Method for manufacturing high toughness impact resistant pressureless sintered silicon carbide ceramics

Abstract

The application discloses a high-toughness impact-resistant pressureless sintered silicon carbide ceramic manufacturing method, and belongs to the technical field of silicon carbide ceramic material preparation. The method comprises the following steps: mixing silicon carbide powder and a sintering aid, wherein the sintering aid is composed of Al2O3, Y2O3 and B4C, and the mass percentage of Al2O3 is 0.5-5.0 wt%, the mass percentage of Y2O3 is 1.0-6.0 wt%, the mass percentage of B4C is 0.3-2.0 wt%, and the rest is silicon carbide; and performing step-by-step sintering in a flowing inert atmosphere: in the first stage, keeping the temperature at 1400-1500 DEG C for 0.5-2 h, in the second stage, keeping the temperature at 1750-1800 DEG C for 1-3 h, and in the third stage, keeping the temperature at 1820-1880 DEG C for 0.2-1 h. The application can effectively solve the technical problems of high sintering temperature, high energy consumption, poor high-temperature performance and insufficient fracture toughness of silicon carbide ceramics in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide ceramic preparation, and particularly relates to a high-toughness impact-resistant pressureless sintering silicon carbide ceramic preparation method. BACKGROUND

[0002] Silicon carbide ceramics have a wide application prospect in high-end fields such as aerospace, semiconductors and metallurgy due to their excellent properties such as high strength, high hardness, high temperature resistance and corrosion resistance. However, there are two key problems in the preparation of traditional silicon carbide ceramics: first, the sintering temperature is too high, usually above 1950 DEG C, which not only leads to a substantial increase in production energy consumption, but also puts strict requirements on the sintering equipment and increases the production cost; second, the high temperature performance is poor, and the Al2O3-Y2O3 binary additive system used in the traditional process will leave SiO2 glass phase at the grain boundary, which is easy to soften and creep at high temperature, resulting in a significant decrease in mechanical properties of the material in high temperature application scenarios, which seriously limits its application in high temperature fields.

[0003] To solve the above problems, there is an urgent need in the field to develop a silicon carbide ceramic preparation method which can reduce the sintering temperature and improve the high temperature stability and mechanical properties of the material. SUMMARY

[0004] The purpose of the present application is to provide a high-toughness impact-resistant pressureless sintering silicon carbide ceramic preparation method, which can effectively solve the technical problems of high sintering temperature, high energy consumption, poor high temperature performance and insufficient fracture toughness of the silicon carbide ceramic in the prior art.

[0005] To solve the above technical problems, the technical solution adopted by the present application is:

[0006] A high-toughness impact-resistant pressureless sintering silicon carbide ceramic preparation method, comprising the following steps:

[0007] Step A: mixing silicon carbide powder and sintering additives, the sintering additives are composed of Al2O3, Y2O3 and B4C, and the mass percentage is as follows: the content of Al2O3 is 0.5-5.0wt%, the content of Y2O3 is 1.0-6.0wt%, the content of B4C is 0.3-2.0wt%, and the balance is silicon carbide;

[0008] Step B: performing step-by-step sintering in a flowing inert atmosphere:

[0009] The first stage is at 1400-1500 DEG C for 0.5-2h, the second stage is at 1750-1800 DEG C for 1-3h, and the third stage is at 1820-1880 DEG C for 0.2-1h.

[0010] In one embodiment of the present disclosure, the silicon carbide powder is alpha-SiC, with purity ≥ 95wt%, and median particle size D50 of 0.3-1.0 μm, which ensures high purity and fine particle size characteristics of the raw material. High purity reduces the adverse effects of impurities on material performance, and fine particle size increases the sintering activity of the powder, which helps to reduce the sintering temperature and improve the densification degree of the green body, laying a foundation for performance optimization in the subsequent sintering process. 50 In one embodiment of the present disclosure, the silicon carbide powder is alpha-SiC, with purity ≥ 95wt%, and median particle size D50 of 0.3-1.0 μm, which ensures high purity and fine particle size characteristics of the raw material. High purity reduces the adverse effects of impurities on material performance, and fine particle size increases the sintering activity of the powder, which helps to reduce the sintering temperature and improve the densification degree of the green body, laying a foundation for performance optimization in the subsequent sintering process.

[0011] In one embodiment of the present disclosure, the particle size of B4C is ≤ 1 μm, which is used to completely react and eliminate the glass phase at the grain boundary, ensuring that B4C can be fully dispersed and react with the SiO2 oxide layer on the surface of SiC. The high reactivity of small particle size B4C can completely consume SiO2, avoiding the residual glass phase at the grain boundary, and solving the problem of high temperature creep caused by the glass phase in the traditional method; at the same time, the completely reacted B4C can generate a uniform fluxing phase and grain inhibitor, further improving the material performance.

[0012] In one embodiment of the present disclosure, in the first stage of the step sintering, B4C reacts with SiO2 on the surface of silicon carbide to generate B2O3 and SiC, and the reaction formula is:

[0013] B4C + SiO2 → B2O3 + SiC + CO↑;

[0014] The reaction consumes the SiO2 oxide layer on the surface of SiC, reduces the grain boundary defects, and at the same time generates B2O3 which has a fluxing effect, reduces the viscosity of the liquid phase, promotes the diffusion of substances, and provides power for the densification of the green body, solving the problem of performance affected by grain boundary impurities.

[0015] In one embodiment of the present disclosure, the sintering aid forms Y3Al5O 12 (YAG) liquid phase and YAl3(BO3)4 grain boundary phase at the grain boundary; the YAG liquid phase fills the gaps between SiC grains during sintering, promoting densification; and YAl3(BO3)4 is a high melting point grain boundary phase (melting point > 1800℃), which can remain stable at high temperatures, avoiding the softening phenomenon of traditional glass phase, significantly improving the high temperature stability of the material, and solving the problem of mechanical property degradation at high temperature.

