Method for preparing composite coating of ultra-high temperature ceramic and refractory metal silicide on surface of refractory alloy

Abstract

The present invention discloses a method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy. A method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicides is designed. The preparation method is as follows: (1) ZrC ceramic powder with good sphericity is prepared by a spray granulation method; (2) a gradient structure ultra-high temperature ceramic / refractory metal ((Zr,Ta)C-Ta(W)) coating is prepared on a Ta-10W substrate by a high-speed laser cladding process; (3) the refractory metal phase in the (Zr,Ta)C-Ta(W) coating is converted into a corresponding silicide phase by an embedded siliconization process, thereby obtaining an ultra-high temperature ceramic / refractory metal silicide ((Zr,Ta)C-TaSi2) composite coating. The novel composite coating of the present invention has the properties of uniform composition, high hardness, high density, continuous multilayer structure, and resistance to high temperature ablation.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-high temperature thermal protective coating preparation, and relates to a method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy. The present invention relates to a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy and a preparation method thereof, and specifically to a method for preparing an ultra-high temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating on the surface of a refractory alloy by using a high-speed laser cladding process and an embedded siliconization process. Background Art

[0002] Ta-10W alloy is widely used in hot-end components of aerospace due to its excellent mechanical properties at high temperatures. However, Ta-10W alloy is highly susceptible to oxidation in high-temperature oxygen-rich environments, necessitating the formation of a thermal protective coating on its surface.

[0003] Ultra-high temperature ceramics have the advantages of high melting point, high temperature strength, good oxidation resistance and ablation resistance, and have great application value in the field of oxidation resistance and ablation resistance of high temperature materials. Ultra-high temperature ceramics mainly include refractory metal borides and carbides, among which ZrC is the most representative, which has good thermal shock resistance, low density, high hardness, high melting point and moderate thermal expansion coefficient, as well as good high temperature mechanical properties and chemical stability. However, as a protective coating for metals, ceramic coatings also face problems such as thermal expansion coefficient mismatch, cracking and peeling of ceramic coatings during oxidation ablation, and effective protection of the substrate. At present, the surface technologies for preparing thermal protective coatings on the surface of refractory alloy substrates (including embedding, slurry sintering, chemical vapor deposition, plasma spraying, etc.) have their own advantages and limitations. Existing coating schemes are limited by material system, thickness, density, or bonding strength, and have always been unable to provide ideal oxidation resistance protection for refractory alloy substrates.

[0004] Ceramic coatings deposited using laser surface technology can form a metallurgical bond with the metal substrate. Furthermore, the rapid cooling and heating during high-speed laser cladding (HSL) results in finer microstructures and denser coatings. However, current research confirms that due to the extremely high laser energy density and the inherent brittleness of ultrahigh-temperature ceramics (UHTC) materials, producing complete UHTC coatings using HSL is difficult. The recent emergence and development of high-speed laser cladding (HSL) technology promises to address these challenges. HSL allows the majority of the laser energy to be applied directly to the powder in flight, while reducing the energy applied to the substrate. This effectively manages the energy balance between the powder and the substrate. (Conventional laser heat source coating deposition techniques, on the other hand, apply nearly all of the energy directly to the substrate (sub)surface or within the melt pool, resulting in brittle cracking and spalling of the resulting UHTC coatings.) However, coatings deposited using HSL inevitably contain small amounts of refractory metal phases, which negatively impact the coating's high-temperature ablation resistance. Therefore, how to combine the advantages of the above processes to prepare a composite coating with excellent anti-oxidation and ablation properties and metallurgical bonding properties is a key challenge faced in the preparation of ultra-high temperature ceramic-based composite coatings.

[0005] At present, the preparation process and advantages and disadvantages of anti-oxidation ablative coatings are as follows:

[0006] (1) Physical vapor deposition: The commonly used method is magnetron sputtering, which can be used to prepare coatings of high-melting-point materials such as SiC, HfB2 and ZrB2. However, the thickness of the prepared coating is thin, usually not exceeding 50 μm, and it takes longer time than other preparation methods;

[0007] (2) Chemical vapor deposition: It can prepare high-melting-point coatings at low temperatures and can precisely control the composition of the coatings. However, the deposition efficiency of the coatings is low, the production cost is high, and the raw gas and waste gas after the reaction are toxic, flammable, and explosive, which can easily cause safety hazards.

[0008] (3) Slurry sintering method: It has the advantages of simple process, low equipment requirements, no influence from substrate shape, low preparation cost and easy industrialization. However, the thickness uniformity of the coating prepared by this process is poor, there are many defects, and the temperature resistance of the prepared silicide system does not exceed 1700℃.

[0009] (4) Embedding method: It has the advantages of simple equipment, simple operation, good bonding between coating and substrate, ability to simultaneously realize co-penetration of multiple elements, ability to prepare coatings with excellent performance for products with complex shapes, and low environmental pollution. However, the coating thickness is difficult to control and may have a certain impact on the substrate. The coating thickness is usually less than 200µm, otherwise the silicide layer is prone to brittle cracking, and the material system is limited to silicide or aluminide, and the oxidation resistance temperature does not exceed 1700℃;

[0010] (5) Plasma spraying: It has the advantages of fast coating deposition rate, easy to control coating thickness, simple operation, and suitability for large-scale production. However, plasma spray coatings have disadvantages such as high porosity and poor bonding with the substrate. Oxygen can easily invade and oxidize the substrate during service.

