyethylene micro powder, and 0.1 kg of stearic acid, add them to a mixing container, and heat to 135°C to completely melt the paraffin wax and polyethylene, forming a homogeneous thermoplastic binder system. Stearic acid acts as a dispersant to reduce interfacial tension and improve powder wettability. Under constant temperature conditions of 120–170°C, the precursor-modified composite powder is slowly added in batches to the molten system, and kneaded under continuous stirring and a certain shearing action for 1 hour to promote uniform dispersion of the powder in the binder system and inhibit particle agglomeration. During the kneading process, by controlling the addition rate and stirring intensity, the system gradually forms a high-solids slurry with stable viscoelastic characteristics, wherein the powder mass fraction is controlled at 66–70 wt%.

[0024] S3, Thermoplastic Compression Flow Orientation Molding The slurry was injected into a metal mold preheated to 100°C, and a staged progressive pressure loading method was adopted (pressure loading rate of 3 MPa / min). First, a pressure of 5 MPa was applied and held for 3 minutes to allow the slurry to spread fully and achieve initial orientation adjustment of the h-BN flake particles. Then, a pressure of 12 MPa was applied and held for 8 minutes to further induce the h-BN flake particles to rotate and rearrange during thermoplastic flow, forming an oriented arrangement structure along the plane of the sealing ring. After cooling and demolding, a preform with an oriented structure was obtained.

[0025] S4, Heat degreasing treatment The resulting preform was subjected to a segmented thermal debinding treatment in an inert atmosphere: the temperature was increased to 300℃ at 1℃ / min and held for 1 hour; then increased to 450℃ at 0.5℃ / min and held for 1 hour; finally, the temperature was increased to 800℃ at 2℃ / min and held for 1 hour. By gradually increasing the temperature, the organic binder was fully decomposed and removed, resulting in a porous inorganic framework that maintained the orientation structure, thereby preserving the orientation structure of the lamellar boron nitride while avoiding structural collapse.

[0026] S5, Reaction Sintering The degreased green body was sintered at high temperature under a nitrogen atmosphere, heated to 1800℃ at a heating rate of 4℃ / min and held for 1.5h. During this process, polycarbosilane and trimethyl borate underwent pyrolysis and in-situ reaction, gradually forming Si-C and BC-related intermediate phases at 1200–1500℃, and transforming into a silicon carbide (SiC) and boron carbide (B4C) composite phase at higher temperatures. The in-situ generated SiC and B4C formed a continuous bridging structure between the h-BN layers, simultaneously achieving preliminary densification and interfacial bonding strengthening of the material, resulting in an initial composite ceramic sintered body with an anisotropic thermal conductivity structure.

[0027] S6, Hot Isostatic Pressing Densification Treatment The initial composite ceramic sintered body after reaction sintering is placed in a hot isostatic pressing furnace and subjected to secondary densification treatment under an inert gas protective atmosphere (preferably argon). Specifically, the temperature is raised to 1600–1750 °C, a gas pressure of 100 MPa is applied, and the temperature is held for 4 h. Under the coupling effect of high temperature and high pressure, the residual pores inside the material are effectively eliminated, and the interfacial bonding is further strengthened, thereby significantly improving the density and mechanical properties of the material, while maintaining the orientation structure of the lamellar boron nitride without significant damage. Finally, a SiC(B4C) / h-BN composite ceramic sealing ring with high density and excellent thermal-mechanical property matching is obtained.

[0028] Performance of the resulting product: The performance of the SiC(B4C) / h-BN composite ceramic sealing ring obtained in this embodiment was tested and found to be as follows: relative density 98.5%, radial thermal conductivity 145 W·m. -1 ·K -1 Axial thermal conductivity 45 W·m -1 ·K -1 Flexural strength 420 MPa, fracture toughness 5.5 MPa·m 1 / 2 The coefficient of friction is 0.22.

[0029] Example 2 The only difference between this embodiment and Example 1 is that the amount of polycarbosilane used in S1 is 1.5 kg and the amount of trimethyl borate is 0.6 kg. The remaining steps are the same as in Example 1.

