A method and application for preparing an antioxidant MoSi2 coating on the surface of Nb-Si based alloys by a single-step slurry melting method.

Abstract

This invention discloses a method and application for preparing an antioxidant MoSi2 coating on the surface of an Nb-Si based alloy using a single-step slurry melting method, relating to the field of high-temperature alloy oxidation protection technology. The coating comprises an oxide diffusion barrier layer and a MoSi2 coating sequentially stacked on the surface of an Nb-Si based superalloy; the oxide diffusion barrier layer is distributed discontinuously at the interface between the Nb-Si based superalloy and the MoSi2 coating; the oxide diffusion barrier layer is prepared by ball milling and mixing nano-Al2O3 particles and SiO2 particles. This invention prepares a MoSi2 coating on the alloy surface using a single-step slurry melting method. This preparation method is simple to operate, requires few materials, is low in cost, and is suitable for large-scale industrial production, yielding a MoSi2 coating with excellent oxidation resistance.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy oxidation protection technology, specifically to a method and application for preparing an anti-oxidation MoSi2 coating on the surface of Nb-Si based alloys by a single-step slurry melting method. Background Technology

[0002] Nb-Si based alloys have low density (approximately 7.2 g / cm³). 3 With advantages such as high melting point (over 1700 ℃) and good high and low temperature mechanical properties, this alloy can operate at a temperature approximately 200 ℃ higher than nickel-based single-crystal superalloys, making it a promising material for aero-engine turbine blades. However, the insufficient high-temperature oxidation resistance of Nb-Si based alloys severely limits their application in the aerospace industry. Although alloying can improve the high-temperature oxidation resistance of Nb-Si based alloys to some extent, it also reduces the alloy's mechanical properties. Surface coating technology is an effective method to improve the high-temperature oxidation resistance of the alloy without compromising its mechanical properties.

[0003] Intermetallic compound MoSi2 possesses advantages such as high melting point, high hardness, and excellent high-temperature oxidation resistance, making it an excellent anti-oxidation protective coating for Nb alloy surfaces and widely used in engineering. In high-temperature, oxygen-rich environments, a continuous SiO2 protective film can form on the MoSi2 surface, effectively preventing oxygen diffusion into the substrate. Furthermore, the coefficient of thermal expansion of MoSi2 (8.1 × 10⁻⁶) is low. -6 K -1 The coefficient of thermal expansion of Nb-Si based alloys is 8.4 × 10⁻⁶. -6 K -1 Therefore, the MoSi2 coating is considered one of the most ideal high-temperature anti-oxidation coatings for Nb-Si based superalloys.

[0004] The slurry sintering method offers advantages such as simple preparation process, ability to coat complex-shaped workpieces, low material consumption, and low cost, making it an important method for preparing silicide coatings. However, the coatings prepared by this method lack sufficient density, significantly impacting their high-temperature protection capabilities. While a two-step method exists for preparing dense MoSi2 coatings, it is cumbersome. Therefore, developing a single-step slurry sintering method for preparing dense MoSi2 coatings is of great significance. Summary of the Invention

[0005] To address the shortcomings of the aforementioned background technology, this invention addresses the issues of poor density in MoSi2 coatings prepared by slurry sintering processes on Nb-Si based alloy surfaces, and the cumbersome steps involved in preparing dense MoSi2 coatings using the slurry sintering method. This invention provides a method and application for preparing an antioxidant MoSi2 coating on the surface of Nb-Si based alloys using a single-step slurry sintering method. This method for preparing MoSi2 coatings on alloy surfaces is simple to operate, requires few materials, is low-cost, and facilitates large-scale industrial production, yielding MoSi2 coatings with excellent antioxidant properties.

[0006] The first objective of this invention is to provide an antioxidant MoSi2 coating prepared on the surface of an Nb-Si based alloy by a single-step slurry melting method. The coating comprises an oxide diffusion barrier layer and a MoSi2 coating sequentially stacked on the surface of the Nb-Si based superheated alloy.

