SiC / SiC composite material as well as preparation method and application thereof

Abstract

The invention discloses a SiC / SiC composite material as well as a preparation method and application thereof, and belongs to the technical field of ceramic matrix composite materials. Aiming at the problems of long period and SiC fiber damage in the densification process of the existing SiC / SiC composite material, the invention provides the preparation method of the SiC / SiC composite material, two times of PIP operation and one time of PI-OP operation are used as a densification period, Hb-PBSZ is used as a ceramic precursor, and a cracking product of the Hb-PBSZ is SiBCN ceramic which can be used as self-healing phase SiBCN ceramic. According to the method, an ideal densification effect can be rapidly achieved only through two densification cycles, meanwhile, a tightly combined coating composed of a self-healing phase and CVI SiC alternately can be formed on the surface of the composite material while densification is conducted, and the finally prepared SiC / SiC composite material has excellent room-temperature bending strength and is suitable for being applied to the field of composite materials. And the service capability of the composite material in a high-temperature oxidizing atmosphere environment is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic-based composite materials, and in particular to a SiC / SiC composite material and a preparation method and application thereof. Background Art

[0002] Continuous Silicon Carbide Fiber Reinforced Silicon Carbide Ceramic Matrix Composites (SiC / SiC) are a typical ceramic-based composite material consisting of continuous SiC fibers, a SiC matrix, and an interface. They offer advantages such as low density, high specific strength, high specific modulus, high temperature resistance, and high oxidation resistance, making them ideal new high-temperature structural materials. In the aerospace and energy sectors, the continuous improvement in the performance of related equipment, such as reentry vehicles, aircraft engines, and gas turbines, has placed higher demands on the high-temperature resistance of SiC / SiC composites.

[0003] The densification process of SiC / SiC composites involves preparing a SiC matrix within an interfaced fiber preform or semi-densified SiC / SiC composite. One approach to improving the high-temperature serviceability of SiC / SiC composites is to modify the matrix and introduce a self-healing phase. These processes are often developed from common SiC / SiC composite densification methods, such as chemical vapor infiltration (CVI), polymer impregnation pyrolysis (PIP), and reactive melt infiltration (RMI). For example, the CVI process can directly deposit modified ceramic matrices, such as BC ceramics and Si-BC ceramics, within a semi-densified fiber preform. Alternatively, the PIP process, leveraging the highly designable and diverse ceramic precursors, can introduce a self-healing phase into the SiC / SiC matrix. However, the CVI process is limited by the reactive gas source, resulting in a limited selection of self-healing phases and a lengthy preparation cycle. However, the PIP process often produces gaseous products during the cracking reaction, which makes the matrix prepared by the PIP process loose and porous, with limited protection effect on the fiber, and often requires more than ten impregnation and cracking cycles.

[0004] Alternating the CVI process and the PIP process can produce a composite material with excellent mechanical properties, but this method also has the problem of a long preparation cycle. The polymer impregnation-online pyrolysis (PI-OP) process is to place the composite material sample after impregnation and curing directly into a CVI furnace for deposition, pyrolysis of the polymer precursor during the heating process of the CVI, and then immediately deposit it. The pyrolysis of some precursors and the deposition of SiC in the CVI are carried out simultaneously. Compared with the ordinary CVI combined with the PIP process, the PI-OP process reduces the number of temperature rises and falls experienced during the sample densification process by half, simplifying the preparation process while reducing the damage to the SiC fiber caused by high temperature, but the optimization effect of this process on the preparation cycle is still not ideal. Summary of the Invention

[0005] In response to the above-mentioned problems, the present invention aims to provide a SiC / SiC composite material, a preparation method and application thereof, and densification treatment of semi-densified SiC / SiC composite materials or fiber preforms with interfaces using a high-strength self-healing phase matrix. Each densification cycle includes two PIP operations and one PI-OP operation. This method can quickly achieve the ideal densification effect through only two densification cycles. At the same time, the SiC / SiC composite material finally prepared also has excellent room temperature flexural strength.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] In one aspect, the present invention provides a method for preparing a SiC / SiC composite material, comprising the following steps:

[0008] S1: Using polymer ceramic precursor, the composite material sample to be processed is subjected to the first polymer impregnation and cracking;

[0009] S2: performing a second polymer impregnation and cracking treatment on the composite material sample after the first polymer impregnation and cracking treatment;

[0010] S3: Performing polymer impregnation online pyrolysis on the composite material sample after the second polymer impregnation pyrolysis treatment to complete a densification treatment cycle;

[0011] S4: Repeat steps S1-S3 to complete two densification cycles to obtain a fully densified SiC / SiC composite material.

