Tantalum-tungsten alloy surface high-temperature anti-oxidation layer thickness ratio gradient structure coating and preparation method thereof

Abstract

The invention discloses a tantalum-tungsten alloy surface layer thickness ratio gradient structure coating and a preparation method thereof, and belongs to the technical field of ultrahigh-temperature anti-oxidation coating preparation. A tantalum-tungsten alloy is used as a substrate, and the surface coating of the tantalum-tungsten alloy is prepared through the following steps: (1) solid-phase embedding boronizing; (2) a ZrB2-MoSi2-ZrSi2 layer is prepared through the combination of slurry fusion sintering and a solid infiltration method; and (3) the ZrB2-TaSi2-Zr6Ta2O17 composite coating slurry is prepared in a sintering mode. The total thickness of the prepared coating ranges from 120 micrometers to 200 micrometers, the thicknesses of all the layers are in an exponential gradient relation: tn = t1 * Kn-1 (t0 = 1, K = 1.2-1.3), the problems of uneven thermal stress distribution between the tantalum-tungsten alloy substrate and the coating and between the layers of the coating and ultra-high-temperature anti-oxidation protection of the tantalum-tungsten alloy are successfully solved, the prepared coating is good in binding force and free of defects such as holes and cracks, and the service life of the coating is prolonged. And the tantalum-tungsten alloy can keep a good anti-oxidation effect for a short time under the extreme high-temperature condition of 2000 DEG C.

Description

Technical Field

[0001] This invention relates to the field of high-temperature antioxidant coating preparation technology, and in particular to a high-temperature antioxidant layer thickness ratio gradient structure coating on the surface of tantalum-tungsten alloy and its preparation method. Background Technology

[0002] Tantalum-tungsten alloys have melting points exceeding 3000℃. Compared to more mature alloys like molybdenum and niobium-tungsten in the same field, tantalum-tungsten alloys exhibit better toughness and lack a brittle transition temperature. They also maintain excellent high-temperature strength, wear resistance, and creep resistance even at high temperatures. However, the oxidation and pulverization phenomenon at temperatures above 400℃ severely limits the application of tantalum-tungsten alloys in critical hot-end components in the aerospace and nuclear industries.

[0003] Currently, there are two main methods to improve the surface oxidation resistance of tantalum-tungsten alloys: alloying protection and surface coating. Alloying protection directly affects the mechanical properties of the alloy substrate itself, leading to the degradation of the material's properties. Antioxidant coatings can isolate the tantalum-tungsten substrate from the oxygen medium or slow down the oxygen permeation rate without damaging the properties of the substrate itself, providing a key guarantee for its long-term stable service in high-temperature environments. Domestic and foreign research on high-temperature antioxidant coatings for tantalum-tungsten alloy surfaces is mainly focused on temperatures below 2000℃, and there is almost no research on protective coatings for short-term service at 2000℃. In the existing tantalum alloy antioxidant protective coating system, there are some defects: (1) There is a certain accumulation of thermal stress between the coating and the substrate, and between coatings. When the accumulated thermal stress exceeds the fracture strength of the coating material, it will cause the coating to crack or peel off directly. Usually, a second phase is added to adjust the thermal expansion coefficient of the coating material or a multi-layer gradient structure coating is prepared to disperse the thermal stress distribution and improve the problem of mismatch in the thermal expansion coefficients between layers. (2) The problem of element interdiffusion during high-temperature oxidation: Si in commonly used silicide coatings exhibits secondary diffusion. When the oxidation temperature exceeds the melting point of SiO2 (1600–1700℃), the viscosity of SiO2 decreases, and the solubility of Si in the coating decreases, the content of self-healing phase decreases, and oxygen permeability increases, making it difficult to provide effective protection. These problems greatly limit the application of tantalum-tungsten alloys in high-temperature fields, and also restrict the development of my country's aerospace and nuclear energy industries.

