A double system forming compound for complex shape silicon carbide ceramics and its preparation method

Abstract

The application discloses a double-system forming combined material for complex-shaped silicon carbide ceramics and a preparation method thereof. The combined material comprises a fine replication slurry and a structure filling slurry; the fine replication slurry comprises fine-particle silicon carbide powder, boron carbide powder, phenolic resin, liquid potassium sodium silicate water glass and ethanol; and the structure filling slurry comprises coarse-particle silicon carbide powder, fine-particle silicon carbide powder, boron carbide powder, phenolic resin, liquid potassium sodium silicate water glass and ethanol. The whole ceramic blank is constructed by the fine replication layer and the structure filling body, and the complex-shaped silicon carbide ceramic product is obtained through carbon dioxide solidification, demolding, pre-burning, shape-following supporting and high-temperature sintering. The application takes into account the forming precision, surface quality, size stability and mechanical properties, and is suitable for the preparation of complex curved surface, thin-walled and special-shaped inner cavity silicon carbide ceramic products.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation technology, specifically to a dual-system molding compound for complex-shaped silicon carbide ceramics and its preparation method. Background Technology

[0002] Silicon carbide (SiC) ceramics possess high hardness, high wear resistance, excellent high-temperature resistance, good chemical stability, and high thermal conductivity, making them promising for applications in aerospace, semiconductor equipment, precision machinery, chemical engineering, and environmental protection. However, the inherent high hardness and brittleness of silicon carbide ceramics make them difficult to machine after sintering. Traditional machining methods are not only inefficient and result in high tool wear, but also struggle to process complex shapes, especially those with internal cavities, thin walls, or suspended structures.

[0003] Currently, the main methods for preparing complex-shaped silicon carbide ceramic products include slip casting, gel casting, injection molding, and direct 3D printing. Slip casting relies on plaster molds, which have long manufacturing cycles, are difficult to demold for complex internal structures, and result in poor uniformity of green body density. While gel casting can achieve relatively complex shapes, the process involves the polymerization of organic monomers, requiring high degassing of the slurry, and is prone to cracking during drying; furthermore, the removal of organic matter is complex. Injection molding requires specialized injection molds, which are costly and uneconomical for small-batch, multi-variety complex-shaped products; additionally, the debinding process is prone to defects. Although direct 3D printing can theoretically produce any complex shape, current silicon carbide 3D printing technologies generally suffer from insufficient forming accuracy, high surface roughness, and low green body density, making it difficult to meet the application requirements of high-precision silicon carbide ceramic products. Furthermore, investment casting typically involves repeatedly applying slurry, sprinkling sand, and dewaxing the outer surface of a wax pattern. The resulting ceramic shell or core is used for subsequent metal casting and is not intended as the final silicon carbide structure ceramic product. Therefore, using the phrase "sacrificial mold coating to form a shell" can easily lead to confusion with the aforementioned casting shell-making process.

[0004] Therefore, there is an urgent need to develop a preparation method that can achieve near-net-shape forming of complex-shaped silicon carbide ceramic products while taking into account high dimensional accuracy, good surface quality and excellent mechanical properties. Summary of the Invention

[0005] The present invention aims to solve the following technical problems existing in the existing silicon carbide ceramic preparation methods: (1) It is difficult to achieve near-net-shape forming of silicon carbide ceramic products with complex curved surfaces, thin walls, suspended structures and irregular internal cavities; (2) The forming accuracy is insufficient, the dimensional deviation is large after sintering, and the surface roughness is high; (3) The green body is prone to cracking, deformation and other defects during demolding and sintering; (4) The density and mechanical properties of the products are difficult to meet the requirements for use.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a dual-system molding composite material for complex-shaped silicon carbide ceramics, comprising independently formulated fine replication slurry and structural filling slurry; By weight, the fine replication slurry comprises: 100 parts of fine-grained silicon carbide micro powder, 0.5 to 1.0 parts of boron carbide micro powder, 5 to 9 parts of phenolic resin, 8 to 14 parts of liquid potassium sodium silicate water glass, and 12 to 20 parts of ethanol. The structural filler slurry comprises, by weight, 35-55 parts of coarse-grained silicon carbide micro powder, 45-65 parts of fine-grained silicon carbide micro powder, 0.5-1.0 parts of boron carbide micro powder, 7-13 parts of phenolic resin, 6-11 parts of liquid potassium sodium silicate water glass, and 8-15 parts of ethanol. The total amount of coarse-grained silicon carbide micro powder and fine-grained silicon carbide micro powder in the structural filling slurry is 100 parts by mass. The fine replication slurry uses fine-grained silicon carbide micro powder as silicon carbide ceramic aggregate to form the fine replication area on the surface of the silicon carbide ceramic green body; the structural filling slurry uses a coarse-fine particle size distribution formed by coarse-grained silicon carbide micro powder and fine-grained silicon carbide micro powder as silicon carbide ceramic aggregate to form the internal solid area of ​​the silicon carbide ceramic green body. After curing, the fine replication slurry and the structural filling slurry form a continuously bonded integral silicon carbide ceramic green body.

[0007] Furthermore, the fine-grained silicon carbide micro powder includes submicron silicon carbide micro powder with a D50 particle size of 0.5 to 1.0 μm and one or more selected from F240, F320, F360, F400, F500 and F600 silicon carbide micro powder, wherein the submicron silicon carbide micro powder accounts for 50 to 80% of the total mass of the fine-grained silicon carbide micro powder.

[0008] Furthermore, the coarse-grained silicon carbide micro powder is selected from one or more of F100, F120, 100# and 120# silicon carbide micro powder.

[0009] Furthermore, the phenolic resin is a thermosetting liquid phenolic resin with a solid content of 65% to 75% and a residual carbon rate of not less than 40%.

[0010] Furthermore, by weight: the fine replication slurry is composed of 100 parts of fine-grained silicon carbide micro powder, 0.6-0.8 parts of boron carbide micro powder, 5-7 parts of phenolic resin, 9-12 parts of liquid potassium sodium silicate water glass, and 15-20 parts of ethanol. The structural filling slurry is composed of 40-50 parts of coarse-grained silicon carbide micro powder, 50-60 parts of fine-grained silicon carbide micro powder, 0.6-0.8 parts of boron carbide micro powder, 8-11 parts of phenolic resin, 7-9 parts of liquid potassium sodium silicate water glass, and 10-15 parts of ethanol, wherein the total amount of the coarse-grained silicon carbide micro powder and the fine-grained silicon carbide micro powder is 100 parts by mass.