[0012] Specifically, the specific operations of step S1 include the following steps:

[0013] S101: pre-treating the composite material sample to be processed;

[0014] S102: preparing a polymer ceramic precursor solution;

[0015] S103: placing the container containing the polymer ceramic precursor solution into a vacuum impregnation system to impregnate the composite sample;

[0016] S104: curing the impregnated composite sample;

[0017] S105: pyrolyzing the cured composite sample.

[0018] Specifically, the composite sample to be treated in step S101 includes a semi-dense SiC / SiC composite sample and a SiC fiber preform plate with a BN interface.

[0019] Specifically, the polymer ceramic precursor solution in step S102 includes an organic solvent and a polymer ceramic precursor, and the volume ratio of the organic solvent to the polymer ceramic precursor is ≤1:1.

[0020] Specifically, the organic solvent includes toluene, and the polymer ceramic precursor includes Hb-PBSZ.

[0021] Specifically, the curing temperature in step S104 is 180-250°C, and the composite sample needs to be turned over during the curing process.

[0022] Specifically, the specific operation of pyrolyzing in step S105 includes the following steps: transferring the cured composite sample into a tube furnace, vacuumizing and filling argon; increasing the temperature to the pyrolysis temperature of the polymer ceramic precursor at a rate of 4-6°C / min, keeping the temperature for 1.5-3h, then cooling to 350-400°C at the same rate, and then cooling with the furnace.

[0023] Specifically, the specific operation of step S3 includes the following steps,

[0024] S301: placing the composite sample after the second polymer impregnation and pyrolysis treatment into a container containing a polymer ceramic precursor solution, and placing the container into a vacuum impregnation system to impregnate the composite sample;

[0025] S302: curing the impregnated composite sample;

[0026] S303: polishing the cured composite sample, and transferring the composite sample into a CVI furnace to perform one cycle of CVI.

[0027] In another aspect, the present application also provides a SiC / SiC composite material prepared by the preparation method as described above.

[0028] In still another aspect, the present application also provides the use of the SiC / SiC composite material as described above in high-temperature harsh environment thermal structural components.

[0029] The beneficial effects of the present invention are:

[0030] 1. The preparation method of the SiC / SiC composite material provided by the present invention combines PIP with PI-OP, and uses two PIP operations and one PI-OP operation as a densification cycle. The PI-OP operation fills the tiny holes remaining in the composite material during the PIP process. Compared with the PI-OP process alone, it can introduce more self-healing phases into the composite material. Two densification cycles can achieve the ideal densification level, and the densification speed is about twice that of the PI-OP process, greatly improving production efficiency. At the same time, the prepared composite material has high strength characteristics, which improves the serviceability of the composite material in high-temperature oxidizing atmosphere environments.

[0031] 2. The present invention combines a semi-densified SiC / SiC composite with a SiC fiber preform with a BN interface, providing a different pretreatment method. Prior to impregnation, the SiC fiber preform with the BN interface undergoes a single cycle of CVI to form a uniform, continuous, and high-strength SiC matrix around the fibers and the interface. This SiC layer protects the fibers from potential damage from multiple impregnation-cracking processes during subsequent densification, improves load transfer efficiency between the composite fiber and matrix, and ultimately ensures the high strength of the composite.

[0032] 3. The preparation method of the present invention can form a tightly bonded coating composed of alternating self-healing phases and CVI SiC on the sample surface while densifying, which can improve the serviceability of the composite material in a high-temperature oxidizing atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of the vacuum impregnation system in the present invention.

[0034] Figure 2 This is the comparison result of the impregnation efficiency between the densification process of the present invention and the PI-OP process in the first application example of the present invention.

[0035] Figure 3 This is a three-dimensional CT image of defects in the composite material sample before and after densification in Application Example 1 of the present invention.

[0036] Figure 4 This is the stress-displacement curve of the three-point bending test of the SiC / SiC composite material prepared in Application Example 1 of the present invention.

[0037] Figure 5 This is an electron microscope photograph of the fracture of the SiC / SiC composite material prepared in Application Example 1 of the present invention.

[0038] Figure 6For the application example two of the present application, the cross-section electron microscope photo of the composite sample after pretreatment.

[0039] Figure 7 For the application example two of the present application, the open porosity and volume density curve of the composite sample during densification.

[0040] Figure 8 For the application example two of the present application, the three-dimensional CT image of the defects of the composite sample before and after densification.

