A method for producing a high-temperature oxidation resistant silicide coating comprising a composite diffusion barrier layer

Abstract

The application relates to a preparation method of a high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer, which comprises an MoSi2 outer layer, a WSi2-YSZ diffusion barrier layer and a relatively thin NbSi2 and Nb5Si3 interdiffusion layer between the outer layer and a substrate, the outer layer provides good high-temperature oxidation resistance for the coating, the diffusion barrier layer can effectively slow down the element interdiffusion between the coating and the substrate, reduces the loss of beneficial element Si, the interdiffusion layer forms a metallurgical bond between the substrate, and can improve the interface bonding between the outer coating and the substrate. After the WSi2-20%YSZ diffusion barrier layer sample is subjected to 100h of constant temperature oxidation at 1400 DEG C, the oxidation weight gain is 1.5mg / cm 2 ; compared with the sintering sample without the diffusion barrier layer, the thickness of the oxidation film and the thickness of the diffusion layer are reduced by 28.5% and 29.2% respectively after 100h of oxidation, the oxidation film does not peel off, the coating and the substrate alloy are well combined.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of refractory metal thermal protection, and particularly relates to a preparation method of a high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer. BACKGROUND

[0002] Nb-based ultrahigh-temperature alloy has the advantages of high melting point (1750℃), moderate density (7.1g / cm3), excellent high-temperature mechanical properties, and good processability, and is expected to replace nickel-based high-temperature alloy to become a new generation of raw material for gas turbine aero-engine blades and other high-temperature structural components. However, its poor high-temperature oxidation resistance and high-temperature surface mechanical properties seriously limit its engineering application.

[0003] At present, the ways to improve the high-temperature oxidation resistance of niobium alloy include alloying method and surface coating method. The alloying method is to add Al, Cr, Ti and other oxidation-resistant elements to the base alloy to improve the oxidation resistance of the alloy, but this method often reduces the melting point and related high-temperature mechanical properties of the alloy, and its improvement degree is far from meeting the actual oxidation resistance needs. In comparison, the surface coating technology can significantly improve the high-temperature oxidation resistance of the alloy without affecting the mechanical properties of the base itself, and the dense protective oxide film on the coating surface can effectively hinder / delay the internal diffusion of oxygen, protecting the alloy from oxidation. MoSi2 has the characteristics of high melting point, good thermal stability and excellent high-temperature oxidation resistance, and is an optimal oxidation-resistant coating material for the surface of refractory metals such as niobium. However, the severe interdiffusion of elements at the MoSi2 / niobium alloy interface at high temperatures will lead to rapid degradation of the composition and microstructure of the MoSi2 coating and interface embrittlement, shortening the service life of the MoSi2 coating, so it is necessary to add a diffusion barrier at the interface of the coating and the alloy to inhibit or delay the interdiffusion of Si and other elements at the interface.

[0004] The present application proposes to combine slurry coating and SPS rapid sintering method to construct a WSi2-YSZ composite diffusion barrier (YSZ: yttria-stabilized zirconia) in situ, because WSi2 and YSZ both have a certain Si diffusion blocking ability, and the chemical reaction and interaction of YSZ, WSi2 and the base alloy at the interface at high temperatures are expected to further improve the interface bonding strength and Si element blocking ability, to solve the problems of insufficient high-temperature blocking ability, low interface bonding strength or excessive mismatch of thermal expansion coefficient of single WSi2 layer or YSZ layer, to improve the oxidation resistance and service life of the surface MoSi2 coating. SUMMARY

[0005] The present application aims to provide a preparation method of a high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer, to solve the problems of insufficient high-temperature blocking ability, low interface bonding strength or excessive mismatch of thermal expansion coefficient of single WSi2 layer or YSZ layer.

