Ti-modified CVD-sic oxidation-resistant coating, and preparation method and application thereof

Abstract

The application discloses a Ti modified CVD-SiC oxidation resistant coating and a preparation method and application thereof, and belongs to the technical field of material preparation. The method comprises the following steps: firstly, preparing a SiC coating on the surface of a C / C composite material by using a chemical vapor deposition method; and then, introducing Ti elements into the SiC coating by using a molten salt reaction and low-temperature heat treatment at 1100 DEG C to 1400 DEG C, thereby in-situ forming a Ti-Si-C layer, and finally obtaining the Ti modified CVD-SiC oxidation resistant coating. The TiO2 and SiO2 generated in the oxidation process are used for mutual diffusion, the viscosity of SiO2 is reduced, the flowability of SiO2 is improved, and then the self-healing efficiency of the SiC coating is improved. Meanwhile, the excess TiO2 plays a role in improving the stability of the surface oxidation film, and the two work together to improve the thermal protection performance of the SiC coating in the low-temperature zone.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material preparation, and particularly relates to a Ti modified CVD-SiC oxidation resistant coating and a preparation method and application thereof. BACKGROUND

[0002] Carbon / carbon (C / C) composite material is one of the candidate materials for the thermal structural components of new generation aircrafts, which has the advantages of low density, low thermal expansion coefficient, high specific strength, and mechanical properties rising with temperature rising. However, the C / C composite material can be oxidized in the oxygen environment above 400 DEG C, and the mechanical properties thereof decrease by 10% when the weight loss percentage is 1%. The silicon-based ceramic coating technology is an important technology for effectively protecting the C / C composite material for a long time. The SiC coating prepared by the chemical vapor deposition method is an ideal oxidation resistant coating material because the SiC coating has a similar thermal expansion coefficient with the C / C composite material, has a small damage to the mechanical properties of the C / C composite material, and can generate SiO2 with self-healing performance at high temperature.

[0003] However, in low- and medium-temperature environments such as 1300℃, the SiO2 generated by the oxidation of SiC coatings is produced at a slow rate, with high viscosity and poor fluidity. This results in the inability to effectively heal defects such as cracks in the coating and thus provides ineffective protection against the C / C matrix. Studies have shown that introducing Ti elements into the coating under low- and medium-temperature oxidation conditions can reduce the viscosity of SiO2, improve its fluidity, promote the healing of defects such as cracks in the coating, and improve the protective effect of the coating. The literature “Y.Wei,L.Zhou,J.Zhang et al.Effect of TiB2 on the self-crack-healing ability of SiC-Si coating at 1300℃[J],Surface Coating Technology,2021,425” describes the introduction of TiB2 into SiC coatings via slurry impregnation combined with vapor-phase silicon diffusion. The interaction between B2O3 and TiO2 with SiO2 enhances the self-healing efficiency of the coating. After oxidation at 1300℃ for 1 hour, the original cracks on the TiB2-SiC coating surface are almost completely healed, while no significant healing is observed on the SiC coating surface. However, this method typically involves complex preparation processes and high temperatures (>1800℃), which can cause mechanical damage to the C / C matrix. The literature “S.Liu,WZLu,YGChen et al.Influence of Substrate Temperature on Microstructure and Properties of Ti-Si-C Film[J].Key Engineering Materials,2016,693:813-820.” describes the preparation of Ti-Si-C coatings using chemical vapor deposition with CH4, (CH3)4Si, TiCl4 and H2 as raw materials. However, this reaction system involves Ti-Si-C co-deposition, and the deposition parameters are usually difficult to control. The invention patent with patent number ZL202211230431.8, entitled "A multi-layer core-shell structure nanowire toughened chemical vapor deposition SiC coating and its preparation method", prepared a TiO2-coated SiC nanowire toughened SiC coating. The introduction of TiO2 improved the self-healing and thermal shock resistance of the coating. The TiO2 was coated on the surface of SiC nanowires by the sol-gel method. However, this method leads to an increase in the diameter of the nanowires and partial collapse of the nanowire network, which reduces the porosity of the nanowires. The resulting coating usually has a high porosity, which is not conducive to the long-term effective protection of the coating.