[0011] Therefore, it is crucial to carry out research on new ultra-high temperature thermal protection coatings to meet the thermal protection needs of the surfaces of refractory metal hot end components serving in extreme ultra-high temperature (≥1800℃) environments. Summary of the Invention

[0012] In response to the problems existing in the ultra-high temperature ceramic coatings in the prior art, and taking into account the advantages and disadvantages of the existing coating preparation processes and materials, as well as the failure modes of anti-ablation coatings, the present invention provides a method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy, a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy and a preparation method thereof, and also an ultra-high temperature ceramic / refractory metal silicide ((Zr, Ta)C-Ta(W)) coating on the surface of a refractory alloy and a preparation method thereof, specifically: first, a gradient structured ultra-high temperature ceramic / refractory metal (Zr, Ta)C-Ta(W) coating is prepared on a Ta-10W substrate by a high-speed laser cladding process; further, an embedded siliconization process is used to convert the refractory metal phase in the (Zr, Ta)C-Ta(W) coating into a corresponding silicide phase, thereby obtaining a highly dense, thick, continuous multi-layered ultra-high temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating.

[0013] The technical solutions of the present invention are as follows:

[0014] A method for preparing a composite coating of ultra-high temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) is as follows:

[0015] (1) ZrC ceramic powder with good sphericity was prepared by spray granulation method;

[0016] (2) A gradient structured ultrahigh temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating was prepared on a Ta-10W substrate using a high-speed laser cladding process.

[0017] (3) The embedded siliconization process is used to convert the refractory metal phase in the (Zr, Ta)C-Ta(W) coating into the corresponding silicide phase, thereby obtaining an ultra-high temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating.

[0018] The novel composite coating prepared in the present invention has the properties of uniform tissue composition, high hardness, high density, continuous multilayer structure, high temperature ablation resistance and the like.

[0019] The purpose of the present invention is achieved through the following technical solutions:

[0020] A method for preparing an ultrahigh-temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating on a refractory alloy surface, also comprising the following steps:

[0021] S1. Spray granulation ZrC powder:

[0022] S1-1. Slurry preparation: High-purity zirconium carbide ceramic powder, purified water, polyvinyl alcohol (PVA), polyethylene glycol (PEG), and n-butanol were mixed in a ratio of 100 g:82 mL:16 g:2 g:1 mL using a mechanical stirrer at a speed of 500 rpm for 2 h to obtain a ceramic slurry for spray granulation.

[0023] S1-2, spray granulation: The ceramic slurry is granulated using a spray granulation device to obtain a nearly spherical ZrC powder, wherein the process parameters of the spray granulation device are: air inlet temperature 240°C, air outlet temperature 160°C, atomizer frequency 50 Hz, and peristaltic pump speed 10 rpm;

[0024] After granulation, the ZrC powder was collected and dried, and sieved with a 180-mesh standard sieve to obtain -180-mesh ZrC powder, which was used for high-speed laser cladding to prepare the coating.

[0025] S2. High-speed laser cladding for ultra-high temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coatings:

[0026] S2-1. Pre-treatment of the Ta-10W substrate surface by rust removal and oil removal: polish the substrate with #200, #400, #600, and #800 sandpaper for 2 minutes each, and then ultrasonically clean the substrate with acetone or anhydrous ethanol to remove oil and impurities on the surface at an ultrasonic power of 150W for a total of 15 minutes;

[0027] S2-2. The ZrC ceramic powder obtained in S1-2 is loaded into a powder feeder of a high-speed laser cladding equipment, and then fed into the high-speed laser cladding equipment equipped with a synchronous powder feeding head. The laser focus formed by the high-speed cladding laser head emitting laser light is aligned with the powder spot focus formed by the synchronous powder feeding head feeding powder. The overlapping position of the two focal points is adjusted to be 1 mm above the surface of the substrate. The substrate is subjected to high-speed laser cladding in a local inert gas protective atmosphere. The zirconium carbide undergoes a phase transformation under the action of the high-energy laser beam to form an ultra-high temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating having both a ceramic phase and a metal phase.

[0028] The process parameters of high-speed laser cladding are as follows: laser power is set to 2500W, scanning rate is 80mm / s, and overlap rate is 85%;

[0029] S3. Ball milling to prepare powder for embedded siliconization process:

[0030] S3-1. Powders for embedded siliconization process: weigh 25% Si powder, 68% Al2O3 powder, 5% Y2O3 powder and 2% NaF powder according to the mass ratio; Si powder is used as silicon source, Al2O3 powder and Y2O3 powder are used as dispersants, and NaF powder is used as activator;

[0031] Among them, the Si powder particle size is 300 mesh, purity 99.99%; the Al2O3 powder particle size is 100 mesh, purity 99.99%; the Y2O3 powder particle size is 100 mesh, purity 99.99%; the NaF powder particle size is 100 mesh, purity 99.99%;

[0032] S3-2. Place the weighed powder raw materials in a ball mill, and use a planetary mill to refine and mix the powders. The ball-to-material ratio is 2:1, the ball mill speed is 250 r / min, and the ball milling time is 5 h to obtain powder for the embedded siliconization process;

[0033] S4. Preparation of ultra-high temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating by embedded siliconization process:

[0034] S4-1: Cut the ultrahigh-temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating prepared in S2 into a 28mm×18mm×5mm rectangular parallelepiped specimen. Use sandpaper to remove wire cutting marks on all surfaces of the specimen except the coating surface until the surface is smooth and free of scratches. Use a 30ml crucible. To ensure a certain distance from the crucible mouth, use 24g of mixed siliconizing agent for a single siliconizing process.

