Silicon carbide coating and its preparation method

Abstract

The present invention relates to a silicon carbide coating and a preparation method thereof. The preparation method comprises the following steps: performing chemical vapor deposition treatment on a substrate to form a silicon carbide coating; wherein, the chemical vapor deposition treatment includes a low-temperature nucleation stage, a medium-temperature growth stage, and a high-temperature growth stage that are carried out in sequence, and the gas sources used in the chemical vapor deposition treatment include a dilution gas, hydrogen, and an organosilicon source gas; the deposition temperature in the low-temperature nucleation stage is 600°C to 800°C; the deposition temperature in the medium-temperature growth stage is 1000°C to 1300°C; the deposition temperature in the high-temperature growth stage is 1350°C to 1500°C. A stepped heating mode is presented between the above-mentioned stages, and the chemical vapor deposition method under the stepped heating conditions reduces the phenomenon of local overheating or condensation of silicon carbide crystals, effectively inhibits the generation of internal stress in the coating, reduces the formation of microcracks and voids, improves the denseness of the coating, and further improves the mechanical properties of the silicon carbide coating.

Description

Technical Field

[0001] The present invention relates to the technical field of materials, and particularly to a silicon carbide coating and a preparation method thereof. Background Art

[0002] Silicon carbide (SiC) materials have been widely used in semiconductor devices such as high temperature, high frequency, high voltage and high power due to their excellent physical and chemical properties and thermodynamic stability.

[0003] Chemical vapor deposition (CVD) is a commonly used surface modification technology for depositing high-quality thin films or coatings on various substrates, such as the preparation of silicon carbide coatings. However, the silicon carbide coatings prepared by the CVD method at present still have problems such as easy occurrence of stress concentration and formation of microcracks, resulting in poor mechanical properties of the coatings. Summary of the Invention

[0004] Based on this, it is necessary to provide a silicon carbide coating with better mechanical properties and a preparation method thereof.

[0005] In the first aspect of the present invention, a preparation method of a silicon carbide coating is provided, including the following preparation steps:

[0006] Performing chemical vapor deposition treatment on a substrate to form a silicon carbide coating;

[0007] Wherein, the chemical vapor deposition treatment includes a low-temperature nucleation stage, a medium-temperature growth stage and a high-temperature growth stage in sequence, and the gas sources used in the chemical vapor deposition treatment include a dilution gas, hydrogen and an organosilicon source gas; the deposition temperature in the low-temperature nucleation stage is 600°C to 800°C; the deposition temperature in the medium-temperature growth stage is 1000°C to 1300°C; the deposition temperature in the high-temperature growth stage is 1350°C to 1500°C.

[0008] In the above method for preparing a silicon carbide coating by chemical vapor deposition, during the chemical vapor deposition process, a low-temperature nucleation stage, a medium-temperature growth stage, and a high-temperature growth stage are sequentially carried out, and the temperature of each stage is controlled at a specific temperature. Among them, in the low-temperature nucleation stage under lower temperature conditions, it is beneficial to provide a good initial growth layer for silicon carbide. This initial growth layer can form an intermediate transition layer between the substrate and the silicon carbide coating, which is conducive to the nucleation and growth of silicon carbide, and at the same time can also achieve a smooth transition of the thermal expansion coefficient from the substrate to the silicon carbide coating; then depositing in the medium-temperature growth stage and the high-temperature growth stage can further improve the overall performance of silicon carbide. The above stages show a stepped heating method. The chemical vapor deposition method under this stepped heating condition reduces the phenomenon of local overheating or condensation of silicon carbide crystals, effectively inhibits the generation of internal stress in the coating, reduces the formation of microcracks and voids, improves the densification of the coating, and further improves the hardness and fracture toughness of the silicon carbide coating, thereby improving the mechanical properties of the silicon carbide coating. Further, the above preparation method can also improve the interfacial bonding force between the coating and the substrate, and at the same time can control the orientation of silicon carbide grains.

