A high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics and its preparation method

Abstract

This invention belongs to the field of 3D printing materials technology, and relates to a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics and its preparation method. The method includes: dispersing silicon carbide powder in a polyethyleneimine aqueous solution, mixing, stirring, heating, filtering, and drying to obtain modified silicon carbide powder; dispersing ceramic whiskers in a precursor solution composed of ammonium metavanadate and boric acid, mixing, stirring, heating, filtering, and drying to obtain precursor whiskers; calcining the precursor whiskers to obtain modified ceramic whiskers; uniformly mixing the modified silicon carbide powder, modified ceramic whiskers, binder, etc., to obtain a composite slurry; obtaining a green body after 3D printing; and sequentially subjecting the green body to static curing, drying, debinding, and sintering to obtain the silicon carbide composite material. The silicon carbide composite material obtained by this invention possesses both complex structure forming capability and excellent mechanical properties, solving the common technical problems of poor slurry performance and low sintering density in silicon carbide ceramic composite materials.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing materials technology, and relates to a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics and its preparation method. Background Technology

[0002] Silicon carbide ceramics have broad application prospects in cutting-edge fields such as aerospace, energy and chemical industry, and semiconductor manufacturing due to their excellent high-temperature strength, wear resistance, chemical stability, and good thermal conductivity. However, the inherent high hardness, high brittleness (low fracture toughness), and difficult sintering characteristics of silicon carbide make its traditional forming and processing (such as machining) extremely difficult and expensive, especially for components with complex geometries, which seriously limits the full realization of its application potential.

[0003] Additive manufacturing (3D printing) technology, especially photopolymerization-based technologies such as stereolithography (SLA) and digital light processing (DLP), has provided new solutions for forming complex silicon carbide ceramic structures. To meet the stringent requirements of 3D printing for slurry leveling and light transmittance, existing technologies typically employ low-solids, low-viscosity slurry formulations. This directly results in low green body density, making the green body prone to significant shrinkage and deformation, and even cracking, during subsequent debinding and sintering processes, making it difficult to guarantee the dimensional accuracy and structural reliability of the components.

[0004] To improve the toughness of silicon carbide ceramics, introducing a second-phase reinforcement is a recognized effective approach. Among these, ceramic whiskers (such as silicon carbide whiskers and silicon nitride whiskers) are ideal toughening materials due to their high strength and modulus. However, introducing whiskers into 3D printing systems faces significant challenges. First, the addition of whiskers significantly alters the rheological properties of the slurry, easily leading to a sharp increase in slurry viscosity and decreased flowability. Simultaneously, the light scattering effect of whiskers severely degrades printing accuracy and interlayer bonding strength. Second, during high-temperature sintering, unfavorable interfacial reactions may occur between the whiskers and the matrix, resulting in whisker damage or passivation, significantly reducing the toughening effect. Current technologies often employ relatively simple whisker modification processes, failing to effectively control their synergy with the slurry system and sintering process, making it difficult to simultaneously achieve good printability, high sintering density, and significant toughening effects. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a high-strength, high-modulus 3D printing silicon carbide composite material for special ceramics and its preparation method. The resulting silicon carbide composite material possesses both complex structure forming capability and excellent mechanical properties, solving common technical problems in 3D printing silicon carbide ceramic composite materials such as poor slurry performance, low sintering density, and high material brittleness.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics, the method comprising:

[0008] S1. Disperse silicon carbide powder in an aqueous solution of polyethyleneimine, add ammonia solution dropwise to adjust the pH value, then mix, stir and heat, and finally filter and dry to obtain modified silicon carbide powder.

[0009] S2. Ammonium metavanadate and boric acid are added to deionized water to obtain a precursor solution. Ceramic whiskers are dispersed in the precursor solution, mixed, stirred and heated, and then filtered and dried to obtain precursor whiskers. The precursor whiskers are calcined to obtain modified ceramic whiskers.

[0010] S3. Mix the modified silicon carbide powder, the modified ceramic whiskers, the binder, the dispersant, the sintering aid, and deionized water evenly to obtain a composite slurry;

[0011] S4. The composite slurry is 3D printed to obtain a green body; the green body is then subjected to static curing, drying, degreasing and sintering in sequence, and cooled to room temperature in the furnace to obtain the silicon carbide composite material.

[0012] This invention first modifies silicon carbide powder with polyethyleneimine to improve its dispersion stability in composite slurry. Then, ceramic whiskers are immersed in a precursor solution composed of ammonium metavanadate and boric acid and sintered, forming a VB2 protective layer with extremely high melting point and hardness on the surface of the ceramic whiskers. This VB2 protective layer greatly protects the structural integrity of the ceramic whiskers during high-temperature sintering. Finally, the modified silicon carbide powder, modified ceramic whiskers, binder, dispersant, sintering aid, and deionized water are mixed uniformly in a specific ratio to prepare a composite slurry suitable for 3D printing. The printed blank is then subjected to static curing, drying, degreasing, and sintering in sequence, ultimately obtaining a silicon carbide composite material that combines the ability to form complex structures with excellent mechanical properties. This solves the common technical problems of poor slurry performance, low sintering density, and high material brittleness in 3D printed silicon carbide ceramic composite materials.

[0013] Unmodified silicon carbide powder has a high degree of surface chemical inertness. When blended with components such as ceramic whiskers, it is prone to agglomeration due to poor interfacial compatibility, which in turn affects the interfacial bonding strength between the ceramic whiskers and the silicon carbide matrix. This invention, under alkaline conditions, modifies the surface of silicon carbide powder with polyethyleneimine, significantly improving the dispersion stability of silicon carbide powder in aqueous composite slurries. This is because the polyethyleneimine molecular chain contains a large number of amine groups. Under alkaline conditions, the amine groups adsorbed on the surface of the silicon carbide powder partially protonate, giving the entire silicon carbide powder surface a positive charge. Through the electrostatic repulsion between positive charges, agglomeration of silicon carbide powder in the composite slurry can be effectively prevented.

[0014] This invention uses a precursor solution composed of ammonium metavanadate and boric acid to treat the surface of ceramic whiskers. After stirring and heating, the ammonium metavanadate and boric acid are adsorbed on the surface of the ceramic whiskers. Then, through calcination, an extremely thin VB2 protective layer is generated in situ on the surface of the ceramic whiskers and is firmly bonded to the ceramic whiskers.

[0015] Ammonium metavanadate (NH4VO3) decomposes into V2O5 during heating, releasing NH3 and H2O in the process. The reaction equation is as follows:

[0016] ;

[0017] During the initial heating stage of calcination, NH4VO3 adsorbed on the surface of silicon carbide whiskers first undergoes thermal decomposition to generate V2O5. V2O5 is deposited on the surface of silicon carbide whiskers in the form of gaseous molecules, forming an active V2O5 layer.

[0018] V₂O₅ reacts with boric acid (H₃BO₃) in a hydrogen reducing atmosphere to produce VB₂. The reaction equation is as follows:

[0019] ;

[0020] Hydrogen in the mixed atmosphere acts as a reducing agent, gradually reducing high-valence V2O5 and boric acid, releasing active vanadium and active boron atoms. Under high temperature, the active vanadium and active boron atoms diffuse into each other on the whisker surface and crystallize to form the target product VB2.

[0021] After the above reaction, the VB2 protective layer completely covers the surface of the silicon carbide whisker. The gaseous products such as NH3 and H2O generated during the reaction will escape, thereby forming a dense and uniform VB2 protective layer on the surface of the whisker.

[0022] The VB2 protective layer serves two main purposes: First, its coefficient of thermal expansion falls between that of the ceramic whiskers and the silicon carbide matrix, allowing it to act as a transition layer. This effectively alleviates internal stress caused by the difference in thermal expansion coefficients between the ceramic whiskers and the silicon carbide matrix during sintering, reducing the formation of microcracks. Second, the VB2 protective layer acts as a load-bearing bridge. When the composite material is subjected to external forces, stress is transferred from the relatively soft silicon carbide matrix to the high-modulus ceramic whiskers. This process is highly dependent on the bonding state at the interface between the two. The VB2 protective layer, through its high strength and excellent interfacial bonding with the ceramic whiskers, ensures that the load is efficiently transferred from the VB2 protective layer to the ceramic whiskers, preventing stress concentration at the interface between the ceramic whiskers and the silicon carbide matrix. This ensures that the ceramic whiskers can fully bear the load, thereby significantly improving the overall strength and modulus of the composite material. On the other hand, the VB2 protective layer has high melting point and high hardness, which can act as a physical barrier to protect the strength and modulus of ceramic whiskers from the influence of subsequent high-temperature sintering processes. It effectively suppresses the adverse interfacial reactions that may occur between ceramic whiskers and silicon carbide matrix, avoids high-temperature damage or passivation of ceramic whiskers, and preserves the inherent high strength and high modulus of ceramic whiskers to the maximum extent.

