Preparation method of high-temperature-oxidation-resistant silicide coating containing composite diffusion-resistant layer

Abstract

The invention relates to a preparation method of a high-temperature oxidation-resistant silicide coating containing a composite diffusion-resistant layer, the high-temperature oxidation-resistant silicide coating comprises a MoSi2 outer layer, a WSi2-YSZ diffusion-resistant layer and a thin NbSi2 and Nb5Si3 mutual diffusion layer between the WSi2-YSZ diffusion-resistant layer and a substrate, the outer layer provides good high-temperature oxidation resistance for the coating, the diffusion-resistant layer can effectively slow down element mutual diffusion between the coating and the substrate, and the high-temperature oxidation-resistant silicide coating has good oxidation resistance. The loss of the beneficial element Si is reduced, metallurgical bonding is formed between the mutual diffusion layer and the matrix, and the interface bonding between the external coating and the matrix can be improved. According to the method, a YSZ resistance diffusion layer sample containing WSi 2-20% is subjected to constant-temperature oxidation at the temperature of 1400 DEG C for 100 h, and then the oxidation weight of the sample is increased by 1.5 mg / cm < 2 >; meanwhile, compared with an unimpeded diffusion layer sintering sample, the thickness of an oxidation film and the thickness of a diffusion layer are reduced by 28.5% and 29.2% respectively after oxidation is conducted for 100 h, the oxidation film does not peel off, and the coating is well combined with a matrix alloy interface.

Description

Technical Field

[0001] The invention belongs to the technical field of heat protection of refractory metals, and in particular relates to a method for preparing a high-temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer. Background Art

[0002] Niobium-based ultra-high temperature alloys have the advantages of high melting point (1750℃), moderate density (7.1g / cm3), excellent high-temperature mechanical properties and good processability. They are expected to replace nickel-based high-temperature alloys and become the raw materials for the new generation of gas turbine aircraft engine blades and other high-temperature structural components. However, their poor high-temperature oxidation resistance and high-temperature surface mechanical properties severely limit their engineering applications.

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

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

[0005] The purpose of the present invention is to provide a method for preparing a high-temperature resistant oxidized silicide coating comprising a composite diffusion-resistant layer, aiming to solve the problems of insufficient high-temperature blocking ability of a single WSi2 layer or YSZ layer, low interface bonding strength or excessive mismatch in thermal expansion coefficient.

[0006] In order to solve the above technical problems, a method for preparing a high temperature oxidation resistant silicide coating including a composite diffusion barrier layer is provided, comprising the following steps:

[0007] S1. Grind the six surfaces of the Nb alloy substrate to make them smooth and the edges and corners rounded;

[0008] S2, put it into anhydrous ethanol for ultrasonic vibration cleaning, pickle it for 5-8s, take it out and rinse it with plenty of clean water, then immerse it in anhydrous ethanol again for ultrasonic vibration cleaning, and finally dry it in a drying oven;

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

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

[0011] S5. Use a brush to evenly coat the slurry on the surface of the Nb alloy. Place it in a drying oven for 30 minutes after each coating. The temperature of the drying oven is set at 50-70°C. Repeat the coating 2-6 times.

[0012] S6. Place the substrate coated with the diffusion barrier layer into an SPS spark plasma sintering mold, spread appropriate Mo and Si mixed powders on the upper and lower surfaces, and sinter at a sintering temperature of 1400°C, a sintering pressure of 40Mpa, and a sintering time of 15min. The heating rate is 100°C / min. During the sintering process, argon gas is introduced for protection. Finally, the substrate is cooled with the furnace to obtain a molybdenum silicide coating containing a composite diffusion barrier layer.

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

[0014] S31. Use a ball mill to grind Mo, Si, WSi2 and YSZ powders respectively, with a ball-to-material ratio of 3:1-5:1 and a ratio of large balls to small balls of 12:50. Add a small amount of anhydrous ethanol for wet grinding. The ball mill speed is 300-500r / min. The ball mill duration is 8-10h to obtain Mo, Si, WSi2 powders and YSZ powders with a particle size of 0.6-1um. During the ball milling process, stop the machine for 10min every 50min of ball milling.

[0015] In the above method, step S3 further comprises the following steps:

[0016] S32. After the ball-milled powder suspension is left to stand for 3-5 hours, it is placed in a drying oven and dried at a constant temperature of 40-60° C. for 8-12 hours to completely dry the powder.