[0006] To solve the above technical problems, a preparation method of a high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer is provided, comprising the following steps:

[0007] S1, polish the six surfaces of the Nb alloy substrate smooth and round the corners;

[0008] S2, ultrasonic vibration cleaning in anhydrous ethanol, and pickling for 5-8s, then rinse with plenty of water, then immerse in anhydrous ethanol again and use ultrasonic vibration cleaning, and finally dry in a drying oven;

[0009] S3, use a ball mill to refine Mo, Si, WSi2 powder and YSZ respectively, wet grinding with anhydrous ethanol, ball mill speed is 300-500r / min, ball milling time is 8-15h, to obtain Mo powder, Si powder and YSZ powder;

[0010] S4, use PVB as binder, content is 1-5wt.%, molar ratio of tungsten and silicon is W:Si=1:2.2, YSZ content is 0-30wt.%, and add anhydrous ethanol as solvent, prepare slurry with solid content of 50-80wt.%, then use polytetrafluoroethylene ball mill tank for 2-6h ball milling, ball mill speed is 200-400r / min;

[0011] S5, use brushing to evenly coat the slurry on the surface of the Nb alloy, dry for 30min in a drying oven after each brushing, drying oven temperature is set to 50-70℃, repeat brushing 2-6 times;

[0012] S6, put the substrate with diffusion barrier layer brushed on it into the SPS discharge plasma sintering mold, put appropriate Mo and Si mixed powder on top and bottom, sinter under the conditions of sintering temperature 1400℃, sintering pressure 40Mpa and sintering time 15min, heating rate is 100℃ / min, protect with argon gas during sintering, finally cool down with the furnace, finally obtain a MoSi coating containing a composite diffusion barrier layer.

[0013] The above method, step S3 includes the following steps:

[0014] S31, use a ball mill to refine Mo, Si, WSi2 and YSZ powder, ball to powder ratio is 3:1-5:1, large ball to small ball number ratio is 12:50, put a small amount of anhydrous ethanol for wet grinding, ball mill speed is 300-500r / min, ball milling duration is 8-10h, to obtain Mo, Si, WSi2 and YSZ powder with particle size of 0.6-1um, stop for 10min every 50min of ball milling.

[0015] The method further comprises the following step in step S3:

[0016] S32, the powder suspension after ball milling is placed in a drying oven for 8-12 hours at a constant temperature of 40-60℃ to completely dry the powder.

[0017] The method further comprises the following step in step S3:

[0018] S33, the dried powder is poured into a mortar and ground thoroughly, and when the powder particles are separated without obvious agglomeration, the powder is sieved through a 260 target screen; the remaining powder that fails to pass through the screen is poured back into the mortar and ground again, and then sieved again until all the powder can pass through the screen, so that the particle size of the powder is uniform.

[0019] The method further comprises the following step in step S4:

[0020] The refined Mo and Si powders are mixed according to an atomic ratio of 1:2.2, and a small amount of B and Y2O3 is added, the content of B is 2-3wt.%, the content of Y2O3 is 1-2wt.%, the solvent is anhydrous ethanol, the rotation speed of the ball mill is 200-300r / min, the ball-to-material ratio is 5:1, the ball milling time is 2-3h, and then the ball milling is processed according to steps S32 and S33 in sequence.

[0021] The method specifically comprises the following steps in step S5:

[0022] The slurry is uniformly brushed on the surface of the Nb alloy substrate by using a brush, and after each brushing, the substrate is placed in a drying oven for 30min, the temperature of the drying oven is set to 40-70℃, the brushing is repeated for 2-6 times, and after the brushing is completed, the substrate is placed in the drying oven for 12h.

[0023] In step S2, the pickling solution for pickling comprises 10-30vol.% nitric acid, 1-10vol.% hydrofluoric acid, and 50-80vol.% distilled water.

[0024] In step S1, the thickness of the Nb alloy substrate is 3-5mm.

[0025] In step S6, the sintered sample is subjected to isothermal oxidation at 1400℃ for 100h to obtain an oxidation film on the surface of the coating.

[0026] The implementation of the embodiment of the application has the following beneficial effects:

[0027] 1、The preparation method of the high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer in the embodiment, which comprises a MoSi2 outer layer, a WSi2-YSZ diffusion barrier layer, and a thin NbSi2 and Nb5Si3 transition layer between the outer layer and the substrate. The outer layer provides good high-temperature oxidation resistance for the coating, the diffusion barrier layer can effectively slow down the element diffusion rate between the coating and the substrate and slow down the loss of beneficial element Si, the transition layer forms a metallurgical bond between the substrate, and the coating and the substrate are tightly combined. The oxidation weight gain of the sample containing the WSi2-20% YSZ diffusion barrier layer is 1.5 mg / cm after 100 h of constant temperature oxidation at 1400℃ 2 Compared with the sample without the diffusion barrier layer, the thickness of the oxidation film and the diffusion barrier layer is reduced by 28.5% and 29.2%, respectively, after 100 h of oxidation, and the oxidation film does not peel off, and the coating and the substrate alloy are well combined. Since the coating times are controllable, it is easier to control the thickness of the WSi2-YSZ diffusion barrier layer. Specifically, first, the powder is refined by ball milling, then a mixed slurry of WSi2 and YSZ in a certain ratio is brushed on the surface of the Nb alloy substrate, and after each brushing, it is dried in a 60℃ drying box for 30 min, and after multiple brushing, it is placed in a 60℃ constant temperature drying box for 12 h, and finally the dried sample is placed in an SPS discharge plasma sintering furnace for sintering, and finally a MoSi2 / WSi2-YSZ composite oxidation-resistant coating is obtained;

[0028] 2、The preparation method of the high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer in the embodiment has the advantages of fast heating rate, low forming pressure, sintering and pressing integration, high efficiency, and good repeatability. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0030] Figure 1 The flow chart of the preparation method of the high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer described in the embodiment of the present application;

[0031] Figure 2 The SEM morphology of the sintered coating in Example 1 of the present application;

[0032] Figure 3 The SEM morphology of the oxidation film surface and cross section of the coating after 100 h of constant temperature oxidation at 1400℃ in Example 1;

[0033] Figure 4The image shows the SEM morphology of the interdiffusion layer after the coating in Example 1 was oxidized at 1400℃ for 100h.

[0034] Figure 5 This is a diagram showing the elemental concentration distribution along the depth direction of the coating in Example 1, which was oxidized at 1400℃ for 100 hours.

[0035] Figure 6 The cross-sectional SEM morphology of the diffusion-resistant composite coating in Example 2 is shown.

[0036] Figure 7 The surface and cross-sectional SEM morphology of the oxide film containing the diffusion-resistant composite coating oxidized at 1400℃ for 100h in Example 2 are shown.

[0037] Figure 8 The image shows the SEM morphology of the interdiffusion layer of the composite coating in Example 2 after being oxidized at 1400℃ for 100 hours.

[0038] Figure 9 This is a diagram showing the elemental concentration distribution along the depth direction of the composite coating in Example 2 after being oxidized at 1400℃ for 100 hours.

[0039] Figure 10 The oxidative weight gain of each coating after being oxidized at 1400℃ for 100 hours is calculated. Detailed Implementation

[0040] This invention discloses a method for preparing a high-temperature resistant silicon oxide coating comprising a composite diffusion barrier layer, comprising the following steps:

[0041] The six sides of the Nb alloy substrate are polished smooth, and the edges are rounded.

[0042] Immerse in anhydrous ethanol for ultrasonic cleaning and acid washing for 5-8 seconds. After removing, rinse with plenty of water. Then immerse in anhydrous ethanol again for ultrasonic cleaning and finally dry in a drying oven.

[0043] Mo, Si, WSi2 powder and YSZ were refined separately using a ball mill. Anhydrous ethanol was used for wet milling. The ball mill speed was 300-500 r / min and the ball milling time was 8-15 h to obtain Mo powder, Si powder and YSZ powder.

[0044] PVB is used as a binder with a content of 1-5 wt.%, the molar ratio of tungsten to silicon is W:Si = 1:2.2, and the content of YSZ is 0-30 wt.%. Anhydrous ethanol is added as a solvent to prepare a slurry with a solid content of 50-80 wt.%. The slurry is then ball-milled in a polytetrafluoroethylene ball mill jar for 2-6 hours at a speed of 200-400 r / min.

[0045] The slurry is evenly coated on the surface of the Nb alloy by brushing, and is placed in a drying oven for 30 min after each brushing, with the drying oven set at a temperature of 50-70°C, and the brushing is repeated 2-6 times;

[0046] The substrate with the diffusion barrier layer is placed in a SPS discharge plasma sintering mold, and appropriate Mo and Si mixed powder is placed on the top and bottom. Sintering is performed at a sintering temperature of 1400°C, a sintering pressure of 40 MPa, and a sintering time of 15 min, with an increase in temperature of 100°C / min. Argon is introduced during the sintering process for protection, and the final product is cooled in the furnace. A molybdenum silicide coating containing a composite diffusion barrier layer is obtained.