[0023] This invention combines modified silicon carbide powder rich in organic functional groups on its surface with modified ceramic whiskers having a VB2 protective layer on its surface in a specific ratio. These are then dispersed together in an aqueous slurry containing a binder, dispersant, and sintering aid. The modified silicon carbide powder serves as the matrix of the composite material, while the modified ceramic whiskers act as the reinforcement. The binder provides sufficient strength to the printed preform, ensuring it maintains its shape during subsequent processing. The dispersant further ensures the uniform and stable dispersion of the modified silicon carbide powder and modified ceramic whiskers in the composite slurry, preventing sedimentation and agglomeration. The added sintering aid melts to form a liquid phase during high-temperature sintering, lowering the sintering temperature, reducing porosity, and promoting densification of the composite material.

[0024] The purpose of static curing and drying is to gently remove some of the moisture from the green body, preventing cracking due to excessively rapid drying. The purpose of the degreasing process is to remove organic components (binders, dispersants, etc.) from the green body, preventing cracking or blistering caused by the rapid decomposition of organic matter and the generation of large amounts of gas. Finally, during the sintering process, high-temperature heating and the action of sintering aids densify the interior of the green body, connecting loosely bound particles into a dense whole, ultimately obtaining a silicon carbide composite material with high strength and high modulus.

[0025] It should be noted that this invention does not impose specific requirements or special limitations on process parameters of the 3D printing process, such as printing speed, printing spacing, and single-layer printing thickness. In order to ensure the integrity and feasibility of the technical solution, based on the viscosity, composition, and subsequent process requirements of the composite slurry provided by this invention, the present invention provides the following optional range of process parameters by way of example:

[0026] (1) The printing speed is set to 5~15mm / s, with the optimal value being 10mm / s. When the printing speed is too slow, the printing efficiency is too low, and the composite slurry is easy to solidify in the nozzle. When the printing speed is too fast, the extrusion pressure is insufficient, and filament breakage or interlayer voids are likely to occur. A printing speed of 5~15mm / s can ensure continuous extrusion of the composite slurry and reduce the impact of vibration on the accuracy of the blank.

[0027] (2) The printing spacing is set to 0.8~1.2mm, with the optimal value being 1mm. The setting range of the printing spacing is matched with the nozzle diameter (the present invention preferably uses a nozzle with a diameter of 1.0mm). If the spacing is too small, it is easy to overlap and bulge, and if it is too large, it will reduce the interlayer bonding strength. The printing spacing of 0.8~1.2mm can ensure that the overlap rate of adjacent paths is about 30%, which can ensure the interlayer density and avoid material accumulation.

[0028] (3) The single-layer printing thickness is set to 0.2~0.4mm, with the optimal value being 0.3mm. When the single-layer printing thickness is too low, the drying shrinkage stress is concentrated and cracking is easy. When the single-layer printing thickness is too high, the uncured slurry in the lower layer may deform under the load. A single-layer printing thickness of 0.2~0.4mm can take into account both molding efficiency and blank strength.

[0029] As a preferred technical solution of the present invention, in S1, the mass fraction of polyethyleneimine in the polyethyleneimine aqueous solution is 1~5wt%, for example, it can be 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt% or 5.0wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In some optional examples, the silicon carbide powder has a particle size D90 of 1.5 μm.

[0031] In some alternative examples, the mass ratio of the silicon carbide powder to the polyethyleneimine in the aqueous polyethyleneimine solution is 100:(3~5), for example, it can be 100:3.0, 100:3.2, 100:3.4, 100:3.6, 100:3.8, 100:4, 100:4.2, 100:4.4, 100:4.6, 100:4.8 or 100:5.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] This invention specifically limits the mass ratio of silicon carbide powder to polyethyleneimine in the aqueous solution to 100:(3~5). Within this range, it can ensure that the surface of silicon carbide powder is fully and uniformly adsorbed and coated by polyethyleneimine molecules, forming an organic adsorption layer of appropriate thickness. This ensures that the surface of silicon carbide powder carries a sufficient number of positive charges to achieve electrostatic repulsion, effectively preventing the agglomeration of silicon carbide powder in the composite slurry. At the same time, it also avoids the large amount of gas generated by thermal decomposition during the subsequent degreasing process due to excessive polyethyleneimine, which would affect the structural integrity of the green body.

[0033] When the amount of polyethyleneimine is lower than the lower limit of the range defined in this invention, the polyethyleneimine molecules cannot completely cover the surface of all silicon carbide powders, resulting in a weak electrostatic repulsion between silicon carbide powders. This cannot completely prevent the silicon carbide powders from agglomerating in the composite slurry, which in turn causes the modified silicon carbide powders to settle in the composite slurry due to agglomeration, affecting the uniformity and stability of the composite slurry, and resulting in structural defects such as pores in the final composite material.

[0034] When the amount of polyethyleneimine exceeds the upper limit defined in this invention, excess polyethyleneimine not adsorbed on the surface of silicon carbide powder will remain free in the solution. These free long-chain polyethyleneimine molecules can simultaneously entangle and adsorb onto the surfaces of multiple coated silicon carbide powders, thereby pulling together the originally uniformly dispersed silicon carbide powders and exacerbating the agglomeration phenomenon. Furthermore, excess polyethyleneimine will decompose upon heating during the subsequent degreasing process, generating more gas. The rapid release of a large amount of gas will create significant pressure inside the green body, significantly increasing the risk of cracking and deformation.

[0035] In some alternative instances, the addition of ammonia solution to adjust the pH to 9-10, for example, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9 or 10.0, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0036] In some optional instances, the mixing and heating temperature is 50~70°C, for example, 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] In some optional instances, the mixing and heating time is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0038] In some alternative instances, the drying temperature is 80 to 100°C, for example, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0039] In some optional instances, the drying time is 8 to 10 hours, for example, 8.0 hours, 8.2 hours, 8.4 hours, 8.6 hours, 8.8 hours, 9.0 hours, 9.2 hours, 9.4 hours, 9.6 hours, 9.8 hours, or 10.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0040] In a preferred embodiment of the present invention, in S2, the ceramic whiskers are silicon carbide whiskers.

[0041] In some optional examples, the silicon carbide whiskers have a diameter of 0.2 μm and a length of 50 μm.

[0042] In some alternative examples, the concentration of ammonium metavanadate in the precursor solution is 0.05 to 0.15 mol / L, for example, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, or 0.15 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0043] In some alternative instances, the concentration of boric acid in the precursor solution is 0.1 to 0.2 mol / L, for example, 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, or 0.2 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0044] In some alternative examples, the mass ratio of the ceramic whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution is 1:(0.1~0.3), for example, it can be 1:0.1, 1:0.12, 1:0.14, 1:0.16, 1:0.18, 1:0.2, 1:0.22, 1:0.24, 1:0.26, 1:0.28 or 1:0.3, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0045] This invention specifically limits the ratio of the mass of the ceramic whisker to the total mass of ammonium metavanadate and boric acid in the precursor solution to 1:(0.1~0.3). Within this range, sufficient vanadium and boron sources can be uniformly adsorbed and covered on the surface of the ceramic whisker. After calcination, a continuous, dense, and moderately thick VB2 protective layer is formed on the surface of the ceramic whisker. The VB2 protective layer can effectively block harmful interfacial reactions between the ceramic whisker and the silicon carbide matrix during subsequent high-temperature sintering, avoiding damage to the ceramic whisker, and can also optimize the interfacial bonding strength between the ceramic whisker and the silicon carbide matrix to facilitate load transfer.

[0046] When the amounts of ammonium metavanadate and boric acid are below the lower limit of the range defined in this invention, the vanadium and boron sources are insufficient to completely cover the surface of all ceramic whiskers. After calcination, only a thin and discontinuous VB2 protective layer can be formed on the surface of the ceramic whiskers. This VB2 protective layer cannot provide effective physical protection for the ceramic whiskers. During the subsequent high-temperature sintering process, elemental diffusion will occur between the silicon carbide matrix and the ceramic whiskers. The surface of the ceramic whiskers not covered by the VB2 protective layer will directly come into liquid phase contact with the silicon carbide matrix or sintering aids, causing the ceramic whiskers to be eroded and dissolved, and their structure to be severely damaged, so that the reinforcing and toughening effect of the ceramic whiskers cannot be effectively exerted.

[0047] When the amount of ammonium metavanadate and boric acid exceeds the upper limit of the range defined in this invention, the excess ammonium metavanadate and boric acid cannot be fully adsorbed on the surface of ceramic whiskers. After calcination, the free ammonium metavanadate and boric acid will generate fine VB2 particles that are free outside the ceramic whiskers and irregularly dispersed inside the composite material. These free VB2 particles will become stress concentration points in the composite material, and are prone to microcracks when subjected to external forces, thereby reducing the mechanical strength of the composite material.

