A method for preparing high-performance silicon nitride ceramics

Abstract

This invention relates to the field of high-performance structural ceramic materials and their corrosion resistance optimization technology, and particularly to a method for preparing high-performance silicon nitride ceramics. Performance improvement is achieved through dynamic optimization of composite sintering aids, closed-loop control of gas pressure sintering, and multi-process data linkage. In the raw material pretreatment stage, a laser particle size analyzer is used to monitor particle size distribution in real time, and surface modification parameters are adjusted accordingly to form a uniform monomolecular coating layer. The ratio of rare earth oxides to alumina in the composite sintering aids is dynamically adjusted according to the mixing torque fluctuations to suppress agglomeration and segregation of the aids. In the gas pressure sintering stage, the argon pressure and heating rate are dynamically adjusted based on the slope of the shrinkage curve, combined with low-temperature nitrogen protection and high-temperature argon densification to promote the directional alignment of β-phase grains. Multi-dimensional process control synergistically optimizes grain boundary composition, structure, and density, significantly improving the corrosion resistance and service life of silicon nitride ceramics in sulfur-containing environments.

Description

Technical Field

[0001] This invention relates to the field of high-performance structural ceramic materials and their corrosion resistance optimization technology, and particularly to a method for preparing high-performance silicon nitride ceramics. Background Technology

[0002] Silicon nitride ceramics are covalent compound ceramics with silicon and nitrogen as the main components. Their three-dimensional network crystal structure endows the material with excellent high-temperature stability and mechanical properties. The overall performance of silicon nitride ceramics prepared by reaction sintering or gas pressure sintering processes can be controlled by adjusting the grain ratio of the internal α-phase and β-phase and the composition of the grain boundary phase. The material maintains high flexural strength at high temperatures due to the strong covalent bonds' ability to resist grain boundary slip; its non-oxide properties provide good oxidation resistance, and oxygen atom diffusion is significantly suppressed below 1200℃. The synergistic effect of low thermal expansion coefficient and high thermal conductivity gives silicon nitride ceramics outstanding thermal shock resistance under thermal cycling loads, making it an ideal candidate material for high-temperature moving parts such as gas turbine blades and bearing rollers. In oil pipeline transportation systems, existing metal sealing components are prone to corrosion in sulfur-containing media, while silicon nitride ceramic seals suffer from insufficient corrosion resistance due to grain boundary phase segregation. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for preparing high-performance silicon nitride ceramics, solving the problem of insufficient corrosion resistance of silicon nitride ceramic seals caused by grain boundary phase segregation in sulfur-containing media environments.

[0004] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows:

[0005] The present invention discloses a method for preparing high-performance silicon nitride ceramics, comprising:

[0006] Step 1: The silicon nitride powder is pretreated by wet ball milling. The particle size distribution of the powder is monitored in real time by a laser particle size analyzer. Based on the particle size data obtained by the laser particle size analyzer, the concentration of silane coupling agent and ultrasonic power in the surface modification process are adjusted. The silane coupling agent is coated on the powder surface to form a monolayer by ultrasonic dispersion.

[0007] Step 2: Mix the surface-modified powder with the composite sintering aid, which is composed of rare earth oxides and alumina in a certain proportion. The mixing speed and time are dynamically adjusted according to the torque data of the planetary mixer during the mixing process. The torque data is collected in real time by the built-in sensor of the planetary mixer to obtain a uniformly dispersed mixture.

[0008] Step 3: The mixture is subjected to gas pressure sintering. The displacement of the mold is monitored by a laser displacement sensor to generate a sintering shrinkage curve. Based on the curve, the argon pressure and heating rate are dynamically adjusted to form a silicon nitride ceramic matrix containing oriented β-phase grains.

[0009] Step 4: Analyze the distribution of rare earth elements in the grain boundary phase of the silicon nitride ceramic matrix using an electron probe microanalysis. If a local discontinuous region of the grain boundary phase is detected, repeat the mixing and sintering steps based on the increase in the proportion of rare earth oxides in the composite sintering aid in Step 2.