[0004] With technological advancements, the challenges faced by hot-end components in high-temperature and high-pressure environments are gradually increasing. To achieve high-temperature oxidation resistance of tantalum-tungsten alloys to adapt to increasingly complex and extreme service environments, it is necessary to consider both internal and external element diffusion. Simultaneously, coating thickness and structural design can, to some extent, alleviate the mismatch in thermal expansion coefficients between the substrate and coating, and between different coating layers. Improving the overall performance of the system and enriching the tantalum-tungsten alloy oxidation-resistant coating systems capable of operating at temperatures above 2000℃ to meet the needs of different application environments are crucial for its successful application at high temperatures. Summary of the Invention

[0005] This invention relates to a high-temperature anti-oxidation layer thickness ratio gradient structure coating on the surface of tantalum-tungsten alloy and its preparation method. The coating system exhibits a gradient change in the layer thickness ratio along the thickness direction, forming a gradient to adjust the interlayer thermal mismatch and bonding problem, which can protect the tantalum-tungsten alloy substrate from oxidation corrosion or slow down the oxidation rate for a short period of time at high temperatures.

[0006] To achieve the aforementioned objectives, this invention employs a solid-phase infiltration method combined with a slurry spraying and sintering method to prepare a layer-thickness gradient structure coating containing a TaB2 diffusion barrier layer on the surface of a tantalum-tungsten alloy. The coating consists of four layers, each with a thickness satisfying t n =t1×K n-1 (Where, t0 = 1, K = 1.2~1.3). The innermost layer near the substrate is a TaB2 diffusion barrier layer, the next layer is a metal-ceramic ZrB2-Mo-Mo5Si3 layer, the transition layer is a ZrB2-MoSi2-ZrSi2 layer, and the top ceramic layer is a ZrB2-TaSi2-Zr6Ta2O layer. 17 Composite coating.

[0007] This invention discloses a high-temperature anti-oxidation layer thickness gradient structure coating on the surface of a tantalum-tungsten alloy. The raw materials used in the boronizing powder (raw materials used in the preparation of the inner layer coating of the coating system) include the following components by mass percentage:

[0008] The Al2O3 content is 55-68%, preferably 55-63%, and more preferably 57-63%.

[0009] The NaF content is 10-20%, preferably 10-18%, and more preferably 11-17%.

[0010] The boron permeating agent comprises 15-30%, preferably 15-26%, and more preferably 18-25%.

[0011] The Y2O3 content is 1-3%, preferably 1-2.5%, and more preferably 1.5-2.5%.

[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 layer thickness gradient structure coating on 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: 44-55%,

[0016] Mo: 35-50%,

[0017] Si: 3-6%.

[0018] This invention discloses a high-temperature anti-oxidation layer thickness gradient structure coating on the surface of a tantalum-tungsten alloy. In the coating preparation process, the raw materials used in the third step of solid-phase embedding and silicon infiltration include the following components by mass percentage:

[0019] The Al2O3 content is 55-68%, preferably 55-65%, and more preferably 58-65%.

[0020] The NaF content is 10-20%, preferably 10-18%, and more preferably 11-17%.

[0021] The silica diffusion agent comprises 15-30%, preferably 15-25%, and more preferably 16-23%.

[0022] The Y2O3 content is 1-3%, preferably 1-2.5%, and more preferably 1.5-2.5%.

[0023] This invention discloses a high-temperature anti-oxidation layer thickness gradient structure coating on the surface of a tantalum-tungsten alloy. In the coating preparation process, the raw materials used in the fourth step comprise the following components by mass percentage:

[0024] ZrB2: 60-70%,

[0025] TaSi2: 15-20%,

[0026] Zr6Ta2O 17 5-10%.

[0027] This invention discloses a high-temperature anti-oxidation layer with a gradient thickness ratio on the surface of a tantalum-tungsten alloy and its preparation method, comprising the following steps:

[0028] Step 1

[0029] Al2O3 powder, NaF powder, boronizing agent and Y2O3 powder were prepared according to the design group ratio. The powders were mixed evenly by dry ball milling and dried to obtain boronized powder. The prepared boronized powder was poured into a corundum crucible and dispersed and embedded in a clean and dry tantalum-tungsten substrate. Then it was kept at 1000-1100℃ in Ar atmosphere to obtain a boride layer preform.

[0030] Step Two

[0031] According to the design group ratio, ZrB2 powder, Mo powder and Si powder are taken, and binder and diluent are added and mixed evenly to prepare a slurry. The slurry is then sprayed onto the surface of the boride blank, vacuum dried, and then vacuum sintered at 800-1000℃ for 90-120 min to obtain a ZrB2-Mo-Si composite coating.