[0041] Figure 9 For the application example two of the present application, the stress-displacement curve of the SiC / SiC composite material prepared by three-point bending test.

[0042] Figure 10 For the application example two of the present application, the fracture electron microscope photo of the SiC / SiC composite material prepared.

[0043] Wherein, 1, vacuum impregnation tank; 101, top cover; 2, iron wire; 3, air pipe; 4, mechanical vacuum pump; 5, first ball valve; 6, second ball valve; 7, vacuum gauge; 8, container. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application are further described below in combination with the drawings and examples.

[0045] Example one:

[0046] Example one provides a preparation method of SiC / SiC composite material, specifically comprising the following steps,

[0047] S1: using polymer ceramic precursor, the first polymer impregnation and pyrolysis of the composite sample to be treated;

[0048] Specifically, S101: pretreatment of the composite sample to be treated;

[0049] In this embodiment, the composite sample to be treated is selected as semi-dense SiC / SiC composite sample. The pretreatment method of semi-dense SiC / SiC composite sample is: using ultrasonic cleaning machine to clean and remove the debris and oil stains of semi-dense SiC / SiC composite sample during mechanical processing, and then placing the composite sample in a 70℃ air drying oven for sufficient drying. The dried composite sample is bundled and fixed with fine iron wire.

[0050] S102: preparation of polymer ceramic precursor solution;

[0051] The polymer ceramic precursor is diluted with an organic solvent until it can flow smoothly at room temperature. To ensure ceramic conversion, the volume ratio of the organic solvent to the polymer ceramic precursor should not exceed 1:1. The diluted polymer ceramic precursor solution is placed in a container 8 that matches the volume of the composite material sample to be processed. The amount of polymer ceramic precursor solution required is estimated based on the capacity of container 8 and the volume of the composite material sample, ensuring that the liquid level of the composite material sample submerged in the solution reaches the highest point of the composite material sample.

[0052] Preferably, in the present invention, the organic solvent is toluene and the polymer ceramic precursor is Hb-PBSZ ceramic precursor. It should be noted that the solvent in the present invention includes but is not limited to toluene, and similarly, the polymer ceramic precursor also includes but is not limited to Hb-PBSZ ceramic precursor.

[0053] S103: placing a container containing a polymer ceramic precursor solution in a vacuum impregnation system to perform an impregnation treatment on the composite material sample;

[0054] Specifically, the structure of the vacuum impregnation system is as shown in the attached Figure 1 As shown, the vacuum impregnation tank 1 includes a top cover 101 on the top of which a wire 2 is passed through. The vacuum impregnation tank 1 uses a vacuum drying dish with good airtightness. The top cover 101 is perforated to allow a wire 2 with a diameter of 2 mm to pass through smoothly. The bottom of the wire 2 is bent into a hook shape. Vacuum sealant is used to fill the gap between the wire 2 and the top cover 101 and fix the position of the wire 2 to prevent it from slipping. The vacuum impregnation tank 1 is connected to a mechanical vacuum pump 4 via an air pipe 3. The air pipe 3 is provided with a first ball valve 5 and a second ball valve 6. The first ball valve 5 is close to the vacuum impregnation tank 1, and the second ball valve 6 is close to the mechanical vacuum pump 4. A vacuum gauge 7 is also connected between the first ball valve 5 and the second ball valve 6 via a three-way valve. After the vacuum impregnation system is assembled, the air tightness of the system needs to be verified. Connect the air line, turn on the switch of the mechanical vacuum pump 4, evacuate the vacuum impregnation tank 1 until the air pressure is lower than 10KPa, and then close the second ball valve 6. The air pressure change in the vacuum impregnation tank 1 should not be higher than 5% within 10 minutes. At this time, the air tightness of the vacuum impregnation system is good.

[0055] Place container 8 containing the polymer ceramic precursor solution in a vacuum impregnation tank 1. Wire 2 is hooked around the composite material sample, suspending it from the wire. Initially, the composite material sample is isolated from the polymer ceramic precursor solution. Connect the air supply, start the mechanical vacuum pump 4, and wait for the vacuum level to stabilize before timing. After 15 minutes, push wire 2 downward to completely immerse the composite material sample in the polymer ceramic precursor solution. After 30 minutes of immersion, turn off the mechanical vacuum pump 4 and slowly open the ball valve of the vacuum impregnation tank 1 until the pressure inside and outside the tank 1 is balanced.