[0010] Step 5: Anneal the sintered ceramic matrix to eliminate residual stress, and then strengthen and seal the internal pores by hot isostatic pressing. The hot isostatic pressing parameters are dynamically adjusted according to the porosity test results of the matrix after sintering in Step 3.

[0011] Furthermore, in the high-performance silicon nitride ceramic preparation method of the present invention, during the wet ball milling pretreatment in step 1, a laser particle size analyzer is used to monitor the particle size distribution of the powder in real time. When the median particle size is found to exceed the range of 0.5-1.0 μm, it is corrected by extending or shortening the ball milling time. The corrected powder particle size data is used to generate a silane coupling agent concentration correction value through the particle size adjustment model in step 1, and the correction value is input into the surface modification process to adjust the silane coupling agent concentration simultaneously.

[0012] Furthermore, in the high-performance silicon nitride ceramic preparation method of the present invention, the composite sintering aid in step 2 is composed of rare earth oxides and alumina, wherein the proportion of rare earth oxides is 60-80 wt%. The proportion is dynamically optimized according to the torque data change trend of the planetary mixer in step 2. The preset threshold is set according to the powder dispersion uniformity requirements of the mixing process. If the torque fluctuation exceeds the preset threshold, the proportion of rare earth oxides is reduced to below 70 wt%, and the mixing uniformity of the adjusted aid is verified by X-ray diffraction analysis.

[0013] Furthermore, in the high-performance silicon nitride ceramic preparation method of the present invention, step 3 of the gas pressure sintering includes a low-temperature stage and a high-temperature stage. In the low-temperature stage, the initial mold displacement data monitored by the laser displacement sensor in step 3 is used to raise the temperature at a rate of 5-10℃ / min and nitrogen is introduced. When the slope of the sintering shrinkage curve reaches the critical value set according to the densification requirements of the sintering process, the process switches to the high-temperature stage. After switching, argon is used and the heating rate is reduced to 2-5℃ / min. At the same time, the argon pressure increase is adjusted according to the slope of the real-time shrinkage curve. The adjusted argon pressure increase is verified by observing the compactness of the β-phase grain arrangement using a metallographic microscope.

[0014] Furthermore, in the high-performance silicon nitride ceramic preparation method of the present invention, in step 4, the distribution of rare earth elements in the grain boundary phase is analyzed by electron probe microanalysis. If local discontinuous regions are detected, the proportion of rare earth oxides in the composite sintering aid in step 2 is increased. The increased proportion is calculated based on the initial proportion of the composite sintering aid in step 2. The adjusted composite sintering aid and surface-modified powder are mixed again in step 2 and sintered in step 3. The continuity of the grain boundary phase is verified again by electron probe microanalysis until the grain boundary phase is continuously distributed.

[0015] Furthermore, in the high-performance silicon nitride ceramic preparation method of the present invention, during hot isostatic pressing in step 5, argon gas is used as the pressure transmission medium. The processing parameters are selected based on the porosity test results of the sintered matrix: when the porosity is higher than 3%, it is treated at 1300℃ and 200MPa for 4 hours; when the porosity is lower than 1%, it is treated at 1200℃ and 150MPa for 2 hours. The porosity test results are determined by Archimedes' displacement method, and the pore sealing effect of the treated ceramic matrix is ​​verified by ultrasonic flaw detection.

[0016] Furthermore, in the high-performance silicon nitride ceramic preparation method of the present invention, before the start of step 1, the specific surface area and oxygen content of each batch of silicon nitride powder are tested. The specific surface area is determined by gas adsorption method and the oxygen content is determined by inert gas melting method. If the difference in specific surface area exceeds ±5% or the oxygen content is greater than 1.5wt%, the ball milling time in step 1 or the proportion of composite sintering aid in step 2 is adjusted according to the deviation between the excess value and the benchmark value. The adjusted powder needs to be retested until the result meets the standard.