[0032] Step 3

[0033] Al2O3 powder, NaF powder, silica diffusion agent and Y2O3 powder were prepared according to the design group ratio. The powders were mixed evenly by dry ball milling and dried to obtain silica-diffused powder. The prepared silica-diffused powder was poured into a corundum crucible and dispersed into the obtained coating sample. Then, it was kept at 1000-1150℃ in Ar atmosphere to obtain ZrB2-MoSi2-ZrSi2 coating.

[0034] ZrB2 powder, TaSi2 powder, and Zr6Ta2O were prepared according to the design group's proportions. 17 The powder is mixed with binder and diluent to form a slurry, which is then sprayed onto the surface of the composite coating sample, vacuum dried, and then sintered at 1500-1650℃ to obtain a multilayer composite coating; vacuum sintering is performed below 800℃, and sintering is performed in an Ar protective atmosphere above 800℃.

[0035] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation layer thickness ratio gradient structure coating on the surface of a tantalum-tungsten alloy. 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 150 to 200 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.

[0036] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation layer thickness ratio gradient structure coating on the surface of a tantalum-tungsten alloy. In step one, the average particle sizes of the Al2O3 powder, NaF powder, boron infiltrator, and Y2O3 powder as raw materials are 40–50 μm, 1–10 μm, 1–5 μm, and 1–5 μm, respectively. As a further preferred embodiment, the average particle sizes of the Al2O3 powder, NaF powder, boron infiltrator, and Y2O3 powder are 45–50 μm, 0.1–10 μm, 1–3 μm, and 1–3 μm, respectively, and the purity of the Al2O3 powder, NaF powder, boron infiltrator, and Y2O3 powder is not less than 99%.

[0037] The boron permeation agent powder mentioned in step one is at least one of B and B4C.

[0038] As a preferred embodiment, a method for preparing a high-temperature anti-oxidation layer thickness ratio gradient structure 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 scheme: after sand grinding 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 clean and dry tantalum-tungsten square block.

[0039] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation layer with a gradient thickness ratio on the surface of a tantalum-tungsten alloy. 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 1000-1100℃ 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 20-25μm.

[0040] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation layer thickness ratio gradient structure coating on the surface of a tantalum-tungsten alloy. In step two, ZrB2 powder, Mo powder, and Si 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, Mo powder, and Si powder are 1 to 5 μm, 1 to 8 μm, and 0.1 to 3 μm, respectively, and the purity of the powder is not less than 99%.

[0041] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation layer thickness ratio gradient structure coating on the surface of a tantalum-tungsten alloy. In step two, the obtained slurry is sprayed onto the surface of the boride blank obtained in step one, and after vacuum drying at 80-100°C for 10-60 min, it is heated to 800-1000°C at a heating rate of 5-15°C / min and vacuum sintered for 90-120 min. After cooling, a composite coating with a boride diffusion barrier layer is obtained on the surface of the tantalum-tungsten alloy.

[0042] As a preferred embodiment, in step three of the present invention, the average particle sizes of the Al2O3 powder, NaF powder, silica penetrant, and Y2O3 powder used as raw materials are 40–50 μm, 1–10 μm, 1–5 μm, and 1–5 μm, respectively. As a further preferred embodiment, the average particle sizes of the Al2O3 powder, NaF powder, silica penetrant, and Y2O3 powder are 45–50 μm, 0.1–10 μm, 1–3 μm, and 1–3 μm, respectively, and the purity of the Al2O3 powder, NaF powder, silica penetrant, and Y2O3 powder is not less than 99%.

[0043] As a preferred embodiment, this invention provides a method for preparing a high-temperature anti-oxidation layer with a gradient structure on the surface of a tantalum-tungsten alloy. In step three, Al2O3 powder, NaF powder, boronizing agent, and Y2O3 powder are selected as raw materials according to the designed proportions. 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. The obtained boronizing powder is poured into an alumina crucible and dispersed into the coating sample. After compaction and sealing, it is placed in the middle of a high-temperature atmosphere furnace. Argon gas is introduced, and the temperature is raised to 1000 to 1150 °C at a heating rate of 5 to 15 °C / min. After holding at this temperature for 20 to 40 min, the temperature is lowered to obtain a silicide layer.