[0016] In one embodiment of the present disclosure, in the second stage of the step sintering, Al2O3 reacts with Y2O3 to generate YAG liquid phase, promoting densification; the liquid phase provides a channel for substance migration, promoting the green body to achieve densification at a lower temperature, reducing the requirement for sintering temperature, and solving the problem of high densification temperature in the traditional method.

[0017] In one embodiment of this invention, during the third stage of stepped sintering, boron (B) diffuses to the SiC grain boundaries to inhibit grain growth, controlling the grain size to 1.5-2.5 μm. This limitation of B diffusion in the third stage inhibits SiC grain growth, controlling the grain size to 1.5-2.5 μm. The fine and uniform grain structure significantly improves the fracture toughness of the material, avoiding performance degradation due to excessively large grains, resulting in a fracture toughness of 4.9-5.8 MPa·m. 1 / 2 This solves the problem of insufficient toughness in traditional silicon carbide ceramics.

[0018] In one embodiment of the present invention, the inert atmosphere is argon gas with a flow rate of 30-100 mL / min; this ensures that the sintering process is carried out in an inert environment to prevent SiC from being oxidized at high temperatures; the stable argon gas flow rate can promptly remove the CO gas generated by the reaction, prevent porosity residue, and maintain stable pressure inside the furnace, providing a stable environment for the reaction of additives and grain growth, and ensuring consistent product performance.

[0019] In one embodiment of the present invention, during the first stage of stepped sintering, the argon gas flow rate is dynamically adjusted by real-time monitoring of the CO generation concentration, with the adjustment range being ±30% of the initial set value. When the CO concentration is >2 vol%, the argon gas flow rate is reduced by 10%-20% to avoid excessive residence time of the reaction gas leading to local impurity accumulation.

[0020] In one embodiment of the present invention, the CO generation concentration is monitored online by a mass spectrometer, and when the concentration is below 0.5 vol%, the argon flow rate is increased by 10%-30%.

[0021] In one embodiment of this invention, an oxygen content sensor is used to monitor the oxygen partial pressure inside the furnace in real time, and combined with an argon purity detector, the oxidation potential index (OPI) is calculated.

[0022]

[0023] Where [O2] represents the partial pressure of oxygen in the furnace and [Ar] represents the purity of argon. The OPI value calculated by this formula is used to determine whether to start the atmosphere circulation filtration system to control the oxidation risk during the sintering process; when OPI>0.05, the atmosphere circulation filtration system is started.

[0024] In one embodiment of the present invention, the SiO2 removal efficiency is verified by the concentration ratio of CO to B2O3 in the exhaust gas. If the CO / B2O3 molar ratio is >2.5, the grain boundary purification is deemed to meet the standard.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention achieves low-temperature pressureless sintering of silicon carbide ceramics by limiting specific content ranges of Al2O3, Y2O3, and B4C and using three-stage stepped sintering parameters. With the synergistic effect of the ternary additives, the sintering temperature is reduced by 70-130℃ compared to the traditional binary additive system, significantly reducing production energy consumption. Simultaneously, the stepped sintering process ensures sufficient reaction of the additives and densification of the green body, solving the problems of high sintering temperature and high energy consumption associated with traditional methods. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the overall principle of the present invention. Detailed Implementation

[0029] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the appendix... Figure 1 The descriptions are considered to be exemplary rather than restrictive in nature.

[0030] The following is in conjunction with the appendix Figure 1 The embodiments of the present invention will be described in detail below.

[0031] Example 1: A method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics, specifically including the following steps:

[0032] Step 1: Select α-SiC powder with a purity of 97wt% and a median particle size D50 of 0.6μm as the matrix material. The sintering aids are as follows by mass percentage: Al2O3 2.0wt%, Y2O3 3.0wt%, B4C 1.0wt%, B4C particle size = 0.8μm, and the balance is SiC powder.

[0033] Specific weighing: 94.0g α-SiC powder, 2.0g Al2O3 powder, 3.0g Y2O3 powder, and 1.0g B4C powder. Add the above raw materials to a planetary ball mill, using silicon carbide balls as the grinding medium and anhydrous ethanol as the dispersant. The ball-to-material ratio is 5:1, and the milling speed is 300 r / min. After ball milling for 4 hours, dry in a vacuum drying oven at 80℃ for 12 hours, and then pass through a 100-mesh sieve to remove agglomerated particles.

[0034] Step 2: The dried mixed powder is loaded into a rubber mold and cold isostatically pressed at 200 MPa for 3 minutes to obtain a cylindrical blank with a diameter of 50 mm and a thickness of 10 mm. The blank density is 2.1 g / cm³. 3 .

[0035] Step 3: Place the green body in a graphite sintering furnace and perform step sintering in a flowing Ar atmosphere at a flow rate of 50 mL / min.

[0036] First stage: The temperature was increased from room temperature to 1450℃ at a rate of 10℃ / min and held for 1 hour. During this stage, the reaction B4C + SiO2 → B2O3 + SiC + CO↑ occurred. CO gas was detected by mass spectrometry, proving that B4C effectively removed the SiO2 oxide layer on the SiC surface.

[0037] Second stage: The temperature was increased to 1780℃ at a rate of 5℃ / min and held for 2 hours. XRD analysis showed that Y3Al5O was generated in this stage. 12 (YAG) liquid phase promotes the initial densification of the green body;

[0038] The third stage: the temperature was increased to 1850℃ at a rate of 3℃ / min and held for 0.5h. SEM observation showed that the green body was further densified and there were no obvious pores at the grain boundaries.

[0039] After sintering, the furnace is cooled at a rate of 8°C / min.

[0040] Example 2: A method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics, specifically including the following steps:

[0041] Step 1: Select α-SiC powder with a purity of 96 wt% and a D50 of 0.6 μm. The sintering aids, by mass percentage, are: Al₂O₃ 3.0 wt%, Y₂O₃ 4.5 wt%, and B₄C 0.5 wt%, with a B₄C particle size of 0.6 μm. Specific weighings are: 92.0 g α-SiC powder, 3.0 g Al₂O₃ powder, 4.5 g Y₂O₃ powder, and 0.5 g B₄C powder. The mixing process is the same as in Example 1, followed by ball milling, drying, and sieving.

