Nb-si based ultrahigh temperature alloy surface oxidation-resistant composite coating and preparation method and application thereof

Abstract

The application discloses a Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating and a preparation method and application thereof, and relates to the technical field of high-temperature alloy oxidation protection.The composite coating comprises a diffusion barrier layer and a MoSi2 coating which are arranged in a stack manner, and the diffusion barrier layer is located on the surface of the Nb-Si-based ultrahigh-temperature alloy.The composite coating is prepared on the alloy surface through two-step slurry melting and sintering, and the preparation method is convenient to operate, low in cost and convenient for large-scale industrial production, and can obtain a dense MoSi2 coating with a good bonding force and containing the diffusion barrier layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature alloy oxidation protection, and particularly relates to a Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating and a preparation method and application thereof. BACKGROUND

[0002] The melting point of the new Nb-Si-based alloy is about 350 DEG C higher than that of the nickel-based high-temperature alloy, the density is about 15% lower than that of the nickel-based high-temperature alloy, and the new Nb-Si-based alloy organically combines the toughness of the Nb-based solid solution (Nbss) and the high-temperature strength of the silicide, and is expected to become one of the high-temperature structural materials of the Nb-based high-temperature alloy. However, the oxidation resistance of the alloy at high temperature is poor, which seriously restricts the application prospect of the alloy in actual hot end components. Since the MoSi2 coating has the characteristics of high melting point, good thermal stability and self-healing ability, the MoSi2 coating is one of the coating materials suitable for the high-temperature oxidation protection of the Nb-Si-based alloy.

[0003] The new Nb-Si-based alloy capable of continuously working at 1200-1450 DEG C, the surface coating of the alloy must also be capable of working in air or other oxidizing atmospheres for a long time, which requires the coating to have stable and longer service life. However, there is a large difference in chemical composition and microstructure between the alloy and the coating, the outward diffusion of the alloy elements and the inward diffusion of the Si elements in the coating will cause the change of the composition and the microstructure of the coating, a thick low-silicide layer such as Mo5Si3 and Nb5Si3 is formed at the interface, the Si source is depleted, and the high-temperature oxidation resistance of the coating is degraded and fails. In order to prevent the element interdiffusion at the coating / substrate interface, it is an effective method to introduce a diffusion barrier layer at the interface of the protective coating / substrate. At present, the diffusion barrier layer of noble metal or refractory metal is studied more, but the diffusion barrier capacity of the diffusion barrier layer is limited. The oxide ceramics such as Al2O3, Y2O3 and CeO2 have excellent diffusion barrier effect and are suitable for being used as the diffusion barrier layer between the silicide coating and the Nb alloy, but the interface bonding is poor. In addition, the slurry melting and sintering method has simple process operation, low cost and can coat parts with complex shapes, but the MoSi2 coating prepared by the slurry melting and sintering method is usually poor in compactness and poor in protection effect. Therefore, it is very important to develop a slurry melting and sintering method for preparing a dense MoSi2 coating and to prepare a diffusion barrier layer at the interface, which has excellent diffusion barrier effect and good bonding. SUMMARY

[0004] In view of the problems in the background art, the present application mainly solves the problem that the outward diffusion of the alloy elements and the inward diffusion of the Si elements in the coating will cause the change of the composition and the microstructure of the coating, a thick low-silicide layer such as Mo5Si3 and Nb5Si3 is formed at the interface, the Si source is depleted, and the high-temperature oxidation resistance of the coating is degraded and fails.

[0005] The application provides a Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating and a preparation method and application thereof.

[0006] The first object of the application is to provide a Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating, which comprises a diffusion barrier layer and a MoSi2 coating arranged in a stack, and the diffusion barrier layer is located on the surface of the Nb-Si-based ultrahigh-temperature alloy.

[0007] Preferably, the mass ratio of the Al2O3 and SiC particles is 1-15:1.

[0008] Preferably, the thickness of the diffusion barrier layer is 2-30 μm.

[0009] Preferably, the thickness of the MoSi2 coating is 50-200 μm.

[0010] Preferably, the thickness of the MoSi2 coating is 50-200 μm.

