A tantalum-tungsten alloy surface high-density gradient composite coating and a preparation method thereof

Abstract

This invention relates to the field of high-temperature anti-oxidation coatings, and particularly to a high-density gradient composite coating for the surface of tantalum-tungsten alloys and its preparation method. The coating consists of a first diffusion barrier layer, a second transition composite layer, and a third anti-oxidation top layer, stacked sequentially. Specifically, the first diffusion barrier layer is prepared by embedding powder containing Al2O3, NaF, B, Si, and Gd2O3 using an embedding infiltration method; the second transition composite layer is prepared by wet mixing ZrB2-MoSi2-TaSi2 with ethanol and a binder to form a slurry, which is then sprayed and sintered; and the third anti-oxidation top layer is prepared by wet mixing ZrB2-MoSi2-8YSZ-La2O3 with ethanol and a binder to form a slurry, which is then sprayed and sintered in stages. The developed coating has strong adhesion to the tantalum-tungsten alloy substrate, with a total thickness of 200~250μm and dense interlayer bonding. It can protect the tantalum-tungsten alloy substrate from oxidation and corrosion or slow down the oxidation rate within 50 minutes above 2000℃ and within 800 seconds above 2050℃, and the number of thermal cycling shocks is not less than 60.

Description

Technical Field

[0001] This invention relates to the field of high-temperature anti-oxidation coatings, and in particular to a high-density gradient composite coating for the surface of tantalum-tungsten alloy and its preparation method. Background Technology

[0002] Tantalum-tungsten alloys have melting points exceeding 3000℃ and exhibit excellent high-temperature strength, wear resistance, and creep resistance even in high-temperature environments. In the aerospace field, tantalum-tungsten alloys are superior missile warhead materials and ideal candidates for hot-swappable components such as valve stems, valve cores, cylinders, and support plates in hypersonic wind tunnel systems.

[0003] However, under atmospheric conditions above 400°C, tantalum-tungsten alloys react with oxygen, exhibiting a "pest" oxidation phenomenon. Furthermore, with increasing temperature, the alloy eventually pulverizes and fails completely, limiting its service life and application range. Two methods to improve the oxidation resistance of tantalum-tungsten alloys are alloying protection and surface coating. Coating methods do not alter the matrix composition and can preserve the alloy's high-temperature mechanical properties to the greatest extent possible.

[0004] Domestic and international research on high-temperature protective coatings for tantalum-tungsten alloy surfaces has largely focused on temperatures below 1900℃, with limited research on protective coatings suitable for temperatures above 2000℃. Existing technologies suffer from the following problems: First, thermal stress concentration arises due to the mismatch in thermal expansion coefficients between the coating and the substrate, and between different coating layers, leading to coating cracking and even peeling. Second, traditional silicide coatings experience rapid consumption of the self-healing phase during long-term oxidation at ultra-high temperatures, resulting in decreased coating density and increased oxygen permeation rate. Third, the coating system design lacks a gradient transition, making it difficult to simultaneously achieve both adhesion and oxidation resistance. Therefore, it is necessary to design a novel gradient composite coating structure and its preparation method to address these issues. Summary of the Invention

[0005] The purpose of this invention is to provide a high-density gradient composite coating on the surface of tantalum-tungsten alloy and its preparation method, so as to solve the technical problems in the prior art, such as insufficient interfacial bonding force, uneven thermal stress distribution, rapid consumption of self-healing phase leading to decreased coating density, and limited ultra-high temperature oxidation resistance life.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A high-density gradient composite coating for the surface of a tantalum-tungsten alloy, the coating being composed of a first coating material, a second coating material, and a third coating material stacked sequentially;

[0008] The composition of the first coating material is: Al2O3 58%~62%, NaF 12%~14%, B 16%~18%, Gd2O3 2%~3%, with the balance being Si; preferably, Al2O3 59%~61%, NaF 12.5%~13.5%, B 16.5%~17.5%, Gd2O3 2.2%~2.8%, with the balance being Si.

[0009] The second coating material has the following composition: ZrB2 48%~52%, MoSi2 34%~38%, TaSi2 10%~14%; preferably ZrB2 49%~51%, MoSi2 35%~37%, TaSi2 11%~13%.

[0010] The composition of the third coating material is: ZrB2 42%~47%, MoSi2 33%~38%, 8YSZ 12%~15%, La2O3 3%~5%; preferably ZrB2 43%~46%, MoSi2 34%~37%, 8YSZ 13%~14%, La2O3 3.5%~4.5%.