[0004] Therefore, in order to achieve long-term effective protection of C / C composites in the low- and medium-temperature range, it is necessary to prepare a self-healing component modified antioxidant coating with high density, excellent self-healing properties, minimal damage to the mechanical properties of the matrix, and low difficulty in controlling the preparation process. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a Ti-modified CVD-SiC antioxidant coating, its preparation method and application, so as to solve the technical problems of high preparation temperature, complex preparation process, difficulty in control and low coating density in the prior art.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention discloses a method for preparing a Ti-modified CVD-SiC antioxidant coating, comprising: firstly, preparing a SiC coating on the surface of a C / C composite material by chemical vapor deposition, and then using a molten salt reaction to perform low-temperature heat treatment at 1100℃~1400℃ to introduce Ti elements into the SiC coating, thereby forming a Ti-Si-C layer in situ and obtaining a Ti-modified CVD-SiC antioxidant coating.

[0008] Preferably, the method for preparing the Ti-modified CVD-SiC antioxidant coating includes the following steps:

[0009] 1) Preparation of C / C composite materials containing SiC coating;

[0010] 2) Weigh out Ti powder, SiC powder and NaCl-KCl mixed powder in a certain proportion, grind them thoroughly and evenly to obtain a mixed powder;

[0011] 3) The C / C composite material containing the SiC coating is embedded in the mixed powder and then placed in a crucible for sealing treatment;

[0012] 4) The sample treated in step 3) was heat-treated in an Ar environment at 1100℃~1400℃ for 0.5~10h. After the treatment, it was washed and dried to obtain the Ti modified CVD-SiC antioxidant coating.

[0013] More preferably, in step 1), H2 is used as the reaction gas, Ar is used as the dilution gas, and methyltrichlorosilane is used as the raw material to deposit a SiC coating on the surface of the C / C composite material under negative pressure.

[0014] More preferably, the temperature during coating deposition is 1100℃~1300℃, the Ar flow rate is 150~700mL / min, the H2 flow rate is 500~1300mL / min, the methyltrichlorosilane flow rate is 0.05~0.3g / min, and the reaction pressure is controlled at 2~8kPa.

[0015] More preferably, in step 2), the molar ratio of the Ti powder and SiC powder mixture to the NaCl-KCl powder mixture is 3:1 to 1:8; the molar ratio of Ti powder to SiC powder is 1:0 to 1:4; the molar ratio of NaCl to KCl in the NaCl-KCl powder mixture is 2:1 to 1:2; and the grinding time is 30 to 60 minutes.

[0016] The purity of Ti powder is 99.5%, and the particle size is 1–10 μm; the purity of SiC powder is 99.5%, and the particle size is 1–3 μm; the purity of NaCl and KCl is 99.5%.

[0017] More preferably, in step 3), the crucible is an alumina crucible, and the reaction powder is wrapped with 2 to 3 layers of graphite paper. The thickness of the powder around the C / C composite material containing the SiC coating should be no less than 5 mm.

[0018] More preferably, in step 4), the sealed crucible is placed in the constant temperature zone of a tube furnace and heat-treated in an environment with atmospheric pressure and an Ar flow rate of 30-60 mL / min.

[0019] Washing involves placing the heat-treated test specimen in water and boiling it multiple times at 100–300°C. Drying involves drying it at 60–75°C.

[0020] This invention discloses a Ti-modified CVD-SiC antioxidant coating prepared by the above-described preparation method. The antioxidant coating comprises a two-layer structure, with an inner uniform and dense SiC layer and an outer uniform Ti-Si-C layer. The thickness of the Ti-Si-C layer can be adjusted by controlling the reaction temperature and reaction time.

[0021] Preferably, the antioxidant coating gains 0.35% in weight after being oxidized in static air at 1300°C for 300 hours, and loses 0.23% in weight after 30 thermal shock tests from 1300°C to room temperature.