[0017] In the above method, step S3 further comprises the following steps:

[0018] S33. Pour the dried powder into a mortar and grind it thoroughly. When the powder particles are separated without obvious agglomeration, use a 260 target sieve to vibrate and sieve. Pour the remaining powder that fails to pass through the sieve back into the mortar and grind it again and sieve it again until all the powder can pass through the sieve to make the powder particle size uniform.

[0019] In the above method, step S4 further includes:

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

[0021] In the above method, step S5 specifically includes:

[0022] Use a brush to evenly apply the slurry on the surface of the Nb alloy substrate. Place it in a drying oven for 30 minutes after each application. The temperature of the drying oven is set at 40-70°C. Repeat the application 2-6 times. After all the application times are completed, place it in a drying oven to dry for 12 hours.

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

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

[0025] The above method further comprises, in step S6, subjecting the sintered sample to constant temperature oxidation at 1400° C. for 100 hours to obtain an oxide film on the surface of the coating.

[0026] Implementing the embodiments of the present invention will have the following beneficial effects:

[0027] 1. The preparation method of the high temperature oxidation resistant silicide coating containing a composite diffusion barrier layer in this embodiment includes a MoSi2 outer layer, a WSi2-YSZ diffusion barrier layer, and a thin NbSi2 and Nb5Si3 transition layer between the substrate and the outer layer, which provides the coating with good high temperature oxidation resistance, and the diffusion barrier layer can effectively slow down the element diffusion rate between the coating and the substrate, slow down the loss of the beneficial element Si, and form a metallurgical bond between the transition layer and the substrate, so that the coating and the substrate are tightly bonded. After the WSi2-20% YSZ diffusion barrier layer sample was oxidized at 1400℃ for 100h, its oxidation weight increased by 1.5mg / cm 2 At the same time, compared with the sample without diffusion barrier layer, the thickness of the oxide film and the diffusion layer after oxidation for 100 hours were reduced by 28.5% and 29.2% respectively, and the oxide film did not peel off, and the coating had a good interface with the base alloy. Since the number of coatings can be controlled, it is easier to control the thickness of the WSi2-YSZ diffusion barrier layer. Specifically: firstly, the powder is refined by ball milling, and then a mixed slurry of WSi2 and YSZ in a certain proportion is brushed on the surface of the Nb alloy substrate. After each brushing, it is placed in a 60℃ drying oven for 30 minutes. After multiple brushings, it is placed in a 60℃ constant temperature drying oven for 12 hours. Finally, the dried sample is placed in an SPS spark plasma sintering furnace for sintering, and finally a MoSi2 / WSi2-YSZ composite anti-oxidation coating is obtained;

[0028] 2. The method for preparing the high temperature resistant oxidized silicide coating including the composite diffusion-resistant layer in this embodiment has the advantages of fast heating rate, low molding pressure, integrated sintering and pressing, high efficiency and good repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 A flow chart of a method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion resistance layer according to an embodiment of the present invention;

[0031] Figure 2 This is the SEM morphology of the cross section of the sintered coating in Example 1 of the present invention;

[0032] Figure 3 The surface and cross-sectional SEM morphology of the oxide film after the coating in Example 1 was oxidized at 1400℃ for 100h;

[0033] Figure 4The SEM morphology of the interdiffusion layer of the coating in Example 1 after isothermal oxidation at 1400°C for 100h;

[0034] Figure 5 The element concentration distribution diagram along the depth direction of the coating in Example 1 after constant temperature oxidation at 1400℃ for 100h;

[0035] Figure 6 The cross-sectional SEM morphology of the diffusion-blocking composite coating in Example 2;

[0036] Figure 7 The surface and cross-sectional SEM morphology of the oxide film containing the diffusion barrier composite coating in Example 2 after constant temperature oxidation at 1400℃ for 100h;

[0037] Figure 8 The SEM morphology of the interdiffusion layer of the composite coating in Example 2 after isothermal oxidation at 1400°C for 100h;

[0038] Fig. 9 The element concentration distribution diagram along the depth direction of the composite coating in Example 2 after constant temperature oxidation at 1400℃ for 100h;

[0039] Fig.10 It is the oxidation weight gain of each coating after constant temperature oxidation at 1400℃ for 100h. DETAILED DESCRIPTION