[0011] This invention also provides a method for preparing complex-shaped silicon carbide ceramic products using a two-system molding compound, comprising the following steps: S1. Prepare a removable sacrificial mold with a molding cavity based on a three-dimensional model of a silicon carbide ceramic product with a complex shape to be prepared. The molding cavity corresponds to the solid material region of the silicon carbide ceramic product to be prepared. The inner wall contour of the molding cavity corresponds to the outer surface contour of the silicon carbide ceramic product to be prepared. The required channels or cavities of the product are defined by molding protrusions set in the molding cavity. The linear dimensions of the molding cavity are enlarged according to the compensation coefficient K=1 / (1-s), where s is a small value of the sintering linear shrinkage rate of the pre-sample prepared using the same ceramic composite material and the same sintering process. A main gas channel and a branch gas channel that communicates with the main gas channel and extends to the inner wall of the molding cavity are provided inside the mold wall of the sacrificial mold. The diameter of the main gas channel is 3 to 10 mm, the diameter of the branch gas channel is 0.5 to 3 mm, and the distance between the outlets of adjacent branch gas channels is 5 to 20 mm. The sacrificial mold is provided with a feed port, an exhaust port and a demolding outlet that are connected to the molding cavity, and is printed using PLA printing material or casting wax 3D printing material; S2. The above-mentioned fine replication paste is applied to the inner wall of the molding cavity to form a fine replication layer with a thickness of 0.3 to 1.2 mm, and then surface-dried at 40 to 60°C for 10 to 30 minutes. S3. The structural filling slurry is added into the molding cavity where the fine replication layer is formed through the feed port, and the gas in the cavity is discharged through the exhaust port, so that the structural filling slurry fills the remaining cavity space within the fine replication layer. The thickness of the structural filler in the thinnest part of the product is 1.5 to 6.0 mm. S4. Industrial carbon dioxide is continuously introduced through the gas channel inside the sacrificial mold wall, maintaining the positive pressure of the gas flow at 0.02-0.15MPa for 30-180s, so that the fine replication layer adjacent to the inner wall of the molding cavity begins to solidify from the sacrificial mold side toward the structural filler. After the surface gel of the fine replication layer is set at intervals of 30 to 150 seconds, the resulting composite is placed in a sealed curing chamber. Industrial carbon dioxide is continuously introduced into the sealed curing chamber to maintain the positive gauge pressure of 0.02 to 0.10 MPa and to ventilate for 60 to 300 seconds. At the same time, the main gas channel, feed port and exhaust port are connected to the carbon dioxide atmosphere in the chamber to allow the structural filler to continue to cure, resulting in an integral solid ceramic body composed of the fine replication layer and the structural filler continuously combined. S5. Remove the sacrificial anti-mode; When the sacrificial mold is a casting wax-based 3D printing material, the temperature is increased to 120-180℃ at a rate of 0.5-2.0℃ / min and held for 1-3 hours to allow the sacrificial mold to melt and be discharged. When the sacrificial mold is PLA printing material, the temperature is increased to 350-500℃ at 0.5-1.5℃ / min under a nitrogen atmosphere and held for 2-5 hours to thermally decompose the sacrificial mold. S6. Place the ceramic blank after removing the sacrificial mold in a graphite crucible, and heat it to 800-1000℃ at 0.5-3℃ / min under a nitrogen or argon atmosphere and hold it for 1-3 hours to further carbonize the phenolic resin to form a carbon bonded phase, thereby obtaining a silicon carbide pre-fired blank. S7. A boron nitride isolation layer with a thickness of 5-20 μm is formed on the surface of the silicon carbide pre-sintered blank. A silicon carbide micro powder support layer with a thickness of 3-10 mm and a D50 particle size of 9-45 μm is provided outside the boron nitride isolation layer. A silicon carbide micro powder breathable layer with a thickness of 10-30 mm and a D50 particle size of 100-150 μm is provided outside the support layer. S8. Under argon protection, the temperature is increased to 2000-2150℃ at 2-8℃ / min and held for 1-4 hours to sinter the silicon carbide ceramic blank. After cooling, the silicon carbide micro powder support layer and silicon carbide micro powder permeable layer are removed to obtain silicon carbide ceramic products with complex shapes.

[0012] Furthermore, the casting wax 3D printing material is selected from either casting white wax or high-temperature resistant red wax.

[0013] Furthermore, the thickness of the fine replication layer is 0.5 to 1.0 mm, and the thickness of the structural filler in the thinnest part of the workpiece is 2.0 to 4.0 mm.

[0014] Furthermore, during the first stage of carbon dioxide curing through the gas channel inside the sacrificial mold wall, the positive pressure of carbon dioxide is 0.05–0.10 MPa, and the ventilation time is 60–120 s; after an interval of 60–100 s, the second stage of carbon dioxide curing is carried out in the sealed curing chamber, where the positive pressure of carbon dioxide is 0.03–0.08 MPa, and the ventilation time is 120–200 s.

[0015] Furthermore, during the sintering process of the silicon carbide ceramic blank, the temperature is increased to 2050-2150℃ at a rate of 3-6℃ / min and held for 2-3 hours.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a strategy combining 3D printing of a removable sacrificial mold with full-volume cavity filling to achieve near-net-shape forming of complex-shaped silicon carbide ceramic products. The sacrificial mold is a negative mold used to define the forming cavity, with its inner wall corresponding to the product surface. Reverse dimensional compensation is implemented based on the sintering linear shrinkage rate of a pre-sample with the same formula and process, using K=1 / (1-s). The fine replication slurry forms a fine surface layer only on the inner wall of the cavity, while the structural filling slurry fills the remaining cavity space, ensuring a continuous and integral solid material area in the product design. This method differs from the process in investment casting where slurry is repeatedly applied to the outside of the wax model to prepare a self-supporting ceramic shell or core. In this invention, the sacrificial mold serves only as a removable forming tool; after demolding, what is retained is the integral silicon carbide blank as the final sintering object, rather than a ceramic shell for subsequent metal casting.

[0017] 2. This invention employs a staged positive pressure carbon dioxide curing process. First, by sacrificing the gas channels inside the mold wall, a fine replica layer tightly adhering to the inner wall of the cavity is preferentially gelled and shaped under a positive gauge pressure of 0.02-0.15 MPa. This fixes the surface contour of the product and inhibits the erosion and displacement of the fine layer by the structural filler slurry. Then, the composite is placed in a sealed curing chamber, and under a positive gauge pressure carbon dioxide atmosphere of 0.02-0.10 MPa, curing is achieved through multiple gas channels, inlets, and outlets, allowing the surface shaping and overall curing to proceed sequentially. This reduces interface cracking, gas retention, and local shrinkage defects caused by simultaneous overall curing. All pressures mentioned above are positive gauge pressures; negative pressure curing is not used.

[0018] 3. This invention employs a boron-carbon composite sintering aid to promote the densification of silicon carbide particles during high-temperature sintering: Phenolic resin is carbonized during pre-firing under a protective atmosphere to form activated carbon. On one hand, activated carbon reacts with the oxide film on the surface of silicon carbide powder to generate a silicon carbide bonding phase in situ, giving the green body sufficient operational strength. On the other hand, activated carbon, together with the boron source provided by boron carbide micropowder, constitutes a silicon carbide pressureless sintering aid system, promoting diffusion mass transfer and densification bonding between silicon carbide particles during the high-temperature sintering stage of 2000-2150℃. Liquid potassium sodium silicate water glass is used as a low-temperature curing agent. The alkali metal components introduced by liquid water glass volatilize and are discharged during the high-temperature sintering process, giving the product excellent mechanical properties.

[0019] 4. This invention employs a double-layer conformal support powder bed composed of a boron nitride isolation layer, a fine-grained silicon carbide micropowder support layer, and a coarse-grained silicon carbide micropowder permeable layer. The fine-grained support layer adheres closely to the surface of the pre-sintered blank, providing uniform conformal support for complex curved surfaces, thin-walled sections, and suspended structures, preventing deformation during high-temperature sintering. The coarse-grained permeable layer provides gas exhaust channels, ensuring the smooth escape of volatiles during sintering. The boron nitride isolation layer prevents the support powder bed from adhering to the product surface during high-temperature sintering. After sintering, the support powder bed is easy to remove without affecting the surface quality of the product. Attached Figure Description

[0020] Figure 1 This is a physical image of the product prepared in Example 1 of the present invention.

[0021] Figure 2 The images show X-ray photoelectron spectroscopy (XPS) analysis of the silicon carbide ceramic product prepared in Example 1 of this invention; where (a) is a high-resolution XPS spectrum of Si2p, (b) is a high-resolution XPS spectrum of C1s, (c) is a high-resolution XPS spectrum of O1s, and (d) is a high-resolution XPS spectrum of B1s. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The parameters of most of the raw materials involved in the embodiments / comparative examples of this application are shown below: Fine-grained silicon carbide micro powders: F240, F320, F360, F400, F500, F600 and high-density silicon carbide micro powders were purchased from Shandong Qingzhou Micro Powder Co., Ltd.; W28 (PS04) silicon carbide micro powders were purchased from Weifang Kaihua Silicon Carbide Micro Powder Co., Ltd.; D50 submicron silicon carbide micro powders with a particle size of 0.5-1.0μm were commercially available industrial-grade products with a purity of not less than 98%.

[0024] Coarse-grained silicon carbide micro powder: purchased from Weifang Kaihua Silicon Carbide Micro Powder Co., Ltd., with specifications including F100 (100F, PS05, D50 approx. 129μm), 120# (D50 approx. 125μm), 150#, 200#, and F120 (D50 approx. 109μm) silicon carbide micro powder purchased from Shandong Qingzhou Micro Powder Co., Ltd., with a purity of not less than 98%.