[0044] As a preferred embodiment, in step four of the present invention, a method for preparing a high-temperature anti-oxidation layer with a gradient thickness ratio structure coating on the surface of a tantalum-tungsten alloy is provided, wherein ZrB2 powder, TaSi2 powder, and Zr6Ta2O are prepared according to the designed group allocation. 17 Using powder as raw material, after dry ball milling to achieve uniformity, binder and diluent are added and wet ball milling is performed to prepare a slurry. The ball-to-powder mass ratio is controlled at 5:1 to 15:1, the ball milling speed is controlled at 200 to 300 r / min, and the milling time is 3 to 4 h. The ZrB2 powder, TaSi2 powder, and Zr6Ta2O are mentioned. 17 The average particle size of the powder is 1-5 μm, 1-8 μm, and 200-800 nm, respectively, and the purity of the powder is not less than 99%. According to the design group, allocate 60-70% ZrB2 powder, 15-25% TaSi2 powder, and 5-10% Zr6Ta2O by mass percentage. 17The powder is placed in a ball mill and dry-mixed for more than 2 hours. Then, binder and diluent are added and wet-milled to obtain a ceramic composite coating slurry. The wet mixing process is 200-300 r / min for 3-4 hours. The obtained slurry is sprayed onto the surface of the silicide composite coating obtained in step 3 and sintered at 1500-1650℃ for 60-150 minutes to obtain the top ceramic coating.

[0045] As a preferred embodiment, the present invention provides a method for preparing a high-temperature anti-oxidation layer with a gradient thickness ratio on the surface of a tantalum-tungsten alloy. In step four, the obtained slurry is sprayed onto the surface of the coating sample obtained in step three. After vacuum drying at 80–100°C for 10–60 min, the temperature is increased to 1500–1650°C at a heating rate of 5–15°C / min and sintered for 60–150 min. Vacuum sintering is performed below 800°C, and the vacuum gauge pressure inside the furnace is less than 1.0 × 10⁻⁶. -1 After Pa, when the temperature is greater than 800℃, high-purity argon gas is introduced until the temperature is raised, held, and cooled to room temperature, a composite coating is obtained on the surface of the tantalum-tungsten alloy with a total coating thickness of 120-200μm.

[0046] After optimization, a high-temperature anti-oxidation layer thickness ratio gradient structure coating for tantalum-tungsten alloy surface was prepared by solid-phase infiltration method combined with slurry melting method. The coating samples had a static isothermal anti-oxidation life of 20-40 min at 2000℃ and a thermal cycling impact of 15-40 times from room temperature to 2000℃. The coating samples had a static isothermal anti-oxidation life of 250-1500 s at 2050℃.

[0047] Principle of this invention

[0048] The TaB2 diffusion barrier layer of the present invention uses Al2O3 powder, NaF powder, boron infiltrator and Y2O3 powder as raw materials. Through high temperature solid phase infiltration method, reactions (1) to (3) occur to form a diffusion barrier layer with TaB2 as the main component on the surface of tantalum-tungsten alloy. Al2O3 is used as an inert filler, NaF is used as an activator, B / B4C is used as a boron infiltrator and Y2O3 is used as a catalyst.

[0049] Ta+2B=TaB2 (1)

[0050] 2Ta + 2B + O2 = TaB2 + TaO2 (2)

[0051] 4Y + 3TaO2 = 2Y2O3 + 3Ta (3)

[0052] The metal-ceramic layer on the surface of the TaB2 diffusion barrier layer of the present invention uses ZrB2 powder, Mo powder and Si powder as raw materials. After high-temperature melting reaction sintering, a coating with ZrB2 and Mo as the main phases and accompanied by a small amount of Mo5Si3, MoB and ZrSi2 phases is formed by (4) to (7).

[0053] 5Mo + 3Si = Mo5Si3 (4)

[0054] 3Mo + Si = Mo3Si (5)

[0055] Mo3Si+Si=3Mo5Si3 (6)

[0056] ZrB2+2Mo+2Si=ZrSi2+2MoB (7)

[0057] The present invention uses Al2O3 powder, NaF powder, silicon powder and Y2O3 powder as raw materials to embed and infiltrate silicon into the metal-ceramic layer to obtain a transition layer mainly composed of ZrB2, MoSi2 and ZrSi2. The main reactions that occur are (8)-(10).