[0009] In some embodiments, the deposition temperature in the low-temperature nucleation stage is 650 °C to 750 °C; and / or,

[0010] the deposition temperature in the medium-temperature growth stage is 1150 °C to 1250 °C; and / or,

[0011] the deposition temperature in the high-temperature growth stage is 1350 °C to 1450 °C.

[0012] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0013] (1) The rate of heating to the deposition temperature in the low-temperature nucleation stage is 0.5 °C / min to 15 °C / min;

[0014] (2) Heating from the deposition temperature in the low-temperature nucleation stage to the deposition temperature in the medium-temperature growth stage at a rate of 2 °C / min to 10 °C / min for 50 °C to 100 °C and holding for 4 min to 6 min;

[0015] (3) Heating from the deposition temperature in the medium-temperature growth stage to the deposition temperature in the high-temperature growth stage at a rate of 2 °C / min to 10 °C / min for 50 °C to 100 °C and holding for 4 min to 6 min.

[0016] In some embodiments, neither hydrogen nor the organosilicon source gas is introduced during the heating process.

[0017] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0018] (1) The low-temperature nucleation stage includes the following steps:

[0019] After the temperature is raised to the deposition temperature of the low-temperature nucleation stage, keep it warm for 1 h to 2 h first, and then introduce the gas source to perform the first chemical vapor deposition. The time of the first chemical vapor deposition is 20 min to 30 min;

[0020] (2) The medium-temperature growth stage includes the following steps:

[0021] When the temperature reaches the deposition temperature of the medium-temperature growth stage, keep it warm for 1 h to 2 h first, and then introduce the hydrogen gas and the silicon source gas to perform the second chemical vapor deposition. The time of the second chemical vapor deposition is 20 min to 80 min;

[0022] (3) The high-temperature growth stage includes the following steps:

[0023] When the temperature reaches the deposition temperature of the high-temperature growth stage, keep it warm for 1 h to 2 h first, and then introduce the gas source to perform the third chemical vapor deposition. The time of the third chemical vapor deposition is 40 min to 100 min.

[0024] In some embodiments, before the chemical vapor deposition treatment of the substrate, the preparation method further includes the step of keeping the substrate warm and pre-treating it under a vacuum condition at 400 °C to 600 °C.

[0025] In some embodiments, the heat preservation time of the heat preservation pre-treatment is 1 h to 2 h.

[0026] In some embodiments, after the high-temperature growth stage is completed, the following steps are further included:

[0027] Cool the temperature from the deposition temperature of the high-temperature growth stage to 700 to 800 °C at a rate of 1 °C / min to 3 °C / min, and keep it warm for 2 to 4 h; then lower it to room temperature at a rate of 0.3 °C / min to 1 °C / min.

[0028] In some embodiments, the organosilicon source is selected from methyltrichlorosilane, dimethyldichlorosilane or dimethylsilane; and / or

[0029] The dilution gas is selected from argon or helium; and / or

[0030] The substrate is selected from graphite, carbon, silicon carbide or ceramic.

[0031] In some embodiments, the flow rate ratio of the dilution gas, the hydrogen gas and the organosilicon source gas introduced is (5 to 20):(5 to 20):1.

[0032] In the second aspect of the present invention, a silicon carbide coating is provided, and the silicon carbide coating is prepared according to the above method. Detailed implementation manners

[0033] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that the purpose of providing these embodiments is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0035] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0036] In one embodiment of the present application, a method for preparing a silicon carbide coating is provided, including the following steps:

[0037] Performing chemical vapor deposition treatment on a substrate to form a silicon carbide coating;

[0038] Wherein, the chemical vapor deposition treatment includes a low-temperature nucleation stage, a medium-temperature growth stage and a high-temperature growth stage carried out in sequence, and the gas sources used in the chemical vapor deposition treatment include a dilution gas, hydrogen and an organosilicon source gas; the deposition temperature in the low-temperature nucleation stage is 600°C to 800°C; the deposition temperature in the medium-temperature growth stage is 1000°C to 1300°C; the deposition temperature in the high-temperature growth stage is 1350°C to 1500°C.