[0042] Step 2: Using the same cold isostatic pressing parameters as in Example 1, a billet density of 2.05 g / cm³ was obtained. 3 .

[0043] Step 3, stepped sintering process: Sintering in a flowing Ar atmosphere at a flow rate of 60 mL / min:

[0044] First stage: 1450℃×1h, B4C deoxygenation reaction is fully carried out;

[0045] Second stage: 1780℃×2h, a large amount of YAG liquid phase is generated with low viscosity;

[0046] Third stage: 1820℃×0.5h, to achieve densification; heating and cooling rates are the same as in Example 1.

[0047] Example 3: A method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics, specifically including the following steps:

[0048] Step 1: Select α-SiC powder with a purity of 95 wt% and a D50 of 0.6 μm. Use an Al2O3-Y2O3 binary additive: 2.5 wt% Al2O3 and 3.5 wt% Y2O3, with no B4C added. Specific weighings: 94.0 g α-SiC powder, 2.5 g Al2O3 powder, and 3.5 g Y2O3 powder. The mixing process is the same as in Example 1.

[0049] Step 2: Cold isostatic pressing parameters are the same as in Example 1, with a billet density of 2.0 g / cm³. 3 .

[0050] Step 3: Sintering process. To achieve densification, the sintering temperature needs to be increased.

[0051] First stage: 1450℃×1h, no B4C deoxygenation reaction, SiO2 residue;

[0052] Second stage: 1800℃×2h;

[0053] Third stage: 1950℃×1h, the temperature is increased by 100℃ compared with Example 1; Ar atmosphere flow rate 50mL / min.

[0054] Example 4 is basically the same as Example 1, except that α-SiC powder with a purity of 98wt% and a D50 of 0.8μm is selected, and the sintering aid ratio is: Al2O3 1.5wt%, Y2O3 2.5wt%, and B4C 1.2wt% (B4C particle size = 1.0μm). The specific weighings are: 94.8g of α-SiC powder, 1.5g of Al2O3 powder, 2.5g of Y2O3 powder, and 1.2g of B4C powder.

[0055] Cold isostatic pressing: 200 MPa × 3 min, billet density 2.12 g / cm³ 3 .

[0056] Sintering: First stage 1480℃×0.8h, second stage 1760℃×2.5h, third stage 1860℃×0.4h, Ar flow rate 40mL / min.

[0057] The performance test results of Examples 1-4 are shown in Table 1:

[0058]

[0059] Examples 1-2 used a ternary additive system, with a third-stage sintering temperature of only 1820-1850℃; while Example 3, without B4C, required a temperature increase to 1950℃ to achieve basic densification, resulting in a 70-130℃ reduction in sintering temperature. The dual role of B4C—the deoxygenation reaction generating a low-viscosity B2O3 flux phase and the synergistic promotion of densification by the YAG liquid phase—is the core of low-temperature sintering. The lower temperature not only reduces production energy consumption by approximately 25%, but also, based on the positive correlation between high-temperature sintering energy consumption and temperature, lowers the high-temperature resistance requirements of the sintering equipment, significantly reducing production costs.

[0060] The relative densities of Examples 1 and 2 reached 99.0% and 98.2%, respectively, while Example 4 reached 98.7%. However, Example 3 only achieved a relative density of 97.1% at a higher temperature. The synergistic effect of the ternary additives—YAG liquid phase filling of grain gaps and B4C purifying grain boundaries to reduce porosity—achieved a higher degree of densification. High density reduces internal defects in the material, laying the foundation for improved mechanical properties and avoiding stress concentration problems caused by porosity.

[0061] Examples 1, 2, and 4 containing B4C had fracture toughnesses of 5.8 MPa·m. 1 / 2 4.9 MPa·m 1 / 2 and 5.5 MPa·m 1 / 2 Example 3 without B4C had a strength of only 3.6 MPa·m. 1 / 2 The toughness is improved by 36%-61%; the diffusion of boron element inhibits the growth of SiC grains. The grain size in Examples 1, 2 and 4 is 1.8-2.2μm, and in Example 3 it reaches 3.5μm. The fine and uniform grain structure can improve fracture toughness through the grain refinement toughening mechanism, so that the material has better fracture resistance and impact resistance during use, thus broadening the application scenarios.

[0062] Example 1 achieved a flexural strength of 465 MPa at 1600℃, with a room temperature strength retention rate of 93%; Examples 2 and 4 achieved 430 MPa and 455 MPa, respectively; however, Example 3 experienced creep fracture at 1600℃ due to softening of the grain boundary glass phase, and its strength could not be effectively measured. The B4C reaction eliminates the SiO2 glass phase and forms a high-melting-point YAl3(BO3)4 grain boundary phase, avoiding the performance degradation caused by high-temperature softening of the glass phase in the traditional system. This allows the material to be stably applied in high-temperature scenarios, such as semiconductor wafer carriers and high-temperature metallurgical components.

[0063] Example 1 showed an oxidative weight gain of only 0.7 mg / cm³ under conditions of 1400℃ / 100h.2 Example 4 showed a concentration of 0.8 mg / cm³. 2 The oxidation rate is significantly lower than that of traditional systems. The absence of SiO2 glass phase at grain boundaries reduces the "channels" for oxidation reactions. At the same time, the dense microstructure and stable grain boundary phase hinder oxygen diffusion and penetration, reduce the oxidation rate, and extend the service life of the material in high-temperature oxidation environments.

[0064] This invention comprehensively solves the problems of high sintering temperature, poor high-temperature performance, and insufficient toughness of traditional silicon carbide ceramics through the synergistic design of ternary additives and the optimization of the step sintering process. The prepared ceramic products exhibit excellent performance in terms of density, toughness, high-temperature stability, and oxidation resistance, and have significant technological innovation and industrial application value.

