A method for preparing a SiC coating

Abstract

The present invention relates to the technical field of semiconductor material preparation, and provides a method for preparing a SiC coating. The preparation method deposits two SiC coatings, namely an inner SiC coating and an outer SiC coating, on the surface of a substrate by chemical vapor deposition twice, and regulates the grain size of the deposited SiC by adjusting the deposition temperature, deposition pressure and precursor flow ratio in the chemical vapor deposition process, so that the grain size of the inner SiC coating is small and the grain size of the outer SiC coating is large, thereby enabling the inner SiC coating to have a better bonding force with the substrate, the outer SiC coating to have higher densification and better uniformity, making the grain sizes of the inner and outer SiC coatings show a gradient distribution, improving the oxidation and ablation resistance and bonding strength of the SiC coating, reducing the risk of cracking and peeling of the SiC coating, and increasing the service life of the SiC coating.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor material preparation, and specifically relates to a method for preparing a SiC coating. Background Art

[0002] Carbon / carbon composites have the advantages of low density, high strength, high specific modulus, high thermal conductivity, low coefficient of thermal expansion, good friction performance, good thermal shock resistance, and high dimensional stability. They are widely used as high-temperature materials in the fields of aviation, aerospace, metallurgy, nuclear energy, solar energy, etc. However, the performance of carbon / carbon composites deteriorates rapidly in an oxygen-containing atmosphere above 350°C, and their ability to resist the erosion of reactive gases is weak. Due to oxidation weight loss, the mechanical properties of C / C composites will decrease significantly, which greatly limits their application as high-temperature refractory materials in an oxidizing atmosphere. Solving the problem of high-temperature oxidation protection has become the key to making full use of C / C composites.

[0003] Antioxidant coatings are currently an effective method commonly used to solve the problem of high-temperature oxidation protection. Since silicon carbide ceramic materials have good physical and chemical compatibility with C / C composites, they are generally used as coating materials in contact with the C / C composite matrix. In order to obtain a uniform and dense silicon carbide coating, the grain size of the existing silicon carbide coating prepared by the embedding method is relatively large, about 20 - 100 μm, and the particles grow in a tangential or cross-intersecting manner. The pores between the grains are relatively large, and the silicon carbide coating is prone to cracking and peeling, thus affecting the effect of high-temperature oxidation protection. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above problems existing in the prior art, and provide a method for preparing a SiC coating, so that the grain sizes of the inner and outer SiC coatings are distributed in a gradient manner (smaller in the inner layer and larger in the outer layer), improving the antioxidant ablation ability and bonding strength of the SiC coating, reducing the risk of cracking and peeling of the SiC coating, and increasing the service life of the SiC coating.

[0005] To achieve the above purpose, the present invention provides a method for preparing a SiC coating, including the following steps:

[0006] (1) After pre-treating the substrate, place it in a chemical vapor deposition device, heat and evacuate the chemical vapor deposition device, and then replace the air in the chemical vapor deposition device with an inert gas;

[0007] (2) Introduce the mixed gas of the first silicon carbide source gas, the first carrier gas, and the first dilution gas into the chemical vapor deposition equipment, and perform the first deposition on the surface of the substrate by chemical vapor deposition to obtain a SiC inner coating; the process parameters of the first deposition include: the first deposition temperature is 1000°C - 1400°C, the first deposition pressure is 10 Kpa - 20 Kpa, the first deposition time is 1 h - 8 h, and the flow ratio of the first silicon carbide source gas to the first carrier gas is 1:(4 - 8);

[0008] (3) Introduce the mixed gas of the second silicon carbide source gas, the second carrier gas, and the second dilution gas into the chemical vapor deposition equipment, and perform the second deposition on the surface of the SiC inner coating by chemical vapor deposition to obtain a SiC outer coating; the process parameters of the second deposition include: the second deposition temperature is 1100°C - 1500°C, the second deposition pressure is 5 Kpa - 16 Kpa, the second deposition time is 1 h - 5 h, and the flow ratio of the second silicon carbide source gas to the second carrier gas is 1:(8 - 10);

[0009] Among them, the SiC grain size in the SiC inner coating is 0.5 μm - 2 μm;

[0010] The SiC grain size in the SiC outer coating is 10 μm - 50 μm.

