Densification production process of porous silicon carbide-boron carbide ceramic matrix composites

Abstract

This application relates to the technical field of ceramic material production, specifically to the densification production process of porous silicon carbide-boron carbide ceramic matrix composites. This process includes: weaving carbon fibers into two-dimensional carbon cloth, laminating and laying it flat and fixing it to obtain a carbon preform; depositing a pyrolytic carbon interface layer on the carbon preform, and continuing to deposit after heat treatment to obtain a porous C / SiC preform; dissolving sodium carboxymethylcellulose and heating it in a water bath, cooling it and adding boron carbide powder and stirring evenly, then performing wet ball milling to obtain a boron carbide slurry; repeatedly performing vacuum infiltration and pressure infiltration on the porous C / SiC preform with the boron carbide slurry to obtain a C / SiC-B4C preform; performing liquid silicon infiltration on the C / SiC-B4C preform, and adjusting the cooling rate of the gas circulation system during the cooling process to obtain a porous silicon carbide ceramic material. The purpose of this application is to improve the density of the porous silicon carbide ceramic material.

Description

Technical Field

[0001] The present application relates to the technical field of ceramic material production, and in particular to a densification production process for porous silicon carbide-boron carbide ceramic-based composite materials. Background Art

[0002] Silicon carbide ceramic materials have excellent properties such as high specific strength, high specific modulus, high temperature stability and oxidation resistance, and are widely used in the thermal protection systems of aerospace engines and aerospace vehicles and nuclear fusion reactors. Silicon carbide ceramic materials are composed of high-strength and high-modulus carbon fibers, pyrolytic carbon (PyC) interface phases with strong plastic deformation ability, and SiC matrix with excellent oxidation resistance. By adding a self-healing phase to the matrix, it can quickly react with the invading oxidizing medium in a high-temperature oxidizing environment to generate a liquid filling phase, which can further protect the fibers and interfaces from oxidation and extend the service life of the composite material.

[0003] Liquid Silicon Infiltration (LSI) is a fast and effective densification method that can prepare dense silicon carbide ceramic materials with a porosity of less than 5%, reducing the diffusion channels of oxidizing media in the service environment. When the silicon carbide ceramic material prepared by the liquid silicon infiltration method is cooled from a higher preparation temperature to room temperature, the difference in thermal expansion coefficients between the fiber and the matrix causes residual thermal stress between the components of the material. The release of thermal stress causes microcracks in the matrix perpendicular to the fiber axis, providing channels for the diffusion of oxidizing gases. The large temperature fluctuations when the porous silicon carbide ceramic material is cooled increases the temperature gradient inside it, thereby increasing the residual thermal stress between the components of the material, resulting in a large number of microcracks in the matrix, reducing its density, and limiting the improvement of the mechanical properties and oxidation resistance of the silicon carbide ceramic material. Summary of the invention

[0004] In view of the above, it is necessary to provide a densification production process for porous silicon carbide-boron carbide ceramic matrix composite materials to solve the above problems.

[0005] An embodiment of the present application provides a densification production process for a porous silicon carbide-boron carbide ceramic matrix composite material, the process comprising: step 1: weaving carbon fibers into a two-dimensional carbon cloth, laying and fixing the layers to obtain a carbon preform; step 2: depositing a pyrolytic carbon interface layer on the carbon preform, and continuing to deposit after heat treatment to obtain a porous C / SiC preform; step 3: dissolving sodium carboxymethyl cellulose and heating it in a water bath, adding boron carbide powder after cooling, stirring evenly, and then wet ball milling to obtain a B4C slurry; step 4: using the B4C slurry to The porous C / SiC preform is repeatedly subjected to vacuum infiltration and pressure infiltration to obtain a C / SiC-B4C preform; Step 5: The C / SiC-B4C preform is subjected to liquid silicon infiltration, and the cooling rate is adjusted during the cooling process to obtain a porous silicon carbide ceramic material; wherein the process of adjusting the cooling rate during the cooling process is specifically as follows: Step 501: Obtain the temperature data at each preset temperature measurement point at each moment, and preset the row mark value and column mark value of each temperature measurement point according to the position of each temperature measurement point ; Step 502: Perform straight line fitting on the temperature data within the preset time period at each temperature measurement point at each moment, and obtain the cooling rate stability of each temperature measurement point at each moment according to the difference between the temperature data before fitting and the temperature data after fitting, combined with the slope of the fitting straight line; Step 503: Obtain the relative distance between the two temperature measurement points according to the row mark value difference and the column mark value difference between the two temperature measurement points; Analyze the temperature data difference at each moment and the average level of the cooling rate stability between all the temperature measurement points in pairs, and obtain the temperature distribution uniformity at each moment in combination with the relative distance; Step 504: Obtain the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix; Calculate the cooling rate adjustment coefficient according to the numerical difference of the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix corresponding to the mean value of the temperature data of all the temperature measurement points at each moment, combined with the temperature distribution uniformity; According to the set cooling rate, combined with the cooling rate adjustment coefficient, obtain the cooling rate of the porous silicon carbide ceramic material at each moment.