[0048] In some optional instances, the mixing and heating temperature is 70~80°C, for example, it can be 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] In some optional instances, the mixing and heating time is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0050] In some alternative instances, the drying temperature is 80 to 100°C, for example, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] In some optional instances, the drying time is 6 to 12 hours, for example, 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours, 10.0 hours, 10.5 hours, 11.0 hours, 11.5 hours, or 12.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0052] As a preferred technical solution of the present invention, in S2, the calcination process is carried out in a mixed atmosphere of argon and hydrogen, wherein the volume fraction of hydrogen in the mixed atmosphere is 3-5%, for example, it can be 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8% or 5.0%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] This invention utilizes a mixed atmosphere of argon and hydrogen during the calcination of precursor whiskers to ensure the smooth reduction of ammonium metavanadate and boric acid, thereby forming a VB2 protective layer on the surface of the ceramic whiskers. Argon, being an inert gas, serves as the main calcination atmosphere, effectively isolating oxygen and preventing the whiskers from oxidation. A small amount of hydrogen is incorporated into the argon atmosphere to create a weakly reducing calcination atmosphere. Under high-temperature conditions, hydrogen reacts with vanadium oxide produced by the decomposition of ammonium metavanadate, removing oxygen and reducing it to metallic vanadium. Simultaneously, boron oxide produced by the decomposition of boric acid is also reduced to boron. Vanadium and boron combine on the whisker surface to form the VB2 protective layer.

[0054] This invention strictly controls the volume fraction of hydrogen within the range of 3-5%, which is sufficient to provide a adequate and stable reducing atmosphere, ensuring the complete reduction of vanadium and boron oxides, thereby forming a continuous and dense VB2 protective layer on the surface of ceramic whiskers. If the hydrogen concentration is too low, the reduction reaction will be incomplete, resulting in a protective layer containing oxygen impurities, which will seriously affect the protective effect of the protective layer on the ceramic whiskers. If the hydrogen concentration is too high, although the reducing power is further enhanced, the excessively rapid reduction reaction will cause the VB2 protective layer to grow too quickly, resulting in a loose structure or even cracks in the formed VB2 protective layer.

[0055] In some optional examples, the heating rate of the calcination is 5~8℃ / min, for example, it can be 5.0℃ / min, 5.2℃ / min, 5.4℃ / min, 5.6℃ / min, 5.8℃ / min, 6.0℃ / min, 6.2℃ / min, 6.4℃ / min, 6.6℃ / min, 6.8℃ / min, 7.0℃ / min, 7.2℃ / min, 7.4℃ / min, 7.6℃ / min, 7.8℃ / min or 8.0℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0056] In some optional instances, the calcination temperature is 1200~1300℃, for example, it can be 1200℃, 1210℃, 1220℃, 1230℃, 1340℃, 1250℃, 1260℃, 1270℃, 1280℃, 1290℃ or 1300℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0057] This invention specifically limits the calcination temperature to 1200~1300℃. Within this temperature range, it ensures that the ammonium metavanadate and boric acid adsorbed on the surface of the ceramic whiskers react fully, generating a VB2 protective layer with good crystallinity and strong bonding to the ceramic whiskers. At this calcination temperature, the oxides of vanadium and boron can be effectively reduced by hydrogen and diffuse to form a stable VB2 protective layer. At the same time, this temperature range allows the generated VB2 particles to have sufficient surface migration ability to connect and form a continuous and dense VB2 protective layer, but it is not enough to cause excessive growth of VB2 grains, resulting in coarse grains.

[0058] When the calcination temperature is below 1200℃, the decomposition and reduction processes of ammonium metavanadate and boric acid become slow and incomplete, resulting in unreacted vanadium oxide or boron oxide remaining in the product. In addition, at relatively low calcination temperatures, atomic diffusion is limited. Even if VB2 particles are generated, it is difficult to effectively connect them through surface diffusion and grain boundary migration to form a dense and complete VB2 protective layer. The final result is a structure in which several small VB2 particles are loosely attached to the surface of ceramic whiskers. This structure cannot provide effective physical protection for ceramic whiskers.

[0059] When the calcination temperature exceeds 1300℃, the excessively high calcination temperature will cause the grains of the VB2 protective layer to coarsen, forming an excessively thick VB2 protective layer with excessive internal stress. This can easily lead to cracking of the VB2 protective layer or peeling off from the surface of the ceramic whiskers. In addition, excessively high calcination temperatures can also cause atomic rearrangement on the surface of the ceramic whiskers, making their inherent sharp edges rounded. This weakens the high strength and high modulus of the ceramic whiskers themselves, seriously affecting the mechanical strengthening and toughening effect of the ceramic whiskers.

[0060] In some optional instances, the calcination holding time is 1 to 3 hours, for example, it can be 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0061] As a preferred technical solution of the present invention, in S3, the mass ratio of the modified silicon carbide powder to the modified ceramic whiskers is 100:(10~20), for example, it can be 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18, 100:19 or 100:20, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0062] This invention specifically defines the mass ratio of modified silicon carbide powder to modified ceramic whiskers as 100:(10~20). Within this range, the modified ceramic whiskers can be uniformly dispersed in the silicon carbide matrix. When the composite material is subjected to stress, these uniformly distributed modified ceramic whiskers can effectively inhibit crack propagation, significantly improving the fracture toughness and strength of the composite material. Simultaneously, excessive use of modified ceramic whiskers will not affect the viscosity of the composite slurry; appropriate addition of modified ceramic whiskers allows the composite slurry to maintain good fluidity, meeting the requirements of 3D printing.

[0063] When the amount of modified ceramic whiskers is lower than the lower limit of the range defined in this invention, the reinforcing and toughening effect of the modified ceramic whiskers cannot be fully exerted, and the mechanical properties of the final composite material cannot be effectively improved.

[0064] When the amount of modified ceramic whiskers exceeds the upper limit defined in this invention, excessive modified ceramic whiskers will significantly increase the viscosity of the composite slurry, resulting in poor flowability and easy clogging of the printhead, leading to printing difficulties. Furthermore, excessive modified ceramic whiskers in the composite slurry are difficult to disperse uniformly and are prone to agglomeration. These agglomerates become structural defects after sintering. Simultaneously, during sintering, excessive and highly rigid modified ceramic whiskers will come into contact with each other, forming a skeletal structure that severely hinders the rearrangement and densification of silicon carbide powder, leading to a decrease in the density of the sintered composite material and significantly affecting its strength and modulus.

[0065] In some optional instances, the amount of binder added is 0.5 to 1.5 wt% of the total mass of the modified silicon carbide powder and the modified ceramic whiskers, for example, it can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, or 1.5 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0066] In some alternative examples, the adhesive is hydroxypropyl methylcellulose.

[0067] In some optional instances, the amount of dispersant added is 1 to 2 wt% of the total mass of the modified silicon carbide powder and the modified ceramic whiskers, for example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%, but is not limited to the values ​​listed, and other unlisted values ​​within this range are also applicable.

[0068] In some alternative instances, the dispersant is ammonium polyacrylate.

[0069] In some optional examples, the sintering aid consists of Al2O3 and Y2O3 in a molar ratio of 5:3.

[0070] In some optional examples, the amount of the sintering aid added is 1 to 3 wt% of the total mass of the modified silicon carbide powder and the modified ceramic whiskers, for example, it can be 1.0 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2.0 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, or 3.0 wt%, but is not limited to the values ​​listed, and other unlisted values ​​within this range are also applicable.

[0071] This invention specifically limits the amount of sintering aid added to 1-3 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The sintering aid, composed of alumina and yttrium oxide in a specific ratio, melts at high temperature to form a liquid phase. This liquid phase wets the surface of the modified silicon carbide powder and modified ceramic whiskers, causing the particles to rearrange through capillary force, filling the pores between the particles, and achieving densification. Within this dosage range, it ensures the generation of an appropriate amount of liquid phase at high temperature, effectively promoting sintering densification, while preventing the formation of a large amount of continuous grain boundary phase after material cooling due to excessive addition of the sintering aid.

[0072] When the amount of sintering aid added is less than 1 wt%, the amount of liquid phase generated in the high-temperature sintering stage is insufficient. Too little liquid phase cannot fully wet the surface of all modified silicon carbide powder, resulting in insufficient particle rearrangement process driven by capillary force. Many large pores cannot be effectively filled, and the final composite material will have a lot of residual pores inside. These pores will become stress concentration points, which seriously affect the strength and modulus of the composite material.

[0073] When the addition of sintering aids exceeds 3 wt%, although more liquid phase is generated, accelerating material densification, the excessive liquid phase, while promoting densification, also forms thicker grain boundary phases between grains. The mechanical, thermal, and chemical stability of these grain boundary phases are far lower than that of silicon carbide. Therefore, the presence of excessive grain boundary phases significantly reduces the overall hardness, high-temperature strength, and creep resistance of the composite material. Furthermore, under high-temperature conditions, excessive liquid phase can also lead to abnormal growth of silicon carbide grains, and coarse silicon carbide grains will adversely affect the mechanical properties of the composite material.