[0025] Phenolic resin: The examples / comparative examples in this application all used RA-L5103 thermosetting liquid phenolic resin purchased from Tongcheng Electronic Materials (Zhenjiang) Co., Ltd., with a solid content of 65%-75% and a residual carbon rate of not less than 40%; the resin liquid purchased from Hebei Zetian Chemical Co., Ltd. was a spare raw material and was not used in the corresponding tests in Table 1.

[0026] Liquid potassium sodium silicate water glass: purchased from Yourui Building Materials Flagship Store (brand: Yourui), model SP-38, modulus 2.2-3.0, Baume degree 38-42°Bé, solid content 35%-40%; the following examples all use water glass with a modulus of 2.6.

[0027] PLA printing material: In the embodiments / comparative examples involving PLA sacrificial molds, the PLA sacrificial molds used were all made of BambuLab PLALite filament, 1.75mm in diameter and white, purchased from the BambuLab JD.com flagship store.

[0028] Casting wax: In the examples / comparative examples of this application involving casting wax sacrificial molds, casting wax filament for FDM printing was purchased from Wuhan Yicheng 3D Technology Co., Ltd.

[0029] High-temperature resistant red wax: In the examples / comparative examples of this application involving high-temperature resistant red wax sacrificial molds, high-temperature resistant red wax filaments for FDM printing, purchased from Wuhan Yicheng 3D Technology Co., Ltd., were used. Boron carbide micro powder: Commercially available industrial-grade boron carbide micro powder, with a D50 particle size of 1-5μm and a purity of not less than 95%.

[0030] Boron nitride isolation spray: Commercially available alcohol-based boron nitride aerosol spray with boron nitride content of 10-20 wt%, used for sintering isolation and protection.

[0031] Carbon dioxide: Purchased from Wuhan Runhuahui Oxygen Cylinder Inspection Co., Ltd., 10L steel cylinder containing industrial carbon dioxide.

[0032] Graphite crucibles: Purchased from Kaifeng Xiaozheng Technology Co., Ltd., high-temperature graphite crucibles, specifications Φ260-150, Φ350-200, Φ400-400.

[0033] Graphite plate: purchased from Yifeng New Materials Co., Ltd. in Dengta City, with specifications of 280×380×8mm.

[0034] Example 1

[0035] This embodiment provides an indirect 3D printing method for complex-shaped silicon carbide ceramics to fabricate integral solid turbine impellers. The specific steps are as follows: S1. Based on the three-dimensional model of the turbine impeller to be prepared, a sacrificial mold can be designed for removal. The sacrificial mold has a forming cavity corresponding to the solid material area of ​​the turbine impeller, and the inner wall contour of the forming cavity corresponds to the outer surface contour of the turbine impeller. According to the sintering linear shrinkage rate of 12.5% ​​measured by the pre-sample with the same formula and process, size compensation is performed according to K=1 / (1-0.125)=1.1429, that is, the linear dimension is enlarged by 14.29% relative to the target shape. A main gas channel and a branch gas channel connected to the main gas channel are set inside the mold wall of the sacrificial mold. The branch gas channel extends to the inner wall of the forming cavity, and one end of the main gas channel extends to the outside of the sacrificial mold to form a gas supply interface. The sacrificial mold is provided with a feed port, an exhaust port and a demolding and glue discharge port connected to the forming cavity. The diameter of the main gas channel is 6mm, the diameter of the branch gas channel is 1.5mm, and the distance between the outlets of adjacent branch gas channels is 10mm. The sacrificial mold is obtained by printing with the above-mentioned casting wax filament for FDM printing.

[0036] S2. Mix 100 parts by mass of fine-grained silicon carbide micro powder (composed of 60 parts by mass of submicron silicon carbide micro powder with D50 of approximately 0.8 μm and 40 parts by mass of F400 silicon carbide micro powder), 0.7 parts by mass of boron carbide micro powder, 6 parts by mass of phenolic resin (RA-L5103), 10 parts by mass of liquid potassium sodium silicate water glass (modulus 2.6), and 18 parts by mass of ethanol in the following order: First, mix the phenolic resin and ethanol evenly, then add the fine-grained silicon carbide micro powder and boron carbide micro powder and mix, and finally slowly add the liquid potassium sodium silicate water glass while stirring; stir at 800 r / min for 40 min, and then degas under vacuum for 10 min to obtain a fine replication slurry.

[0037] S3. Mix 45 parts by weight of coarse-grained silicon carbide micro powder F100 (D50 approximately 129 μm), 55 parts by weight of fine-grained silicon carbide micro powder (composition same as in step S2), 0.6 parts by weight of boron carbide micro powder, 9 parts by weight of phenolic resin (RA-L5103), 8 parts by weight of liquid potassium sodium silicate water glass, and 13 parts by weight of ethanol in the order described in step S2, stir at 800 r / min for 40 min, and degas under vacuum for 10 min to obtain the structural filling slurry.

[0038] S4. Using an dip-coating method, the fine replication slurry is applied to cover the inner wall of the mold cavity of the sacrificial mold, forming a fine replication layer with a thickness of 0.8 mm. After surface drying at 50°C for 20 min, structural filling slurry is filled into the mold cavity through the inlet, and the gas in the cavity is discharged through the vent until the structural filling slurry fills the remaining cavity space within the fine replication layer. The thickness of the structural filler at the thinnest solid part of the blade is 3.5 mm. The inlet and vent are then sealed to obtain the sacrificial mold-fine replication layer-structural filler composite.

[0039] S5. Carbon dioxide is introduced through the gas channel inside the sacrificial mold wall, with a positive pressure of 0.08 MPa and a gas flow time of 90 s, so that the fine replication layer begins to solidify from the mold side towards the structural filler. After a 90-s interval to allow the surface of the fine replication layer to gel and set, the sacrificial mold-fine replication layer-structural filler composite is placed in a sealed curing chamber. Carbon dioxide is introduced into the sealed curing chamber, with the positive pressure controlled at 0.05 MPa and a gas flow time of 180 s. At the same time, the main gas channel, inlet, and outlet are connected to the carbon dioxide atmosphere in the chamber, so that the structural filler continues to solidify, resulting in a solid ceramic body.

[0040] S6. Place the entire solid ceramic blank on a graphite plate with the demolding outlet facing down for demolding treatment; heat to 150℃ at 1.0℃ / min and hold for 2 hours to melt the casting wax sacrificial mold and discharge it through the demolding outlet and the outside of the mold. During the heat preservation process, the phenolic resin is cured by heat.

[0041] S7. The ceramic blank after removing the sacrificial mold is placed into a covered graphite crucible with an exhaust hole. The crucible is heated to 900℃ at 1.5℃ / min under a nitrogen atmosphere and held for 2 hours to further carbonize the phenolic resin and form a carbon bonded phase, thus obtaining a silicon carbide pre-fired blank.

[0042] S8. Spray a 10μm thick boron nitride isolation layer on the surface of the silicon carbide pre-sintered billet, then lay a 6mm thick F400 silicon carbide micro powder (D50 about 17μm) support layer on the surface of the silicon carbide pre-sintered billet, and lay a 20mm thick F100 silicon carbide micro powder (D50 about 129μm) permeable layer on the outside of the support layer, so that the complex curved blade parts of the turbine impeller are all supported by the shape.

[0043] S9. Place the graphite crucible containing the silicon carbide pre-sintered blank and the silicon carbide support powder bed, with a crucible lid equipped with an exhaust hole, in a carbon tube furnace under argon protection. Control the argon pressure to 0.05 MPa gauge pressure, raise the temperature to 2050℃ at 5℃ / min, and hold for 2.5h to sinter and bond the silicon carbide particles. After sintering, cool the furnace to room temperature.

[0044] S10. Remove the sintered body, clean the silicon carbide support powder bed on the surface, and perform surface cleaning and local finishing to obtain a silicon carbide ceramic product with a complex turbine impeller shape. See the actual product image below. Figure 1 As shown.