[0006] Among them, the specific operation of depositing the pyrolytic carbon interface layer on the carbon preform is: the precursor gas source used is propylene, the deposition temperature is 890~960ºC, the deposition pressure is 5kPa, and the deposition time is 36h; the specific operation of the heat treatment is: heat treatment at 1800ºC in a high-temperature vacuum furnace for 2~3h, and argon protection is used during the heat treatment process.

[0007] The specific process of the continued deposition is as follows: trichloromethylsilane is used as a precursor gas source, argon is used as a diluent gas, H2 is used as a carrier gas, and trichloromethylsilane is introduced into the reaction chamber by bubbling, wherein the molar mixing ratio of H2 and MTS is 10:1, the deposition temperature is 1000ºC, the deposition pressure is 5~10kPa, and the deposition time is 320h.

[0008] The specific operation of the vacuum infiltration is as follows: suspending the porous C / SiC preform in a glass container containing B4C slurry, placing the glass container in a vacuum device, and evacuating the glass container until the air pressure is lower than -0.09 MPa. After maintaining the vacuum for 15 to 20 minutes, the preform is immersed in the B4C slurry for 30 to 45 minutes. The specific operation of the pressure infiltration is as follows: immersing the preform in the B4C slurry, placing it in a closed container and pressurizing it to 0.8 MPa for 30 to 45 minutes.

[0009] The specific operation of liquid silicon infiltration is as follows: embedding the C / SiC-B4C preform with silicon powder and then wrapping it with graphite paper to prevent the outflow of molten silicon at high temperature; then placing it in a vacuum siliconizing furnace, rapidly heating it to 1600°C under vacuum conditions, and keeping it warm for 20 to 30 minutes.

[0010] The step of obtaining the cooling rate stability at each temperature measurement point at each moment includes: recording a sequence of temperature data of a preset time period at each temperature measurement point at each moment as a temperature sequence, obtaining a temperature fitting straight line of the temperature sequence, and obtaining a difference between a slope of the temperature fitting straight line and a preset slope, which is recorded as a first difference;

[0011] The difference between the temperature data at each moment in the temperature sequence and the fitting value on the temperature fitting straight line is recorded as the deviation value; the number of elements in the temperature sequence at each moment is obtained, and the difference between the number of elements and the serial number value of each element in the temperature sequence is calculated, which is recorded as the second difference; the ratio of the deviation value of each element in the temperature sequence to the second difference is obtained, all the ratios in the temperature sequence are fused, and based on the fusion result and the first difference, the cooling rate stability at each temperature measurement point at each moment is obtained.

[0012] Among them, the relative distance between the two temperature measurement points is obtained by: recording the column mark value difference and the row mark value difference between any two temperature measurement points as the third difference and the fourth difference, respectively; obtaining the difference between the maximum column mark value of all temperature measurement points and the fourth difference, which is recorded as the fifth difference; obtaining the minimum value of the fourth difference and the fifth difference, and merging it with the third difference to obtain the relative distance between the any two temperature measurement points.

[0013] Among them, the method of obtaining the temperature distribution uniformity at each moment includes: for each moment, obtaining the mean value of the cooling rate stability of any two temperature measurement points, combining it with the negative correlation mapping of the relative distance and temperature value difference between the any two temperature measurement points, and obtaining the distribution difference of the any two temperature measurement points; and taking the mean value of the distribution difference of all the temperature measurement points combined in pairs as the temperature distribution uniformity at each moment.

[0014] The calculation of the cooling rate adjustment coefficient is specifically as follows: calculating the difference between the mean value of the temperature data of all temperature measurement points at each moment and the room temperature at each moment, recorded as the sixth difference; obtaining the absolute value of the difference between the thermal expansion values ​​corresponding to the mean value of the temperature data at each moment on the thermal expansion curve of the carbon fiber and the SiC-SiBC matrix, recorded as the seventh difference; obtaining the cooling rate adjustment coefficient at each moment based on the sixth difference, the seventh difference and the uniformity of the temperature distribution; wherein the cooling rate adjustment coefficient is negatively correlated with the sixth difference and the seventh difference, and is positively correlated with the uniformity of the temperature distribution.

[0015] The formula for the cooling rate of the porous silicon carbide ceramic material at each moment is:

[0016] ;

[0017] in, , Respectively represent the preset minimum cooling rate and the preset maximum cooling rate of the silicon carbide ceramic material;

[0018] c represents the cooling rate adjustment coefficient at each moment; Indicates the cooling rate at each moment.