[0022] The present invention also discloses the application of the above-mentioned Ti-modified CVD-SiC antioxidant coating in the preparation of thermal structural components for aircraft.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention discloses a method for preparing a Ti-modified CVD-SiC antioxidant coating. Ti is introduced into the CVD-SiC coating via a molten salt reaction. First, a SiC coating is prepared on the surface of a carbon / carbon (C / C) composite material using chemical vapor deposition. Then, Ti is introduced into the SiC coating via a molten salt reaction, forming a Ti-Si-C layer in situ, thus obtaining the Ti-modified CVD-SiC antioxidant coating. It can be seen that this method can prepare a high-density Ti-modified CVD-SiC coating at a relatively low temperature, as low as 1100℃, without the need for high-temperature reactions or complex co-deposition. This invention utilizes the interdiffusion of TiO2 and SiO2 generated during oxidation to reduce the viscosity of SiO2 and improve its fluidity, thereby improving the self-healing efficiency of the SiC coating. Simultaneously, excess TiO2 enhances the stability of the surface oxide film; both factors synergistically improve the thermal protection performance of the SiC coating in the low-temperature region. This effectively solves the technical problems of high preparation temperature, complex preparation process, difficulty in control, and low coating density in existing technologies.

[0025] Furthermore, in this invention, the SiC-coated C / C composite material is embedded in the mixed powder and placed in an alumina crucible. An alumina crucible is used instead of a graphite crucible to avoid the raw material reacting with the graphite crucible and being consumed in large quantities.

[0026] Furthermore, when using an alumina crucible, it should be covered with graphite paper in 2-3 layers to effectively prevent the introduction of impurity Al elements. At the same time, when filling the crucible with powder, it should be sprinkled evenly to avoid pressing and compacting. The powder thickness around the sample should be no less than 5 mm.

[0027] The Ti-modified CVD-SiC anti-oxidation coating prepared by the method of this invention consists of a uniform and dense SiC layer inside and a uniformly thick Ti-Si-C layer on the outside. The thickness of the Ti-Si-C layer can be adjusted by controlling the reaction temperature and reaction time. The introduction of Ti element does not significantly change the surface morphology of the coating, which is beneficial for maintaining the aerodynamic shape of components during practical applications. This coating exhibits good self-healing properties and anti-oxidation and thermal shock resistance at 1300℃. After oxidation in static air at 1300℃ for 300 hours, the weight gain is approximately 0.35%, while the SiC coating loses 1.37% after 36 hours of oxidation. After 30 thermal shock tests from 1300℃ to room temperature, the weight loss is approximately 0.23%, which is also superior to the SiC coating (weight loss after 30 thermal shocks is approximately 0.87%). The main reason is that the TiO2-embedded Ti-Si-O glass film generated during the oxidation process not only improves the crack healing ability of SiO2 but also enhances the stability of the glass film. Attached Figure Description

[0028] Figure 1XRD patterns of Ti-modified CVD-SiC coating and CVD-SiC coating;

[0029] Figure 2 SEM images of Ti-modified CVD-SiC coating and CVD-SiC coating;

[0030] Figure 3 SEM images of oxidation curves and surface morphology of Ti-modified CVD-SiC coatings at 1300℃;

[0031] Figure 4 Thermal shock curves of Ti-modified CVD-SiC coating and CVD-SiC coating at 1300℃. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0034] The present invention will now be described in further detail with reference to the accompanying drawings:

[0035] This invention discloses a method for preparing a Ti-modified CVD-SiC antioxidant coating, comprising the following steps:

[0036] Step 1: Place the polished and cleaned C / C composite material in the constant temperature zone of a vertical chemical vapor deposition furnace. Use H2 as the reaction gas, Ar as the dilution gas, and methyltrichlorosilane (MTS) as the raw material. Deposit the coating under negative pressure. During the deposition process, process parameters must be strictly controlled to obtain a SiC coating that is easy to react with the Ti source and not easy to fall off.

[0037] Step 2: Weigh out Ti powder, SiC powder and NaCl-KCl mixed powder of appropriate particle size in a certain proportion, place them in a mortar and mix for 30-60 minutes.

[0038] Step 3: Embed the SiC-coated C / C composite material obtained in Step 1 into the above-mentioned mixed powder and place it in an alumina crucible. The alumina crucible should be covered with graphite paper to avoid the introduction of Al impurities. Finally, seal the crucible.