[0045] like Figure 2 As shown, the Si2p spectrum decomposes into three components located at 100.3 eV, 101.6 eV, and 103.1 eV. The strong peak at 100.3 eV is attributed to the Si-C bonds in the silicon carbide lattice and is the main contributor to the Si2p spectrum, indicating that the sample surface is dominated by Si-C chemical bonds. The weak peak near 101.6 eV corresponds to the Si-CO transition oxidation state, indicating that a small amount of surface SiC underwent slight oxidation during sintering. The small peak at 103.1 eV is attributed to the Si-O bonds, mainly originating from the naturally formed SiO_x / SiO_2 oxide layer on the sample surface. The C1s spectrum can be decomposed into four peaks at 282.9 eV, 284.8 eV, 286.2 eV, and 288.6 eV, corresponding to the C-Si, CC / C=C, CO, and OC=O chemical environments, respectively. The C-Si peak occupies the majority, further indicating that the carbon elements on the sample surface are mainly in the C-Si chemical environment, containing only a small amount of residual free carbon and oxygen-containing carbon species on the surface. The O1s spectrum consists of three components at 531.6 eV, 532.6 eV, and 533.5 eV, corresponding to defect oxygen / C=O, Si-O-Si or Si-OC structures, and adsorbed hydroxyl / water molecules, respectively, indicating limited oxidation and adsorption on the sample surface. The B1s spectrum shows weak signals near 188.0 eV, 190.5 eV, and 192.2 eV, attributed to BC, BN, and BO bonds, respectively, indicating that residual elements from sintering aids or the boron nitride isolation layer exist only in trace amounts. The BN peak near 190.5 eV corresponds to the BN signal at approximately 398.0 eV in the N1s spectrum, indicating a small amount of boron-nitrogen species remaining on the ceramic surface. These XPS results are used to characterize the elemental chemical state of the sample surface and are not used as a basis for determining the bulk or crystalline phase.

[0046] Example 2

[0047] This embodiment provides an indirect 3D printing method for complex-shaped silicon carbide ceramics to prepare integral thin-walled irregular tubes with designed cavities, using lower limit values ​​for parameters. The specific steps are as follows: S1. Based on the three-dimensional model of the thin-walled shaped tube to be prepared, a sacrificial mold can be designed for removal. The forming cavity of the sacrificial mold corresponds to the solid wall area of ​​the thin-walled shaped tube. The inner wall of the cavity and the forming protrusion together define the outer surface of the thin-walled shaped tube and the designed tube boundary. Based on the sintering linear shrinkage rate of 10.6% measured by the pre-sample with the same formula and process, size compensation is performed according to K=1 / (1-0.106)=1.1186, that is, the linear size is enlarged by 11.86% relative to the target contour. A gas channel is set inside the wall of the sacrificial mold. One end of the main gas channel extends to the outside of the sacrificial mold to form a gas supply interface, and a feed port, an exhaust port and a demolding discharge port are set. The diameter of the main gas channel is 3mm, the diameter of the branch gas channel is 0.5mm, and the distance between the outlets of adjacent branch gas channels is 5mm. The sacrificial mold is obtained by printing with the above-mentioned casting wax filament for FDM printing.

[0048] S2. Mix 100 parts by weight of fine-grained silicon carbide micro powder (composed of 80 parts by weight of submicron silicon carbide micro powder with D50 of approximately 0.8 μm and 20 parts by weight of F600 silicon carbide micro powder), 0.5 parts by weight of boron carbide micro powder, 5 parts by weight of phenolic resin, 8 parts by weight of liquid potassium sodium silicate water glass, and 12 parts by weight of ethanol in the following order: First, mix the phenolic resin and ethanol evenly, then add the fine-grained silicon carbide micro powder and boron carbide micro powder and mix, and finally slowly add the liquid potassium sodium silicate water glass while stirring; stir at 500 r / min for 20 min, and degas under vacuum for 5 min to obtain a fine replication slurry.

[0049] S3. Mix 35 parts by weight of coarse-grained silicon carbide micro powder F120 (D50 about 109μm), 65 parts by weight of fine-grained silicon carbide micro powder (composition same as in step S2), 0.5 parts by weight of boron carbide micro powder, 7 parts by weight of phenolic resin, 6 parts by weight of liquid potassium sodium silicate water glass, and 8 parts by weight of ethanol in the order described in step S2, stir at 500r / min for 20min, and degas under vacuum for 5min to obtain structural filling slurry.

[0050] S4. Using a brushing method, the fine replication slurry is applied to cover the inner wall of the molded cavity of the sacrificial mold and the surface of the molded protrusion used to define the design cavity, forming a fine replication layer with a thickness of 0.3 mm. After surface drying at 40°C for 30 min, structural filling slurry is filled into the molded cavity through the inlet and the gas in the cavity is discharged through the vent until the remaining cavity space is filled. The thickness of the structural filler at the thinnest solid wall part is 1.5 mm. The inlet and vent are sealed to obtain the sacrificial mold-fine replication layer-structural filler composite.

[0051] S5. Carbon dioxide is introduced through the gas channel inside the sacrificial mold wall, with a positive pressure of 0.02 MPa and a gas introduction time of 30 s. After a 30 s interval to allow the surface gel of the fine replication layer to set, the sacrificial mold-fine replication layer-structure filler composite is placed in a sealed curing chamber. Carbon dioxide is introduced into the sealed curing chamber, with the positive pressure inside the chamber controlled at 0.02 MPa and a gas introduction time of 60 s. At the same time, the gas channel, feed port, and exhaust port are kept connected to the carbon dioxide atmosphere inside the chamber to obtain an integral solid ceramic green body.

[0052] S6. Place the entire solid ceramic blank on a graphite plate with the demolding outlet facing down, heat it to 120℃ at 0.5℃ / min and keep it at that temperature for 1 hour. This allows the cast white wax sacrificial mold to melt and be discharged through the demolding outlet and the outside of the mold. During the heat preservation process, the phenolic resin is also heated and cured.

[0053] S7. The ceramic blank after removing the sacrificial mold is placed into a covered graphite crucible with an exhaust hole. The crucible is heated to 800℃ at 0.5℃ / min under a nitrogen atmosphere and held for 1 hour to further carbonize the phenolic resin and form a carbon bonded phase, thus obtaining a silicon carbide pre-fired blank.

[0054] S8. Spray a 5μm thick boron nitride isolation layer onto the surface of the silicon carbide pre-sintered billet, then lay a 3mm thick F600 silicon carbide micro powder (D50 about 9μm) support layer on the surface of the silicon carbide pre-sintered billet, and lay a 10mm thick F120 silicon carbide micro powder (D50 about 109μm) breathable layer on the outside of the support layer.

[0055] S9. Place the graphite crucible containing the silicon carbide pre-sintered blank and the supporting powder bed, with a crucible lid equipped with an exhaust hole, in a carbon tube furnace protected by argon gas. Control the argon gas pressure to 0.02 MPa gauge pressure, raise the temperature to 2000℃ at 2℃ / min, hold for 1 hour, and cool to room temperature with the furnace after sintering.

[0056] S10. Remove the sintered body, remove the surface support powder bed, and after cleaning and local trimming, obtain a thin-walled irregular tube complex-shaped silicon carbide ceramic product.

[0057] Example 3

[0058] This embodiment provides an indirect 3D printing method for complex-shaped silicon carbide ceramics, used to prepare an integral precision nozzle with a designed flow channel, employing upper limit values ​​for parameters. The specific steps are as follows: S1. Based on the three-dimensional model of the precision nozzle to be prepared, a sacrificial mold can be removed. The molding cavity of the sacrificial mold corresponds to the solid material area of ​​the precision nozzle. The inner wall of the cavity and the molding protrusion together define the outer surface of the precision nozzle and the design flow channel boundary. According to the sintering linear shrinkage rate of 13.1% measured by the pre-sample with the same formula and process, size compensation is performed according to K=1 / (1-0.131)=1.1507, that is, the linear size is enlarged by 15.07% relative to the target contour. A gas channel is set inside the mold wall of the sacrificial mold. One end of the main gas channel extends to the outside of the sacrificial mold to form a gas supply interface, and a feed port, an exhaust port and a demolding discharge port are set. The diameter of the main gas channel is 10mm, the diameter of the branch gas channel is 3mm, and the distance between the outlets of adjacent branch gas channels is 20mm. The sacrificial mold is obtained by printing with the above-mentioned BambuLab PLALite filament.