[0030] The tested sealing ring exhibits the following properties: relative density 97.8%, radial thermal conductivity 132 W·m. -1 ·K -1 Axial thermal conductivity 42 W·m -1 ·K -1 Flexural strength 368 MPa, fracture toughness 5.0 MPa·m 1 / 2 The coefficient of friction is 0.24.

[0031] Example 3 The only difference between this embodiment and Example 1 is that the amount of polycarbosilane used in S1 is 3.5 kg and the amount of trimethyl borate is 1.4 kg. The remaining steps are the same as in Example 1.

[0032] The tested sealing ring exhibits the following properties: relative density 97.5%, radial thermal conductivity 128 W·m. -1 ·K -1 Axial thermal conductivity 40 W·m -1 ·K -1 Flexural strength 390 MPa, fracture toughness 4.9 MPa·m 1 / 2 The coefficient of friction is 0.26.

[0033] Example 4 The only difference between this embodiment and embodiment 1 is that in S3, a pressure of 3 MPa is applied first (held for 3 min), followed by a pressure of 6 MPa (held for 8 min), and the rest of the steps are the same as in embodiment 1.

[0034] The tested sealing ring exhibits the following properties: relative density 97.2%, radial thermal conductivity 130 W·m. -1 ·K -1 Axial thermal conductivity 41 W·m -1 ·K -1 Flexural strength 365 MPa, fracture toughness 4.8 MPa·m 1 / 2 The coefficient of friction is 0.25.

[0035] Example 5 The only difference between this embodiment and embodiment 1 is that in S3, a pressure of 6 MPa is applied first (held for 3 min), followed by a pressure of 18 MPa (held for 8 min), and the rest of the steps are the same as in embodiment 1.

[0036] The tested sealing ring exhibits the following properties: relative density 98.0%, radial thermal conductivity 138 W·m. -1 ·K -1 Axial thermal conductivity 44 W·m -1 ·K -1Flexural strength 388 MPa, fracture toughness 5.2 MPa·m 1 / 2 The coefficient of friction is 0.23.

[0037] Example 6 The only difference between this embodiment and embodiment 1 is that in S2, the amount of paraffin wax is increased to reduce the powder mass fraction in the thermoplastic slurry to 60 wt%, and the remaining steps are the same as in embodiment 1.

[0038] The tested sealing ring exhibits the following properties: relative density 96.8%, radial thermal conductivity 120 W·m. -1 ·K -1 Axial thermal conductivity 38 W·m -1 ·K -1 Flexural strength 355 MPa, fracture toughness 4.6 MPa·m 1 / 2 The coefficient of friction is 0.27.

[0039] Example 7 The only difference between this embodiment and Embodiment 1 is that the powder mass fraction in the thermoplastic material described in S2 is increased. By reducing the amount of paraffin, the powder mass fraction in the thermoplastic slurry is increased to 72-74 wt%. The remaining steps are the same as in Embodiment 1.

[0040] The tested sealing ring exhibits the following properties: relative density 98.2%, radial thermal conductivity 140 W·m. -1 ·K -1 Axial thermal conductivity 44 W·m -1 ·K -1 Flexural strength 392 MPa, fracture toughness 5.3 MPa·m 1 / 2 The coefficient of friction is 0.23.

[0041] Example 8 The only difference between this embodiment and embodiment 1 is that the heating regime in the heat degreasing stage of S4 is different: the temperature is increased to 450°C at 3°C / min and held for 1 hour, and then increased to 800°C at 5°C / min and held for 1 hour. The remaining steps are the same as in embodiment 1.

[0042] The tested sealing ring exhibits the following properties: relative density 96.5%, radial thermal conductivity 118 W·m. -1 ·K -1 Axial thermal conductivity 37 W·m -1 ·K -1 Flexural strength 350 MPa, fracture toughness 4.5 MPa·m 1 / 2 The coefficient of friction is 0.28.

[0043] Example 9 The only difference between this embodiment and Embodiment 1 is that the reaction sintering temperature in S5 is reduced: the degreased green body is heated to 1700°C at 4°C / min under an argon atmosphere and held for 1.5h. The remaining steps are the same as in Embodiment 1.

