Pressureless sintered silicon carbide ceramic special-shaped beam and preparation method thereof

Abstract

The present application relates to the technical field of silicon carbide ceramic special-shaped beam preparation, in particular to a pressureless sintering silicon carbide ceramic special-shaped beam and a preparation method thereof, which comprises the following composition and structure: material composition: the base material is silicon carbide powder; the particle size is in bimodal distribution, the main phase is 3-5 microns, and the nano phase is 0.5-1 micron; and a composite sintering aid is used; through the innovative design of material composition and structure, the present application realizes multi-scale synergistic strengthening and surface gradient protection; the base uses bimodal distribution silicon carbide powder, through the synergistic effect of micron particle skeleton and nano particle filling pores, internal cracks caused by uneven shrinkage of special-shaped cross section are significantly reduced, meanwhile, the composite sintering aid can inhibit abnormal grain growth, synergistically reduce the sintering temperature, reduce the deformation risk of multi-cavity structure, and greatly improve the corner crack propagation resistance through gradient reinforcement, and the problem of uneven hardening layer at special-shaped corners is solved through deep silicon infiltration strengthening.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation of silicon carbide ceramic special-shaped beams, and particularly relates to a pressureless sintering silicon carbide ceramic special-shaped beam and a preparation method thereof. BACKGROUND

[0002] The pressureless sintering silicon carbide ceramic special-shaped beam is a pressureless sintering process manufactured silicon carbide ceramic load-bearing structure with a non-rectangular cross-section. The pressureless sintering silicon carbide ceramic special-shaped beam is a core load-bearing component of high-end industrial kilns and high-temperature equipment. With the structural stability, long service life and energy-saving characteristics in extreme environments, the pressureless sintering silicon carbide ceramic special-shaped beam becomes the preferred material to replace metals and conventional ceramics, especially in the scene of customized cross-section design.

[0003] As shown in the application No. CN202310133308.2 and the authorization announcement date of 20230620, a pressureless liquid phase sintering silicon carbide ceramic and a preparation method thereof. The silicon carbide ceramic is obtained by sequentially subjecting a green body to heating and degumming and pressureless liquid phase sintering. The green body is pressed from granulated powder. The granulated powder is obtained by centrifugal spray granulation of a slurry. The components of the slurry include deionized water. In addition to the deionized water, the slurry also includes the following components in parts by weight: 100 parts of silicon carbide raw powder, 3-5 parts of sintering aid, 0.5-1.5 parts of polyvinyl alcohol, 0.5-1.5 parts of tetramethylammonium hydroxide, 0.5-1.5 parts of urea, and 0.5-1 parts of release agent. The sintering aid is a water dispersion liquid containing yttrium oxide powder and aluminum oxide powder. The present application reduces the possibility of surface overburning and internal underburning of the ceramic product, improves the sintering success rate, and reduces the waste of silicon carbide raw powder.

[0004] As shown in the application No. CN201510369366.0 and the authorization announcement date of 20190426, a high-thermal-conductivity pressureless sintering silicon carbide ceramic material and a preparation method thereof. It is composed of the following mass percentage of raw materials: silicon carbide 75-95wt.%, graphene 0.5-10wt.%, surfactant 1-3wt.%, dispersant 0.5-2.5wt.%, binder 2-10wt.%, boron carbide 0.5-3.5wt.%. The present application is prepared by specific proportioning of silicon carbide, graphene and boron carbide, pressure forming into a green body, and pressureless sintering under vacuum conditions to obtain a SiC ceramic material. Graphene is uniformly distributed in the SiC matrix material and forms a close bond with SiC, avoiding the reduction of thermal conductivity caused by the scattering of internal pores in the material, offsetting and exceeding the effect of the introduction of graphene on the improvement of thermal conductivity. The present application ensures the densification of the ceramic material and achieves high thermal conductivity, ensuring the uniformity of the material.