[0017] Beneficial effects of this invention;

[0018] This invention systematically improves the corrosion resistance of silicon nitride ceramics through dynamic optimization of composite sintering aid ratios, closed-loop control of gas pressure sintering parameters, and a multi-process data linkage mechanism. In the grain boundary phase optimization stage, the proportion of rare earth oxides is iteratively adjusted based on electron probe microanalysis results to promote the formation of a continuous network structure in the grain boundary region, effectively blocking the penetration and diffusion paths of sulfur-containing media. During the gas pressure sintering stage, the argon pressure and heating rate are dynamically adjusted in conjunction with the slope of the shrinkage curve to directionally control the β-phase grain arrangement and reduce grain boundary defect density. The raw material pre-inspection and hot isostatic pressing (HIP) strengthening processes are linked, and a porosity-graded treatment strategy balances densification efficiency and microstructural integrity, reducing corrosion-sensitive areas caused by grain boundary stress concentration. This multi-dimensional process control creates a synergistic optimization effect on grain boundary composition, structure, and density, ultimately enabling long-term stable service of silicon nitride seals in sulfur-containing environments. Attached Figure Description

[0019] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating a method for preparing high-performance silicon nitride ceramics, as provided in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The technical solutions provided by various embodiments of this invention will be described in detail below with reference to the accompanying drawings. To better understand the objectives of this invention, it will be described in further detail below.

[0022] Please see Figure 1 The present invention discloses a method for preparing high-performance silicon nitride ceramics, comprising:

[0023] Step 1: The silicon nitride powder is pretreated by wet ball milling. The particle size distribution of the powder is monitored in real time by a laser particle size analyzer. Based on the particle size data obtained by the laser particle size analyzer, the concentration of silane coupling agent and ultrasonic power in the surface modification process are adjusted. The silane coupling agent is coated on the powder surface to form a monolayer by ultrasonic dispersion.

[0024] Step 2: Mix the surface-modified powder with the composite sintering aid, which is composed of rare earth oxides and alumina in a certain proportion. The mixing speed and time are dynamically adjusted according to the torque data of the planetary mixer during the mixing process. The torque data is collected in real time by the built-in sensor of the planetary mixer to obtain a uniformly dispersed mixture.

[0025] Step 3: The mixture is subjected to gas pressure sintering. The displacement of the mold is monitored by a laser displacement sensor to generate a sintering shrinkage curve. Based on the curve, the argon pressure and heating rate are dynamically adjusted to form a silicon nitride ceramic matrix containing oriented β-phase grains.

[0026] Step 4: Analyze the distribution of rare earth elements in the grain boundary phase of the silicon nitride ceramic matrix using an electron probe microanalysis. If a local discontinuous region of the grain boundary phase is detected, repeat the mixing and sintering steps based on the increase in the proportion of rare earth oxides in the composite sintering aid in Step 2.

[0027] Step 5: Anneal the sintered ceramic matrix to eliminate residual stress, and then strengthen and seal the internal pores by hot isostatic pressing. The hot isostatic pressing parameters are dynamically adjusted according to the porosity test results of the matrix after sintering in Step 3.

[0028] In the wet ball milling pretreatment stage, silicon nitride powder is homogenized through wet ball milling. A laser particle size analyzer monitors the particle size distribution in real time. When the particle size data deviates from the target range, the system automatically adjusts the ball milling time to correct the particle size deviation. The corrected particle size data is then simultaneously input into the surface modification process. By establishing a linear relationship model between particle size and silane coupling agent concentration, the ultrasonic power and coupling agent concentration parameters are dynamically matched. The ultrasonic cavitation effect is used to promote the directional adsorption of coupling agent molecules on the powder surface, forming a uniform monomolecular coating layer. This particle size control step provides a basic guarantee of powder quality for subsequent mixing processes.