[0044] The tested sealing ring exhibits the following properties: relative density 96.9%, radial thermal conductivity 122 W·m. -1 ·K -1 Axial thermal conductivity 39 W·m -1 ·K -1 Flexural strength 360 MPa, fracture toughness 4.7 MPa·m 1 / 2 The coefficient of friction is 0.26.

[0045] Example 10 The only difference between this embodiment and Embodiment 1 is that the reaction sintering temperature in S5 is increased: the degreased green body is heated to 1900℃ at 4℃ / min under an argon atmosphere and held for 1.5h. The remaining steps are the same as in Embodiment 1.

[0046] The tested sealing ring exhibits the following properties: relative density 97.9%, radial thermal conductivity 135 W·m. -1 ·K -1 Axial thermal conductivity 43 W·m -1 ·K -1 Flexural strength 380 MPa, fracture toughness 5.1 MPa·m 1 / 2 The coefficient of friction is 0.24.

[0047] Comparative Example 1 The only difference between this comparative example and Example 1 is that: in S1, the precursor solution coating treatment is not performed, but the boron nitride powder, silicon carbide powder and boron carbide powder are dry mechanically mixed in the same mass ratio as in Example 1, and the remaining steps are the same as in Example 1.

[0048] The tested sealing ring exhibits the following properties: relative density 95.5%, radial thermal conductivity 105 W·m. -1 ·K -1 Axial thermal conductivity 36 W·m -1 ·K -1 Flexural strength 285 MPa, fracture toughness 3.5 MPa·m 1 / 2 The coefficient of friction is 0.30.

[0049] Comparative Example 2 The only difference between this comparative example and Example 1 is that in S3, a single cold pressing molding at room temperature is used with a molding pressure of 10 MPa, and thermoplastic molding orientation treatment is not performed. The remaining raw material composition and steps S1, S2, S4, S5, and S6 are the same as in Example 1.

[0050] The tested sealing ring exhibits the following properties: relative density 94.8%, radial thermal conductivity 100 W·m. -1 ·K -1 Axial thermal conductivity 34 W·m -1 ·K -1 Flexural strength 270 MPa, fracture toughness 3.3 MPa·m 1 / 2 The coefficient of friction is 0.31.

[0051] Comparative Example 3 The only difference between this comparative example and Example 1 is that no reinforcing precursor system is introduced in S1, and only boron nitride powder is used as a single masterbatch, that is, no polycarbosilane and trimethyl borate are added. The remaining steps are the same as in Example 1.

[0052] The tested sealing ring exhibits the following properties: relative density 96.2%, radial thermal conductivity 115 W·m. -1 ·K -1 Axial thermal conductivity 38 W·m -1 ·K -1 Flexural strength 295 MPa, fracture toughness 3.7 MPa·m 1 / 2 The coefficient of friction is 0.24.

[0053] Comparative Example 4 The only difference between this comparative example and Example 1 is that: in S1, only polycarbosilane (PCS) is used for coating treatment, and trimethyl borate (TMB) is not added. The amount of polycarbosilane added is the same as in Example 1, and the remaining steps are the same as in Example 1.

[0054] The tested sealing ring exhibits the following properties: relative density 96.8%, radial thermal conductivity 120 W·m. -1 ·K -1 Axial thermal conductivity 39 W·m -1 ·K -1 Flexural strength 305 MPa, fracture toughness 3.9 MPa·m 1 / 2 The coefficient of friction is 0.27.

[0055] Comparative Example 5 The only difference between this comparative example and Example 1 is that in S1, only trimethyl borate (TMB) is used for treatment, and polycarbosilane (PCS) is not added. The amount of trimethyl borate added is the same as in Example 1, and the remaining steps are the same as in Example 1.

[0056] The tested sealing ring exhibits the following properties: relative density 96.5%, radial thermal conductivity 118 W·m. -1 ·K -1 Axial thermal conductivity 38 W·m -1 ·K-1 Flexural strength 300 MPa, fracture toughness 3.8 MPa·m 1 / 2 The coefficient of friction is 0.28.

[0057] Comparative Example 6 The only difference between this comparative example and Example 1 is that the S6 hot isostatic pressing densification treatment is omitted. The remaining steps S1-S5 are the same as in Example 1.