[0011] Further preferred, in the first coating material, the particle size of Al2O3 powder, NaF powder, B powder, Si powder, and Gd2O3 powder is all less than 50 μm, preferably 1~30 μm, and the purity is greater than 99.9%; in the second and third coating materials, the particle size of ZrB2 powder, MoSi2 powder, TaSi2 powder, 8YSZ powder, and La2O3 powder is all less than 50 μm, preferably 1~20 μm, and the purity is greater than 99.9%.

[0012] The present invention also provides a method for preparing the above-mentioned high-density gradient composite coating on the surface of tantalum-tungsten alloy, comprising the following steps:

[0013] The components of the first coating material are mixed and then placed in a ball mill for grinding. After grinding, the powder is dried to obtain the first layer of coating.

[0014] The pretreated substrate is placed in a crucible and completely filled with the first layer of coating embedding powder. Then the crucible is placed in an atmosphere furnace for high-temperature sintering. The sintering temperature is controlled at 1150~1250℃ and the holding time is 2~4 hours. High-purity argon gas is continuously introduced for protection throughout the sintering process. After sintering, the furnace is cooled to room temperature, thus obtaining the first diffusion barrier layer on the surface of the substrate.

[0015] The second coating material is mixed with anhydrous ethanol and binder, and then placed in a ball mill for wet grinding. After being mixed evenly, the second coating slurry is obtained.

[0016] The obtained second coating slurry was uniformly sprayed onto the surface of the substrate on which the first diffusion barrier layer had been prepared. After the sprayed sample was dried in an oven, it was placed in a vacuum sintering furnace for sintering treatment. The sintering temperature was 1350~1400℃ and the holding time was 60~90 minutes. During the sintering process, when the temperature was below 1000℃, the vacuum gauge pressure in the furnace was controlled to be less than 0.5Pa. When the temperature rose above 1000℃, high-purity argon gas was introduced for protection. After the sintering was completed, the furnace was cooled, and the second transition composite layer was obtained on the surface of the first layer.

[0017] The third coating material is mixed with anhydrous ethanol and binder, and then placed in a ball mill for wet grinding. After being mixed evenly, the third coating slurry is obtained.

[0018] The obtained third coating slurry was uniformly sprayed onto the surface of the substrate with the first and second coatings. After spraying, the sample was dried in an oven and then placed in a vacuum sintering furnace for segmented sintering: First, the temperature was raised to 800℃ under vacuum and held for 30 minutes. During this stage, the vacuum gauge pressure in the furnace was less than 0.1 Pa. After the holding period, high-purity argon gas was introduced into the furnace, and the temperature was raised to 1500~1550℃ and held for 90~120 minutes. After sintering, the sample was cooled with the furnace, thus obtaining the third antioxidant top layer on the surface of the second layer.

[0019] The first diffusion barrier layer, the second transition composite layer, and the third anti-oxidation top layer, which are connected in sequence, together constitute the high-density gradient composite coating on the surface of the tantalum-tungsten alloy, with a total thickness of 200~250μm.

[0020] Further preferred, the ball milling process for the first coating material is a ball-to-material ratio of 8:1, a rotation speed of 250 r / min, and ball milling for 5 hours; the ball milling process for the second coating material is a ball-to-material ratio of 5:1, a rotation speed of 300 r / min, and ball milling for 8 to 10 hours; the ball milling process for the third coating material is a ball-to-material ratio of 5:1, a rotation speed of 350 r / min, and ball milling for 10 to 12 hours.

[0021] Further preferably, the binder is polyvinyl butyral, and the amount added is 0.8%~1.2% of the total mass of the powder; the spraying is carried out using a pneumatic spray gun, the spraying pressure is 0.3~0.4MPa, and the wet film thickness is controlled at 250~350μm; the drying process after spraying is to first pre-dry at 80℃ for 1~2 hours, and then vacuum dry at 120℃ for 4 hours.

[0022] Further preferred, during the second layer sintering process, the vacuum gauge pressure is less than 0.5 Pa when the temperature is below 1000℃, and high-purity argon gas is introduced when the temperature is above 1000℃; in the third layer segmented sintering, the gauge pressure inside the vacuum section is less than 0.1 Pa, and the argon section is under slight positive pressure protection.