[0007] The oxide diffusion barrier layer is distributed in a discontinuous state at the interface between the Nb-Si based superalloy and the MoSi2 coating.

[0008] The oxide diffusion barrier layer is prepared by ball milling and mixing nano-Al2O3 particles and SiO2 particles.

[0009] Preferably, the molar ratio of the nano-Al2O3 particles to the SiO2 particles is (0.5~2):1; and the particle size of both the nano-Al2O3 particles and the SiO2 particles is 25~35 nm.

[0010] Preferably, the thickness of the MoSi2 coating is 100~200 μm.

[0011] Preferably, the thickness of the oxide diffusion barrier layer is 3~15 μm.

[0012] The second objective of this invention is to provide a method for preparing an antioxidant MoSi2 coating on the surface of a Nb-Si based alloy using a single-step slurry melting method, comprising the following steps:

[0013] Al2O3 powder and SiO2 powder were mixed to form slurry I;

[0014] Mo powder and Si powder are mixed to form slurry II;

[0015] Slurry I and slurry II were sequentially coated onto the surface of Nb-Si based ultra-high temperature alloy, and vacuum sintered at 1400~1500 ℃ for 0.5~2 h to obtain an anti-oxidation MoSi2 coating on the surface of Nb-Si based alloy.

[0016] Preferably, the slurry I is prepared according to the following steps:

[0017] Weigh out 5-17% Al2O3 powder, 5-10% SiO2 powder, 0.5-2% binder and 70-85% solvent by mass percentage, and mix them evenly by ball milling to obtain the product;

[0018] The adhesive is polyvinyl butyral;

[0019] The solvent is ethanol.

[0020] Preferably, the slurry II is prepared according to the following steps:

[0021] Mo powder and Si powder are weighed in an atomic percentage ratio of (1~3):(2~8), and then 0.5~2% of PVB as a binder is added as a total mass of Mo powder and Si powder, and anhydrous ethanol is used as a solvent. The mixture is then uniformly mixed to obtain the final product.

[0022] Preferably, when applying slurry II, multiple brushings are performed until the MoSi2 slurry coating thickness is 100~300 μm.

[0023] Preferably, when applying slurry I, the coating thickness on the surface of the Nb-Si-based ultra-high temperature alloy is 3~15 μm.

[0024] The third objective of this invention is to provide an application of MoSi2 coating in the oxidation resistance of Nb-Si based alloy surfaces.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention provides a method and application for preparing an antioxidant MoSi2 coating on the surface of Nb-Si based alloys by a single-step slurry melting method. This invention solves the technical problem of the cumbersome steps in preparing a dense MoSi2 coating by the slurry melting method, and reduces the porosity of the single-step slurry melting MoSi2 coating. The area porosity of the MoSi2 coating is reduced from 31.6% without an oxide diffusion barrier layer to 16%.

[0027] The low-porosity MoSi2 coating of this invention exhibits excellent high-temperature oxidation resistance. After isothermal oxidation at 1250 °C for 100 h, it can still effectively protect the substrate, with a weight gain of only 9.4 mg / cm² per unit area. 2 .

[0028] The nano-oxide diffusion barrier layer and MoSi2 coating of the present invention are prepared by a single-step slurry melting method, which is simple and easy to operate, highly efficient, low in cost, and highly controllable, making it suitable for industrial production.

