Preparation method for preparing silicide coating at low temperature by taking carbide as template

Abstract

The invention relates to the technical field of coating materials, and discloses a preparation method for preparing a silicide coating at low temperature by taking carbide as a template, and the preparation method comprises the following steps: weighing transition metal powder, sodium chloride and potassium chloride according to a preset proportion, and uniformly mixing to prepare mixed molten salt; embedding the carbon material into the mixed molten salt, reacting in a molten salt furnace, and cooling to room temperature after the reaction is finished, so as to prepare the carbon material with a carbide coating on the surface; and embedding the carbon material with the carbide coating on the surface as a template in a silicon source, carrying out high-temperature reaction, and naturally cooling to room temperature to prepare the carbon material with the silicide coating on the surface. According to the preparation method, the silicide coating can effectively protect the base material in an extreme high-temperature oxidation environment.

Description

Technical Field

[0001] The present invention relates to the technical field of coating materials, and particularly to a preparation method for preparing a silicide coating at low temperature using a carbide as a template. Background Art

[0002] Silicide coatings are a type of high-temperature protective coatings mainly composed of silicides (such as titanium silicide, tantalum silicide, hafnium silicide, chromium silicide, molybdenum silicide, etc.), and are widely used in the surface protection of high-temperature structural materials in fields such as aerospace and energy chemical engineering. Silicide coatings have high melting points, high hardness, excellent oxidation resistance and corrosion resistance, and can effectively protect the substrate material in extremely high-temperature oxidation environments.

[0003] Currently, the main preparation methods for silicide coatings include physical vapor deposition, chemical vapor deposition, thermal spraying, pack cementation, etc. Physical vapor deposition represented by magnetron sputtering bombards the target material with high-energy particles to deposit silicide on the substrate surface. This method has good uniformity but low deposition efficiency; the coatings prepared by chemical vapor deposition have good denseness, but the process temperature is high, which may cause thermal damage to the substrate material; the thermal spraying method heats the silicide powder to the molten state and then sprays it on the substrate surface. This method is suitable for the preparation of large-area coatings, but there is a deficiency in the low bonding strength between the coating and the substrate material. The pack cementation method places the substrate material in a silicide powder or gas environment and forms a silicide coating on the substrate surface through a high-temperature diffusion reaction. This method is suitable for substrates with complex shapes, but the process time is relatively long. In addition, when preparing a silicide coating by sintering, it is necessary to pre-coat a mixture of silicon and metal powder and sinter it at a high temperature in an inert atmosphere, and the reaction temperature is 1600 - 2200 °C; during the process of laser cladding of a silicide coating, the reaction powder is heated to the melting point and a coating is made by rapidly solidifying the powder through laser beam focusing, and the reaction temperature is 1500 - 1900 °C. The reaction temperatures are all relatively high, which may cause thermal damage to the substrate material. The above methods are the main methods for preparing silicide antioxidant coatings at present, but they all have common disadvantages: (1) The interfacial bonding strength between the silicide coating and the substrate material is relatively low, and the thermal shock resistance is limited. (2) Due to the mismatch of the thermal expansion coefficients of the coating and the substrate material, there are large thermal stresses in the coating at high temperatures, resulting in cracks or even peeling of the coating. Therefore, it is necessary to propose a preparation method for preparing a silicide coating at low temperature using a carbide as a template to solve the above problems. Summary of the Invention

[0004] Based on the above, the object of the present invention is to provide a preparation method for preparing a silicide coating at low temperature using a carbide as a template, so that the silicide coating can also effectively protect the substrate material in an extremely high-temperature oxidation environment.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, the method includes the following steps:

[0007] Weigh a preset ratio of transition metal powder, sodium chloride, and potassium chloride and mix them evenly to obtain a mixed molten salt;

[0008] Bury the carbon material in the mixed molten salt and react in a molten salt furnace. After the reaction is completed, cool it to room temperature to obtain a carbon material with a carbide coating on its surface;

[0009] Use the carbon material with the carbide coating on its surface as a template and embed it in the silicon source. React at high temperature and naturally cool it to room temperature to obtain a carbon material with a silicide coating on its surface.

[0010] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, the molar ratio of the transition metal powder, sodium chloride, and potassium chloride is (0.3 - 1):5:5.