[0011] The second object of the application is to provide a preparation method of a Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating, which comprises the following steps:

[0012] A certain amount of SiC powder and Al2O3 powder is configured into a slurry and then coated on the surface of the Nb-Si-based ultrahigh-temperature alloy, dried and sintered at 800-1000 ℃ in air for 1-5 h to obtain a glass layer containing Al2O3 and SiC particles.

[0013] A certain amount of Mo powder and Si powder is configured into a slurry and then coated on the glass layer, dried and vacuum sintered at 1300-1600 ℃ for 0.5-2 h to obtain the Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating.

[0014] Preferably, the glass layer containing Al2O3 and SiC particles is prepared according to the following steps:

[0015] 2-10% SiC powder, 10-30% Al2O3 powder, 50-80% liquid potassium silicate and 2-10% deionized water are weighed according to the mass percentage, and the prepared slurry is uniformly ball-milled and mixed.

[0016] The ball-milled slurry is uniformly sprayed on the surface of the Nb-Si based super high temperature alloy, and then dried at room temperature, 70℃, 120℃ and 260℃ in sequence to obtain a slurry coating, and then sintered at 900℃ in air for 1-5h to obtain a glass layer containing Al2O3 and SiC particles.

[0017] Preferably, during the spraying process, the air pressure of the spray gun is 0.6Mpa, the distance between the Nb-Si based super high temperature alloy surface and the nozzle is about 15cm, and the spraying is performed for multiple times, each time lasting for 1s.

[0018] Preferably, when a certain amount of Mo powder and Si powder is configured into a slurry, the Mo powder and the Si powder are weighed according to an atomic percentage of 3:1, 1% of the total mass of the Mo powder and the Si powder is added as a binder, anhydrous ethanol is used as a solvent, and a uniformly mixed MoSi2 slurry is obtained.

[0019] Preferably, when the MoSi2 slurry is brushed on the glass layer, the brushing is performed for multiple times until the thickness of the MoSi2 slurry is 100-300μm.

[0020] The third object of the present application provides an application of the above-mentioned composite coating in the oxidation resistance of the surface of the Nb-Si based super high temperature alloy.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The Nb-Si based super high temperature alloy surface oxidation resistant composite coating, the preparation method and the application thereof provided by the present application solve the technical problem of poor densification of the MoSi2 coating obtained by slurry melting and sintering of the Nb-Si based alloy surface, realize the complete densification of the MoSi2 coating, and reduce the area porosity of the coating from 50.3% without the diffusion barrier layer to 3.4%.

[0023] The dense MoSi2 coating containing the diffusion barrier layer has excellent high-temperature oxidation resistance, and after 100h of constant temperature oxidation at 1250℃, the oxidation film is dense and complete without falling off, and the unit area weight gain is 2.11mg / cm 2 , which is significantly lower than 6.63mg / cm 2 .

[0024] The glass phase diffusion barrier layer containing Al2O3 and SiC particles significantly inhibits the element interdiffusion at the interface, and the thickness of the interdiffusion zone (IDZ) is reduced from 62.66μm without the diffusion barrier layer to 3.83μm with the diffusion barrier layer, which is reduced by about 93.9%.

[0025] The glass phase diffusion barrier layer and the MoSi2 coating are both prepared by the slurry melting and sintering method, which is simple and easy to operate, has easy synthesis conditions, and is suitable for industrial production.

[0026] The glass phase diffusion barrier layer introduced in the present application can cut off the Si chemical potential gradient between the MoSi2 coating and the Nb-Si based super high temperature alloy, prevent the diffusion of Si to the substrate, and ensure sufficient Si source to react with Mo to form a dense coating during the slurry melting and sintering process. Moreover, the glass phase diffusion barrier layer has chemical reactions with the substrate alloy and the MoSi2 coating, can achieve chemical bonding, and has good interface bonding conditions. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A process schematic diagram for preparing the dense MoSi2 coating with a diffusion barrier layer for the present application examples 1, 2 and 3;

[0028] Figure 2 BSE images of the cross section of the MoSi2 coating without a diffusion barrier layer (a) and the dense MoSi2 coating with a diffusion barrier layer (b) prepared for the present application example 2;