[0035] S4-2: Take out the siliconized powder after ball milling in S3-2, weigh 12g, and place it in a crucible and compact it. Place the sample to be siliconized in the center area. Then weigh another 10g of powder for the embedded siliconizing process and cover the sample and compact it. Mix appropriate amounts of neutral alumina and silica sol to prepare a sealing slurry to seal the crucible lid and the crucible. Place the sealed crucible on a corundum boat and push it to the center of the tube furnace heating tube so that the crucible is fixed in the highest temperature area during heating and insulation, and is heated evenly.

[0036] S4-3: Place the crucible on a corundum boat and place it in the center of a tube furnace. Evacuate the crucible and continue evacuating for 10 minutes after the pressure inside the tube drops to 0.1 MPa. Then turn off the mechanical pump. Introduce argon until the pressure inside the tube reaches atmospheric pressure. 10 minutes later, start heating and continue ventilating. The argon flow rate is 100 ml / min. Set the heating and cooling programs of the tube furnace with a heating rate of 10°C / min, a holding temperature of 1200°C, a holding time of 24 hours, and a cooling rate of 10°C / min to room temperature. A composite coating of ultrahigh temperature ceramics and refractory metal silicide ((Zr, Ta)C-TaSi2) on the surface of a refractory alloy is obtained. The composite coating of ultrahigh temperature ceramics and refractory metal silicide on the surface of a refractory alloy has a continuous multilayer structure, with a top layer of (Zr, Ta)C-TaSi2 and a transition layer of (Zr, Ta)C-Ta(W), the coating and the substrate have a metallurgical bonding interface; density>98.5%, thickness ≥300μm, average hardness>1568.34 Hv 0.5 (The highest hardness is 1673.67 Hv 0.5 ), can maintain 300 seconds under plasma beam ablation conditions of 2000-2100℃ to completely protect the substrate from being damaged.

[0037] The present invention also relates to a composite coating of ultrahigh temperature ceramics and refractory metal silicides on the surface of a refractory alloy, which is obtained by using the above-mentioned method for preparing a composite coating of ultrahigh temperature ceramics and refractory metal silicides on the surface of a refractory alloy. The obtained composite coating of ultrahigh temperature ceramics and refractory metal silicides on the surface of a refractory alloy has a continuous multilayer structure, a top layer of (Zr, Ta)C-TaSi2, a transition layer of (Zr, Ta)C-Ta(W), and a metallurgical bonding interface between the coating and the substrate; the density is greater than 98.5%, the thickness is greater than 300 μm, and the average hardness is greater than 1568.34 Hv 0.5 (The highest hardness is 1673.67 Hv 0.5 ), can maintain complete protection of the substrate from damage for 300 seconds under plasma beam ablation conditions of 2000-2100℃; significantly superior to existing technologies, this process has the advantages of short preparation cycle, controllable coating thickness, and the ability to prepare complex shapes. Specifically:

[0038] ① The composite coating has a density of >98.5%, effectively blocks oxygen, and has controllable thickness. Thick coatings exceeding 300μm can be prepared as required, achieving a continuous transition from ultra-high temperature ceramic / refractory metal silicide composite coating, ultra-high temperature ceramic / refractory metal transition layer to refractory alloy substrate;

[0039] ② The composite coating was subjected to ablation test under a plasma beam. After 300 seconds of ablation at 1900°C, an oxide layer was produced on the surface of the ablation center area. As the temperature changed, the composition of the oxide layer also changed to a certain extent, mainly consisting of ZrO2 and SiO2. That is, after ablation, the coating surface was transformed from a mixture of multiple ceramic phases of Al2O3, TaSi2, and ZrSi2 into an oxide layer composed of Al2O3, ZrO2, and SiO2, which together resisted the erosion of subsequent high-temperature airflow. The siliconized layer below was not affected by the ablation and was in a completely protected state.

[0040] ③ After 300s of plasma beam ablation at 2000-2100℃, the coating surface is slightly damaged, and the generated oxides such as SiO2 are washed away, causing the subsequent sub-surface layer to be oxidized, but the coating can still completely protect the substrate from oxidation.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] 1. The present invention discloses a method for preparing a composite coating of ultrahigh-temperature ceramic and refractory metal silicide on a refractory alloy surface. A method for preparing an ultrahigh-temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating on a refractory alloy surface is proposed. ZrC ceramic powder with micron-sized particles and good sphericity is prepared by spray granulation. By combining the advantages of a high-speed laser cladding process and an embedded siliconization process, a composite coating with excellent oxidation and ablation resistance and metallurgical bonding properties is prepared. A gradient-structured ultrahigh-temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating is first prepared on a Ta-10W substrate by a high-speed laser cladding process. Furthermore, an embedded siliconization process is used to convert the refractory metal phase in the composite coating into a corresponding silicide phase, thereby obtaining a highly dense, thick, continuous multilayered ultrahigh-temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating.

[0043] 2. A method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicide on a refractory alloy surface according to the present invention:

[0044] ① The micron-sized ZrC ceramic powder with good sphericity obtained by spray granulation method has a particle size of 80 µm, good fluidity, and is not easy to get stuck, which is conducive to subsequent high-speed laser cladding;

[0045] ② The gradient structure of the ultra-high temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) composite coating prepared on the Ta-10W substrate by high-speed laser cladding technology has the advantage of metallurgical bonding, and there is no need to worry about the potential risk of thermal protection coating falling off during service;

[0046] ③ The (Zr, Ta)C-Ta(W) coating undergoes silicification treatment via an embedded siliconization process, transforming the refractory metal phase within the (Zr, Ta)C-Ta(W) coating into the corresponding silicide phase, resulting in an ultra-high-temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating. The longer the embedded siliconization holding time, the thicker the siliconized layer. During the embedded siliconization process, the formation of silicides causes a certain degree of expansion in the coating, which positively impacts its internal density and reduces porosity. This expansion also generates compressive stress in the coating, and prolonged high-temperature treatment improves the bonding strength between the coating and the substrate.

