A method for surface modification of a titanium-aluminum alloy and its application

Abstract

The present invention discloses a method for surface modification of titanium aluminide alloy and its application, specifically relating to the field of coating materials. The present invention modifies the surface of the titanium aluminide alloy by introducing an SiO 2 coating, and a flux is added to the SiO 2 coating to reduce the softening point of the coating. Specifically, the flux forms a compound with a lower melting point with a part of the SiO 2 in the SiO 2 coating. In this compound, the original densification grid structure of the SiO 2 is damaged. Therefore, the compound can form a liquid phase at the service temperature of the titanium aluminide alloy below the melting point of SiO 2 , while the other part of the SiO 2 in the coating retains the densification grid structure and remains in the solid phase. Therefore, overall, the SiO 2 coating can be softened at a temperature below the melting point of SiO 2 , and the softening point of the SiO 2 coating is reduced. The compound forming the liquid phase can flow and fill the cracks and pores generated during the preparation of the coating, improving the density of the SiO 2 coating, and can prevent the diffusion of oxygen to the titanium aluminide alloy matrix at high temperatures, improving the high-temperature oxidation resistance of the matrix.

Description

Technical Field

[0001] The invention relates to the field of coating materials, and more specifically to a method for modifying the surface of a titanium-aluminum alloy and an application thereof. Background Art

[0002] Since the mid-twentieth century, the aviation industry has developed rapidly. Nickel-based alloys are widely used in the manufacture of aircraft engines, gas turbines, and high-temperature corrosion-resistant parts due to their good oxidation resistance, corrosion resistance, high-temperature strength, organizational stability, and fatigue performance. However, with the iteration of the aviation industry, people's requirements for aircraft thrust-to-weight ratios have gradually increased. Titanium-based alloys have the characteristics of low density, high specific strength, good corrosion resistance, low thermal conductivity, and strong surface decorativeness. They are widely used in aerospace, chemical, automotive, construction and other fields. Among them, Ti-Al intermetallic compounds have become popular high-temperature structural materials due to their excellent high-temperature performance and good environmental stability, and are expected to replace traditional Ni-based alloys. However, when the operating temperature exceeds 800°C, the high-temperature oxidation resistance of TiAl alloys deteriorates rapidly, greatly limiting the scope of use of TiAl alloys. This is mainly because a layer of TiO on the surface of the TiAl alloy is formed in a high-temperature environment. 2 , the middle part is Al 2 O 3 , the interior is TiO 2 and Al 2 O 3 Loose mixed oxide film.

[0003] In order to improve the high temperature oxidation resistance of titanium aluminum alloy, surface modification technology of applying protective coating on the surface of titanium aluminum alloy is a common method. By introducing protective coating on the surface of titanium aluminum alloy, its high temperature oxidation resistance can be improved without changing the performance of titanium aluminum alloy itself. Currently, common covering coatings include metal coatings, ceramic coatings and composite coatings formed by combining several coatings. Among them, SiO 2 Coatings are often used to provide oxidation protection for alloy materials due to their dense meshed silicon-oxygen tetrahedral structure and good high-temperature chemical stability. However, pure SiO prepared by traditional methods such as spraying, dipping, and spin coating 2 Coatings often produce cracks and pores during the preparation process. 2 The melting point (>1500℃) is much higher than the service temperature of 900℃. 2 The coating is difficult to soften and the defects therein are difficult to heal, which further leads to the inability to control the density of the coating and poor bonding with the substrate, limiting the protective performance of the coating.