[0019] This application has at least the following beneficial effects:

[0020] The embodiment of the present application uses a liquid silicon infiltration method to prepare porous silicon carbide ceramic materials, generates a liquid filling phase in a high-temperature oxidizing environment, and protects the fibers and interfaces from oxidation. The temperature data is analyzed to obtain the stability of the cooling rate, which has the beneficial effect of measuring the stability of the cooling rate of the crucible temperature measurement point at each moment; the temperature distribution uniformity is obtained, which has the beneficial effect of reflecting the distribution of temperatures at different positions of the porous silicon carbide ceramic material; the cooling rate adjustment coefficient is calculated, and the cooling rate is adjusted, which has the beneficial effect of reducing the probability of a large temperature gradient inside the porous silicon carbide ceramic material, avoiding the expansion of the residual thermal stress between the matrix and the fiber inside the material, reducing the cracks caused by thermal expansion mismatch between the matrix and the fiber during the cooling process, and improving the material density, thereby improving the mechanical properties and oxidation resistance of the silicon carbide ceramic material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a densification production process for a porous silicon carbide-boron carbide ceramic matrix composite material provided in the present application;

[0022] Figure 2 A specific flow chart for adjusting the cooling rate during the cooling process provided in this application. DETAILED DESCRIPTION

[0023] In the description of the embodiments of the present application, words such as "exemplary", "or", "for example" and the like are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "or", "for example" and the like is intended to present related concepts in a concrete manner.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0025] It should also be noted that the terms "first" and "second" in this application and its drawings are used to distinguish similar objects, rather than to describe a specific order or sequence. The method disclosed in the embodiments of the present application or the method shown in the flow chart includes one or more steps for implementing the method. Without departing from the scope of protection of this application, the execution order of multiple steps can be interchanged with each other, and some steps can also be deleted.

[0026] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0027] Example 1

[0028] Example 1 of the present application proposes a densification production process for porous silicon carbide-boron carbide ceramic matrix composite materials, which is applied in the technical field of ceramic material production. Figure 1 The process comprises: step 1, weaving carbon fibers into two-dimensional carbon cloth, stacking and fixing the layers to obtain a carbon preform.

[0029] The T-300 carbon fiber with a yarn count of 1k is woven into a two-dimensional carbon cloth with a 0° / 90° distribution direction by a plain weave method, and then cut into a certain size. The size in this embodiment is The number of carbon cloth layers is selected according to the thickness of the carbon preform, and the carbon cloth is laminated on the graphite mold. Fibers are inserted in a direction perpendicular to the carbon cloth at a certain density to make the carbon cloth firm. In this embodiment, the density is Finally, the four sides of the mold are tightened and fixed with graphite bolts to obtain a carbon preform.

[0030] Step 2, depositing a pyrolytic carbon interface layer on the carbon preform, and continuing to deposit after heat treatment at high temperature to obtain a porous C / SiC preform.

[0031] The PyC interface layer was deposited on the two-dimensional carbon cloth of the carbon preform using a chemical vapor deposition (CVD) process. The specific deposition process parameters are as follows: propylene (C3H6) was selected as the precursor gas source, the deposition temperature was 890°C, the deposition pressure was maintained at 5kPa, and the deposition process lasted for 36 hours.

[0032] Next, the material was heat treated in a high-temperature vacuum furnace at 1800°C for 2 hours. During the heat treatment, argon gas was used for protective atmosphere control, and the purity of argon gas was 99.999%.

[0033] Finally, the SiC matrix is ​​deposited on the carbon preform with the PyC interface deposited by the CVD process to obtain a porous C / SiC preform. The advantage is that the SiC matrix deposited by the CVD process can protect the fiber from being corroded by the molten silicon in the subsequent process, thereby improving the in-situ strength of the carbon fiber. Deposition process parameters:

[0034] Trichloromethylsilane (CH3SiCl3, MTS for short) was used as the precursor gas source, argon as the diluent gas, and hydrogen (H2) as the carrier gas, and MTS was introduced into the reaction chamber by bubbling. In this process, the molar ratio of H2 to MTS was 10:1.

[0035] The temperature of the deposition process was set to 1000°C, the deposition pressure to 5 kPa, and the deposition time to 320 h.

[0036] Step 3, dissolving sodium carboxymethyl cellulose and heating in a water bath, adding boron carbide powder after cooling, stirring evenly, and then wet ball milling to obtain B4C slurry.

[0037] First, dissolve sodium carboxymethyl cellulose (CMC-Na) in distilled water and heat it in a water bath at 80°C until the CMC-Na is completely dissolved and forms a uniform solution;

[0038] After the solution is cooled, boron carbide (B4C) powder with a particle size of 1.5 μm and a purity of 91% is added and stirred evenly. The impurities mainly include free carbon and boron oxide (B2O3). Among them, the mass ratio of CMC-Na to distilled water is 1:100, and the mass ratio of CMC-Na solution to B4C powder is 2:1.

[0039] Next, the prepared B4C slurry was transferred to a ball mill, corundum balls with a particle size ranging from 10 mm to 20 mm were added, and wet ball milling was performed in a drum ball mill for 24 h to prepare a uniform B4C slurry, wherein the mass ratio of B4C slurry to corundum balls was 4:3.

[0040] Step 4: Repeat vacuum infiltration and pressure infiltration of the porous C / SiC preform using B4C slurry to obtain a C / SiC-B4C preform.