[0047] 3. The method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy described in the present invention realizes the overall preparation of a new ultra-high temperature multiphase ceramic coating (i.e., a composite of ultra-high temperature ceramics and high temperature silicide ceramic phases). The thermal protective coating has a density of >98.5%, can effectively block oxygen, and has controllable thickness. A thick coating with a thickness exceeding 300μm can be prepared according to demand; and a continuous transition from the ultra-high temperature ceramic / refractory metal silicide composite coating, the ultra-high temperature ceramic / refractory metal transition layer to the refractory alloy substrate is realized.

[0048] 4. The present invention describes a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy. The coating sample was subjected to ablation test under a plasma beam. After 300 seconds of beam ablation at 1800-1900°C, an oxide layer was generated on the surface of the ablation center area. As the temperature changes, the composition of the oxide layer also changes to a certain extent, mainly consisting of two components: ZrO2 and SiO2. That is, after ablation, the coating surface is transformed from a mixture of multiple ceramic phases such as Al2O3, TaSi2, and ZrSi2 into an oxide layer composed of Al2O3, ZrO2, and SiO2, which together resist the subsequent erosion of high-temperature airflow, so that the sub-surface siliconized layer below is not affected by ablation and is in a completely protected state. After 300 seconds of beam ablation at 2000-2100°C, the coating surface is slightly damaged, and the oxides such as SiO2 generated at the same time are washed away, so that the subsequent sub-surface layer is oxidized, but the coating can still completely protect the substrate from oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with Example 1 of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention.

[0050] Figure 1 This is a SEM image of ZrC powder prepared by spray granulation in the method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicide on the surface of a refractory alloy according to the present invention;

[0051] Figure 2 A cross-sectional SEM image of an ultrahigh-temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating according to the method for preparing a composite coating of ultrahigh-temperature ceramic and refractory metal silicide on a refractory alloy surface according to the present invention;

[0052] Figure 3 This is a cross-sectional SEM image of a composite coating of ultrahigh-temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 on the surface of a refractory alloy prepared in Example 1 of the present invention;

[0053] Figure 4 XRD pattern of a composite coating of ultrahigh-temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 on the surface of a refractory alloy prepared in Example 1 of the present invention;

[0054] Figure 5 The ablation curve of a composite coating of ultra-high temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 on a refractory alloy surface prepared in Example 1 of the present invention after ablation at 1800-1900°C for 300s, as well as the surface morphology of the coating during ablation;

[0055] Figure 6 Cross-sectional morphology of a composite coating of ultra-high temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 on a refractory alloy surface prepared in Example 1 of the present invention after ablation at 1800-1900°C for 300s:

[0056] Figure 7 The ablation curve of a composite coating of ultra-high temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 on a refractory alloy surface prepared in Example 2 of the present invention after ablation at 2000-2100°C for 300s, as well as the surface morphology of the coating during ablation;

[0057] Figure 8 This is a cross-sectional morphology of a composite coating of ultra-high temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 on a refractory alloy surface prepared in Example 2 of the present invention after ablation at 2000-2100°C for 300s;

[0058] Figure 9 This is a macroscopic morphology of the surface of the ultra-high temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating prepared in the comparative example of the present invention after ablation at 2000-2100°C for 12s. DETAILED DESCRIPTION

[0059] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0060] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0062] The present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, identical elements are represented by similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0063] Features described and / or illustrated with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0064] Example 1:

[0065] A method for preparing a composite coating of ultra-high temperature ceramic and refractory metal silicide on the surface of a refractory alloy comprises the following steps:

[0066] Step 1: Prepare slurry: High-purity zirconium carbide ceramic powder, purified water, PVA (polyvinyl alcohol), PEG (polyethylene glycol), and n-butanol are stirred in a ratio of 100 g:82 mL:16 g:2 g:1 mL using a mechanical stirrer (speed 500 rpm) for 2 h to obtain a ceramic slurry for spray granulation.

[0067] Step 2: Spray granulation: The ceramic slurry is granulated using a spray granulation device to obtain a nearly spherical ZrC powder. The process parameters of the spray granulation device are: air inlet temperature 240°C, air outlet temperature 160°C, atomizer frequency 50Hz, and peristaltic pump speed 10rpm. After granulation, the collected powder is dried and sieved using a 180-mesh standard sieve to obtain a -180-mesh powder for high-speed laser cladding coating preparation.

[0068] Step 3: Pre-treat the Ta-10W substrate surface by removing rust and oil: polish the substrate with #200, #400, #600, and #800 sandpaper for 2 minutes each, and then use acetone or anhydrous ethanol to ultrasonically clean the surface to remove oil and impurities at an ultrasonic power of 150W for a total of 15 minutes.

[0069] Step 4: Load ZrC ceramic powder into the powder feeder of the high-speed laser cladding equipment and feed it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head. The laser focus formed by the high-speed cladding laser head emitting laser light is aligned with the powder spot focus formed by the synchronous powder feeding head. The overlapping position of the two focal points is then adjusted to be 1 mm above the substrate surface. The substrate is then subjected to high-speed laser cladding under a local inert gas protective atmosphere. The zirconium carbide undergoes a phase transformation under the action of the high-energy laser beam, forming a composite coating with both ceramic and metallic phases. The process parameters for high-speed laser cladding are: laser power set to 2500W, scanning rate of 80mm / s, and overlap rate of 85%.