[0011] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, the transition metal powder includes one or more of Ti, Zr, Hf, Ta, and Mo.

[0012] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, the carbon material includes one or more of carbon / carbon composite materials, graphite, diamond, amorphous carbon, and carbon fiber.

[0013] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, during the process of burying the carbon material in the mixed molten salt and reacting in the molten salt furnace, heat the molten salt furnace to 800 - 1400 °C at a rate of 10 - 20 °C / min in an inert gas atmosphere and keep it at this temperature for 2 - 7 h.

[0014] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, the carbide coating includes one or more of TiC, TaC, HfC, ZrC, NbC, and Mo 2 C.

[0015] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, the silicon source includes one or more of elemental silicon, a mixed powder of silicon and silicon dioxide, and SiO powder.

[0016] As a preferred embodiment of a preparation method for preparing a silicide coating at low temperature using a carbide as a template, when using the carbon material with the carbide coating on its surface as a template and embedding it in the silicon source, during the high-temperature reaction process, heat it to 1000 - 1600 °C at a heating rate of 10 - 20 °C / min in an inert gas atmosphere and react for 0.5 - 4 h.

[0017] As a preferred embodiment of a preparation method for low-temperature preparation of a silicide coating using a carbide as a template, the silicide coating includes one or more of titanium silicide, tantalum silicide, hafnium silicide, zirconium silicide, and molybdenum silicide.

[0018] As a preferred embodiment of a preparation method for low-temperature preparation of a silicide coating using a carbide as a template, the preparation methods of the carbide coating and the silicide coating further include a molten salt method, a carbothermal reduction method, a slurry sintering method, a sol-gel method, and a chemical vapor deposition method.

[0019] The beneficial effects of the present invention are as follows:

[0020] The present invention provides a preparation method for low-temperature preparation of a silicide coating using a carbide as a template. First, a carbide coating with a gradient structure is prepared on the surface of a graphite substrate, and then the silicide coating is prepared by directly reacting with a silicon source using the carbide as a template. The preparation method of the silicide coating is simple, the process conditions are mild, and the preparation temperatures of the carbide coating and the silicide coating are low. Compared with the silicide coating prepared by the traditional method, the silicide coating prepared by the present invention retains the gradient structure existing between the original carbide coating and graphite, enhances the bonding force between the silicide coating and the carbon matrix, reduces the thermal stress between the silicide coating and the matrix caused by the mismatch of the expansion coefficients, improves the thermal shock resistance of the coating, and solves the problem of easy cracking of the coating. In addition, the formation temperature of the silicide coating on the substrate surface is relatively low, the grain size is small, the coating is uniform and dense, and the porosity is low, having strong oxidation resistance, and broadening the application scenarios and scope of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments of the present invention. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the content of the embodiments of the present invention and these drawings.

[0022] Figure 1 Optical images of carbon materials with different coatings on the surface, where (a) is graphite with a silicon carbide coating on the surface, and (b) is graphite with a carbon disilicide coating on the surface;

[0023] Figure 2 XRD spectrum of the graphite with a tantalum disilicide coating on the surface prepared in Example 1;

[0024] Figure 3 Surface pattern of the graphite with a tantalum disilicide coating on the surface prepared in Example 1, where (a) is an SEM image and (b) is a scanning energy spectrum;

[0025] Figure 4 Cross-sectional line spectrum of graphite with tantalum disilicide coating prepared in Example 1, where (a) is an SEM image and (b) is a scanning energy spectrum

[0026] Figure 5 Pore image of graphite with tantalum disilicide coating prepared in Example 1 after adjusting the gray threshold of tantalum disilicide on the surface. Detailed implementation mode

[0027] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosed content of the present invention more thorough and comprehensive. Unless otherwise defined, all technical and scientific terms used in the present invention belong to the technical field of the present invention.

[0028] This embodiment provides a preparation method for low-temperature preparation of a silicide coating using a carbide as a template, which is characterized by including the following steps:

[0029] S100. Weigh a preset ratio of transition metal powder, sodium chloride, and potassium chloride and mix them evenly to obtain a mixed molten salt;

[0030] Specifically, the molar ratio of the transition metal powder, sodium chloride, and potassium chloride is (0.3 - 1):5:5, preferably (0.5 - 0.7):5:5; the transition metal powder includes one or more of Ti, Zr, Hf, Ta, and Mo.