[0005] The above-mentioned and the preparation method of pressureless sintering silicon carbide ceramic in the prior art are difficult to accurately predict and control sintering shrinkage and deformation for complex multi-cavity special-shaped cross-section members, which easily leads to insufficient size precision and internal stress concentration; and the effect of the existing method is limited or the process is complex, and the effective strengthening means for the stress concentration area such as the special-shaped beam corner is insufficient, it is difficult to uniformly form a deep dense protective layer with high hardness and high bonding force on the complex surface, and the stability of the overall performance of the member is insufficient. SUMMARY

[0006] The purpose of the present application is to provide a pressureless sintering silicon carbide ceramic special-shaped beam and a preparation method thereof to solve the above-mentioned problems in the prior art.

[0007] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0008] A pressureless sintering silicon carbide ceramic special-shaped beam, comprising the following composition and structure:

[0009] Material composition:

[0010] The base material is silicon carbide powder: the particle size is bimodal distribution, the main phase is 3-5 μm, and the nano phase is 0.5-1 μm;

[0011] Composite sintering agent: composed of Al2O3, Y2O3, MgO and CeO2 in a mass ratio of 4:3:1:1, the total addition amount is 3-5% of the mass of the base material, the molar ratio of Al2O3 to Y2O3 in the composite sintering agent is 1:0.58, and the molar ratio of MgO to CeO2 is 1:1;

[0012] Reinforcing phase: graphene and Ti3SiC2 are selected, the total addition amount of graphene is 0.5-2% of the mass of the base material, the graphene is a sheet structure, the single-layer thickness is ≤5 nm, the lateral size is 1-5 μm, and the surface is subjected to hydroxylation modification treatment and uniformly dispersed in the base material; the total addition amount of Ti3SiC2 is 5-15% of the mass of the base material;

[0013] The surface of the special-shaped beam is subjected to silicon infiltration treatment to form a dense layer with a thickness of 10-30 μm, and the surface hardness is ≥2800 HV; the silicon source for silicon infiltration treatment is a polycarbosilane precursor, the treatment temperature is 1600-1700 ℃, and the silicon infiltration time is 2-4 h;

[0014] The cross section of the special-shaped beam is a multi-cavity special-shaped structure, and the number of sides is ≥4.

[0015] A preparation method of a pressureless sintering silicon carbide ceramic special-shaped beam, comprising the following steps:

[0016] Step 1. Data collection and modeling: Collecting past data of special-shaped beam preparation and expert analysis data, establishing a three-dimensional virtual model of special-shaped beam, inputting real-time collected slurry viscosity, injection molding pressure and temperature data into the three-dimensional virtual model of special-shaped beam to simulate sintering shrinkage rate and stress distribution, predicting shrinkage rate, dynamically adjusting mold size, optimizing powder grading scheme, and predicting the best sintering curve;

[0017] The three-dimensional virtual model of special-shaped beam integrates sintering kinetics model and LSTM algorithm shrinkage rate model.

[0018] The three-dimensional virtual model of special-shaped beam real-time predicts the grain growth rate (error ≤8%) and synchronously optimizes the coarse / medium / fine particle grading ratio to (3.5-4.5):(2.5-3.5):(2.5-3.5), then predicts the shrinkage rate, and dynamically adjusts the mold size (compensation 0.5-1.2%).

[0019] Step 2. Material preparation and green body preparation:

[0020] (1) Mix silicon carbide powder, composite sintering aid and graphene in proportion, ball mill for 24-48h to obtain slurry, then place the slurry in a constant temperature and humidity environment for a period of time to form uniform mud; the slurry viscosity is controlled at 3000-5000 mPa·s and the solid content is ≥55 vol%; during the constant temperature and humidity standing of the slurry: temperature 20-30℃, humidity 50-70%, time 5-7 days.

[0021] (2) Disperse the obtained uniform mud in an acrylamide system with pH=10-11, then inject into a gypsum mold to form a shaped green body;

[0022] (3) Then immerse the green body in a tung oil-glutinous rice slurry composite liquid with a mass ratio of 1:2, and low-temperature drying to form a pre-reinforced network; during immersion, adopt a six-dip-six-bake process, and the tung oil-glutinous rice slurry composite liquid needs to add nano-silica sol with a particle size of 20-50 nm and a mass fraction of 5-10%; after immersion, expose to sunlight or dry at 60℃ to form a three-dimensional organic-inorganic composite network, and the green body bending strength is improved by more than 30%.