[0039] Step 4: Place the sealed crucible in the constant temperature zone of a tube furnace and perform heat treatment in an Ar environment at atmospheric pressure. After heat treatment, place the sample in deionized water and boil it multiple times at 100-300℃, then dry the sample in a 70℃ oven.

[0040] Preferably, in step 1, the temperature during coating deposition is 1100℃~1300℃, the Ar flow rate is 150~700mL / min, the H2 flow rate is 500~1300mL / min, the MTS flow rate is 0.05~0.3g / min, and the furnace pressure is controlled at 2~8kPa.

[0041] Preferably, in step 2, the molar ratio of the mixed Ti powder and SiC powder to the NaCl-KCl mixed powder is 3:1 to 1:8, the molar ratio of Ti powder to SiC powder is 1:0 to 1:4, and the molar ratio of NaCl to KCl is 2:1 to 1:2. The purity of Ti powder is 99.5% and the particle size is 1 to 10 μm; the purity of SiC powder is 99.5% and the particle size is 1 to 3 μm; and the purity of NaCl and KCl is 99.5%.

[0042] Preferably, in step 3, an alumina crucible is used instead of a graphite crucible to avoid excessive consumption due to reaction between the raw material and the graphite crucible. To avoid the introduction of Al impurities, the crucible should be wrapped with 2-3 layers of graphite paper. When loading the powder into the crucible, it should be sprinkled evenly, avoiding pressing or compaction. The powder thickness around the sample should be no less than 5 mm.

[0043] Preferably, in step 4, the heat treatment temperature is 1100℃~1400℃, the heat treatment time is 0.5~10h, and the Ar flow rate is 30-60mL / min.

[0044] Example 1

[0045] The cleaned and polished C / C composite material was placed in the isothermal zone of a chemical vapor deposition (CVD) furnace. A vacuum of 4 kPa was then applied, followed by pressure holding. If the airtightness was good, the temperature of the isothermal zone was increased to 1200℃ at a heating rate of 5℃ / min, with an Ar flow rate of 200 ml / min. After reaching the set temperature, H2 and MTS were introduced, with an H2 flow rate of 800 ml / min and an MTS flow rate of 0.15 g / min. After deposition, the heating power was turned off, and the sample was allowed to cool down with the furnace, while the Ar flow rate remained at 200 ml / min. After cooling to room temperature, the C / C composite material with a SiC coating, i.e., the CVD-SiC coating, was obtained.

[0046] Approximately 3.5 g of Ti powder (1–10 μm particle size), 1 g of SiC powder, 2.9 g of NaCl, and 3.7 g of KCl were weighed and ground in an agate mortar for 30 min. The SiC-coated C / C composite material was then embedded in the mixed powder in an alumina crucible, which was subsequently sealed. The sealed crucible was placed in the isothermal zone of a horizontal tube furnace and heat-treated at 1100℃ in an Ar environment for 8 h. After the heat treatment, the heating power was turned off, and the sample was cooled with the furnace. The heat-treated sample was then boiled in deionized water at 300℃ until no change in mass was observed, and then dried in a 70℃ oven for 2 h to obtain a Ti-modified CVD-SiC coating with a thickness of approximately 25 μm.

[0047] See Figure 1 The figures show the XRD patterns of the Ti-modified CVD-SiC coating and the CVD-SiC coating prepared in Example 1. As can be seen from the figures, the treated sample surface is bright yellow, while the untreated sample surface is gray. The XRD results show that, in addition to SiC, the treated sample also contains Ti3SiC2 phase and Ti... x Si y The phase indicates that Ti element was successfully introduced into the SiC coating.

[0048] See Figure 2 The images show SEM images of the Ti-modified CVD-SiC coating and the CVD-SiC coating prepared in Example 1. As can be seen from the images, the surface morphology of the samples did not change significantly after treatment. The cross-sectional images show that the total coating thickness did not change significantly, but a Ti-containing phase was formed on the coating surface.