[0047] Example 1

[0048] The preparation method of a high-temperature oxidation-resistant silicide coating containing a composite diffusion barrier layer in Example 1 is performed according to the following steps:

[0049] (1) Prepare the sample. Select Nb alloy as the experimental substrate raw material, and cut the Nb alloy rod with a diameter of 10 mm into thin slices with the same thickness. The thickness of the slices should not be too thin, and should be controlled within 3-5 mm. The substrate is too thin and is prone to warping under high pressure, causing mechanical strain. The six sides of the Nb alloy substrate are polished smooth and the corners are rounded to reduce stress concentration during sintering.

[0050] (2) Treat the substrate. Place the substrate in anhydrous ethanol and ultrasonically clean it. Then, acid wash for 5-8 s, take it out and rinse it with plenty of water. Then, immerse it in anhydrous ethanol again and clean it using ultrasonic vibration. Finally, dry it in a drying oven.

[0051] (3) Prepare the powder. Use a ball mill to ball mill Mo and Si powders separately. The ball mill speed is 500 r / min, and the ball milling duration is 8 h to achieve powder refinement. The particle size of the Mo and Si elemental powders obtained is 0.6-1 um. During the ball milling process, stop every 50 min to avoid overheating.

[0052] (4) After 4 hours of standing, place the ball-milled powder suspension in a drying oven at a constant temperature of 60°C for 12 hours to ensure that the water in the suspension is completely evaporated and the powder is completely dried.

[0053] (5) Pour the dried powder into a mortar and grind it thoroughly to ensure that the powder particles are separated and there is no obvious clumping. Then, use a 260 target sieve to vibrate the powder. Pour the remaining powder that did not pass through the sieve back into the mortar and grind it again before sieving again until all the powder passes through the sieve, ensuring that the particle size of the powder is uniform.

[0054] (6) mixing powder, the refined Mo, Si powder is mixed and ball milled according to the atomic ratio 1:2.2 and a small amount of B and Y2O3 is added to improve the high-temperature oxidation resistance of the MoSi2 coating, the content of B is 2%, the content of Y2O3 is 1%, the solvent is anhydrous ethanol, the rotation speed of the ball mill is 300 r / min, the ball-to-material ratio is 5:1, the ball milling time is 3 h, and then the ball milling is processed according to steps (4) and (5);

[0055] (7) the substrate is placed into an SPS discharge plasma sintering mold, and appropriate Mo, Si, B and Y2O3 mixed powder is laid on the upper and lower parts, sintering is carried out under the conditions of a sintering temperature of 1400°C, a sintering pressure of 40 Mpa and a sintering holding time of 15 min, the sintering heating rate is 100°C / min, argon is introduced for protection during the sintering process, and finally the furnace is cooled to obtain a MoSi2 coating, the sintering coating surface and cross section are as shown in Figure 2 , the coating and substrate interdiffusion layer detail view is as shown in Figure 2 , and the coating surface product is as shown in the X-ray diffraction analysis result of Figure 4 ;

[0056] (8) the sintered sample is subjected to a 1400°C constant temperature oxidation experiment, and after oxidation for 100 h, the coating cross section is as shown in Figure 4 , a continuous and dense SiO2 film is generated, the diffusion layer thickness increases, and the element concentration distribution measured by EDS along the depth direction is as shown in Figure 5 .

[0057] Example 2

[0058] A method for preparing a high-temperature oxidation resistant silicide coating containing a composite diffusion barrier layer in Example 2 is carried out according to the following steps:

[0059] (1) preparing a sample, selecting high-purity Nb as the experimental substrate raw material, cutting a Nb alloy rod with a diameter of 10 mm into thin slices with the same thickness, the thickness of the slices should not be too thin, and is controlled to be 3-5 mm, the substrate is too thin and is easy to warp under high pressure, causing mechanical strain, polish the six surfaces of the Nb alloy substrate to be smooth and round the corners to reduce stress concentration during sintering;

[0060] (2) substrate treatment, the substrate is placed into anhydrous ethanol and ultrasonically vibrated for cleaning; then it is pickled for 5-8 s, taken out and washed with a large amount of water, then immersed into anhydrous ethanol again and ultrasonically vibrated for cleaning, and finally dried in a drying box;

