A high-temperature oxidation-resistant multilayer coating on a tantalum-tungsten alloy surface and a preparation method thereof

Abstract

The application discloses a high-temperature oxidation-resistant multilayer coating on a tantalum-tungsten alloy surface and a preparation method thereof, and is characterized by comprising the following steps: (1) preparing a composite diffusion barrier layer by a solid phase package infiltration method; (2) preparing a ZrB2-TaB2-HfB2-YB4 gradient transition layer by slurry spraying; and (3) preparing an oxidation-resistant top layer by slurry spraying in combination with the solid phase package infiltration method. The composite multilayer coating has three layers, the thermal expansion coefficients thereof present a step change, the distribution of thermal stress is effectively relieved, and an element barrier layer is further formed between the substrate and the coating at high temperature, which can effectively prevent the interdiffusion of the oxide-forming elements in the oxidation-resistant coating and the substrate elements, thereby slowing down the consumption of the oxidation-resistant elements. The prepared coating has strong bonding strength with the tantalum-tungsten alloy substrate, can protect the tantalum-tungsten alloy substrate from oxidation corrosion or slow down the oxidation rate at a higher temperature (above 2050 DEG C) for more than 500 s.

Description

Technical Field

[0001] This invention relates to the field of high-temperature antioxidant coatings, and in particular to a high-temperature antioxidant multilayer coating for tantalum-tungsten alloy surfaces and its preparation method. Background Technology

[0002] Tantalum-tungsten alloys, as a class of excellent refractory metal alloys, have melting points above 3000℃, excellent high-temperature mechanical strength, good creep resistance and weldability. They are key candidate substrates for high-end high-temperature fields such as hot-end components of aerospace engines, high-temperature melting crucibles, and high-temperature core components of nuclear power plants, and have the core conditions to become a new generation of high-temperature structural materials.

[0003] However, its high-temperature oxidation resistance has inherent defects. Tantalum-tungsten alloys are prone to oxidation reactions in medium- and high-temperature oxygen environments. At temperatures above 500°C, "pest" oxidation and powdering failure will occur. The higher the temperature, the more intense the oxidation reaction. The generated oxides are loose and easy to peel off. Some oxidation products are also volatile, leading to rapid corrosion of the alloy matrix, damage to structural integrity, and ultimately component failure that cannot continue to be used. These defects have become the core bottleneck restricting its reliable engineering service. Therefore, it is necessary to improve the oxidation resistance of tantalum-tungsten alloys. Currently, there are two common ways to improve oxidation resistance: alloying and adding a coating. Although alloying can increase its oxidation resistance, it is easy to cause changes in its physical properties. Coating does not change the physical structure of tantalum-tungsten alloys and can retain its excellent high-temperature performance. However, existing coatings still have some problems. Their main defects are as follows: (1) The coating is not firmly bonded to the substrate and is easy to peel off and fail; (2) Poor thermal compatibility and easy to generate cracks; (3) Insufficient high-temperature service stability and easy to consume or fail; (4) The coating itself has limitations in design and modification.

[0004] To address the aforementioned shortcomings, there has been considerable research both domestically and internationally on the high-temperature oxidation resistance of tantalum-tungsten alloys. However, research on temperatures above 2000℃ remains significantly lacking. Many tantalum-tungsten alloy hot-end components operate at temperatures around 1900℃, and some even require short-term use at 2200℃. Therefore, developing a comprehensive high-temperature oxidation-resistant coating system capable of operating above 2000℃ is crucial. Summary of the Invention

[0005] To address issues such as poor adhesion between the coating and the substrate, poor thermal compatibility, and insufficient high-temperature service stability, this invention provides a high-temperature anti-oxidation multilayer coating for tantalum-tungsten alloys and its preparation method. The coating system, through a layer sequence design and composition optimization of "composite diffusion barrier layer - gradient functional transition layer - multi-element composite anti-oxidation top layer," effectively blocks oxygen diffusion and element interdiffusion while achieving gradient mitigation of thermal stress and high-temperature structural stability, significantly improving the service performance of tantalum-tungsten alloys under extreme high-temperature conditions.