[0039] In the above method for preparing a silicon carbide coating by chemical vapor deposition, a low-temperature nucleation stage, a medium-temperature growth stage, and a high-temperature growth stage are sequentially carried out during the chemical vapor deposition process, and the temperature of each stage is controlled at a specific temperature. Among them, the low-temperature nucleation stage under lower temperature conditions is conducive to providing a good initial growth layer for silicon carbide. This initial growth layer can form an intermediate transition layer between the substrate and the silicon carbide coating, which is conducive to the nucleation and growth of silicon carbide, and at the same time can also achieve a smooth transition of the coefficient of thermal expansion from the substrate to the silicon carbide coating; then depositing in the medium-temperature growth stage and the high-temperature growth stage can further improve the overall performance of silicon carbide. The above stages show a stepped heating method. The chemical vapor deposition method under this stepped heating condition reduces the phenomenon of local overheating or condensation of silicon carbide crystals, effectively inhibits the generation of internal stress in the coating, reduces the formation of microcracks and voids, improves the density of the coating, and further improves the hardness and fracture toughness of the silicon carbide coating, and improves the mechanical properties of the silicon carbide coating. Further, the interfacial bonding force between the coating and the substrate can be improved by the above method, and at the same time, the orientation of silicon carbide grains can be controlled.

[0040] The above "deposition temperature in the low-temperature nucleation stage is 600 °C to 800 °C" can be understood as the temperature in the low-temperature nucleation stage can be 600 °C, 620 °C, 650 °C, 670 °C, 700 °C, 720 °C, 750 °C, 770 °C or 800 °C. Further, the deposition temperature in the low-temperature nucleation stage can be a range value formed by any two of the above point values as the end values. Preferably, the deposition temperature in the low-temperature nucleation stage is 650 °C to 750 °C. In the lower temperature range, the reaction rate is moderate, and the thermal kinetic barrier for nucleation is small, which is conducive to the formation of uniform, stable and dense SiC nuclei.

[0041] The above "deposition temperature in the medium-temperature growth stage is 1000 °C to 1300 °C" can be understood as the deposition temperature in the medium-temperature growth stage can be 1000 °C, 1020 °C, 1050 °C, 1070 °C, 1100 °C, 1120 °C, 1150 °C, 1170 °C, 1200 °C, 1250 °C or 1300 °C. Further, the deposition temperature in the medium-temperature growth stage can be a range value formed by any two of the above point values as the end values. Preferably, the deposition temperature in the medium-temperature growth stage is 1150 °C to 1250 °C. In the medium-temperature growth stage under specific temperature conditions, it ensures the uniform growth of nuclei and reduces the generation of defects.

[0042] The above "deposition temperature in the high-temperature growth stage is 1350°C to 1450°C" can be understood as that the deposition temperature in the high-temperature growth stage can be 1350°C, 1370°C, 1400°C, 1420°C or 1450°C. Further, the deposition temperature in the high-temperature nucleation stage can be a range value formed by any two of the above point values as the end values. Preferably, the deposition temperature in the high-temperature nucleation stage is 1150°C to 1250°C. In the high-temperature growth stage at a specific temperature, the reaction rate increases, which is beneficial to the rapid thickening of the SiC crystal.

[0043] In some embodiments, in the above preparation method: the rate of heating to the deposition temperature in the low-temperature nucleation stage is 0.5°C / min to 15°C / min.

[0044] In some embodiments, in the above preparation method: heat from the deposition temperature in the low-temperature nucleation stage to the deposition temperature in the medium-temperature growth stage at a rate of 2°C / min to 10°C / min for 50°C to 100°C and hold for 4 min to 6 min.

[0045] As an example, to heat the temperature from the deposition temperature of 750°C in the low-temperature nucleation stage to the deposition temperature of 1150°C in the medium-temperature growth stage, the heating can be carried out as follows: heat from 750°C to 850°C at a rate of 10°C / min and hold for 5 min; then continue to heat to 950°C at a rate of 10°C / min and hold for 5 min; then continue to heat to 1050°C at a rate of 10°C / min and hold for 5 min; then heat to 1150°C again at a rate of 10°C / min to reach the deposition temperature in the medium-temperature growth stage.