[0074] In some optional examples, the viscosity of the composite slurry is 2000~3000 mPa·s, for example, it can be 2000 mPa·s, 2100 mPa·s, 2200 mPa·s, 2300 mPa·s, 2400 mPa·s, 2500 mPa·s, 2600 mPa·s, 2700 mPa·s, 2800 mPa·s, 2900 mPa·s or 3000 mPa·s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0075] As a preferred technical solution of the present invention, in S3, the process of mixing the modified silicon carbide powder, modified ceramic whiskers, binder, dispersant, sintering aid and deionized water includes low-speed ball milling and high-speed ball milling performed sequentially.

[0076] In some optional instances, the ball milling speed of the low-speed ball mill is 100 to 200 rpm, for example, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm or 200 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0077] In some optional instances, the ball milling time of the low-speed ball mill is 5 to 10 minutes, for example, it can be 5.0 minutes, 5.5 minutes, 6.0 minutes, 6.5 minutes, 7.0 minutes, 7.5 minutes, 8.0 minutes, 8.5 minutes, 9.0 minutes, 9.5 minutes or 10.0 minutes, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0078] In some optional instances, the high-speed ball mill has a milling speed of 400 to 500 rpm, such as 400 rpm, 410 rpm, 420 rpm, 430 rpm, 440 rpm, 450 rpm, 460 rpm, 470 rpm, 480 rpm, 490 rpm or 500 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0079] In some optional instances, the ball milling time of the high-speed ball mill is 30 to 40 minutes, for example, 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes or 40 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0080] In some alternative instances, the high-speed ball milling is performed under a vacuum of -0.09 to -0.1 MPa, such as -0.09 MPa, -0.091 MPa, -0.092 MPa, -0.093 MPa, -0.094 MPa, -0.095 MPa, -0.096 MPa, -0.097 MPa, -0.098 MPa, -0.099 MPa, or -0.1 MPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0081] This invention employs a staged ball milling method to achieve uniform mixing of the components. In the low-speed ball milling stage, the dry powder and liquid are initially mixed to form a uniform paste. In the high-speed ball milling stage, the rolling and impact of the grinding balls apply shearing and impact forces to the agglomerated powder, effectively breaking up the agglomeration between particles. This ensures that each particle is uniformly coated with liquid and additives, which is beneficial for obtaining a uniformly dispersed composite filler. The high-speed ball milling stage is carried out under negative pressure, which removes air bubbles introduced into the composite slurry during the high-speed ball milling process, preventing pores from appearing inside the printed blank.

[0082] As a preferred technical solution of the present invention, in S4, the static curing time is 12~24h, for example, it can be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0083] In some optional instances, the static curing temperature is 25°C and the humidity is 60%RH.

[0084] In some alternative instances, the drying temperature is 50-60°C, for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0085] In some optional instances, the drying time is 24 to 48 hours, for example, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0086] As a preferred technical solution of the present invention, in S4, the degreasing process includes low-temperature degreasing and high-temperature degreasing performed sequentially.

[0087] In some optional examples, the heating rate of the low-temperature degreasing is 0.3~0.5℃ / min, for example, it can be 0.3℃ / min, 0.32℃ / min, 0.34℃ / min, 0.36℃ / min, 0.38℃ / min, 0.4℃ / min, 0.42℃ / min, 0.44℃ / min, 0.46℃ / min or 0.48℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0088] In some optional instances, the low-temperature degreasing temperature is 400~500℃, for example, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 480℃, 490℃ or 500℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0089] In some optional instances, the holding time for the low-temperature degreasing is 1 to 2 hours, for example, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0090] In some optional instances, the heating rate of the high-temperature degreasing is 1~2℃ / min, for example, it can be 1.0℃ / min, 1.1℃ / min, 1.2℃ / min, 1.3℃ / min, 1.4℃ / min, 1.5℃ / min, 1.6℃ / min, 1.7℃ / min, 1.8℃ / min, 1.9℃ / min or 2.0℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0091] In some optional instances, the high-temperature degreasing temperature is 600~700℃, for example, it can be 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃ or 700℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0092] In some optional instances, the heat treatment time for the high-temperature degreasing is 1 to 2 hours, for example, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0093] This invention employs a two-stage degreasing process, first at low temperature and then at high temperature, to thoroughly remove organic components from the green body while avoiding structural defects during the degreasing process. The organic matter in the green body mainly includes hydroxypropyl methylcellulose as a binder, ammonium polyacrylate as a dispersant, and polyethyleneimine coating the surface of silicon carbide powder. These organic substances have different thermal decomposition temperatures. If a single, rapid heating degreasing method is used, it will cause all types of organic substances to decompose violently and simultaneously, generating a large amount of gas in a short time. This gas is difficult to diffuse and escape quickly from the green body, accumulating inside and creating high pressure, leading to blistering, swelling, and even cracking of the green body.

[0094] During the low-temperature degreasing stage, the billet is heated to 400-500℃ and held at a controlled heating rate (0.3~0.5℃ / min). This process gently decomposes organic compounds with shorter molecular chains and relatively poor thermal stability, such as some polyethyleneimine molecular chain segments and small molecule components in the dispersant. The slow heating process allows the organic molecular chains in the billet to gradually break down, giving the generated gas sufficient time to slowly diffuse and escape through the micropores within the billet. This effectively avoids bubbling, swelling, or cracking of the billet caused by a rapid increase in internal gas pressure due to the rapid and violent decomposition of large amounts of organic matter in a short period. Therefore, low-temperature degreasing not only removes some easily decomposed organic components, but more importantly, the slow decomposition and gas generation of organic matter create interconnected pore channels within the billet. In the subsequent high-temperature degreasing stage, the remaining large amount of organic matter will rapidly decompose, generating a large amount of gas in a short time. This large amount of gas can quickly escape through the pore channel network formed during the low-temperature degreasing stage, preventing a sudden increase in internal gas pressure caused by rapid gas accumulation within the billet.

[0095] The purpose of high-temperature debinding is to further remove organic components with higher thermal decomposition temperatures, mainly the binder hydroxypropyl methylcellulose. The heating rate during the high-temperature debinding stage is appropriately increased to 1-2℃ / min. This is because after low-temperature debinding, most of the easily decomposable organic components in the green body have been removed, forming a network of pore channels within the green body. This enhances the structural strength of the green body and reduces the resistance to gas escape, thus allowing for a more appropriate heating rate. Setting the temperature at 600-700℃ ensures that the remaining organic components are completely decomposed and vaporized. If the sintering temperature during the high-temperature debinding stage is too low, the remaining organic components will not decompose completely, and the residual organic matter will further decompose and vaporize during subsequent sintering, ultimately forming pore defects within the composite material. If the sintering temperature during the high-temperature debinding stage is too high, trace impurities in the green body will melt prematurely, blocking the already formed pore channels and hindering densification in subsequent sintering stages.

[0096] As a preferred technical solution of the present invention, in S4, the sintering process is carried out under an argon atmosphere, including low-temperature sintering and high-temperature sintering performed sequentially.

[0097] In some optional instances, the heating rate of the low-temperature sintering is 3~5℃ / min, for example, it can be 3.0℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min, 4.0℃ / min, 4.2℃ / min, 4.4℃ / min, 4.6℃ / min, 4.8℃ / min or 5.0℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0098] In some optional instances, the low-temperature sintering temperature is 1400~1600℃, for example, it can be 1400℃, 1420℃, 1440℃, 1460℃, 1480℃, 1500℃, 1520℃, 1540℃, 1560℃, 1580℃ or 1600℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0099] In some optional instances, the holding time for the low-temperature sintering is 0.5 to 1 hour, for example, it can be 0.5 hours, 0.55 hours, 0.6 hours, 0.65 hours, 0.7 hours, 0.75 hours, 0.8 hours, 0.85 hours, 0.9 hours, 0.95 hours or 1 hour, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0100] In some optional examples, the heating rate of the high-temperature sintering is 5~8℃ / min, for example, it can be 5.0℃ / min, 5.2℃ / min, 5.4℃ / min, 5.6℃ / min, 5.8℃ / min, 6.0℃ / min, 6.2℃ / min, 6.4℃ / min, 6.6℃ / min, 6.8℃ / min, 7.0℃ / min, 7.2℃ / min, 7.4℃ / min, 7.6℃ / min, 7.8℃ / min or 8.0℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0101] In some optional instances, the high-temperature sintering temperature is 1900~2100℃, for example, it can be 1900℃, 1920℃, 1940℃, 1960℃, 1980℃, 2000℃, 2020℃, 2040℃, 2060℃, 2080℃ or 2100℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0102] In some optional instances, the holding time for the high-temperature sintering is 1 to 2 hours, for example, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0103] The invention employs a two-stage gradient sintering process, first at a low temperature and then at a high temperature. The heating rate during the low-temperature sintering stage is relatively low (3~5℃ / min), which facilitates uniform heat transfer and reduces thermal stress. When the sintering temperature reaches 1400~1600℃, the sintering aid composed of Al2O3 and Y2O3 begins to melt and form a liquid phase. During the 0.5~1h holding period, the liquid phase has sufficient time to spread evenly and wet the surface of the modified silicon carbide powder and modified ceramic whiskers. Under the action of capillary force in the liquid phase, the particles undergo preliminary rearrangement, and some large, irregular pores are filled, resulting in preliminary densification of the green body.