[0070] Step 5: The powders used in the embedded siliconization process are Si powder as the silicon source, Al2O3 and Y2O3 powders as dispersants, and NaF powder as the activator. According to the mass ratio, 25% Si powder, 68% Al2O3, 5% Y2O3 and 2% NaF are weighed. Among them, the Si particle size is 300 mesh and the purity is 99.99%, the Al2O3 particle size is 100 mesh and the purity is 99.99%, the Y2O3 particle size is 100 mesh and the purity is 99.99%, and the NaF particle size is 100 mesh and the purity is 99.99%.

[0071] Step 6: Place the weighed powder raw materials in a ball mill and use a planetary mill to grind the powder into fine powder and mix it evenly; the ball-to-material ratio is 2:1, the ball mill speed is 250r / min, and the ball milling time is 5h;

[0072] Step 7: Cut the high-speed laser cladding ZrC ultra-high temperature ceramic coating into a 28mm×18mm×5mm rectangular parallelepiped sample. Use sandpaper to remove the wire cutting marks on all surfaces of the sample except the coating surface until the surface is smooth and free of scratches. Use a 30ml crucible. To ensure a certain distance from the crucible mouth, the mixed siliconizing dosage used for a single siliconizing is 24g.

[0073] Step 8: Take out the siliconized powder after ball milling, weigh 12g and put it into the crucible and compact it, put the sample to be siliconized into the center area, and then weigh 10g of the infiltrant powder again to cover the sample and compact it; mix the neutral alumina and silica sol in appropriate amounts to prepare a sealing slurry to seal the crucible cover and the crucible; place the sealed crucible on the corundum boat and push it to the center of the tube furnace heating tube, so that the crucible is fixed in the highest temperature area during heating and insulation and is heated evenly;

[0074] Step 9: Place the crucible on the corundum boat and place it in the center of the tube furnace. Evacuate the tube until the pressure inside the tube drops to 0.1 MPa and continue to evacuate for 10 minutes, then turn off the mechanical pump; introduce argon until the pressure inside the tube rises to atmospheric pressure for 5 minutes, then start heating and continue ventilating; the argon flow rate is 100 ml / min; set the tube furnace heating and cooling program with a heating rate of 10°C / min, a holding temperature of 1200°C, a holding time of 24 hours, and a cooling rate of 10°C / min to cool to room temperature;

[0075] Step 10: Plasma beam ablation test was performed on the ultra-high temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating sample using a plasma beam at an ablation temperature of 1800-1900°C and an ablation time of 300s.

[0076] By observing and analyzing the surface of the sample after ablation, the coating surface has slight ablation marks and a small amount of ablation holes, but no obvious cracks on the surface;

[0077] result:

[0078] In view of the fact that in Example 1, after the prepared coating was ablated under a beam at 1800-1900°C for 300s, only the surface of the coating suffered obvious ablation damage, and the inner layer of the coating remained intact, having good anti-oxidation and ablation performance, in Example 2, the coating was tested by ablation under a beam at 2000-2100°C for 300s, and the test results are shown in Example 2.

[0079] Figure 1 This is a SEM image of ZrC powder prepared by spray granulation in the method for preparing a composite coating of ultrahigh temperature ceramic and refractory metal silicide on the surface of a refractory alloy described in step 2 of Example 1;

[0080] Figure 2 This is a cross-sectional SEM image of an ultrahigh temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating according to the method for preparing an ultrahigh temperature ceramic and refractory metal silicide composite coating on a refractory alloy surface described in step 4 of Example 1;

[0081] Figure 3 This is a cross-sectional SEM image of the composite coating of ultrahigh temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) after the embedded siliconization process in step nine of Example 1;

[0082] Figure 4 This is the XRD pattern of the surface of the ultra-high temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating after the embedded siliconization process in step nine of Example 1;

[0083] Figure 5The ablation curve of the ultrahigh temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 composite coating ablated at 1800-1900°C for 300s in step 10 of Example 1, and the surface morphology of the coating during ablation;

[0084] Figure 6 This is a cross-sectional morphology of the ultrahigh temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 composite coating after ablation at 1800-1900°C for 300s in Step 10 of Example 1.

[0085] Example 2

[0086] A method for preparing a composite coating of ultra-high temperature ceramic and refractory metal silicide on the surface of a refractory alloy comprises the following steps:

[0087] Step 1: Prepare slurry: High-purity zirconium carbide ceramic powder, purified water, PVA (polyvinyl alcohol), PEG (polyethylene glycol), and n-butanol are stirred in a ratio of 100 g:82 mL:16 g:2 g:1 mL using a mechanical stirrer (speed 500 rpm) for 2 h to obtain a ceramic slurry for spray granulation.

[0088] Step 2: Spray granulation: The ceramic slurry is granulated using a spray granulation device to obtain a nearly spherical ZrC powder. The process parameters of the spray granulation device are: air inlet temperature 240°C, air outlet temperature 160°C, atomizer frequency 50Hz, and peristaltic pump speed 10rpm. After granulation, the collected powder is dried and sieved using a 180-mesh standard sieve to obtain a -180-mesh powder for high-speed laser cladding coating preparation.