[0023] Further preferably, the substrate is a tantalum-tungsten alloy.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The first layer of the present invention adopts a boron-silicon-aluminum composite encapsulation system. Through the synergistic effect of Al2O3, NaF, B, Si and Gd2O3, a dense diffusion barrier layer is generated in situ on the surface of tantalum-tungsten alloy, which effectively blocks the interdiffusion of elements and improves the interfacial bonding strength.

[0026] (2) The second layer of the present invention adopts a ZrB2-MoSi2-TaSi2 ternary composite system, which has good high temperature stability and self-healing ability. At the same time, as a component transition layer, it alleviates the difference in thermal expansion coefficient between the first layer and the third layer.

[0027] (3) The third layer of the present invention is modified by composite modification of 8YSZ and La2O3. 8YSZ provides thermal barrier effect and phase stability, while La2O3 serves as a rare earth oxide sintering aid and grain boundary modifier. The synergistic effect of the two significantly improves the high-temperature compactness and oxidation resistance of the coating. At the same time, the introduction of La2O3 effectively slows down the consumption rate of the self-healing phase during high-temperature oxidation, so that the coating can still maintain a dense structure under ultra-high temperature long-term oxidation conditions. This solves the problem proposed in the background art that the rapid consumption of the self-healing phase leads to a decrease in coating compactness and an increase in oxygen permeation rate.

[0028] (4) The total thickness of the coating prepared by the present invention is 200~250μm, the interlayer bonding is dense, and there are no defects such as cracks or pores. The test shows that the coating sample prepared by the present invention has a static isothermal oxidation life of not less than 50 minutes at 2000℃, a thermal cycling impact number of not less than 60 times from 2000℃ to room temperature, and a static isothermal oxidation life of not less than 800 seconds at 2050℃.

[0029] (5) The preparation process of this invention is simple, the equipment requirements are low, the operation is highly controllable, and it is applicable to tantalum-tungsten alloy components of different shapes and sizes, and has good industrial application prospects. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope image of the surface morphology of the coating prepared in Example 1 of the present invention.

[0031] Figure 2 The image shows the surface morphology of the coating prepared in Example 1 of this invention after oxidation at 2000℃ using a scanning electron microscope. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0033] Example 1

[0034] A 10mm × 10mm × 1mm tantalum-tungsten alloy (Ta-10W) specimen was selected as the substrate. The surface was successively polished with 400#, 800#, and 1500# sandpaper until glossy, followed by sandblasting with 180-mesh brown corundum abrasive at a pressure of 0.4 MPa for 30 seconds. Then, it was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, and finally dried in an 80℃ vacuum oven for 2 hours for later use.

[0035] (1) Preparation of the first diffusion barrier layer: 60% Al2O3 powder, 13% NaF powder, 17% B powder, 3% Gd2O3 powder, and the balance of 7% Si powder were weighed by mass percentage. The particle size of each powder was less than 50 μm and the purity was greater than 99.9%. The above powder was placed in a planetary ball mill, using zirconia balls as grinding balls, with a ball-to-material mass ratio of 8:1, a rotation speed of 250 r / min, and dry ball milling for 5 hours. After uniform mixing, the embedded powder was obtained.

[0036] (2) Pour the embedding powder obtained in step (1) into a corundum crucible, embed the pretreated matrix, ensuring that the matrix is ​​completely covered by the powder, and seal the crucible with the lid. Place the crucible in a tube furnace, evacuate it, and then fill it with high-purity argon to a slightly positive pressure. Increase the temperature to 1150℃ at 10℃ / min and hold for 3 hours. After the holding period, cool it to below 100℃ with the furnace and remove it from the furnace. Clean the loose powder on the surface with a brush to obtain the first diffusion barrier layer with a thickness of 35μm.

[0037] (3) Preparation of the second transition composite layer: Weigh 50% ZrB2 powder, 36% MoSi2 powder, and 14% TaSi2 powder by mass percentage. The particle size of the three powders is less than 50 μm and the purity is greater than 99.9%. Place the weighed powders into a ball mill jar, add 1.0% polyvinyl butyral as a binder and 80% anhydrous ethanol as a solvent, with a ball-to-powder ratio of 5:1, and wet ball mill at 300 r / min for 10 hours to prepare a uniform slurry.