[0011] The research of the present invention finds that by depositing two SiC coatings, namely the SiC inner coating and the SiC outer coating, on the surface of the substrate through two chemical vapor depositions, and by adjusting the deposition temperature, deposition pressure, and precursor flow ratio (the flow ratio of the silicon carbide source gas to the carrier gas) in the chemical vapor deposition process to control the SiC grain size of the deposition, the SiC inner coating has a small grain size and the SiC outer coating has a large grain size, so that the SiC inner coating has a better bonding force with the substrate, the SiC outer coating has higher densification and better uniformity, the SiC grain sizes of the inner and outer coatings show a gradient distribution (smaller in the inner layer and larger in the outer layer), improving the oxidation ablation resistance and bonding strength of the SiC coating, reducing the risk of cracking and peeling of the SiC coating, and increasing the service life of the SiC coating.

[0012] To more clearly explain the solution of the present invention, each step will be explained one by one below.

[0013] Step (1)

[0014] Chemical vapor deposition (CVD) is a process in which gaseous or vaporous substances react on the gas phase or gas-solid interface to form solid deposits. Optional chemical vapor deposition equipment includes high-temperature deposition furnaces, hot-wall reactors, low-pressure chemical vapor deposition equipment, vapor phase epitaxy equipment, metalorganic chemical vapor deposition equipment, plasma-enhanced chemical vapor deposition equipment, etc.

[0015] In the present invention, the substrate pretreatment includes grinding, ultrasonic cleaning and drying of the substrate. Among them, grinding can be carried out with sandpaper to a roughness between 1 μm and 2 μm, which is beneficial to the bonding between the substrate and the SiC inner coating and improves the bonding strength between the substrate and the SiC inner coating.

[0016] In the present invention, the substrate is a carbon-based material and / or a carbon-silicon-based composite material.

[0017] In the present invention, the substrate includes at least one of graphite, C f / C, C f / SiC, SiC f / C, and the substrate is more preferably a graphite substrate. As a reactor material, the graphite substrate can withstand high temperatures and chemical corrosion and has low chemical reaction activity.

[0018] In the present invention, the chemical vapor deposition equipment is heated and evacuated. Specific operations are, for example, starting the heating system of the chemical vapor deposition equipment to heat the inside of the chemical vapor deposition equipment, and at the same time continuing to evacuate the deposition furnace until the temperature in the deposition furnace reaches 1100°C - 1500°C and the vacuum is pumped to 10 Pa - 800 Pa.

[0019] In the present invention, the inert gas refers to a gas with stable chemical properties that does not participate in chemical reactions, such as argon. The inert gas is circulated and introduced multiple times to ensure complete replacement of the air in the chemical vapor deposition equipment and avoid residual air affecting the chemical vapor deposition of the SiC coating.

[0020] Step (2)

[0021] Step (2) is a process step of performing the first deposition on the surface of the substrate to obtain a SiC inner coating.

[0022] In the present invention, the "carbon-silicon source gas" refers to a gas that can provide carbon and silicon elements, that is, the raw material gas for providing the precursor for preparing SiC.

[0023] In the present invention, the first silicon-carbon source gas is selected from at least one of trichloromethylsilane, trichlorosilane and tetrachlorosilane, and trichloromethylsilane is preferred.

[0024] In the present invention, the first carrier gas is hydrogen.

[0025] In the present invention, the first dilution gas is selected from at least one of argon and nitrogen, and argon is preferred. The delivery flow rate of the first dilution gas is 1 - 100 L / min.

[0026] In the present invention, the first deposition temperature is 1000°C - 1400°C, and for example, it can be 1000°C, 1100°C, 1200°C, 1300°C, 1400°C. When the deposition temperature is within the above range, it can promote the growth of silicon carbide crystals, make the grain size smaller, and the silicon carbide crystal structure more dense.