[0089] Step 3: Pre-treat the surface of the Ta-10W substrate by removing rust and oil; polish the substrate with #200, #400, #600, and #800 sandpaper for 2 minutes each, and then ultrasonically clean the substrate with acetone or anhydrous ethanol to remove oil and impurities on the surface at an ultrasonic power of 150W for a total of 15 minutes;

[0090] Step 4: Load ZrC ceramic powder into the powder feeder of the high-speed laser cladding equipment and feed it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head. The laser focus formed by the high-speed cladding laser head emitting laser light is aligned with the powder spot focus formed by the synchronous powder feeding head. The overlapping position of the two focal points is then adjusted to be 1 mm above the substrate surface. The substrate is then subjected to high-speed laser cladding under a local inert gas protective atmosphere. The zirconium carbide undergoes a phase transformation under the action of the high-energy laser beam, forming a composite coating with both ceramic and metallic phases. The process parameters for high-speed laser cladding are: laser power set to 2500W, scanning rate of 80mm / s, and overlap rate of 85%.

[0091] Step 5: The powders used in the embedded siliconization process are Si powder as the silicon source, Al2O3 and Y2O3 powders as dispersants, and NaF powder as the activator. According to the mass ratio, 25% Si powder, 68% Al2O3, 5% Y2O3 and 2% NaF are weighed. Among them, the Si particle size is 300 mesh and the purity is 99.99%, the Al2O3 particle size is 100 mesh and the purity is 99.99%, the Y2O3 particle size is 100 mesh and the purity is 99.99%, and the NaF particle size is 100 mesh and the purity is 99.99%.

[0092] Step 6: Place the weighed powder raw materials in a ball mill and use a planetary mill to grind the powder into fine powder and mix it evenly; the ball-to-material ratio is 2:1, the ball mill speed is 250r / min, and the ball milling time is 5h;

[0093] Step 7: Cut the high-speed laser cladding ZrC ultra-high temperature ceramic coating into a 28mm×18mm×5mm rectangular parallelepiped sample. Use sandpaper to remove the wire cutting marks on all surfaces of the sample except the coating surface until the surface is smooth and free of scratches. Use a 30ml crucible. To ensure a certain distance from the crucible mouth, the mixed siliconizing dosage used for a single siliconizing is 24g.

[0094] Step 8: Take out the siliconized powder after ball milling, weigh 12g and put it into the crucible and compact it, put the sample to be siliconized into the center area, and then weigh 10g of the infiltrant powder again to cover the sample and compact it; mix the neutral alumina and silica sol in appropriate amounts to prepare a sealing slurry to seal the crucible cover and the crucible; place the sealed crucible on the corundum boat and push it to the center of the tube furnace heating tube, so that the crucible is fixed in the highest temperature area during heating and insulation and is heated evenly;

[0095] Step 9: Place the crucible on the corundum boat and place it in the center of the tube furnace. Evacuate the tube until the pressure inside the tube drops to 0.1 MPa and continue to evacuate for 10 minutes, then turn off the mechanical pump; introduce argon until the pressure inside the tube rises to atmospheric pressure for 5 minutes, then start heating and continue ventilating; the argon flow rate is 100 ml / min; set the tube furnace heating and cooling program with a heating rate of 10°C / min, a holding temperature of 1200°C, a holding time of 24 hours, and a cooling rate of 10°C / min to cool to room temperature;

[0096] Step 10: Use plasma beam to conduct ultra-high temperature ablation test on the ultra-high temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating sample, with an ablation temperature of 2000-2100℃ and an ablation time of 300s.

[0097] result:

[0098] After 300s of beam ablation at 2000-2100℃, the coating surface is slightly damaged, and the generated oxides such as SiO2 are washed away, causing the subsequent sub-surface layer to be oxidized, but the coating can still completely protect the substrate from oxidation.

[0099] Figure 7 The ablation curve of the ultrahigh temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 composite coating ablated at 2000-2100°C for 300s in step 10 of Example 2, and the surface morphology of the coating during ablation;

[0100] Figure 8 This is a cross-sectional morphology of the ultrahigh temperature ceramic and refractory metal silicide (Zr, Ta)C-TaSi2 composite coating after ablation at 2000-2100°C for 300s in Step 10 of Example 2.

[0101] Comparative Example:

[0102] The difference between the comparative example and Example 1 is that the comparative example 1 does not perform the embedded siliconization process step, and the ablation test is directly performed on the ultra-high temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) coating, while Example 1 performs the embedded siliconization process step and performs an ablation test on the embedded siliconized high temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating;

[0103] The preparation method of the comparative example comprises the following steps:

[0104] Step 1: Prepare slurry: High-purity zirconium carbide ceramic powder, purified water, PVA (polyvinyl alcohol), PEG (polyethylene glycol), and n-butanol are stirred in a ratio of 100 g:82 mL:16 g:2 g:1 mL using a mechanical stirrer (speed 500 rpm) for 2 h to obtain a ceramic slurry for spray granulation.

[0105] Step 2: Spray granulation: The ceramic slurry is granulated using a spray granulation device to obtain a nearly spherical ZrC powder. The process parameters of the spray granulation device are: air inlet temperature 240°C, air outlet temperature 160°C, atomizer frequency 50Hz, and peristaltic pump speed 10rpm. After granulation, the collected powder is dried and sieved using a 180-mesh standard sieve to obtain a -180-mesh powder for high-speed laser cladding coating preparation.