[0023] Step 3. Pressureless step sintering: Put the green body obtained in the above steps into a sintering furnace, perform micro-hammering on the surface of the green body before sintering, energy density 0.5-1.2 J / mm², induce grain directional arrangement, and fracture toughness at corners is improved to 7.2 MPa·m¹ / ², then start the sintering furnace for sintering treatment, which is divided into three stages as follows:

[0024] Debinding stage: heat up to 800℃ at 2-3℃ / min, and keep for 1.5-2h;

[0025] Pre-sintering stage: increase temperature to 1400℃ at 5℃ / min, keep for 0.4-0.6h, then increase temperature to 1600℃ at 3℃ / min, keep for 0.8-1h;

[0026] Final sintering stage: increase temperature to 2050-2150℃ at 8℃ / min, keep for 2-4h;

[0027] During sintering, the temperature / shrinkage data are fed back by the embedded optical fiber sensor (the selected embedded optical fiber sensor monitors the frequency of ≥10Hz, and the change gradient of the temperature increasing rate is ≤2℃ / min when dynamically adjusting the parameters), then input into the special-shaped beam three-dimensional virtual model to predict the deformation and stress distribution, and dynamically adjust the sintering parameters, if the predicted deformation is >0.5%, the temperature increasing rate is automatically reduced to 4℃ / min;

[0028] Step 4. Post-processing and verification: after sintering, the obtained sample is sent into a hot isostatic pressing equipment, and then kept for a period of time in an argon environment, and during the hot isostatic pressing, the temperature is 1600-2000℃, the pressure is 140-160MPa, and the pressure keeping time is 0.8-1.2h; and during the pressure keeping, the temperature and pressure are adjusted (the SiCl4 vapor partial pressure is controlled at 0.3-0.5MPa during the initial silicon infiltration treatment, and the thickness of the β-SiC nanocrystalline layer is negatively correlated with the porosity (R²≥0.92)), the SiCl4 vapor is introduced to react to generate a β-SiC nanocrystalline layer in a high-temperature environment, the initial silicon infiltration is carried out, after the pressure keeping is completed, the polycarbosilane precursor is coated on the surface of the beam body, and the secondary silicon infiltration is carried out in a vacuum furnace for a period of time (the temperature is 1600-1700℃, and the time is 2-4h during the secondary silicon infiltration), after the silicon infiltration is completed, the sample is sent into a reduction furnace to form a Fe3O4 protective film in a high-temperature environment, and during the reduction, the real-time spectrum is monitored to dynamically adjust the flow of Fe(CO)5, the flow of Fe(CO)5 vapor and the temperature gradient satisfy the formula ΔQ=0.0005T²-0.12T+0.8 (T is the temperature in ℃, and ΔQ is in L / min), the thickness of the film layer is controlled at 2-5μm, the laser micro-texture treatment is increased, the staggered micro-grooves with a depth of 50-100μm and a width of 20-30μm are formed on the surface, the crack propagation path is lengthened by 300%, and finally the final product is obtained, and the final product is verified by thermal shock cycling >50 times at 1500-2000℃. 3+ / Fe 2+ ratio (1.8-2.2), and the flow of Fe(CO)5 is dynamically adjusted, and during the formation of the Fe3O4 protective film, the flow of Fe(CO)5 vapor and the temperature gradient satisfy the formula ΔQ=0.0005T²-0.12T+0.8 (T is the temperature in ℃, and ΔQ is in L / min), the thickness of the film layer is controlled at 2-5μm, the laser micro-texture treatment is increased, the staggered micro-grooves with a depth of 50-100μm and a width of 20-30μm are formed on the surface, the crack propagation path is lengthened by 300%, and finally the final product is obtained, and the final product is verified by thermal shock cycling >50 times at 1500-2000℃.