[0027] In the present invention, the first deposition pressure is 10 KPa - 20 KPa, and for example, it can be 10 KPa, 12 KPa, 14 KPa, 16 KPa, 18 KPa, 20 KPa. When the deposition pressure is within the above range, it can increase the deposition rate, improve the quality and uniformity of SiC, avoid high production costs caused by excessive deposition pressure, and at the same time avoid low SiC density and slow deposition rate caused by too low deposition pressure.

[0028] In the present invention, the first deposition time is not limited and can be adjusted according to the thickness of the SiC inner coating. For example, the first deposition time is 1 h - 8 h.

[0029] In the present invention, the flow rate ratio of the first silicon carbide source gas to the first carrier gas is 1:(4 - 8), and for example, it can be 1:4, 1:5, 1:6, 1:7, 1:8. When the flow rate ratio of the first silicon carbide source gas to the first carrier gas is within the above range, a coating with smaller SiC grain size can be obtained.

[0030] In the present invention, in the step (2), the delivery flow rate of the first silicon carbide source gas is 1 L / min - 80 L / min, and the delivery flow rate of the first carrier gas is 1 L / min - 180 L / min.

[0031] In the present invention, the SiC grain size in the SiC inner coating is 0.5 μm - 2 μm, making the SiC inner coating more dense and uniform, and improving the bonding force between the SiC inner coating and the substrate.

[0032] In the present invention, the SiC grain size is tested by EBSD (electron backscatter diffraction), and EBSD is a test method used to study the crystal structure and crystal orientation of materials.

[0033] Step (3)

[0034] Step (3) is a process step of performing a second deposition on the surface of the SiC inner coating of the substrate to obtain a SiC outer coating.

[0035] In the present invention, the second silicon carbide source gas is selected from at least one of trichloromethylsilane, trichlorosilane, and tetrachlorosilane, and preferably trichloromethylsilane.

[0036] In the present invention, the second carrier gas is hydrogen.

[0037] In the present invention, the second dilution gas is selected from at least one of argon and nitrogen, preferably argon. The delivery flow rate of the second dilution gas is 1 - 100 L / min.

[0038] In the present invention, the second deposition temperature is 1100°C - 1500°C, and for example, it can be 1100°C, 1200°C, 1300°C, 1400°C, 1500°C. When the deposition temperature is within the above range, the growth of silicon carbide crystals can be promoted, making the grain size of the outer coating larger than that of the inner coating, and improving the densification and uniformity of the silicon carbide outer coating.

[0039] In the present invention, the second deposition pressure is 5 Kpa - 16 Kpa, and for example, it can be 5 Kpa, 8 Kpa, 10 Kpa, 12 Kpa, 14 Kpa, 16 Kpa. When the second deposition pressure is within the above range, the deposition rate can be increased, and the quality and uniformity of SiC can be improved.

[0040] In the present invention, the second deposition time is not limited and can be adjusted according to the thickness of the SiC inner coating. For example, the second deposition time is 1 h - 5 h.

[0041] In the present invention, the flow rate ratio of the second silicon carbide source gas to the second carrier gas is 1:(8 - 10), and for example, it can be 1:8, 1:8.5, 1:9, 1:9.5, 1:10. When the flow rate ratio of the carbon silicon source gas to the second carrier gas is within the above range, the formation of the silicon carbide outer coating can be well promoted, making the grain size of the outer coating larger than that of the inner coating.

[0042] In the present invention, in the step (3), the delivery flow rate of the second silicon carbide source gas is 20 L / min - 100 L / min, and the delivery flow rate of the second carrier gas is 10 L / min - 200 L / min.

[0043] In the present invention, the second deposition temperature is 50°C - 100°C higher than the first deposition temperature, that is, the value of the second deposition temperature is larger than that of the first deposition temperature, and the difference between the second deposition temperature and the first deposition temperature can be 50°C - 100°C. For example, the difference can be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C. If the temperature difference is too small, the crystal form difference between the first deposition and the second deposition will be too small, and the matrix cannot be effectively filled and covered; if the temperature difference is too large, there will be a large stress between the SiC inner coating and the SiC outer coating during use, which is likely to cause the coating to fall off.