[0029] During the mixing process of surface-modified powder and composite sintering aids, the planetary mixer's built-in sensors collect torque data in real time, and the dispersion uniformity of the powder and aids is judged by analyzing the torque fluctuation amplitude. When the torque fluctuation exceeds a preset threshold, the system reduces the mixing speed and extends the mixing time, while optimizing the aid ratio based on the thermodynamic compatibility of rare earth oxides and alumina. The mixing uniformity is verified by the change in the full width at half maximum (FWHM) of the X-ray diffraction pattern, ensuring that there is no segregation of the aid phase distribution. The dispersion uniformity of the mixture directly affects the grain boundary liquid phase migration efficiency during the sintering stage.

[0030] During the gas pressure sintering stage, a laser displacement sensor monitors the mold displacement in real time, generating a sintering shrinkage curve to reflect the material densification process. In the low-temperature stage, nitrogen is introduced to suppress powder surface oxidation, and the heating rate is set based on the initial mold displacement. When the slope of the shrinkage curve exceeds a critical value, the process switches to a high-temperature stage and reduces the heating rate. Simultaneously, the argon pressure is dynamically increased according to the curve slope to promote the directional growth of β-phase grains along the pressure gradient. After sintering, the grain interlocking structure is observed using a metallographic microscope to verify the directional alignment effect.

[0031] In the grain boundary phase optimization stage, electron probe microanalysis is used to analyze the distribution of rare earth elements in the grain boundary region. When local element enrichment or depletion is detected, the deviation between the current additive ratio and the target value is calculated, and the rare earth oxide content is increased proportionally. The adjusted additive is then remixed and sintered with the powder to form a highly continuous grain boundary phase network. The iterative optimization process uses a second electron probe scan to confirm that the grain boundary phase continuity meets the standard, thus blocking the penetration path of corrosive media.

[0032] In the hot isostatic pressing (HIP) strengthening stage, the porosity of the sintered matrix was determined using the Archimedes' displacement method. Treatment parameters were selected based on the pore distribution characteristics: high-pressure argon gas was applied to high-porosity regions to promote plastic flow and fill the pores, while milder parameters were used in low-porosity regions to prevent excessive grain growth. Annealing eliminated thermal stress through gradient cooling. The HIP matrix was then subjected to ultrasonic testing to verify the pore-sealing effect, resulting in a dense, defect-free final product.

[0033] Specifically, in the high-performance silicon nitride ceramic preparation method of the present invention, during the wet ball milling pretreatment in step 1, a laser particle size analyzer is used to monitor the particle size distribution of the powder in real time. When the median particle size is found to exceed the range of 0.5-1.0 μm, it is corrected by extending or shortening the ball milling time. The corrected particle size data is used to generate a silane coupling agent concentration correction value through the particle size adjustment model in step 1, and the correction value is input into the surface modification process to adjust the silane coupling agent concentration simultaneously.

[0034] During the wet ball milling pretreatment stage, a laser particle size analyzer collects silicon nitride powder particle size distribution data in real time at a sampling frequency of once per second. When the system detects that the median particle size deviates from the range of 0.5-1.0 μm, the operating time of the ball mill is dynamically adjusted through a PID control algorithm: if the particle size is too large, the ball milling time is extended to 1.2 times the target value; if it is too small, it is shortened to 0.8 times. The corrected particle size data is input into a particle size-concentration mapping model based on multiple linear regression. This model is trained using a historical process database to obtain the silane coupling agent concentration correction coefficient, with the correction value adjusted in increments of 0.1 wt%. The adjustment command is synchronously transmitted to the ultrasonic dispersion equipment in the surface modification process via a PLC control system. The ultrasonic power is automatically matched according to the direct proportional relationship with the concentration correction value, so that the coupling agent molecules form a single-layer coating structure on the powder surface. The data linkage mechanism between particle size control and surface modification realizes closed-loop optimization of the powder pretreatment process, providing a raw material basis with uniform particle size and consistent surface activity for subsequent mixing processes.

[0035] Specifically, in the high-performance silicon nitride ceramic preparation method of the present invention, the composite sintering aid in step 2 is composed of rare earth oxides and alumina, wherein the proportion of rare earth oxides is 60-80 wt%. The proportion is dynamically optimized according to the torque data change trend of the planetary mixer in step 2. The preset threshold is set according to the powder dispersion uniformity requirements of the mixing process. If the torque fluctuation exceeds the preset threshold, the proportion of rare earth oxides is reduced to below 70 wt%, and the mixing uniformity of the adjusted aid is verified by X-ray diffraction analysis.