[0006] To achieve the above objectives, the technical solution of the present invention adopts a composite process combining solid-phase infiltration and slurry spraying and melting, in which three layers of coating with different functions are sequentially constructed on the surface of tantalum-tungsten alloy. The total thickness and the thickness of each layer follow a specific exponential growth relationship to optimize the distribution of thermal stress.

[0007] This invention discloses a high-temperature anti-oxidation multilayer coating for a tantalum-tungsten alloy surface. The boronizing powder used in the coating (the raw material used in the preparation of the inner layer of the coating system) comprises the following components by mass percentage:

[0008] Al2O3: 50-65%, preferably 50-60%, more preferably 55-60%

[0009] NaF: 10-15%, preferably 10-13%, more preferably 11-13%

[0010] B / B4C: 15-30%, preferably 15-25%, further preferably 16-25%

[0011] Y2O3: 3~5%, preferably 3~4.5%, even more preferably 3.5~4.5%

[0012] The selected boronizing agent is chosen from at least one of B and B4C;

[0013] In step one, a boride barrier layer was prepared using a solid-state infiltration method. Before sintering, a vacuum was applied to a vacuum level of 1.5~2.5×10⁻⁶. 1 Pa, under conditions of a small amount of residual oxygen, is heated and held at a temperature to obtain a boride preform;

[0014] This invention discloses a high-temperature anti-oxidation multilayer coating for the surface of a tantalum-tungsten alloy. In the coating preparation process, the raw materials used in the second step comprise the following components by mass percentage:

[0015] ZrB2: 35-55%, preferably 35-50%, more preferably 37-50%.

[0016] The TaB2 content is 35-50%, preferably 35-48%, and even more preferably 37-48%.

[0017] HfB2: 10-30%, preferably 10-26%, more preferably 12-26%.

[0018] YB4: 3-6%, preferably 3-5%, further preferably 3.5-5%

[0019] This invention discloses a high-temperature anti-oxidation multilayer coating for the surface of a tantalum-tungsten alloy. In the coating preparation process, the raw materials used in the second step comprise the following components by mass percentage:

[0020] The ZrB2 content is 35-55%, preferably 35-50%, and even more preferably 37-50%.

[0021] The content of MoSi2 is 35-50%, preferably 35-48%, and more preferably 37-48%.

[0022] The HfB2 content is 10-30%, preferably 15-25%, and even more preferably 16-23%.

[0023] YB4 is 3-6%, preferably 3-5%, and even more preferably 3.5-5%.

[0024] The raw materials used in the solid-phase infiltration method include the following components by mass percentage:

[0025] A12O3: 55~70%

[0026] NaF: 8~25%

[0027] B: 20~40%.

[0028] The thickness design of the above three coating layers satisfies the following gradient relationship:

[0029] t n =t0×K n-1

[0030] Where t0 is the design reference thickness of the composite diffusion barrier layer, K is the layer thickness ratio coefficient, ranging from 1.4 to 1.6, and n is the layer number. Based on this relationship, the final total coating thickness prepared on the tantalum-tungsten alloy surface is 250–300 μm. This gradient structure design makes the change in the coefficient of thermal expansion within the coating more gradual, significantly reducing the peak thermal stress caused by drastic temperature changes and effectively preventing cracking or interface delamination of the coating due to stress accumulation during thermal cycling.

[0031] This invention discloses a high-temperature anti-oxidation multilayer coating for tantalum-tungsten alloy surfaces and its preparation method, comprising the following steps:

[0032] Step 1

[0033] According to the design group ratio, Al2O3 powder, NaF powder, boronizing agent and Y2O3 powder are mixed evenly by dry ball milling and dried to obtain boronized powder; the obtained boronized powder is poured into a corundum crucible and dispersed and embedded in a clean and dry tantalum-tungsten alloy substrate; then it is kept at 1000~1200℃ in Ar atmosphere to obtain boride layer blank.

[0034] Step Two

[0035] ZrB2 powder, TaB2 powder, HfB2 powder, and YB4 powder were prepared according to the designed proportions. A binder and diluent were added and mixed thoroughly to obtain a slurry. This slurry was then sprayed onto the surface of a boride preform, vacuum dried, and then vacuum sintered at 800–1000℃ for 90–120 min to obtain a ZrB2-TaB2-HfB2-YB4 composite coating.

