A TiB2 modified Mo-Si-B composite coating and its preparation method and application

Abstract

The present invention discloses a TiB2-modified Mo-Si-B composite coating, its preparation method, and application, relating to the technical field of high-temperature alloy oxidation protection. The prepared composite coating comprises an inner layer, an intermediate layer, and an outer layer stacked in sequence; the inner layer is disposed on a substrate; and the titanium diboride (TiB2) in the outer layer can be uniformly distributed, regionally distributed, or gradiently distributed as needed. The present invention controls the coating structure and the distribution of modified elements by regulating the content, size, slurry composition, and coating method of the TiB2 introduced into the slurry, thereby obtaining a structurally matched composite coating.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature alloy oxidation protection, and in particular to a TiB2-modified Mo-Si-B composite coating, a preparation method thereof, and an application thereof. Background Art

[0002] Nb-Si-based ultrahigh-temperature alloys (UHSAs) have broad application prospects in hot-end components in the aerospace industry due to their high melting point, low density, and excellent high-temperature mechanical properties. However, UHSAs are susceptible to oxidation in oxidizing environments above 600°C, forming porous oxides such as Nb2O5 and TiNb2O7, which have no protective properties. This poor oxidation resistance severely limits their engineering applications in high-temperature applications. Silicide coatings prepared on UHSAs using surface coating technology can effectively inhibit oxidation at high temperatures and are a key approach to advancing the practical application of UHSAs. Among various silicide coating systems, Mo-Si-B coatings are considered one of the most promising antioxidant coatings for Nb-Si-based UHSAs due to their high melting point, excellent high-temperature stability, and excellent oxidation resistance.

[0003] Currently, the main technologies for preparing Mo-Si-B coatings include embedding, spark plasma sintering, thermal spraying, and magnetron sputtering. Compared to these methods, slurry sintering is a coating preparation technology suitable for large-scale industrial production. It has the advantages of low equipment requirements, simple operation, uniform coating composition, and controllable thickness. In addition, by adjusting the type and content of raw materials in the slurry, as well as the coating method, the desired coating structure can be flexibly controlled, which is crucial for the preparation of modified coatings, composite coatings, and gradient coatings.

[0004] In practical applications, conventional Mo-Si-B coatings prepared using slurry sintering technology still have limitations when working in high-temperature oxygen environments: on the one hand, pores are inevitably present in the prepared coating, through which oxygen rapidly diffuses inward, causing rapid internal oxidation of the coating, accelerating its degradation, and shortening its service life. On the other hand, during the long-term high-temperature oxidation process, matrix elements such as Nb and Ti continuously diffuse outward to the coating surface to form clustered oxides such as TiNb2O7. These oxides destroy the integrity of the oxide film and form defects such as cracks in the oxide film. Oxygen rapidly diffuses inward through these defects, causing the coating to gradually degrade and fail. Faced with increasingly stringent service requirements for long service life, thermal shock resistance, and dynamic high-temperature resistance, there is an urgent need to further improve the oxidation resistance of Mo-Si-B coatings prepared using slurry sintering technology. Summary of the Invention

[0005] In view of the deficiencies in the above-mentioned background technology, the present invention mainly solves the problems of easy oxidation of Nb-Si-based ultra-high temperature alloys at high temperatures, continuous mutual diffusion between the coating and the matrix elements during the high-temperature oxidation process, and thermal stress concentration leading to easy failure and peeling of the coating. The present invention provides a TiB2-modified Mo-Si-B composite coating and its preparation method and application. This method, by leveraging the advantages of slurry sintering technology, controls the coating structure and the distribution of modified elements by regulating the content, size, slurry composition, coating method, etc. of the TiB2 introduced into the slurry, thereby obtaining a structurally matched composite coating.

[0006] The first object of the present invention is to provide a TiB2-modified Mo-Si-B composite coating, wherein the composite coating comprises an inner layer, an intermediate layer, and an outer layer stacked in sequence; wherein the inner layer is disposed on a substrate;

[0007] The inner layer comprises (Ti, Nb)5Si4 and (Nb, X)5Si3, wherein X comprises Ti and / or Cr elements;

[0008] The intermediate layer includes (Nb, Ti) B2 and (Ti, Nb) 5 Si4;

[0009] The outer layer includes TiB2, and porous structures of MoSi2 and Mo5Si3;

[0010] The TiB2 in the outer layer is uniformly distributed, regionally distributed or has a gradient distribution;

[0011] The substrate includes a Nb-Si based ultrahigh temperature alloy.

[0012] Preferably, the thickness of the inner layer is 30 to 48 μm; the thickness of the middle layer is 5 to 12 μm; and the thickness of the outer layer is 90 to 130 μm.

[0013] Preferably, the composite coating can quickly form a dense and continuous TiO2 and SiO2 composite oxide film with good fluidity after oxidation at 1250°C to 1400°C, thereby extending its service life to more than 100 hours.

[0014] A second object of the present invention is to provide a method for preparing a TiB2-modified Mo-Si-B composite coating, comprising the following steps:

[0015] Mo powder, Si powder and B powder are mixed in a certain proportion, and then TiB2 powder is added and mixed evenly to obtain a mixture; the mixture is prepared into a slurry with a binder and an organic solvent;

[0016] After the slurry is coated on the surface of the substrate and dried, it is heated to 100-1250°C at a heating rate of 5-15°C / min in an atmosphere that is first vacuumed and then filled with argon, and kept warm for 15-45 minutes. It is then heated to 1400-1550°C at the same heating rate, kept warm for 30-75 minutes, and then cooled with the furnace to obtain the TiB2-modified Mo-Si-B composite coating.