[0029] Figure 3 Unit area weight gain curves of the MoSi2 coating without a diffusion barrier layer and the dense MoSi2 coating with a diffusion barrier layer prepared for the present application example 2 after oxidation at 1250℃ in an atmospheric environment for 100h;

[0030] Figure 4 Cross section BSE images of the MoSi2 coating without a diffusion barrier layer (a and a') and the dense MoSi2 coating with a diffusion barrier layer (b and b') prepared for the present application example 2 after oxidation at 1250℃ for 100h;

[0031] Figure 5 Thickness of the interface interdiffusion zone (IDZ) of the MoSi2 coating without a diffusion barrier layer and the dense MoSi2 coating with a diffusion barrier layer prepared for the present application example 2 after oxidation at 1250℃ for 100h. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific examples and drawings, but the examples are not limiting to the present application.

[0033] The present application provides a Nb-Si based super high temperature alloy surface oxidation resistant composite coating, which comprises a diffusion barrier layer and a MoSi2 coating arranged in a stack, and the diffusion barrier layer is located on the surface of the Nb-Si based super high temperature alloy.

[0034] The diffusion barrier layer is a glass layer containing Al2O3 and SiC particles.

[0035] The mass ratio of the Al2O3 and SiC particles is 1-15:1.

[0036] The diffusion barrier layer has a thickness of 2-30 microns.

[0037] The MoSi2 coating has a thickness of 50-200 microns.

[0038] The application provides a preparation method of a Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating.

[0039] A certain amount of SiC powder and Al2O3 powder is configured into a slurry and coated on the surface of the Nb-Si-based ultrahigh-temperature alloy, and then dried and sintered at 800-1000 DEG C in air for 1-5 hours to obtain an Al2O3 and SiC particle-containing glass layer.

[0040] A certain amount of Mo powder and Si powder is configured into a slurry, and then coated on the glass layer, dried, and vacuum sintered at 1300-1600 DEG C for 0.5-2 hours to obtain the Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating.

[0041] The Al2O3 and SiC particle-containing glass layer is prepared according to the following steps:

[0042] 2-10% SiC powder, 10-30% Al2O3 powder, 50-80% liquid potassium silicate and 2-10% deionized water are weighed according to the mass percentage, and then the prepared slurry is ball-mixed uniformly.

[0043] The ball-mixed slurry is uniformly sprayed on the surface of the Nb-Si-based ultrahigh-temperature alloy, and then sequentially dried at room temperature, 70 DEG C, 120 DEG C and 260 DEG C to obtain a slurry coating, which is then sintered at 900 DEG C in air for 1-5 hours to obtain the Al2O3 and SiC particle-containing glass layer.

[0044] During the spraying process, the spraying gun air pressure is 0.6 Mpa, the distance between the Nb-Si-based ultrahigh-temperature alloy surface and the nozzle is about 15 cm, and spraying is performed multiple times, each time lasting 1 s.

[0045] Further, when a certain amount of Mo powder and Si powder is configured into a slurry, the Mo powder and Si powder are weighed according to the atomic percentage of 3:1, 1% of the total mass of the Mo powder and Si powder is added as a binder, and anhydrous ethanol is used as a solvent to obtain a uniformly mixed MoSi2 slurry.

[0046] When the MoSi2 slurry is brushed on the glass layer, brushing is performed multiple times until the MoSi2 slurry brushing thickness is 100-300 microns.

[0047] The application also provides a use of the composite coating in the Nb-Si-based ultrahigh-temperature alloy surface oxidation resistance.

[0048] In order to illustrate the effect of the present application, the Nb-Si based alloy is taken as the substrate, the dense MoSi2 coating containing the diffusion barrier layer is prepared by using the above two-step slurry sintering on the surface thereof, and the isothermal oxidation test is carried out on the coating at 1250℃ in the atmospheric environment for 100h.

[0049] It should be noted that the experimental methods used in the present application are conventional methods unless otherwise specified; the reagents and materials used are commercially available unless otherwise specified.

[0050] The Nb-Si based ultrahigh-temperature alloy used in the following examples is Nb-22Ti-16Si-4Cr-2Al-1.5Hf (at %).