[0058] The tested sealing ring exhibits the following properties: relative density 94.2%, radial thermal conductivity 116 W·m. -1 ·K -1 Axial thermal conductivity 40 W·m -1 ·K -1 Flexural strength 245 MPa, fracture toughness 3.2 MPa·m 1 / 2 The coefficient of friction is 0.27.

[0059] The performance test results of each embodiment and comparative example are shown in Table 1.

[0060] Table 1: Performance test results of the examples and comparative examples

[0061] As shown in Table 1, Example 1 exhibits the best overall performance, with a relative density of 98.5% and a radial thermal conductivity of 145 W·m. -1 ·K -1 The axial thermal conductivity is 45 W·m. -1 ·K -1 Flexural strength 420 MPa, fracture toughness 5.5 MPa·m 1 / 2 The coefficient of friction is 0.22.

[0062] Comparing Examples 1 and 2-3, it can be seen that when the ratio of polycarbosilane to trimethyl borate deviates from 2.5:1 (the amount is reduced in Example 2 and increased in Example 3), the density, thermal conductivity and mechanical properties of the material all decrease, indicating that the ratio of the two precursors has a significant impact on the final performance.

[0063] Comparing Example 1 with Examples 4-5, it can be seen that as the molding pressure increases (from 3→6 MPa primary pressure, 6→18 MPa secondary pressure), the radial thermal conductivity and bending strength of the material gradually increase. This indicates that higher molding pressure is beneficial to enhancing the directional alignment of the lamellar boron nitride, thereby improving the anisotropic thermal conductivity and mechanical properties.

[0064] Comparing Examples 1 with Examples 6-7, it can be seen that a low solid content in the thermoplastic slurry (Example 6, 60 wt%) leads to a decrease in density and thermal conductivity; while a high solid content (Example 7, 73 wt%) increases density, the thermal conductivity and strength are slightly lower than in Example 1, indicating that a suitable solid content range (66-70 wt%) helps to obtain good overall performance.

[0065] Comparing Example 1 and Example 8, it can be seen that a rapid heating rate (5℃ / min) during thermal degreasing significantly reduces the relative density, thermal conductivity, and strength of the material, indicating that segmented slow degreasing is beneficial for maintaining the integrity of the orientation structure.

[0066] Comparing Examples 1 and 9-10, it can be seen that when the sintering temperature is too low (1700℃), the material density and thermal conductivity are insufficient; when the sintering temperature is too high (1900℃), the performance decreases slightly, possibly due to the partial decomposition of h-BN, indicating that the optimal sintering temperature is around 1800℃.

[0067] Comparative Example 1 used directly mechanically mixed powder without precursor coating. Although the composition was the same, its relative density, thermal conductivity and mechanical properties were significantly lower than those of Example 1, which confirms that precursor interface coating is crucial for improving interfacial bonding strength and material density.

[0068] Comparative Example 2 was not subjected to thermoplastic compression molding and orientation. The sheet-like boron nitride was randomly distributed, and its radial thermal conductivity (100 W·m) was... -1 ·K -1 The strength of the oriented structure is much lower than that of Example 1, and the bending strength and fracture toughness are significantly reduced, proving that the orientation structure is the key to achieving anisotropic thermal conductivity and mechanical enhancement.

[0069] Comparative Example 3, without the addition of any reinforcing precursors, only sintered h-BN, had extremely low mechanical properties despite its acceptable relative density, with a bending strength of only 295 MPa. This indicates that the SiC-B4C bond plays a decisive role in the relative material strength.

[0070] The performance of Comparative Example 4 (PCS only) and Comparative Example 5 (TMB only) was lower than that of Example 1, indicating that a single precursor system cannot achieve the synergistic enhancement effect of SiC and B4C, and a dual precursor system is a necessary condition for obtaining excellent overall performance.

[0071] Comparative Example 6, without hot isostatic pressing (HIP), showed a significant decrease in the relative density and mechanical properties of the material, with a bending strength of only 245 MPa. In contrast, Example 1, after HIP, showed an increase in bending strength to 420 MPa, demonstrating that HIP can effectively eliminate residual pores and strengthen interfacial bonding, making it a key step in improving the density and mechanical properties of materials.