[0044] In the present invention, the second deposition pressure is 3 Kpa - 6 Kpa less than the first deposition pressure, that is, the value of the second deposition pressure is smaller than that of the first deposition pressure, and the difference between the first deposition pressure and the second deposition pressure can be 3 Kpa - 6 Kpa. For example, it can be 3 Kpa, 3.5 Kpa, 4 Kpa, 4.5 Kpa, 5 Kpa, 5.5 Kpa, 6 Kpa.

[0045] During the second deposition process for preparing the SiC outer coating, increasing the deposition temperature, decreasing the deposition pressure, and increasing the gas flow rate can make the grain size of the outer coating larger than that of the inner coating.

[0046] In the present invention, the SiC grain size in the SiC outer coating is 10 μm - 50 μm.

[0047] In the present invention, the SiC inner coating further includes nano SiC grains with a grain size of 500 nm - 1000 nm.

[0048] The present invention studies and finds that by adjusting the process parameters during the first deposition to control the SiC grain size and promote the formation of nano fine grains (nano SiC grains), the surface gaps of the substrate can be effectively covered, and the bonding force between the SiC inner coating and the substrate can be increased. Then, by regulating the process parameters of the second deposition to control the grain size, the SiC outer coating can have higher densification and uniformity, play a role in linking and fixing during the crack propagation process, fully absorb the energy at the crack tip, and effectively inhibit the unstable propagation of cracks. It can effectively solve the problems of the SiC coating being non-dense, easy to crack, and easy to fall off caused by the traditional embedding method and single deposition, and extend the service life of the coating.

[0049] In the present invention, in the SiC inner coating, the area ratio of the nano SiC grains is 3 - 30%, for example, the ratio can be 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%. In the present invention, the area ratio of the nano SiC grains refers to the ratio of the total area of the nano SiC grains to the total area of all SiC grains in the SiC inner coating. The test method for the area ratio of the nano SiC grains includes: in the electron microscope image at 500 times magnification, select three fields of view with a size of 20 μm * 20 μm, calculate the area ratio of the nano SiC grains respectively, and take the average value.

[0050] The present invention studies and finds that by adjusting the process parameters during the first deposition and controlling the area ratio of the nano SiC grains within the above range, the surface gaps of the substrate can be covered more effectively, the bonding force between the SiC inner coating and the substrate can be increased, and further the risk of the SiC coating being easy to crack and fall off can be reduced.

[0051] In the present invention, the step (2) further includes a step of treating the surface of the SiC inner coating: grinding and cleaning the substrate after the first deposition. Specifically, diamond or silicon carbide can be selected for grinding, or other grinding processes in the art can be selected for grinding, ensuring that there are no obvious particles on the surface of the substrate after the first deposition (i.e., the surface of the SiC inner coating), and it does not affect the second deposition of the SiC outer coating. The cleaning can include steps of pickling, water washing and drying. The pickling solution can be selected from conventional organic acids and / or inorganic acids in the art to remove surface impurities.

[0052] In order to further increase the bonding strength and service life of the SiC coating, the present invention also provides a technical solution for preparing a multi-layer silicon carbide inner coating, which is introduced in detail as follows:

[0053] In some embodiments, the silicon carbide inner coating includes a first silicon carbide inner coating, a second silicon carbide inner coating and a third silicon carbide inner coating, and the carbon content of the silicon carbide inner coating gradually decreases along the deposition direction of the silicon carbide inner coating.

[0054] In some embodiments, in the first silicon carbide inner coating, the C / Si molar ratio is (1.45 - 1.55):1, for example, it can be 1.45:1, 1.48:1, 1.5:1, 1.52:1, 1.55:1, and preferably 1.5:1.

[0055] In some embodiments, in the second silicon carbide inner coating, the C / Si molar ratio is (1.25 - 1.35):1, for example, it can be 1.25:1, 1.28:1, 1.3:1, 1.32:1, 1.35:1, and preferably 1.3:1.

[0056] In some embodiments, in the third silicon carbide inner coating, the C / Si molar ratio is (1.05 - 1.15):1, for example, it can be 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.15:1, and preferably 1.1:1.