[0036] In the composite sintering aid mixing process, the ratio of rare earth oxides to alumina is set to 60-80 wt%, a range determined based on the synergistic effect of the rare earth silicate liquid phase formation temperature and the alumina grain boundary strengthening effect. A planetary mixer with a built-in torque sensor collects torque data twice per second during the mixing process. The powder dispersion uniformity is assessed by calculating the standard deviation of the torque fluctuation amplitude. When the standard deviation exceeds a preset threshold (pre-calibrated based on the functional relationship between powder specific surface area and aid density), the system triggers an aid ratio adjustment program: the proportion of rare earth oxides is gradually reduced in 5 wt% increments until the torque fluctuation amplitude returns to the threshold range. The adjusted mixture is then subjected to X-ray diffraction analysis. The uniformity of aid dispersion is judged by comparing the changes in the full width at half maximum (FWHM) of the diffraction peaks. If the FWHM shrinks to below 80% of the baseline value, the mixing uniformity is considered satisfactory. This dynamic optimization mechanism, through the linkage between torque data feedback and aid ratio adjustment, suppresses the risk of grain boundary phase segregation caused by aid agglomeration, providing a stable mixture foundation for subsequent sintering processes.

[0037] Specifically, in the high-performance silicon nitride ceramic preparation method of the present invention, step 3 of the gas pressure sintering includes a low-temperature stage and a high-temperature stage. In the low-temperature stage, the initial mold displacement data monitored by the laser displacement sensor in step 3 is used to raise the temperature at a rate of 5-10℃ / min and nitrogen is introduced. When the slope of the sintering shrinkage curve reaches the critical value set according to the densification requirements of the sintering process, the process switches to the high-temperature stage. After switching, argon is used and the heating rate is reduced to 2-5℃ / min. At the same time, the argon pressure increase is adjusted according to the slope of the real-time shrinkage curve. The adjusted argon pressure increase is verified by observing the compactness of the β-phase grain arrangement using a metallographic microscope.

[0038] In the gas pressure sintering process, during the low-temperature stage, the initial mold displacement data is collected in real time with a laser displacement sensor at an accuracy of 0.1 mm. Based on the displacement change trend, a heating rate of 5-10℃ / min is set, and nitrogen atmosphere is used to suppress the formation of an oxide layer on the powder surface. When the slope of the sintering shrinkage curve exceeds the critical value calculated based on the material theory densification rate model, the system switches to the high-temperature stage. Argon replaces nitrogen to enhance the fluidity of the liquid phase at grain boundaries, while the heating rate is reduced to 2-5℃ / min to match the grain growth kinetics requirements. The slope change of the real-time sintering shrinkage curve is converted into an argon pressure adjustment signal through a differential algorithm. The pressure increase is dynamically increased in a direct proportional relationship with the slope, promoting the directional alignment of β-phase grains along the pressure gradient. After the high-temperature stage, a cross-sectional sample of the ceramic matrix is ​​taken, and the aspect ratio of the β-phase grains and the angle between adjacent grain boundaries are observed using a metallographic microscope. If the aspect ratio is greater than 3:1 and the angle is less than 15°, the grain interlocking structure is considered to meet the standard. This segmented temperature and pressure control mechanism achieves coordinated control of the densification process and grain orientation through data-driven methods, providing a structural basis for grain boundary phase optimization.

[0039] Specifically, in the high-performance silicon nitride ceramic preparation method of the present invention, in step 4, the distribution of rare earth elements in the grain boundary phase is analyzed by electron probe microanalysis. If local discontinuities are detected, the proportion of rare earth oxides in the composite sintering aid in step 2 is increased. The increased proportion is calculated based on the initial proportion of the composite sintering aid in step 2. The adjusted composite sintering aid and surface-modified powder are mixed again in step 2 and sintered in step 3. The continuity of the grain boundary phase is verified again by electron probe microanalysis until the grain boundary phase is continuously distributed.