[0056] S104: curing the impregnated composite material sample;

[0057] Open the lid 101 of the vacuum impregnation tank 1 and transfer the impregnated composite material sample to a heating platform with a temperature range of 50-400°C for curing. A 200mm x 200mm, 5mm thick aluminum tray is used to separate the heating platform and the composite material sample. The curing temperature is 200°C. After 30 minutes, turn the composite material sample over and continue curing for another 30 minutes.

[0058] S105: cracking the fixed composite material sample;

[0059] The cured composite sample was transferred to a tube furnace and evacuated and filled with argon three times. The temperature was raised to the precursor cracking temperature at a rate of 5°C / min, held at that temperature for 2 hours, and then cooled to 400°C at a rate of 5°C / min. The sample was then removed from the furnace, completing the first polymer impregnation and cracking process.

[0060] Further, S2: performing a second polymer impregnation and cracking treatment on the composite material sample after the first polymer impregnation and cracking treatment;

[0061] Specifically, a diamond file is first used to grind away the polymer-converted ceramic on the surface of the composite material sample after the first polymer impregnation and cracking, and then the second polymer impregnation and cracking is performed according to the operating method in step S1.

[0062] Further, S3: performing polymer impregnation online pyrolysis on the composite material sample after the second polymer impregnation pyrolysis treatment to complete a densification treatment cycle;

[0063] Specifically, S301: first, using a diamond file to grind away the polymer-converted ceramic on the surface of the composite material sample after the second polymer impregnation and pyrolysis treatment, then placing the composite material sample after the second polymer impregnation and pyrolysis treatment in a container containing a polymer ceramic precursor solution, placing the container in a vacuum impregnation system, and performing an impregnation treatment on the composite material sample;

[0064] S302: curing the impregnated composite material sample;

[0065] The specific operation process of step S301 and step S302 is the same as the dipping and curing operation in step S1.

[0066] S303: polishing the cured composite material sample to be smooth, and transferring the composite material sample to a CVI furnace for one cycle of CVI;

[0067] After curing in step S302, the composite material sample was polished flat with a diamond file and transferred to a CVI furnace for one cycle of CVI. The CVI process uses standard procedures, with specific parameters including: trichloromethylsilane (MTS) as the precursor, Ar as the diluent gas, and H2 as the carrier gas, with MTS introduced into the reaction chamber by bubbling. The reaction pressure was maintained at 5 kPa, the deposition temperature was 1000°C, and the actual deposition time per cycle was 60 hours, completing one densification cycle.

[0068] S4: Repeat steps S1-S3 to complete two densification cycles to obtain a fully densified SiC / SiC composite material.

[0069] Example 2:

[0070] The only difference between Example 2 and Example 1 is that in step S101, the composite material sample to be processed is a SiC fiber preform plate deposited with a BN interface. The pretreatment method of the SiC fiber preform plate deposited with a BN interface is specifically as follows: first, the composite material sample is processed into a desired shape using a mechanical processing method such as wire cutting, and then an ultrasonic cleaning machine is used to clean and remove debris and oil stains remaining on the composite material sample during mechanical processing, and then the composite material sample is placed in a 70°C forced air drying oven to be fully dried.

[0071] The dried composite sample was transferred to a CVI furnace for a single SiC deposition cycle. The CVI process followed standard parameters: trichloromethylsilane (MTS) was used as the precursor, Ar was used as the diluent, and H₂ was used as the carrier gas. MTS was bubbled into the reaction chamber. The reaction pressure was maintained at 5 kPa, the deposition temperature was 1000°C, and the deposition time was 60 hours.

[0072] The composite material sample after CVI treatment is bound and fixed with thin iron wires, and then the subsequent steps S102-S105 and S2-S5 are performed.

[0073] Application Example 1:

[0074] This example uses a three-dimensional four-directional (3D 4D) structure woven with domestic second-generation fibers, with an average open porosity of 27.3±2% and an average bulk density of 2.0±0.1g / cm 3The semi-dense SiC / SiC composite material sample is used as the densification starting point, and hyperbranched polyborosilazane (Hb-PBSZ) is used as the polymer ceramic precursor. The pyrolysis product of the ceramic precursor of hyperbranched polyborosilazane (Hb-PBSZ) is SiBCN ceramic, which can be used as SiBCN ceramic of self-healing phase. This example is processed using the densification method described in Example 1, and finally a SiC / SiC composite material sample modified with a self-healing phase matrix is ​​prepared. The specific processing process includes the following steps:

[0075] S1: Using polymer ceramic precursor, the composite material sample to be processed is subjected to the first polymer impregnation and cracking;

[0076] Specifically, S101: pre-treating the composite material sample to be processed;

[0077] An ultrasonic cleaner was used to clean the semi-dense SiC / SiC composite samples to remove debris and oil residue from machining. Specifically, the samples were placed in a 100mL glass beaker, covered with clean water, and then placed in an ultrasonic cleaner for 10 minutes. After discarding the dirty water, the samples were rinsed again with clean water for another 10 minutes until the water was clear and translucent. The composite samples were then dried in a 70°C forced air drying oven for 12 hours. After drying, the composite samples were secured with 0.5mm diameter wire.