[0059] S2. Mix 100 parts by weight of fine-grained silicon carbide micro powder (composed of 50 parts by weight of submicron silicon carbide micro powder with a D50 of approximately 1.0 μm and 50 parts by weight of F240 silicon carbide micro powder), 1.0 part by weight of boron carbide micro powder, 9 parts by weight of phenolic resin, 14 parts by weight of liquid potassium sodium silicate water glass, and 20 parts by weight of ethanol in the following order: First, mix the phenolic resin and ethanol evenly, then add the fine-grained silicon carbide micro powder and boron carbide micro powder and mix, and finally slowly add the liquid potassium sodium silicate water glass while stirring; stir at 1000 r / min for 60 min, and degas under vacuum for 15 min to obtain a fine replication slurry.

[0060] S3. Mix 55 parts by weight of coarse-grained silicon carbide micro powder F120 (D50 about 109μm), 45 parts by weight of fine-grained silicon carbide micro powder (composition same as in step S2), 1.0 part by weight of boron carbide micro powder, 13 parts by weight of phenolic resin, 11 parts by weight of liquid potassium sodium silicate water glass and 15 parts by weight of ethanol in the order described in step S2, stir at 1000r / min for 60min, and degas under vacuum for 15min to obtain structural filling slurry.

[0061] S4. Using a pouring method, the fine replication slurry is used to cover the inner wall of the molded cavity of the sacrificial mold and the surface of the molding protrusion used to define the design flow channel, forming a fine replication layer with a thickness of 1.2 mm. After surface drying at 60°C for 10 min, structural filling slurry is filled into the molded cavity through the inlet and the gas in the cavity is discharged through the vent until the remaining cavity space is filled. The thickness of the structural filler at the thinnest solid part is 6.0 mm. The inlet and vent are closed to obtain the sacrificial mold-fine replication layer-structural filler composite.

[0062] S5. Carbon dioxide is introduced through the gas channel inside the sacrificial mold wall, with a positive gauge pressure of 0.15 MPa and a gas introduction time of 180 s. After a 150 s interval to allow the surface gel of the fine replication layer to set, the sacrificial mold-fine replication layer-structure filler composite is placed in a sealed curing chamber. Carbon dioxide is introduced into the sealed curing chamber, with the positive gauge pressure inside the chamber controlled at 0.10 MPa and a gas introduction time of 300 s. At the same time, the gas channel, feed port, and exhaust port are kept connected to the carbon dioxide atmosphere inside the chamber to obtain an integral solid ceramic green body.

[0063] S6. Place the entire solid ceramic blank on a graphite plate with the demolding outlet facing down, and heat it to 500℃ at 1.5℃ / min under a nitrogen atmosphere and hold it for 5 hours to allow the PLA sacrificial mold to thermally decompose. The decomposition gas is discharged through the feed port, vent port and demolding outlet.

[0064] S7. The ceramic blank after removing the sacrificial mold is placed into a covered graphite crucible with an exhaust hole. The crucible is heated to 1000℃ at 3℃ / min under a nitrogen atmosphere and held for 3h to further carbonize the phenolic resin and form a carbon bonded phase, thus obtaining a silicon carbide pre-fired blank.

[0065] S8. Spray a 20μm thick boron nitride isolation layer on the surface of the silicon carbide pre-sintered blank, then lay a 10mm thick F240 silicon carbide micro powder (D50 about 44μm) support layer on the surface of the silicon carbide pre-sintered blank, and lay a 30mm thick F120 silicon carbide micro powder (D50 about 109μm) breathable layer on the outside of the support layer.

[0066] S9. Place the graphite crucible containing the silicon carbide pre-sintered blank and the supporting powder bed, along with a crucible lid with vent holes, into a carbon tube furnace protected by argon gas. Control the argon gas pressure to 0.1 MPa gauge pressure, raise the temperature to 2150℃ at 8℃ / min, hold for 4 hours, and cool to room temperature with the furnace after sintering.

[0067] S10. Remove the sintered body, remove the surface support powder bed, and after cleaning and local trimming, obtain a silicon carbide ceramic product with a complex shape and a precision nozzle.

[0068] Example 4

[0069] The difference between this embodiment and Embodiment 1 is that the sacrificial mold material is replaced by the aforementioned casting white wax filament for FDM printing with the aforementioned high-temperature resistant red wax filament for FDM printing. The remaining steps and parameters are the same as in Embodiment 1. Specifically, the demolding process step S6 is adjusted to: heating to 165°C at a rate of 1.5°C / min and holding at that temperature for 2.5 hours, so that the high-temperature resistant red wax sacrificial mold melts out and is discharged through the opening.

[0070] Example 5

[0071] This embodiment provides an indirect 3D printing method for complex-shaped silicon carbide ceramics, using the lower limit value of optimized ratio parameters. The specific steps are as follows: S1. Based on the three-dimensional model of the silicon carbide ceramic product to be prepared, a sacrificial mold can be designed for removal. The molding cavity of the sacrificial mold corresponds to the solid material area of ​​the product, and the inner wall contour of the molding cavity corresponds to the outer surface contour of the product. According to the sintering linear shrinkage rate of 11.8% measured by the pre-sample with the same formula and process, size compensation is performed according to K=1 / (1-0.118)=1.1338, that is, the linear size is enlarged by 13.38% relative to the target contour. A gas channel is set inside the mold wall of the sacrificial mold. One end of the main gas channel extends to the outside of the sacrificial mold to form a gas supply interface, and a feed port, an exhaust port and a demolding and glue discharge port are set. The diameter of the main gas channel is 5mm, the diameter of the branch gas channel is 1.0mm, and the distance between the outlets of adjacent branch gas channels is 8mm. The sacrificial mold is obtained by printing with the above-mentioned casting wax filament for FDM printing.

[0072] S2. Mix 100 parts by weight of fine-grained silicon carbide micro powder (composed of 70 parts by weight of submicron silicon carbide micro powder with D50 of approximately 0.8 μm and 30 parts by weight of F360 silicon carbide micro powder), 0.6 parts by weight of boron carbide micro powder, 5 parts by weight of phenolic resin, 9 parts by weight of liquid potassium sodium silicate water glass, and 15 parts by weight of ethanol in the following order: First, mix the phenolic resin and ethanol evenly, then add the fine-grained silicon carbide micro powder and boron carbide micro powder and mix, and finally slowly add the liquid potassium sodium silicate water glass while stirring; stir at 700 r / min for 30 min, and degas under vacuum for 8 min to obtain a fine replication slurry.

[0073] S3. Mix 40 parts by weight of coarse-grained silicon carbide micro powder F120 (D50 about 109μm), 60 parts by weight of fine-grained silicon carbide micro powder (composition same as in step S2), 0.6 parts by weight of boron carbide micro powder, 8 parts by weight of phenolic resin, 7 parts by weight of liquid potassium sodium silicate water glass, and 10 parts by weight of ethanol in the order described in step S2, stir at 700r / min for 30min, and degas under vacuum for 8min to obtain structural filling slurry.

[0074] S4. The fine replication slurry is applied to the inner wall of the mold cavity of the sacrificial mold by dip coating to form a fine replication layer with a thickness of 0.5 mm. After surface drying at 50°C for 15 min, the structural filling slurry is filled into the mold cavity through the inlet and the gas in the cavity is discharged through the vent until the remaining cavity space is filled. The thickness of the structural filler at the thinnest solid part is 2.5 mm. The inlet and vent are sealed to obtain the sacrificial mold-fine replication layer-structural filler composite.