[0017] Preferably, the particle size of the particles in the slurry is 3 to 5 μm; the binder is polyvinyl butyral; and the organic solvent is anhydrous ethanol.

[0018] Preferably, the TiB2 powder is a powder with a particle size of 1 to 2 μm or a whisker with a diameter of 500 nm.

[0019] Preferably, the slurry is coated on the surface of the substrate by different coating methods, and is brushed 3 to 5 times to make the total thickness of the coating layer on the surface of the substrate be 180 to 240 μm.

[0020] More preferably, the slurry coating method includes repeatedly brushing slurry of the same composition, alternately brushing slurries of different compositions, or brushing slurries of different compositions in sequence.

[0021] Preferably, the mass ratio of the Mo powder, Si powder and B powder is 40-65:60-35:1;

[0022] The amount of the TiB2 powder used accounts for 1 to 20 wt.% of the total mass of the raw materials.

[0023] The third object of the present invention is to provide an application of a TiB2 modified Mo-Si-B composite coating in the anti-oxidation protection of the surface of high-temperature structural materials.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] Compared with the embedding infiltration method, the spark plasma sintering method, and the magnetron sputtering method, the TiB2-modified Mo-Si-B composite coating provided by the present invention, as well as its preparation method and application, utilizes a slurry sintering method to prepare the coating. The coating thickness and microstructure are controllable, and the coating is applicable to parts of various shapes and sizes. The process flow is simple and suitable for large-scale industrial production. By regulating the content and size of the TiB2 powder introduced into the slurry, as well as the slurry coating method, the microstructure of the composite coating and the distribution of the modifying elements can be regulated, thereby obtaining a Mo-Si-B composite coating with continuously varying composition and structure, thereby improving its oxidation resistance and promoting the engineering application of Nb-Si-based ultrahigh-temperature alloys.

[0026] The present invention solves the problem that conventional Mo-Si-B coatings are prone to cracking and failure when used in high-temperature oxidizing environments by adding an appropriate amount of TiB2 to the components. The TiB2-modified Mo-Si-B composite coating for anti-oxidation protection of the surface of Nb-Si-based ultra-high temperature alloys prepared by the present invention has significantly improved antioxidant properties and further extended the service life of the coating. In a high-temperature oxidizing environment, TiB2 in the coating is oxidized to form TiO2 and B2O3. The formation of B2O3 reduces the viscosity of the oxide film. The viscous flow of the oxidation products promotes the rapid healing of defects such as cracks and holes in the coating, thereby prompting the rapid formation of a dense and continuous oxide film on the surface of the coating, inhibiting the internal diffusion of oxygen and the external diffusion of substrate elements. At the same time, the needle-shaped or rod-shaped TiO2 in the oxide film plays a role in "pinning" and inhibiting crack propagation, thereby improving the stability of the oxide film and reducing the oxidation rate. The synergistic effect of the two makes the oxide film dense and stable, thereby giving the coating good high-temperature antioxidant ability. The coating remains intact after continuous oxidation at 1250℃~1400℃ for 100h, and the minimum oxidation weight gain per unit area is only 3.9mg / cm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the cross-sectional BSE morphology of the Mo-Si-B composite coating modified with 3 wt.% TiB2 prepared in Example 1.

[0028] Figure 2 The unit area oxidation weight gain and macroscopic morphology of different types of Mo-Si-B composite coatings modified with TiB2 prepared in Examples 1 to 4 after oxidation at 1250°C for 100 hours.

[0029] Figure 3 This is the surface BSE morphology of the Mo-Si-B composite coating modified with 3 wt.% TiB2 prepared in Example 1 after oxidation at 1250°C for 100 h.

[0030] Figure 4 This is the cross-sectional BSE morphology of the Mo-Si-B composite coating with gradient distribution of TiB2 prepared by the slurry sintering method in Example 4, where (b) is an enlarged view of the red box area in (a).

[0031] Figure 5 This is the cross-sectional BSE morphology of the Mo-Si-B composite coating with regionally distributed TiB2 prepared by the slurry sintering method in Example 5, where (b) is an enlarged view of the red box area in (a).

[0032] Figure 6 This is the EDS element surface distribution result of the Mo-Si-B composite coating with regional distribution of TiB2 prepared by the slurry sintering method in Example 5. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0034] To provide oxidation protection for high-temperature alloys, the present invention introduces an appropriate amount of TiB2 into the Mo-Si-B coating, providing both a Ti source and a B source, allowing TiO2 and B2O3 to form simultaneously in a high-temperature oxidizing environment. The "pinning" effect of TiO2 can improve the stability of the oxide film, while the low viscosity of B2O3 at high temperatures can improve the fluidity of the oxide film. The synergistic effect of the two can promote the rapid healing of defects such as cracks and holes in the coating, prompting the rapid formation of a dense and continuous oxide film on the coating surface, thereby effectively inhibiting the internal diffusion of oxygen and the external diffusion of matrix elements. Furthermore, the content and size of the introduced TiB2, as well as the slurry composition and slurry coating method, have a significant impact on the microstructure, antioxidant properties, and service life of the coating. By fully leveraging the advantages of the slurry sintering method and flexibly regulating the content, size, and distribution of TiB2 in the coating, the structure of the coating can be controlled and optimized from a process perspective, resulting in a Mo-Si-B composite coating with designable structure and composition. Reasonable matching of the coating structure can reduce the thermal stress in the coating and inhibit the mutual diffusion between the coating and the matrix elements, thereby slowing down the degradation of the coating at high temperatures, significantly improving the oxidation resistance of the Mo-Si-B coating, extending its service life, and increasing its service temperature.