[0029] In the above technical solution, the present application provides a pressureless sintering silicon carbide ceramic special-shaped beam and a preparation method thereof, and has the following beneficial effects:

[0030] (1) The present application realizes multi-scale synergistic reinforcement and surface gradient protection through innovative design of material composition and structure. The base body adopts bimodal distribution of silicon carbide powder, which significantly reduces internal cracks caused by uneven shrinkage of the special cross-section through the synergistic effect of micron particle skeleton and nanoparticle filling pores. The composite sintering agent can inhibit abnormal grain growth, synergistically reduce sintering temperature, reduce the risk of deformation of multi-cavity structure, greatly improve the corner crack propagation resistance through gradient reinforcement phase, and solve the problem of uneven hardening layer at the special corner through deep silicon infiltration strengthening.

[0031] (2) The present application realizes real-time prediction of the shrinkage and stress distribution of the special-shaped beam through a three-dimensional virtual modeling system integrating sintering kinetics model and LSTM algorithm, and improves the accuracy of mold size compensation by using bimodal distribution of silicon carbide powder and dynamic particle grading optimization, significantly improves the size accuracy of complex multi-cavity structure, and effectively suppresses sintering deformation.

[0032] (3) The present application adopts surface micro-hammering to induce grain directional arrangement, and forms a three-dimensional organic-inorganic composite network through six-dipping and six-drying process, which improves the fracture toughness at the corner. The subsequent laser micro-texture forms a deep 50-100μm staggered micro groove on the surface, which prolongs the crack propagation path by 300%, effectively solving the brittle fracture problem in the stress concentration area of the special-shaped part. At the same time, through the synergistic effect of hot isostatic pressing and twice silicon infiltration, the wear resistance and corrosion resistance of complex surface are greatly improved.

[0033] (4) The present application solves the four technical bottlenecks of size accuracy, stress concentration, corner brittleness and surface strengthening of the special-shaped beam through the synergistic effect of bimodal powder + multi-phase reinforcing material design, gradient silicon infiltration + blank pretreatment process innovation and LSTM model + real-time sensing intelligent control, which significantly improves the structural stability and life in extreme environment. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art based on these drawings.

[0035] Figure 1 The structure section view provided for the embodiment of the present application of a pressureless sintered silicon carbide ceramic special-shaped beam and its preparation method.

[0036] Figure 2 The method flowchart provided for the embodiment of the present application of a pressureless sintered silicon carbide ceramic special-shaped beam and its preparation method. DETAILED DESCRIPTION

[0037] In order to make the technical personnel in the art better understand the technical solutions of the present application, the present application will be further described in detail below with reference to the drawings.

[0038] As Figure 1 shown, the embodiment of the present application provides a pressureless sintering silicon carbide ceramic special-shaped beam, comprising the following components and structures:

[0039] Material composition:

[0040] The base material is silicon carbide powder: the particle size is bimodal distribution, the main phase is 3-5 μm, and the nano phase is 0.5-1 μm;

[0041] Composite sintering agent: composed of Al2O3, Y2O3, MgO and CeO2 in a mass ratio of 4:3:1:1, the total addition amount is 3-5% of the mass of the base material, the molar ratio of Al2O3 to Y2O3 in the composite sintering agent is 1:0.58, and the molar ratio of MgO to CeO2 is 1:1;

[0042] Reinforcing phase: graphene (graphene surface is hydroxylated and modified to enhance its dispersibility in the matrix), Ti3SiC2, the total addition amount of graphene is 0.5-2% of the mass of the base material, the graphene is in a sheet structure, the single-layer thickness is ≤5 nm, the lateral size is 1-5 μm, and the surface is hydroxylated and modified, and uniformly dispersed in the matrix; the total addition amount of Ti3SiC2 is 5-15% of the mass of the base material;

[0043] The surface of the special-shaped beam is treated by silicon infiltration to form a dense layer with a thickness of 10-30 μm, and the surface hardness is ≥2800 HV; the silicon source for silicon infiltration treatment is polycarbosilane precursor, the treatment temperature is 1600-1700 ℃, and the silicon infiltration time is 2-4 h;

[0044] The cross section of the special-shaped beam is a multi-cavity special-shaped structure, and the number of sides is ≥4.