[0029] The nano-oxide diffusion barrier layer introduced in this invention can prevent the diffusion of liquid-phase Si into the substrate during sintering, ensuring sufficient Si source to react with Mo to form a dense coating during slurry melting. The discontinuous distribution of the nano-oxide diffusion barrier layer at the interface ensures the metallurgical bond between the coating and the substrate. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the process of preparing the MoSi2 coating containing the diffusion barrier layer in Examples 1, 2, and 3 of the present invention;

[0031] Figure 2 BSE morphology images of the cross-sections of the MoSi2 coating (a) without a diffusion barrier layer and the dense MoSi2 coating (b) with a diffusion barrier layer prepared in Example 2 of the present invention;

[0032] Figure 3 The weight gain per unit area of ​​the MoSi2 coating without a diffusion barrier layer and the dense MoSi2 coating with a diffusion barrier layer prepared in Example 2 of the present invention after oxidation for different times in an atmospheric environment at 1250 °C;

[0033] Figure 4 Cross-sectional BSE morphology images of the MoSi2 coating (a) without a diffusion barrier layer and the dense MoSi2 coating (b) with a diffusion barrier layer prepared in Example 2 of the present invention after oxidation at 1250 °C for 10 h;

[0034] Figure 5 The cross-sectional BSE image of the MoSi2 coating containing the diffusion barrier layer prepared in Example 2 of the present invention after oxidation at 1250 °C for 100 h is shown. Detailed Implementation

[0035] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0036] The first aspect of the present invention provides an antioxidant MoSi2 coating prepared on the surface of an Nb-Si based alloy by a single-step slurry melting method, characterized in that the coating comprises an oxide diffusion barrier layer and a MoSi2 coating sequentially stacked on the surface of the Nb-Si based superheated alloy.

[0037] The oxide diffusion barrier layer is distributed in a discontinuous state at the interface between the Nb-Si based superalloy and the MoSi2 coating.

[0038] The oxide diffusion barrier layer is prepared by ball milling and mixing nano-Al2O3 particles and SiO2 particles.

[0039] The molar ratio of the nano-Al2O3 particles to the SiO2 particles is (0.5~2):1; the particle size of both the nano-Al2O3 particles and the SiO2 particles is 25~35 nm.

[0040] The thickness of the MoSi2 coating is 100~200 μm.

[0041] The thickness of the oxide diffusion barrier layer is 3~15 μm.

[0042] The nano-oxide diffusion barrier layer introduced in this invention can prevent the diffusion of liquid-phase Si into the substrate during sintering, ensuring sufficient Si source to react with Mo to form a dense coating during slurry melting. The discontinuous distribution of the nano-oxide diffusion barrier layer at the interface ensures the metallurgical bond between the coating and the substrate.

[0043] The coating provided by the present invention includes an oxide diffusion barrier layer at the interface and a MoSi2 coating. The diffusion barrier layer is distributed in a discontinuous state at the interface between the Nb-Si-based superalloy and the MoSi2 coating. The diffusion barrier layer is a mixed oxide of nano-Al2O3 and SiO2 particles.

[0044] A second aspect of the present invention provides a method for preparing an antioxidant MoSi2 coating on the surface of a Nb-Si based alloy by a single-step slurry melting method, comprising the following steps:

[0045] Al2O3 powder and SiO2 powder were mixed to form slurry I;

[0046] Mo powder and Si powder are mixed to form slurry II;

[0047] Slurry I and slurry II were sequentially coated onto the surface of Nb-Si based ultra-high temperature alloy, and vacuum sintered at 1400~1500 ℃ for 0.5~2 h to obtain an anti-oxidation MoSi2 coating on the surface of Nb-Si based alloy.

[0048] The slurry I is prepared according to the following steps:

[0049] The following components are weighed by mass percentage: 5-17% Al2O3 powder, 5-10% SiO2 powder, 0.5-2% binder, and 70-85% solvent. These components are then ball-milled and mixed uniformly to obtain the final product. The binder is polyvinyl butyral, and the solvent is ethanol. When applying slurry I, a coating thickness of 3-15 μm is brushed onto the surface of the Nb-Si based ultra-high temperature alloy.

[0050] It should be noted that during the brushing process of the nano-oxide diffusion barrier layer, only one brushing is performed, and the thickness of the nano-oxide diffusion barrier layer brushed on the surface of the Nb-Si-based superalloy is controlled to be 3~15 μm.