[0046] In some embodiments, the above heating step includes: heating from the deposition temperature in the medium-temperature growth stage to the deposition temperature in the high-temperature growth stage at a rate of 2°C / min to 10°C / min for 50°C to 100°C and hold for 4 min to 6 min.

[0047] As an example, to heat the temperature from the deposition temperature of 1150°C in the medium-temperature growth stage to the deposition temperature of 1350°C in the high-temperature growth stage, the heating can be carried out as follows: heat from 1150°C to 1200°C at a rate of 10°C / min and hold for 5 min; then continue to heat to 1250°C at a rate of 10°C / min and hold for 5 min; then continue to heat to 1300°C at a rate of 10°C / min and hold for 5 min; then heat to 1350°C again at a rate of 10°C / min to reach the deposition temperature in the high-temperature growth stage.

[0048] In some embodiments, hydrogen and organosilicon source gases are not introduced during the above heating process.

[0049] In some embodiments, no gas source is introduced during the process of raising the temperature to the deposition temperature of the low-temperature nucleation stage. That is to say, during the process of raising the temperature to the deposition temperature of the low-temperature nucleation stage, neither the dilution gas, hydrogen gas nor the organosilicon source gas is introduced.

[0050] In some embodiments, no hydrogen gas and organosilicon source gas are introduced during the process of raising the temperature from the deposition temperature of the low-temperature nucleation stage to the deposition temperature of the medium-temperature growth stage. It can be understood that during the process of raising the temperature from the deposition temperature of the low-temperature nucleation stage to the deposition temperature of the medium-temperature growth stage, no hydrogen gas and organosilicon source gas are introduced, while the dilution gas is continuously introduced. By continuously introducing the dilution gas, the air pressure value in the deposition chamber can be kept stable, and the operation safety of the equipment can be improved.

[0051] In some embodiments, no hydrogen gas and organosilicon source gas are introduced during the process of raising the temperature from the deposition temperature of the medium-temperature growth stage to the deposition temperature of the high-temperature growth stage. It can be understood that during the process of raising the temperature from the deposition temperature of the medium-temperature growth stage to the deposition temperature of the high-temperature growth stage, no hydrogen gas and organosilicon source gas are introduced, while the dilution gas is continuously introduced. By continuously introducing the dilution gas, the air pressure value in the deposition chamber can be kept stable, and the operation safety of the equipment can be improved.

[0052] In some embodiments, the low-temperature nucleation stage includes the following steps:

[0053] After raising the temperature to the low-temperature nucleation stage, keep the temperature for 1 h to 2 h first, and then introduce the above gas source to perform the first chemical vapor deposition. The time of the first chemical vapor deposition is 20 min to 30 min. It can be understood that during the process of keeping the temperature for 1 h to 2 h in the low-temperature nucleation stage, neither the above dilution gas, hydrogen gas and organosilicon source gas are introduced, nor the chemical vapor deposition treatment is carried out; after the insulation process is completed, the above gas source is introduced to perform the first chemical vapor deposition.

[0054] In some embodiments, the medium-temperature growth stage includes the following steps:

[0055] When the temperature reaches the deposition temperature of the medium-temperature growth stage, keep the temperature for 1 h to 2 h first, and then introduce hydrogen gas and silicon source gas to perform the second chemical vapor deposition. The time of the second chemical vapor deposition is 20 min to 80 min. It can be understood that during the process of keeping the temperature for 1 h to 2 h in the medium-temperature growth stage, neither hydrogen gas and organosilicon source gas are introduced, nor the chemical vapor deposition treatment is carried out; only the dilution gas is introduced during the insulation process to keep the air pressure in the chemical vapor deposition chamber stable; after the insulation process is completed, hydrogen gas and organosilicon source gas are introduced to perform the second chemical vapor deposition.

[0056] Further, the time of the second chemical vapor deposition can be 40 min, 50 min, 60 min, 70 min or 80 min. Even further, the time of the second chemical vapor deposition can be a range value formed by any two of the above point values as the end values.