[0045] A pressureless sintering silicon carbide ceramic special-shaped beam preparation method, as Figure 2 shown, comprises the following steps:

[0046] Step 1. Data acquisition and modeling: collect past special-shaped beam preparation data and expert analysis data, establish a three-dimensional virtual model of the special-shaped beam (input parameters include powder particle size distribution, sintering agent melting point and graphene thermal conductivity), collect real-time data of slurry viscosity, injection molding pressure and temperature, input the three-dimensional virtual model of the special-shaped beam to simulate sintering shrinkage rate and stress distribution, predict the shrinkage rate, dynamically adjust the mold size, and then optimize the powder grading scheme to predict the optimal sintering curve;

[0047] The three-dimensional virtual model of the special-shaped beam integrates a sintering kinetics model and an LSTM algorithm shrinkage rate model;

[0048] The special-shaped beam three-dimensional virtual model predicts the grain growth rate in real time (error ≤8%) and synchronously optimizes the coarse / medium / fine particle size ratio to (3.5-4.5):(2.5-3.5):(2.5-3.5), and then predicts the shrinkage rate and dynamically adjusts the mold size (compensation amount 0.5-1.2%).

[0049] Step 2. Material preparation and green body preparation:

[0050] (1) Mix the silicon carbide powder, composite sintering agent and graphene according to the proportion, ball mill for 24-48h to obtain a slurry, and then place the slurry in a constant temperature and humidity environment for a period of time to form a uniform mud; the slurry viscosity is controlled at 3000-5000 mPa·s, and the solid content is ≥55 vol%; during the constant temperature and humidity standing of the slurry: temperature 25℃, humidity 60%, time 6 days.

[0051] (2) Disperse the obtained uniform mud in an acrylamide system with pH=10-11, and then inject it into a gypsum mold to form a shaped green body;

[0052] (3) Then immerse the green body in a tung oil-waxy rice slurry composite liquid with a mass ratio of 1:2, and low-temperature drying to form a pre-reinforced network; six-dip-six-bake process is adopted during immersion, and nano-silica sol with a particle size of 20-50 nm and a mass fraction of 5-10% is added to the tung oil-waxy rice slurry composite liquid, and after immersion, sunlight exposure or 60℃ drying is carried out to form a three-dimensional organic-inorganic composite network, and the green body bending strength is increased by more than 30%.

[0053] Step 3. Pressureless step sintering: put the green body obtained in the above step into a sintering furnace, and perform micro-hammering on the surface of the green body before sintering, with an energy density of 0.5-1.2 J / mm², to induce directional arrangement of grains, and the fracture toughness at the corners is increased to 7.2 MPa·m¹ / ², and then the sintering furnace is started for sintering treatment, which is divided into three stages, as shown below:

[0054] Debinding stage: heat up to 800℃ at a rate of 2-3℃ / min, and keep for 1.5-2h;

[0055] Pre-sintering stage: heat up to 1400℃ at a rate of 5℃ / min, keep for 0.4-0.6h, and then heat up to 1600℃ at a rate of 3℃ / min, keep for 0.8-1h;

[0056] Final sintering stage: heat up to 2050-2150℃ at a rate of 8℃ / min, keep for 2-4h;

[0057] The temperature / shrinkage data is fed back by the embedded optical fiber sensor (the selected embedded optical fiber sensor monitors a frequency of greater than or equal to 10 Hz, and the dynamic adjustment parameter changes at a rate of less than or equal to 2℃ / min) during the sintering process, and then input into the special-shaped beam three-dimensional virtual model to predict the deformation and stress distribution, and dynamically adjust the sintering parameters. If the predicted deformation is greater than 0.5%, the heating rate is automatically reduced to 4℃ / min.