[0041] Slurry Infiltration (SI) includes two steps: vacuum infiltration and pressure infiltration:

[0042] The porous C / SiC preform was suspended in a glass container containing B4C slurry, and the container was placed in a vacuum device. The pressure in the container was reduced to below -0.09 MPa by vacuuming, and the vacuum state was maintained for 15 minutes. Then, the preform was completely immersed in the B4C slurry and kept immersed for 30 minutes;

[0043] The glass container and the preform are taken out together, the preform is kept immersed, and placed in a sealed container and pressurized to 0.8 MPa for 30 minutes.

[0044] Finally, the preform was taken out from the B4C slurry, placed in an oven for drying for 2 hours, and then taken out. After removing the excess B4C slurry on the surface, the weight change of the preform was weighed and recorded.

[0045] Repeat vacuum infiltration and pressure infiltration to introduce as many B4C particles as possible into the preform until the preform no longer increases in weight, thereby obtaining a C / SiC-B4C preform.

[0046] Step 5, infiltrating the C / SiC-B4C preform with liquid silicon, adjusting the cooling rate during the cooling process, and obtaining a porous silicon carbide ceramic material.

[0047] The C / SiC-B4C preform is placed in the crucible of a vacuum siliconizing furnace for liquid silicon infiltration, i.e. LSI, specifically:

[0048] The C / SiC-B4C preform is embedded with silicon powder and then wrapped with graphite paper to prevent the outflow of molten silicon at high temperature. The particle size of the silicon powder is 45μm and the purity is 99.3%;

[0049] Then it is placed in a vacuum siliconizing furnace, and the temperature is rapidly raised to 1600°C under vacuum conditions and kept at this temperature for 25, so that the molten silicon and the B4C slurry react fully and the matrix is ​​rapidly densified. Finally, during the cooling process, the cooling rate of the gas circulation system is adjusted to room temperature to obtain a porous silicon carbide ceramic material, namely, a modified C / SiC-SiBC.

[0050] The specific steps for adjusting the cooling rate during the cooling process are as follows:

[0051] Step 501, obtaining the temperature data at each preset temperature measurement point at each moment, and presetting the row mark value and column mark value of each temperature measurement point according to the position of each temperature measurement point.

[0052] At the bottom of the crucible, L temperature measurement points are evenly arranged along the circumferential direction of the bottom of the crucible, one of which is selected as the initial measurement point, and its row mark value is numbered as 1. The row mark values ​​of the remaining measurement points are numbered in clockwise order in the top view direction, and the column mark values ​​of the L measurement points at the bottom are all set to 1. In this embodiment, the value of L is 5.

[0053] Along each bottom temperature measurement point, L-1 temperature measurement points are evenly set along the crucible axis, and their column marking values ​​are numbered from small to large according to their height. In this embodiment, the row marking value and column marking value numbering both start from 1 and increase by 1 in sequence according to their respective numbering order;

[0054] So far, a total of M temperature measurement points are obtained, and the value of M in this embodiment is 25.

[0055] The room temperature data is obtained by installing a temperature sensor outside the vacuum siliconizing furnace. The temperature data of each measuring point is obtained by installing M thermocouple temperature sensors at M temperature measuring points on the crucible, wherein the temperature data acquisition frequency of the thermocouple temperature sensor is once per second.

[0056] The temperature data at each moment obtained from each temperature measurement point is taken as the end data, and the temperature data of N-1 moments are taken forward to form a temperature sequence of each temperature measurement point at each moment. In this embodiment, N is taken as 60, and the time period composed of each moment and the previous N-1 moments is the preset time period.

[0057] Step 502: Perform straight line fitting on the temperature data of each temperature measurement point within a preset time period at each moment, and obtain the cooling rate stability of each temperature measurement point at each moment based on the difference between the temperature data before fitting and the temperature data after fitting and the slope of the fitting straight line.

[0058] During the cooling process of porous silicon carbide ceramic materials, the difference in thermal expansion coefficients between the fiber and the matrix leads to residual thermal stress between the components of the material, and the large temperature fluctuation during cooling increases the temperature gradient inside the material, thereby increasing the residual thermal stress between the components of the material, resulting in a large number of microcracks in the matrix, which reduces its density and mechanical properties on the one hand, and provides a channel for the diffusion of oxidizing gases on the other hand, reducing the material's antioxidant properties. By adjusting the cooling rate of the gas circulation system, the temperature of the porous silicon carbide ceramic material can be slowly reduced, thereby achieving the purpose of reducing the temperature gradient inside the material and reducing the generation of microcracks.

[0059] The faster cooling rate of porous silicon carbide ceramic materials will produce uneven temperature distribution inside the material, thereby aggravating the thermal expansion mismatch between different components, increasing the residual thermal stress inside the matrix, and further increasing the risk of matrix cracks.