[0058] Mo5Si3+7Si=5MoSi2 (8)

[0059] ZrB2+4Si+3Mo=ZrSi2+MoSi2+2MoB (9)

[0060] Mo + 2Si = MoSi² (10)

[0061] This invention uses ZrB2 powder, TaSi2 powder and Zr6Ta2O 17 The powder, used as the anti-oxidation top coating in the tantalum-tungsten alloy substrate surface coating system, densifies after sintering of the slurry, forming a coating composed of ZrB2, TaSi2, and Zr6Ta2O. 17 The coating is mainly composed of Ta5Si3 phase and a small amount of solid solution phase, and the reaction formula is (11-12).

[0062] ZrB2+Ta→(Zr,Ta)B2 (11)

[0063] 5TaSi2=Ta5Si3+7Si (12)

[0064] The boride inner layer prepared by this invention is produced using a solid-phase infiltration method, which is simple to implement. The resulting inner layer coating is uniform and dense, and during the reaction and sintering process with the secondary layer slurry, a Mo-Si-B phase with a low diffusion coefficient is formed. This not only effectively mitigates the infiltration of harmful elements but also slows down the consumption of beneficial elements, thereby significantly improving the coating's oxidation resistance. The secondary layer slurry is doped with a small amount of Si to ensure the further formation of the silicon-infiltrated layer; the ceramic top layer uses nano-sized Zr6Ta2O powder. 17 As a modifier, it has high temperature stability, high toughness and low oxygen diffusivity, and compared with other silicide modifiers, it does not have the problem of rapid dissipation under extreme conditions.

[0065] Compared to existing coating systems, the advantages of this invention are as follows:

[0066] (1) The layer thickness ratio gradient structure coating of the present invention effectively alleviates the thermal stress distribution. At the same time, the elements between the substrate and the coating layers have a certain degree of interdiffusion at high temperature, which strengthens the interlayer bonding.

[0067] (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.

[0068] (3) The present invention has optimized the design of multilayer 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.

[0069] (4) Experiments show that the coating samples prepared by this invention have a static isothermal oxidation resistance life of 20-40 min at 2000℃ and a thermal cycling impact of 15-40 cycles from room temperature to 2000℃; the coating samples have a static isothermal oxidation resistance life of 250-1500 s at 2050℃.

[0070] (5) The coating prepared by this invention will generate self-healing phases B2O3 and SiO2 at medium to high temperatures, filling the framework of ZrO2 and ZrSiO4, and the Zr6Ta2O in a molten state at high temperatures will also be formed. 17 Used to fill pores, it can effectively block oxygen penetration throughout the heating system, giving the coating good oxidation resistance.

[0071] (6) The present invention provides a simple preparation process for a high-temperature anti-oxidation layer thickness ratio gradient structure coating on the surface of tantalum-tungsten alloy, with low production cost. It is applicable to tantalum-tungsten alloy substrates of various shapes and sizes and can be used for large-scale production applications. Attached Figure Description

[0072] Figure 1 The images show the SEM surface morphology, cross-sectional view, and XRD pattern of the boride diffusion barrier layer on the surface of the tantalum-tungsten alloy obtained in Example 1.

[0073] Figure 2 The image shows the SEM surface morphology and XRD pattern of the transition layer coating of the tantalum-tungsten alloy surface thickness gradient structure coating obtained in Example 2.

[0074] Figure 3 This is a schematic diagram of the coating structure of the tantalum-tungsten alloy surface thickness ratio gradient structure coating obtained in Example 2;

[0075] Figure 4The images show the macroscopic and microscopic morphology of the tantalum-tungsten alloy surface thickness gradient structure coating obtained in Example 2 after static isothermal oxidation at 2000℃ for 30 min. Detailed Implementation

[0076] The present invention will be further described below with reference to specific embodiments.