[0036] Step 3

[0037] According to the design group ratio, ZrB2 powder, MoSi2 powder, HfB2 powder, and YB4 powder were added to binder and diluent and mixed evenly to prepare a slurry. The slurry was then sprayed onto the surface of the composite coating sample and vacuum dried. This process was repeated five times. Next, according to the design group ratio, Al2O3 powder, NaF powder, and B powder were taken, and the powders were mixed evenly using dry ball milling and dried to obtain boron-infiltrating powder. The prepared boron-infiltrating powder was poured into an alumina crucible and dispersed and embedded in the dried coating sample. The sample was sintered at 1500~1650℃ for 60~150 min to obtain the ceramic top coating.

[0038] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation multilayer coating on a tantalum-tungsten alloy surface. In step one, Al2O3 powder, NaF powder, boronizing agent, and Y2O3 powder are taken as raw materials according to the designed composition ratio; the ball-to-material mass ratio is controlled at 5:1 to 15:1, the ball milling speed is 160 to 240 r / min, and the ball milling time is 4 to 7 h to obtain the boronizing powder for later use. As a further preferred embodiment, the mass ratio of ball milling media to raw materials is 10:1 to 15:1.

[0039] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation multilayer coating on a tantalum-tungsten alloy surface. In step one, the average particle sizes of the Al2O3 powder, NaF powder, boron infiltrator, and Y2O3 powder used as raw materials are 40~50μm, 1~10pm, 1~5μm, and 1~5μm, respectively. As a further preferred embodiment, the average particle sizes of the Al2O3 powder, NaF powder, boron infiltrator, and Y2O3 powder are 45~50μm, 0.1~10pm, 1~3μm, and 1~3μm, respectively, and the purity of the Al2O3 powder, NaF powder, boron infiltrator, and Y2O3 powder is not less than 99%.

[0040] The boron permeation agent powder mentioned in step one is at least one of B and B4C.

[0041] As a preferred embodiment, a method for preparing a high-temperature anti-oxidation multilayer coating on the surface of a tantalum-tungsten alloy is provided. In step one, the tantalum substrate with a clean and dry surface is prepared by the following method: after sand milling pretreatment, the tantalum-tungsten substrate is washed with water, alkali, and acid, then ultrasonically cleaned in alcohol, and dried in a drying oven to obtain a square block of tantalum-tungsten with a clean and dry surface.

[0042] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation multilayer coating on a tantalum-tungsten alloy surface. In step one, the prepared boronizing powder is poured into an alumina crucible and dispersed and embedded in a clean and dry tantalum-tungsten substrate. After compaction and capping, the crucible is placed in the center of a high-temperature atmosphere furnace, and a vacuum is drawn to a vacuum degree of 1.5~2.5×10⁻⁶. 1 Pa is used to make the furnace contain a small amount of residual oxygen. Argon gas is introduced and the temperature is raised to 1000-1200℃ at a heating rate of 5-15℃ / min. After holding at this temperature for 1-4 hours, the temperature is lowered to obtain a boride layer with a thickness of 40-60μm.

[0043] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation multilayer coating on a tantalum-tungsten alloy surface. In step two, ZrB2 powder, TaB2 powder, HfB2 powder, and YB4 powder are selected as raw materials according to the designed group allocation. After being uniformly milled by dry ball milling, a binder and a diluent are added and wet ball milling is performed to prepare a slurry. The ball-to-material mass ratio is controlled at 5:1 to 15:1, the ball milling speed is controlled at 200 to 300 r / min, and the ball milling time is 3 to 4 hours. The average particle size of the ZrB2 powder, TaB2 powder, HfB2 powder, and YB4 powder are 1 to 3 μm, 0.8 to 10 μm, 1 to 10 μm, and 18 to 75 μm, respectively, and the purity of the powder is not less than 99%.