[0004] The prior art discloses a carbon fiber surface densification sintered TiO 2A method for coating, using titanate as the titanium source and a low-melting-point salt as a sintering aid (flux). First, a precursor solution containing the sintering aid and the titanium source is prepared through hydrolysis. Then, carbon fibers are impregnated in the precursor solution, dried, and sintered to obtain a densified TiO coating on the surface of the carbon fibers. 2 Although the preparation of a dense coating is achieved by the action of the flux, the TiO coatings disclosed in the prior art are of rutile structure or anatase structure, which are not as dense as the grid structure of the SiO coatings. It is difficult to contain the diffusion of oxygen at high temperatures, and there are many anion vacancies in the TiO structure, with a relatively high oxygen solubility. This makes TiO not suitable as an oxidation-resistant coating for high-temperature metal structural materials and difficult to improve the high-temperature oxidation resistance of titanium-aluminum alloy materials. 2 2 2 2 Summary of the Invention

[0005] To solve the problem of the too-high softening temperature of the SiO coating used for surface modification of titanium-aluminum alloy in the prior art, the present invention provides a method for surface modification of titanium-aluminum alloy. SiO particles are added to a flux solution to prepare a suspension, which is then coated on the surface of the substrate, dried, and heat-treated to obtain a SiO coating on the surface of the substrate. The low-melting-point compound formed by the flux and SiO enables the prepared SiO coating to have a lower softening point, and it can fill the cracks and pores inside itself when serving in a high-temperature environment below the melting point of SiO, improving the high-temperature oxidation resistance of the titanium-aluminum alloy substrate. 2 2 2 2 2 2

[0006] Another object of the present invention is to provide an application of the above method for surface modification of titanium-aluminum alloy in the preparation of titanium-aluminum alloy.

[0007] The above objects of the present invention are achieved through the following technical solutions:

[0008] A method for surface modification of titanium-aluminum alloy specifically includes the following steps:

[0009] S1. Remove the oxide scale on the surface of the titanium-aluminum alloy substrate, wash, and dry.

[0010] S2. Dissolve the flux in water or absolute ethanol to obtain a flux solution with a molar concentration of 0.01 - 1 mol·L -1 , add SiO particles to the flux solution to form a suspension, and the mass concentration of SiO particles in the suspension is 0.1 - 10 g·L 2 2 -1 ;​​​​​​​​​​​​

[0011] S3. Coat the suspension on the substrate surface and dry it to obtain an initial coating on the substrate surface;

[0012] S4. Heat-treat the sample in a gas environment at 700-1000 °C for 1-5 h, and then air-cool to obtain a SiO 2 coating on the substrate surface;

[0013] The flux in step S2 is selected from any one or more of Li, Na, K, and Ca salts.

[0014] SiO 2 The SiO coating has a dense structure and good high-temperature chemical stability. It can be used as a shielding layer to effectively prevent the diffusion of external oxygen to the titanium aluminide alloy substrate and the diffusion of metal ions in the substrate to the external environment, providing good high-temperature oxidation resistance for the titanium aluminide alloy substrate. However, the melting point of the pure SiO 2 coating is too high, and the cracks and pores generated during the preparation process are difficult to be repaired during the high-temperature oxidation process, providing a channel for the contact between oxygen and the substrate, resulting in coating deterioration and reduced lifespan. The introduction of the flux can destroy the grid structure of the SiO 2 coating to form a compound with a lower melting point. The compound turns into a liquid phase under the high-temperature environment where the titanium aluminide alloy is in service. The SiO 2 coating softens accordingly, and the original cracks and pores in the coating are filled with the compound formed into a liquid phase. At the same time, part of the SiO 2 components still retain a complete grid structure, so that at the temperature at which the titanium aluminide alloy is in service, this SiO 2 coating can retain a certain hardness, and the reaction between the compound formed into a liquid phase and the substrate can enhance the bonding force at the coating-substrate interface, ultimately significantly improving the high-temperature oxidation resistance of the alloy substrate.

[0015] The flux introduced into the SiO 2 coating is selected from any one or more of Li, Na, K, and Ca salts. The principle that the flux can form a compound with a lower melting point with SiO 2 is that elements such as Li and Na in it can enter the dense structure of the SiO 2 coating and occupy the vacancies outside the silicon-oxygen tetrahedrons. In the SiO 2 coating, after part of the SiO 2 forms a compound with a lower melting point with the flux, the dense grid structure of this part of the SiO 2 will be destroyed under the high-temperature environment at which the alloy is in service and lower than the melting point of SiO 2 , which is why this part of the SiO 2 forming a compound with the flux will liquefy at high temperature; but when the temperature decreases, this part of the SiO2 The meshed structure can be reconstructed, and the SiO 2 coating is re-cured. Meanwhile, after cooling, after the SiO 2 coating forms a continuous and dense whole, components containing elements such as Al, Zr, and Si can be continuously added to the coating to re-connect the meshed structure and reduce the oxygen diffusion rate at high temperatures.