[0038] (4) Use a pneumatic spray gun to uniformly spray the slurry obtained in step (3) onto the surface of the first layer obtained in step (2), and control the wet film thickness to 250 μm. Place the sprayed sample horizontally in an 80℃ oven for pre-drying for 1 hour, and then transfer it to a 120℃ vacuum drying oven for drying for 4 hours.

[0039] (5) Place the dried sample from step (4) into a vacuum sintering furnace, evacuate to a pressure below 0.5 Pa, raise the temperature to 1380 °C at 5 °C / min, then introduce high-purity argon into the furnace to atmospheric pressure and hold for 75 minutes. After holding, cool with the furnace under argon protection to obtain the second transition composite layer with a thickness of 90 μm.

[0040] (6) Preparation of the third antioxidant top layer: Weigh 45% ZrB2 powder, 35% MoSi2 powder, 15% 8YSZ powder, and 5% La2O3 powder by mass percentage. The particle size of all four powders is less than 50 μm and the purity is greater than 99.9%. Place the weighed powders into a ball mill jar, add 1.0% polyvinyl butyral and 80% anhydrous ethanol by mass of the powders, with a ball-to-powder ratio of 5:1, and wet ball mill at 350 r / min for 12 hours to prepare a slurry.

[0041] (7) Use a spray gun to uniformly spray the slurry obtained in step (6) onto the second layer surface obtained in step (5), and control the wet film thickness to 200 μm. Place the sprayed sample horizontally in an 80°C oven for pre-drying for 1 hour, and then transfer it to a 120°C vacuum drying oven for drying for 4 hours.

[0042] (8) Place the dried sample from step (7) into a vacuum furnace, evacuate to less than 0.1 Pa, and heat to 800°C at 3°C / min, holding for 30 minutes to remove the adhesive. After holding, fill the furnace with high-purity argon to a slightly positive pressure, and continue heating to 1520°C at 8°C / min, holding for 100 minutes. After holding, cool the furnace to room temperature with argon gas continuously to obtain the third antioxidant top layer with a thickness of 80 μm.

[0043] The scanning electron microscope (SEM) morphology of the high-density gradient composite coating on the tantalum-tungsten alloy surface prepared in this embodiment is as follows: Figure 1 As shown, the surface morphology of the tantalum-tungsten alloy prepared in this embodiment after oxidation at 2000℃ using scanning electron microscopy is as follows. Figure 2 As shown.

[0044] Measurements showed that the total thickness of the coating prepared in this embodiment was approximately 205 μm, with a smooth surface, no cracks or peeling, a dense cross-sectional structure, and good interlayer bonding.

[0045] Example 2

[0046] A 10mm × 10mm × 1mm tantalum-tungsten alloy (Ta-10W) specimen was selected as the substrate. The surface was successively polished with 400#, 800#, and 1500# sandpaper until glossy, followed by sandblasting with 180-mesh brown corundum abrasive at a pressure of 0.4 MPa for 30 seconds. Then, it was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, and finally dried in an 80℃ vacuum oven for 2 hours for later use.

[0047] (1) Preparation of the first diffusion barrier layer: 58% Al2O3 powder, 14% NaF powder, 18% B powder, 2% Gd2O3 powder, and the balance being 8% Si powder were weighed by mass percentage. The particle size of each powder was less than 50 μm and the purity was greater than 99.9%. The above powder was placed in a planetary ball mill, using zirconia balls as grinding balls, with a ball-to-material mass ratio of 8:1, a rotation speed of 250 r / min, and dry ball milling for 5 hours. After uniform mixing, the embedded powder was obtained.

[0048] (2) Pour the embedding powder obtained in step (1) into a corundum crucible, embed the pretreated matrix, ensuring that the matrix is ​​completely covered by the powder, and seal the crucible with a lid. Place the crucible in a tube furnace, evacuate it, and then fill it with high-purity argon to a slightly positive pressure. Heat the furnace to 1180℃ at 10℃ / min and hold for 2.5 hours. After holding, cool the furnace to below 100℃ and remove it from the furnace. Clean the loose powder on the surface with a brush to obtain the first diffusion barrier layer with a thickness of 32μm.

[0049] (3) Preparation of the second transition composite layer: Weigh 52% ZrB2 powder, 35% MoSi2 powder, and 13% TaSi2 powder by mass percentage. The particle size of the three powders is less than 50 μm and the purity is greater than 99.9%. Place the weighed powders into a ball mill jar, add 1.0% polyvinyl butyral as a binder and 80% anhydrous ethanol as a solvent, with a ball-to-powder ratio of 5:1, and wet ball mill at 300 r / min for 10 hours to prepare a uniform slurry.