[0044] As a preferred embodiment, in step three of the present invention, the average particle sizes of the ZrB2 powder, MoSi2 powder, HfB2 powder, YB4 powder, Al2O3 powder, NaF powder, and B powder used as raw materials are 1~3μm, 0.2~3μm, 1~10μm, 18~75μm, 40~50μm, 1~10μm, and 1~5μm, respectively. As a further preferred embodiment, the average particle sizes of the ZrB2 powder, MoSi2 powder, HfB2 powder, and YB4 powder are 1~2.8μm, 0.8~3μm, 1~8μm, 18~70μm, 43~50μm, 180μm, and 1~4μm, respectively, and the purity of the ZrB2 powder, MoSi2 powder, HfB2 powder, YB4 powder, Al2O3 powder, NaF powder, and B powder is not less than 99%.

[0045] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation multilayer coating on a tantalum-tungsten alloy surface. In step three, Al2O3 powder, NaF powder, and B powder are taken as raw materials according to the designed grouping ratio; the ball-to-material mass ratio is controlled at 5:1 to 15:1, the ball milling speed is 150 to 200 r / min, and the ball milling time is 4 to 7 h to obtain boronizing powder for later use; ZrB2 powder, MoSi2 powder, HfB2 powder, and YB4 powder are taken as raw materials according to the designed grouping ratio, and dry-mixed in a ball mill for more than 2 h, then a binder and a diluent are added and wet-milled to obtain a gradient transition coating slurry. The wet mixing process is 200 to 300 r / min for 3 to 4 h. The obtained slurry was sprayed onto the surface of the composite coating prepared in step two, and dried in a vacuum drying oven at 70°C for 2 hours. This operation was repeated five times. Then, the prepared silica-infiltrating powder was poured into an alumina crucible and dispersed into the coating sample. After compaction and sealing, the sample was placed in the middle of a high-temperature atmosphere furnace. Argon gas was introduced, and the temperature was raised to 1500-1650°C at a heating rate of 5-15°C / min. Sintering was carried out for 60-150 minutes. Vacuum sintering was performed below 800°C, with the vacuum gauge pressure inside the furnace less than 1.0 × 10⁻⁶. -1 After heating to a temperature greater than 800℃, high-purity argon gas is introduced until the temperature is raised, held, and then cooled to room temperature, resulting in a composite coating on the surface of the tantalum-tungsten alloy. The total thickness of the coating is 250~300μm.

[0046] Compared to existing coating systems, the advantages of this invention are as follows:

[0047] (1) The composite multilayer coating of the present invention has three layers, and the coefficient of thermal expansion shows a step-like change, which effectively alleviates the distribution of thermal stress. At the same time, at high temperature, the elements between the substrate and the coating have a certain degree of interdiffusion, which strengthens the interlayer bonding.

[0048] (2) The coating system prepared by the present invention will further form an element barrier layer between the substrate and the coating at high temperature, which can effectively prevent the interdiffusion of oxide generating elements and substrate elements in the antioxidant coating, thereby slowing down the consumption of antioxidant elements.

[0049] (3) The present invention has optimized the design of each coating thickness, spraying process and embedding process through a large number of experiments, so that the prepared coating has better oxidation resistance and mechanical properties.

[0050] (4) The test results show that the coating sample prepared by the present invention has a static isothermal oxidation resistance life of not less than 30 min at 2000℃, a thermal cycling impact number of more than 30 times from room temperature to 2000℃, and a static isothermal oxidation resistance life of not less than 500 s at 2050℃.

[0051] (5) The coating prepared by the present invention will generate self-healing phases B2O3 and SiO2 at medium and high temperatures, which fill the skeleton of ZrO2 and Y2O3. At high temperatures, the molten ZrO2 and Y2O3 are used to fill the pores, which can effectively block the penetration of oxygen in the entire heating system, so that the coating exhibits good oxidation resistance. Attached Figure Description

[0052] Figure 1 A schematic diagram of the structure of a high-temperature anti-oxidation multilayer coating on a tantalum-tungsten alloy surface obtained by implementing the following example;

[0053] Figure 2 The image shows the SEM surface morphology of the high-temperature anti-oxidation multilayer coating on the tantalum-tungsten alloy surface obtained in Example 2.