[0016] The molar concentration of the flux solution in step S2 is 0.01 - 1 mol·L -1 , and the mass concentration of SiO 2 particles in the suspension is 0.1 - 10 g·L -1 . When the concentrations of the flux solution and SiO 2 particles are within the above ranges, the flux can form a sufficient amount of compounds with lower melting points with SiO 2 to fill the original cracks and pores in the SiO 2 coating in the high-temperature environment where the titanium aluminide matrix serves. This is because, if the molar concentration of the flux in the suspension is higher, the mass concentration of SiO 2 particles is too low, and the SiO 2 coating provided by the present invention exhibits the properties of low-melting-point compounds, with reduced density and enhanced fluidity at high temperatures, and is prone to slipping from the surface. When there is too little flux in the suspension, the SiO 2 concentration is too high, and the coating exhibits the properties of pure SiO 2 , with an increase in pores and cracks at high temperatures and insufficient high-temperature oxidation resistance.

[0017] The conditions for heat treatment in step S4 are to heat-treat the specimen in a gas environment at 700 - 1000 °C for 1 - 5 h. The heat treatment temperature is an important factor determining whether the densification process of the coating can occur. Although the flux has a low melting point, 700 °C is the lowest temperature at which the compound formed by it and SiO 2 can liquefy and flow. Once the heat treatment temperature is lower than 700 °C, although a small amount of liquid-phase compounds may still form in the SiO 2 coating, its densification process is very long, and some pores and cracks are difficult to disappear. When the temperature is higher than 1000 °C, it may cause a violent reaction at the coating-matrix interface, affecting the interface stability.

[0018] It should be noted that the surface modification method for titanium aluminide provided by the present invention is applied to titanium aluminide. Specifically, the titanium aluminide is selected from one of Ti 3 -Al, Ti-Al, Ti-Al 3 , Ti-6Al-4V, TiAlNb, Ti-47Al-2Cr-2Nb.

[0019] In addition, when preparing the SiO 2 coating in the present invention, the flux reacts directly with the prepared SiO 2 particles rather than their precursors. The SiO 2 particle content and the flux content in the SiO 2 coating can both be precisely controlled, the method has strong reliability, and the success rate of coating preparation is high.

[0020] In a specific embodiment of the present invention, the specific operation of removing the oxide scale on the surface of the titanium-aluminum alloy in step S1 is to polish the titanium-aluminum alloy substrate with sandpaper.

[0021] Preferably, the concentration of the flux solution in step S2 is 0.05 - 0.5 mol·L -1 . For example, it can be 0.1 mol·L -1 in Example 1, 0.5 mol·L -1 in Example 6, 0.01 mol·L -1 in Example 7, or 0.05 mol·L -1 in Example 8.

[0022] More preferably, the concentration of the flux solution in step S2 is 0.1 mol·L -1 .

[0023] The content of the flux in the flux solution determines the content of elements such as Li, Na, K, and Ca in the coating, and thus determines the fluidity and viscosity of the liquid-phase compound in the coating, that is, the bonding force to the substrate. When the concentration of the flux solution in step S2 is lower than 0.05 mol·L -1 , the finally obtained SiO 2 coating has too low fluidity at the service temperature of the titanium-aluminum alloy, and it is difficult to densify through the softening of the coating and the flow of the liquid phase; while when the concentration of the flux solution is higher than 0.5 mol·L -1 , the fluidity of the coating at the service temperature of the titanium-aluminum alloy is too high, which easily causes the coating to directly slide off the titanium-aluminum alloy substrate during service. When the concentration of the flux solution is 0.1 mol·L -1 , the fluidity and viscosity of the SiO 2 coating at the service temperature of the titanium-aluminum alloy can achieve the best balance.