[0065] Example 5 is basically the same as Example 1, except that in this example,

[0066] Step 1: The raw materials are the same as in Example 1.

[0067] Step 2: The preparation of the blank is the same as in Example 1.

[0068] Step 3: Add dynamic control to the stepped sintering process:

[0069] First stage: Incubate at 1450℃ for 1 hour, with an initial Ar flow rate of 50 mL / min, and monitor the CO concentration in real time using a mass spectrometer; when the CO concentration is <0.5 vol%, it indicates that the reaction is weakening, and the flow controller is automatically triggered to increase the Ar flow rate to 65 mL / min; continue monitoring until the CO concentration stabilizes at zero, confirming that the SiO2 removal is complete, and the residual amount is <1.5%.

[0070] Second stage: Hold at 1780℃ for 2 hours, oxygen sensor monitors oxygen partial pressure [O2] in furnace = 15ppm, argon purity 99.99%, calculate OPI = 0.015 (<0.05), filter not started.

[0071] Third stage: heat treatment at 1850℃ for 0.5h, the tail gas spectroscopy showed that the CO / B2O3 molar ratio was 3.2 (>2.5), indicating that the grain boundary purification met the standard.

[0072] Example 6 is basically the same as Example 1, except that in this example, step 3: the Ar flow rate is fixed at 50 mL / min and is not dynamically adjusted;

[0073] The rest is the same as in Example 5:

[0074] During the first phase, the CO concentration remained below 0.3 vol%, and flow compensation was not triggered.

[0075] SEM images after sintering showed approximately 4.1% residual SiO2 at the grain boundaries, compared to 1.5% in Example 5; the fracture toughness was only 5.1 MPa·m. 1 / 2 This is lower than the 5.7 MPa·m in Example 5. 1 / 2 .

[0076] The performance test results for Examples 5 and 6 are shown in Table 2:

[0077]

[0078] This invention adjusts the argon flow rate by feedback of CO concentration, thereby reducing the residual SiO2 content from 5% in the original scheme to <2% (data from Example 5), and further reducing the grain boundary glass phase.

[0079] Example 5, by adding a dynamic control mechanism to the stepped sintering process, achieved precise process control and improved product performance. In the first stage, the CO concentration was monitored in real time using a mass spectrometer, and the argon flow rate was dynamically adjusted. When the CO concentration was <0.5 vol%, the flow rate was increased to 65 mL / min to ensure that the reaction between B4C and SiO2 on the SiC surface proceeded fully. Ultimately, the residual SiO2 content was reduced to <1.5%, far lower than the 4.1% in traditional fixed flow rate processes, such as in Example 6. The grain boundary glass phase was almost completely eliminated, laying the foundation for the material's high-temperature and mechanical properties.

[0080] The second stage precisely controls the furnace atmosphere by calculating the oxidation potential index (OPI = 0.015 < 0.05) to prevent oxygen infiltration. The flexural strength reaches 470 MPa at 1600℃, and the room temperature strength retention rate is increased to 95%; the oxidation weight gain at 1400℃ / 100h is only 0.5 mg / cm³. 2 It is significantly better than Example 1 (0.7 mg / cm³). 2 This indicates that the material is more stable in high-temperature oxidizing environments.

[0081] The third stage verified the compliance of grain boundary purification by measuring the CO / B2O3 molar ratio in the exhaust gas (3.2 > 2.5), with the grain size controlled at 1.7 μm and the fracture toughness reaching 5.7 MPa·m. 1 / 2 The relative density was increased to 99.2%, and the overall performance was balanced and superior to the embodiment without dynamic control. The dynamic control mechanism enabled real-time feedback and adjustment of the reaction process, avoiding the incomplete reaction problems that may occur under traditional fixed parameters, ensuring the consistency of product quality for each batch, and providing a stable process reference for industrial production.

[0082] In Example 6, the CO concentration remained below 0.3 vol% without triggering flow compensation, resulting in 4.1% residual SiO2 at the grain boundaries and a fracture toughness of only 5.1 MPa·m. 1 / 2 In stark contrast to Example 5, this clearly demonstrates the crucial role of "CO concentration feedback adjustment of argon flow rate" in grain boundary purification and toughness improvement. Performance data under fixed parameters (such as relative density of 97.8% and high-temperature strength retention of 90%) quantifies the shortcomings of traditional fixed processes in densification and grain boundary control, further highlighting the innovation and advantages of the newly added dynamic control technology in this invention.

[0083] In the first stage of stepped sintering, the argon flow rate is dynamically adjusted by real-time monitoring of CO generation concentration, with an adjustment range of ±30% of the initial set value, enabling more precise control of the gas atmosphere during the sintering process. In this stage, B4C reacts with SiO2 on the silicon carbide surface to generate CO. The CO generation concentration is a key indicator of the reaction progress and the effectiveness of SiO2 removal. Dynamically adjusting the argon flow rate by real-time monitoring of CO generation concentration allows for timely adjustments to the reaction environment. When the CO concentration is high, appropriately reducing the argon flow rate allows the reactant gas to have a more suitable residence time in the furnace, promoting a more complete reaction. When the CO concentration is low, increasing the argon flow rate quickly removes the generated CO, preventing it from adversely affecting subsequent reactions and product quality. Compared to the traditional method of fixing the argon flow rate, this dynamic adjustment mechanism significantly improves the controllability of the reaction during sintering, creating more favorable conditions for subsequent compaction of the green body and grain boundary purification.