[0054] Figure 3 The image shows the microstructure of the tantalum-tungsten alloy surface after static isothermal oxidation at 200°C for 30 minutes following the high-temperature anti-oxidation multilayer coating obtained in Example 2. Detailed Implementation Detailed Implementation

[0056] The present invention will be further described below with reference to specific embodiments.

[0057] Example 1

[0058] (1) Matrix pretreatment: Tantalum-tungsten alloy was selected as the matrix with dimensions of 10mm×10mm×1mm. The sample surface was polished to a mirror finish using 800#, 1000#, 2000# and 4000# sandpaper respectively. After sandblasting, the sample was washed with water, alkali, and acid. Then it was ultrasonically cleaned with alcohol and placed in an oven to dry.

[0059] (2) Preparation of boron-impregnated powder: 60% Al2O3 powder, 10% NaF powder, 22% boron impregnating agent and 8% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle sizes of the four powders were 50μm, 8μm, 5μm and 2μm, respectively, and the purity of the four powders was not less than 99%. The prepared powder was poured into a ball mill jar with a ball-to-powder ratio of 15:1, a ball milling speed of 180 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for use.

[0060] (3) Preparation of boride preform: The obtained boronizing powder is poured into an alumina crucible and dispersed and embedded in a clean and dry tantalum-tungsten substrate. After compaction and capping, it is placed in the middle of a high-temperature atmosphere furnace and evacuated to a vacuum degree of 1.5~2.5×10⁻⁶. 1 Pa is used to make the furnace contain a small amount of residual oxygen. The temperature is raised to 1050℃ under an argon atmosphere, held for 90 minutes, and then cooled to obtain a boride layer with a coating thickness of about 50μm.

[0061] (4) Slurry preparation: Weigh 40% ZrB2 powder, 40% TaB2 powder, 15% HfB2 powder and 5% YB4 powder by mass percentage. The average particle size of the four powders is 2μm, 5μm, 5μm and 30μm respectively. The purity of the four powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball powder ratio is 1.1:15:1, the ball mill speed is 250r / min, mix evenly to make a slurry, and then spray it onto the surface of the (3) boride layer with a pneumatic spray gun. Vacuum sinter at 900℃ for 90min to obtain a gradient transition layer.

[0062] (5) Preparation of boron-impregnated powder: 60% Al2O3 powder, 10% NaF powder and 30% B powder were weighed and mixed according to the mass percentage. The average particle sizes of the three powders were 50 μm, 5 μm and 3 μm, respectively, and the purity of the three powders was not less than 99%. The prepared powder was poured into a ball mill jar with a ball-to-powder ratio of 15:1, a ball milling speed of 180 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for use.

[0063] (6) Preparation of top slurry: Weigh 45% ZrB2 powder, 35% MoSi2 powder, 15% HfB2 powder and 5% YB4 powder by mass percentage and mix them. The average particle size of the four powders are 2μm, 2μm, 5μm and 30μm respectively, and the purity of the four powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball powder ratio is 0.9:15:1, the ball mill speed is 250r / min, and mix evenly to make a slurry.

[0064] (7) Preparation of top coating slurry: The slurry prepared in (6) is sprayed onto the surface of the gradient transition layer in (4) using a pneumatic spray gun. It is dried in a vacuum drying oven at 70°C for 2 hours. The above operation is repeated five times. Then, the dried sample is dispersed and embedded in the boron-infiltrated powder in (5). Vacuum sintering is carried out at <800°C. Argon protective gas is introduced at >800°C. Sintering is carried out at 1500°C for 2 hours. The total thickness of the coating is about 265μm.

[0065] (8) The high-temperature anti-oxidation multilayer coating on the surface of the tantalum-tungsten alloy prepared in the example has a static isothermal anti-oxidation life of about 35 min at 2000℃, a resistance to 35 cycles of thermal shock, and a static isothermal anti-oxidation life of about 560 s at 2050℃.