[0057] When three layers of inner coatings are provided, controlling the C / Si molar ratio of each inner coating within the above range can better improve the bonding strength between the silicon carbide composite coating and the substrate and reduce the risk of coating cracking and detachment.

[0058] In some embodiments, adjust the flow ratio of the first silicon carbide source gas and the first carrier gas to 1:(4 - 4.5) to obtain the first silicon carbide inner coating;

[0059] In some embodiments, adjust the flow ratio of the first silicon carbide source gas and the first carrier gas to 1:(5 - 6.5) to obtain the second silicon carbide inner coating;

[0060] In some embodiments, the flow rate ratio of the first silicon carbide source gas to the first carrier gas is adjusted to 1:(7.5 - 8) to obtain a third silicon carbide inner coating.

[0061] When preparing different silicon carbide inner coatings, the flow rate ratio of the first silicon carbide source gas to the first carrier gas is adjusted within different ranges, thereby obtaining silicon carbide inner coatings with different C / Si molar ratios.

[0062] The present invention adopts the above technical solutions and has the following beneficial effects:

[0063] (1) The method for preparing the SiC coating provided by the present invention improves the oxidation and ablation resistance and bonding strength of the SiC coating, reduces the risk of cracking and peeling of the SiC coating, and improves the service life of the SiC coating.

[0064] (2) The method for preparing the SiC coating provided by the present invention has a relatively small difference in the thermal expansion coefficient between the gradient-distributed silicon carbide inner coating and the substrate, increasing the bonding ability between the SiC coating and the substrate.

[0065] (3) The method for preparing the SiC coating provided by the present invention is simple, easy to operate, can be produced without complex equipment and harsh conditions, and is suitable for large-scale industrial production.

[0066] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values between each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In this article, unless otherwise specified, data ranges include endpoints. Description of the Drawings

[0067] Figure 1 The SEM image of the SiC inner coating in Example 1 of the present invention is shown.

[0068] Figure 2 The SEM image of the SiC outer coating in Example 1 of the present invention is shown.

[0069] Figure 3 The SEM image of the cross-section of the SiC coating in Example 1 is shown. Detailed Embodiments

[0070] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0071] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as those commonly understood by those skilled in the technical field to which the present invention pertains.

[0072] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0073] The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels without special instructions.

[0074] The present invention will be described in detail below in combination with specific embodiments, and these embodiments are for understanding rather than limiting the present invention.

[0075] Example 1

[0076] A method for preparing a SiC coating includes the following steps:

[0077] (1) The graphite substrate is polished with sandpaper until the surface roughness is between 1 and 2, ultrasonically cleaned and dried; then the pretreated substrate is placed in a deposition furnace; the heating system of the deposition furnace is started to heat the inside of the furnace, and at the same time, the inside of the deposition furnace is continuously evacuated until the temperature inside the deposition furnace reaches 1000°C - 1400°C, then held for a certain period of time. After the temperature zone is stable, argon is filled to make the pressure inside the deposition furnace reach a certain value, and at the same time, the turntable is started to drive the graphite substrate to rotate; then argon is continuously filled; such cyclic operations are performed multiple times to displace the air inside the deposition furnace with argon;

[0078] (2) The first deposition to prepare the SiC inner coating: Trichloromethylsilane (the first silicon carbide source gas), hydrogen (the first carrier gas), and argon (the first dilution gas) are simultaneously introduced into a heating box to form a mixed gas. The heating box preheats the mixed gas to fully vaporize it and mix it fully with the mixed gas, and then the mixed gas with trichloromethylsilane is introduced into the deposition furnace; the flow rate ratio of trichloromethylsilane to hydrogen is 1:8; after the deposition furnace is heated to 1300°C at a rate of 2 - 10°C / min, the deposition pressure is 15 Kpa. After depositing for 4 h, H2 and MTS are turned off to obtain the SiC inner coating;

[0079] (3) The Ar flow rate is adjusted to 50 L / min, and the deposition furnace is cleaned and maintained for 1 - 2 h; the temperature is lowered and then the inside of the deposition furnace is inflated. After the pressure reaches atmospheric pressure, the furnace body is opened; after taking out the product, the surface of the substrate after the first deposition is polished, pickled, washed with water and dried with a silicon carbide grinding block to ensure that there are no obvious particles on the surface affecting the secondary deposition of the outer coating;