[0040] The present invention provides a method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer, comprising the following steps:

[0041] The six surfaces of the Nb alloy substrate are polished to be smooth and the edges and corners are polished to be rounded;

[0042] Put it in anhydrous ethanol for ultrasonic vibration cleaning, pickle it for 5-8 seconds, take it out and rinse it with plenty of water, then immerse it in anhydrous ethanol again for ultrasonic vibration cleaning, and finally dry it in a drying oven;

[0043] Mo, Si, WSi2 powder and YSZ were respectively refined by ball mill, and wet milling was performed by anhydrous ethanol. The ball mill speed was 300-500r / min, and the ball milling time was 8-15h to obtain Mo powder, Si powder and YSZ powder;

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

[0045] Use a brush to evenly coat the slurry on the surface of the Nb alloy. Place it in a drying oven for 30 minutes after each coating. The temperature of the drying oven is set at 50-70°C. Repeat the coating 2-6 times.

[0046] The substrate coated with the diffusion barrier layer is placed in an SPS spark plasma sintering mold, and appropriate Mo and Si mixed powders are spread on the upper and lower surfaces. It is sintered at a sintering temperature of 1400°C, a sintering pressure of 40Mpa, and a sintering time of 15min. The heating rate is 100°C / min. Argon is introduced during the sintering process for protection. Finally, it is cooled with the furnace to obtain a molybdenum silicide coating containing a composite diffusion barrier layer.

[0047] Example 1

[0048] The method for preparing a high temperature oxidation resistant silicide coating including a composite diffusion-blocking layer in Example 1 is carried out according to the following steps:

[0049] (1) Prepare the sample. Select Nb alloy as the raw material of the experimental matrix. Cut the Nb alloy rod with a diameter of 10 mm into thin slices of the same thickness. The thickness of the slice should not be too thin and should be controlled within 3 to 5 mm. If the matrix is ​​too thin, it is easy to warp under high pressure, causing mechanical strain. The six surfaces of the Nb alloy matrix are polished smooth and the edges and corners are polished round to reduce stress concentration during sintering.

[0050] (2) Matrix treatment: the matrix is ​​placed in anhydrous ethanol and cleaned by ultrasonic vibration; then pickled for 5 to 8 seconds, taken out and rinsed with a large amount of clean water, then immersed in anhydrous ethanol again and cleaned by ultrasonic vibration, and finally dried in a drying oven;

[0051] (3) Prepare powders, use a ball mill to refine Mo and Si powders respectively, the ball mill speed is 500r / min, the ball milling duration is 8h, so as to achieve powder refinement and obtain Mo and Si single substance powders with a particle size of 0.6 to 1um. During the ball milling process, the machine is stopped for 10min every 50min of ball milling to avoid overheating;

[0052] (4) After the ball milling treatment, the powder suspension was placed in a drying oven for 4 hours and dried at a constant temperature of 60° C. for 12 hours to ensure that the water in the suspension was completely evaporated and the powder was completely dry;

[0053] (5) Pour the dried powder into a mortar and grind it thoroughly to ensure that the powder particles are separated without obvious agglomeration, and then vibrate and sieve it using a 260-degree screen. Pour the remaining powder that fails to pass through the screen back into the mortar and grind it again, then sieve it again until all the powder can pass through the screen, ensuring that the powder particle size is uniform;

[0054] (6) Mixing powders: The refined Mo and Si powders are mixed and ball-milled according to an atomic ratio of 1:2.2 and a small amount of B and Y2O3 are added to improve the high-temperature oxidation resistance of the MoSi2 coating. The B content is 2%, the Y2O3 content is 1%, the solvent is anhydrous ethanol, the ball mill speed is 300 r / min, the ball-to-material ratio is 5:1, the ball milling time is 3 h, and after ball milling, the treatment is carried out according to steps (4) and (5);

[0055] (7) The substrate was placed in an SPS spark plasma sintering mold, and appropriate Mo, Si, B, and Y2O3 mixed powders were placed on the upper and lower surfaces. The substrate was sintered at a sintering temperature of 1400°C, a sintering pressure of 40 MPa, and a sintering holding time of 15 min. The sintering heating rate was 100°C / min. Argon was introduced during the sintering process for protection. Finally, the substrate was cooled with the furnace to obtain a MoSi2 coating. The surface and cross-section of the sintered coating were as shown in FIG. Figure 2 The details of the interdiffusion layer between the coating and the substrate are shown in Figure 2 As shown, the coating surface products are Figure 4 As shown by the X-ray diffraction analysis results;

[0056] (8) The sintered sample was subjected to a constant temperature oxidation test at 1400°C. After oxidation for 100 hours, the cross section of the coating was as follows: Figure 4 As shown in Figure 2, 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 shown in Figure 2. Figure 5 shown.