[0057] In some embodiments, the high-temperature growth stage includes the following steps:

[0058] After the temperature reaches the deposition temperature of the high-temperature growth stage, first keep the temperature for 1 h to 2 h, and then introduce hydrogen and a silicon source gas for the third chemical vapor deposition. The time of the third chemical vapor deposition is 40 min to 100 min. It can be understood that during the process of keeping the temperature for 1 h to 2 h in the high-temperature growth stage, hydrogen and an organosilicon source gas are not introduced, and no chemical vapor deposition treatment is performed; only a dilution gas is introduced during the temperature-holding process to keep the air pressure in the chemical vapor deposition chamber stable; after the temperature-holding process is completed, hydrogen and a silicon source gas are introduced for the third chemical vapor deposition.

[0059] Further, the time of the third chemical vapor deposition can be 40 min, 50 min, 60 min, 70 min or 80 min. Even further, the time of the third chemical vapor deposition can be a range value formed by any two of the above point values as the end values.

[0060] In some embodiments, before the chemical vapor deposition treatment of the substrate, the above preparation method further includes a step of pre-treating the substrate by keeping it at a constant temperature under a vacuum condition of 400 °C to 600 °C.

[0061] The above “400 °C to 600 °C” can be understood as that the substrate can be pre-treated by keeping it at a constant temperature under the conditions of 400 °C, 450 °C, 500 °C, 550 °C or 600 °C. Further, the pre-treatment temperature of the substrate can be a range value formed by any two of the above point values as the end values. Preferably, the temperature of the substrate pre-treatment by keeping it at a constant temperature is 450 °C to 550 °C. Pre-treating the substrate by keeping it at a constant temperature under specific temperature conditions can remove impurities and moisture on the surface of the substrate, and at the same time make the surface of the substrate have a stronger adsorption capacity for SiC crystal nuclei, improving the bonding force between the silicon carbide coating and the substrate.

[0062] In some embodiments, the vacuum degree during the pre-treatment of the substrate by keeping it at a constant temperature is lower than 10 Pa.

[0063] In some embodiments, the temperature-holding time of the pre-treatment by keeping it at a constant temperature is 1 h to 2 h.

[0064] In some embodiments, after the high-temperature growth stage is completed, the following steps are further included:

[0065] Cool the temperature from the deposition temperature in the high-temperature growth stage to 700 - 800 °C at a rate of 1 °C / min to 3 °C / min, and keep the temperature for 2 - 4 h; then reduce the temperature to room temperature at a rate of 0.3 °C / min to 1 °C / min. By adopting the above specific gradient cooling, the thermal stress concentration in the silicon carbide coating can be further reduced, and the hardness and fracture toughness of the silicon carbide coating can be further improved.

[0066] In some embodiments, hydrogen and organosilicon source gases are not introduced during the process of cooling after the high-temperature growth stage is completed. It can be understood that hydrogen and organosilicon source gases are not introduced throughout the process of cooling the temperature from the deposition temperature in the high-temperature growth stage to 700 - 800 °C, keeping the temperature for 2 - 4 h, and then reducing the temperature to room temperature, while the dilution gas is continuously introduced.

[0067] In some embodiments, the organosilicon source is selected from methyltrichlorosilane, dimethyldichlorosilane, or dimethylsilane.

[0068] In some embodiments, the dilution gas is argon or helium.

[0069] In some embodiments, the substrate can be selected from graphite, carbon, silicon carbide, or ceramics. Further, the ceramic is an oxide ceramic, including but not limited to alumina ceramic. It can also be silicon nitride ceramic.

[0070] In some embodiments, the flow rate ratio of the above dilution gas, hydrogen, and organosilicon source gas is (5 - 20):(5 - 20):1.

[0071] In some embodiments, the flow rate ratios of the dilution gas, hydrogen, and organosilicon source gas introduced in the low-temperature nucleation stage, medium-temperature growth stage, and high-temperature growth stage can be the same.

[0072] In some embodiments, the chemical vapor deposition treatment is carried out under the condition of a pressure of 9.8 KPa to 12 KPa.

[0073] In one embodiment of the present application, a silicon carbide coating is provided, and the silicon carbide coating is prepared according to the above method.