[0106] Step 3: Pre-treat the surface of the Ta-10W substrate by removing rust and oil; polish the substrate with #200, #400, #600, and #800 sandpaper for 2 minutes each, and then ultrasonically clean the substrate with acetone or anhydrous ethanol to remove oil and impurities on the surface at an ultrasonic power of 150W for a total of 15 minutes;

[0107] Step 4: Load ZrC ceramic powder into the powder feeder of the high-speed laser cladding equipment and feed it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head. The laser focus formed by the high-speed cladding laser head emitting laser light is aligned with the powder spot focus formed by the synchronous powder feeding head. The overlapping position of the two focal points is then adjusted to be 1 mm above the substrate surface. The substrate is then subjected to high-speed laser cladding under a local inert gas protective atmosphere. The zirconium carbide undergoes a phase transformation under the action of the high-energy laser beam, forming a composite coating with both ceramic and metallic phases. The process parameters for high-speed laser cladding are: laser power set to 2500W, scanning rate of 80mm / s, and overlap rate of 85%.

[0108] Step 5: Use plasma beam to perform ultra-high temperature ablation test on the sample, with the ablation temperature of 2000-2100℃ and the ablation time of 12s;

[0109] result:

[0110] By comparing the comparative example with Examples 1-2, the coatings obtained in Examples 1 and 2 can achieve ideal anti-ablation performance only after being treated with the embedded siliconization process, while the coating obtained in Comparative Example 1 was not treated with the embedded siliconization process, so the coating was ablated and damaged after ablation at 2000-2100°C for 12s.

[0111] Figure 9 The surface morphology of the sample after ablation at a temperature of 2000-2100°C and ablation time of 12s in step 5 of the comparative example is shown in FIG. Figure 9 As shown in Figure 3, the (Zr, Ta)C-Ta(W) coating that has not been treated with the embedded siliconization process undergoes destructive ablation after being ablated for 12 seconds at 2000-2100℃, and the substrate is exposed and melted.

[0112] Results and Discussion

[0113] As can be seen from the above examples, the present invention provides a method for preparing an ultrahigh-temperature ceramic and refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating on a refractory alloy surface. Combining the advantages of high-speed laser cladding and embedded siliconization, a gradient-structured ultrahigh-temperature ceramic / refractory metal ((Zr, Ta)C-Ta(W)) composite coating is first fabricated on a Ta-10W substrate using the high-speed laser cladding process. This coating offers the advantages of metallurgical bonding, eliminating the risk of potential thermal protective coating shedding during service. The (Zr, Ta)C-Ta(W) coating is then silicided using an embedded siliconization process to transform the refractory metal phase in the composite coating into its corresponding silicide phase, resulting in an ultrahigh-temperature ceramic / refractory metal silicide ((Zr, Ta)C-TaSi2) composite coating exhibiting both excellent oxidation and ablation resistance and metallurgical bonding properties.

[0114] It can be seen from the comparative examples that when the coating is not combined using the process used in the present invention, the presence of the metal phase in the coating will cause the coating to fail quickly during the ablation process.

[0115] In summary, the present invention achieves the fabrication of a novel ultrahigh-temperature composite ceramic coating (i.e., a composite of ultrahigh-temperature ceramic and high-temperature silicide ceramic phases). This composite coating exhibits a density exceeding 98.5%, effectively blocks oxygen, and has controllable thickness, enabling the production of coatings exceeding 300 μm on demand. A continuous transition from the ultrahigh-temperature ceramic / refractory metal silicide composite coating, the ultrahigh-temperature ceramic / refractory metal transition layer, to the refractory alloy substrate is achieved. Coating samples were subjected to plasma beam ablation testing. Under beam ablation at 1800-1900°C, an oxide layer formed on the surface of the ablated central region. The composition of the oxide layer varied with temperature, primarily consisting of ZrO₂ and SiO₂. Consequently, after ablation, the coating surface transformed from a mixture of various ceramic phases, including Al₂O₃, TaSi₂, and ZrSi₂, into an oxide layer composed primarily of Al₂O₃, ZrO₂, and SiO₂, which together resisted subsequent high-temperature airflow erosion. This protected the underlying subsurface siliconized layer from ablation, leaving it completely protected. Under beam ablation at 2000-2100℃, the coating surface is slightly damaged, and the generated oxides such as SiO2 are washed away, causing the subsequent sub-surface layer to be oxidized, but the coating can still completely protect the substrate from oxidation.

[0116] It is important to note that although the present invention uses zirconium carbide (ZrC) ultra-high temperature ceramics as powder feed, the scope of protection is not limited to ZrC ultra-high temperature ceramics. Other ultra-high temperature ceramic systems (such as ZrB2, etc.) can also be tried and should be included in the scope of protection of this patent.

[0117] Similarly, although the present invention uses Ta-10W refractory metal as the matrix material, the scope of protection is not limited to Ta-10W refractory metal. Other refractory metal systems (such as Ta-12W, molybdenum alloy, etc.) can also be tried and should also be included in the scope of protection of this patent.