[0077] Example 1

[0078] (1) Pretreatment of the substrate: Tantalum-tungsten alloy was selected as the substrate with a size of 10mm×10mm×1mm. The surface of the sample was polished to a mirror finish with 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 dried in an oven.

[0079] (2) Preparation of boron-impregnated powder: 60% Al2O3 powder, 15% NaF powder, 25% boron impregnating agent and 2% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle sizes of the four powders were 50μm, 5μm, 3μm 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 150 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for later use.

[0080] (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 1050℃ under an argon atmosphere, held for 90 minutes, and then cooled to obtain a boride layer with a coating thickness of about 25μm.

[0081] (4) Slurry preparation: Weigh 55% ZrB2, 40% Mo and 5% Si by mass percentage. The average particle size of the three powders is 5μm, 5μm and 3μm respectively. The purity of the three powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball 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 using a pneumatic spray gun. Dry it in a vacuum drying oven for 9h.

[0082] (5) Preparation of embedded silica powder: 60% Al2O3 powder, 15% NaF powder, 25% silica diffusion agent and 2% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle size of the four powders were 50μm, 5μm, 3μm and 2μm respectively. 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. The ball milling speed was 150r / min and the ball milling time was 5h to obtain the silica powder for use.

[0083] (6) Silicon infiltration treatment: The prepared silicon infiltration powder was poured into the corundum crucible and dispersed and embedded in the coating sample in (4). After compaction and sealing, it was placed in the middle of the high temperature atmosphere furnace and heated to 1150℃ under argon atmosphere. After holding for 30 minutes, it was cooled down and the coating thickness was measured to be about 95μm.

[0084] (7) Preparation of top coating slurry: Weigh out 65% ZrB2, 25% TaSi2, and 10% Zr6Ta2O by mass percentage respectively. 17 The average particle size of the three powders is 5μm, 5μm, and 400nm, and the purity of the three powders is not less than 99%. The prepared powders are poured into a ball mill jar, with ethanol as the solvent and the solvent to ball ratio is 0.9:15:1. The ball milling speed is 250r / min. After mixing evenly to form a slurry, it is sprayed onto the surface of the (3) boride layer using a pneumatic spray gun. It is dried in a vacuum drying oven for 9h, and then vacuum sintered at <800℃. Argon protective gas is introduced at >800℃, and it is kept at 1500℃ for 2h. The total thickness of the coating is about 145μm.

[0085] (8) The tantalum-tungsten alloy surface thickness gradient structure coating prepared in the example has a static isothermal oxidation resistance life of about 37 min at 2000℃, a resistance to 28 cycles of thermal shock, and a static isothermal oxidation resistance life of about 500 s at 2050℃.

[0086] Example 2

[0087] (1) Pretreatment of the substrate: Tantalum-tungsten alloy was selected as the substrate with a size of 10mm×10mm×1mm. The surface of the sample was polished to a mirror finish with 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 dried in an oven.

[0088] (2) Preparation of boron-impregnated powder: 65% Al2O3 powder, 15% NaF powder, 20% boron impregnating agent and 2% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle size of the four powders were 50μm, 5μm, 3μm and 1μm, 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 150 r / min and a ball milling time of 5 h to obtain the boron-impregnated powder for use.

[0089] (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 was used to introduce a small amount of residual oxygen into the furnace. The temperature was raised to 1050℃ under an argon atmosphere, held for 3 hours, and then cooled to obtain a boride layer. The coating thickness was measured to be approximately 29 μm.

[0090] (4) Slurry preparation: Weigh 45% ZrB2, 50% Mo and 5% Si by mass percentage. The average particle size of the three is 5μm, 5μm and 3μm respectively. The purity of the three powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball 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 using a pneumatic spray gun. Dry it in a vacuum drying oven for 9h.

[0091] (5) Preparation of embedded silica powder: 60% Al2O3 powder, 15% NaF powder, 25% silica diffusion agent and 2% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle size of the four powders were 50μm, 5μm, 3μm and 2μm respectively. 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. The ball milling speed was 150r / min and the ball milling time was 5h to obtain the silica powder for use.

[0092] (6) Silicon infiltration treatment: The prepared silicon infiltration powder was poured into the corundum crucible and dispersed and embedded in the coating sample in (4). After compaction and sealing, it was placed in the middle of the high temperature atmosphere furnace and heated to 1150℃ under argon atmosphere. After holding for 30 minutes, it was cooled down and the coating thickness was measured to be about 105μm.