[0050] (4) Use a pneumatic spray gun to uniformly spray the slurry obtained in step (3) onto the surface of the first layer obtained in step (2), and control the wet film thickness to 250 μm. Place the sprayed sample horizontally in an 80℃ oven for pre-drying for 1 hour, and then transfer it to a 120℃ vacuum drying oven for drying for 4 hours.

[0051] (5) Place the dried sample from step (4) into a vacuum sintering furnace, evacuate to a pressure below 0.5 Pa, raise the temperature to 1400 °C at 5 °C / min, then introduce high-purity argon into the furnace to atmospheric pressure and hold for 60 minutes. After holding, cool with the furnace under argon protection to obtain the second transition composite layer with a thickness of 95 μm.

[0052] (6) Preparation of the third antioxidant top layer: Weigh 47% ZrB2 powder, 38% MoSi2 powder, 12% 8YSZ powder, and 3% La2O3 powder by mass percentage. The particle size of the four powders is less than 50 μm and the purity is greater than 99.9%. Place the weighed powders into a ball mill jar, add 1.0% polyvinyl butyral and 80% anhydrous ethanol by mass of the powders, with a ball-to-powder ratio of 5:1, and wet ball mill at 350 r / min for 12 hours to prepare a slurry.

[0053] (7) Use a spray gun to uniformly spray the slurry obtained in step (6) onto the second layer surface obtained in step (5), and control the wet film thickness to 200 μm. Place the sprayed sample horizontally in an 80°C oven for pre-drying for 1 hour, and then transfer it to a 120°C vacuum drying oven for drying for 4 hours.

[0054] (8) Place the dried sample from step (7) into a vacuum furnace, evacuate to less than 0.1 Pa, and heat to 800°C at 3°C / min, holding for 30 minutes to remove the adhesive. After holding, fill the furnace with high-purity argon to a slightly positive pressure, and continue heating to 1500°C at 8°C / min, holding for 120 minutes. After holding, cool the furnace to room temperature with argon gas continuously to obtain the third antioxidant top layer with a thickness of 85 μm.

[0055] Measurements showed that the total thickness of the coating prepared in this embodiment was approximately 212 μm, with a smooth surface, no cracks or peeling, a dense cross-sectional structure, and good interlayer bonding.

[0056] Example 3

[0057] A 10mm × 10mm × 1mm tantalum-tungsten alloy (Ta-10W) specimen was selected as the substrate. The surface was successively polished with 400#, 800#, and 1500# sandpaper until glossy, followed by sandblasting with 180-mesh brown corundum abrasive at a pressure of 0.4 MPa for 30 seconds. Then, it was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each, and finally dried in an 80℃ vacuum oven for 2 hours for later use.

[0058] (1) Preparation of the first diffusion barrier layer: 62% Al2O3 powder, 12% NaF powder, 16% B powder, 4% Gd2O3 powder, and the balance being 6% Si powder were weighed by mass percentage. The particle size of each powder was less than 50 μm and the purity was greater than 99.9%. The above powder was placed in a planetary ball mill, using zirconia balls as grinding balls, with a ball-to-material mass ratio of 8:1, a rotation speed of 250 r / min, and dry ball milling for 5 hours. After uniform mixing, the embedded powder was obtained.

[0059] (2) Pour the embedding powder obtained in step (1) into a corundum crucible, embed the pretreated matrix, ensuring that the matrix is ​​completely covered by the powder, and seal the crucible with the lid. Place the crucible in a tube furnace, evacuate it, and then fill it with high-purity argon to a slightly positive pressure. Increase the temperature to 1200℃ at 10℃ / min and hold for 2 hours. After the holding period, cool it to below 100℃ with the furnace and remove it from the furnace. Clean the loose powder on the surface with a brush to obtain the first diffusion barrier layer with a thickness of 38μm.

[0060] (3) Preparation of the second transition composite layer: Weigh 48% ZrB2 powder, 38% MoSi2 powder, and 14% TaSi2 powder by mass percentage. The particle size of the three powders is less than 50 μm and the purity is greater than 99.9%. Place the weighed powders into a ball mill jar, add 1.0% polyvinyl butyral as a binder and 80% anhydrous ethanol as a solvent, with a ball-to-powder ratio of 5:1, and wet ball mill at 300 r / min for 10 hours to prepare a uniform slurry.