[0051] The slurry II is prepared according to the following steps:

[0052] Mo powder and Si powder were weighed in an atomic percentage ratio of (1~3):(2~8), and then 0.5~2% PVB (by mass of the total Mo and Si powder) was added as a binder. Anhydrous ethanol was used as a solvent, and the mixture was stirred evenly to obtain the final product. When applying slurry II, multiple brushings were performed until the MoSi2 slurry thickness reached 100~300 μm. In other words, when applying the MoSi2 slurry to the nano-oxide diffusion barrier layer, multiple brushings were performed until the MoSi2 slurry thickness reached 100~300 μm.

[0053] The nano-oxide diffusion barrier layer and MoSi2 coating of this invention are prepared using a single-step slurry sintering method. This process is simple, efficient, low-cost, and highly controllable, making it suitable for industrial production. The nano-oxide diffusion barrier layer is relatively stable at high temperatures, so most of the nano-oxide particles remain at the coating substrate / interface throughout the sintering process. During coating sintering, the nano-oxide diffusion barrier layer at the interface effectively blocks some of the Si diffusion, thereby increasing the coating density. Because the granular nano-oxide diffusion barrier layer is not continuous and dense, metallurgical bonding can occur between the coating and the substrate. After sintering, the diffusion barrier layer is distributed in a discontinuous granular form at the coating / substrate interface.

[0054] A third aspect of the present invention provides the application of MoSi2 coating in the oxidation resistance of Nb-Si based alloy surfaces.

[0055] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0056] The Nb-Si based superalloy used in the following examples is Nb-22Ti-15Si-5Cr-3Al-3Hf (at.%)

[0057] Example 1

[0058] A method for preparing an anti-oxidation MoSi2 coating on the surface of an Nb-Si based superalloy, see [link to relevant documentation]. Figure 1 As shown, it includes the following steps:

[0059] (1) The Nb-Si based alloy was cut into 7mm×6mm×4mm block samples by wire cutting. The six surfaces of each sample were polished smooth with 80~1000# SiC water sandpaper, ultrasonically cleaned in anhydrous ethanol and then dried with cold air for later use.

[0060] (2) Weigh out Al2O3 powder (17%), SiO2 powder (5%), binder polyvinyl butyral (1%) and solvent ethanol (77%) by mass percentage, and ball mill and mix the prepared slurry evenly.

[0061] (3) Weigh the refined Mo powder and Si powder according to Mo: Si=3:1 (at%), add 1% of PVB as a binder and anhydrous ethanol as a solvent (50% of the total mass of the slurry), put the nylon can containing the mixed slurry into a planetary ball mill and ball mill at 400 r / min for 4 h to obtain a uniformly mixed slurry.

[0062] (4) The ball-milled slurry from step (2) is evenly brushed onto each surface of the base alloy after step (1). The slurry is brushed once, and the thickness of the brushed slurry is measured using a micrometer. The thickness is controlled to be around 5 μm.

[0063] (5) The ball-milled slurry from step (3) is evenly brushed onto each surface of the sample after step (4). After brushing three times, the thickness of the brushed slurry is measured using a micrometer screw gauge to control the thickness of the MoSi2 slurry brushing to be 260 μm.

[0064] (6) The sample coated in step (5) was vacuum dried at 60 and 120 °C for 1 h, and vacuum sintered at 1450 °C for 1 h to obtain a MoSi2 coating containing a nano-oxide diffusion barrier layer; this is the method for preparing an anti-oxidation MoSi2 coating on the surface of Nb-Si based super high temperature alloy.

[0065] Analysis revealed that the coating consisted of nano-oxides (Al2O3 and SiO2) and a MoSi2 layer at the interface, with a porosity of 24% and good interfacial bonding.