[0058] Step 4. Post-processing and verification: After sintering, the obtained sample is sent to a hot isostatic pressing device, and then isostatic pressing is performed in an argon environment for a period of time. During the hot isostatic pressing, the temperature is 1800℃, the pressure is 150MPa, and the isostatic pressing time is 1h. The heating and cooling rates during the hot isostatic pressing are 10℃ / min. During the isostatic pressing, the temperature and pressure are adjusted (the SiCl4 vapor partial pressure is controlled at 0.3-0.5MPa during the initial silicon infiltration treatment, and the thickness of the β-SiC nanocrystalline layer is negatively correlated with the porosity (R²≥0.92)). SiCl4 vapor is introduced to react to form a β-SiC nanocrystalline layer in a high-temperature environment, and the initial silicon infiltration is performed. After the isostatic pressing is completed, the polycarbosilane precursor is coated on the surface of the beam body, and high-temperature silicon infiltration is performed in a vacuum furnace for a period of time to perform secondary silicon infiltration (the temperature during the secondary silicon infiltration is 1600-1700℃, and the time is 2-4h). After the silicon infiltration is completed, the sample is sent to a reduction furnace to form a Fe3O4 protective film in a high-temperature environment. During the reduction, the Fe 3+ / Fe 2+ ratio (1.8-2.2) is dynamically adjusted, and the Fe(CO)5 vapor flow and temperature gradient satisfy the formula ΔQ=0.0005T²-0.12T+0.8 (T is the temperature in ℃, and ΔQ is in L / min) during the formation of the Fe3O4 protective film. The thickness of the film layer is controlled at 2-5μm. Laser micro-texturing is added to form staggered micro-grooves with a depth of 50-100μm and a width of 20-30μm on the surface, and the crack propagation path is extended by 300%. The final product is obtained, and the final product is verified by thermal shock cycling at 1500-2000℃ for more than 50 times.

[0059] Embodiment (scheme of the present application)

[0060] Raw material ratio:

[0061] SiC powder: bimodal distribution (main phase 4μm accounts for 70wt%, nanophase 0.8μm accounts for 30wt%);

[0062] Sintering aid: Al2O3 / Y2O3 / MgO / CeO2=4:3:1:1 (total addition amount 4wt%);

[0063] Reinforcing phase: hydroxylated graphene (1.5wt%) + Ti3SiC2 (10wt%).

[0064] Preparation method:

[0065] 1. Digital modeling:

[0066] Input 12 parameters such as powder D50 = 3.8 μm, graphene thermal conductivity 5300 W / (m·K), etc.

[0067] Dynamic compensation mold size: shrinkage prediction value 1.05% (actual measurement 1.08%, error 0.03%).

[0068] 2. Ancient immersion:

[0069] Tung oil-nuomi slurry composite liquid (1:2) + 8wt% nano silicon sol;

[0070] Six immersion and six sun cycle parameters:

[0071] ;

[0072] Green body opening porosity decreased to 4.7%.

[0073] 3. Sintering control:

[0074] Micro hammering energy: 0.8 J / mm 2 (KIC = 7.3 MPa·m 1 / 2 );

[0075] Optical fiber sensor feedback: predicted deformation amount 0.52% at 1600℃ → automatic speed reduction to 4℃ / min.

[0076] 4. Surface treatment:

[0077] First silicon infiltration: SiCl4 partial pressure 0.45 MPa (thickness 28 μm, HV = 2980);

[0078] Secondary silicon infiltration: PCS precursor viscosity 180 cP (thickness deviation ±1.5 μm);

[0079] Blue burning process: Fe(CO)5 flow Q = 0.05×890 2 -1.2×890+8=35.2 mL / min → Fe3O4 film thickness 3.8 μm.

[0080] Verification results:

[0081] ;

[0082] Comparative Example 1 (without ancient immersion)

[0083] 1. Changes:

[0084] Delete tung oil-nuomi slurry immersion and six immersion and six sun process;

[0085] Green body directly dried and sintered;

[0086] 2. Performance comparison:

[0087] Open hole porosity: 9.8% (↑108% compared with Example 1);

[0088] Bending strength: 521 MPa (↓22%);

[0089] Thermal shock cycle failure times: 32 times (↓45%).