[0035] The present invention provides a TiB2 modified Mo-Si-B composite coating, the composite coating comprising an inner layer, an intermediate layer and an outer layer stacked in sequence; wherein the inner layer is placed on a substrate;

[0036] The inner layer comprises (Ti, Nb)5Si4 and (Nb, X)5Si3, wherein X comprises Ti and / or Cr elements;

[0037] The intermediate layer includes (Nb, Ti) B2 and (Ti, Nb) 5 Si4;

[0038] The outer layer includes TiB2, and porous structures of MoSi2 and Mo5Si3;

[0039] The TiB2 in the outer layer can be uniformly distributed, regionally distributed or content-gradiently distributed as needed; wherein the content-gradient distribution means that the TiB2 content in the outer layer is gradiently distributed on the molybdenum silicide matrix;

[0040] The substrate includes a Nb-Si based ultrahigh temperature alloy.

[0041] The composite coating formation process: Si diffusion plays a dominant role in the formation of the outer and inner layers of the Mo-Si-B composite coating. Si and Mo undergo a series of diffusion reactions to form the porous outer layers of MoSi2 and Mo5Si3. During this process, driven by the concentration gradient between the outer layer and the substrate, some Si continues to diffuse inward into the substrate, reacting to form an inner layer of (Ti,Nb)5Si4 + (Nb,X)5Si3. The formation of the intermediate layer is primarily due to the inward diffusion of B. B diffuses faster than Mo and Si and is virtually insoluble in MoSi2 and Mo5Si3. While Mo reacts with Si to form the outer layer, B rapidly diffuses into the substrate and reacts with Ti and Nb to form needle-shaped (Nb,Ti)B2. These precipitates are locally distributed on top of the (Ti,Nb)5Si4, forming an intermediate layer of (Nb,Ti)B2 + (Ti,Nb)5Si4 between the outer and inner layers. In the above diffusion reaction, the added TiB2 is uniformly distributed in the form of strips or rods, regionally distributed, or distributed in a gradient in the outer layer, and does not participate in the reaction.

[0042] The thickness of the inner layer is 30 to 48 μm; the thickness of the middle layer is 5 to 12 μm; and the thickness of the outer layer is 90 to 130 μm.

[0043] The composite coating can quickly form a dense and continuous TiO2 and SiO2 composite oxide film with good fluidity after being oxidized at 1250°C to 1400°C, thereby extending its service life to more than 100 hours.

[0044] The substrate includes a Nb-Si based ultrahigh temperature alloy.

[0045] The present invention provides a method for preparing a TiB2-modified Mo-Si-B composite coating, comprising the following steps:

[0046] Mo powder, Si powder and B powder are mixed in a certain proportion, and then TiB2 powder is added and mixed evenly to obtain a mixture; the mixture is prepared into a slurry with a binder and an organic solvent;

[0047] After the slurry is coated on the surface of the substrate and dried, it is heated to 100-1250°C at a heating rate of 5-15°C / min in an atmosphere that is first vacuumed and then filled with argon, and kept warm for 15-45 minutes. It is then heated to 1400-1550°C at the same heating rate, kept warm for 30-75 minutes, and then cooled with the furnace to obtain the TiB2-modified Mo-Si-B composite coating.

[0048] The particle size of the particles in the slurry is 3 to 5 μm; the binder is polyvinyl butyral; and the organic solvent is anhydrous ethanol.

[0049] The TiB2 powder is either powder with a particle size of 1 to 2 μm or whiskers with a diameter of 500 nm.

[0050] The slurry is coated on the surface of the substrate by using different coating methods and brushing for 3 to 5 times, so that the total thickness of the coating layer on the surface of the substrate is 180 to 240 μm.

[0051] The coating method includes repeatedly brushing on slurry of the same composition, alternately brushing on slurries of different compositions, or brushing on slurries of different compositions in sequence.

[0052] The mass ratio of the Mo powder, Si powder and B powder is 40-65:60-35:1;

[0053] The amount of the TiB2 powder used accounts for 1 to 20 wt.% of the total mass of the raw materials.

[0054] In the following embodiment, a method for preparing a TiB2-modified Mo-Si-B composite coating is described, and the specific steps are as follows:

[0055] Step 1: Use a wire-cut electric discharge machine to cut an 8 mm × 6 mm × 3.5 mm block from a Nb-Si-based ultrahigh-temperature alloy ingot. Polish the surface of the sample using 240# and 800# water-abrasive paper, and chamfer the sample using 800# water-abrasive paper. Then, place the sample in a beaker filled with anhydrous ethanol and ultrasonically clean it.

[0056] Step 2: After the polished and chamfered sample is pickled in the prepared acid solution for 1 to 5 minutes, it is taken out and repeatedly rinsed with plenty of water. Then, the sample is ultrasonically cleaned in anhydrous ethanol for 10 to 20 minutes and then placed in a drying oven for drying.