[0049] See Figure 3The images show the oxidation curves and SEM images of the Ti-modified CVD-SiC coating and the CVD-SiC coating prepared in Example 1 at 1300℃. The oxidation curves show that the modified coating can protect against C / C for approximately 300 hours, while the unmodified coating provides protection for less than 60 hours. The surface morphology shows that the unmodified coating has no obvious oxidation marks and contains large-sized cracks, while the modified coating has a large amount of glassy phase, which is beneficial for the healing of surface cracks.

[0050] See Figure 4 The figures show the thermal shock curves of the Ti-modified CVD-SiC coating and the CVD-SiC coating prepared in Example 1 at 1300℃. It can be seen that after 30 thermal shock cycles from 1300℃ to room temperature, the unmodified coating sample lost approximately 0.87% of its weight, while the modified coating sample lost only 0.23%. The coatings exhibit good thermal shock resistance.

[0051] Example 2

[0052] The cleaned and polished C / C composite material was placed in the isothermal zone of a chemical vapor deposition (CVD) furnace. A vacuum of 4 kPa was then applied, followed by pressure holding. If the airtightness was good, the temperature of the isothermal zone was increased to 1150°C at a rate of 5°C / min, with an Ar flow rate of 300 ml / min. After reaching the set temperature, H2 and MTS were introduced, with an H2 flow rate of 1000 ml / min and an MTS flow rate of 0.2 g / min. After deposition, the heating power was turned off, and the sample was allowed to cool down with the furnace, while the Ar flow rate remained at 300 ml / min. After cooling to room temperature, the C / C composite material with a SiC coating was obtained.

[0053] Approximately 3.5 g of Ti powder (1–10 μm particle size), 1 g of SiC powder, 5.8 g of NaCl, and 7.4 g of KCl were weighed and ground in an agate mortar for 30 minutes. The SiC-coated C / C composite material was then embedded in the mixed powder in an alumina crucible, which was subsequently sealed. The sealed crucible was placed in the isothermal zone of a horizontal tube furnace and heat-treated at 1400℃ in an Ar environment for 2 hours. After the heat treatment, the heating power was turned off, and the sample was cooled with the furnace. The heat-treated sample was then boiled in deionized water at 100℃ until no change in mass was observed, and then dried in a 70℃ oven for 2 hours to obtain a Ti-modified CVD-SiC coating with a thickness of approximately 55 μm.

[0054] Example 3

[0055] The cleaned and polished C / C composite material was placed in the isothermal zone of a chemical vapor deposition (CVD) furnace. A vacuum of 4 kPa was then applied, followed by pressure holding. If the airtightness was good, the temperature of the isothermal zone was increased to 1300℃ at a heating rate of 5℃ / min, with an Ar flow rate of 300 ml / min. After reaching the set temperature, H2 and MTS were introduced, with an H2 flow rate of 1000 ml / min and an MTS flow rate of 0.3 g / min. After deposition, the heating power was turned off, and the sample was allowed to cool down with the furnace, while the Ar flow rate remained at 300 ml / min. After cooling to room temperature, the C / C composite material with a SiC coating was obtained.

[0056] Approximately 3.5 g of Ti powder, 2.5 g of SiC powder, 11.6 g of NaCl, and 14.8 g of KCl with a particle size of 1–10 μm were weighed and ground in an agate mortar for 30 min. The SiC-coated C / C composite material was then embedded in the mixed powder in an alumina crucible, which was subsequently sealed. The sealed crucible was placed in the isothermal zone of a horizontal tube furnace and heat-treated at 1100℃ in an Ar environment for 2 h. After the heat treatment, the heating power was turned off, and the sample was cooled with the furnace. The heat-treated sample was then boiled in deionized water at 300℃ until no change in mass was observed, and then dried in a 70℃ oven for 2 h to obtain a Ti-modified CVD-SiC coating with a thickness of approximately 10 μm.