[0090] Example 2 (without digital twin regulation)

[0091] 1. Changes:

[0092] Fixed sintering curve (5℃ / min to 2050℃) is adopted;

[0093] Optical fiber sensor and dynamic parameter adjustment are cancelled;

[0094] 2. Performance comparison:

[0095] Crack density at corners: 15 / cm (3 / cm in Example 1);

[0096] Size deviation: +1.85% (0.65pt beyond compensation range);

[0097] Final sintering deformation: 1.2% (triggering automatic stop).

[0098] Example 3 (single silicon infiltration treatment)

[0099] 1. Changes:

[0100] SiCl4 gas phase silicon infiltration is cancelled, only PCS liquid phase silicon infiltration is retained;

[0101] MgAl2O4 composite strengthening is not added in the bluing process;

[0102] Performance comparison:

[0103] ;

[0104] 2. Mechanism analysis: The organic-inorganic network formed by six dipping and six drying significantly reduces the porosity of the green body, and the real-time deformation correction of digital twin makes the sintering stress distribution uniform; the double composite silicon infiltration layer blocks the crack propagation path by 300% through the interpenetrating structure of β-SiC nanocrystals (gas phase) and SiC whiskers (liquid phase).

[0105] The foregoing merely illustrates some exemplary embodiments of the application, and no doubt numerous modifications and alterations thereto will be apparent to those skilled in the art. Accordingly, the above description is intended for purposes of illustration only and should not be construed as limiting the scope of the application.

Claims

1. A method for preparing a pressureless sintered silicon carbide ceramic beam of irregular shape, characterized in that, Comprising the following steps: Step 1. Data acquisition and modeling: Collecting past special-shaped beam preparation data and expert analysis data, establishing a three-dimensional virtual model of the special-shaped beam, inputting real-time collected slurry viscosity, injection molding pressure and temperature data into the three-dimensional virtual model of the special-shaped beam to simulate sintering shrinkage rate and stress distribution, and to predict shrinkage rate, dynamically adjusting the mold size, optimizing the powder grading scheme, and predicting the optimal sintering curve; Step 2. Material preparation and green body preparation: Mixing silicon carbide powder, composite sintering agent and graphene in proportion, ball milling for 24-48h to obtain slurry, and then placing the slurry in a constant temperature and humidity environment for a period of time to form uniform mud; The particle size of the silicon carbide powder is bimodal distribution, the main phase is 3-5μm, and the nano phase is 0.5-1μm; The total addition amount of graphene is 0.5-2% of the mass of the base material, the graphene is a sheet structure, the single layer thickness is ≤5nm, the lateral size is 1-5μm, and the surface is modified by hydroxylation and uniformly dispersed in the matrix; The total addition amount of Ti3SiC2 is 5-15% of the mass of the base material; Disperse the obtained uniform mud in an acrylamide system with pH=10-11, then inject into a gypsum mold to form a green body; Then immerse the green body in a tung oil-glutinous rice slurry composite liquid with a mass ratio of 1:2, and low-temperature drying to form a pre-reinforced network; Step 3. Pressureless step sintering: Put the green body obtained in the above step into a sintering furnace, then start the sintering furnace for sintering treatment, which is divided into three stages, as shown below: Degreasing stage: heat to 800℃ at 2-3℃ / min, and keep for 1.5-2h; Pre-sintering stage: heat to 1400℃ at 5℃ / min, keep for 0.4-0.6h, then heat to 1600℃ at 3℃ / min, keep for 0.8-1h; Final sintering stage: heat to 2050-2150℃ at 8℃ / min, keep for 2-4h; During the sintering process, the temperature / shrinkage data is fed back through the embedded optical fiber sensor, then input into the three-dimensional virtual model of the special-shaped beam to predict the deformation and stress distribution, and dynamically adjust the sintering parameters; Step 4. Post-processing and verification: After sintering, the obtained sample is sent into a hot isostatic pressing device, then pressurized for a period of time in an argon environment, and during the pressurization, the temperature and pressure are adjusted, SiCl4 vapor is introduced to react to form a β-SiC nanocrystalline layer in a high-temperature environment for primary silicon infiltration, after the pressurization is completed, polycarbosilane precursor is coated on the surface of the beam, and high-temperature silicon infiltration is carried out in a vacuum furnace for a period of time for secondary silicon infiltration, after the silicon infiltration is completed, the sample is sent into a reduction furnace to form a Fe3O4 protective film in a high-temperature environment to obtain the final product, and the final product is verified by heat shock cycling >50 times at 1500-2000℃; The cross section of the special-shaped beam is a multi-cavity special-shaped structure, and the number of sides is ≥4; In step 4: The temperature for secondary silicon infiltration is 1600-1700℃, and the time is 2-4h; The Fe was monitored by real-time spectrum during reduction 3+ / Fe 2+ The ratio was 1.8-2.2, and the flow of Fe(CO)5 was dynamically adjusted. During the formation of the Fe3O4 protective film, the flow of Fe(CO)5 vapor and the temperature gradient met the condition ΔQ=0.0005T²-0.12T+0.8, where T was the temperature in ℃, ΔQ was in L / min, and the thickness of the film was controlled to be 2-5 μm.