[0118] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a composite coating of ultra-high temperature ceramics and refractory metal silicide on the surface of a refractory alloy, characterized by: The following steps are involved: S1. Spray granulation ZrC powder: S1-1. Slurry preparation: high-purity zirconium carbide ceramic powder, purified water, polyvinyl alcohol, polyethylene glycol, and n-butanol were stirred in a mechanical stirrer at a ratio of 100 g:82 ml:16 g:2 g:1 ml at a speed of 500 rpm for 2 h to obtain a ceramic slurry for spray granulation; S1-2, spray granulation: The ceramic slurry is granulated using a spray granulation device to obtain a nearly spherical ZrC powder, wherein the process parameters of the spray granulation device are: air inlet temperature 240°C, air outlet temperature 160°C, atomizer frequency 50 Hz, and peristaltic pump speed 10 rpm; After granulation, the ZrC powder was collected and dried, and sieved with a 180-mesh standard sieve to obtain -180-mesh ZrC powder, which was used for high-speed laser cladding to prepare the coating. S2. High-speed laser cladding to prepare ultra-high temperature ceramic / refractory metal coatings: S2-1. Pre-treatment of the Ta-10W substrate surface by rust removal and oil removal: polish the substrate with #200, #400, #600, and #800 sandpaper for 2 minutes each, and then ultrasonically clean the substrate with acetone or anhydrous ethanol to remove oil and impurities on the surface at an ultrasonic power of 150W for a total of 15 minutes; S2-2. The ZrC ceramic powder obtained in S1-2 is loaded into a powder feeder of a high-speed laser cladding equipment, and then fed into a high-speed laser cladding equipment equipped with a synchronous powder feeding head. The laser focus formed by the high-speed cladding laser head emitting laser light is overlapped with the powder spot focus formed by the synchronous powder feeding head feeding powder. The overlapping position of the two focal points is then adjusted to be 1 mm above the surface of the substrate. The substrate is subjected to high-speed laser cladding in a local inert gas protective atmosphere. The zirconium carbide undergoes a phase change under the action of the high-energy laser beam to form an ultra-high temperature ceramic / refractory metal coating having both a ceramic phase and a metal phase. The process parameters of high-speed laser cladding are as follows: laser power is set to 2500W, scanning rate is 80mm / s, and overlap rate is 85%; S3. Ball milling to prepare powder for embedded siliconization process: S3-1. Powders for embedded siliconization process: weigh 25% Si powder, 68% Al2O3 powder, 5% Y2O3 powder and 2% NaF powder according to the mass ratio; Si powder is used as silicon source, Al2O3 powder and Y2O3 powder are used as dispersants, and NaF powder is used as activator; Among them, the Si powder particle size is 300 mesh, purity 99.99%; the Al2O3 powder particle size is 100 mesh, purity 99.99%; the Y2O3 powder particle size is 100 mesh, purity 99.99%; the NaF powder particle size is 100 mesh, purity 99.99%; S3-2. Place the weighed powder raw materials in a ball mill, and use a planetary mill to refine and mix the powders. The ball-to-material ratio is 2:1, the ball mill speed is 250 r / min, and the ball milling time is 5 h to obtain powder for the embedded siliconization process; S4. Preparation of ultra-high temperature ceramic / refractory metal silicide composite coating by embedded siliconization process: S4-1: Cut the ultra-high temperature ceramic / refractory metal coating prepared in S2 into a 28mm×18mm×5mm rectangular parallelepiped specimen. Use sandpaper to remove wire cutting marks on all surfaces of the specimen except the coating surface until the surface is smooth and free of scratches. Use a 30ml crucible. To ensure a certain distance from the crucible mouth, the mixed siliconizing agent used for a single siliconizing is 24g. S4-2: Take out the siliconized powder after ball milling in S3-2, weigh 12g, and place it in a crucible and compact it. Place the sample to be siliconized in the center area. Then weigh another 10g of powder for the embedded siliconizing process and cover the sample and compact it. Mix appropriate amounts of neutral alumina and silica sol to prepare a sealing slurry to seal the crucible lid and the crucible. Place the sealed crucible on a corundum boat and push it to the center of the tube furnace heating tube so that the crucible is fixed in the highest temperature area during heating and insulation, and is heated evenly. S4-3: Place the crucible on a corundum boat and place it in the center of a tube furnace. Evacuate the crucible. After the pressure in the tube drops to 0.1 MPa, continue to evacuate for 10 minutes, and then turn off the mechanical pump. Add argon until the pressure in the tube reaches atmospheric pressure. 5 minutes later, start heating and continue venting. The argon flow rate is 100 ml / min. Set the heating and cooling programs of the tube furnace at a heating rate of 10°C / min, a holding temperature of 1200°C, a holding time of 24 hours, and a cooling rate of 10°C / min to room temperature to obtain a composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy. The obtained composite coating of ultra-high temperature ceramics and refractory metal silicides on the surface of a refractory alloy has a continuous multilayer structure, with a top layer of (Zr, Ta)C-TaSi2 and a transition layer of (Zr, Ta)C-TaW. The coating and the substrate have a metallurgical bonding interface. The composite coating has a density of >98.5%, a thickness of ≥300 μm, and an average hardness of >1568.34 HV 0.5 , the highest hardness reaches 1673.67 HV 0.5 , it can maintain complete protection of the substrate from damage for 300 seconds under plasma beam ablation conditions of 2000-2100℃.

2. A composite coating of ultra-high temperature ceramics and refractory metal silicide on the surface of a refractory alloy, characterized by: The method for preparing a composite coating of ultrahigh-temperature ceramics and refractory metal silicides on a refractory alloy surface according to claim 1 is used to obtain the composite coating. The composite coating has a continuous multilayer structure, a top layer of (Zr, Ta)C-TaSi2, a transition layer of (Zr, Ta)C-TaW, and a metallurgical bonding interface between the coating and the substrate. The composite coating has a density of >98.5%, a thickness of ≥300 μm, and an average hardness of >1568.34 HV. 0.5 , the highest hardness reaches 1673.67 HV 0.5 , it can maintain complete protection of the substrate from damage for 300 seconds under plasma beam ablation conditions of 2000-2100℃.

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