[0080] (4) Preparation of SiC outer coating by secondary deposition: Repeat the steps of (5), adjust the flow ratio and deposition temperature. The flow ratio of trichloromethylsilane to hydrogen is 1:9. After the deposition furnace is heated to 1350 °C at a rate of 2 - 10 °C / min, the deposition pressure is 12 Kpa. After depositing for 4 h, turn off H2 and MTS to obtain a dense SiC outer coating.

[0081] (5) After a certain deposition time, keep the delivery of argon and hydrogen, flush the by-products in the deposition furnace and cool down the deposition furnace through a water cooling device. Then, inflate the deposition furnace. After the pressure reaches atmospheric pressure, open the furnace body and take out the product.

[0082] The product prepared in Example 1 was observed by a scanning electron microscope (SEM, Scanning Electronic Microscopy), as Figure 1 is the SEM image of the SiC inner coating, Figure 2 is the SEM image of the SiC outer coating, Figure 3 is the SEM image of the cross-section of the SiC coating. Among them, the horizontal line indicated by the arrow is the boundary between the SiC inner coating and the SiC outer coating. Among them, the grain structures of both the SiC inner coating and the SiC outer coating are tetrahedral SiC crystals, and the crystal form is β-SiC.

[0083] Example 2

[0084] Refer to Example 1, the difference is to adjust the process parameters of the first deposition and the second deposition:

[0085] In step (2), for the first deposition to prepare the SiC inner coating: the flow ratio of trichloromethylsilane to hydrogen is 1:4. After the deposition furnace is heated to 1000 °C at a rate of 2 - 10 °C / min, the deposition pressure is 10 Kpa;

[0086] In step (4), for the second deposition to prepare the SiC outer coating: the flow ratio of trichloromethylsilane to hydrogen is 1:8. After the deposition furnace is heated to 1100 °C at a rate of 2 - 10 °C / min, the deposition pressure is 5 Kpa.

[0087] Example 3

[0088] Refer to Example 1, the difference is to adjust the process parameters of the first deposition and the second deposition:

[0089] In step (2), for the first deposition to prepare the SiC inner coating: the flow ratio of trichloromethylsilane to hydrogen is 1:8. After the deposition furnace is heated to 1400 °C at a rate of 2 - 10 °C / min, the deposition pressure is 20 Kpa;

[0090] In step (4), the SiC outer coating is prepared by the second deposition: the flow rate ratio of trichloromethylsilane to hydrogen is 1:10; after the deposition furnace is heated to 1500 °C at a rate of 2-10 °C / min, the deposition pressure is 16 Kpa.

[0091] Example group 4

[0092] This group of examples is used to illustrate the influence of the change of the second deposition temperature, which causes the difference between the second deposition temperature and the first deposition temperature, on the performance of the silicon carbide coating.

[0093] Example 4a: Conducted with reference to Example 1, the difference is that the second deposition temperature is 1380 °C, and the second deposition temperature is 80 °C higher than the first deposition temperature;

[0094] Example 4b: Conducted with reference to Example 1, the difference is that the second deposition temperature is 1400 °C, and the second deposition temperature is 100 °C higher than the first deposition temperature;

[0095] Example 4c: Conducted with reference to Example 1, the difference is that the second deposition temperature is 1330 °C, and the second deposition temperature is 30 °C higher than the first deposition temperature;

[0096] Example 4d: Conducted with reference to Example 1, the difference is that the second deposition temperature is 1500 °C, and the second deposition temperature is 200 °C higher than the first deposition temperature.

[0097] Example group 5

[0098] This group of examples is used to illustrate the influence of the change of the second deposition pressure, which causes the difference between the second deposition pressure and the first deposition pressure, on the performance of the silicon carbide coating.