[0060] A straight line is fitted to the temperature data within a preset time period at each temperature measurement point at each moment, and the cooling rate stability at each temperature measurement point at each moment is obtained according to the difference between the temperature data before fitting and the temperature data after fitting, combined with the slope of the fitting line: the temperature sequence of each temperature measurement point at each moment is used as input, and the temperature fitting line of each temperature measurement point at each moment is obtained by the least squares method, and the difference between the preset slope and the slope of the temperature fitting line is obtained, which is recorded as the first difference; the difference between the temperature data at each moment in the temperature sequence and the fitting value on the temperature fitting line is recorded as the deviation value; the number of elements in the temperature sequence at each moment is obtained, and the difference between the number of elements and the serial number value of each element in the temperature sequence is calculated, which is recorded as the second difference; the ratio of the deviation value of each element in the temperature sequence to the second difference is obtained, all the ratios in the temperature sequence are fused, and based on the fusion result and the first difference, the cooling rate stability at each temperature measurement point at each moment is obtained.

[0061] In this embodiment, the first difference is specifically the ratio between the slope of the temperature fitting line and the preset slope, wherein the preset slope is -0.017, which represents the slope of the temperature fitting line corresponding to the minimum cooling rate, and the minimum cooling rate of the porous silicon carbide ceramic material is set to 1ºC / min, and the maximum cooling rate is 5ºC / min;

[0062] The deviation value is specifically the sum of the squares of the difference between the two values; the second difference is measured by the difference;

[0063] The fusion of multiple variables is in the form of accumulation;

[0064] The fusion result of all the ratios in the temperature series is recorded as A;

[0065] The first difference is recorded as B, and the formula of the cooling rate stability is: ;

[0066] in, represents an exponential function with a natural constant as the base, and ln() represents a logarithmic function with a natural constant as the base.

[0067] It should be understood that the stability of the cooling rate reflects the stability of the cooling rate of the crucible temperature measurement point at each moment. The minimum cooling rate is used as the evaluation benchmark for the material cooling rate to avoid too low a production rate on the one hand, and to reduce the generation of a large temperature gradient inside the material on the other hand. During the cooling process of the porous silicon carbide ceramic material, the slope of the temperature fitting line is negative. When the slope of the temperature fitting line is greater than the preset slope, the smaller the first difference, the slower the cooling rate, and the smaller the impact on the stability of the cooling rate; when the slope of the temperature fitting line is less than the preset slope, the larger the first difference, the faster the cooling rate, and the greater the impact on the stability of the cooling rate;

[0068] In addition, the greater the fitting deviation of the temperature data, the greater the temperature fluctuation of the temperature measurement point. At the same time, the larger the temperature data serial number, the closer it is to each moment. When the difference with the fitting straight line is the same, the larger the temperature data serial number, the greater the instability of the corresponding moment, the greater the impact on the adjustment of the cooling rate at each moment, and the greater the stability of the obtained cooling rate.

[0069] Step 503: Obtain the relative distance between the two temperature measurement points according to the row mark value difference and the column mark value difference between the two temperature measurement points; analyze the temperature data difference at each moment and the average level of the cooling rate stability between all the temperature measurement points in pairs, and obtain the temperature distribution uniformity at each moment in combination with the relative distance.

[0070] The temperature data distribution at different temperature measurement points reflects the temperature distribution at different positions of the porous silicon carbide ceramic material. When the temperature distribution at different positions of the crucible is more uniform, the temperature gradient generated by the material is smaller, and the residual thermal stress between the material fiber and the matrix is ​​smaller.

[0071] Considering that the temperature distribution of temperature measurement points at different positions reflects the temperature gradient during the cooling process of porous silicon carbide ceramic materials, the relative position relationship is obtained according to the row mark value and column mark value of the measurement point. Since the measurement points are evenly distributed in the circumferential direction of the crucible, the minimum value of the row mark value interval between two measurement points and the difference between the number of circumferential measurement points and the row mark value interval reflects the relative distance between the two in the circumferential direction of the crucible.

[0072] Based on this, firstly, the relative distance between the two temperature measurement points is obtained according to the row mark value difference and column mark value difference between the two temperature measurement points:

[0073] The difference in column mark values ​​and row mark values ​​between any two temperature measurement points are recorded as the third difference and the fourth difference, respectively;

[0074] Obtain the difference between the maximum column mark value of all temperature measurement points and the fourth difference, and record it as the fifth difference;

[0075] The minimum value of the fourth difference and the fifth difference is obtained, and is merged with the third difference to obtain the relative distance between the arbitrary two temperature measurement points.

[0076] In this embodiment, the column mark value difference and the row mark value difference are measured by the absolute value of the difference;

[0077] The fifth difference is specifically the difference between the maximum column mark value of all temperature measurement points and the fourth difference;

[0078] Multiple differences are fused in an additive manner.

[0079] Furthermore, the temperature data differences and the cooling rate stability between all the temperature measurement points in pairs at each moment are analyzed, and the temperature distribution uniformity at each moment is obtained by combining the relative distance:

[0080] At each moment, the mean value of the cooling rate stability between any two temperature measurement points is obtained, and combined with the negative correlation mapping of the relative distance and the temperature value difference between the any two temperature measurement points, the distribution difference of the any two temperature measurement points is obtained;

[0081] The mean of the distribution differences of all pairwise combinations of temperature measurement points is taken as the temperature distribution uniformity at each moment.