[0061] (4) Use a pneumatic spray gun to uniformly spray the slurry obtained in step (3) onto the surface of the first layer obtained in step (2), and control the wet film thickness to 250 μm. Place the sprayed sample horizontally in an 80℃ oven for pre-drying for 1 hour, and then transfer it to a 120℃ vacuum drying oven for drying for 4 hours.

[0062] (5) Place the dried sample from step (4) into a vacuum sintering furnace, evacuate to a pressure below 0.5 Pa, raise the temperature to 1360 °C at 5 °C / min, then introduce high-purity argon into the furnace to atmospheric pressure and hold for 90 minutes. After holding, cool with the furnace under argon protection to obtain the second transition composite layer with a thickness of 88 μm.

[0063] (6) Preparation of the third antioxidant top layer: Weigh 43% ZrB2 powder, 37% MoSi2 powder, 15% 8YSZ powder, and 5% La2O3 powder by mass percentage. The particle size of the four powders is less than 50 μm and the purity is greater than 99.9%. Place the weighed powders into a ball mill jar, add 1.0% polyvinyl butyral and 80% anhydrous ethanol by mass of the powders, with a ball-to-powder ratio of 5:1, and wet ball mill at 350 r / min for 12 hours to prepare a slurry.

[0064] (7) Use a spray gun to uniformly spray the slurry obtained in step (6) onto the second layer surface obtained in step (5), and control the wet film thickness to 200 μm. Place the sprayed sample horizontally in an 80°C oven for pre-drying for 1 hour, and then transfer it to a 120°C vacuum drying oven for drying for 4 hours.

[0065] (8) Place the dried sample from step (7) into a vacuum furnace, evacuate to less than 0.1 Pa, and heat to 800°C at 3°C / min, holding for 30 minutes to remove the adhesive. After holding, fill the furnace with high-purity argon to a slightly positive pressure, and continue heating to 1550°C at 8°C / min, holding for 90 minutes. After holding, cool the furnace to room temperature with argon gas continuously, obtaining the third antioxidant top layer with a thickness of 78 μm.

[0066] Measurements showed that the total thickness of the coating prepared in this embodiment was approximately 204 μm, with a smooth surface, no cracks or peeling, a dense cross-sectional structure, and good interlayer bonding.

[0067] The coating samples prepared in Examples 1-3 were subjected to high-temperature static oxidation and thermal shock tests. The static oxidation test temperatures were 2000℃ and 2050℃, and the oxidation environment was static air. The time to complete coating failure was taken as the oxidation resistance lifetime. The thermal shock test involved holding the sample at 2000℃ for 5 minutes and then rapidly immersing it in room temperature water for cooling. This process was repeated until the coating peeled off 5% of the area, at which point the number of thermal shocks was recorded.

[0068] The test results show that: the coating prepared in Example 1 has a static oxidation lifetime of 52 minutes at 2000℃, a static oxidation lifetime of 820 seconds at 2050℃, and a thermal shock cycle of 62 times from 2000℃ to room temperature; the coating prepared in Example 2 has a static oxidation lifetime of 50 minutes at 2000℃, a static oxidation lifetime of 800 seconds at 2050℃, and a thermal shock cycle of 60 times from 2000℃ to room temperature; the coating prepared in Example 3 has a static oxidation lifetime of 51 minutes at 2000℃, a static oxidation lifetime of 810 seconds at 2050℃, and a thermal shock cycle of 61 times from 2000℃ to room temperature.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any variations, equivalent substitutions, or improvements that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A high-density gradient composite coating on the surface of a tantalum-tungsten alloy, characterized in that... The high-temperature anti-oxidation gradient composite coating consists of a first coating material, a second coating material, and a third coating material stacked sequentially. The composition of the first coating material is as follows: Al2O3 58~62wt%, NaF 12~14wt%, B powder 16~18wt%, Gd2O3 2~3wt%, with the balance being Si. The composition of the second coating material is: ZrB2 48~52wt%, MoSi2 34~38wt%, TaSi2 10~14wt%. The composition of the third coating material is as follows: ZrB2 42~47wt%, MoSi2 33~38wt%, 8YSZ 12~15wt%, and La2O3 3~5wt%.