[0104] The high-temperature sintering stage primarily focuses on the complete densification of the green body. At this stage, the heating rate is increased to 5-8℃ / min. Having already achieved a certain strength and density through the low-temperature sintering stage, the green body exhibits relative structural stability and can withstand a relatively rapid heating rate. Simultaneously, the sintering temperature is increased to 1900-2100℃. At this temperature, the liquid phase viscosity further decreases, fluidity further increases, and the solubility of silicon carbide in the liquid phase significantly increases. The tiny pores in the green body are completely filled, and strong connections are formed between the grains. Under the physical protection of the VB2 protective layer, the ceramic whiskers maintain structural stability and integrity, effectively hindering the rapid growth of silicon carbide matrix grains and playing a role in grain refinement and strengthening. Holding at this temperature for 1-2 hours is sufficient to ensure a thorough and complete densification process, allowing sufficient time for the removal of any remaining tiny pores in the green body.

[0105] In a second aspect, the present invention provides a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics, prepared by the preparation method described in the first aspect.

[0106] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0107] This invention first modifies silicon carbide powder with polyethyleneimine to improve its dispersion stability in composite slurry. Then, ceramic whiskers are immersed in a precursor solution composed of ammonium metavanadate and boric acid and sintered, forming a VB2 protective layer with extremely high melting point and hardness on the surface of the ceramic whiskers. This VB2 protective layer greatly protects the structural integrity of the ceramic whiskers during high-temperature sintering. Finally, the modified silicon carbide powder, modified ceramic whiskers, binder, dispersant, sintering aid, and deionized water are mixed uniformly in a specific ratio to prepare a composite slurry suitable for 3D printing. The printed blank is then subjected to static curing, drying, degreasing, and sintering in sequence, ultimately obtaining a silicon carbide composite material that combines the ability to form complex structures with excellent mechanical properties. This solves the common technical problems of poor slurry performance, low sintering density, and high material brittleness in 3D printed silicon carbide ceramic composite materials. Attached Figure Description

[0108] Figure 1A process flow diagram for preparing high-strength, high-modulus 3D printing silicon carbide composite materials for special ceramics is provided for this invention.

[0109] Figure 2 Infrared spectra of silicon carbide powder, polyethyleneimine, and modified silicon carbide powder prepared in Example 1 of this invention;

[0110] Figure 3 This is a transmission electron microscope (TEM) image of the modified ceramic whiskers prepared in Example 1 of the present invention.

[0111] Figure 4 This is a scanning electron microscope image of the composite slurry prepared in Example 1 of the present invention. Detailed Implementation

[0112] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0113] The CAS number of ammonium metavanadate used in the various embodiments and comparative examples of this application is 7803-55-6.

[0114] Example 1

[0115] This embodiment provides a method for preparing high-strength, high-modulus silicon carbide composite materials for 3D printing of special ceramics, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0116] S1. Silicon carbide powder with a particle size D90 of 1.5 μm was dispersed in a 1 wt% aqueous solution of polyethyleneimine, with a mass ratio of silicon carbide powder to polyethyleneimine in the aqueous solution of 100:3. A 10 wt% aqueous solution of ammonia was added dropwise to the aqueous solution of polyethyleneimine to adjust its pH value to 9. The mixture was heated at 300 rpm at 50°C for 3 h, and then filtered. The residue was dried at 80°C for 10 h to obtain modified silicon carbide powder.

[0117] S2. Ammonium metavanadate and boric acid were added to deionized water to obtain a precursor solution. The concentration of ammonium metavanadate in the precursor solution was 0.05 mol / L, and the concentration of boric acid was 0.1 mol / L. Silicon carbide whiskers with a diameter of 0.2 μm and a length of 50 μm were dispersed in the precursor solution. The mass ratio of silicon carbide whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution was 1:0.1. The mixture was heated at 70°C and 300 rpm for 3 hours. Then, it was filtered. The residue was dried at 80°C for 12 hours to obtain the precursor whiskers.

[0118] The precursor whiskers were placed in a mixed atmosphere of argon and hydrogen (hydrogen volume fraction of 3%), heated to 1200℃ at a heating rate of 5℃ / min and held for 3h to complete the calcination, so as to form a VB2 protective layer on the surface of silicon carbide whiskers and obtain modified ceramic whiskers.

[0119] S3. Modified silicon carbide powder, modified ceramic whiskers, hydroxypropyl methylcellulose, ammonium polyacrylate, sintering aid and deionized water are mixed in proportion. After mixing, the mixture is ball-milled at 100 rpm for 10 min, and then ball-milled at 400 rpm under a vacuum of -0.09 MPa for 40 min to obtain a composite slurry.

[0120] The mass ratio of modified silicon carbide powder to modified ceramic whiskers in the composite slurry is 100:10. The amount of hydroxypropyl methylcellulose added is 0.5 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The amount of ammonium polyacrylate added is 1 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The sintering aid is composed of Al2O3 and Y2O3 in a molar ratio of 5:3. The amount of sintering aid added is 1 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The viscosity of the composite slurry is controlled at 2000 mPa·s by controlling the amount of deionized water added.

[0121] S4. 3D print the composite slurry. Set the printing speed to 10mm / s, the printing spacing to 1mm, and the single-layer printing thickness to 0.3mm. After printing, a blank is obtained. Then, the blank is statically cured at 25℃ and 60%RH for 12 hours. After curing, it is dried at 50℃ for 48 hours.

[0122] After drying, the dried blank is heated to 400℃ at a heating rate of 0.3℃ / min and held for 2 hours to complete low-temperature degreasing. Then, it is heated to 600℃ at a heating rate of 1℃ / min and held for 2 hours to complete high-temperature degreasing.

[0123] After degreasing, the degreased blank was heated to 1400℃ at a heating rate of 3℃ / min and held for 1 hour to complete low-temperature sintering. Then, it was heated to 1900℃ at a heating rate of 5℃ / min and held for 2 hours to complete high-temperature sintering. The blank was then cooled to room temperature in the furnace to obtain the silicon carbide composite material.

[0124] Figure 2 The infrared spectra of silicon carbide powder, polyethyleneimine, and the modified silicon carbide powder prepared in this example are shown in the figure. As can be seen from the figure, in the spectral curve of polyethyleneimine, the 3300 cm⁻¹... -1 A broad and strong absorption peak appears at 2900 cm⁻¹, which is attributed to the NH stretching vibrations of the primary and secondary amines in the polyethyleneimine molecule; -1 The absorption peak at 1640 cm⁻¹ is attributed to the symmetric and asymmetric stretching vibrations of the methylene group (-CH₂-) in the polyethyleneimine molecular chain; -1 The absorption peaks at 1000–1100 cm⁻¹ are attributed to the bending vibration of NH₄⁺ and the stretching vibration of CN₄, which are typical characteristic peaks of polyethyleneimine. In the spectral curve of silicon carbide powder, the absorption peaks in the 1000–1100 cm⁻¹ range are also characteristic. -1 The relatively broad absorption band appearing within the range is a characteristic peak of the stretching vibration of the Si-C bond. This peak is retained in the spectral curve of modified silicon carbide powder in the 1000–1100 cm⁻¹ range. -1 The characteristic absorption peak of the Si-C bond at 3300 cm⁻¹ is observed. -1 A broad absorption peak, identical to that of polyethyleneimine, appeared at 2900 cm⁻¹. -1 An absorption peak for CH bonds also appeared at the surface, indicating that polyethyleneimine molecules have been successfully adsorbed onto the surface of silicon carbide powder.

[0125] Figure 3 The image shows a transmission electron microscope (TEM) image of the modified ceramic whiskers prepared in this embodiment. As can be seen from the image, the modified ceramic whiskers have a complete overall morphology and a relatively smooth surface. A continuous and dense thin film coating layer with a contrasting appearance to the internal matrix is ​​wrapped around the modified ceramic whiskers. This is the VB2 protective layer formed on the surface of the silicon carbide whiskers during the high-temperature calcination process. The VB2 protective layer is tightly bonded to the silicon carbide whisker body, without obvious peeling or cracks.

[0126] Figure 4 The image shows a scanning electron microscope (SEM) image of the composite slurry prepared in this embodiment. As can be seen from the image, the modified ceramic whiskers are uniformly dispersed in the modified silicon carbide powder. The modified ceramic whiskers play a good bridging and skeletal support role, which helps to promote the densification of the green body and effectively transfer the load during the subsequent sintering process.