[0031] S200. Burry the carbon material in the mixed molten salt and react in a molten salt furnace. After the reaction is completed, cool it to room temperature to obtain a carbon material with a carbide coating on the surface;

[0032] Specifically, the carbon material includes one or more of carbon / carbon composites, graphite, diamond, amorphous carbon, and carbon fiber, preferably graphite; during the reaction process, the molten salt furnace is heated to 800 - 1400 °C at a rate of 10 - 20 °C / min in an inert gas atmosphere, and kept warm for 2 - 7 h. The preferred reaction temperature is 1000 - 1200 °C; the carbide coating includes one or more of TiC, TaC, HfC, ZrC, NbC, and Mo 2 C.

[0033] S300. Use the carbon material with a carbide coating on the surface as a template and embed it in a silicon source, react at high temperature, and naturally cool it to room temperature to obtain a carbon material with a silicide coating on the surface.

[0034] Specifically, the silicon source includes one or more of elemental silicon, a mixed powder of silicon and silicon dioxide, and SiO powder; during the high-temperature reaction process, the temperature is raised to 1000-1600 °C at a heating rate of 10-20 °C / min in an inert gas atmosphere, and the reaction is carried out for 0.5-4 h. The reaction temperature is preferably 1200-1400 °C; the silicide coating includes one or more of titanium silicide, tantalum silicide, hafnium silicide, zirconium silicide, and molybdenum silicide.

[0035] More specifically, the preparation method of the carbide coating and the silicide coating in this embodiment is the embedding method. In other embodiments, the preparation methods of the carbide coating and the silicide coating also include the molten salt method, the carbothermal reduction method, the slurry sintering method, the sol-gel method, and the chemical vapor deposition method.

[0036] The present invention will be further described below through specific examples.

[0037] Example 1

[0038] A preparation method for preparing a silicide coating at low temperature with a carbide as a template includes the following steps:

[0039] Weigh Ta powder, sodium chloride, and potassium chloride in a molar ratio of (0.3-0.5):5:5 and mix them evenly to obtain a mixed molten salt;

[0040] Embed graphite into the mixed molten salt powder, and raise the temperature of the molten salt furnace to 800-1000 °C at a rate of 10-20 °C / min in an argon atmosphere, keep it warm for 2-3 h, and cool it to room temperature after the reaction to obtain tantalum carbide-coated graphite;

[0041] Then, using the tantalum carbide-coated graphite as a template, embed it in silicon powder, and raise the temperature to 1000-1200 °C at a heating rate of 10-20 °C / min in an argon atmosphere, react for 0.5-1 h, and naturally cool it to room temperature to obtain tantalum disilicide-coated graphite.

[0042] The tantalum disilicide coating prepared in this example uniformly covers the surface of graphite and the coating structure is dense. The thickness of the tantalum disilicide coating is 5.8 μm.

[0043] Example 2

[0044] A preparation method for preparing a silicide coating at low temperature with a carbide as a template includes the following steps:

[0045] Weigh Ta powder, sodium chloride, and potassium chloride in a molar ratio of (0.5-0.7):5:5 and mix them evenly to obtain a mixed molten salt;

[0046] Embed graphite into the mixed molten salt powder. In an argon atmosphere, heat the molten salt furnace to 1000 - 1200 °C at a rate of 10 - 20 °C / min, hold for 1 - 2 h, and after the reaction is completed, cool to room temperature to obtain tantalum carbide-coated graphite;

[0047] Then, using the tantalum carbide-coated graphite as a template, embed it in silicon powder. In an argon atmosphere, heat it to 1200 - 1400 °C at a heating rate of 10 - 20 °C / min, react for 1 - 2 h, and naturally cool to room temperature to obtain tantalum disilicide-coated graphite.

[0048] The tantalum disilicide coating prepared in this example uniformly covers the surface of the graphite and the coating structure is dense. The thickness of the tantalum disilicide coating is 7.1 μm.