[0074] In some embodiments, the Vickers hardness of the above silicon carbide coating is greater than 2500 HV. Further, the Vickers hardness of the silicon carbide coating is 2500 HV to 3000 HV.

[0075] In some embodiments, the fracture toughness of the above silicon carbide coating is greater than 3 MPa·m 1 / 2 . Further, the fracture toughness of the silicon carbide coating is 3 MPa·m 1 / 2 ~8 MPa·m 1 / 2 .

[0076] In order to make the objectives, technical solutions and advantages of the present invention more concise and clear, the present invention will be described by the following specific embodiments. However, the present invention is by no means limited to these embodiments. The embodiments described below are only the preferred embodiments of the present invention and can be used to describe the present invention, but should not be construed as a limitation on the scope of the present invention. It should be noted that any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0077] To better illustrate the present invention, the content of the present invention will be further described below in conjunction with embodiments. The following are specific embodiments.

[0078] Embodiment 1:

[0079] (1) Clean the graphite substrate, place it in a chemical vapor deposition chamber, evacuate, heat it to 500 °C within 1 h, and keep it warm for 1 h.

[0080] (2) Then, heat it to 700 °C at a rate of 0.85 °C / min and keep it warm for 1 h; then introduce argon, hydrogen and methyltrichlorosilane (MTS) for deposition according to a flow rate ratio of 10:10:1, and the deposition time is 25 min; and control the pressure in the chemical vapor deposition chamber to be 10000 ± 100 Pa; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon. The pressure in the chemical vapor deposition chamber is always controlled within the range of 10000 ± 100 Pa.

[0081] (3) Then gradually heat it up, heat it to 1200 °C at a rate of 5 °C / min by heating 100 °C and keeping it warm for 5 min, and keep it warm for 1 h; resume introducing argon, hydrogen and methyltrichlorosilane for deposition, and the deposition time is 25 min; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon; during the process, the pressure in the chemical vapor deposition chamber is always controlled at 10000 ± 100 Pa;

[0082] (4) Then gradually heat it up, heat it to 1400 °C at a rate of 5 °C / min by heating 100 °C and keeping it warm for 5 min, and keep it warm for 1 h; resume introducing argon, hydrogen and methyltrichlorosilane gas for deposition, and the deposition time is 95 min; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon; during the process, the pressure in the chemical vapor deposition chamber is always controlled at 10000 ± 100 Pa.

[0083] (5) Cool the temperature in the chemical vapor deposition chamber to 700 °C at a rate of 1 °C / min and keep it warm for 3 h; then cool it to room temperature at a rate of 0.5 °C / min, and repeatedly replace it with argon three times before opening the furnace lid; obtain a silicon carbide coating.

[0084] Comparative Example 1:

[0085] (1) Clean the graphite substrate, place it in the chemical vapor deposition chamber, evacuate the chamber, heat it to 500 °C within 1 h, and keep it at this temperature for 1 h.

[0086] (2) Heat it to 1200 °C at a rate of 2.33 °C / h and keep it at this temperature for 1 h; then introduce argon, hydrogen, and methyltrichlorosilane (MTS) for deposition at a flow rate ratio of 10:10:1. The deposition time is 145 min; and control the pressure in the chemical vapor deposition chamber to be 10000 ± 100 Pa; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon. The pressure in the chemical vapor deposition chamber is always controlled within the range of 10000 ± 100 Pa.

[0087] (3) Cool the temperature in the chemical vapor deposition chamber to 700 °C at a rate of 1 °C / min and keep it at this temperature for 3 h; then cool it to room temperature at a rate of 0.5 °C / min. Before opening the furnace lid, replace the gas with argon three times repeatedly; obtain a silicon carbide coating.

[0088] Comparative Example 2:

[0089] (1) Clean the graphite substrate, place it in the chemical vapor deposition chamber, evacuate the chamber, heat it to 500 °C within 1 h, and keep it at this temperature for 1 h.