[0084] The mass spectrometer possesses extremely high detection accuracy and sensitivity, enabling real-time and accurate online monitoring of CO generation concentration. When the CO concentration falls below 0.5 vol%, it indicates a weakened reaction. At this point, increasing the argon gas flow rate by 10% to 30% allows for timely replenishment of fresh argon gas, providing a better mass transfer environment for the reaction and accelerating the reaction process of unreacted SiO2 with B4C, ensuring that SiO2 is removed as completely as possible. As shown in Example 5, through this precise control, the residual SiO2 content was reduced from 5% in the original scheme to <2%, further reducing the grain boundary glass phase and significantly improving grain boundary quality. This, in turn, enhances the high-temperature performance and mechanical properties of silicon carbide ceramics, effectively avoiding problems such as high-temperature softening and creep caused by excessive residual grain boundary glass phase.

[0085] During the sintering process of silicon carbide ceramics, even trace amounts of oxygen can react with SiC to cause oxidation, affecting product quality. By monitoring the oxygen partial pressure and argon purity in the furnace in real time and calculating the OPI, the oxidation risk of the furnace atmosphere can be quantitatively assessed. When the OPI > 0.05, the atmosphere circulation filtration system is activated to promptly remove oxygen and other harmful impurities from the furnace and block oxygen permeation pathways. In Example 5, at 1600℃, the oxidation weight gain was only 0.5 mg / cm³ under OPI index control. 2 Compared with Example 1, 0.7 mg / cm 2 This significantly reduces the risk of oxidation and improves the stability and reliability of products in high-temperature environments, which is of great significance for silicon carbide ceramic products used in high-temperature fields such as aerospace and metallurgy.

[0086] During sintering, the SiO2 removal efficiency directly affects the degree of grain boundary purification, thus influencing the performance of ceramic materials. The concentration ratio of CO to B2O3 in the exhaust gas is closely related to the SiO2 removal reaction. CO is one of the products of the reaction between B4C and SiO2, while B2O3 is another product. By monitoring the molar ratio of CO to B2O3 in the exhaust gas, the SiO2 removal efficiency can be directly reflected. When the CO / B2O3 molar ratio is >2.5, the grain boundary purification is considered to be up to standard, ensuring the consistency of grain boundary purification effect for each batch of products. This makes quality control during the production process more scientific and accurate, and the product toughness fluctuation range is reduced from ±0.4 MPa·m. 1 / 2 Narrowed to ±0.2 MPa·m 1 / 2 This greatly enhances process stability and is conducive to the large-scale industrial production of high-quality silicon carbide ceramic products.

[0087] Example 7 discloses a method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics, the method comprising:

[0088] By segmenting and controlling the temperature curve inside the sintering furnace, precisely adjusting the heating rate and setting the holding time in stages, and combining the chemical reaction between B4C and the oxide layer on the surface of silicon carbide ceramics, data on the reaction products are obtained to determine the degree of oxide removal.

[0089] Specifically, thermodynamic simulation software was used to process the reaction product data. Combined with the physical properties of B4C particle size ≤1μm and SiC powder D50=0.6μm, the degree of SiO2 oxide layer removal at 1450℃ was calculated. If the B2O3 residue was less than 5%, the grain boundary purification effect was confirmed to meet the standard, and the oxide removal degree data was obtained.

[0090] Based on the reaction product data, the argon flow rate is adjusted in real time and the argon purity is detected online. Combined with the filtration of the atmosphere circulation system, the gas input pressure is adjusted to determine whether the flowing argon meets the threshold requirements of the preset oxidation conditions, so as to obtain stable environmental protection parameters.

[0091] Specifically, if the oxidation potential index is lower than the preset threshold, the filtration program is started through the atmosphere circulation system to adjust the gas input pressure to the set range and obtain stable environmental protection parameters.

[0092] If the flow argon parameters meet the preset threshold, the oxidation reaction rate data can be obtained by monitoring the oxygen content during the sintering stage, combined with the adsorption of residual oxygen in the furnace and the uniform distribution of the atmosphere flow field, to determine the degree to which the oxidation reaction is suppressed.

[0093] By analyzing oxygen partial pressure data and the B4C reaction rate (B4C + SiO2 → B2O3 + SiC + CO↑), the oxidation reaction rate constant is calculated. Combined with the YAG liquid phase formation rate, the degree to which the oxidation reaction is inhibited is determined.

[0094] Based on the oxidation reaction rate data, a threshold control algorithm is used, combined with the optimization of uniform thermal field distribution and dynamic balance of furnace pressure, to adjust the segmented control of the temperature curve and the precise control of gas humidity in the sintering furnace, to determine whether the weight gain of silicon carbide ceramics is lower than the fourth threshold, and to obtain a sintering state that meets the preset oxidation conditions.

[0095] Specifically, based on the thermal field uniformity parameters and pressure distribution data, the stepped heating curve inside the sintering furnace is adjusted. A segmented control algorithm is adopted to set temperature curves of 1450℃×1h, 1780℃×2h, and 1850℃×0.5h, obtain temperature stability data for each stage, and obtain the temperature control status of the sintering process.

[0096] By analyzing sintering state data, combined with material surface reaction rate analysis and exhaust gas emission composition analysis, the residual amount of oxide layer on the surface of silicon carbide ceramics is obtained. Using a support vector machine model and combined with the atmosphere switching during the cooling stage, the oxidation trend in the subsequent sintering process is predicted, and the final process parameter optimization scheme is determined.

[0097] Specifically, the concentration data of CO and B2O3 in the combustion tail gas are obtained, the proportion of tail gas emission components in the 1450℃ deoxygenation stage is determined by mass spectrometry analysis, and the oxide layer removal efficiency is calculated by combining the SiO2 residual data to obtain the degree of grain boundary purification.

[0098] This embodiment uses segmented temperature control, precise adjustment of heating rate and holding time, and the chemical reaction between B4C and the oxide layer to obtain reaction product data to determine the degree of oxide removal. By real-time adjustment of argon flow rate, online detection of argon purity, and filtration through an atmosphere circulation system, the flowing argon is ensured to meet preset oxidation condition thresholds. Oxygen content monitoring and thermal field distribution optimization dynamically balance furnace pressure and suppress oxidation reaction rates. Finally, a support vector machine model is used to analyze reaction rate and exhaust gas composition, predict oxidation trends, and optimize process parameters. This invention significantly reduces the residual oxide layer on the surface of silicon carbide ceramics, ensures stable sintering, and improves ceramic material performance and process reliability.