[0078] S102: preparing a polymer ceramic precursor solution;

[0079] The Hb-PBSZ ceramic precursor was diluted with toluene in a 100 mL beaker at a volume ratio of 1:1 to obtain a total volume of 25 mL of the precursor solution.

[0080] S103: placing a container containing a polymer ceramic precursor solution in a vacuum impregnation system to perform an impregnation treatment on the composite material sample;

[0081] The vacuum impregnation tank 1 uses a 250mm plastic vacuum drying dish with good airtightness. The inner diameter of the air pipe 3 is 6mm and the outer diameter is 8mm. The vacuum degree of the mechanical vacuum pump 4 is 7KPa and the flow rate is 113L / min. After confirming that the vacuum impregnation system is airtight, the impregnation operation begins.

[0082] Place container 8 containing the polymer ceramic precursor solution in a vacuum impregnation tank 1. Wire 2 is hooked around the composite material sample, suspending it from the wire. Initially, the composite material sample is isolated from the polymer ceramic precursor solution. Connect the air supply, start the mechanical vacuum pump 4, and wait for the vacuum level to stabilize before timing. After 15 minutes, push wire 2 downward to completely immerse the composite material sample in the polymer ceramic precursor solution. After 30 minutes of immersion, turn off the mechanical vacuum pump 4 and slowly open the ball valve of the vacuum impregnation tank 1 until the pressure inside and outside the tank 1 is balanced.

[0083] S104: curing the impregnated composite material sample;

[0084] Open the lid 101 of the vacuum impregnation tank 1 and transfer the impregnated composite material sample to a heating table with a temperature range of 50-400°C for curing. The heating table is equipped with a 250mm x 250mm heating plate. A 200mm x 200mm, 5mm thick aluminum tray is used to separate the heating plate and the composite material sample. The curing temperature is 200°C. After 30 minutes, turn the composite material sample over and continue curing for another 30 minutes.

[0085] S105: cracking the fixed composite material sample;

[0086] The cured composite sample was transferred to a tube furnace and evacuated and filled with argon three times. The temperature was raised to the precursor cracking temperature at a rate of 5°C / min, held at that temperature for 2 hours, and then cooled to 400°C at a rate of 5°C / min. The sample was then removed from the furnace, completing the first polymer impregnation and cracking process.

[0087] S2: performing a second polymer impregnation and cracking treatment on the composite material sample after the first polymer impregnation and cracking treatment;

[0088] Specifically, a diamond file is first used to grind away the polymer-converted ceramic on the surface of the composite material sample after the first polymer impregnation and cracking, and then the second polymer impregnation and cracking is performed according to the operating method in step S1.

[0089] S3: Performing polymer impregnation online pyrolysis on the composite material sample after the second polymer impregnation pyrolysis treatment to complete a densification treatment cycle;

[0090] Specifically, the composite material sample is impregnated and cured according to the procedures in step S1. The cured composite material sample is then polished flat with a diamond file and transferred to a CVI furnace for a single CVI cycle. The CVI process uses standard techniques, with specific process parameters including: trichloromethylsilane (MTS) as the precursor, Ar as the diluent gas, H2 as the carrier gas, and MTS introduced into the reaction chamber by bubbling. The reaction pressure is maintained at 5kPa, the deposition temperature is 1000°C, and the actual deposition time per cycle is 60 hours.

[0091] S4: Repeat steps S1-S3 to complete two densification cycles to obtain a fully densified SiC / SiC composite material.

[0092] During the densification process, the changes in density and porosity of the composite samples were recorded and compared using a separate PI-OP operation. The results are shown in the attached figure. Figure 2 As shown. Figure 2 As can be seen from the figure, compared with composite samples densified using the same ceramic precursor using the PI-OP process with the same initial open porosity and bulk density, the densification process using two PIPs and one PI-OP in the present invention can effectively increase the sample densification speed, quickly reduce the sample open porosity and increase the sample density. Two densification cycles can achieve the ideal densification effect. The average open porosity of the SiC / SiC composite sample obtained after densification is 1.9±0.6%, and the bulk density is 2.49±0.02g / cm 3 , the average room temperature flexural strength is 839.5±262MPa.