[0090] (2) Heat it to 1400 °C at a rate of 2.5 °C / min and keep it at this temperature for 1 h; then introduce argon, hydrogen, and methyltrichlorosilane (MTS) for deposition at a flow rate ratio of 10:10:1. The deposition time is 145 min; and control the pressure in the chemical vapor deposition chamber to be 10000 ± 100 Pa; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon. The pressure in the chemical vapor deposition chamber is always controlled within the range of 10000 ± 100 Pa.

[0091] (3) Cool the temperature in the chemical vapor deposition chamber to 700 °C at a rate of 1 °C / min and keep it at this temperature for 3 h; then cool it to room temperature at a rate of 0.5 °C / min. Before opening the furnace lid, replace the gas with argon three times repeatedly; obtain a silicon carbide coating.

[0092] Comparative Example 3

[0093] (1) Clean the graphite substrate, place it in the chemical vapor deposition chamber, evacuate the chamber, heat it to 500 °C within 1 h, and keep it at this temperature for 1 h.

[0094] (2) Then, heat it up to 700 °C at a rate of 0.85 °C / min and hold for 1 h; then introduce argon, hydrogen, and methyltrichlorosilane (MTS) in a flow ratio of 10:10:1 for deposition, and the deposition time is 25 min; and control the pressure in the chemical vapor deposition chamber to be 10000 ± 100 Pa; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon. The pressure in the chemical vapor deposition chamber is always controlled within the range of 10000 ± 100 Pa.

[0095] (3) Then gradually heat it up. Each time, heat it up by 100 °C at a heating rate of 5 °C / min and hold for 5 min until it reaches 1400 °C and hold for 1 h; resume introducing argon, hydrogen, and methyltrichlorosilane for deposition, and the deposition time is 25 min; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon; during the process, the pressure in the chemical vapor deposition chamber is always controlled at 10000 ± 100 Pa.

[0096] (4) Then cool it down. Cool it down to 1200 °C at a heating rate of 5 °C / min and hold for 1 h; resume introducing argon, hydrogen, and methyltrichlorosilane for deposition, and the deposition time is 95 min; after the deposition is completed, cut off methyltrichlorosilane and hydrogen, and keep argon; during the process, the pressure in the chemical vapor deposition chamber is always controlled at 10000 ± 100 Pa;

[0097] (5) At a rate of 1 °C / min, lower the temperature in the chemical vapor deposition chamber to 700 °C and hold for 3 h; then lower the temperature to room temperature at a rate of 0.5 °C / min. Before opening the furnace lid, replace it with argon three times repeatedly; obtain a silicon carbide coating.

[0098] Performance testing:

[0099] Vickers hardness: Test it according to the method specified in GB / T 7997-2014.

[0100] Fracture toughness: Test the silicon carbide coating by the indentation method.

[0101] Roughness: Test the surface of silicon carbide with a stylus roughness instrument.

[0102] Adhesion: Test the adhesion between the silicon carbide coating and the graphite substrate according to the method specified in GB / T 5210-2006.

[0103] The performance tests of the silicon carbide coatings of each example and the comparative example are shown in Table 1 below.

[0104] Table 1

[0105]

[0106] As can be seen from Table 1, the coating obtained in Example 1 has a small surface roughness, a flat surface, a Vickers hardness of 2824.8 HV, and a fracture toughness of 6.53 MPa·m 1 / 2 ; the bonding strength between the silicon carbide coating and the substrate reaches 9.26 MPa.

[0107] When preparing the silicon carbide coating by the methods of Comparative Example 1 and Comparative Example 2, chemical vapor deposition was carried out only under one temperature condition, and the surface flatness of the obtained silicon carbide coating was relatively poor, and its performance in terms of roughness, Vickers hardness, fracture toughness and bonding strength with the substrate was also inferior to that of Example 1.

[0108] In the preparation of the silicon carbide coating in Comparative Example 3, chemical vapor deposition was first carried out under a lower temperature condition, then under a higher temperature condition, and then under a medium temperature condition. As a result, the obtained silicon carbide coating had poor uniformity, a Vickers hardness of 2684.1 HV, and a fracture toughness of 4.23 MPa·m 1 / 2 , and the bonding strength with the substrate was only 8.48 MPa, which was inferior to that of Example 1.