[0051] Example 1

[0052] A method for preparing a surface oxidation-resistant composite coating of a Nb-Si based ultrahigh-temperature alloy, as shown in Figure 1 The method comprises the following steps:

[0053] (1) The Nb-Si based alloy is cut into 7mm×7mm×5mm block samples by wire cutting, 6 surfaces of each sample are polished smooth with 80-1000# SiC water sandpaper, and then ultrasonic cleaned in anhydrous ethanol and dried by cold air for standby;

[0054] (2) SiC powder (5%), Al2O3 powder (12%), liquid potassium silicate (80%) and deionized water (3%) are weighed according to the mass percentage, and the prepared slurry is ball-mixed uniformly;

[0055] (3) The slurry ball-mixed in step (2) is uniformly sprayed to each surface of the substrate alloy treated in step (1), the spraying gun pressure is 0.6Mpa, the distance between the sample and the nozzle is about 15cm, and each surface of the substrate is sprayed 4 times, each time for 1s;

[0056] (4) The slurry coating obtained in step (3) is dried at room temperature, 70℃, 120℃ and 260℃ in turn, and then sintered at 900℃ in air for 1h, to obtain a glass layer containing Al2O3 and SiC particles;

[0057] (5) The refined Mo powder and Si powder are weighed according to Mo:Si=3:1 (at %), 1% of the total mass of the powder is added as a binder, anhydrous ethanol is used as a solvent (50% of the total mass of the slurry), the nylon tank containing the mixed slurry is put into a planetary ball mill at a rotating speed of 400r / min for 4h, and a uniformly mixed slurry is obtained;

[0058] (6) use a brush to dip the slurry prepared in step (5) in a ball mill jar, then brush the slurry on the glass layer obtained in step (4), brush the slurry for two to three times, and then measure the thickness of the brushed slurry using a screw micrometer, the pre-prepared MoSi2 slurry is brushed to a thickness of 200 μm;

[0059] (7) vacuum dry the sample brushed in step (6) at 60 and 120 °C for 1 h respectively, and then vacuum sinter the sample at 1300 °C for 0.5 h to obtain a dense MoSi2 coating layer containing a diffusion barrier layer; namely, a method for preparing a Nb-Si based ultrahigh-temperature alloy surface oxidation-resistant composite coating.

[0060] Analysis shows that the obtained coating layer is composed of a glass layer containing Al2O3 and SiC particles and a MoSi2 layer, the porosity is 35%, and the interface is well bonded.

[0061] Example 2

[0062] A method for preparing a Nb-Si based ultrahigh-temperature alloy surface oxidation-resistant composite coating, as shown in Figure 1 , comprises the following steps:

[0063] (1) cut the Nb-Si based alloy into a block sample with a size of 7 mm x 7 mm x 5 mm using a wire saw, polish the six surfaces of each sample to be smooth using 80-1000# SiC water sandpaper, ultrasonically clean the sample in anhydrous ethanol, and then dry the sample with cold air for standby;

[0064] (2) weigh SiC powder (7%), Al2O3 powder (15%), liquid potassium silicate (75%), and deionized water (3%) according to the mass percentage, and mix the prepared slurry uniformly by ball milling;

[0065] (3) uniformly spray the slurry prepared in step (2) to each surface of the substrate alloy treated in step (1), the spraying gun pressure is 0.6 MPa, the distance between the sample and the nozzle is about 15 cm, and each surface of the substrate is sprayed 4 times, each time for 1 s;

[0066] (4) dry the slurry coating obtained in step (3) at room temperature, 70 °C, 120 °C, and 260 °C in turn, and then sinter the coating at 900 °C in air for 1 h to obtain a glass layer containing Al2O3 and SiC particles;

[0067] (5) weigh the refined Mo powder and Si powder according to Mo: Si = 3: 1 (at%), add 1% of the total mass of the powder as a binder, use anhydrous ethanol as a solvent (50% of the total mass of the slurry), put the nylon jar containing the mixed slurry into a planetary ball mill, and ball mill at a speed of 400 r / min for 4 h to obtain a uniformly mixed slurry;

[0068] (6) use a brush to dip the slurry prepared in step (5) in a ball mill jar, then brush the slurry on the glass layer obtained in step (4), brush the slurry for two to three times, and then measure the thickness of the brushed slurry using a screw micrometer, the brushing thickness of the MoSi2 slurry is 200 μm;

[0069] (7) vacuum dry the sample brushed in step (6) at 60 and 120 °C for 1 h respectively, and then vacuum sinter the sample at 1350 °C for 0.75 h to obtain a dense MoSi2 coating layer containing a diffusion barrier layer, which is a Nb-Si based ultrahigh-temperature alloy surface oxidation-resistant composite coating preparation method.