[0082] In this embodiment, for two temperature measurement points, the temperature value difference is measured by the square value of the temperature value difference, which is recorded as C, the relative distance between the temperature measurement points is recorded as D, and the mean value of the cooling rate stability is recorded as E. The formula form of the distribution difference is: ; In order to prevent the formula from being meaningless when the denominator is 0, a preset value greater than zero is added to the denominator, which is 1.

[0083] It should be understood that the cooling rate stability reflects the stability of the cooling rate at the current crucible temperature measurement point. The greater the cooling rate stability, the smaller the probability of temperature gradient inside the porous silicon carbide ceramic material, and the greater the uniformity of the calculated temperature distribution. For the difference in temperature data at the same time, the smaller the relative distance between the two temperature measurement points, the greater the temperature gradient inside the material, the greater the influence of residual thermal stress, and the more uneven the temperature distribution.

[0084] Step 504: obtaining thermal expansion curves of the carbon fiber and the SiC-SiBC matrix; calculating a cooling rate adjustment coefficient based on the numerical difference of the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix corresponding to the mean values ​​of the temperature data of all temperature measurement points at each moment, combined with the temperature distribution uniformity; obtaining the cooling rate of the porous silicon carbide ceramic material at each moment according to the set cooling rate, combined with the cooling rate adjustment coefficient.

[0085] When the porous silicon carbide ceramic material is cooled from the preparation temperature to room temperature, the difference in thermal expansion coefficients between the carbon fiber and the matrix causes residual thermal stress between the components of the material. The greater the difference in thermal expansion coefficients, the greater the residual thermal stress between the carbon fiber and the matrix. Considering that the thermal expansion coefficients of the carbon fiber and the SiC-SiBC matrix vary with temperature, that is, the residual thermal stresses of the two are different at different temperatures. When the residual thermal stress is large, a smaller cooling rate is set to reduce the temperature gradient inside the material to avoid expanding the influence of the residual thermal stress between different components of the material.

[0086] Based on this, the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix are obtained; the cooling rate adjustment coefficient is calculated according to the numerical difference of the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix corresponding to the mean value of the temperature data of all temperature measurement points at each moment, combined with the uniformity of the temperature distribution:

[0087] Calculate the difference between the mean value of the temperature data of all temperature measurement points at each moment and the room temperature at each moment, which is recorded as the sixth difference; obtain the absolute value of the difference between the thermal expansion values ​​corresponding to the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix of the mean value of the temperature data at each moment, which is recorded as the seventh difference;

[0088] Based on the sixth difference, the seventh difference and the temperature distribution uniformity, the cooling rate adjustment coefficient at each moment is obtained; wherein the cooling rate adjustment coefficient is negatively correlated with the sixth difference and the seventh difference, and is positively correlated with the temperature distribution uniformity.

[0089] In this embodiment, the temperature distribution uniformity is recorded as F, the sixth difference is recorded as G, and the seventh difference is recorded as H. The formula of the cooling rate adjustment coefficient is: ;

[0090] It should be noted that in order to prevent the denominator from being 0, a preset value greater than 0 needs to be added to the denominator, and the value is 1.

[0091] Furthermore, according to the set cooling rate, combined with the cooling rate adjustment coefficient, the cooling rate of the porous silicon carbide ceramic material at each moment is obtained: ;in, , They represent the preset minimum cooling rate and the preset maximum cooling rate of the silicon carbide ceramic material, respectively, and their values ​​are 1ºC / min and 5ºC / min; c represents the cooling rate adjustment coefficient at each moment; Indicates the cooling rate at each moment, so as to achieve the production rate of porous silicon carbide ceramic material while reducing cracks caused by residual thermal stress between fiber and matrix.

[0092] It should be understood that the greater the difference from room temperature, the greater the probability that the porous silicon carbide ceramic material is in a liquid state, and the greater the risk of a large temperature gradient inside it, so a lower cooling rate is set to ensure uniform distribution of temperature at different positions of the material during the cooling process. At the same time, the smaller the uniformity of the temperature distribution, the greater the temperature gradient in the material, and a smaller cooling rate is set. In addition, in order to avoid expanding the influence of residual thermal stress between different components of the material, the greater the difference in thermal expansion coefficients between the porous silicon carbide ceramic material fiber and the matrix at the current temperature, the smaller the cooling rate is set, which reduces the residual thermal stress between the fiber and the matrix, thereby reducing the risk of matrix cracks.

[0093] The gas circulation system of the vacuum siliconizing furnace adjusts the gas flow and pressure to achieve the cooling process of the porous silicon carbide ceramic material at the set cooling rate, wherein the process atmosphere of the cooling process adopts argon gas with a purity of 99.999%. The cooling rate of the porous silicon carbide ceramic material currently obtained is input into the gas circulation system, and the gas flow and pressure are adjusted to slowly cool the porous silicon carbide ceramic material to room temperature. When the average value of the temperature data obtained at M measurement points is equal to the room temperature data, the gas circulation system is closed to complete the densification production of the porous silicon carbide ceramic material.