2. The high-density gradient composite coating on the surface of a tantalum-tungsten alloy according to claim 1, characterized in that... The particle size of the Al2O3 powder, NaF powder, B powder, Si powder, Gd2O3 powder, ZrB2 powder, MoSi2 powder, TaSi2 powder, 8YSZ powder, and La2O3 powder is less than 50 μm, and the purity is greater than 99.9%.

3. The method for preparing a high-density gradient composite coating on a tantalum-tungsten alloy surface according to claim 1 or 2, characterized in that... It includes the following steps: (1) The components of the first coating material are mixed and then placed in a ball mill for grinding. After grinding, the powder is dried to obtain the first layer of coating. (2) Place the pretreated substrate in a crucible and completely fill it with the first layer of coating embedding powder obtained in step (1). Then place the crucible in an atmosphere furnace for high-temperature sintering treatment. The sintering temperature is controlled at 1150~1250℃ and the holding time is 2~4 hours. High-purity argon gas is continuously introduced for protection throughout the sintering process. After sintering, the furnace is cooled to room temperature, thus obtaining the first diffusion barrier layer on the surface of the substrate. (3) The second coating material is mixed with anhydrous ethanol and binder, and then placed in a ball mill for wet grinding. After mixing evenly, the second coating slurry is obtained. (4) The second coating slurry obtained in step (3) is uniformly sprayed onto the surface of the substrate with the first diffusion barrier layer. After the sprayed sample is dried in an oven, it is placed in a vacuum sintering furnace for sintering treatment. The sintering temperature is 1350~1400℃ and the holding time is 60~90 minutes. During the sintering process, when the temperature is below 1000℃, the vacuum gauge pressure in the furnace is controlled to be less than 0.5Pa. When the temperature rises above 1000℃, high-purity argon gas is introduced for protection. After the sintering is completed, the furnace is cooled, and the second transition composite layer is obtained on the surface of the first layer. (5) The third coating material is mixed with anhydrous ethanol and binder, and then placed in a ball mill for wet grinding. After mixing evenly, the third coating slurry is obtained. (6) The third coating slurry obtained in step (5) is uniformly sprayed onto the surface of the substrate with the first and second coatings. After the sprayed sample is dried in an oven, it is placed in a vacuum sintering furnace for segmented sintering: First, the temperature is raised to 800°C under vacuum and held for 30 minutes. During this stage, the vacuum gauge pressure in the furnace is less than 0.1 Pa. After the holding period, high-purity argon gas is introduced into the furnace, and the temperature is raised to 1500~1550°C and held for 90~120 minutes. After sintering, the furnace is cooled, and the third anti-oxidation top layer is obtained on the surface of the second layer. The first diffusion barrier layer, the second transition composite layer, and the third antioxidant top layer, which are connected in sequence, constitute a high-temperature antioxidant gradient composite coating.

4. The method for preparing a high-density gradient composite coating on a tantalum-tungsten alloy surface according to claim 3, characterized in that: The ball milling process for the first coating material is a ball-to-material ratio of 8:1, a rotation speed of 250 r / min, and ball milling for 5 hours; the ball milling process for the second coating material is a ball-to-material ratio of 5:1, a rotation speed of 300 r / min, and ball milling for 8 to 10 hours; the ball milling process for the third coating material is a ball-to-material ratio of 5:1, a rotation speed of 350 r / min, and ball milling for 10 to 12 hours.

5. The method for preparing a high-density gradient composite coating on a tantalum-tungsten alloy surface according to claim 3, characterized in that: The binder added in steps (3) and (5) is 0.8% to 1.2% polyvinyl butyral.

6. The method for preparing a high-density gradient composite coating on a tantalum-tungsten alloy surface according to claim 3, characterized in that: During the second layer sintering process, the vacuum gauge pressure is less than 0.5 Pa when the temperature is below 1000℃, and high-purity argon gas is introduced when the temperature is above 1000℃; during the third layer segmented sintering, the gauge pressure inside the vacuum section is less than 0.1 Pa, and the argon section is under slight positive pressure protection.

7. The method for preparing a high-density gradient composite coating on a tantalum-tungsten alloy surface according to claim 3, characterized in that: The substrate is a tantalum-tungsten alloy, and the final coating has a total thickness of 200~250μm.

8. The method for preparing a high-density gradient composite coating on a tantalum-tungsten alloy surface according to claim 3, characterized in that: In steps (4) and (6), a pneumatic spray gun is used as the coating spraying tool, and the spraying pressure is 0.3~0.4MPa.

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