[0075] S5. Carbon dioxide is introduced through the gas channel inside the sacrificial mold wall, with a positive gauge pressure of 0.05 MPa and a gas introduction time of 60 s. After the surface gel of the fine replication layer is set after an interval of 60 s, the sacrificial mold-fine replication layer-structure filler composite is placed in a sealed curing chamber. Carbon dioxide is introduced into the sealed curing chamber, and the positive gauge pressure inside the chamber is controlled at 0.03 MPa. The gas introduction time is 120 s. At the same time, the gas channel, feed port and exhaust port are kept connected to the carbon dioxide atmosphere inside the chamber to obtain the integral solid ceramic green body.

[0076] S6. Place the entire solid ceramic blank on a graphite plate with the demolding outlet facing down, heat it to 140℃ at 1.0℃ / min and hold it for 1.5h, so that the casting white wax sacrificial mold melts and is discharged through the demolding outlet and the outside of the mold. During the heat holding process, the phenolic resin is cured by heat.

[0077] S7. The ceramic blank after removing the sacrificial mold is placed into a covered graphite crucible with an exhaust hole. The crucible is heated to 850°C at 1°C / min under a nitrogen atmosphere and held for 1.5 hours to further carbonize the phenolic resin and form a carbon-bonded phase, thus obtaining a silicon carbide pre-fired blank.

[0078] S8. Spray an 8μm thick boron nitride isolation layer onto the surface of the silicon carbide pre-sintered blank, then lay a 5mm thick F360 silicon carbide micro powder (D50 about 23μm) support layer on the surface of the silicon carbide pre-sintered blank, and lay a 15mm thick F120 silicon carbide micro powder (D50 about 109μm) breathable layer on the outside of the support layer.

[0079] S9. Place the graphite crucible containing the silicon carbide pre-sintered blank and the supporting powder bed, along with a crucible lid with vent holes, into a carbon tube furnace protected by argon gas. Control the argon gas pressure to 0.03 MPa gauge pressure, raise the temperature to 2000℃ at 3℃ / min, hold for 2 hours, and cool to room temperature with the furnace after sintering.

[0080] S10. Remove the sintered body, remove the surface support powder bed, and after cleaning and local trimming, obtain silicon carbide ceramic products with complex shapes.

[0081] Example 6

[0082] This embodiment provides an indirect 3D printing method for complex-shaped silicon carbide ceramics, using the upper limit of optimized proportioning parameters. The specific steps are as follows: S1. Based on the three-dimensional model of the silicon carbide ceramic product to be prepared, a sacrificial mold can be designed for removal. The molding cavity of the sacrificial mold corresponds to the solid material area of ​​the product, and the inner wall contour of the molding cavity corresponds to the outer surface contour of the product. According to the sintering linear shrinkage rate of 12.9% measured by the pre-sample with the same formula and process, size compensation is performed according to K=1 / (1-0.129)=1.1481, that is, the linear size is enlarged by 14.81% relative to the target contour. A gas channel is set inside the mold wall of the sacrificial mold. One end of the main gas channel extends to the outside of the sacrificial mold to form a gas supply interface, and a feed port, an exhaust port and a demolding and glue discharge port are set. The diameter of the main gas channel is 8mm, the diameter of the branch gas channel is 2.0mm, and the distance between the outlets of adjacent branch gas channels is 15mm. The sacrificial mold is obtained by printing with the above-mentioned casting wax filament for FDM printing.

[0083] S2. Mix 100 parts by weight of fine-grained silicon carbide micro powder (composed of 70 parts by weight of submicron silicon carbide micro powder with D50 of approximately 0.8 μm and 30 parts by weight of F360 silicon carbide micro powder), 0.8 parts by weight of boron carbide micro powder, 7 parts by weight of phenolic resin, 12 parts by weight of liquid potassium sodium silicate water glass, and 20 parts by weight of ethanol in the following order: First, mix the phenolic resin and ethanol evenly, then add the fine-grained silicon carbide micro powder and boron carbide micro powder and mix, and finally slowly add the liquid potassium sodium silicate water glass while stirring; stir at 800 r / min for 40 min, and then degas under vacuum for 10 min to obtain a fine replication slurry.

[0084] S3. Mix 50 parts by weight of coarse-grained silicon carbide micro powder F120 (D50 about 109μm), 50 parts by weight of fine-grained silicon carbide micro powder (composition same as in step S2), 0.8 parts by weight of boron carbide micro powder, 11 parts by weight of phenolic resin, 9 parts by weight of liquid potassium sodium silicate water glass, and 15 parts by weight of ethanol in the order described in step S2, stir at 800r / min for 40min, and degas under vacuum for 10min to obtain structural filling slurry.

[0085] S4. The fine replication slurry is applied to the inner wall of the mold cavity of the sacrificial mold by dip coating to form a fine replication layer with a thickness of 1.0 mm. After surface drying at 55℃ for 18 min, the structural filling slurry is filled into the mold cavity through the inlet and the gas in the cavity is discharged through the vent until the remaining cavity space is filled. The thickness of the structural filler at the thinnest solid part is 5.0 mm. The inlet and vent are sealed to obtain the sacrificial mold-fine replication layer-structural filler composite.

[0086] S5. Carbon dioxide is introduced through the gas channel inside the sacrificial mold wall, with a positive pressure of 0.12 MPa and a gas introduction time of 120 s. After the surface gel of the fine replication layer is set after 120 s intervals, the sacrificial mold-fine replication layer-structure filler composite is placed in a sealed curing chamber. Carbon dioxide is introduced into the sealed curing chamber, and the positive pressure inside the chamber is controlled at 0.08 MPa. The gas introduction time is 240 s. At the same time, the gas channel, feed port and exhaust port are kept connected to the carbon dioxide atmosphere inside the chamber to obtain the integral solid ceramic green body.

[0087] S6. Place the solid ceramic blank on a graphite plate with the demolding outlet facing down, heat it to 160℃ at 1.5℃ / min and hold it for 2.5h, so that the casting white wax sacrificial mold melts and is discharged through the demolding outlet and the outside of the mold. During the heat holding process, the phenolic resin is cured by heat.

[0088] S7. The ceramic blank after removing the sacrificial mold is placed into a covered graphite crucible with an exhaust hole. The crucible is heated to 950°C at 2°C / min under a nitrogen atmosphere and held for 2.5 hours to further carbonize the phenolic resin and form a carbon-bonded phase, thus obtaining a silicon carbide pre-fired blank.

[0089] S8. Spray a 15μm thick boron nitride isolation layer on the surface of the silicon carbide pre-sintered blank, then lay an 8mm thick F360 silicon carbide micro powder (D50 about 23μm) support layer on the surface of the silicon carbide pre-sintered blank, and lay a 25mm thick F120 silicon carbide micro powder (D50 about 109μm) breathable layer on the outside of the support layer.

[0090] S9. Place the graphite crucible containing the silicon carbide pre-sintered blank and the supporting powder bed, along with a crucible lid with vent holes, into a carbon tube furnace under argon protection. Control the argon pressure to 0.08 MPa gauge pressure, raise the temperature to 2100℃ at 6℃ / min, hold for 3 hours, and cool to room temperature with the furnace after sintering.

[0091] S10. Remove the sintered body, remove the surface support powder bed, and after cleaning and local trimming, obtain silicon carbide ceramic products with complex shapes.

[0092] Comparative Example 1 Except for explicitly changed technical conditions, the raw materials used in the following comparative examples are the same as those in Example 1, and all are actual purchased raw materials of the above-mentioned sources and specifications.

[0093] The difference between this comparative example and Example 1 is that the partitioned structure of the fine replication layer-structure filler is eliminated, and only a single fine replication slurry is used to fill the entire molding cavity. Specifically, in steps S3 and S4, no structure-filling slurry is prepared, and a whole filler with a total thickness of 4.3 mm is formed using fine replication slurry. The remaining steps and parameters are the same as in Example 1.

[0094] Comparative Example 2 The difference between this comparative example and Example 1 is that it does not employ the phased approach of prioritizing the shaping of the fine replication layer followed by the curing of the structural filler. Specifically, in step S5, the sacrificial mold-fine replication layer-structural filler composite is placed in a sealed curing chamber, and carbon dioxide is simultaneously introduced for 270 seconds through the gas channels, inlet, and outlet of the sacrificial mold wall for overall synchronous curing. The remaining steps and parameters are the same as in Example 1.