[0040] In the grain boundary phase optimization stage, an electron probe microanalysis (EPMA) analyzes the rare earth element distribution in the cross-section of the silicon nitride ceramic matrix using a surface scanning mode. When the standard deviation of element concentration exceeds 15% of the baseline value, it is identified as a local discontinuity region. Based on the initial ratio data of the composite sintering aid recorded in step 2, the system calculates the incremental ratio of rare earth oxides according to the area ratio of the defect region. For every 1% increase in defect area, the rare earth oxide content is increased by 0.5 wt%. The adjusted aid and surface-modified powder are re-introduced into the planetary mixer, and the mixing time is extended to 1.5 times the original cycle to ensure uniform dispersion. After the mixture is treated with the same gas pressure sintering parameters, a new cross-section sample is cut again. Secondary EPM analysis focuses on the original defect region. If the standard deviation of concentration drops to within 5% of the baseline value and the element distribution gradient is continuous, the grain boundary phase continuity is considered to be up to standard. If it is still not up to standard, the ratio adjustment-mixing sintering-detection verification process is iteratively executed until the grain boundary phase forms a fully closed network structure. This closed-loop control mechanism eliminates corrosion resistance defects caused by grain boundary segregation through data feedback and process parameter adjustment.

[0041] Specifically, in the high-performance silicon nitride ceramic preparation method of the present invention, during hot isostatic pressing (HIP) strengthening in step 5, argon gas is used as the pressure transmission medium. The processing parameters are selected based on the porosity test results of the sintered matrix: when the porosity is higher than 3%, it is treated at 1300℃ and 200MPa for 4 hours; when the porosity is lower than 1%, it is treated at 1200℃ and 150MPa for 2 hours. The porosity test results are determined by Archimedes' displacement method. The pore sealing effect of the treated ceramic matrix is ​​verified by ultrasonic flaw detection.

[0042] During the hot isostatic pressing (HIP) strengthening stage, when determining the porosity of the sintered matrix using the Archimedes' displacement method, the sample needs to be pretreated with ethanol to eliminate gas interference in open pores. The closed-pore rate is calculated by averaging three weighings. When the closed-pore rate is higher than 3%, the system automatically matches the parameter combination of 1300℃ and 200MPa, utilizing the plastic deformation characteristics of the material at high temperature to induce the argon gas pressure transmission medium to penetrate into the pores. Creep closure of submicron-level pores is achieved through four hours of pressure holding. When the closed-pore rate is lower than 1%, a mild parameter of 1200℃ and 150MPa is used for two hours to avoid excessive densification and stress concentration at grain boundaries. After treatment, the matrix is ​​wire-cut to prepare test samples, and C-scan imaging is performed using a 20MHz high-frequency ultrasonic probe. The pore sealing effect is evaluated by comparing the difference between the reflected wave amplitude attenuation rate and that of the reference sample. If the difference in attenuation rate is less than 5%, it is considered qualified. The process parameter selection mechanism and testing verification form a closed-loop control, and the high-low porosity zoning treatment strategy balances the densification efficiency and the microstructure integrity requirements.

[0043] Specifically, in the high-performance silicon nitride ceramic preparation method of the present invention, before the start of step 1, the specific surface area and oxygen content of each batch of silicon nitride powder are tested. The specific surface area is determined by gas adsorption method and the oxygen content is determined by inert gas melting method. If the difference in specific surface area exceeds ±5% or the oxygen content is greater than 1.5wt%, the ball milling time in step 1 or the proportion of composite sintering aid in step 2 is adjusted according to the deviation between the excess value and the benchmark value. The adjusted powder needs to be tested again until the result meets the standard.