[0049] Example 3

[0050] A preparation method for preparing a silicide coating at low temperature using a carbide as a template, comprising the following steps:

[0051] Weigh Ta powder, sodium chloride, and potassium chloride according to the molar ratio of tantalum powder, sodium chloride, and potassium chloride of (0.7 - 1):5:5, mix them evenly to obtain a mixed molten salt;

[0052] Embed graphite into the mixed molten salt powder. In an argon atmosphere, heat the molten salt furnace to 1000 - 1200 °C at a rate of 10 - 20 °C / min, hold for 2 - 5 h, and after the reaction is completed, cool to room temperature to obtain tantalum carbide-coated graphite;

[0053] Then, using the tantalum carbide-coated graphite as a template, embed it in silicon powder. In an argon atmosphere, heat it to 1400 - 1600 °C at a heating rate of 10 - 20 °C / min, react for 2 - 3 h, and naturally cool to room temperature to obtain tantalum disilicide-coated graphite.

[0054] The tantalum disilicide coating prepared in this example uniformly covers the surface of the graphite and the coating structure is dense. The thickness of the tantalum disilicide coating is 9.8 μm.

[0055] Example 4

[0056] A preparation method for preparing a silicide coating at low temperature using a carbide as a template, comprising the following steps:

[0057] Weigh Ta powder, sodium chloride, and potassium chloride according to the molar ratio of tantalum powder, sodium chloride, and potassium chloride of (0.5 - 0.7):5:5, mix them evenly to obtain a mixed molten salt;

[0058] Embed graphite into the mixed molten salt powder. In an argon atmosphere, heat the molten salt furnace to 1200 - 1400 °C at a rate of 10 - 20 °C / min, hold for 4 - 7 h, and after the reaction is completed, cool to room temperature to obtain tantalum carbide-coated graphite;

[0059] Then, using tantalum carbide-coated graphite as a template, embed it in silicon powder, and heat it to 1200-1400 °C at a heating rate of 10-20 °C / min in an argon atmosphere, react for 1-4 h, and naturally cool to room temperature to obtain tantalum disilicide-coated graphite.

[0060] The tantalum disilicide coating prepared in this example uniformly covers the graphite surface and the coating structure is dense, and the thickness of the tantalum disilicide coating is 11.8 μm.

[0061] Perform relevant tests on the graphite with a tantalum disilicide coating on the surface prepared in Example 1. Figure 1 Figure 9 is an optical image of carbon materials with different coatings on the surface. Among them, (a) is graphite with a silicon carbide coating on the surface, and (b) is graphite with a carbon disilicide coating on the surface. After a tantalum carbide coating grows on the graphite surface, it has an obvious metallic luster, indicating the formation of the tantalum carbide coating on the graphite surface. When the tantalum carbide coating reacts with silicon powder, the graphite surface changes from golden yellow to gray, and a new phase is formed after the surface carbide coating reacts with silicon powder. Figure 2 Figure 11 is the XRD pattern of the graphite with a tantalum disilicide coating on the surface prepared in Example 1. The diffraction peaks near 2θ = 21.5°, 25.5°, 35.0°, 40.1°, 59.0°, and 70.1° in the figure correspond to the (101), (102), (111), (210), (301), and (302) crystal planes of TaSi 2 in turn, indicating that TaSi has been successfully prepared on the graphite surface using TaC as a template. 2 coating; Figure 3 Figure 17 is the surface map of the graphite with a tantalum disilicide coating on the surface prepared in Example 1. Among them, (a) is the SEM image, and (b) is the scanning energy spectrum; it is again shown that the reaction-formed coating is a silicide coating, and the coating structure is uniform without obvious pores; Figure 4 Figure 19 is the cross-sectional line map of the graphite with a tantalum disilicide coating on the surface prepared in Example 1. Among them, (a) is the SEM image, and (b) is the scanning energy spectrum. It can be seen from the figure that the thickness of the TaSi 2 layer on the graphite surface is 5.8 μm, and there is a gradient structure between the tantalum silicide coating and the graphite, and they are closely combined.