[0093] The defects of the composite material samples were scanned by CT three-dimensional scanning before and after densification treatment. The results are shown in the attached figure. Figure 3 As shown in the figure, (a) is the three-dimensional CT image of the defects of the composite material sample before densification; (b) is the three-dimensional CT image of the defects of the composite material sample after densification. Figure 3 It can be seen that compared with the samples before densification, the maximum defect volume and defect volume ratio of the composite material samples after densification are significantly reduced, indicating that the process of the present invention has a good densification effect.

[0094] The SiC / SiC composite material prepared in this example was subjected to a three-point bending test, and the stress-displacement curve was obtained as shown in the attached figure. Figure 4 As shown in the figure, in order to prove the effectiveness of this method, three-point bending tests were performed on two SiC / SiC composites through repeated experiments. Figure 4As can be seen in the figure, all SiC / SiC composites exhibit pseudoplastic curve characteristics: after the loading phase reaches its maximum stress, the samples do not immediately fracture, and the stress does not drop suddenly to zero. Instead, it remains at a high value and slowly decreases. This result demonstrates that the composite samples densified using the process of this invention possess excellent room-temperature flexural strength.

[0095] Furthermore, the fracture electron microscope photos of the SiC / SiC composite material prepared in this example were collected, and the results are shown in the attached Figure 5 As shown. All electron microscope images are backscattered electron images. Since the backscattered electron signal is sensitive to the atomic number and PDC SiBCN ceramics contain more light elements than CVI SiC matrix, PDC SiBCN ceramics are darker than CVI SiC in electron microscope images. Figure 5 It can be seen that the PDC SiBCN ceramics and the CVI SiC matrix are tightly bonded, and the PDC SiBCN ceramics are successfully introduced.

[0096] Application Example 2:

[0097] This example uses a three-dimensional four-directional (3D 4s) structure woven with domestic second-generation fibers, with an average open porosity of 33.6±0.4% and an average bulk density of 1.86±0.02g / cm 3 The SiC fiber preform plate with a BN interface is used as the densification starting point, and hyperbranched polyborosilazane (Hb-PBSZ) is used as the ceramic precursor as the impregnation raw material. The pyrolysis product of the ceramic precursor of hyperbranched polyborosilazane (Hb-PBSZ) is SiBCN ceramic, which can be used as a SiBCN ceramic of the self-healing phase. This example is processed using the densification method described in Example 2, and finally a SiC / SiC composite material sample modified with a self-healing phase matrix is ​​prepared. The specific processing process includes the following steps:

[0098] S1: Using polymer ceramic precursor, the composite material sample to be processed is subjected to the first polymer impregnation and cracking;

[0099] Specifically, S101: pre-treating the composite material sample to be processed;

[0100] The SiC fiber preform plate with BN interface deposited thereon was machined into a three-point bending sample with dimensions of 40x5x3mm using a wire cutting machine. The composite sample was cleaned using an ultrasonic cleaning machine to remove debris and oil remaining after machining. Specifically, the sample was placed in a 100mL glass beaker and covered with clean water. The sample was cleaned in the ultrasonic cleaning agent for 10 minutes. After the dirty water was poured out, the sample was cleaned again with clean water for 10 minutes. This process was repeated until the water was clear and free of dust. Then, the sample was placed in a 70℃ drying oven for 12 hours.

[0101] The dried composite sample was transferred to a CVI furnace for one cycle of SiC deposition. The CVI process used standard parameters, as follows: trichloromethylsilane (MTS) was used as the precursor, Ar was used as the dilution gas, and H2 was used as the carrier gas. The MTS was introduced into the reaction chamber by bubbling. The reaction pressure was maintained at 5kPa, the deposition temperature was 1000℃, and the actual deposition time was 60 hours. The CVI process covered the surface of the sample fiber with a CVI SiC layer about 7μm thick, as shown in FIG. 1. Then, the composite sample was fixed by binding with a thin iron wire with a diameter of 0.5mm. Figure 6

[0102] S102: Preparation of a polymer ceramic precursor solution;

[0103] In a 100mL beaker, the Hb-PBSZ ceramic precursor was diluted with toluene at a volume ratio of 1:1 to obtain a precursor solution with a total volume of 25ml.

[0104] S103: The container containing the polymer ceramic precursor solution was placed in the vacuum impregnation system, and the composite sample was subjected to impregnation treatment;

[0105] The vacuum impregnation tank 1 was a 250mm plastic vacuum drying dish with good air tightness. The inner diameter of the air pipe 3 was 6mm, and the outer diameter was 8mm. The vacuum degree of the mechanical vacuum pump 4 was 7KPa, and the flow rate was 113L / min. After confirming that the vacuum impregnation system had good air tightness, the impregnation operation was started.