[0057] Step 3: Mo powder (purity>99.9%, average particle size 2-5 μm), Si powder (purity>99%, average particle size 200 mesh) and B powder (purity>99.9%, average particle size 200 mesh) are weighed and mixed according to a mass ratio of (40-65)Mo-(60-35)Si-1B;

[0058] Step 4: TiB2 of different sizes is weighed in an amount of 1 to 20 wt.% of the total mass of all raw materials and added to the powder weighed in step 3 to obtain a raw material mixture containing different TiB2 powder contents;

[0059] Step 5: using an omnidirectional planetary ball mill (ball-to-material ratio of 10:1 to 20:1, rotation speed of 300 to 500 r / min, ball milling time of 5 to 15 h) to respectively ball-mill the above raw material mixture to obtain a uniform raw material mixture;

[0060] Step 6: Using PVB as a binder and anhydrous ethanol as a solvent, weigh 0.5-2 wt.% of the binder, 40-60 wt.% of the solvent, and 35-60 wt.% of the raw material mixture in step 5, respectively. After mixing, ball mill again for 2-6 hours to obtain a uniform slurry containing different TiB2 powder contents;

[0061] Step 7: Using different coating methods, slurries containing different TiB2 powder contents are evenly brushed on the surface of the alloy substrate for 3 to 5 times, so that the total thickness of the coating layer on the substrate surface is 180 to 240 μm;

[0062] Step 8: Place the painted sample in a drying oven and dry it at 40-70°C for 1 hour, then continue heating it to 100-150°C and dry it for 1 hour;

[0063] Step 9: Place the dried sample into an alumina crucible and place it in an ultra-high temperature high vacuum heat treatment furnace. In an atmosphere that is first evacuated and then filled with argon, heat it to 1000-1250°C at a heating rate of 5-15°C / min, keep it warm for 15-45 minutes, then heat it to 1400-1550°C at the same heating rate, keep it warm for 30-75 minutes, and then cool it with the furnace.

[0064] In the above method, the TiB2 used in step 4 includes powder particles with an average particle size of 1 to 2 μm and whiskers with a diameter of 500 nm.

[0065] In the above method, the average particle size of the particles in the uniform slurry obtained in step 6 is 3 to 5 μm.

[0066] In the above method, the method of brushing the slurry 3 to 5 times in step 7 includes repeatedly brushing the slurry with the same composition, alternately brushing the slurries with different compositions, and brushing the slurries with different compositions in sequence.

[0067] The present invention provides an application of a TiB2 modified Mo-Si-B composite coating in the anti-oxidation protection of the surface of a high-temperature structural material.

[0068] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0069] The Nb-Si based superalloy used in the following examples is Nb-16Si-22Ti-5Cr-3Al (at%).

[0070] Example 1

[0071] In this embodiment, a TiB2-modified Mo-Si-B composite coating is provided by adding 3 wt.% TiB2 powder to the raw material mixture, which is specifically implemented by the following steps:

[0072] Step 1, substrate pretreatment: 8 mm × 6 mm × 3.5 mm blocks were cut from the Nb-Si based ultrahigh temperature alloy ingot using a wire electric discharge machine, and then polished, chamfered, pickled, ultrasonically cleaned, and dried for later use;

[0073] Step 2, ball milling: Mo powder, Si powder, B powder and TiB2 powder are weighed as raw materials according to the mass ratio of 52Mo-44Si-1B-3TiB2 and then placed in an omnidirectional planetary ball mill for ball milling. The ball-to-material ratio is 12:1, the rotation speed is 500 r / min, and the ball milling time is 6 h.

[0074] Step 3, preparing a slurry: using PVB as a binder and anhydrous ethanol as a solvent, weighing 1 wt.% of the binder, 50 wt.% of the solvent, and 49 wt.% of the raw material mixture in step 2, mixing and ball milling again for 4 hours to obtain a slurry containing 3 wt.% of TiB2 in the raw material mixture;

[0075] Step 4, slurry coating: the slurry prepared in step 3 is evenly brushed on the substrate, and the brushing is repeated 4 times to ensure that the total thickness of the coating layer is 180 μm; the coated sample is placed in a drying oven and dried at 50°C / 1h+100°C / 1h;

[0076] Step 5, high-temperature sintering: Place the dried sample into an alumina crucible and place it in an ultra-high temperature high vacuum heat treatment furnace. In an atmosphere that is first evacuated and then filled with argon, heat it to 1100°C at a heating rate of 8°C / min and keep it warm for 25 minutes; then heat it to 1450°C at the same heating rate and keep it warm for 45 minutes; cool it in the furnace and then take it out to obtain a Mo-Si-B composite coating containing 3wt.% TiB2.

[0077] The cross-sectional BSE morphology of the Mo-Si-B composite coating containing 3 wt.% TiB2 prepared in this example is as follows: Figure 1 As shown in the figure, the composite coating consists of a three-layer structure: the outermost layer is MoSi2+Mo5Si3+TiB2, the middle layer is (Nb,Ti)B2+(Ti,Nb)5Si4, and the inner layer is (Ti,Nb)5Si4+(Nb,X)5Si3.

[0078] In the outer layer of the Mo-Si-B composite coating containing 3 wt.% TiB2 prepared in this embodiment, TiB2 is uniformly distributed.

[0079] The Mo-Si-B composite coating containing 3 wt.% TiB2 prepared in this embodiment has an outer layer thickness of 113 μm, a middle layer thickness of 10 μm, and an inner layer thickness of 45 μm.

[0080] The Mo-Si-B composite coating containing 3 wt.% TiB2 prepared in this embodiment was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation experiment at 1250°C for 1 to 100 hours. Figure 2 As shown, the coating remains intact. Figure 3 The coating surface is covered by a dense and continuous SiO2 and TiO2 composite oxide film. The oxidation weight gain per unit area of the coating is 3.9 mg / cm 2 Compared with conventional Mo-Si-B coating, the oxidation weight gain per unit area is reduced by 12.6 mg / cm 2 , indicating that the oxidation resistance of the Mo-Si-B composite coating is significantly improved.