[0094] In the cooling process, the cooling rate is adjusted as follows: Figure 2 shown.

[0095] Example 2

[0096] Example 2 of the present application proposes a densification production process for porous silicon carbide-boron carbide ceramic matrix composite materials, which is applied in the technical field of ceramic material production. Figure 1 The process comprises: step 1, obtaining a carbon preform by the same method as in Example 1; step 2, obtaining a porous C / SiC preform by the same process as in Example 1; wherein the deposition temperature in the CVD process is 960°C. Heat treatment is performed for 3 hours; and the deposition pressure when depositing the SiC substrate is 7 kPa.

[0097] Step 3, obtaining B4C slurry by the same method as in Example 1; wherein the wet ball milling time is 30 hours.

[0098] Step 4, obtaining a C / SiC-B4C preform by the same method as in Example 1; wherein, during vacuum infiltration, the preform is completely immersed in the B4C slurry and kept immersed for 45 minutes; during pressure infiltration, the preform is placed in a sealed container and pressurized to 0.8 MPa for 45 minutes; the preform is taken out of the B4C slurry, placed in an oven for drying for 3 hours, and then taken out.

[0099] Step 5, infiltrating the C / SiC-B4C preform with liquid silicon using the same method as in Example 1, adjusting the cooling rate during the cooling process to obtain a porous silicon carbide ceramic material, wherein the insulation time is 20 minutes.

[0100] Example 3

[0101] Example 3 of the present application proposes a densification production process for porous silicon carbide-boron carbide ceramic matrix composite materials, which is applied in the technical field of ceramic material production. Figure 1 The process comprises: step 1, obtaining a carbon preform by the same method as in Example 1; step 2, obtaining a porous C / SiC preform by the same process as in Example 1; wherein the deposition temperature in the CVD process is 900°C. The heat treatment is performed for 2.5 hours; and the deposition pressure when depositing the SiC substrate is 10 kPa.

[0102] Step 3, obtaining B4C slurry by the same method as in Example 1;

[0103] The wet ball milling time is 25 hours.

[0104] Step 4, obtaining a C / SiC-B4C preform by the same method as in Example 1;

[0105] Among them, during vacuum infiltration, the vacuum state is maintained for 30 minutes;

[0106] After the preform is taken out from the B4C slurry, it is placed in an oven for drying for 3 hours and then taken out.

[0107] Step 5: Infiltrate the C / SiC-B4C preform with liquid silicon using the same method as in Example 1, and adjust the cooling rate during the cooling process to obtain a porous silicon carbide ceramic material.

[0108] Finally, the statistical results of the density and porosity of the porous silicon carbide ceramic material with the cooling rate adjusted at each moment (Example) and without adjusting the cooling rate (Comparative Example) are shown in Table 1:

[0109] Table 1: Test results of examples and comparative examples

[0110] <![CDATA[Density (g / cm 3 )]]> Porosity(%) Example 1 2.68 4.0 Example 2 2.70 3.7 Example 3 2.73 3.5 Comparative Example 1 2.25 11.6 Comparative Example 2 2.53 8.2 Comparative Example 3 2.39 10.3

[0111] Among them, all parameters except the cooling rate in Comparative Examples 1, 2, and 3 are consistent with those in Example 1;

[0112] Comparative Example 1 is natural cooling, that is, the gas circulation system is closed; Comparative Examples 2 and 3 are fixed cooling rates, wherein the cooling rate of Comparative Example 2 is 3ºC / min, and the cooling rate of Comparative Example 3 is 5ºC / min.

[0113] The flowchart and block diagram in the accompanying drawings show the possible architecture, function and operation of the system, method and computer program product according to the embodiment of the present application. In this regard, each box in the flowchart or block diagram can represent a module, a program segment or a part of the code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. In some alternative implementations, the function marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two continuous boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, which can depend on the functions involved. In the description corresponding to the flowchart and the block diagram in the accompanying drawings, the operations or steps corresponding to different boxes can also occur in a different order from the order disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two continuous operations or steps can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, which can depend on the functions involved. Each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented by a dedicated hardware-based system that performs the specified functions or actions, or may be implemented by a combination of dedicated hardware and computer instructions.