[0062] In addition, porosity tests and oxidation resistance tests were also carried out on the graphite with tantalum disilicide coating prepared in Examples 1-4. The porosity test method was as follows: ImageJ software was used to calculate the porosity. After importing the microscopic image of the material into ImageJ software, pores and the matrix were distinguished by gray threshold segmentation to generate a binary image. Subsequently, the pixel area ratio of the pore region was statistically analyzed and combined with the image scale to calculate the material porosity. Three images on the surface of the specimen were randomly selected, and the porosity of SiC on the surface of the specimen was calculated by ImageJ software and the average value was taken. The pore image of the graphite with tantalum disilicide coating prepared in Example 1 after adjusting the gray threshold of tantalum disilicide on the surface is as Figure 5 shown. Static oxidation resistance detection method: A constant temperature oxidation test at 900 °C for 10 h was used to test the high-temperature oxidation resistance of the coating specimens with different components. First, the mass M 1 of the carbon material coated with a silicide coating was measured, and then the specimen was placed in a corundum crucible and put into a muffle furnace. The heating rate was 10 °C / min. When the temperature was raised to the set temperature of 900 °C, heat preservation started for 10 h. After the oxidation test, the specimen was cooled to room temperature with the furnace, and the coated specimen was weighed and recorded as M 2 . After the oxidation test, the weight loss rate of the specimen was Δω = (M 2 - M 1 ) / M 1 (where Δω is the mass change rate, M 1 is the mass of the coated specimen before oxidation, and M 2 is the mass of the coated specimen after oxidation).

[0063] Through testing, it was obtained that the porosity of Example 1 was 2.7%, the porosity of Example 2 was 2.4%, the porosity of Example 5 was 2.1%, and the porosity of Example 4 was 1.7%. The above porosities were all relatively low and met the application requirements; in the static oxidation resistance test, the weight loss rate of Example 1 was 9.37%, the weight loss rate of Example 2 was 8.91%, the weight loss rate of Example 3 was 7.47%, and the weight loss rate of Example 4 was 6.75%. During the constant temperature static oxidation process of the specimen at 900 °C for 10 hours, the weight loss rate of the graphite with tantalum disilicide coating prepared by this method (Example 1) was 9.37%. The weight loss rate of the graphite with tantalum disilicide coating prepared by the plasma spraying method in the prior art was 17.89%, and the weight loss rate of the graphite without coating was 35%. Therefore, the weight loss rate of the graphite with tantalum disilicide coating prepared by this application was lower, and it had excellent oxidation resistance.

[0064] The above are only the preferred embodiments of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein. Various obvious changes, re-adjustments, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it may also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for preparing a silicide coating at low temperature using carbide as a template, characterized in that: The following steps are involved: Weighing a preset ratio of transition metal powder, sodium chloride and potassium chloride and mixing them evenly to prepare a mixed molten salt; The carbon material is buried in the mixed molten salt and reacted in a molten salt furnace, and after the reaction is completed, the mixture is cooled to room temperature to obtain a carbon material with a carbide coating on the surface; The carbon material with a carbide coating on the surface is used as a template and embedded in a silicon source, reacted at high temperature, and naturally cooled to room temperature to obtain a carbon material with a silicide coating on the surface.

2. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The molar ratio of the transition metal powder, sodium chloride and potassium chloride is (0.3-1):5:

5.

3. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The transition metal powder includes one or more of Ti, Zr, Hf, Ta and Mo.

4. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The carbon material includes one or more of carbon / carbon composite materials, graphite, diamond, amorphous carbon and carbon fiber.

5. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The carbon material is buried in the mixed molten salt, and during the reaction in the molten salt furnace, the molten salt furnace is heated to 800-1400° C. at a rate of 10-20° C. / min in an inert gas atmosphere and kept warm for 2-7 hours.

6. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The carbide coating includes one or more of TiC, TaC, HfC, ZrC, NbC and Mo2C.

7. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The silicon source includes one or more of elemental silicon, mixed powder of silicon and silicon dioxide, and SiO powder.

8. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The carbon material with a carbide coating on the surface is used as a template and embedded in a silicon source. During the high-temperature reaction, the temperature is increased to 1000-1600° C. at a heating rate of 10-20° C. / min in an inert gas atmosphere for 0.5-4 hours.

9. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The silicide coating includes one or more of titanium silicide, tantalum silicide, hafnium silicide, zirconium silicide, and molybdenum silicide.

10. The method for preparing a silicide coating at low temperature using carbide as a template according to claim 1, characterized in that: The preparation methods of the carbide coating and the silicide coating also include molten salt method, carbon thermal reduction method, slurry sintering method, sol-gel method and chemical vapor deposition method.

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