[0127] Example 2

[0128] This embodiment provides a method for preparing high-strength, high-modulus silicon carbide composite materials for 3D printing of special ceramics, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0129] S1. Silicon carbide powder with a particle size D90 of 1.5 μm was dispersed in a 2 wt% aqueous solution of polyethyleneimine, with a mass ratio of silicon carbide powder to polyethyleneimine in the aqueous solution of 100:3.5. A 10 wt% aqueous solution of ammonia was added dropwise to the aqueous solution of polyethyleneimine to adjust its pH value to 9.2. The mixture was heated at 55°C and 300 rpm for 2.8 h. Then, it was filtered and the residue was dried at 85°C for 9.5 h to obtain modified silicon carbide powder.

[0130] S2. Ammonium metavanadate and boric acid were added to deionized water to obtain a precursor solution. The concentration of ammonium metavanadate in the precursor solution was 0.08 mol / L, and the concentration of boric acid was 0.12 mol / L. Silicon carbide whiskers with a diameter of 0.2 μm and a length of 50 μm were dispersed in the precursor solution. The mass ratio of silicon carbide whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution was 1:0.15. The mixture was heated at 72°C and 300 rpm for 2.8 h. Then, it was filtered, and the residue was dried at 85°C for 10 h to obtain the precursor whiskers.

[0131] The precursor whiskers were placed in a mixed atmosphere of argon and hydrogen (hydrogen volume fraction of 3.5%), heated to 1220℃ at a heating rate of 6℃ / min and held for 2.5h to complete the calcination, so as to form a VB2 protective layer on the surface of silicon carbide whiskers and obtain modified ceramic whiskers.

[0132] S3. Modified silicon carbide powder, modified ceramic whiskers, hydroxypropyl methylcellulose, ammonium polyacrylate, sintering aid and deionized water are mixed in proportion. After mixing, the mixture is ball-milled at a low speed of 120 rpm for 8 min, and then ball-milled at a high speed of 420 rpm for 38 min under a vacuum of -0.092 MPa to obtain a composite slurry.

[0133] The mass ratio of modified silicon carbide powder to modified ceramic whiskers in the composite slurry is 100:12. The amount of hydroxypropyl methylcellulose added is 0.8 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The amount of ammonium polyacrylate added is 1.2 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The sintering aid is composed of Al2O3 and Y2O3 in a molar ratio of 5:3. The amount of sintering aid added is 1.5 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The viscosity of the composite slurry is controlled at 2200 mPa·s by controlling the amount of deionized water added.

[0134] S4. 3D print the composite slurry. Set the printing speed to 10mm / s, the printing spacing to 1mm, and the single-layer printing thickness to 0.3mm. After printing, a blank is obtained. Then, the blank is statically cured at 25℃ and 60%RH for 15h. After curing, it is dried at 52℃ for 42h.

[0135] After drying, the dried blank was heated to 420℃ at a heating rate of 0.35℃ / min and held for 1.8h to complete low-temperature degreasing. Then, it was heated to 620℃ at a heating rate of 1.2℃ / min and held for 1.8h to complete high-temperature degreasing.

[0136] After degreasing, the degreased blank was heated to 1450℃ at a heating rate of 3.5℃ / min and held for 0.8h to complete low-temperature sintering. Then, it was heated to 1950℃ at a heating rate of 6℃ / min and held for 1.8h to complete high-temperature sintering. The blank was then cooled to room temperature in the furnace to obtain the silicon carbide composite material.

[0137] Example 3

[0138] This embodiment provides a method for preparing high-strength, high-modulus silicon carbide composite materials for 3D printing of special ceramics, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0139] S1. Silicon carbide powder with a particle size D90 of 1.5 μm was dispersed in a 3 wt% aqueous solution of polyethyleneimine, with a mass ratio of silicon carbide powder to polyethyleneimine in the aqueous solution of 100:4. A 10 wt% aqueous solution of ammonia was added dropwise to the aqueous solution of polyethyleneimine to adjust its pH value to 9.5. The mixture was heated at 60°C and 300 rpm for 2.5 h. Then, it was filtered and the residue was dried at 90°C for 9 h to obtain modified silicon carbide powder.

[0140] S2. Ammonium metavanadate and boric acid were added to deionized water to obtain a precursor solution. The concentration of ammonium metavanadate in the precursor solution was 0.1 mol / L, and the concentration of boric acid was 0.15 mol / L. Silicon carbide whiskers with a diameter of 0.2 μm and a length of 50 μm were dispersed in the precursor solution. The mass ratio of silicon carbide whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution was 1:0.2. The mixture was heated at 75°C and 300 rpm for 2.5 h, followed by filtration. The residue was dried at 90°C for 8 h to obtain the precursor whiskers.

[0141] The precursor whiskers were placed in a mixed atmosphere of argon and hydrogen (hydrogen volume fraction of 4%), heated to 1250℃ at a heating rate of 6℃ / min and held for 2h to complete the calcination, so as to form a VB2 protective layer on the surface of silicon carbide whiskers and obtain modified ceramic whiskers.

[0142] S3. Modified silicon carbide powder, modified ceramic whiskers, hydroxypropyl methylcellulose, ammonium polyacrylate, sintering aid and deionized water are mixed in proportion. After mixing, the mixture is ball-milled at a low speed of 150 rpm for 7 min, and then ball-milled at a high speed of 450 rpm under a vacuum of -0.095 MPa for 35 min to obtain a composite slurry.

[0143] The mass ratio of modified silicon carbide powder to modified ceramic whiskers in the composite slurry is 100:15. The amount of hydroxypropyl methylcellulose added is 1 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The amount of ammonium polyacrylate added is 1.5 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The sintering aid is composed of Al2O3 and Y2O3 in a molar ratio of 5:3. The amount of sintering aid added is 2 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The viscosity of the composite slurry is controlled at 2500 mPa·s by controlling the amount of deionized water added.

[0144] S4. 3D print the composite slurry. Set the printing speed to 10mm / s, the printing spacing to 1mm, and the single-layer printing thickness to 0.3mm. After printing, a blank is obtained. Then, the blank is statically cured at 25℃ and 60%RH for 18h. After curing, it is dried at 55℃ for 36h.

[0145] After drying, the dried blank is heated to 450℃ at a heating rate of 0.4℃ / min and held for 1.5h to complete low-temperature degreasing. Then, it is heated to 650℃ at a heating rate of 1.5℃ / min and held for 1.5h to complete high-temperature degreasing.

[0146] After degreasing, the degreased blank was heated to 1500℃ at a heating rate of 4℃ / min and held for 0.7h to complete low-temperature sintering. Then, it was heated to 2000℃ at a heating rate of 6℃ / min and held for 1.5h to complete high-temperature sintering. The blank was then cooled to room temperature in the furnace to obtain the silicon carbide composite material.

[0147] Example 4

[0148] This embodiment provides a method for preparing high-strength, high-modulus silicon carbide composite materials for 3D printing of special ceramics, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0149] S1. Silicon carbide powder with a particle size D90 of 1.5 μm was dispersed in a 4 wt% aqueous solution of polyethyleneimine, with a mass ratio of silicon carbide powder to polyethyleneimine in the aqueous solution of 100:4.5. A 10 wt% aqueous solution of ammonia was added dropwise to the aqueous solution of polyethyleneimine to adjust its pH value to 9.8. The mixture was heated at 65°C and 300 rpm for 2.2 h. Then, it was filtered and the residue was dried at 95°C for 8.5 h to obtain modified silicon carbide powder.

[0150] S2. Ammonium metavanadate and boric acid were added to deionized water to obtain a precursor solution. The concentration of ammonium metavanadate in the precursor solution was 0.12 mol / L, and the concentration of boric acid was 0.18 mol / L. Silicon carbide whiskers with a diameter of 0.2 μm and a length of 50 μm were dispersed in the precursor solution. The mass ratio of silicon carbide whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution was 1:0.25. The mixture was heated at 78°C and 300 rpm for 2.2 h, followed by filtration. The residue was dried at 95°C for 7 h to obtain the precursor whiskers.

[0151] The precursor whiskers were placed in a mixed atmosphere of argon and hydrogen (hydrogen volume fraction of 4.5%), heated to 1280℃ at a heating rate of 7℃ / min and held for 1.5h to complete the calcination, so as to form a VB2 protective layer on the surface of silicon carbide whiskers and obtain modified ceramic whiskers.

[0152] S3. Modified silicon carbide powder, modified ceramic whiskers, hydroxypropyl methylcellulose, ammonium polyacrylate, sintering aid and deionized water are mixed in proportion. After mixing, the mixture is ball-milled at a low speed of 180 rpm for 6 min, and then ball-milled at a high speed of 480 rpm for 32 min under a vacuum of -0.098 MPa to obtain a composite slurry.