[0095] Comparative Example 3 The difference between this comparative example and Example 1 is that the supporting powder bed is omitted, and the silicon carbide micro powder support layer and the permeable layer are not used during sintering. Specifically, in step S8, no supporting powder bed is laid, and the silicon carbide pre-sintered blank is directly placed in a graphite crucible for sintering. The remaining steps and parameters are the same as in Example 1.

[0096] Comparative Example 4 The difference between this comparative example and Example 1 is that the thickness of the fine replication layer is too thin (0.1 mm). Specifically, the thickness of the fine replication layer in step S4 is adjusted to 0.1 mm, while the remaining steps and parameters are the same as in Example 1.

[0097] Comparative Example 5 This comparative example is used to evaluate the overall impact of rapid heating in the three stages of demolding, pre-firing, and sintering. The difference from Example 1 is that the heating rate in all three stages is increased. Specifically, the demolding heating rate in step S6 is adjusted to 5°C / min, the pre-firing heating rate in step S7 is adjusted to 5°C / min, and the sintering heating rate in step S9 is adjusted to 10°C / min. The remaining steps and parameters are the same as in Example 1.

[0098] Comparative Example 6 The difference between this comparative example and Example 1 is that no gas channel is provided inside the sacrificial mold wall. Specifically, in step S1, no main gas channel and branch gas channel are provided inside the sacrificial mold wall, and in step S5, carbon dioxide is only brought into contact with the structural filler and cured for 270 seconds through the inlet and outlet. The remaining steps and parameters are the same as in Example 1.

[0099] Comparative Example 7 The difference between this comparative example and Example 1 is that the sintering temperature is too low (1700℃). Specifically, in step S9, the temperature is increased to 1700℃ at a rate of 5℃ / min and held for 2.5h. The remaining steps and parameters are the same as in Example 1.

[0100] The silicon carbide ceramic products prepared in Examples 1-6 and Comparative Examples 1-7 were subjected to the following performance tests: (1) Bending strength of the furnace-fed specimens: According to GB / T 6569-2006, the three-point bending method was used for testing. The span was 30 mm, the loading rate was 0.5 mm / min, and the test specimen size was 3 mm × 4 mm × 36 mm. The specimens were furnace-fed specimens prepared with the same slurry, process and furnace as the products of each embodiment and comparative example. Five specimens were tested in each group and the average value was taken. The bending strength listed in Table 1 are all results of the furnace-fed specimens and do not directly characterize the local structural strength of complex products.

[0101] (2) Bulk density: determined by Archimedes' water displacement method in accordance with GB / T25995-2010.

[0102] (3) Linear shrinkage rate: The linear dimensional change rate of the sample in the critical dimension direction before and after sintering is measured. The ceramic blank size L0 after demolding and before sintering is used as the reference, and the size L1 after sintering is used as the final value. It is calculated by s=[(L0-L1) / L0]×100%. The average value is taken for each sample in 3 directions. When used for sacrificing the size of the reverse mold, s is converted to a decimal and the compensation coefficient is calculated by K=1 / (1-s).

[0103] (4) Surface roughness Ra: According to the Ra parameter specified in GB / T 1031-2009, a stylus-type surface roughness measuring instrument is used to randomly select 5 positions on the outer surface of the product formed by the replication of the inner wall of the sacrificial mold cavity or the surface of the designed cavity, and measure them under the same sampling length, evaluation length and filtering conditions, and take the average value.

[0104] (5) Dimensional deviation: In accordance with GB / T 1958-2017, a coordinate measuring machine is used to measure the maximum deviation between the key dimensions of the product and the design dimensions.

[0105] (6) Appearance integrity: Visually inspect the surface of the product for defects such as cracks, deformation, and damage.

[0106] The performance test results are summarized in Table 1.

[0107] Table 1. Performance test results of silicon carbide ceramic products in Examples 1-6 and Comparative Examples 1-7

[0108] As shown in Table 1, the products of each embodiment achieved a balanced technical effect in terms of density, mechanical properties, dimensional accuracy, and surface quality: the boron source provided by boron carbide micropowder and the active carbon source formed by the carbonization of phenolic resin constitute a boron-carbon composite sintering aid system, which promotes diffusion mass transfer and densification between silicon carbide particles during the argon-protected sintering stage at 2000-2150℃, enabling the products and the furnace-fed samples to obtain higher bulk density and flexural strength; the measured sintering linear shrinkage rate of each embodiment is 10.6%-13.1%, and the molding cavity of the sacrificial mold is based on the linear shrinkage rate of the pre-sample with the same formula and process, and reverses the size compensation according to K=1 / (1-s), thereby ensuring a small dimensional deviation; the submicron silicon carbide micropowder in the fine replication layer can closely adhere to the inner wall of the mold cavity and replicate surface details, while the coarse-fine particle gradation in the structural filler fills the remaining solid material area of ​​the product to be produced, forming an integral blank with a continuous combination of the surface fine layer and the internal carrier, taking into account surface quality, volume density, and appearance integrity. Comparative Examples 1-4 and 6-7 each changed a single key condition, while Comparative Example 5 simultaneously increased the heating rates during demolding, pre-firing, and sintering stages to evaluate the overall impact of rapid heating. All comparative examples showed performance degradation consistent with the corresponding process deviations: after filling all cavities with only fine-grained replica slurry, the internal skeleton reinforcement effect of the coarse-fine particle gradation was insufficient, leading to decreased resistance to deformation during demolding and sintering, and stress-concentrated microcracks at the blade roots; when the fine-grained replica layer and the structural filler were simultaneously cured with carbon dioxide, the surface layer was disturbed by internal gel shrinkage and gas migration before it was fully formed, resulting in delamination and penetrating microcracks at the interface, and a significant decrease in flexural strength; after eliminating the conformal support powder bed, complex curved surfaces, thin walls, and suspended parts lost the uniform support of the fine-grained support layer during the high-temperature sintering stage, and the lack of exhaust channels in the coarse-grained permeable layer caused gravity deformation of the products, resulting in a significant increase in dimensional deviations; When the thickness of the fine replication layer is below the lower limit, the replication of the surface details of the inverse mold cavity is incomplete, and pinholes and local exposed defects appear on the surface of the product, increasing the surface roughness. During the rapid heating of the three heat treatment stages in Comparative Example 5, the melting or decomposition products of the sacrificial inverse mold, the carbonized volatiles of phenolic resin, and the sintering volatiles are concentrated and escaped, forming through cracks under the combined effect. When there is no gas channel inside the sacrificial inverse mold wall, the fine replication layer cannot preferentially gel and solidify from the inverse mold side, and the gas supply from the inlet and outlet only causes uneven overall curing, resulting in blistering and cracking on the surface of the product. When the sintering temperature is below the lower limit, the diffusion mass transfer of the boron-carbon additive system is not fully activated, the sintering necks between particles are not fully developed, and the density and linear shrinkage rate of the product are significantly lower. The actual shrinkage deviates from the compensation design of the inverse mold cavity calculated based on the shrinkage rate of the pre-sample, and the dimensional deviation increases accordingly. The strength is also at a low level due to insufficient bonding phase.The above results demonstrate that the present invention, through the synergistic effect of sacrificing the full-volume filling of the inverse model cavity, the partitioned construction of the finely replicated layer-structure filler, the staged positive pressure carbon dioxide curing, and the boron-carbon composite sintering aid and the double-layer conformal support powder bed, jointly ensures the near-net-shape forming quality and comprehensive performance of silicon carbide ceramic products with complex shapes.