[0070] The cross-sectional BSE morphology of the obtained coating layer is shown in Figure 2 (b). It can be seen that the coating layer is composed of a glass layer containing Al2O3 and SiC particles and a MoSi2 layer, both layers are dense, the porosity is 1.8%, and the interface is well bonded. The coating layer without the diffusion barrier layer has a large number of pores, as shown in Figure 2 (a). The area porosity of the coating layer is reduced from 50.3% without the diffusion barrier layer to 3.4%. The oxidation experiment of the coating sample at 1250 °C in the atmospheric environment for 100 h shows that the surface oxide film is dense and complete, and there is no peeling phenomenon Figure 4 ), the weight gain per unit area is 2.11 mg / cm 2 , which is significantly lower than 6.63 mg / cm 2 of the coating layer without the diffusion barrier layer (as shown in Figure 3 ). The MoSi2 coating layer without the diffusion barrier layer is oxidized as a whole Figure 4 . As shown in Figure 5 , the glass phase diffusion barrier layer containing Al2O3 and SiC particles significantly inhibits the interdiffusion of elements at the interface, and the interdiffusion zone (IDZ) thickness is reduced from 62.66 μm without the diffusion barrier layer to 3.83 μm with the diffusion barrier layer, which is reduced by about 93.9%.

[0071] Example 3

[0072] A Nb-Si based ultrahigh-temperature alloy surface oxidation-resistant composite coating preparation method, as shown in Figure 1 , comprises the following steps:

[0073] (1) cut the Nb-Si based alloy into a block sample with a size of 7 mm x 7 mm x 5 mm using a wire saw, polish the six surfaces of each sample to be smooth using 80-1000# SiC water sandpaper, ultrasonic clean the sample in anhydrous ethanol, and then dry the sample with cold air for standby;

[0074] (2) weigh SiC powder (10%), Al2O3 powder (12%), liquid potassium silicate (75%), and deionized water (3%) according to the mass percentage, and mix the prepared slurry uniformly in a ball mill jar;

[0075] (3) The slurry prepared in step (2) is uniformly sprayed on each surface of the substrate alloy treated in step (1), the spraying gun pressure is 0.6 MPa, the distance between the sample and the nozzle is about 15 cm, and each surface of the substrate is sprayed 4 times, each time lasting 1 s;

[0076] (4) The slurry coating obtained in step (3) is dried at room temperature, 70°C, 120°C and 260°C in turn, and then sintered at 900°C in air for 1 h to obtain a glass layer containing Al2O3 and SiC particles;

[0077] (5) The refined Mo powder and Si powder are weighed according to Mo: Si = 3: 1 (at%), 1% of the total mass of the powder is added as a binder, anhydrous ethanol is used as a solvent (50% of the total mass of the slurry), the nylon tank containing the mixed slurry is put into a planetary ball mill to ball mill at a speed of 400 r / min for 4 h to obtain a uniformly mixed slurry;

[0078] (6) The slurry prepared in step (5) is dipped in the ball mill tank with a brush, and then the slurry is brushed on the glass layer obtained in step (4), the brushing thickness is measured using a screw micrometer after brushing two to three times, and the brushing thickness of the prepared MoSi2 slurry is 200 μm;

[0079] (7) The sample brushed in step (6) is vacuum dried at 60 and 120°C for 1 h respectively, and vacuum sintered at 1450°C for 0.5 h to obtain a dense MoSi2 coating containing a diffusion barrier layer; that is, the Nb-Si-based ultrahigh-temperature alloy surface oxidation-resistant composite coating preparation method.

[0080] Analysis shows that the obtained coating is composed of a glass layer containing Al2O3 and SiC particles and a MoSi2 layer, the porosity is 1%, and the interface is well combined. The coating sample is subjected to an oxidation experiment at 1250°C in an atmospheric environment for 100 h, and the results show that the surface oxide film is dense and complete without peeling.