[0024] Preferably, the mass concentration of SiO 2 particles in the suspension in step S2 is 0.5 - 2.0 g·L -1 . For example, it can be 1.0 g·L -1 in Example 1, 10 g·L -1 in Example 2, 0.5 g·L -1, or it can also be 2.0 g·L in Example 4 -1 .

[0025] More preferably, in step S2, the mass concentration of SiO 2 particles in the suspension is 1.0 g·L -1 .

[0026] If the mass concentration of SiO 2 particles in the suspension obtained in step S2 is too low, the SiO 2 coating provided by the present invention is likely to exhibit the properties of a low-melting compound, that is, it is easily liquefied at high temperatures, the coating density decreases, the fluidity increases, and thus it is likely to slide off the substrate surface. When the concentration of SiO 2 particles in the suspension is too high, the coating is likely to exhibit the properties of a pure SiO 2 coating, that is, the pores and cracks in the coating increase at high temperatures, and the high-temperature oxidation resistance is insufficient. When the mass concentration of SiO 2 particles in the suspension is 1.0 g·L -1 , the SiO 2 coating prepared by the present invention better balances the contradiction between density and fluidity and has the best high-temperature oxidation resistance.

[0027] Preferably, the preparation method of SiO 2 particles in step S2 specifically includes the following steps:

[0028] Mix ammonia water: water: absolute ethanol: siloxane reagent in a volume ratio of (1-4):(10-20):(20-40):(1-10), stir and react at 20-30 °C for 0.5-5 h; centrifuge the reaction liquid obtained, take the precipitate, add absolute ethanol to redissolve; centrifuge again, take the precipitate, and the obtained precipitate is pure SiO 2 particles.

[0029] SiO 2 There are various methods for preparing SiO 2 particles, and the above method is the sol-gel method. The sol-gel method can prepare a coating with molecular-scale uniformity in a very short time, and the reaction can be carried out at a relatively low reaction temperature. The SiO 2 particles prepared by the sol-gel method have a smaller and controllable particle size and a higher surface energy, and can be transformed into a continuous and dense SiO

[0030] More preferably, in the preparation of SiO 2 particles, ammonia water: water: absolute ethanol: siloxane reagent are mixed in a volume ratio of 4:18:32:5, the reaction temperature is 30 °C, and the reaction time is 1 h.

[0031] SiO prepared at this volume ratio of the reactants 2 particles, with a smaller particle size (less than 1 μm), are suitable as raw materials for preparing coatings.

[0032] Preferably, the flux in step S2 is LiNO 3 , NaNO 3 , KNO 3 , Ca(NO 3 ) 2 any one or more of them.

[0033] More preferably, the flux in step S2 is any one of KNO 3 , Ca(NO 3 ) 2 .

[0034] Most preferably, the flux in step S2 is KNO 3 .

[0035] The low-melting compounds formed by different fluxes and SiO 2 particles are different, and their properties are also different. Preferably, salts of Li, Na, K, Ca such as KNO 3 , Ca(NO 3 ) 2 are used as fluxes because the compounds formed by them and SiO 2 particles have a melting point near the service temperature of the titanium-aluminum alloy, and SiO 2 coatings can be prepared by simple condition adjustment, and the heat treatment temperature is lower, the energy consumption is less, and the densification process is easier to carry out. Among them, the compound formed by KNO 3 and SiO 2 particles can achieve coating densification at a melting point of 700 °C below the service temperature of the titanium-aluminum alloy.

[0036] By selecting different types and contents of fluxes, the softening point of the SiO 2 coating can also be regulated, and then the density of the coating can be regulated, and finally a SiO 2 coating with a balance of softening point - density is obtained.

[0037] It should be noted that in step S3, the coating method is selected from any one of the four traditional methods of drop coating, spraying, dip coating, and spin coating.

[0038] Preferably, the specific coating method in step S3 is drop coating or spraying.

[0039] More preferably, the specific coating method in step S3 is drop coating.