[0072] In summary, this invention successfully prepared a SiC(B4C) / h-BN composite ceramic sealing ring with high density, anisotropic thermal conductivity, and excellent mechanical properties through a combination of precursor interface coating, thermoplastic molding orientation, in-situ reaction sintering of two precursors, and hot isostatic pressing densification treatment.

[0073] The above embodiments are only used to illustrate the technical methods of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical methods of the present invention without departing from the spirit and scope of the technical methods of the present invention.

Claims

1. An anisotropic SiC(B4C) / h-BN composite ceramic sealing ring, characterized in that, include: The thermally conductive framework structure formed by h-BN sheet-like particles; A SiC-B4C composite phase formed by high-temperature in-situ conversion of silicon-containing and boron-containing precursors; The h-BN flake particles are oriented along the plane of the sealing ring and form a continuous in-plane thermally conductive network structure, which makes the thermal conductivity of the sealing ring in the radial direction higher than that in the axial direction. The SiC-B4C composite bonding phase is distributed between and at the interface of the lamellar boron nitride, which enhances the interfacial bonding strength and improves the overall density.

2. The composite ceramic sealing ring according to claim 1, characterized in that, The silicon-containing precursor is polycarbosilane, and the boron-containing precursor is trimethyl borate.

3. The composite ceramic sealing ring according to claim 1, characterized in that, The h-BN flake particles have an aspect ratio of 5 to 10 and a volume fraction of 30% to 70%.

4. The composite ceramic sealing ring according to claim 1, characterized in that, The relative density of the composite ceramic sealing ring is not less than 95%.

5. A method for preparing a composite ceramic sealing ring as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Polycarbosilane is dissolved in an organic solvent to form a precursor solution, and then mixed with flake boron nitride to form a coating layer on the surface of boron nitride; subsequently, trimethyl borate is added for deposition treatment to obtain precursor-modified composite powder. S2. The composite powder is mixed with a thermoplastic binder system composed of paraffin, polyethylene and stearic acid, and sheared and kneaded under heating conditions to prepare a uniform slurry. S3. The slurry is placed in a mold, and thermoplastic molding flow orientation is performed in the molten state of the bonding system. By gradually applying pressure in stages, the sheet boron nitride rotates and rearranges during the melting flow and pressure process, and is oriented along the plane of the sealing ring to form a blank with an orientation structure. S4. Perform hot degreasing treatment on the green body to remove paraffin, polyethylene and stearic acid; S5. High-temperature sintering is carried out under a protective atmosphere to transform polycarbosilane and trimethyl borate in situ to form a composite phase and construct a continuous radial thermally conductive network structure. S6. The sintered body is subjected to hot isostatic pressing treatment. Under the action of high temperature and inert gas pressure, the material is further densified and the interfacial bonding is strengthened to obtain the final composite ceramic sealing ring.

6. The preparation method according to claim 5, characterized in that, In step S1, the mass ratio of polycarbosilane to trimethyl borate is 2.5:1, and the amount of polycarbosilane used is 1.5 to 3.5 parts by weight, while the amount of trimethyl borate used is 0.6 to 1.4 parts by weight.

7. The preparation method according to claim 5, characterized in that, In step S3, the phased progressive pressure loading includes: First, apply a pressure of 3-6 MPa to achieve slurry spreading and preliminary orientation adjustment of h-BN flake particles; Subsequently, a pressure of 8–18 MPa is applied to further induce the h-BN flake particles to rearrange along the plane of the sealing ring and form an oriented arrangement structure.

8. The preparation method according to claim 5, characterized in that, In step S4, the thermal degreasing process is carried out in a segmented heating manner, with a heating rate of 0.5 to 3 °C / min.

9. The preparation method according to claim 5, characterized in that, In step S5, the sintering temperature is 1700–1900°C, and the sintering atmosphere is an inert gas.

10. The preparation method according to claim 5, characterized in that, The hot isostatic pressing (HIP) treatment is performed at a temperature of 1600–1750°C, a pressure of 100–150 MPa, and a holding time of 2–6 h. The atmosphere for the HIP treatment is argon.

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