[0153] The mass ratio of modified silicon carbide powder to modified ceramic whiskers in the composite slurry is 100:18. The amount of hydroxypropyl methylcellulose added is 1.2 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The amount of ammonium polyacrylate added is 1.8 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The sintering aid is composed of Al2O3 and Y2O3 in a molar ratio of 5:3. The amount of sintering aid added is 2.5 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The viscosity of the composite slurry is controlled at 2800 mPa·s by controlling the amount of deionized water added.

[0154] S4. 3D print the composite slurry. Set the printing speed to 10mm / s, the printing spacing to 1mm, and the single-layer printing thickness to 0.3mm. After printing, a blank is obtained. Then, the blank is statically cured at 25℃ and 60%RH for 21h. After curing, it is dried at 58℃ for 30h.

[0155] After drying, the dried blank was heated to 480℃ at a heating rate of 0.45℃ / min and held for 1.2h to complete low-temperature degreasing. Then, it was heated to 680℃ at a heating rate of 1.8℃ / min and held for 1.2h to complete high-temperature degreasing.

[0156] After degreasing, the degreased blank was heated to 1550℃ at a heating rate of 4.5℃ / min and held for 0.6h to complete low-temperature sintering. Then, it was heated to 2050℃ at a heating rate of 7℃ / min and held for 1.2h to complete high-temperature sintering. The blank was then cooled to room temperature in the furnace to obtain the silicon carbide composite material.

[0157] Example 5

[0158] This embodiment provides a method for preparing high-strength, high-modulus silicon carbide composite materials for 3D printing of special ceramics, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0159] S1. Silicon carbide powder with a particle size D90 of 1.5 μm was dispersed in a 5 wt% aqueous solution of polyethyleneimine, with a mass ratio of silicon carbide powder to polyethyleneimine in the aqueous solution of 100:5. A 10 wt% aqueous solution of ammonia was added dropwise to the aqueous solution of polyethyleneimine to adjust its pH value to 10. The mixture was heated at 70°C and 300 rpm for 2 h. Then, it was filtered and the residue was dried at 100°C for 8 h to obtain modified silicon carbide powder.

[0160] S2. Ammonium metavanadate and boric acid were added to deionized water to obtain a precursor solution. The concentration of ammonium metavanadate in the precursor solution was 0.15 mol / L, and the concentration of boric acid was 0.2 mol / L. Silicon carbide whiskers with a diameter of 0.2 μm and a length of 50 μm were dispersed in the precursor solution. The mass ratio of silicon carbide whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution was 1:0.3. The mixture was heated at 80°C and 300 rpm for 2 hours. Then, it was filtered. The residue was dried at 100°C for 6 hours to obtain the precursor whiskers.

[0161] The precursor whiskers were placed in a mixed atmosphere of argon and hydrogen (hydrogen volume fraction of 5%), heated to 1300℃ at a heating rate of 8℃ / min and held for 1h to complete the calcination, so as to form a VB2 protective layer on the surface of silicon carbide whiskers and obtain modified ceramic whiskers.

[0162] S3. Modified silicon carbide powder, modified ceramic whiskers, hydroxypropyl methylcellulose, ammonium polyacrylate, sintering aid and deionized water are mixed in proportion. After mixing, the mixture is ball-milled at a low speed of 200 rpm for 5 min, and then ball-milled at a high speed of -0.1 MPa vacuum and 500 rpm for 30 min to obtain composite slurry.

[0163] The mass ratio of modified silicon carbide powder to modified ceramic whiskers in the composite slurry is 100:20. The amount of hydroxypropyl methylcellulose added is 1.5 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The amount of ammonium polyacrylate added is 2 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The sintering aid is composed of Al2O3 and Y2O3 in a molar ratio of 5:3. The amount of sintering aid added is 3 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. The viscosity of the composite slurry is controlled at 3000 mPa·s by controlling the amount of deionized water added.

[0164] S4. 3D print the composite slurry. Set the printing speed to 10mm / s, the printing spacing to 1mm, and the single-layer printing thickness to 0.3mm. After printing, a blank is obtained. Then, the blank is statically cured at 25℃ and 60%RH for 24 hours. After curing, it is dried at 60℃ for 24 hours.

[0165] After drying, the dried blank is heated to 500℃ at a heating rate of 0.5℃ / min and held for 1 hour to complete low-temperature degreasing. Then, it is heated to 700℃ at a heating rate of 2℃ / min and held for 1 hour to complete high-temperature degreasing.

[0166] After degreasing, the degreased blank was heated to 1600℃ at a heating rate of 5℃ / min and held for 0.5h to complete low-temperature sintering. Then, it was heated to 2100℃ at a heating rate of 8℃ / min and held for 1h to complete high-temperature sintering. The blank was then cooled to room temperature in the furnace to obtain the silicon carbide composite material.

[0167] Comparative Example 1

[0168] This comparative example provides a method for preparing a high-strength, high-modulus 3D printing silicon carbide composite material for special ceramics. The difference from Example 1 is that in S1, the mass ratio of silicon carbide powder to polyethyleneimine in the polyethyleneimine aqueous solution is adjusted to 100:1. Other operating steps and process parameters are exactly the same as in Example 1.

[0169] Comparative Example 2

[0170] This comparative example provides a method for preparing a high-strength, high-modulus 3D printing silicon carbide composite material for special ceramics. The difference from Example 1 is that in S1, the mass ratio of silicon carbide powder to polyethyleneimine in the polyethyleneimine aqueous solution is adjusted to 100:8. Other operating steps and process parameters are exactly the same as in Example 1.

[0171] Comparative Example 3

[0172] This comparative example provides a method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics. The difference from Example 1 is that in S2, the ratio of the mass of ceramic whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution is adjusted to 1:0.05. Other operating steps and process parameters are exactly the same as in Example 1.

[0173] Comparative Example 4

[0174] This comparative example provides a method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics. The difference from Example 1 is that in S2, the ratio of the mass of ceramic whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution is adjusted to 1:0.5. Other operating steps and process parameters are exactly the same as in Example 1.

[0175] Comparative Example 5

[0176] This comparative example provides a method for preparing a high-strength, high-modulus 3D printing silicon carbide composite material for special ceramics. The difference from Example 1 is that in S2, the calcination temperature is adjusted to 1000℃, while the other operation steps and process parameters are exactly the same as in Example 1.

[0177] Comparative Example 6

[0178] This comparative example provides a method for preparing a high-strength, high-modulus 3D printing silicon carbide composite material for special ceramics. The difference from Example 1 is that in S2, the calcination temperature is adjusted to 1500℃, while the other operation steps and process parameters are exactly the same as in Example 1.

[0179] Comparative Example 7

[0180] This comparative example provides a method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics. The difference from Example 1 is that in S3, the mass ratio of modified silicon carbide powder to modified ceramic whiskers is adjusted to 100:5, while other operating steps and process parameters are exactly the same as in Example 1.

[0181] Comparative Example 8

[0182] This comparative example provides a method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics. The difference from Example 1 is that in S3, the mass ratio of modified silicon carbide powder to modified ceramic whiskers is adjusted to 100:30, while other operating steps and process parameters are exactly the same as in Example 1.

[0183] Comparative Example 9

[0184] This comparative example provides a method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics. The difference from Example 1 is that in S3, the amount of sintering aid added is 0.5 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. Other operating steps and process parameters are exactly the same as in Example 1.

[0185] Comparative Example 10

[0186] This comparative example provides a method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics. The difference from Example 1 is that in S3, the amount of sintering aid added is 5 wt% of the total mass of modified silicon carbide powder and modified ceramic whiskers. Other operating steps and process parameters are exactly the same as in Example 1.

[0187] The flexural strength, elastic modulus, and bulk density of the high-strength, high-modulus silicon carbide composite materials for special ceramics prepared in Examples 1-5 and Comparative Examples 1-10 were tested. The specific test steps are as follows:

[0188] (1) Bending strength: Bending strength is one of the most critical indicators for evaluating the mechanical properties of structural ceramic materials. It directly reflects the material’s ability to resist fracture under complex stress conditions. In this invention, the bending strength is tested using GB / T6569-2006 “Test Method for Bending Strength of Fine Ceramics”.

[0189] (2) Elastic modulus: Elastic modulus is an index that measures the ability of a material to resist elastic deformation. The higher the value, the greater the stiffness of the material. In this invention, the elastic modulus is tested according to GB / T10700-2006 "Test Method for Elastic Modulus of Fine Ceramics".

[0190] (3) Bulk density: Bulk density is the most direct indicator for evaluating the degree of densification of sintered ceramic bodies. It is closely related to the mechanical and thermal properties of materials. High density is a prerequisite for obtaining high strength and high modulus. In this invention, the bulk density is tested according to GB / T25995-2010 "Test Method for Density and Apparent Porosity of Fine Ceramics".

[0191] The test results are shown in Table 1.

[0192] Table 1. Performance test results of high-strength, high-modulus silicon carbide composite materials for special ceramics prepared in Examples 1-5 and Comparative Examples 1-10.