[0040] The preparation methods such as spraying, drop coating, and spin coating adopted in the present invention are simple and convenient to operate, with high efficiency and easy to implement. However, the coating thickness prepared by the dip coating method is insufficient, making it difficult to improve the high-temperature oxidation resistance of metal materials. The spin coating method has requirements for the size of the alloy substrate, and not only is it prone to sagging, but also wastes a large amount of raw materials. Drop coating and spraying can better coat the raw materials on the surface of the specimen, and the operation is simple and convenient. Drop coating is the simplest operation and has extremely low requirements for equipment.

[0041] Preferably, the operations of coating and drying in step S3 are carried out 1 to 5 times.

[0042] More preferably, the operations of coating and drying in step S3 are carried out 3 times.

[0043] When the operations of coating and drying in step S3 are carried out only once, a SiO 2 coating with a reduced softening point and increased density can be obtained on the surface of the titanium-aluminum alloy substrate; when the operations of coating and drying in step S3 are carried out 2 to 5 times, multiple SiO 2 layers can be obtained on the surface of the substrate, increasing the thickness of the SiO 2 coating and enhancing its function of blocking oxygen diffusion at high temperatures. On the premise that the number of coating and drying times is greater than 1, based on the design of the flux content in each SiO 2 layer and the coating position of this layer, the internal SiO 2 layer close to the substrate in the multiple SiO 2 layers can also retain some pores, making the prepared SiO 2 coating have a structure with a dense exterior and porous interior. The porous structure is prone to crack deflection of the coating itself, and crack deflection can absorb fracture stress, improving the toughness of the SiO 2 coating; at the same time, because the porous structure can also store some air, the thermal conductivity is low, which fundamentally hinders the high-temperature oxidation of the titanium-aluminum alloy substrate, so the high-temperature oxidation resistance of the SiO 2 coating can be further improved. However, the number of coating and drying times should not be further increased to more than 5, otherwise problems such as the mismatch of thermal expansion coefficients between the too thick coating and the substrate may lead to stress concentration and the coating will crack. Therefore, when the operations of coating and drying in step S3 are carried out 1 to 5 times, the prepared SiO 2 coating has better high-temperature oxidation resistance; when the operations of coating and drying are carried out 3 times, the SiO 2 coating has the best effect on improving the high-temperature oxidation resistance of the substrate.

[0044] In the specific embodiment of the present invention, the gas environment in which the specimen is heat-treated in step S4 can be selected from any one of a vacuum environment, an air environment, and an argon environment.

[0045] Preferably, the gas environment in the heat treatment in step S4 is selected from any one of an air environment and an argon environment.

[0046] Performing heat treatment in the above gas environment requires lower requirements for equipment.

[0047] More preferably, the gas environment in the heat treatment in step S4 is an air environment.

[0048] Preferably, the temperature of the heat treatment in step S4 is 800 - 950 °C.

[0049] More preferably, the temperature of the heat treatment in step S4 is 800 - 900 °C.

[0050] Most preferably, the temperature of the heat treatment in step S4 is 900 °C.

[0051] Although the melting point of the flux is low, 700 °C is the lowest temperature at which the compound formed by it and SiO 2 can liquefy and flow. Once the heat treatment temperature in step S4 is lower than 700 °C, although a small amount of liquid-phase compound will still form in the SiO 2 coating, the densification process of the coating is very long, and some pores and cracks are difficult to disappear. When the heat treatment temperature is higher than 1000 °C, the heat treatment may cause a violent reaction at the coating-substrate interface, affecting the interface stability. Heat treatment at 800 - 950 °C can not only achieve the densification of the coating with good density, but also control the densification time within 5 h. Among them, after heat treatment in an air environment at 900 °C, the SiO 2 coating has the highest density and the best high-temperature oxidation resistance.