[0081] The preferred embodiments and their effects are described. However, once the basic creative concept is known to those skilled in the art, additional changes and modifications can be made to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0082] Although the embodiments of the present application 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 present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. An anti-oxidation composite coating for the surface of an Nb-Si based ultra-high temperature alloy, characterized in that, The composite coating includes a diffusion barrier layer and a MoSi2 coating stacked together, wherein the diffusion barrier layer is located on the surface of the Nb-Si-based superalloy. The diffusion barrier layer is a glass layer containing Al2O3 and SiC particles; The mass ratio of Al2O3 to SiC particles is 1~15:1; The thickness of the diffusion barrier layer is 2~30 μm; The thickness of the MoSi2 coating is 50~200 μm; The Nb-Si based super-high temperature alloy surface anti-oxidation composite coating is prepared according to the following steps: Weigh out 2-10% SiC powder, 10-30% Al2O3 powder, 50-80% liquid potassium silicate and 2-10% deionized water by mass percentage, prepare the slurry, and then ball mill and mix them evenly. The ball-milled slurry was uniformly sprayed onto the surface of the Nb-Si-based ultra-high temperature alloy and then dried sequentially at room temperature, 70 ℃, 120 ℃, and 260 ℃. The resulting slurry coating was then sintered in air at 900 ℃ for 1-5 h to obtain a glass layer containing Al2O3 and SiC particles. After preparing a slurry from a certain amount of Mo powder and Si powder, the slurry is coated onto a glass layer. After drying, it is vacuum sintered at 1300~1600 ℃ for 0.5~2 h to obtain an anti-oxidation composite coating on the surface of Nb-Si based ultra-high temperature alloy. When a certain amount of Mo powder and Si powder are prepared into a slurry, the Mo powder and Si powder are weighed in an atomic ratio of 3:1, and 1% of PVB by mass of the total Mo powder and Si powder is added as a binder. Anhydrous ethanol is used as a solvent to prepare a uniformly mixed MoSi2 slurry.

2. A method for preparing an anti-oxidation composite coating on the surface of an Nb-Si based ultra-high temperature alloy as described in claim 1, characterized in that, Includes the following steps: Weigh out 2-10% SiC powder, 10-30% Al2O3 powder, 50-80% liquid potassium silicate and 2-10% deionized water by mass percentage, prepare the slurry, and then ball mill and mix them evenly. The ball-milled slurry was uniformly sprayed onto the surface of the Nb-Si-based ultra-high temperature alloy, and then dried sequentially at room temperature, 70 ℃, 120 ℃, and 260 ℃. The resulting slurry coating was then sintered in air at 900 ℃ for 1-5 h to obtain a glass layer containing Al2O3 and SiC particles. After preparing a slurry from a certain amount of Mo powder and Si powder, the slurry is coated onto a glass layer. After drying, it is vacuum sintered at 1300~1600 ℃ for 0.5~2 h to obtain an anti-oxidation composite coating on the surface of Nb-Si based ultra-high temperature alloy. When a certain amount of Mo powder and Si powder are prepared into a slurry, the Mo powder and Si powder are weighed in an atomic ratio of 3:1, and 1% of PVB by mass of the total Mo powder and Si powder is added as a binder. Anhydrous ethanol is used as a solvent to prepare a uniformly mixed MoSi2 slurry.

3. The method for preparing an anti-oxidation composite coating on the surface of an Nb-Si based ultra-high temperature alloy according to claim 2, characterized in that, During the spraying process, the air pressure of the spray gun is 0.6 MPa, the distance between the Nb-Si based ultra-high temperature alloy surface and the nozzle is about 15 cm, and multiple sprayings are performed, each lasting 1 second.

4. The method for preparing an anti-oxidation composite coating on the surface of an Nb-Si based ultra-high temperature alloy according to claim 2, characterized in that, When brushing the MoSi2 slurry onto the glass layer, brush it multiple times until the MoSi2 slurry thickness is 100~300 μm.

5. The application of the composite coating of claim 1 in the oxidation resistance of Nb-Si based superalloy surfaces.

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