[0044] In the raw material pre-inspection process, the specific surface area of ​​silicon nitride powder is determined by BET gas adsorption method. Before testing, the powder needs to be degassed in a vacuum environment at 300℃ for 2 hours to remove adsorbed impurities. The specific surface area benchmark value is pre-calibrated according to the powder synthesis process type. Oxygen content is detected using inert gas melting-infrared absorption method. After the powder sample is crushed and sieved to below 100 mesh, it is placed in a graphite crucible and pulse-heated to 2500℃ in a helium atmosphere to release oxygen. The oxygen content value is calculated by comparing it with the calibration curve of the standard sample. When the specific surface area difference exceeds ±5%, the system adjusts the ball milling time in step 1 according to the direction of the deviation: for a positive deviation, the ball milling time is shortened to 80%-90% of the benchmark value, and for a negative deviation, it is extended to 110%-120%. When the oxygen content exceeds the standard, the proportion of rare earth oxides in the composite sintering aid in step 2 is reduced by 0.5wt% for every 0.1wt% excess. The adjusted powder needs to be resampled and subjected to double sampling testing. If the retest results still fail to meet the standards, the raw material batch replacement procedure will be initiated. The mapping relationship between test data and process parameter adjustments is established through training on historical data from the process database, forming a predictive mechanism that links raw material quality control with process parameters, thus avoiding the risk of abnormal grain boundary phases caused by raw material fluctuations.

[0045] This invention solves the problem of grain boundary phase segregation in silicon nitride ceramic seals in sulfur-containing media through the synergistic effect of three technical means.

[0046] During the sintering aid mixing stage, the ratio of rare earth oxides to alumina in the composite aid is adjusted in real time based on torque data to suppress component segregation caused by aid agglomeration. After electron probe microanalysis to detect the rare earth element distribution in the grain boundary region, for local discontinuous areas, the increment is calculated according to the initial ratio, and mixing and sintering are repeated. Through iterative optimization, a continuous network grain boundary phase is formed. This structure effectively blocks the penetration path of sulfur-containing media and reduces the risk of grain boundary corrosion.

[0047] During the gas pressure sintering stage, a shrinkage curve is generated by monitoring the mold displacement using a laser displacement sensor. The argon pressure and heating rate are dynamically adjusted to promote the directional alignment of β-phase grains and reduce grain boundary defects. Subsequent hot isostatic pressing (HIP) strengthens the process by matching high-pressure parameters based on porosity detection results. The plastic flow characteristics of the argon gas pressure transmission medium are utilized to seal submicron-level pores and eliminate sulfide diffusion channels.

[0048] Wet ball milling pretreatment adjusts surface modification parameters based on particle size data feedback to ensure uniform powder dispersion. Raw material batch testing involves strict grading based on surface area and oxygen content; if standards are exceeded, ball milling time or additive ratios are adjusted accordingly. Real-time data acquisition, parameter adjustment, and effect verification across multiple processes form a closed-loop control system, systematically suppressing the impact of raw material fluctuations and process deviations on grain boundary phase stability, ultimately improving corrosion resistance.

Claims

1. A method for preparing high-performance silicon nitride ceramics, characterized in that, include: Step 1: The silicon nitride powder is pretreated by wet ball milling. The particle size distribution of the powder is monitored in real time by a laser particle size analyzer. Based on the particle size data obtained by the laser particle size analyzer, the concentration of silane coupling agent and ultrasonic power in the surface modification process are adjusted. The silane coupling agent is coated on the powder surface to form a monolayer by ultrasonic dispersion. Step 2: Mix the surface-modified powder with the composite sintering aid, which is composed of rare earth oxides and alumina in a certain proportion. The mixing speed and time are dynamically adjusted according to the torque data of the planetary mixer during the mixing process. The torque data is collected in real time by the built-in sensor of the planetary mixer to obtain a uniformly dispersed mixture. Step 3: The mixture is subjected to gas pressure sintering. The displacement of the mold is monitored by a laser displacement sensor to generate a sintering shrinkage curve. Based on the curve, the argon pressure and heating rate are dynamically adjusted to form a silicon nitride ceramic matrix containing oriented β-phase grains. Step 4: Analyze the distribution of rare earth elements in the grain boundary phase of the silicon nitride ceramic matrix using an electron probe microanalysis. If a local discontinuous region of the grain boundary phase is detected, repeat the mixing and sintering steps based on the increase in the proportion of rare earth oxides in the composite sintering aid in Step 2. Step 5: Anneal the sintered ceramic matrix to eliminate residual stress, and then strengthen and seal the internal pores by hot isostatic pressing. The hot isostatic pressing parameters are dynamically adjusted according to the porosity test results of the matrix after sintering in Step 3.