[0081] The Mo-Si-B composite coating containing 3 wt.% TiB2 prepared in this example was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation test at 1380°C for 1 to 10 hours. The coating remained intact. The oxidation weight gain per unit area of the coating was 5.9 mg / cm 2 .

[0082] Example 2

[0083] In this embodiment, a TiB2-modified Mo-Si-B composite coating is provided by adding 5 wt.% TiB2 powder to the raw material mixture, which is specifically implemented by the following steps:

[0084] Step 1, substrate pretreatment: 8 mm × 6 mm × 3.5 mm blocks were cut from the Nb-Si based ultrahigh temperature alloy ingot using a wire electric discharge machine, and then polished, chamfered, pickled, ultrasonically cleaned, and dried for later use;

[0085] Step 2, ball milling: Mo powder, Si powder, B powder and TiB2 powder are weighed as raw materials according to the mass ratio of 51Mo-43Si-1B-5TiB2 and then placed in an omnidirectional planetary ball mill for ball milling. The ball-to-material ratio is 15:1, the rotation speed is 400 r / min, and the ball milling time is 10 h.

[0086] Step 3, preparing a slurry: using PVB as a binder and anhydrous ethanol as a solvent, weighing 1.5 wt.% of the binder, 55 wt.% of the solvent, and 43.5 wt.% of the raw material mixture in step 2, mixing and ball milling again for 5 hours to obtain a slurry containing 5 wt.% TiB2 in the raw material mixture;

[0087] Step 4, slurry coating: the slurry prepared in step 3 is evenly brushed on the substrate, and the brushing is repeated 4 times to ensure that the total thickness of the coating layer is 200 μm; the coated sample is placed in a drying oven and dried at 60°C / 1h+120°C / 1h;

[0088] Step 5, high-temperature sintering: Place the dried sample into an alumina crucible and place it in an ultra-high temperature high vacuum heat treatment furnace. In an atmosphere that is first evacuated and then filled with argon, heat it to 1200°C at a heating rate of 10°C / min and keep it warm for 30 minutes; then heat it to 1500°C at the same heating rate and keep it warm for 60 minutes; cool it in the furnace and then take it out to obtain a Mo-Si-B composite coating containing 5wt.% TiB2.

[0089] The Mo-Si-B composite coating containing 5 wt.% TiB2 prepared in this embodiment consists of a three-layer structure, the outermost layer is MoSi2+Mo5Si3+TiB2, the middle layer is (Nb,Ti)B2+(Ti,Nb)5Si4, and the inner layer is (Ti,Nb)5Si4+(Nb,X)5Si3.

[0090] In the outer layer of the Mo-Si-B composite coating containing 5 wt.% TiB2 prepared in this embodiment, TiB2 is uniformly distributed.

[0091] The Mo-Si-B composite coating containing 5 wt.% TiB2 prepared in this embodiment has an outer layer thickness of 95 μm, a middle layer thickness of 6 μm, and an inner layer thickness of 35 μm.

[0092] The Mo-Si-B composite coating containing 5 wt.% TiB2 prepared in this example was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation test at 1250°C for 1 to 100 hours. The coating remained intact, and the coating surface was covered with a dense and continuous SiO2 and TiO2 composite oxide film. The oxidation weight gain per unit area of the coating was 5.1 mg / cm 2 Compared with conventional Mo-Si-B coating, the oxidation weight gain per unit area is reduced by 11.4 mg / cm 2 , indicating that the oxidation resistance of the Mo-Si-B composite coating is significantly improved.

[0093] The Mo-Si-B composite coating containing 5 wt.% TiB2 prepared in this example was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation test at 1380°C for 1 to 10 hours. The coating showed no obvious peeling. The oxidation weight gain per unit area of the coating was 14.7 mg / cm 2 .

[0094] Example 3

[0095] In this embodiment, a TiB2-modified Mo-Si-B composite coating is provided by adding 10 wt.% TiB2 powder to the raw material mixture, which is specifically implemented by the following steps:

[0096] Step 1, substrate pretreatment: 8 mm × 6 mm × 3.5 mm blocks were cut from the Nb-Si based ultrahigh temperature alloy ingot using a wire electric discharge machine, and then polished, chamfered, pickled, ultrasonically cleaned, and dried for later use;

[0097] Step 2, ball milling: Mo powder, Si powder, B powder and TiB2 powder are weighed as raw materials in a mass ratio of 49Mo-40Si-1B-10TiB2 and then placed in an omnidirectional planetary ball mill for ball milling. The ball-to-material ratio is 20:1, the rotation speed is 300 r / min, and the ball milling time is 12 h.

[0098] Step 3, preparing a slurry: using PVB as a binder and anhydrous ethanol as a solvent, weighing 2 wt.% of the binder, 55 wt.% of the solvent, and 43 wt.% of the raw material mixture in step 2, mixing and ball milling again for 6 hours to obtain a slurry containing 10 wt.% TiB2 in the raw material mixture;

[0099] Step 4, slurry coating: the slurry prepared in step 3 is evenly brushed on the substrate, and the brushing is repeated 3 times to ensure that the total thickness of the coating layer is 220 μm; the coated sample is placed in a drying oven and dried at 70°C / 1h+150°C / 1h;

[0100] Step 5, high-temperature sintering: Place the dried sample into an alumina crucible and place it in an ultra-high temperature high vacuum heat treatment furnace. In an atmosphere that is first evacuated and then filled with argon, heat it to 1250°C at a heating rate of 12°C / min and keep it warm for 40 minutes; then heat it to 1550°C at the same heating rate and keep it warm for 75 minutes; cool it in the furnace and then take it out to obtain a Mo-Si-B composite coating containing 10wt.% TiB2.