[0106] The container 8 containing the polymer ceramic precursor solution was placed in the vacuum impregnation tank 1, and the iron wire 2 was hooked on the composite sample. The composite sample was hung on the iron wire 2, and the initial state was that the composite sample had no contact with the polymer ceramic precursor solution. The air path was connected, the mechanical vacuum pump 4 was started, and the vacuum degree was stabilized. After 15 minutes, the iron wire 2 was pushed down, and the composite sample was completely immersed in the polymer ceramic precursor solution. After 30 minutes of impregnation, the mechanical vacuum pump 4 was turned off, and the ball valve of the vacuum impregnation tank 1 was slowly opened until the air pressure inside and outside the vacuum impregnation tank 1 was balanced.

[0107] S104: Solidification of the impregnated composite sample; ​

[0108] Open the lid 101 of the vacuum impregnation tank 1 and transfer the impregnated composite material sample to a heating table with a temperature range of 50-400°C for curing. The heating table is equipped with a 250mm x 250mm heating plate. A 200mm x 200mm, 5mm thick aluminum tray is used to separate the heating plate and the composite material sample. The curing temperature is 200°C. After 30 minutes, turn the composite material sample over and continue curing for another 30 minutes.

[0109] S105: cracking the fixed composite material sample;

[0110] The cured composite sample was transferred to a tube furnace and evacuated and filled with argon three times. The temperature was raised to the precursor cracking temperature at a rate of 5°C / min, held at that temperature for 2 hours, and then cooled to 400°C at a rate of 5°C / min. The sample was then removed from the furnace, completing the first polymer impregnation and cracking process.

[0111] S2: performing a second polymer impregnation and cracking treatment on the composite material sample after the first polymer impregnation and cracking treatment;

[0112] Specifically, a diamond file is first used to grind away the polymer-converted ceramic on the surface of the composite material sample after the first polymer impregnation and cracking, and then the second polymer impregnation and cracking is performed according to the operating method in step S1.

[0113] S3: Performing polymer impregnation online pyrolysis on the composite material sample after the second polymer impregnation pyrolysis treatment to complete a densification treatment cycle;

[0114] Specifically, the composite material sample is impregnated and cured according to the procedures in step S1. The cured composite material sample is then polished flat with a diamond file and transferred to a CVI furnace for a single cycle of CVI. The CVI process uses standard techniques, with specific process parameters including: using trichloromethylsilane (MTS) as the precursor, Ar as the diluent gas, and H2 as the carrier gas, with MTS introduced into the reaction chamber by bubbling. The reaction pressure is maintained at 5kPa, the deposition temperature is 1000°C, and the actual deposition time per cycle is 60 hours.

[0115] S4: Repeat steps S1-S3 to complete two densification cycles to obtain a fully densified SiC / SiC composite material.

[0116] During the densification process, the changes in density and porosity of the composite samples were recorded. The results are shown in the attached figure. Figure 7 As shown in the attached Figure 7It can be seen that after two densification cycles, the average open porosity of the densified SiC / SiC composite samples is 6.1±1.0%, and the bulk density is 2.37±0.01 g / cm 3 .

[0117] The defects of the composite material samples were scanned by CT three-dimensional scanning before and after densification treatment. The results are shown in the attached figure. Figure 8 As shown in the figure, (a) is the three-dimensional CT image of the defects of the composite material sample before densification; (b) is the three-dimensional CT image of the defects of the composite material sample after densification. Figure 8 It can be seen that compared with the samples before densification, the maximum defect volume and the defect volume ratio of the composite material samples after densification are significantly reduced, indicating that the process of the present invention has a good densification effect.

[0118] The SiC / SiC composite material prepared in this example was subjected to a three-point bending test, and the stress-displacement curve was obtained as shown in the attached figure. Figure 9 As shown in the figure, in order to prove the effectiveness of this method, three-point bending tests were performed on two SiC / SiC composites through repeated experiments. Figure 9 As can be seen from the graph, all composite samples exhibited pseudoplastic curve characteristics: after the loading phase and the material stress reached its maximum value, the samples did not immediately fracture, and the stress did not suddenly drop to zero. Instead, it remained at a high value and slowly decreased. This result demonstrates that the composite samples densified using the process of this invention possess excellent room-temperature flexural strength.