[0109] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dual-system molding compound for complex-shaped silicon carbide ceramics, characterized in that, This includes independently formulated fine replication slurries and structural filling slurries; By weight, the fine replication slurry comprises: 100 parts of fine-grained silicon carbide micro powder, 0.5 to 1.0 parts of boron carbide micro powder, 5 to 9 parts of phenolic resin, 8 to 14 parts of liquid potassium sodium silicate water glass, and 12 to 20 parts of ethanol. The structural filler slurry comprises, by weight, 35-55 parts of coarse-grained silicon carbide micro powder, 45-65 parts of fine-grained silicon carbide micro powder, 0.5-1.0 parts of boron carbide micro powder, 7-13 parts of phenolic resin, 6-11 parts of liquid potassium sodium silicate water glass, and 8-15 parts of ethanol. The total amount of coarse-grained silicon carbide micro powder and fine-grained silicon carbide micro powder in the structural filling slurry is 100 parts by mass. The fine replication slurry uses fine-grained silicon carbide micro powder as silicon carbide ceramic aggregate to form the fine replication area on the surface of the silicon carbide ceramic green body; the structural filling slurry uses a coarse-fine particle size distribution formed by coarse-grained silicon carbide micro powder and fine-grained silicon carbide micro powder as silicon carbide ceramic aggregate to form the internal solid area of ​​the silicon carbide ceramic green body. After curing, the fine replication slurry and the structural filling slurry form a continuously bonded integral silicon carbide ceramic green body.

2. The dual-system molding assembly for complex-shaped silicon carbide ceramics according to claim 1, characterized in that, The fine-grained silicon carbide powder includes submicron silicon carbide powder with a D50 particle size of 0.5 to 1.0 μm and one or more selected from F240, F320, F360, F400, F500 and F600 silicon carbide powder, wherein the submicron silicon carbide powder accounts for 50 to 80% of the total mass of the fine-grained silicon carbide powder.

3. The dual-system molding assembly for complex-shaped silicon carbide ceramics according to claim 1, characterized in that, The coarse-grained silicon carbide micro powder is selected from one or more of F100, F120, 100# and 120# silicon carbide micro powder.

4. The dual-system molding assembly for complex-shaped silicon carbide ceramics according to claim 1, characterized in that, The phenolic resin is a thermosetting liquid phenolic resin with a solid content of 65% to 75% and a residual carbon rate of not less than 40%.

5. The dual-system molding assembly for complex-shaped silicon carbide ceramics according to claim 1, characterized in that, By weight: the fine replication slurry is composed of 100 parts of fine-grained silicon carbide micro powder, 0.6-0.8 parts of boron carbide micro powder, 5-7 parts of phenolic resin, 9-12 parts of liquid potassium sodium silicate water glass and 15-20 parts of ethanol. The structural filling slurry is composed of 40-50 parts of coarse-grained silicon carbide micro powder, 50-60 parts of fine-grained silicon carbide micro powder, 0.6-0.8 parts of boron carbide micro powder, 8-11 parts of phenolic resin, 7-9 parts of liquid potassium sodium silicate water glass, and 10-15 parts of ethanol, wherein the total amount of the coarse-grained silicon carbide micro powder and the fine-grained silicon carbide micro powder is 100 parts by mass.

6. A method for preparing complex-shaped silicon carbide ceramic articles using a dual-system molding compound for complex-shaped silicon carbide ceramics as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Prepare a removable sacrificial mold with a molding cavity based on a three-dimensional model of a silicon carbide ceramic product with a complex shape to be prepared. The molding cavity corresponds to the solid material region of the silicon carbide ceramic product to be prepared. The inner wall contour of the molding cavity corresponds to the outer surface contour of the silicon carbide ceramic product to be prepared. The required channels or cavities of the product are defined by molding protrusions set in the molding cavity. The linear dimensions of the molding cavity are enlarged according to the compensation coefficient K=1 / (1-s), where s is a small value of the sintering linear shrinkage rate of the pre-sample prepared using the same ceramic composite material and the same sintering process. A main gas channel and a branch gas channel that communicates with the main gas channel and extends to the inner wall of the molding cavity are provided inside the mold wall of the sacrificial mold. The diameter of the main gas channel is 3 to 10 mm, the diameter of the branch gas channel is 0.5 to 3 mm, and the distance between the outlets of adjacent branch gas channels is 5 to 20 mm. The sacrificial mold is provided with a feed port, an exhaust port and a demolding outlet that are connected to the molding cavity, and is printed using PLA printing material or casting wax 3D printing material; S2. The fine replication paste according to any one of claims 1 to 5 is applied to the inner wall of the molding cavity to form a fine replication layer with a thickness of 0.3 to 1.2 mm, and then surface-dried at 40 to 60°C for 10 to 30 minutes. S3. The structural filling slurry is added into the molding cavity where the fine replication layer is formed through the feed port, and the gas in the cavity is discharged through the exhaust port, so that the structural filling slurry fills the remaining cavity space within the fine replication layer. The thickness of the structural filler in the thinnest part of the product is 1.5 to 6.0 mm. S4. Industrial carbon dioxide is continuously introduced through the gas channel inside the sacrificial mold wall, maintaining the positive pressure of the gas flow at 0.02-0.15MPa for 30-180s, so that the fine replication layer adjacent to the inner wall of the molding cavity begins to solidify from the sacrificial mold side toward the structural filler. After the surface gel of the fine replication layer is set at intervals of 30 to 150 seconds, the resulting composite is placed in a sealed curing chamber. Industrial carbon dioxide is continuously introduced into the sealed curing chamber to maintain the positive gauge pressure of 0.02 to 0.10 MPa and to ventilate for 60 to 300 seconds. At the same time, the main gas channel, feed port and exhaust port are connected to the carbon dioxide atmosphere in the chamber to allow the structural filler to continue to cure, resulting in an integral solid ceramic body composed of the fine replication layer and the structural filler continuously combined. S5. Remove the sacrificial anti-mode; When the sacrificial mold is a casting wax-based 3D printing material, the temperature is increased to 120-180℃ at a rate of 0.5-2.0℃ / min and held for 1-3 hours to allow the sacrificial mold to melt and be discharged. When the sacrificial mold is PLA printing material, the temperature is increased to 350-500℃ at 0.5-1.5℃ / min under a nitrogen atmosphere and held for 2-5 hours to thermally decompose the sacrificial mold. S6. Place the ceramic blank after removing the sacrificial mold in a graphite crucible, and heat it to 800-1000℃ at 0.5-3℃ / min under a nitrogen or argon atmosphere and hold it for 1-3 hours to further carbonize the phenolic resin to form a carbon bonded phase, thereby obtaining a silicon carbide pre-fired blank. S7. A boron nitride isolation layer with a thickness of 5-20 μm is formed on the surface of the silicon carbide pre-sintered blank. A silicon carbide micro powder support layer with a thickness of 3-10 mm and a D50 particle size of 9-45 μm is provided outside the boron nitride isolation layer. A silicon carbide micro powder breathable layer with a thickness of 10-30 mm and a D50 particle size of 100-150 μm is provided outside the support layer. S8. Under argon protection, the temperature is increased to 2000-2150℃ at 2-8℃ / min and held for 1-4 hours to sinter the silicon carbide ceramic blank. After cooling, the silicon carbide micro powder support layer and silicon carbide micro powder permeable layer are removed to obtain silicon carbide ceramic products with complex shapes.

7. The method according to claim 6, characterized in that, The casting wax 3D printing material is selected from either casting white wax or high-temperature resistant red wax.

8. The method according to claim 6, characterized in that, The thickness of the fine replication layer is 0.5 to 1.0 mm, and the thickness of the structural filler in the thinnest part of the product is 2.0 to 4.0 mm.

9. The method according to claim 6, characterized in that, During the first stage of carbon dioxide curing through the gas channel inside the sacrificial mold wall, the positive pressure of carbon dioxide is 0.05–0.10 MPa, and the ventilation time is 60–120 s; after an interval of 60–100 s, the second stage of carbon dioxide curing is carried out in the sealed curing chamber, where the positive pressure of carbon dioxide is 0.03–0.08 MPa, and the ventilation time is 120–200 s.

10. The method according to claim 6, characterized in that, During the sintering process of the silicon carbide ceramic green body, the temperature is increased to 2050-2150℃ at a rate of 3-6℃ / min and held for 2-3 hours.

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