[0093] (7) Preparation of top coating slurry: Weigh out 60% ZrB2, 30% TaSi2, and 10% Zr6Ta2O by mass percentage. 17The average particle size of the three powders is 5μm, 5μm and 400nm, and the purity of the three powders is not less than 99%. The prepared powders are poured into a ball mill jar, with ethanol as the solvent and the solvent to ball ratio is 0.9:15:1. The ball milling speed is 250r / min. After mixing evenly to form a slurry, it is sprayed onto the surface of the (3) boride layer using a pneumatic spray gun. It is dried in a vacuum drying oven for 9h, and then vacuum sintered at <800℃. Argon protective gas is introduced at >800℃, and it is kept at 1500℃ for 2h. The total thickness of the coating is about 160μm.

[0094] (8) The tantalum-tungsten alloy surface thickness gradient structure coating prepared in the example has a static isothermal oxidation resistance life of about 32 min at 2000℃, a resistance to 27 cycles of thermal shock, and a static isothermal oxidation resistance life of about 550 s at 2050℃.

[0095] Comparative experimental group 1

[0096] (1) Pretreatment of the substrate: Tantalum-tungsten alloy was selected as the substrate with a size of 10mm×10mm×1mm. The surface of the sample was polished to a mirror finish with 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 dried in an oven.

[0097] (2) Slurry preparation: Weigh 45% ZrB2, 50% Mo and 5% Si by mass percentage. The average particle size of the three is 5μm, 5μm and 3μm respectively. The purity of the three powders is not less than 99%. Pour the prepared powder into a ball mill jar, use ethanol as solvent, the solvent to ball 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 (3) boride layer using a pneumatic spray gun. Dry in a vacuum drying oven for 9h.

[0098] (3) Preparation of embedded silica powder: 60% Al2O3 powder, 15% NaF powder, 25% silica diffusion agent and 2% Y2O3 powder were weighed according to the mass percentage and mixed. The average particle size of the four powders were 50μm, 5μm, 3μm and 2μm respectively. 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. The ball milling speed was 150r / min and the ball milling time was 5h to obtain the silica powder for use.

[0099] (4) Silicon infiltration treatment: The prepared silicon infiltration powder was poured into the corundum crucible and dispersed and embedded in the coating sample in (4). After compaction and sealing, it was placed in the middle of the high temperature atmosphere furnace and heated to 1150℃ under argon atmosphere. After holding for 30 minutes, it was cooled down and the coating thickness was measured to be about 75μm.

[0100] (5) Preparation of top coating slurry: Weigh out 60% ZrB2, 30% TaSi2, and 10% Zr6Ta2O by mass percentage. 17 The average particle size of the three powders is 5μm, 5μm and 400nm, and the purity of the three powders is not less than 99%. The prepared powders are poured into a ball mill jar, with ethanol as the solvent and the solvent to ball ratio is 0.9:15:1. The ball milling speed is 250r / min. After mixing evenly to form a slurry, it is sprayed onto the surface of the (3) boride layer using a pneumatic spray gun. It is dried in a vacuum drying oven for 9h, and then vacuum sintered at <800℃. Argon protective gas is introduced at >800℃, and it is kept at 1500℃ for 2h. The total thickness of the coating is about 130μm.

[0101] (6) The tantalum-tungsten alloy surface thickness gradient structure coating prepared in the example has a static isothermal oxidation resistance life of about 15 min at 2000℃, a resistance to 23 cycles of thermal shock, and a static isothermal oxidation resistance life of about 230 s at 2050℃.