[0099] The invention will be further illustrated below with reference to practical applications. The specific steps are as follows:

[0100] Step S101: By segmenting and controlling the temperature curve inside the sintering furnace, the heating rate is precisely adjusted and the holding time is set in stages. Combined with the chemical reaction between B4C and the oxide layer on the surface of silicon carbide ceramic, the reaction product data is obtained to determine the degree of oxide removal.

[0101] The reaction product data were processed using thermodynamic simulation software. Combined with the physical properties of B4C particle size ≤1μm and SiC powder D50=0.6μm, the degree of SiO2 oxide layer removal at 1450℃ was calculated. If the SiO2 residue was less than 5%, the grain boundary purification effect was confirmed to be up to standard, and the oxide removal degree data was obtained.

[0102] Specifically, the temperature curve inside the sintering furnace is controlled by information technology. First, a precise heating rate adjustment algorithm is adopted, with the initial temperature set at 25℃ and the target sintering temperature at 1800℃. The heating process is divided into three stages: heating from 25℃ to 800℃ at 5℃ / min, heating from 800℃ to 1400℃ at 3℃ / min, and heating from 1400℃ to 1800℃ at 2℃ / min. Based on the PID control algorithm, the proportional coefficient Kp = 0.5, the integral time Ti = 120s, and the derivative time Td = 30s. The furnace temperature data is collected in real time by thermocouples, with the error controlled within ±2℃. The temperature curve data is generated and stored in the database.

[0103] The heat preservation time is set in two stages: 30 minutes at 1400℃ and 60 minutes at 1800℃. The system automatically records the heat preservation time with an error controlled within ±10 seconds. The data is correlated with the temperature through timestamps and stored in a MySQL database for subsequent analysis.

[0104] The chemical reaction between B4C and the oxide layer on the surface of silicon carbide ceramic was studied. The reaction environment was set as an argon atmosphere with an oxygen content of 0.1%. The amount of oxidation products (such as B2O3 and SiO2) generated was calculated based on a thermodynamic model using the mass conservation equation.

[0105] m(B4C)+m(SiO2)=m(B2O3)+m(SiC)+m(CO);

[0106] m(B4C) represents the mass of boron carbide involved in the reaction;

[0107] m(SiO2) is the mass of silicon dioxide in the oxide layer on the SiC surface;

[0108] m(B2O3) is the mass of boron trioxide produced in the reaction;

[0109] m(SiC) is the mass of silicon carbide produced in the reaction;

[0110] m(CO) is the mass of carbon monoxide gas produced in the reaction.

[0111] The oxide peak intensity ratio was detected by X-ray diffraction (XRD) analysis of the samples before and after the reaction, and the oxide removal rate was calculated. Assuming that the initial oxide layer thickness was 10 μm and the thickness was reduced to 2 μm after the reaction, the removal rate reached 80%.

[0112] The types of products were further verified by Fourier transform infrared spectroscopy (FTIR), with the absorption peak located at 1380 cm⁻¹. -1 and 850cm -1 The presence of B2O3 and SiO2 was confirmed.

[0113] All data were processed automatically using Python scripts to generate a mass distribution map of reactants. Combined with temperature curve analysis, the relationship between oxide removal degree and temperature and holding time was determined to obtain the optimal process parameters: holding at 1800℃ for 60 minutes, with a removal rate of up to 85%.

[0114] If optimization is needed, the heating rate can be adjusted to 1.5℃ / min and the holding time at 1800℃ can be extended to 75 minutes, which is expected to increase the removal rate to 88%. The stability of the process can be verified by comparing with the database.

[0115] Step S102: Based on the reaction product data, the argon flow rate is adjusted in real time and the argon purity is detected online. Combined with the filtration of the atmosphere circulation system, the gas input pressure is adjusted to determine whether the flowing argon meets the threshold requirements of the preset oxidation conditions, thereby obtaining stable protective environmental parameters.

[0116] If the oxidation potential index is lower than the preset threshold, the filtration program is started through the atmosphere circulation system to adjust the gas input pressure to the set range and obtain stable environmental protection parameters.

[0117] Specifically, in order to achieve argon protection environment control based on reaction product data, the oxygen content in the reaction products is first monitored in real time by online sensors. Assuming that the detected oxygen concentration is 0.05%, which is lower than the preset threshold of 0.1%, it indicates that the reaction products meet the low oxidation conditions.

[0118] Based on this, a PID algorithm is used to adjust the argon flow rate. The target flow rate is set to 10 L / min, the initial flow rate is 8 L / min, the error is e = 2, the proportional coefficient Kp = 0.5, the integral coefficient Ki = 0.1, and the derivative coefficient Kd = 0.05. The output adjustment is calculated as follows:

[0119] u=Kp*e+Ki*∫edt+Kd*de / dt,

[0120] The obtained flow rate increment was 1.2 L / min, and the adjusted flow rate was 9.2 L / min, which is close to the target value.

[0121] Subsequently, the purity of the argon gas was detected using a laser-induced fluorescence spectrometer. Assuming the detected purity was 99.995%, which is higher than the minimum requirement of 99.99%, the gas quality was confirmed to be qualified.

[0122] To further optimize the system, the atmosphere circulation system activated its filtration module, utilizing molecular sieves to adsorb residual moisture and oxygen with a filtration efficiency of 98%, reducing the oxygen content in the circulating gas to 0.01%. Finally, based on pressure sensor data (current pressure 2.0 bar, target pressure 2.5 bar), a linear regression algorithm was used to predict the pressure adjustment amount. The calculation formula is P = 0.8 * Q + 0.5 (where Q is the flow rate), indicating that a pressure increase of 0.4 bar is required. This pressure was then automatically adjusted to 2.4 bar by the servo valve, approaching the target value.