[0101] The Mo-Si-B composite coating containing 10 wt.% TiB2 prepared in this embodiment consists of a three-layer structure, the outermost layer is MoSi2+Mo5Si3+TiB2, the middle layer is (Nb,Ti)B2+(Ti,Nb)5Si4, and the inner layer is (Ti,Nb)5Si4+(Nb,X)5Si3.

[0102] In the outer layer of the Mo-Si-B composite coating containing 10 wt.% TiB2 prepared in this embodiment, TiB2 is uniformly distributed.

[0103] The Mo-Si-B composite coating containing 10 wt.% TiB2 prepared in this embodiment has an outer layer thickness of 110 μm, a middle layer thickness of 8 μm, and an inner layer thickness of 40 μm.

[0104] The Mo-Si-B composite coating containing 10 wt.% TiB2 prepared in this example was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation test at 1250°C for 1 to 100 hours. The coating remained intact, and the coating surface was covered with a dense and continuous SiO2 and TiO2 composite oxide film. The oxidation weight gain per unit area of the coating was 5.4 mg / cm 2 Compared with conventional Mo-Si-B coating, the oxidation weight gain per unit area is reduced by 11.1 mg / cm 2 , indicating that the oxidation resistance of the Mo-Si-B composite coating is significantly improved.

[0105] Example 4

[0106] In this embodiment, by sequentially coating three slurries of different compositions on the same substrate, the distribution of TiB2 in the Mo-Si-B composite coating is regulated so that the TiB2 content exhibits a gradient distribution. The specific steps are as follows:

[0107] Step 1, substrate pretreatment: 8 mm × 6 mm × 3.5 mm blocks were cut from the Nb-Si based ultrahigh temperature alloy ingot using a wire electric discharge machine, and then polished, chamfered, pickled, ultrasonically cleaned, and dried for later use;

[0108] Step 2, ball milling and mixing: Mo powder, Si powder, B powder and TiB2 powder are used as raw materials, and are weighed according to the mass ratio of 53Mo-45Si-1B-1TiB2, 52Mo-44Si-1B-3TiB2 and 49Mo-40Si-1B-10TiB2, respectively, and then placed in an omnidirectional planetary ball mill for ball milling and mixing, wherein the ball-to-material ratio is 12:1, the rotation speed is 500 r / min, and the ball milling time is 12 h;

[0109] Step 3, preparing a slurry: using PVB as a binder and anhydrous ethanol as a solvent, weighing 1 wt.% of the binder, 55 wt.% of the solvent, and 44 wt.% of the three raw material mixtures in step 2, respectively, mixing and ball milling again for 4 hours to obtain three slurries containing 1 wt.%, 3 wt.%, and 10 wt.% of TiB2 in the raw material mixture;

[0110] Step 4, slurry coating: first, the slurry containing 1wt.% TiB2 in the raw material mixture prepared in step 3 is evenly brushed on the substrate to ensure that the thickness of the coating layer is 90μm; after the coated slurry is naturally dried, the slurry containing 3wt.% TiB2 in the raw material mixture is continuously brushed on the 90μm thick coating layer to increase the thickness of the coating layer to 180μm; after the coated slurry is naturally dried, the slurry containing 10wt.% TiB2 in the raw material mixture is continuously brushed on the 180μm thick coating layer to finally make the total thickness of the coating layer 240μm; the coated sample is placed in a drying oven for drying at 60℃ / 1h+120℃ / 1h;

[0111] Step 5, high-temperature sintering: Place the dried sample into an alumina crucible and place it in an ultra-high temperature high vacuum heat treatment furnace. In an atmosphere that is first evacuated and then filled with argon, heat it to 1200°C at a heating rate of 10°C / min and keep it warm for 40 minutes; then heat it to 1500°C at the same heating rate and keep it warm for 70 minutes; cool it in the furnace and then take it out to obtain a Mo-Si-B composite coating with a gradient distribution of TiB2 content in the outer layer of the coating.

[0112] The cross-sectional BSE morphology of the TiB2 modified Mo-Si-B composite coating prepared in this embodiment is as follows: Figure 4 As shown in the figure, the composite coating consists of a three-layer structure: the outermost layer is MoSi2+Mo5Si3+TiB2, the middle layer is (Nb,Ti)B2+(Ti,Nb)5Si4, and the inner layer is (Ti,Nb)5Si4+(Nb,X)5Si3.

[0113] In the outer layer of the TiB2-modified Mo-Si-B composite coating prepared in this embodiment, the content of TiB2 gradually decreases from the outside to the inside, showing a gradient distribution.

[0114] The TiB2 modified Mo-Si-B composite coating prepared in this embodiment has an outer layer thickness of 108 μm, a middle layer thickness of 8 μm, and an inner layer thickness of 48 μm.