[0119] Furthermore, the fracture electron microscope photos of the SiC / SiC composite material prepared in this example were collected, and the results are shown in the attached Figure 10 As shown, (a) is the overall morphology of the fracture, (b) is the matrix morphology between the three fiber bundles, and (c) is an enlarged view of (b). All electron microscope images are backscattered electron images. Since the backscattered electron signal is sensitive to the atomic number and PDC SiBCN ceramics contain more lightweight elements than CVI SiC matrix, PDC SiBCN ceramics are darker than CVI SiC in electron microscope images. Figure 10 As can be seen from (a), each fiber bundle has a long pull-out length. Figure 10As can be seen in (b), when observing outward in the direction perpendicular to the surface of the fiber bundle, there are CVI SiC and a layer of continuous PDC SiBCN ceramics in sequence. Although the sample underwent multiple (2 densification cycles, a total of 4 times) PIP processes during the preparation process, no stratification phenomenon similar to that between CVI SiC matrices from different furnaces was observed inside the PDC SiBCN phase, which indicates that the Hb-PBSZ precursor can remain stable after multiple vacuum impregnations, and the latter PIP process can effectively fill the cracks formed during the high-temperature decomposition of the precursor in the previous PIP process. The PDC ceramics introduced into the composite material through the PIP process can effectively enter the surface of the fiber bundle and the small angle gaps between the fiber bundles. A transition zone with a thickness of about 10μm can be observed between the inner layer of CVI SiC and the PDC SiBCN ceramics, see Appendix. Figure 10 In the dotted rectangular box (c), the existence of the transition zone is beneficial to alleviate the thermal mismatch between PDC ceramics and CVISiC.

[0120] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a SiC / SiC composite material, characterized in that: The following steps are included: S1: Using polymer ceramic precursor, the composite material sample to be processed is subjected to the first polymer impregnation and cracking; S2: performing a second polymer impregnation and cracking treatment on the composite material sample after the first polymer impregnation and cracking treatment; S3: Performing polymer impregnation online pyrolysis on the composite material sample after the second polymer impregnation pyrolysis treatment to complete a densification treatment cycle; S4: Repeat steps S1-S3 to complete two densification cycles to obtain a fully densified SiC / SiC composite material.

2. The method for preparing a SiC / SiC composite material according to claim 1, wherein: The specific operation of step S1 includes the following steps: S101: pre-treating the composite material sample to be processed; S102: preparing a polymer ceramic precursor solution; S103: placing a container containing a polymer ceramic precursor solution in a vacuum impregnation system to perform an impregnation treatment on the composite material sample; S104: curing the impregnated composite material sample; S105: cracking the cured composite material sample.

3. The method for preparing a SiC / SiC composite material according to claim 2, wherein: The composite material sample to be processed in step S101 includes a semi-dense SiC / SiC composite material sample and a SiC fiber preform plate with a BN interface.

4. The method for preparing a SiC / SiC composite material according to claim 2, wherein: The polymer ceramic precursor solution in step S102 includes an organic solvent and a polymer ceramic precursor, and the volume ratio of the organic solvent to the polymer ceramic precursor is ≤1:

1.

5. The method for preparing a SiC / SiC composite material according to claim 4, characterized in that: The organic solvent includes toluene, and the polymer ceramic precursor includes Hb-PBSZ.

6. The method for preparing a SiC / SiC composite material according to claim 2, characterized in that: In step S104 , the curing temperature is 180-250° C., and the composite material sample needs to be turned over during the curing process.

7. The method for preparing a SiC / SiC composite material according to claim 2, wherein: The specific operation of pyrolysis in step S105 includes the following steps: transferring the cured composite material sample to a tube furnace, evacuating and filling it with argon; raising the temperature to the pyrolysis temperature of the polymer ceramic precursor at a rate of 4-6°C / min, keeping it at that temperature for 1.5-3 hours, and then cooling it to 350-400°C at the same rate, and then cooling it with the furnace.

8. The method for preparing a SiC / SiC composite material according to claim 2, characterized in that: The specific operation of step S3 includes the following steps: S301: placing the composite material sample after the second polymer impregnation and cracking treatment in a container containing a polymer ceramic precursor solution, placing the container in a vacuum impregnation system, and performing an impregnation treatment on the composite material sample; S302: curing the impregnated composite material sample; S303: Grinding the cured composite material sample to make it smooth, and transferring the composite material sample to a CVI furnace for one cycle of CVI.

9. A SiC / SiC composite material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the SiC / SiC composite material according to claim 9 in thermal structural components under high temperature and harsh environment.

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