[0123] The above steps form a closed-loop control through sensor data acquisition, algorithm calculation, and automatic adjustment to ensure that the argon environment is stable and meets the oxidation threshold requirements. Logically, each step is interconnected, and the final output is a stable protective environmental parameter.

[0124] Step S103: If the flowing argon parameters meet the preset threshold, the oxidation reaction rate data is obtained by monitoring the oxygen content during the sintering stage, combined with the adsorption of residual oxygen in the furnace and the uniform distribution of the atmosphere flow field, to determine the degree to which the oxidation reaction is suppressed.

[0125] By analyzing oxygen partial pressure data and the B4C reaction rate:

[0126] 4B4C + 7Si O2 → 2B2O3 + 7SiC + 5CO↑. Calculate the oxidation reaction rate constant and, combined with the YAG liquid phase formation rate, determine the degree to which the oxidation reaction is inhibited.

[0127] Specifically, the system first monitors the parameters of the flowing argon gas in real time through sensors, and sets preset thresholds of argon gas flow rate of 20L / min, purity of 99.999%, and pressure of 0.1MPa.

[0128] When the sensor detects a flow rate of 21 L / min, a purity of 99.9995%, and a pressure of 0.09 MPa, the system uses a comparison algorithm:

[0129] Threshold comparison: |actual value - preset value| / preset value < 5%; if the parameter meets the requirements, automatically proceed to the next stage.

[0130] Next, the system uses an oxygen sensor to monitor the oxygen content inside the furnace during the sintering stage. The sampling frequency is set to 1Hz to acquire oxygen concentration data, such as concentration values ​​of 0.02%, 0.019%, and 0.021% over 10 consecutive seconds. By calculating the average value (0.02%) and standard deviation (0.001%), the stability of the oxygen content is analyzed to determine whether it is below the target threshold of 0.05%.

[0131] Subsequently, the system used CFD (Computational Fluid Dynamics) simulation to analyze the uniformity of the atmosphere flow field inside the furnace. Assuming the furnace size is 1m×0.5m×0.5m and the argon inlet velocity is 0.5m / s, the k-ε turbulence model was used, and the calculated flow field uniformity index was 0.95 (close to 1 indicates uniformity).

[0132] Based on the residual oxygen adsorption model, the system is based on the Langmuir adsorption isotherm:

[0133] q = q m *K*C / (1+K*C), where q m =0.01mol / g, K = 100L / mol, C is the oxygen concentration of 0.02%, the calculated adsorption capacity q = 0.0098mol / g, indicating that the residual oxygen was effectively adsorbed; where q is the amount of residual oxygen adsorbed on the adsorbent material in the furnace. m denoted as the maximum adsorption capacity of the adsorbent material, K as the adsorption equilibrium constant, and C as the oxygen concentration in the furnace.

[0134] Finally, the system yields the oxidation reaction rate equation:

[0135] r=k*[O2]^n, k=0.01, n=1, [O2]=0.02%;

[0136] Where r is the oxidation reaction rate on the SiC surface, and k is the reaction rate constant, which is taken as 0.01s in this embodiment. -1 [O2] represents the volume fraction of oxygen in the furnace, and n represents the reaction order. In this embodiment, the oxidation reaction is a first-order reaction, so n = 1.

[0137] The calculated reaction rate r = 0.0002 mol / (L·s) was compared with the standard rate of 0.001 mol / (L·s), indicating that the oxidation reaction was inhibited by 80%. If the flow field uniformity is insufficient, the system can adjust the argon inlet velocity to 0.6 m / s and recalculate until the requirements are met, thus forming a closed-loop control logic.

[0138] Step S104: Based on the oxidation reaction rate data, a threshold control algorithm is used, combined with the optimization of uniform thermal field distribution and dynamic balance of pressure inside the furnace, to adjust the segmented control of the temperature curve and the precise control of gas humidity inside the sintering furnace, and to determine whether the weight gain of silicon carbide ceramic is lower than the fourth threshold, so as to obtain a sintering state that meets the preset oxidation conditions.

[0139] Based on the thermal uniformity parameters and pressure distribution data, the stepped heating curve inside the sintering furnace was adjusted. A segmented control algorithm was adopted to set temperature curves for 1450℃×1h, 1780℃×2h, and 1850℃×0.5h, and temperature stability data for each stage were obtained to obtain the temperature control status of the sintering process.

[0140] Specifically, based on the oxidation reaction rate data, it is assumed that the oxidation weight gain rate of silicon carbide ceramics in the sintering furnace varies with temperature and humidity, with an initial oxidation rate of 0.05 g / h and a target weight gain threshold of 0.03 g / h.

[0141] A threshold control algorithm is adopted. By monitoring the oxidation weight gain in real time, a fourth threshold is set to 0.03 g / h. When the weight gain rate is lower than this value, it is determined that the preset oxidation conditions are met.

[0142] First, by optimizing the uniformity of the thermal field distribution, the temperature field inside the furnace was simulated based on finite element analysis. The initial temperature distribution was 1450℃ at the center and 1400℃ at the edge, with a deviation of ±25℃. The algorithm controlled the uniformity of the thermal field by adjusting the power of the heating elements, aiming to reduce the deviation to ±10℃. Specifically, a PID algorithm was used to adjust the power output, with a proportional coefficient Kp = 0.5, an integral time Ti = 120s, and a derivative time Td = 30s. After iterative calculation, the temperature difference between the center and the edge converged to 1425±10℃.

[0143] Next, combining the dynamic balance of pressure inside the furnace, with an initial pressure of 1.2 atm and a fluctuation of ±0.1 atm, a dynamic pressure control algorithm is adopted. By adjusting the opening of the inlet and outlet valves, and based on pressure sensor data (sampling frequency 10Hz), the pressure is stabilized at 1.2 ± 0.02 atm. The control equation is as follows:

[0144] P(t) = PO + Kv·ΔQ, where Kv is the valve gain of 0.01 atm / (L / s) and ΔQ is the gas flow difference.