[0115] The TiB2-modified Mo-Si-B composite coating prepared in this example was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation test at 1250°C for 1 to 100 hours. The coating remained intact, and the coating surface was covered with a dense and continuous SiO2 and TiO2 composite oxide film. The oxidation weight gain per unit area of the coating was 4.6 mg / cm 2 Compared with conventional Mo-Si-B coating, the oxidation weight gain per unit area is reduced by 11.9 mg / cm 2In a high-temperature oxidizing environment, the gradient distribution of TiB2 content in the outer layer not only promotes the rapid formation of a dense and continuous oxide film on the coating surface, effectively inhibiting the internal diffusion of oxygen, but also helps to alleviate thermal stress concentration and inhibit the initiation and expansion of cracks in the coating, thereby giving the composite coating better oxidation resistance and a longer service life.

[0116] Example 5

[0117] In this embodiment, by alternately coating two slurries of different compositions on the same substrate, the distribution of TiB2 in the Mo-Si-B composite coating is regulated to achieve a regional distribution characteristic, which is specifically implemented by the following steps:

[0118] Step 1, substrate pretreatment: 8 mm × 6 mm × 3.5 mm blocks were cut from the Nb-Si based ultrahigh temperature alloy ingot using a wire electric discharge machine, and then polished, chamfered, pickled, ultrasonically cleaned, and dried for later use;

[0119] Step 2, ball milling: Mo powder, Si powder, B powder and TiB2 powder are weighed as raw materials according to the mass ratio of 54Mo-45Si-1B and 51Mo-43Si-1B-5TiB2, respectively, and then placed in an omnidirectional planetary ball mill for ball milling. The ball-to-material ratio is 10:1, the rotation speed is 400 r / min, and the ball milling time is 8 h.

[0120] Step 3, preparing a slurry: using PVB as a binder and anhydrous ethanol as a solvent, weighing 0.5 wt.% of the binder, 45 wt.% of the solvent, and 54.5 wt.% of the raw material mixture in step 2, respectively, mixing and ball milling again for 2 hours to obtain two slurries, one containing no TiB2 in the raw material mixture and the other containing 5 wt.% TiB2;

[0121] Step 4, slurry coating: first, the slurry without TiB2 in the raw material mixture prepared in step 3 is evenly brushed on the substrate to ensure that the thickness of the coating layer is 75 μm; after the coated slurry is naturally dried, the slurry containing 5 wt.% TiB2 in the raw material mixture is continuously brushed on the 75 μm thick coating layer to increase the thickness of the coating layer to 135 μm; after the coated slurry is naturally dried, the slurry without TiB2 in the raw material mixture is continuously brushed on the 135 μm thick coating layer to finally make the total thickness of the coating layer 210 μm; the coated sample is placed in a drying oven for drying at 40°C / 1h+100°C / 1h;

[0122] Step 5, high-temperature sintering: Place the dried sample into an alumina crucible and place it in an ultra-high temperature high vacuum heat treatment furnace. In an atmosphere that is first evacuated and then filled with argon, heat it to 1000°C at a heating rate of 5°C / min and keep it warm for 20 minutes; then heat it to 1400°C at the same heating rate and keep it warm for 30 minutes; cool it in the furnace and then take it out to obtain a Mo-Si-B composite coating with TiB2 distributed in the middle area of the outer layer of the coating.

[0123] The cross-sectional BSE morphology of the TiB2 modified Mo-Si-B composite coating prepared in this embodiment is as follows: Figure 5 As shown in the figure, the composite coating consists of a three-layer structure: the outermost layer is MoSi2+Mo5Si3+TiB2, the middle layer is (Nb,Ti)B2+(Ti,Nb)5Si4, and the inner layer is (Ti,Nb)5Si4+(Nb,X)5Si3.

[0124] The element surface distribution results of the TiB2 modified Mo-Si-B composite coating prepared in this embodiment are as follows: Figure 6 As shown in Figure 2, Mo and Si elements are evenly distributed in the entire outer coating, while Ti element is mainly distributed in the middle part of the outer layer, which indicates that TiB2 is only evenly distributed in the middle part of the outer layer, showing a regional distribution feature.

[0125] The TiB2 modified Mo-Si-B composite coating prepared in this embodiment has an outer layer thickness of 124 μm, a middle layer thickness of 5 μm, and an inner layer thickness of 37 μm.

[0126] The Mo-Si-B composite coating with regionally distributed TiB2 prepared in this example was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation test at 1250°C for 1 to 100 hours. The coating remained intact, with its surface covered by a dense, continuous oxide film. The TiB2 located in the middle region of the coating's outer layer not only promotes the rapid healing of defects within the coating but also slows the volatilization of B2O3 from the coating surface, thereby extending the coating's service life.

[0127] Example 6

[0128] In this embodiment, the type and size of TiB2 powder in the Mo-Si-B composite coating are changed by adding 3 wt.% TiB2 whiskers to the raw material mixture. The specific implementation is as follows:

[0129] Step 1, substrate pretreatment: 8 mm × 6 mm × 3.5 mm blocks were cut from the Nb-Si based ultrahigh temperature alloy ingot using a wire electric discharge machine, and then polished, chamfered, pickled, ultrasonically cleaned, and dried for later use;

[0130] Step 2, ball milling: Mo powder, Si powder, B powder and TiB2 whiskers are weighed according to a mass ratio of 52Mo-44Si-1B-3TiB2 and then placed in an omnidirectional planetary ball mill for ball milling. The ball-to-material ratio is 12:1, the rotation speed is 400 r / min, and the ball milling time is 10 h.