[0066] Example 2

[0067] (1) Matrix pretreatment: Tantalum-tungsten alloy was selected as the matrix with dimensions of 10mm×10mm×1mm. The sample surface was polished to a mirror finish using 800#, 1000#, 2000# and 4000# sandpaper respectively. After sandblasting, the sample was washed with water, alkali, and acid. Then it was ultrasonically cleaned with alcohol and placed in an oven to dry.

[0068] (2) Preparation of boron-impregnated powder: 58% Al2O3 powder, 10% NaF powder, 24% boron impregnating agent and 8% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle sizes of the four powders were 50μm, 8μm, 5μm and 2μm, respectively, and the purity of the four powders was not less than 99%. The prepared powder was poured into a ball mill jar with a ball-to-powder ratio of 15:1, a ball milling speed of 180 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for use.

[0069] (3) Preparation of boride preform: The prepared boronizing powder is poured into an alumina crucible and dispersed and embedded in a clean and dry tantalum-tungsten substrate. After compaction and capping, it is placed in the middle of a high-temperature atmosphere furnace and evacuated to a vacuum degree of 1.5~2.5×10⁻⁶. 1 Pa is used to make the furnace contain a small amount of residual oxygen. The temperature is raised to 1100℃ under an argon atmosphere, held for 90 minutes, and then cooled to obtain a boride layer with a coating thickness of about 48μm.

[0070] (4) Slurry preparation: Weigh 38% ZrB2 powder, 42% TaB2 powder, 16% HfB2 powder and 4% YB4 powder by mass percentage. The average particle size of the four powders is 2μm, 5μm, 5μm and 30μm respectively. The purity of the four powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball powder ratio is 1.1:15:1, the ball mill speed is 250r / min, mix evenly to make a slurry, and then spray it onto the surface of the (3) boride layer with a pneumatic spray gun. Vacuum sinter at 950℃ for 90min to obtain a gradient transition layer.

[0071] (5) Preparation of boron-impregnated powder: Weigh 55% Al2O3 powder, 15% NaF powder and 30% B powder by mass percentage and mix them. The average particle sizes of the three powders are 50 μm, 5 μm and 3 μm, respectively, and the purity of the three powders is not less than 99%. Pour the prepared powder into a ball mill jar with a ball-to-powder ratio of 15:1, a ball milling speed of 180 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for later use.

[0072] (6) Preparation of top slurry: Weigh out 38% ZrB2 powder, 39% MoSi2 powder, 18% HfB2 powder and 5% YB4 powder by mass percentage and mix them. The average particle size of the four powders are 2μm, 2μm, 5μm and 30μm respectively, and the purity of the four powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball powder ratio is 0.9:15:1, the ball milling speed is 250r / min, and mix evenly to make a slurry.

[0073] (7) Preparation of top coating slurry: The slurry prepared in (6) is sprayed onto the surface of the gradient transition layer in (4) using a pneumatic spray gun. It is dried in a vacuum drying oven at 70°C for 2 hours. The above operation is repeated five times. Then, the dried sample is dispersed and embedded in the boron-infiltrated powder in (5). Vacuum sintering is carried out at <800°C. Argon protective gas is introduced at >800°C. Sintering is carried out at 1500°C for 2 hours. The total thickness of the coating is about 270μm.

[0074] (8) The high-temperature anti-oxidation multilayer coating on the surface of the tantalum-tungsten alloy prepared in the example has a static isothermal anti-oxidation life of about 38 min at 2000℃, a resistance to 40 cycles of thermal shock, and a static isothermal anti-oxidation life of about 580 s at 2050℃.

[0075] Example 3

[0076] (1) Matrix pretreatment: Tantalum-tungsten alloy was selected as the matrix with dimensions of 10mm×10mm×1mm. The sample surface was polished to a mirror finish using 800#, 1000#, 2000# and 4000# sandpaper respectively. After sandblasting, the sample was washed with water, alkali, and acid. Then it was ultrasonically cleaned with alcohol and placed in an oven to dry.

[0077] (2) Preparation of boron-impregnated powder: 55% Al2O3 powder, 12% NaF powder, 23% boron impregnating agent and 10% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle sizes of the four powders were 50μm, 8μm, 5μm and 2μm, respectively, and the purity of the four powders was not less than 99%. The prepared powder was poured into a ball mill jar with a ball-to-powder ratio of 15:1, a ball milling speed of 180 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for use.