[0066] Example 2

[0067] A method for preparing an anti-oxidation MoSi2 coating on the surface of an Nb-Si based superalloy, see [link to relevant documentation]. Figure 1 As shown, it includes the following steps:

[0068] (1) The Nb-Si based alloy was cut into 7mm×6mm×4mm block samples by wire cutting. The six surfaces of each sample were polished smooth with 80~1000# SiC water sandpaper, ultrasonically cleaned in anhydrous ethanol and then dried with cold air for later use.

[0069] (2) Weigh out Al2O3 powder (12%), SiO2 powder (7.5%), binder polyvinyl butyral (0.5%) and solvent ethanol (80%) by mass percentage, and ball mill and mix the prepared slurry evenly.

[0070] (3) Weigh the refined Mo powder and Si powder according to Mo:Si=3:1 (at%), add 1% of PVB as a binder and anhydrous ethanol as a solvent (50% of the total mass of the slurry), put the nylon can containing the mixed slurry into a planetary ball mill and ball mill at 400 r / min for 4 h to obtain a uniformly mixed slurry.

[0071] (4) The ball-milled slurry from step (2) is evenly brushed onto each surface of the base alloy after step (1). The slurry is brushed once, and the thickness of the brushed slurry is measured using a micrometer. The thickness is controlled to be around 5 μm.

[0072] (5) The ball-milled slurry from step (3) is evenly brushed onto each surface of the sample after step (4). After brushing three times, the thickness of the brushed slurry is measured using a micrometer screw gauge to control the thickness of the MoSi2 slurry brushing to be 260 μm.

[0073] (6) The sample coated in step (5) was vacuum dried at 60 and 120 °C for 1 h, and vacuum sintered at 1450 °C for 1 h to obtain a MoSi2 coating containing a nano-oxide diffusion barrier layer; this is the method for preparing an anti-oxidation MoSi2 coating on the surface of Nb-Si based super high temperature alloy.

[0074] The cross-sectional BSE morphology of the obtained coating is as follows Figure 2 As shown in (b), the coating consists of a discontinuously distributed oxide diffusion barrier layer and a MoSi2 layer, with a porosity of 16.3% and a metallurgical bond at the interface. The coating without the diffusion barrier layer, however, has lower density. Figure 2 As shown in (a), the area porosity of the coating decreased from 31.6% without the diffusion barrier to 16.3%. An oxidation experiment was conducted on the coated sample at 1250 °C for 100 h in an atmospheric environment. The results showed that after oxidation at 1250 °C for 100 h, the coating surface was covered with a dense oxide film (as shown in (a)). Figure 5 The weight gain per unit area of ​​the coating was 9.4 mg / cm³. 2 The MoSi2 coating without a diffusion barrier layer showed significant peeling after oxidation at 1250 °C for 10 h. Figure 4 The weight gain per unit area of ​​the coating was 10.6 mg / cm³. 2 .

[0075] It should be noted that, Figure 2 Below (a) and (b) are enlarged images corresponding to the red boxes; Figure 4 Below (a) and (b) are enlarged images corresponding to the yellow boxes; Figure 5 The image on the right is an enlarged view corresponding to the one in the yellow box.

[0076] Example 3

[0077] (1) The Nb-Si based alloy was cut into 7mm×6mm×4mm block samples by wire cutting. The six surfaces of each sample were polished smooth with 80~1000# SiC water sandpaper, ultrasonically cleaned in anhydrous ethanol and then dried with cold air for later use.

[0078] (2) Weigh out Al2O3 powder (5%), SiO2 powder (10%), binder polyvinyl butyral (2%) and solvent ethanol (83%) by mass percentage, and ball mill and mix the prepared slurry evenly.

[0079] (3) Weigh the refined Mo powder and Si powder according to Mo:Si=3:1 (at%), add 1% of PVB as a binder and anhydrous ethanol as a solvent (50% of the total mass of the slurry), put the nylon can containing the mixed slurry into a planetary ball mill and ball mill at 400 r / min for 4 h to obtain a uniformly mixed slurry.