[0099] Example 5a: Conducted with reference to Example 1, the difference is that the second deposition pressure is 9 Kpa, and the second deposition pressure is 6 Kpa lower than the first deposition pressure;

[0100] Example 5b: Conducted with reference to Example 1, the difference is that the second deposition pressure is 15 Kpa, and the second deposition pressure is the same as the first deposition pressure;

[0101] Example 5c: Conducted with reference to Example 1, the difference is that the second deposition pressure is 7 Kpa, and the second deposition pressure is 8 Kpa lower than the first deposition pressure.

[0102] Example 6

[0103] Conducted with reference to Example 1, the difference is that for the preparation of the SiC inner coating by the first deposition: the deposition temperature is 1450 °C and the deposition pressure is 17 Kpa.

[0104] Example 7

[0105] It is carried out with reference to Example 1, except that in step (2), three layers of SiC inner coating are provided:

[0106] The flow rate ratio of MTS to H2 is 1:4, and the feeding time is 1 h to obtain the first silicon carbide inner coating, and the C / Si molar ratio is about 1.5:1;

[0107] The flow rate ratio of MTS to H2 is 1:6, and the feeding time is 1 h to obtain the second silicon carbide inner coating, and the C / Si molar ratio is about 1.3:1;

[0108] The flow rate ratio of MTS to H2 is 1:8, and the feeding time is 2 h to obtain the third silicon carbide inner coating, and the C / Si molar ratio is about 1.1:1.

[0109] Comparative Example 1

[0110] It is carried out with reference to Example 3, except that the second deposition to prepare the SiC outer coating is not carried out.

[0111] Comparative Example 2

[0112] It is carried out with reference to Example 3, except that the process parameters of the first deposition are used for both the first deposition and the second deposition.

[0113] Comparative Example 3

[0114] It is carried out with reference to Example 2, except that the process parameters of the second deposition are used for both the first deposition and the second deposition.

[0115] The silicon carbide materials in the above examples and comparative examples are subjected to relevant performance tests, and the test methods are described as follows:

[0116] (1) Test the grain size of the silicon carbide material

[0117] The test is carried out by EBSD (electron backscatter diffraction), and the test results are recorded in Table 1.

[0118] (2) Area ratio of nanograins

[0119] In the electron microscope images at 500 times magnification, the area ratios of nano-SiC grains are calculated respectively in three fields of view with a size of 20 μm * 20 μm, and the average value is taken.

[0120] (3) Test the bonding strength of the SiC coating

[0121] Referring to the standard GB / T 31541-2015 "Test method for interfacial tensile and shear bond strength of fine ceramics - Cross-cross method", a universal testing machine is used to measure the bonding strength between the substrate and the coating interface, including the following steps:

[0122] Measure the width and thickness of the sample, and place the sample on a fixture with a span of 4 mm; turn on the software and connect it to the machine, select the test method as bending strength, and set the speed to 0.5 mm / min; input the width and thickness of the sample, zero all of the force, displacement, time, and speed, and click Start; combine with the strength calculation formula: In the formula: Rm—bonding strength; FM—maximum load; A—cross-sectional area.

[0123] (4) Oxidation resistance performance test

[0124] Keep the silicon carbide product in a muffle furnace at 800 °C for 4 h, take it out and air-cool it, wait for it to cool down and then weigh it, record the weight loss of the sample to evaluate the oxidation resistance performance of the product, repeat the above steps 12 times, oxidation weight loss rate = (weight of the product before ablation - weight of the product after ablation) / weight of the product before ablation * ‰, take the average value, the smaller the weight loss rate of the sample, the better the oxidation resistance performance.

[0125] Table 1

[0126]

[0127]

[0128] “ / ” indicates not tested.

[0129] It can be seen from the results in Table 1 that the present invention regulates the SiC grain size of the deposition by adjusting the deposition temperature, deposition pressure, and precursor flow ratio in the chemical vapor deposition process, so that the grain size of the SiC inner coating is small and the grain size of the SiC outer coating is large (the grain size shows a gradient distribution), making the bonding force between the SiC inner coating and the substrate better, the compactness of the SiC outer coating higher, and the uniformity better, improving the oxidation and ablation resistance ability and bonding strength of the SiC coating, reducing the risk of cracking and peeling of the SiC coating, and increasing the service life of the SiC coating.