[0102] 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 gradient-thickness-ratio 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 diffusion barrier layer using a solid-phase infiltration method; The boronized powder is prepared by mixing four powders with a mass percentage content of 55-68% Al2O3 powder, 10-20% NaF powder, 15-30% boronizing agent, and 1-3% Y2O3 powder. The average particle size of the four powders is 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 then dried to obtain boronized powder. The process is as follows: ball-to-powder ratio is 5:1-15:1, rotation speed is 150-200 r / min, and time is 4-7 h. A clean tantalum-tungsten square base is embedded in the boronized powder and kept at 1000-1100℃ 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 metal-ceramic composite coating by slurry spraying and sintering. According to the design group, 44-55% ZrB2 powder, 35-50% Mo powder and 3-6% Si powder by mass percentage are taken and put into a ball mill for dry mixing for more than 2 hours. Then, binder and diluent are added and wet ball milling is performed to obtain metal-ceramic composite coating slurry. The wet mixing process is 200-300 r / min for 3-4 hours. The obtained slurry is sprayed onto the surface of the boride blank obtained in step one and vacuum sintered at 800-1000℃ for 90-120 min to obtain ZrB2-Mo-Si composite coating. Step 3 involves preparing a silicon-infiltrated layer using a solid-phase infiltration method; A transition layer was prepared by embedding and silicating to increase the content of self-healing phase elements. The embedding powder was formulated with 55-68% Al2O3 powder, 10-20% NaF powder, 15-30% Si powder, and 1-3% Y2O3 powder. The average particle sizes of the four powders were 40-50 μm, 1-10 μm, 1-5 μm, and 1-5 μm, respectively, and the purity of each powder was not less than 99%. The powder was mixed uniformly by dry ball milling and dried to obtain silicating powder. The process was as follows: ball-to-powder ratio of 5:1 to 15:1, rotation speed of 150-200 r / min, and time of 4-7 h. The coating sample obtained in step two was dispersed and embedded in the silicating powder and kept at 1000-1150℃ in an Ar atmosphere for 20-40 min to obtain a transition layer containing silicide. Step four involves preparing the top ceramic coating by slurry spraying and sintering; According to the design group, allocate 60-70% ZrB2 powder, 15-25% TaSi2 powder, and 5-10% Zr6Ta2O by mass percentage. 17 The powder is placed in a ball mill and dry-mixed for more than 2 hours. Then, binder and diluent are added and wet-milled to obtain a ceramic composite coating slurry. The wet mixing process is 200-300 r / min for 3-4 hours. The obtained slurry is sprayed onto the surface of the silicide composite coating obtained in step 3 and sintered at 1500-1650℃ for 60-150 minutes to obtain the top ceramic coating.

2. The tantalum-tungsten alloy surface layer thickness ratio gradient structure coating and its preparation method according to claim 1, characterized in that, Includes the following steps: (1) The raw materials used to prepare the boride in the innermost layer of the coating are Al2O3, NaF, B, and Y2O3, with the following composition: Al2O3: 55-68% NaF: 10-20% B / B4C: 15-30% Y2O3: 1-3% (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 TaB2, and the thickness of the barrier layer is 20-25 μm. (4) A composite coating prepared by slurry spraying and sintering combined with solid-phase embedding and silicon infiltration method, the main components of the metal-ceramic layer are ZrB2, Mo and a small amount of Mo5Si3, and a transition layer containing silicide is obtained by holding it at 1000-1150℃ in Ar atmosphere for 20-60 min, the main components of which are ZrB2, MoSi2 and ZrSi2. (5) In step four, an antioxidant coating top layer is prepared using a slurry spraying method and then sintered in a tube furnace at a temperature of 1500–1650℃. Vacuum sintering is performed below 800℃ during the sintering process, with the vacuum gauge pressure inside the furnace 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 tantalum-tungsten alloy surface layer thickness ratio gradient structure coating and its preparation method according to claims 1 and 2, characterized in that, The substrate for the step is a tantalum-tungsten alloy.

4. The tantalum-tungsten alloy surface layer thickness ratio gradient structure coating and its preparation method according to claims 1-3, characterized in that, The high-temperature anti-oxidation layer, consisting of a boride barrier layer, a metal-ceramic layer, a silicide transition layer, and a ceramic top layer connected sequentially, has a thickness gradient structure that basically satisfies the relationship: t n =t1×K n-1 (where t0 = 1, K = 1.2 to 1.3), the total thickness of the final coating prepared on the surface of the tantalum-tungsten alloy substrate is 120 to 200 μm.

5. The tantalum-tungsten alloy surface layer thickness ratio gradient structure coating and its preparation method according to claims 1-4, characterized in that, All the slurry spray coatings are applied using a siphon spray gun.

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