[0080] (4) The ball-milled slurry from step (2) is evenly brushed onto each surface of the base alloy after step (1). The slurry is brushed once, and the thickness of the brushed slurry is measured using a micrometer screw gauge. The thickness is controlled to be around 10 μm.

[0081] (5) The ball-milled slurry from step (3) is evenly brushed onto each surface of the sample after step (4). After brushing three times, the thickness of the brushed slurry is measured using a micrometer screw gauge to control the thickness of the MoSi2 slurry brushing to be 260 μm.

[0082] (6) The sample coated in step (5) was vacuum dried at 60 and 120 °C for 1 h, and vacuum sintered at 1450 °C for 1 h to obtain a MoSi2 coating containing a nano-oxide diffusion barrier layer; this is the method for preparing an anti-oxidation MoSi2 coating on the surface of Nb-Si based super high temperature alloy.

[0083] To illustrate the effects of the present invention, a dense MoSi2 coating containing a nano-oxide diffusion barrier layer was prepared on the surface of an Nb-Si based alloy using a single-step slurry melting process, and then subjected to a 100-h isothermal oxidation test at 1250 °C in an atmospheric environment.

[0084] Figure 3 The weight gain per unit area of ​​the MoSi2 coating without a diffusion barrier layer and the dense MoSi2 coating with a diffusion barrier layer prepared in Example 2 are shown in the oxidation curves at 1250 °C for different times. Figure 3As can be seen from the oxidation weight gain curve per unit area, at 1250 °C, the oxidation weight gain of the MoSi2 coating with the diffusion barrier layer is much smaller than that of the MoSi2 coating without the diffusion barrier layer. The MoSi2 coating without the diffusion barrier layer reaches a weight gain of 9.36 mg / cm³ after oxidation at 1250 °C for 10 h. 2 The MoSi2 coating containing the diffusion barrier layer showed a weight gain of only 10.57 mg / cm³ after oxidation at 1250 °C for 100 h. 2 Furthermore, the weight gain due to oxidation follows a parabolic pattern.

[0085] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an oxidation resistant MoSi2 coating on the surface of a Nb-Si based alloy by a single step tape casting and melt infiltration process, characterized in that, Comprising the following steps: (1) The Nb-Si based alloy is cut into 7mm x 6mm x 4mm block samples by wire cutting, and the 6 surfaces of each sample are polished smooth with 80-1000# SiC water sandpaper, then ultrasonic cleaned in anhydrous ethanol and dried with cold air for standby; (2) Al2O3 powder 17%, SiO2 powder 5%, binder polyvinyl butyral 1% and solvent ethanol 77% are weighed according to the mass percentage, and the prepared slurry is ball-mixed uniformly; (3) The refined Mo powder and Si powder are weighed according to the atomic percentage of 3:1, 1% of the total mass of the powder is added as a binder, anhydrous ethanol is used as a solvent, the nylon tank containing the mixed slurry is put into the planetary ball mill at a speed of 400 r / min for 4 h, and a uniformly mixed slurry is obtained; (4) The slurry ball-mixed in step (2) is uniformly brushed on each surface of the substrate alloy treated in step (1), brushed once, and the thickness of the brushed slurry is measured using a screw micrometer, and the thickness is controlled to be 5 μm; (5) The slurry ball-mixed in step (3) is uniformly brushed on each surface of the sample treated in step (4), brushed three times, and the thickness of the brushed slurry is measured using a screw micrometer, and the MoSi2 slurry brushed thickness is controlled to be 260 μm; (6) The sample brushed in step (5) is vacuum dried at 60 and 120 ℃ for 1 h respectively, and vacuum sintered at 1450 ℃ for 1 h, to obtain a MoSi2 coating containing a nano-oxide diffusion barrier layer.