[0109] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0110] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims, and the description can be used to explain the content of the claims.

Claims

1. A method for preparing a silicon carbide coating, characterized in that, It includes the following steps: A step of heat-preserving and pre-treating the substrate under a vacuum condition at 400 °C to 600 °C; the heat-preserving time of the heat-preserving pre-treatment is 1 h to 2 h; Performing chemical vapor deposition treatment on the substrate after the heat-preserving pre-treatment to form a silicon carbide coating; Among them, the chemical vapor deposition treatment includes a low-temperature nucleation stage, a medium-temperature growth stage, and a high-temperature growth stage that are carried out in sequence. The gas sources used in the chemical vapor deposition treatment include a dilution gas, hydrogen, and an organosilicon source gas; the deposition temperature in the low-temperature nucleation stage is 600 °C to 800 °C; the deposition temperature in the medium-temperature growth stage is 1000 °C to 1300 °C; the deposition temperature in the high-temperature growth stage is 1350 °C to 1500 °C; The chemical vapor deposition treatment includes: Heating to the deposition temperature of the low-temperature nucleation stage at a rate of 0.5 °C / min to 15 °C / min; when the temperature reaches the deposition temperature of the low-temperature nucleation stage, first heat-preserve for 1 h to 2 h, and then introduce the gas source to perform the first chemical vapor deposition, and the time of the first chemical vapor deposition is 20 min to 30 min; Stop introducing the hydrogen and organosilicon source gases; heat up from the deposition temperature of the low-temperature nucleation stage to the deposition temperature of the medium-temperature growth stage at a rate of 2 °C / min to 10 °C / min and heat-preserve for 4 min to 6 min by raising the temperature by 50 °C to 100 °C; when the temperature reaches the deposition temperature of the medium-temperature growth stage, first heat-preserve for 1 h to 2 h, and then introduce the hydrogen and the silicon source gas to perform the second chemical vapor deposition, and the time of the second chemical vapor deposition is 20 min to 80 min; Stop introducing the hydrogen and organosilicon source gases; heat up from the deposition temperature of the medium-temperature growth stage to the deposition temperature of the high-temperature growth stage at a rate of 2 °C / min to 10 °C / min and heat-preserve for 4 min to 6 min by raising the temperature by 50 °C to 100 °C; when the temperature reaches the deposition temperature of the high-temperature growth stage, first heat-preserve for 1 h to 2 h, and then introduce the hydrogen and the silicon source gas to perform the third chemical vapor deposition, and the time of the third chemical vapor deposition is 40 min to 100 min; After the high-temperature growth stage is completed, it further includes the following steps: Cooling the temperature from the deposition temperature of the high-temperature growth stage to 700 - 800 °C at a rate of 1 °C / min to 3 °C / min and heat-preserving for 2 - 4 h; then reducing to room temperature at a rate of 0.3 °C / min to 1 °C / min.

2. The preparation method according to claim 1, characterized in that, The deposition temperature in the low-temperature nucleation stage is 650 °C to 750 °C; and / or, The deposition temperature in the medium-temperature growth stage is 1150 °C to 1250 °C; and / or, The deposition temperature in the high-temperature growth stage is 1350 °C to 1450 °C.

3. The preparation method according to any one of claims 1 to 2, characterized in that, Heat-preserving and pre-treating the substrate under a vacuum condition at 500 °C.

4. The preparation method according to any one of claims 1 to 2, characterized in that, The heat-preserving time of the heat-preserving pre-treatment is 1 h.

5. The preparation method according to any one of claims 1 to 2, characterized in that, The organosilicon source is selected from methyltrichlorosilane, dimethyldichlorosilane, or dimethylsilane; and / or The dilution gas is selected from argon or helium; and / or The substrate is selected from graphite, carbon, silicon carbide, or ceramic.

6. The preparation method according to any one of claims 1 to 2, characterized in that, The flow rate ratio of the dilution gas, the hydrogen gas, and the organosilicon source gas is (5-20):(5-20):

1.

7. A silicon carbide coating, characterized in that, The silicon carbide coating is prepared by the method according to any one of claims 1 to 2.

Images