[0057] Example 2

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

[0059] (1) Prepare the sample. Select high-purity Nb as the raw material of the experimental matrix. Cut the Nb alloy rod with a diameter of 10 mm into thin slices of the same thickness. The thickness of the slice should not be too thin and should be controlled within 3 to 5 mm. If the matrix is ​​too thin, it is easy to warp under high pressure, causing mechanical strain. The six surfaces of the Nb alloy matrix are polished smooth and the edges are rounded to reduce stress concentration during sintering.

[0060] (2) Matrix treatment: the matrix is ​​placed in anhydrous ethanol and cleaned by ultrasonic vibration; then pickled for 5 to 8 seconds, taken out and rinsed with a large amount of clean water, then immersed in anhydrous ethanol again and cleaned by ultrasonic vibration, and finally dried in a drying oven;

[0061] (3) preparing powders, using a ball mill to refine Mo, Si, WSi2 and YSZ powders (20wt.%) respectively, with a ball mill speed of 500r / min and a ball milling duration of 8h to achieve powder refinement and obtain Mo, Si, WSi2 and YSZ powders with a particle size of 0.6 to 1um. During the ball milling process, the machine was stopped for 10min every 50min to avoid overheating;

[0062] (4) After the ball milling treatment, the powder suspension was placed in a drying oven for 4 hours and dried at a constant temperature of 60° C. for 12 hours to ensure that the water in the suspension was completely evaporated and the powder was completely dry;

[0063] (5) Pour the dried powder into a mortar and grind it thoroughly to ensure that the powder particles are separated without obvious agglomeration, and then vibrate and sieve it using a 260-degree screen. Pour the remaining powder that fails to pass through the screen back into the mortar and grind it again, then sieve it again until all the powder can pass through the screen, ensuring that the powder particle size is uniform;

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

[0065] (7) Preparation of diffusion barrier layer slurry: PVB is used as a binder with a content of 1 wt.%, YSZ accounts for 20% of the total mass according to the mass ratio, and anhydrous ethanol is added as a solvent to prepare a slurry with a solid content of 60 wt.%, and then the slurry is ball-milled for 2 h in a polytetrafluoroethylene ball mill at a speed of 300 r / min. The speed does not need to be too high to achieve a sufficient mixing effect;

[0066] (8) Use a brush to evenly apply the slurry on the surface of the Nb alloy substrate. Place it in a drying oven for 30 minutes after each application. The temperature of the drying oven is set at 60°C. Apply the slurry three times. After all the application times are completed, place it in a drying oven at 60°C and dry it for 12 hours.

[0067] Finally, the substrate coated with the diffusion barrier layer was placed in the SPS spark plasma sintering mold, and appropriate powders were placed on the upper and lower surfaces. The substrate was sintered at 1400°C, sintering pressure 40Mpa, and sintering holding time 15min. Argon was introduced during the sintering process for protection. After sintering, the substrate was cooled with the furnace, and finally the MoSi2 / WSi2-YSZ composite coating was obtained. The cross section of the coating is shown in Figure 2. Figure 6 shown.

[0068] (9) The sintered sample was subjected to a constant temperature oxidation test at 1400°C. The morphology of the oxide film on the coating surface after oxidation for 100 hours was as follows: Figure 6 The interface morphology between the composite coating and the substrate is shown in Figure 8 As shown, the EDS element concentration distribution along the depth direction of the interface is as follows Fig. 9 The oxidation weight gain results of each sample after constant temperature oxidation at 1400℃ for 100h are shown in Fig.10 As shown, it can be seen that the oxidation resistance of the composite coating can be improved to a certain extent after the diffusion barrier layer is added. When the YSZ addition amount is 20wt.%, its oxidation resistance is better. At this time, the oxide film is dense and has fewer structural defects such as microcracks, and the thickness of the oxide film is relatively small.