[0193] Example 1 498.4 428.7 3.07 Example 2 506.8 421.9 3.09 Example 3 512.5 435.6 3.08 Example 4 487.6 442.2 3.06 Example 5 495.2 417.4 3.10 Comparative Example 1 421.1 385.5 2.89 Comparative Example 2 398.7 362.8 2.82 Comparative Example 3 378.3 352.2 2.80 Comparative Example 4 405.6 348.8 2.88 Comparative Example 5 392.5 366.9 2.78 Comparative Example 6 435.2 339.5 2.91 Comparative Example 7 452.9 392.6 2.93 Comparative Example 8 368.4 401.3 2.75 Comparative Example 9 362.9 335.7 2.72 Comparative Example 10 423.2 387.3 2.95

[0194] As can be seen from the test data of Example 1, Comparative Example 1, and Comparative Example 2 in Table 1, when the amount of polyethyleneimine is too low (Comparative Example 1), the dispersion of silicon carbide powder is poor, resulting in a decrease in the uniformity of the composite slurry. The composite material obtained after sintering has more internal defects, and the flexural strength, elastic modulus, and bulk density of the composite material all show a significant decrease. When the amount of polyethyleneimine is too high (Comparative Example 2), the excessive free polyethyleneimine molecules cause silicon carbide powder agglomeration and generate more gas during the debinding process, damaging the structure of the preform and ultimately leading to a significant decrease in the flexural strength, elastic modulus, and bulk density of the composite material.

[0195] As can be seen from the test data of Example 1, Comparative Example 3, and Comparative Example 4 in Table 1, when the dosage of ammonium metavanadate and boric acid is too low (Comparative Example 3), the generated VB2 protective layer is discontinuous and not dense, and cannot effectively protect the ceramic whiskers during high-temperature sintering. This leads to the ceramic whiskers being eroded by high temperature, and their reinforcing and toughening effects cannot be effectively exerted, ultimately resulting in a significant decrease in the flexural strength and elastic modulus of the composite material. When the dosage of ammonium metavanadate and boric acid is too high (Comparative Example 4), the excess VB2 exists in the green body in the form of free particles, becoming stress concentration points, and cracking occurs due to the excessive thickness of the VB2 protective layer, ultimately leading to a significant decrease in the flexural strength and elastic modulus of the composite material.

[0196] As can be seen from the test data of Example 1, Comparative Example 5, and Comparative Example 6 in Table 1, when the calcination temperature is too low (Comparative Example 5), the reaction is incomplete, the crystallinity of the VB2 protective layer is poor, and the bond between it and the ceramic whiskers is not strong, thus failing to provide effective physical protection. Simultaneously, the densification process of the green body is also affected, ultimately leading to a significant decrease in the flexural strength, elastic modulus, and bulk density of the composite material. When the calcination temperature is too high (Comparative Example 6), it causes structural damage to the ceramic whiskers themselves, severely affecting the reinforcing and toughening effect of the ceramic whiskers. Furthermore, excessively high calcination temperatures can also lead to abnormal grain growth, ultimately resulting in a significant decrease in the flexural strength and elastic modulus of the composite material.

[0197] As can be seen from the test data of Example 1, Comparative Example 7, and Comparative Example 8 in Table 1, when the amount of modified ceramic whiskers is too low (Comparative Example 7), the reinforcing and toughening effect of the modified ceramic whiskers cannot be fully utilized, ultimately resulting in limited improvement in the flexural strength and elastic modulus of the composite material. When the amount of modified ceramic whiskers is too high (Comparative Example 8), it will seriously affect the rheological properties of the composite slurry, resulting in a low bulk density of the printed green body, which hinders the densification of the green body during sintering. At the same time, the modified ceramic whiskers are prone to agglomeration in the composite slurry, becoming stress concentration points, ultimately leading to a significant decrease in the flexural strength, elastic modulus, and bulk density of the composite material.

[0198] As can be seen from the test data of Example 1, Comparative Example 9, and Comparative Example 10 in Table 1, when the amount of sintering aid is too small (Comparative Example 9), the amount of liquid phase generated at high temperature is insufficient, which cannot fully promote particle rearrangement and pore filling, resulting in low density of the sintered body. Ultimately, this leads to a significant decrease in the flexural strength, elastic modulus, and bulk density of the composite material. When the amount of sintering aid is too large (Comparative Example 10), the excess liquid phase will form a continuous low-performance phase at the grain boundaries, becoming a weak area in the material, ultimately leading to a significant decrease in the flexural strength and elastic modulus of the composite material.

[0199] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing high-strength, high-modulus silicon carbide composite materials for 3D printing of special ceramics, characterized in that, The preparation method includes: S1. Disperse silicon carbide powder in a polyethyleneimine aqueous solution, wherein the mass ratio of silicon carbide powder to polyethyleneimine in the polyethyleneimine aqueous solution is 100:(3~5). Add ammonia solution dropwise to adjust the pH value, then mix, stir and heat, and finally filter and dry to obtain modified silicon carbide powder. S2. Ammonium metavanadate and boric acid are added to deionized water to obtain a precursor solution. Ceramic whiskers, which are silicon carbide whiskers, are dispersed in the precursor solution. The mass ratio of the ceramic whiskers to the total mass of ammonium metavanadate and boric acid in the precursor solution is 1:(0.1~0.3). The mixture is stirred and heated, then filtered and dried to obtain precursor whiskers. The precursor whiskers are calcined in a mixed atmosphere of argon and hydrogen at a temperature of 1200~1300℃ to obtain modified ceramic whiskers. S3. The modified silicon carbide powder, the modified ceramic whiskers, the binder, the dispersant, the sintering aid, and deionized water are mixed evenly to obtain a composite slurry. The sintering aid is composed of Al2O3 and Y2O3, and the molar ratio of Al2O3 to Y2O3 is 5:

3. The mass ratio of the modified silicon carbide powder to the modified ceramic whiskers is 100:(10~20), and the amount of sintering aid added is 1~3 wt% of the total mass of the modified silicon carbide powder and the modified ceramic whiskers. S4. The composite slurry is 3D printed to obtain a green body; the green body is then subjected to static curing, drying, degreasing and sintering in sequence, and cooled to room temperature in the furnace to obtain the silicon carbide composite material.

2. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S1, The polyethyleneimine in the aqueous solution has a polyethyleneimine mass fraction of 1-5 wt%. The pH value is adjusted to 9-10 by adding ammonia solution dropwise; The mixing and heating temperature is 50~70℃, and the time is 2~3h.

3. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S2, The concentration of ammonium metavanadate in the precursor solution is 0.05~0.15 mol / L; The concentration of boric acid in the precursor solution is 0.1~0.2 mol / L; The mixing and heating temperature is 70~80℃, and the time is 2~3h.

4. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S2, The volume fraction of hydrogen in the mixed atmosphere is 3-5%; The heating rate of the calcination is 5~8℃ / min; The calcination holding time is 1 to 3 hours.

5. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S3 The amount of binder added is 0.5~1.5 wt% of the total mass of the modified silicon carbide powder and the modified ceramic whiskers; The adhesive is hydroxypropyl methylcellulose; The amount of the dispersant added is 1-2 wt% of the total mass of the modified silicon carbide powder and the modified ceramic whiskers; The dispersant is ammonium polyacrylate; The viscosity of the composite slurry is 2000~3000 mPa·s.

6. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S3 The process of mixing the modified silicon carbide powder, modified ceramic whiskers, binder, dispersant, sintering aid and deionized water includes sequential low-speed ball milling and high-speed ball milling. The low-speed ball mill has a milling speed of 100~200 rpm and a milling time of 5~10 min; The high-speed ball mill has a milling speed of 400~500 rpm, a milling time of 30~40 min, and a vacuum degree of -0.09~-0.1 MPa.

7. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S4, The static curing time is 12~24 hours; The drying temperature is 50~60℃, and the time is 24~48h.

8. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S4, The degreasing process includes sequential low-temperature degreasing and high-temperature degreasing; The heating rate for the low-temperature degreasing is 0.3~0.5℃ / min, the temperature is 400~500℃, and the holding time is 1~2h; The heating rate for the high-temperature degreasing is 1~2℃ / min, the temperature is 600~700℃, and the holding time is 1~2h.

9. The method for preparing a high-strength, high-modulus silicon carbide composite material for 3D printing of special ceramics according to claim 1, characterized in that, In S4, The sintering process is carried out in an argon atmosphere and includes sequential low-temperature sintering and high-temperature sintering. The heating rate for the low-temperature sintering is 3~5℃ / min, the temperature is 1400~1600℃, and the holding time is 0.5~1h; The high-temperature sintering process involves a heating rate of 5-8℃ / min, a temperature of 1900-2100℃, and a holding time of 1-2 hours.

10. A high-strength, high-modulus 3D-printed silicon carbide composite material for special ceramics prepared by the preparation method of any one of claims 1 to 9.

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