2. The preparation method of the pressureless sintered silicon carbide ceramic special-shaped beam according to claim 1, characterized in that, Composite sintering agent: composed of Al2O3, Y2O3, MgO and CeO2 in a mass ratio of 4:3:1:1, with a total addition amount of 3-5% of the mass of the matrix material; the surface of the shaped beam is subjected to silicon infiltration treatment to form a dense layer with a thickness of 10-30 μm.

3. The method of claim 1, wherein the method further comprises the step of: In the step 2: ​ The viscosity of the slurry at the end of ball milling is controlled at 3000-5000 mPa·s, and the solid content is ≥55 vol%; When the slurry is kept at constant temperature and humidity, the temperature is 20-30℃, the humidity is 50-70%, and the time is 5-7 days.

4. The method of claim 1, wherein the method further comprises: In the step 2: The six-dipping-six-drying process is adopted during the dipping, and the nano-silica sol with a particle size of 20-50 nm and a mass fraction of 5-10% is further added to the tung oil-glutinous rice slurry composite liquid, and after dipping, the three-dimensional organic-inorganic composite network is formed by sunlight exposure or 60℃ drying, and the bending strength of the green body is improved by more than 30%.

5. The method of claim 1, wherein the method further comprises the step of: In the step 3: ​ The sintering body surface is micro-hammered before sintering, with an energy density of 0.5-1.2 J / mm 2 , which induces directional arrangement of grains and improves the fracture toughness at corners to 7.2 MPa·m 1 / 2 ; The selected embedded optical fiber sensor has a monitoring frequency of ≥10 Hz, and the temperature rising rate change gradient is ≤2℃ / min when dynamically adjusting the parameters.

6. The method of claim 1, wherein the method further comprises: In the step 3: If the predicted deformation is >0.5%, the temperature rising rate is automatically reduced to 4℃ / min.

7. The method of claim 1, wherein the method further comprises the step of: In the step 4: ​ During hot isostatic pressing: temperature 1600-2000℃, pressure 140-160 MPa, pressure holding time 0.8-1.2h; The SiCl4 vapor partial pressure is controlled at 0.3-0.5 MPa in the initial silicon infiltration treatment, and the thickness of the β-SiC nanocrystalline layer generated in the reaction is negatively correlated with the porosity, R 2 ≥0.

92.

8. The method of claim 1, wherein the method further comprises the step of: In the step 4: ​ Increase the laser micro-texture treatment, form staggered microgrooves with a depth of 50-100 μm and a width of 20-30 μm on the surface, and extend the crack propagation path by 300%.

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