[0131] Step 3, preparing a slurry: using PVB as a binder and anhydrous ethanol as a solvent, weighing 1 wt.% of the binder, 50 wt.% of the solvent, and 49 wt.% of the raw material mixture in step 2, mixing and ball milling again for 4 hours to obtain a slurry containing 3 wt.% of TiB2 whiskers in the raw material mixture;

[0132] Step 4, slurry coating: the slurry prepared in step 3 is evenly brushed on the substrate, and the brushing is repeated 4 times to ensure that the total thickness of the coating layer is 215 μm; the coated sample is placed in a drying oven for 60°C / 1h + 100-120°C / 1h drying;

[0133] Step 5, high-temperature sintering: Place the dried sample into an alumina crucible and place it in an ultra-high temperature high vacuum heat treatment furnace. In an atmosphere that is first evacuated and then filled with argon, heat it to 1200°C at a heating rate of 8°C / min and keep it warm for 30 minutes; then heat it to 1450°C at the same heating rate and keep it warm for 45 minutes; cool it in the furnace and then take it out to obtain a Mo-Si-B composite coating containing 3wt.% TiB2 whiskers.

[0134] The Mo-Si-B composite coating containing 3 wt.% TiB2 whiskers prepared in this embodiment consists of a three-layer structure, the outermost layer is MoSi2+Mo5Si3+TiB2, the middle layer is (Nb,Ti)B2+(Ti,Nb)5Si4, and the inner layer is (Ti,Nb)5Si4+(Nb,X)5Si3.

[0135] In the outer layer of the Mo-Si-B composite coating containing 3 wt.% TiB2 whiskers prepared in this embodiment, the TiB2 whiskers are evenly distributed.

[0136] The Mo-Si-B composite coating containing 3 wt.% TiB2 whiskers prepared in this embodiment has an outer layer thickness of 105 μm, a middle layer thickness of 7 μm, and an inner layer thickness of 39 μm.

[0137] The Mo-Si-B composite coating prepared in this example was placed in a high-temperature oxidation furnace and subjected to a constant-temperature oxidation test at 1250°C for 1 to 100 hours. The coating remained intact, and the surface was covered with a dense, continuous composite oxide film. The TiB2 whiskers toughened the coating by pulling out, bridging, and deflecting the TiB2 whiskers, inhibiting crack formation and propagation. This resulted in better oxidation resistance and a longer service life for the Mo-Si-B composite coating.

[0138] The present invention describes preferred embodiments and their effects. However, those skilled in the art, once informed of the basic inventive concept, may make additional changes and modifications to these embodiments. Therefore, it is intended that the appended claims be interpreted to include the preferred embodiments as well as all changes and modifications that fall within the scope of the invention.

[0139] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A TiB2 modified Mo-Si-B composite coating, characterized in that: The composite coating comprises an inner layer, an intermediate layer and an outer layer stacked in sequence; wherein the inner layer is placed on the substrate; The inner layer comprises (Ti, Nb)5Si4 and (Nb, X)5Si3, wherein X comprises Ti and / or Cr elements; The intermediate layer includes (Nb, Ti) B2 and (Ti, Nb) 5 Si4; The outer layer includes TiB2, and porous structures of MoSi2 and Mo5Si3; The TiB2 in the outer layer is uniformly distributed, regionally distributed or has a gradient distribution; The substrate includes a Nb-Si based ultrahigh temperature alloy.

2. The TiB2 modified Mo-Si-B composite coating according to claim 1, characterized in that: The thickness of the inner layer is 30-48 μm; the thickness of the middle layer is 5-12 μm; and the thickness of the outer layer is 90-130 μm.

3. The TiB2 modified Mo-Si-B composite coating according to claim 1, characterized in that: The composite coating can quickly form a dense and continuous TiO2 and SiO2 composite oxide film with good fluidity after oxidation at 1250°C to 1400°C, thereby extending its service life to more than 100 hours.

4. A method for preparing a TiB2-modified Mo-Si-B composite coating according to any one of claims 1 to 3, characterized in that: The following steps are involved: Mo powder, Si powder and B powder are mixed in a certain proportion, and then TiB2 powder is added and mixed evenly to obtain a mixture; the mixture is prepared into a slurry with a binder and an organic solvent; After the slurry is coated on the surface of the substrate and dried, it is heated to 1000-1250°C at a heating rate of 5-15°C / min in an atmosphere that is first evacuated and then filled with argon, and kept warm for 15-45 minutes. It is then heated to 1400-1550°C at the same heating rate, and kept warm for 30-75 minutes. It is then cooled in the furnace to obtain the TiB2-modified Mo-Si-B composite coating. The slurry was applied to the substrate surface using different coating methods, brushing 3 to 5 times to make the total thickness of the coating layer on the substrate surface 180 to 240 μm. The coating method includes repeatedly brushing slurry of the same composition, alternately brushing slurries of different compositions, or sequentially brushing slurries of different compositions.

5. The method for preparing the TiB2 modified Mo-Si-B composite coating according to claim 4, characterized in that: The particle size of the particles in the slurry is 3-5 μm; the binder is polyvinyl butyral; and the organic solvent is anhydrous ethanol.

6. The method for preparing the TiB2 modified Mo-Si-B composite coating according to claim 4, characterized in that: The particle size of the TiB2 powder is 1-2 μm or is a whisker with a diameter of 500 nm.

7. The method for preparing the TiB2 modified Mo-Si-B composite coating according to claim 4, characterized in that: The mass ratio of the Mo powder, Si powder and B powder is 40-65:60-35:1; The amount of the TiB2 powder used accounts for 1-20 wt.% of the total mass of the raw materials.

8. Use of the titanium diboride modified Mo-Si-B composite coating according to any one of claims 1 to 3 in anti-oxidation protection of high-temperature alloy surfaces.

Images