[0057] Example 4

[0058] The cleaned and polished C / C composite material was placed in the isothermal zone of a chemical vapor deposition (CVD) furnace. A vacuum of 4 kPa was then applied, followed by pressure holding. If the airtightness was good, the temperature of the isothermal zone was increased to 1200℃ at a heating rate of 5℃ / min, with an Ar flow rate of 200 ml / min. After reaching the set temperature, H2 and MTS were introduced, with an H2 flow rate of 1000 ml / min and an MTS flow rate of 0.2 g / min. After deposition, the heating power was turned off, and the sample was allowed to cool down with the furnace, while the Ar flow rate remained at 200 ml / min. After cooling to room temperature, the C / C composite material with a SiC coating was obtained.

[0059] Approximately 6g of Ti powder (1–10 μm particle size), 2g of SiC powder, 11.6g of NaCl, and 14.8g of KCl were weighed and ground in an agate mortar for 40 minutes. The SiC-coated C / C composite material was then embedded in the mixed powder in an alumina crucible, which was subsequently sealed. The sealed crucible was placed in the isothermal zone of a vertical tube furnace and heat-treated at 1100℃ in an Ar environment for 6 hours. After the heat treatment, the heating power was turned off, and the sample was cooled with the furnace. The heat-treated sample was then boiled in deionized water at 200℃ until no change in mass was observed, and then dried in a 70℃ oven for 2 hours to obtain a Ti-modified CVD-SiC coating of approximately 20 μm.

[0060] Comparative Example 1

[0061] Unlike Example 1, the heat treatment temperature was 1500°C.

[0062] The cleaned and polished C / C composite material was placed in the isothermal zone of a chemical vapor deposition furnace. A vacuum of 4 kPa was then applied, followed by pressure holding. If the airtightness was good, the temperature of the isothermal zone was increased to 1100℃ at a heating rate of 5℃ / min, with an Ar flow rate of 200 ml / min. After reaching the set temperature, H2 and MTS were introduced, with an H2 flow rate of 1000 ml / min and an MTS flow rate of 0.3 g / min. After deposition, the heating power was turned off, and the sample was allowed to cool down with the furnace, while the Ar flow rate remained at 200 ml / min. After cooling to room temperature, the C / C composite material with a SiC coating was obtained.

[0063] Approximately 3.5 g of Ti powder (1–10 μm particle size), 1 g of SiC powder, 4.4 g of NaCl, and 5.6 g of KCl were weighed and ground in an agate mortar for 30 minutes. The SiC-coated C / C composite material was then embedded in the mixed powder in an alumina crucible, which was subsequently sealed. The sealed crucible was placed in the isothermal zone of a horizontal tube furnace and heat-treated at 1500℃ in an Ar environment for 2 hours. After the heat treatment, the heating power was turned off, and the sample was cooled with the furnace. The heat-treated sample was then boiled in deionized water at 200℃ until no change in mass was observed, and then dried in a 70℃ oven for 2 hours. The resulting Ti-modified CVD-SiC coating was severely eroded, and significant peeling occurred.

[0064] The comparative results show that heat treatment temperature has a significant impact on the coating. Excessive heat treatment temperature may cause severe molten salt corrosion of the coating, and the generated Ti3SiC2 will decompose. Both of these factors will reduce the stability of the coating and eventually lead to the coating peeling off.

[0065] Comparative Example 2

[0066] Unlike Example 1, SiC powder was not introduced into the mixed powder in order to accelerate the reaction rate.

[0067] The cleaned and polished C / C composite material was placed in the isothermal zone of a chemical vapor deposition (CVD) furnace. A vacuum of 4 kPa was then applied, followed by pressure holding. If the airtightness was good, the temperature of the isothermal zone was increased to 1100℃ at a heating rate of 5℃ / min, with an Ar flow rate of 200 ml / min. After reaching the set temperature, H2 and MTS were introduced, with an H2 flow rate of 800 ml / min and an MTS flow rate of 0.2 g / min. After deposition, the heating power was turned off, and the sample was allowed to cool down with the furnace, while the Ar flow rate remained at 200 ml / min. After cooling to room temperature, the C / C composite material with a SiC coating was obtained.