2. The method for preparing high-performance silicon nitride ceramics according to claim 1, characterized in that, During the wet ball milling pretreatment in step 1, a laser particle size analyzer is used to monitor the particle size distribution of the powder in real time. When the median particle size is found to be outside the range of 0.5-1.0 μm, the ball milling time is extended or shortened for correction. The corrected particle size data is used to generate a silane coupling agent concentration correction value through the particle size adjustment model in step 1, and this correction value is input into the surface modification process to adjust the silane coupling agent concentration simultaneously.

3. The method for preparing high-performance silicon nitride ceramics according to claim 1, characterized in that, In step 2, the composite sintering aid is composed of rare earth oxides and alumina. The proportion of rare earth oxides is 60-80 wt%. The proportion is dynamically optimized based on the torque data of the planetary mixer in step 2. The preset threshold is set according to the powder dispersion uniformity requirements of the mixing process. If the torque fluctuation exceeds the preset threshold, the proportion of rare earth oxides is reduced to below 70 wt%, and the uniformity of the adjusted additives is verified by X-ray diffraction analysis.

4. The method for preparing high-performance silicon nitride ceramics according to claim 1, characterized in that, Step 3, gas pressure sintering, includes a low-temperature stage and a high-temperature stage. In the low-temperature stage, the initial mold displacement data monitored by the laser displacement sensor in step 3 is used to raise the temperature at a rate of 5-10℃ / min and nitrogen is introduced. When the slope of the sintering shrinkage curve reaches the critical value set according to the densification requirements of the sintering process, the process switches to the high-temperature stage. After switching, argon is used and the heating rate is reduced to 2-5℃ / min. At the same time, the argon pressure increase is adjusted according to the slope of the real-time shrinkage curve. The adjusted argon pressure increase is verified by observing the compactness of the β-phase grain arrangement using a metallographic microscope.

5. The method for preparing high-performance silicon nitride ceramics according to claim 1, characterized in that, In step 4, the distribution of rare earth elements in the grain boundary phase is analyzed by electron probe microanalysis. If local discontinuities are detected, the proportion of rare earth oxides in the composite sintering aid in step 2 is increased. The increased proportion is calculated based on the initial proportion of the composite sintering aid in step 2. The adjusted composite sintering aid and surface-modified powder are mixed again in step 2 and sintered in step 3. The continuity of the grain boundary phase is verified again by electron probe microanalysis until the grain boundary phase is continuously distributed.

6. The method for preparing high-performance silicon nitride ceramics according to claim 1, characterized in that, In step 5, during hot isostatic pressing (HIP), argon gas is used as the pressure transmission medium. The processing parameters are selected based on the porosity test results of the sintered matrix: when the porosity is higher than 3%, it is treated at 1300℃ and 200MPa for 4 hours; when the porosity is lower than 1%, it is treated at 1200℃ and 150MPa for 2 hours. The porosity test results are determined by Archimedes' displacement method. The pore sealing effect of the treated ceramic matrix is ​​verified by ultrasonic flaw detection.

7. The method for preparing high-performance silicon nitride ceramics according to claim 1, characterized in that, Before starting step 1, the specific surface area and oxygen content of each batch of silicon nitride powder are tested. The specific surface area is determined by gas adsorption method and the oxygen content is determined by inert gas melting method. If the difference in specific surface area exceeds ±5% or the oxygen content is greater than 1.5wt%, the ball milling time in step 1 or the proportion of composite sintering aid in step 2 is adjusted according to the deviation between the excess value and the benchmark value. The adjusted powder needs to be tested again until the results meet the standards.

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