[0130] In addition, the SiC inner coating is set to three SiC inner coatings with different C / Si molar ratios, which can better improve the bonding force between the silicon carbide composite coating and the substrate and reduce the risk of coating cracking and detachment.

[0131] It should be noted that in this text, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent in such a process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including that element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. Additionally, the features described with reference to certain examples may be combined in other examples.

[0132] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a SiC coating, characterized in that, It includes the following steps: (1) After pre-treating the substrate, place it in a chemical vapor deposition device, heat and evacuate the chemical vapor deposition device, and then replace the air in the chemical vapor deposition device with an inert gas; (2) Introduce a mixed gas of a first silicon carbide source gas, a first carrier gas, and a first dilution gas into the chemical vapor deposition device, and perform a first deposition on the surface of the substrate by chemical vapor deposition process to obtain a SiC inner coating; The process parameters of the first deposition include: the first deposition temperature is 1000°C - 1400°C, the first deposition pressure is 10Kpa - 20Kpa, the first deposition time is 1h - 8h, and the flow rate ratio of the first silicon carbide source gas to the first carrier gas is 1:(4 - 8); (3) Introduce a mixed gas of a second silicon carbide source gas, a second carrier gas, and a second dilution gas into the chemical vapor deposition device, and perform a second deposition on the surface of the SiC inner coating by chemical vapor deposition process to obtain a SiC outer coating; The process parameters of the second deposition include: the second deposition temperature is 1100°C - 1500°C, the second deposition pressure is 5Kpa - 16Kpa, the second deposition time is 1h - 5h, and the flow rate ratio of the second silicon carbide source gas to the second carrier gas is 1:(8 - 10); Among them, the SiC grain size in the SiC inner coating is 0.5μm - 2μm; The SiC grain size in the SiC outer coating is 10μm - 50μm; The SiC inner coating further includes nano-SiC grains with a grain size of 500nm - 1000nm; In the SiC inner coating, the area ratio of the nano-SiC grains is 3 - 30%; The second deposition temperature is 50°C - 100°C higher than the first deposition temperature; The second deposition pressure is 3Kpa - 6Kpa lower than the first deposition pressure.

2. The method according to claim 1, characterized in that, The first silicon carbide source gas and the second silicon carbide source gas are independently selected from at least one of trichloromethylsilane, trichlorosilane, and tetrachlorosilane; And / or, the first carrier gas and the second carrier gas are independently selected from hydrogen.

3. The method according to claim 1, wherein The first dilution gas and the second dilution gas are each independently selected from at least one of argon and nitrogen.

4. The method according to claim 1, wherein In the step (2), the delivery flow rate of the first silicon carbide source gas is 1L / min - 80L / min, and the delivery flow rate of the first carrier gas is 1L / min - 180L / min; And / or, in the step (3), the delivery flow rate of the second silicon carbide source gas is 20L / min - 100L / min, and the delivery flow rate of the second carrier gas is 10L / min - 200L / min.

5. The method according to claim 1, characterized in that, The silicon carbide inner coating includes a first silicon carbide inner coating, a second silicon carbide inner coating, and a third silicon carbide inner coating, and the carbon content of the silicon carbide inner coating gradually decreases along the deposition direction of the silicon carbide inner coating; And / or, in the first silicon carbide inner coating, the C / Si molar ratio is (1.45 - 1.55):1; And / or, in the second silicon carbide inner coating, the C / Si molar ratio is (1.25 - 1.35):1; And / or, in the third silicon carbide inner coating, the C / Si molar ratio is (1.05 - 1.15):

1.

6. The method according to claim 5, wherein Adjust the flow rate ratio of the first silicon carbide source gas and the first carrier gas to 1:(4 - 4.5) to obtain the first silicon carbide inner coating; And / or, adjust the flow rate ratio of the first silicon carbide source gas and the first carrier gas to 1:(5 - 6.5) to obtain the second silicon carbide inner coating; And / or, adjust the flow rate ratio of the first silicon carbide source gas and the first carrier gas to 1:(7.5 - 8) to obtain the third silicon carbide inner coating.

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