2. A method for preparing an oxidation resistant MoSi2 coating on the surface of a Nb-Si based alloy by a single step tape casting and melt infiltration process, characterized in that, Comprising the following steps: (1) The Nb-Si based alloy is cut into 7mm x 6mm x 4mm block samples by wire cutting, and the 6 surfaces of each sample are polished smooth with 80-1000# SiC water sandpaper, then ultrasonic cleaned in anhydrous ethanol and dried with cold air for standby; (2) Al2O3 powder 17%, SiO2 powder 5%, binder polyvinyl butyral 1% and solvent ethanol 77% are weighed according to the mass percentage, and the prepared slurry is ball-mixed uniformly; (3) The refined Mo powder and Si powder are weighed according to the atomic percentage of 3:1, 1% of the total mass of the powder is added as a binder, anhydrous ethanol is used as a solvent, the nylon tank containing the mixed slurry is put into the planetary ball mill at a speed of 400 r / min for 4 h, and a uniformly mixed slurry is obtained; (4) The slurry ball-mixed in step (2) is uniformly brushed on each surface of the substrate alloy treated in step (1), brushed once, and the thickness of the brushed slurry is measured using a screw micrometer, and the thickness is controlled to be 5 μm; (5) The slurry ball-mixed in step (3) is uniformly brushed on each surface of the sample treated in step (4), brushed three times, and the thickness of the brushed slurry is measured using a screw micrometer, and the MoSi2 slurry brushed thickness is controlled to be 260 μm; (6) The sample brushed in step (5) is vacuum dried at 60 and 120 ℃ for 1 h respectively, and vacuum sintered at 1450 ℃ for 1 h, to obtain a MoSi2 coating containing a nano-oxide diffusion barrier layer.

3. A method for preparing an oxidation resistant MoSi2 coating on the surface of a Nb-Si based alloy by a single step tape casting and melt infiltration process, characterized in that, Comprising the following steps: (1) The Nb-Si-based alloy is cut into 7mm×6mm×4mm block samples by wire cutting, and the 6 surfaces of each sample are polished smooth with 80-1000# SiC water sandpaper, then ultrasonic cleaned in anhydrous ethanol and dried by cold air for standby; (2) Al2O3 powder 5%, SiO2 powder 10%, binder polyvinyl butyral 2% and solvent ethanol 83% are weighed according to the mass percentage, and the prepared slurry is ball-mixed uniformly; (3) The refined Mo powder and Si powder are weighed according to the atomic percentage of 3:1, and 1% of the total mass of the powder is added as a binder, and anhydrous ethanol is used as a solvent, and the nylon tank containing the mixed slurry is placed in a planetary ball mill at a speed of 400 r / min for 4 h to obtain a uniformly mixed slurry; (4) The slurry ball-mixed in step (2) is uniformly brushed on each surface of the substrate alloy treated in step (1), and the brushing thickness is measured by using a screw micrometer, and the thickness is controlled to be 10 μm; (5) The slurry ball-mixed in step (3) is uniformly brushed on each surface of the sample treated in step (4), and after brushing three times, the brushing thickness of the MoSi2 slurry is measured by using a screw micrometer, and the brushing thickness of the MoSi2 slurry is controlled to be 260 μm; (6) The sample brushed in step (5) is vacuum dried at 60 and 120 ℃ for 1 h respectively, and vacuum sintered at 1450 ℃ for 1 h to obtain a MoSi2 coating containing a nano-oxide diffusion barrier layer.

4. An oxidation resistant MoSi2 coating prepared on the surface of a Nb-Si based alloy by the method of any one of claims 1 to 3, characterized in that, The coating comprises an oxide diffusion barrier layer and a MoSi2 coating arranged in sequence on the surface of the Nb-Si-based ultrahigh-temperature alloy; The oxide diffusion barrier layer is distributed in a discontinuous state at the interface between the Nb-Si-based ultrahigh-temperature alloy and the MoSi2 coating; The oxide diffusion barrier layer is prepared by ball-mixing nano-Al2O3 particles and SiO2 particles.

5. Application of the MoSi2 coating of claim 4 in the surface oxidation resistance of Nb-Si-based alloys.

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