[0068] Approximately 3.5 g of Ti powder (3–5 μm particle size), 2.9 g of NaCl, and 3.7 g of KCl were weighed and ground in an agate mortar for 30 minutes. The SiC-coated C / C composite material was then embedded in the mixed powder in an alumina crucible, which was subsequently sealed. The sealed crucible was placed in the isothermal zone of a horizontal tube furnace and heat-treated at 1100℃ in an Ar environment for 2 hours. After the heat treatment, the heating power was turned off, and the sample was allowed to cool down with the furnace. It can be seen that due to severe sintering of the Ti powder, the sample could not be effectively removed, and the surface coating of the sample was severely damaged.

[0069] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a Ti-modified CVD-SiC antioxidant coating, characterized in that, include: First, a SiC coating was prepared on the surface of the C / C composite material by chemical vapor deposition. Then, Ti element was introduced into the SiC coating by low-temperature heat treatment at 1100 ℃~1400 ℃ using molten salt reaction, and a Ti-Si-C layer was formed in situ to obtain a Ti-modified CVD-SiC antioxidant coating. The specific method includes the following steps: 1) Preparation of C / C composite materials containing SiC coating; 2) Weigh out Ti powder, SiC powder, and NaCl-KCl mixed powder in a certain proportion, grind them thoroughly and evenly to obtain a mixed powder; the molar ratio of Ti powder to SiC powder mixed powder and NaCl-KCl mixed powder is 3:1~1:8; the molar ratio of Ti powder to SiC powder is 1:0~1:4; the molar ratio of NaCl to KCl in NaCl-KCl mixed powder is 2:1~1:2; the grinding time is 30~60 min. The purity of Ti powder is 99.5%, and the particle size is 1~10 μm; the purity of SiC powder is 99.5%, and the particle size is 1~3 μm; the purity of NaCl and KCl is 99.5%. 3) The C / C composite material containing the SiC coating is embedded in the mixed powder and then placed in a crucible for sealing treatment; 4) The sample treated in step 3) was heat-treated in an Ar environment at 1100 ℃~1400 ℃ for 0.5~10 h. After the treatment, it was washed and dried to obtain the Ti modified CVD-SiC antioxidant coating.

2. The method for preparing the Ti-modified CVD-SiC antioxidant coating according to claim 1, characterized in that, In step 1), H2 is used as the reaction gas, Ar is used as the dilution gas, and methyltrichlorosilane is used as the raw material. A SiC coating is deposited on the surface of the C / C composite material under negative pressure.

3. The method for preparing the Ti-modified CVD-SiC antioxidant coating according to claim 2, characterized in that, During the coating deposition process, the temperature was 1100 ℃~1300 ℃, the Ar flow rate was 150~700 mL / min, the H2 flow rate was 500~1300 mL / min, the methyltrichlorosilane flow rate was 0.05~0.3 g / min, and the reaction pressure was controlled at 2~8 kPa.

4. The method for preparing the Ti-modified CVD-SiC antioxidant coating according to claim 1, characterized in that, In step 3), an alumina crucible is used, and the reaction powder is wrapped with 2 to 3 layers of graphite paper. The powder thickness around the C / C composite material containing the SiC coating should be no less than 5 mm.

5. The method for preparing the Ti-modified CVD-SiC antioxidant coating according to claim 1, characterized in that, In step 4), the sealed crucible is placed in the constant temperature zone of a tube furnace and heat-treated in an environment with atmospheric pressure and an Ar flow rate of 30-60 mL / min. Washing involves placing the heat-treated test specimen in water and boiling it multiple times at 100-300°C. Drying involves drying it at 60-75°C.

6. A Ti-modified CVD-SiC antioxidant coating prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The antioxidant coating comprises a two-layer structure: an inner uniform and dense SiC layer and an outer uniform Ti-Si-C layer; the thickness of the Ti-Si-C layer can be adjusted by controlling the reaction temperature and reaction time.

7. The Ti-modified CVD-SiC antioxidant coating as described in claim 6, characterized in that, The antioxidant coating gained 0.35% weight after being oxidized in static air at 1300℃ for 300 hours, and lost 0.23% weight after 30 thermal shock tests from 1300℃ to room temperature.

8. The application of the Ti-modified CVD-SiC antioxidant coating as described in claim 6 or 7 in the preparation of thermal structural components for aircraft.

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