[0069] After experimental testing, Figure 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 coated sample, but also delay the interdiffusion of elements (especially Si element) at the coating / matrix alloy interface, and reduce the growth rate of the interdiffusion layer. When the YSZ addition amount is 20wt.%, its oxidation resistance is relatively good. At this time, the oxide film has fewer microcracks and a smaller thickness, so it can effectively improve the oxidation resistance of the composite coating at high temperatures.

[0070] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion barrier layer, characterized in that: The following steps are involved: S1. Grind the six surfaces of the Nb alloy substrate to make them smooth and the edges and corners rounded; S2, put it into anhydrous ethanol for ultrasonic vibration cleaning, pickle it for 5-8s, take it out and rinse it with plenty of clean water, then immerse it in anhydrous ethanol again for ultrasonic vibration cleaning, and finally dry it in a drying oven; S3, using a ball mill to refine Mo, Si, WSi2 powder and YSZ respectively, using anhydrous ethanol wet grinding, the ball mill speed is 300-500r / min, the ball milling time is 8-15h, and Mo powder, Si powder and YSZ powder are obtained; S4, using PVB as a binder, the content of which is 1-5wt.%, the molar ratio of tungsten to silicon is W:Si=1:2.2, the content of YSZ is 0-30wt.%, and anhydrous ethanol is added as a solvent to prepare a slurry with a solid content of 50-80wt.%, and then using a polytetrafluoroethylene ball mill to mix for 2-6 hours, and the speed of the ball mill is 200-400r / min; S5. Use a brush to evenly coat the slurry on the surface of the Nb alloy. Place it in a drying oven for 30 minutes after each coating. The temperature of the drying oven is set at 50-70°C. Repeat the coating 2-6 times. S6. Place the substrate coated with the diffusion barrier layer into an SPS spark plasma sintering mold, spread appropriate Mo and Si mixed powders on the upper and lower surfaces, and sinter at a sintering temperature of 1400°C, a sintering pressure of 40Mpa, and a sintering time of 15min. The heating rate is 100°C / min. During the sintering process, argon gas is introduced for protection. 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 oxidation resistant silicide coating comprising a composite diffusion-blocking layer according to claim 1, characterized in that: Step S3 includes the steps of: S31. Use a ball mill to grind Mo, Si, WSi2 and YSZ powders respectively, with a ball-to-material ratio of 3:1-5:1 and a ratio of large balls to small balls of 12:

50. Add a small amount of anhydrous ethanol for wet grinding. The ball mill speed is 300-500r / min. The ball mill duration is 8-10h to obtain Mo, Si, WSi2 powders and YSZ powders with a particle size of 0.6-1um. During the ball milling process, stop the machine for 10min every 50min of ball milling.

3. The method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer according to claim 2, characterized in that: Step S3 also includes the steps of: S32. After the ball-milled powder suspension is left to stand for 3-5 hours, it is placed in a drying oven and dried at a constant temperature of 40-60° C. for 8-12 hours to completely dry the powder.

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

5. The method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer according to claim 4, characterized in that: Step S4 also includes: The refined Mo and Si powders are mixed and ball-milled in an atomic ratio of 1:2.2, and a small amount of B and Y2O3 are added. The B content is 2-3wt.%, the Y2O3 content is 1-2wt.%, the solvent is anhydrous ethanol, the ball mill speed is 200-300r / min, the ball-to-material ratio is 5:1, the ball milling time is 2-3h, and after ball milling, the steps S32 and S33 are followed in sequence.

6. The method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer according to claim 1, characterized in that: Step S5 specifically includes: Use a brush to evenly apply the slurry on the surface of the Nb alloy substrate. Place it in a drying oven for 30 minutes after each application. The temperature of the drying oven is set at 40-70°C. Repeat the application 2-6 times. After all the application times are completed, place it in a drying oven to dry for 12 hours.

7. The method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer according to claim 1, characterized in that: In step S2, the pickling solution for pickling is 10-30 vol. % nitric acid, 1-10 vol. % hydrofluoric acid and 50-80 vol. % distilled water.

8. The method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer according to claim 1, characterized in that: In step S1, the thickness of the Nb alloy substrate is 3-5 mm.

9. The method for preparing a high temperature oxidation resistant silicide coating comprising a composite diffusion-blocking layer according to claim 1, characterized in that: Step S6 also includes subjecting the sintered sample to constant temperature oxidation at 1400° C. for 100 hours to obtain an oxide film on the surface of the coating.

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