[0078] (3) Preparation of boride preform: The prepared boronizing powder is poured into an alumina crucible and dispersed and embedded in a clean and dry tantalum-tungsten substrate. After compaction and capping, it is placed in the middle of a high-temperature atmosphere furnace and evacuated to a vacuum degree of 1.5~2.5×10⁻⁶. 1 Pa is used to make the furnace contain a small amount of residual oxygen. The temperature is raised to 1000℃ under an argon atmosphere, held for 90 minutes, and then cooled to obtain a boride layer with a coating thickness of about 42μm.

[0079] (4) Slurry preparation: Weigh 36% ZrB2 powder, 45% TaB2 powder, 14% HfB2 powder and 5% YB4 powder by mass percentage. The average particle size of the four powders is 2μm, 5μm, 5μm and 30μm respectively. The purity of the four powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball powder ratio is 1.1:15:1, the ball mill speed is 250r / min, mix evenly to make a slurry, and then spray it onto the surface of the (3) boride layer with a pneumatic spray gun. Vacuum sinter at 900℃ for 90min to obtain a gradient transition layer.

[0080] (5) Preparation of boron-impregnated powder: 58% Al2O3 powder, 10% NaF powder and 32% B powder were weighed and mixed according to the mass percentage. The average particle sizes of the three powders were 50 μm, 5 μm and 3 μm, respectively, and the purity of the three powders was not less than 99%. The prepared powder was poured into a ball mill jar with a ball-to-powder ratio of 15:1, a ball milling speed of 180 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for use.

[0081] (6) Preparation of top slurry: Weigh 42% ZrB2 powder, 38% MoSi2 powder, 16% HfB2 powder and 4% YB4 powder by mass percentage and mix them. The average particle sizes of the four powders are 2μm, 2μm, 5μm and 30μm, respectively, and the purity of the four powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball powder ratio is 0.9:15:1, the ball mill speed is 250r / min, and mix evenly to make a slurry.

[0082] (7) Preparation of top coating slurry: The slurry prepared in (6) is sprayed onto the surface of the gradient transition layer in (4) using a pneumatic spray gun. It is dried in a vacuum drying oven at 70°C for 2 hours. The above operation is repeated five times. Then, the dried sample is dispersed and embedded in the boron-infiltrated powder in (5). Vacuum sintering is carried out at <800°C. Argon protective gas is introduced at >800°C. Sintering is carried out at 1600°C for 2 hours. The total thickness of the coating is about 272μm.

[0083] (8) The high-temperature anti-oxidation multilayer coating on the surface of the tantalum-tungsten alloy prepared in the example has a static isothermal anti-oxidation life of about 40 min at 2000℃, a resistance to 38 cycles of thermal shock, and a static isothermal anti-oxidation life of about 600 s at 2050℃.