[0052] The present invention also protects the application of the above method for surface modification of titanium aluminide in the preparation of titanium aluminide.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] The method for surface modification of titanium aluminide provided by the present invention can introduce a dense SiO 2 coating on the titanium aluminide substrate, which has good high-temperature chemical stability and can provide good high-temperature oxidation resistance for the titanium aluminide substrate; the flux introduced into the SiO 2 coating can realize the regulation of the softening point of the SiO 2 coating, so that the SiO 2 coating can soften and fill the original cracks and pores when serving at a high temperature lower than its own melting point, and then regulate the density of the SiO 2 coating to prepare a SiO 2The coating has an excellent effect on improving the high-temperature oxidation resistance of the titanium-aluminum alloy matrix. The titanium-aluminum alloy modified by this method has a weight gain per unit area due to high-temperature oxidation as low as 1 mg / cm even after 100 h of isothermal oxidation at 900 °C. 2 or so. Specific embodiments

[0055] The present invention will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventional raw material reagents purchased.

[0056] Example 1

[0057] A method for surface modification of a titanium-aluminum alloy specifically includes the following steps:

[0058] S1. Polish the titanium-aluminum alloy specimen (Ti-Al alloy, with a titanium-aluminum atomic ratio of 1:1) with sandpaper to remove the surface oxide scale, then ultrasonically clean it in acetone and ethanol for 10 min in sequence, and finally dry it with hot air for standby;

[0059] S2. Dissolve the flux KNO 3 in absolute ethanol to prepare a flux solution with a molar concentration of 0.1 mol·L -1 . Add SiO 2 particles to the flux solution to form a suspension. The mass concentration of SiO 2 particles in the suspension is 1.0 g·L -1 ;

[0060] S3. Drop the suspension onto the surface of the substrate and dry it, and repeat the operation 2 more times, that is, perform 3 coating and drying operations to obtain an initial coating on the surface of the titanium-aluminum alloy substrate;

[0061] S4. Heat-treat the specimen in an air environment at 900 °C for 1 h, and then air-cool it to obtain a SiO 2 coating on the surface of the substrate.

[0062] Among them, the SiO 2 particles in step S2 are prepared by the following method:

[0063] Mix ammonia water: water: absolute ethanol: siloxane reagent in a volume ratio of 4:18:32:5, stir and react at 30 °C for 1 h; centrifuge the reaction liquid obtained, take the precipitate, add absolute ethanol to redissolve it; centrifuge again, take the precipitate, and the obtained precipitate is pure SiO 2 particles.

[0064] Example 2

[0065] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is as follows:

[0066] In step S2, the mass concentration of SiO 2 particles in the suspension is 10 g·L -1 .

[0067] Example 3

[0068] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is as follows:

[0069] In step S2, the mass concentration of SiO 2 particles in the suspension is 0.5 g·L -1 .

[0070] Example 4

[0071] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is as follows:

[0072] In step S2, the mass concentration of SiO 2 particles in the suspension is 2.0 g·L -1 .

[0073] Example 5

[0074] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is as follows:

[0075] In step S2, the concentration of the flux solution is 0.5 mol·L -1 .

[0076] Example 6

[0077] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is as follows:

[0078] In step S2, the concentration of the flux solution is 0.01 mol·L -1 .

[0079] Example 7

[0080] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is as follows:

[0081] In step S2, the concentration of the flux solution is 0.05 mol·L -1 .

[0082] Example 8

[0083] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is as follows:

[0084] The concentration of the flux solution in step S2 is 1 mol·L -1 .

[0085] Example 9

[0086] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is that:

[0087] The temperature of the heat treatment in step S4 is 700 °C.

[0088] Example 10

[0089] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is that:

[0090] The temperature of the heat treatment in step S4 is 800 °C.

[0091] Example 11

[0092] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is that:

[0093] The temperature of the heat treatment in step S4 is 1000 °C.

[0094] Comparative Example 1

[0095] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is that:

[0096] In step S2, SiO 2 particles are directly added to water to form a suspension, that is, the concentration of the flux solution is 0.

[0097] Comparative Example 2

[0098] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is that:

[0099] The concentration of the flux solution in step S2 is 3 mol·L -1 .

[0100] Comparative Example 3

[0101] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is that:

[0102] In the suspension in step S2, the mass concentration of SiO 2 particles is 15 g·L -1 .