[0061] (3) Preparation of powder, using a ball mill Mo, Si, WSi2 and YSZ powder (20wt.%) respectively ball milling refinement, ball mill speed of 500 r / min, ball milling duration of 8 h, to achieve powder refinement, the particle size of Mo, Si, WSi2 and YSZ powder is 0.6-1 um, ball milling process every 50 min stop 10 min, to avoid overheating;

[0062] (4) The powder suspension after ball milling is placed in a drying oven for 4 hours, and dried at 60°C for 12 hours to ensure that the water in the suspension is completely evaporated and the powder is completely dried;

[0063] (5) The dried powder is poured into a mortar and ground thoroughly to ensure that the powder particles are separated and there is no obvious agglomeration, then it is sieved through a 260 target screen. The remaining powder that does not pass through the screen is poured back into the mortar and ground again, then sieved again until all the powder passes through the screen, ensuring that the particle size of the powder is uniform;

[0064] (6) Mixing powder, the refined Mo, Si powder is mixed according to the atomic ratio of 1:2.2 and a small amount of B and Y2O3 is added to improve the high temperature oxidation resistance of MoSi2 coating. The content of B is 2%, the content of Y2O3 is 1%, the solvent is anhydrous ethanol, the ball mill speed is 300 r / min, the ball to powder ratio is 5:1, and the ball milling time is 3 h. After ball milling, follow steps (4) and (5);

[0065] (7) Preparation of diffusion barrier layer slurry, using PVB as binder with a content of 1wt.%, according to the mass ratio, YSZ accounts for 20% of the total mass, and adding anhydrous ethanol as solvent, preparing a slurry with a solid content of 60wt.%, then using a polytetrafluoroethylene milling jar for 2h ball milling, the ball mill speed is 300 r / min, which does not need to be too high, as long as it can achieve sufficient mixing;

[0066] (8) Using a brush to evenly brush the slurry on the surface of the Nb alloy substrate, placing it in a drying oven for 30 min after each brushing, setting the temperature of the drying oven to 60°C, and brushing 3 times; after completing the brushing, placing it in a 60°C drying oven for 12h;

[0067] Finally, the substrate with the brushed diffusion barrier layer is placed in an SPS discharge plasma sintering mold, appropriate powder is placed on top and bottom, and sintering is carried out at 1400°C, sintering pressure of 40Mpa and sintering holding time of 15 min. Argon is introduced for protection during sintering. After sintering, the mold is cooled in the furnace. The final sintered MoSi2 / WSi2-YSZ composite coating is obtained. The cross section of the coating is shown in Figure 6

[0068] ​(9) The sintered sample was subjected to 1400 DEG C isothermal oxidation experiment, and the coating surface oxide film after oxidation for 100 h was as shown in Figure 6 The interface morphology of the composite coating and the substrate was as shown in Figure 8 The EDS element concentration distribution along the depth direction of the interface was as shown in Figure 9 The oxidation weight gain of each sample after isothermal oxidation at 1400 DEG C for 100 h was as shown in Figure 10 As shown in

[0069] Through experimental detection, from Figures 9-10 It can be seen that the addition of the diffusion barrier layer can not only reduce the high-temperature oxidation weight gain of the sample containing the coating, but also delay the interdiffusion of the elements at the coating / substrate alloy interface (especially the Si element), and can reduce the growth rate of the interdiffusion layer. When the YSZ addition amount is 20wt.%, the oxidation resistance is relatively good, at this time the oxide film has less microcracks and smaller thickness, and thus the oxidation resistance of the composite coating at high temperature can be effectively improved.