[0114] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A densification production process for porous silicon carbide-boron carbide ceramic matrix composite material, characterized in that: The process includes: Infiltrating a C / SiC-B4C preform with liquid silicon, the preform including carbon fibers, adjusting the cooling rate during cooling to obtain a porous silicon carbide-boron carbide ceramic matrix composite material; The process of adjusting the cooling rate during the cooling process is specifically as follows: Step 01: Obtain the temperature data at each preset temperature measurement point at each moment, and preset the row mark value and column mark value of each temperature measurement point according to the position of each temperature measurement point; Step 02: Record the sequence composed of the temperature data of the preset time period at each temperature measurement point at each moment as the temperature sequence, obtain the temperature fitting straight line of the temperature sequence, obtain the difference between the slope of the temperature fitting straight line and the preset slope, and record it as the first difference B; record the difference between the temperature data at each moment in the temperature sequence and the fitting value on its temperature fitting straight line as the deviation value; obtain the number of elements in the temperature sequence at each moment, calculate the difference between the number of elements and the serial number value of each element in the temperature sequence, and record it as the second difference; obtain the ratio of the deviation value of each element in the temperature sequence to the second difference, merge all the ratios in the temperature sequence, and obtain the cooling rate stability at each temperature measurement point at each moment based on the fusion result A and the first difference B. The formula form of the cooling rate stability is: ; Step 03: The column mark value difference and row mark value difference between any two temperature measurement points are recorded as the third difference and the fourth difference respectively; the difference between the maximum column mark value of all temperature measurement points and the fourth difference is obtained, which is recorded as the fifth difference; the minimum value of the fourth difference and the fifth difference is obtained, and the difference is merged with the third difference to obtain the relative distance between any two temperature measurement points; at each moment, for two temperature measurement points, the temperature value difference is measured by the square value of the temperature value difference, which is recorded as C, the relative distance between the temperature measurement points is recorded as D, the mean value of the cooling rate stability is recorded as E, and the distribution difference is calculated. The formula of the distribution difference is: ; The mean of the distribution differences of all the temperature measurement points in pairs is taken as the temperature distribution uniformity at each moment; Step 04: Obtain the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix; calculate the difference between the mean value of the temperature data of all temperature measurement points at each moment and the room temperature at each moment, recorded as the sixth difference G; obtain the absolute value of the difference between the thermal expansion values ​​corresponding to the mean value of the temperature data at each moment on the thermal expansion curves of the carbon fiber and the SiC-SiBC matrix, recorded as the seventh difference H; record the temperature distribution uniformity as F, calculate the cooling rate adjustment coefficient, and the formula form of the cooling rate adjustment coefficient is ; Calculate the cooling rate of the porous silicon carbide ceramic material at each moment, the calculation formula is: ;in, , They respectively represent the preset minimum cooling rate and the preset maximum cooling rate of the silicon carbide ceramic material; c represents the cooling rate adjustment coefficient at each moment; Indicates the cooling rate at each moment.

2. The densification production process of the porous silicon carbide-boron carbide ceramic matrix composite material according to claim 1, characterized in that: The method for obtaining the C / SiC-B4C preform comprises the following steps: Step 1: Weave carbon fibers into two-dimensional carbon cloth, lay them flat and fix them to obtain a carbon preform; Step 2: depositing a pyrolytic carbon interface layer on the carbon preform, and continuing deposition after heat treatment to obtain a porous C / SiC preform; Step 3: Dissolve sodium carboxymethyl cellulose and heat in a water bath, add boron carbide powder after cooling, stir evenly, and then wet-ball mill to obtain B4C slurry; Step 4: Repeat vacuum infiltration and pressure infiltration of the porous C / SiC preform using B4C slurry to obtain a C / SiC-B4C preform.

3. The densification production process of the porous silicon carbide-boron carbide ceramic matrix composite material according to claim 2, characterized in that: The specific operation of depositing the pyrolytic carbon interface layer on the carbon preform is: the precursor gas source used is propylene, the deposition temperature is 890~960ºC, the deposition pressure is 5kPa, and the deposition time is 36h; the specific operation of the heat treatment is: heat treatment at 1800ºC in a high-temperature vacuum furnace for 2~3h, and argon protection is used during the heat treatment process.

4. The densification production process of the porous silicon carbide-boron carbide ceramic matrix composite material according to claim 2, characterized in that: The specific process of the continued deposition is: using trichloromethylsilane as a precursor gas source, argon as a diluent gas, and H2 as a carrier gas, trichloromethylsilane is introduced into the reaction chamber by bubbling, wherein the molar mixing ratio of H2 and MTS is 10:1, the deposition temperature is 1000ºC, the deposition pressure is 5~10kPa, and the deposition time is 320h.

5. The densification production process of the porous silicon carbide-boron carbide ceramic matrix composite material according to claim 2, characterized in that: The specific operation of the vacuum infiltration is: suspending the porous C / SiC preform in a glass container containing B4C slurry, placing the glass container in a vacuum device, and evacuating the glass container until the air pressure is lower than -0.09MPa, maintaining the vacuum for 15 to 20 minutes, and then immersing the preform in the B4C slurry for 30 to 45 minutes; the specific operation of the pressure infiltration is: immersing the preform in the B4C slurry, placing it in a closed container and pressurizing it to 0.8MPa for 30 to 45 minutes.

6. The densification production process of the porous silicon carbide-boron carbide ceramic matrix composite material according to claim 2, characterized in that: The specific operation of liquid silicon infiltration is: embedding the C / SiC-B4C preform with silicon powder and then wrapping it with graphite paper to prevent the molten silicon from flowing out at high temperature; then putting it into a vacuum siliconizing furnace, rapidly heating it to 1600°C under vacuum conditions, and keeping it warm for 20 to 30 minutes.

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