[0103] Comparative Example 4

[0104] A method for surface modification of a titanium-aluminum alloy, wherein the difference from Example 1 is that:

[0105] The temperature of the heat treatment in step S4 is 1200 °C.

[0106] Performance test

[0107] High-temperature oxidation resistance performance test: At 900 °C, the titanium aluminide alloy specimens treated by the above-mentioned surface modification method of titanium aluminide alloy were subjected to isothermal oxidation for 100 h, and the weight gain per unit area (mg / cm 2 ) of the titanium aluminide alloy specimens was measured; oxidation will cause the weight gain of the alloy specimens. Therefore, the greater the weight gain per unit area of the alloy specimens after high-temperature heat treatment, the worse the high-temperature oxidation resistance performance of the alloy.

[0108] The test results are shown in Table 1 below:

[0109] Table 1. Performance test results of Examples 1-11 and Comparative Example 1

[0110] Heat treatment temperature °C <![CDATA[Weight gain mg / cm 2 > Example 1 900 0.926 Example 2 900 1.564 Example 3 900 1.121 Example 4 900 1.012 Example 5 900 1.542 Example 6 900 2.027 Example 7 900 0.986 Example 8 900 1.986 Example 9 700 1.542 Example 10 800 1.152 Example 11 1000 1.356 Comparative Example 1 900 6.691 Comparative Example 2 900 2.714 Comparative Example 3 900 2.058 Comparative Example 4 1200 2.546

[0111] Examples 1-4 and Comparative Example 3 reveal the influence of the mass concentration of SiO 2 particles in the suspension on the high-temperature oxidation resistance performance of the coating. The mass concentration of SiO 2 particles in Examples 3-4 is within the preferred range of 0.5-2.0 g·L -1 of the present invention, and Example 1 is the most preferred 1.0 g·L -1 ; while the mass concentration of SiO 2 particles in Example 2 is as high as 10 g·L -1 . A higher mass concentration of SiO 2 particles instead results in a higher oxidation weight gain of the coating at a service temperature of 900 °C, because when the mass concentration of SiO 2 particles is high, the coating is prone to exhibit the properties of a pure SiO 2 coating, that is, the pores and cracks in the coating increase at high temperatures, and the high-temperature oxidation resistance performance is insufficient. The mass concentration of SiO 2 particles in Comparative Example 3 is as high as 15 g·L -1 , which is not within the protection scope of the present invention; when serving at the same 900 °C, the high-temperature oxidation resistance of the coating is worse than that of Examples 1-12. Therefore, the mass concentration of SiO 2 particles in the suspension should be within a certain range.

[0112] The result comparison between Examples 1, 5-8 and Comparative Examples 1-2 reflects the influence of the concentration of the flux solution on the high-temperature oxidation resistance performance of the coating. The flux solutions prepared in Examples 1, 5 and 7 have a concentration within the preferred range of 0.05-0.5 mol·L -1The coatings within this range, while in Examples 6 and 8, the concentration of the flux solution is within a non-preferred range. It can be seen that when the concentration of the flux solution is the most preferred 0.1 mol·L -1 at this time, the prepared SiO 2 coating has the best high-temperature oxidation resistance, with the lowest oxidation weight gain after 1 h of high-temperature oxidation at 900°C; when the concentration of the flux solution is within the range of 0.05 - 0.5 mol·L -1 within this range, the high-temperature oxidation resistance of the coating is also relatively good; the increase in the flux concentration will cause the fluidity of the SiO 2 coating to increase, and it is easy to slide off the substrate surface, resulting in a decrease in the improvement effect of the coating on the high-temperature oxidation resistance of the substrate. Therefore, the oxidation weight gain of the coating in Example 8 is relatively high; too low a flux is difficult to promote the densification of the whole coating in a short time, so the oxidation weight gain of the coating in Example 6 is also high. In addition, due to the lack of the effect of the flux promoting the densification of the coating, the SiO 2 coating in Comparative Example 1 has the worst high-temperature oxidation resistance. After heat treatment at 900°C for 1 h, the oxidation weight gain is as high as 6.691 mg / cm 2 . At the same time, in Comparative Example 2, the flux concentration is too high, exceeding 1 mol·L -1 protected by the present invention. The prepared SiO 2 coating has too strong fluidity and is extremely easy to slide off the substrate surface. Therefore, the improvement effect of the coating on the high-temperature oxidation resistance of the substrate is further reduced, and the oxidation weight gain of the coating in Comparative Example 2 also increases.