[0070] The above-described embodiments only express several embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A method for preparing a high-temperature resistant silicon oxide coating comprising a composite diffusion barrier layer, characterized in that, Includes the following steps: S1. Prepare the sample by polishing the six sides of the Nb alloy substrate until smooth and rounding the edges. S2. Matrix treatment: The Nb alloy matrix is ​​placed in anhydrous ethanol for ultrasonic vibration cleaning and acid pickling for 5-8 seconds. After removal, it is rinsed with plenty of water and then immersed in anhydrous ethanol for ultrasonic vibration cleaning again. Finally, it is dried in a drying oven. S3. Prepare powders and refine Mo, Si, WSi2 powder and YSZ powder separately using a ball mill. Use anhydrous ethanol for wet milling. The ball mill speed is 300-500 r / min and the ball milling time is 8-15 h to obtain Mo powder, Si powder, WSi2 powder and YSZ powder. S4. Mix the powders: Mix the refined Mo and Si powders at an atomic ratio of 1:2.2 and ball mill them, adding a small amount of B and Y2O3. The content of B is 2-3 wt.% and the content of Y2O3 is 1-2 wt.%. The solvent is anhydrous ethanol. The ball mill speed is 200-300 r / min, the ball-to-material ratio is 5:1, and the ball milling time is 2-3 h. S5. Preparation of the diffusion barrier slurry: PVB is used as a binder with a content of 1-5 wt.%. WSi2 powder and YSZ powder are added, with YSZ content of 10-20 wt.%. Anhydrous ethanol is added as a solvent to prepare a slurry with a solid content of 50-80 wt.%. The slurry is then ball-milled in a polytetrafluoroethylene ball mill jar for 2-6 hours at a speed of 200-400 r / min. S6. Apply the slurry evenly to the Nb alloy surface by brushing. After each brushing, place the surface in a drying oven for 30 minutes. Set the temperature of the drying oven to 50-70 ℃. Repeat the brushing 2-6 times. S7. Place the substrate coated with the diffusion barrier slurry into the SPS discharge plasma sintering mold, and spread appropriate Mo and Si mixed powders on the top and bottom. Sinter at a sintering temperature of 1400℃, a sintering pressure of 40MPa, and a sintering time of 15min. The heating rate is 100℃ / min. Argon gas is introduced for protection during the sintering process. Finally, the substrate is cooled with the furnace to obtain a molybdenum silicide coating containing a composite diffusion barrier layer.

2. The method for preparing a high-temperature silicide coating containing a composite diffusion barrier layer according to claim 1, characterized in that, Step S3 includes the following steps: S31. Mo, Si, WSi2 and YSZ powders are refined by ball milling using a ball mill with a ball-to-powder ratio of 3:1-5:1 and a large ball to small ball ratio of 12:

50. A small amount of anhydrous ethanol is added for wet milling. The ball mill speed is 300-500 r / min and the ball milling time is 8-10 h to obtain Mo, Si, WSi2 and YSZ powders with a particle size of 0.6-1 μm. The ball mill is stopped for 10 min every 50 min of ball milling.

3. The method for preparing a high-temperature silicide coating containing a composite diffusion barrier layer according to claim 2, characterized in that, Step S3 also includes the following steps: S32. After the ball milling process, the powder suspension is left to stand for 3-5 hours and then placed in a drying oven. It is then dried at a constant temperature of 40-60℃ for 8-12 hours to ensure that the powder is completely dry.

4. The method for preparing a high-temperature silicide coating containing a composite diffusion barrier layer according to claim 3, characterized in that, Step S3 also includes the following steps: S33. Pour the dried powder into a mortar and grind it thoroughly. When the powder particles are separated without obvious lumps, use a 260-mesh sieve to vibrate and sieve it. Pour the remaining powder that fails to pass through the sieve back into the mortar and grind it again, then sieve it again until all the powder can pass through the sieve, so that the particle size of the powder is uniform.

5. The method for preparing a high-temperature silicide coating comprising a composite diffusion barrier layer according to claim 1, characterized in that, Step S6 specifically includes: The slurry was evenly brushed onto the surface of the Nb alloy substrate. After each brushing, the substrate was placed in a drying oven for 30 minutes. The temperature of the drying oven was set at 40-70℃. The brushing was repeated 2-6 times. After all brushing was completed, the substrate was placed in the drying oven to dry for 12 hours.

6. The method for preparing a high-temperature silicide oxide coating comprising a composite diffusion barrier layer according to claim 1, characterized in that, In step S2, the pickling solution is composed of 10-30 vol.% nitric acid, 1-10 vol.% hydrofluoric acid, and 50-80 vol.% distilled water, with the sum of the volume contents of the above three components being 100%.

7. The method for preparing a high-temperature silicide coating comprising a composite diffusion barrier layer according to claim 1, characterized in that, In step S1, the thickness of the Nb alloy matrix is ​​3-5 mm.

8. The method for preparing a high-temperature silicide coating comprising a composite diffusion barrier layer according to claim 1, characterized in that, Step S7 also includes subjecting the sintered sample to constant-temperature oxidation at 1400℃ for 100 hours to obtain an oxide film on the coating surface.

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