[0145] Precise humidity control is achieved through humidity sensor monitoring. The initial humidity is 30% RH, and the target is 25 ± 2% RH. A proportional control algorithm is used to adjust the humidifier's spray volume. The control equation is as follows:

[0146] H(t) = H0 + Kh·ΔM, where Kh is 0.1%RH / (g / s) and ΔM is the difference in spray volume. The mixture is iteratively adjusted until the humidity stabilizes.

[0147] Ultimately, the oxidation weight gain rate is monitored in real time by a mass sensor, and the data stream is input into a threshold control algorithm. When the current weight gain rate v.028g / h is lower than 0.03g / h, the system determines that the sintering state meets the preset conditions.

[0148] The uniformity of the thermal field affects the oxidation rate, stable pressure ensures uniform gas distribution, and humidity control optimizes the reaction environment, all of which together reduce the weight gain rate to below the target threshold.

[0149] Step S105: By analyzing sintering state data, combined with material surface reaction rate analysis and exhaust gas emission component analysis, the residual amount of oxide layer on the surface of silicon carbide ceramic is obtained. Using a support vector machine model and combined with the atmosphere switching during the cooling stage, the oxidation trend in the subsequent sintering process is predicted, and the final process parameter optimization scheme is determined.

[0150] The concentration data of CO and B2O3 in the combustion tail gas were obtained. The proportion of exhaust gas components in the deoxygenation stage at 1450℃ was determined by mass spectrometry analysis. Combined with the SiO2 residual data, the oxide layer removal efficiency was calculated to obtain the degree of grain boundary purification.

[0151] Specifically, by processing sintering state data through information technology, data such as temperature (e.g., 1450℃), atmosphere (nitrogen to oxygen ratio of 9:1), and sintering time (2 hours) of silicon carbide ceramics during the sintering process are first collected. Combined with surface reaction rate analysis, a kinetic model is used to calculate the oxide layer formation rate.

[0152] Assuming the surface oxidation reaction follows the Arrhenius equation, the reaction rate constant is:

[0153] k = A·exp(-Ea / RT), where A is 10 4 s -1 The activation energy Ea is 200 kJ / mol, R is 8.314 J / (mol·K), T is 1723 K, and the calculated k is approximately 0.012 s, with the oxide layer thickness growth rate being approximately 0.1 m / min.

[0154] The exhaust gas composition was analyzed by infrared spectroscopy, and the CO2 concentration was detected to be 500 ppm and the O2 concentration to be 2%. Based on the mass conservation principle, the residual oxide layer was calculated. Assuming the initial silicon carbide sample mass was 100 g and the mass of SiO2 generated by the oxidation reaction was 0.5 g, the residual oxide layer thickness was approximately 1.2 μm.

[0155] The oxidation trend was predicted using a Support Vector Machine (SVM) model. Input features included temperature, atmosphere ratio, and time; the output was the oxide layer thickness. The RBF kernel function was selected, with C = 1.0 and γ = 0.1. The training dataset contained 1000 samples (80% training, 20% testing). By simulating the effect of atmosphere change on the oxidation rate during the cooling stage (from oxygen to argon at a switching point of 1000℃), the subsequent sintering oxide layer thickness increment was predicted to be 0.3 μm.

[0156] The final optimized process parameters were: sintering temperature reduced to 1420℃, oxygen ratio reduced to 5%, sintering time shortened to 1.8 hours, oxide layer thickness controlled within 0.8μm, and tail gas CO2 emissions reduced to 400ppm.

[0157] The entire process forms a closed-loop logic through data acquisition, algorithm modeling, and simulation optimization, relying on information technology to achieve automated analysis and prediction.

[0158] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0159] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics, characterized in that, Includes the following steps: Step A: Mix silicon carbide powder with a sintering aid, wherein the sintering aid is composed of Al2O3, Y2O3 and B4C, and by mass percentage: Al2O3 content is 0.5-5.0 wt%, Y2O3 content is 1.0-6.0 wt%, B4C content is 0.3-2.0 wt%, and the balance is silicon carbide; the particle size of the B4C is ≤1 μm; Step B: Perform stepped sintering in a flowing argon atmosphere; the argon flow rate is 30-100 mL / min; The first stage involves holding the temperature at 1400-1500℃ for 0.5-2 hours. The second stage involves maintaining the temperature at 1750-1800℃ for 1-3 hours. The third stage involves holding the temperature at 1820-1880℃ for 0.2-1 hour. The silicon carbide powder is α-SiC, with a purity ≥95wt% and a median particle size D. 50 The thickness is 0.3-1.0 μm; In the first stage of stepped sintering, the argon gas flow rate is dynamically adjusted by real-time monitoring of CO generation concentration. The adjustment range is ±30% of the initial set value. When the CO concentration is > 2 vol%, the argon gas flow rate is reduced by 10%-20% to avoid the reaction gas from accumulating local impurities due to excessive residence time.

2. The method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics according to claim 1, characterized in that: In the first stage of the stepped sintering, B4C reacts with SiO2 on the silicon carbide surface to generate B2O3 and SiC.

3. The method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics according to claim 1, characterized in that: The sintering aid forms Y3Al5O at the grain boundaries. 12 Liquid phase and YAl3(BO3)4 grain boundary phase.

4. The method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics according to claim 1, characterized in that: In the second stage of the stepped sintering, Al2O3 reacts with Y2O3 to generate a YAG liquid phase, which promotes densification.

5. The method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics according to claim 1, characterized in that: In the third stage of the stepped sintering, the B element diffuses to the SiC grain boundaries to inhibit grain growth, and the grain size is controlled at 1.5-2.5μm.

6. The method for manufacturing high-toughness, impact-resistant, pressureless sintered silicon carbide ceramics according to claim 1, characterized in that: The CO generation concentration is monitored online using a mass spectrometer. When the concentration is below 0.5 vol%, the argon flow rate is increased by 10%-30%.

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