[0113] Examples 1, 9 - 11 and Comparative Example 4 reveal the influence of the heat treatment temperature on the high-temperature oxidation resistance of the coating. Example 9 is the SiO 2 coating prepared at 700°C. It can be seen that when the heat treatment temperature decreases, the high-temperature oxidation resistance of the coating also decreases relatively. This is because, at a lower heat treatment temperature, the densification process of the SiO 2 coating proceeds relatively slowly; when the heat treatment temperature reaches 1000°C (Example 11), due to high temperature causing more intense reactions at the coating-substrate interface and affecting the interface stability, the obtained SiO 2 coating has reduced high-temperature oxidation resistance; and when the heat treatment temperature reaches 1200°C (Comparative Example 4), the oxidation weight gain of the coating further increases and the high-temperature oxidation resistance is poor, which may be caused by the instability of the coating-substrate interface. The SiO 2 coatings (Examples 1 and 10) prepared within the preferred heat treatment temperature range of 800 - 950°C protected by the present invention have better high-temperature oxidation resistance.

[0114] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for surface modification of a titanium-aluminum alloy, characterized in that, specifically includes the following steps: S1. Remove the oxide scale on the surface of the titanium-aluminum alloy substrate, clean and dry; S2. Dissolve the flux in water or absolute ethanol to obtain a flux solution, and add SiO 2 particles to form a suspension, where the mass concentration of SiO 2 particles in the suspension is 0.1 - 10 g·L -1 ; S3. Coat the suspension on the surface of the substrate and dry to obtain an initial coating on the surface of the substrate; S4. Heat-treat the specimen in a gas environment at 700~1000 °C for 1~5 h, and then air-cool to obtain an SiO 2 coating on the substrate surface; The flux in the step S2 is KNO 3 , Ca(NO 3 ) 2 or one or two of them; The concentration of the flux solution in the step S2 is 0.05~0.5 mol·L -1 ; The gas environment in step S4 is any one of a vacuum environment, an air environment, and an argon environment.

2. The method for surface modification of a titanium-aluminum alloy according to claim 1, characterized in that, The concentration of the flux solution in the step S2 is 0.1 mol·L -1 .

3. The method for surface modification of a titanium-aluminum alloy according to claim 1, characterized in that, In the step S2, the mass concentration of SiO 2 particles in the suspension is 0.5 to 2.0 g·L -1 .

4. The method for surface modification of a titanium-aluminum alloy according to claim 3, characterized in that, In the step S2, the mass concentration of SiO 2 particles in the suspension is 1.0 g·L -1 .

5. The method for surface modification of a titanium-aluminum alloy according to claim 1, characterized in that, The preparation method of the SiO 2 particles specifically includes the following steps: Mix ammonia water: water: absolute ethanol: siloxane reagent in a volume ratio of (1~4):(10~20):(20~40):(1~10), and stir and react at 20~30°C for 0.5~5 h; centrifuge the resulting liquid, take the precipitate, and redissolve it in absolute ethanol; centrifuge again, take the precipitate, and the resulting precipitate is pure SiO 2 particles.

6. The method for surface modification of a titanium-aluminum alloy according to claim 1, characterized in that, The heat treatment temperature in step S4 is 800-950 °C.

7. The method for surface modification of a titanium-aluminum alloy according to claim 6, characterized in that, The heat treatment temperature in step S4 is 900 °C.

8. Application of the method for surface modification of a titanium-aluminum alloy according to any one of claims 1-7 in the preparation of a titanium-aluminum alloy.