[0084] The above description merely illustrates preferred embodiments of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A high-temperature anti-oxidation multilayer coating on the surface of a tantalum-tungsten alloy and its preparation method, characterized in that: Includes the following steps: Step 1 involves preparing a composite diffusion barrier layer using a solid-phase infiltration method: The powders consist of 50-65% Al2O3 powder, 10-15% NaF powder, 15-30% boronizing agent, and 6-10% Y2O3 powder. The average powder diameters of the four powders are 40-50 μm, 1-10 μm, 1-5 μm, and 1-5 μm, respectively, and the purity of each powder is not less than 99%. The powders are mixed evenly by dry ball milling and dried to obtain boronized powder. The process is as follows: ball-to-powder ratio is 5:1-15:1, rotation speed is 160-240 r / min, and time is 5-7 h. A clean tantalum-tungsten alloy substrate is embedded in the boronized powder and held at 1000-1200℃ in an Ar atmosphere for 1-4 h to obtain a boride preform. The boron permeating agent is selected from at least one of B and B4C; Step two involves preparing a gradient transition layer by spraying and sintering a slurry. According to the design group, take 35-55% ZrB2 powder, 35-50% TaB2 powder, 10-30% HfB2 powder and 3-6% YB4 powder by mass percentage, put them into a ball mill and dry mix for more than 2 hours. Then add binder and diluent and wet ball mill to obtain a gradient transition coating slurry. The wet mixing process is 200-300 r / min for 3-4 hours. Spray the obtained slurry onto the surface of the boride preform obtained in step one, and vacuum sinter at 800-1000℃ for 90-120 min to obtain a ZrB2-TaB2-HfB2-YB4 composite coating. Step 3 involves preparing a multi-component composite antioxidant top layer using a combination of slurry spraying and solid-phase infiltration. According to the design composition, 35-55% ZrB2 powder, 35-50% MoSi2 powder, 10-30% HfB2 powder, and 3-6% YB4 powder by mass percentage are placed in a ball mill and dry-mixed for at least 2 hours. Then, binder and diluent are added, and the mixture is wet-milled to obtain the top coating slurry. The wet mixing process is 200-300 r / min for 3-4 hours. The embedding powder is formulated according to the composition ratio of 55-70% Al2O3 powder, 8-25% NaF powder, and 20-40% B powder. The average particle size of the three powders is 40-50 μm. The powders have a particle size of 1-10 μm and 1-5 μm, and a purity of not less than 99%. The powders are mixed evenly by dry ball milling and dried to obtain silica-infiltrated powder. The process is as follows: the ball-to-powder ratio is 5:1 to 15:1, the rotation speed is 150-200 r / min, and the time is 4-7 h. The obtained slurry is sprayed onto the surface of the composite coating obtained in step two and dried in a vacuum drying oven at 70°C for 2 h. The above operation is repeated five times. Then, the dried sample is dispersed and embedded in the silica-infiltrated powder and sintered at 1500-1650°C for 60-150 min to obtain the top ceramic coating.

2. The high-temperature anti-oxidation multilayer coating on the surface of a tantalum-tungsten alloy and its preparation method according to claim 1, characterized in that, Includes the following steps: (1) The raw materials used to prepare the innermost layer of the coating are Al2O3, NaF, B, and Y2O3, with the following composition: Al2O3: 50~65% NaF: 10~15% B / B4C: 15~30% Y2O3: 3~5% (2) In step one, a boride barrier layer is prepared using a solid-phase infiltration method. Before sintering, a vacuum is drawn to a vacuum level of 1.5~2.5×10⁻⁶. 1 Pa, under conditions of a small amount of residual oxygen, is heated and held at a temperature to obtain a boride preform; (3) The boride barrier layer prepared by solid-phase infiltration method in step one is mainly composed of Y2O3 and the thickness of the barrier layer is 40~60μm. (4) In step three, an antioxidant top layer is prepared by slurry spraying combined with solid-phase infiltration, and then sintered in a tube furnace at a temperature of 1500~1650℃. During the sintering process, vacuum sintering is carried out at a temperature below 800℃, and the vacuum gauge pressure inside the furnace is less than 1.0×10⁻⁶. -1 Pa, after the temperature is greater than 800℃, high-purity argon gas is introduced to raise the temperature, hold the temperature, and then cool it to room temperature.

3. The high-temperature anti-oxidation multilayer coating on the surface of a tantalum-tungsten alloy and its preparation method according to claim 1 or 2, characterized in that, The substrate for the step is a tantalum-tungsten alloy.

4. The high-temperature anti-oxidation multilayer coating on the surface of a tantalum-tungsten alloy and its preparation method according to claim 1 or 2, characterized in that, The high-temperature antioxidant composite multilayer coating has a three-layer structure consisting of a boride barrier layer, a boride transition layer, and a ceramic top layer, with their thicknesses generally satisfying the relationship: t n =t0×K n-1 (where t0=1, K=1.4~1.6), the total thickness of the coating finally prepared on the surface of the tantalum-tungsten alloy substrate is 250~300μm.

5. The high-temperature anti-oxidation multilayer coating on the surface of a tantalum-tungsten alloy and its preparation method according to claim 1 or 2, characterized in that, All the slurry spray coatings are applied using a siphon spray gun.

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